Dieter Urban - Polymer dispersion and their industrial applications - 2002.pdf

Polymer Dispersions and Their Industrial Applications.Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. KGaA ISBNs: 3-527-30286-7 (Hardback); 3-527-60058-2 (Electronic) Polymer Dispersions and Their Industrial Applications Edited by Dieter Urban and Koichi Takamura Polymer Dispersions and Their Industrial Applications. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. KGaA ISBNs: 3-527-30286-7 (Hardback); 3-527-60058-2 (Electronic) Polymer Dispersions and Their Industrial Applications edited by Dieter Urban and Koichi Takamura IV Polymer Dispersions and Their Industrial Applications. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. KGaA ISBNs: 3-527-30286-7 (Hardback); 3-527-60058-2 (Electronic) Editors Dr. Dieter Urban Dr. Koichi Takamura BASF Corp. 11501 Steele Creek Road Charlotte, NC 28273, USA This book was carefully produced. Nevertheless, editors, authors and publisher do not warrant the information contained therein to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate. Library of Congress Card No.: applied for British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. Die Deutsche Bibliothek – CIP Cataloguingin-Publication Data A catalogue record for this publication is available from Die Deutsche Bibliothek © 2002 Wiley-VCH Verlag GmbH, Weinheim All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law. Scanning electron micrograph of a hollow sphere created by the deposition of 7.9 µm polystyrene particles on a nitrogen bubble during their preparation in the microgravity environment of the Space Shuttle Challenger (courtesy of the Emulsion Polymers Institute, Lehigh University, Bethlehem, PA, USA). Cover photograph Printed in the Federal Republic of Germany Printed on acid-free paper Typesetting TypoDesign Hecker GmbH, Leimen Printing betz-druck GmbH, Darmstadt Binding Großbuchbinderei J. Schäffer GmbH & Co. KG, Grünstadt ISBN 3-527-30286-7 Polymer Dispersions and Their Industrial Applications. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. KGaA ISBNs: 3-527-30286-7 (Hardback); 3-527-60058-2 (Electronic) Contents Preface XIII 1 Introduction 1.1 1.2 1.3 1.4 1.5 Names and Definitions 1 Properties of Polymer Dispersions 3 Important Raw Materials 8 Commercial Importance of Polymer Dispersions Manufacturers of Polymer Dispersions 12 References 14 1 10 2 Synthesis of Polymer Dispersions 15 2.1 2.2 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 2.2.6 2.3 2.3.1 2.3.2 2.3.3 2.3.4 Introduction 15 Chemistry 17 Mechanism of Emulsion Polymerization 17 Major Monomers 23 Functional Monomers 26 Surfactants 27 Initiator Systems 30 Other Ingredients 32 Manufacturing Processes 34 Types of Process 34 Influence of Process Conditions on Polymer/Colloidal Properties Equipment Considerations 39 Safety Considerations 40 References 40 3 Characterization of Aqueous Polymer Dispersions 41 3.1 3.2 3.2.1 3.2.2 3.2.3 3.2.4 Introduction 41 Polymer Dispersions 42 General Characterization of Dispersions 42 Characterization of Polymer Particles 48 Residual Volatiles 56 Aqueous Phase Analysis 57 37 V VI Contents 3.3 3.3.1 3.3.2 3.3.3 Polymer Films 58 Film Formation 59 Macroscopic Characterization of Polymer Films Microscopic Characterization of Polymers 68 References 72 60 4 Applications in the Paper Industry 75 4.1 4.2 4.3 4.4 4.4.1 4.4.2 4.4.3 4.4.4 4.4.5 4.5 Introduction 75 The Paper Industry 76 Surface Sizing 79 Paper Coating 81 Coating Techniques 84 Pigments used in Coating Colors 86 Co-binders and Thickeners used in Coating Colors Binders used in Coating Colors 90 Test Methods 97 Concluding Remarks 100 Acknowledgments 100 References 101 5 Applications for Printing Inks 103 5.1 5.1.1 5.1.2 5.2 5.2.1 5.2.2 5.2.3 5.2.4 5.2.5 5.3 5.3.1 5.3.2 5.3.3 5.4 5.4.1 5.4.2 5.5 5.5.1 5.5.2 5.5.3 5.6 5.6.1 5.6.2 5.7 Introduction 103 Flexographic Ink 104 Gravure Ink 106 Ink Composition 106 Pigment Dispersion 108 Emulsion Vehicle 109 Solution Vehicle 112 Waterborne Wax Emulsions and Powders 113 Ink Additives 113 Physical Properties and Test Methods 114 Typical Properties 114 Application Tests 115 Test Method Abstracts 115 Inks for Flexible Substrates (Films) 117 Surface Print Film 118 Lawn and Garden Bags 118 Inks for Paper Board Substrates 118 Folding Cartons 118 Direct Print Corrugated Packages 119 Pre-print Corrugated Packages 119 Inks for Poly-coated Board 120 Milk Cartons 120 Cup and Plate 120 Inks for Paper Products 120 87 Contents 5.7.1 5.7.2 5.7.3 5.7.4 Multiple Wall Bags 121 Gift Wrap and Envelopes Newspapers 121 Towel and Tissue 122 References 122 121 6 Applications for Decorative and Protective Coatings 123 6.1 6.1.1 6.1.2 6.1.3 6.2 6.2.1 6.2.2 6.2.3 6.2.4 6.2.5 6.3 6.3.1 6.3.2 6.3.3 6.3.4 6.4 6.4.1 6.4.2 6.4.3 6.5 6.5.1 6.5.2 6.5.3 6.6 6.6.1 6.6.2 6.6.3 6.7 6.7.1 6.7.2 6.7.3 6.8 6.8.1 6.8.2 6.8.3 6.8.4 6.8.5 6.8.6 Introduction 123 Market Overview 123 Coating Industry Trends 124 Coatings Provide Decoration and Protection 124 Overview of Coating Formulations 125 Volume Solids and Pigment Volume Content 125 Polymer Matrix 127 Film Formation 128 Typical Polymer Compositions 129 Pigments, Extenders, and Additives 132 Decorative Coatings 137 Emulsion Polymers in Decorative Coatings 137 Polymer Compositions used for Emulsion-based Decorative Coatings 137 Regional Distinctions in Decorative Coatings 138 Market Size of Decorative Coatings 138 Interior Decorative Coatings 139 Key Performance Features 139 Interior Decorative Coating Formulations 140 Standard Application and Performance Tests 142 Exterior Decorative Coatings 146 Key Performance Features 146 Exterior Decorative Coating Formulations 147 Standard Application and Performance Tests 147 Elastomeric Wall Coatings 149 Key Performance Features 149 Typical Elastomeric Wall Coating Formulations 150 Standard Application and Performance Tests 151 Primer Coatings 151 Key Performance Features 152 Primer Formulations 152 Standard Application and Performance Tests 153 Protective and Industrial Coatings 154 Copolymers used in Protective and Industrial Coatings 154 Market Size 155 Industrial Maintenance Coatings 155 Key Performance Features 155 Formulation Characteristics for Industrial Maintenance Coatings 156 Standard Application and Performance Tests 156 VII VIII Contents 6.9 6.9.1 6.9.2 6.9.3 6.9.4 Traffic Marking Paints 158 Description of Traffic Paint Market 158 Key Performance Features 159 Typical Traffic Paint Formulation 159 Standard Application and Performance Tests 159 References 161 7 Applications for Automotive Coatings 163 7.1 7.1.1 7.2 7.2.1 7.2.2 7.2.3 7.3 7.3.1 7.3.2 7.3.3 7.3.4 7.3.5 7.3.6 7.4 7.5 7.6 7.6.1 7.7 Introduction 163 History of Automotive Coating 164 Automotive Coating Layers 166 Electrocoat 170 Primer 172 Basecoat 173 Properties of Water-borne Binders used for Automotive Coatings Emulsion Polymers 176 Microgels 177 Miniemulsions 177 Selection of Monomers, Initiators, and Surfactants 178 Secondary Acrylic Dispersions 179 Secondary Polyurethane Dispersions 179 Rheology 181 Crosslinking 183 Application Properties 185 Metallic Effect 186 Environmental Aspects and Future Trends 186 References 187 8 Applications in the Adhesives and Construction Industries 191 8.1 8.2 8.2.1 8.2.2 8.2.3 8.3 8.3.1 8.3.2 8.3.3 8.4 8.4.1 8.4.2 8.4.3 8.4.4 8.4.5 8.4.6 Introduction 191 Pressure-sensitive Adhesives 193 Self-adhesive Labels 194 Self-adhesive Tapes 207 Test Methods 210 Laminating Adhesives 217 Flexible Packaging 217 Glossy Film Lamination 219 Furniture and Automotive 222 Construction Adhesives 224 Floor-covering Adhesives 224 Sub-floor and Wall Mastics 231 Sealants 233 Ceramic Tile Adhesives 238 Polymer-modified Mortars 241 Waterproofing Membranes 244 176 Contents 8.4.7 Elastomeric Roof Coatings Acknowledgments 250 References 251 247 9 Applications in the Carpet Industry 253 9.1 9.2 9.3 9.4 9.5 9.5.1 9.5.2 9.5.3 9.5.4 9.5.5 Introduction 253 History of Carpet 253 Present Day Carpet Business 255 Carpet Backing Binders 256 Carpet Laminating 259 Background 259 Carpet Terminology 260 Back-coating Applications 261 Back-coating Formulations and Ingredients 262 Industry Issues 264 References 266 10 Non-wovens Application 267 10.1 10.2 10.2.1 10.2.2 10.3 10.4 Introduction 267 Manufacturing Systems 270 Web Formation 271 Web Consolidation 272 Polymer Dispersions for Chemical Bonding Application Test Methods 275 References 281 11 Applications in the Leather Industry 283 11.1 11.2 11.3 11.3.1 11.3.2 11.3.3 11.3.4 11.3.5 11.3.6 11.3.7 11.4 11.4.1 11.4.2 11.4.3 11.5 11.5.1 11.5.2 11.5.3 Introduction 283 Market Situation 284 Leather Finishing 286 Modern Finishing 287 General Construction of Finishing Coats Spray Dyeing 287 Grain Impregnation 287 Base Coat 287 Pigment Coat 288 Top Coat 288 Application Methods 288 Spraying 289 Roll Coating 289 Curtain Coater 289 Binders 291 Polyacrylate Dispersions 291 Polybutadiene Dispersions 291 Polyurethane Dispersions 292 273 287 IX 1 12.7.9 Production of Selected Leather Articles 292 Shoe Upper Leather 292 Apparel Leather 293 Automotive Leather 294 Furniture Leathers 295 Test Methods in Leather Finishing 296 Flexing Endurance 297 Rub-fastness 298 Dry and Wet Adhesion 299 Fastness to Ironing 299 Hot Air Fastness 299 Aging resistance 299 Fogging test 300 Light-fastness 300 Hot light aging 300 References 300 12 Applications for Asphalt Modification 301 12.4 12.2 12.2.2 12.3.2 13.3.3.4 13.7 11.5 Introduction 329 Manufacturing of Redispersible Powders 330 Dry Mortar Technology 332 Markets and Application Areas of Redispersible Powders 333 Adhesives for Ceramic Tiles 334 Tile Grouts 340 Exterior Insulation and Finish Systems and Top Coats 341 Self-leveling Underlayments 345 Patch and Repair Mortars 346 Waterproof Membranes 350 Summary 353 329 .7.7.1 12.7.4.5 11.2 12.4.6.7.3 13.4 13.6.7.1 12.2 11.5 Introduction 301 Hot Mix Asphalt Paving 303 Asphalt Specification 304 In-line Injection (Pump-in) 311 Paving with Asphalt Emulsion 313 Applications of Asphalt Emulsions 314 Asphalt Emulsion Tests 317 Polymer Honeycomb Structure in Cured Asphalt Emulsion 317 Asphalt Emulsion Residue Characterization 319 Application Tests for Chip Seal and Microsurfacing 321 Eco-efficiency Analysis 323 Concluding Remarks 326 Acknowledgement 326 References 326 13 Applications of Redispersible Powders 13.1 13.6 11.3 11.4 11.4 12.3.7.2 11.1 11.6.3 13.4.X Contents 11.7.7 11.5 12.7.3 12.4.3 12.4 11.6.2.6 11.3 11.4.6 13.1 11.3.2 13.5 13.1 13.4.8 11. 4 15.1 14.1 14.5.4.4.3.1 14.4 15.2 15.3 15.2.2 14.4.2 15.3.1 15.3 14.5.5 15.1 14.4.4 14.Contents References 354 14 Applications for Modification of Plastic Materials 355 14.4.2 14.3 15.1 15.2 Introduction 383 Polymers Used by the Dipping Industry 384 Principles of Dipping 385 Dipping Synthetic Polymer Emulsions in Practice 386 Former Design 386 Mix Design 388 Coagulant 390 The Dipping Process 390 The Testing of Synthetic Gloves 395 Non-safety-critical Gloves 395 Safety-critical Gloves 396 References 398 Index 399 XI .1 15.2 Introduction 355 Emulsion Polymerization and Isolation Technology 356 Isolation Technology 357 Processing Aids 358 Processing Aids for PVC 359 Processing Aids for Other Resins 366 Impact Modifiers 367 Impact Modifiers for PVC 368 Engineering Resins 375 Acknowledgment 378 References 379 15 Applications for Dipped Goods 383 15.4. gloves.g. The chapters on synthesis and characterization should be regarded as an introduction and should aid understanding of the applications. Finally. bitumen. for binders or foams. wood or paper. 3-527-60058-2 (Electronic) Preface Aqueous polymer dispersions are important raw materials used in a variety of industrial processes. North Carolina. or cement. and are used as binders for pigments. and leather against water and microorganisms. The strongest development of polymer dispersions occurred in Europe and North America in the middle of the 20th century. e. They consist of very small polymer particles dispersed in water and appear as milky fluids. The applications of aqueous polymer dispersions have developed differently. When finally processed and providing the function for which they were selected. and latex foams for mattresses are polymeric materials which are made directly from polymer dispersions. and fibers and to finish the surfaces of metal. Charlotte. The differences between these two regions are emphasized. binding. In most applications the water will be evaporated and a functional polymer remains. they are used for coatings or as adhesives. We are specially grateful to all the authors who helped us make this global comparison and acknowledge the authors’ companies. and in liquid soap. The huge variety of applications continues into the area of solid plastic materials – impact modifiers are added to improve the properties of plastic materials. Even small amounts of polymer dispersion are able to improve considerably the properties of different binders. fillers. Regulatory issues have contributed to these differences. USA Dieter Urban Koichi Takamura XIII . wood. Polymer dispersions are used to protect metal. This book focuses on the applications of aqueous polymer dispersions. and finishing are the essential effects achieved by use of polymer dispersions. Accordingly. both historically and regionally. there are also applications in which polymer dispersions remain in their liquid form – they are used as drug carriers. for approving and supporting this work. Dipping goods. they are barely visible. This can be hard or tacky. plastic or elastic.g. It is even possible to reconcile these classically contradictory properties by proper design of a single dispersion or by mixing several.Polymer Dispersions and Their Industrial Applications. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. e. transparent or opaque. KGaA ISBNs: 3-527-30286-7 (Hardback). in medical diagnosis. starch. for clear coat varnishes or opacifiers. Protecting. Sunitha Grandhee BASF Corporation 26701 Telegraph Road Southfield. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. UK Dr. MI 48674. Essex. NC 28210. Westervoortsedijk 71 NL-6827 AV Arnhem. Germany Richard Scott BASF Corporation 475 Reed Road NW Dalton.V. USA Wacker Polymer Systems. 24 D-84489 Burghausen.B1 D-67056 Ludwigshafen. Onno Graalmann BASF Nederland B. CM20 2BH. Werner Kirchner BASF Aktiengesellschaft EV/CS – H201 D-67056 Ludwigshafen. Templefields. 3-527-60058-2 (Electronic) List of Authors Peter Blanpain Dr. Germany Dr. USA Richard Groves Synthomer LTD Central Road. Mary Burch Rohm & Haas Company 727 Norristown Road Spring House. GA 30720. PA 19477. Harlow. PA 19477. USA XV . Germany Dr. Johannes Peter Dix BASF Aktiengesellschaft EVL/I – G100 D-67056 Ludwigshafen. MI 49221. 13 Bristol. USA Dr. P. Brough Richey Rohm & Haas Company 727 Norristown Road Spring House. Chuen-Shyong Chou Rohm & Haas Company Rt. USA Dr. USA Dr. MI 48034. Germany Dr. Dieter Distler BASF Aktiengesellschaft GKD . Do Ik Lee The Dow Chemical Company 1604 Building Midland. Jürgen Schmidt-Thümmes BASF Aktiengesellschaft GKD/S – B1 D-67056 Ludwigshafen. Germany Andrew Lanham Synthomer Ltd. UK Dr. Elmar Schwarzenbach BASF Aktiengesellschaft EDP/MB – H201 D-67056 Ludwigshafen. Hermann Lutz Wacker Polymer Systems GmbH&CoKG Johannes-Hees-Str. PA 19007. Christoph Hahner 7834 Covey Chase Drive Charlotte. CM20 2BH.Polymer Dispersions and Their Industrial Applications. The Netherland Dr. USA Dr. Central Road. Essex. Harlow. Germany Dr. USA Dr. Templefields. Luke Egan BASF Corporation 11501 Steele Creek Road Charlotte. NC 28273. L. 413 and Old Rt. KGaA ISBNs: 3-527-30286-7 (Hardback). 3301 Sutton Road Adrian. USA Dr. NC 28273. Essex. Koichi Takamura BASF Corporation 11501 Steele Creek Road Charlotte. The Netherland K. Central Road.V. UK Barna Szabo Flint Ink Corporation 4600 Arrowhead Drive Ann Arbor. Templefields. MI 48105. Taylor BASF Corporation 11501 Steele Creek Road Charlotte. USA Dr. NC 28273. CM20 2BH. Westervoortsedijk 71 NL-6827 AV Arnhem. Weier Rohm & Haas Company Rt. USA . NC 28273. NC 28273. Germany Marilyn Wolf BASF Corporation 11501 Steele Creek Road Charlotte. Jane E. 13 Bristol. NC 28273. USA Jim Tanger BASF Corporation 11501 Steele Creek Road Charlotte. USA Dr. Spenceley Synthomer Ltd.XVI J. Harlow. USA Dr. 413 and Old Rt. USA Michael A. PA 19007. Dieter Urban BASF Corporation 11501 Steele Creek Road Charlotte. Harm Wiese BASF Aktiengesellschaft GKD/N – B1 D-67056 Ludwigshafen. Arthur Smith BASF Nederland B. USA Dr. KGaA ISBNs: 3-527-30286-7 (Hardback). 1-3 Particle morphologies. supercalendered Coated grade. supercalendered Fig. Raspberry structure Core/shell structure Acorn structure Uncoated grade.Polymer Dispersions and Their Industrial Applications. 3-527-60058-2 (Electronic) Color Plates Color Plates Fig. XVII . Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. 4-7 Effect of coated paper on offset printing. Coating head Steam Dryer Laminating station Release liner Schematic representation of PSA label coater. Fig. Backing Fig.XVIII Color Plates Coated gravure paper Uncoated gravure paper Fig. 8-9 Unwind Rewind Latex Polymer Network Photomicrograph demonstrating spontaneous formation of polymer network upon curing of the CRS-2 asphalt emulsion modified with 3 % cationic SBR latex. 4-8 Effect of coated paper on rotogravure printing. 12-15 50 µm . which essentially consists of fat droplets in water. calcium hydroxide above the solubility limit in water. The temperature and stress duration are other important factors. KGaA ISBNs: 3-527-30286-7 (Hardback). Portuguese. in dispersions and emulsions. Polish. If the finely dispersed phase and the continuous phase.g. Romanian. 3-527-60058-2 (Electronic) 1 Introduction Dieter Urban and Dieter Distler 1. Finally. Hungarian. This behavior of polymers between liquid and solid is one reason why aqueous synthetic organic polymer colloids are referred to as dispersions (Danish. Dutch. The term “organic” needs to be added to exclude inorganic polymers like silica. The term “polymer colloid” defines a state of subdivision in which polymolecular particles dispersed in a medium have at least in one direction a dimension of roughly between 1 nm and 1000 nm [1]. depending on the language. An example of a dispersion is whitewash. the liquid is water. the droplets are stabilized by proteins. they are viscous or elastic materials. if Tg and molecular weight are high. polymers are viscous liquids at low Tg and low molecular weight or they will be tough to brittle solids. Dealing with organic polymers being the dispersed substance it is difficult to define precisely whether they are solid or liquid. Depending on the glass transition temperature (Tg) and chain length. In both cases.1 Names and Definitions Most precisely the subject of this book is called “aqueous synthetic organic polymer colloids”. while in emulsions it is liquid. Finnish. excluding e. Japanese.Polymer Dispersions and Their Industrial Applications. the continuous phase is therefore a liquid. Korean. organic solvents. In dispersions. the term “aqueous” ensures that the continuous medium is only water. German. However. In general the term “dispersion” characterizes a two phase system consisting of finely dispersed solid particles in a continuous liquid phase. the term “emulsion” will be used. Norwegian. if organic polymers of natural origin like natural rubber should be excluded. while above this temperature or in the case of long stress times. Greek. in all of our examples. To be more precise the term “synthetic” will be added. polymers behave like glasses. the geographical region and the field of application there are many other names commonly used (Fig. An example is milk. both are liquid. Russian. the finely disperse substance is solid. 1 . Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. At temperatures below the glass transition temperature or in the case of very short stress duration. Spanish. 1-1). 1-1 colloids. Commonly used names for aqueous synthetic organic polymer .2 1 Introduction Fig. “emulsion” and “latex” are used synonymously. for example by aminoor hydroxyl-containing monomers or protective colloids. One particle contains 1–10 000 macromolecules. droplet) is derived from the naturally occurring rubber milk and is most widely used for aqueous synthetic organic polymer colloids. The products are referred to as emulsion polymers or simply emulsions. especially for the substitution products of natural latex. Each mL of dispersion contains about 1015 particles with diameters of 50–500 nm. according to the preference of the authors the terms “polymer dispersion”. 1-2). 1. freezing. Another reason for the use of emulsion or emulsion polymer comes from the most important production process for these products. If we want only water to be the continuous phase. etc.” Since we will not cover inorganic dispersions. or by incorporation of ionic groups into the polymer. The polymer may be organic or inorganic. for example by adsorption of anionic or cationic surfactants. Industrially important polymer dispersions usually contain 40–60 % of polymer in water. Turkish) and emulsions (Arabic. Finally a polymer block and a substantially polymer-free water phase will be formed. However.” The continuous phase can be a liquid. In contrast to this the name latex (Latin: latex. and each macromolecule contains about 100–106 monomer units (Fig. The special nature of the particle surface. Latex is defined as “A colloidal dispersion of polymer particles in an aqueous medium. Polymer dispersions used in industry usually are stabilized by both mechanisms (ionic and nonionic). Driving force for the agglomeration of particles is the gain of energy by reducing the internal surface. Greek: λαταξ. shear. nonionic type of stabilization takes place via hydrophilic groups on the particle surface.1. the particles are usually provided with ionic groups. This coagulation can be accelerated by salts. Chinese. which differs from the particle interior. 3 . plays an important role in all applications. Another. To obtain highly stable polymer dispersions. Therefore this book has been called “Polymer Dispersions and Their Industrial Applications”. butadiene-styrene copolymer emulsions. In industrial applications non-aqueous polymer dispersions are negligible. Malay). The very large internal surface area of up to 100 m2 mL–1 of dispersion requires stabilization of the particle surfaces in order to suppress phase separation and coagulation. aqueous is added. The Union for Pure and Applied Chemistry recommends two names: Latex and polymer dispersion [2]. acids. the emulsion polymerization. Indonesian. this book should have been called “Organic Latices and Their Industrial Applications”. solid or gas. solvents.2 Properties of Polymer Dispersions The aggregate state of a polymer dispersion is thermodynamically unstable. “dispersion”. Polymer dispersion is defined as “A dispersion in which the disperse phase consists of polymer particles. which seems to be a pleonasm because the use of latex is generally associated with organic material. liquid. “emulsion polymer”. Italian. English.2 Properties of Polymer Dispersions Swedish. the possibility of cross-linking between the polymer chains and finally separated phases of different polymers in a particle allow a virtually unlimited variety in this product class. which is caused by Bragg scattering at a crystalline superstructure of close packing of the particles. This enables product properties with even contradictory requirements to be achieved better. 1-3). . If all the particles are of the same size. The water phase of many polymer dispersions contains a whole range of water-soluble oligomers. the term “monodisperse dispersions” will be used. The flow property of polymer dispersions is a particular advantage of this aggregate state. Besides the polymer content. Polymer dispersions normally consist of spherical particles. This Mie scattering is utilized for particle size measurement. Polymer dispersions with a heterogeneous particle structure – a special particle morphology consisting of a number of phases – have recently become of interest. The particle morphology may be thermodynamically preferred. particle size distribution and electrolyte content. it is mostly kinetically controlled morphologies that are frozen. the viscosity is also affected by dissolved constituents in the aqueous phase. auxiliaries and additives which contribute to the application properties as well. but maximum blocking resistance or hardness of the polymer (Fig. 1-2 What is a polymer dispersion? These figures give an impression of the possible variation. if just the molecular weight (or molecular weight distribution) and particle size (or particle size distribution) of homo-polymers will be considered. particles with a raspberry structure. in the case of polymers with reduced chain mobility or even in the case of relatively low cross-linking. Dispersions can have a polymer content which is a multiple higher than polymer solutions. The flow behavior is also an important parameter. for example low film formation temperature. yet still be freeflowing. Examples are particles with a core/shell structure or two coexistent polymer phases. They are frequently recognized from a certain particle size merely from the iridescent appearance.4 1 Introduction Fig. The random incorporation of various monomers in the chains. particle size. etc. The dispersed particles scatter the light and are the cause of the milky appearance. Very small polymer particles hardly scatter visible light at all. those polymer dispersions have a translucent appearance. The viscosity of polymer dispersions is usually dependent on the shear rate. very broad or bimodal particle size distributions are needed (Fig. for example. Fig. Raspberry structure Core/shell structure Acorn structure To obtain readily free-flowing dispersions with low viscosity at high polymer contents of >60 % by volume. A distinction is made between pseudoplastic behavior (viscosity decreases with increasing shear).2 Properties of Polymer Dispersions Fig. by means of a shear gradient. possibly with a flow limit. 1-3 Particle morphologies. so that significantly larger agglomerates are present alongside the small primary particles. by freezing or by addition of an agglomeration aid. Electron photomicrograph of a bimodal polymer dispersion. 1-4 This can be achieved during the polymerization or by partial agglomeration. 1-4).1. thixotropic behavior (viscosity decreases with in- 5 . Ethylene/vinyl acetate copolymers form elastic films and are fairly resistant to oxygen and light. versatic esters. Depending on the composition and/or processing temperature. elastic and solvent resistant polymers are obtained. The polymer dispersions are spray dried to obtain a polymer powder. Acrylic dispersions (pure acrylics and styrene acrylics) are extremely versatile. The main application areas are coatings and adhesives. Carboxylated styrene/butadiene (XSB) dispersions contain acrylic. This polymer class is resistant to hydrolysis at all pH values since it does not contain ester units which tend to hydrolyze especially at very high pH. The main applications are paper coating and carpet backing. Most dispersions are therefore provided with biocides. by the morphology of the polymer particles and by the morphology of the polymer film. which are used for dipping goods. They are used as synthetic rubber for tires and molded foam. the molecular weight and the molecular weight distribution. yeast). it becomes yellow and brittle. tack. The rheology of concentrated polymer dispersions is complex. often being dependent on the shear rate and previous history. These properties are determined by the chemical composition of the copolymers. Acrylics are resistant against oxidation by air and degradation by light.2 and 2. Important polymer classes are: Styrene/butadiene dispersions are used for their elastic properties since molecular weight and cross-linking of the polymer can be adjusted widely by choosing the degree of conversion and the amount of chain transfer agents. When styrene is replaced by acrylonitrile. etc. Owing to the content of surface-active substances. which is widely used in construction industry. fumaric or itaconic acid. maleic. Antifoam agents reduce foaming. the foaming behavior is an important property for many applications.6 1 Introduction creasing shear time) and dilatant behavior (viscosity increases with increasing shear). elongation at break. This is prevented by adding antioxidants. The big variety of available acrylic and methacrylic esters together with styrene offer almost unlimited opportunities to choose for the glass transition temperature and the hydrophilic/hydrophobic properties.3 double bonds of butadiene favor autoxidation of the polymer. methacrylic esters in contrast form polymer chains which are not cross-linked. In most applications. Acrylic esters tend to form cross-linked polymers by abstraction of the α-hydrogen atom. Most common co-monomers are ethylene. glass transition temperature. To stabilize the polymer particles often polyvinyl alcohol is used as protective colloid. The remaining 1. a polymer film or powder is formed. The biodegradability of many additives makes the dispersions susceptible to attack by microorganisms (bacteria. The carboxylic groups provide stabilization of the polymer particles and a good interaction with fillers (calcium carbonate. clay) and pigments. solvent and environmental resistance. . vinyl chloride or acrylic esters. Vinyl acetate dispersions are widely used for coatings and adhesives as well. methacrylic. the water is evaporated from the dispersions. transparency. The properties of the polymer now come into play: strength. while further emulsifiers and rheology modifiers increase the foaming or stabilize the foam once formed. elasticity. They are used as thickeners. a whole range of periodicals focuses on polymer dispersions [14–18].1. They are used in paper coating to improve gloss. are used as temporary protective films. 1-5 Polymer dispersions with a high amount of acrylic/methacrylic acid convert to aqueous solutions or gels when pH is increased. Films of acrylic dispersions. In addition to excellent reviews [3–13]. Polystyrene dispersions have a glass transition temperature of 105 ºC.2 Properties of Polymer Dispersions Polymer dispersion with a high content of vinylidene chloride form polymer films with crystalline areas. Permeability of polymer films. especially for food packaging (Fig. And the use of polymer dispersions is increasing worldwide. emulsion polymerization is an inexpensive production process for these products. and are used as barrier coatings in packaging materials. oxygen and water vapor. and water is environmentally friendly. which are cross-linked with metal ions and re-dispersible with an aqueous solution of ammonia. the fluid form of polymer dispersions is easy to handle. The complex colloidal and chemical behavior of polymer dispersions is an interesting working area for many scientific disciplines and is important for many applications. Films made from polyurethane dispersions combine elastic properties with high tensile strength. These PVDC films are highly impermeable for both. The main reasons for this are: the variety of polymer properties achievable by emulsion polymerization is virtually unlimited. They are both commodities and specialties. 1-5). in liquid soaps to provide opacity and in medical diagnosis as carrier for active ingredients. 7 . Fig. All those examples elucidate that polymer dispersions are used in both big volume and small volume applications. There are currently about 200 steam crackers worldwide. This process is started by preparing a monomer emulsion consisting of monomer droplets in water. the Middle East and North America. such as chain transfer agents. bases. The largest plants have an annual capacity of more than 800 000 tons of naphtha.. Fig. free-radical-polymerizable monomers. The monomer droplets are stabilized by emulsifiers and/or protective colloids. reached a world capacity of about 80 million tons per year in 1995.8 1 Introduction 1. biocides.3 Important Raw Materials The most important production process for polymer dispersions is emulsion polymerization [19]. with the steam cracker as reactor. Liquid hydrocarbons (naphtha or liquefied natural gas LNG) are broken down (“cracked”) into short-chain hydrocarbons at 800–850 °C with addition of steam as diluent (Fig. Further auxiliaries. . the most important petrochemical feedstock today. predominantly ethane and propane from natural gas are used. emulsifiers and/or protective colloids and initiators. acids. the starting material is mostly naphtha. When adding an initiator polymerization is started converting the monomers into polymer particles (Chapter 2). In Europe. The production of polymer dispersions by emulsion polymerization requires deionized water. 1-6) [20]. however. in this connection as a feedstock for the production of vinyl chloride. styrene and vinyl acetate. anti-aging agents. Ethene. 1-6 Steam cracker products. Latin America and South-East Asia. Almost half is polymerized to give polyethylene. can be used. while in North Africa. The most important source of the main monomers used or their precursors is petroleum chemistry. It plays only a secondary role for emulsion polymerization in vinyl acetateethene copolymers and in polyethylene waxes. It is important. buffers. etc. It is. polyvinyl-pyrrolidone. crosslinking within the particles (difunctional acrylates. styrene. Reactive monomers which still contain a latently reactive group even after incorporation into the polymer. for example the particle surface. alkylpolyglycol ethers. however. such as hydroxyacrylates). but is so far mainly of academic interest. for example glycidylmethacrylate or N-methylol(meth)acrylamide. etc. and can be used directly for emulsion polymerization.3 Important Raw Materials Propene cannot be polymerized by means of free radicals. acrylates and acrylonitrile. polyvinyl alcohols.1. Besides the monomers. Butadiene is extracted from the C4 fraction from the steam cracker. a free-radical initiator which forms free radicals at elevated temperatures (60–100 ºC) is needed. For the polymerization to start and maintain. γ-rays. but are preferentially moved to the area of greatest effectiveness. methacrylamide). In addition. The polymerization can also be initiated by UV. These specific polar groups are frequently not distributed homogeneously over the particle cross-section. sulfonate. have not yet been used in practice. Ethylene oxidepropylene oxide block copolymers. or a redox system. the elasticity.) or hydrophilic properties (OH-containing monomers. The combination of initiator. can form a network between various particles and polymer molecules after film formation. etc. although these. control important properties such as colloid-chemical stabilization (acrylic acid. hexadecyl or alkylbenzene) and a hydrophilic end group. sulfosuccinic acid. phosphate. Auxiliary monomers. for example hydrogen peroxide/ascorbic acid with Fe2+ salts. a feedstock for acrylic acid. the emulsifiers are important constituents. 9 . The principal monomers butadiene. electron beams or strong sound or shear fields.and surface-active properties (inisurf) or surfaceactive and monomer properties (surfmer) in a single molecule is possible. usually <5 %. the water absorption capacity. vinyl acetate.and 3-block copolymers. which are frequently used in combination with ionic emulsifiers. hydrogen peroxide. The hydrophilic group may be anionic (sulfate. (meth)acrylates and acrylonitrile essentially determine the material properties of films made from the corresponding dispersions: the glass transition temperature. which are only used in a small proportion. for example sodium peroxodisulfate. etc. amphiphilic 2. there is a whole series of nonionic emulsifiers and protective colloids. carboxylate) or cationic (quaternary ammonium salts) or have a zwitterionic structure (betaine groups). apart from UV initiation. divinylbenzene. Emulsifiers (surfactants) consist of a long-chain hydrophobic group (dodecyl. methacrylic acid. acrylamide. organic peroxides or azo compounds. 4 Commercial Importance of Polymer Dispersions Polymers were discovered in the 1920s.10 1 Introduction 1. 1-7). The major polymer classes – polyolefins. bonding and finishing. but not by the chemical composition. Million Metric tons 200 180 189 160 140 120 114 100 80 60 68 40 20 0 Fig. During World War II large industrial scale production was established and since the 1950s production and use of polymers have grown strongly (Fig. They essentially perform the functions of protecting. Combinations of the various product classes make a significant contribution toward the variety of end products made of plastic materials and synthetic fibers. and the extremely low energy content (as product and in production). This growth is due to two factors: the ability of polymers to combine properties such as light weight. strength. electrical insulation. ethene. In the chapters dealing with applications. The possibility of energy recovery. recycling of the raw material or even of the polymer after use conserves resources. This growth is ongoing. The class of polymer dispersions is only described by the state of aggregation.. and production of synthetic polymers has reached about 189 million metric tons with a total value of more than US$ 200 billion worldwide by the year 2000. etc. propene. Functional polymers are used as polymer solutions. films. vinyl chloride and styrene (Fig. polyvinyl chloride and polystyrene – are defined by their monomers. we will also see that for a particular application a number of polymer classes are suitable. binding. polymer dispersions or polymer powders. These three groups together account for 64 % of synthetic polymers. etc. materials. 1-8). We encounter a wide range of polymers every day in the form of fibers. the specific . 1-7 8 1960 32 1970 1980 1990 2000 Growth of plastics production. in virtually all products we use in everyday life.. The variety of functional polymers is even greater than for plastics and fibers. state of aggregation of the dispersions is consequently often more important than the monomer combinations. They are not sold as dispersions. vinyl ester. and polyacrylates. or 15 million metric tons (wet). but further processed directly by the manufacturers. only about 15 % is sold as latex with a solids content of 60 %. assuming an average polymer content of 50 %. Other polymer dispersions contain copolymers of ethylene. These figures also omit impact modifiers for plastics. 11 . vinylidene chloride. is. The most important product classes of polymer dispersions are butadiene-styrene copolymers. chloroprene and polyurethane (Fig. 1-9). The most important dispersion. vinyl chloride. natural latex from Hevea brasiliensis with about 6 million metric tons (dry).5 million metric tons (dry) polymer. 4 % polymer dispersions correspond to about 7. The majority is coagulated and used predominantly in the tire industry. About 1 million metric ton (dry) of impact modifiers is produced worldwide. styrene. 1-8 Polymer Dispersions (dry) 4% Production by polymer class [21].4 Commercial Importance of Polymer Dispersions PVC 14% Polyolefin 43% Polyester 14% Polystyrene 7% Polyurethane 4% Other 14% Fig. not included here.1. as a natural product. vinyl acetate homopolymers and copolymers. 1-10 major suppliers of polymer dispersions are listed in alphabetical order.5 Manufacturers of Polymer Dispersions Worldwide there are far more than 500 companies producing and offering polymer dispersions. Acrylic dispersions include pure acrylics and styrene acrylics. The product lines as well as the information about the main application areas and the trade names were mainly taken from the company’s web sites [22–49]. DOW Chemical. etc. vinyl chloride. chloroprene. The product lines are defined by the main monomers used. However.12 1 Introduction Vinylacetate 28% Acrylate 30% Other 5% Styrene Butadiene 37% Fig. only 20 companies account for about half of the global market. Rohm and Haas – have an annual production capacity of more than 1 million metric tons (wet) and cover about 20 % of the world market. specialty dispersions consist of monomers like vinyl pyridine. .. In Fig. 1. vinylidene chloride. 1-9 Aqueous polymer dispersions by product class. The leading 3 suppliers – BASF. A. NeoRad. Resyn Nitrilatex Adh. Carbobond. Tex Aqueous XPD. Con. UCAR Latex Eastman Chem. Valtac. Tex Mowilith. NB Adh. Tex Lucidene. Carbotac. Applications: Adh adhesives. AcrylGen. AcrylPrint. Eastarez. VAc. I/GA inks/graphic arts. OmnaBloc.C. NB. Nitriflex [1-36] NB. Con. SB. Pap. Tylac Adh Durabond Adh. Pap. Pap. Con. Appretan Coat. Tex Rhodopas. PU. SB A. Pap. SB A. NB. Sp A. NB. Wacker SMK Raisio Group [1-40] Reichold [1-41] Fig.1. 1-10 Major suppliers of aqueous polymers dispersions. Coat. Sp National Starch [1-35] A. SB. Dur-o-cryl. Rovace Adh Gelva Adh. Con. Butonal. EVA. Tex Dow Latex. EVA. Primal. Con. Coat. Sun Wrap Adh. SB. Luhydran. GenFlo. Sp Adh. Lipaton. NB A. Tex Rikabond Adh. Coat. Waterborne Polymer Adh. VAc Adh. VAc vinyl acetate dispersions. I/GA. VAc. Coat. Plextol. Tex Vinamul. Pliotec Adh. A. I/GA. Coat. Sunbond Adh. Tex Nipol Omnova [1-38] A. Pap Glasca. Bunatex. Rhodotak. SB. A. EVA. Pap. I/GA. GenTac. Dur-o-set. NB. Rhoximat Adh. Coat. Airflex. Valbond. SB styrene butadiene dispersions. Pace. Tex Acralen. Flexcryl. Con construction/building products. Tex Elvace. SunCryl. Coat. Coat. I/GA. Coat. VAc. SB. Pap paper. VAc. Sp EVA. Tex Intex. Coat. Product lines: A acrylic dispersions. Tex Acronal. Vancryl. 13 . Coat. I/GA. Butofan. Coat. Tex Airbond. Con. Lipolan. Vycar Adh. Styronal Adh. PU BASF [1-25] A. Hystrech. Tex Zeon Corp. Johnson [1-33] Mitsubishi Chem [1-34] A. Tex Pliolite. Pap. Con. Con. Europrene. Con. Luphen. Coat. Con. Pap. Sp Clariant [1-26] Dow [1-27] VAc. Coat. I/GA. Coat. Con. Vac A. VAc SB. EVA. PU. Tex carpet/textile/non-woven. EVA. Sequabond. Pap. Vinac Adh. VAc. I/GA. Con. NB acrylonitrile butadiene dispersions. Plyamul. EVA. Pap. Coat. [1-45] Synthomer [1-46] UCB [1-47] Wacker [1-48] A A. [1-28] Elf Atochem [1-29] Enichem [1-30] Goodyear [1-31] BFGoodrich [1-49] now Noveon JSR Corporation [1-32] S. Coat. EVA ethylene vinyl acetate dispersions. Ucecoat Adh. Mowiplus. SB. Sp A. GenCryl. Con. Baypren. Emuldur. Carboset. SCX Adh. Coat coatings/paints. SB A. Sp Polymer Latex [1-39] Revertex [1-42] Rhodia [1-43] Rohm&Haas [1-44] A. Sp A. Sp specialty dispersions. SB. Pap. A Asahi Kasei [1-23] Avecia[1-24] A. NeoPac. GenCal. Flexbond. Tex Raisional Adh. Con Vinnapas. Sancure. PU A. Rhobond. PU Solutia Inc. Nacrylic. Perbunan Pap. [1-37] A. Synthemul. Rhopaque. Styrofan. Coat Polytron. Haloflex Adh. Dynaflow Adh. Basonal. Coat. Tex AcryGen. Con. Pap. NB. PU. Tex Repolem Adh. Diofan. SB. Polyco. I/GA Joncryl. Pap. PU EVA. PU A. I/GA Eastek.5 Manufacturers of Polymer Dispersions Company Product lines Applications Air Products [1-22] VAc. I/GA. Con. I/GA NeoCryl. Con. Coat Ucecryl. SB. VAc. Tex Adh. Con. SB. PU polyurethane dispersions. Pap. Latice Adh. Coat. Sp Trade names Adh. NeoRes. PU. VAc. Rhoplex. Baystal. VAc A. Goodrite. VAc. Hycar. Pap. 1972. 1994. Benn..atofina. 19 Gilbert. H. American Chemical Society. R. 335). Emulsion Polymerisation. Weissermel. H. Kluwer Academic Publishers. New York. New York.nitriflex. Berlin. 1991. Corner.Vinamulpolymers. London. London.. 1995. Colloid Polym. Vol. Weinheim. Properties.rhodia. Science.ucb. 1997.enichem. 1972. Engelmann. 1997. I. H. Chem.com http://www. Springer. Berlin. Hölscher. 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 A Mechanistic Approach. Emulsion Polymerisation. Emulsion Polymerisation. The Application of Synthetic Resin Emulsions. F. Lovell.synthomer..com/ http://www. Encyclopedia of Polymer Science and Engineering. Marcel Dekker.. T. London. Emulsion Polymer Technology. P. Applied Science.. P..eastman.jsr. Blackley.be/ http://www. (NATO ASI Series E: Appl. Dispersions of Synthetic High Polymers.com http://www.basf. Baum.. ACS Journal of Surfaces and Colloids..it/english/ http://www. New York.rohmhaas. 1982.. Steinkopf. Nachrichten aus der Chemie.jp/asahi/ english/kasejusi.. Pure Appl. G. K.. C.com/ http://www. See also ISO 12000 Plastics/rubber-Polymer dispersions and rubber latices – Definitions and review of test methods.com/neoresins/ http://www.co.. G. Dispersion Sci.wacker. 18 J. Poehlein. Emulsion Polymerisation.. 49/3.co. 1966. Asua. Academic Press..jp/ http://www.. Coden.airproducts.m-kagaku.com/ http://www. Verlag Chemie.avecia. D.raisiogroup. Colloid Interface Sci.html http://www. 2001. two volumes. J. Elsevier. El-Asser.solutia. Elsevier Applied Science. D.. Athey.jp/ http://www. D. Piirma. 1975. 1985.com/ http://www.omnova. Academic Press.jp/main/english/ http://www. http://www.polymerlatex.goodyear. Part II. Technol. Academic Press. Theory and Practice.htm http://www. A. Wiley.asahi-kasei. Warson. Arpe. R. R.. S. London.de/de/dispersionen/ products http://www. C. J.com.com/ http://www.com/ http://www.dow.14 References 1 Everett. Polymer Colloids. 368f. J. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 579–638.com/vip/ produktion/wacker/website/polymersystems/index_en. J.de/ http://www.com/ http://www. J.com/ http://www.com/ http://www.html http://www. Polymeric Dispersions: Principles and Applications. New York.reichhold.br/ http://www. Preparation. 1986. Stagemann.co.com/ http://www. Part I. D. Industrial Organic Chemistry. Wiley. Dispersions of Synthetic High Polymers. Use.. Springer. Colloids Surf.com/ http://www.scjohnsonwax.bfgsolutions..com/ http://www. M.clariant.com/emulpoly/ index. Blackley. Major Organic Precursors and Intermediates. F. Reinhard.. Emulsion Polymerisation and Emulsion Polymers.zeon. MacLaren. 31(4). Sci. H.revertexfinewaters.com . J.-J. IUPAC Proposal for The nomenclature for Polymerization Processes and Polymers in Dispersed Systems.com/ http://www. Volume 6. High Polymer Lattices. Dordrecht. London.. Buscall. Testing.. Langmuir. 1969. M.co. 1969.. scale-up from laboratory to manufacturing gives good duplication of polymeric and colloidal properties. The larger quantities involved in continuous poly- 15 . heat losses often exceed heat generated by the reaction. do not normally pose any problems for cooling. often limits production rates in large-scale reactors. With non-pressure reactors. to produce specific polymeric and colloidal properties. In order to achieve a similar degree of mixing in vessels of different sizes. but there are still large gaps in the knowledge needed to translate this into application behavior. Taylor 2. In general. while pumps or inert gas pressure may be used for pressurized systems. Figures 2-1 and 2-2 show modern laboratory facilities for non-pressure and pressure emulsion polymerization. Laboratory reactors. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. with their large cooling surface to volume ratio and the large heat capacity of the reactor relative to the contents. While the equipment used in preparing an emulsion polymer is relatively simple. and the mechanism of the important reactions are fairly well understood. laboratory reactors have significant limitations. necessitating heat input to maintain reaction temperature. the most important scale-up criteria is usually to maintain the same power input per unit volume. a consequence of which is increased shear on the emulsion.Polymer Dispersions and Their Industrial Applications. and laboratory equipment normally consists of simple stirred reactors. the development of new and improved products is often still carried out in a somewhat empirical fashion. Recipe and process conditions can frequently be designed. Unfortunately.1 Introduction The intent of this chapter is to give a short overview of the chemistry and manufacturing processes involved in the synthesis of emulsion polymers. usually glass for non-pressure polymerizations. KGaA ISBNs: 3-527-30286-7 (Hardback). for the study of process characteristics. Both batch and semi-batch reactions are regularly carried out on laboratory scale. Therefore. this translates to a higher agitation speed as reactor size reduces. ingredients may be added under gravity. Two important process features that are not reproduced well between small and large-scale reactors are heat transfer and shear. Heat transfer. 3-527-60058-2 (Electronic) 2 Synthesis of Polymer Dispersions Mike A. In fact. on the other hand. with a means of maintaining temperature control of the exothermic reaction. based on a theoretical knowledge. Fig.1). tacky/non-tacky.16 2 Synthesis of Polymer Dispersions Typical laboratory apparatus for emulsion polymerization at atmospheric pressure (photograph courtesy BASF Corporation). A simple recipe. etc. stable/unstable.3. Subsequent sections of this chapter give greater detail on materials used to produce emulsion polymers. although the kinetics of a chain of multiple continuous stirred-tank reactors can be simulated with a batch reaction (Sect. is shown in Tab.) . a very wide range of polymers with significant differences in polymer and latex properties can be produced (soft/hard. low/high molecular weight. which could be used to demonstrate the influence of ingredients and process on polymer and colloidal properties. With just these two monomers and one functional monomer. 2-2 merization generally rule out this process for laboratory scale reproduction. This recipe could be utilized for investigating both batch and semi-batch emulsion polymerization at a range of temperatures. 2-1 Laboratory equipment for emulsion polymerization at high pressures (photograph courtesy BASF Corporation). Fig. 2. Reactions at low temperatures require the provision of refrigerated coolant. 2-1. surfactant. Molecular wt. In many cases. through a 17 .5–3. and/or give stability to the growing particles.0 t-Dodecyl mercaptan Divinylbenzene 0–1. a modifier to control the molecular weight of the polymer or a cross-linking agent to control the amount of gel. viscosity. ingredients used to control polymerization behavior will also exert their own influence on application properties of the final emulsion. reaction kinetics. colloidal stability. emulsion polymerization can take place in a system with only three components. viscosity. minimum film-forming Glass transition temp.. a monomer that forms the structure of the polymer. reaction kinetics Particle size.1–1. surfactants. rheology. characterized as a molecule containing at least one carbon-carbon double bond. water that acts as the continuous medium in which the polymer particles are dispersed. and an initiator that produces free radicals which start and maintain the polymerization process. and which. at the very least the system will almost invariably contain a fourth ingredient. while often determining the number of particles and their stability. colloidal stability.2.2 Chemistry 2.0 0–0. In addition.2 Chemistry Tab. C=C. minimum film-forming Colloidal stability. can also have significant effects on such properties as adhesion. filler tolerance and many others. reaction kinetics Particle size. viscosity Glass transition temp. However.2. reaction kinetics Cross-linking/gel 1 Parts per hundred parts of monomer 2. molecular wt. for example. Particularly.1 Mechanism of Emulsion Polymerization Strictly speaking. Ingredient Quantity (phm1) Influence Water Styrene 100–150 0–95 n-Butyl acrylate 0–95 Methacrylic acid 0–5 Sodium lauryl sulfate 0. 2-1 Model system for the study of some aspects of emulsion polymerization.5 Solids content. Rarely can the best of everything be achieved.0 Ammonium persulfate 0. The basic building block of any polymer is the monomer. most commercial recipes would normally include other ingredients to impart specific properties to the final polymer or emulsion. which can provide the initial site. from which polymer particles subsequently grow. The overall formulation of an emulsion polymer is therefore often a compromise to obtain an optimum balance of properties. suspension and emulsion.2. building up long chains of monomer units. can also cause termination to occur. solution. To exert additional control over molecular weight. The process continues. Many different monomers (Sect. The difference between the processes is the environment. the average molecular weight of the polymer chains is controlled primarily by the temperature of polymerization and the quantity of initiator. but in this case the monomer is diluted with a fully miscible solvent and the final polymer is in solution in the solvent. With chain transfer. The free radical that terminates the chain can be an original radical.18 2 Synthesis of Polymer Dispersions free radical mechanism. Polyacrylic acid. In bulk polymerization there exists only one phase. Both polystyrene and poly(methyl methacrylate) are produced in large quantities by bulk polymerization. or a “polymeric radical” when the ends of two propagating chains terminate each other. Polymerization is started when a free radical. for example bulk. where R is typically a twelve to fourteen hydrocarbon (t-dodecyl or n-dodecyl being the most common). until the free radical at the end of the chain comes into contact with some species other than a monomer molecule. Other species. normally another free radical. initially the monomer. with the solvent being water. a growing polymer chain is terminated but at the same time another radical is generated which can initiate polymerization of a further monomer unit. comes into contact with a monomer molecule and adds on at the site of the C=C double bond. originating from the decomposition of the initiator (Sect. more usually. These three main stages of polymerization are termed initiation.2) are in use commercially for producing emulsion polymers. In suspension polymer- . This creates a monomer unit that is then itself a free radical and can in turn add on to another monomer molecule. propagation and termination and can be denoted schematically as follows: Initiation Propagation Ι → 2R• (decomposition of initiator) M + R• → R–M• R–M(n)• + M → R–M(n + 1)• or transfer to polymer leading to branching Termination or R–M(n)• + R–M(m)–R → R–M(n) + R–M•(m)–R R–M(n + 1)• + R• → R–M(n + 1)R R–M(n)• + R–M(m)• → R–M(n + m)–R In such a system. R–SH. Chain Transfer R–M(n)• + R–SH → R–M(n)–SH + R• These four mechanisms are common to all types of free-radical polymerizations. then as polymerization progresses a solution of the polymer in its own monomer. thus starting another polymer chain. can add on to itself. ultimately forming very large molecules of repeating units. 2. at which time the growing polymer chain is terminated. is produced by this technique. from the decomposition of the initiator. Solution polymerization is similar in that there is only one phase present. Widely used chain transfer agents are the mercaptans.5). as combinations of monomers to give specifically desired properties. a molecular weight modifier (chain transfer agent) is used. such as inhibitors and short-stopping agents if present. either as the sole monomer or. 2.2. with the high concentration of the hydrophobic portions of the surfactant. In most cases. and monomer could contain 1017–1019 monomer-swollen micelles per liter.2. In the case of micellar nucleation. Emulsion polymerization is also carried out in a continuous water phase. When a sparingly water-soluble monomer (which describes most of the monomers used in emulsion polymerization) is added to an aqueous solution containing these micelles. or a pre-formed polymer particle of very small size. a dispersion of 50 weight percent monomer droplets in water would contain typically about 1010 monomer droplets per liter. but in this case the site of polymerization is a far smaller entity than dispersed monomer droplets. and the decomposition. The size of these micelles is typically about 4 nm. many surface active agents. Also. the initiators used in emulsion polymerization are water soluble. which is used as the seed for further polymerization. with free radicals initiating monomer molecules in 19 . as is the size of the final polymer particles. soap solution at a concentration greater than the CMC. monomer is “solubilized” within clusters of surfactant molecules. and as a consequence the ratio of the surface areas is similarly large. when dissolved in water above a certain concentration (Critical Micelle Concentration or CMC). which form the nucleus of the polymer particle. It is most probable that polymerization also starts in the aqueous phase. the free radical has a far greater probability of entering a micelle and initiating polymerization than it has of entering a monomer droplet. whereas a system containing water. This early model is still basically accepted today. termed micelles. is greatly enhanced in the micellar system. Polyvinyl chloride dispersions are made in this way. monomer molecules in solution in the water. the monomer is dispersed in droplet form in a continuous medium that is usually water. which is the rate per particle multiplied by the number of polymerizing particles. The inside of the micelle. usually less than 50 nm. and monomer molecules that diffuse into the micelles. surfactant and monomer. with the hydrophobic portion of the molecule oriented toward the center of the cluster and the hydrophilic portion toward the outside. the general shape being either spherical or lamellar. and is described briefly as follows. relatively large monomer droplets stabilized by surfactant molecules at the droplet surface. This represents a total surface area of the swollen micelles approximately 105 times that of the monomer droplets. Harkins [1. The size of the droplets is typically in the range ten to one hundred microns.2 Chemistry ization. but where the polymer is insoluble in the monomer. This process would be favored where an aqueous based polymer is required. provides an attraction for the hydrophobic monomer that diffuses through the water and swells the micelle. will form ordered clusters of molecules. The number of monomer-swollen micelles in such a system is orders of magnitude greater than the number of monomer droplets present. For example. In this process. These monomer-swollen micelles are limited in size by hydrodynamic forces and interfacial tension. the overall rate of polymerization. to produce free radicals takes place in this phase. either thermal or with the use of a reducing agent. 2] developed a quantitative theory describing emulsion polymerization in an ideal system. The consequence of this is that when free radicals are produced in the aqueous phase of a system containing water. it becomes distributed in three sites. 2-3 Emulsion polymerization [7]. If termination occurs. .2.6). such as chain transfer agents. and much practiced today in industry. normally less than 50 nm. diffusion through the aqueous phase. 2. such as monomer droplets. which act as the nucleus for further polymer growth.2. the particle will then remain “dead” until another radical enters and initiates a new chain. The solubilization of the monomer in the micelles and the mechanism of growth of the polymer particles are depicted in Fig. With polymerization taking place within a particle and fresh monomer entering.2. 2-3. Stability is maintained by further adsorption of surfactant molecules at the surface. but can be a limit on other processes (Sect.4. Polymerization will continue within the particle until either all of the monomer has been depleted or another radical enters the particle and terminates the growing chain. to enter the growing polymer particles.20 2 Synthesis of Polymer Dispersions Fig. the particle obviously increases in size during the process. the monomer within a growing particle will be replenished by diffusion from the droplet through the aqueous phase and into the particle. along with other mechanisms discussed in Sects 2. Other sparingly water-soluble ingredients. solution in water.3 and 2. is the use of preformed polymer particles of very small and uniform size. An alternative to micellar nucleation. these “oligomeric radicals” increase in hydrophobicity and hence the probability of entering a monomer-swollen micelle increases. As long as there is a source of monomer outside the micelles. This is known as seeded emulsion polymerization. Diffusion of molecules into particles is not usually a limiting step in the overall rate of polymerization. follow the same route. the driving force being the affinity of the monomer for the polymer. As monomer units are added on. A radical which enters a micelle will then continue to add on monomer using the reservoir within. termination of the chain will occur almost instantly. This gives rise to an increase in the overall rate of polymerization in the system (region 3). and an entering radical can co-exist with an already growing chain. the monomer concentration in the swollen particles. with a constant number of particles at a constant temperature. and chain entanglement and cross-linking all contribute toward reduced mobility within the particle. assuming an active radical is present. the rate of polymerization is dependent on the particular monomer and the concentration of monomer in the monomer-polymer mixture. and with an av– .2. As long as there is a 21 . and is referred to as the gel effect. Figure 2-4 shows this relationship. During this period the average number of radicals per particle can be much less than unity. giving the overall rate of polymerization in mol s–1. the swollen size of the particles being limited by entanglement and crosslinking of polymer within the chain and by hydrodynamic forces and interfacial tension. viscosity of the mixture increases. While the particles are small and still have high concentrations of monomer. therefore. It then remains at this value until overall conversion reaches 50–60 %. following which a period occurs during which the entry rate of free radicals into particles is less than the exit rate (region 1). then drops rapidly when polymerization begins. the average number of radicals per particle does not usually exceed two. when a radical enters a particle which already contains a growing polymer radical. It is evident that. that is the average number of radicals per particle is about one half. As particles grow larger and the polymer/monomer ratio increases. that is. On average. the overall rate will change according to the average number of radicals per particle and the monomer concentration in the particle. the overall rate of polymerization erage number of radicals per particle denoted by n is given by: R = k p ⋅ N ⋅ n ⋅ [M ] [M].2 Chemistry Within an individual particle. where exit of radicals from particles becomes negligible. Typically the weight fraction of monomer in the monomer-polymer mixture is limited to about 0. Monomer concentration starts off at one hundred percent in the monomerswollen micelles. kp. The rate of addition of a monomer molecule onto a growing polymer chain is known as the propagation rate of the monomer. The polymer formed is not infinitely swellable. Thus in a system with N total particles. a maximum of one growing radical is thought to exist per particle. where they describe three regions. Region 2 is quickly reached. Smith and Ewart [3] developed an early quantitative theory to predict the rate of polymerization in an emulsion system. only one half of the total number of particles will be actively polymerizing at any given instant. In this case termination is not instantaneous. diffusion of radicals within the particles and mobility of the polymer chains is unrestricted. In a styrene-butadiene system. is normally expressed as mol L–1. Under these circumstances. distances within the particle become greater. this being temperature dependent with increasing temperature giving increasing propagation rate.45 maximum. Typically there is a short induction period as the flux of free radicals builds up. but with butyl acrylate polymerization values of twenty and higher often occur. reaching zero at one hundred percent conversion.45. the rate of reaction increases as n constant rate period. very shortly after the start of polymeriza– and [M] become constant. . At around sixty percent conversion. 2-4 n . the weight fraction in the particles will remain at 0.4 1. Fig. This is followed by a induction period.Av.6 0.2 1 0.6 1. with the excess in the form of monomer droplets. In his book on emulsion polymerization. 2-4 and 2-5 that. The normal type of conversion-time curve for a batch polymerization is shown in Fig.6 0.8 0.2 0 0 20 40 60 80 100 % Conversion greater quantity of monomer in the total system. 2-5. which thereafter decreases. Blackley [4] gives a comprehensive review of the development of the theory of the subject. both n sult of this is a constant rate of polymerization over this period. usually to beyond 50–60 % conversion.2 Synthesis of Polymer Dispersions Typifying the variation of average number of radicals per particle with conversion.8 0. (SB system).4 0. Weight Fraction Monomer M/(M+P) 22 1 0.4 0. the rate often shows an in– has a greater influence than decreasing [M]. radicals/particle 1. 2-5 0 0 20 40 60 % Conversion 80 100 It can be seen in Figs. where an increasing n decreasing monomer concentration has the biggest influence on rate. After a short – increases. This is depicted in Fig. 2-6. Fig. When the monomer droplets have been exhausted.2 Typical monomer concentration in the polymer particles as a function of conversion. the weight fraction of monomer in the particles will reduce. The retion. Finally the crease. Wm2 … are the weight fractions of the different monomers making up the final polymer composition. being normally greater than five percent of the final polymer composition. Tg1.2 Major Monomers The major monomers are considered as those that make up the bulk of the final polymer chains. either by themselves to give homopolymers containing recurring monomer units of the same type or. 100 % Conversion Fig. A large number of major monomers are used in emulsion polymerization. Table 2-2 lists a number of widely used major monomers in order of increasing Tg. 2-6 80 60 40 20 0 0 1 2 3 4 5 6 7 8 9 10 11 Time h 2.2 Chemistry Conversiontime curve for a typical batch emulsion polymerization. with 1. Tg. Generally. The Tg of polymers made up from mixtures of different monomers can be approximated by use of the Fox equation [5]: 1 Wm1 Wm2 W = + + … + mn Tg Tg1 Tg2 Tgn where Tg refers to the final polymer. a copolymer can be made with any desired Tg in the 23 .2. This is the temperature at which the polymer changes from a glassy state to an elastomeric material.3. which are generally used at levels of less than five percent of the total composition. more frequently. and which are used to impart certain special properties to the latex or polymer.3-butadiene and methyl methacrylate as monomers. One of the major determining factors in the choice of a monomer is the glass transition temperature. and Wm1.2. Tg2 … refer to the individual homopolymers. However. 2. the different reactivities of free radicals with different monomers does lead to uneven distribution of monomers throughout the polymer chains. of the homopolymer. as mixtures giving copolymers (two different monomer units). discussed in Sect. It can be seen that. a change that takes place over a relatively narrow temperature range. Not included here are the so-called functional monomers. free-radical polymerization is a random process with the different monomer units distributed randomly in the polymer molecules. terpolymers (three different monomer units) or polymers with even higher order.2. acrylonitrile can impart solvent resistance. A third alternative. cis-1. As a polymer latex dries and the water evaporates. characterized by having two C=C double bonds. This can occur in one of three different ways: First. Figure 2-7 shows these three possibilities. The presence of this second double bond results in both differences in the polymerization mechanism of a diene relative to a vinyl monomer and in the subsequent behavior of the polymer. During free-radical polymerization.4 and there are two possible isomeric forms. by a process of electron transfer. the movement of molecules is too restricted to allow this interpenetration between particles. One of the important attributes of polymers which is related to the Tg is the film-forming temperature. normally very close to the Tg. This repeat unit is called 1. Many other polymer properties are of importance.4 with the carbon atoms of the double bond on opposite sides of the chain. For example. This incorporation is known as 1. and trans-1.3butadiene is a member of the diene group of monomers. if the polymer is at a higher temperature than the Tg then the molecules in an individual particle have enough freedom of movement to penetrate and intertwine with molecules in an adjacent particle.24 2 Synthesis of Polymer Dispersions Tab. Monomer Structure 1. are characterized by having only one C=C double bond. the remaining C=C double bond being between carbon atoms 2 and 3.2. with the butadiene linked into the chain through carbon atoms 1 and 2. and a coherent film cannot form. All of the monomers listed in Tab. 2-2 Some major monomers used in emulsion polymerization. has the C=C double bond hanging off the chain as a pendant vinyl group. Isoprene is another common diene monomer. 2-1. acrylates tend to give good heat and light aging properties. In this way. Of course in the design of a polymer.4 with the carbon atoms of the double bond both on the same side of the backbone chain.3-Butadiene n-Butyl acrylate 2-Ethylhexyl acrylate CH2=CH–CH=CH2 CH2=CH–C(O)–O–(CH2)3–CH3 CH2=CH–C(O)–O–CH2– CH(CH2CH3)–(CH2)3–CH3 CH2=CH–C(O)–CH3 CH2=CH–O–C(O)–CH3 CH2=CH–Cl CH2=CH–CN CH2=CH–(C6H5) CH2=C(CH3) CH3C(O)–O–CH3 Methyl acrylate Vinyl acetate Vinyl chloride Acrylonitrile Styrene Methyl methacrylate Normal b. (°C) Tg of homopolymer (°C) –4. Below the Tg. the butadiene molecules become incorporated into the polymer chain through one of the C=C bonds. the choice of monomers is not only made on the basis of the required Tg. vinyl chloride may be used where fire retardency is required. However.4 148 –85 –54 216 80 73 –13 77 145 100 –50 10 32 81 97 100 105 range –85 °C to +105 °C. . Isoprene can be incorporated in four different ways. and are known as vinyl monomers.p. apart from one. 1. the polymer can form a coherent film. the molecule can be linked into the chain through carbon atoms 1 and 4. acrylonitrile or methyl methacrylate Low Tg monomers like n-butyl acrylate or butadiene Avoid crosslinking.3. On the negative side. butadiene Use 2-ethylhexyl or hexyl acrylate Use crosslinking monomers N-methylol(meth)acrylamide.2.4 H n H * The presence of these additional C=C bonds in the polymer. generally referred to as unsaturation.2 (pendant vinyl) H C * H C H Hn trans -1. Some ways in which desired properties can be achieved are shown in Tab.2 Chemistry Possible methods of incorporation of butadiene during free-radical polymerization.4 * H H H C H H C H C C C H H * C * C n C H H C C H H 1. Fig. so that crosslinking actually occurs during propagation. the 1. molecular weight and distribution. Desired property Possible polymer design Stiffness Soft hand Tackiness Water resistance Use methacrylates..2 pendant vinyl groups compete with monomer for addition onto a growing free radical. can be of benefit or it can be deleterious to polymer properties. This can be controlled to some degree by the choice of process conditions (Sect. gel and crosslinking. styrene Use n-butyl acrylate. Use hydrophobic monomers like n-butyl acrylate or styrene Crosslinking monomers and/or acrylonitrile High Tg monomers like styrene. the residual double bonds being attacked by oxygen. The process of vulcanization uses controlled amounts of sulfur to achieve a desired degree of crosslinking and producing a thermosetting polymer. Also. Of course this Table only shows a few possibilities in polymer Tab. acrylonitrile. 2. crystallinity. 2-7 * cis -1. eventually leading to yellowing and brittling of the polymer. 2-3 Some aspects of polymer design through composition. UV radiation etc.2). The general characteristics that control a polymer’s behavior are basic chemical composition. 2-3. ethyl acrylate. but cannot be completely eliminated. the presence of unsaturation in diene polymers leads to inferior heat and light aging properties relative for example to acrylics. The double bonds in the backbone chain can be used to give controlled crosslinking between chains. Use thermoplastic monomers like styrene Use high amounts of polymerizable acids like acrylic acid Resistance to organic solvents High tensile strength High elongation Thermoformability High alkali swellability 25 . glass transition temperature. during free-radical polymerization. The ions and counterions are referred to as the electric double layer and the thickness of this layer is very dependent on the pH of the continuous medium. 2. with Itaconic and Fumaric acids as common dibasic acids. It should be noted that the presence of watersoluble polymer in the latex could also contribute strongly to viscosity increase with increasing pH. typically 2–5 % of the dry polymer. so that the particle surface has a negative charge at each acid site (–COO–). not just adsorbed at the particle surface.2. Acrylic and Methacrylic acids are the most widely used monobasic carboxylic acids. particles repelling each other due to the like charges. each with variations in molecular weight. These acids.. At low pH (high H + concentration) the layer is compressed and at its minimum thickness. 2-4 Commonly used functional monomers. Tab. The negative charge at the surface imparts a high degree of stability to the polymer particles. the layer of negative ions is balanced by an adjacent layer of cationic counterions.3 Functional Monomers Certain monomers are characterized as functional monomers. Functional monomer Structure Acrylic acid Methacrylic acid Itaconic acid Fumaric acid Hydroxyethyl acrylate Acrylamide CH2=CH–C(O)–OH CH2=C(CH3)–C(O)–O–H CH2=C(C(O)–OH)–CH2–C(O)–O–H H–O–C(O)–CH=CH–C(O)–O–H CH2=CH–C(O)–O–CH2–C(OH)H2 CH2=CH–C(O)–NH2 . There are vast numbers of different potential combinations of monomers available to choose from. The acid group is ionized in water. branching. but due to the highly polar carboxyl group (COOH) tend to be at the surface of the polymer particles (polymer-water interface) with the carboxyl group orientated toward the aqueous phase. due to stretching of the chains. and is one reason for increasing viscosity as pH increases. The thickness of this double layer contributes to the effective diameter of the latex particle. giving almost infinite possibilities in the balance of properties obtained.26 2 Synthesis of Polymer Dispersions design. This stabilizing influence is the same as that produced by surfactants. the layer expands outward from the particle. participate in the free-radical polymerization and become incorporated in the main polymer. but with the added advantage that the carboxylic acid is bound into the polymer chains. through the C=C bond. They are normally used in relatively small amounts. As the pH is increased (reducing H + concentration). crosslinking etc. To maintain overall electrical neutrality across the interface. so called because in addition to having the polymerizable C=C double bond they contain a functional group such as a carboxylic acid or amide. These monomers are important because they can impart special properties to both the polymer and the colloidal system. Table 2-4 lists some of the commonly used functional monomers. 1. reducing incorporation into the polymer and at worst.1. which gives an ionic crosslink between carboxyl groups. surface tension reaches a minimum then begins to increase. interfacial tension reaches a minimum and osmotic pressure almost plateaus. A key phenomenon observed with surfactants is a marked change in a number of physical properties of an aqueous solution that takes place at a certain critical concentration. The optimum choice of surfactant for one role may produce undesirable performance in other roles.2 Chemistry In addition to the greatly enhanced mechanical stability imparted to the emulsion by these functional monomers. stability to electrolytes is generally improved. Below this concentration. These high molecular weight polyelectrolytes can act as very effective coagulants for the latex. for example zinc oxide. as with acrylic and methacrylic acids. surfactant molecules are in normal random solution in the water. The break in the behavior of solution properties represents the change from a true solution to a colloidal solution. forming the primary sites for nucleation – stabilization of growing polymer particles – enhancement of application properties of the finished latex A single surfactant may satisfy all three roles. Mechanical strength of the polymer films is increased. and the number of molecules of surfactant which form one micelle is called the agglomeration number. with ionic surfactants. 2. Polymerization of the acid functional monomers is usually carried out under conditions of relatively low pH. a compromise is often required in the choice of surfactant. as is filler tolerance of the latex. For example. The main characteristic of a surfactant is that its molecular structure consists of two parts. phenol-formaldehyde. normally considered to be spherical but other geometry such as lamellar is also possible. The presence of the carboxyl groups also allows crosslinking through the use of urea-formaldehyde. Addition of further surfactant above the CMC all goes toward increasing the number of micelles. and in fact can be increased further by the use of. surface-active materials are normally an essential ingredient in emulsion polymerization. or there may be a requirement for multiple surfactants. The concentration of surfactant at which this change takes place is known as the Critical Micelle Concentration (CMC). melamine-formaldehyde and various epoxy resins. 2.2. They can be used in any or all of the following roles: – micellar solubilization of monomers. the surfactant molecules aggregate into ordered clusters known as micelles. Neutralization of the acid favors partitioning in the aqueous rather than the organic phase. equivalent conductivity exhibits a sharp reduction. As the critical concentration is reached. the formation of polyacrylic acid salts in the aqueous phase. a lyophobic (solvent hating) portion and a lyophilic (solvent loving) por- 27 .2. where homo-polymerization of the acid is a possibility.4 Surfactants As first discussed in Sect. and there may be positive or negative synergism exhibited when multiple surfactants are used. As with many other aspects of emulsion polymerization. although other structures are possible. sulfate. often polyoxyethyleneated long chain alcohols or alkylphenols. alkylnaphthalene residues.6 × 10–1 4.3 × 10–5 9. long chain alkylbenzene residues. The effect of increasing linear alkyl chain length in a series of sodium alkyl sulfonates is Tab. where the hydrophilic group has a negative charge. with both positive and negative charge on the hydrophilic group.7 × 10–3 2. because of the source of the alkyl group. the presence of an aromatic group or the incorporation of propylene oxide units. The hydrophobic portion of a surfactant is usually a longchain hydrocarbon or oxygenated hydrocarbon. – Cationic. these two groups are referred to respectively as hydrophobic and hydrophilic. Anionic and cationic surfactants are not compatible with one another.5 × 10–3 7. rosins and high molecular weight propylene oxide polymers.3 × 10–5 . The hydrophilic group is either ionic or highly polar. sulfonate and phosphate groups. Certain zwitterionics become cationic at low pH and anionic as the pH is increased. and in most cases. When the solvent is water. 2-5 Some structural influences on surfactant properties (Rosen [6]).6 × 10–3 1. with no charge on the hydrophilic group.8 × 10–3 5. branching or unsaturation. The alkyl groups are generally 3–20 carbon atoms long.9 × 10–5 7. – Non-ionic. with or without incorporation of ethylene oxide units. The properties of the surfactant depend on the length of the hydrophobic group. Surfactants are classified according to the nature of the hydrophilic group of the molecule: – Anionic. Some of the structures that can make up the hydrophobic group are straight or branched long alkyl groups. Surfactant Formula Agglomeration number / T (°C) CMC at 40 °C (mol L–1) Sodium octyl sulfonate Sodium decyl sulfonate Sodium dodecyl sulfonate Sodium tetradecyl sulfate Sodium hexadecyl sulfate Sodium dodecyl sulfate Branched sodium alkyl sulfate Sodium dodecyl ethoxylate (2EO) Dodecyl alcohol ethoxylate (5EO) Dodecyl alcohol ethoxylate (7EO) Dodecyl alcohol ethoxylate (8EO) C8H17SO3– Na+ C10H21SO3– Na+ C12H25SO3– Na+ C14H29SO3– Na+ C16H33SO3– Na+ C12H25SO4– Na+ C12H25CH(SO4– Na+)C3H7 C12H25(OC2H4)2SO4– Na+ C12H25(OC2H4)5OH C12H25(OC2H4)7OH C12H25(OC2H4)8OH 25 / 23 40 / 30 54 / 40 80 / 60 1. Long chain quaternary ammonium salts and long chain amines and amine salts. the hydrophobic/hydrophilic balance being controlled by the number of moles of ethylene oxide.0 × 10–2 1.1 × 10–2 2. Rosen [6] discusses the influence of different hydrophobic and hydrophilic groups in detail. – Zwitterionic. Non-ionic and zwitterionic types are compatible and can be used with either anionics or cationics. Examples are carboxylic.28 2 Synthesis of Polymer Dispersions tion. where the hydrophilic group has a positive charge. a particular surfactant will actually be a mixture of various chain lengths.0 × 10–4 8. Table 2-5 gives an example of the influence of some different structures on agglomeration number and CMC. 2 Chemistry seen. – Salts of sulfated linear alcohols. but the use of cationics and anionics in the same equipment is generally avoided. Below pH 7. normally being used at pH 10–12. Cationics are used in polymerization for some applications. for a specific surfactant the number of polymer particles initiated is approximately proportional to [surfactant concentration]0. anionic and non-ionic surfactants are the most common choice during the polymerization stage. Seeded processes significantly reduce this variation and eliminate the requirement for the initial surfactant. Overall. Addition of too much surfactant during polymerization can. Inclusion of the sulfate anion on a non-terminal carbon atom increases the CMC. In emulsion polymerization. These materials are only useful at pH values greater than 7. for example temperature. if the CMC is exceeded. 29 . as a general rule. Some common surfactants used in emulsion polymerization are: – Sodium and potassium salts of naturally occurring fatty acids (oleic. The difficulty of balancing nucleation and stability is exacerbated by the fact that many factors influence nucleation.2. the insoluble acids are precipitated. which give improved electrolyte stability and are not subject to hydrolysis in acid media as are the sulfated alcohols. usually polyoxyethyleneated. Then. balancing the two requirements can be difficult. It is possible to produce an emulsion polymer with either an anionic or a cationic surfactant. and the introduction of polyethylene oxide (2 mol) into the sulfate reduces CMC. For micelle formation. – Salts of alkylphosphates. with seeded processes. Sodium dodecylbenzene sulfonate is widely used. Zwitterionics are not common in emulsion polymerization. linoleic) and rosin acids. It is therefore often the case that the amount of surfactant required to give the desired ultimate particle size is insufficient to provide continued stabilization as the particles grow. and all stabilizing function is lost. the total amount of surfactant is often considerably less than with micellar nucleation.6. and as a consequence it is usually necessary to add additional surfactant as polymerization progresses. – A range of the salts of alkylbenzene sulfonates and alkylnaphthalene sulfonates. Finally. If the surfactant is serving the dual purpose of providing nucleation sites and subsequently stabilizing the growing particles. cause another family of particles to be initiated. This can occur almost anywhere within the normal particle size range. the concentration of surfactant must be at or above its CMC. pH and any impurities that either retard or increase polymerization. and subsequently switch to an oppositely charged species along with a controlled pH change. concentration of initiator/surfactant/electrolyte. are widely used in the emulsion polymerization of functionalized styrene–butadiene polymers and many acrylic esters. increasing the moles of ethylene oxide in the non-ionic series of polyoxyethyleneated straight chain alcohols is seen to increase the CMC. increasing carbon number giving rise to reducing agglomeration number and CMC. These soaps are used in large quantities in the production of styrenebutadiene latex for both dry rubber production and latex applications. The sulfate group is seen to give a lower CMC than the sulfonate. for example sodium lauryl sulfate. Unfortunately as a general rule.5 Initiator Systems The initiator system in emulsion polymerization is the source of free radicals. and even to a large extent nucleation. where the molecule contains a polymerizable C=C double bond. persulfates can still be used in conjunction with a reducing agent such as sodium bisulfite. Light or other radiation can generate free radicals. sodium and potassium persulfate and a wide range of organic peroxides and hydroperoxides. The three persulfates have a similar half-life and their effectiveness in emulsion polymerization is therefore also similar. the choice of surfactant is usually not too critical. where the length of the alkyl group and the moles of ethylene oxide can be varied.) are often caused. the lower water solubility of the potassium salt makes it less commonly used than the others. known as “polymerizable surfactants”. the presence of surfactant in the final dry polymer causes reduced water resistance. etc. In an attempt to mitigate against migration of surfactant. Also. By far the most common thermal systems are peroxy compounds. This list is by no means exhaustive. and production of free radicals takes place in the aqueous phase of the emulsion. From the aspect of particle stabilization during the emulsification process. substances which thermally decompose to produce free radicals and substances which produce free radicals when part of a redox system. The . However. 2. loss of tack. and can provide an appropriate choice for most normal polymerization temperatures. By far the biggest factor in the choice of surfactant is the application performance of the final product.30 2 Synthesis of Polymer Dispersions – non-ionic surfactants in wide use in emulsion polymerization include polyoxyethyleneated alkylphenols and straight chain alcohols.) Examples are the Noigen and Hitenol series of products from DaiIchi Kogyo Seiyaku (polyethoxylated alkylpropenyl phenyl ethers and polyethoxylated alkylpropenyl phenyl ether sulfates respectively). defined as the time taken at a particular temperature for the concentration of a solution of the material to reduce to one half of its initial value through thermal decomposition. This again demonstrates the compromise often necessary in emulsion polymer synthesis. The rate of decomposition of these materials is usually specified by the “half-life”. Persulfates are generally used for polymerization in the temperature range 50–100 °C. where deleterious effects (cloudiness at the surface. there is a tendency for surfactant molecules to diffuse to the polymer/air or polymer/substrate interface. and polyoxyethyleneated polypropylene glycols. At lower temperatures. (This is a functional monomer because it does not form micelles. there are certain products available. ammonium. there being an almost limitless choice of surfactants or combinations of surfactants available.2. decomposition is usually too fast to give efficient use of the free radicals due to radical recombination. but is not widely used for emulsion polymerization. The organic peroxides and hydroperoxides cover a wide range of half-life. At higher temperatures. block copolymers where the moles of ethylene and propylene oxides can be varied to adjust the hydrophilic/hydrophobic balance. There are two major types of system used. the faster that initiation occurs. the peroxides and hydroperoxides are used at lower temperatures. along with their half-life. it adsorbs surfactant from solution thus reducing the possible number of micelles in the system.27 8.2 14 90 °C 0.55 0.2 70 110 °C 0.29 1. Half-life (h)1 Substance Dicyclohexyl peroxydicarbonate Ammonium persulfate Dilauryl peroxide Dibenzoyl peroxide t-Butyl peroxybenzoate Dicumyl peroxide Cumene hydroperoxide t-Butyl hydroperoxide 40 °C 50 °C 70 °C 18 4. Table 2-6 lists some of the commonly used thermally dissociating initiators. then the greater will 31 . An organic peroxide decomposes as follows: ROOR → 2RO• and the reduction of a hydroperoxide by iron(II): ROOH + Fe2+ → RO• + HO– + Fe3+ During the nucleation stage of emulsion polymerization. according to the mechanism: S2O82– → 2SO4–• SO4 + H2O → HSO4– + HO• 2OH• → H2O + 1⁄2O2 –• It is generally accepted that the primary initiating species is the sulfate anion radical. An initiated particle grows very rapidly as polymer is formed.13 6 23 570 130 °C 150 °C 0.2 Chemistry Tab.26 20 70 1 Approximate values only. pH and the presence of other components can significantly influence decomposition differing solubilities in water also determine if the free radicals are produced in either the aqueous or the monomer phase. as a part of a redox system. The thermal decomposition of persulfate produces both sulfate and hydroxyl radicals. it is expected that most polymer chains would contain two sulfur atoms. and to the extent that termination is predominantly caused by another sulfate initiated radical species. the concentration of initiator exerts an influence on the number of polymer particles formed.3 100 520 0. 2-6 A range of thermally dissociating initiators (from manufacturers’ product literature). As the particle increases in surface area.7 2. This is generally found to be the case.2. Most commonly.1 192 50 0. On the negative side. these sulfate groups also increase the water sensitivity of dried polymer films.4 3. Often persulfates are chosen in preference to the organic peroxides because of the increase in colloidal stability that results from the sulfate end groups on the polymer chains. 0–50 °C. Therefore. that a plot of log [S] against log [M]. 2. should be a straight line with slope ε. One entering radical initiates polymerization. As stated. which is the ratio of rate of the chain transfer step to the propagation step: Ks R–M(n)–SH + R• R–M(n) • + R–SH → • Kp R–M(n) + M → R–M(n + 1)• Ks =ε Kp It can be shown that. 2.2. not the rate of radical production.4. In general. the time available for a polymer chain to grow is dependent on the rate at which free radicals enter the particle. This is because the rate-determining step for mercaptan consumption can often be the diffusion of mercaptan through the aqueous phase into the reaction zone in the polymer particle. the greater will be the rate of radical production and the shorter the initiation period. Because the thermal decomposition of the initiator is first order with respect to its concentration.32 2 Synthesis of Polymer Dispersions be the number of polymer particles formed before micellar surfactant is exhausted. subsequent changes in the initiator concentration (assuming a certain minimum) have little effect on the rate of polymerization.6 Other Ingredients The use of chain transfer agents in emulsion polymerization was briefly discussed in Sect.2. rosin acid salts. the higher the concentration. ε. neglecting all other reactions of monomer and chain transfer agent.1. where [S] and [M] are the concentrations of modifier and monomer respectively. and therefore the consequent rate of polymerization is also proportional to [Initiator]0. because.2. the next normally terminates the chain. This is due to the fact that the number of particles remains fairly constant. 4-vinylcyclohexene (butadiene dimer) amongst many others. Although this effect on molecular weight is significant. for example carbon tetrachloride. The number of polymer particles formed is approximately proportional to the concentration of initiator to the power of 0. 2.1. The effectiveness of a chain transfer agent is denoted by its transfer constant. which may also include impurities in other raw materials. the higher the rate of production of radicals and the higher the rate of entry of radicals into a particle. the overall rate of polymerization is proportional to the number of polymer particles. This linear relationship is generally found to hold true in emulsion polymerization. chain transfer agents often exerts a bigger influence. However. the fewer the number of carbon atoms in the alkyl group of the . neglecting other influences. but the slope is often not equal to ε as determined from bulk polymerization.4. although a wide range of other compounds also exert a modifying effect during polymerization. the most commonly used chain transfer agents are the mercaptans (thioalcohols) RSH. The molecular weight of the polymer is however influenced by the initiator concentration. The higher the concentration of initiator. after completion of the nucleation stage. As discussed in Sect. and the average number of radicals per particle is dependent on the environment within the particle. certain disulfides. usually when a dried polymer film is heated). Cross-linking then takes place between two methylol groups. the closer the apparent transfer constant in emulsion polymerization becomes to that measured in bulk (faster diffusion). | | CH2–CH–C(O)–NH–CH2–NH–C(O)–CH–CH2  Electrolytes. the number of cross-links introduced would be less than one per thousand monomer units. either to form cross-links during the polymerization (increasing the gel in the polymer. The structure of N-methylolacrylamide is as follows: CH2=CH–C(O)–NH–CH2–OH Incorporation into the polymer backbone takes place through the vinyl double bond. or increasing the so-called “green strength”) or to form cross-links subsequent to polymerization. two commonly used monomers are N-methylolacrylamide and N-methylolmethacrylamide. Finally. so one can see that. Thus the short chain modifiers tend to exert a greater modifying influence during the early stages of a batch emulsion polymerization. the overall effect of the chain transfer agent can also be controlled by making injections at appropriate times during polymerization. when a diene is one of the monomers in an emulsion polymerization. other monomers that are commonly used to produce cross-links during the polymer formation are divinyl benzene and a range if diacrylates and triacrylates. <0. and this is an additional means of controlling the number of polymer particles formed. To introduce heat sensitivity into the polymer (cross-linking which occurs after polymerization. whereas the longer chain alkyl groups tend to be more effective toward the end of polymerization. for example butanediol diacrylate and trimethylolpropane triacrylate. These materials would normally be incorporated at low levels. This means that the shorter chain mercaptans tend to disappear more quickly than the longer chains. especially during the polymerization process. As previously discussed. electrolytes are often used as part of a buffer system to minimize pH variation during polymerization. Electrolytes are also used to reduce the viscosity of the polymer emulsion. or with semi-batch reactions by having continuous (linear or non-linear) feeds of modifier. In the absence of a diene. Of course. by heat application or chemical means. most often alkali metal phosphates or sulfates. High concentrations of electrolytes will generally cause de-stabilization and agglomeration of polymer particles. When present in a micelleforming surfactant solution.1 weight percent of the monomer. the second double bond in the diene will lead to a considerable degree of cross-linking during the polymer formation. electrolytes can increase the aggregation number of the micelles (the number of soap molecules per micelle). are utilized in emulsion polymerization systems for a variety of reasons. on average. Thus with increasing electrolyte concentration the number of micelles is reduced. an effect that is achieved through compression of the electric double layer. hence the very common use of n-dodecyl and t-dodecyl mercaptans. Polymerizable cross-linking agents are often included in emulsion polymerization recipes. C12 chains often show the best balance between these extremes. 33 .2.2 Chemistry mercaptan. some type of filtration or screening to remove any coagulum from the latex and a final stage where post additions of other ingredients may be made along with final adjustment of latex properties such as pH and solids content. A plug-flow continuous reactor is one in which the reacting mixture passes through the reactor without any forward or backward mixing. Occasionally there may be a concentration of the latex to reduce the water content. 2. semi-batch or continuous. the product from one being the feed for the next in the chain. Distance along the reactor is equiva- . a purification stage to remove residual organic volatile components. particularly calcium.3 Manufacturing Processes 2. in emulsion polymerization recipes. In a batch emulsion polymerization. and for some processes there may be some purification of raw materials. The greater the number of CSTRs in a chain. magnesium and iron. The processes differ not only in equipment type and economics of operation but also in the specific properties imparted to the polymer and the emulsion. and often gives more consistent initiation of polymerization. Here the conditions in the reactor remain constant with time. generally leads to lower coagulum levels in the final latex. or multiple CSTRs in a chain. the production of emulsion polymers is relatively simple in terms of the unit operations required. where the reactants continuously enter a stirred vessel and the product continuously exits. all ingredients are added to a vessel. There may be only one CSTR. the closer the properties approach those from a batch reaction. stirred-tank reactor. In low temperature systems with redox initiators. In this type of system. a chelating agent is often a part of the redox system.3. or recovery and recycling of raw materials. conditions in the reactor gradually change from monomer + water → polymer + water. polymerization is initiated and the reaction proceeds to completion over a period of time. Use of this compound to chelate metal ion impurities in the system. normally a salt of ethylenediamine tetraacetic acid (EDTA). used to complex the iron component and prevent precipitation. the composition being equal to the exit composition. The use of a chelating agent protects against the “hardness” salts. at any given position in the reactor. Industrial chemical processes are categorized as batch. and the manufacture of emulsion polymers is carried out in all these process types. It is fairly common practice in the manufacture of emulsion polymers at higher temperatures to use untreated (non-deionized) water as the continuous media. as for example in a tubular reactor. Typically there is a reaction stage.1 Types of Process Compared with many other types of chemical manufacture. where the polymer is made. passing through all intermediate ratios of monomer/polymer. the composition is constant with time.34 2 Synthesis of Polymer Dispersions It is common to include a chelating agent. Thus. A continuous polymerization may be carried out in a continuous. Figure 2-8 shows the typical progression of the monomer/polymer composition profile in these main process types and Fig. conditions in the reactor change rapidly when the feeds start (monomer → monomer + polymer). (D) continuous plug flow. The reactor type and the process conditions exert large influences on the resulting properties as discussed in Sect. only a portion of the total ingredients is added to the reactor initially.3.4) semi-batch is the preferred manufacturing process. heavy fouling of the reactor and the difficulties of cleaning. Although emulsion polymerization in a continuous tubular reactor has been the subject of much research in the past. 2-9 is a diagrammatic representation of the processes. alcohols from hydrolysis of vinyl esters. Fig. 2. products formed from 35 .3.2. polymerization is initiated and the remainder of the ingredients is added over a period of time until the desired filling volume is reached. as are combinations of the processes. 2.2. along with volatile impurities from many sources. Such impurities may include a range of solvents originating from various raw materials. The material is then discharged and the process repeated. and change rapidly again when the feed stops (monomer + polymer → polymer). dimers and co-dimers either present in monomers or formed during the polymerization. (A) (B) 100 % Conversion % Conversion 100 80 60 40 20 0 80 60 40 20 0 0 1 2 3 4 5 6 0 1 2 3 (C) 5 6 (D) 70 100 60 CSTR 5 50 CSTR 4 40 30 CSTR 3 20 CSTR 2 10 CSTR 1 % Conversion % Conversion 4 Time Time 80 60 40 20 0 0 0 Reactor number in chain 1 2 3 4 5 6 Distance along reactor Variation of monomer/polymer in different processes expressed as % conversion of added monomer: (A) batch.3 Manufacturing Processes lent to time in the batch reactor. (C) chain of five CSTRs. (B) semi-batch. For safety reasons (Sect. 2-8 There are novel variations of these processes in use. In the semi-batch process. In a semi-batch process. remain relatively constant for the majority of the feed period. The product from emulsion polymerization reactors usually contains a small amount of non-reacted monomers. this process is not commonly used because of the poor degree of mixing. (b) semi-batch. it is normal to further polymerize this residual monomer.36 2 Synthesis of Polymer Dispersions Feed Feed Final Level a) b) Initial Level Product Product Product c) Feed Feed d) Product Types of process used for emulsion polymerization: (a) batch. physical separation techniques are often employed. (c) continuous stirred tank (chain of three). Of course many of the organic impurities are either not polymerizable or cannot be polymerized under typical emulsion polymerization conditions. the rate of polymerization is relatively slow. so that the residual monomers are often <1 %. and with reactor time normally being at a premium this “chemical stripping” is carried out in separate. In some cases. (d) continuous plug flow (tubular). Fig. In many cases. solvent extraction. membrane separation or adsorption processes may be used. Because of the low monomer concentration at this stage. and a whole range of saturated and unsaturated organics coming from the monomers. polymerization is taken to a high degree of conversion in the reactors (>99 %). Steam distillation is the most widely used technique. lower cost equipment. either in batch strippers or in continuous processes such as a column stripper. . 2-9 organic initiators. often using a redox initiator system. To remove these contaminants. However. Slow feed rates (monomer starved) lead to high branching and crosslinking. Centrifugation is also used. residual butadiene is flashed off under vacuum. and final adjustments to properties such as pH and solids content are carried out usually in simple stirred tanks. With such large amounts of residual monomer. filter presses to quite complex selfcleaning filters of various types. the system is monomer flooded and the product will be close in properties to the batch reaction. in order to limit the crosslinking reaction from the pendant vinyl groups in the butadiene units. a batch process. A semi-batch process can be operated at both ends of the scale. both with and without the use of filter aids such as diatomaceous earth. With very fast feed rates. After the polymerization stage.3. there still exists the need to remove coagulum during various stages of the process. are competitive and dependent on the relative quantities of monomer and polymer at the reacting site. will give the least branched polymer with the lowest degree of crosslinking. 2. Because many of the chemical reactions occurring during emulsion polymerization. economics force the recovery and recycling of both butadiene and styrene. Post additions to the latex product. and although much progress has been made in the industry to minimize these problems. band filters. Increasing the number of CSTRs in a chain will lead to a reduction in branching and crosslinking. Crosslinking increases rapidly as con- 37 . condensed and also returned to the reactor. compressed. from simple filter bags and static screens through wiped screens.1. typically 70–80 %. The opposite end of the scale is represented by a single CSTR operating at a high conversion which will tend to give a highly branched and crosslinked polymer.3 Manufacturing Processes The production of styrene-butadiene rubber emulsions is one case where polymerization is deliberately stopped at a low conversion. and styrene is steam stripped in a column stripper. given the same reaction temperature. cooled and returned to the reactor feed. which has the highest average monomer concentration through the process. In particular. the density difference between polymer and the disperse medium is too small to make this an efficient process. such as branching. Therefore. the three main types of reaction process differ in the monomer/polymer concentration profile throughout the reaction. improved control of process parameters). better stabilization systems. it can be seen that all of these will be influenced by reactor type. Coagulum formed during the manufacture of emulsion polymers can cause problems with application processes. the influence of monomer/polymer ratio is highly significant.2 Influence of Process Conditions on Polymer/Colloidal Properties As shown in Sect. 2. Branching and crosslinking are favored at high polymer concentrations. although continuous in-line mixing may also be practiced. vibrating screens. (improved recipe design. in systems containing butadiene where the pendant vinyl groups contribute strongly to crosslinking.3.2. crosslinking and propagation. All types of filtration equipment are used in the industry. although with many lattices. 2-11 Influence of number of particles on the instantaneous conversion in a semi-batch emulsion polymerization of styrene-butadiene 45:55 with a feed time of 4. for a given feed rate. the influence of temperature is enhanced because reducing the temperature at a constant feed rate causes a reduction in polymerization rate and hence a reduction in the instantaneous conversion. both normally reducing with lower temperatures. the larger the number (smaller final particle size) the faster the overall rate. Figure 2-11 shows this influence.00005 0 0 20 40 60 80 100 % Conversion version increases (Fig.00035 Variation in the relative degree of crosslinking with percentage conversion during the emulsion polymerization of styrene/butadiene 25:75 in a batch system at 30 °C. Molecular weight tends to increase with reducing temperature. the number of particles exerts an influence on instantaneous conversion and thus all of the properties previously discussed under conversion. . 2-10 0.0002 0. and has been one of the driving forces to100 % Instantaneous Conversion 38 90 80 70 60 50 40 30 20 10 0 0 2 4 6 Time in Hours PD = 135 nm PD = 155 nm PD = 175 nm 8 Fig.0004 0. 2-10) necessitating shortstopping of the polymerization at low conversion when a polymer with high elongation is required. (average number of cross-links per monomer unit in polymer) Fig. The number of particles in the polymerization system influences the rate of reaction. Therefore in a semi-batch reactor or a CSTR.Relative X-linking 2 Synthesis of Polymer Dispersions 0.5 h at 85 °C.00025 0. This control over polymer properties by the number of particles in the system makes it critical to control particle number.00015 0.0003 0.0001 0.00045 0. Temperature similarly influences branching and crosslinking. In a semi-batch and a CSTR. dimpled. Carbon steel.3.3 Equipment Considerations The reactors used for the manufacture of emulsion polymers are normally relatively simple. paddles. Because of the tendency of emulsion polymers to cause deposits in the process. although some operations will require full vacuum rating. half-pipe). all pipework associated with feeds into and product from the reactor would be stainless steel construction. with the majority being in the range 15–100 m3. and “moving parts”. stripping columns. surfactant concentration. The use of seed reduces the variability of the nucleation stage. the reactor may be fitted with internal cooling coils or cooled baffles. To control the temperature of these highly exothermic reactions. there may be supplemental cooling systems such as reflux condensers. particularly if high shear is imparted to the latex. filtration equipment and mixing vessels are all in use to a varying extent downstream of the reaction stage. The most common temperature range for emulsion polymerization is 60–100 °C. The choice of impeller is very much dependent on the properties of the emulsion polymer being made (stability. it has become common to replace glass-lined reactors with either stainless steel or carbon steel with stainless steel cladding. reactors are fitted with a variety of cooling systems. a wide variety of impeller types are in use. Ease of cleaning is paramount. the secret of successful operation is usually to keep equipment simple. electrolyte concentration etc. It is normal to neutralize the latex after the reaction stage. batch strippers.2. anchor agitators and many other proprietary designs. both axial and radial flow turbines. making it less dependent on temperature. Pressure ratings of reactors range from atmospheric to >100 bar with temperature of operation in the range 5–200 °C. agitated vessels. This may be a jacket around the reactor (annular. As emulsion stability has been improved over the years. propellers. viscosity etc.1.). Of course this is in turn dependent upon the seed itself being a consistent raw material. glass-lined construction used to be the standard (the glass surface minimizing polymer deposition) for polymerization under acid or slightly alkaline conditions.3 Manufacturing Processes ward the use of seed polymer. or heat exchangers of various types through which the reaction mixture is circulated. High-pressure equipment is not usually necessary downstream of the reactor. (in certain special cases sub-zero temperatures may be achieved through the use of anti-freeze agents in the emulsion). For agitation. For high pH systems (for example those based on the alkali metal salts of fatty acids and using redox initiator systems) carbon steel reactors are the standard. 2.3. Typically. 39 . Latex may be transferred through subsequent parts of the process either using inert gas pressure or with a variety of low shear pumps. thus greatly increasing stability. should be avoided where possible. 2. to avoid contamination from metal ions. and better cleaning techniques have been developed (high pressure water jets). ranging in size from 5 m3 (less than this is normally considered to be pilot plant scale) to 200 m3. As discussed in Sect. Emulsion Polymerisation Theory and Practice. Chem. Sci. D. 5. the pressure which can develop under a worst case scenario should always be less than the design pressure of the reactor. The correct sizing of relief systems for emulsion polymerization reactors is also not a trivial exercise. P. 1948. Soc. 1947. It has to be questioned whether or not relief devices are ever really appropriate – in reality. 1989. with smaller quantities of monomer in the reactor at any given time. Blackley. J. G. although the reactor may be protected. 217. Chem. the pressure) will increase in an exponential manner. environment). 1428. D. Ewart. and the safety systems which are in place to ensure that the maximum reactor working pressure can never be exceeded. Phys. D. R. V. quench tanks. Surfactants and Interfacial Phenomena. Rosen. which in turn means a large problem outside the reactor. despite the loss in some polymeric properties which often accompanies this change. Am. the rate and efficiency of removing heat from the system. Harkins. 581. Emulsion Polymers Institute. Anderson. has been the inherently safer aspects of semi-batch. a potentially hazardous situation is being transferred elsewhere (vent tanks. . the temperature (and in an enclosed system. El-Aasser. Phys. A major driving force for the change from batch to semi-batch polymerization processes. 7 The schematic diagram is a courtesy of C. H. References 1 W. 6 M. the major capacity limitation in the process can be seen to be a function of the pressure rating of the reactor. J. J. 1950. J. J. 1975. 21. Applied Science.3. Very large relief devices are often indicated. 16. S. Thus. C. if the generated heat is not removed from the system. Appl. resulting in rupture of the vessel or its associated piping if the system is not protected by appropriate relief devices. Lehigh University. Flory. Fox. The pressure can rapidly exceed the design pressure of the containing vessel. 5 T. 69. Harkins. 592. 1950. Polym.40 2 Synthesis of Polymer Dispersions 2. 4 D. 3 W.4 Safety Considerations To carry out emulsion polymerization safely. As with any highly exothermic chemical reaction. M. 2 W. Bethlehem Pennsylvania. Smith. John Wiley and Sons. J. in part because it is difficult to define a worst case scenario and in part because emulsion and polymer properties at extreme reaction conditions are not well known. 2. In addition to determining the macroscopic properties of the dispersion (Sect. a large number of application-specific tests exist.2. the residual volatile content (Sect. this article can only hope to provide a broad overview of this vast subject area.1) and to be able to describe the macroscopic and microscopic properties of the film (Sects 3. 3. 3.3). Given the large number of parameters and the numerous techniques employed to measure them. Beyond the general physical and chemical characterization of dispersions and polymer films. In this chapter. these systems possess a marked heterogeneity at the mesoscopic level and their characterization is therefore a difficult task. space does not permit discussion of these tests nor of the wide variety of the formulations used in the different applications.3) and the aqueous phase (Sect.2).3. Other areas which have had to be excluded are the on-line and off-line methods of monitoring emulsion polymerization [1] and techniques for determining the microbial contamination of polymer dispersions.2.4). characterization requires investigating the polymer particles themselves (Sect. 3. 3.1 Introduction Aqueous polymer dispersions and the polymer films that form from them exhibit a diverse and complex range of properties. the reader is referred to the literature. 41 . For more detailed descriptions of the various measurement methods. Moreover.3. It is also important to understand the process of film formation (Sect.1).Polymer Dispersions and Their Industrial Applications. 3-527-60058-2 (Electronic) 3 Characterization of Aqueous Polymer Dispersions Harm Wiese 3. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. 3.2 and 3.2. KGaA ISBNs: 3-527-30286-7 (Hardback).3. ISO 1625) and the solids content is then expressed as the percentage ratio of the dry matter to the total mass of the sample. The dry matter comprises the polymer. To accelerate the drying process.42 3 Characterization of Aqueous Polymer Dispersions 3. The amount of residue is expressed as a fraction of the original dispersion mass. The residue is rinsed with water. grit particles can be detected by their refraction and diffraction effects.2 Polymer Dispersions 3. particularly in transparent coatings and must be prevented during the polymerization process. Because of a possible thermal decomposition of the polymer or emulsifiers however the temperature of the sample must not be allowed to rise much above the temperature range specified above. Coagulum and grit In many applications polymer dispersions must only contain a very small fraction of agglomerates with diameters greater than 1 µm. dried and weighed. To characterize the fraction of grit present. the dispersion is dried to constant mass at a temperature of between 100 and 140 °C (see. If the skin bursts material can be lost from the sample tray. The grit is undesirable in many applications. since it is the polymer and not the water which is used in the final product. microwaves and infrared radiators. emulsifiers and inorganic salts (formed by the decomposition of the initiators and from neutralization). most modern laboratories make use of alternative drying techniques such as halogen lamps. A comparison of the theoretical solids content (that is assuming complete monomer conversion) to the experimental value therefore provides a means of assessing how far polymerization has proceeded to completion. When viewed with transmitted light. Furthermore.1 General Characterization of Dispersions Solids content In most of the applications the determination of the solids content is the first part of any routine characterization of emulsion polymers. The type of filter and the mesh size should be specified. the filtered dispersion is cast on to a glass plate using film applicators with specified gap size (for example 45 or 125 µm). Mesh sizes of between 45 and 180 µm are typical. Fine agglomerates or large polymer particles which cannot be separated by filtration but are still visible in the wet or dry polymer film are known as grit.2. The filter residue is known as the coagulum content or sieve residue. A determination of sieve residue according to ISO 4576 may involve pre-diluting the dispersion with water before filtering it through stainless steel filters having the above mesh size. Normally. The number of grit particles per unit area . Coarse components may be removed by filtration. for example. the assessment is performed on the dry film. Typically. The volatile part includes the water and monomers which were not converted during the polymerization reaction. the drying rate should not be too high since this may cause skin formation on the surface of the sample. The densities of most polymer dispersions are close to 1 g cm–3 as the corresponding polymers (with the exception of polyvinyl chloride and poly(vinylidene chloride)) have densities in the range 1. Densities can. it is often necessary to dilute the dispersion before measurement. a thin ring of platinum wire. In this method. for instance. the hanging drop method or by using a stalagmometer [4]. Possible sources of error in assessing grit content are wetting defects and occluded gas bubbles. Surface tension measurements can be made by the Du Nouy ring method (see ISO 1409). is withdrawn from the dispersion and the tensile force exerted by the liquid lamella that extends from the ring to the bulk liquid is measured just before it ruptures. the change in the resonant frequency of the tube. because the density of the monomer is usually lower than that of the polymer (densitometry [1]). which depends on its total mass. gas bubbles are blown 43 . The surface tension of a polymer dispersion is of major importance in the coating of substrates. it is also important how fast the surface tension of a freshly generated surface is able to decrease. Problems however often arise due to film formation on the glass membrane. Density measurements have been used in the past to follow the course of emulsion polymerization reactions. Good wetting of the substrate is achieved with a dispersion of low surface tension (Sect. the surface tensions of polymer dispersions generally lie some 20 to 40 units below that for water (73 mN m–1).2). is measured when the dispersion is placed in it.2 g cm–3 [2]. be determined quite simply with a pycnometer (see ISO 2811). pH. As a result of the emulsifiers used in emulsion polymerization. which is generally easy to determine experimentally. A device which permits this dynamic surface tension to be measured is the maximum bubble pressure tensiometer [5]. Very high precision density measurements (±5 × 10–6 g cm–3) are possible with a vibrating-tube densimeter [3].2 Polymer Dispersions is counted or the grit pattern classified by comparison with standard samples. the shape or volume of a drop of the dispersion as it emerges from a capillary is used to compute the surface tension. In this method. The ring method enables the static surface tension of the dispersion to be determined.3. A general approach to obtain information on the wetting properties of a dispersion is by measuring its surface tension in air. density and surface tension pH is an important factor in both the stabilization and the formulation of polymer dispersions. 3. When polymer dispersions are applied on large-scale coating machines. For example. sedimentation is usually only a problem in emulsion polymers if they contain very coarse particles. Since the densities of the polymer particles almost match the density of the aqueous phase. In the latter two techniques. suspended in the dispersion parallel to the surface. pH measurements can be performed using a standard combination electrode (see ISO 976).3. dispersions that contain carboxylic acids are usually adjusted to a pH of between 7 and 9 in order to improve their stability and to increase viscosity.0 to 1. As this method requires relatively low dispersion viscosities (< 200 mPa s). In the Du Nouy ring method. It is essential that the sample is wholly free of gas bubbles. Other factors affecting flow behavior are the electrostatic charges of the polymer particles. a “memory” of these forces. In contrast to polymer solutions. 3-1 and ISO 3219).44 3 Characterization of Aqueous Polymer Dispersions through a capillary into the dispersion. in certain cases. should form smooth surfaces. but should not sag when applied to a wall and should not spatter during brush application. The surface tension can be calculated on the basis of the pressure changes during bubble formation. The dispersion is sheared in a cup by an immersed rotating cylinder (spindle). processing parameter [6]. It is worth noting that the hanging drop and stalagmometer techniques are also dynamic methods. Paints. In practice. The effect of shear forces can be investigated by measuring a flow curve with a rotational viscometer (Fig. Flow behavior The flow behavior of a polymer dispersion or of its formulation is a central. the dynamical processes during the growth of the surface can be accessed. In many industrial applications. albeit much more slowly than the gas exiting the capillary in the maximum bubble pressure tensiometer. see below). and often critical. Apart from solids content. molecular weight and polymer composition do not have a significant effect on the rheology of a polymer dispersion. The flow curve is the plot of the torque acting on the cylinder (or the shear stress τ which can be derived from it) as a function of the . their surface composition and water-soluble oligomers in the aqueous phase. developing. for example. particle charge has only a relatively minor influence because the ionic strength of the aqueous phase is generally high enough (due to the presence of ions arising from the decomposition of the initiator and from neutralization) to restrict to a few nanometers the range over which the electrostatic forces are effective. This behavior is caused by the particle interactions that become apparent when the solids content is high. the rheological properties of dispersions with a solids content above roughly 25 % are complex and strongly dependent upon the forces applied. that is the time taken for a known volume of dispersion to exit the cup through the orifice. because the dispersion is continuously emerging from the capillary. must be easy to apply. The measurement variable is the efflux time. much greater shear forces are applied (for example in coating machines) and these forces often have a strong effect on the rheological properties of the dispersion (non-Newtonian behavior. particle size and particle size distribution play a crucial role. By varying the gas speed. It is important to be aware of the fact that a variety of cups are in use and that each type of cup produces a different efflux time. Even relatively small amounts of watersoluble polymers have a pronounced influence on the flow properties of a dispersion and this fact is used in practice to adjust the viscosity of the dispersion to the desired level (thickeners). The most common types are the ISO cups (complying with ISO 2431) and the Ford cups used in the ASTM D 1200 test procedure. In contrast to conventional liquids. The efflux time characterizes the low-shear flow behavior of a dispersion flowing under its own weight. In the measurement the velocity gradient (or shear rate) between the outer surface of the cylinder and the inner surface of the stationary cup is varied. A simple crude assessment of flow behavior can be achieved on-site using socalled flow cups – funnel-shaped vessels with specified orifices in their bases. however. 2 Polymer Dispersions Rotational viscometer Flow curve shear stress τ shear stress shear rate shear rate D Measuring a flow curve using a rotational viscometer. For this reason. 3-1 is typical of thixotropic dispersions. Figure 3-2 presents a number of τ/D and η/D curves which summarize the various phenomenological descriptions of how dispersion viscosity depends upon shear rate or time. 3-3). 3-1) by measuring the shear stress both as a function of increasing shear rate and as a function of decreasing shear rate. Because of the technical limitations of the shear-force transducers. Increasing the shear rate further induces a strong dilatancy and possibly also coagulation. 3-1 0 viscosity η = τ / D shear rate D. The Brookfield type of viscometer. LV and so forth) is rotated in the sample dispersion. a measurement range of between one and several thousand mPa s must be accessible. in which one of a number of different spindle types (RV. the flow curve is recorded (as shown in Fig. also enjoys widespread use for viscosity measurements (see ISO 2555 and 1652). Shear rates of up to about 1000 s–1 can be accessed with conventional rotational viscometers. 45 . Figure 3-3 shows a viscosity/shear rate dependence which is often observed for polymer dispersions. As both low viscous aqueous-like and highly viscous dispersions are used. one observes shear thinning (viscosity decreases with increasing shear rate) and thixotropic behavior (viscosity falls with time at a constant shear rate). In this log-log plot. Fig. The hysteresis visible in Fig. The shear thinning is assumed to be caused by the onset of ordering within the dispersion as the polymer particles align themselves in parallel layers (Fig. different cylinder/cup sizes are usually required in order to cover both low-viscosity to high-viscosity dispersions.3. The (dynamic) viscosity is defined as the quotient of shear stress and shear rate at every point along the flow curve. The disadvantages associated with this type of viscometer are that the shear rate is not well defined and that the results of measurements made using different spindle types cannot be compared with one another. The dilatancy is thought to be the result of the temporary formation of aggregates which can only pass by one another with difficulty. In many cases. an high initial plateau at low shear rates is followed by a region of shear thinning which leads to a lower plateau at high shear rates. shear yield stress rate. 3-3 shear-induced ordering aggregation When processing dispersions. A key objective in the formulation and production of polymer dispersions is therefore to adjust the shear-rate profile to meet the demands of the particular application. shear thickng. In rheology it is more commonly used than the alternative solids content of the dispersion. Fig.46 3 Characterization of Aqueous Polymer Dispersions Phenomenological classification of the flow behavior of polymer dispersions (τ. t. viscosity. η D D plastic η D D D Time dependence (constant shear rate) η thixotropy η rheopexy t t log (viscosity) shear thinning dilatancy log (shear rate) statistical distribution Typical dependence of the viscosity of a polymer dispersion on the shear rate. The volume fraction is normalized to unity. Semi-empirical expressions . shear stress. a particular viscosity is often desired both at low and at high shear rates. and these viscosities may be very different. time). One way in which this can be achieved is by the addition of polymeric thickeners. shear thinning η dilatant. Figure 3-4 shows schematically how the viscosity of a polymer dispersion varies as a function of the volume fraction φ of the particles. Shear rate dependence τ τ Fig. which influence the viscosity at low and at high shear rates differently depending upon their structure and molecular weight. D. η. 3-2 τ τ η D Newtonian η D D pseudoplastic. A characteristic steep increase in the viscosity is observed as one approaches a maximum volume fraction φm. studies of the extensional flow of polymer dispersions are still in their infancy. which can lead to coagulation. To avoid these problems. However. Low viscosity at high volume fractions can be achieved with a bimodal or broad size distribution where the interstitial spaces between the larger particles are filled with the smaller ones. Little use is also made of viscoelastic techniques where the sample is subjected to low-amplitude oscillatory shear and the amplitude and phase of the oscillating stress is measured (usually as a function of the frequency of the oscillation). any changes can be inspected visually or quantified using the methods available for assessing the coagulum. sedimentation. If the volume fraction is constant. These changes are generally due to instabilities of the polymer particles. This is the reason why dispersions containing fine particles have higher viscosities than those containing coarser ones. for certain applications.2 Polymer Dispersions Dependence of viscosity on the particle volume fraction.3. 47 . 3-4 viscosity shear rate: low high φm volume fraction φ exist which provide more or less reasonable approximations of the experimental curves. which is the value associated with hexagonal close packing. also subjected to freeze-thaw cycles. For the purposes of illustration the Dougherty–Krieger equation is reproduced here: η  φ  = 1 −  η0  φm  −2. the steep rise in viscosity can occur at smaller volume fractions (often at around 0. Because of the lack of commercially available test equipment.74. Fig. The theoretical upper limit for the maximum volume fraction φm of monodisperse spheres is 0. decreasing particle size results in a decrease in the distance between the particles and an increase in the total particle surface area. Stability The production. the viscosity or the particle size distribution. transport and processing of polymer dispersions expose these materials to significant degree of mechanical and thermal stress. polymer dispersions are routinely tested for mechanical and storage stability and.6).55 to 0. depending upon the type of packing and the distance over which the interparticle forces act. After testing. Machine processing exposes dispersions not only to shear but also to tensile stresses (extensional flow).5φm (3-1) where η0 is the viscosity of the aqueous phase. phase separation or changes in viscosity. In the majority of applications. Storage stability: Accelerated testing is achieved by storing the dispersion at enhanced temperature for a particular time (for example for 15 h at 80 °C). for example in ISO 2006 where the sample is agitated for 10 min at 14 000 rotations min–1. 3. particle size and particle size distribution are highly significant factors that determine the properties of a polymer dispersion. the particle size is between 100 and 250 nm. For many applications (for example spray coating) foaming must be suppressed by the addition of defoaming agents. A broad range of . A known quantity of the dispersion is placed on the frit. One common method uses a graduated cylinder whose base is sealed by a porous glass frit through which gas can enter the cylinder. Good reproducibility requires careful temperature control and thoroughly clean cylinders and frits. the gas flow initiated and the height of the foam within the cylinder is then recorded as a function of time. The additives are added either directly or. solvents. Testing is often conducted on diluted dispersions to permit simple visual inspections to be carried out. Stability with respect to additives: For many formulations. 3.2 Characterization of Polymer Particles This chapter restricts itself to a presentation of the methods used to characterize the size and the surface of the polymer particles. Analysis of the polymer itself or the particle morphology is usually performed on the polymer film or on the dried particles and is therefore treated later in Sect. The test involves subjecting the dispersion to repeated freeze-thaw cycles (for example 16 h at –20 °C followed by 8 h at + 23 °C).2. An alternative approach is to measure the foam height after beating the dispersion within a cylinder with a perforated plate for a set time. such as its flow behavior or its stability (Sect. though the conclusions that can be drawn from these qualitative assessments are naturally limited. fillers and pigments. must be tested.2. Measuring particle size is thus an important element when developing polymer dispersions and is also used in in-process control.3.3. polymer dispersions tend to foam. with any changes of the dispersion being assessed as described above. for example ISO 1147. where necessary. such as electrolytes. See. Freeze-thaw stability: This test provides information about the re-dispersibility of a dispersion after having been frozen. Typically. Foaming behavior Because of the presence of emulsifiers. The tendency of a dispersion to foam can be assessed by a number of application oriented methods which can be used for relative measurements [7]. defined stirring (using a serrated stirring disk or rotor/stator units) as. Particle size Polymer dispersions contain particles with diameters ranging from 10 to about 1500 nm. appropriately diluted.1). 3.48 3 Characterization of Aqueous Polymer Dispersions Mechanical stability: The dispersion is subjected to intensive. the stability of the dispersion with respect to various additives. It is caused by light scattering of the polymer particles due to the difference in the refractive indexes of the polymer (typically 1. w/w dispersions. LT2. m = refractive index of the polymer/refractive index of water. white light). … of the respective mass fractions m1.15 200 300 400 500 600 diameter / nm For polydisperse dispersions. the measured light transmission is the inverse geometric mean of the relative transmissions LT1. The link between the scattering behavior of a dispersion of spherical particles and their diameter is provided by Mie theory [9] and is shown in Fig. 3-5 60 m =1.3.3. 3-6) involves directing a laser beam into a highly diluted sample of the dispersion and recording the scattered light impinging on a photomultiplier at a particular angle. The measurement can be performed within a matter of seconds using a simple arrangement of lamp.5 cm cuvette. 3-5 for the relative transmission of white light through various 0. Fig. Electron microscopy is dealt with later in Sect.33). m. LT = transmission through water/transmission through dispersion (2.3 which discusses the characterization of particle and film morphology.4 to 1. also called quasielastic light scattering QELS or photon correlation spectroscopy PCS) has established itself as the most important technique of measuring particle size in polymer dispersions [10].2 Polymer Dispersions methods are available for determining particle size [8] of which only light-scattering and sedimentation techniques as well as modern fractionation methods will be discussed here. 3.01 %. cell and photocell detector.01 % polymer dispersions as a function of particle diameter for different relative refractive indexes.20 (polystyrene) 20 0 0 100 m =1. The measurement (Fig. m2. LT / % 100 80 Relative light transmission LT of 0. …: LT −1 = LT1− m 1 ⋅ LT2− m 2 ⋅ … (3-2) Laser light scattering Of the many methods based on laser light scattering. If the relative refractive index is known. and provides a simple way of accessing the mean particle size in the dispersion. 49 . Light transmission A distinctive feature of polymer dispersions is their turbidity. dynamic light scattering (DLS. Transmission increases as particle size falls or with decreasing relative refractive index (refractive index of the polymer/refractive index of water).10 (polyacrylate) 40 m =1. Fig. 3-5 can be used to determine the mean average particle size from the observed relative light transmission.6 [2]) and water (1. the measurements must be carried out on highly dilute samples (10–5 to 10–2 %. which takes only a few minutes to perform. can be used to determine particle diameters of between 5 nm and 5 µm. As a rule of thumb. the scattered waves have a fixed phase relationship to one another which is determined by the geometrical arrangement of the scattering particles. DLS is used as a routine means of determining particle size in monodisperse polymer dispersions. Experimental set-up and intensity fluctuations. A further fact which complicates the analysis of polydisperse samples is that the diffusion coefficients are weighted according to the scattering intensity. However. Fig. 3-6 sample scattering angle polarizer analyzer intensity photomultiplier time The intensity of the scattered light reaching the detector is determined by the mutual interference of the light waves scattered from the individual particles in the dispersion. w/w).50 3 Characterization of Aqueous Polymer Dispersions laser Dynamic light scattering. the particle diameters of two fractions must differ by a factor of 3 or 4 if they are to be clearly differentiated. 3-6). Typical systems employ a red helium-neon laser (wavelength: 633 nm) and a scattering angle of 90°. non-interacting spheres is assumed. In order to avoid complications due to multiple scattering of the laser light and due to particle interactions. Because laser light is highly coherent. The mean frequency of these fluctuations. The Brownian motion of the particles causes a statistical variation of the phase relationship in time. D. The measurement. the hydrodynamic diameter is equal to the particle diameter. the resolution achievable with such systems when measuring polydisperse samples is generally quite low. which influence diffusion. which in DLS is determined by autocorrelation of the scattering intensity. and η the viscosity of the aqueous phase. using the Stokes–Einstein equation: D= kT 3πηd (3-3) where k is Boltzmann’s constant. According to . A hydrodynamic particle diameter d can then be calculated from the measured diffusion coefficient. T temperature. is proportional to the diffusion coefficient of the particles. producing corresponding fluctuations in intensity at the detector (Fig. If the approximation of hard. 3.2 Polymer Dispersions Mie theory, the scattering intensity of light on particles whose diameter d is approximately equal to the wavelength λ of the light is a complex function of d, λ, the refractive indexes of the particles and the scattering angle. This fact considerably complicates the calculation of the exact mass fractions. For this reason, most equipment manufacturers make use of simple approximate descriptions of the dependence of scattering intensity on particle size. A more accurate approach is to measure the absolute scattering intensities and intensity fluctuations at a number of angles and then to use Mie theory (assuming that the refractive indexes of the particles are known) to convert the measured data to a particle size distribution [11]. Compared with DLS, static light scattering, in which the absolute intensity of the scattered light is analyzed as a function of scattering angle, has become less relevant as a method of determining polymer particle size. Static measurements are today mainly used for characterizing dissolved macromolecules (with gyration radii <100 nm) and for particles with a diameter greater than 1 µm (Fraunhofer diffraction). The reader is referred to the literature for further details on these techniques [12, 13]. Centrifugation Centrifugation methods allow a detailed and comprehensive characterization of polymer dispersions. Figure 3-7 is a schematic view of an analytical ultracentrifuge (AUC) equipped with two types of optical detection systems (schlieren optics and turbidity measurement at fixed radial position, “turbidity optics”) [14]. Particle size determination with an AUC exploits the different sedimentation rates of the particles in the centrifugal field. According to Stokes’ law, the sedimentation time, ts, for the path between the radial position of the meniscus, rm, and the position of the detection optics r (Fig. 3-7) in a centrifuge rotating at a constant angular velocity, ω, is given by: ts = 18η ln(r/rm ) (3-4) ( ρ – ρm )d 2ω 2 where η is the viscosity of the aqueous phase, ρ – ρm the difference in density between the particles and the aqueous phase, and d is the particle diameter. Thus particle size determination requires the precise knowledge of the particle densities. schlieren optics turbidity optics photomultiplier video camera schlieren plate Schematic diagram of an analytical ultracentrifuge (ω is the angular velocity of the rotor). Fig. 3-7 ω sample cuvette rm r lamp laser 51 52 3 Characterization of Aqueous Polymer Dispersions The measurement of the particle size distribution (PSD) is performed on dilute samples (typical concentration: 0.05 to 2 %, w/w) in a so-called sedimentation velocity analysis using the turbidity optics (Fig. 3-7). At the start of the measurement the dispersion is uniformly distributed throughout the cell and the detector registers an attenuated laser beam. As soon as the first particle fraction has migrated under the influence of the centrifugal field out of the optical path, the signal at the detector increases. Particle size can then be determined by measuring the time at which the signal begins to rise. By applying Mie scattering theory (knowledge of particle diameter and refractive index required) the mass fraction of that particular particle fraction can be computed from the increase in signal amplitude. Measurements can be performed with high resolution in the diameter range between 20 and 2000 nm. Figure 3-8 illustrates the result of a sedimentation velocity analysis on a mixture of ten polystyrene calibration latexes. Measurements on such broadly distributed samples are usually performed with an exponentially increasing rotation speed and require centrifuges capable of reaching 60 000 rotations min–1 (Eq. 3-4); a measurement typically lasts 1 h. Machines designed to allow simultaneous determinations with eight sample cells per rotor are described in the literature [14]. Particle size distribution (differential and cumulative) of a mixture of ten polystyrene calibration latexes (sedimentation velocity analysis). Fig. 3-8 By carrying out the sedimentation velocity analysis not only in H2O but also in D2O and in a 1:1 H2O:D2O mixture (H2O/D2O analysis), both the PSD and information on the density (and thus chemical uniformity) of the individual particle fractions may be obtained. Apart from the sedimentation velocity analysis, the AUC may also be used to perform a so-called density gradient analysis. In a density gradient analysis, a water-soluble substance of high density (CsCl or the iodinated sugar metrizamide) is added to the sample so that in the liquid phase a radial density gradient is established at equilibrium in the centrifugal field. The various particle fractions migrate along the gradient to the point having their own density, thus allowing the densities – as in the H2O/D2O analysis – to be determined. I this case the schlieren optics (Fig. 3-7), 3.2 Polymer Dispersions which detect changes in the refractive index along the radial axis, is used for the analysis. In contrast to the turbidity optics, a photo of the entire cell is taken once equilibrium has been established. Normally between 10 and 20 h are needed to achieve equilibrium. The advantage of using the schlieren optics is that in addition to the particle fractions also dissolved macromolecules can be studied with respect to chemical composition and molecular weight. Like the polymer particles, the macromolecules migrate along the density gradient to their isodensity point. However, the small size of the macromolecules means that the bands are diffusion broadened. If the scaling law that relates the diffusion coefficient to the molecular weight is known, the latter can be calculated. The considerable amount of information obtainable by AUC analyses must be viewed in the light of the considerable technical expense and effort needed to run such a machine. At present, only a few laboratories have access to this technology. Disc centrifuges are a cost-effective alternative (rotation speeds of up to 15 000 rotations min–1). Because of the lower rotation speeds in a disc centrifuge a different analysis technique has to be employed. The cell is first filled with a spin fluid and then a sample layer is injected on top of the fluid while the disc is rotating. By this means the particle fractions migrate past the detection optics layer by layer according to their differing sedimentation velocities. Unfortunately, it is often difficult to achieve a uniform injection layer in practice (because of disruptions of the sample flow front). For this reason, and also because of the low density difference between the polymer particles and the aqueous phase, disc centrifuge sedimentometry is not widely used for the characterization of polymer dispersions. Modern fractionation methods In recent years a number of new fractionation techniques, such as capillary hydrodynamic fractionation (CHDF) [15] and field field-flow fractionation (F-FFF) [16], have established themselves as reliable alternatives to centrifugation in PSD analysis. Only CHDF will be discussed here. The technique involves injecting a small amount of the sample into an aqueous eluent containing an emulsifying agent. The eluent is pumped through a glass capillary tubing (inner diameter 7–10 µm) and in so doing adopts a laminar flow profile (Fig. 3-9). The larger the particles, the less able they are to approach the capillary wall during thermal Brownian motion. Large particles are therefore, on average, flowing in faster stream lines than smaller ones and are transported more rapidly through the capillary. The particle fractions are detected using a UV-detector. Complications due to specific interactions between the particles themselves or between the particles and the wall are eliminated by using a particular type and amount of emulsifier and working at low ionic strength. When the apparatus has been calibrated with particles of known size, the PSD of a sample can be determined from its elution curve. As is the case for AUC, calculating the mass fractions requires application of Mie scattering theory, but this is not implemented in CHDF equipment currently available on the market. The manufacturers content themselves with a relative conversion based on the extinction coefficients 53 54 3 Characterization of Aqueous Polymer Dispersions glass capillary parabolic flow field Capillary hydrodynamic fractionation (CHDF): the principle. Fig. 3-9 inaccessible regions (shown for two different particle sizes) particle of polystyrene calibration latexes. Typically, CHDF is able to measure particle diameters in the range 10 to 400 nm. By using capillaries with a larger inner diameter, the range can be extended to include particles about 1 µm in diameter, but the resolution achievable at the lower end of the particle size range is then reduced. A measurement takes about 10 minutes to complete. Particle surface The surface characterization of a polymer particle involves investigating the adsorption of ions and amphiphilic molecules (emulsifiers, oligomers), determining the number of covalently bonded functional groups and acquiring information on the structure of the interfacial layer (swollen state or ‘hairy layers’). Presently this task can not be solved satisfactorily. The main methods used are titrimetric analyses on purified dispersions, soap titration and electrokinetics. Titrimetric methods Titrimetric analysis of polymer dispersions is mainly used to quantitatively determine acidic and basic groups covalently bonded to the particle surface (from initiators or comonomers). Before titration the dispersion has to be cleaned thoroughly, that is all traces of amphiphilic and ionic components have to be removed. The recommended purification technique employs a combination of anionic and cationic ion-exchange resin beads [17]. The beads have to be thoroughly purified themselves before use. After purification, the dispersion is titrated potentiometrically to determine the quantity of residual, that is covalently bonded, acid or base groups [17]. When titrating for acids, the different pKa values enable distinction of sulfuric/sulfonic acid and carboxylic acid. Fundamental questions that arise in connection with this method are (1) whether all of the bonded acid groups can be neutralized because of the high resulting charge density, and (2) to what extent the particle surface reorganizes during neutralization. The increasing hydrophilicity might, for instance, cause particle swelling and a migration of acid groups from the particle interior to the surface. 3.2 Polymer Dispersions Soap titration Soap titration is employed to determine the emulsifier coverage of the polymer particles in the dispersion. Emulsifier coverage is defined as the percentage of the particles’ total occupiable surface area that is covered by emulsifier. In soap titration the surface tension of the dispersion is measured, for example using the Du Nuoy ring method [4], as a function of the emulsifier added (Fig. 3-10). The emulsifier molecules distribute themselves between the particle surfaces, the aqueous phase and the dispersion/air interface where the surface tension is measured. As a rule the equilibrium lies well over in favor of adsorption on the particle surface, so that if the surfaces are not fully covered, only a few of the added emulsifier molecules are found at the dispersion/air interface where, as a consequence, relatively high surface tension values γ are recorded. As more and more emulsifier is added, γ gradually decreases (Fig. 3-10). When the surface of the particles is completely covered, the excess emulsifiers must be taken up by the aqueous phase, leading eventually to the formation of micelles. From this point on the aqueous phase can accommodate large amounts of emulsifier and γ remains essentially constant. The sharp change in the gradient of the curve shown in Fig. 3-10 determines the critical micelle concentration (CMC) of the particular emulsifier in the dispersion under test. The soap titration is usually carried out at a series of solids contents (for example, 2.5, 5, 7.5 and 10 %, w/w) in order to eliminate the amount of emulsifier required for micelle formation. Plotting the resulting CMC values against the solids content produces a straight line whose slope is inversely proportional to the emulsifier coverage α (Maron plot, see [18, 19]). If the size of the particles is known, the effective molecular surface area of the emulsifier occupied on the particle can be calculated. Studies have shown that the emulsifier molecular surface area is determined not only by the type of polymer, but also by the way in which comonomers and initiator residues are incorporated into the particle surface. air emulsifier polymer particle model dispersion 100% coverage of particle surface micelle formation surface tension Fig. 3-10 Soap titration. Determination of the emulsifier coverage of the polymer particles. cmc log(emulsifier conc.) 55 56 3 Characterization of Aqueous Polymer Dispersions The soap titration technique is strictly only applicable for dispersions which contain one type of emulsifier. However, many polymer dispersions are stabilized by a combination of emulsifiers, often both ionic and non-ionic types. One approach in such cases is to perform the study with the emulsifier mixture, though there is the problem of exchange processes occurring on the particle surfaces if one of the emulsifiers is preferentially adsorbed. The results may also be affected by adsorbed amphiphilic oligomers generated during the emulsion polymerization. Electrokinetics Electrokinetic measurements [20] are used to access the electrophoretic mobility µe of the polymer particles and thereby to get information on their charges. Because of the relatively small particle size of 100 to 250 nm, the measurement technique used for polymer dispersions is laser Doppler electrophoresis. Sample preparation and experimental set-up correspond to those of a dynamic light scattering experiment (Sect. 3.2.2, Fig. 3-6). The only difference is a pair of electrodes immersed in the sample between which the particles are moved backwards and forwards by an alternating voltage. The electrophoretic mobility, µe, is related to the zeta potential, ζ, which is defined as the electric potential at the surface of shear of the particles and is therefore a measure of their total charge. Unfortunately, the electrophoretic mobility of dispersion particles does not depend solely on the zeta potential, but also in a complex way on particle size and on the ionic strength and viscosity of the aqueous phase [21]. It is only at the limits of very high and very low ionic strength that ζ can be directly computed from the measured µe values (Helmholtz–Smoluchowski or Hückel approximations). These complex dependencies and some experimental difficulties (for example, due to electro-osmotic convection) are the reason why electrokinetic measurements are still of only minor importance in the characterization of polymer dispersions. On the other hand, the technique provides a simple means by which the adsorption of amphiphilic components (emulsifiers, protective colloids and so forth) on the particle surfaces can be followed at least qualitatively. 3.2.3 Residual Volatiles The increased attention paid to ecological and environmental issues in recent years has lead to a growing significance of residual volatile determination in polymer dispersions. Depending upon the production process, polymer dispersions may contain small quantities of residual monomers, monomer impurities, substances formed by the decomposition of the initiator or from chemical reactions between the various components in the reaction mixture. The European Union has defined such substances as volatiles, if they have a boiling point below 250 °C. The determination of the residual volatiles is usually performed by capillary column gas chromatography [22]. Different sampling techniques are described. In the headspace technique (see ISO 13741-2) a diluted dispersion sample is mixed with an 3.2 Polymer Dispersions internal standard and a polymerization inhibitor. The sample is then heated in a sealed vial (for example at 90 °C for 1 h) and, after equilibration, a small part of the headspace vapors is introduced into the chromatography column. In the direct liquid injection method (see ISO 13741-1) a diluted dispersion sample is mixed with an internal standard and directly injected on to the hot insert liner (temperature 150–200 °C) of the chromatograph causing the dispersion to vaporize instantly. In both techniques the column (typically coated with a 1 µm thick layer of polydimethylsiloxane, PDMS) is initially thermostatted at 50 °C causing the injected volatiles to condense at the entrance part of the column. The temperature of the column is then raised linearly to 250 °C and the component substances are fractionated by the column in the order of their volatility and detected for example by a flame ionization detector (FID). Careful calibration is necessary in order to assign elution time and signal height to the type and amount of the components. With this technique, the typical residual volatiles of polymer dispersions can be quantitatively determined in a range between 10 and approximately 10,000 ppm (measurement duration about 45 minutes). 3.2.4 Aqueous Phase Analysis In common practice the aqueous phase, or serum, of a polymer dispersion is only investigated for its pH (Sect. 3.2.1). On the other hand, the aqueous phase contains a host of substances which play an important role in many applications. These substances include: (a) emulsifiers, (b) initiator residues, (c) electrolytes from the neutralization process or from initiator decomposition (for example sodium sulfate from sodium peroxodisulfate), (d) unreacted water-soluble monomers such as acrylic acid or vinyl sulfonic acid, and (e) water-soluble oligomers formed from this kind of monomers. To analyze the aqueous phase for any of these substances, it must first be separated from the polymer particles. Both flocculation and membrane filtration techniques can be used for this purpose and they are described in more detail below. The detection of the substances listed above can then be performed with the usual array of analytical methods used for characterizing aqueous media. For the determination of emulsifiers, electrolytes and water-soluble monomers, ion chromatography (IC) and high-performance liquid chromatography (HPLC) are particularly suitable. The techniques of choice for characterizing oligomers are gel permeation chromatography (GPC) and capillary electrophoresis (CE). As these analytical techniques are not specific to colloidal chemistry, they will not be described further here and the reader should consult the literature for more information. Serum separation techniques Flocculation techniques The dispersion is for instance flocculated by the addition of acids or salts (typically containing polyvalent ions). Examples of salts of this type are aluminum sulfate or 57 58 3 Characterization of Aqueous Polymer Dispersions the combination of K4Fe(CN)6 and ZnSO4 (Carrez precipitation). Subjecting the dispersion to freeze-thaw cycles also often proves successful. A further possibility is centrifugation. If the centrifugal forces are high enough, the dispersion flocculates at the base of the cell allowing the aqueous phase to be subsequently drawn off. In the case of well-stabilized dispersions, high-performance centrifuges are required. Two disadvantages of the flocculation methods should be mentioned. First, the flocculated polymer particles can release considerable amounts of emulsifier into the aqueous phase. Secondly, centrifugation may cause components in the aqueous phase to be flocculated along with the polymer particles. Membrane filtration techniques In this case, the polymer particles are separated from the aqueous phase by a membrane through which the particles cannot permeate. Suitable membranes include dialysis tubes (molecular weight cut-off: 10 000–15 000 g mol–1) or, for example, Nucleopore membranes, which are available with pore diameters from 15 nm to several micrometers. In dialysis the dispersion is placed in a well-sealed tube and immersed for several days in water, which should be changed regularly. Before being analyzed, the dialysate usually has to be concentrated. Changing the water and concentrating the dialysate can both be carried out easily if the dialysis tube is placed inside a Soxhlet apparatus. In the diafiltration method [23], which uses the Nucleopore membranes, the dispersion is filtered under pressure through the membrane. Like the dialysis method, diafiltration can be used not only to separate the aqueous phase, but also to ‘purify’ a polymer dispersion, that is to separate all the water-soluble components. When used for the latter purpose, the dispersion is continuously rinsed with water during the diafiltration process. Filter cake formation is prevented by adopting a cross-flow filtration arrangement in which, for example, a stirrer is used to create a convective current parallel to the surface of the membrane. 3.3 Polymer Films In the typical applications such as paints, adhesives, textiles and non-wovens the dispersions or their formulations are subjected to a drying process. The properties of the dispersion itself are for this reason only of relevance during processing. It is the properties of the polymer film that are of importance to the end product, and these properties are essentially determined by the polymer itself. Characterizing the properties of the polymer films is thus a subject of central relevance to the typical dispersion applications. In the description of methods presented in this chapter, the focus is on pure polymer films. However, these methods are equally applicable to characterizing formulated films such as paints. Commercial equipment usually has shallow channels engraved in the plate which facilitate the spreading of the dispersion. are present. for example. Once completely dry. emulsifiers. the film is visually inspected for the presence of cracks and cloudiness. the micro domains can merge to form macro domains. but also by the conditions under which the dispersion is dried. Rapid drying. air humidity.3. Immediately after its formation. The drying has to be performed in a controlled atmospheric environment. in particular. below which no compact film can be formed. thus hindering the controlled drying of the dispersion below. thorough drying of the film is essential if the measurement results are to be meaningful.1 Film Formation In the drying stage at the end of water evaporation the particles adopt a hexagonal close-packed geometry. the dispersion is usually cast on to the substrate using either a drawdown film applicator or a roller applicator. The interstitial regions will still house the water-soluble components (salts. such as are used for mechanical strength testing. The MFFT is the lowest temperature at which a homogeneous and crack-free film forms. such as certain film-forming agents. or more rapidly if subjected to higher temperatures. If low-volatility substances. can be formed by pouring the dispersion into flexible polyethylene or silicone rubber trays. Minimum film formation temperature (MFFT) The minimum film formation temperature is determined according to ISO 2115 by spreading the dispersion at defined layer thickness (for example at 200 µm wet) on a plate along which a linear temperature gradient is established (for example from 0 to 40 °C).3 Polymer Films 3. it is necessary to control such parameters as wet film thickness. Films with thicknesses in the millimeter range. polyethylene terephthalate or teflon. In multiphase films.3. The determination of the MFT is discussed below. air convection currents. which facilitate the removal of the film after drying. oligomers and so forth) and multiphase particles. Emulsion polymers therefore possess a so-called minimum film formation temperature (MFT). To achieve reproducible results when characterizing polymer films. The phases formed directly after drying are not in thermodynamic equilibrium with one another. will initially give films with micro domains. polyethylene. Good subsequent film formation requires a high level of polymer particle deformability and the rapid interdiffusion of polymer chains between the particles. can cause a skin to form on the surface of dispersion. The quality of a polymer film is therefore influenced not only by the properties of the constituent polymer. the properties of the polymer film are still mainly determined by the particulate structure of the dispersion. and drying and storage times. Suitable substrates are glass. An example of such changes is the tendency of the water-soluble components to group together or to migrate to the surface of the film. To create a film with a defined (dry film) thickness of up to about 200 µm. drying temperature. Changes in these micro domains can occur gradually with time. The MFFT is either displayed by built-in temperature sensors or can be determined using a surface temper- 59 . for example on coating machines. In this case. which is the negative quotient of ∆T and R. particle size and the water-soluble substances such as auxiliary monomers or emulsifiers also play an important role. For this reason a number of different definitions of the glass transition temperature can . the MFFT is strongly dependent upon morphology. However. As long as the water is present the mobility of the polymer chains is increased and interdiffusion thus favored. An example of this type of system are the core-shell particles with copolymers of differing glass temperature discussed below. and the temperature difference ∆T between the sample and the reference is then recorded over the temperature ramp. The MFFT of a dispersion can therefore be lowered by inclusion of auxiliary monomers. This is the temperature below which a cloudy film forms and above which a clear. The method also enables the so-called white-point temperature to be determined.3. Mechanical stress may develop during film formation (particularly when crosslinking is involved) which leads to crack formation above a certain layer thickness. Usually.2 Macroscopic Characterization of Polymer Films Thermal characterization Thermal characterization of an emulsion polymer essentially means the measurement of the glass transition temperature Tg. Figure 3-11 is a schematic representation of a DSC measurement in which a glass transition and a melting process are shown. 3-11). A glass transition is not a second-order transition between two defined equilibrium states. transparent film results. Normally Tg is measured by differential scanning calorimetry (DSC [25]). Polymers whose Tg lies well above room temperature are designated as ‘hard’. The effect of these substances is to retard the rate at which water leaves the interstitial region. As an aqueous dispersion can only dry above 0 °C. In the case of multiphase polymer particles. The sample and the reference are placed on a sensor plate of defined thermal resistance R. The discrepancy is caused by kinetic limitations in water evaporation and polymer interdiffusion [24]. glass-like polymer film becomes viscous or rubber-like. The main factors determining the MFFT of an emulsion polymer are the composition. the difference between the heat absorbed per unit time by the polymer film to that absorbed by a thermally inert reference material is recorded during a linear temperature ramp. the MFFT and white-point temperature are only defined above this value. The white-point temperature always lies a few degrees below the MFFT. The control of the polymer layer thickness is crucial for the measurements. 3. the heat flow difference. that is the temperature above which the hard. A further point which should be considered is that very short drying times are often used in dispersion processing. those with a Tg much lower than room temperature as ‘soft’. is plotted as a function of temperature (Fig. It therefore occurs over a relatively wide temperature range and depends upon the rate of temperature change.60 3 Characterization of Aqueous Polymer Dispersions ature probe. In this technique. molecular weight and crosslinking density of the main copolymer [24]. the MFFT may well lie above the value determined according to ISO 2115. should extend to 150 °C. Tg should always be determined during the second heating ramp. in the case of soft adhesives. enthalpy of melting). should start at –110 °C and. The investigated temperature range. The glass transition temperature of an emulsion polymer is the temperature above which the polymer chains become mobile and it is therefore directly related to the minimum film formation temperature MFFT. Tg.3. In crosslinked polymers. for example due to the presence of residual water. for instance. Tg values of several important homopolymers are listed in reference [2].5 and 20 K min–1 and recommends the repeat heating of the sample (that is heat/cool/heat). the MFFT is influenced by the drying process. in the case of hard coatings. which is known as “Tg/MFFT splitting”. the MFFT can be lowered significantly. Melting processes are uncommon in the emulsion polymers described in this book. The Gordon–Taylor equation usually produces reliable results: 61 . different definitions of the melting point. glass transition Tpeak β∆Cp Tonset Tg temperature be found in the literature. glass transition temperature. In contrast to Tg. heat capacity difference of the polymer in the temperature regions below and above Tg. 3-11 is that of the so-called “midpoint” definition. Investigation of glass transitions and melting processes in polymer films (β. The values were determined on samples of non-crosslinked emulsion polymers. “Tg/MFFT splitting” is important for all applications in which a hard film with a low MFFT is required. heating rate. Tonset and Tpeak. A number of approximations for calculating the Tg of copolymers have been proposed in the literature [26]. This repeat heating helps to eliminate any influence of the thermal history and the drying process. ∆Cp.3 Polymer Films melting process heat flow difference β∆Hs increasing endothermicity Fig. This phenomenon. water is able to solubilize part of the copolymer during the coalescence of the particles at the end of the drying stage. If. 3-11 DSC. Tg is shifted to higher temperatures as a result of the restricted chain mobility. The Tg shown in Fig. The ISO 11357-1 standard specifies a heating and cooling rate of between 0. ∆Hs. Exceptions are the melting and crystallization phenomena observed with ethylene oxide chains when highly ethoxylated emulsifiers or protective colloids are employed in the polymerization process. which is essentially determined by the main copolymer. is typical of vinyl acetate emulsion polymers but also observed for other polymer types when large amounts of hydrophilic monomers are used in the polymerization process. 30 mm long and 5–10 mm wide) is loaded into a tensile testing machine and the stress (force per unit area) recorded as a function of tensile strain (elongation over original length) at a constant drawing speed (typically 10–100 mm min–1) until the test sample ruptures [27]. the stress-strain curve is linear and the film behaves elastically. Mechanical characterization is typically performed by recording the stress-strain curve up until film rupture takes place (large deformations) or by dynamic mechanical analysis within the elastic limit (small deformations).62 3 Characterization of Aqueous Polymer Dispersions Tg = Tg(1)m 1 + αTg( 2)m 2 m 1 + αm 2 (3-5) Here m1 and m2 are the mass fractions of the monomers 1 and 2 and α is defined as ∆β(2)/∆β(1). If a film contains two phases. on the other hand. Figure 3-12 shows a typical form of a stress-strain diagram measured for a polymer film. In a similar way. only one glass transition is recorded and this lies between those of the individual components. with ∆β the difference in the coefficient of expansion of the molten and glass states of the respective homopolymer. differential scanning calorimetry also provides a simple means of investigating polymer compatibility and phase separation in polymer films. If. This requires drying of the dispersion on a substrate of low surface energy (such as Teflon or silicone rubber) from which it can be lifted without applying strong mechanical forces. Mechanical characterization The mechanical characterization of a polymer film is performed on a free film. Great care is required when preparing such free films as defects or deformations caused by mechanical stress have a detrimental effect on the reproducibility of the measurements. Stress-strain measurements A stress-strain measurement on a free polymer film is performed as a uniaxial tensile test. the Fox equation can be used to provide a simple estimate: 1 m1 m 2 = + Tg Tg(1) Tg( 2) (3-6) For statistical copolymers. At small levels of deformation. this shows up as two glass transition regions in the DSC scan. Other parameters available from this test are the tensile strength and the elongation at break. Beyond enabling the glass transition temperature to be measured. The relative fraction of the phases can be determined by the ratio of the measured heat capacities. The transition broadens with increasing inhomogeneity of the monomer distribution within and between the polymer chains. the compatibility of the polymer to low molecular weight substances such as plasticizers can be examined. If α is not known. The film (typical geometry: 250 µm thick. The gradient of the curve in this region is called the elastic modulus (or Young’s modulus) of the material under test. the width of the glass transition corresponds approximately to that of the homopolymers. the constituent polymers are wholly compatible. The integral under the curve . Dynamic mechanical analysis In dynamic mechanical analysis (DMA [27]) of a polymer film. 3-12 Typical stress-strain curve for a polymer film. the tensile stress passes through a maximum after which it remains relatively constant over a certain deformation range (before rising again shortly before rupture). the stress follows the strain in a sinusoidal manner. stress tensile strength work of fracture elongation at break strain to failure represents the energy per unit volume required to rupture the sample (work of fracture or toughness).3. Curves of this type are found in crosslinked films above the glass transition and in non-crosslinked films in the so-called entanglement region (see dynamic mechanical analysis below).1 % and 1 Hz respectively). non-crosslinked films (in the vicinity of Tg) are elastic at small elongations and start to deform plastically above a critical value. Hard. In conventional DMA. 3-12 is typical of the elastomeric response of a polymer film. These materials show essentially elastic behavior up until rupture. a sample with the same dimensions as in the tensile stress-strain analysis described above is slightly pre-tensioned and then subjected to a low-amplitude and low-frequency sinusoidal deformation (typically 0. E″ the loss modulus and i = √(–1). in which the process of polymer chain interdiffusion in n-butyl methacrylate films was followed by monitoring the films work of fracture. The stress-strain behavior shown in Fig. highly crosslinked films below their glass transition temperature are characterized by their relatively small elongation at break and their high tensile strength. On the other hand. the storage and loss moduli are recorded as a function of the oscillation frequency. In this case. has been reported elsewhere [28]. The amplitude ratio and the phase difference between the stress and strain oscillations enables the dynamic elastic modulus E* to be calculated: E* = E′ + iE″ (3-7) –––––– where E′ is the so-called storage modulus. As the measurement is performed below the material’s elastic limit. Stress-strain measurements are also a useful tool for studying film formation in polymer films. This phenomenon is known as necking. E′ is a measure of the (recoverable) energy stored in the film during deformation and E″ is the (irrecoverable) energy that is dissipated in the film as heat. Such an investigation.3 Polymer Films Fig. Of more widespread application are DMA measurements 63 . E″ = 0 (3-8) where ρ is the film density. the storage and loss moduli measured above the glass transition region remain relatively constant or exhibit a slightly positive temperature dependence (crosslinking plateau). After passing through the glass transition region. R the gas constant. the temperature scan provides the same information as the frequency scan. For non-crosslinked polymers. Equation (3-8) shows that in this ideal case the storage modulus of a crosslinked film increases linearly with temperature and provides a direct means of accessing the crosslinking density ν of the polymer (ν = ρ/Mc). a further increase in temperature causes the film to undergo plastic flow. the moduli decrease more weakly with temperature as a result of polymer chain entanglement and crosslinking within the film. This molecular weight corresponds to the polymer chain length above which physical chain entanglement (temporary crosslinking) can occur (entanglement molecular weight).2). In the case of non-crosslinked polymers.64 3 Characterization of Aqueous Polymer Dispersions Dynamic mechanical analysis. T the temperature and Mc the average molecular weight between two crosslinking sites. the entanglement region is only observed above a critical molecular weight (typically between 2000 and 10 000 g mol–1). A high storage modulus is measured in the glassy state. Fig. . According to the theory of rubber-elasticity. This maximum can be used as an alternative definition of the glass transition temperature of the sample (compare with Sect. Figure 3-13 shows a typical DMA measurement (temperature scan) on a non-crosslinked polymer film. E″ assumes significantly lower values than E′. For crosslinked polymer films. the storage and loss moduli in this region have the following values: E′ = 3ρRT/Mc. The loss modulus passes through a maximum at the beginning of the glass transition region. As a result of the time-temperature superposition principle. 3-13 in which E′ and E″ are measured at a constant frequency over a temperature range. Storage (E′) and loss (E″) moduli as a function of temperature for a polymer film of poly(2-ethylhexyl methacrylate). 3. The storage and loss moduli can be seen to vary over several orders of magnitude across the temperature range. It decreases rapidly in the glass transition region as the film softens.3. optical measurements on polymer films are often performed using black foils as substrate (for example pigment blackened PVC). These liquids can wet. the results will be influenced by film thickness and by the choice of substrate (color. Behavior with respect to liquids In a multitude of applications. transparency and so forth). angles of incidence and detection (relative to the surface normal). Despite the fact that a multitude of optical techniques are available for such measurements (UVvisible spectroscopy. DMA is also able to provide information on the effects of plasticizers. To characterize these processes (with the exception of wetting) simple gravimetric methods are normally used. Wetting If a series of liquids with increasing surface tension γL are brought into contact with a polymer film.3 Polymer Films When analyzing multiphase samples. The advantage is that the film is placed between two plates rather than being clamped at its ends. G* is measured by exerting a small sinusoidal torsional displacement of one of the plates. complete wetting will occur below a critical surface tension γC and partial wetting (that is droplet formation) will be observed above this value (see Fig. that is diffuse illumination and detection of the scattered light at 0° to the film surface normal. laser scattering and so forth). swell. Measurements of film gloss are performed by recording the intensity of light reflected at a specified angle to the normal (usually 20. Film opacity is usually measured by the transmission of white light through a free film. The complete optical characterization of a polymer film would require measuring the optical response of the film as a function of wavelength. resins and fillers on the polymer film. 65 .3. 60 or 85°). In colormeasuring instruments. For this reason. in most applications simple techniques using white light are employed [29]. In the case of soft films which tend to flow it is easier to measure the dynamic shear modulus G* = G′ + iG″ than the elastic modulus E*. film thickness and type of substrate. Optical characterization The transparency. Films with a high γC are easy to wet. wavelength-dependent measurements are conducted at known angles of incidence and detection and the results then converted to color values. polymer films get in contact with water or organic solvents. ellipsometry. The information content of the shear moduli curves corresponds to that of the elastic moduli ones. permeate or even dissolve the film. The critical surface tension γC is a characteristic of the polymer film and a measure of its surface energy. those with a low γC value can only be wetted with difficulty. It is important to realize that when investigating films that are not wholly opaque to the wavelength concerned. gloss and color of a film are important in many applications. it may be possible to detect several glass transitions in a DMA measurement as was the case in the thermal characterization of multiphase polymer films described above. The back-scattering power is determined using an integrating sphere photometer. 3-14). 31]). In addition to their use in determining the critical surface energy γC. 3-14 Wetting is quantified by measuring the contact angle. conversely. For evaluating the data a number of procedures have been published (see for example the Good-Girifalco-Fowkes method [30. After a defined period of immersion (for example 24 h). Swelling. The contact angle is measured either by image analysis (sessile drop method) or by using a Wilhelmy balance [4. which is the angle subtended by the drop at the point of contact to the film. Fig. a value of 180° represents complete non-wetting (see Fig. 3-14). the polymer film is suspended vertically from the balance and then lowered slowly until it is in contact with the liquid. the film is removed . contact angle measurements can also provide information on the polarity of the film surface. the contact angle can be calculated from the difference in sample weight when in and out of contact with the liquid. dissolution and permeation The usual means of characterizing swelling and dissolution processes involves storing weighed films in the solvent of interest (for example water or tetrahydrofuran). In this case the measurements are conducted with a series of liquids of different polarity (for example isopropanol-water mixtures).66 3 Characterization of Aqueous Polymer Dispersions Determination of the critical surface energy γC of polymer films using the Zisman method (θ is the contact angle). 30]. A contact angle of 0° reflects complete wetting. If the surface tension at the liquid-air interface is known. In contrast. The Wilhelmy method can also be used to investigate dynamic wetting processes by recording the formation of the liquid lamella in time or by immersing and withdrawing the polymer film into and from the liquid at constant rate. In the Wilhelmy balance method. Time-dependent measurements are also useful for examining cases in which liquid is taken up after the polymer film has been wetted or. in which the liquid dissolves film components such as emulsifiers. 3 Polymer Films from the liquid. 3. Further parameters of interest are the volume changes that accompany the swelling and the subsequent drying. but also of the physical entanglement of the chains in these high-molecular-weight emulsion polymers. 3-8). what is sought is the greatest possible compatibility or incompatibility between a polymer film and a particular solvent. the greater the swelling the better the compatibility. liquid adhering to the surface of the film is removed and the sample is weighed in its wet and dry state. The percentage increase of the wet film relative to its initial weight prior to immersion is known as the solvent or water uptake. The permeation of a polymer film by a liquid can be investigated by filling the liquid into a container whose base is made of the polymer film under test.3. Full dissolution is hindered if a gel fraction is present. Measurements conducted for different storage periods provide information on the kinetics of the sorption and dissolution processes. In many applications. Sorption and dissolution measurements on polymer films in various solvents are also the basis for determining the solubility parameters of a polymer [33]. The loss of 67 .3. which are a measure of its solvent compatibility. The gel fraction is the result not only of covalent crosslinking between polymer chains. Quantifying the solvent uptake and extraction loss is therefore a simple means for characterizing this type of crosslinking. the greatest level of compatibility is achieved at the maximum solution viscosity. This phenomenon is caused by refractive index inhomogeneities created in the film when water penetrates the interstitial regions between the particles. In the case of a crosslinked polymer film. Soluble and insoluble film parts are frequently referred to as the sol and gel fractions. ρ is the polymer density. Interparticle crosslinking (that is crosslinking after film formation) reduces the swelling and dissolution of the polymer film strongly. The gel fraction is often higher in polymer films which have been subjected to longer drying times as the chain segments then have the opportunity for greater interdiffusion. The weight loss of the dried film compared to the initial sample weight specifies the extraction loss and is due to the partial dissolution (leaching) of film components in the liquid. Many of the methods used for the characterization of the emulsion polymer macromolecules (see Sect. In a crosslinked film. In the case of a non-crosslinked polymer film.5 − χ (3-9) where Q is the swelling ratio by volume. Characterization of film whitening can be done with conventional techniques as discussed above. the mean molecular weight Mc between two crosslinking sites can be calculated from by the degree of swelling in a particular solvent using the Flory-Huggins equation [32]: Mc = ρVS (Q 5/ 3 − Q / 2) 0. Swelling – particularly due to the uptake of water – often creates opacity within the film (whitening) which is undesirable in many applications. The speed with which the wet film dries may also be of significance for certain applications. VS the molar volume of the solvent and χ the Flory-Huggins interaction parameter for the polymersolvent pair (see also Eq.3) require the polymer film to be dissolved in a solvent. An alternative or complementary method is pyrolysis gas chromatography. Polymer composition can also be determined by 1H and 13C NMR [38] on dilute samples of the polymer in an organic solvent. 3. the film samples examined must be free of pores. As in the liquid permeation studies.68 3 Characterization of Aqueous Polymer Dispersions liquid is then recorded gravimetrically as a function of time. for instance by monitoring the pressure drop across the film or by the specific determination of a gas component that permeates the film. Because of their high molecular weight and their partial crosslinking. Some of the measurements are performed on solutions of the polymer in organic solvents such as tetrahydrofuran or dimethylformamide. the container is filled with a material which acts as a strong absorber for a particular gas (for example sodium dihydrogen phosphate for water vapor or sodium hydroxide for carbon dioxide). Quantitative analysis involves comparison of the spectra obtained with those of standard calibration substances. rather than being filled with a liquid. complete dissolution of an emulsion polymer is often difficult (see Sect. For this reason the investigations are performed on the dry polymer film or on freeze-dried samples. If.2).3. In this technique the polymer is rapidly heated causing depolymerization or decomposition and the products are separated and detected gas chromatographically [34]. conventional gas analytical techniques may be used to examine permeability. 3. Chemical composition The chemical composition of an emulsion polymer sample can for instance be determined by Fourier transform infrared (FTIR) spectroscopy [37]. Such measurements are only reproducible if pore-free films can be produced.3 Microscopic Characterization of Polymers Macromolecules Most of the methods used for the microscopic characterization of emulsion polymers in terms of their macromolecular composition.3. Films can be tested for the absence of pores by examining their gas tightness. gas permeation into the container can also be monitored. Gas permeation The permeability of polymer films to vapors can be measured gravimetrically in analogy to liquid permeability (above). and the information that can be provided by these methods is in such cases rather limited. NMR analysis also enables end group analysis and to a limited extent monomer sequence studies (for example in terms of triad distributions). with the difference that the film now acts as the lid rather than the base of a container partially filled with the liquid forming the vapor. The measurement is performed on a polymer film. The methods employed are the standard techniques of polymer characterization [34–36]. . As an alternative to these gravimetric methods. molecular weight and crosslinking require the removal of water. the amount of the good solvent in the eluent is gradually raised which leads to the re-dissolution and fractionation of the copolymer. Normally. Because emulsion polymers are prepared by a radical polymerization process. The copolymer is dissolved in the good solvent and then injected into the LC column with the non-solvent as eluent.3 Polymer Films In recent years there has been increased interest in using gradient HPLC techniques. M. The solubility gradient is created by mixing a solvent in which the polymer dissolves well with one in which it does not dissolve (the so-called non-solvent). is given by the Mark-Houwink equation:  1 η( c ) − η0  α (3-10) [η ] = lim   = AM c →0  c η0   where c is the polymer concentration. alternative methods of absolute molecular weight characterization (static light scattering. The dependence of the intrinsic viscosity and the molecular weight. end-group analysis. for determining the compositional distribution of copolymers. such as gradient polymer elution chromatography (GPEC [39]). other techniques such as FTIR spectrometry and light scattering are now used to characterize the individual fractions as they elute from the column. density gradient analysis in an analytical ultracentrifuge. In addition to simple UV and refractive index detectors. The measurement is normally made using a capillary viscometer and involves recording the solution viscosity as a function of polymer concentration c and then extrapolating the data to zero concentration (see ISO 1628-1). η0 the solvent viscosity and A and α are quantities which are constant at specified temperature for the solvent-polymer pair. The Mark-Houwink equation (Eq. In this technique the polymers are embedded in a matrix made of a strong UV absorber which enables the unfragmented ionization of the macromolecules by a UV laser pulse. Absolute molecular weight determination is achieved in this mass spectrometer by time-of-flight measurement. also referred to as SEC. the molecular weight distribution (MWD) is generally quite broad. In doubtful cases. 3-10) assumes that the polymer in solution is present in the form of random statistical coils. GPC fractionates a polymer solution according to coil size by passing it through a micro-porous gel with a defined pore size distribution [34]. Molecular weight The determination of the molecular weight of the polymer is also carried out in organic solution. with the result that the copolymer precipitates at the entrance of the column. A modern alternative is that of matrix-assisted laser desorption ionization mass spectrometry (MALDI MS [40]). membrane osmometry. A simple method is to measure the intrinsic viscosity [η] of the solution [34]. During gradient elution. The latter two detectors enable both the chemi- 69 .3. For a given molecular weight. In such cases viscosity is only measured at one particular (low) concentration and used as a relative measure for the molecular weight of the investigated polymer. size exclusion chromatography). MWD is usually characterized by gel permeation chromatography (GPC. and so forth) should be used for comparison purposes [34–36]. the c → 0 extrapolation is too involved for routine measurements. branching and crosslinking in the macromolecule lead to a lower viscosity. a lateral resolution of around 1 nm is achievable. while molecular weight can be determined by the density gradient analysis in an analytical ultracentrifuge or by static light scattering. The hydrodynamic volume is best accessed by viscosity measurements or dynamic light scattering. they have to be placed separately on a suitable . interparticle crosslinking.70 3 Characterization of Aqueous Polymer Dispersions cal composition and the molecular weight of the individual polymer fractions to be accessed directly. but a significant restructuring of the phases can occur as a function of time (leading for example to larger domains). High molecular weights coupled with small hydrodynamic volumes indicate extensive crosslinking. Fig. 44]) and NMR spin-diffusion and spin-relaxation techniques [45]. Film and particle morphology Polymer particles can be produced in a number of morphologies. atomic force microscopy (AFM. Transmission electron microscopy In transmission electron microscopy [46] the dry sample has to be transferred into ultrahigh vacuum and is illuminated by a high-energy beam of electrons (for example 100 keV). which occurs after film formation. On the other hand. 3-15 Morphologies of polymer particles. [43. However these methods are not in widespread use and their ability to characterize the composition. Other techniques are small angle X-ray and neutron scattering (SAXS [41] and SANS [42]). Since sample preparation is rather involved. The reader is referred to the literature for further details. significantly reduces the solubility of the polymer film. The morphology of the film. Figure 3-15 shows examples of structures that have been observed. will be determined by the structure of the particles. In an ideal case. Micro-gel fractions are a common feature of emulsion polymers because of intraparticle crosslinking. directly after its formation. In order to examine individual particles. size. In this latter case. TEM is not a routine technique. The major technique used to characterize particle and film morphology is transmission electron microscopy (TEM). Crosslinking Internally crosslinked polymer particles (“micro-gels”) can be characterized by comparing hydrodynamic volumes and molecular weight. shape and superstructure of the domains is somewhat limited. which is described below. crosslinking is characterized by performing swelling experiments in organic solvents. The freezing process has to be fast enough to avoid crystallization of the water phase. H. Dr A. Sometimes it is also possible to directly deposit a particle monolayer on a substrate by drying the dispersion at the right dilution. In the same way a possible phase restructuring taking place in the film of these particles can be studied. for example. For the TEM inspection of a polymer film a thin section containing only one particle layer is required (typical thickness <100 nm). The sample is then cryo-transferred to the electron microscope where it is fractured. Mächtle. Improved contrast can be achieved by staining the polymer with heavy-metal compounds such as RuO4. Dr R. Transmission electron micrographs directly show the size and shape of the individual polymer particles. For example. OsO4 or uranyl acetate. is the freeze-fracture technique.3 Polymer Films substrate under conditions which prevent film formation (that means high dilution of the sample and drying below the minimum film formation temperature). Nissler. Lamprecht. on the other hand. Dr H.3. Acknowledgments I wish to thank Dr J. Krause for their assistance in the preparation of the manuscript. which causes low contrast in the images. The fracture surfaces can then be imaged using. Heiter. However. A fundamental problem of using electron microscopy to analyze polymer samples is their low electron density. and S. Acrylates. These compounds are incorporated into the polymer network directly or via a suitable coupling agent. polystyrene and polybutadiene can be selectively stained with RuO4. albeit a rather involved one.-J. Staining agents which exhibit high selectivity for certain polymers also form the basis of morphology studies. Baumstark. in which the dispersion is shock frozen by being poured into liquid nitrogen. 71 . require treatment with hydrazine and OsO4. The thin-cut can only be done at a temperature below the glass transition temperature of the polymer. Dr W. An alternative to the above preparation methods. A core-shell particle with a polystyrene core and an acrylate shell can thus be characterized by staining the core with RuO4. Zosel. to draw any reliable conclusions on the distribution of particle size or shape the laborious counting of a large number of particles is required (>1000!). replica techniques. Cornell University Press. Zosel. C. 1989. I. 1987. S. S. Lovell. El-Aasser (eds). P. Harding. 7.). Colloid Sci. Colloid. M. VI: Determination of Thermodynamic Properties. 1994. J. A. M. 1995. W. Koch in: Physical Methods of Chemistry. 135. Unterforsthuber. 1981. Hunter. P. Ley. C. Sci. Kratochvil. W. Principles of Colloid and Surface Science. Botana. Rowe. Syst. 1990. Munich. Absorption and Scattering of Light by Small Particles. MNL 17. II. A. El-Aasser. G. DosRamos. New York. 89 (1988). Oxford. Charact. J. Mark. 388 (1980). S. G. I. Silebi.). M. Chapter 6. Wiley. N. N. Baetzold (eds). C. New York. Flory. Lesko. Vol. 59–62. A. G. Fainerman. A. Schaller in: Emulsion Polymerization and Emulsion Polymers. G. K. Brown. Foundations of Colloid Science. D. Wiley. W. W. 73. ASTM. B. J. Vol. S. . W. Rossiter. Microcolumn Sep. Giddings. 395 (1995). Horton (eds). F. pp. Cambridge. Bascom. A. Ithaca. J. M. Tausk. A. Clarendon Press. Davis. Penzel in: Ullmann's Encyclopedia of Industrial Chemistry. E. C. Maron. Lovell. Hunter. J. Ahmed.72 References 1 W. E. Elder. Adamson. 21. Joos. B. Barton. 1997. 1983. Lüddecke. C. A. Weinheim. J. London. Oxford University Press. Calorimetry and Thermal Analysis of Polymers. W. Chapters 40–42. 85. Bohren. Oxford. G. Physical Chemistry of Surfaces. CRC Handbook of Solubility Parameters and Other Cohesion Parameters. Chapter 13. pp. New York. M. Brown (ed. pp. A. Asua (ed. New York. New York. V. El-Aasser (eds). p. R. J. W. P. Menges. Vol. F. J. Berlin. J. Mechanical Properties of Solid Polymers. 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 R. Colloid Polym. S. 147–175. Koleske (ed. V. M. J. Sci. E. Oxford. Marcel Dekker. pp. G. M. P. K. 2222 (1993). J. Wiley. T. 619–655. 1983. Lovell. Vanderhoff. Wu. Zeta Potential in Colloid Science. Baugh (ed. 165 (1990). B. 1992. M. 76 (1960). Brodnyan. R. Barth. Ward.. Sci. New York. Classical Light Scattering from Polymer Solutions. 731 (1994). Van den Hul. G. 1992. L. M. M. 9. 17 J. H. New York. Overberger. Miller. 437–466. El-Aasser (eds). pp. S. J. 267–288. Wiley. E. Mathot (ed. Wiley. V. Lilge. R. Collins in: Emulsion Polymerization and Emulsion Polymers. M. Philadelphia. 89 (1954). Adv. Boca Raton. E. 15. Kroschwitz (eds) Encyclopedia of Polymer Science and Engineering. 1973. W. J. 1987. Principles of Polymer Chemistry. P. Vanderhoff. The Netherlands. Sperry in Emulsion Polymerization and Emulsion Polymers.-D. Ratanathanawongs. J. 539. F. G.). Overbeek in: Clean Surfaces. Dynamic Light Scattering. J. M. P. J. H. F. Gas Chromatography. J. Amsterdam. 1970. C. G. P. J. I. Huffman. D. Vol. R. W. A. Part. 1997. G. E. R. Hiemenz. P. H. J. 1986. Royal Society of Chemistry. C. Paint and Coating Testing Manual. H. P. 1992. J. New York. J. Verlag Chemie. Wiley. 1953. Hanser. Macromolecules 26. Bikerman. Bikales.). New York. Poehlein. Oxford University Press.). New York. S. 145–149 (1994). Polym. 1984. Wiley. Goldfinger (ed. Foams. Colloid Interface Sci. Ulevitch. J. H. D. Springer. pp. J. 1992. Hergeth in: Polymeric Dispersions: 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Principles and Applications. Colloid Interface Sci. New York. pp. Wiley. S. G. S. D. C. Wiley. R. 272. Mächtle in: Analytical Ultracentrifugation in Biochemistry and Polymer Science. CRC Press. P. ASTM manual series. 1997. Elsevier. A. Modern Methods of ParticleSize Analysis. 385–436. Part. J. Pauli. 1983. Academic Press. Horn. 7. 157–178. 1997. Marcel Dekker.). Kluwer Academic Publishers. 1993. Sci: Part B: Polym. D. Polymer Characterization. 41 R. Didier. G. Mater. Hanser. pp. W. Arndt. D. J. Polym. Phys. Booth. Macromolecules 29. Price (eds).). 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M. 7. 1988. Comprehensive 35 36 37 38 39 Polymer Science. Adv. Washington. J. 1993. Berlin. Colloid Polym. C. C. Oxford. Blackie. H. 563 (1993). 1. E. J. 4-1 The 1998 world demand for emulsion polymers by market and region. 75 . 4-2 shows the demand forecast in 2003 [1]. respectively. Other Markets (18%) Paints & Coatings (26%) Carpet Backing (11%) Adhesives Paper & Paperboard (22%) (23%) By market Other Regions (21%) North America (35%) Japan (12%) Western Europe (32%) By region The 1998 World Emulsion Polymer Demand: 7.4 million metric tons and is forecasted to increase to 8. and Do Ik Lee 4.6 % [1]. Of this 1998 world demand. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. The world demand for emulsion polymers in 1998 is shown by market and region in Fig.4 Million Metric Tons Fig. while Fig. while about 23 % was for paper and paperboard coatings. For this reason.1 Introduction In 1998. they will account for about half of the world consumption of emulsion polymers. If the world-wide uses of emulsion polymers for both paper and paperboard coatings and paints and coatings are combined. KGaA ISBNs: 3-527-30286-7 (Hardback). Elmar Schwarzenbach.8 million metric tons in 2003 with an annual growth rate of 3. 3-527-60058-2 (Electronic) 4 Applications in the Paper Industry Jürgen Schmidt-Thümmes. along with the industry for paints and coatings. the world demand for emulsion polymers (dry) was 7. about 35 % and 32 % were consumed in North America and Western Europe. 4-1.Polymer Dispersions and Their Industrial Applications. the industry for paper and paperboard coatings is a core market for emulsion polymers. respectively [2].76 4 Applications in the Paper Industry Other Markets (17%) Paints & Coatings (26%) Carpet Backing (10%) Adhesives Paper & Paperboard (23%) (24%) By market Other Regions North America (24%) (34%) Japan (11%) Western Europe (31%) By region The 2003 World Emulsion Polymer Demand Forecast: 8. 4-1 The Western European market for emulsion polymers in the paper industry [2]. Table 4-1 shows the amounts of emulsion polymers used for these applications in Western Europe: 3 % and 97 %. Since information on the breakdown in the uses of emulsion polymers for surface sizing and paper coating is not readily available in the world markets. 4-2 This chapter will cover the applications of emulsion polymers in the paper industry. The original paper was made in China from rags. The invention of paper has been attributed to Ts’ai Lun in AD 105.2 The Paper Industry 4. Market segment Amount of polymer dispersions in metric tons and percent (1997) Surface sizing Paper coating Total 35 000 ( ~3 %) 1 150 000 (~97 %) 1 185 000 4. In China.2. strips of bamboo or wood were used for writing and drawing before the discovery of paper. Tab. especially in surface sizing and paper coating. bark . it is hoped that information available on the Western Europe market would provide some perspectives on their relative uses of emulsion polymers.1 History The precursors of paper were papyrus and parchment. which were used for writing as early as 3000 BC in Egypt. Fig.8 Million Metric Tons The 2003 world demand forecast for emulsion polymers by market and region. who produced a uniform writing-material paper from felted plant fibers [3]. synthetic additives comprise only about one third so that overall synthetic additives make up only about 1 % of the 77 . The main raw material used to make paper is wood. This type of pulp is less well suited for paper manufacture. increasing levels of trade and for other reasons.4. cellulose. The plants were crushed in mortars and water was added to create a homogeneous fiber pulp. Numerous raw materials were used for paper manufacture and there were rapid developments in industrial papermaking with the first papermaking machine being built in 1799. and incrustations have been removed by the refining process to leave high-grade cellulose fiber that is particularly well suited to paper manufacture.2 The Paper Industry Today In 1998. a surprisingly small amount compared to the other constituents such as recycled paper. and pigments. – Paper made of pure cellulose is designated as “wood-free” paper. 4. Typically. The art of papermaking finally reached Central Asia by AD 751 and Baghdad by 793. but also for high-quality paper. large amounts of recycled papers are also used in today’s papermaking industry. Even today. In an effort to protect wood resources. As a result of further discoveries. the world production of paper and paperboard excluding newsprint and tissue totaled approximately 240 million metric tons and is expected to grow to approximately 290 million metric tons in 2003 with an annual growth rate of 4 % [1]. – Mechanical pulp. resins.2. and in 1809 John Dickinson invented the first cylinder machine [4]. Of this 3 %. The intermediate stage between the raw materials and the finished paper is socalled half stuff (pulp). as the incrustations are still present to a large extent and the properties of the pulp are determined by fiber bunches and fragments inevitably present. The proportion of the chemical additives used as fillers in both paper and coatings is about 3 %.2 The Paper Industry fiber. the level of paper consumption continued to rise. paper was made one sheet at a time by dipping a frame or mold with a screen bottom into a vat of pulp. By dipping a hand wire screen into the suspension. Nicholas-Louis Robert constructed the first papermaking machine. Modern technology combined with appropriate process chemicals enables this secondary raw material to be used not only for paperboard. With the invention of the printing press by J. the brothers Henry and Sealy Fourdrinier improved Robert’s machine. A few years later. Later. it landed in the New Continent. these are still the fundamental steps in the papermaking process. Both softwoods (long fiber) and quick-growing hardwoods (short fiber) are processed. paper assumed a previously unimagined importance and there was a massive increase in the demand for paper. Using a moving screen belt. whereas that made from mechanical wood is called “wood-containing” paper. a thin layer of the pulp was removed and then dried. and bamboo. Gutenberg in the middle of the fifteenth century. which is produced from wood that has been ground or refined by mechanical means. and by the 14th century there were paper mills in several parts of Europe [4]. this is: – Cellulose from which lignin. The pulp is prepared for the paper machine in an upstream unit. Fig. wire section. In this unit.0% Synthetic chemical additives 0. 8% Process chemicals used in the papermaking. 4-4.5% Starch 8% 35% 11% Waste paper Mechanical pulp Pigment/Filler The proportion of chemical additives relative to the total global raw material demand of the paper industry in 1996.78 4 Applications in the Paper Industry Chemical additives Chemical pulp 43% 3% 1. as shown in Fig. flocculants. pressing section. 4-4 5% Retention drainage aids. sizing agents can be monomeric or polymeric. OBA Fig. In the latter case. The two most important groups of the synthetic additives are the synthetic binders (50 %) and the sizing agents (25 %).5% Alum 1. the wood is ground. cleaners 8% 3% 6% Sizing agents 25% Wet strength resins Bleaching chemicals Dyes. .etc. The paper machine itself is a single continuous production line with a length that today may exceed 200 m and comprises the following main sections: headbox. and finishing section. While synthetic binders are composed of emulsion polymers. 4-3 total content (Fig. they are in the form of polymer dispersions. washed. 4-3). curing agents. and then fiber concentration and consistency are adjusted to the desired levels. and sorted. drying section. deaerators Dispersants. Additives relevant to paper properties Additives relevant to manufacturing process (Functional chemicals) (Process chemicals) Synthetic binders 50% (Paper coating) 1% 1% 1% Biocides Defoamers. A wide range of production and finishing processes guarantees that even the most demanding quality requirements can be met. for printing paper and board.e. So in a size press formulation starch clearly dominates with more than 95 % of the solids content. in combination with starch. The state-of-the-art papermaking and finishing machines are up to 10 m wide in web widths and up to 2000 m min–1 (120 km h–1) in production speeds. The size of today’s paper production lines is enormous. the surface sizing agents. and coating equipment.1 to 0. In the pressing section. the penetration and spreading of print colors are controlled and the loss of strength in the wet state is reduced. The application will be on-line to the paper machine by either a size press or a film press. To meet these demands. the physical characteristics of the paper or board must ensure both good processability and good printability. the machine calendering cylinder. The requirements that these materials must meet include: – high degree of uniformity and smoothness – good optical properties of which brightness and gloss are the most important – high opacity and high strength In short. On passing through the drying section.3 Surface Sizing In the headbox. will be applied. 79 . also known as graphic arts. Thus. the web is dried to a final moisture content that is in equilibrium with the ambient air.4. the surface sizing agent hydrophobicizes the paper sheet.25 % (w/w) of sizing agents. 4. The paper or board web is wound onto rolls in the finishing section which also contains roll handling and wrapping equipment. the following two processing stages are incorporated into the drying section of the papermaking line: – surface sizing – paper coating The use of emulsion polymers in the paper industry is essentially restricted to these two processes which are described in more detail in the following sections. i. the pulp suspension is spread across the entire width of the web and passed onto the wire mesh at the correct speed. water is driven out of the wet mat by applying pressure to the web. In relation to the paper mass usually 3 to 5 % (w/w) of starch and 0.3 Surface Sizing Surface sizing means a pigment-free application of hydrophobicizing substances. various types of calenders. each calculated as solid. The sheet is formed as the water drains from the mesh and the fibers are fixed into their final orientation while still in the wet mat stage. Examples of such devices are the size press. The web enters the pressing section with a dry content of about 20 % which increases to 40–50 % as the web leaves this section of the machine. The drying section is often equipped with additional devices which improve the surface properties of the paper or board. thereby reducing the absorbency of the paper. The largest part of the papers produced today is for printing. Starch enhances the strength of the paper. Only dispersions stabilized by protective colloids are able to form such a coherent hydrophilic/hydrophobic raster. preventing a rupture of the film during drying and shrinking of the starch.200 nm Fig. Polymer particles in the interior improve the wet strength and delay the dissolution of starch and the flow of aqueous media within the starch layer. and binding strength of the polymer. Polymer particles sitting at the interphase between starch film and fiber surface support the fixation of the starch film to the fiber. mostly polymeric sizing agents are used. 4-6). For surface sizing. The most important product classes are acrylic copolymer dispersions stabilized by protective colloids. glass transition temperature. 4-5). In this process step. 4-5 Structure of a polymer-based sizing agent. viscous flow. The hydrophobic effect of surface sizing stems from the formation of a stable coherent film at the paper surface providing a halftone-like screen (raster) formed from well defined hydrophobic barriers and areas of hydrophilic character (Fig. It renders stability to the dispersions during storage and against the high shear stress during application. . The particles of the sizing agent consist of a hydrophobic polymer core and a hydrophilic shell formed out of the protective colloid (Fig. The protective colloid tightly fixed to the polymer core acts as a compatibilizer between starch and hydrophobic polymer core.80 4 Applications in the Paper Industry An alternative to surface sizing is internal sizing. It also plays an important role in the interaction between starch and sizing agent. Charged hydrophilic protective colloid + + + + + + + + + Hydrophobic core + + + + + + Charged hydrophilic protective colloid 70 . The hydrophilic shell is highly swollen in water and normally carries either an anionic or cationic charge. exclusively low molecular weight sizing agents like rosin acids or alkyl ketene dimers (AKD) are applied. The composition of the polymeric core influences hydrophobicity. however. Polymer particles at the surface reduce the wettability of the surface. the addition of a sizing agent to the wet end before the formation of the paper sheet. 4 Paper Coating Starch Polymer protective colloid Polymer core Hydrophilic Hydrophobic Fiber Fig. The hydrophilic/hydrophobic balance of the surface can be individually controlled by: – the ratio between starch and hydrophobic polymer – properties of the starch-like film formation. The interaction between hydrophobic toner and polymer particle enhances the toner adhesion in case of photocopy papers. Thereby. 4. a hydrophilic/hydrophobic raster on the paper surface results in a highly accurate fixation of the dye right to the spot at the paper surface. Applied to ink jet papers. Whereas the hydrophilic areas allow a fast dewatering of the printing ink. color density and outline sharpness can be further improved. and viscous flow of the polymer particles Also. Furthermore. and water uptake – hydrophobicity. Coating is typically applied onto paper and board for printing or packaging 81 . Additional modification of the starch/polymer film by cationic groups results in an additional fixation of the anionic dyes by ionic interaction.4. swelling. The method involves coating the surface of the paper with a water-based pigmented coating color.4 Paper Coating Paper coating is the most important surface finishing process for paper in terms of both the amount of paper that is coated and the quantity of emulsion polymers consumed in the coating process. The emulsion polymer used in the coating color formulation binds the individual pigment particles together and helps the entire pigment layer to adhere to the surface of the paper. This proves to be very helpful in cases where the process conditions in the copier are insufficient to guarantee complete melting of the toner on the paper surface. emulsion polymers are also added to improve the processability and/or runnability of the coating color. the hydrophobic points prevent a spreading parallel to the paper surface. the addition of polymer dispersions to surface sizing formulations can lead to positive effects. in special paper applications like photocopy and ink jet papers. 4-6 Formation of a starch-polymer film. average particle size. mostly to the interior of the paper sheet. . wallpaper. Other specialty kinds of paper that undergo coating are labels. when the printing on one side of the paper can be seen from the other side) is to be prevented. The surface of an uncoated paper will contain fibers which are approximately 1–3 mm (1000–3000 µm) long and approximately 10 µm thick. The fibers are thus the limiting factor dictating image definition. the pigments used in the coating color can be easily ground to a particle size of less than 1 µm. Coating paper or board increases the homogeneity of the surface and considerably improves its optical characteristics such as gloss. Uncoated grade. smoothness. The crucial factor determining opacity is the volume of the coating. supercalendered Fig. While fillers are naturally better than cellulose in increasing opacity. The properties of the pulp severely limit the surface homogeneity achievable with uncoated papers. Low basis-weight papers require a high degree of opacity if show-through (i. The opacity of an uncoated paper is determined by the cellulose fibers and any fillers it contains. coated paper exhibits more uniform ink receptivity and better holdout than uncoated papers. 4-7 Effect of coated paper on offset printing. especially when using a rotogravure process (Fig. If this paper is printed by the halftone process using a 50 lines/cm screen. brightness. and opacity. the dots (200 µm) are smaller than the dimensions of the fiber. by contrast. they are unable to provide the opacity levels attainable by coating. the surface of a coated paper is. respectively. For the reasons given above. In contrast. 4-9). Figures 4-7 and 4-8 demonstrate clearly the differences in the quality of offset and rotogravure printing on coated and uncoated paper surfaces. and non-printed silicone papers which act as the backing sheets for self-adhesive labels. uniform and homogeneous in structure. While the surface of an uncoated paper comprises numerous individual fibers of varying degrees of hardness. Coating also produces a much smoother paper surface that is particularly a significant factor when printing individual dots.82 4 Applications in the Paper Industry applications.e. supercalendered Coated grade. since this determines . Fig. 83 . 4-8 Effect of coated paper on rotogravure printing.4.4 Paper Coating Coated gravure paper Uncoated gravure paper Fig. 4-9 the area of the pigment–air interface (within the coating layer) at which the scattering of incident light occurs. typical dotsize critical area for missing dots Result of printing paper of insufficient smoothness by the rotogravure printing process. unbleached). Figures 4-10a–c illustrate the common coating methods. along with the range of coating weights that can be achieved.. In this way. The major components of a coating color are: – inorganic pigments to cover the surface of the base paper – co-binder and thickener for controlling the processing properties – binder (water-soluble or disperse systems or a combination of the two) . either by purely mechanical means (calendering).1 Coating Techniques A number of different coating machines exist for applying the coating color onto the base paper. or by controlled addition of gloss-imparting pigments. the required level of solid content. and the viscosity of the coating colors. Calendering is only able to improve the gloss of an uncoated paper surface to a limited extent. Stiff blades are more commonly used in North America. These requirements must be taken into account when formulating a coating color for a particular application.g. a full range of coated papers from highgloss to semi-gloss to matte are easily obtained. opacifying pigments such as titanium dioxide (TiO2) and special techniques such as double or triple coating are used. The degree of brightness can be controlled by selecting appropriate pigments. It is apparent that the various coating methods place different demands on the rheological properties of the coating color.84 4 Applications in the Paper Industry Gloss is a critical property when assessing the quality of printing. The gloss of a coated paper surface can be varied over a wide range. If the base paper is of low brightness (e.4. 4. while bent blades are more widely used in Europe. The brightness of a coated paper also depends strongly on that of the base paper. by the coating process itself. but can also be adjusted by the use of optical brighteners or toning dyes or both. The quantities given here always refer to the amount of active ingredient required. the paper is smoothed as part of the calendering process.4. A more detailed description of the constituents of a coating color is presented in Sects 4.1–3 parts of other additives. Coating color compositions common in both North America and Europe for sheet-fed offset and rotogravure printing processes are listed in Tab. pigments are the principal constituent of any coating color.4. Once coated.2–4.4. binders being used in relatively small amounts. bent blade. For every 100 parts pigment. 4-2. (A) Stiff blade. Quantitatively. there are typically about 5–20 parts binder and 0. (B) Air-knife. and roll blade. 4-10 Coating equipment.4 Paper Coating Fig. (C) Pre-metered size press. Calendering involves subjecting the paper surfaces to high temperatures and pressures in or- 85 .4. In the soft-nip calender process. 4-2 Typical coating color compositions for sheet-fed offset and rotogravure printing processes in both North America and Europe. glossy surface. with typically twelve rolls in a supercalender stack. A distinction is made between soft-nip calendered and supercalendered papers. i. Sheet-fed offset Rotogravure North American formulation 75 parts fine kaolin clay 25 parts fine ground calcium carbonate 12 parts emulsion polymer 3 parts starch 0. immediately after the coating process and that the bulk of the paper does not decrease as much as in supercalendering.5 parts co-binder 0. and higher temperatures and lower pressures are used.75 parts calcium stearate der to create a smooth. 4.. The advantages of the soft-nip calendering are that it can be performed “on-line”.5 parts calcium stearate European formulation 80 parts fine ground calcium carbonate 20 parts fine kaolin clay (high gloss clay) 12 parts emulsion polymer 0.4. In the supercalender.5 parts calcium stearate North American formulation 85 parts delaminated clay 15 parts talc 5 parts emulsion polymer 2 parts starch 0. By varying temperature and pressure in a controlled manner.e.86 4 Applications in the Paper Industry Tab.5 parts optical brightener European formulation 50 parts talc 50 parts kaolin clay (coarse or high aspect ratio) 5 parts rotogravure sole binder 0. The smoothest and glossiest paper surfaces are achieved by supercalendering. the number of nips used to smooth the paper is greater. the number of nips is kept low. compared to the supercalender process. which serve to cover the surface of the base paper and thus to improve its optical properties.5 parts curing agent 0. a very broad range of gloss levels can be achieved. natural or precipitated – titanium dioxide .2 Pigments used in Coating Colors The main constituents of a coating color formulation are the inorganic pigments. Coating pigments must therefore satisfy the following requirements: – high purity – high brightness and opacity – high refractive index – good dispersibility and desirable rheological properties – amount of binder required should be low The most important pigments are: – kaolin clay (often referred to simply as china clay) – calcium carbonate. 3 Co-binders and Thickeners used in Coating Colors Pumping. the actual coating method require certain rheological properties of the coating colors. 4-3) lists the amount of binder required by various pigments to achieve a given level of binding strength (pick strength) for sheet-fed offset printing paper. There are a great number of different types in each of the two pigment groups: the calcium carbonate grades being distinguished mainly by particle size. whereas Newtonian or structurally viscous (i. The different pigments require different amounts of binder in order to ensure adequate adhesion of the coating to the surface of the paper and sufficient binding between the pigment particles. and. the use of ground calcium carbonate pigments in North America has been steadily increased so that the differences in coating color formulations between North America and Europe are being narrowed. In the recent years. immobilization point. 87 .4. Pigment Kaolin clay Ground calcium carbonate Precipitated calcium carbonate Titanium dioxide Binder demand (%) Paper Board 12 11 15 14 14 12 18 16 More binder is needed when coating board to ensure good glueability in folded cardboard boxes. Low-shear and highshear viscosities (shear rates of 10 to >106 s–1) and water retention values are highly important parameters. 4. These are aqueous dispersions which by using dispersing agents such as tetrasodium pyrophosphate or sodium polyacrylate can have a solid pigment content of greater than 70 %. solid content.e. pseudoplastic or shear-thinning) flow at high shear rates is important for all blade coating techniques. in roll coating applications. The pigments used in the preparation of coating colors are prepared as slurries. transfer. most particularly. Kaolin clay and calcium carbonate are the most commonly used pigments. and water retention capacity. For example. not one but a combination of several pigments is used in coating color formulations. For this reason. it is important to keep the specified binder-to-pigment ratios when formulating coating colors. re-circulation. The following table (Tab. while the plate-like kaolin clays are classified according to their so-called aspect ratio (ratio of surface diameter to thickness) and particle size. Coating colors are characterized by their viscosity.4 Paper Coating Nearly in all cases. Tab. 4-3 Amount of binder in coating colors as a function of pigment type. the thixotropic behavior of the coating color is particularly important.4. and glueability of the paper. co-binders and thickeners are added to coating color formulations.COO . influence the rheology of the coating color in a complex manner and are still not fully understood.1–3 parts of co-binder or thickener to 100 parts pigment and approximately 12 parts binder. If possible. printability. smoothness. These include natural products such as starch and synthetic water-soluble polymers such as polyvinyl alcohol and carboxymethylcellulose. Dispersion Solution pH < 7 pH > 7 Hydrophobic polymer chains in form of small balls (dispersion particles) .COOH Alkali . This high degree of hydrophilicity means that the particulate nature of the dispersion is lost when the acidic dispersion (pH < 7) is added to the alkaline environment of the coating color formulation (pH > 7). The resulting structures. Apart from the increase in the viscosity of the aqueous phase due to the dissolved polymer molecules. Typical amounts are 0. polymer chains stretch and dissolve Alkali MAIN MONOMERS CH2=CH-COOH Acrylic acid CH2=C(CH3)-COOH Methacrylic acid CH2=CH-COO-R Acrylic acid esters Acrylonitrile CH2=CH-CN CH2=CH-O-CO-CH3 Vinyl acetate Fig. The chemical composition and the behaviors of co-binders and thickeners with respect to pH are shown in Fig. other substances are used as co-binders and thickeners. those employed as cobinders and thickeners contain large fractions of hydrophilic (typically carboxyl-rich) monomers. these additives should be chosen to have a positive influence on the gloss. binding strength. which range from massively swollen polymer networks to polymer chains dissolved in the aqueous phase. 4-11 Chemical structure of synthetic co-binders. brightness. which are present as stiff chains at the pH of the coating color . In addition to the emulsion polymers described in greater detail below. 4-11.88 4 Applications in the Paper Industry To adjust these properties to the required level.COOH Anionic charges repel each other. In contrast to the emulsion polymers used as binders. and they should certainly not have a detrimental effect on any of these properties.COO . These structures. polymer bridges also form between the pigment particles (Fig. 4-12).4. A Dispersion + Alkali (pH>7) Solution Carboxylate groups with anionic charges Functional groups with high polarity Additional hydrophobic side chains Anionic charges repel each other Adsorption on pigment surfaces Associative interactions between polymers Extended polymer chains in the aqueous phase Polymer bridges between pigment particles Additional network structures (micelles) Viscosity in the aqueous phase High viscosity at low shear Very high viscosity at low shear B Latex particles Extended polymer chains Bridges between pigments Associative thickening Fig. 89 . the resulting associative interaction between the dissolved chains enables the low-shear viscosity to be increased still further. in addition. which are strongly dependent on the state of shear in the coating color. 4-12 Thickening mechanisms with various types of alkali-soluble co-binders and thickeners. (A) Alkali solubilization and thick- ening behaviors of various acrylate copolymers. result in a rise in its low-shear viscosity. If. (B) Various thickening mechanisms of synthetic co-binders and thickeners. one succeeds in incorporating hydrophobic side chains into the polymer.4 Paper Coating formulation. to improve the colloidal and rheological properties of coating color formulations and the printing and/or packaging properties of coated papers and paperboards. are: – styrene and butadiene – styrene and butyl acrylate – poly(vinyl acetate) – acrylates – vinyl ester and acrylic ester – ethylene and vinyl ester These synthetic binders commonly known as latexes are mostly modified with functional monomers such as vinyl acids. When the coating of paper began more than one hundred years ago. Synthetic binders. unlike the synthetic products.e.. whereas potato starch is more prevalent in Europe..4 Binders used in Coating Colors Both natural and synthetic binders are used in the paper coating. Partly because of their high price. Choosing the right thickener or cobinder for a coating color which is to be formulated for use in a particular type of coating machine is a complex task that requires good product knowledge and a considerable degree of practical experience. corn. and size of the pigments used as well as on the solid content of the formulation.90 4 Applications in the Paper Industry All effects induced by the co-binder and thickener in the coating color are very strongly dependent on the shape. The natural products of more lasting significance were starch (from potatoes. combine the characteristics of binder and cobinder. . though it is now frequently used in combination with synthetic binders. and rice) and casein (from milk). starch and casein cannot be added directly to the pigments. but must first be pre-processed. only treated (i. like the synthetic sole binders. Both are binders which. Corn starch is more common in the USA.g. polyvinyl alcohol represents a special case among synthetic binders. amides. Native starch containing two fractions of amylose (linear chain) and amylopectin (branched chain) is not suitable for coating paper and board because the amylose fraction tends to undergo retrogradation and the viscosity of coating colors made with native starch is too high [5]. Binders from natural sources are used in the form of aqueous solutions and include: – starch – soy protein – cellulose derivatives such as carboxymethylcellulose (CMC). 4. However. Table 4-4 presents a general comparison of natural and synthetic binders. gelatin in the manufacture of photopaper). charge distribution. animal glues and gelatin were used as binders. etc. acrylonitrile. For these reasons. Most paper mills carry out their own starch preparations in-house. As a water-soluble substance. The most important natural binder still in use today is starch.4. these materials are no longer used today except in a few specialty applications (e. which are prepared as aqueous polymer dispersions. depolymerized) or chemically modified starches are used. but also of securing them at the coating surface and of anchoring them to the base paper. Advantages Disadvantages Low-price binder Improves runnability. thermoplastic. The pigment particles at the coating surface must be held sufficiently tightly so that the coated paper can be smoothed in calendering and subsequently printed. 4-6. However.4 Paper Coating Tab. the most economical method of modification is enzymatic degradation to prepare enzyme-converted starches. The binder in a coating color formulation must be capable not only of binding the pigment particles together. ranging from soft to hard. low wet-pick strength Not compatible with satin white Risk of non-uniform printing in an offset printing Variable quality of commercial products Liable to rot In addition to starch. elastic Yes No Practically none High-very high Very good The properties of the starch depend on how it is treated or modified. another natural binder still used in North America is soy protein. 4-5 Evaluation of starch as a binder. The mechanical stress experienced by the surface of the paper depends very much on the printing process used and on the tack of the chosen 91 . Natural binders and polyvinyl alcohol Synthetic binders Sold as Quality consistency Dissolution/digestion needed Concentration in aqueous form Viscosity in aqueous form Film properties Solid (powder) Good to poor Yes Maximum 10–20 % High Very hard and brittle Tendency to foam Bacterial decay Water retention Binding strength (pick strength) Water resistance Casein yes.4. Tab. The advantages and disadvantages of these synthetic binders are summarized in Tab. starch no Yes High Medium high Poor Dispersion Very good No 50 % Low Variable. 4-4 Comparison of natural binders including polyvinyl alcohol with synthetic binders. Emulsion polymers were first used successfully as coating color binders in the nineteen forties. The best results are achieved by ethylation. It is mainly used for recycled board coatings. Table 4-5 compares the advantages and disadvantages of using starch as a binder. oxidized starches are widely used in North America. particularly well-suited for roll coating (thixotropic coating colors can be prepared) Coating colors with a high solid content can be prepared Low binding strength compared to synthetic binders Highly soluble in water. Also. Table 4-7 provides a rough guide to the amounts of binder required for the various types of printing process. causing set-off in the stack (i. Tab. depending on the printing process used. but also can be detrimental to quality. high levels of solid content possible Freeze-sensitive Water resistance of coating is higher than that achieved with natural binders No acceptor sites for optical brighteners Better gloss and smoothness attainable Simple to use: – no digestion needed – feed can be controlled via a flow meter printing ink. Using too much binder not only increases the price of a coating color unnecessarily. 4-7 The dependence of binder quantity on printing process. is repelled by the surface.. 4-6 Advantages and disadvantages of emulsion polymers as binders. More binder is needed for coated board in order to meet such additional requirements as folding strength and glueability. Printing process Amount of binder per 100 parts of pigment Letterpress printing Sheet-fed offset process Web offset process Flexographic printing Rotogravure process 8–15 parts 10–20 parts 10–18 parts 10–18 parts 4–10 parts The amount of binder in coating colors used to coat board that is to be printed by rotogravure. the transfer of wet ink from a newly printed sheet to the reverse side of the following sheet).e. in extreme cases. The amount of binder added to the coating color formulation must therefore be chosen appropriately. or the sheet-fed offset process is usually somewhat greater than in coating color formulations for paper. . flexography. Large amounts of binder can cause the porosity of the coating to decrease so much that the printing ink does not transfer properly to the surface or. Advantages Disadvantages Binder properties can be optimized to meet requirements of printing process High transportation costs (50 % water) Does not affect coating color viscosity.or water-resistance. Drying times increase considerably as a result. Special papers are an exception to this rule because in these materials the binder not only determines the paper’s printability. but also performs other functions such as controlling its oil. The binder accounts for approximately 15 to 40 % of the total cost of a coating color.92 4 Applications in the Paper Industry Tab. etc.e. However.5.4 Paper Coating In addition to the amount of binder used. gloss) and on printability (ink absorption. the most important methods of testing coated papers will be described. low number of missing dots) from the rotogravure cells to the paper. requires paper which is both smooth and compressible. Once printed. The most exacting requirements on binder strength must be met by paper grades to be printed by the sheet-fed offset process.e. To guarantee the even and error-free transfer of the printing inks (i. The extent to which a coated paper needs to fulfil the various requirements listed above depends on the printing process to be used. the paper in a web offset press passes through a drier in order that the printing ink solvents and any residual water within the base paper can evaporate. Pruefbau) – gloss (specular reflection intensity) – brightness (reflection of visible light λ = 475 nm) – opacity (hiding opposite to transparency) – smoothness (Parker Surface Roughness Test. the requirements on the binding strength for paper printed by the web offset process are not so high. Because an aqueous fountain solution is used in the offset process. the paper must exhibit high resistance to blistering. which is a dominant factor determining the binding strength. These important properties are: – pick resistance (dry pick strength.4.) – porosity – compressibility (rotogravure) – stiffness (more important for light-weight papers) – drying/setting of printing inks – mottling (uneven uptake of ink) – water absorption capacity (the capacity of the paper to absorb water. Pruefbau) – water resistance or wet pick resistance (wet pick strength. the demands made on optical parameters (brightness. It therefore has the lowest requirements in terms of the pick strength of the paper. the binding strength of the moist paper) is crucially important. the wet pick strength (i. As the sheet-fed offset process is principally used to create high-quality prints. thus permitting the transfer of inks to moist surfaces) – ink absorption capacity (the capacity of the paper to absorb ink and to prevent ink being transferred from the freshly printed areas to the rubber blanket of the following printing station) – blistering in web offset process (blister-free printing) – glueability of board and packaging paper In Sect. the type of binder is also of crucial significance in determining the properties that influence the appearance and classification of paper and board. the water vapor can become trapped causing blistering and detachment of the coating layer. IGT method. absence of mottling) are particularly stringent. 93 . 4. If the porosity of the coating is too low. As the printing inks used in a web offset press have less tack than those used in the sheet-fed offset process. IGT method.4. The rotogravure process uses inks with a very low viscosity. Fig. porosity. Acrylic ester copolymers are significantly less prone to thermal or UV-induced yellowing (as shown clearly in Figs 4-13 and 4-14) and these are the copolymers of choice for the production of high-quality. stiffness. Generally speaking. The most common combinations are styrene with butadiene or acrylic esters and vinyl acetate combined with ethylene or acrylic esters. These are: – nature of the constituent monomers – glass transition temperature – particle size and particle size distribution – molecular structure of polymers As mentioned at the beginning of this section. gloss. long-life prints. . The high smoothness and compressibility required for paper grades used in the rotogravure printing process are achieved by using binders with a much lower glass transition temperature (<0 °C). binders based on polyvinyl acetate or on styrene-acrylate produce a more porous coating than do binders based on a butadiene copolymer. An important difference between styrene-butadiene binders and styrene-acrylic ester binders is the tendency of the binder to yellow under the influence of UV radiation or heat. Paper used in offset printing contains binders whose glass transition temperature lies between 0 °C and 30 °C. the binders used in coating color formulations are based on combinations of different monomers. Products containing a butadiene-based binder are considerably more susceptible to yellowing due to the much greater fraction of double bonds in the polymer. one generally focuses on those four parameters whose effect on binder properties is sufficiently well known. 4-13 Thermal yellowing as a function of the chemical composition of the binder. Figure 4-15 shows the typical dependence of dry and wet pick strength. The glass transition temperature of a polymer is determined by the amounts of its different monomer constituents. and evenness of offset printing on the glass transition temperature.94 4 Applications in the Paper Industry When choosing or developing a suitable binder for one of the various printing processes. Goal .e.. Binders based on a styrene-butadiene combination therefore have a more cross-linked and branched polymer structure. In contrast to the other possible monomer components.printability Glass transition temperature (Tg) Particle size and particle size distribution are influenced by the choice and amounts of emulsifiers and protective colloids that a polymer dispersion contains.porosity Goal Fig. butadiene possesses two double bonds both of which can act as polymerization sites.dry pick .paper gloss . filtered. 4-15 Dependence of paper properties on the glass transition temperature of the binder. binders used in the paper coating process have particle sizes of between 100 and 300nm. Figures 4-16 and 4-17 demonstrate that both the viscosity of the coating color and the wet pick strength of the coated paper are strongly dependent on particle size. enabling it to be conveyed.wet pick . The extent of cross-linking affects the dry and wet pick strength. which is a highly significant parameter in 95 . These components are added to stabilize the dispersion thus making it both processable (i. 4-14 UV-induced yellowing as a function of the chemical composition of the binder. Typically.4.print gloss . .) and storable. the print gloss and the degree of blistering. Variations in the emulsion polymerization process also have a major effect on the size and size distribution of the polymer particles.4 Paper Coating Brightness Loss 14 After 8 hours of UV exposure 12 10 8 6 4 2 0 Base paper Chemical Basis Styrene/Acrylate Chemical Basis Styrene/Butadiene/Acrylate Chemical Basis Styrene/Butadiene Fig. etc. metered. Additional information on paper coating can also be found elsewhere [6–14]. mPas 1200 1000 800 600 400 200 0 50 100 150 200 250 300 350 Particle size (D). Wet pick strength 100 50 Wet pick strength of paper and board coatings improves with decreasing particle size 0 100 150 200 250 Particle size (D). binding strength and blister resistance show a mutually opposed dependence on the relative molecular weight of the polymers. 4-16 Dependence of the viscosity of binder dispersions on particle size. binding strength and blister resistance tend to oppose one another and cannot therefore be optimized by the choice of binders alone (Fig. 4-19). can be controlled in the two classes of binders by careful adjustment of the polymerization conditions and by the addition of a so-called chain transfer agent. nm Fig. A very similar dependence is observed with the styrene-acrylate binders (Fig. The polymer structure. nm Fig. In this case. 4-17 Dependence of the wet pick strength of binder dispersions on particle size.96 4 Applications in the Paper Industry Viscosity. web offset printing. 4-18). Unfortunately. and thus the desired balance between binding strength and blister resistance. . The printability and the final print quality can often be successfully predicted on the basis of these relatively simple tests. 4-19 Relationship between blister resistance and binding strength for styreneacrylate binders. The following tests simulate the stresses experienced by the paper surface during the printing process. the most important methods of testing coated papers will be described. Dry pick strength Molecular weight of Styrene/Acrylate copolymers 4. Whether or not the paper is dampened prior to printing is also of considerable importance. in particular ink splitting during the offset process (Fig. 4-18 Relationship between blister resistance and binding strength for styrene-butadiene binders. Coating strength tests The strength required for a paper surface is to a large part determined by the tack of the ink used in the printing process.4 Paper Coating Blister resistance Pick strength Pick strength Blister resistance Low % Gel content High Fig. 97 .4. particularly in the offset process. Blister resistance Fig.5 Test Methods In this section. 4-20).4. However. After wetting the test strip at constant speed and uniform pressure to create a precisely defined moisture content. When plotted as a function of printing speed. Dry pick test This test determines the tensile strength of the coating strip when subjected to ink splitting during the printing process: The test strip is printed at a precisely defined plate pressure while being accelerated through the printing zone. since in practice. the paper passes through not one but several printing presses (4–8 in the offset process). the color density values are a measure of the water resistance of the paper strip. blanket printing ink ink splitting paper or board Cylinder Wet pick test This is a test to determine the water resistance of a coated paper. the measuring dots used to determine color density are chosen randomly. the strip is printed with the testing ink while moving at constant or increasing speed through the press. This is the so-called offset test.98 4 Applications in the Paper Industry Fig. Using a hole template to define ten separate measuring dots (representing precisely defined strip speeds). Ink splitting in offset printing. The location of the first picking point and the position at which picking is visible right across the test strip are determined by inspection and analyzed quantitatively with the aid of a computer program. a further test can be performed to examine the effects of this sequential stressing of the paper surface. When the paper strip is printed at constant speed. . 4-20. the color density of each of the ten dots is measured using a densitometer and then expressed relative to the full tone of the printed surface. Printability tests Mottle test This test determines the evenness of the printing. If the coating on the paper is unevenly distributed. Rotogravure test This test determines the suitability of paper or board for printing by the rotogravure printing process: To perform this test. In North America. The counter strip will pick up some of the non-dried printing ink from the original strip.4 Paper Coating Offset test This test simulates repeated ink splitting caused by contact between the printed area and the rubber blanket during the printing process. the rate of ink setting and the number of passes-to-fail must be balanced.4. the ink gloss is measured using a gloss meter. Paper-Ink Stability Test (P&I Test) is widely used [15]. Printing is carried out at a constant speed 99 . The number of passes at which the first signs of picking become apparent is recorded. Ink set-off test This test measures the speed at which the oils in the printing ink penetrate the coating of the paper during the drying (setting) process: A test strip is printed from an inked plate applied at a precisely defined pressure and a constant printing speed. The test measures the rate of ink setting by calculating the slope of the ink splitting force as a function of the number of impressions taken at a given time interval. Measurement of ink gloss A test strip is printed using a precisely defined plate pressure and constant printing speed. The inhomogeneity of the printed image is either ranked visually or with a mottle tester (which measures fluctuations in color density). the faster the rate of ink setting. The gravure cylinder is inked and the excess ink removed from the non-printing areas by the blade. this test measures the number of passes-to-fail. A blank counter strip is pressed against the original strip once every 15 s during the duration of the test (900 s). the printed image may appear cloudy as a result. for press runnability. The color density of any ink transferred to the counter strip is measured using a densitometer. a gravure cylinder and blade must be added to a standard IGT tester. In general. Therefore. Ink is transferred to the test strip from an inked plate at an exactly specified plate pressure and a defined constant speed. Once the test strip is dried. the lower the number of passes-to-fail. and subsequently split three times by an offset rubber blanket-covered cylinder. Ink is transferred to the test strip from a plate at an exactly specified plate pressure and a constant known printing speed. Also. The printed region is subsequently reprinted five times at 10-s intervals using the same plate but without re-inking. The Paper-Ink Stability Test mentioned as an offset test can provide information on ink set-off in terms of the ink setting rate [15]. Elmar Schwarzenbach.and Graphischen Industrie. coating. This chapter has been based on an English translation of the Paper Industry portion of Chapter 5 Anwendung in der Papier. stiffness relationship as well as by using recycled and secondary fibers more effectively. etc. Some of the challenges are conservation of raw materials. environmentally friendly papermaking. .). 1998. especially trees as fiber source. There are many challenges confronting the paper industry. It will be interesting to see how well the paper industry can succeed in the 21st century. coating. by improving the current basis weight vs. better quality coated paper and paperboard products at lower costs.5 Concluding Remarks Science and technology in the fields of paper surface sizing and paper coating have been significantly advanced over the past two decades and will be continued to move forward to meet the needs in the paper industry. These challenges will require us to continuously innovate in papermaking. This particular test method is known as Helio test. Acknowledgments One of the co-authors (DIL) would like to thank his two other co-authors (JS-T and ES) for letting him contribute to this chapter. by Jürgen Schmidt-Thümmes. Wiley-VCH. and finishing processes.100 4 Applications in the Paper Industry and a defined force exerted by the impression cylinder. Dieter Distler (ed. and finishing. 4. Each test strip is examined to determine the length at which 20 missing dots have occurred. and Berhard Prantl in Polymerdispersionen. Latimer. 38. John Wiley and Sons. 10 A. New York. Heiser. De Groot. Booth. World Emulsion Polymers.. W. Chapter 1 in: Pulp and Paper: Chemistry and Chemical Technology. 1975. Tappi Monograph Series. Gaspar. 15 N. BASF Corporation. Tappi Monograph Series. 37. Coating Equipment and Processes. 9 R. L. L. F. I. 1980. 13 J. 1975. 1976. Ita. L. .).W. C. Göttsching. A. Tappi Mono- graph Series. S. 1987. 120–136. Paper.101 References 1 P. Cellulose and Hemicellulose. Lancashire. 37. 37. 1–38. Starch and Starch Products in Paper Coating. Tappi Press. 37. Tappi Monograph Series. 1994. Sinclair. Econ Verlag. pp. Pita. 98–119. 11 E. L. The Essential Guide to Aqueous Coating of Paper and Board. Casey (ed. September. Vol. Vienna. 1990. P. 211. Cogan. 1975. F. New York. 1975. H. 3rd edn. 1975. 22–63. Jezerec. Kaulakis. Tappi Monograph Series. Shafizadeh. 2 3 4 5 6 7 The Freedonia Group. p. F. Hagemeyer. P. T. P. 14 R. Vol. W. McGinnis. Düsseldorf. Walsh. G. H. Sandreuter. 126. 12 T. Encyclopaedia Britannica. 1990.). UK. G. Kearney. The New Encyclopaedia Britannica. Tappi Mono- graph Series. R. Maurer (ed. 64–69. J. Lockwood. Tappi Coating Confer- ence Proc. A. 1997. 9. 8 G. Papier in unserer Welt. 1999. R Dean. J. 1970. J. R. D. 37. one-half solvent in an estimated flexographic ink market of 27 000 tons. Approximately one-half of flexographic ink consumed is water based. The total Japanese ink market for all six printing processes is over 400 000 tons for year 2000 or approximately 1. gravure. 3-527-60058-2 (Electronic) 5 Applications for Printing Inks Barna Szabo 5. greater than twothirds solvent based in an estimated flexographic ink market of 34 000 tons.4 billion $US. approximately two-fifths of flexographic ink is water based. threefifths is solvent based in an estimated flexographic ink market of 180 000 tons.1 Introduction The major printing processes used worldwide are: lithographic. Letterpress is one of the smallest.5 billion $US.5 billion $US. The total European ink market for all six printing processes is estimated at over 0. In the United States. Oil. The total Latin American ink market for all printing processes is over 125 000 tons for year 2000 or approximately 750 million $US. letterpress and digital. water based gravure volumes are negligible in Europe and Latin America. The flexo ink market in Japan is very small. In Europe. The major volume of water based flexo ink consumed in the United States is for printing corrugated containers.9 million tons for year 2000 or approximately 4. Lithography is the largest volume printing process. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. flexographic. one-third is solvent based in an estimated flexographic ink market of 200 000 tons. Solvent based ink is used mostly for printing gravure. In Latin America less than one-third of flexographic ink is water.Polymer Dispersions and Their Industrial Applications. The total US ink market for all six printing processes listed above is estimated at over 1. Both water and solvent based inks are used in screen and digital printing.1 million tons for year 2000 or approximately 4. 103 . Less than 23 000 tons per year of water based ink are used for gravure printing in the US and less than 14 000 tons in Japan.and solvent-based ink systems are used in the lithographic and letterpress processes. KGaA ISBNs: 3-527-30286-7 (Hardback). approximately two-thirds of flexographic ink is water based. these consume comparatively small volumes of ink. Flexography is the only printing process that consumes significant quantities of water based (aqueous) ink. although it is readily adaptable to aqueous ink. screen. 5-1. 5-1 The aqueous ink market in 2000. Molecular weight. rosin fumarates (i. Flexo and gravure inks are referred to as fluid inks because of their low viscosity. They are low cost. multi-wall bags. paperboard cartons. Emulsion polymers provide a wide range in properties and low viscosity. A flexo ink is comprised of low boiling point solvents for low temperature evaporation and fast drying.2. estimated 2/3 2/5 <1/3 1/2 200 180 34 27 1100 910 125 400 1/3 3/5 >2/3 1/2 Emulsion polymers are used in flexographic and gravure ink for printing flexible packages. Pigment dispersion stability. The “support” resin is a low to medium molecular weight styrene acrylic or other water soluble resin. 5. Most presses are equipped with air circulating dryers. It comprises up to 60 % solids content of the emulsion and replaces up to 90 % of surfactant stabilizers. estimated Water and solvent Total printing ink × 103 tons.1 Flexographic Ink A flexo ink is a low viscosity (fluid ink) suitable for transfer from an ink fountain via anilox roll to the plate cylinder and substrate. and other flexible substrates (films) and paper products. The level of styrene monomer used in ink grade emulsion polymers is maximized due to film hardness requirements of paper and paperboard materials and its low price. 5. Rosin based resins have been used in printing ink since the early days of letterpress printing. US Europe Latin America Japan Flexo ink Solvent-based Water-based Total flexo ink × 103 tons.1. and ink re-solubility are important properties to consider in the design of emulsion polymers for printing ink. Aqueous rosin based resin solutions provide the performance properties similar to use of rosin phenolic and rosin maleic pentaerythritol esters in a lithographic printing ink. Tab.e. Prior to the mid 1970s. and particle size distribution are key properties that are varied to meet specific ink requirements. a wider range in properties than possible with rosin became important. newspapers. Tg (glass transition temperature). and are easily modified to vary viscosity and hardness. When aqueous flexo and gravure printing began displacing solvent based systems. . give inherently good pigment dispersion properties. Cost is a key factor in ink raw material suitability for most ink systems. sodium and amine rosin salts) were the main resins used in aqueous ink. It dries by evaporation of the solvent (water). Styrene acrylic based emulsion polymers are most commonly used in printing ink applications.2) is used in most ink grade emulsions to maintain these properties. A “support” resin (Sect. corrugated boxes.104 5 Applications for Printing Inks The aqueous ink market in 2000 is summarized in Tab. room temperature film formation. A diagram of a flexographic press is given in Fig. isopropyl alcohol).1 Introduction Fig. 5-1 Flexographic press [1]. – An impression cylinder (smooth and polished chrome). Only aqueous ink is discussed in this chapter. The composition and solvency is limited to prevent swelling of rubber or photopolymer-based rolls. 105 . and minor levels of aliphatics such as heptane are mostly used. minimal concentrations of acetates (i.5.5 cm). A smooth polished chrome cylinder that holds the substrate in contact with the printing plate. Water. 5-1.e. The printing plate’s raised surface replicating the image contacts the substrate to transfer ink. A photopolymer printing plate is attached to the plate cylinder. The anilox is engraved with cells (of inverted pyramid shapes) varying in density (size) between 80 to 1000 cells per linear inch (2. A flexographic printing press consists of: – An ink fountain roll (rubber). The fountain roll rotates in a reservoir of ink and transfers a large volume of ink to the anilox roll. – A printing plate cylinder (steel). A reverse angle doctor blade is used to wipe excess ink. alcohols. The anilox supplies a precise volume of ink to the raised surface (print image) of the printing plate. – An Anilox ink metering roll (chrome plated or ceramic coated). ethyl. Acetates and aliphatics are used to solubilize polyurethane and polyamide resins used in solvent based laminating ink. The cylinder rotates through the ink fountain. Ink rheology. solvent. Fig. 5-2. 5-2 Gravure press [2]. The gravure cylinder is engraved with cells of varying sizes replicating the print image. surfactant. Its function is to control ink transfer. An excess is wiped by a doctor blade. crosslinker. pigment. Ink is transferred directly from cylinder to substrate. Gravure utilizes various environmentally compliant solvents as required by specific printing applications. Only water based ink is discussed in this chapter. The polymer (resin) functions as the “vehicle” for carrying the pigment. The ink is drawn out of the cells of the print cylinder by means of impression pressure and capillary action.1. A diagram of a gravure press is given in Fig. It is also a key component for achieving printing . and additives. – An impression cylinder. Ink fills the cells.2 Ink Composition An aqueous flexo or gravure printing ink is composed of polymer. electron charge and surface energy are key variables that effect transfer. A gravure printing press consists of: – A gravure print cylinder (chrome). An ESA (electrostatic assist) mechanism is sometimes used to assist in the capillary action. The impression cylinder is a rubber coated cylinder that keeps the substrate in contact with the print cylinder.106 5 Applications for Printing Inks 5.2 Gravure Ink A gravure ink is a low viscosity (fluid ink) with rheological characteristics suitable for transfer “out of” small cells of an engraved cylinder to the substrate. wax. 5. A gravure ink is comprised of low boiling point solvents for low temperature evaporation and fast drying. w/w) Gravure ink Component Amount (%.2). and heptane are also used in flexo and gravure ink. moisture.2. A printing ink formula is frequently modified to meet exact color reproduction specifications and/or a customer’s changing performance requirement.3) Amine neutralizer Wax emulsion compound Wax powder Surfactant Crosslinking additive Silica additive Corrosion inhibitor Defoamer Other additives Total Amount (%. emulsion vehicle (Sect. 5. An average consumer would not purchase a food item (i.2 Ink Composition performance properties.1) Emulsion vehicle (Sect. The smooth surface provides gloss for desirable visual effects.1). oxidation. solution vehicle(Sect. w/w) Dispersion varnish Organic pigment Total 55–70 30–45 100 35–50 25–35 10–20 0. Colorfastness and lightfastness is important to maintain desirable visual effects of printed materials.2. 5.2. 5. The polymer provides viscosity and rheology characteristics necessary for transfer of ink from press to substrate. 5. 5-2 is a generic formulation for an aqueous flexographic or gravure ink. toluene. Using intermediates minimizes the number of raw materials handled at the ink manufacturing or blend- 107 .3). This effect would convey a message about its lack of freshness.5–1.5. Aqueous flexographic ink Component Pigment dispersion (Sect. and wax emulsion compound (Sect.2. 5. It provides resistance to environmental conditions such as: heat and temperature.2) Solution vehicle (Sect.2. 5. Organic pigments are used in most cases for lightfastness and transparency. freeze–thaw. It provides adhesion to the substrate. Water is used mainly in flexo and gravure printing processes.25–0. Other solvents such as ethyl-isopropyl alcohol. Oxidized or crosslinked polymer structures provide resistance to “chemicals” that contact printed packages. The pigment provides the color.5 100 Most commercially manufactured printing inks are made from intermediates such as: pigment dispersion (Sect.5 0–2 2–5 0–1 0–1 0.2. light. etc. but only aqueous flexo and gravure inks are discussed in this chapter. Tab.5 2–5 0–2 1–1. box of cereal) with faded or shifted colors. ozone.4). Water (solvent) is used to solubilize the resin or polymer. The polymer is the material or compound for dispersing a pigment and preventing its re-agglomeration. The branched network of the polymer provides hold-out on porous substrates. 5-2 Generic aqueous flexo or gravure ink formulation.2.e. 5. It provides resistance to scuffing or rubbing. Illustrated in Tab. ethyl-isopropyl acetate. Most pigments used in pigment dispersions for printing ink are surface treated with a resin or polymer compatible with the pigment surface chemistry. The poly- . Most emulsion polymers used in printing ink vary between 20 nm to 200 nm. The most common polymers used to disperse pigments are: low to mid-molecular weight styrene acrylics. 5-3 Solution polymers used for pigment dispersions. 5. Non-polar intermediate sections of a polymeric anion add adsorbed layer thickness [3]. the smaller emulsion polymer particles are not suitable for forming stable dispersions of organic pigment particles and agglomerates. ink viscosity stability. Tab. or as chips. It facilitates the production of ink in blending plants with minimal equipment and at locations close to the customer and/or printer.. A presscake is dried by various drying processes to yield pigment agglomerates in a large range of particle sizes. SMA (styrene maleic anhydride). Chips are a dry form of dispersed pigment particles in a polymer. Tg (°C) Mw (g mol–1) Acid number (mg KOH g–1) 140–170 NA NA 125–145 70–125 15– 20 45–110 80– 90 12000– 18000 30000– 35000 50000–150000 2000– 10000 210–240 65– 70 165–285 115–200 The stabilization of organic pigment dispersions is achieved by use of polymeric anionic surfactants that provide strong adsorption on the polar surface of the pigment and hydroxyl groups for interaction with the aqueous phase.02 to 100 µm.02 to 100 µm (aggregate size).5 to 1. between 0. Producing ink from intermediates offers flexibility in modifying formulas to meet color reproduction specifications and changing customer application requirements. Table 5-3 illustrates the physical properties of polymers used for dispersing pigments. Because of a pigments relatively large particle size and its wide range in particle size distribution. Styrene acrylic I Styrene acrylic II SMA ester Rosin fumarate ester Softening point (°C) Glass transition temp. or rosin fumarate ester resins. transparency and pH drift are controlled by use of polymers such as those containing salt groups and hydroxyl functionality. The degree of stabilization of a pigment dispersion (which relates directly to color strength development).108 5 Applications for Printing Inks ing site. High speed mixers are used to disperse a pigment from a dried form or an aqueous slurry. A presscake is a high solids dispersion of pigment in water. The particle size distribution of particles in a pigment dispersion are typically 0.2. A typical organic pigment particle size ranges between 0.1 Pigment Dispersion The pigment dispersion is made from dry pigment (which is surface treated) dispersed in an aqueous polymer solution. Pigments used in aqueous flexo and gravure ink are supplied as a presscake. in dry form.5 µm. They do not have sufficient mobility to wet the surface area. For example.e. It is important that resins or polymers used in the surface treatment of pigment.2 Emulsion Vehicle The emulsion vehicle provides the “workhorse” performance characteristics of an ink (i. chemical resistance. A fumarated rosin polyamine condensation resin is explained in a second Westvaco patent – Modified Rosin Resins for Waterbased Inks. Viscosity is not dependent on molecular weight but only on solids content and particle size distribution.5.2. A resinated pigment minimizes agglomeration. Compared to other polymers (i. contributes to increased color value and improves the efficiency of the dispersion process. terpolymers of styrene-α-methylstyrene and other acrylate monomers (i. Furthermore. thus more flexible polymers.e. and poor printability (e. gloss. A pigment is surface treated or “resinated” as part of the pigment manufacturing process. Higher levels of styrene give higher Tg. high molecular weights (>200 000 g mol–1) are achievable at low viscosity. An explanation about the type of resins and polymers used for surface treatment of pigment is a separate segment of ink-pigment technology that is not covered in this chapter. Emulsion vehicles are prepared by emulsion polymerization in water in the presence of surfactant stabilizers.2 Ink Composition mer is added as a dissolved aqueous solution during the “pigment striking” step. butyl acrylate. acrylic acid. adhesion. are compatible and do not react with the resins and polymers used in the pigment dispersion. increased low shear viscosity (known as “thixotropy”) leading to a change in ink rheology. This type of resin has high softening point and gives relatively stable low viscosity ink [4]. They are used to achieve specific ink application properties not obtainable by the conventional resins and polymers discussed above. 2 hydroxyethyl acrylate. The condensation reaction product of polyamines with certain rosin-based polycarboxylic acids results in an efficient pigment dispersion resin and gives a stable viscosity over a wide range in pH. Surface treated pigments are known as “resinated” pigments. heat. amino acrylate). These resins and others not discussed provide alternatives for dispersing pigments. Emulsions with small par- 109 .e. low viscosity. between 8. As a result. Higher levels of butyl and 2-ethylhexyl acrylate give lower Tg. methacrylic acid. and chemical resistance at low cost).g. printability. they must be compatible with the emulsion and solution vehicles of the ink. or adhesion to films and lamination ink (cohesive) bond strength. In addition there are various hybrid resins in use to disperse a pigment. It adheres to the pigment surface via physical and/or chemical attraction. a glycerol ester of fumarated rosin is further esterified with a styrene-allyl alcohol as taught in Westvaco Chemical Corporation’s patent – Rosin-Based Grind Resins for Aqueous Printing Ink. polyurethanes) styrene acrylics do not give good alkali resistance. Incompatibility between these components may cause: pigment re-agglomeration (resulting in a loss of color strength). Most printing ink emulsion vehicles are polymer dispersions composed of styrene acrylics. ethyl acrylate. variable ink transfer) performance. methyl methacrylate..5 to 10. re-solubility in water.5 [5]. 5. 2-ethylhexyl acrylate. and insure film coalescence. Air Products. Most printing ink emulsions are “resin supported”. after evaporation of water from the ink. A support resin provides ink re-wettability. Polyurethanes are known to give excellent chemical and product resistance properties but increase cost. Goodrich and others. Outlined in Tab. They are produced by emulsion polymer manufacturers such as: SC Johnson Polymer. 5-4 are: applications. Westvaco. Printing ink emulsion polymers contain a “support” resin to reduce MFFT (minimum film forming temperature). a fumarated rosin ester offers advantages such: as improved gloss. An emulsion vehicle comprises 25 to 35 % of the total ink formula. The crosslinking reaction between ketone groups and a bishydrazide proceeds rapidly at room temperature. may be used. Rosin based support resins are lower cost. Inc. B. Emulsion polymers are supplied in bulk quantities at solids levels between 45 and 60 %. then used as a support resin in ink grade styrene acrylic emulsions. Avecia. pH stability. Westvaco’s US Patent 5 656 679 teaches that a rosin fumarate reacted with an alkanolamine containing at least one secondary amine and one hydroxyl group is used as a support resin for ink grade emulsions for providing improved adhesion to films [7]. Polyurethane supported styrene acrylic emulsion polymers may be used to balance the high cost of polyurethanes and provide improved chemical resistance [8]. improves compatibility with pigment dispersions. The Air Products novel dispersion contains a quaternary ammonium polyurethane acrylic hybrid carboxylate salt and pendant acrylate epoxide that selfcrosslink upon evaporation of water and ammonia. The table is sorted by increasing Tg. Akzo’s novel polymer contains a diacetone acrylamide reactive monomer and a bishydrazide. According to Westvaco’s US Patent 5 216 064 [6]. . A water soluble polyurethane is made by adding acid modified monomer to the polymer backbone. low polarity. A rosin fumarate ester can be used as a “support” resin for ink grade emulsions. and physical properties of the styrene acrylic emulsion vehicles used in flexo and gravure ink. absence of residual glycol used in processing a styrene acrylic. near Newtonian rheology. the polymer is neutralized with amine. an aqueous dispersion of an acid functional polyurethaneepoxy acrylate hybrid (self crosslinking for improved chemical resistance) [9] patented by Air Products and Chemicals.F. and improves ink transfer and printability. emulsion characteristics.110 5 Applications for Printing Inks ticle sizes impart properties similar to solution resins with advantages of: low viscosity. For printing inks that require specific properties not obtainable by conventional styrene acrylic emulsions. and insolubility after drying for immediate water resistance. A “support resin” also decreases the need for surfactants. A higher solids emulsion gives faster drying. Support resins are typically styrene acrylic polymers with acid functionality that are amine neutralized. Rohm & Haas. or a self crosslinking styrene acrylic emulsion which reacts upon evaporation of water [10] patented by Akzo Nobel Resins BV. and higher resin solids. 48–52 45–50 45–50 25–40 20–25 47–49 S.C. (%) 8.2–8.7 7.9–8.5 8.5–9.5 6.0–7.9 7.9–8.3 8.2–8.4 pH 150– 500 150– 500 150– 500 45–2500 2500–6000 700– 900 Viscosity (mPa s) >200000 >200000 >200000 ~100000 70000–100000 >200000 Mw (g mol–1) 40– 55 40– 55 40– 55 125– 50 120–130 35– 50 A.N. (mg KOH g–1) 95–105 95–105 40– 48 30– 35 10– 35 –30 to 1 Tg (°C) P.S., number average particle size distribution in nanometer; S.C., solids content; A.N., acid number; MFFT, minimum film forming temperature 180–220 55– 65 Folding carton Flexo news 40– 50 160–180 Direct print corrugated Cup, plate, multi-wall bag, gift wrap 65– 75 120–140 Pre-print corrugated P.S. (nm) Surface print Application Tab. 5-4 Typical styrene acrylic emulsion vehicles used in flexo and gravure printing inks sorted by increasing Tg. >60 >60 >45 <24 <24 < 7 MFFT (°C) 5.2 Ink Composition 111 112 5 Applications for Printing Inks 5.2.3 Solution Vehicle Solution vehicles consist of water soluble polymers not manufactured by emulsion polymerization. The solution vehicle is an alkali soluble polymer in aqueous solution or a blend of polymers with combined properties into a single waterborne varnish. Soluble polymers are made by free radical polymerization in a processing solvent or as addition or condensation products with heat reaching temperatures up to 265 °C. Solution vehicles are mixtures of soluble resins unlike emulsion polymers. A solution vehicle is used to increase adhesion to film and improve ink printability or transfer to meet specific performance requirements. The solution vehicle provides pigment dispersion stabilization, transparency, low film forming temperature, gloss and re-solubility. An alkali soluble resin is a carboxylic acid functional polymer neutralized (solubilized) with ammonia, amine or sodium hydroxide. The acid numbers are generally above 100. Ammonia or volatile amines are used in most aqueous inks except for news print inks. After evaporation of the amine, the resin becomes insoluble and resistant to water spray or other water contact. The ink is re-solubilized with alkaline water for the clean-up cycle. For news print ink, the polymers are solubilized with sodium hydroxide to maintain re-solubility (open time) of the ink on the press. News print ink pressman prefer unlimited open time and fewer clean-up cycles. Water resistance is not required since ink penetrates the news print paper fibers. The key solution polymers (resins) used in printing ink are styrene or rosin based. Styrene-α-methylstyrene monomer and acid functional co-monomers (i.e. acrylic or methacrylic acid) comprise the bulk of styrene acrylic solution vehicles used in printing ink. Rosin acid reacted with fumaric acid gives a tri-functional “adduct”. The “adduct” is partially esterified with polyols such as pentaerythritol, glycerin, diethylene glycol, etc. to achieve a range of acidity, viscosity, Tg and molecular weight. The viscosity of aqueous polymer solutions is strongly dependant on molecular weight. High performance characteristics such as rub resistance and heat resistance are compromised since low ink viscosity is required for flexo and gravure fluid ink printing. The volatile amines used to neutralize acid functionality results in pH shifts, unstable viscosity, reduced pigment dispersion stability, and poor alkali resistance. Water soluble styrene acrylics are processed via free radical polymerization in glycol ether solvents. The solvent is stripped by conventional or proprietary processes. Rosin based resins are processed molten at high temperatures up to 265 °C. These materials are flaked or pelletized and packaged in bags or bulk storage for further conversion. There are various hybrid polymers and co-polymers in use to achieve specific ink application properties not obtainable by conventional resins and polymers. Water soluble fatty acid epoxy esters provide improved heat resistance. For example, an aqueous fatty acid-acrylic acid epoxy ester patented by Reichold Chemical, which crosslinks via heat and auto-oxidation is used to provide water and heat resistance [11]. Typical solution polymers are listed in Tab. 5-5. 5.2 Ink Composition Tab. 5-5 Typical solution polymers. Surface print Folding carton Direct print corrugated Pre-print corrugated Alternative folding carton Direct print corrugated Pre-print corrugated Multi-wall bags and gift wrap Milk carton Cup and plate Towel and tissue Resin/Polymer Softening point (°C) Tg (°C) Styrene acrylic resin 145 73 4500– 7500 108–213 Rosin fumarate ester resin 125–145 80–90 2000–10000 115–200 Fatty acid (Castor oil)/ >125 acrylic epoxy ester Styrene acrylic Water and amine neutralizer >100 75–100 Mw (g mol–1) Acid number 30000–40000 50–60 6000–10000 200–230 5.2.4 Waterborne Wax Emulsions and Powders Both natural and synthetic waxes are used in ink. Waxes provide increased block, rub, scuff and/or water resistance. Waterborne wax emulsions are produced in a range of particle sizes between 35 to 175 nm (number average particle size distribution) by Michelman, Shamrock Wax, and others. Polyethylene and Fischer-Tropsch emulsions improve the rub and scuff resistance of an ink. Carnauba paraffin and polypropylene emulsions are used to prevent blocking and improve water resistance of an ink. Certain waxes are micro-pulverized to yield particle sizes smaller than a dispersed pigment particle. A micro-pulverized wax is “stirred” into ink as a powder. Recycled PTFE (Teflon) is supplied in small particle powder form. 5.2.5 Ink Additives An amine neutralizer is added to solubilize resins containing carboxylic acid functionality. The amine reacts with the resin carboxylic acid to form a water soluble salt. Volatile amines such as dimethylaminoethanol (DMAE), morpholine or ammonia are used to insure that a printed product becomes water resistant upon drying or evaporation of the amine. The type of amine used is selected based on press speed, pH requirement and evaporation rate and press drying capacity. Sodium hydroxide is commonly used in news print ink to maintain re-solubility (“open time”) of the ink on the press. A crosslinking compound is added to provide covalent branching to a polymer for enhanced printed film tensile strength and chemical resistance characteristics. Com- 113 114 5 Applications for Printing Inks pounds such as zinc ammonium complexes or zinc oxide react with available carboxylic acid functionality. Self crosslinking emulsion polymers may be used as explained in Sect. 5.2.2. A surfactant is added to reduce the surface tension to give increased ink spreading and substrate wetting particularly when printing untreated or partially treated films. The surface tension of water is approximately 72 dynes cm–1 whereas a polyethylene film is approximately 30–40 dynes cm–1 after surface treatment. Surfactants increase the foaming tendency of an ink. Therefore levels of surfactant and defoamer are carefully balanced. A defoamer is added to reduce foaming. A fine particle size silica powder is added to increase the viscosity and modify print film slip or abrasion properties. A corrosion inhibitor is added to prevent corrosion of press parts made of steel. 5.3 Physical Properties and Test Methods Viscosity, pH and color strength are the main properties that relate to press performance and print quality. Viscosity is critical for satisfactory ink transfer or printability. A gravure ink has slightly lower viscosity than a flexo ink. The pH is controlled since it effects viscosity, viscosity stability and compatibility with other components. The viscosity changes with change in pH, but is readily adjusted by adding amine or water. Color accuracy (ink color strength) is important for achieving satisfactory print color and to maximize profitability. The color strength of a pigment dispersion intermediate is carefully controlled to narrow tolerances. Therefore, color adjustments in the ink manufacturing step are minimized. 5.3.1 Typical Properties The typical properties or specifications of aqueous flexo and gravure ink are: Viscosity, Zahn efflux cup (ref. ASTM D4212-99) @ 25 °C: Flexo ink shipping viscosity, Zahn #3 25–30 s Gravure ink shipping viscosity, Zahn #3 21–25 s Flexo ink printing viscosity, Zahn #3 18–22 s Gravure ink printing viscosity, Zahn #2 18–22 s Zahn #3 8–10 s pH 9.0–9.5 Color accuracy (ASTM D2244-93) <2.0 Delta E* (CIELAB total color difference) versus standard Fineness of grind, (ASTM D1316-93) <2.0 Residue (ref. ASTM F311-97) <15 mg per 100 g ink 5.3 Physical Properties and Test Methods 5.3.2 Application Tests Application specific pass/fail tests are specified to guarantee that an ink shipment gives satisfactory performance. The application properties are measured relative to a standard sample. The results are reported as pass or fail versus the standard. The following application tests are performed on aqueous flexo and gravure ink: – Abrasion resistance, dry/wet rub resistance, Sutherland Rub Tester – Adhesion at surface tension of 38–44 dynes cm–1, Scotch 610 Tape Test – Block resistance – COF (coefficient of friction), ink to ink, static at 26.6° slide angle – COF (coefficient of friction), ink to ink, kinetic at 19.3° slide angle – Crinkle resistance at room temperature or that of ice water – Drying with a 1 millimicron or 2 mil fineness of grind gauge – Freeze-thaw resistance, two cycles – Heat resistance, 98 °C – Milk carton wet rub – Product resistance – acid, fertilizer, limestone, wood oil – Re-wetting – Rub test – metal corrugator – Surface tension of film – Viscosity, Zahn efflux cup – Water resistance, 24 h, immersion at 25 °C 5.3.3 Test Method Abstracts – Abrasion resistance – Sutherland Rub Tester: A test strip (18.8 cm) is rubbed by a four pound test block with a 15 cm × 7.5 cm strip affixed. The test is run either: ink-to-ink or unprinted paper-to-ink, 20 to 40 rub cycles according to specifications. A subjective comparison is made to a photograph standard or control sample that is tested subsequently. This test method simulates scuffing that may occur during in-line filling, handling or transporting of a package. Wax emulsions or micro-pulverized powders are added to adjust the abrasion resistance properties of an ink. For heated abrasion resistance, the four pound test block is held in an oven for twenty minutes at a temperature specified. The test simulates scuffing that may occur on hot filling lines or under high friction conditions. For wet-rub resistance (approximately twelve drops) water is applied to a 18.8 cm test strip with a pipette. Un-printed paper is used to test paper or board substrates. A swatch of cotton material is used to test film substrates. The test simulates rubbing of a package by cotton clothing. – Adhesion/Scotch 610 Tape Test: A 2.5 cm wide 3-M 610 tape is attached to the ink and pulled off at an angle of 180 degrees. Ink removal of greater than 10 % is a failure. This test is performed to flag unusual problems associated with poorly treated films or ink composition errors 115 116 5 Applications for Printing Inks – Block resistance – wet/dry – ink to ink and ink to substrate: The exposure time, pressure, and temperature are specified by the end use requirement (i.e. 3 min at 1034 bar, 50 °C for surface print ink (5.4) – The ink surface’s resistance to heat and pressure is subjectively measured. Ink properties that effect blocking results are: “hardness”, adhesion, cohesion, and slip. The polymer glass transition temperature (Tg), molecular weight, and surface compatibility effect the block resistance test. – Coefficient of friction measurement, TMI slip and friction tester: The peak angle (static) and average force (kinetic) are measured. An emulsion polymer with low glass transition temperature is required for high slide angles. – Crinkle resistance test at room temperature or at the temperature of ice water: The print is immersed in ice water for one hour (re-ice water crinkle). Two surfaces of ink are rubbed ink to ink for 10 cycles. Perform a subjective comparison between a test sample and a standard. – Drying test with a 1.0 mil (25 µm) or 2.0 mil (50 µm) fineness of grind gauge: Drying time is measured subjectively by finger tapping and a stopwatch. A polymer’s glass transition temperature, MFFT and emulsion particle size distribution effect drying. – Freeze–thaw test: A sample of ink is placed in a freezer at –15 °C for 4 h. Changes in viscosity, homogeneity, and seeding tendency are observed. – Heat resistance test at 100 °C – Sentinel heat seal tester: Set-up a Sentinel heat sealer according to heat pressure and time interval specified. A one by three inch (2.5 cm × 7.5 cm) print sample is folded ink surface-to-ink surface and placed between the sealer bars. The heat sealer is operated. After the sample has been cooled, the sheets are separated and a subjective comparison is made for cling, ink transfer and picking. The polymer glass transition temperature (Tg), molecular weight, and surface compatibility affect heat resistance. – Milk carton wet rub test: A test print is immersed in milk at 1 to 7 °C for 24 h. A rub resistance test is performed using a Sutherland rub tester (see abrasion resistance). Specific polymers (Sect. 5.6.1) are used to give resistance to milk. – Product resistance and/or chemical resistance – acid, fertilizer, limestone, wood oil, etc : Three drops of an appropriate chemical solution is applied using a 3-mL pipette. After a specified time interval, a cotton swab is rubbed through the drop over the print surface with moderate pressure. A comparison is made for discoloration, ink removal, or blistering. A polymer composition, branching structure and crosslinking density have the largest effect on chemical resistance of an ink. – Re-wetting test: A #4 Meyer bar drawdown is allowed to dry for 20 min at RT (room temperature). A drop of water is placed on the ink surface and subsequently wiped with a cloth. A subjective comparison is made versus a standard sample. Solution polymers are neutralized with volatile amines (Sect. 5.2.3) to prevent resolubilization after the ink print dries. – Rub test – metal corrugator: For pre-print liner board, this test simulates the effects of a corrugator. The extent of scuffing/marring is subjectively compared to a photographed standard. The emulsion polymer’s soft segment, glass transition 5.4 Inks for Flexible Substrates (Films) temperature (Tg), and molecular weight have the largest effect on the rub resistance properties of an ink. – Surface tension of film: Accudyne level pens or solutions are used to estimate the surface tension of treated films. A targeted range of 38–42 dynes cm–1 is specified for most printing applications. The surface tension of most aqueous styrene acrylic based pigmented inks are greater than 38–42 dynes cm–1. – Viscosity, Zahn efflux cup (ref. ASTM D4212-99), seconds: A Zahn efflux cup is a fast and effective instrument for measuring viscosity of flexo and gravure ink. Viscosity is an important property for maintaining printability. For a flexo press, consistency of ink flow into the pan or well of the doctor blade system, ink-transfer to the anilox roller, and release of ink from anilox roller are largely effected by ink viscosity. On a gravure press the release of a consistent volume of ink out of the cylinder cell is effected by viscosity. Viscosity changes due to pH drift or evaporation of solvent (water) should be corrected immediately. – Water resistance, 24 h, immersion at 25 °C: A Crinkle test is performed. Two surfaces of ink are rubbed ink-to-ink for 10 cycles. A subjective comparison is made between a test sample and a standard. 5.4 Inks for Flexible Substrates (Films) The ink used for printing flexible substrates (films) contains a soft film forming emulsion polymer based on styrene and co-monomers such as butyl acrylate, and 2-ethylhexyl acrylate. Solvent based inks have continued use in high performance printing applications such as packages requiring lamination bonds (i.e. candy wrappers, potato chip bags). Flexo and gravure printing companies have invested in solvent incinerators to remain compliant with environmental regulations. Examples of materials used for flexible packaging films are: LDPE Low density polyethylene (i.e. fruit and vegetable produce bags) MDPE Medium density polyethylene (i.e. department store merchandize bags) HDPE High density polyethylene (i.e. grocery item bags) LLDPE Linear low density polyethylene (i.e. department store merchandize bags) PP Polypropylene (i.e. salt, fertilizer bags) PP-EVA Ethylene vinyl acetate modified polypropylene OPP Oriented polypropylene PP-NO Non-oriented polypropylene PP-AC Acrylic coated polypropylene PP-PVDC Poly(vinylidene chloride)-coated polypropylene PET Polyethylene terephthalate PVDC Poly(vinylidene chloride) (Saran) 117 118 5 Applications for Printing Inks 5.4.1 Surface Print Film Surface print inks are designed for printing on polyethylene substrates used in utility bags, department store merchandize bags, grocery bags, and general purpose surface film applications. The films are surface treated via corona discharge increasing to a surface tension of 38–41 dynes cm–1 before printing. A corona discharge induces ions and free radicals to oxidize the surface of a film to form polar functionality. This change in surface chemistry and roughness increases surface energy and improves wetting of ink on film. A surface print ink is composed of a soft film forming styrene acrylic emulsion vehicle to provide adhesion. A solution vehicle composed of low molecular weight styrene acrylic resin is added to adjust printability. Typical properties of the emulsion polymers and solution resins used in ink for surface print films are listed in Tabs 5-3 and 5-4. 5.4.2 Lawn and Garden Bags Lawn and garden bag inks are designed for printing on polyethylene or polypropylene substrates used in fertilizer, salt, mulch, potting soil, manure, feeds and wood bark bags. Lawn and garden bags require resistance to: weak acids, bases, fertilizers, limestone dust, wood oils (i.e. cedar, pine), etc. A typical Lawn and garden bag ink has a similar composition to surface inks. A crosslinking compound (i.e. zinc oxide, carbodiimide, polyfunctional aziridine) adds covalent branching, increases modulus and enhanced print film adhesion and resistance to chemicals. As an alternative, a self crosslinking styrene acrylic emulsion which reacts upon evaporation of water may be used according to the Akzo Nobel Resins paper presented at the 44th NPIRI Technical Conference [10]. 5.5 Inks for Paper Board Substrates 5.5.1 Folding Cartons Folding carton inks are designed for printing on paper board (or boxboard) substrates used in: fast food carry out packages, pastry cartons, cereal boxes, mail containers, auto parts boxes, beverage carriers, milk and juice cartons, and other packages. Folding cartons are made from solid bleached kraft or solid bleached sulfate (SBS), unbleached kraft, solid unbleached sulfate (SUS), clay coated unbleached kraft, recycled paperboard, and coated paperboard. For beverage carriers, one substrate type is used consistently in most of the US market. Many beverage carriers are over-coated with a clear protective coating layer. high gloss. As an alternative. Direct print corrugated ink is made from styrene acrylic colloids. heat resistant. and SBS coated paper board substrates. and scuff resistant coating. mottled kraft.e.5 Inks for Paper Board Substrates A folding carton ink is composed of a hard non-film forming styrene acrylic emulsion vehicle and a styrene acrylic solution vehicle. 119 .4 and 5. A direct print corrugated ink is composed of a styrene acrylic emulsion colloid vehicle and a rosin fumarate ester and/or styrene acrylic solution vehicle.9–9. They are used in low cost ink systems for printing on porous substrates such as corrugated paper board.3 Pre-print Corrugated Packages Pre-print corrugated inks are designed for printing on standard kraft. clay coated. a film forming styrene acrylic emulsion vehicle and rosin fumarate ester solution vehicle are used. Colloids have molecular weights in the range of 25 000– 100 000 g mol–1. The physical properties of emulsions and resins used in pre-print corrugated ink are listed in Tabs 5. bleached kraft. and marring/scuffing conditions of the subsequent paperboard corrugating process. Many producers of corrugated packages have installed flexo presses for pre-printing linerboard before making the corrugated board.5 for. They are supplied at low solids concentrations typically between 20 % to 40 %. Corrugated board is manufactured by laminating flat sheets of paper to a corrugated inner layer to give an increased stiffness-to-weight ratio [12].5. a mixture of colloid solution with a film forming emulsion provides the overall corrugated ink properties.2 Direct Print Corrugated Packages Direct print corrugated inks are designed for printing on standard kraft paper board substrates.3 Density (g cm–3/lbs gal–1) Dry rub 100 rubs/1. propylene glycol) and solvent (i. Colloids are polymers produced by emulsion polymerization followed by neutralization of available carboxyl functionality. 5. Most pre-print packages are coated with a clear. A pre-print corrugated ink is composed of a styrene acrylic emulsion colloid vehicle and a rosin fumarate ester resin and/or styrene acrylic resin solution vehicle. Printing on a smoother surface gives improved print quality.07–1. These inks must withstand heat (175–200 °C).5.5. Direct print corrugated ink specifications: Residue <15 mg per 100 g ink 1. NPIRI <2 5. As an alternative.e. pressure. This results in uncoiling of the colloidal particle to form a colloid solution. Colloids are also supplied in solid form for dissolving in water by neutralization with an amine.11/8. Colloid solutions give a high viscosity. n-propyl alcohol) are added to folding carton ink to improve printability and insure coalescence at room temperature.8 kg (4 lb) weight Grind. The coating adds resistance properties and gloss. A plasticizer (i. 6 Inks for Poly-coated Board Inks for polymer coated paper board are designed for printing on polyethylene coated SBS (solid bleached sulfate) paper board substrates used in milk cartons. 5. A fatty acid acrylic epoxy ester [11] is the key resin used in this type of ink.e. styrene acrylic emulsion vehicle. and envelopes are composed of a hard non-film forming styrene acrylic emulsion combined with a solution vehicle comprising a rosin fumarate ester to balance printability and coalescence. propylene glycol) and coalescing solvents (i.1 Milk Cartons Milk carton ink must have resistance to alkaline detergent based chain lubricants. ice cream cartons. A typical ink for coated board is composed of an epoxy ester based pigment dispersion. They should meet the requirements for general purpose paper plate use. and an epoxy ester solution vehicle. Alternative polymers that may be used in inks for coated board are: aziridine (ethylene imine) crosslinking styrene acrylic or a VAE (vinyl acetate ethylene) self crosslinking emulsion polymer.120 5 Applications for Printing Inks Plasticizers (i.2 Cup and Plate Cup and plate inks must have tolerance for hot wax coatings and resistance to hot and cold fluids. A polymer with high molecular weight and Tg fast drying via fast: resin-solvent (water) separation. glycol ether) are added to maintain satisfactory printability and satisfactory MFFT (minimum film formation temperature).3). and paper plates. Special pigment dispersions are used based on the same epoxy ester since conventional styrene acrylic based pigment dispersions are not stable in epoxy ester based systems. .e. 5. penetration of paper and brightness of color via “holdout” of pigment particles on the paper surface.6. The system undergoes oxidation to give moisture and alkali resistance [11]. A hard non-film forming styrene acrylic emulsion combined with hot-air drying (by oxidation) fatty acid-acrylic epoxy ester [11] provide the resistance requirements. beverage cups. The epoxy resin commonly used is an ester of drying or semi-drying fatty acid and acrylic acid (Sect 5.6. gift wrap. 5.7 Inks for Paper Products A typical ink used for printing multiple wall bags.2. 5. Therefore it was necessary to target certain newspaper market segments with higher value products. During the 1980’s the remaining letterpress printers began to switch to the flexographic process and water based ink. Offset news ink is composed of carbon black or organic pigments dispersed in high boiling point aliphatic petroleum solvent based vehicles.1 Multiple Wall Bags Inks for Multiple Wall bags are designed for printing on kraft: brown.2 Gift Wrap and Envelopes Gift wrap is used for seasonal gifts. Flexographic printing is the most used process for multi-wall bags. Low cost black ink was mostly used. Aqueous flexo news ink is based on higher cost emulsion polymers than typical petroleum hydrocarbon resin based offset inks. clay coated. 5.7. soybean oil). Envelope ink is made from the same mix of polymers as gift wrap ink. Multi-wall and other paper bags are made of one or more walls of paper glued together and treated to provide moisture resistance.7 Inks for Paper Products 5. A letterpress black ink is composed of carbon black dispersed in high boiling point aliphatic petroleum solvent (ink oil).5.3 Newspapers Newspapers were originally printed by the letterpress printing process. and uncoated paper substrates. mottled (compressed thin layers of bleached pulp on top of brown pulp). A typical flexographic news ink is composed of a hard semi-film-forming styrene acrylic emulsion vehicle. 5. Heavy duty bags used as shipping sacks have three or more plies.7. liquor boxes. and overall increased color coverage per newspaper. Bags used for packaging consumer products (i. A flexographic news ink contains a high molecular weight. candy and other products. By 1995 the majority of newspapers converted to the offset lithographic printing process. 121 .e. The vehicles are resin solutions in ink oil and/or vegetable oils (i. The paper used in bags for packaging consumer products has been upgraded in recent years to bleached kraft and clay coated. retail wrapping. Gravure is the most used process for printing gift wrap. sugar. Flexographic newspaper printing introduced brighter colors to comics and advertising. or bleached. flower) have two plies. styrene acrylic emulsion with high Tg (glass transition temperature) to provide fast drying. The substrates used are 90 % paper and 10 % foil [12].e.7. pet food. Inks for Gift Wrap are composed of a hard non-film-forming styrene acrylic emulsion combined with a solution vehicle to adjust printability and balance coalescence. W. US Patent: 5.977. Mao. . Akzo Nobel Resins BV. Schilling.679. Dispersions in Aqueous Media. C.064. Westvaco Corporation. P.054. Pappas. J.. Ph. A. J. Chapter 20.... de Krom.245. Rosin Ester-Amide Support Resins for Acrylic Latexes. Jones. Wiley-Interscience. K.. Meeske. E.. A Comparison of Water-borne Chemical Resistant Technologies and the Variables that Affect their Performance.166.. US Patent 4. Air Products and Chemicals. Beck. US Patent: 5. H. N.122 5 Applications for Printing Inks 5. D.216... J. The colorants used are mostly dyes or pigments that are not dermatological irritants.. Jack- 9 10 11 12 son. Tien. 2nd edn. Westvaco Chemical Division. 8 Biggerstaff. J. 395. 1992.D. The components of a towel and tissue ink are re-pulpable for ease in recovery of waste and/or off-grade material to achieve satisfactory economies of paper towel tissue converting.. C. Zuraw.656.208. Modified Rosin Resins for Waterbased Inks.wmich.215. S.. 1999. October 18–20.. 1979. Reichold Chemicals. P.7. A. 2000. Snyder. Inc. Jr. G. Water Dispersible Epoxy resin Copolymers and Methods of Making Same...edu/ppse/flexo/. US Patent: 5. Racey. P.. 1993. Jelmar Publishing. A.3.edu/ppse/gravure/. Westvaco Corporation.P.. US Patent: 5. US Patent 5.. The resin should give a waterproof bond and be low cost. Eldred. M. Westvaco Corporation. Low Temperature Self-Crosslinking. C.. M. Science and Technology. Gravure Process. Van der Tuin.4 Towel and Tissue The same styrene acrylic emulsions used for sizing tissue paper to provide wet strength are used in the ink. C.. M. Self-Crosslinking Acrylic Dispersions Outperform Conventional Solventborne Liquid Inks. Westvaco Corporation . Rosin-Based Resin-Fortified Emulsion Polymers Hutter. 43rd NPIRI Technical Conference. F. Flexographic Process Western Michigan University Web Site: http://www. F. in: Organic Coatings.319. R. Aqueous Dispersions of Urethane–Vinyl Polymers for Coating Applications. Reuther. Rivera. J. A. Rosin-Based Grind Resins for Aqueous Printing Ink. Wicks. 44th NPIRI Technical Conference.wmich. References 1 Western Michigan University Web Site: 2 3 4 5 6 7 http://www. Mulder. P. Zuraw. N. J... Z. H.166. 1999. p. Mestach. Package Printing.. September 15–17. 3-527-60058-2 (Electronic) 6 Applications for Decorative and Protective Coatings Brough Richey and Mary Burch 6. However.1 Introduction Decorative and protective coatings are used in a great variety of applications. ranging from the familiar such as coatings for buildings. Most coating applications have historically utilized solution polymers as the binder component. it will not be possible to address them all. and specialized coatings for optical fibers and electronic components. paper coatings. Annual growth is typically the range of 1–3 % world wide. furniture. The use of emulsion polymers for coating applications has increased tremendously over the past fifty years and they are now represented in nearly every segment of the industry.Polymer Dispersions and Their Industrial Applications. manufacture. and is generally linked to the combined gross domestic product of the major industrialized and developing nations. representing world wide sales of about $60 billion US [1]. to less well known applications such as removable coatings. and large industrial structures. the toxicity of solvents.1. coatings based on emulsion polymers frequently set the performance standards and lead the market in many areas. and we have chosen instead to focus on selected application areas which we believe will provide the reader with a useful foundation in a variety of coating applications. In fact. automobiles. concerns over pollution. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. The objective of this chapter is to give the reader an overview of the use of emulsion polymers in decorative and protective coatings. Because of the great variety of specific applications.1 Market Overview The development. KGaA ISBNs: 3-527-30286-7 (Hardback). and ease of use and clean-up have driven the development of new emulsion polymer technologies to meet the needs of the coatings industry. sale and application of decorative and protective coatings comprise a large business and we estimate that approximately 20 billion liters of decorative and protective coatings are manufactured and applied each year. 6. Growth rates for 123 . it can be also be misleading. Again.2 Coating Industry Trends The most significant trend in the decorative and protective coatings markets has been the move to more environmentally friendly coating materials. in the 3–6 % range. 6. the combination of continued technical innovation with improved cost efficiency presents the central challenge to the coatings industry as we move into the twenty-first century. it follows that the world wide production of emulsion polymer for coating applications is about 3 billion wet kg (6–7 billion wet pounds) per year. and its associated raw material suppliers [2]. While this is admittedly a rough estimate. we can estimate an “average” water based paint has about 30 % volume solids. and powder coatings is a key consequence of this trend. with the dry volume of binder representing about 50 % of this value. We can obtain an estimate for the annual world wide production of emulsion polymers for decorative and protective coatings as follows.1. This change has been driven by a variety of regulatory pressures aimed at reducing air pollution by lowering the volatile organic content (VOC) of coating materials.3 Coatings Provide Decoration and Protection It is common to divide the general class of coatings into two subclasses: decorative and protective coatings. While this division can be useful. particularly in the area of decorative coatings for homes and offices. Automotive coatings systems provide a familiar illustration of this dual role: they are . the vast majority of coatings systems provide both decoration and protection. Assuming an average polymer dry density of 1.5 billion liters of solid emulsion polymer produced per year. it nevertheless serves to illustrate the enormous size of the water based coatings market and the large amount of polymer emulsion needed to supply it. If we assume that water based coatings make up about 50 % of the total world wide volume. 6. high solids coatings.1. then approximately 10 billion liters of water based paint are manufactured each year.124 6 Applications for Decorative and Protective Coatings water based coatings have been higher. Related to these pollution concerns is the desire to increase the safety of the end use application process. world wide economic conditions have led to consolidation in the paint manufacturing industry. this has caused a shift away from traditional solvent borne technologies toward newer technologies with improved health and safety profiles. The shift away from traditional solvent borne technologies to newer technologies based on waterborne emulsion polymers. In our view. with most of the extra growth due to the switch from solvent based coatings.1 kg L–1 and an average emulsion solids level of 50 % by weight. Finally. These economic factors have created a strong movement towards cost reduction and increases in production and distribution efficiency across the coatings industry. This yields an estimated 1. To estimate the amount of emulsion polymer manufactured to yield this amount of coating material. Many optimized formulations contain more than one member of each of these classes. 6. and meet the appearance and performance requirements of the intended application. It typically is reported as a percentage. Interior decorative finishes provide an example at the other end of the decorative-protective continuum. In this chapter. the color and appearance of automotive finishes are vital factors which influence the customer’s purchase decision. water will be the carrier liquid. These formulations usually have on the order of 10–20 raw material components. which provides as the liquid character of the coating while in the wet state (before drying).2 Overview of Coating Formulations foremost a protective coating. and (iii) carrier liquid. surfactants to improve colloidal stability and promote substrate wetting. These types of coatings are also commonly referred to as latex paints. While used primarily for decorative purposes. which holds the film together and provides coating integrity. a biocide to prevent microbial spoilage. apply correctly to the substrate. which provides color and opacity to the coating (ii) binder. 6. and yet. The primary technical challenge of coatings formulation is to develop cost effective coating formulations which are stable indefinitely in the wet state. the specific nature of which depends on the intended application. a dispersed emulsion polymer acting as the binder.6. A more realistic formulation would include: dispersed solids such as pigments and fillers stabilized by a polymeric dispersing agent. Volume solids is the simplest of these relationships. presumably in reference to the similarities in appearance between the emulsion polymer binders and unprocessed natural rubber.2. we will focus on coatings utilizing emulsion polymer binders.2 Overview of Coating Formulations Decorative and protective coatings consist of three main components: (i) pigment. and consequently. 4]. and must protect the automobile body from damage by weathering and the environment.1 Volume Solids and Pigment Volume Content The relative ratios between the volumes of different formulation components control many of the key appearance and performance properties of a coating [3. Commercial paint formulations are usually complex and typically contain more than the three main components described above. coalescents and co-solvents to promote film formation and optimize the drying process. it is the ratio between the volume of solid components in a coating and the total volume of the wet coating. Volume solids is a useful quantity because it allows one to 125 . and a neutralizing agent to adjust the pH. dry into defect free films. a thickener to provide proper rheology. the stain resistance and cleanability of interior finishes are important performance characteristics which often provide differentiation in this competitive market. a defoamer to reduce foaming during manufacturing and application. The pigment volume content (PVC) is another useful volume relationship which is frequently used in coatings formulation development. above critical. formulations high in water content (and low in volume solids) tend to have lower raw material costs. the dry coating begins to develop small voids between the solid components of the film. and. in conceptual terms. and coatings with high PVCs have a low binder content with higher levels of pigment and extender. with values ranging up to 60 % for some specialty applications. This point is termed the critical PVC. or CPVC. and low- . This is because the higher surface area of the smaller PS pigment will require a higher level of polymer to uniformly cover the pigment surfaces. Coatings with low PVCs have a high binder content. This results in a higher binder demand. Note the high porosity and variety of extenders in the above CPVC coating. and suggest that these two types of coatings would have very different performance profiles. The value of the CPVC for a particular formulation will depend on the chemical and physical nature of the pigments. If several versions of a particular formulation are prepared with different PVCs. and in the other case the paint is formulated with a larger PS version of the same pigment. The CPVC of the paint with the smaller PS pigment would be lower than the CPVC of the paint with the larger PS pigment. To illustrate this. extender. It can also be used to estimate the quality of a coating when comparing coating formulations of a given class. flat ceiling coating at the same magnification. it has proven to be a useful and practical conceptual tool for coatings formulation development. represents the PVC where the polymeric components of a film no longer form a continuous phase surrounding the pigment and extender particles. rather than the wet coating. is usually reported as a percentage. polymer rich surface which is typical of a water based enamel formulated significantly below CPVC. Since water is an inexpensive raw material. we consider two paints formulated with the same total volume of pigment and binder (equal PVC). Figure 6-1 is a scanning electron micrograph which provides a vivid illustration of the differences between above and below CPVC coatings: Figure 6-1A shows the smooth. leading to an abrupt change in the performance features of the coating. Figure 6-1B shows the surface of a highly extended. Typical emulsion polymer coatings for decorative and protective applications have volume solids in the range of 25–45 %. Above CPVC.126 6 Applications for Decorative and Protective Coatings calculate the thickness of a dried coating from the applied wet paint thickness. and thus it is not a truly fundamental characteristic of a film. The value of CPVC for a coating depends somewhat on the property used to measure it. and like volume solids. a transition point will be observed at which many performance features of the coatings change abruptly. It is important to recognize that PVC represents a property of the dry film. the white spots are TiO2 particles sticking through the surface of the gray polymer matrix. In one case the paint is formulated with a smaller particle size (PS) pigment. ranging from lower to higher values. Nevertheless. The differences in the surface features of these two emulsion polymer coatings are striking. and binder solids). PVC is an important quantity because it relates to many of the performance properties of a dry paint film. extenders and the binder. It is the ratio of pigment and extender solids to the total coating solids (pigment. or from the spread rate (the volume of wet coating applied per unit of area). 2 Overview of Coating Formulations Field Emission Scanning Electron Micrographs of Below and Above CPVC Coatings. A high molecular weight polymeric material is generally used as the binder in order to provide the toughness and resistance properties needed to protect the substrate and ensure a durable coating. Polymers with molecular weight below this value generally do not have the required toughness properties needed for coating applications: lower molecular weight crystalline materials are generally too brittle and can chip or flake. In practical systems the minimum molecular weight of thermoplastic polymers targeted for coating applications is around 50 000 g mol–1 [5–7]. 6. (B) shows Fig. Coatings formulated above CPVC generally have lower gloss.2. Coatings formulated at PVCs below CPVC tend to have higher gloss. ers the PVC at which CPVC is reached. Since PVC level is usually adjusted upward by increasing the levels of low cost extenders. Decorative and protective coatings are generally designed to perform their function over the temperature range of –20 °C to +45 °C.2 Polymer Matrix The polymer or binder component holds the coating together and provides many of the performance features needed for specific coating applications. Comparing the actual PVC of a coating to the CPVC can provide useful information regarding a coating’s physical properties and suitability for a particular application. better flexibility and better barrier properties. (A) shows the surface image obtained from a gloss enamel coating which has been formulated significantly below CPVC. higher porosity. PVC can provide a useful gauge of formulation cost (and quality). since these coatings contain little or no low cost extenders and consist primarily of higher cost resins and pigments. lower flexibility and lower total cost. while non-crystalline materials such as amorphous waxes do not have high enough moduli to provide the film integrity needed for most coating applications.6. PVC is a less useful measure of quality in coatings formulated below CPVC. 6-1 the surface image obtained from a flat ceiling coating which has been formulated significantly above CPVC. lower porosity. This measure is most useful for coatings formulated above CPVC. Note the porosity and variety of extenders present in the coating formulated above CPVC. The polymers used for coating 127 . the ubiquity of water in our environment would make the utility of such coatings very limited. Since film formation involves the interpenetration of polymer chains between adjacent polymer particles. In the second phase. however. In the third and final phase. pigment-polymer composite. If film formation were reversible. it has been observed that if the polymer Tg is higher than the ambient film formation temperature. In the first step.3 Film Formation Coatings based on emulsion polymers exist as stabilized colloidal dispersions while in the wet state. but the concepts can also be applied in a less formalized way to thermoset coatings (temperature dependent reactive polymerization systems). Tg. interstitial water diffuses out of the film and the emulsion polymer particles coalesce into a continuous. as well as the drying rate of the applied coating. resulting in a poor quality film with diminished integrity. 6. These generalizations are most applicable to thermoplastic polymers. inter-particle polymer network. However. the wet paint is stable indefinitely. Properly designed and formulated. the MFFT of an emulsion polymer is not a precisely defined physical quantity and its value can depend on several factors in addition to Tg including polymer molecular weight and composition. The irreversibility of the film formation process is a key technical factor underlying the successful utilization of emulsion based polymers for decorative and protective coating applications.128 6 Applications for Decorative and Protective Coatings applications are usually random copolymers or terpolymers with monomer compositions such that the polymer glass transitions. Empirically.2. The effective volume solids of the coating rises significantly. Polymers with glass transition temperatures below 0 °C are not useful in most coating applications because their films are tacky and weak under normal ambient temperature conditions. the final coalescence step of the process may break down. water evaporates and the film dries and cures into the final coating. It should not be a surprise that there is a general relationship between the polymer Tg and the MFFT. the drying and film formation processes are effectively irreversible and result in a final film which is a tough. MFFTs are usually determined empirically by moni- . fall in the middle to upper end of this range. the latex and pigment particles begin to pack together to create a contiguous film. water evaporates from the continuous phase of the liquid coating and the polymer and pigment particles begin to crowd together. then dried coatings could be degraded by contact with liquid water. Upon application to the substrate. Hence. The minimum temperature at which an emulsion polymer will form a good film is referred to as the MFFT (minimum film formation temperature) and is generally a few degrees lower than the polymer Tg. Film formation from emulsion polymers is a complex process but for simplicity it can be taken to consist of three phases. a reasonable amount of chain mobility must exist for this process to proceed. The detailed physics and chemistry of the film formation process are still not completely understood and are affected by many factors [8–10]. Polymers with Tg significantly above 50 °C tend to be brittle and inflexible under normal ambient conditions and are less commonly used in coating applications. which we will highlight below in the context of specific examples of coating applications. To be effective. In practice.6. 6. more useful coating. Typical polymer compositions were 65 % styrene with 35 % butadiene.2 Overview of Coating Formulations toring film formation as a function of temperature under a set of standardized drying conditions. This presents a problem: polymers with desirable dry film performance frequently have Tg which are too high to form a good film under typical drying conditions. styrene-butadiene copolymers were the first emulsion polymers to be used for coating applications. coatings formulators temporarily lower polymer Tg and MFFTs by use of coalescing agent. While paints based on styrene-butadiene emulsion polymers opened the door for the development of synthetic latex paints. To circumvent this problem. allowing the effective Tg to rise and yielding a tougher. Oxygenated solvents of moderate polarity are commonly used for this purpose. Styrene-butadiene copolymers Historically.4 Typical Polymer Compositions A variety of polymer compositions are used as binders in decorative and protective coating applications. disrupting the packing of the polymer chains.2. Most coatings are applied under ambient temperature conditions (either on a job site or in a factory) with typical application temperatures between 10 and 40 °C. the coating formulation and the intended application. 129 . The choice of a coalescent depends on the polymer composition. Coalescents work by partitioning into the emulsion polymer particles. The choice of polymer system depends on many factors. their cost-performance profiles were not particularly competitive with the solvent borne coatings present at that time or with the other emulsion polymer technologies which would be developed later. By definition. but even with this restriction there are a number of different polymer classes which can be used for a given application. They now occupy only a very small segment of the coatings market. these include various ether-esters of propylene and ethylene glycols. In this section we give an overview of the major emulsion polymer classes and discuss their general performance characteristics. the coalescent will slowly diffuse to the film surface and evaporate. polymer Tg values would need to be in the 10–15 °C range. and thus lowering the effective polymer Tg. emulsion polymers are based on vinyl monomers. To ensure good film formation at the lower end of this range. and ester-alcohols. it has been found that polymers with higher Tg are usually needed to provide optimized performance in many coating applications. but should also evaporate from the film reasonably quickly in order to allow performance properties to develop. These polymers were based on technology developed for synthetic rubber production during WW II. It should also have a moderate vapor pressure: the coalescent needs to remain in the film long enough to optimize film formation. particularly for coatings formulated at lower PVCs where the binder content is high. After the film is applied. the coalescent must be reasonably compatible with the polymer phase and relatively low in molecular weight in order to partition into the polymer matrix. VA-BA copolymers have proven to be very successful in interior decorative paint applications. and like styrene-butadiene polymers. Typical VAE copolymers used in coating applications are about 90 % VA with 10 % ethylene by weight. VAEs have been most successful in interior decorative coatings. The performance profiles of VAEs are similar to that of VA-BAs. In spite of this drawback. ethylene serves as an internal plasticizer for VA. Because of their relatively low cost. Since ethylene is a gas at ambient temperature. the use of VA-BA emulsion polymers in coating applications increased substantially. Most frequently. However. the exterior durability of styrene acrylics is often adequate to meet the performance requirements for many exterior applications.130 6 Applications for Decorative and Protective Coatings Vinyl acetate copolymers Vinyl acetate (VA) homopolymers were also used in early latex paints. high quality films. were also not particularly successful in the market. although they are often used for less demanding exterior coatings when low raw material costs are a primary formulation factor. lowering the Tg of the copolymer into the useful ambient temperature range. Styrene acrylic copolymers Homopolymer styrene has a high Tg (100 °C) and thus needs to be copolymerized with a soft monomer for use in coating applications. Vinyl acetate can also be copolymerized with ethylene (E) in an emulsion polymerization process. and styrene-butyl acrylate copolymers used in coating applications typically have a composition of around 50 % styrene with 50 % butyl acrylate by weight. VAE emulsion copolymers need to be manufactured in specialized reactors. The main problems were that the high Tg of VA homopolymers made it difficult for these coatings to form strong. Again. While more resistant than VA homopolymers. However. particularly in comparison to vinyl acetate polymers. like VA-BA copolymers. and photons of this wavelength are energetic enough to induce photochemical processes which ultimately lead to polymer degradation and reduced exterior durability. paints based on styrene acrylic polymers tend to be resistant to water transport and provide good barrier properties. Typical vinyl acetate-butyl acrylate copolymers compositions are 80 % VA with 20 % BA by weight. While ethylene is a low cost monomer. designed for high pressure use. the cost advantage relative to BA can be lost because of the higher manufacturing costs associated the use of pressurized reactor systems. VA-BA copolymers can still be degraded by alkaline hydrolysis and their polar character can yield films which are relatively water sensitive. Styrene is a relatively low cost monomer (although styrene costs have fluctuated widely over the years) which is produced widely around the world. butyl acrylate is chosen for this purpose. vinyl acetate can be copolymerized with butyl acrylate (BA) in an emulsion polymerization process. When large quantities of BA monomer became commercially available in the 1960s. and the mottling and loss of film integrity caused by hydrolysis of VA when applied over masonry (alkaline) substrates. styrene has a strong absorption band in the near UV region of the electromagnetic spectrum. These factors can limit the use of VA-BA copolymers in demanding exterior applications. resulting in internally plasticized copolymers with MFFTs in the ambient temperature range and improved resistance to hydrolysis. Because styrene is relatively hydrophobic. particularly those where low . Steric stabilization is based on attaching low molecular weight. Both coulombic and steric stabilization inhibit un- 131 . Their barrier properties and resistance to alkaline hydrolysis make styrene acrylics particularly popular in coatings for masonry applications. methyl methacrylate is a higher cost monomer than VA or styrene. The coulombic repulsion between these negatively charged particles can provide an effective barrier to thermally induced aggregation processes. water soluble polymers to the particle surface. they are most popular in exterior applications and can be engineered to provide cost-effective performance features for interior applications as well. This layer of soluble polymers on the particle surface provides an entropically based repulsive interaction between particles.2 Overview of Coating Formulations formulation cost is a primary consideration. Specialty monomers Most emulsion polymers used in coating applications are based on the general copolymer compositions outlined above. and often for stain blocking primers. Unlike styrene. acrylic polymers do not absorb light in the near UV region. Good colloidal stability (resistance to particle–particle aggregation processes) is required in order to provide long term storage stability and to deliver the intended performance features. Usually an acidic monomer such as acrylic or methacrylic acid is used. Acrylic copolymers are used in a wide variety of coating applications. commercial polymers usually utilize small amounts of specialty monomers to provide added performance features desirable for specific applications. where their good barrier properties help provide effective corrosion resistance when applied over ferrous substrates. Colloidal stability can be enhanced by utilizing coulombic or steric stabilization methodologies. and to bring the Tg of acrylic copolymers down into the ambient temperature range. which upon neutralization with a suitable base. and thus they are resistant to photochemically induced polymer degradation processes. emulsion polymer coatings exist in the form of a densely crowded colloidal dispersion. Acrylic copolymers Homopolymers of methyl methacrylate have a high Tg (100 °C) and.6. However. butyl acrylate is commonly used to provide internal plasticization. As a class. Most anionic surfactants associate with the surface of dispersed emulsion particles. Typical acrylic compositions for coating applications are around 50 % methyl methacrylate and 50 % butyl acrylate by weight. thus conferring additional colloidal stability. like styrene and VA. Styrene acrylics are also commonly used in industrial maintenance applications. and coatings based on acrylic binders tend to have higher raw material costs. are too hard for typical coating applications. and involves including a small amount of ionizable species (<10 %) in the polymer composition. However. and they can also be used to increase coulombic stability in emulsion polymer systems. Coulombic stabilization is the most commonly used method. In the wet state. provides a layer of net negative charge on the particle surface. acrylics generally exhibit the best exterior durability of emulsion polymers commonly used in coating applications. Again. as well as helping to optimize the film formation process. For example. hydroxyethyl methacrylate can be used to provide hydroxyl functionality to acrylic resins. . and n-butyl methacrylate can be used to enhance the durability of BA-MMA acrylics. Colored pigments function by absorbing a portion of the visible light spectrum. pigments usually exists as a colloidal dispersion of sub-micron or micron sized particles. A wide variety of other specialty monomers are also used to provide specialized performance properties for coating applications. with the aim of providing the reader with a background sufficient to understand the formulations and examples discussed later in this chapter. In this section we will give a brief overview of these other components. Specialized monomers can also be used to improve exterior durability. Pigments are dispersed into a liquid by a high shear rate grinding processes. extenders. TiO2. or inorganic materials such as titanium dioxide (TiO2) and iron oxide [11]. amine functional monomers can be used to improve adhesion to aged alkyd substrates. and they are carefully processed and formulated in order to maximize their performance. gives a white color and excellent hiding because its high index of refraction and carefully optimized particle size allow it to uniformly and efficiently scatters light across the visible spectrum. and the unabsorbed spectral components are scattered back from the film. and Additives While the polymeric binder is usually a major component of a coating formulation. and additives) also play a vital role in ensuring a coating will meet the desired cost and performance targets.5 Pigments. Pigments make up a substantial portion of a coating’s total raw material cost. Specialty monomers are also used to provide specific chemical functionality to polymer compositions. giving rise to its color.2. 6. For example. For coatings based on emulsion polymers. for example VEOVA (vinyl ester of vesatic acid) monomers can improve the hydrolysis resistance of vinyl acetate polymers.132 6 Applications for Decorative and Protective Coatings desired particle aggregation in the wet coating and this enhances storage and shear stability. they frequently provide the performance features needed for the successful application of emulsion polymers in many coating areas. They can be either organic materials. usually in the presence of specific dispersing agents (specialized surfactants or low molecular weight polyacid resins) which provide colloidal stability and help optimize color efficiency. it is important to recognize that the other components (pigments. It is the selective absorption and scattering of visible light by the pigment particles which provides color and opacity to a coating. Polymer hydrophobicity can be fine tuned by varying the levels of hydrophobic and hydrophilic monomers in the composition and styrene or ethyl hexyl acrylate are used to increase film hydrophobicity and reduce water permeability in BA-MMA systems. such as phthalocyanine blue and carbon black. Pigments provide the color and hiding properties of a coating. allowing these polymers to be used in cross-linkable thermoset coatings which cure via melamine chemistry. Extenders. While specialty monomers are used at relatively low levels in polymer compositions. the most common pigment used in coating applications. Extenders are inorganic materials which are processed to yield particle sizes on the micron scale. aided by dispersing agents. Dispersants are generally low molecular weight. the extenders in an emulsion based coating exist as a stable dispersion in the water phase. dispersing resins associate with polar functional groups on the pigment surface.2 Overview of Coating Formulations Extenders provide a low cost way to adjust the solids level of a coating formulation. For example. or HEC). silicas. dispersants act by increasing the coulombic stability of the pigment particles. HASE thickeners are high molecular weight emulsion polymers which are activated. There are three main classes of thickeners or rheology modifiers which are commonly used in emulsion polymer coatings: Cellulosic (a class of modified natural products. they can have a significant impact on the performance of a coating. Dispersing resins also facilitate the wetting and breakdown of pigment and extender agglomerates in the initial milling and/or grinding process and help to stabilize and reduce the viscosity of the millbase (the millbase is a concentrated dispersion prepared from the pigment and extender powders). A variety of extender materials are commonly used in coating applications. Dispersants provide enhanced colloidal stability to pigment and extender particles when formulating coatings based on emulsion polymers. feldspars. HEC polymers were one of the original materials utilized for thickening water based coatings and they are still in common use. Cellulosics are relatively high molecular weight water soluble polymers which thicken by raising the viscosity of the water phase of the coating. The proper choice of a thickener and optimizing its level allows the coating’s rheology to be adjusted to meet the needs of the intended application. In coatings based on emulsion polymers. these include: calcium carbonates.6. HASE (a class of synthetic polymers termed hydrophobically modified alkali swellable emulsions) and HEUR (a class of synthetic polymers termed hydrophobically modified ethylene oxide urethanes). and are used at levels of 0. While extenders are relatively inexpensive. A high shear rate milling process. Thickeners are used to provide emulsion based coatings with the desired application rheology. primarily in low sheen decorative coating applications. by neutralization with a base such as ammonia. and the ionized acidic groups on the resin backbone provide strong anionic stabilization to the particles under neutral or basic pH conditions. the 133 . extenders differ from inorganic pigments because they do not significantly absorb or scatter visible light. water soluble. Careful selection of extender components is needed in order to optimize the cost-performance balance of a coating formulation. coatings formulated above CPVC generally contain high levels of extenders. sodium hydroxide or potassium hydroxide. or swelled. Functionally.5 to 1. vinyl resins with high levels of acid functionality. this range of volume solids would be too low to provide adequate viscosity for most coating applications. because it would be cost prohibitive to raise the PVC this high by use of TiO2 alone. They are usually neutralized with a base such as ammonium hydroxide. and in the absence of a thickening system. Like the binder and pigment components. clays. Coatings formulated with emulsion polymers generally have volume solids in the range of 25–40 %. and talcs [12]. In contrast to conventional HEC. usually hydroxy ethyl cellulose. is used to create the dispersion.0 % by weight solids on pigment and extender solids. and with hydrophobic domains on the surface of the emulsion polymer particles. thereby increasing scattering efficiency and improving hiding. water resistance. Above this level. (In the wet state before the film dries. the opacity or hiding power of a coating increases linearly with TiO2 content up to about 10 PVC. They are particularly useful for demanding applications of decorative and protective coatings where higher gloss. Hollow sphere particles also make a direct contribution to hiding. The sample is presented as seen from above. Since TiO2 levels are usually reduced when hollow sphere opacifying aids are utilized. but they are lower in molecular weight (50 000 g mol–1) and do not have the alkali swellable component of the HASE thickeners. In spite of this decrease in efficiency. HEUR thickeners make a positive contribution to the colloidal stability of a coating. which can associate with hydrophobes from other thickener molecules. and they are not generally preferred for demanding exterior applications.134 6 Applications for Decorative and Protective Coatings HASE polymer backbone is modified by pendant hydrophobic functional groups. and while total hiding continues to rise. Common opacifying aids fall into two main classes: hollow sphere particles and small particle size extenders. HASE thickeners are cost effective and they are used in a variety of decorative coating applications. and effective barrier properties are needed. hiding efficiency (hiding scaled to the amount of TiO2) starts to fall off.) The air void effectively increases the difference in refractive index between the TiO2 scattering centers and their surrounding medium. because their central air voids provide a certain amount of intrinsic scattering to the dry film. and thereby allow coating manufacturers to reduce formulated raw material costs while maintaining hiding performance. Figure 6-2 presents a transmission electron micrograph of a commercial hollow sphere opacifying aid. and the hiding contribution is substantially reduced. . This hydrophobic association gives HASE thickeners improved efficiency. HEUR thickeners are also hydrophobically modified synthetic polymers. individual TiO2 particles begin to crowd or interfere with each other. with the polymer shells appearing as a dark rings and the voids as the lighter cores. coating manufactures careful optimize the rheology modifier package in order to ensure that the coating applies correctly. hydrophobes from surfactant molecules. and helps them resist volume exclusion flocculation. At low TiO2 levels. However. coatings manufacturers generally utilize TiO2 levels in the range of 15–25 PVC to provide adequate wet and dry film opacity. and that it meets the appearance and performance needs of the intended application. Opacifying aids work by improving TiO2 efficiency. the central air void is filled with water. hiding efficiency is also improved through a reduction in TiO2 crowding. Opacifying aids are frequently included in coating formulations to enhance the hiding performance of TiO2. non-associating polymers. The particle size is quite uniform with particle diameters of roughly 300 nm. Again. Hollow sphere particles are sub-micron sized hollow polymer beads which enhance TiO2 hiding in the dry film by bringing a low index of refraction air void in close proximity to the TiO2 particle. an undesirable aggregation process associated with high molecular weight. Because of their lower molecular weight and associative character. the alkali swellable component of their composition can increase the water sensitivity of a film. or they may be deposited by rain or from the atmosphere. Particles are approximately 300 nm in diameter. Small particle size extenders are the other class of opacifying aids. although other chemistries are used as well. and the hollow cores appear as the light areas within the rings.) In the past. unless they are inactivated and are unable perform their function. The use of anti-microbial agents. 6.2 Overview of Coating Formulations Fig. Contrast was increased by staining with RuO4. (Apparently.5 µm). In the wet state. The primary particle size of these specialized extenders is quite small (typically <0.6. Coatings based on vinyl emulsion polymers have better resistance to microbial growth than traditional alkyd coatings. they increase the average distance between TiO2 particles in a film. and trace minerals. they may leach out from the substrate. paint film mildewcides based 135 . in general. or biocides. and the coating itself. a source of carbon and nitrogen.2 Transmission Electron Micrograph of a Hollow Sphere Opacifying Aid. is generally required to prevent water based paints from spoiling while being transported and stored. Polymer shells appear as dark rings. leading to poorer intrinsic mildew resistance. acting as spacers. Preservatives are used at low levels and generally do not affect the performance properties of a coating. Paint film mildewcides are commonly used in exterior coatings formulations to prevent defacement of the coating surface by mold and mildew. support microbial growth on the paint film surface. Biocides protect coatings from attack by microbial organisms. causing deterioration of the film itself. the natural oil components of alkyd resins make them more readily metabolized by microorganisms. Isothiazolones. seriously affecting decorative performance. thereby disrupting the function of vital cellular components. and in severe cases. but paint film mildewcides are usually included in exterior formulations to provide additional protection. and materials based on formaldehyde are most often used for this purpose. These materials. and the colloidal components of a coating need to be properly formulated and stabilized in order for these materials to work effectively. The microbial growth process can eventually lead to unsightly mildew and algae growth on the coating surface. preservatives used in these applications are electrophilic compounds which function by reacting with nucleophilic groups within the cell or on the cell surface. A variety of materials are used as in-can preservatives for water based coatings. thereby reducing crowding effects. water based coatings possess the basic ingredients needed to support microbial growth: water. Sample was prepared by diluting polymer dispersion with water and then drying a small quantity on an electron microscope sample grid. The surface of an exterior coating can accumulate nutrient compounds from the local environment. Different wetting aids are used to ad- . they partition strongly into the polymeric domains of the coating. and it must be properly balanced or it can result in film defects or loss of activity. thickeners and defoamers) this can affect the amount of free surfactant available to reduce the surface tension. appearance and performance characteristics of a coating. and if they are released into the environment by the weathering process. including hydrocarbon and silicone based materials. Defoamers are used to prevent or to dissipate foam in coatings based on emulsion polymers. and while the surfactants present in a water based coating can reduce this to values in the 25–30 mN m–1 range.136 6 Applications for Decorative and Protective Coatings on organomercury compounds provided cost effective protection in emulsion polymer coatings. This marginal incompatibility is an important factor in defoamer effectiveness. extenders. Wetting aids are used to improve the ability of water based coatings to form defect free films over a variety of substrates. isothiazolone and chlorothalonil chemistries. Combinations of organic biocides are sometimes used to provide increased protection against a broad spectrum of microorganisms. but environmental and health concerns now strongly limit their use. this may not be adequate to allow proper wetting (and thus adhesion) to low surface energy substrates such as plastics or certain re-paint surfaces. Defoamers are used in a formulation to destabilize and to speed the breakup of foam in the liquid coating. Over the life of a film. Small air bubbles can be introduced into the liquid coating during the manufacturing or application processes. A wide variety of non-ionic and ionic surfactants are used. the water phase and the coating surface. If these bubbles are stabilized or long lived. The most common organic paint film mildewcides in use today are based on iodopropynylcarbamate. as well as improving the application. Used properly. While typically used at low levels (<1 % by weight). They are generally hydrocarbon or silicone based dispersions or emulsions which have limited compatibility with both the water and polymer phases of the coating. modern paint film mildewcides offer a safe and cost effective means to significantly extend the service life of exterior coatings. 73 mN m–1 [9]. Modern organic mildewcides have significantly improved environmental risk profiles. defoamers can significantly enhance the paint manufacturing process. Typically wetting aids are surfactants or very low molecular weight oligomeric polymers. The equilibrated surface tension of a formulated coating will ultimately depend on the complex distribution of surfactants molecules between these colloidal particles. and formulators commonly include zinc oxide in order to provide longer term protection from mildew growth. they are present at extremely low concentrations so that they can be broken down and metabolized by microorganisms in the soil. They are generally selected by a combination of previous experience and direct testing. Also. Unfortunately. and the judicious use of wetting aids can be used to supplement colloidal stability and to promote proper wetting of the substrate. surfactants can potentially interact with all the colloidal materials in a coating formulation (pigments. the surfactants which are used in the manufacture of emulsion polymers and water based coatings can also act to stabilize foam. or leave unwanted voids in the dried film. they can interfere with the efficiency of manufacturing. these biocides slowly diffuse to the coating surface where they act to control microbial growth. Pure water has a high surface tension. and these terms include flat. floor paints for masonry and wood. they can play a vital role in enabling water based coatings to meet specific appearance and performance requirements. 6. While typically used at low levels (<1 %). exterior wall and exterior trim. with the 137 . VA-BAs. 6. offices and other architectural structures by providing color.3 Decorative Coatings The primary role of decorative coatings is to enhance the esthetic appeal of homes. there are still a variety of technical issues which remain to be addressed by both raw material suppliers and paint manufacturers. driveway sealers and arts and crafts finishes. interior trim. Space limitations prevent a detailed discussion of these specialized coating applications.6.3. solvent borne drying oils and alkyds were the predominant polymer technologies used throughout most of the twentieth century. EVAs and styrene acrylics are commonly used for interior flat wall coatings. However. Clearly. rising environmental and health concerns.3. such as masonry finishes. or combine them. texture and sheen to interior and exterior surfaces. arguably extending back to prehistoric times with paintings on the walls of cave dwellings. have allowed water based coatings to move into the leading positions in the decorative application areas. EVAs.1 Emulsion Polymers in Decorative Coatings The history of decorative coatings is long one. including poor substrate adhesion. While emulsion polymers are now the market leaders in most decorative applications. and coating manufactures commonly break these classes down further. semi-gloss and gloss. in order to enhance the marketability of their products. 6. and acrylics being most popular. clear and stain finishes for wood. product performance and product differentiation remain. with VA-BAs. The sheen level of the coating is also commonly characterized. styrene acrylics. coupled with improvements in the performance of emulsion polymer coatings. regulatory pressure to drive down VOC emissions continues to increase throughout the world. Decorative coatings are commonly classified by their intended application.3 Decorative Coatings dress a variety of coating problems. and the challenges of balancing the often conflicting objectives of product cost. There are also many kinds of more specialized decorative coatings. Focusing on more recent times. but much of the information we present here can be easily adapted to these coatings. poor flow and leveling and poor color acceptance. These distinctions are not rigid or comprehensive. and these include interior wall.2 Polymer Compositions used for Emulsion-based Decorative Coatings A variety of thermoplastic emulsion polymers are used in decorative coating applications. North America (NA). For example.138 6 Applications for Decorative and Protective Coatings choices between them generally based on regional economic and performance characteristics. heavily industrialized countries have a relatively higher proportion of protective and product finishes. Differences in building materials and. 6. account for roughly 40 % of worldwide coatings production. and the use of styrene acrylics for decorative segments in Europe and Asia. high performance coating. 6. and in labor costs.4 Market Size of Decorative Coatings Decorative coatings. acrylics and styrene acrylics are commonly used. consequently. and the specific choices made by paint formulators are based on a complex mixture of factors. underlie many of these distinctions. can affect how end users balance the higher initial costs associated using a more durable. the substrates to which coatings are commonly applied.3. Regional economic factors also influence the choice of polymer used in coating applications: differences in raw material costs. Australia – New Zealand (ANZ) and Scandinavia all have relatively high levels of wood substrates. would give the total production of decorative coatings to be roughly 8 billion liters per year worldwide. The ratio can vary from country to country. Starting with the world wide coating production estimate of 20 billion liters per year [1]. raw material cost. and specific performance needs. versus the higher deferred costs associated with using a less durable coating having a more frequent re-paint cycle.3. and taking the fraction of decorative finishes to be 40 %. whereas masonry substrates are more common in Europe. VA-BAs. this drives the use of VA-BA polymers for the low cost interior flat segments of NA and ANZ. while less industrialized countries often have a higher proportion of decorative finishes. the use of elastomeric wall coatings for masonry applications in Europe.3 Regional Distinctions in Decorative Coatings There are significant regional distinctions in the formulation of decorative coatings. as defined here. Acrylics and styrene acrylics are the preferred chemistries for exterior applications. and styrene acrylics and VA-BA polymers predominate in these markets. decorative paints are commonly designed for both interior and exterior applications. Latin America (LA) and Asia. while for interior semi-gloss applications. The availability of supplies of low cost monomers is another important factor affecting the choice of polymer composition. These are generalizations. Substrate differences are a major factor in the preference of acrylics for exterior wood applications in NA. Acrylics and styrene acrylics are both used for interior and exterior gloss and semi-gloss applications. ANZ and Scandinavia. including regional custom. again with regional economic factors and performance characteristics driving specific choices. In Latin America. local availability. Assuming that about 50 % of this is based on emulsion polymer technology leads to an esti- . and the choice of styrene acrylics for masonry applications in LA and Asia. 1 Key Performance Features Interior flat wall coatings have a low or “flat” sheen. and this in turn requires a correspondingly large number of formulations and raw materials.4. coat- 139 . semi-gloss and gloss. an important characteristic in re-paint applications. We estimate the North American market to be a third of this value or about 1. we will focus our discussion on two of the major segments of the interior decorative market. satin. differences in sheen and color are readily observable in these coatings. and use them to highlight performance and formulation concepts of this market segment. Coatings manufacturers produce a wide variety products to meet the different needs of this large market segment. End users expect decorative coating to have good hiding characteristics.5 billion liters per year. If we estimate the average retail selling price to be $4–5 US per liter. fast dry. Again it is important to emphasize that these are very rough estimates. and assuming an average retail selling price of roughly 4–5 Euros per liter. and thus sheen and color uniformity of the applied coating are key performance attributes. The popularity of water based paints in interior decorative applications is due to many factors. good appearance and color stability. and the ease of soap and water clean-up. Paints based on emulsion polymer technology now account for most of this segment. flat interior wall paints and interior trim enamels. Because of space limitations. sheen and color to the interior walls and ceilings of homes and offices.4 Interior Decorative Coatings mated annual production of about 4 billion liters of water-based decorative coatings world wide. and are generally applied by roller in re-paint applications. this gives a total NA market value of $6–8 billion US per year for decorative coatings. would give a total European market value of about 6–8 billion Euros per year for decorative coatings. trim and ceiling. Paints for this application are designed for a variety of specific applications such as kitchen and bath. and are intended to give the reader a general picture of market size. and they are usually formulated with an 85° gloss level below about 4 %. Good application characteristics are important as well. wall. 6. Formulating with associative thickeners (typically HASE) can help reduce roller splatter.4 Interior Decorative Coatings Interior decorative paints are designed to provide texture. interior flat wall paints are frequently spray applied in new construction applications. including their ease of use. low odor. The volume of the European decorative coating market is roughly comparable in size to the North American market.5 billion liters per year. Taking the annual European production estimate to be also 1.6. and while true one-coat hiding remains an elusive goal. Low sheen levels are usually achieved by using large particle size extenders at relatively high PVCs. they also provide different sheen levels such as flat. While low sheen levels help to hide defects in the substrate. 6. since they are routinely applied to living areas (with higher potential for dirt and stains). and they also help to lower raw material costs by reducing TiO2 levels. although recently developed binders for interior flat coatings can often be formulated with very little or no added coalescent. 6. film integrity and optimum appearance characteristics. respectively. aged water based enamels. Trim enamels are frequently brush applied so good flow and leveling characteristics are important. A coalescing agent is usually included to enhance film formation. windows and kitchen areas. Opacifying aids are commonly used to help achieve high hiding levels. Finally. more resistant coating is needed to provide substrate protection. Interior Enamels Polymer performance plays a more significant role in the formulation of enamel coatings than in flat coatings. and to improve the freeze thaw resistance of the wet paint during storage. Interior flat coatings also need to have good cleanability characteristics. decorative moldings around doors and windows. It is also desirable that the coating’s hardness develop quickly so that objects can be placed on painted surfaces without marking the film. Table 6-1 provides an example of a typical interior flat coating formulation.4. Enamels are generally formulated at higher sheen levels. Finally. base boards. cupboards and shelving. These surfaces often have a high level of day to day human contact and a tougher. trim enamels need good stain resistance and cleanability. Thus. They are applied over a variety of substrates. Enamel coatings are frequently applied to trim surfaces such as doors. Acrylic and styrene acrylic emulsion polymers are .2 Interior Decorative Coating Formulations Flat Interior Wall Coatings Cost is one of the most important factors for interior flat coatings and drives many of the choices in formulations and raw materials. primed wood or metal. and the coating’s ability to be easily cleaned can add significantly to its service life and user satisfaction. window frames. Trim enamels should also have good block resistance so that adjacent painted surfaces can be pressed into contact without sticking to each other. Propylene glycol is commonly used as a pigment grinding aid. and thus they must have good adhesion characteristics. since the polymer component makes up a higher volume fraction of the dried film. PVCs are generally high.140 6 Applications for Decorative and Protective Coatings ing manufacturers carefully balance hiding performance and cost in these formulations. including aged alkyd. and are usually above CPVC. because they are applied in high use areas such as doors. with HASE and cellulosic thickeners being most commonly used. anionic and non-ionic surfactants are commonly added to optimize colloidal stability and enhance color development and uniformity. Rheology modifiers are chosen to provide the desired rheology profile. with values for semi-gloss and gloss coatings ranging from 30–85 % at 60°. Vinyl acetate and styrene based copolymers are most frequently used as binders for this market and cost considerations also drive the use of relatively high levels of low cost extenders. 07 0.16 0.04 52.18 0. and are used to a limited extent in semi-gloss coatings. 6-1 Interior decorative flat formulation.73 13. Extenders and opacifying aids are not commonly used in gloss enamel coatings.36 100.6.56 4. with vinyl acrylics playing a role in the lower performance/lower cost end of the market.65 9.84 1. they provide excellent flow and leveling with brush application and generally allow for higher gloss levels. Material Weight % Grind Water Propylene Glycol Dispersant Defoamer Biocide Aminomethylpropanol Titanium Dioxide Calcined Clay Extender Calcium Carbonate Extender Grind sub-total 13. Again. The harder polymers used in enamel coatings generally require higher levels of coalescing agents to provide good film formation. and enamels are formulated significantly below critical PVC.58 1.18 16.18 1.4 Interior Decorative Coatings Tab.52 0. grind aid Interior grade Coarse grade Add to grind with good agitation 55 % Solids Ester alcohol. 141 . generally in the range of 15–25 % PVC.18 10. Performance considerations limit the PVCs of these coatings.34 0.09 Let down VA-BA Emulsion Polymer Hollow Sphere Opacifying Aid Coalescent Defoamer Water HEUR Thickener Ammonia (28 %) HASE Thickener Total Property Total PVC Volume Solids Weight Solids Comments Prepare in a high speed disperser 19. film formation Hydrocarbon dispersion 25 % solids Base Emulsion Value 63 % 33 % 47 % most commonly used in this segment.00 Grind and freeze-thaw aid Polyacid Hydrocarbon dispersion Isothiazolone preservative Base.72 0. HEUR and HASE thickeners are often used as rheology modifiers. Table 6-2 provides an example of a typical interior/exterior gloss enamel formulation. anionic and non-ionic surfactants are commonly added to optimize colloidal stability and enhance color development and uniformity.72 6. Decorative coatings are often stored for long periods of time under sub-optimum conditions before they are sold or applied.39 Let down Acrylic Emulsion Polymer Water Diethylene glycol butyl ether Coalescent Phosphate Surfactant HEUR Thickener A HEUR Thickener B Defoamer Total Property Total PVC Volume Solids Weight Solids 50.36 2.00 Comments Prepare in a high speed disperser Grinding aid Isothiazolone preservative Hydrophobically modified polyacid Non-ionic pigment wetting aid Silicone emulsion Universal Grade Add to grind with good agitation Specialized gloss enamel vehicle Co-solvent Ester alcohol.09 2. film formation Wetting Aid 20 % solids 25 % solids Silicone emulsion Value 21 % 32 % 45 % 6.16 0.142 6 Applications for Decorative and Protective Coatings Tab. In the warmer regions of the world.58 2.10 1.4.10 0. Heat age and freeze-thaw stability testing protocols have been developed to assess the storage stability of coating products.36 0.67 15. 6-2 Interior/exterior decorative gloss enamel. appearance and resistance properties of interior decorative coatings. The reader is referred to the specific ASTM and ISO test methods given in Tab. Heat Age Stability is tested by placing the paint in an oven for a specific time and temperature. Material Weight % Grind Propylene Glycol Water Biocide Dispersant Surfactant Defoamer Titanium Dioxide Grind sub-total 3.50 0. Our objective in this section.28 28. In the colder regions of the world.05 100. and the cited references [13–14] for a more detailed description of test method protocols. and in the subsequent application and performance test sections.02 21. will be to identify the key performance features and to give the reader an overview of how these tests are conducted.12 0. 6-3.43 0. coatings are frequently stored in warehouses where temperatures can reach 45 °C for extended periods of time. and then testing the coating for key performance . coatings can be subjected to repeated freeze-thaw cycling when stored at an unheated job site.3 Standard Application and Performance Tests Many specialized tests have been developed to measure the application.19 0. D4587. G26. 6-3). Defects in the applied coating should be minimal.6. 6-3 Selected coating applications test methods. D4213 D3450. Also. changes in viscosity and other key performance properties are then evaluated. G85 D2370 D1653 D 1640 – Modified D711.4 Interior Decorative Coatings Tab. Application properties are particularly important with products designed for professional painters. D4541 D2486.D713 1147 2813 2814. D661. without excessive sagging. and field trials under realistic application conditions. D2805 D4946 D2064 D3359. Decorative coatings are commonly applied by brush. D662.org ** ISO test methods can be obtained from the ISO web site – http://www. or spray techniques. G151 D610. D3719.ch properties.iso. and easily repairable. D1014 D2803. Testing protocols include laboratory testing under carefully controlled conditions.astm. typically 3–5 cycles of temperature changes between –20 °C and room temperature. since these features are vital to reducing call backs and maintaining high productivity. 11997 7783 ** ASTM test methods can be obtained from the ASTM web site – http://www. Good initial appearance is an important factor in determining customer satisfaction in any coating application. but is particularly vital for decorative finishes. D6677 D2297. and provides a uniform coating to the substrate. The applied coating is expected have the right color and the right sheen level. The objective is to develop a coating which applies correctly. Many different time-temperature protocols are used. 11341 4628 7253. many specialized tests have been developed to as- 143 . has a rheology profile which allows good flow and leveling. G53. Freeze-thaw stability is tested by subjecting the coating to repeated freeze-thaw cycles. and coatings manufacturers generally design their products to perform well when applied by any of these methods. A variety of standardized laboratory instruments have been developed to measure sheen. D4828 D6686 D660. two common ones are 10 days at 60 °C or 30 days at 50 °C. Application test ASTM method* ISO method** Freeze-thaw resistance Heat age stability Low temperature film formation Gloss Color acceptance Hiding Block resistance Print resistance Adhesion – qualitative Adhesion – quantitative Scrub resistance Stain removal (top coat) Stain blocking (tannin) Durability – exterior Durability – accelerated Corrosion – exterior Corrosion – accelerated Tensile testing Permeability testing Early washout (traffic paint) No pickup test (traffic paint) D2243 D1849 D3793 D523 D5326 D344. D4214 D4141. 6504 3678 2409 4624 11998 4586 4628 4892. roller. D772. hiding and color development (Tab. allowing the coating to dry for a specified time. but rather. While it is desirable to have a coating exhibit cohesive failure in lab tests. and then testing the adhesion of the applied coating by attempting to separate it from the substrate. cross hatch/tape pull. variations in color uniformity can have a significant impact on end user satisfaction. This is generally indicative of good adhesion performance. mustard. steel or aluminum. Adhesion is a key performance factor and several tests have been developed to measure this parameter. Adhesive failure occurs when the applied coating separates from the substrate at the interface between the coating and the substrate. and this can result in a color which appears different from adjacent areas coated under the lower shear rate of roller application. . or measured quantitatively with a color spectrophotometer. the coating is allowed to dry for a specified time (usually a week) and then common staining materials such as coffee. and then a section of the coating is either rubbed with the finger or brushed until the coating starts to dry. Experience and careful comparisons against known standards are generally required in order to obtain useful performance predictions in these cases. and then filled in by roller application to the center sections. or by destruction of the substrate. they impact user satisfaction by affecting the service life of the coating. Adhesion can be tested under wet or dry conditions (wet adhesion is usually a more severe test than dry adhesion). such as using knife peel. Problems in this area are generally related to poor colloidal stability. In laboratory testing of this property. coatings which exhibit adhesive failure often show good adhesion performance in actual exposure testing. and the coating is usually scored or cut in order to minimize the confounding effects of film integrity. because it provides a controlled and accelerated measure of performance features which may take years to become evident in actual end use applications. Failures of this type can be assessed via subjective or quantitative measurements.144 6 Applications for Decorative and Protective Coatings sess appearance properties under specific application conditions. Laboratory testing plays a key role in assessing the resistance properties of coatings. fruit juice. For example the color rub-up test assesses the color variability of a coating when applied by brush or roller application techniques. a lightly flocculated pigment dispersion can be temporarily dispersed by the high shear conditions of brushing. or a quantitative measurement of the force to peel. tea. In the stain resistance test. Cohesive failure occurs when the coating remains bound at the film–substrate interface and separation occurs within the coatings itself. Color differences between the low shear rate draw-down region and the high shear rate rub up or brushed region are then assessed subjectively. The cleanability of a coating is generally assessed by stain resistance or scrub tests. Resistance properties In contrast to the appearance and applications properties of a coating. but it can sometimes be misinterpreted when a coating has extremely poor film integrity (giving a false positive reading). Since large interior wall areas are usually painted by brush application around the perimeters. All adhesion tests follow the general protocol of applying the test coating to a defined substrate such as chalky or aged alkyd. a draw-down of uniform film thickness is first applied. resistance properties are not assessed by the user during and immediately after the application. painted surfaces are placed in contact in routine operation. In this test. such as books or vases. The test squares are then pulled apart and rated subjectively for self adhesion. The test is allowed to progress for a specified time and temperature (usually one week at 25 °C. The force necessary to separate the test areas is then measured quantitatively. as described above. Both tests are subject to high levels of variability and carefully controlled experiments are needed to produce accurate and reproducible results. and these test areas are placed together. This is an important feature for coatings which are applied to windows and doors. the coating is washed with a cleaning formulation and then is rated for stain removal relative to controls. A coating of defined thickness is applied to a vinyl chart and dried for a specified time. on a horizontal coated surface.5 kg weight on a surface area of approximately 5 cm2) is applied for a specified period of time and temperature (typically 12 h at 25 °C or 4 h at 50 °C). and then the coating is evaluated subjectively against controls for its ability to resist permanent marking or defacement. In a variation of this test. and allowed to dry under controlled conditions for a specified time (typically ranging from 8 h to 4 weeks). After a specified contact time.4 Interior Decorative Coatings ketchup. the coating can be applied to a rigid substrate such as glass or metal. Ideally. and measurers the ability of a coating to resist abrasion by a stiff brush and an abrasive cleaner. or cleaning solution. The print resistance test measures the ability of a coating to resist permanent imprinting caused by the placement of heavy objects. under pressure. Dry time and contact pressure are important factors affecting block resistance and are the primary variables which are controlled in laboratory testing. A defined pressure (generally in the form of a 0. such as a rough cloth is placed on the coated surface with a defined pressure (typically about 1 kg per 5 cm2). Block resistance is a measure of a coating’s ability to resist destructive self adhesion when placed into contact with itself. the test coating is placed in the testing machine for a fixed number of cycles using either the abrasive medium or a cleaning solution. pen or felt tip marker are applied to the surface. usually a week. Failure is noted when the film is visibly damaged upon separation. or one day at 50 °C). 145 . In another variation of the scrub test. and then a heavily textured object. leaving no film damage. The coating is cast on a non-rigid substrate such as a coated paper chart. Small squares of the coated substrate are then cut out and placed with the coated sides facing together. The operator assesses the number of scrub cycles needed to wear through the coating to the substrate. The scrub test assesses cleanability differently. pencil. the two test squares separate with minimal force. since in these components. and then cleaned and dried. A specialized scrub testing machine is used to scrub the coating with a brush and a standardized abrasive medium. Performance is assessed by measuring the weight of coating lost during the scrub process.6. a coating is cast onto a metal substrate. chalk resistance – the ability of a coating to resist the surface powdering caused by UV and moisture induced polymer degradation. Because exterior coatings are generally viewed from a distance. the coating should be resistant to darkening caused by adsorption of dirt and soot from the external environment. appearance and resistance features characterizing interior decorative coatings.5. and resistance to cracking and adhesion loss – the ability of a coating to resist grain cracking and the subsequent flaking and loss of adhesion when applied over wood substrates. but over the past 30 years coatings based on emulsion polymers have advanced and are now the preferred technology for this application. Historically. leading to poor tint retention and premature chalking. they can eventually lead to film embrittlement and subsequent cracking over dimensionally unstable substrates. They share many of the application. Finally. exterior decorative coatings are expected to protect their substrates from the harmful effects of weathering for the lifetime of the coating. Acrylic based polymers are more resistant to these different degradation processes and. alkyd and oil based coatings were commonly used in exterior decorative applications. This is primarily manifested in three important areas: tint and gloss retention – the ability of a coating to maintain its original color and gloss level during exposure. the ester linkages of oil and alkyd based coatings are susceptible to alkaline based hydrolysis. with the obvious and important difference that they are expected to provide these features while being subjected to the deleterious effects of UV radiation and weathering. consequently. most of the other performance features de- . Of course. Good dirt pick-up resistance is also important. The primary reason for this is the superior durability of acrylic emulsion polymers (and to a lesser extent vinyl-acrylic and styrene-acrylic polymers) in exterior applications. apartments and offices.1 Key Performance Features Exterior durability is the key factor which differentiates the performance of exterior decorative coatings. Additionally.5 Exterior Decorative Coatings Exterior decorative coatings are used to provide aesthetic and protective features to the exterior walls and trim of houses. The UV absorption characteristics of these materials make them quite susceptible to UV degradation. Adhesion to a variety of architectural substrates is also an important performance feature. While the cure processes are quite efficient. particularly over freshly prepared concrete. 6. particularly in re-paint applications where weathered substrates present particular challenges. appearance properties such as flow and leveling are somewhat less important than they are in many interior applications. Alkyd and oil based coatings rely on oxidative cure processes to develop resistance properties.146 6 Applications for Decorative and Protective Coatings 6. In addition. most alkyd resins are made by the esterification of phthalic anhydride with unsaturated fatty acids or natural drying oils. a polymer degradation process which can be accelerated by the basic pH conditions present in many masonry applications. have become the performance standards for exterior decorative coatings. 5. Most raw material suppliers and many coating manufacturers have set up their own exposure sites. visible on tinted films) in horizontal face down applications. but normally would include several different types of wood and masonry in both new and re-paint applications. In contrast to interior flat paints. 6. A typical experimental design for an exposure experiment would include experimental and control coatings which are applied. A typical formulation for an exterior flat decorative coating is given in Tab. 6. the tint retention and chalk resistance of exterior flat coatings can be enhanced by favoring the use of coarse silica or nephiline syenite over clays.2 Exterior Decorative Coating Formulations Acrylic emulsion polymers are generally preferred for exterior decorative applications because of their good exterior durability characteristics. Durable grades of TiO2. particularly in flat and satin formulations. Styrene acrylics and vinyl acrylics are also popular. sometimes leading to poor dirt pick-up resistance. while HEURs are commonly used in gloss and semi-gloss formulations. Carbonates can also can show frosting (the appearance of a hard white exudate. Based on our experience.3 Standard Application and Performance Tests Exterior exposure testing is the most direct and reliable method to evaluate the durability of exterior decorative coatings. are generally chosen for exterior applications. and the vast majority of exterior exposure testing is done via controlled exposure experiments carried out at established exposure sites around the world. particularly in regions of the world where lower labor costs reduce the economic barrier to a more frequent re-paint cycle. The choice of substrates depends on the intended market segment and region. The most representative and general exposure protocol is to actually apply the coating to test homes or buildings. the cost and logistics of such large scale trials limit their use. Calcium carbonates generally have good tint retention. Because good moisture resistance generally is required for exterior applications. but they can degrade in regions with acid rain. in replicate. to test areas (on the order of 15 cm × 30 cm) over a variety of representative substrates. Finally. a paint film mildewcide is generally included in exterior formulations. exterior flat paints are generally formulated below CPVC in order to provide improved durability. to provide this capability. and to then evaluate the performance over a long period of time. South vertical exposures are 147 . cellulosic and HEUR thickeners are generally chosen as rheology modifiers for exterior applications. However. cellulosics are commonly used in exterior flat formulations. coated with inorganic materials to provide improved UV resistance.5. to minimize mildew growth on the coating after application.6. or use commercial exposure services. In the Northern hemisphere. The choice of extenders can also have a significant impact on the performance of exterior coatings.5 Exterior Decorative Coatings scribed above for interior decorative coatings also apply to their exterior counterparts. 6-4. grain cracking. selecting woods with poor dimensional stability as substrates. even with these methods. and applying thinner layers of coating (one coat applications). this exposure angle increases the flux of UV energy incident on the sample. Material Weight % Grind Cellulosic Thickener (2.87 0. Exposures at South 45° can be used to accelerate failure modes linked to UV radiation and moisture.64 Let down Acrylic Emulsion Polymer (60 %) 22.25 0.17 0.17 100.5 %) Water Dispersant KTPP Non-Ionic Surfactant Defoamer Biocide Mildewcide Titanium Dioxide Zinc Oxide Nepheline Syenite Extender Functional Extender Grind sub-total 10.17 1. and the data obtained from these experiments should be interpreted with caution.17 8.5 % in water Value 50 % 35 % 54 % commonly chosen to accentuate failure modes which are linked to UV exposure.09 2.86 Ester Alcohol Coalescent Ethylene Glycol Defoamer HEC Thickener Water Total Property Total PVC Volume Solids Weight Solids 0.83 0.52 0.07 7. . these include gloss loss. Exterior exposure testing is not a rapid process.11 16.14 0.08 0.42 60. 6-4 Exterior decorative flat formulation. as well as increasing the intensity and duration of moisture contact brought about by the daily dew cycle and rain.00 Comments Prepare in a high speed disperser HEC thickener Hydrophobically modified polyacid Co-dispersant Pigment wetting aid Hydrocarbon dispersion Isothiazolone preservative Isothiazolone mildewcide Exterior universal grade Mildew protection Coarse grade Thixotropic clay Add to grind with good agitation Enhanced adhesion to alkyd and chalky re-paint Film formation Co-solvent and freeze-thaw aid Hydrocarbon dispersion 2. it can still take 2 years or more to develop a clear picture of a coating’s durability characteristics. some failure modes can take several years to develop. chalking and color fading.148 6 Applications for Decorative and Protective Coatings Tab. However.71 7.08 0. 45° exposures are generally uncommon in real world applications. However. coatings scientists can accelerate the exposure testing process. North vertical exposures are used to evaluate mildew resistance and discoloration by dirt pick up. By using specialized exposure techniques such as: exposing samples at South 45°.25 21. 6. The use of such soft polymers would normally lead to coatings with poor dirt pick up resistance and tackiness. While a variety of exposure instruments and devices have been developed. Elastomeric coatings also prevent the penetration of wind driven rain and water into the substrate by sealing these cracks. but proprietary technologies are usually employed to address these problems. Their function is to enhance the appearance and durability of exterior masonry surfaces present on large buildings such as apartments. allows them to bridge cracks in the substrate and to stretch and shrink with thermally driven building movement.6. and because masonry construction is widely used around the world. The elastic character of these coatings. Elastomeric coatings can significantly enhance the durability of many masonry surfaces. applied over dimensionally stable substrates. Elastomeric coatings improve the appearance of masonry surfaces by covering these small cracks with a smooth elastic film. caused by uneven thermal expansion and contraction. Emulsion polymers used for elastomeric wall coatings generally have low Tg (typically less than –20 °C) in order to provide the elastic character needed for effective crack bridging.6 Elastomeric Wall Coatings Accelerating the process for assessing the durability of exterior coatings is of obvious interest to raw material suppliers. These types of structures often have large uniform surfaces which can be disfigured by small cracks and fractures. we have found that these instruments do not always provide information consistent with exterior exposures. This is currently an area of active research and a variety of efforts are under way to improve the predictive ability of accelerated weathering protocols [15]. thus improving the durability of the underlying masonry material. along with the use of thicker applied films. and are commonly used to provide accelerated exposure information. and they enhance the durability of masonry substrates by preventing the intrusion of water into these defects.1 Key Performance Features Elastomeric wall coatings are designed provide a high quality decorative and protective finish for large masonry surfaces. Accelerated exposure devices have proven to be most useful when evaluating specific failure modes. 149 . 6. 6. hotels and offices. the use of elastomeric wall coatings has grown significantly over the past 20 years. and comparing the performance of coatings of similar composition.6 Elastomeric Wall Coatings Specialized elastomeric wall coatings were first introduced into European markets in the early 1980s. coating manufacturers and end users. 09 0.89 100. it is recommended that the total dry film thickness be in the range of 300 to 500 µm.2 Typical Elastomeric Wall Coating Formulations Elastomeric coatings are formulated to yield tough films which maintain a balance of tensile strength and elongation characteristics across a broad temperature range (–10 to +30 °C). non-ionic Specialized elastomeric vehicle Hydrocarbon dispersion Isothiazolone class Solid . A typical elastomeric coating formulation is given in Tab.20 26.150 6 Applications for Decorative and Protective Coatings 6. For optimum long-term performance. Tab. These coatings are formulated with relatively low levels of hiding pigments.20 0.55 54.27 0.84 Let down Surfactant Acrylic Emulsion Polymer Defoamer Mildewcide HEC Thickener Water Total Property Total PVC Volume Solids Weight Solids Comments Prepare with high speed disperser 0. They are usually extended with fillers such as calcium carbonate. Coatings of this thickness need a carefully optimized rheology profile in order to prevent sagging during the application and drying processes. Cellulosics. in order to provide for thicker dried films.6. either alone or in combination with HEUR thickeners.21 43. much thicker than typically used in architectural applications.09 0. Volume solids are typically high.44 0. An effective paint film mildewcide is also need in order to prevent discoloration of the coating surface by mildew growth.18 0. 6-5 Elastomeric wall coating formulation.67 2. Elastomeric wall coatings are generally formulated to be applied by professional painters using either roller or spray application techniques. since thick coatings are generally utilized. in the in range of 50 % to 60 %. These coatings are generally formulated at relatively low PVCs (typically in the range of 30–45 %) to provide the dried film with good elasticity and barrier properties.35 6. are generally preferred for this application.75 0.12 2.00 Value 31 % 49 % 61 % Grind aid and freeze-thaw Polyacid Co-dispersant Hydrocarbon dispersion Exterior Grade Fine grade Mildew protection Add to grind with good agitation Wetting aid. Material Weight % Grind Water Ethylene Glycol Dispersant KTPP Defoamer Titanium Dioxide Calcium Carbonate Extender Zinc Oxide Grind sub-total 5. 6-5. Permeability is then calculated from the rate at which water is lost through the film. is measured by mass difference over the course of one week.6. lower strain rates yield higher values for elongation. In the laboratory. since the topcoat can be independently optimized to provide these and other performance features. (ii) they prevent the transport of a variety of different types of colored stains from the substrate to the topcoat. They usually are not designed to provide high hiding or intrinsic weathering resistance. (iv) they serve as a flexible linkage between dimensionally unstable substrates and the topcoat. 151 . Testing is performed at a constant rate of jaw separation with load cells adequate to measure the tensile forces generated. Primers generally provide many or all of the following features: (i) they promote effective adhesion to a variety of substrates.6. The sample is fastened between the jaws of the tester and is stretched apart at a constant strain rate until it breaks. generally. permeability is evaluated by sealing a dried paint film of specified thickness over a cup of water and placing the assembly in a constant temperature and humidity room. providing a smoother and more uniform surface for the topcoat. Values for the percent elongation and tensile strength at break are then calculated. and samples are cut with a die from a dried film which was drawn down over a Teflon release plate. (iii) they enhance corrosion resistance. Testing sample dimensions are usually about 500 µm thick × 2 cm long × 1 cm wide.7 Primer Coatings Primer coatings are used to provide a functional boundary layer between the substrate and the topcoat. These properties are commonly evaluated in the laboratory at ambient and below ambient temperatures by use of a tensile testing instrument (Instron type or equivalent).3 Standard Application and Performance Tests The tensile and elongation properties of an elastomeric coating are important performance features which characterize the coating’s ability to bridge cracks in the substrate. coupled with lower values for tensile strength at break. and (v) they reduce irregularities and imperfections in the substrate. and are usually formulated at relatively low PVCs and high volume solids. 6. Water loss from the cup. through the film. Coating manufacturers design a variety of specialized primers to enhance total system performance for a variety of coating applications.7 Primer Coatings 6. The permeability of an elastomeric coating is crucial for determining whether the coating will allow adequate passage of water vapor through the coating. Decorative and protective primers generally have demanding performance specifications. These values depend somewhat on the strain rate used. 7. and (ii) the primer is formulated with specialized ingredients. which lock (by interacting with) stain molecules into the film. wood. it is effectively locked into the film and does not lead to discoloration of the topcoat. water stains and nicotine stains. The performance characteristics of primers can be greatly affected by the choice of thickener and dispersant. Table 6-6 illustrates a typical formulation used in stain blocking primer applications. Stain blocking primers are one of the most popular types.1 Key Performance Features Primer vehicles based on emulsion polymer technology were introduced in the 1970s and have shown a steady increase in market share over the past 30 years. While the stain may be visible at the surface of the primer coating after drying. children’s marker stains. and are used to prevent discoloration of topcoats by a variety of materials. lower PVCs and higher volume solids formulations are preferred because these characteristics provide tighter and more flexible films. In general. . Since this level of performance may not be needed. Water based primers generally block the transport of stains by two principle mechanisms: (i) the primer acts as a physical barrier and blocks the migration of stains from the substrate to the topcoat (this is similar to the way in which solvent based primers block stain transport). and water based primers are formulated to adhere to a variety of substrates including metal. and chalky or aged re-paint surfaces. including tannin stains from wood.152 6 Applications for Decorative and Protective Coatings 6. such as zinc oxide or other functionalized extenders.2 Primer Formulations Primers based on emulsion polymers typically are formulated with PVCs in the range 25 to 45 % and volume solids in the range 30 to 40 %. in many topcoat formulations. Primers are expected to have excellent adhesion. Primer formulations frequently (but not always) contain some type of reactive pigment or specialized extender to enhance performance features: stain blocking primers frequently utilize functionalized extenders to lock stains while anti-corrosive primers utilize reactive pigments to passivate ferrous substrates. effective primers are formulated with a high degree of colloidal stability and reduced levels of water sensitive materials in order to improve performance characteristics. HEUR rheology modifiers along with relatively hydrophobic dispersants are generally preferred in this application.7. They are used in a variety of exterior and interior coating applications. 6. or achievable. the use of specialized primers offers a flexible and cost effective way to meet the performance needs of many different coating applications with a limited number of optimized topcoat products. Binders for stain blocking primers are usually based on relatively hydrophobic emulsion polymers with acrylic or styrene acrylic compositions. 19 0.25 65.7 Primer Coatings Tab. to wooden panels with high tannin levels such as western red cedar or redwood.18 27.10 1. along with a suitable topcoat. Material Weight % Grind Water Biocide Dispersant Defoamer Titanium Dioxide Calcium Carbonate Extender Dispersant Zinc Oxide Grind sub-total 4.00 Isothiazolone preservative Hydrophobically modified polyacid Hydrocarbon dispersion Exterior grade Coarse grade Acrylic acid type Functional extender – stain blocking Add to grind with good agitation 25 % solids Specialized primer vehicle Film formation Co-solvent and freeze-thaw aid Isothiazolone mildewcide Hydrocarbon dispersion HASE (30 %) pH adjustment 25 % solids 20 % solids Value 19 % 37 % 49 % 6.7.21 1.) is needed to obtain meaningful results. a careful experimental design (comparisons on the same panel.25 1.07 Let down HEUR Thickener A Acrylic Emulsion Polymer Ester Alcohol Coalescent Ethylene Glycol Biocide Defoamer Thickener B Ammonia (28 %) Water HEUR Thickener A HEUR Thickener B Total Property Total PVC Volume Solids Weight Solids Comments Prepare in a high speed disperser 0.40 2.67 4.24 0. the performance is rated by a visual comparison against the controls. etc.3 Standard Application and Performance Tests Application testing for stain blocking primers is focused on the ability of the primer to block stains and to provide a suitable substrate for the topcoat.20 0. Because of the high degree of panel to panel variability inherent with a natural substrate such as wood. Laboratory testing for tannin stain resistance is performed by applying the primers.03 100. replication. The panels are allowed to dry for a short time and they are then placed in a high moisture environment such as a fog box or mist chamber. the 153 .16 1.15 0. 6-6 Stain blocking decorative primer formulation.17 14. Laboratory testing of marker stain resistance is done in a similar manner.6.39 0. After the panels are removed from the fog box and allowed to dry.89 0.73 0.90 0.90 0. Because of this.8. acrylics. and more specialized applications such as coil coatings. or to products produced in an industrial production process. there are a great number of different types of application areas which use protective or industrial coatings. However. with solvent-borne alkyds. Samples dry overnight and are then rated relative to controls by a visual comparison. Recently. acrylic emulsion polymers are the most common compositions chosen for these applications. We will not include automotive coatings in our current discussion.1 Copolymers used in Protective and Industrial Coatings A variety of synthetic polymer resins are used in coatings for protective and industrial finishes. since they are covered in Chapter 7 of this volume. Solvent borne coatings are the historical market leaders in protective and industrial coating markets. Acrylic emulsion polymers for protective and industrial coating applications are generally designed with Tg in the range 30 to 60 °C. marine coatings and traffic marking coatings. Testing is usually carried out with several water based and solvent based markers. Even with these limitations. significantly higher than binders used for decorative appli- . 6. and they still hold this position in most applications. polyurethanes and emulsified alkyds are also used. The performance requirements of coatings designed for protective and industrial applications are generally more demanding than those of decorative coatings. In the context of waterborne coatings. new developments in polymer design and formulation technologies have allowed waterborne finishes to make significant inroads into many areas of protective and industrial coatings. such as bridges and factories. epoxies and polyesters being most common. allowed to dry for a short period (usually 2–4 h) and then coated with a suitable topcoat. which are applied to draw-down charts. metal containers. urethanes. these include coatings for industrial structures. we will define protective and industrial finishes as coatings which are applied to large industrial structures. has led to significant growth in the use of waterborne coatings for these applications. high solids coatings (based on solvent borne polymers designed for formulation with low levels of solvent) and powder coatings have also made significant inroads into the protective and industrial coatings areas.8 Protective and Industrial Coatings The distinctions between protective and decorative coatings are often a matter of degree. wood furniture and flat stock. and the wide variety of applications. although significant amounts of waterborne epoxies. 6. the shift to coatings based on waterborne emulsion polymers has not been as pronounced as it has been in the decorative area. coupled with an increasingly stringent regulatory environment. The trial primers are then drawn down over the test area. This.154 6 Applications for Decorative and Protective Coatings performance of primer-topcoat combinations are evaluated for their ability to resist discoloration relative to a set of pass and fail controls. machinery and equipment. and for our purposes. without suffering the drawbacks usually associated with using higher Tg polymers in many decorative applications.2 Market Size Based on the analysis presented in the earlier sections of this chapter. coatings used in protective and industrial (non-decorative) applications represent about 60 % of annual world wide production. and electrical power plants. and 0. and epoxies and urethanes showing very good growth in recent decades due to their strong performance profiles. 6.6. Since most protective and industrial finishes are applied to dimensionally stable substrates. Solvent borne coatings predominate in this high performance application. 6.3 Industrial Maintenance Coatings Industrial maintenance coatings are designed to provide corrosion control and extend the service life of large metal and concrete structures associated with manufacturing. which utilize melamine or other types of crosslinking chemistry. 6.8. as we have defined them.8 Protective and Industrial Coatings cations. Again. chemical plants. assuming a value of 25 % yields an estimated annual production rate for waterborne protective and industrial finishes to be on the order of 2 billion liters world wide. oven bake applications.5–0. we emphasize the approximate nature of these estimates and provide them to give the reader a general idea of market size. are also used in many factory applied.7 billion liters per year in North America. Better barrier properties were needed to im- 155 . Thermosetting acrylic systems. water treatment plants. The penetration of waterborne coatings has been less in these markets than in decorative areas. or roughly 12 billion liters per year. chemical processing and transportation. water tanks. Typical applications include bridges. or roughly 2 to 3 billion liters per year.8. The use of waterborne coatings in the light and medium duty segments of this market has grown significantly over recent years. polymers with harder compositions can be utilized in order to provide improved performance characteristics.4 Key Performance Features Early water based coatings for industrial maintenance applications utilized polymers developed for exterior decorative coatings. with alkyds historically holding the largest share. and we estimate they now account for approximately 20 % of these segments in North America. Assuming that automotive and other applications outside the traditional finish applications represent roughly a third of this value. storage towers. we estimate the world wide annual production to be approximately 8 billion liters per year for protective and industrial finishes. they were not optimized to provide good corrosion or chemical resistance.8. North American production is estimated to be about 1/4 to 1/3 of this value. Although these polymers provided good gloss and tint retention in exterior applications. oil refineries. based on zinc. mar aids to increase abrasion resistance and glycols for improved pigment grinding and freeze-thaw stability. resulting in reduced gloss.8.156 6 Applications for Decorative and Protective Coatings prove these performance features. application and resistance tests used for decorative coatings. roller and brush application. Effective coalescing agents are needed. Good colloidal stability is particularly important in maintenance coatings. Urethane rheology modifiers are generally used to provide a more Newtonian rheology profile (good flow and leveling) as well as to avoid the weak flocculation and water sensitivity associated with cellulosic and HASE thickeners. particularly in applications where resistance to gasoline and aromatic solvents is desirable.6 Standard Application and Performance Tests Industrial maintenance coatings are evaluated by many of the standard stability. defoamers. these coatings are often formulated with reactive pigments which can be difficult to stabilize. these can include dispersants and surfactants for pigment incorporation and stabilization. A wide variety of reactive pigments are often used to enhance corrosion resistance. 6. drying time and wetting characteristics. Finally.5 Formulation Characteristics for Industrial Maintenance Coatings Industrial maintenance coatings are usually enamels. In addition to these features. since harder polymer compositions are generally used. Table 6-7 illustrates a typical formulation used in industrial maintenance applications. A properly balanced composition is needed for optimum performance in maintenance applications. all acrylic polymers provide excellent durability characteristics. and a combination of two or more coalescing agents is often used to optimize film formation. as well as for . Like decorative finishes. and specialized maintenance binders were developed by reducing polymer molecular weight (to promote improved film formation) and utilizing more hydrophobic compositions (to provide better resistance to water and ion transport). Many of these materials are inorganic salts. good hardness development and enamel-like resistance to marking and abrasion. and are generally evaluated for performance in spray. calcium or barium cations with anions of phosphate.8. or poor storage characteristics. Acrylonitrile is sometimes incorporated in order to improve chemical resistance. They should also have good appearance and application properties. or metaborate. 6. like decorative enamels. a variety of additives are commonly included in these formulations. and are formulated in a manner similar to decorative gloss enamels: they are formulated significantly below critical PVC in order to enhance gloss. barrier properties and toughness. respectively. industrial maintenance coatings should show good adhesion to metal substrates. particularly in primer formulations. they are applied in the field and need to have good heat-age and freeze-thaw stability. borate. but are generally supplemented with more hydrophobic monomers such as styrene or ethylhexyl acrylate in order to provide improved barrier properties and corrosion resistance. placed in the test chamber.73 0.8 Protective and Industrial Coatings Tab. non-ionic Base Universal grade Yellow iron oxide Mix the following with good agitation Specialized maintenance vehicle Add with good agitation Alkyl acetate ester Co-solvent. the exterior durability of industrial maintenance coatings are commonly evaluated by exterior exposure testing. industrial maintenance coatings are also evaluated in the laboratory for corrosion resistance. relative to controls. Salt spray and prohesion testing are commonly used and both of these techniques use aqueous salt solutions and high humidity to accelerate the corrosion of steel test panels. with particular emphasis being placed on corrosion resistance.94 20. for blistering and corrosion on the face and at the scribe. In contrast to most decorative finishes. gloss retention and color retention.75 0.94 6. then add the following ingredients Coalescent Propylene Glycol Methanol Sodium Nitrite (15 %) Ammonia (15 %) Thickener Total Property Total PVC Volume Solids Weight Solids Comments Prepare in a high speed disperser 4. The test panels are then scribed to expose bare steel beneath a portion of the coating.19 0. freeze-thaw aid Co-solvent. Samples are prepared by coating steel test panels with a film of defined thickness and then drying for a specific time under controlled temperature and humidity conditions. Panels are subjectively rated. 6-7 Yellow industrial maintenance coating. Like exterior decorative finishes.96 0.34 0.21 0. and color uniformity. freeze-thaw aid Flash rust inhibitor Base HEUR (25 %) Value 11 % 35 % 44 % gloss.51 0.00 Hydrophobically modified polyacid Silicone emulsion Pigment wetting aid. Material Weight % Grind Water Dispersant Defoamer Surfactant Ammonia (28 %) Titanium Dioxide Yellow Pigment Grind sub-total 5.32 Let down Add the grind to the above premix.11 6.49 Premix Styrene Acrylic Emulsion Polymer Ammonia (15 %) 68.6.21 0.48 1. 157 . and evaluated at periodic time intervals.25 100.07 3. In the early 1990s. This is due not only to increased environmental sensitivity. In spite of the simplicity and speed of these tests. are the best way to obtain useful information regarding the corrosion resistance of industrial maintenance coatings.05 % NaCl). and there is some question regarding whether they actually accelerate corrosion processes present under normal use conditions.158 6 Applications for Decorative and Protective Coatings Salt spray and prohesion testing both suffer from the general problem discussed above in regard to accelerated exposure testing: corrosion resistance in laboratory tests does not always correlate well with performance in real world applications.9. they also offer improved glass bead reten- . with the North American market representing about 120 million liters of this total. 6. which were later replaced by alkyds or chlorinated rubber blends. We estimate the total world wide market for traffic marking paints to be around 400 million liters per year. These products use proprietary technology to provide waterborne traffic paints with the ability to dry rapidly under a wide range of relative humidity and airflow conditions. Due to their acrylic compositions. and alternating cycles of salt spray and drying. Prohesion testing utilizes lower salt levels (0. at ambient temperature and 35 °C. however. walkways and airport runways. but also is due to improved performance features which have been incorporated into waterborne acrylic emulsion polymers for traffic marking paints. it is generally acknowledged that realistic exterior exposures. parking lots. Early paints were based on oilmodified phenol-formaldehyde resins. 6. Since the late 1980s. traffic paint technologies have changed dramatically over this period. waterborne traffic markings have enjoyed strong growth in the United States and in parts of Europe and Asia. The enabling technology which allowed for the widespread use of waterborne traffic paints was the development of fast drying acrylic emulsion polymers in the late 1980s. Laboratory corrosion tests use a combination of aqueous salt spray and high humidity conditions to speed corrosion processes.1 Description of Traffic Paint Market Road-marking paints have been in use since the 1920s.9 Traffic Marking Paints Traffic marking paints are used to control the flow of vehicle and pedestrian traffic on a variety of surfaces such as roadways. preferably in the form of trials on actual metal structures such as bridges or storage tanks. respectively. the technology shifted toward more environmentally friendly and higher performing waterborne acrylic systems. but slower evaluation.35 % ammonium sulfate and 0. Most of the traffic paint market in North America has shifted over to waterborne technology and the share of water based traffic coatings is now estimated to be greater than 80 %. Salt spray testing uses a high salt concentration (5 % NaCl by weight) and 100 % humidity at elevated temperature (35 °C) to provide a more aggressive testing environment. to provide a somewhat more realistic. defoamers. and (iii) retain a large percentage of the glass beads applied to the coating surface for nighttime visibility. and a modification of the standard coating dry-through test (also called the early washout test) is used to evaluate the time needed for a traffic paint to become resistant to washing off with water (presumably rain). opacity.4 Standard Application and Performance Tests Fast drying is an important characteristic for traffic marking paints. Table 6-8 illustrates a typical formulation for paint used in traffic marking applications. They contain many of the components found in the waterborne coatings discussed previously. and rheology modifiers. The volume solids of waterborne traffic paints are quite high.6. In addition. in the range of 55–60 %. percent solids. As with any paint. While the coating has not dried in the conventional sense by this time (all moisture has not yet left the film).9. In this test. Traffic paints are also formulated near or above CPVC. 159 .3 Typical Traffic Paint Formulation Formulations for waterborne traffic markings differ substantially from those of decorative coatings. various governmental agencies can mandate specific requirements for viscosity. 6.9 Traffic Marking Paints tion. (ii) adhere to the road surface (concrete or asphalt) during the expected lifetime of the coating.9. VOC content. the values obtained in the dry-through test provide a useful measure of the time needed for a coating to become resistant to being washed away by rain. to provide higher porosity and increased drying speed. The dry-through time is defined as the time required for there to be no surface deformation when the test operator’s thumb is twisted through an arc of 90° with minimal pressure on the paint film. such as dispersants.9. around 60 %. 6. these components must be chosen with care so as to not detract from the desired performance characteristics. etc. a draw-down with a film thickness of 330 µm wet is placed in a humidity chamber maintained at 90 % relative humidity with negligible air flow. which leads to better retention of retro-reflectivity (the ability of a material to reflect light back towards the source from a variety of incidence angles) and nighttime visibility. and to thereby speed the drying process. in order to minimize the amount of water. color. 6.2 Key Performance Features The success or failure of road-marking paints depends on their ability to: (i) dry quickly enough to prevent damage by traffic following the striping truck. 36 0. The retention of retro-reflectance is determined in the field. . is rolled over the surface of the drying paint film at specified times. The auto-no-track test is a complementary field evaluation method which also measures the time for a traffic marking paint to become resistant to tire pickup. Requirements can vary.5 % in water. This property is commonly evaluated in the laboratory by the no-pick-up test.68 1.34 100. a steel cylinder. A traffic marking paint also needs to quickly become resistant to tire pickup after application to the roadway. It is measured either by a portable or truck-mounted retro-reflectomer.07 94. reflective glass beads which are dropped onto the coating surface during the coating application process. and add with good agitation Co-solvent Ester-alcohol.13 1. outfitted with rubber O-rings. specifications will call for initial minimum values as well as some minimum throughout the lifetime of the marking.11 54.20 0.21 7.18 0. 6-8 Traffic marking paint. and is related to the ability of a traffic marking paint to retain small. The no-pick-up time is defined as the point at which paint does not adhere to the rubber rings when the cylinder is rolled across the film.160 6 Applications for Decorative and Protective Coatings Tab. polyacid White pigment Coarse grade Mix grind for 15 minutes. and determining the minimum time required for there to be no indication of pick-up and re-deposition of the line by an observer standing at a distance of 15 m. 150 mcd m–2 lux–1) owing to their lower TiO2 content.00 Property Total PVC: Volume Solids: Weight Solids: Value 60 % 61 % 78 % Comments Prepare in a high speed disperser Utilizes rapid set technology Ammonia neutralized. but typical initial values for white markings are on the order of 250 mcd m–2 lux–1 while yellow markings are somewhat less (ca. Often. Material Weight % Grind Acrylic Traffic Paint Emulsion Dispersant Wetting Agent Defoamer Titanium Dioxide Calcium Carbonate Extender Grind sub-total 32.40 0. Retro-reflectance is a quantitative measure of a traffic marking’s nighttime visibility.35 Let down Methanol Coalescent Defoamer HEC Thickener Water Total 2.31 0. In this test. film formation Hydrocarbon type 2. This test is carried out by passing a moving automobile over a freshly applied transverse or diagonal marking line. Jones F. in: Waterborne Coatings. C. Lesko. pp. 39–52. Z. 126–204. pp. S. Langmuir. J. (eds). V.. Lowell. H. J.. Coatings. 3. Acrylic Polymers as Coatings Binders in Paint and Coatings Testing Manual. Organic Coatings. Leman. Kroschwitz. W.. S. Snyder. T.5100 C. 1435–1442. Jr.N. 1995. Wicks. II. Wiley-Interscience. New York. 1992. Washington. A. in: Surface Coatings – 2... Sivers.). Chemical Economics Handbook. A. Pappas. 14th edn of the Gardner Sward Handbook. Paint in: Encyclopedia of Chemical Technology. 2001. Patton.02. Tulo. 1994. London. . Prosser. SRI International. American Society for Testing and Materials. Elsevier Applied Science. in: Encyclopedia of Polymer Science and Engineering. S. Wiley-Interscience. Hare. Nicholson. News 2000. Vol. 1995. D.. Pappas.. J. 4th edn. Philadelphia.. 1999.. Annual Book of ASTM Standards. 1994. Eng. New York.. 2 3 4 5 6 7 8 9 Paint and Coatings Overview. J. Science and Technology. 10. A. Winnik. Vol. 11 12 13 14 15 M. 1996. Wiley-Interscience. J. 1049–1069. A.. N. M. Chem. 37–62. 1999. W. Y. P. 1994. O’Dowd. 1988. Jones F. P. 615–675.. (ed. Pittsburgh. D. Dinsdale.. V. Protective Coatings. I.. Friel. L. 592. M. Ishikawa-Yamaki. C. 1979. A. Koleske. Wicks. 1–38. Jr. Vol.. R.. P.. Wiley-Interscience.. I. New York. Paint and Coatings Testing Manual. J. E. Wiley-Interscience. M. 10 Wang. 1992. Organic Coatings. Juhue. A Systems Approach.. pp.. Bauer. 14th edn of the Gardner Sward Handbook. J. 19–28.. (ed. J. pp. (ed. Langmuir. American Chemical Society/Oxford University Press.).C. Kats. H. Koleske.). Sperry.. Wilson. American Society for Testing and Materials. 17.. American Society for Testing and Materials. 55–64.. New York. Nicholson. (ed. 35–48. W. Vols 6. D. Kroschwitz. J. B. R. Service Life Prediction of Organic Coatings. pp. Science and Technology.. 2619–2628. Fundamentals of Chemistry and Composition. Technology Publishing Company. (eds). Martin. R. J. A. H..161 References 1 Connolly. J.).. R. Paint Flow and Pigment Dispersion. 1985. 78(41). Philadelphia. I. 8. Philadelphia. 2nd edn.W. P. Vol. pp.. M. W.01 and 6. Z. New York. 163 . LEPC is tackling the technical challenge of developing paint-related technologies to reduce or eliminate VOC from automotive coatings. polyurethanes. the latest water-borne coatings are much more robust in terms of usage or application friendliness and require significantly less heating or air-conditioning than two decades ago. Furthermore.Polymer Dispersions and Their Industrial Applications. the United States Council for Automotive Research (USCAR) which now is the umbrella for 11 other research consortia including the Low Emissions Paint Consortium (LEPC). Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co.3 million by 2003 [1]. An approach to this problem is by the appropriate modification of acrylic primary dispersions to suit automotive coating requirements or solvent-free secondary dispersions of conventional resin types like epoxies. employing 4 million people. It is estimated that motor vehicle production on a global basis will rise from 54. Daimler-Chrysler. The biggest manufacturing industry in the world today is the auto industry. or changed in color. Ford and General Motors in the United States.1 Introduction The automotive coatings industry is faced with new challenges as we enter into the new millennium. manufacturers often want their coatings modified so that they can be used at faster production rates. Increasingly stringent environmental legislation and tougher market conditions require that modern coating systems must bring. 3-527-60058-2 (Electronic) 7 Applications for Automotive Coatings Sunitha Grandhee 7. In the United States over 15 million cars are produced annually. cost and quality in addition to globalization and market constraints are driving new developments.9 million in 1998 to some 59. with over seventy separate companies or subsidiaries. Need to reduce VOC has led to change in many raw materials that were traditionally used in coatings. Environment legislation. not just enhanced product performance but also reduced overall production costs to paint producers. polyesters. Today. baked at lower temperatures. has formed a consortium. The movement towards lower to zero VOC involves many types of coatings technologies. They still require some additional dehydration or special kinds of flashes before going into ovens to help remove the water. KGaA ISBNs: 3-527-30286-7 (Hardback). and Latin America.1 billion on OEM coatings (Fig. “You can have a car any color you like as long as it is black. Henry Ford always said.9 billion. Phillips. The coating was then sanded smooth and refinished in the same manner. Demand for motor vehicle coatings is forecast to rise by 1. 7-1 Original equipment manufacturers (OEM) coatings demand 1999. the Middle East.1.0 million metric tons by 2003. These products were not colorful. Latin America $1. The market for automotive OEM coatings alone is growing at 3. 4].5 billion in OEM end markets. consumes $1. with OEM coatings posting 1. Middle East. with faster economic growth than Europe or North America. Mixtures of ground pigments and linseed oil – like old wood coatings used for carriages and stagecoaches – were brushed on the surface and allowed to dry.5 % growth per year to 1.1 History of Automotive Coating The history of automotive paint dates back to the beginning of the 20th century. 7-1). offering a wider range of color choices to the market.2 % per year [2]. In 1999.5 B Fig. Asia.8 % per year to 2.6 billion in OEM coatings.” In the 1920s nitrocellulose-based enamels were applied. last year spent $3. Europe was the largest market for coatings for OEM end markets at $8. North America was second having used $7. 7.164 7 Applications for Automotive Coatings Europe $8. according to P.2 million metric tons.9 B Asia $3.6 B North America $7. .G. The rest of the world. when the mass production of automobiles started [3. which includes Africa.1 B Africa. 7. still wet. Using polyisocyanates dramatically magnified and improved acrylic enamel’s performance qualities like gloss. They were also successful at providing the consumer with metallics or metal flake paints. Throughout the 50s and 60s. During the 1970s Japanese and European major paint companies developed the next technology change. 4]. Out of the 99 North American assembly plants. was durable and was oven cured to produce a hard and colorful surface. These enamels were selected to improve gloss and gloss retention. Baking the vehicle in a large oven caused the solvents to evaporate and the product to flow to a uniform smooth finish. Dupont. They did this after realizing that consumers made a vehicle purchase using mainly their eyes: “shiny sells”. In this process electrically charged paint particles are deposited from aqueous solution onto metallic substrates by application of an electrical field. It had a very high gloss. Acrylic lacquer. This product was also applied with a spray gun. eliminating corrosion as a major cause of automotive failure [5]. Cationic electrodeposition of a protective coating was the major invention in the late 1960s. Ford also decided that they liked many of the properties that the early acrylic resins provided. The coating was applied to the vehicle surface with a spray gun. Automotive paint systems are now well within VOC limits and comply with EPA standards for emissions. and very high gloss [3. In 1960 the Ford Motor Company went back to the stoving methods. The technology is a one-stage acrylic flat basecoat followed immediately by a high gloss urethane crosslinked clearcoat. The main suppliers of OEM coatings are PPG. This results in excellent durability to corrosion and stone chips. The introduction of the spray gun technique made automotive coating much faster than using the brush method. Today. This product and process was the system of choice for most vehicle manufacturers until the 1950s [3. Today approximately 14 million vehicles are coated with water-borne technology each year. At that point the product. did possess one outstanding trait: it was incredibly fast drying as compared to enamels of the time. 4]. German automakers influenced this change with their color-plus-clear combinations on such premium vehicles as Mercedes Benz. BASF. In the mid 1950s the next great technology leap happened. In the late 80s and early 90s new laws were enacted that governed the content and application of paints. 4].1 Introduction During the early 30s the auto industry started using “stoving enamels” based on alkyd resins. hardness. corrosion was the major cause limiting automobile’s life span. 99 % of all vehicles manufactured use some type of electrocoat process. 165 . Alkyds as a whole proved to be more durable and faster drying than nitrocellulose enamels. durability [3. while not markedly better in terms of performance qualities over alkyd enamels. Automobile companies such as General Motors immediately saw the production time savings as a real plus. The amounts of volatile organic compounds (VOC) were lowered using water-borne binder systems. It minimized sanding between coatings and applied the product evenly. They went to work with yet another new group of suppliers to create “acrylic stoving enamels”. Nippon and Kansai Paint company. 33 plants are using water-borne based coats [6]. contained a large amount of solvents. the application of two-coat acrylic painting systems: basecoat/clearcoat. Hence. This method is used commercially by Daimler-Chrysler in Europe. solvent resistance and uniformity of appearance. therefore corrosion protection is one of the most important functions of automotive coatings. just prior to painting. the surface is coated (phosphate coating) by dipping into . Generally. A new clearcoat system has been introduced.2 Automotive Coating Layers Current automotive coatings are made up of a number of distinct layers (Fig. and is stabilized in water [7]. a variation on this theme is to use slurries of powder in water as automotive clearcoats. however.166 7 Applications for Automotive Coatings Another approach to VOC reduction is the use of powder coatings. Clearcoat Basecoat Primer Electrocoat (+) ( -) Automotive OEM coating layers. to make polyurethane coatings [8]. 7. Drying and curing usually involves energy input such as heat and UV radiation to produce coatings of higher toughness. with their thickness and functions. Trying to make water the carrier for isocyanates was no easy task. Bayer modified isocyanate molecules to stabilize them in water. basecoat and primer are spray applied while the electrocoat is electro-deposited by dip application.2. are shown in Tab. one of the raw materials for polyurethanes. 7-2 7. that offers zero emissions. The various coating layers. Typically the clearcoat. 7-2). is powder dispersed. 7-1. so customers can apply them together with polyols. there is a lot of cost in converting existing spray booths to suit powder application. Bayer recently won the Presidential Green Chemistry Challenge Award for its twocomponent water-borne polyurethane system. Stringent conditions are established for surface preparation. the coatings are either spray applied or electrodeposited. Automobile bodies are generally fabricated from steel [9–11]. Low bake temperatures are desired to save energy cost. Fig. are unstable in water. isocyanates. The layers should cure to a desired finish and should have a wide tolerance for bake conditions. application and curing.1 Spray Coating OEM automotive coatings are those used for painting trucks and cars on fast moving assembly lines. After the fabrication of the car body. electrocoat. Tab. The use of plastics as a substitute for metals began accelerating in the 1970s to achieve a weight reduction in order to improve fuel economy. as shown in Fig. Furthermore basecoat here. in this chapter is referred to an independent layer. 7-2 Water-borne binders used for automotive coatings. primers and basecoats.e. plastic and rubber components are used. Clearcoat polymers are primarily still solventborne. even though basecoat is considered as part of the automotive topcoat system. 7-1 Function and typical thickness of automotive coating layers. a chemically crosslinked matrix is formed between the main resin molecules. For parts of the exterior. Automotive OEM coatings are thermosetting coatings. Layer Thickness Function Clearcoat 40 µm Basecoat Primer Electrocoat 15 µm 35 µm 20 µm Withstand solar radiation. For the purpose of this chapter’s discussion. Coating Resin chemistry Dispersion Type Electrocoat Primer Basecoat Basecoat Basecoat Basecoat Basecoat Epoxy-amine Polyesters Polyacrylics Polyacrylics Polyesters Polyurethanes Polyurethane-acrylics Secondary Secondary Secondary Primary Secondary Secondary Secondary Cationic Anionic Anionic Anionic Anionic Anionic/nonionic Anionic Water-borne emulsion polymers are used in formulating automotive coatings for electrocoat. aggressive chemicals like road salts and caustic detergents) Optimum appearance and long lasting color Good adhesion and resistance to chipping Long-term corrosion protection an aqueous solution containing primary zinc phosphate Zn2(H2PO4)2 as the major component. 167 . A powder dispersed in water (powder slurry) has been developed as a binder for clearcoats [7]. This matrix cannot be returned to its original form by use of solvent or heat. i. 7-2 and Tab. Most current automotive passenger cars are coated with four coating layers in addition to the phosphate coating. is not referred to as primer since an additional layer is present before the vehicle is top coated. bird droppings.7. which in some cases are completely coated before assembly. 7-1. Polymers used as binder Table 7-2 shows the emulsion polymers most often used in the various automotive layers. atmospheric pollution (acid rain.2 Automotive Coating Layers Tab. – secondary dispersions: the polymer is synthesized in an organic solvent and later dispersed in water. 7-4 17–24 2– 3 1– 2 71–80 Primer 35–45 5– 7 2– 3 45–58 Base coat Metallic Solid color 23–25 10–15 2– 3 57–65 25–30 10–15 2– 3 52–63 Function of ingredients in an automotive coating formulation. The higher the concentration of the polar groups. E-coat Solids (resins. 7-3. the greater is the solubility of the polymer. mechanical properties Reacts with functional groups on main resin to form crosslinked matrix Provides color. Based on the nature of the solubilizing group. 7-3 Main ingredients (%) of for automotive coatings. Tab. 7-4. hiding Provides appearance effect Reduces viscosity. controls rate of drying and film formation Inhibits degradation of film by sunlight Drives crosslinking reaction Pigment dispersion. sag.168 7 Applications for Automotive Coatings Aqueous polymer dispersions used in automotive water-borne coatings are classified as: – primary dispersions: polymerization is carried out in the presence of water by emulsion or mini emulsion polymerization. Incorporation of functional groups in the polymer skeleton is necessary for stabilization in aqueous phase [12]. wetting agents) Water Tab. pigments) Solvents Additives (RCA. 7-5. the polymer is classified as anionic. RCA: rheology control agent. Formulation ingredients The amounts of main ingredients present in a water-borne automotive coating formulation are shown in Tab. flow. Pigment dispersion Flake pigments Solvents UV absorber Catalyst Secondary resins Antifoamer/defoamer Rheology control agents (RCA) Other additives Standard test methods The standard test methods for automotive water-borne coatings are summarized in Tab. crosslinker(s). etc. . defoamer. Ingredient Function Aqueous polymer dispersion Crosslinker Film formation. cationic or nonionic. pop tolerance. aligns aluminum flakes (metallic basecoats) Improve substrate wetting. adhesion promotion Decrease foaming tendencies Control leveling. the functions of these ingredients are summarized in Tab. Performance properties include physical properties of hardness.SAE. stability to extremes of temperature and humidity. stone-chip resistance. primer. orange peel. primer UV ASTM D3363 ASTM D5420 ASTM D1735. primer Xenon lamp SAE J1960 Topcoat.e. Florida exposure Outdoor weathering of exterior materials The J tests were developed by the Society of Automotive engineers. primer Basecoat. primer Gravelometer ASTM D562 ASTM D4287 ASTM D2196 ASTM D1200 ASTM 4212 ASTM D1186. primer E-coat. These layers are now described in more detail. curing efficiency. adhesion and overall resistance to chipping damage by stones Hardness Hardness Adhesion and appearance. Condensing humidity (D2247) and water soak (D1735) Appearance (gloss. testing coating flexibility.org) The test methods for automotive layers are designed to stimulate conditions likely to occur in the field and are of two types – appearance and performance. ASTM D4585. J2334 preferred to B117 Chip resistance testing. ISO 4623 ASTM B117. USA (www. primer Basecoat. 169 . primer. ASTM D2247. 7-5 Test methods for automotive coatings. adhesion. impact resistance. primer Basecoat.2 Automotive Coating Layers Tab. primer Topcoat. SAE J2334. ISO 7253. primer ASTM D3359 SAE J 951 SAE J 1976 Corrosion. cold crack resistance i. basecoat Hardness (pencil) Impact (Gardner) Humidity Topcoat. Polymer dispersions are applied as coating binder mainly in three of the four layers: electrocoat. cracking . DIN 53167 J 400 E-coat E-coat E-coat. DIN 53209 SAE J2020 Topcoat. primer Topcoat. mottle. chalking) Weathering test Accelerated test to check for gloss loss Accelerated test to check for gloss loss Adhesion Durability. flexibility. distinctness of image. primer and basecoat.7. Test Method Description E-coat Basecoat. Appearance includes gloss. primer Sunshine/ carbon arc Tape test Exposure Exposure ASTM G 152 Topcoat. basecoat Stomer ICI cone/plate Brookfield Ford viscosity Dip type Film build Viscosity Viscosity Viscosity Viscosity Viscosity Thickness E-coat Salt spray resistance E-coat. PPG introduced the first cathodic primer. the blocked isocyanate reacts with a hydroxyl group to form a urethane crosslink. with continuous improvement.2 Electrocoat Electrocoat or e-coat or Elpo is the first pigmented coating layer. Until mid 1970. 2-ethylhexyl alcohol). Cationic electrocoat applied by dipping process is used worldwide for coating autobodies and its adoption in 1970s and 1980s led to major improvement in the corrosion resistance of cars. which is the most critical factor for corrosion protection. It serves as a bridge between the metal and the overlaying coating layers. fatty acids [19] and fatty monoepoxies [20]. Combined with the more recent introduction of galvanized sheet metal. Blocked isocyanates which are used as crosslinking agent are stable in the slightly acidic water system. has become the standard of the automotive industry worldwide. Polymers used The resins used in electrocoat.2. Bisphenol A epoxy resins are reacted with polyamines to yield a resin with amine and hydroxyl groups. The resulting polymer is reacted with a polyisocyanate. Cationic polyurethane dispersions are obtained by incorporating tertiary amine functionality into the backbone. This complete coverage ensures excellent corrosion protection to the automobile. These are dispersed in water by neutralizing the amino groups with organic acids such as formic. Most current cathodic systems are based on modified epoxy resins containing amino groups. which is applied over the phosphate coating of the fabricated car steel body.g. acetic or lactic acid. low-Tg aliphatic epoxies [18]. Requirements Current systems are characterized by excellent corrosion protection. which is partially blocked with an alcohol (e. Mannich reactions or re-esterification. Salts are formed with the amine groups with a low molecular weight carboxylic acid. In 1976.170 7 Applications for Automotive Coatings 7. acrylic grafts [17]. The epoxy backbone is made flexible by various ways by incorporation of polyester and polyether diols [16]. perhaps owing to strong interaction between the amine groups and the substrate surface that increases wet adhesion. The resins are crosslinked by blocked isocyanates. whereas melamine formaldehyde resins are not. either by introducing tertiary amine groups in the . car manufacturers are now able to offer ten years warranties against corrosion. and this technology. 20 µm. During baking. Dip application has the advantage to fill the smallest recessed areas of the automobile body. This coating layer is applied in a dip application by cathodic electrodeposition to the steel automobile body. electrocoat was of the anodic type [13–15]. Amine-substituted resin binders provide greater corrosion protection for steel. must have excellent hydrolytic stability and resistance to salt accelerated corrosion and the chemical composition of the resin also allows for excellent adhesion of the next coating layer. good throwing power and good filling properties at film thickness of ca. A coating of uniform thickness is obtained after baking at 150–180 °C for ca.5–1. 20 min. The application technique allows coating of complicated shapes and even internal areas. squeezing the water out of the deposited coating and leaving it in a firm state. followed by quaternization with an alkylating agent or protonation with a suitable acid [21]. improved uniform coverage is achieved in recessed areas and on sharp edges as well as on flat surfaces. Lead also catalyzes the curing reaction. the consequent transfer of electrons provides an electrically neutral film deposit. With this process. 20 %. The applied voltage causes the dispersed particles and pigments to migrate to the car body. Application The car body is coated on a production line by immersing the body in a tank containing the aqueous primer dispersion and subjecting it to a direct current charge.7.2 Automotive Coating Layers diol. 171 . Composition Most of the commercial cathodic electrocoat formulas are two-pack formulas consisting of a pigment dispersion intermediate and the principal resin components [24]. The body is baked to coalesce and cure the primer film with much less sagging occurring.g. Special lead-containing pigments e. Pigment dispersion: Aqueous dispersion resin (epoxy amine isocyanate adduct) Extenders Anticorrosive pigments Organometallic oxides Deionized water Principal resin component: Epoxy amine adduct Crosslinker Organic acid Organic solvent Deionized water 10–15 % 20–30 % 3–7 % 1–2 % 65–46 % 20–25 % 10–12 % 0. During the process electroendoosmosis occurs. Solvent content is low (typically less than 2 % based on total volume). instead of a carboxylic group. As they are deposited.0 % 1–3 % 68–69 % Pigments commonly used are titanium dioxide and extender pigments. however the trend nowadays is eliminate lead from electrocoat. silicates are used as anticorrosive agents. Other coating systems contain cationically modified copolymers obtained by polymerization of acrylic monomers in presence of unsaturated polyurethane macromonomer [22]. The solids content is ca. and water-dilutable dispersions of cationically modified and urethane modified methacrylic copolymers obtained by solution polymerization [23]. With the advent of electrocoat in the automotive industry corrosion resistance has become less of a issue for spray primers.3 Primer Primer or primer surfacer is spray applied over the electrocoat before applying the basecoat. The primer also protects the light sensitive cathodic electrodeposition layer from exposure to light. It is designed to be especially resistant to impact by stones thrown up from a road against the car body. The main function is to minimize surface roughness and improve adhesion of the basecoat. . Polyesters which are dissolved or dispersed in water by neutralizing acid groups with amines are crosslinked with a suitable melamine resin.2.5 mS cm–1 Cure schedule at metal temperature: 165–170 °C for 20 min 7. chip resistance. leveling. A chip-resistant primer called anti-chip is frequently applied over the electrocoat on the lower parts of the car body.172 7 Applications for Automotive Coatings Electrocoat bath: Coatings stable at a pH a little below 7 are preferred.8–1. Weakness in the layer will lead to UV radiation degradation causing loss of adhesion of primer to basecoat/clearcoat and ultimately delamination. Polymers used The development of chip resistant water-borne primer-surfacers has benefited from the use of predominantly water-borne polyester and polyester-polyurethane resins. adhesion. sandability. The uniform thickness provided by the e-coat. Other properties that are presently of great concern for spray primers are yellowing. The corrosion function of spray primers has centered around protecting against sanding cut throughs (sanding to bare metal) on the electrocoat primer. Viscosity: 20–50 mPa s at 25 °C Bath solids: 15–25 % (1 h at 110 °C) Water: 64 % Deionized water Solvents: 1–4 % Organic solvent Bath pH: 5. the colors are picked for use under a group of top coats with related colors.0–6. Presently the main purpose of spray primer is the preparation of a surface to receive a top coat (basecoat/clearcoat). Requirements The primer must have good chip resistance and exterior durability. UV durability and smoothness of the coating with respect to the surrounding coatings (electrocoat and topcoat).0 Bath conductivity (20 °C): 0. A current trend is to use color key primers. Aqueous polyurethane or acrylic modified polyurethane systems are also slowly entering the primer market. Historically the basic function for spray primers has been corrosion resistance and preparation of a surface to receive a top coat. makes it smooth and glossy which makes the adhesion to basecoat very difficult. sanding. Water-borne polyesters which are of the acrylics-grafted type form stable aqueous dispersion. to give amine salt solutions in solvent that can be diluted with water to give reasonable stable dispersions of aggregates of resin molecules swollen with water and solvent. For the anti-chip-appearance. presumably because the polymers are more hydrophobic. UV absorbers and HALS stabilizers can be added to improve UV resistance. the polyesters are copolymerized with hydrophilic monomers. This layer is covered by the transparent coating (clearcoat). humidity resistance). they are cured with various melamines and blocked isocyanates. 7. Composition of primer Primers are highly pigmented systems. humidity sensitivity. To avoid emulsifiers. weight per gallon. 2-amino-2-methyl-1-propanol). solids. viscosity. containing titanium dioxide in combination with extender pigments such as silicates or barium sulfate. In addition to the steric effect. polyethylene glycol are copolymerized. Application and testing Primer coating are spray applied onto the electrocoated substrate. it has been shown that polyols with low water solubility give polyesters that are more stable against hydrolysis under basic conditions than those with higher water solubility. 173 . often sodium 5-sulfoisophthalic acid. Usual acid numbers are in the range of 35–60 mg KOH g–1 resin.2 Automotive Coating Layers Water-borne polyesters used for automotive coatings have both hydroxyl and carboxylic groups as terminal groups. sag and solvent pop and gravelometer-chip resistance test are used. 2. appearance. settling .2. However. The pH of the system is maintained between 7 and 8. filterability and sand scratch telegraph. Small particle diameters were obtained by use of polyesters having the largest amount of unsaturated bonds unless gelation occurs [24–30].7. To give acid functionality. They consist of “core-shell” particles with a core of high molecular weight polyester. In the case of linear high molecular weight polyesters.2. carefully selected to improve the paint attributes (leveling. weight per gallon. Typical wet phase testing includes seed check. viscosity. Since many of the polymers are hydroxyl functional. topcoat adhesion. Hydrolytic stability is also affected by the choice of the polyol. Thermosetting water based polyester resin coating composition prepared from polyalkadienediol may be directly applied to wet electrodeposited coating [31].-bis(hydroxymethyl)propionic acid is used as one of the diol components. the copolymerization increases the melt viscosity and decreases water resistance and adhesion. gloss. impact resistance. The polymers are mainly stabilized in the water phase by neutralization of anionic groups with amines which are volatile (dimethylethanolamine.4 Basecoat Basecoat is the layer which contains the color pigments. solvent resistance. polyacrylic acids [33] and pigment like additives (metasilicates. Water-borne basecoats also contain rheology modifiers e. Basecoat-clearcoat finishes provide a “wet” appearance. Water-borne basecoats contain crosslinker building a polymer network and ensuring film stability and durability. Solvents help in achieving good flow and leveling of the coating after it is sprayed.174 7 Applications for Automotive Coatings Basecoats – along with the clearcoat also called the topcoat system – form protective layers over the car body surface and are very important as decoration. Metallic pigments are frequently incorporated into the basecoat to provide the appearance phenomenon known as the geometric metamerism or “color-travel”. HALS stabilizers are added to improve UV resistance. A UV absorber in the top coat that strongly absorbs UV in the wavelength range of 290–380 nm also helps to protect the primer from degradation.g. They have the characteristics of: – full and deep gloss – highly brilliant solid or metallic color effects – long-lasting resistance against weather and chemical influences – easy to repair and polish In terms of appearance. water-borne basecoats have been developed. Because of the smoothness of the surface and clarity of the film of the clearcoats. the trend now is to eliminate solvents . Both layers are cured together at about 120–140 °C. colloidal silicon dioxide). In order to reduce the emissions of VOC. The trend nowadays is to go with HAPS (Hazardous Air PollutantS) compliant solvents like monoethers of propylene glycol. They also help in proper alignment of the metal flakes of a metallic coating. Composition of basecoat The pH of the system is maintained between 7. water-borne coatings have been the most popular approach to VOC reduction and there has been a substantial reduction of solvents on going from solvent-borne systems to water-borne systems.0. a significant trend in automotive original equipment finishes has been influenced the dramatic growth in the use of basecoat-clearcoat finishes to replace single-stage pigmented topcoats. which may contain only up to 20 % co-solvents. The basecoat/clearcoat system consists of a colored layer (basecoat) which is overcoated after a brief flash off time with a protective layer of clearcoat. Even though.0 and 8. This effect is used by automotive stylists who specify metallic basecoat–clearcoat finishes to draw viewers eye the subtle contrast in hue and brightness found in styling lines and curvatures in the vehicle. Coatings with geometric metamerism display different hue and brightness when viewed at different angles. previously associated with European vehicles. Approximately 10–15 % by weight is comprised of solvents. polyurethane thickeners [32]. in that the appearance of the basecoat is enhanced by the transparent clearcoat. The basecoat contains pigments which provide solid (straight) shades or metallic finishes. the gloss and distinctness of the image of these multi-stage finishes has been widely accepted as the standard of appearance in both the automotive original equipment and refinish coatings markets. miniemulsion polymers.2 Automotive Coating Layers Solvent-borne basecoats Water-borne basecoats Resin 22% Resins 23% Pigment 2% Pigment 2% Organic Solvent 12% Water 63% Organic Solvent 76% Fig. temperature and fallout against pollution) coated panels are exposed for several years in special places (Florida. Application and testing Typically. color matching.g. different types of dispersions of acrylic resins in water and amino resins. Fig. Binders used Anionic coatings systems for water-borne topcoats are emulsion polymers. there is the possibility to run shorter test times in accelerated weather machines (weather-o-meter) which try to model the natural conditions. film failures (popping. light.7. polyurethane dispersions. a southern Japanese isle and Alunga in northern Australia). almost completely. flow and leveling. seeding). There are many other requirements including: resistance to car brushes. bird drop- 175 . There are different stability tests: mechanical stability (hardness and flexibility) and stability against environmental influences (rain. alkoxy silanes. line speeds for spray application of basecoats are lower in Europe compared to United States. water-borne polyesters. while piston pumps are used in Europe. viscosity. humidity. e. stability at room temperature/hot box 43 °C/56 °C. 7-3 shows the differences in composition between solventborne basecoats and water-borne basecoats. turbine pumps are used for circulation of water-borne basecoats in United States. carbodiimides can be used. The main tests for basecoats paints are: solids content. The polymers are mainly stabilized in the water phase by neutralization of anionic groups with volatile amines (2-amino-2-methyl-1-propanol). polyurethanes. Basecoat–clearcoat testing depends strongly upon customer requirements. higher temperature). Arizona. humidity. Furthermore. Okinava. cratering. For trials. gloss and effect (in case of metallic systems). To test the stability of topcoats against the effects of weather (mainly sunlight. Many of the polymers are hydroxyl containing and cured with various melamines and blocked isocyanates. blocked epoxy resins. Cross-linkers like aminoplast resins. 7-3 Solvent and water-borne basecoat compositions. Compositions containing methylol(meth)acrylamide can be used for very low VOC water-borne coatings. blocked isocyanates. adhesion. because of their low cost and processing requirements. wherein core shell polymers have been suggested to be used for waterborne basecoats. To achieve good flow properties. acid rain. a low minimum film-forming temperature. the core material is hard and the shell is soft and the latter is made of strongly hydrophobic monomers and a relatively large proportion of monomers carrying carboxyl groups [34–36]. and easy clean-up.176 7 Applications for Automotive Coatings pings. Water-soluble or a water-dispersible alkylated melamine formaldehyde crosslinking agent or a polymeric partially methylated melamine formaldehyde resin having a degree of polymerization of approximately 1–3 are used frequently. Such compositions have been used for automotive quality clear coat and/or pigmented color coat for automobiles and for an automotive quality primer composition [48]. in addition to their well-known features including safe handling. low odor. sudden thunder showers on a car that has been sitting in the hot sun. good stability to agitation and good adhesion to other coating layers.3.3 Properties of Water-borne Binders used for Automotive Coatings 7.1 Emulsion Polymers Emulsion polymers are binders of choice for automotive water-borne basecoats applications. because of their resistance to photodegradation and low cost. derivatives of acrylic or methacrylic acid. amide carbamate. Functionalized latexes in baked coatings can be crosslinked with aminoplast resins. A number of patents exist in the literature. Acrylic core-shell polymers have been used as principal polymers for aqueous metallic basecoat paints [37–40]. Relatively low-Tg polymers that coalesce well without coalescing solvents are applied and subsequent crosslinking will give the required film properties. For thermoset automotive coatings cross-linkable polymer dispersions are used [41–47]. Acrylic latexes are increasingly becoming popular for basecoat automotive applications. etc. low toxicity. 7. biochemical activity. alkoxy silanes. where the latex particles are small in size. postpolymerization reactions. The anionic shell allows pseudoplastic flow behavior which ensures parallel orientation of the aluminium pigments in the wet paint film. These functional groups can provide sites for crosslinking. gasoline spillage and so on. . compatibility with other polymers. This orientation and the low solids content are responsible for the metallic gloss and high color flop (change in color observed on varying the viewing angle) of the basecoats. epoxy resins and many other cross-linkers. A particularly valuable element of acrylic emulsion polymer chemistry is the ability to incorporate a broad range of functional chemical groups into the polymer chain via ester. multiphase emulsion polymers are used. the impact of pieces of gravel striking the car. Thus. have shown that incorporation of polyester into each acrylic latex particle. The chemical composition and degree of crosslinking of the microparticle may be such that it has a Tg below room temperature in which case the microparticles will be rubbery in nature. confers upon the film derived from the latter.3 Miniemulsions Significant advances have been made in recent years in applying miniemulsions for making water-borne polymers for the coating industry. therefore a successful basecoat/clearcoat system cannot be achieved. 7. that is to say the particles will be hard and glassy. stable water-based latex coatings can be prepared that also have the ability to cure (by crosslinking). even at low solids contents. alternatively. The polymer particle size is between 50 and 500 nm. prepared via miniemulsion polymerization. The presence of the crosslinked polymer microparticles in the basecoat composition. the desired ability to withstand subsequent application of the topcoat composition without disturbance of the film or of the pigmentation. The hydrophobic nature of the polyester resin makes it impossible to be accommodated by traditional emulsion polymerization due to mass-transfer limitations in crossing the aqueous phase to micellar nucleation sites. allyl methacrylate or divinylbenzene.2 Microgels Microgels are used as rheology control agents (RCA) for solvent-borne basecoats and clearcoats. branched vinyl esters with long hydrophobic chains can be used [49].3 Properties of Water-borne Binders used for Automotive Coatings To improve the water resistance. Shork et al. the dispersion contains a few if any multi-particle aggregates. This gives the advantage of the flip tone effect as well as the gloss to produce the ever popular metallic finishes for the automotive industry [51]. which it contains and without which. They are insoluble in the aqueous medium and are stable towards gross flocculation. Emulsion polymerization is carried out as a semi-continuous batch process [50]. in particular metallic pigmentation.7.The above hybrid miniemulsion polymerization was successfully used to incorporate an oil modified polyurethane in the acrylic 177 . Microgel dispersions having a pseudoplastic or thixotropic character have been used for formulating metallic pigments in the basecoat composition. Miniemulsions are routinely prepared using some kind of high shear device.3. in most cases this being an ultrasonifier or a microfluidizer [58]. 7. Since the introduction of miniemulsion polymerization in the early 1970s [52] many investigators have studied the subject and have used many different methods to prepare miniemulsions [53–57]. They are crosslinked microparticles made by emulsion polymerization using monomers like ethylene glycol dimethacrylate. leads to an effective in situ grafting of the acrylic and polyester systems [59]. The polymer micro-particles can be dispersed in the basecoat composition in a state in which.3. it may be such that the Tg is above room temperature. so in general anionic surfactants are used at levels of 0. Sometimes di. These dispersions of microparticles are produced by high stress dispersion followed by polymerization of the vinyl monomers in the presence of cellulose ester within the micro-particles. This technique was successfully used to core-shell polymers for use in making water-borne basecoats [64. To improve acid rain etch resistance. Typically a low particle size in the range of 50–300 nm is preferred.4′-azo-bis(cyanovaleric acid) has also been used for making acrylic latexes [70]. Latexes and coatings are stabilized by biocides or water-miscible solvents to prevent microbiological contamination and deterioration [71]. since some nonionic surfactants plasticize the latex polymer. used for clearcoats. a . 61]. The most common initiators are peroxydisulfate salts. The effects of acid monomers on stability and viscosity are maximized when they are incorporated in the last part of the monomer feed and the polymerization medium is acidic. wherein the carbamate groups crosslink with melamine. These coating compositions have good leveling and flow characteristics and exhibit good humidity resistance.5–2 % (w/w) based on polymer. carbamate functional monomers are included. A water soluble azo initiator 4. Acrylic acid (AA) or the somewhat less water-soluble methacrylic aid (MAA) are used in the order of 1–2 % (w/w) of the monomer charge. Whitening of films may occur sometimes due to the hydrophilicity of the salts like ferrous thiosulfate.178 7 Applications for Automotive Coatings droplets to give stable miniemulsions which were polymerized to give hybrid latexes [60. and an acrylic polymer and a surfactant has been used for coating compositions. 7. less sensitive to changes in pH. appearance.3. Hydrophilicity. Initiators. Stable aqueous dispersion of polymeric microparticles containing cellulose ester. and Surfactants Glass transition temperature is usually the first design property considered for the application. Choice of surfactant can also affect film formation temperature. especially ammonium peroxydisulfate.4 Selection of Monomers. 68]. Chain transfer agents are sometimes added to control the molecular weights and the distribution.or tri-functional cross-linking monomers are included. Nonionic surfactants may be added in stabilizing the latex against coagulation during freeze-thaw cycling making it less sensitive to coagulation by salts. Choice of surfactants are critical for automotive paint application due to their foaming tendency. 65]. ability to impart water sensitivity to paint films and change gloss characteristics. The aminoplast cured coating system combines acid resistance with excellent coating properties providing protection against etching by acid rain [69]. Additionally. acid-base properties. Thermal initiation is preferred to redox initiation. hydrophobicity. crosslinking ability are other properties [67. adhesion and chip resistance when used in a “low bake repair” process as well as a good automotive quality finish [66]. The hybrid polyurethane modified miniemulsion latexes have been successfully used in formulating coatings for basecoats [62–64]. miniemulsions made using a mixture of polyurethane and acrylic monomers were used to make latexes using a semi-continuous feed. leading to lower Tg and hence. but the higher ethoxylated surfactants are more effective latex stabilizers [72].6 Secondary Polyurethane Dispersions Another important class of materials used for OEM coatings are aqueous polyurethanes due to their versatility in their properties [74–80]. mar and chemical resistance. glycol ethers and other oxygen-containing solvents that are soluble or miscible with water. the carboxyl groups are neutralized with an amine which is subsequently dispersed in water and 179 . butyl alcohols) are polymerized by freeradical mechanisms. Organic solvents used are generally alcohols. Thermoplastic latexes are of higher Tg (upwards of 60 °C) are used for higher toughness. Typical monomers used are MMA/BA/BMA.5 Secondary Acrylic Dispersions Automotive coatings containing acrylic resins as binders are well known. and – dispersions containing both the non-ionic and the ionic groups. while acrylic acid monomers are used to impart water solubility. Azo initiators are typically used. HEA are used. Anionic PU dispersions In the first step of the synthesis. – ionic type. For example. the carboxyl monomers can provide cure with epoxies. the Tg depends on the molecular mass. In the next step.3. The hydroxylic monomers can be incorporated for cure with melamine and isocyanate resins.7. 1-(n-propoxy)-2-propanol. 2-(dimethylamino)ethanol is widely used [73]. they have enjoyed considerable interest and commercial acceptance. Typically. In the low-molecular-mass range (<6000 g mol–1).or polyester-based isocyanate-terminated prepolymer is obtained by condensation polymerization of a diol and a diol containing a carboxyl function. The choice of amine is crucial. nonylphenylethoxylate nonionic surfactants with less than nine ethoxy units reduce film formation temperature as compared to 20 to 40 ethoxylate units. Hydroxy monomers like HEMA. After polymerization the carboxylic acid groups are neutralized.g. a conventional polyether. Subsequent cross-linking leads to an increase of Tg which is dependant on the cross-linking density.3. aziridines and carbodiimides. 2-butoxyethanol. Polyurethane dispersions can be classified into three main groups: – non-ionic type. preferably reacting the hydroxyl groups of dimethylol propionic acid with isocyanate groups. 7. 7.3 Properties of Water-borne Binders used for Automotive Coatings lower temperature for coalescence. since heat is available for film formation. equivalent weight equals 56 100/acid number). these resins have acid numbers of 40–60 (acid number is determined by titration and is defined as mg of KOH required to neutralize 1 g of resin solids. Since the introduction of polyurethane dispersions in 1960s. Acrylic resins made in solvents (e. resulting in wrinkled finish and loss of DOI (Distinctness of image). Polyurethane particles can exhibit core-shell morphology with the shell having higher molecular weight and higher urea functionality than the core. High-performance OEM-clearcoats have been produced with good chemical resistance with excellent mar resistance. which leaves during baking. volatile amines used to salt these carboxylic acid-functional resins. 81]. thereby hindering the cure of the strong acid-catalyzed acrylic-melamine clearcoats. The different morphology exhibited by aqueous polyurethanes and acrylics explains why the minimum film forming temperatures of polyurethane dispersions (PUD) are lower than that of acrylics with equal hardness [82]. it can be used directly as a seed for subsequent free radical polymerization. glass transition temperature and durability. and the limited rheological stability with metallic formulations which contain certain rheology control agents. A number of diols. The most widely utilized technique for making hybrids is to free radically polymerize a combination of monomers in the presence of a pre-formed polymer which may or may not be intrinsically dispersible. Some limitations of using anionic water-borne polyurethanes are. they show lower reactivity with water and carboxylic groups. because beside conferring good durability. tertiary amines are preferred compared to other amines to prevent unwanted side reactions with isocyanates. nonionic polyurethane dispersions were developed [87. In response to these limitations. 85]. Water-borne basecoats containing polyurethanes have been produced with a formulation containing less than three pounds per gallon and lower temperatures than solvent-borne systems [86]. Non-ionic Dispersions In the non-ionic types. anionic PU resins have generally not given satisfactory application properties and paint stability. Aliphatic isocyanates are preferred. In certain formulations. isocyanates and amine raw materials can be used to adjust the mechanical properties. A two coat one bake coating process which does not give environmental problems has been developed using aqueous PUD [84. As neutralizing bases.180 7 Applications for Automotive Coatings chain extended in order to obtain high-molecular-weight materials by reacting with a diamine in further steps. This effect was found to be quite pronounced with isophorone diisocyanate-based polyurethane dispersions [83]. 88]. While water-borne acrylic resins and polyurethanes have been widely used as polymers for automotive coatings. . Rapid-drying polyurethanes have been used for industrial finishing and automotive refinish with a well-balanced range of properties at low VOC level. If the preformed polymer is water dispersible. both water-borne resins are inferior to corresponding solvent based counterparts because of hydrophilic functional groups or surfactants which are introduced to impart dispersion stability to these resins. the hydrophilic centers comprise of polyether chain segments [75. Hybrid systems The blending of resins is a simple and useful technique for improving paint properties. Further aliphatic isocyanates favor very rapid reaction with diamines in the chain extension step. Table 7-6 shows some of the advantages and disadvantages of polyurethane and acrylic resins. the thickener. the viscosity needs to be very low. “Hybrid” acrylic-urethane latexes have been made by simultaneous polymerization of acrylic monomers and chain extension of urethane prepolymers giving structures similar to interpenetrating network polymers. In a well designed system. such as is present at the nozzle during the spraying process. Since polyurethanes are generally more hydrophilic than the acrylic copolymer. with mechanical properties exceeding those. in the formulation. however its viscosity needs to be very high so as to prevent sagging on vertical surfaces and clouding. sag resistance and leveling properties.7. reduced water sensitivity. The paint must have a good intrinsic viscosity. The viscosity of the paint must be very low at the spray gun in order to ensure a good and uniform atomization. simultaneously. 7-6 Acrylics Polyurethanes Advantages Disadvantages Hardness Weatherability Chemical resistance Gloss Affinity for pigments Cost Mar resistance Elongation Softness and adhesion Toughness Mar resistance Elongation Cost Urethane acrylic aqueous dispersions prepared by an acrylic polymerization in the presence of an aqueous polyurethane can possess a range of advantages over the corresponding blends. the particles coalesce on film formation to give a film with a continuous polyurethane phase. i.e. Tab. e.4 Rheology A major concern in developing water-borne automotive coatings is to achieve a distinct rheology profile providing good sprayability. The flow behavior of the aqueous basecoat therefore has to be adjusted by including a rheology additive. ability to prepare in the cosolvent form. After the paint meets the car body.4 Rheology Advantages and disadvantages of polyurethane and acrylic resins. it is virtually unaffected 181 . If the paint then meets the car body. In water-borne systems rheology control agents (RCA) are added to control sag and flake orientation. microgels and water-soluble resins have yielded excellent aqueous binders for various coatings [25]. the viscosity must depend on the shear rate. Combination of special emulsions. In low solids solvent-borne systems. controlling the rate of solvent loss controls viscosity and sagging and metal flake orientation. 7. if blended [89].g. the polyurethane concentrates at the particle surface. With a high shear force. sample D 49. it has been observed that higher degree of pseudoplasticity led to a better flake orientation when compared to samples with lower metallic flop index values. Values of this parameter for basecoat/clearcoat typically range from 45 for a coating with poor travel to 70 for a coating with very good metallic flake orientation. When light strikes a surface. sample C 58. scattered. A pseudoplastic (“shear thinning”) behavior is ideal for coating materials. However. 7-4 10 1 10 100 Shear Rate [1/s] A Zeiss multiangle goniospectrophotometer MMK-111 with 45° illumination angle was used to measure the lightness values of the basecoat/clearcoat film at different angles. sample B 57.7 Applications for Automotive Coatings by the shear strength and the viscosity must rise to very high values with almost the same solids content so that the paint does not sag and the aluminum platelets do not lose their alignment. TEM and analytical ultracentrifuge techniques [90]. Nevertheless. At higher shear rates. Attempts to correlate various rheological parameters to good metallic appearance have not been found to be successful [91]. some of the light penetrates where it can then be absorbed. Specular reflectance is the reflectance of the incident light. Interactions between thickener and latex particles in water-borne automotive coatings and the corresponding microstructures were investigated using dynamic mechanical spectroscopy. When incident light falls on the coating surface. (Fig. a certain . the viscosity is reduced which allows easy handling and application of materials. because of the change in refractive index between air and most substances. Viscosity is fairly high at low shear rates which avoids settling in the can and gives good anti-sag properties. cryo-replication. The degree of “travel” was estimated using the following mathematical calculation [92]: Metallic flop (MF) index = 50(L25 – L70)/L70 where L25 and L70 is the lightness value at 25° and 70° off of specular reflectance. in the case of four samples with varying metallic flop index values. metallic flop index values: sam1000 ple A 62. 7-4) Steady Shear Viscosity Profile 10000 Sample A Viscosity [mPas] 182 Sample B Sample C 1000 Sample D 100 Viscosity versus shear rate. Fig. or even transmitted if the layer is sufficiently thin. [104]. Light that is reflected by the substance itself is called body reflectance. such as hardness. hardness and flexibility) no longer exist. By examining the frequency bands in which the rate of change in the refractive index is high. Dynamic mechanical measurements showed that films from slightly or moderately cross-linked particles behave like homogeneous networks in the linear viscoelastic range [105]. Lower solvent content and the replacement of conventional solvent-borne paints by water-based paints meant that the molecular mass of the binders had to be lowered to a range where the required paint properties (film formation. A further impetus was given by increasingly stringent environmental legislation. the index of refraction of the polymer from the microgel is nearly identical with that of the crosslinked acrylic binder polymer so that light scattering does not interfere with color flop. 98].7. many properties can be greatly improved. The paints exhibit outstanding gloss and durability [103]. These properties therefore had to be obtained by increasing the molecular mass by crosslinking after application. 7-5). The effect of the gel particles depends on the interaction with the low molecular weight resin. Melamine formaldehyde cross-linkers have been 183 . the chemical reaction after application also provides advantages of high molecular mass dispersions.130 °C and is effected by acid catalysis (Fig. specular reflectance measures the energy that is reflected off the surface of a sample or its refractive index. Instead of examining the energy that passes through the sample. the glass transition temperature and film hardness are increased. By crosslinking the resin used in the coating. users can make assumptions regarding the absorbency of the sample. The angular distribution of this light depends upon the nature of the surface but light that is reflected at the opposite angle to the incident light is called specular reflectance. All coating layers uses resins which need to be crosslinked. 7.5 Crosslinking Thermoset coatings (chemically crosslinked film) play a very important role in the automotive coatings industry. The rheological properties of the systems are discussed elsewhere [99]. mar resistance and solvent resistance.5 Crosslinking proportion of the incident light is reflected directly from the surface. A widely used method of cross-linking paint films consists of reacting of hydroxyl containing acrylates or carbamate containing acrylates with melamine-formaldehyde resins or urea-formaldehyde resins [100–102]. Acrylic microgels have been developed that impart thixotropic flow using swollen gel particles [52. 93–96]. Crosslinking is carried out at ca. In the final film. Crosslinking reactions became important in the 1950s with the introduction of acrylic resins in the automotive sector. Thixotropic agents are added to increase the viscosity at low shear rates to minimize sagging [97. The possibility of making cross-linkable latexes by emulsion polymerization in the presence of etherified melamine-formaldehyde resins has been demonstrated by Jones et al. Furthermore. 7-5 O OH O Crosslink reactions. 7-5) [111–114]. Michael adducts [110] sulfonium stabilized polymers. Other crosslinking mechanisms that have been studied are use of addition polymers. Mannich bases. Melamine-Hydroxyl reaction R' N OR N + N N HO OR N R' ROH N OR N H+ R' O N R' Alkoxylated Melamine Hydroxyl-functional Acrylic Melamine Ether Isocyanate-Hydroxyl reaction + R NCO HO R N O O Hydroxyl-functional Acrylic Isocyanate Urethane Melamine-Carbamate reaction OCNH2 OCNH2 O OR N N N 250 F N N OR N N N N N N N Fig. The mechanism involves the reaction of an isocyanate group (NCO) with the hydroxy group of the epoxy backbone and liberation of the blocking group. alkoxy. transesterification reaction of hydroxy. A practical and effective crosslinking mechanism in cathodic electrocoating is done with polyfunctional blocked isocyanates. water-reducible polyester–polyurethanes and acrylic latexes [106–109] in automotive water-borne basecoats. amido and ester systems with hydroxy functional cathodic backbone (Fig. C O N H OR .184 7 Applications for Automotive Coatings used with water-reducible acrylics. temperature and air flow. and crater formation. On account of the viscosity anomaly. water is used as the solvent or diluent. They can be formulated to have a high gloss due to their good pigment wetting and stabilization. Water-borne coatings themselves vary depending whether they are latexes. Coating films formed from some water-soluble binders tend to be water-sensitive because of their hydrophilic solubilizing groups. which may take up to several days. The high dipole moment of water is also responsible for its high surface tension. oven drying). The film may. the required application viscosity of waterborne emulsion paints is generally obtained by adding a small volume of water. Aqueous dispersions generally contain a few per cent of high boiling solvents which act as temporary plasticizers and lower the minimum film-forming temperature.30–40 %) and require relatively large amounts of organic solvents (up to 15 %) to ensure water solubility and film formation. The water molecules have a high dipole moment and associate with one another. They can also have a high level of corrosion protection. only low gloss and. The physical properties of water and organic solvents differ. As a result of the particulate nature of the acrylic latex polymers. The latter determines adhesion to the substrate and diffusion of water and oxygen through the paint film.7. They also have the advantage of a broad drying spectrum (physical. In the case of paints made from emulsion polymers. thus allowing film formation to occur.g. in some cases. however they are of only limited use for electrostatic coating and dipping applications due to their rapid drying properties. Water-borne viscosity characteristics are distinctly different and application. Water-borne coatings based on dispersions can be applied by spraying. Critical surface tension (at 20 °C) of water is 72. Some of these properties have to be taken into account when water is used as a paint solvent. In the production and application of water-borne paints. This means that water has a high boiling point and high latent heat of evaporation despite its low molecular mass. A film of sufficient hardness is obtained only after complete evaporation of solvent. plastics or unsatisfactorily greased metals) this leads to inadequate wetting. gloss and gloss retention. dispersion (semi-soluble) resins or a combination of the two. only limited corrosion protection can be obtained.6 Application Properties Water-borne coatings initially presented a number of difficulties. With substrates having a low critical surface tension (e. which depends on the corrosion-inhibiting pigments used and the chemical nature of the binder. this reduces its water resistance.5 mN m–1. The evaporation behavior of polymer dispersions is similar to that of conventional solvent-based paints. however be somewhat hydrophilic due to the presence of carboxyl groups and emulsifier residues. film formation and drying behavior are dependant on humidity and phase distribution of solvents as well as the usual factors of solids. 185 . water-borne paints based on water-soluble binders have a relatively low solids content (ca.6 Application Properties 7. unsatisfactory edge covering. This in turn results in fairly long evaporations or in the need to supply energy in the form of heat to evaporate the water and dry the paint film. The main problems arise due to the relatively high . lower energy consumption in spray cabins. The key factor is the rapid rise in viscosity on the car which results in the aluminum flakes effectively frozen in an orientation parallel to the surface. all contribute to the overall economy of water-borne coating materials. If rust is present in the circulation system. savings in insurance premiums.g. which also reduces surface distortion during subsequent application of the clear coat [117]. The lower film thickness of the basecoat and the flash-off time required before applying the clear top coat reduces the popping problem.1 Metallic Effect Typically in solvent-borne systems. pH 7. thicker film thickness and poor aluminium alignment all reduce specular reflectance within the sprayed basecoat paint film [109–115]. it can react with the paint resins. use of respirators) must be taken depending on the workplace concentration. 7. and drying ovens. Savings in organic solvents as diluents. 7. These basecoats are cured at 130–140 °C [116]. Nevertheless. lungpenetrating paint mists (aerosols) of water-based paints present a health hazard and appropriate protective measures (e. These are supplied to the European and world automotive industry for production line applications. Control of sagging during application requires that the waterborne basecoat is shear thinning. Water-borne coatings can generally be classed as less toxicologically harmful than corresponding solvent-based paints. ventilation zones. which results in the so-called flip effect.g. Surface tension in turn controls amount of picture framing and film thickness. The slower rate of evaporation of water means that a water-borne basecoat cannot rely upon water evaporation to achieve his rapid viscosity rise. through its patented microgel technology has managed to stimulate the rapid viscosity rise. The prospects for the increasing use of automotive water-borne coatings lies in their economic advantages and in the possibility of reducing solvent emissions during application to comply with legal requirements. ICI.6. the basecoat requires high solvent or low solids content in order to achieve perfect orientation of aluminium flakes.6. The microgel pseudoplastic rheology means that the paint at the spray gun tip behaves like a thin liquid while the paint on the car panel is highly viscous. creating gel lumps which under circulation trap the metal flake hindering flake alignment.186 7 Applications for Automotive Coatings Circulation studies of water-borne metallic basecoats demonstrate a few reasons why specular reflectance is lost during circulation. The microgel particles are acrylic-based and swell rapidly in the presence of small amounts of organic co-solvents such as butyl cellusolve in alkaline solution e.7 Environmental Aspects and Future Trends Water-borne coatings for automotive applications have a broad application spectrum. The flow induced stress of circulation reduces flake size and produces cycles in liquid surface tension. Smaller flakes. 2nd edn. 55 (707). Sci. EP 798323 (October 1. 2000. etc. Appl. Eng. 6 M. Rosenberger. Coat. US Pat. W. 1998. 50 (642). US Pat. Chem. 1995. Ohguchi J. 89. 4104174 assigned to PPG. US Pat. Padget. 78 (2).: Polym. Kaji. 392. Vogt-Birnbrich. 22 3 http://www. 281. B. M. 19. Weigel: Elektrophorese-Lacke. Fettis. 1998 33. A. S. 9 B. Org. in order to avoid toxicity caused by these components. J. Although water-borne systems are not considered toxic. 4177124 assigned to Dupont. Yabuta. March 2001. P. Higashiura. 86. 4170579.com/Paint. 66. D. 187 . VCH. 24 25 26 istics Affecting Coatings. US Pat. Technol. Tullo. J. Pat. D. p. H. 91. S. US Pat. Future approaches will encompass improvements in scratch and environmental etch resistance. 1994. J. Gobel. Coat. 1978. J. Horibe. 1 C. US Pat. Freitag. Jr. 4698141 assigned to Dow. Blackley. Stuttgart 1967.htm 4 http://www. Wojtkowiak. T.org/autoinc/ may2001/paint. Technol. Sci. they require careful selection of resin/binders and additives such as biocides. 1998. 1975. H. G. M. 2001. Automotive Coatings. A. 4419467. Wiley-VCH. C. M. Mitsuji. 839. Vanderhoff. A. Esposito. 2000. Okumura (Kansai Paint Co) EP 785034 (July 23 1997). New York. Wiley. 1995. S. 108. Greissel. Jones. New York. Dietrich. Coatings World. 1983. Coatings. D. Nagara. Fettis Automotive Paints and Coatings. K. Z. 1985. 108–116.7 Environmental Aspects and Future Trends freezing point. G.7. 72. W. Org. 43. Polym. US Pat. 4113682 assigned to Nippon. Yasuhara Nakayama. October 2000. Coat. Coatings and Solvents. J. coalescing agents. Bender. Verlagsgesellschaft. Federation of Societies for Coatings Technology. El-Aasser. Weinheim. 38. Prog. International Sterling Publications. Haneishi. cosolvents. N. 161–198. Wiley. S. Lovell (eds) Emulsion polymerization and Emulsion Polymers. Wis- senschaftl. Emulsion polymerization. 1997. Polym. better performance features all at a lower cost to the manufacturer. F. 1994. 9(3). Organic Coatings Science and Technology. . H. better color options. Moreover the presence of water causes rusting problems of ferrous substrates and also make the water-borne systems very prone to attach by microorganisms. Coatings 1981. high surface tension and low evaporation rates of water compared to organic solvents. A. Prog. J. C. (Herberts GmbH) Eur. 7 J. Maeda. Wicks. E. 1997).asashop. S. 8 M. 4139510 assigned to Celanese.protectall. 37. PA. 2nd edn. Symp. References General M. M. US Pat. 22. October 9. J. Perfetti. Industrial Paint and Powder. Y. Woltering. Appl. J. Theory and Practice. Shimizu. Paint and Coatings Industry Magazine. W. Blue Bell. Stoye. Paints. Peter Pappas. Acknowledgment The author wish to thank BASF Coatings Division for their support in writing this chapter.. Automotive Paints and Coatings. 4423166. News. Metal Surface Character- 10 11 12 13 14 15 16 17 18 19 20 21 2 A. C.htm 23 5 K. September 2000. Technol. S. 65. J. Paint Coat. 60. Appl. R. J. J. S. 50 (647). Polym. 1978. Hansen. A 0238108 (1986). Rosthauser. US Pat. S. 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Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. But it was not until 1930 that phenol-formaldehydes and urea-formaldehyde condensates developed by C. Polymerization processes discovered in the 1920s resulted in a large number of new thermoplastics and elastomers. the first semi-synthetic plastic. Thermally stable plastics were more recently developed which enable adhesive bonds that withstand temperatures up to 350 °C. polychloroprene. 8-1).or fully synthetic products are used for a wide variety of bonding applications (Fig. The products discovered in 1872 by Adolf Baeyer by polycondensation of phenol with formaldehyde were the basis for the first fully synthetic plastic. Polyurethanes and epoxies – developed in the mid-1930s – further broadened the range of adhesive raw materials. natural rubber and starches. in particular. i. whose ethereal solution was used by the shoe industry in 1910 for bonding leather. Adhesives of natural origin were mainly used prior to the beginning of the 20th century and by early civilizations as long ago as 2000 BC. casein. which was obtained by Bakeland in 1909 by thermally curing reactive phenolic pre-condensates. These included animal glue. As such.1 Introduction Adhesives are high-molecular-weight substances which bond materials to one another without significantly changing their structure. The action of adhesives is based on two key properties: they must firstly “wet” solid surfaces and adhere to them. they must be cohesive.Polymer Dispersions and Their Industrial Applications. The development of synthetic adhesives paralleled the development of plastics which began in 1845 with the nitration of cellulose to give cellulose nitrate. classical connection meth- 191 . Goldschmidt in 1896 (Kaurit) were used widely as adhesives. sandwich construction) now makes it possible to adhere a multitude of various materials to one another. and polyisobutylene were used as the basis for new adhesive technologies. Bakelite. and secondly. 3-527-60058-2 (Electronic) 8 Applications in the Adhesives and Construction Industries Dieter Urban and Luke Egan 8. KGaA ISBNs: 3-527-30286-7 (Hardback). Concurrent development of new bonding technologies (e. have internal strength. screwing. continue to be replaced by adhesive bonding techniques.4 billion in North America [11]. cellulose ether Synthetic rubber (polychloroprene. bone glue) Casein Blood albumin Vegetable glue Albumin. 8-1 Synthetic and natural adhesive raw materials. artificial gum Natural gum. sewing. pectin Starches. A particularly impressive example of new adhesive technology is in aircraft and rocket construction. furniture.192 8 Applications in the Adhesives and Construction Industries Natural adhesives Animal glue Gluten (hide glue..5 million tons of adhesives (dry weight) were used in 1996 [10] compared to 2. about 1. melamine. ods. tragacanth Natural rubber. etc. vinyl esters. such as welding. construction and packaging. copolymers of butadiene with acrylonitrile or styrene) Copolymers of acrylics. wheat. The world market in 1996 for adhesives and sealants was about US$ 21 billion compared to approximately US$ 6. Adhesive bonding has now become a routine joining method in a host of various industries – including automobile.and solvent-borne adhesives) Cellulose ester. vinyl ethers Derivatives of natural rubber (chlorinated or cyclized rubber) Polyurethane elastomers Bonding by cooling (hot melt) Ethylene copolymers Polyalkylene terephthalate Polyamide Butadiene or isoprene based block copolymers Chemical reacting adhesives Urethanes. natural resins (colophony) Synthetic adhesives Physical binders Bonding by evaporation (water. In Western Europe. shoe. (meth)acrylates Fig. where supporting structures are adhesively bonded on assembly lines [1–9]. . silicones Urea.3 million tons in North America [11]. gum rosin. epoxides. gum arabic. and phenolic resins Cyanoacrylate. riveting. Avery [15] invented a coating unit for self-adhesive paper labels using a wooden cigar box filled with an adhesive solution. This was probably the first curtain coating process. signs) began at virtually the same time.8. They were produced on an industrial scale for the first time at the beginning of the 1940s. Furthermore.g. Solvent-based rubber/resin mixtures and comparatively smaller amounts of acrylate solutions were processed almost exclusively. This excellent property also made it possible to use dispersions for electrical insulation tapes. As so often it occurs in new technical developments. viscoelastic liquids which adhere to virtually all surfaces when pressed down gently. A new branch of industry began to coat various support materials with pressure sensitive adhesives and to make self-adhesive products from them. systematic work in the 1970s on high speed coatings technologies [16]. They are used in manufacturing “easy to apply” self-adhesive products. A continuous increase in pressure sensitive adhesive dispersion production occurred throughout 1960s. die cutting and stripping). The crucial factor was the ground-breaking.2 Pressure-sensitive Adhesives 8. The rapid development of a number of new applications accelerated this process. so that further curing operations after applying the tape or label are generally unnecessary. The first areas of application were self-adhesive book binding and map protection films. It was also found that existing “solvent” coating units could be modified to permit economical processing of aqueous dispersions. Until the beginning of the 1970s. slitting. It was then possible for the first time to make flexible PVC films self-adhesive without the need for a primer. The adhesive dripped through holes cut in the bottom. In 1935. promotional graphics. such as labels and tapes. This increased efforts to use aqueous polyacrylate dispersions as pressure sensitive adhesives. However. The development of new application equipment and corresponding high-solids dispersions has enabled coating rates to be increased from less than 60 m min–1 to as high as 600–1000 m min–1 today. R.2 Pressure-sensitive Adhesives Pressure sensitive adhesives (PSA) are highly viscous. The first water-based acrylate dispersions were developed as long ago as the 1930s. The inherent properties of polyacrylates made by emulsion polymerization enabled hitherto unknown speeds during down-stream converting operations (i. 193 . Day [13] and in Germany in 1882 by P. Pressure sensitive adhesives typically have permanent tack and adequate cohesion.H. which were developed in the USA in 1845 by the medical doctor H.e. completely unexpected advantages became evident with newly developed acrylic dispersions. The first self-adhesive products were adhesive plasters [12].S. The use of self-adhesive tapes for industrial purposes marked the beginning of “dry-adhesion” technology. acrylate dispersions for pressure sensitive adhesives were not introduced into the market until the beginning of the 1950s. Beiersdorf [14]. acrylate dispersions satisfied the demand for removability without leaving a residue. on to a roll of paper that ran below. The use of self-adhesive films in advertising applications (e. pressure sensitive articles were produced mainly by coating from organic solutions. The importance of acrylic dispersions continues to increase for reasons of environmental protection (nonflammable.1 Self-adhesive Labels Self-adhesive labels (and decals) are pieces of paper. barcodes. no hazardous solvents). price stickers.2. and technical data. About 30 % in North America and 45 % in Europe are applied from organic solution while hot melts have a share of 40 % in North America and 15 % in Europe [17. Japanese paper label manufacturers started converting from rubber solutions to water-borne systems because of very strict environmental protection regulations. The most important adhesive raw material compositions for adhesive labels are polyacrylate dispersions. product or package contents. Permanent and removable UV-cross-linkable acrylic hot-melt adhesives have recently also been introduced [19–22]. In North America 3. styrene-butadiene rubber solutions. and the control of the molecular weight and process parameters [26–29]. 31]) at various temperatures is shown in Fig. instructions. In the 1970s. . and excellent coating and processing properties. corresponding to 35 % of world production. They are typically used to convey various kinds of information – for example. this corresponds to a demand for adhesives of 70 000 dry tons year–1 in Europe. At average application rates of 24 g m–2. 8-2.5 billion m2 of self adhesive labels were produced in 1999. and styrene-butadienestyrene (SBS) and styrene-isoprene-styrene (SIS) hot-melt adhesives. Some examples are given below. Assuming the same coating weight. Aqueous polymer dispersions have a share of about 30 % in North America and 40 % in Europe. the adhesive demand in North America was 84 000 dry tons year–1. About 2. resulting in acrylic dispersions becoming the most important group of PSA raw materials in Japan. high solids contents. 8. plastic film or metal foil coated with pressure sensitive adhesives which adhere to any solid surfaces after removal from a release liner. good aging resistance. the conversion was carried out in the 1980s and now the use of acrylic dispersions in self-adhesive products is widespread and well advanced. 85 % of the PSA label market was solvent born in 1975 [23] but in 1991 approximately two-thirds of the market was waterborne [24]. In Europe. Polyacrylate dispersions Adhesion and cohesion of polyacrylate dispersions can be varied over a broad range and matched to many applications through the type and combination of low Tg (“soft”) and high Tg (“hard”) monomers.194 8 Applications in the Adhesives and Construction Industries The total market demands for pressure sensitive adhesives (tapes and labels) is about 300 000 tons of polymer in North America and about 200 000 tons in Europe.9 billion m2 of self-adhesive labels were produced in Europe in 1996. In North America. 18]. Zosel [30. the choice of auxiliaries. The influence of glass transition temperature (Tg) of acrylic homopolymers on tack (according to A. If the K-value is increased further. For use at room temperature. and variation of the polymerization process [27]. A practical measure for assessing the average degree of polymerization. Besides polymer composition. in particular for process control. the molecular weight of the polymer also affects adhesion properties. The peel strength is low at very low K-values and high at a K-value of 50 (cohesive fracture). the lower the tack or adhesion. This characteristic constant. 8-2 It can be seen that tack is greatest at temperatures 50–80 °C above the Tg of the homopolymers. the failure mechanism changes from cohesive into adhesive. the peel strength drops slightly. At K-values above 50. Acrylic dispersions of identical composition. The higher the K-value.2 Pressure-sensitive Adhesives Tack of polyacrylates as a function of composition and temperature. but of different K-value. the tack increases with increasing hydrocarbon chain length of the acrylic monomer.8. which can be determined quickly and simply at a single concentration. enables a rough estimate of the intrinsic viscosity and molecular weight [27]. mixing high-molecularweight with low-molecular-weight components. is Fikentscher’s K-value. were investigated (Fig. the higher the internal strength of the film and the worse the wetting. polyethylhexyl and polybutyl acrylate have the greatest tack [27]. i. which is obtained by measuring the relative viscosity of a dilute polymer solution [32]. and the peel strength drops to a low value. 195 . The following measures may be used for varying degree of polymerization: addition of a chain transfer agent. The following example is intended to clarify the effect of molecular weight. varied through different amounts of a chain-transfer agent. crosslinking additives. 8-3) [27]. the cohesion of the film is very low. In addition.e. Fig. Substrate wetting and polymer cohesion strength are responsible for these results. Although wetting is good at low K-values. Druschke [27]. This can be seen in Fig. according to W. Druschke [27]. Fig. but also by the molecular weight distribution. adhesion is not affected by the average molecular weight alone. 8-4.196 8 Applications in the Adhesives and Construction Industries peel strength in N / 2 cm peel rate 300 mm / min 20 cohesion failure adhesion failure 15 10 5 0 20 50 80 K-value Fig. 8-3 Peel strength as a function of molecular weight (K-value). However. which shows the peel strength in N / 2 cm peel rate 300 mm / min 20 cohesion failure adhesion failure 15 10 5 0 10:0 8:2 6:4 4:6 2:8 0:10 lower/higher molecular weight component Peel strength as a function of the content of high-molecularweight component. according to W. 8-4 . 2 Pressure-sensitive Adhesives peel strength of various mixtures of relatively high molecular weight acrylic polymer (K-value ca. i. The maximum peel strength is obtained at a high molecular weight component content of 80 % [27].8. which crosslink on recombination. results in an increase in cohesion (Fig. 90) with low molecular weight material having the same composition (K-value ca. 8-5 shows. the actual performance of the mixtures can deviate strongly from a linear mixing relationship. As Fig.e. copolymerized functional monomers like acrylic acid. an increase in the average degree of polymerization. The two contradictory requirements for high tack and needed internal strength can be best achieved in polyacrylate dispersions when adhesive and cohesive components are produced stepwise during the emulsion polymerization. Crosslinking affects the viscoelastic behavior in two ways: by slightly raising the glass transition temperature and by increasing the modulus level above the glass transition region. 8-6) and produces a significant increase in the shear strength. This behavior is pronounced in polyacrylates and can be 197 . With increasing content of high-molecular-weight component. the transition from cohesive to adhesive fracture occurs again with a sudden drop in the measured peel values. The transfer of free radicals to pre-formed polymer chains results in the formation of branches. It also reduces the mobility of the crosslinked polymer chains. Shear values at 20 °C and low temperature peel strength at –23 °C depending on the mixing ratio of a high peel dispersion A and a high shear dispersion B [33] Fig. 8-5 Interestingly. the shear values are significantly reduced by small amounts of dispersion A and low temperature peel strength drops to zero at only 20 % of component B. for example. 55). When an acrylic dispersion with good low temperature peel strength (A) is mixed with one having high cohesive strength (B). 500 g peel strength in N / inch 20 time in min 100 80 15 60 10 40 5 20 0 0 0 0. The maximum peel strength is achieved at 0.198 8 Applications in the Adhesives and Construction Industries shear in min 1/2 inch x 1/2 inch. Figure 8-7 shows that even small amounts of chain transfer agent cause a significant reduction in cohesion. 8-6 1 000 500 0 0 1 2 acrylic acid in pphm used to improve cohesion. 8-7 . Fig.3 0. An optipeel (Cr) [N/inch] 300 mm/min quick-stick (Cr) [N/inch] 300 mm/min cohesion [min] 1/2 x 1/2 inch.4 chain transfer agent in pphm 0. which suppresses crosslinking and produces lower molecular weights. Adhesion can be improved using a chain transfer agent.2 0.2 pphm and the maximum quick-stick (or loop tack) at 0. 500g 1 500 Shear strength as a function of copolymerized acrylic acid.1 0.5 Effect of the chain transfer agent on the adhesive properties of an acrylic dispersion.3 pphm of chain transfer agent. Fig. The formulator can take advantage of this effect to impart opacity to a substrate. and – matching of the viscosity.g. rheology and wetting behavior of the adhesive to the proposed coating method and substrate. water resistance of the dried films can be affected in unexpected ways (Fig. against plasticizers). This is generally done by mixing acrylic dispersions with one another. Polymers used in pressure sensitive applications have glass transition temperatures of between –60 and –20 °C. But it is important to note that when blending acrylics and SBR. Dispersion mixtures In some self-adhesive products (for example. cohesive products with good tack are admixed. Wetting agents. a blend of acrylic dispersions. 8-8).8. for example. brown adhesive tapes for packaging) or to achieve special effects (e. However. natural latex. bottles). The polyacrylate dispersions optimized in this way for pressure sensitive adhesives are produced and supplied with solids contents between 50 % and 70 %. – optimization of the formulation from a commercial point of view.2 Pressure-sensitive Adhesives mum balance between plasticity and bond strength is clearly achieved at a certain degree of crosslinking. Technical or economic considerations often make modification necessary [34]: – optimization and refinement of the adhesion properties. In wet labeling applications (e. and adding tackifying resins and plasticizers.g. produce dry films which are opaque – because of differences in refractive index. a dispersion with superior resistance can be mixed in certain proportions to increase the overall formulation performance. zinc oxide in medical tapes). protective films). dispersions with a high solids content (> 60 %) and low viscosity (<500 mPa s) need to have a bimodal or multimodal particle size distributions. In certain applications requiring chemical resistance (e.g. Note that blends of acrylics and styrene-butadiene latex (SBR). In order to improve the tack. Fillers or pigments are used to color the adhesive material (e. – production of a large number of self-adhesive products using a small number of starting materials. These products are based on special self-crosslinking acrylics. which previously used “natural adhesives” such as casein. the goal is a weak tack which does not increase after extended bonding times. The viscosities of most commercial products are generally between 10 and 1000 mPa s but high-viscosity dispersions – greater than 10 000 mPa s – are also used in certain packaging applications. Average particle sizes are typically between 100 nm and 1000 nm.g. defoamers and thickeners are added to adapt the adhesive to the prevailing coating conditions. Formulation modifications Acrylate dispersions can be used directly in only a small number of applications. and wax dispersion have been employed. 199 . . The most suitable products for improving the tack of polyacrylates are modified natural resins. If these resins are combined with softer resins. resin dispersions should be used instead of resin solutions. They must be compatible with the polymer (i. Resin dispersions are available. Polymeric tackifier has been reported to increase the elastic properties of a pressure sensitive adhesive resulting in improved peel strengths. DRT/ND Dispersions (France. for example. from Akzo Nobel/EKA Chemicals (Netherlands. addition of resin also specifically increases the adhesion to polyolefin surfaces. pressure sensitive adhesives with high shear strength but relatively low tack are obtained. the water resistance. USA). the addition of resin may impair the aging resistance of the adhesive. and Hercules (Germany. carpet laying tapes). In addition. is often reduced. after 24hrs) 200 50 40 30 20 10 0 100/0 80/20 50/50 20/80 0/100 PSA Blend Ratio (Acrylate / SBR) Water resistance of dried PSA films depending on the blend ratio acrylic/styrene-butadiene latex. However. USA). evident from blushing. USA). substrate wetting. especially at high peel rates [36]. Preferred applications for acrylate–resin combinations are paper labels and double-sided adhesive tapes (for example. Fig. With resins whose softening points are about 70 °C. the tack is significantly increased. To retain the advantage of the “solvent-free” feature offered by polymer dispersions. such as dimerized or hydrogenated gum rosins and esterified abietic acids. However. mixture has a single Tg) and modify its viscoelastic properties resulting in improved polymer flow characteristics.8 Applications in the Adhesives and Construction Industries 70 60 Water Update (%. Besides the general increase in tack. Hydrocarbon resins based on petroleum oil derivatives are preferred for tackifying styrene–butadiene dispersions [24.e. it should be noted that a resin dispersion generally reduces cohesion to a greater extent than does a resin solution – because of the surfactants present. 8-8 Addition of tackifying resins Resins are used to improve the tack of pressure sensitive adhesives. and adhesive bond formation. 35]. This naturally occurs at the expense of cohesion and heat resistance. the surface tension of the pressure sensitive adhesive dispersion must be matched to that of the substrate to be coated (film or silicone 201 .e. modify the rheology for optimum coatability and speed. phthalates such as DOP. the proportion of thickener should always be minimized. A high resistance to flow (i.e. In this case. however. which normally increase the Tg of the adhesive polymer. precise metering and suitable selection and combination of the protective colloids and thickeners are necessary.and hydroxyethylcellulose). cellulose derivatives (methyl-. Even surfaces with extremely low surface tension. fish eyes). polyvinyl alcohols. They increase the viscosity and water retention. The tack-increasing effect of resins can be augmented by addition of small amounts of plasticizers. This product has now proven highly successful in a number of applications (including pressure sensitive adhesives. vegetable gum.2 Pressure-sensitive Adhesives Addition of plasticizers Plasticizers increase the flow properties of the adhesive film. The situation is quite different. casein. such as silicone paper and corona treated polyolefin film. In contrast to resins. A resin-plasticizer combination consequently increases the tack very effectively. The main plasticizers used are the classical plasticizers (i. polyacrylic acids.g. high viscosity) prevents subsequent dewetting and minimizes the occurrence of coating flaws (e. carboxymethyl. acrylic sealants and paints). DBP and DIDP). which is initially uniformly distributed on the surface. in high speed. amongst others. but are rarely used owing to price reasons and their somewhat lower compatibility. re-coalesces relatively quickly if its surface tension is excessively high. alginates. This results in faster wetting of the substrate surface to be bonded and consequently increases the initial peel strength. can be wetted under the uniform pressure imparted by the liquid adhesive on to the substrate during the coating operation.8. Thickening of pressure sensitive adhesive dispersions Suitable protective colloids and thickeners include animal glues. plasticizers decrease the Tg and make the polymer softer. Adipates are also suitable as polymeric plasticizers. polyacrylamides and polyvinylpyrrolidones. dextrins. has extremely good compatibility with acrylate polymers and does not migrate. Since the water resistance of polymer films from dispersion decreases with increasing addition of thickener. and in addition generally also improve the mechanical stability and compatibility of the dispersions with electrolytes and fillers. enzymatically digested starches. Particularly in the case of resins with high softening point that have a deadening action on the adhesive. Small amounts of plasticizer (2–5 %) are frequently added to the acrylic dispersions in order to obtain gentler removal. A special polymeric plasticizer polypropylene glycol alkyl phenyl ether (Plastilit 3060) from BASF. Addition of wetting agents Thickened dispersions generally have little problem wetting various surfaces. low viscosity coating systems such as modern vario-gravure where the dispersion film. In order to achieve optimum results. gelatin. addition of a small amount of plasticizer results in a lowering of the softening point. In labels made from relatively thin paper. Muenzig Chemie. Addition of fillers or pigments Fillers cause significant deadening of the adhesive. the tack can no longer be measured. or aliphatic hydrocarbons with non-ionogenic constituents. BASF AG/Corporation. i. NJ (USA). Middlesbrough (England). Zinc oxide has proven successful as an antiseptic. In contrast. BASF. non-ionogenic acetylenic compounds. for example higher alcohols. Ludwigshafen/Mount Olive (Germany/USA). sprayed directly on to the foam surface by means of an atomizer if needed. the most effective antifoam for each adhesive must be determined experimentally. or Drew Ameroid Europe. Düsseldorf (Germany). This is prevented by addition of antifoams. Heibronn (Germany).e. If necessary.. moisture-absorbent filler in rubber-based medical adhesive tapes. varies depending on the other auxiliaries present in the formulation and in addition can drop with increasing storage time. Companies which offer suitable antifoams include: Air Products and Chemicals Inc. white coloration is produced using TiO2. This is achieved by adding corresponding surfactants. which rapidly results in flaws (pinholes. fisheyes) in the coating. NJ (USA). Ashland Chemical Co. It is therefore recommended that the dilute antifoam only be added immediately before processing or. one part of wetting agent and 0.. These surfactants naturally increase the risk of foaming and in some cases increase the water sensitivity of the adhesive film. Drew Industrial Division. which results in coating defects particularly when operating at high speeds. Fine sand (SiO2) also has a very strong deadening action. which can be compensated again by a slightly increased amount of tackifier.. Even on addition of only 10 %. It should be noted that excessive amounts can impair flow of the dispersion. Ultra Additives Inc. is no longer available at the liquid–air interface where it is needed. for example. The effectiveness of antifoams. A general rule of thumb is that the amount of antifoam in initial experiments is 10 % of the amount of wetting agent. These contain virtually no filler. Aerosol OT70-PG.202 8 Applications in the Adhesives and Construction Industries paper). Owing to interaction with the auxiliaries in the dispersion. Calcium carbonate filler exhibits much . ICI Surfactants.1 part of antifoam per 100 parts of dispersion. small amounts of fillers or pigments can be added in order to increase the hiding power. Cytec) is a relatively low-foaming surfactant whose particular effectiveness as wetting agent arises due to its tendency to migrate to newly formed surfaces very quickly. The amount added should again be kept as low as possible. settle or diffuse into the polymer and thus. Boonton. Patterson. Henkel AG. even better. The antifoam may float. The sodium salt of a sulfosuccinic acid ester (Lumiten I-SC. modern medical adhesive tapes with non-woven or woven fabric as support material use polyacrylates owing to their lower skin irritation action. Allentown PA (USA). so-called wetting agents. Addition of antifoams Surfactants (emulsifiers and wetting agents) often cause foaming. it is advantageous to prepare a paste with a little water. †Akzo Nobel. USA).8. USA. if used.5 0–2 0–2 203 . Benkiser. Ontario. Philadelphia. a pigment and/or filler paste. Additives to the water. DE. one part of Calgon N (sodium polyphosphate. one part of Pigment Dispersant A (BASF).5 0. Guiding formulations 1. USA and Manchester.5–1. Avecia. Ladenburg) and 97 parts of water. UK). DE. A “wetting fluid” comprising one part of ammonia. dilution and addition of wetting agent. Wilmington. plasticizers and. Wilmington. Valboonne-Cedex. 116 36.5–8. Connecticut. Rohm and Haas France SA. Acrylic permanent paper label (resin tackified) Polymer dispersion Tackifier dispersion Defoamer Wetting agent Neutralizing agent Water Rheology modifier Application rate: 20 g solid m–2 Acrylic dispersion. NC. 60–70 % Tacolyn 1070. For homogeneous incorporation of fillers or pigments. Other preservative suppliers include Riedel-de Haën AG (Germany). 57 %† Drewplus L-108‡ Lumiten I-SC§ Ammonia (10 %) to pH 7. 55 %* or Snowtack 880G. Protection against microorganisms The risk of bacterial. aid in dispersing and also prevent the filler particles from subsequently re-agglomerating. General notes on modification The following is a suitable compounding procedure: the pH of the starting dispersion is firstly increased in order to improve compatibility. France and Cheshire. Preservatives used include formols. Charlotte. ‡ Ashland/Drew Chemical. followed by resin solution or resin dispersion. France). Troy Corporation. but this is relatively expensive. §BASF.2 Pressure-sensitive Adhesives better behavior. has proven successful. Secondary acrylate dispersions are then added. PA. NJ (USA) and Arch Chemicals (Paris.4 0. yeast or fungal contamination is naturally the greatest in the neutral or weakly basic pH range. Toronto. USA Wet wt. This pH range is in most cases established during modification as it also provides the best compatibility of the dispersion with formulation additives. such as ammonia.1–0. 65 % solids As needed for coating head Suppliers: *Hercules. Rohm and Haas. Florham Park. benzisothiazolinones (Proxel. The final step is adjustment to the processing solids content and viscosity by thickening. polyacrylic acid salts and polyphosphates. isothiazolones (Kathon . other tackifiers. to which the pigments are mixed to yield a paste.5 As required to max. USA. Canada. The smallest reduction in tack is caused by titanium dioxide. SBR used in pressure sensitive adhesives are produced by emulsion polymerization with butadiene contents typically between 25 and 45 %.5–8. Charlotte. This subsequently translates into slower line speeds and/or higher energy demand during the drying operation. 51 %* Tackifier dispersion Aquatack 6085.204 8 Applications in the Adhesives and Construction Industries 2. 50–55 %). Compared to tackified acrylic PSA. An antioxidant would be recommended for SBR applications requiring extended stability against heat exposure or oxygen attack. SBR are compatible with both commercial rosin and hydrocarbon based tackifying resins. styrene and butadiene feed rates) and ingredient feed levels (chain transfer agent. and surfactant stabilizers in tackifier dispersions can have a significant impact on the peel-shear balance of the formulated product [26]. styrene-butadiene based systems normally require significantly increased tackifier contents (up to 2 times) to achieve desired tack and peels levels. With careful control of process conditions (temperature. Arizona Chemical. softening point. when clear films with long-term UV or heat aging resistance are required. SBR based systems are primarily used in cost-sensitive paper label applications. While the hydrophobic nature of SBR promotes superior initial tack and adhesion to low energy substrates.2 Suppliers: *BASF Corporation. All-temperature paper label (non-tackified) Polymer dispersion Acrylic dispersion Neutralizing agent Ammonia (10 %) to pH 7. intermediate molecular weight. and rheology modifiers added as needed. this feature also makes them susceptible to plasticizer attack. USA.5–1 0–2 Suppliers: #Cytec Styrene-butadiene dispersions In North America approximately 5–10 % of the dispersions used for labels are based on styrene-butadiene rubber (SBR) [24]. Differences in chemical composition. Application rate: 20 g solid m–2 Wet wt. FL. 60 % Defoamer. USA . wetting agent. Since commercial SBR are available at relatively low solids contents (ca.5 Wetting agent Aerosol OT70-PG# Rheology modifier As needed for coating head Water To maximum 65 % solids Application rate: 20 g solid m–2 100 3–5 0. 63. initiator. Guiding formulation SBR permanent paper label (resin tackified) Polymer dispersion Butonal NS 166. monomers). lightly cross-linked elastomers having an excellent balance of cohesive and adhesive properties can be obtained. NC. they are not used. Panama City.8 36. the formulated adhesives have higher water contents compared to those based on acrylics. and slot die technologies are available. a roll with a different grid must be used. reliability. In reverse-roll coating. vario gravure (600+ m min–1). coating weight is found to drop off drastically above about 300 m min–1. 8-10) with 14 to 18 lines cm–1 give a dry coating weight of about 20 g m–2. Knife coaters and reverse roll coaters are traditional systems originally developed for coating solvent-based adhesives. reverse gravure (300 m min–1). coating speeds of only 100–120 m min–1 are possible with these coating methods – at application rates of about 20 g m–2. Adhesive is transferred from the pan into the recesses of the gravure roll and then on to the web. For higher production speeds. Coating head Steam Dryer Laminating station Release liner Schematic representation of PSA label coater. Meyer rod (150–250 m min–1). Gravure rolls (Fig. so short that the gravure line cells are no longer completely 205 . A gravure roll with 36 lines cm–1 gives. When high reverse-gravure coating speeds (600+ m min–1) are attempted..e. the adhesive is transferred to the substrate web after being taken up by an application roll rotating in a direction opposite to that of the web. and product quality led to lower production costs and continuation of the trend to waterbased emulsion coating technologies. For significant changes. for example. Various coating methods are used to ensure the correct amount of adhesive is applied per unit area of substrate [37–40]. If desired. High viscosity adhesives can be applied using a knife-over-roll coater. 8-9). paper stock. The blade and roll assembly are primarily responsible for metering on the correct quantity of wet adhesive and establishing a consistent. 8-9 Unwind Backing Rewind Reverse gravure was introduced by BASF at the beginning of the 1980s for pressure sensitive adhesive processing and basically consists of a blade pressed on to a gravure cylinder rotating in a pan of wet adhesive in a direction opposite to that of the web. about 10 g m–2 (in each case with an approximately 50 % solids adhesive). coating consistency.8. defect free adhesive coating. Fig. But with aqueous dispersions. the coating weight can be varied slightly by adjusting the blade position and by modifying the viscosity of the adhesive.2 Pressure-sensitive Adhesives Coating Self-adhesive labels and films are produced by coating support materials such as silicone release liner. Improvements in coating speeds. and film webs with pressure sensitive adhesives (Fig. This behavior occurs at high speeds because of the shorter residence time of the gravure roll in the dispersion reservoir – i. These systems require lowviscosity dispersions and their development in the 1960s paved the way for a major breakthrough by acrylate dispersions for mass-produced pressure sensitive articles in Europe. (b) 10–15 µm nickel layer. For example. 8-10 Portion of a gravure roll (left). which simultaneously prevents air being drawn in and results in very low air entrainment (i. providing pressure release and lubrication. Two grooves. it is possible to vary coating weight over a broader range. (d) steel base roll. Rubber parts are also built into the margin wipes to seal the side edges of the coating blade – the entire “casting box” assembly is sealed by a lateral force applied on to the sides of two margin wipes. (a) 10–20 µm chrome layer. However. Vario gravure is a substantial refinement of the standard reverse gravure method (Fig. 8-11). in PSA dispersion . even with a constant number of lines. substrate adhesive blade adjustment margin wipe out blade adjustment Fig. The side seal consists of two polyethylene “margin wipes” pressed against the polished ends of the gravure roll. low foaming). are incorporated into each margin wipe. filled and too little dispersion is applied to the web.e. if the dispersion is forced into the engraving under pressure.206 8 Applications in the Adhesives and Construction Industries Fig. 8-11 Vario gravure coating head. (c) 70–250 µm copper layer. cross-sectional schematic (right). The upper blade is additionally pressed against the gravure roll surface. application rates from 15 to 30 g m–2 can be achieved at 600 m min–1 with an 18 lines cm–1 gravure roll and from 20 to 40 g m–2 with a 14 lines cm–1 gravure roll. The flow rate of wet adhesive through the pump can also be coupled to the web speed in order to keep coating weight constant during speed changes. designed to operate without pulsation (Mohno pump). 8. 8-12 Slot-die coating head. Due to the excess pressure prevailing in the casting box (0. Uniform distribution of medium-viscosity adhesive over the web width is achieved with a special die geometry where the outlet aperture is larger at the web edges than in the center.6 bar). masking tapes and other adhesive tapes (medical tapes. resinmodified rubber solutions. but a film. adhesive substrate width adjustment of slot die opening die die lip offset adjustment Fig.e. Water based pessure sensitive adhesives can also be directly applied on to the substrate web using a slot die coater (Fig.2 Pressure-sensitive Adhesives Coating weight is controlled mainly via the pump pressure.3 billion m2 of adhesive tapes were produced in Europe in 1996 [41]. office tapes and protective films).2. not only are the recesses of the gravure roll surface filled. but is only used occasionally in Europe. About 4. i. electrical insulation tapes. are still dominant in this segment. Seventy percent of these are packaging tapes. 60–70 % of total label production). used mainly for packaging adhesive tapes. 8-12). Solvent-based. while the remainder are double-sided adhesive tapes. PSA dispersion feed line Coating weight can be easily varied over a broad range at different web speeds.2–0. household tapes.2 Self-adhesive Tapes Self-adhesive tapes are flexible substrates coated with pressure sensitive adhesives which are wound up in roll form and cut to different widths. This is the only way that a coating weight of 20 g m–2 can be maintained at higher speeds (400–600+ m min–1).8. The stringent requirements on tack and cohesion for tapes 207 . is also applied on to the roll. This method provides an impressive final coating – characterized by unusual levelness. an excess. Die coating is widespread in the USA (est. Paper backed tapes. Packaging tapes Packaging tapes are required to form the contact points necessary for box or carton closure (typically corrugated). acrylate dispersions have been used in the manufacture of electrical tapes for more than four decades. In Europe. Some foil tapes use strands of fiber reinforcement laminated between foil and kraft paper layers to improve tensile strength [24]. require coating weights in the 30–60 g m–2 range. for pipe insulation. used in North America for heating. this corresponds to a polymer demand of 180 000 tons year–1. about 4. the rest is used for consumer. However. As a result. carton sealing tapes made from oriented polypropylene and water-borne acrylic PSA are also produced. Coating weights of about 15–35 g dry adhesive m–2 are typically used. Assuming an average coating weight of 40 g m–2.208 8 Applications in the Adhesives and Construction Industries have still not been achieved by any other adhesive system in such a balanced way.5 billion m2 of adhesive tapes were produced in 1999. the adhesive is covered with a release liner to prevent adhesion to the top side of the foil and subsequent blocking of the tape roll. 25 g dry adhesive m–2 are typically used. The main requirements for this application are withstanding the continuous shear and low-angle peel forces transmitted to the tape at the carton closure. even on gentle pressure. In North America. In North America. Although acrylate dispersions have better aging resistance. The proportion of water-borne adhesives used in the European tape market is about 14 % [19]. natural rubber is predominately used to meet these requirements. Once coated. Waterborne systems are used mainly to produce carton-sealing tapes. Water-borne adhesives are mainly used for double-sided adhesive tapes and electrical insulation tapes. Of prime . Their advantage is that they can be coated on to flexible PVC films without a primer. In Europe. the use of dispersions requires a high level of knowledge of the compositions and interactions between particular flexible PVC substrates and acrylic adhesives. This means that the adhesive must have high tack and good adhesion. Anchoring of the dispersion adhesive to the polypropylene film is achieved by corona pretreatment. are constructed of 50 µm aluminum foil coated with 50–100 µm of an acrylic dispersion PSA to provide high adhesion and functionality at extreme “use” temperatures. it is necessary to use more than one dispersion type to achieve required performance levels. they have lower tack at the high cohesion levels needed. surgical. Coating weights of ca. About 70 % are used for industrial and packaging tapes. ventilation and air conditioning systems. electrical and masking tapes [18]. Foil duct tapes Foil duct tapes. such as masking tapes. Electrical tapes Flexible PVC tapes of various types are predominately used for electrical insulation purposes and to a lesser extent. Experiments have shown that the lower tack values can be fully compensated through increased positioning or “application” pressure. A release coating is not necessary. suitable dispersions must be carefully selected and in many cases. A range of support substrates are used. Coating weights of about 5 g dry adhesive m–2 are employed. etc. Here too. 45 g m–2 dry adhesive are used. anodized aluminum. Double-sided adhesive tapes Double-sided adhesive tapes or “mounting” tapes have been used to replace conventional attachment methods in a range of different end-use applications.and polyester films [24]. acrylic sheets. nails and screws). They are used on a wide variety of surfaces. for example. The central support substrate used includes non-wovens. Nonetheless. While acrylate dispersions are often used. support-free mounting tapes are also available. self-crosslinking emulsion adhesives providing crucial cohesion and anchoring to PE films have been developed especially for protective films [24. PE-. flexible PVC. Key requirements of masking tapes include adequate adhesion and then easy removability without leaving a residue – even after extended storage times or after exposure at high ambient temperatures. Coating weights of ca. dispersions having high solids contents have been advantageous to increase drying rates during the coating operation. foams and other materials and in some cases.g. the most demanding applications employ solvent based acrylates that are subsequently crosslinked chemically or thermally to achieve performance requirements.2 Pressure-sensitive Adhesives importance are plasticizer resistance screening tests on the adhesive. as an assembly aid in the automotive industry. The support material used is crepe paper of various quality and extensibility with natural rubber predominately used in the adhesive. Protective films Protective films are used to protect high-value items like painted or polished metal surfaces (e.g. PP. Masking tapes This term covers tapes for protecting surfaces during painting. in graphic arts for plate mounting and in home and office uses that previously required mechanical fasteners (e. 209 . adhesives made from mixtures of certain acrylate dispersions are highly suitable for “painters-grade” masking tapes. lacquered furniture surfaces and automotive carpets from scratching. acrylate dispersions are being used instead of the cross-linkable acrylate solutions used in the past. automobile paint finish). carried out in order to examine for undesired changes in adhesive properties due to plasticizer migration from the PVC film. In particular. In applications requiring exceptionally high adhesive coating weights (up to 100 g dry adhesive m–2). 42]. sand blasting. shipping and installation. including paper. Foam mounting tapes are especially useful because the foam provides stress distribution for increased shear strengths.8. textile fabrics. soiling and marring during manufacture. a distinction must be made between the performance at room temperature and at elevated temperatures. When assessing shear strength. adhesion permanent labels packaging tapes removable labels protective films cohesion Fig.3 Test Methods Tack. depending on the formulation. The peel strength (adhesion) is a measure of the separating force necessary to peel a label or tape off from the surface to which it was applied. 8-13). adhesion and cohesion are the three main properties required of a pressure sensitive adhesive. as well as hot-melt contact adhesives. While acrylic dispersions exhibit only a slight change in shear strength at elevated temperatures (due to internal gel structure). hot-melt adhesives tend to soften and the shear strength drops significantly.210 8 Applications in the Adhesives and Construction Industries 8. Rubber adhesives and hot-melt contact adhesives exhibit high peel values after only a relatively short contact time. Depending on the use. The shear strength (cohesion) is the ability of a pressure sensitive adhesive to withstand applied forces or loads. 8-13 Adhesion level of self-adhesive articles. i. meet the usual demands. Good shear strength is required when labels are stuck to curved surfaces and for processing purposes. A pressure sensitive adhesive with good tack forms the contact points necessary for adhesion of the tape or label after only brief contact with a substrate. The term describes the strength of adhesion or “grab” to a surface. different requirements are made of pressure sensitive adhesives with respect to adhesion and cohesion (Fig. Acrylate compositions require a few hours before achieving full adhesion. . The tack is the ability of a pressure sensitive adhesive to adhere immediately to a surface. Solvent based rubber adhesives can have very good tack. slitting and to minimize edge-ooze of roll products. Pressure sensitive adhesives designed having adequate room temperature shear strengths should also be formulated to resist failure at higher service temperatures. die-cuttability. Acrylate solutions and dispersions.2.e. after a certain dwell or bonding time. 44].2 Pressure-sensitive Adhesives A protective film must be removable without leaving a residue. By contrast. Conditioned test strips with a certain width are rolled on to test panels using a roller with a defined weight. contact pressure and temperature. therefore. In the first phase of the test. However. only individual. which are different in each measurement method [27. contact formation and separation. the bonding time is a maximum of 1 min in the PSTC test.e. or alternatively at 90°. One common feature of these established test methods is that they are all destructive measurements. For example. must have very low adhesion. depending on the applied pressure. a packaging tape must stick immediately and durably. high adhesion is needed in order to ensure rapid bonding to the various surfaces. even after long bonding times. i. During the second phase. There are various standards for the peel strength test which differ essentially through the type of cleaning of the test panels and the bonding times. Muny [43]. It is conceivable to carry out nondestructive measurement of an adhesive joint using nuclear magnetic resonance methods (NMR imaging). For better comparison of the properties of pressure sensitive adhesives. while the cohesion need only be sufficiently high to avoid formation of adhesive filaments during label stamping and stripping operations. are influenced by the test conditions. and adsorbate layers. in which the force which occurs on peeling the adhesive layer off from a substrate is measured. 8-14.P.e. But in both cases. Other important influencing factors are contact time. a bond is formed on contact of pressure sensitive adhesive with the substrate. Removable labels have low adhesion and sufficient cohesion for removal. Contact formation is.e. such as surface tension. 211 . determined by mechanical behavior and surface properties. the bond is separated under the action of a tensile force. in conjunction with high cohesive strength. and high cohesion. Peel strength The most common adhesion test is peel strength testing [27]. Since the dwell time has a significant effect on the level of adhesion. with the bond being deformed.8. Numerous methods are available for quantifying these different property profiles. different values are obtained by the two methods mentioned [27]. viscous flow and wetting of the substrate with the adhesive. Stainless steel with a surface of defined roughness is used in method PSTC-1 while glass is employed in the FINAT method. standardized test methods have been developed by various organizations. must have both very high adhesion. whose number and size increase during the contact phase due to elastic deformation. i. small points of adhesion form. the peel measurement is carried out in a mechanical testing machine at constant peel rate and at a peel angle of either 180° as in Fig. even after brief contact. i. such methods are still under development [45]. and 20 min and 24 h in the FINAT method. including: – FINAT – Fédération Internationale des Fabricants et Transformateurs d’Adhésifs et Thermocollants sur Papiers et autres Supports – PSTC – Pressure Sensitive Tape Council. roughness. In paper labels for permanent bonding. Both processes. These and other PSA test methods were compared in a review article by R. 30. Initially. a bonding time of 24 h. He has shown that the peel strength is dependent on the moduli of elasticity and the thicknesses of both the adhesive and the support.6 1h 5. according to W. corresponding to FINAT test method 1 [27]. and the interaction forces at the adhesive-substrate interface [27]. the peel strength increases with increasing peel rate.5 24 h 8.R. 51]. film) test substrate (steel. At a given temperature. glass.F. a measurement is therefore often taken after. 10 min max. 8-15).0 30 min 4. Druschke [27]. for example. Besides numerous other authors [46–49]. Peel strength also depends on temperature and peel rate. on the peel angle.A. the main contributor to understanding of the very complex peel mechanism in self-adhesive tapes is Kaelble [50. Even after a bonding time of 1 h. 8-14 Peel strength at 180° [27].E. 8-15 Peel strength of an acrylic pressure sensitive adhesive depending on the dwell time. 1 min FINAT 20 min 24 h clamp Fig.3 3h 5.212 8 Applications in the Adhesives and Construction Industries clamp support substrate (paper. 4001 PSTC-1 dwell time max. At low peel rates the viscous properties are dominant. Besides the immediate value. . polyolefin) adhesive method A.0 Fig. the wetting process is not complete in all cases (Fig. polymer moledwell time peel strength in N / 2 cm 10 min 4. 9. IA 319-337-8247) specifies a loop tack test and within their manual. probe tack. in which peeling is carried out at an angle of 90° without formation of a loop [55]. The best known tack measurement methods are quick-stick. Tack Tack is defined as the limiting value of the adhesion as the contact time approaches zero. and so the polymer modulus or “stiffness” increases. 8-16. includes a host of useful TAPPI and ASTM methods for testing paper and plastic film substrates used in pressure sensitive labels. as shown in Fig. the peel strength will decrease as well – at a constant peel rate [52]. 213 . brought into contact with a glass plate and then immediately peeled off again.8. The Tag and Label Manufacturers Institute (TLMI. In the quick-stick method corresponding to FINAT test method No. glass. to disentangle and to dissipate energy. 54]. At high peel rates the elastic properties of the polymer network predominate.2 Pressure-sensitive Adhesives cules have time to slide past one another. Zosel tack and rolling ball [27]. which still plays significant role in forming a qualitative practical opinion [27]. This FINAT method differs from the PSTC (PSTC-5) quick-stick method. Iowa City. a test strip is formed into a loop. With this aim. All these methods are ultimately a refinement of the subjective finger test. polyolefin) Fig. respectively. Since the mobility of polymer chains increase with increasing temperature. a number of methods have been developed [53. clamp support substrate adhesive clamp support substrate adhesive test plate (steel. the polymer molecules are not able to disentangle. Targets for tack measurements are shortest possible contact time and lowest possible contact pressure. 8-16 Quick-stick tack measurement [27]. Zosel [30–31] for fundamental studies [58–63] on the theory of adhesion operates on a similar principle to the probe tack method (Fig. The instrument allows measurements from –50 °C to 200 °C.2 cm2 means that only small areas of the adhesive layer are measured. the very small ram contact area of only 0. Air inclusions in the adhesive layer can result in incomplete wetting of the piston surface [27]. The shortest contact time that can be set is 0.214 8 Applications in the Adhesives and Construction Industries The advantage of the quick-stick methods compared with other tack measurement methods is that the test can be carried out in any mechanical test machine with only minimal contact pressures. Disadvantages of the method include a relatively long contact time. 8-17 Polyken Probe Tack method [27]. surface tension of the test piston. contact force. contact time and approach speed of the tack experiment. In addition. 8-18). the peel angle is not constant in the FINAT method. a cylindrical ram with a diameter of 0. different contact times within a test area and different contact areas.5 cm is pressed from below against the adhesive layer at a defined pressure and speed and removed again at a defined speed after a certain contact time (see ASTM D2979-71). Contact times in the region of 0. In this method. 8-17). With the aid of an electric motor. substrate adhesive weight weight support support piston Fig. The fact that the measurements can be carried out simply and quickly and the conditions varied easily and widely is advantageous. This method also allows basic studies with variation of other key parameters. An instrument developed at BASF by A. known as the Polyken probe tack method (Fig. . the sample platform within the test chamber is moved against the piston and then away again in the opposite direction after contact. The piston is connected to a piezoelectric force transducer. Variable parameters are the piston area. A widespread tack measurement method is the probe tack method proposed by Wetzel [56] and refined by Hammond [57]. The polymer to be tested is applied to a flat steel plate in a defined layer thickness and dried. However. Moreover.1 s are possible using this method. a very complex instrument is necessary. 65].01 s. such as separation speed. and composition of the adhesive layer [64. For adhesive layers whose tack is not too low. as shown in Fig. The adhesive values are relatively dependent on the viscosity and on the thickness of the adhesive layer [27]. The distance traveled before the ball stops is a measure of the tack. the rolling ball test requires simple equipment and is easy to carry out. The meaningfulness of the method is also impaired by the following characteristics: The surface of the ball can change its nature even during the first rotation. Fig. because of transfer of traces of adhesive – ball contamination. 8-19. In accordance with PSTC-6. The main difference to the other tack measurement methods is the fact that the rolling ball method does not measure force.2 Pressure-sensitive Adhesives force transducer rod test chamber sample steel support electrical motor raises and lowers test chamber Fig. 8-19 Rolling ball method [27]. 8-18 Zosel tack measurement. In contrast to the other tack measurement methods mentioned above. the rolling ball tack method may be used [66].8. 215 . a steel ball of defined diameter is rolled down an inclined plane at a certain tilt angle on to the adhesive test strip. the scatter is lower for methods with longer contact times. 8-21 Shear strength measurement. 8. Prerequisites for such results are very uniformly defined test specimens and exact compliance with defined test conditions [27].3 N/2 cm 10.9 J m–2 3. The standard surface used is glass.3 N cm–12 13. 8-20 Statistical evaluation of the test results [27]. 8-21).67 J m–2 1. a 12. depending on the test. Shear strength The cohesive properties of a pressure sensitive adhesive are generally determined by measuring the shear strength.9 cm 0. .5 × 12. Apart from the very low scatter in the quick-stick method.24 N cm–12 4.2 N/2 cm 11. Fig.46 cm 8 5 3 11 34 38 Fig.5 mm adhesive contact area on corrugated or stainless steel is subjected to a 1 kg load and the time to adhesive failure is recorded. The scatter in the values after exclusion of outliers is 3–38 % of the mean. Test Number of samples Mean Standard deviation Coefficient of variation (%) Peel strength after 10 min Peel strength after 24 h Quick-stick Sample tack Zosel tack Rolling ball tack 25 42 50 43 25 50 3.54 N/2 cm 0. Corresponding to FINAT test method No. the shear strength is the time required for a certain area (25 mm × 25 mm) of a self-adhesive material to slide off a standard surface in the parallel direction to the surface with a load of 1 kg (Fig. In PSTC-7.8 N/2 cm 9.34 N/2 cm 1.31 N/2 cm 0.216 8 Applications in the Adhesives and Construction Industries Reproducibility of adhesion measurements Figure 8-20 shows a statistical evaluation of tests on a commercially available adhesive tape. juice pouches and boil-in-bag meals where oxygen barrier. In the packaging industry. Depending on the sector of industry and product class. and in many cases more. where plastics are melted and extruded in thin layers through an extrusion die.8. crosslinking polyurethanes. solvent-containing adhesives have already been replaced by environmentally friendly water-borne adhesives in a number of applications. drying. to boiling water) are also important. such as cheeses. distinct layers in the total construction. snack foods (potato chips). A wide variety of flexible laminates can be produced on fast. high-performance laminating machines using suitable adhesives.3 Laminating Adhesives 8.3 Laminating Adhesives Laminating adhesives are used to permanently bond various types of substrate webs together in industrial manufacturing processes. Materials with specific properties are utilized in each layer which altogether impart the performance attributes needed for the particular application. and oil or fat barrier characteristics are required.1 Flexible Packaging The process of laminating single-layer web materials to give flexible multilayer film structures has been an established method for many years. water-based polyurethanes – the latter have been increasing in importance in recent years because of environmental pressures. for example. water and heat resistance. Multilayer structures are widely used in packaging of foods.g. 8.3. bacon. for example. consists of polyethylene so that the pack is heat-sealable. and two-component. Alternate production techniques include extrusion coating and co-extrusion. glossy film lamination and technical lamination applications such as furniture assembly. and a polyester film for mechanical strength and good printability. The choice of adhesive depends on the type of film to be bonded and on the end use application. These multi-layer laminated products are generally known as laminates and can consist of three. Film laminates are produced by coating adhesive on to one side of the primary film. In food packaging. a distinction is made below between film-to-film lamination for flexible packaging. and then laminating a second film on to the dried adhesive layer under 217 . Therefore. The term lamination has gained general acceptance for this industrial process. Common laminating adhesives include solvent containing and solvent free. Polymer dispersions The prime advantage of aqueous polyurethane and polyacrylate dispersions over solvent-containing systems is that recovery or disposal of significant amounts of solvent is unnecessary. The multilayer film for vacuum-packed coffee. an aluminum foil layer for aroma retention and light barrier. food regulations and the resistance of the adhesive (e. potential for residual solvent traces in the adhesive and subsequent migration into food are also major concerns. dispersions are employed as the only adhesive component. If this time is exceeded. Application rates between 1 and 3. but also significantly increases adhesion to most films [68]. Achievable adhesion levels with PU dispersions are in many cases higher than with acrylates. The majority of the adhesion increase is attributable to the formation of hydrogen bonds predominantly formed between OH and NH groups and polar groups of the individual substrate. Adhesive purchases into flexible packaging applications (including paper and plastic laminates) totaled in USA approximately 150 million dollars in 1997 [67]. PU can be crosslinked for use in .5 g dry adhesive m–2 are typical. higher pH result in shorter pot-lives. pH must be maintained between 3 and 4.218 8 Applications in the Adhesives and Construction Industries heat and pressure. depending on the film or web type the adhesive used. Additionally. covalent reaction occurs to a small extent owing to steric factors. water-dispersible polyisocyanates. from 3 to 5 % of a suitable curing agent should be added – e.g. 8-22 Reaction of a two-component aqueous lamination adhesive (acrylate dispersion + water-dispersible triisocyanate) with corona-pretreated films. Fig. A mixture of polymer dispersion and polyisocyanate has a maximum processing time of about 5–7 h. In low-performance laminates. however. the laminate adhesion and hence peel strength drops. If additional boiling resistance or sterilization capability is required. Polyurethane dispersions adhere strongly to a broad range of corona-pretreated plastic films. As mentioned above. Addition of curative of this type results in a significant increase in adhesive strength. Figure 8-22 shows the reaction of a trifunctional polyisocyanate with an acrylate polymer and the OH groups of a corona-pretreated film. The water-dispersible polyisocyanate does not just act as crosslinking agent yielding increased heat resistance.. Multiple layer structures are typically built up by applying further adhesive and film layers at subsequent coating and laminating stations. peel strength (i. adhesive pot-life issues are eliminated because of the absence of a reactive second component. therefore. a special form of film lamination. eliminating the need for additional adhesive. laminates can be used immediately after production – thus. or used alone to produce medium-performance laminates.3. bleaching and moisture). cohesive failure. thus. and adhesive failure to either of the film surfaces involved (including printed layers). Due to the rapid development of peel strengths. predominates. Examples include book covers. oriented polypropylene (OPP) films with a pre-applied heat-sealable adhesive layer are thermally bonded to the substrate.e. possibilities include film tear. The test is usually carried out with 15 mm wide test strips where the film layers are peeled apart using a tensile tester. Moreover. laminate adhesion) is typically measured. The peel strength is specified in N/15 mm. 219 . 8. aliphatic polyisocyanate. Other methods besides film lamination are used to “finish” print products. The process improves the brightness of the printing inks and protects the printed material from external influences (e. the aim is to form the strongest possible laminate. advertising and packaging materials. scratching. Glossy film lamination is used to a large extent in Europe but in North America. Guiding formulation Two-component polyurethane laminating adhesive Wet parts Dispersion Crosslinking agent Polyurethane dispersion (40 %) anionically stabilized Water-dispersible.g. A specially designed high performance acrylic dispersion that does not require addition of crosslinking agent and which yields excellent green strengths has been developed [69].2 Glossy Film Lamination Glossy film lamination involves the covering of printed paper or board products with an optically clear. including both physically and chemically cured coating systems. In either case. In thermolamination. it can take as many as seven days to achieve final laminate peel strengths (by chemical reaction of isocyanates with hydroxyl groups). NCO content approximately 18 % 100 3–5 Test methods With film laminates made by adhesive bonding. making it necessary to store laminate rolls temporarily prior to downstream converting. eliminating the need for inventory storage. The test report should furthermore indicate the failure mode. Moreover. high-gloss plastic film.3 Laminating Adhesives higher-end applications. called “thermo-lamination” [70].8. low initial “green-strengths” after forming the laminate bond are common. The peel strength in the region of a heat-sealed seam is known as the seal seam strength. Crosslinking takes place at room temperature using a reactive ketone-dihydrazide chemistry designed into the polymer dispersion (Fig. However. However. Fig. A considerable advance was made. such adhesive films would then be too soft and would result in partial separation between film and board during subsequent bending and embossing operations. however. self-crosslinking dispersions with shelf lives equal to those of standard polymer dispersions were developed. 8-23). One-component. on film formation. 8-23 Chemical crosslinking reaction of a one-component acrylic adhesive. The polymer particles contain co-polymerized carbonyl groups which. solving the pot life problem. Efforts to eliminate solvents to comply with more stringent emission regulations likewise here resulted in the use of aqueous polymer dispersions. the limited pot lives of two-component systems require increased care from the processor. A similar process also occurs between corona-pretreated polypropylene film and the emulsion adhesive thereby significantly increas- . Wetting and flow of the adhesive on the film are the main prerequisites for high clarity lamination. This requires the polymer dispersion adhesive layer to be as plastic and film-forming as possible during the lamination process. react with hydrazide groups of the water-soluble acid dihydrazide to form hydrazone. two-part solventcontaining polyurethanes with crosslinking agents. Embossable paper board laminates were only made possible by high adhesion. after the film has formed. with the development of aqueous acrylate-based polymer dispersions which crosslink after evaporation of the water. Increased cohesion strength results due to both inter-particle and intraparticle crosslinking reactions. Lamination is frequently still carried out using solvent-containing adhesives.220 8 Applications in the Adhesives and Construction Industries High-gloss film laminates have been available in Europe since the 1960s. as evidenced by pale strips or spots in the otherwise high-gloss. 8-18). Resistance to Delamination After allowing sufficient crosslinking time. This can be carried out using the Zosel tack measurement tester described in Sect. Domke u. which can then react with the dihydrazide crosslinking agent.4 corona treated PE film unteated PE film (according to W. This enables measurement of the separation work of adhesive layers throughout the course of drying.2. Steinke) 0.2 1900 1800 1700 1600 1500 wave number in cm-1 ing the adhesion strength of the laminate. Steinke [71]. if possible dark.6 0. In practice. in order to maintain film-to-film bonding [72]. Formed and embossed laminates are classified as “failures” if the film is observed to have delaminated in the high-stress zones. As shown in the IR spectra for the PE films in Fig. according to W. the lamination is formed. H. this means that bending and embossing of freshly produced board laminates should only be carried out after this time period.3 (Fig.-D. 221 . 8. Domke and H.3 Laminating Adhesives Fig. absorption 0. Test methods Drying The progress of crosslinking over time can be recorded by measuring the surface tack. additional carbonyl and carboxyl groups are observed on the film surface after pretreatment [71]. 8-24. 8-24 Infrared spectrum of polyethylene films.8.-D. embossed and evaluated after certain time intervals. lamination. The measurement of peel strengths after drying shows that significant crosslinking occurs after only approximately 2 h and is complete after about 48 h.8 C=O COOH 0. insufficient drying. hot-melt. In North America. or coalescence of the adhesive during lamination. and water-based dispersion adhesives are typically used in producing technical laminates for the furniture and automotive industries. dashboards. the total automotive adhesive market is estimated to be roughly $ 200 million (in 1997) [74].3 Furniture and Automotive Solvent based. After the adhesive has dried. On cooling. which make a significant contribution to the internal strength.222 8 Applications in the Adhesives and Construction Industries Yellowing High-quality. Accelerated tests can be carried out. door interior panels) [73]. 8-26). The polyurethane adhesive is applied using a spray gun. recrystallization produces a rapid increase in strength. The market share for aqueous dispersions is about 40 %. The polyester–polyol component can be designed to form crystalline structures (Fig. Evident “graying” is an indication of tiny air bubbles between board and film. been established. The cohesive polyester-polyol crystals of commercially available PU adhesives melt at about 50 °C – the lamination adhesive is thermally activated and becomes soft and capable of heat-sealing (Fig. Optical microscopy has also proven useful in confirming defect types in laminates. the assessment of surface film gloss is best carried out visually. Gloss No reliable test methods for measuring the surface gloss of film laminates have. 8. and the fiberboard elements can be stacked. for example. In addition to adhesive. which provide excellent adhesion and extremely high bond strengths to a range of substrates. One-component acrylic adhesives perform very well in this respect.3. using a Q-UV type exposure instrument with a radiation spectrum and intensity matched to that of natural sunlight. During cooling. This is necessary to counter the re- . These may be caused by inadequate application of adhesives. while conventional solvent-containing two-component polyurethane adhesives yellow after a relatively short exposure time. They are then pressed with the decorative sheet at 60–80 °C. the behavior of the top film layer and underlying paper and printing should also be evaluated by including appropriate control samples light exposure tests. 8-25). for example in a membrane press. The main products are “heat-activatable” polyurethane dispersions. After polymerization water is added followed by solvent removal. the polyester–polyol segments recrystallize. in which the polyurethane dispersion is usually mixed with a reactive crosslinking agent. This effect is utilized in furniture lamination. As such. a blocking-resistant film forms.g. durable laminates are expected to maintain print color and gloss levels even after prolonged light exposure. so far. Polyurethane dispersions are secondary dispersions typically produced by polymerization of isocyanates and diols in organic solvent. Important applications are furniture lamination (lamination of medium density fiberboard to decorative sheeting) and the lamination of moldings for interior automotive parts (e. resulting in a rapid increase in the internal strength of the adhesive film. 3 Laminating Adhesives Fig. covery forces in the thermoformed decorative sheet which are effective in the first minutes after pressing. by contrast.8. 8-26 Differential heat flow measurement of a water-borne PU adhesive. Fig. The reversible melting of the polyester-polyol segments is the physical basis for the thermal activation ability. 8-25 Crystalline structures of a polyurethane adhesive. with the final strength only being achieved after days. The increase in cohesion due to the crosslinking reaction of water-dispersible isocyanate is. The possibility of heat activation is a very important ad- 223 . a slower process. the addition of crosslinking agents improves adhesion and water resistance and increases the heat resistance. these were unsuitable for the new PVC floor-coverings on the market. It is also an example of switchable properties of polymers. vinyl composition tile (VCT). although this also results in a reduction in heat resistance. Leverkusen. These contact adhesives had to be applied to both . The main driving force for the development of modern floor-covering adhesives is the need for reduced volatile organic content (VOC).224 8 Applications in the Adhesives and Construction Industries vantage of polyurethane adhesives. Though there are regional differences. where heat is the switch. ceramic and parquet. However. felt backed vinyl.* or Dispercoll U 53§ Water-dispersible polyisocyanate Wet parts 100 5 Suppliers: *BASF AG. for which solvent-containing polychloroprene adhesives consisting of 75 % of organic solvents and 25 % of polychloroprene and resins were used. and various vinyl and polyurethane backed carpet tile products. Germany Test methods The static peel strength of the laminate made from PVC furniture sheet and MDF is assessed visually for delamination after storage at elevated temperature. Guiding formulation Two-component polyurethane dispersion for furniture lamination Dispersion Crosslinking agent Luphen D 200 A. homogeneous vinyl sheet. reducing emissions of organic solvents is a worldwide consumer driven trend based on environmental and health concerns (sick building syndrome). In Europe at the beginning of the 1960s. are not included here. §Bayer AG. flexible floor-coverings (such as linoleum) were bonded using alcohol-soluble resin adhesives. 40 %. The reactivity of the crosslinking agents is reduced by various methods so that an adequate processing time is available. Mixing with other acrylic dispersions allows the properties to be modified and the costs of the adhesive to be reduced. rubber.4. In contrast. such as natural stone. Germany. Formulation modifications The addition of suitable resin dispersions and small amounts of plasticizer enables the thermal activation temperature to be reduced. These include secondary and unitary backed carpets. Ludwigshafen. The crosslinking agents used are water-dispersible triisocyanates. Rigid coverings. carbodiimides and polyaziridines.4 Construction adhesives 8. 8.1 Floor-covering Adhesives The term floor-covering adhesives denotes all materials for laying flexible floor-coverings. Polychloroprene adhesives develop their bond strength through recrystallization of the elastomer from solution. which were laid after the solvent had evaporated. A severe disadvantage of contact adhesives with a solvent content of 50 to 70 % was the emission of large amounts of solvents.e.4 Construction adhesives sides. Although plasticizers are not solvents in the sense of TRGS 610. a film-formation phase occurs in which the polymer film. Poor ventilation and the presence of an ignition source resulted in explosions. Adhesives formulated in this way have proven adhesive properties and are solvent-free substitutes as defined in the Technical Rules for Hazardous Materials. post-flow of the polymers on to the substrate surfaces results in an increased contact area and consequently in an increase in adhesive strength. At the beginning of the 1970s. During evaporation of the water. solvents. The final strength is then achieved by two processes occurring in parallel: Firstly. has particularly high tack and low cohesion. The adhesive consisted of 40 parts of Acronal 80 D (50 %). and the bond strengths which could be achieved for PVC floor-coverings corresponded to the level of polychloroprene contact adhesives. the tackifying resin solution was replaced by a resin melt.8. The next generation of floor-covering adhesives was developed in 1994. This technique was soon also used for bonding high-quality carpeting. The absence of the action of these two proven starting materials was compensated by a larger proportion of the softer and tackier acrylate dispersion Acronal A 200 or Primal CA-187 (see guide formulation 2) [76]. could not be corrected once laid. rapid growth commenced for back-coated textile floor-coverings. 40 parts of chalk and – to improve the wet tack – 20 parts of balsam resin solution (70 % in toluene). In these. plasticizers and resins were deliberately omitted. 225 . burns and even fatalities. In these. the polymer particles are initially swollen by the resin solution. secondly. TRGS 610 [75]. At the end of the 1980s. solvent-free floor-covering adhesives were produced for the first time with Acronal A 323 in combination with a plasticizer. further advantages of the new type of adhesive were: – application of adhesive to one side only – the floor-coverings could be corrected – good aging resistance – fresh adhesive residues could be removed from the floor-covering and tools using water Solvent based polychloroprene adhesives have a different setting mechanism compared to water based flooring adhesives. A precise laying technique was vital as the floor-coverings. The first polyacrylate dispersion for the production of aqueous floor-covering adhesives became available in Europe in the mid 1960s. Resins were omitted because the usual abietic acid derivatives are odor carriers. due to the residual solvent. evaporation of the residual solvent and recrystallization of the small and rigid abietic acid molecules increase the cohesion of the polymer film to its final strength. which were also bonded using one-side adhesives. they are nevertheless low-molecular-weight substances with a certain vapor pressure and are consequently a source of emissions. In addition to significantly reducing the risk of accident. i. The solvent content was only 6 %. to the back of the floor-covering and to the floor. In the case of emulsion adhesives. In North America reductions in solvent levels in floor-covering adhesives have been essentially driven by environmental and VOC concerns.6 billion square meters. These adhesives are typically formulated employing non-carboxylated. the long-term total emissions of volatile organic compounds (TVOC) to be determined after 240 h (consumer protection). workplaces and hospitality facilities are installed employing specially designed or multipurpose adhesive systems. Other state agencies are expected to implement similar solvent and VOC criteria in years to come. Flooring mastics based on non-carboxylated SBR HSL are employed primarily in carpet and mineral fiber or felt-backed vinyl glue-down applications over most common sub-floor surfaces. tack-strip). in floor-covering adhesives from approximately 150–200 g L–1 to approximately 50–70 g L–1. Total North American carpet consumption in 1999 was approximately 1. founded in Germany) at the beginning of 1997. and fillers as the primary components. Rule 1168. to reduce solvent levels. Carefully selected resin–oil systems are employed for both cost and property reasons (early wet tack . split between two main sectors.226 8 Applications in the Adhesives and Construction Industries The adhesive formulated in this way has very low emissions as defined in the requirements published by the Association of Emission-Controlled Laying Materials (Gemeinschaft Emissionskontrollierter Verlegewerkstoffe. acrylic copolymer based floor-covering adhesives are employed in direct vinyl contact applications where plasticizer resistance is required. which enables firstly. Residential carpets are typically installed using glue-less installation techniques (e. surfactant. such adhesives were formulated with resin solutions based on hydrocarbon solvents (e. hospitals. Such SBR based adhesives are not recommended for “unbacked” vinyl (PVC) applications due to plasticizer migration from PVC to the adhesive and bond loss issues. The main constituents of the SBR HSL based flooring adhesive are the resin–oil blend. For all classes the maximum emission of carcinogenic compounds after 24 hours has to be less than 10 µg m–3. Corresponding to the TVOC after 240 h. These regulatory changes necessitate a further shift from solvent-rich adhesive systems towards water-based adhesive technology. Environmental pressures led to near elimination of solvents and plasticizers in the 1990s and introduction of increasingly lower VOC adhesives made with increasingly higher viscosity “naphthenic” oils. specifically non-exempt VOC. EC 2 low emissions (500 to 1500 µg m–3) and EC 3 not low emissions (TVOC >1500 µg m–3). The emissions are measured using a chamber test method (see Test Methods). hydrocarbon resin-oil blends. high-solids. styrene-butadiene lattices (SBR HSL). three emission classes are defined: EC 1 very low emissions (TVOC <500 µg m–3). but are based on a voluntary self-commitment by the member companies for processor and consumer protection. In the past. In March 2001. volatile carcinogenic (suspected or proven) constituents to be identified and measured after 24 h (processor protection) and secondly. the California South Coast Air Quality Management District (SCAQMD) approved a proposal.g. carpets in commercial installations including schools. These requirements have no legal foundation. residential (75 %) and commercial (25 %). Conventional “felt” backings provide an effective barrier to plasticizer migration. retail establishments. latex and filler (see guiding formulation 1).g. In contrast. However. mineral spirits) and/or plasticizers. High solids content styrene butadiene (HSL) and naphthenic oil based flooring adhesive for carpet and felt backed vinyl floor-coverings with emissions satisfying CRI Green Label TVOC requirements. too much filler or too little resin and/or oil will result in inferior properties. The method employs a small chamber test apparatus described in ASTM D-5116. formulation technology based on high solids content styrene butadiene lattices and naphthenic oils are widely used in the market place. Floor-coverings are bonded using an application rate of about 250–500 g m–2. legging or webbing. In North America. Like many other SBR based adhesives. Not surprisingly. Guiding formulations 1. Excess water will result in slower drying. respectively. initial or “green” strength. high performance adhesives for carpet and felt-back vinyl floorcoverings. 24-h emission rates from adhesives must be <10 mg m–2 h–1 for TVOC. defined as the Green Label Program in North America. HSL based flooring mastics include in-can and dry-film preservatives as well as an antioxidant package to ensure long-term performance. Alkali sensitive emulsions (e. In the mid 1990s. TVOC and formaldehyde are quantitated employing thermal desorption GC–MS and HPLC techniques. For CRI Green Label certification. 20 % KOH) is added to neutralize the rosin acid and to achieve sufficiently high pH so that when the non-carboxylated HSL is added. The rosin acid and non-ionic surfactants in this formulation serve to stabilize the oil in water emulsion during compounding and to provide end-product in-can stability. and <0. Latekoll D) are added for thickening purposes. Caustic solution (e.g.4 Construction adhesives development. 227 . <3 mg m–2 h–1 of 2-ethylhexyl alcohol. clay/latex ratio and resin/latex ratio. The key parameters to control are formulation water content. Webbing and bond strength are also sensitive to formulation latex content. Urea can be employed to achieve freeze-thaw resistance (low molecular weight alcohols and/or glycols can also be considered). final bond strength. typically in the order of 10–15 %. pH shocking effects with coagulation are avoided. and probably the need for more “water sensitive” thickeners. The total volatile organic content (TVOC) is a key property of floor-covering adhesives.g.8.05 mg m–2 h–1 for formaldehyde. depending on the desired adhesive cost structure. Low TVOC products have evolved to meet the CRI Green Label requirements and to provide cost-effective. Such adhesives are not recommended for homogeneous or solid vinyl sheet goods where plasticizer migration is a concern. the Carpet and Rug Institute (CRI) introduced a voluntary TVOC specification for floor-covering adhesives. aging resistance and low VOC). Clay is added for reinforcement purposes and for cost–performance optimization. Floor-covering adhesives made from water-based polymer emulsions contain approximately 10–20 % dry polymer in both European and North American systems. GA. 300 g m–2). §Rhone-Poulenc. and thickener are then added to the resin emulsion in the order indicated above.7 Hydrocarbon resin Neville LX 1200* Rosin acid Melhi 2. Germany. USA. Wrens. ‡‡Omya. Ludwigshafen. These methods. The clay.c.2 Surfactant Igepal CO-897 (70 %)§ Surfactant Igepal CO-530 0.9 Thickener Latekoll D 2 %** Resin melt Gum resin WW: Plastilit 3431 = 8:2 16. Very low emissions corresponding to the requirements of the German association of Emission-Controlled Laying Materials (GEV) Wet parts Dispersion Acrylic dispersion 24. after a certain curing time at room temperature or 60 °C.0 Chalk Ulmer white XM‡‡ 10. Germany.0 Plastiziser Plastilit 3431** 0. USA. urea and KOH solution are slowly added under mild agitation to form an emulsion.4 Neutralizing agent Potassium hydroxide (2.M.4 2. Germany. are fundamentally quite similar to methods developed in Germany through a .0 Naphthenic oil Tufflo 1200‡ 0. SBR. Drafts of European test standards for measuring peel and shear strengths of floor and wall coverings were submitted for approvals in early 1999 by Technical Committee CEN/TC193. **BASF. PA. Cologne.2 12. Wilmington. stir until homogeneous.0 4.7 41. after 20 min the carpet or vinyl is laid and pressed down at room temperature. the floor-covering is peeled off at 90° angle using a tensile tester. §§ Erbsloeh. USA.1 Anti freeze Urea (50 %) 1. NJ. However. and. referred to as prEN 1372 and prEN 1373 respectively. USA.4 Filler Huber 95 (70 % clay slurry)# 20.228 8 Applications in the Adhesives and Construction Industries Wet parts 9. Huber Corp. USA. methods are under development by ASTM committee D14.4 HSL dispersion Butonal NS 104 (71 % s. 2. Cranbury. Surfactant. Germany Test methods North American industry standard test methods for floor-covering adhesives are currently not available. Carpet Adhesives. NC. ‡Lyondell Lubricants.70. Pittsburgh.0 Resin Poli melt 15§§ Total 100 Suppliers: *Neville Chemical Company.2 Antifoam Agitan 282†† 0. As a guiding method for evaluating carpet to plywood peel strength the adhesive is troweled on to plywood (application weight ca. ††Münzing Chemie.5 Dispersant Pigment dispersant NL** 42. DE. †Hercules Incorporated. TX. USA. Houston. then cool to 95–98 °C. Krefeld.)** 3. Heilbronn. Charlotte. # J..12.5 %) 8.9 Thickener Latekoll D (pH adjusted 8 % solution)** Total 100 Procedure: Add resins to oil at 140–150 °C. preferably using a fixed weight roller (e. 8-27 Measurement of peel resistance. 2. 50 °C) can also be evaluated using variations of this general method. Adhesive areas of 1000 mm2 (ca. After a storage time under standard laboratory conditions.27). a 5 cm × 30 cm floor-covering strip is laid on to the adhesive bed and pressed down. water resistance. and accelerated oven aging (e. According to regional requirements. the adhesive is applied to plywood. The shear 229 .g.5 cm × 5 cm) are produced on plywood or other cementitious substrates using a template and trowel.g. after a certain “open” or evaporation time. and adhesive and raw material producers. per unit width of floor-covering. 1 N mm–1). Fig. The peel forces which occur during this operation are measured and specified in N mm–1. German test standards and specifications for peel and shear strength discussed below are summarized in DIN 16860 for PVC floor-coverings and in DIN 53269 for textile floor-coverings. cement board or other substrate using a trowel spreader and. Peel resistance The peel resistance is the force. which results when peeling-off a bonded sample perpendicular to the original adhesive bond line.g. After a storage time under defined standard laboratory conditions. According to DIN 16860. Other factors such as early bond strength development. official test institutes.4 Construction adhesives collaboration between floor-covering manufacturers. Shear strength The shear strength is the force per unit area which results in fracture of bonded samples parallel to the bond joint. the average peel strength must have a certain minimum value (e. 5 kg).8. 8. the floor-covering is removed parallel to the adhesive join at a defined speed using a tensile testing machine. then the floor-covering is laid on to the adhesive area and pressed down. the floor-covering strip is peeled perpendicular to the adhesive join at a certain speed using a tensile testing machine (Fig. For this reason. the German Association of Emis- . 30. After exceeding the open time. 0. As with green strength development. Depending on drying conditions and adhesive composition. Typically. which occur during this operation are measured and specified in N/5 cm strip. 60 and 90 min airing times and pressed down. 50 % rel. VOC are collected onto adsorption tubes containing suitable adsorbents after flowing purified air through the chamber at a controlled rate. While not necessarily correlated with final adhesive bond strength. The curing of water-based adhesives is typically dependent on temperature and humidity conditions. The peel forces. The floor-covering is immediately peeled off at a certain speed perpendicular to the adhesive join.3 N mm–2) to be considered “passing”. 45. because of slower water evaporation from the adhesive itself). a 5 cm wide floor-covering specimen is placed in the partially dried emulsion adhesive after 30. However. Chamber method for emission measurement North American “CRI Green Label” and European chamber TVOC methods for flooring adhesives are fundamentally similar. humidity). and then pressed down. The CRI Green Label method requires volatile and formaldehyde samples be collected at the 24 h point. it has proven useful in the development of water-based adhesives for carpets and other floor-coverings to also test peel strength as a function of time. and 60 min.g. These two methods have a reproducibility of ±20 %. unacceptably low peel strengths and poor adhesive grab on to the floor-covering substrate are observed. temperature and humidity conditions also have a significant impact on the open time actually found under installation conditions. 20. peel strengths on the order of 10–15N/5 cm strip should be expected within 15–30 min after applying the floor-covering strip. 23 °C. the mean of the shear strength must have a certain minimum value (e.230 8 Applications in the Adhesives and Construction Industries forces which occur during this operation are measured and specified in N mm–2 . According to DIN 16860. it is equally important to also report the degree of web or leg development as a function of time. installers nevertheless commonly look for early web development as an indication of adhesive quality. Floor-covering specimens are peeled off at a certain speed perpendicular to the adhesive join after a further 10. the adhesive sample is applied to a stainless steel or glass plate and immediately sealed in a stainless-steel test chamber carefully maintained under well defined temperature and humidity conditions (e. There are two additional test methods for this: Green strength development The 5 cm wide floor-covering strip is laid in the wet emulsion adhesive after a 10–20 min drying time.g. longer open times and delayed green strength development are expected at higher humidity and lower installation temperatures (i. When peel testing SBR HSL based mastics in particular. which occur during this operation are measured and specified in N/5 cm. To quantify this parameter. Open time Open time represents the maximum recommended time after troweling that the floor-covering should be laid into the adhesive. The peel forces. In both cases.e. 0 air exchanges per hour in the ASTM protocol). ASTM D 3498 is quite similar to the AFG-01 standard originally written by the American Plywood Association. Sub-floor type mastics are typically used for fixing plywood subflooring to lumber floor joists and more recently applied to secure plywood roof sheathing to roof rafters and trusses of existing roofs. but also that long-term emissions be determined after 10 days.5 chamber volumes per hour (1. is a mandrel flexibility check on films of dried mastic after exposure to oxygen at high temperature in an oxygen bomb apparatus. 8-28). The long term emissions are quantified using toluene as standard substance for volatile substances in low concentration. In both of these applications. Water based mastics formulated with acrylics or styrene-acrylic polymer dispersions typically pass oxidation resistance requirements. low VOC water-based mastics. After desorption.e. 8-29). in wind exposure tests [77].8. Loading of the chamber should be at 0. For example. moisture-cure polyurethanes. five of which involve shearing plywood to lumber wood block specimens in compression mode after various carefully controlled material conditioning and specimen curing protocols (Fig.4 Construction adhesives sion-Controlled Laying Materials specifies that substances known or suspected of being carcinogenic must be determined at the 24 h point (in accordance with Hazardous Materials Regulation/TRGS 905). An estimated 75 % of the mastic products sold in North America indicate compliance to stringent AFG-01 (i. adhesives were found to increase resistance to wind uplift forces by factors of 2–3 compared to traditional nail down methods. Sub-floor mastics are generally supplied in cartridge form (310 cm3 and 860 cm3 tubes) and applied as a 6 mm bead using standard caulk gun applicators. “Adhesives for Field Gluing”) requirements.4. The most challenging pa- 231 . These methods define a series of six test specifications (Fig. nails are also used to hold the plywood in place. important for homes and buildings in areas prone to tornadoes and hurricanes. the emitted substances are determined by gas chromatography (GC-MS coupling) or liquid chromatography. The sixth test. The market consists predominately of formulated solvent based styrene–butadiene polymers. Improved mastic systems are required which are compatible with commercial oriented strand boards (OSB) used increasingly in place of standard plywood in both sub-floor and roofing constructions. Plywood-lumber sub-floor mastics are employed in quality construction systems to eliminate nail pops and floor squeaking. but the adhesive greatly augments the structural strength.2 Sub-floor and Wall Mastics Sub-floor and wall mastics are employed in a host of building and home construction applications. called oxidation resistance. Overall market in North America for this class of adhesive is approximately $35 million year–1 with 3 % growth per annum. Increasing VOC concerns coupled with lower solvent threshold limits in California [78] are driving the eventual movement to environmentally friendly. 8. and high performance water based acrylic systems.4 m2 m–3 and the air exchange rate at 0. Adhesive Bond Line Plywood Lumber Conditioning of materials Assembly curing Test specifications Dry lumber Wet lumber 48 h. standard conditions 28 days.g. 37 °C/30 % rh 48 h soak lumber. 8-29 Performance specifications for Adhesives for Field Gluing Plywood to wood framing (AFG-01) rh relative humidity. The wall mastic market in North America is roughly twice the size of the sub-floor market mentioned above. Typical wall mastic applications include: – wood bonding to concrete walls and floors – bonding drywall or gypsum board and paneling to studs and framing structures . standard conditions 28 days. rameters to balance. 22 °C/50 % rh 3 cycles of 4 h H2O/o. glycols.v. <10 % bond failure Gap filling 48 h. 4 °C/50 % rh 7 days recovery Shear >667 N Moisture resistance 48 h. involve moisture resistance and frozen lumber.232 8 Applications in the Adhesives and Construction Industries Fig.n. however. 500 h. Levels of such additives are kept to a minimum in order maintain maximum resistance to moisture. 22 °C/50 % rh. 2 days. over night. –14 °C for lumber and plywood 5 days. Frozen lumber adhesion is promoted through the use a combination of coalescents and freeze-thaw aids (e. alcohols). 37 °C/90 rh for Plywood 28 days. 22 °C/50 % rh (16 gauge wire) Shear >667 N 3 days. dry 37 °C 7 day recovery Shear >1000 N. 37 °C/30 % rh 28 days.2248 lbf. 48 h. 8-28 Force Plywood on lumber shear test (AFG-01). –14 °C 21 days. 70 °C/20bar O2 bend over 6 mm Mandrel: no cracking Oxidation resistance Fig. o. 48 °C/50 % rh. 1 N = 0. 37 °C/90 % rh Shear >1000 N Shear >1000 N Frozen lumber 48 h soak lumber 48 h. USA. USA. ††ECC International. 40 % polymer on dry AFG-01 testing: Moisture resistance: 3100 N (>1000 N required) Frozen lumber: 880 N (>667 N required) Bond failure: None (<10 % required) Suppliers: *BASF Corporation. §Eastman Chemical Company.7 Filler Clay†† 0. pH 9. sealants are considered higher end products that must additionally perform after repeated extension-compression cycles originating from material temperature and humidity fluctuations.3 Coalescent Eastman DBA§ 11. insects). ‡Akzo Nobel. Like sub-floor mastics. use of adhesives eliminate the need for time consuming drilling operations and prevents damage to the concrete substrate. eliminating passage of the “elements” through the joint (i. Charlotte. TN. polyurethane and water based formulations. Test specifications for drywall adhesives are described in ASTM C-557. NC. Kingsport. wall mastics are also manufactured in solvent based. GA.3 Thickener Latekoll D* Total 100 Ingredients are combined in the order indicated above at room temperature with high-speed agitation. drywall mastics are typically filled to a higher degree and thus.7 Dispersion Acronal DS 2159* 0. Due to reduced strength requirements (i. Adhesive properties: 70 % solids content. Atlanta.4 Filler Duramite†† 22.8.e.6 Tackifier Snowtack 301 A‡ Anti freeze Ethylene glycol 3. thus. USA. hot or cold air.1 Dispersant Pigment disperser N* Dispersant Sodium tripolyphosphate 0. Drywall adhesives are used increasingly as builders look for ways to replace time consuming hammer and nail approaches [79].4. Historically. Adhesives for Fastening Gypsum Wallboard to Wood Framing. moisture.3 Sealants Sealants or caulks in accordance with ISO 6927 are materials which remain plastic or elastic and are used for sealing a joint between two separate construction parts. USA 8. mixed with chalk to give window putty. Guiding formulation Solvent-free plywood-lumber sub-floor adhesive Wet parts 56.e. PA.4 Construction adhesives In concrete bonding applications. the starting point for sealants was the natural raw material linseed oil. Ambler.1 0. 233 .05 Defoamer Nopco NXZ† 3. are less costly compared to AFG-01 sub-floor mastics. USA.0 2. Woodstock. While a caulk needs only fulfill the above general purpose. relatively low inherent strength of drywall). CT. †Henkel. with acrylic emulsion sealants comprising approximately 15 % of the total market. . Water based sealants. polyurethanes and polysulfides set through a chemical reaction. The majority of emulsion sealants are composed of acrylic emulsions and to a lesser extent vinylacrylic and other copolymers. and by the type and amount of the fillers and/or pigments. cement panels. excessive plasticizer detrimentally affects film strength. aerated concrete. evaporation of the water. for example fumed silica or SiO2. Thixotropic fillers. plasticizers and coalescents reduce the glass transition temperature of the polymeric component and thereby enhance low-temperature flexibility and film elongation. polyisobutenes and Plastilit 3060 have proven successful. With Plastilit 3060 (propylene glycol alkylphenyl ether) as plasticizer. plasticizers and thickeners [81]. for example DIN 18540. The total caulk and sealant market in North America is estimated 500 000 tons of formulated sealants [80]. reduce the surface tack while simultaneously stiffening the film. tack and therefore. The movement of components must be absorbed and compensated by the joint sealant. Fillers also reduce formulation costs and affect the technical properties of the sealant itself. barium sulfate and silicic acids. The importance of these sealants in the construction industry has also increased considerably through the increased use of prefabricated elements. connecting joints (internal and external) and expansion joints (internal and external) with a movement capability of 10–15 %. dirt pickup resistance. the white pigment used is usually titanium dioxide. and 23 000 tons dry acrylic resin. such as concrete. water based emulsion sealants achieve their functional end state by simple physical drying. polyurethanes. While silicones. dibenzoates. the joint design is stipulated in the relevant standards. aluminum silicate (clay). Experimental testing to ensure long-term polymer-plasticizer compatibility and minimum tendency to volatilize or migrate to the exposed surface is always recommended. Pigments are used to color sealants. improve the gunnability and reduce the sag of the compositions. Finely divided fillers. or shear. sealants with faster skin formation after application and lower Shore hardness which are particularly elastic at low temperatures are obtained. These movements can be expansion. polysulfides. phthalates.e. are used predominately in construction applications whereas reactive urethanes and silicones are used in more demanding construction and automotive applications. They are used for sealing all types of internal joints. For the production of polymer emulsion sealants. Common fillers for sealants are calcium carbonate (chalk). While improving formulation cost. contraction.234 8 Applications in the Adhesives and Construction Industries Synthetic polymers suitable as binders for the production of caulks and sealants include silicones. sold primarily in cartridge tubes. Depending on the degree of compatibility. In Europe. Formulation ingredients The properties of an emulsion caulk or sealant are affected by the type of emulsion. and aqueous polymer emulsions. i. such as talc and Microdol 1. plaster and wood. Fillers reinforce and increase the volume of the sealant. Polymer emulsion sealants can be used on all sorptive substrates. Sealant types Three types of water-based sealant are commercially available. low molecular weight polycarboxylic acid salts are used. they reduce adhesion performance and film elongation. formulation solids content is essentially defined by the solids content of the polymer dispersion used. Relatively hard acrylic copolymers (Tg = –10 to +10 °C) are needed in clear sealants to minimize surface tack and subsequent dirt pick-up. but has low sag after removal of the shear stress. Both “wet phase” biocides and “dry film” preservatives should also be added to the sealants produced using polymer dispersions in order to achieve adequate protection against microbiological attack. thickeners. In general. and dried film strength. Since fillers are not used. glass. Because of the “stiffening” effect of most fillers. The majority of the market (>75 %) consists of the filled variety. preservatives. protects the sealants against freezing during storage and transport. Filled sealants are typically formulated with approximately 25–35 wet parts polymer dispersion per 100 parts total formula. for example ethylene glycol. Clear and translucent sealants are used when a clear or translucent “look” is desired and in applications requiring higher adhesion performance. Clear and translucent sealants consist primarily of polymer dispersion (ca. Higher water contents promote slower sealant drying rates. associative thickeners and fumed silica are used to adjust the rheological behavior of sealants. formulation solids contents in the vicinity of 90 % are possible. Highly disperse fumed silica with a average particle diameter of from 10 to 30 µm is used as thixotropic agent to ensure that the sealant flows out of the cartridge well even under gentle pressure. Addition of suitable antifreeze agents. is typically <65 %. With high filler loads. with filler to binder ratios in the range from 2 to 4. and freeze-thaw agents. Figure 8-30 shows the tensile stress of a sealant at 50 % elongation as a function of time under various climatic drying conditions. The mechanical properties of water-based sealants are essentially determined by the ambient temperature and atmospheric humidity.4 Construction adhesives Dispersing aids and surfactants improve the incorporation of fillers and pigments and improve the sealants’ storage stability. thus. and filled sealants. filled sealants are pro- 235 .g. Silane-based coupling agents can be employed to improve adhesion to difficult substrates (e. which for currently available materials. defoamers. 75–95 % by weight) and various formulation auxiliaries such as plasticizers. aluminum). elongation. Translucent sealants are formulated similarly but with small amounts of fumed silica thickener to adjust flow properties. While fillers serve to reduce formulation cost and surface tack. improve storage stability and provide desired enhanced adhesion performance even after extended package aging. clear. A new class of hydrolysis resistant silanes are now available [82] which minimize self-crosslinking reactions. translucent.8. Anionic thickeners based on polycarboxylic acids. Sealants containing small amounts of silane adhesion promoter are referred to as “siliconized”. dirt pickup. The suitability of these preservatives must be established and monitored experimentally. Filled sealant with good elasticity (even at low temperatures) and a broad adhesion spectrum Wet parts Dispersion Acrylic dispersion.5 Filler.7 Thixotropic agent Silicic acid HDK H 20‡ Total 100 Sealant properties: filler/binder ratio = 2. solids content = 89 % Polymer dispersion properties: 65 % solids.71.5 2 Plasticizer Plastilit 3060* 10 Pigment paste Plastilit 3060/Kronos 2056 TiO2† (1:1) 0. relative humidity. CaCO3 0. Tg = –30 °C . r. pH 8 with NaOH 20 % 31. duced either with lower Tg emulsion polymers (–40 to –30 °C) and low plasticizer levels or with higher Tg copolymers (<0 °C) and higher levels plasticizers which “soften” the dried sealant film.h. Guiding formulations 1. 8-30 Tensile stress values of a dispersion sealant at 50 % elongation and various climatic influences.236 8 Applications in the Adhesives and Construction Industries Fig.2 Emulsifier Lumiten N-OG* 0.1 Dispersant Pigment dispersant N* Omya BLP 3† 55. USA. The plasticizer is then added directly. High solids. 237 . ‡ Wacker-Chemie.3 Surfactant Emulphor OPS 25. This suppresses the formation of pigment particle agglomerates. †Omya GmbH. 50968 Cologne. low cost formulation for common gap filling applications. solids content = 90 % Polymer dispersion properties: 60 % solids. ASTM C-736).8. rapid drying. Ridgefield Park. DIN 52458. and after 24 h the separation is measured after release (EN 27389. C-9 phthalate* 0. USA. For the measurement. after each addition. 81737 Munich. Production of sealants Vacuum planetary mixers have proven particularly successful for the production of water-based polymer emulsion sealants. the mixture is stirred for about 5 min until smooth.4 Construction adhesives 2. Test methods Resistance to flow The resistance to flow is the property of a sealant to remain in the specified shape after processing. DE. The homogeneous mixture is then deaerated for about 5 min under a vacuum of 900 mbar with stirring at 20 rpm and then packed into polyethylene or foil carton cartridge tubes. CaCO3 61 Sealant properties: filler/binder ratio = 4.6 Dispersant Pigment disperser N* Filler Mikrodol 1. NC. Tipure R901-01 TiO2 also available from Dupont Chemical. two concrete test specimens are joined together. DIN 52454. After the final addition of filler. NJ. paintable Wet parts Dispersion Acrylic dispersion 23. Aerosil 200 fumed silica also available from Degussa Corporation. ISO 7389. Thickener and dispersant are then added. Elastic recovery Elastic recovery is the magnitude of the recovery of a sealant after prior elongation followed by release. non-ionic* 0. USA. It has proven favorable in experiments to grind finely divided pigments (for example titanium white and iron oxide black) with the same amount of plasticizer in a roll mill and to incorporate the resultant pigment paste into the dispersion before the fillers. Germany. A minimum shelf life of 6 months can be assumed in properly sealed cartridges. the stirring arms are scraped and stirring is continued for a further 5 min. Germany. The speed is then gradually increased to about 80 rpm. the fillers are added in 3 or 4 portions. a U-profile is filled with sealant (EN 27390. Tg = –10 °C Suppliers: *BASF Corporation. The dispersion is adjusted to pH 8 using 20 % sodium hydroxide solution.3.8 10 Plasticizer Palatinol N. Wilmington. which can otherwise easily occur. ASTM D-2202). the joint is stretched by 50 %. After a stirring time of about 8 min at 30–40 rpm. Charlotte. and the mixture is stirred briefly at low speed. ISO 7390. For testing. Notes for use Water-based sealants generally adhere sufficiently well to sorptive substrates without pre-coating.g. gypsum wallboard. However. The thickness of the adhesive bed is variable and depends both on the size of the tiles and on the nature of the tile undersurface. In general.e. Jointing should not be carried outside in the rain or at temperatures below +5 °C since the dispersion is still water-sensitive after application. However. underlayment grade plywood or prefabricated con- .15 N mm–2 and an elongation at break of 200–300 %. ASTM C-735). the thin-bed method can only be used if the substrate surface is relatively flat. cementitious self-leveling repair underlayments and floor patching compounds) and industry proven construction materials. polyurethane and advanced acrylic emulsion technologies are typically designed to satisfy the ASTM C-920 standard. the thin-bed method involves adhesive bonding. ISO 8339. in order to achieve greater reliability. These are actually umbrella specifications constructed from a host of individual ASTM test methods [83]. The greatest advantages of the thin-bed method are the high application speeds and lower mortar coat or application weights (i. 8. However. latex sealants are typically unsuitable for sealing joints which are constantly exposed to water or subjected to strong expansion movements.238 8 Applications in the Adhesives and Construction Industries Adhesion-elongation test Two concrete test specimens are joined together and pulled apart in a tensile testing machine at 6 mm min–1 until the breaking point is reached (DIN 52455. sealants can be developed which satisfy the specifications defined in ASTM C-834 for “latex sealing compounds”. pre-coating of the joint edges with dilute sealant (for example 1 part of sealant with 3 parts of water) has proven successful in practice. Tools should be cleaned with water immediately after use as the residues can only be removed mechanically once they have dried. such as cementitious backerboard. cost). a tensile stress of 0.4 Ceramic Tile Adhesives In contrast to the traditional thick-bed method in which tiles are laid in thick layers of mortar.4. The sealant is introduced into the joint using a manual or compressed-air caulking gun. The mechanical properties of a good emulsion-based sealant should be an elastic recovery of 60–70 %. it requires 30–60 min to form a sufficiently thick skin on the surface.1–0. This prerequisite is achieved in most cases by using appropriate substrate preparation techniques (e. In North America ASTM C-834 and C-920 are used. Depending on the temperature and relative atmospheric humidity. Higher performance “elastomeric joint sealants” based on silicone. in particular to bind dust particles. This means that the tiles are laid into a wet adhesive bed trowel applied on to a substrate. The surface is then smoothed using a wet flat brush. EN 28340. ASTM C-920 class A sealants are those that can withstand deformations as high as 50 % while class B sealants tolerate deformations as high as 25 %. They have a broad adhesion spectrum. thus. impact strength. including improved bond strength. water resistant ceramic tile mastic without film forming aids Wet parts Diluent Water 6. In thin-bed ceramic tile applications.4 Construction adhesives crete panels. Recently styrene acrylics or straight acrylics and styrene butadiene copolymer powders gain an increasing market share. Ethylene vinyl acetate copolymers (EVA) are the predominant powder polymer base used in one component polymer modified thinsets. styrene-acrylic and SBR polymer emulsions in the admix component.8. ready to use ceramic tile mastics are used in interior residential and light commercial applications where only intermittent water exposure is expected. They are used both for professional tile setting and – owing to their simple processing properties – in the “do it yourself” (DIY) market. they are described in Chapter 13.1 Filler Calcium carbonate (7 µm) 17 Total 100 Suppliers: *Henkel Corporation. USA. IL. Mastics are generally water based and are supplied as a smooth trowelable paste for setting smaller sized tiles (<15 cm × 15 cm).4 0. a long working time and form a flexible adhesive film. improved moisture and alkali resistance. Ambler. USA 239 . Guiding formulation Low emission. improved mix workability. flexibility. Polymer modification imparts a wide range of performance improvements to ceramic tile mortar adhesives. Two component thinsets systems combine a cementitious powder mix and a separate polymer dispersion admixture. PA. Ceramic tile adhesive mastics One component.16 mm) 39 Filler Calcium carbonate (23 µm) 17. Two component thinset adhesives employ acrylic. both cementitious adhesives (mortar) and non cementitious systems (mastics) are applied. †US Silica. Both one component polymer modified thinsets and two component cementitious adhesives are used. freeze-thaw resistance. The benefit of a styrene-acrylic polymer compared to a straight acrylic backbone involves increased hydrophobicity. ammonia-free.6 Thickener Natrosol CG 450 † Dispersion Acrylic dispersion 20 Filler Silica sand (0. Ottawa. Ceramic tile mortar adhesives (thinsets) Thinset mortars are employed in demanding interior and exterior floor and wall applications where there may be standing water or high moisture exposure. water resistance. Polymers also aid in promoting adhesion to difficult substrates such as plywood and vitreous tiles (porcelain).1 Defoamer Nopco NXZ* 0. 240 8 Applications in the Adhesives and Construction Industries Action of the additives Cellulosic thickeners (Natrosol) are used to adjust the viscosity and regulate mix consistency, working time and spreadability. Special thickeners (Attagel 50, an attapulgite clay) are used to generate a flow barrier, so that the tiles do not slip under their own weight. In cementitious systems, cellulosics are used to provide water for cement hydration over an extended time period due to their natural tendency to retain water. Surfactants improve the homogeneity and shelf life of adhesives with high filler content and also have a tendency to extend open time. Preparation of polymer-emulsion-based CTA mastics Additives are incorporated into the polymer emulsion in the stated sequence. The additives are added in portions, and the mixture is stirred after each addition until it is smooth again. These high-viscosity mastic adhesives (ca. 500 000 mPa s) can in principle be prepared using any mixing equipment with an appropriate stirrer geometry. Planetary mixers and turbulent mixers are particularly recommended. Preservatives are added to the adhesives to protect them against microbiological attack. Test methods for assessing tile adhesives Well defined test methods are available in North America and Europe for evaluating ceramic tile adhesives. Test methods used in Germany for emulsion-based mastics are described in DIN EN 1324 (adhesive shear strength) and DIN EN 1346 (correction or adjustment time). Cementbased CTA are tested by DIN EN 1348 (pull of strength) and again DIN EN 1346 (open time). Classification is determined for both types of adhesives by prDIN EN 12004. North American test methods and specifications for tile adhesives are described in the following American National Standards Institute (ANSI) standards: One-component CTA mastics with glazed wall tiles ANSI 136.1 Latex-Portland cement mortar with glazed wall tile, quarry tile and porcelain and/or mosaic tile ANSI 118.4 Latex-Portland cement mortar with quarry tile on plywood ANSI 118.11 DIN Methods In the pull-off strength test performed with cementions CTA, the tile adhesive is first applied to concrete. After 20 min, earthenware tiles (50 mm × 50 mm) are pressed into the adhesive bed. After a storage time under standard atmospheric conditions, tension anchors (50 mm × 50 mm) are attached to the smooth tile surface using a two-component adhesive (epoxy). A tensile tester is used to measure the force needed to detach the tile from the concrete; it must be greater than 0.5 N mm–2. To estimate adjustment time, earthenware tiles are laid in the adhesive bed as described above, rotated by 90° after 10 min and then rotated back into the original position. The adhesion pull strength after storage must still be at least 0.5 N mm–2. Also described in DIN 18156 Part 3 is a method for evaluating vertical slip of tiles under their own weight. 8.4 Construction adhesives ANSI Methods The key mechanical tests defined in ANSI 136.1 involves tile-to-tile shear strength after dry conditioning and after water immersion. In this method, adhesive mastic is applied to the unglazed back of a 108 mm × 108 mm test tile using a specified template to produce a pattern of equally spaced circles of adhesive on the back of the tile. After 2 min airing time, the unglazed back of a second tile is carefully oriented on to the adhesive bed – tile to tile separation is controlled with the use of spacer rods. Test assemblies are then subjected to compression under a 6.8 kg load for a period of 3 min. Bonded tile assemblies are then dried for 72 h at 50 % rel. humidity and 22 °C and then further conditioned for 21 days in an air circulating oven set at 49 °C. Wet, type 1 shear strengths are determined by shearing wet test specimens at a defined rate using a tensile tester, immediately after immersing the bonded test assemblies in a water bath for 7 days. The minimum ANSI wet, Type 1 shear strength specification for CTA mastics is 3.5 kg cm–2 (50 psig). ANSI 118.4 includes a complete series of methods to evaluate application properties (initial and final set, open time, adjustability, vertical sag) of latex–Portland cement mortars and shear strength of bonded tile assemblies. 8.4.5 Polymer-modified Mortars Polymer modified Portland cement mortars are used in a range of primary construction and concrete and mortar repair applications (Fig. 8-31) [86, 90]. Damaged Concrete Fig. 8-31 Waterproof Membrane Fine screed Repair Mortar Application of repair mortar. They are applied in bridge decking and airport runway applications, in repair applications, where the mortar layer can be as much as 5–8 cm thick, in industrial floor screeds, where up to a 5 cm layer is applied over standard concrete, in fine screeds or patching compounds, where up to 1.5 cm of repair mortar is applied on floors, in self-leveling underlayments, where thickness from 2–3 cm to “feather edging” are common. Fundamentals of concrete and Portland cements, hydration chemistry and classification of admix agents were reviewed by Kosamatka, Panarese and Soroka [84, 85]. Polymers are added to Portland cement based mortar systems for a number of reasons. Firstly, polymers improve the key properties of the fresh, non hardened mortar, i.e. adhesion, workability and open time. Polymer additives also tend to have a plasticizing effect on cementitions mortars, there by reducing the amount of added water to achieve needed workability and mortar flow properties. Minimizing added water results in fewer capillary pores, lower porosity and stronger cements. Secondary, the properties of a hardened cement mortar are improved. Properly selected 241 242 8 Applications in the Adhesives and Construction Industries polymers, i.e., those with Tg lower than 15 °C, form a film within the mortar matrix [86] thereby filling voids, pores and reducing the potential for ingress of water and dissolved salts. This reduced permeability to salts (e.g. chloride) provides protection against corrosion of underlying steel reinforcing elements. With reduced water ingress, polymer modification also promotes improved freeze-thaw resistance of the mortar – a feature which is especially important in exterior or cold climate applications. Improved tensile, compressive and flexural strength are generally realized in polymer modified cement mortars, provided sufficient levels of defoamer are added to counteract the tendency of emulsion polymer additives to induce excessive foam generation. Similarly, concrete used, e.g. in critical bridge decking applications is typically polymer modified in North America to extend service life and reduce repair costs by minimizing deterioration caused by exposure to the many forces of nature (Fig. 8-32). Deterioration of concrete concrete surface H 2O Filler particle Crack Steel corrosion - Rust CaCl Reinforcing steel SO2 Pores Concrete damage pH = 12 - 13 CO2 Carbonation zone Fig. 8-32 Deterioration of concrete. As with ceramic tile thinset mortars, styrene-acrylics, acrylics and SBR polymer emulsions and their dry polymer analogs, including EVA powders, are employed across the range of polymer modified cementitious applications. While polymermodified mortars are used widely, for cost reasons, polymer modified concretes are seldom used – with the exception of bridge decks where SBR are almost exclusively employed. However, in Europe the use of additives in construction concrete is regulated by technical guide lines. When developing new polymer modified mortars these days, formulators should also consider the impact of alkali exposure on long-term hydrolytic stability of the polymer and the subsequent impact of any degradation on application performance 8.4 Construction adhesives and service life. By their very nature, SBR are inherently resistant to alkali induced hydrolysis compared to some vinyl acetate containing polymers which, by virture of the vinyl ester linkage, are more prone to hydrolysis. Guiding Formulations Repair mortar Part A: Liquid Component Dispersion Diluent Part B: Dry Component Filler Cement Filler Carboxylated SB Hydration water Wet parts 54 83 Silica sand Portland cement Microsilica 721 273 6 Polymer/cement ratio Water/cement ratio Performance after Flexural strength (bar) Compressive strength (bar) 0.1 0.4 1 day 60 270 28 days 110 560 Test methods The test methods are summarized in Chapter 13. 8.4.6 Waterproofing Membranes Concrete is the most prevalent building material used in the world today [84, 86]. While concrete typically exhibits tremendously high strengths, the fact remains that it is nevertheless porous in nature and thus, is susceptible to direct moisture penetration and water vapor ingress. Additionally, acids (i.e. CO2, SO2) may penetrate into the concrete and lower the pH of cementitious materials. Along with migration of chloride and other salts dissolved in water deep within the concrete, this may cause severe irreversible damage to steel reinforcements present (i.e. corrosion). Certain additives can be introduced into the concrete mix to minimize water and salt penetration (e.g. latex admixture, calcium stearate), but due to the costs involved, these approaches are employed in only the most demanding applications, such as, bridge decks and parking garages. Moreover, concrete admixtures do not protect the concrete surface layer nor are they able to eliminate moisture penetration in cases where direct hydrostatic pressure forces exist – protective waterproofing membranes are needed. A host of different commercial waterproofing systems have been developed to protect against the harmful effects associated with water intrusion into concrete. These can be broken down into pre-formed membrane sheets and applied coating systems. 243 244 8 Applications in the Adhesives and Construction Industries Pre-formed membrane sheets typically consist of rubber modified bitumen supported on a polyethylene web with a release liner to protect the highly adhesive bitumen layer. These products are available in rolls with total membrane thickness of approximately 1–2 mm and can be fiberglass-reinforced to provide improved membrane dimensional stability. The adhesive nature of the rubber-modified bitumen assures excellent sealing at the roll overlaps. A host of applied coating systems exist based on rubberized bitumen emulsions, solvent borne synthetic rubber and asphalt solutions, two-part epoxies, two-part self-curing bitumen-free liquid applied membranes [91], one-component water-based elastic coatings, and flexible one or twocomponent cementitious waterproofing slurries. Water based systems employing polymer emulsion binders will be discussed further below. Waterproofing products are used in a wide range of construction and repair applications, applied directly on to pre-formed concrete, concrete blocks, bricks, and stone products. The most important applications include foundation building walls, bridges, balconies and terraces, tunnels, basements, planters, silos, and parking decks. Coating systems are typically applied to uniform thickness (1–3 mm) using a brush, roller, trowel or spray system. In all cases, strong adhesion and intimate contact of the waterproofing layer to the underlying substrate, as well as proper waterproof system design, are required to eliminate water seepage through or around the membrane. Depending on the application, waterproofing membranes should also exhibit chemical resistance (e.g. to oils and acids), should remain flexible over all potential use temperatures and be capable of resisting hydrostatic pressures, even over cracks. Both, one-component, water-based elastic coatings and one or two-component flexible cementitious waterproofing slurries have the advantage that, by virtue of the water carrier, they are environmentally friendly and easy to clean after application. They both yield monolithic, seamless, puncture resistant and watertight layers after curing but which nevertheless allow water vapor to escape from the inside to the outside. Cementitious systems are particularly ideal on damp substrates – because of hydration reactions which occur in the freshly applied membrane. As they consist of polymeric binder, sand and Portland cement, through hydration reaction chemistry they become integrally bonded to and thereby become a part of the underlying concrete. Minor cracks can be bridged at low temperatures, if a sufficiently low Tg, flexible polymer dispersion binder component is selected [87, 93]. Elastic waterproofing membranes used on the exterior of concrete structures should also exhibit resistance to the damaging effects of UV radiation, sulfur dioxide and acid rain, carbon dioxide (carbonation), and repeated freeze-thaw cycles. Rubber based waterproofing systems are typically based on styrene-butadiene copolymers and SBS resins while acrylic and styrene-acrylic dispersions are employed in most flexible one-component and two-component cementitious membrane systems. In Europe, new regulations defined in ZTV-SIB (Additional Technical Contract Conditions and Regulations for the Protection and Restoration of Concrete Building Components) specify crack-bridging at –20 °C [88]. As a result, lower Tg polymer systems have been developed, which yield membrane flexibility and hairline crack 8.4 Construction adhesives bridging at lower use temperatures. The industry has moreover shifted to systems containing, as a rule, higher proportions of polymer binder (0.8 < polymer/cement ratio < 1) compared with earlier membrane systems. Guiding formulations 1. One-component flexible waterproofing membrane (500 µm dry film) Wet parts Diluent Water 123.0 5.5 Defoamer BYK 035* Freeze–thaw additive Propylene glycol 27.1 5.5 Pigment disperser Pigment disperser NL† 1.6 Surfactant Triton X-405‡ 0.8 Thickener Natrosol 250 MXR§ 134.5 White pigment Kronos 2101 TiO2# 318.2 Filler Duramite** 16.4 Filler Atomite** 99.5 Filler Microtalc MP 10-52†† 3.3 Biocide Proxel GXL‡‡ Grind until smooth, then add Polymer binder Acrylic dispersion Defoamer BYK 035* Thickener Natrosol 250 MXR Neutralizing agent Ammonium hydroxide Total Pigment volume concentration: 42.3 %; solids content: 72.8 % 2. Two-component flexible cementitious waterproofing membrane Dry component 28.0 F-110 Silica sand§§ 27.3 F-95 Silica sand§§ 19.6 Portland cement type I/II## 0.2 Pigment disperser N† Lumiten E-P3108 defoamer 1.6 Styrene acrylic dispersion – Antifoam – Water (to desired flow) – 475.7 7.4 2.8 1.8 1223 Wet component – – – – – 20.6 0.2 0.5 Mix dry and wet components separately, then blend dry mix into the wet phase. Apply two or three layers of 400–600 µm each. Water/cement ratio: 0.45; sand/cement ratio: 2.82; dry polymer/cement ratio: 0.60 245 246 8 Applications in the Adhesives and Construction Industries 3. Waterproofing membrane Polymer binder Defoamer Thickener Total Styrofan D 422† BYK 035* Rheolate 300*** Wet parts 98.4 0.1 1.5 100 Formulation 3 is intended for sealing interior walls and floors in bathrooms and other damp areas – preventing underlying moisture damage. Compounds based on Styrofan D 422 can also serve as “wet” concrete curing compound (by spray application), preventing premature concrete drying during the critical hydration stage. Suppliers: *BYK Chemie, Wallingford, CT, USA: †BASF Corporation, Charlotte, NC, USA; ‡ Union Carbide, Danbury, CT, USA; §Aqualon, Wilmington, DE, USA; #Kronos, Houston, TX, USA; **ECC International, Atlanta, GA, USA; ††Pfizer, Easton, USA; ‡‡Zeneca Biocides, Wilmington , DE, USA; §§US Silica, Ottawa, IL, USA; ##Leghigh Portland Cement Co., Allentown, PA, USA; ***Rheox, Hightstown, NJ, USA Test methods The ANSI 118.10 test specification describes key test requirements for load bearing, bonded, waterproof membranes for thinset ceramic tile and dimension stone installation. The standard applies to trowel applied, liquid, and sheet membranes. Requirements include a seam strength evaluation, membrane tensile or breaking strength, shrinkage or dimensional stability, “waterproofness” in accordance with ASTM D 4068, and shear strength of ceramic tile and cement mortar applied on the waterproofing membrane. Membrane water vapor transmission is typically determined according to ASTM E 96, employing a permeation cup apparatus (Fig. 8-33). Waterproof membranes in Europe are tested according to [92]. Waterproofness is an indication of a particular membrane material’s ability to withstand a 60 cm hydrostatic pressure head. The apparatus employed in this test is shown in Fig. 8-34. The membrane film is affixed at the bottom end of the J-tube and water is then carefully introduced to an overall height of 60 cm above the level of the membrane. Fig. 8-33 assembly. Moisture vapor transmission cup test 8.4 Construction adhesives Fig. 8-34 J-Tube apparatus for measuring the hydrostatic pressure resistance of water-proofing membranes. Fracture of the membrane or evidence of wetness on top of the material (even the formation of a single droplet) within the first 48 h exposure, are considered as visible signs of water penetration and require rejection of the material. The performance of a concrete curing compound is assessed by measuring the water loss of green concrete according to ASTM C 156-94, the water loss after three days may not be higher than 0.7 kg m–2, acievable with SB coatings (Fig. 8-35) Water loss (kg/m2) 4 3 without coating 2 1 ASTM Spec. with SB coating 0 Water loss of green concrete according to ASTM C 156-94. Fig. 8-35 4 24 48 72 Time (hours) 247 Buildings covered with white coatings. and upon drying forms a continuous film or coating membrane. that are applied by spray or roller coating to a sloped roof surface. <20 °C). In particular. reduce building heating and/or cooling costs [89]. While field exposure conditions can vary. A typical “white” roof coating formulation consists of polymer dispersion mixed with various fillers and pigments and small amounts of additives to provide stability and to build viscosity to the roof coating mixture. compared to black asphalt type roofs. Crosslinking occurs both on the membrane surface and throughout the coating providing required elastomeric film properties with only very slight residual surface tack – thereby maximizing dirt pick up resistance and long-term reflectivity. the Tg for an elastomeric copolymer should be lower than the minimum low temperature for a given geographic region where the roof coating is to be applied (i.4. . This coating membrane must also be sufficiently flexible to withstand the movement of the substrate due to the diurnal cycle. This program is aimed at promoting energy efficient buildings and in doing so. prevent the roof membrane from cracking under contraction stresses. The program requires the roof membrane to demonstrate both a minimum initial solar reflectivity and maintenance of that solar reflectance after three years field exposure (by ASTM E 903). Elastomeric roof coatings are used in repair applications to seal existing roof structures and also in new building construction applications. Low-Tg (–20 °C) pure acrylic dispersions provide excellent adhesion to polyurethane roofing foam and many other construction substrates. reflect rather than absorb light radiation resulting in cooler surface temperatures and reduced cooling demands for buildings located in hot climates.7 Elastomeric Roof Coatings Water based elastomeric roof coatings can be described as formulated liquid products. in two or more coats. Acrylic polymer dispersions are ideal for the manufacture of water based liquid elastomeric roof coatings. which have the ability to form a continuous protective polymer film over the substrate upon evaporation of the water. the membrane will remain flexible and thus. It also has to provide resistance to water intrusion. This helps assure that during cold weather. white pigmented roof coating membranes are becoming increasingly prevalent as a result of a new EPA program called “Energy Star”. cracking. The demand for dispersions in this market is estimated to be on the order of 20 000 tons wet per annum. The mixture is applied to a clean roofing substrate.e. and weathering while maintaining adhesion to the substrate under all exposure conditions. They may contain internal crosslinking agents that crosslink the polymer film after the water has evaporated. Elastomeric polymer films require a proper balance of properties for the film to expand and contract and return to its original state every time external stress-strain forces have been applied and removed.248 8 Applications in the Adhesives and Construction Industries 8. particularly for protecting polyurethane insulating foam roofs. The polymeric component binds the materials in a monolithic state and forms the film. 42. Wilmington.91 Suppliers: *BASF. USA. These specifications are based on a somewhat Film physical property After 14 days drying at room temperature Tensile strength D2370 % Elongation at break After 1000 h aging in a xenon arc weatherometer % Elongation at break Accelerated weathering checking Low-temperature mandrel flexibility Adhesion (wet) C 794 Water swelling (%) Permeance – inverted (perms) Tear resistance (lbf in–1) Fungi resistance (after 28 days) Fig. DE. Houston. †BYK-Chemie USA. 8-36).27 0. A Div.22 12. then add Binder Acrylic dispersion Thickener Natrosol 250 MXR†† Neutralizing agent Ammonia Solution Defoamer BYK 035† Weight % solids = 72.23 0. 8-36 roofing.88 2. CT. 59 % Pigment volume concentration = ca.45 28. viscosity (Krebs) = ca. §ECC International.17 26. DE.4 Construction adhesives Guiding formulation Water based elastomeric roof coating Diluent Water Freeze Thaw Propylene glycol Dispersing aid 30 % Pigment Disperser NL* Binder Acrylic dispersion Defoamer BYK 035† Kronos 2101‡ TiO2 pigment Filler Duramite§ Filler Atomite§ Filler Microtalc MP 10-52# Biocide Proxel GXL** Grind. USA. NC. TX.45 0. Wilmington.34 18. of Hercules. ††Aqualon. Charlotte. #Pfizer. **Zeneca Biocides. Roswell.23 0. ASTM D 6083-97a (Fig. Wallingford. was issued for determining the acceptable performance of liquid acrylic flexible roof coating mixtures based on laboratory testing. 105 Wet parts (g) 6. USA Test methods In 1997 an American National Standard. USA. ‡Kronos.36 1. USA. USA. ASTM test Requirement ≥200 psig D2370 ≥100 % D2370 D4798 ≥100 % No cracking and D522 Pass (1/2 in at –15 °F) >2 lb in–1 D471 D1653 D624 G21 <20 % <50 >60 (die C) Zero observed Standard specification for liquid applied acrylic coating used in 249 .45 11. PA. volume % solids = ca.34 0.78 0. USA. GA.8. Easton. H. F. Jäger. W. TorresLosa. Maempel. Schuler. K. J. Neumann.-H. These tests are carried out at various specified temperatures.250 8 Applications in the Adhesives and Construction Industries broader set of test requirements described in Dade County Florida. Licht. Schwarz. The standard has minimum specifications. Türk. Protocol PA 12995 and Protocol PA 143-95. These tests are carried out after a minimum of 14 days drying at standard lab conditions (22 °C and 50 % relative humidity). L. Fickeisen. Krobb. H. A. Mächtle. Auchter. Seibert. Anders. Fitzgerald. Acknowledgments The authors would like to express their sincere thanks to the following colleagues for friendly assistance in writing the “Applications for Adhesive and Construction Industries” chapter and for critical checking of the manuscript: H. O. Pakusch. tensile strength. adhesion to various substrates. Zosel . W. P. J. relative humidity and aging conditions.J. H. Druschke. Füßl. B. U. A. M. when testing the free film for tensile strength. G. Zettl. Drewery. J.W. H. Müller. permeability and tear resistance. water swelling. elongation at break and mandrel flexibility. J. The coated film must also meet standards for. Aydin. Schumacher. J. P. J. R. Fricke. elongation at break. 1882. Trans. German Patent 20057. Muny. Adhäsion. M. 40. L. Mallon. 1975. Polym. Die Technologie der Klebstoffe. 21(3/4). Medina. Age 1963. Varanese. Adhes. New York. Türk. pp.und Kunststoff-Verarbeiter. Hagan... J. Adhes. 1963. Schwartz. 1996. H. 19. New York. April 2000. Blümich. 10. De Bruyne-Houwink. 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Wistuba. 1997. Adhes. J. Adhäsion 1990. 1988. 6. Kleben und Dichten Adhäsion. http//www. Pittsburgh. S. Oct/Nov. Adhäsion. 1979. Rubber. C. H. E. www. pp. Conn. Steinke. 14–18. 1997.htm http//www. Satas and Associates. Maempel. Technical brochure. Chemical Publishing Co. 279. Van Nostrand Reinhold. L. in: Handbook of Pressure 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 Sensitive Adhesives Technology. J. US Patent 5763014. 13–19. Farbe Lack. Pakusch. R.com/articles. Illinois. Recent progress in Concrete–Polymer Composites. T. . 77 Adhes. Zosel in: Advances in Pressure Sensitive Adhesives Technology 1. Zosel. 1989. H. 64. A. Boca Raton. 1963. Ohama. Zosel.gov/ Y. Zosel. ASTM Special Technical Publication No. 14–20. Hummerich. 1994. Chandra. 44. Kamagata. A. 6 billion m2 and $11. Onno Graalmann. the largest user of polymer dispersions. 9. with an estimated [2] sales volume and value of 1. A Turkish knotted pile rug. It is known that the Egyptians of 3000 BC wove linen carpets ornamented by sewn on pieces of colored woolen cloth. and J. Scott.13 billion m2 [3] and 284 million m2 soft floor covering respectively. and adhesive applications. During 1999.1 Introduction This chapter covers the use of synthetic polymer dispersions in the carpet industry. Richard L. Europe and the Asia-Pacific countries produced during the same period an estimated 1. dispersion usage during 1999 has been estimated at respectively 400 kt [3] and 100 kt wet. carpet accounted for approximately 60 % [1] of the volume of all floor coverings (soft and hard) sold in the USA. Carpet backing is the fourth largest user of synthetic dispersions in North America (NA) after paints and coatings.7 billion respectively. KGaA ISBNs: 3-527-30286-7 (Hardback). give improved dimensional stability. Blanpain. is dominant with an estimated 1. Of this volume.2 History of Carpet The history of the manufacturing of rugs and carpets began with weaving.Polymer Dispersions and Their Industrial Applications. was found in 253 . In Western Europe and the Asia-Pacific regions. dated back to 500 BC. paper. hand. which represents around 9 % of the estimated 5. the tufted carpet and rug segment.4 billion m2. The function of the polymeric binder in carpet backings is primarily to anchor the pile fibers in place. J. Evidence obtained from excavations near the Caspian Sea indicates that the spinning and weaving of sheep and goat wool was practiced as early as 6000 BC. dispersion consumption in carpet backings was around 490 kt (wet) [4].300 kt total dispersions (wet) produced in the USA. 3-527-60058-2 (Electronic) 9 Applications in the Carpet Industry Peter R.3 billion m2. In 1999. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. and resistance to fraying or tuft loss at cut edges of the carpet. Synthetic polymer dispersions have been used as binders for the backing of carpet since the late nineteen-forties. with broadloom’s share accounting for approximately 1. Arthur Smith 9. into an unbleached muslin base cloth. reshaped the industry. increased costs. and cutting the surface loops of the yarn so they would fluff out. The chartering of carpet weavers in Wilton and Axminster in 1701. when a Dalton (Georgia. Germany. Deep-pile rugs. Catherine Evans Whitener. During the early 1800s. as carpet became more popular. produced bedspreads by sewing thick cotton yarns with a running stitch. During the late 1920s and early 1930s. This resulted in woven carpet production declining in England by about 70 % by the1970s. called Savonneries.” and by the 1930s there were around 10 000 “Tufters” in the Dalton area. was the beginning of the establishment of England as the world’s major woven carpet producer. and the introduction of carpet production in Kidderminster around the 1740s. This. and the establishment of Belgium. which made the mass production of woven carpet possible. The tufted carpet industry had its beginning in the late 19th century. This situation continued until the 1960s. and by the late nineteen-fifties. Bedspreads led to other small tufted goods such as toilet covers. The woven carpet industry continued to thrive until the end of the nineteen-forties and the advent of tufted carpets. robes. and in 1839 Erastus Bigelow’s invention of the power loom. The Spanish in the 13th century. USA) woman. increases in loom widths. the mechanization of looms. the material was washed to cause the muslin to shrink around the tufts to mechanically hold them in place. together with the invention of the Axminster loom in 1876 to produce woven carpets with a wide range of designs and colors. Oriental rugs were carried to Europe by the Saracen conquerors of Spain. The US carpet industry had its modest beginning in 1791 when William Sprague founded the first woven carpet mill in Philadelphia. Continued domination by British imports. The Netherlands. and Great Britain as Europe’s major tufted carpet manufacturers. and small “scatter rugs. were first produced in Paris during the early 17th century. Before the 1790s. when technology developed in America for tufted carpet production was introduced into Europe. The weaving of hand-knotted rugs spread throughout the Orient. and Persia (Iran) became the predominant manufacturer. The Netherlands and Germany. The revocation of the Edict of Nantes in the late 17th century. and falling prices due to increased competition. carpet affordable to virtually . and generated so much interest that a thriving cottage industry started. and Pennsylvania. stimulated efforts to improve methods of production. resulted in the development of multi-needle tufting machines. and later Italian merchants. were the first Europeans to make hand-pile rugs. the carpet business in the USA was monopolized by expensive woven imports from The United Kingdom. New York. that had guaranteed religious and civil freedom to French Protestants. She sold the first bedspread in 1900. Moorish weavers were probably taken from Spain in the 13th century to start the early French carpet weaving industry at Aubusson. further stimulated the expansion of the US woven carpet industry. Tufting machines for producing carpet appeared in the late nineteen-forties.254 9 Applications in the Carpet Industry Siberia in the nineteen-fifties. by returning Crusaders. and building of looms of greater width in order to meet demands for more bedspreads. other factories were established in New England. After tufting. where they made significant contributions to the early development of the spinning and weaving industries in these countries. and other advances in technology. drove French and Walloon Protestants (the Huguenots) into England. 3 Present Day Carpet Business In 1999 [2].3 Present Day Carpet Business every home owner in the USA.3 billion m2 in 1999. using nylon fiber. recreational vehicles. manufactured housing. multifamily units.6 billion square meters of carpet floor coverings. 9-1. is constructed for use in three markets: – consumer residential: purchases for use in a home by members of a family. apartments. with a value of $11. Woven carpet has almost disappeared and today only represents around 2 % of the total carpet manufactured. Tab. The state of Georgia accounts for 74 % of US production nearly all of which is concentrated in the northwest corner of the state around the city of Dalton [7]. as indicated in Tab. was being produced in twelve foot widths. etc. with broadloom carpet representing around 90 % of the tufted volume. As shown in Tab.7 billion. The evolution of the US carpet industry since this time is depicted below in Tab. etc. – contract residential: purchases by persons other than the home owner for new homes.9. 255 . and jute as the secondary backing cloth. This represents 45 % of the total world carpet production. 9-3. knotted. In the USA tufted broadloom carpet. 9-2. the most important segment of the tufted carpet business with an estimated 1. is somewhat different in that woven (13 %) and needlepunched (26 %) carpet floor coverings still have an appreciable share of the total. 9-2 1999 US carpet production (in million). needlepunched. Tab. 9-1 Evolution of the US carpet industry (in million m2). Second largest are the carpets grouped under others (knitted. the US carpet industry produced an estimated 1. Total Tufted Woven Other Total m2 US $ 1432 34 129 1595 10692 450 548 11690 The situation in Europe. Year Tufted carpet Woven carpet Total 1950 [5] 1974 [5] 1992 [6] 1998 [6] 1999 [2] 16 724 1094 1404 1432 65 61 19 30 34 81 785 1113 1434 1466 9.) with around 8 % of the total. condominiums. tufted carpet is by far the largest carpet type produced with approximately 90 % of the total carpet volume. The late nineteen-fifties saw the development of carboxylated styrene-butadiene dispersions (XSB) and their introduction as binders for carpet backings. the polymers usually being vulcanized to obtain good strength. the major binders were natural latex. institutional buildings and industrial buildings. m2 Tufted Woven Needlepunched Total 682 143 296 1121 I* 6656 1746 441 8843 *Courtesy: GUT e. Type m2 % Consumer residential Contract residential Contract commercial Total broadloom 707 262 339 1308 54 20 26 100 In all three. 9-4.V. 1999’s production forecast (USA) [1] for the three types of carpet is summarized in Tab. 9-4 Broadloom carpet by market type (in million). which began to replace the sulfur cure SB. The 70s through to the early nineteen-eighties was the era of the attached SBR foam cushion backings. the type and formulation of the backing adhesives differ significantly. whilst the binder used for construction may be the same.256 9 Applications in the Carpet Industry Tab. together with insight into their end use property requirements. the starches and natural gums initially used as binders for improved tuft bind. as a result of the easier and less costly compounding. and improved performance in terms of specific adhesion to the fabric substrates. 9. 9-3 1999 European carpet production (in million). school rooms. Tab.. Aachen. In the nineteen-fifties. faster drying rate. were largely replaced by rubber dispersions. banks. for producing the three carpet types will be detailed in sections following. motels. cold SB (styrene-butadiene) and hot SB dispersions. college dormitories. These XSB dispersions. In terms of square meters and market share percent. The formulations employed. have since become the workhorse of the carpet backing industry. business offices.4 Carpet Backing Binders During the late nineteen-forties. and methods of adhesive application. Such carpets were con- . Germany – contract commercial: purchases other than by a home owner for hotels. as each category of carpet has different performance specifications. The mid nineteen-fifties saw the introduction of non-cure hot SB dispersions. accelerators). chalk and emulsifier together with air is frothed. the highly competitive situation prevailing at the time. the growth in the market being almost entirely restricted to secondary backed products. Foam backing is a process in which a high solids SB dispersion. but at a much slower speed. In 1975 it was estimated that one third of all the broadloom carpet produced in the USA had an attached SBR cushion. The wet foam structure needs to be maintained until vulcanization takes place. Unfortunately. In the late nineteen-nineties environmental pressure. This can be achieved by gelling agents which destabilize the polymer particles by smoothly decreasing pH and coagulating the latex within the membranes of the wet foam. 257 . A similar situation to that observed in the USA has been experienced for similar reasons. An alternative more ecologically friendly product was required. and the market share of foam backed carpet being gradually eroded.9. this has decreased to approximately 20 % in 2000. The situation in Europe is somewhat different to that of the United States of America. Several of the ingredients used in the formulations for HSL foam in the floor coverings industry were brought into ecological question. a vulcanizing agent (suspension of sulfur. Non-gel foam is stabilized with emulsifiers which maintain the foam structure during the evaporation of water until vulcanization takes place. Since 1998. In general the styles of carpet produced in Europe have a much lower face fiber content. the pile height being much lower and pile density higher. The transfer of heat into the foam product is much easier.5 to 1:2. today HSL foam backed carpet has virtually disappeared in the USA. when foam backed carpets made up approximately 45 % of textile floor coverings in Europe. zinc oxide. In North America carpet underlays made of polyurethane foam are commonly used to provide the soft comfort of residential carpets. Vulcanization is carried out at about 100 °C resulting in an elastic polymer network. As consequence of the bad name that attached SBR cushions obtained in the eyes of consumers. compelled manufacturers to reduce the cost of the attached foam by either increasing the level of the cheap calcium carbonate filler and/or reducing foam application weights and density. with the exception of a few specialty floor coverings such as bath mats. and enabled higher production speeds to be achieved than were possible in the USA. The polymer/filler ratio varies from 1:0.4 Carpet Backing Binders structed using a compounded XSB dispersion pre-coat or tie-coat to bind the tufts in place. The foam backing was also generally of higher density therefor thinner for an equivalent weight. This inevitably adversely affected the durability of the foam to such an extent that failure occurred resulting in premature wear of the carpet. to provide under foot comfort. followed by the application of a foamed compound of a high solids styrenebutadiene latex (HSL). particularly in Germany. and prolong the useful life of the carpet. resulted in a very steep decline in the consumption of HSL for floor coverings. The consumption of HSL for foam backing remained fairly static for many years. In Europe this was achieved by replacing the HSL foam by a needlefelt product which is adhered to the carpet by means of an XSB latex. Ongoing advances in polymerization technology have enabled tailoring of the physical and polymeric properties of dispersions to better meet the evolving demands of present day backing machines and performance requirements. the remaining volume being shared by ethylene-vinyl acetate. the US carpet industry consumed approximately 490 kt wet dispersion. They are usually selected not only for good stability and low foaming during the dispersion manufacturing process. the dispersion producers have radically improved their XSB manufacturing processes to minimize the level of residual organic compounds. and the advent of “Sick Building components (VOC): Syndrome”. Polymer type: Bound styrene: Carboxylation: Carboxylated styrene butadiene dispersion (XSB) Typically in the range 60–67 % Typically less than 3 % by weight of the polymer. 9-5. The XSB binders of today are considerably different from those at the time of their introduction into carpet backings. Volatile organic Over the last 10–12 years. some typical characteristics of the dispersions commercially available today are given below. However. Polymer Products. but also to impart the required foaming properties to the backing binder formulations during processing in the customer’s plant. Southeastern Latex and Textile Rubber.0 Particle size: Up to 10 years ago. Omnova.258 9 Applications in the Carpet Industry Over the years. The actual type/level of carboxylation is proprietary information to each producer. it is fair to say that virtually every type of polymer available in dispersion form has been tried for use in the backing compound for tufted carpet. Today. polyvinyl chloride and polyurethane dispersions. because of its versatility and cost-effectiveness. Dow Chemical. with a minor proportion being supplied by so-called re-sellers or compounders such as General Latex. particle sizes are generally within the 140–155 nm range. 170–200 nm used to be the norm. as consequence of the need to reduce 4-PCH content. The carboxylic acid may be itaconic acid alone or blends of itaconic acid with either acrylic acid or methacrylic acid. Whilst the dispersion formulations are the proprietary information of the producers.5–9. During 1999. Solids content: 51–53 % dry weight pH: 7. Today. for the four major VOC are given in Tab. . of which 463 kt were XSB [4]. in ppm on wet dispersion. Surfactants: Type and level is the proprietary information of the individual producers. the maximum target values. it is the carboxylated styrene-butadiene (XSB) polymer dispersions that hold the major share of this business today with an estimated 95 % of the volume sold in 1999. The majority of the XSB is supplied direct to the carpet mills by the three major dispersion producers BASF. For cut-loop combinations. the unfinished tufted carpet will be dyed. followed by a finishing step to add a compound and usually a secondary backing material. Carpet laminating or backcoating is an essential step in the carpet manufacturing process. Both the long term performance and the aes- 259 . Stepping. needle bars and individually controlled needles greatly expand patterning possibilities. a special looper and conventional cutting knife are used. Tufting has reached a high degree of specialization utilizing a variety of patterning devices. knitted. with other factors. timed with the needles to catch the yarn and hold it to form loops. Below the needle plate are loopers. although they still work in the same basic way. Other advanced tufting techniques are loop over loop and loop over cut (LOC) machines. After completion of tufting. if precolored yarns are not used. The first tufting machines were very similar to a giant sewing machine that uses thousands of threaded needles in a row across the width of the machine. the yarns are passed overhead through guide tubes to puller rolls. or rack of yarn cones. a looper and knife combination is used to cut the loops. determines the carpet’s pile height. devices shaped like inverted hockey sticks.9. If a cut pile is called for. Today’s machines are far more complex and sophisticated. From the creel.5 Carpet Laminating Tab. needlepunch. Styrene Ethylbenzene 4-Vinylcyclohexene 4-Phenylcyclohexene Total North America Europe* Denmark 35 10 15 60 200 50 50 200 <400 40 20 10 50 *Defined by EPDLA (European Polymer Dispersion and Latex Association) and GuT (Association for environmental friendly carpet) 9. The needles. which number up to 2000 for very fine gauge machines. and tufted are subjected to the latex laminating procedure [8].5. By far the most prevalent carpet construction method is tufting. are located in front of the tufter. the attributes it imparts to the finished carpet are rarely appreciated. The speed of the puller rolls controls the amount of yarn that is supplied to the tufter and. insert the yarn into a primary backing supplied from a roll of material located in front of the machine. many of which are computer-controlled. The creel. Since the backcoating is hidden from view. 9-5 Maximum limits (ppm) of volatile organic components.1 Background Several types of carpets including woven. Spiked rolls on the front of the tufting machines feed the backing through the machine.5 Carpet Laminating 9. or zigzag moving. Such patterned carpet is frequently referred to as a graphic pattern. 2 Carpet Terminology Before proceeding further with carpet laminating. Physicals and terminology for a level loop carpet would be the same as for cut pile. vertical burn – resistance to edge fraying – odor 9. A level loop carpet would appear the same but the tops of the tufts would not be cut. 9-1 Carpet terminology.260 9 Applications in the Carpet Industry thetic value of the installed carpet are vitally dependent upon a correctly formulated and a properly applied backcoating.5. Figure 9-1 illustrates a typical cut pile carpet and the physicals associated with it. Fig. smoke. a review of carpet terminology would be useful. radiant panel. light. Among the most important performance requirements of a backcoating are: – high tuftlock – minimum pilling and fuzzing – adhesion to secondary backing – dimensional stability – bundlewrap – proper hand – durability – water resistance – resistance to heat. tunnel. and atmospheric contaminants – flammability-pill. . since physical properties imparted by the SB latex backcoating relate directly to its construction. 3 Back-coating Applications Over the last few years. Tuftbind: The force expressed in pounds required to remove a single tuft from its primary backing (ASTM D 1335) Pill and fuzz: Hairy effect on the carpet surface caused by slippage of individual filaments or fibers Bundlewrap: A subjective rating. Variations of this include a roll over roll for the pre-coat application and a roll over roll or Tillitson application for the adhesive.5 Carpet Laminating Tuft: Bundle: Filament: Primary: One cut or uncut loop of a pile fabric A continuous tufted collection of fibers or filaments A single continuous strand of fiber Woven or non-woven fabric into which the pile yarn is inserted by tufting Secondary: A woven or non-woven fabric laminated to the tufted primary to provide dimensional stability Delamination: The force expressed in lb/inch required to remove the secondary backing from the primary carpet (ASTM D 3936. This schematic shows a set up utilizing a bed-plate for the application of the pre-coat and a pan for the application of the adhesive scrim coat.9. 261 . usually expressed as a percentage. poor pickup) – better visual weight control (puddle gain or loss seen immediately) – faster drying due to lighter densities Figure 9-2 depicts a typical direct coating unit with scrim coat. The major advantages associated with direct coating are: – less waste (mill and disposal savings) – easier clean up – overall ease of operation – uncoated selvages (cost and clean up savings) – uniform weight control side to side – uniform coating side to side – fresh compound always available – less problems with filler fallout – higher compound solids – immediate response to cup weight changes – short lag time for compound changes – elimination of density variations (airing up or collapsing in pans) – thixotropic effects eliminated (troughing. to indicate the degree of latex encapsulating the yarn Bundle penetration: A subjective rating. to indicate the degree of penetration into the yarn Hand: A subjective rating to indicate the stiffness of the finished carpet 9. ISO 11857). usually expressed as a percentage.5. direct coating with scrim lock has replaced pan application as the preferred method for back-coating carpet. Miscellaneous ingredients include pigment. delamination. and combinations of ALS and long chain alcohol are commonly used. Its primary purpose is to securely lock the tufts into the primary backing. They impart the proper viscosity and rheology to allow proper placement of the compound.5. and thickener.262 9 Applications in the Carpet Industry Direct coating with scrim coat. penetrant. aid in the dispersion of the filler. surfactant. The froth machine lowers the density thus allowing for proper placement and weight control. Along with latex. chelating agent. Backcoating residential carpets involves two latex compounds. sodium sulfosuccinamate. and flammability. Sodium lauryl sulfate (SLS) and ammonium lauryl sulfate (ALS). the pre-coat compound would typically contain water. if a back-coating needs a specific appearance or specialized performance property. Other properties affected by the pre-coat are pill and fuzzing. 9-2 9. Typical pre-coat loadings are between 400 and 600 parts per 100 parts dry latex. filler. To enhance flame retardant properties. Miscellaneous ingredients occasionally will be used. One is highly loaded with filler and is deposited directly onto the tufted primary after having passed through a mechanical froth machine. defoamer. Its grind and purity are critical for compound stability and runability.4 Back-coating Formulations and Ingredients Direct coating is used to back-coat both residential and commercial carpets. The filler is almost always calcium carbonate due to its universal availability and economical price. Thickeners are almost always sodium polyacrylates. Water is used to adjust the solid content of the compound. This compound is usually referred to as the pre-coat or undercoat. dispersant. They also help to suspend the filler in the compound. Surfactants are used to increase stability and frothability of the compound. anti-blistering . Fig. aluminum trihydrate can be substituted for all or part of the filler in the pre-coat. hand. and extend shelf life. 2–0.7 786 Solids content of the formulation 83 %.6 Solids content of the formulation 82 %. the need for a secondary backing is eliminated. A typical pre-coat formulation used in North America is represented in Tab.6 579. surfactant is eliminated from the formulation. Loadings between 350 and 400 parts of filler per 100 parts of dry latex are typical. The second compound used in residential carpet coating is referred to as the adhesive scrim or skip coat. 9-6 Pre-coat formulation (US). since a stronger compound is required for the adhesive coating. This coating provides the strength necessary to sufficiently adhere the secondary backing to the primary backing. First. The configuration of the coating machines determines the compound to be used. On average the viscosity is 5 Pa s. and viscosity of 3–5 Pa s. Water XSB latex Calcium carbonate Surfactant Polyacrylate thickener Total Solids content (%) Dry parts Wet parts – 53 100 35 13 83 – 100 550 2 1 653 35 188 550 5. viscosity 9–10 Pa s In Europe the ingredients for secondary backing compounds are similar but the filler loads can vary from 0–450 parts per hundred part of dry latex. 9-7 Adhesive scrim coat formulation (US).7 7.4 dry parts).6 475. In general they contain more filler (600–1000 dry parts of calcium carbonate). The adhesive scrim coat formulation is similar to the pre-coat with two exceptions.9. since the compound is not frothed. 9-6. which in turn imparts dimensional stability to the carpet. Tab. Since most commercial contract carpets are glued directly to the substrate. Tab.5 Carpet Laminating agent. and stabilizer. viscosity 17–18 Pa s In Europe a typical pre-coat formulation does not exist due to widely differing styles and quality requirements. filler loading is reduced. Water XSB latex Calcium carbonate Polyacrylate thickener Total Solids content (%) Dry parts Wet parts – 53 100 13 82 – 100 375 0. antistatic agent.5 dry parts). Secondly. less surfactant (0.6 12 188 375 4. Thus most commercial contract carpets 263 . It is applied by means of a pan and lick roll directly to the secondary backing. and less thickener (0. Table 9-7 is representative of a typical adhesive formulation. Filler levels are typically in the range of 150–200 parts of filler per 100 dry parts of latex.5 Industry Issues Although direct coat has been universally accepted as the latex application technique of choice.5 0. XSB latex Calcium carbonate Surfactant Polyacrylate thickener Total Solids content (%) Dry parts Wet parts 53 100 35 13 73 100 150 0. 9-8 Unitary backing formulation (US).9 188. As the industry becomes even more competitive. Feed forward application systems are beginning to be used by some manufacturers. Table 9-8 illustrates a typical North American unitary formulation. viscosity 9–10 Pa s European unitary formulations would be very similar both in ingredients and filler loads to the above North American formulation. Typical viscosity is 5 to 7 Pa s. High density is achieved by using low surfactant levels and lightly frothing the unitary compound.6 150 1. 9.1 343. there still exist large variations in processing speeds due to a wide range of dryer configurations and their efficiencies. This system produces a more consistent compound application resulting in enhanced performance.4 3. high speed finishing ovens – increased use of computerized froth machines . manufacturers will be forced to continue to reduce fixed and variable costs.5. Tab.264 9 Applications in the Carpet Industry are coated with a single high strength compound referred to as a unitary coating. Electronic monitoring from the compounding area to final inspection is reducing manpower requirements and increasing dryer efficiency dramatically. 50–90 N) and pill and fuzzing. The two most important properties of a unitary coating are high tuft-bind requirements (11–20 lb. Utilizing computerized frothing machines eliminates the need to sample for density control and allows for a more consistent latex application due to the consistent froth produced.1 Solids content of the formulation 73 %. To meet the enhanced performance requirements of commercial contract carpets a high density. Current processing speeds for a light weight carpet can range between 10 to 60 m min–1. low filled compound is used. More and more high speed dryers will replace slow inefficient ones. Computerized froth machines will become more common as mills focus on reducing variable costs.4 250. Following is a list of process improvements currently being implemented or anticipated for implementation in the future: – movement toward high efficiency. and economics. As a result. the SBLC member companies have reduced VOC emissions by 95 % since 1988. Even though carpet emissions have been declared to produce no adverse health effects. It is formed by a DielsAlder reaction of styrene and 1. the issue of new carpet odor had to be addressed. In the early nineteen-nineties allegations stemming from flawed scientific work arose connecting a chemical (4-PCH) emitted from carpeting to adverse health effects. and adverse health effects. the EPA declared 4-PCH to be an “unremarkable chemical” [9]. Due to its performance.3-butadiene and is responsible for “new carpet odor”.9. the trend toward ammonia free latex is also creating a more worker friendly environment in the manufacturing site.5 Carpet Laminating – feed forward application systems – some carpet producers beginning to question delamination testing as best indicator of “fit for use” – increased use of polypropylene fibers for commercial carpet resulting in greater need for latex that has an affinity for polypropylene – greater need for blister resistant latex due to higher heat and more efficient ovens – increased commitments through quality partnerships by both latex producers and carpet manufacturers in the use of statistical process control – movement towards low/zero ammonia systems to reduce emissions into the workplace – quality issues have replaced VOC issues as the primary concern of carpet manufacturers. Even though alternative backing systems are available. versatility. 4-phenyl cyclohexene or 4-PCH is a byproduct of the SB latex manufacturing process and has a low odor threshold. SB latex continues to afford the carpet manufacturer the best value in back-coating systems today and for the foreseeable future. As a result of the allegations the Styrene Butadiene Latex Council (SBLC). 265 . As well as creating an odor free environment for the carpet consumer by reducing VOCs. Since 1988 there has been a heightened awareness of volatile organic compounds (VOC) emitted from carpet. With present low VOC latex and proper drying technique. the trade association of US latex producers and the EPA (Environmental Protection Agency) undertook extensive animal toxicological testing to investigate whether there was a link between 4-PCH and adverse health effects. carpet manufacturers today can produce odor free carpet. EPA has repeatedly concluded that valid scientific data showed no link between 4-PCH or any other carpet VOC emission. SB latex still accounts for over 90 % of the carpet back-coating market. After exhaustive testing and numerous reviews. Statistical Report 2 3 4 5 ’99. 2000. 1997.266 References 1 Floor Covering Weekly. 8 Carpet and Rug Institute. Bureau of Census. 9 55 Federal Register 17404. . 1999. Martino. 2000. D. Carpet Primer. December. April 24. US Department of Commerce. The Pride of Georgia. 1990. Carpet and Rugs. History and Current Statistics. 2000. 49(19). 6 Carpet and Rug Institute. 7 CRI The Tufted Carpet Industry. 1999 Industry Review. Brunswick Corporation. American Plastics Council Monthly Statistical Report. Carpet Backfinishing Review. Current Industrial Reports. 1999. 2000. Intercontuft. 1975. L. July 17/24. as shown in Fig.8 billion [7] and disposables account for nearly 70 % in value. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. or filaments by mechanical. They are not made by weaving or knitting and do not require converting the fibers to yarn. They are categorized according to application as either disposables or durables. KGaA ISBNs: 3-527-30286-7 (Hardback). or very durable. strength. yarns. 3-527-60058-2 (Electronic) 10 Non-wovens Application Koichi Takamura. molten plastic or plastic film. They provide specific functions such as absorbency. followed by North America (30 %).1 Introduction Non-wovens are described as flat. non-woven fabrics provide a spectrum of products with diverse properties.0 billion pounds) in 1999 [4–6]. They are porous sheets that are made directly from separate fibers. Marilyn Wolf. chemical. softness. Non-woven fabrics are engineered fabrics that may be of single-use. Western Europe accounts for approximately 35 % of the world production of non-woven products. Japan (12 %) and others. 10-1. or solvent means. Double-digit growth is expected in these countries. industrial. 10-1 [1–3]. China (12 %). flame retardancy. The worldwide production of non-wovens is estimated at 2. thermal. China and Japan dominate non-wovens production in Asia followed by Taiwan and Korea as shown in Fig. health care. In combination with other materials. The non-woven industry in North America is expected to grow at 2–3 % annually and to be $3. resilience.Polymer Dispersions and Their Industrial Applications. porous sheet or web structures produced by binding and interlocking fibers. home furnishing. cushioning. Some familiar products made with non-wovens are listed in Tab. and Jim Tanger 10. and production in China and Japan reached to 350 000 tons each in 2000 with an an- 267 . engineering. 10-2. liquid repellency. These properties are often combined to create fabrics suited for specific jobs.7 million tons (or 6. and are used alone or as components of apparel. limited life. stretch. while achieving a good balance between product uselife and cost. filtering. bacterial barrier and sterility. The value of nonwoven product shipment in North America reached an all-time high in 1997 with an approximate value of $2. and consumer goods.2 billion in 2002. washability. 5 billion yards (13 billion m2) and 900 million pounds (400 000 tons) of material. sanitary napkins and tampons Sterile wraps. Western Europe and Asia produced approximately 35 % each. tags and labels Insulation and house wraps Roofing products Civil engineering fabrics/geotextiles Global Production of Nonwovens W.268 10 Non-wovens Application Tab. Fig.e. Europe Asia Global non-woven production reached to 2. high loft padding and backing Wall coverings Agricultural coverings and seed strips Electronic components (i. polishing cloth. Disposable products Diapers. masks Drapings used in the medical field Household and personal wipes Filtration media Laundry aids (fabric-dryer sheets) Embroidery backing Durable products Apparel interlining Carpet backing and upholstery fabrics. China non-woven production increased 87 times during the last two decades from 4000 tons in 1980.9 billion in 1997.7 million tons in 1999. but fewer than 20 % Nonwoven Production in Asia Taiwan 100 kton Japan 315 kton China 315 kton China and Japan are two major non-woven producers in Asia. 10-1 North America nual growth rate of 11 % [5. 10-1 Some familiar products made with non-wovens. 10-3. As seen in Fig. gowns. etc. filtration and medical applications represent nearly 60 % of the dollar value. Fig. caps. battery separations. They reported 11 % annual growth in 2000.) Envelopes. and represent roughly 15. 10-2 Korea 100 kton . disk liners. 6]. insulation liners. The North American market for disposable applications was approximately $1. 1 billion yard 2 (2. 10-4. Total $ 0. 10-3 1997 figures show disposable products account for nearly 70 % in the dollar value and 85 % in volume in North America. but furniture. Cover stock applications dominate disposable volume. 10-5 comparing total weight of products in 1999. Europe has a longer history in the use of durable non-wovens. of disposable square yard volume. and Furniture/Bedding/Home applications account for approximately 55 % of $0. where disposable non-wovens play a stronger role as discussed above. but furniture related applications are the largest in volume. 10-4 Electronic. Electronic. and approximately 80 % of this volume is used for diaper production [7]. This is in contrast to the North American market.9 billion non-woven materials in durable applications in the North American market.9 billion Total 3.10.9 billion 2 2 Total 15.5 billion yard (13 billion m ) Dryer Sheets Wipes Wipes Dryer Sheets Filtration Filtration Medical Cover Stock Cover Stock Medical Fig. bedding and home furnishing applications are the largest volume (42 %) of non-wovens in this durable category as shown in Fig. The volume for durable non-wovens exceeds that used for disposables in Europe. Interlining. European and Japanese markets are shown in Fig. in particular geotextiles and roofing substrates. North American.6 billion m2 ) Automotive Electronic Construction Materials Construction Materials Automotive Electronic Interlining Coating/ Laminates Coating/ Laminates Interlining Geotextiles Geotextiles Furniture/ Bedding/Home Furniture/ Bedding/Home Fig. interlining and furniture related applications account for 55 % of $ 0.1 Introduction Total $1. Hygiene (cover stock in North America and consumer goods in Japan) medical products and wipes account for greater than 50 % of 269 .9 billion in durable applications in North America. proprietary technology was used to produce fabric structures that performed not only better than items they were designed to replace. Europe and Japan are compared by weight of products in 1999. but often when traditional fabrics could not. 10-5 Non-woven applications in North America. though consumer goods in Japan appear to include some durable products. The basic non-woven manufacturing systems have four principal elements or phases: fiber selection and preparation. As a result. During this initial phase. Many non-woven products listed in Fig 10-5 were virtually non-existent a generation ago. medical and wipes account for greater than 50 % in all these continents. web consolidation. .2 Manufacturing Systems Early thrust in non-woven usage emphasized replacing traditional knits and woven fabrics in low-end applications. web formation. 10. new applications and markets were established and the industry expanded. total production in these continents.270 10 Non-wovens Application North American Production (800 kton) European Production (910 kton) Coaging/ Laminates Civil Engineering Geotextitle Coating Substrates Filtration Automotive Carpet Backing Building Medical Furniture/ Bedding/ Home Hygiene Construction Materials Others Interlining Electronic CoverStock Garments Wipes Dryer Sheets Footwear/ Leather Goods Floor Coverings Wipes Upholstery/ Bed Linen Japanese Production (315 kton) Others Medical Interlinings Filtration Consumer Goods Industrial Products Construction Medical Fig. Hygiene. and finishing treatments. mineral.1 Web Formation Four basic methods are used to form a web. Products produced by the spun-laid technique account for 20–25 % of the market in Japan and China [5. this cannot be regarded as the principal method of bonding. North American Market by Process European Market by Process Wetlaid Wetlaid Spunlaid Spunlaid Drylaid Drylaid Other Fig. Detailed description of these technologies can be found elsewhere [1. and non-wovens are usually referred to by one of these methods: dry-laid. The wet-laid process is similar to paper making. wet-laid and other techniques. polymer granules are melted and molten polymer is extruded through spinnerets. but raw material flexibility is more restricted. since most textile fibers and bonding systems can be utilized and conventional textile fiber processing equipment can be readily adapted with minimum additional investment.2. as melt-blown and flash spun web formation methods. 10-6.2 Manufacturing Systems 10. The spun-laid process (also known as spun-bonded) has the advantage of giving non-wovens greater strength. Spun-laid and dry-laid are two preferred processes both in North America and Europe. 4]. Other 271 . The continuous filaments are cooled and deposited on to a conveyor to form a uniform web. Other techniques include a group of specialized technologies in which the fiber production.10. The dry-laid processes provide maximum product versatility. In the spun-laid process. where a dilute slurry of water and fibers are deposited on a moving wire screen and drained to form a web. spun-laid and dry-laid are two preferred processes both in North America and Europe. garnetting and air-laying are examples of the dry-laid processes. Carding. and synthetic fibers of varying length can be used. As seen in Fig. The spun-laid process showed the strongest growth during a last decade [1. 10-6 Comparison of web formation technologies in North America and Europe. Even though filaments adhere to one another during this cooling process. web structure and bonding usually occur at the same time and in the same place. spun-laid. 7]. A wide range of natural. 6]. Factors to consider when consolidating a web with binder are the end-use characteristics. Carded thermally bonded technology is losing significant share in the cover stock market in North America and spun-bonded non-wovens accounted for 75 % of cover stock in 1999 (Fig. whereas hydro-entanglement is mainly applied to carded or wet-laid webs. Air Laid . Cover Stock Wipes Melt Blown Carded Thermal Bounded Unbounded Carded Web Other Carded Thermal Bounded Hydroentangled Unbounded Carded Web Carded Chemical Bounded Wet Laid Spunbounded Fig. mechanical and chemical. process compatibility. The thermal bonding uses the thermoplastic properties of certain synthetic fibers to form bonds under controlled heating. Hydro-entangled products are expected to grow in wipes. thermal. Chemical bonding mainly refers to the application of a latex dispersion based bonding agent to the web. and foaming. but often a low melt fiber or bi-component fiber is introduced at the web formation stage to perform the binding function later in the process. Hydro-entangled products are expected to grow due to superior strength and softness [7]. printing. drying capacity and cost [1]. 10-7 Spun-bonded products dominate the cover stock market in North America due to better performance and lower cost. the type of web substrate that is used. In some cases the web fiber itself can be used.2 Web Consolidation Webs produced with the above described processed have limited strength in their unbonded form and need to be consolidated. Needle punching and hydro-entanglement (also known as spunlace) are two main mechanical bonding processes. There are three basic types of bonding. Needle-punching can be used on most fiber types. 10-7). In contrast widely different technologies are utilized to produce non-wovens for wipes.2. line speed. spraying.272 10 Non-wovens Application 10. In mechanical bonding the strength of the web is obtained through the physical entanglement of the fibers. The major binder application methods include saturation. 8]. stiffness. absorbency. Characteristics of these latex binders and typical applications of non-woven products are summarized in Tab. flame retardancy. An article by Wiaczek [3] estimates that total latex consumption in the US non-wovens market will reach 160 000 dry tons in 2001. color fastness. They are less costly than acrylics. 10-8 [1. water repellency. and maintain excellent toughness. abrasion resistance. 273 . It also provides hydrophobicity and durability to products. tear resistance. Ethylene vinyl acetate binders provide high tensile strength and excellent absorbency. 10-2.10.3 Polymer Dispersions for Chemical Bonding 10. 10-8 Acrylics are the predominant binders used in non-wovens. durability. Vinyl acetate binders offer good dry strength and toughness but tend to be hydrophilic. such as glass transition temperature. smoothness. especially together with antimony oxide [11]. heat sealability. Latex binders fall into following two categories: those that provide rigidity to a product and those that render a web soft and drapeable. color stability and dry/wet performance. Vinyl Acrylic Vinyl Chloride/ Others Vinyl Acetate Acrylic Ethylene Vinyl Acetate Fig. dry cleanability. colloidal stability and specific surface functionality for post chemical reactions. Chlorinated polymers such as poly(vinyl chloride) and ethylene vinyl polymers promote flame retardancy. resiliency. Styrene-butadiene latex offers an excellent combination of flexibility and toughness. non-linting. monomer compositions are optimized to obtain desired physicochemical properties. Vinyl acrylics are more hydrophobic than vinyl acetate binders. Acrylics are the predominant binders used in non-wovens as shown in Fig. pilling resistance. Tg. flexibility and better color stability. molecular mass. cross-linking density.3 Polymer Dispersions for Chemical Bonding Most non-wovens use 5 % to 50 % of polymer binder to provide one or more of following characteristics: softness. and bulkiness [1]. dry and wet tensile strength. but the vinyl acetate ethylene latex showed strongest growth during the last decade StyreneButadiene For all these latices. They are versatile and offer the ultimate in durability. dry-cleanability. good adhesion. g Solids. moderate durability. industrial. Tab. 10-3. coverstock Ethylene-vinyl acetate Good softness. foam impregnation or print bonding as shown in Tab. % Acrylic latex Water Defoamer Surfactant 100 120–450 0.1 0–1 55 Acrylic latex Water* Ammonia* Surfactants 100 80–150 55 100 150–450 55 0–5 50 Acrylic latex Water1 Dye2 Thickener1 *Adjust to 10-25% solids 100 50 *Adjust to 15-30% solids and pH=8 Typical foam weight of 70–150 g/liter 1 2 Adjust to 10–15% solids and 10Pas viscosity Add to the desired color . limited washability and dry-cleanability Highloft webs. can be plasticized.274 10 Non-wovens Application Tab. dry-cleanability Synthetic leather As shown in Fig. carder. home furnishings Acrylic Excellent adhesion. good cross-linking Coverstock. Latex binder type Characteristics Typical applications Polyvinyl acetate Resilient. wipes. air-laid pulp Styrene-butadiene Good tear and tensile Filters. g Solids. excellent durability. wipes. somewhat stiff. g Solids. highloft webs Poly(vinyl alcohol) Resilient. launderability. widely different technologies are utilized to produce wipes. Saturation Foam Impregnation Print Bonding Materials Weight. % Materials Weight. good solvent resistance Medical and/or surgical. heat sealable. home furnishings Poly(vinyl chloride) Stiff to soft. stiff to soft. The acrylic latex can be applied through saturation. fabric softener. filter media. filter media. medical Acrylonitrile-butadiene copolymer Resilience. 10-7. durability and adhesion Coverstock. wall covering Ethylene-vinyl chloride Excellent mechanical stability Underpads. launderability. foam and print bonding methods. interlinings medical/ health care. wet wipes Vinyl acetateacrylic copolymer Flexibility. % Materials Weight. heat sealable. 10-2 Basic characteristics and typical applications of latex binders used for non-wovens pro- duction. 10-3 Typical latex-based formulations for wipes with saturation. low temperature cure Scouring pads. wipes. water absorbent Filter media. This is also applicable to the binder application method. INDA (Association of the Non-woven Fabrics Industry) Standard Test [2] and EDANA (European Disposables and Non-wovens Association) Recommended Test Method [4] are two major standards for non-wovens.10. and some corresponding EDANA.4 Application Test Methods 10. government and university research institutes. the stiffness was measured by the Handle-O-Meter (IST 90. International Standardization Organization (ISO) and the American Society for Testing and Materials (ASTM) refine and approve a wide range of test methods developed by these trade organizations. 10-9 Improvement in the stiffness of an acrylic latex bonded non-woven sheet as a function of the latex level.3). INDA Standard Test Methods. The crosslinking resins such as melamine can be used to enhance wet and dry tensile strength. 60 275 .4 Application Test Methods A series of well-defined standardized test methods have been established through various trade organizations. 10-4. mN 250 with 10% Melamine 200 150 100 with 5% Melamine 50 without Melamine 0 0 20 40 % Acrylic in Sheet Fig. moisture resistance. ASTM and ISO test methods are listed in Tab. where a fabric specimen is pushed through a slot with a blade on an arm at a constant rate and the resultant force on the center point of the fabric measured. heat resistance and solvent resistance (dry-cleanability) of non-woven fabrics. Here. Figure 10-9 illustrates examples of the stiffness improvement of an acrylic latex bonded non-woven sheet as a function of the latex level in the sheet at two different levels of the melamine resin [12]. Dent [13] recently reported through theoretical analysis that the initial slope of the load-deflection curve Handle-O-Meter Reading. 2 IST 10.1 IST 10.4 IST 20. ASTM and ISO tests.2 IST 40.1 IST 30. ERT 80.2 IST 20.6 ISO 276 10 Non-wovens Application .3-99 ERT 230.3 IST 20.1 IST 40.IST GL non-wovens IST GL felts IST 1 IST 10.3-99 ERT 1.1 IST 20.3 IST 20.6 IST 30.3-99 EDANA recommended test method ASTM D3786-87 ASTM D3886-92 ASTM D3885-99 ASTM D4157-92 ASTM D3884-92 ASTM D4966-98 ASTM D4158-92 ASTM D1117-99 ASTM method ISO 9073-6 ISO 13938-1 ISO 12947-3 ISO 9073.5 IST 20.2 Absorption Non-woven absorption Rate of sorption of wiping materials Demond absorbency Abrasion resistance Inflated diaphragm Flexing and abrasion Oscillatory cylinder Rotary platform Martindale Uniform abrasion method Bursting strength Diaphragm Non-woven burst Electrostatic properties Surface resistivity Decay INDA standard test method Guideline test methods for evaluating non-woven felt Non-woven vocabulary Guideline test methods for non-woven fabrics Description Tab. 10-4 INDA Standard Test Methods for non-wovens and the corresponding EDANA.0-99 ERT 10. 1 IST 90.IST 50.8 IST 80.2 IST 90.4 IST 80.0-99 ERT 120.2 IST 60.1 IST 60.4 IST 80.1-78 EDANA recommended test method ASTM D5732-95 ASTM D737-96 ASTM D5908-96 ASTM D4770-00 ASTM method IS09073-7 ISO 811-1981 ISO 811-1981 ISO 4920-1981 (E) ISO 9073 8:1995 ISO 2471-198 ISO 2470-1997 ISO 10.7 IST 80.5-99 ERT 152.4 Optical properties Opacity Brightness Permeability Air permeability Water vapor transmission (multiple tests) Liquid strike-through time Water vapor transmission (Mocon) Repellence Surface wetting spray test Penetration by water (rain test) Penetration by water (spray impact test) Penetration by water (hydrostatic pressure test) Penetration by saline solution (automated mason jar test) Water resistance hydrostatic pressure test) Penetration by oil (hydrocarbon resistance) Alcohol repellence of non-woven fabrics Non-wovens run-off Stiffness Cantilever Gurley Handle-O-meter Drape INDA standard test method Binder properties Resin binder distribution and penetration Appearance and integrity of highloft batting Description ERT 90.3 IST 80.2 IST 70.5 IST 80.1-99 ERT 110.1-78 ERT 100.4-99 ERT50.6 IST 80.1 IST 70.1-80 ERT 170.1-80 ERT 150.4-99 ERT 140.0-89 ERT 120.1 IST 80.4 Application Test Methods 277 .3 IST 70.9 IST 90.2 IST 80.2 IST 70.1 IST 50.3 IST 90. 2-89 ERT 70. IST 120.3-90 ERT 30.4 IST 120.Continue.5-99 ERT 20.4 Tensile Grab Seam strength Internal bond strength Strip Thickness Thickness of non-woven fabrics Highloft non-wovens Highloft compression and recovery (measurematic) Highloft compression and recovery (plates and weights.2 IST 110. 10-4 ERT 220-0-96 & 300-84 ERT 40.1 IST 100.3 IST 110.3 INDA standard test method Tear strength Elmendorf Trapezoid Tongue Description Tab. high temperature.1 IST 150.2 IST 120.3 Weight Non-wovens mass per unit area Friction Static arid kinetic Dry-cleaning Resistance Appearance and integrity of highloft batting Linting Particulate shedding (dry) Particulate shedding (wet) Fibrous debris from non-woven fabrics IST 120.4-99 EDANA recommended test method ASTM D2724-87 ASTM D5729-97 ASTM D5736-95 ASTM D5035-95 ASTM D5034-95 ASTM D1683-90A ASTM D5734-95 ASTM D5733-95 ASTM method ISO 9073-2:1995(E) ISO 9073-3 ISO 13934-2:1999 ISO 1974-1974(E) ISO 9073-1997(E) ISO 278 10 Non-wovens Application .1 IST 160.5 IST 140.5 IST 130. room temperature) Highloft Compression and Recovery (plates and weights.1 IST 110. high humidity) IST 100.2 IST 100.1 IST 150.2 IST 160.3 IST 110.2 IST 160.1 IST 120. A specimen support consisting of a non-absorbent material 100 × 100 mm with a central hole of approx. burette stand.1 g Wire basket. light source Swatch or skein to fit tightly over embroidery hoop As directed in EDANA 10. Record time for the basket to sink completely below the surface of the liquid Wire basket. max.. stopwatch. weight 3 to 8 g. liquid.01 mL are the amounts used. weight 3 ± 1 g. 2 cm mesh.INDA IST 10.1-95 According to ASTM D 1776 In MD direction cut 75 mm and a length sufficient so the strip weight is 5 ± 0.1 mL and 0.1 g Condition test specimens according to ERT 60. number 20 to 26 gage B&S copper wire. It is important to condition the fabric.4 Application Test Methods 279 . Drop measuring device. diameter 5 cm.3-99 As directed in EDANA 10. diameter 5 cm. stopwatch Drop basket from height of 25 mm into liquid.3-99 Excerpt from 2000 Global Comparison of Test Methods for non-woven absorption [10]. 40 mm diameter Approximately 100 mm × 100 mm According to TAPPI T 402 TAPPI T432 OM-94 ISO ISO9073-6 Absorbency in s (of bleached textiles) 5 Deliver one drop of water (21 ± 3 °C) 1. liquid container.3-99 At moisture According to equilibrium ISO 139 65 ± 2 % RH.2-99 EDANA ERT 10. 0. Burette. stopwatch In MD direction cut 76 ± 1 mm wide and a length so the strip weight is 5 ± 0. height 8 cm. 21 ± 1 °C AATCC 79-1995 10. or more.0 ± 0. liquid container.1 cm from hoop.3-99 5 As directed in EDANA 10. and minimum absorption time in s.5 mm diameter stainless steel wire. 2 cm mesh. the volume used. and type of paper used 10 Drop liquid from height of at least 10 mm on to the specimen. Time for specimen to become completely wet is measured 5 Absorbency time in s Properties Sample conditioning Test specimen size Equipment used Procedure Number of tests Properties reported Liquid absorbency time in s 5 Drop basket from height of 25 ± 1 mm into room temp. Embroidery hoop 15 cm dia. (Absorption – Liquid Absorbency Time) Tab.3-99 As directed in EDANA 10.0 mL 0. height 8 cm. 1. delivering 15–25 drops per mL. 10-5 ASTM Average. six hydro-entangled. which is placed on a stainless steel pan. imparted through creping or stitch-bonding exhibited superior “wipe-dry”. a single measurement can measure two basic parameters governing the fabric “hand” or “feel”. while the ratio of maximum load to initial slope gives the fabric friction or smoothness. he describes results of the dynamic wiping efficiency. Table 10-5 is an excerpt from the Absorption – Liquid Absorbency Time. which conveniently compares standard test methods by the above listed organizations. or “wipe-dry” test. In addition. a wiper is affixed to the bottom side of a 1 kg sled. A known amount of the liquid challenge was placed in front of the sled pulled into and through the pool at a wiping speed of 25 cm s–1.2. Thus.280 10 Non-wovens Application gives the fabric stiffness or flexural rigidity. TAPPI (Technical Association of the Pulp and Paper Industry) is active in the wet-form non-woven segment of the industry [9]. Some of the standard test methods established by AATCC (American Association of Textile Chemists and Colorists) are also applicable to non-wovens. INDA recently published “2000 Global Comparison of Test Methods” [10].1 and 10. The test tries to simulate manual wiping operations. two knitted polyester and one woven cotton. In this test. which demonstrates two different principles used to quantify similar properties. In addition to the static absorption measurements specified by IST 10. His results demonstrate that fabrics with bulky character. Oathout [14] has discussed the water-absorption characteristics of eleven wiping materials including one 100 % wood pulp with binder. . paper making process. Flame Retardant Nonwovens. www. Determining the Dynamic Efficiency with which Wiping Materials Remove Liquids from Surface. 1992. 2000. International Non-wovens Journal. USA. Cary. North Carolina. GA. North Carolina. 10 11 12 13 14 TAPPI Press. Non-wovens World 2 3 4 5 6 7 8 Factbook 1991. 1998. An analysis of fabric ‘Hand’ and ‘Feel’. 1999. D. J. USA.com Association of the Non-woven Fabrics Industry. TAPPI Press. P. Belgium. Miller Freeman Publications. W. www. ISBN 0-87930-227-5. . 221–248. M. Vaughn. Wiaczek. Wallace. M. Crosslinker resins in non-woven binder systems.tappi. 2000. 1988. 9. www. Oathout.org 2000 Global Comparison of Test Methods. 2000. TAPPI PRESS. Vol. www. Vinyl Copolymer Materials. Atlanta. 1988.gr. Cary. A. Non-wovens Binders and Additives Seminar. Non-wovens Binders and Additives Seminar. Vol. Brussels. B. International Non-wovens Journal. R. www. Association for the Non-woven Fabrics Industry.281 References 1 E. Analysis – The Non-woven Industry in North America. Principles of Non-wovens.chinanonwovens. 1991. EDANA – European Disposables and Non-wovens Association. 9.org P.org All Nippon Non-wovens Association.edana. 9 1998-1999 TAPPI Test Methods.INDA. Comparison of Trends in Latex Emulsions for Non-wovens and Textiles: China and the United States. Dent. Weil. D. Association of the Non-woven Fabrics Industry. 53-61. E. International Non-wovens Journal.anna. Koltisko. Association of the Non-woven Fabrics Industry.jp China Non-woven Technical Association. Methods for converting the fresh animal hide into leather (Fig. a naturally occurring aluminum sulfate (mineral tanning). Fig. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. 11-1 Structure of leather. for example.1 Introduction Leather making is an ancient art. Tanning with vegetable tannins (vegetable tanning) and with alum. Stone Age man. KGaA ISBNs: 3-527-30286-7 (Hardback). then became established in the Middle Ages. used smoke or fat for preserving the hides. Dix and Werner Kirchner 11. economical manner. 283 . 3-527-60058-2 (Electronic) 11 Applications in the Leather Industry Johannes P. It was only about 100 years ago that the development of chrome tanning (tanning with chromium salts) produced the decisive breakthrough which has made it possible to produce leather in an efficient. 11-1) have been known for approximately 100 000 years [1].Polymer Dispersions and Their Industrial Applications. It is this function that is performed by leather finishing [1–7]. This has led and is still leading to a relocation of leather manufacture from the traditional industrialized countries of Europe and from the U. 7.S. Costs of leather production in Europe: ca. It is driven by the high proportion of leather processing and leather production costs attributable to wages (Fig. At the same time. the industry. especially in the Far East (Fig. 11-2). 11. The articles made from leather differ greatly.2 Market Situation To describe the economic importance of polymer dispersions. which is predominantly based on small and medium size companies. The leather industry has undergone global changes in the last decades. a brief look at the structure of the leather industry is helpful.284 11 Applications in the Leather Industry The excellent properties of chrome-tanned leather opened up new fields of use and made possible the mass production of leather goods. Livestock is bred world-wide. Fig. 11-3). to low wage countries. Accordingly. It is closely coupled to raw hide production and hence to meat consumption. for example in the shoe or apparel leather sector. This structural change is still not complete. The leather industry is one of the oldest and most complex industries world-wide. 11-3 . ranging from shoe upper leather to apparel leather and to automotive leather. tanneries are located all around the globe. 11-2 Regional distribution of finished leather production.5 e/m2 Breakdown of leather production costs (without raw hide costs) in Europe. Fig. is undergoing a process of consolidation. This created the need for fashionable styling of these leather goods and for making them resistant to soiling and damage. 10 %. finishing dyes and finishing auxiliaries (Fig. goat) at about 30 % and pork leather at ca. the solvent-containing lacquers still account for a relatively large share today. 0.5 billion world-wide. the annual growth rate of leather produced is only small (ca. The finishing segment subdivides into the categories of binders/top coats.2 Market Situation Since finished leather production is determined by raw hide production (Fig. Polyacrylate or polybutadiene dispersions are preferred here. However. 11-4 World-wide raw hide production in 1990 to 1995.75 billion Fig. 11-6). 30 %). here too increasingly tougher environmental regulations are driving a changeover to solvent-reduced and waterborne systems. The largest segment by far in terms of value is the product range for tanning (ca. followed by small-animal skins (sheep. Fig. followed by finishing (ca. depending on the end use. aqueous systems based on polyurethane dispersions are used as well as.11.11-4). The market volume of chemicals used in leather manufacture is about Euro 2. At about 20 %. 60 %). this share will in future decrease further in favor of polyurethane dispersions. Finishing market volume: ca.8 % year–1). 285 . solvent-containing lacquers or emulsions. About 180 000 tons annum–1 of binders are estimated to be used in leather finishing world-wide. Base coats and pigmented coats are today already commonly applied in low-solvent and solvent-free processes. The predominant portion of leather produced is cattle hide (ca. still. 11-5 Distribution of market volume in leather finishing between individual product ranges. 50 %). Polyurethane dispersions and casein formulations are used as well. about 60 % are polyacrylate and polybutadiene dispersions and about 12 % polyurethane dispersions (Fig. 11-5). e 0. However. In the case of top coats. Of that. The leather is also dyed. The thermoplasticity of polymer dispersions makes it possible to emboss the leather surface and so create any desired surface texture. A surface coating provides better protection against wetness. The use of polymer dispersions provides not only better adhesion of the finish to the leather. strength. The finishing of buffed leather or split leather permits the use and upgrading of otherwise less suitable leather qualities. Similarly. luster or feel and also light. water repellency) is substantially determined by the retanning and the fat-liquoring operations. At the same time. Interestingly.or rub-fastness are imparted or improved. leather damages or unlevelness (grain defects.286 11 Applications in the Leather Industry World-wide use of binders in leather finishing. scratches) are covered up. This was the first polymer dispersion on the market and the starting point for the immense development of polymer dispersions for other applications too. This is followed by the further processing of the dried leather (crust). The further processing takes place in two stages: In wet finishing. This is done using soluble dyes. Farben commercialized a dispersion based on poly(methyl acrylate) in 1931. It is this operation which is commonly referred to as finishing. i. but also highly flexible finishes that are stable to light and aging. It is accordingly no surprise that polymer dispersions have become widely established in leather finishing. soiling and mechanical action. Surface properties such as hue. They make it possible to apply thicker finish coats on the leather.. usually becomes a sailable article with an upgrading post-treatment. It makes a significant contribution to enhancing the performance characteristics.3 Leather Finishing The tanned animal hide. .e. many fashion effects are not possible without finishing.G. leather finishing was one of the first industrial applications for polymer dispersions. the leather. the then I. 11-6 11. the immense potential of polymer dispersions as binders for finishing was soon recognized. While Corialgrund E was primarily used as a barrier to avoid migration of the plasticizer out of the nitrocellulose lacquers then used and thus to counteract finish embrittlement. the character of the leather article (softness. Fig. In Corialgrund E. 11.3. Adequate adhesion is the precondition for many application properties and important to achieve the required physical fastnesses for the ready-produced leather articles. Leather finishing is therefore regarded as being more an art than a science.3. 11.4 Grain Impregnation Grain impregnation is used to improve the firmness of the buffed grain layer. are used to dye.3. 287 . Soft. damages to the finish in the course of the use of the leather article are less pronounced.2 General Construction of Finishing Coats The finish is generally made up of a number of coats. finely divided polyurethane dispersions have won out in this sector over polyacrylate dispersions. finely divided acrylate dispersions (solids content about 10 %) are applied in combination with capillary-active substances known as penetrators. but need not be. the binders used or the method of application. the adhesion of the finish layer to the leather has to be improved in some cases by means of a separate base coat. As a result. or correct the hue of the surface of leathers which have not been drum dyed and to match it to the hue of the finish. Frequently there are many different ways of producing the desired article. To this end.3 Spray Dyeing Metallized dyes.3. The impregnating float or liquor has to absorb into the leather and must not become deposited at the surface. It depends primarily on the type of leather used and the effect desired. say. 11.1 Modern Finishing The various leather articles with their specific requirements each require a specific optimized process in the tannery. Each coat has a certain purpose. 11. very dilute. Classifying leather finishes according to. The coating technique can be the same for each coat. for example.5 Base Coat Depending on the crust leather used.3 Leather Finishing 11.3.11. the appearance or the ready-produced leather article is thus possible only to a limited extent. . good film formation despite relatively high hardness). These are usually polyurethane dispersions which. nappa). Finely divided acrylate dispersions (<100 nm) are useful for less hiding finishes. polyacrylate dispersions are used in the pigment coat. tend to be tacky and cause processing problems in leather production. Polyurethane dispersions are used in the pigment coat in particular when very high fastness properties are required..g. Soft binders.3. soft leather types (e. Instead of organic. . The degree of luster of the finish is controlled using matting agents (e.3.6 Pigment Coat Its components are pigments. The butadiene-based dispersions used in leather finishing have high filling effect and can enhance the hiding power of the finish. As well as the degree of hiding. solvent-containing lacquers and top coats (e.4 Application Methods The application method used depends not only on the processing step but also on the type of leather and the desired finishing effect. Auxiliaries (waxes and fillers) can be used to reduce the tackiness within certain limits. nitrocellulose emulsions).288 11 Applications in the Leather Industry 11.g. the hardness/softness balance of the pigment coat has a significant influence on application and processing properties. The choice of binders is made according to the finishing effect and fastness profile desired.. The glass transition temperatures of the polyacrylate dispersions used are typically between –10 and +10 °C.g. 11. Generally. are superior to polyacrylate dispersions in application terms. Especially on thin.g.7 Top Coat The top coat determines the ultimate appearance and the feel of the leather surface. today there is an increasing trend towards waterborne top coat systems. silica derivatives). It further substantially influences the fastness properties of the finish.. owing to their specific properties (no emulsifier. semi-aniline finish) and high hiding finishes which receive the desired grain structure through embossment. binders and auxiliaries such as waxes and fillers. however. 11. The pigment coat imparts the desired appearance to the leather and levels out the leather surface. Currently applied methods of coating will now be briefly described. hard pigment coats lead to an unwanted doubleskin appearance. A distinction is made between finishes which preserve the natural character of the leather (e. The horizontal leather passes through this vertically descending curtain. Rotating spray guns inside spray machines (Fig. 11-8) is the second most important method for application after spraying.2 Roll Coating Roll coating (Fig. As well as the HVLP process there is the airless process whereby the spray jet is not mixed with compressed air.4 Application Methods 11. 11. low pressure conditions to reduce spray drift.4.11. Soft leathers can be processed on this machine only if the rolls turn in the same direction. Fig. Modern spray units are equipped with computer-controlled spray guns which recognize the outlines of the leather and so minimize overspray. these types of leather can be roll coated only with finishes that do not require high amounts.4.4. The top roll transfers the relatively viscous color to the leather. 11-7 Spray machine. The leather passes between two rolls (color print roll and transportation roll) by means of a transportation belt. but is generated by very high pressure in the spray nozzle. Even soft leathers can be processed by this technique. The texture and the direction of rotation (synchronous or reverse) of the color print roll determine the amounts applied.1 Spraying Spraying is the most widely used method of application in leather finishing. They further operate under high volume. Consequently. 11-7) apply the low-viscosity finish liquor to the horizontal leather. Casting finds application in particular in 289 . In this process (Fig. 11-9) a casting head creates a curtain of liquid. 11.3 Curtain Coater The casting process comes from the surface coating of wood. This method is suitable for high amounts applied. This application technology places particularly high demands with regard to shear stability and foam control on the dispersions used. Fig.290 11 Applications in the Leather Industry Fig. grain impregnation and in pigment finish applications for patent leather and buffed leather. 11-9 coater. This technique is not suitable for processing very soft leathers. since they buckle as they pass through the curtain of liquid. Curtain . The use of antifoams is limited by wetting and flow-out requirements. 11-8 Roll coater. In addition. Their advantage is the substantial flexibility in thick layers. hardness and softness. As the hiding component. As well as from binders and pigment preparations. These systems are typically crosslinked using zinc oxide.11. Aqueous finishes generally utilize aqueous polymer dispersions. as required in the finishing of split leathers for example. polyacrylate dispersions are relatively inexpensive. coldflex stability and hiding power. elasticity. which have no inherent affinity for leather. they do not (as yet) meet the highest requirements. and protect the leather surface through their filmforming property. heat) and sensitive to heavy metals. whether it is a pigment finish or a top coat.2 Polybutadiene Dispersions The polybutadiene dispersions used are customarily copolymers based on butadiene. the effect of process conditions and the colloid-chemical properties of the dispersions make for an immense range of binder properties that can be obtained. They provide finishes having good application properties. These include.5 Binders 11. Owing to their different chemistries. crosslinker and handle modifier. matting agent. styrene and acrylonitrile.5. Owing to the monomers on which they are based. However.5 Binders Binders are among the most important components of a finish system. flow control agents. polybutadiene dispersions are also used in combination with polyacrylate dispersions. the various molecular weight distributions and degrees of crosslinking of the polymers. 11. finishes are prepared from rheological additives (thickeners. the three types of polymer dispersion differ in their application properties: 11.1 Polyacrylate Dispersions Typical leather-finishing polyacrylate dispersions are based on ethyl acrylate or copolymers of butyl acrylate with acrylonitrile or methyl methacrylate. The double bonds in the polymer make polybutadiene dispersions susceptible to oxidative aging (light. for example. 291 . The polyacrylate dispersions used are lightfast and compatible in the color batch. as required for automotive leather for example.5. Glass transition temperatures range from –10 °C to +10 °C. water resistance. film formation in the course of drying has a decisive effect on many fastnesses of the finish. They bind the color-conferring pigments. The following product classes are available as polymer dispersions: – polyacrylate (copolymers) – polybutadiene (copolymers) – polyurethanes The multiplicity of possible monomer combinations and their different blend ratios. solvents in appropriate cases). polyurethanes form stable – usually anionically stabilized – dispersions in water. Finish requirements are dictated not only by the performance characteristics but also greatly by the particular processing methods in the footwear industry. the use of polyurethane dispersions is mainly restricted to applications where the special properties of polyurethane dispersions are essential. and rub-fastness (after crosslinking) meet the highest standards. Owing to the incorporation of hydrophilic groups in the polymer.6. The finisher has to adapt these guideline recipes to the leather to be finished and to the final properties demanded (feel. The somewhat less costly aromatic systems. there are polyetherurethanes and polyesterurethanes. 11. Owing to the hydrophilic groups. The shoe sole is injection molded on in a further operation. The finish coat therefore has to be solvent-fast and the dyes may not migrate into the shoe sole. polyurethane dispersions can be made without an emulsifier.1 Shoe Upper Leather In terms of area. fastness). So the finish has to be heat resistant. Flexing endurance. for example. appearance. The folds appearing at the round edges of the shoe are smoothed away by heat treatment with a hot air blower or a smoothing iron (the leather shrinks at these high temperatures). In shoe making. even at low temperatures. Shoe upper leather is the largest sector by far.5. Their chemistry makes carboxylate-stabilized systems pH-sensitive. polyurethane dispersions possess very good adhesion to leather. Depending on the polyol component used. however. With regard to the isocyanate component. do not meet the extreme aging resistance requirements of automotive leathers. In addition. 11.6 Production of Selected Leather Articles Guideline recipes for finishes for some selected leather articles will now be used by way of example to discuss the particular requirements that have to be met by the polymer dispersions used. Since monomer costs are distinctly above those of the acrylates. the previously moistened leather is wiped (pulled) over the last by heated irons. the finish must not scratch under the rubbing by the irons. a distinction is made between aromatic and aliphatic monomers.292 11 Applications in the Leather Industry 11.3 Polyurethane Dispersions Polyurethanes are polyaddition compounds of isocyanates with polyols and/or NH-functional compounds. about 60 % of all leather produced is further processed as shoe upper leather. Finishes with polyurethane dispersions are notable for a very high fastness level. . Unlike the systems described above. but in some cases also calf leather. One important performance characteristic is the light-fastness of the finish. Useful top coats include a nitrocellulose lacquer or an aqueous system with a very hard and hence plating-fast polyurethane dispersion. Other decisive aspects are wear properties such as softness and feel. the latter can be crosslinked to improve the rubfastness. Apparel leathers preferably utilize sheep and goat leathers. 11.6. Rub-fastness is of minor importance. 80 g m–2). An example of a finish recipe for shoe upper leather is: Leather type: Cattle leather box-type Base coat: (depending on crust) Pigment finish: Pigments 100 parts Polyacrylate dispersion (40 %) 200 parts Waxes (40 %) 50 parts Casein binder (20 %) 100 parts Water 350 parts Top coat: Polyurethane dispersion (35 %) 400 parts Waxes (40 %) 20 parts Crosslinker (50 %) 30 parts Water 550 parts Thickener to a 4 mm Ford cup viscosity of approximately 24 s Processing: Pigment coat: 2 × spraying (each ca. With regard to processing.6 Production of Selected Leather Articles Shoe upper leather requires good flexing endurance and good adhesion of the finish. fashion aspects are of primary importance with apparel leathers. 50 g m–2).2 Apparel Leather Apparel leather is the second largest sector after shoe upper leather.11. Flexing endurance and rub-fastness are of lesser importance. If necessary. Inevitably. 50 g m–2). dry Plating: 2 s at 80 °C and 150 bar 1 × spraying (ca. dry Top coat: 2 × spraying (each ca. 293 . It accounts for about 20 % of leather production in terms of area. the finish does not have to meet special requirements. dry The non-thermoplastic casein binder ensures processability in the wiping process by reducing sensitivity to heat and improving hot rub resistance. e. i. dry Top coat: 2 × spraying (each ca. for example. less coated appearance may be obtained for the finish. The pigment content in the pigment coat has been reduced in favor of the spray dyes in order that a more transparent. these leathers have to be aging resistant. but. dry Plating: 2 seconds at 80 °C and 30 bar 5 × spraying (each ca. 50 g m–2).6. This is intensified by means of low concentration of the pigment finish and the large number of spray applications. finishing chemical demand greatly outweighs those for shoe upper leather or apparel leather.3 Automotive Leather Although the amount of leather processed in the automotive sector. . rub-fastness has to meet extreme requirements: >1000 rubs wet and a swelling resistance of >2000 rubs.294 11 Applications in the Leather Industry An example of a finish recipe for apparel leather is: Leather type: Sheepskin Pigment coat: Pigment 50 parts Spray dye 50 parts Polyacrylate dispersion (40 %) 200 parts Wax (40 %) 100 parts Water 600 parts Top coat: Nitrocellulose emulsion (15 %) 500 parts Wax (40 %) 20 parts Water 480 parts Processing: Pigment coat: 2 × spraying (each ca. as with shoe upper leather. dry Hydraulic ironing: 0. 40 g m–2). UV light and moisture. In addition. 11. as leather seats or steering wheel leather.. 23 °C) of 100 000 cycles and 30 000 cycles at –10 °C. they have to have adequate flexing endurance and rubfastness even after simultaneous exposure to heat. At present. Nor may any color shifts occur. 50 g m–2).5 s at 120 °C and 30 bar Apparel leathers generally are not provided with a base coat. there is an increasing trend toward the use of aqueous top coats. These high fastness requirements in the automotive leather sector include – depending on the specific requirements of the automotive manufacturer – adhesions of greater than 4 N cm–1. flexing endurance’s (dry. because of the high fastness requirements. Similarly. amounts to only about 2 % in terms of area of total leather production (and rising). solvent-containing top coats are still customary for apparel leathers. To achieve these very high fastnesses it is predominantly necessary to use polyurethane dispersions. As an alternative to the application method described. the base and pigment coats can also be applied by synchronous roll coating. the polyurethane dispersions used in the pigment coat are of medium hardness. Light-fastness is an exception. dry Top coat: 2 × spraying (each ca. for example.6 Production of Selected Leather Articles A guideline recipe for automotive leather is: Leather type: Cattle hide Base coat: Polyurethane dispersion (20 %) 200 parts Water 600 parts Pigment coat: Pigment 100 parts Polyurethane dispersion (35 %) 250 parts Polyacrylate dispersion (40 %) 100 parts Waxes (40 %) 80 parts Matting agent 80 parts Water 290 parts Thickener to a 4 mm Ford cup viscosity of 16–18 s Top coat: Polyurethane dispersion (35 %) 500 parts Waxes (40 %) 20 parts Crosslinker (50 %) 60 parts Water 420 parts Thickener to a 4 mm Ford cup viscosity of approximately 24 s Processing: Base coat: 1 × spraying (ca. need less high fastnesses. unlike automotive leathers. A portion of the polyurethane dispersions may also be replaced by polyacrylate dispersions.6. dry Hydraulic ironing: 2 s at 80 °C and 80 bar Pigment coat: 1 × spraying (70–100 g m–2). 50 g m–2). dry Press embossing: 5 s at 80 °C and 250 bar 1 × spraying (50–70 g m–2). Useful crosslinkers include. The high rub-fastnesses are primarily achieved by the crosslinking of the top coat. In contrast.11. The leathers are strongly embossed to conform the surface structure of the leathers to the interior styling of the car. for this the recipe needs to be adjusted to a smaller water quantity and a higher color batch viscosity (about 50 s in 6 mm Ford cup). 100 g m–2). Primary furniture leather criteria are the feel properties and the visual appearance of the leather.4 Furniture Leathers Furniture leathers. The use of soft polyacrylate dispersions has proved 295 . dry The polyurethane dispersions used in the base coat are soft and very finely divided. These must not have an adverse effect on the cold flexing endurance and so the polyacrylate dispersions used must have a low glass transition temperature. However. 11. modified aliphatic polyisocyanates. the corresponding test descriptions (e. The greater use of inferior leather grades increasingly forces the use of binders that provide high covering. hydrophilicity.g. leather thickness. surface structure. The test results . For aesthetic reasons. The different leather types vary greatly in thickness. 11. 50 g m–2). Furniture leathers are softer than automotive leathers. dry Hydraulic ironing: 0.296 11 Applications in the Leather Industry advantageous here. the top coat is less crosslinked and the applied amount is lower. many test methods simulate the stresses to which the finished leathers are exposed in use.7 Test Methods in Leather Finishing The primary purpose of the test methods is to ensure that the finished leathers are as a whole suitable for the stated purpose. It must always be noted in this context that the leather itself has a substantial influence on the tests as well as the finish coat on the leather. etc. For example. softness. dry Top coat: 1 × spraying (ca. Embossing is accordingly done under less pressure. Even a single hide is not homogeneous in itself. fiber density. buffed Base coat: (depending on crust leather used) Pigment coat: Pigment 100 parts Matting agent 80 parts Wax (40 %) 80 parts Polyacrylate dispersion (40 %) 200 parts Polybutadiene dispersion (40 %) 100 parts Water 290 parts Thickener to a 4 mm Ford cup viscosity of 16–18 s Top coat: Polyurethane dispersion (35 %) 400 parts Waxes (40 %) 50 parts Crosslinker (50 %) 30 parts Water 520 parts Thickener to a 4 mm Ford cup viscosity of 24 s Processing: Pigment coat: 2 × spraying (each ca.. the leather is briefly plated after the application of the top coat. DIN or ISO standards) provide precise definitions of the areas of the leather from which the test specimens are to be taken. An example of a recipe for furniture leather is: Leather type: Cattle hide. pore structure and absorbency are different in the belly than in the butt. 80 g m–2). For this reason. Since the fastness requirements are lower. 50 g m–2). dry Embossing: 3 s at 80 °C and 150 bar 1 × spraying (ca. Accordingly.5 s at 120 °C and 30 bar The requisite hiding performance is achieved through the partial use of the polybutadiene dispersion. The German DIN sheets for testing leather have in most cases been conformed to the above methods.U.1 Flexing Endurance This test describes the behavior of the finish coat on repeated flexing of the leather. 11. apparel leather and leather for bags and suitcases.7 Test Methods in Leather Finishing depend not only on the sampling position but also on the moisture content of the leather specimens.U. It is described in DIN 53351 or I. The test is carried out both on dry and on wet leathers. methods) and “Methods of physical leather testing” (I.11. From experience. the test methods prescribe that the test specimens must be conditioned under standard atmospheric conditions (e. For this reason. The rectangular leather specimens are clamped into a flexometer (Bally flexometer.7. either designed for certain leather articles or required by certain customers.U. the harder and less elastic are the leather fibers. In addition.. The International Union of Leather Technologists’ and Chemists’ Societies has developed. 11-10) with a fold. methods).U. 20. The following methods are only the most important tests in common use. It is among the most important tests of the finish. 11-10 Bally flexometer.F.g. mostly binding. Since finished leathers are predominantly used in the shoe industry.P. these test methods are also suitable for evaluating other leather articles such as upholstery leather. (International Union Fastness) describes guidelines and test methods drawn up by the International Fastness Commission for leather dyes and dyed leathers. The rotational movement of the up- Fig.P. “Methods of chemical leather analysis” (I. 297 . test methods are largely adapted to these requirements. I. The fastness level to be achieved varies from article to article. 50 % relative humidity and 23 °C or 65 % and 20 °C). The drier the leather is. there are a multiplicity of specific test methods. Fig.C. 35 000. In this test a rotating pad of felt acts on the leather surface under a certain pressure and at a defined speed of rotation. by the shoe industry for work and sports footwear. the test specimen is evaluated according to the degree of damage of the finish coat. The leather is stretched 10 %. Rub-fastnesses are also tested using the SATRA rub-fastness tester. dry felt Wet rub-fastness: dry leather. The test is carried out on the VESLIC rub-fastness tester (Fig. For particularly demanding requirements. The leather is evaluated after fixed numbers of cycles. 10 000.U. 11. The finish is assessed after 1000. 11-11).7. abrasion or transfer of color from the pigment coat under both dry and moist conditions. The test is customarily carried out in three variations: Dry rub-fastness: dry leather. The felt is 10 mm × 10 mm in size and weighted with 1 kg. 50 000 flexes. This method provides data on the sensitivity of the finished leather surface to rubbing through. leather seats) also have to meet such high requirements. 11-11 VESLIC rubfastness tester.F.g.298 11 Applications in the Leather Industry per axis makes the fold move back and forth on the surface of the leather.2 Rub-fastness The rub-fastness test examines resistance of the pigment coat to abrasion and the transfer of color to other surfaces (crocking). Fig. But leathers for the automotive sector (e. .. dry felt The damage or change in the finish coat and the transfer of color to the rubbing element are assessed after fixed rubbing intervals. This test is likewise carried out with both a dry and a wet felt pad. the test is continued to 100 000 flexes. for example. After visual examination. 450. On a stretched leather a felt is rubbed back and forth. This test is governed by the standards DIN 53339 and I. 20 000. High flexibility is demanded. A variation of this test is flexing endurance at temperatures below freezing. Any more will dry the leather too much. 5000. wet felt Swelling resistance: wet leather. Typical requirements are 30 000 flexes at –10 °C or 10 000 flexes at –20 °C. Wet specimens are flexed only 20 000 times at most. Strips of leather having a certain length and width are glued to a fixed basis using a defined adhesive. The damage to the finish and the change in hue are then assessed. in this test. the leather samples are subjected for 1 min to the flow of hot air from a hair dryer (150 °C). defined test liquids: perspiration rub-fastness. Ideally. 11. etc. The result is assessed in each case after five rubs. the adhered specimens are immersed in water and tested after a predetermined time. the finish can only be pulled off together with the grain layer. 299 . yellowing or a change in the flexing endurance. The tensile tester is then used to pull this leather away from the basis at an angle of 90°. These arise in particular when excessive auxiliary quantities (especially waxes) are used or the crosslinking of the preceding layer is excessive. 11. A more sensitive version of this test is carried out on the VESLIC rub-fastness tester using a heatable test punch. They are then assessed to see whether heat aging has resulted in embrittlement.6 Aging resistance The leather specimens are aged (a) at 50 °C for 7 days or (b) at 80 °C for 3 days.7. which is likewise important for shoe leathers. An iron is moved once back and forth across the leather surface over a slightly rounded edge as a preliminary test.11. the test can be carried out under exposure to various.3 Dry and Wet Adhesion This test determines the adhesion of the finish coat to the leather surface. The force measured during the pulling is recorded and its average reported.5 Hot Air Fastness In this test.7 Test Methods in Leather Finishing As a further variation. the adhesion of the finish to the leather is such that. The damage to the finish and any shift in hue are then evaluated. chemical rub-fastness. Again the temperatures are increased in intervals of 20 °C.7. 11. To test the wet adhesion. This test is repeated at least four times with half the test specimens being punched out along the backbone and the other half at right angles to it.7. 11. It also provides evidence of possible inter-adhesion problems within the finish coat.7. The test temperatures are increased in intervals of 20 °C.4 Fastness to Ironing This test is important for finished shoe upper leathers (see above) in particular. in: Herfeld. W. Eduard Roetherdruck. The leather strip to be tested is exposed to the light together with a light-fastness scale.U. Lederzurichtung. Proc. The color change of the leather is compared with the color change of the light-fastness scale. 3 Heidemann.300 11 Applications in the Leather Industry 11. 4 Schubert. Leather Finishing... Colomb. R.) Bibliothek des Leders.8 Light-fastness The test is carried out using not only daylight (I. H. Finished leather strips are exposed to a defined dose of radiation in a test chamber at 20 % relative humidity. Osgood. the reflectometric method describes the clouding of the cooled glass plate after 3 h at 100 °C. Heenemann Verlagsgesellschaft. The Society of Leather Technologists and Chemists. heat and moisture on the flexing endurance. Chapter 9. 1977. 1993.. E. and references cited therein. Berlin. (Ed. 11. H.) Lehrbuch der Lacke und Beschichtungen. Frankfurt am Main. R. G.. 6. A. for example after 16 h at 100 °C. Gerbereichemie und Gerberei- 5 Science and Technology for Leather technologie. which is important for automotive leathers in particular. Vol.7 Fogging test This test.7.7. Requirements differ from one car producer to the other. Akademie Verlag. Fundamentals of Leather Manufacturing. Vol. XXV IULTCS Congress. Darmstadt. F. (Ed. 1999. Tata McGraw-Hill. M. There are two different methods of measurement: (a) the reflectometric method and (b) the gravimetric method.. determines the condensation on cooled glass panes of volatiles from the leather or the finish coat. Weinheim. 2 Schubert. The light-fastness scale is made up of eight colored cotton strips having different. 11.F. 6 Wood. 1982. Umschau Verlag. Ullmanns Enzyklopädie der technischen Chemie. Oberflächenbehandlung des Leders. into the next Millennium. the rub-fastness after the third cycle and the color fastness once more after the last cycle.U. . in Leather Technologists Pocket Book. the rub-fastness and the color fastness of the leather finish. The color fastness is examined after the first cycle. 1999. While the gravimetric method indicates the condensed mass.. A15 (Leather). Verlag Chemie.F. 1967. 5.. E. the flexing endurance after the second cycle. It is described in DIN 75201. 1999. It assesses the effect of light.7. Vol. Berlin. 402).9 Hot light aging This test is important for automotive leather in particular. References 1 Stather. New Delhi. defined light-fastness. in: Kittel. 7 Heidemann. 401) but also artificial light (xenon lamp) (I. 3-527-60058-2 (Electronic) 12 Applications for Asphalt Modification Koichi Takamura 12. 12-1 [2]. Global Asphalt Consumption Asia/ Australia Fig. 12-1 The annual global asphalt consumption. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. 12-2) with an annual road budget of $85 billion [2]. Two thirds of that is con- 301 .Polymer Dispersions and Their Industrial Applications. The other 6 % (200 000 km) are paved with Portland cement concrete. the West Coast (11 %). which is primarily used for the heavy traffic area of the interstate highway [1]. The Midwest has the highest production (40 %). the East Coast (17 %). North America and Europe consume two-thirds of total 90 000 000 tons. and asphalt roads account for 94 % (3 270 000 km) of the paved roads in the US. followed by the Gulf Coast (25 %).1 Introduction The annual worldwide consumption of asphalt was over 90 000 000 metric tons in 1995 and the US used approximately one-third of that total [1]. 12-2) asphalt used in the US for non-paving purposes is sold to the roofing industry. There are more than 6 000 000 km (4 000 000 miles) of roads. Over 90 % (16 % of total asphalt consumption as in Fig. KGaA ISBNs: 3-527-30286-7 (Hardback). The global asphalt consumption in 1996 is represented in Fig. Others North America Europe Asphalt production is not very uniform throughout the US. Federal Highway Trust Fund Authorizations reached nearly $21 billion in 1996. and the Rocky Mountains. Greater than 85 % of 30 000 000 metric tons consumed in USA was used to maintain and improve more than 3 000 000 km (2 000 000 miles) of asphalt roads (Fig. The remaining 10 % of the paving asphalt usage (approximately 7 % of the total asphalt consumption) is comprised of asphalt emulsions. Asphalt has been modified to: – stiffen binders and mixtures at high temperatures to minimize rutting and reduce the detrimental effects of load induced moisture damage – soften binders at low temperatures to improve relaxation properties and strain tolerance. – reduce raveling by improving abrasion resistance. Almost 90 % of US paving asphalt consumption is for hot mix. particularly in environments where higher strains are imposed on the asphalt concrete mixture – improve asphalt–aggregate bonding to reduce stripping. – permit thicker films of asphalt on open-graded aggregates for increased durability. 4]. – minimize tender mixes. The use of polymer modified asphalts for hot mix and asphalt emulsions has grown significantly in the US during the last 10 years. – improve resistance to aging or oxidation. or segregation during construction. thus minimizing non-load associated thermal cracking – improve fatigue resistance. – rejuvenate aged asphalt binders. 12-2 Others Use of asphalt in the US. and the other third is used in commercial built-up roof. slurry seal and microsurfacing. and – improve overall performance as viewed by the highway user. primarily used for preventive maintenance and rehabilitation techniques such as chip seal. – replace Portland cement concrete with asphalt construction methods that reduce lane closure times and user delay costs. – reduce flushing or bleeding. Roofings Asphalt Cement for Paving sumed in the manufacture of shingles for houses. – replace asphalt cement as an extender. .302 12 Applications for Asphalt Modification Emulsions for Paving Fig. – stiffen hot mix asphalt (HMA) layers to reduce required structural thickness. Emulsified asphalts are also used for construction in recycling of old paving materials. – improve pavement durability with an accompanying net reduction in life cycle costs. The National Center for Asphalt Technology (NCAT) has published a list of reasons for the use of asphalt modification [3. drain-down. but have more recently been replaced by other types of elastomeric polymers such as styrene-butadiene-styrene. primarily in Canada and the Western United States [7]. 8]. The aggregate-asphalt mixture is then transported to the job site. Natural rubber latex.12. Recent emphasis on sustainable development and the concern about global warming has encouraged further development of cold paving technology using asphalt emulsions. Neoprene modified asphalts have been used for many years. neoprene latex was introduced in the 1950s and found a small but steady market. Test projects were placed in Europe beginning in the 1930s [6]. thus corresponding to approximately 3 000 000 metric tons a year in the US. Water based styrene-butadiene rubber (SBR) latex has found wide usage as an additive to asphalt emulsions to improve chip retention. resulting in less than 100 000 metric tons of polymers being used for this application. application and/or performance benefits. spread and compacted.2 Hot Mix Asphalt Paving Hot mix paving and cold paving with asphalt emulsion are the two types of paving technologies used for producing asphalt-based pavements [3]. 3 % by weight. the synthetic and natural lattices account for approximately 30 % of the total polymer annually consumed in the United States. Asphalt emulsions for paving already account for more than 40 % of total asphalt consumption in France and nearly 30 % in Spain [2]. Asphalt emulsions will be discussed in Sect. primarily in water-based emulsion applications such as microsurfacing. The mix has to be sufficiently hot to be compacted adequately within the specified density. The typical cold paving method includes mixing aggregates with asphalt emulsion and thus it does not involve heating the components used to produce the asphaltbased formulation. there are considerable energy requirements and cost associated with the hot mix process. SBS block co-polymers. is still being used today. on average. which is at a temperature as high as 160–180 °C [3. 12. energy. In North America. Because of the need for the aggregate and the asphalt to be at high temperatures. 303 . In general.3. The introduction of polymers into asphalt emulsions allows them now to be successfully used for almost any paving application. [3]. Although the exact figure is not available. The polymer content in these modified asphalt is. Polymer modified asphalt accounts for less than 10 % of total asphalt consumption for paving in the US. one of the materials mentioned in the earliest patents. In hot mix paving. In fact heating aggregates accounts for nearly 90 % of the total energy usage of hot mix paving. Approximately 1 000 000 metric tons of polymer modified asphalt were used in Europe in 1996 and 70 % of these are modified with elastomeric polymers. 12. aggregates are heated to a temperature above 200 °C to remove residual water and mixed with molten asphalt.2 Hot Mix Asphalt Paving According to the article by King et al. the job site has to be within a 1-h transportation distance from the mix plant. The polymers are added to alleviate pavement problems and to realize economic. environmental. patents for modifying asphalt with natural and synthetic polymers were granted as early as 1843 [5]. The Superpave asphalt binder tests try to determine physical properties that can be directly related to field performance in terms of rutting.g. RTFOT. 4. For asphalt paving technology. The SHRP study also developed Superpave® Performance Graded (PG) asphalt binder specifications based on the pavement’s temperature range [3. The study also defined the laboratory testing procedures and specifications for both the asphalt-aggregate mix. the binder becomes brittle during cold winter nights. Cold characterization is based on the asphalt binder after the pressurized aging vessel. and at the periods of time when distresses are most likely to occur. aggregate specification and compaction method. Changes in crude sources and refinery processes caused deterioration of pavements during the energy crisis in the late 1970s to early 1980s. The specification is based on the rutting. fatigue and cold fracture resistance of the asphalt binder and defined by two numerical values representing the upper and lower temperature limits of particular asphalt in °C (e. The problem was recognized by the Federal government and led to the development of the Strategic Highway Research Program (SHRP) to examine the entire paving technology for both Portland cement and asphalt based pavements. The freshly applied pavement is most susceptible to rutting. which is called rutting.2. but it becomes more susceptible to fatigue fracture when the asphalt binder is oxidized and loses its flexibility during usage. In contrast. 10]. rutting. The asphalt binder becomes too fluid during hot summer days under strong sun resulting in permanent deformation. or 25 °C (77 °F) penetration graded asphalt conforming to AASHTO M20. rutting and fatigue resistances are based on the fresh asphalt and after the rotating thin film oven test. Therefore. fatigue cracking and low temperature cracking. Superpave characterizes asphalt at the actual pavement temperatures it will experience.1 Asphalt Specification Asphalt used for paving has been graded with regards to its viscosity at 60 °C (140 °F) conforming to American Association of State Highways and Transportation Officials. The World Road Association (PIARC) in France has been active in developing similar international specifications [9.304 12 Applications for Asphalt Modification 12. emphasizing importance of international recognition. A perpendicular crack across the pavement lane develops when the stress generated by thermal contraction exceeds a critical value. This test simulates asphalt heat aging during the hot mix process. These specifications are based on properties at one specified temperature and do not necessarily predict asphalt performance over the wide range of climatic conditions that the pavement is subjected to in its lifetime. 8]. PG64-22). PG Grading The Superpave asphalt mix design system includes the performance grade (PG) asphalt binder specification. All Superpave specifications are based on the SI unit. AASHTO M226 specifications. (such as a compaction method for core sample preparation). PAV. these studies included the entire road construction procedure. test which is intended to reproduce 7–10 years of oxidative aging of the asphalt binder on the road. fatigue and cold fracture testing of prepared samples. A part of the Superpave binder specification is . minimum 1. (°C) 135 Dynamic shear. at 60 s (°C) –61 –12 –18 0 *110 °C PAV for the desert climate 22 19 16 34 31 28 25 22 19 –24 –30 0 –6 –12 –18 –24 –30 305 . G*sin(δ ). m-value minimum.00 MPa. Tab.30 kPa. test temp. minimum 5. 0. at 10 rad s–1 (°C) 64 70 Pressure aging vessel residue PAV aging temperature (°C) 100 100 (110)* Dynamic shear.12. 11]. 300 MPa. maximum.00 Dynamic shear. Test temp.2 Hot Mix Asphalt Paving shown in Tab. G*/sin(δ ). test temp. procedures and the PG specification can be found elsewhere [8. maximum. Detailed specifications as well as test apparatus. at 10 rad s–1 (°C) 64 70 Rolling thin film oven residue Mass loss. minimum 2. Performance grade PG64 –10 PG70 –16 –22 –28 –34 –40 –10 –16 –22 –28 –34 –40 Average 7-day maximum pavement design temperature (°C) <64 <70 Minimum pavement design temperature (°C) >–10 >–16 >–22 >–28 >–34 >–40 >–10 >–16 >–22 >–28 >–34 >–40 Original binder Flash-point temp. test temp. S. G*/sin(δ ). test temp.. 12-1 Example of Superpave binder specification.. % 1. at 10 rad s–1 (°C) 31 28 25 Creep stiffness. minimum (°C) 230 Viscosity maximum 3 Pa s.300.00 kPa. 12-1. If the creep stiffness is too high. The complex modulus can be considered as the total resistance of the binder to deformation under repeated shear. asphalt pavement shrinks. the asphalt will behave in a brittle manner. Low-temperature cracking: When the pavement temperature decreases. The asphalt binder will not recover or rebound from deformation if δ = 90°. this part of the specification addresses these properties using binder aged in both the RTFO and PAV. A minimum m-value of 0. The rate that the binder stiffness changes with time at low temperatures is regulated through the m-value. The bending beam rheometer is used to apply a small creep load to a binder beam specimen and measure the creep stiffness. As a part of the Superpave activities. thus promotes the use of compliant. a low temperature crack occurs. The relative amounts of recoverable and non-recoverable deformation are indicated by the phase angle. A high m-value is desirable since this leads to smaller tensile stresses in the binder and less chance for low temperature cracking.00 kPa for the original binder and 2. To prevent this cracking. G′ and loss modulus. An example of the Superpave analysis of one of the MRL asphalt. Since low temperature cracking usually occurs after the pavement has been in service for some time. the Superpave specification promotes the use of stiff. chemical and physical properties of more than 70 asphalt samples commonly used in the United States were analyzed. Since fatigue generally occurs at low to moderate pavement temperatures after the pavement has been in service for a period of time. the specification addresses these properties using binder aged in both RTFO and PAV. DSR. In practice. This is represented by G*/sin(δ ). Fatigue cracking: The Superpave specifies G*sin(δ ) < 5. A rotational viscometer (ASTMD4402) is used. AAA-1 (Lloydminster) modified with 3 % Butonal® NS175 (SBR latex from . elastic binders to address fatigue cracking. tensile stresses buildup in the pavement. elastic binders. δ.20 kPa after aging the binder using the RTFO procedure. Permanent deformation: The rutting resistance of the binder is represented by the stiffness of the binder at high temperatures that one would expect in use.59 Hz).00 MPa. These asphalt samples were available through the Material Research Library (MRL) for researchers in the field [12]. Since friction against the lower pavement layer inhibits movement. and cracking is more likely to occur. When these stresses exceed the tensile strength of the asphalt mix. G″ (recoverable and non-recoverable components). to minimize rutting. To address rutting resistance. measured at 10 rad s–1 (1.300 after 60 s of loading is required by the Superpave binder specification. G*/sin(δ ) must be a minimum of 1. where G* is the complex shear modulus and δ is the phase angle determined by the dynamic shear rheometry. creep stiffness has a maximum limit of 300 MPa.306 12 Applications for Asphalt Modification Pumping and handling: The maximum viscosity of the unaged binder should be below 3 Pa s at 135 °C to ensure that the binder can be pumped and handled at the hot mix facility. and consists of elastic modulus. 38 MPa at 7 and 10 °C.38 Creep stiffness. 12-2. 12-2. viscous component.2 kPa at 69 °C. The rotational viscosity measured by the Brookfield viscometer is 1. which gives the phase angle δm = 78° at the same temperature. respectively with phase angle δu = 88° at 64 °C. respectively. S. 12-2 Example of Superpave characterization of SBR modified asphalt.98 2.91 and 0. G*/sin(δ ) of the original (unaged) asphalt were 1.80 kPa.47 and 1. The upper limiting (rutting resistance) temperature of this asphalt is 67 °C and thus this modified asphalt meets specification of PG64. The same measurement for the RTFO residue gave G*/sin(δ ) = 3. at G*/sin(δ) = 1. at G*/sin(δ) = 2. elastic component.364 67 69 67 –29 –24 –34 64–34 The Superpave analysis specifies the PAV temperature of 100 °C for 20 h for this sample (Tab. m value at –24 °C Rate of change of S. Viscosity at 135 °C (Pa s) Rutting resistance by DSR Original asphalt After RTFO Fatigue resistance by DSR After RTFO and PAV Low-temp. S. m value at –18 °C 186 108 0. The DSR analysis of the PAV residue gave G*sin(δ ) = 2. which allow us to estimate G*/sin(δ ) = 1. m value at –30 °C Rate of change of S.80 kPa.80 kPa.37 kPa upon modification with 3 % SBR latex but non-recoverable. crack resistance by BBR After RTFO and PAV Temp. G′ increased nearly 11× to 0. Polymer modification improves the rutting and fatigue resistance mostly through enhancement in the recoverable.91 kPa as shown in Tab.2 Hot Mix Asphalt Paving BASF Corporation) is shown in Tab.11 G*/sin(δ ) at 64 °C (Pa) G*/sin(δ ) at 70 °C (Pa) G*/sin(δ ) at 64 °C (Pa) G*/sin(δ ) at 70 °C (Pa) 1. respectively. These values are significantly lower than the requirement for the PG64 asphalt. at –18 °C (MPa) Rate of change of S. thus G*/sin(δ ) = 2. The elastic and loss moduli.30 (°C) Limiting low temperature (°C) PG grading (°C) 1. This resulted in G*/sin(δ ) = 1.89 kPa at the same temperatures. at m = 0. 12-1). at S = 300 MPa (°C) Temp.59 kPa at 64 and 70 °C.11 Pa s at 135 °C.035 and 0. G″ showed only moderate increase of 2. resulting G*/sin(δ ) = 0.91 0.298 0.0 kPa at 67 °C.89 G*sin(δ ) at 7 °C (MPa) G*sin(δ ) at 10 °C (MPa) 2.3× to 1.2 kPa (°C) Limiting high temperature (°C) Temp.98 and 2.0 kPa (°C) Temp.59 3. G′ and G″ of the unmodified asphalt were 0. which is within the specification of <3 Pa s.12. 12-3. The phase angle δ alone makes only a limited contribution for determination of the rutting re- 307 . at –24 °C (MPa) Creep stiffness. Tab.47 1. G′ of the asphalt as seen in Fig. The bending beam rheometry (BBR) of the PAV residue was conducted to establish the low limiting temperature of the modified asphalt. it was confirmed that by raising the test temperature 10 °C. Thus. Thus. –34 °C would be the low temperature limit from the BBR measurement. using the concept of time–temperature superposition. 12-3 where Superpave analysis of unmodified and modified with 3 % Butonal NS175 for AAA-1 and AAK-1 (Boscan) asphalt are compared. S would be 300 MPa about at –29 °C and m would be 0. Taking the higher value. The polymer modification results in 11× increase in the elastic component.981 at δu = 88° and δm = 78°. and the m-values were 0. G″. We conclude that this asphalt meets the PG64-34 specifications as shown in Tab. –24 °C is the low temperature limit of this asphalt determined at a condition of 60-s loading.12 Applications for Asphalt Modification sistance since sin(δ ) = 0. such as ductility (ASTM D113). softening point (ASTM D36) and absolute viscosity measured at 60 °C (ASTM D2171) are also included. for the unmodified and modified asphalt.300 at approximately –24 °C. 12-3 Complex modulus G* of unmodified and 3 % SBR latex modified asphalt measured at 64 °C. respectively. respectively (Tab.298 and 0. Improvement in both the rutting and cold fracture resistance of the asphalt with the polymer modification are demonstrated in Tab.01 0. 10 G* G" (Viscous Behavior). penetration (ASTM D5). However. In addition to the Superpave analysis. The creep stiffness values were 186 and 108 MPa. G′ with moderate increase in viscous component. 12-2). . values of conventional measures of unmodified and modified asphalt.364 determined at –24 and –18 °C. equal creep stiffness could be obtained after a 60-s loading. The desired value of creep stiffness was originally developed as a correlation between thermal cracking of in-service asphalt pavement and binder stiffness values estimated at 2 h loading time. 12-1.01 0.999 and 0. kPa 1 Fig.1 G' (Elastic Behavior).1 δm δu 0. kPa 308 Unmodified 1 G * SBR Modified 0. it is expected that the use of polymer modified binders will increase as these specifications are implemented during the late 1990s and the early 2000s.086 69 –29 –24 67 –34 64–34 >150 11 56 0. 309 . Because many Performance Grade asphalt specifications can only be met with polymer modification. varies widely dependent on the crude source. at G*–sin(δ) = 2. and no agency reported they will be using less modified binder [14].30 (°C) Limiting high temperature (°C) Limiting low temperature (°C) PG Grading Ductility at 4 °C Penetration (mm) at 25 °C Softening Point (°C) Absolute viscosity at 60 °C (Pa s) AAA-1 AAK-1 Unmodified Modified Unmodified Modified 280 58 1100 67 560 63 2000 79 58 –21 –24 58 –31 58–28 >150 16 44 0. The polymer is mixed in the asphalt and stored at elevated temperature. One of the primary benefits of polymer modified asphalt binders is a reduced susceptibility to temperature variation [13].33 78 –19 –14 78 –24 76–22 86 4.34 65 –14 –17 63 –24 64–22 28 6.5 63 1. A new DSR procedure is under development for the better prediction of fatigue resistance. 12 agencies reported they will be using the same amount of modified binders. the chemical composition.12. the molecular mass. at G*sin(δ) = 1 kPa (°C) Temp. The degree of swelling.2 Hot Mix Asphalt Paving Tab. which could cause chemical reaction within polymer chains and with some components in the asphalt. that is highly swollen with aromatic components in the asphalt. Storage Stability A polymer-modified asphalt is a two phase system. Integration of the bending beam rheometry data and direct tension measurement in the near future will provide a better description of the benefits of the polymer-modified asphalt.2 kPa after RTFO (°C) Temp.7 49 0. the refining process and the grade of the base asphalt used. the refining process and the grade of the base asphalt [15–17]. Asphalt Properties Brookfield viscosity at 135 °C (mPa s) Temp.6 The results of modifying asphalt with additives are highly dependent upon the concentration. and thus the microscopic morphology of the polymer phase. at S = 300 MPa (°C) Temp at m = 0. and microscopic morphology of the additive as well as the crude source. Superpave binder specifications are successful in predicting the rutting resistance and cold fracture resistance of the unmodified asphalt. forming a continuous fine polymer network. A 1997 survey of state highway agencies found that 35 agencies reported that they will be using greater quantities of modified binders. 12-3 Superpave analysis of unmodified and SBR modified asphalts. The asphalt composition in the polymer rich phase is vastly different from the original asphalt. These polymer blobs migrate to the top due to the density difference. The polymer phase transfers to macroscopic polymer globules without agitation when the sample is slowly heated to 170 °C. One of their results with Asphalt E modified with 5 % SBS polymer is shown in Fig. which would have negative effects on low temperature flexibility of asphalt. 12-4 Difference in asphalt composition among original asphalt and the polymer rich and asphalt phases developed during storage. thus concentrating the asphaltenes and polar resin fractions in the asphalt phase. which allows us to observe changes in the polymer morphology at the mixing and storage conditions. . with SBS modified asphalts [16]. was modified with 3 % Butonal NS175. Here. The phase separation during storage can be visualized with hot stage optical microscopy. the other MRL asphalt. This potentially leads to reduced swelling of asphaltenes. Photomicrographs shown in Fig. resulting in an increase in the asphaltenes/aromatic ratio. Polymer phase Original Asphalt E Asphaltene Saturate Resin Asphalt phase Aromatic Fig. 12-4.310 12 Applications for Asphalt Modification When the chemical and physical properties of the polymer and asphalt are not matched to each other. The aromatic and saturate components preferentially partition to the polymer phase. 12-5 illustrate the presence of a fine polymer network in the freshly mixed sample observed at 110 °C at ×200 magnification. a polymer rich phase could develop near the surface of the asphalt when stored at 160–170 °C for a few days without agitation as reported by Brûlé et al. The majority of asphaltenes are retained in the asphalt phase. AAB-1 (Wyoning Sour). a highly viscoelastic fluid dispersed in a less viscous one. Cross-linking reduces solvent swelling and increases the visco-elasticity of the polymer phase. The photomicrograph shown here (Fig. 12.2 Hot Mix Asphalt Paving Fig. which often involve introduction of a controlled cross-link reaction in the polymer phase. a fine polymer network remains even when the modified asphalt is observed at 170 °C for 10 min. 12-5) demonstrates that polymer modified asphalt behaves as a dispersion consisting of two immiscible fluids. 12-5 Photomicrographs of conventional SBR modified asphalt taken at 110 and 170 °C.2. The dispersed phase elongates to fine fluid columns under agitation. This process eliminates potential separation of 311 . Numerous inventions are reported in the literature to overcome the polymer incompatibility in the modified asphalt.2 In-line Injection (Pump-in) Pre-blending infers that the latex and asphalt have been mixed at a central location using a batch process as discussed above. even though only fine structures existed in the modified binder observed at room temperature using fluorescence microscopy. Stable polymer structures of this latex also extend the low temperature limits of certain modified asphalts. 12-6. which is the traditional method of studying polymer morphology [15–17].12. these elongated columns transfer to a series of spherical droplets as minimizing the total surface area and thus the total energy. In-line injection (also known as pump-in) implies that the latex and asphalt are blended immediately before being applied to the aggregate at the hot-mix plant. as determined by the direct tension measurement. Wegan et al. When the agitation is removed. Butonal NX1129 is an example of the new type of SBR latex. As shown in Fig. [17] reported observing similar macroscopic polymer globules and/or a polymer layer surrounding the aggregate surface in the paved asphalt mixtures. With the pre-blending process. 12-7 . Photomicrograph demonstrating the presence of polymer networks in the asphalt prepared by the in-line injection (pump-in) process. Fig. polymer and asphalt are thoroughly mixed and the binders can be tested and certified before application to the aggregates. polymer and asphalt during transportation and storage of incompatible materials. 12-6 Butonal NX1129 maintains stable.312 12 Applications for Asphalt Modification Fig. 12-7. fine polymer network even at 170 °C. An optical photomicrograph demonstrating polymer networks in the asphalt prepared by the direct injection process is shown in Fig. thus reducing handling costs. Recent advancement in quality control at the mixing process guarantees adequate mixing and performance of the asphalt produced by the in-line injection process. and the need for an asphalt storage tank for the polymer modified asphalt. 3 Paving with Asphalt Emulsion 12. or setting. in most cases. which is determined by the type of the emulsifying agent used.1). Addition to the aqueous phase is the most commonly used method. Asphalt emulsions are classified with their charge and on the basis of how quickly the asphalt will coalesce.3 to 20 µm. 12-8 Particle size distribution and photomicrograph of a typical asphalt emulsion.5 mm. based on the electrical charge of the asphalt particles. 12-9. and an SS emulsion is designed to mix with fine aggregate. as schematically shown in Fig. The emulsions are further subdivided by a series of numbers and letters related to the viscosity of the emulsions and the hardness of the base asphalt cements. The letter “C” in front of the emulsion type denotes 313 . 12-8.3 Paving with Asphalt Emulsion Asphalt emulsions used in road construction and maintenance are either anionic or cationic. MS and SS have been adopted to simplify and standardize this classification. 12.3. The terms RS. They are relative terms only and mean rapid-setting. A latex modified asphalt emulsion can be prepared using several methods: addition of the latex in the aqueous emulsifier solution. The colloid mill has a high-speed rotor that revolves at 1000–6000 rpm with mill-clearance settings in the range of 0.12. Asphalt emulsion properties depend greatly upon the emulsifier used for their preparation. An RS emulsion has little or no ability to mix with an aggregate.2 to 0. The asphalt contents of these emulsions are. direct injection in the asphalt line just ahead of the colloid mill or post-addition to the pre-manufactured emulsion. an MS emulsion is expected to mix with coarse but not fine aggregate. Fig. medium-setting and slowsetting. from 55 to 75 % and prepared using a high shear mechanical device such as a colloid mill. The direct injection process often helps to produce an emulsion with a desired high viscosity for chip seal application (Sect. which is commonly referred to as breaking. This is due to the narrow particle size distribution of the asphalt emulsion produced with this process. A typical asphalt emulsion has a mean particle size of 2–5 µm in diameter with distribution from 0. A photomicrograph and typical size distribution of an asphalt emulsion are shown in Fig. we will limit our discussion to chip seal and slurry surfacing. ASTM and the American Association of State Highway and Transportation Officials (AASHTO) have developed standard specifications for the grades of emulsions. 12. Surface treatments applied to an existing pavement for preventive maintenance are the most significant application of polymer modified asphalt emulsion. For example. which utilizes milled old asphalt pavement mixed with asphalt emulsion.3. 19]. but in this chapter. is gaining popularity for rehabilitating deteriorating roadways. In this method. The “HF” preceding some of the MS grades indicates high-float. Latex Asphalt Water Emulsifier Acid or Base Latex Storage Colloidal Mill Latex cationic. Then. materials are mixed together.314 12 Applications for Asphalt Modification Fig. An inplace aggregate base can also be incorporated or new aggregates can be added to the old materials and asphalt emulsion added. . easy to place. High float emulsions have a specific quality that permits a thicker asphalt film coating on the aggregate particles. Detailed descriptions as well as recommended performance guidelines of various paving technologies using asphalt emulsions can be found elsewhere [18. There are several types of surface treatment. Slow setting SS and CSS asphalt emulsions are used currently without polymer modification. as measured by the Float Test (ASTM D139 or AASHTO T 50). respectively. and compacted. The absence of the “C” denotes anionic. the old asphalt pavement is crushed. They are economical. CRS-2 is a cationic rapid setting emulsion typically used for chip seal application. 12-9 Schematic illustration for latex modified asphalt emulsion production.1 Applications of Asphalt Emulsions The Cold-mix recycling operation. often in place. shown in Tabs 12-4 and 12-5 for anionic and cationic emulsions. spread to a uniform thickness. The “h” that follows certain grades means that harder base asphalt is used. resist traffic abrasion and provide a long lasting waterproof cover over the underlying structure. 5 cm min–1 (cm) 100–250 <40 100–400 65 100–250 <40 50–450 65 CMS-2 CRS-1 20–100 60 Medium-setting Rapid-setting CRS-2 65 100+ 100–200 <40 1200 20–100 20–100 55 HFMS-1 40–90 <40 50–450 65 CMS-2h MS-2h 100–200 100–200 40–90 <40 <40 <40 44 20–100 Selected requirements for cationic asphalt emulsion (ASTM D2397). (dmm) Ductility. 100 g. Saybolt Furol at 50 °C (s) Minimum residue by distillation (%) Test Tab. Test on emulsion Viscosity. 25 °C. Saybolt Furol at 50 °C (s) Minimum residue by distillation (%) Test Tab. 5 cm min–1 (cm) Float test. Saybolt Furol at 25 °C (s) Viscosity.75–400 63 75–400 63 65 100+ 100–250 <40 Test on residue from distillation Penetration at 25 °C. (dmm) 100–200 100–200 100–200 <40 <40 <40 Ductility. Saybolt Furol at 25 °C (s) Viscosity. 100 g. Test on emulsion Viscosity. 12-4 100+ 100+ 65 100–250 <40 57 20–100 CSS-1 Slow-setting 100–200 40–90 <40 <40 1200 1200 100+ 100+ 65 20–100 20–100 57 SS-1h 40–90 <40 57 20–100 CSS-1h 100–200 40–90 <40 <40 20–100 20–100 57 HFMS-2 HFMS-2h SS-1 Slow-setting 12. 5 s.3 Paving with Asphalt Emulsion 315 . 12-5 Test on residue from distillation Penetration at 25 °C. 5 s. 60 °C (s) 1200 55 20–100 MS-2 MS-1 HFRS-2 RS-1 RS-2 Medium-setting Rapid-setting Selected requirements for anionic asphalt emulsion (ASTM D977). 25 °C. Fig. 12-10. Aggregate Particle Emulsion Residue Schematic diagram illustrating chip seal paving. TB147A. polymer modified asphalt emulsion. Quick-setting (QS) asphalt emulsion is used when early opening to traffic is necessary. . mineral filler.316 12 Applications for Asphalt Modification Chip seal: This treatment involves spraying asphalt material (heated asphalt or asphalt emulsion) followed immediately by a thin (one stone thick) aggregate cover as schematically shown in Fig.3.5). TB-144 and TB-113) confirming compatibility of the aggregate. respectively. A small amount of mineral filler. hydrated lime. and other additives is essential for successful slurry seal and microsurfacing operations. aids in setting the slurry. though a medium setting MS. Polymer modified CSS-1h asphalt emulsion (ASTM D2397 and AASHTO M208) is used with a minimum polymer level of 3 %. A rapid setting RS. The microsurfacing mix has to set quickly enough to accept traffic within 1 h after placement [20]. The International Slurry Seal Association has established recommended performance guidelines A105 and A143 for the slurry seal and microsurfacing. 12-11. CSS-1 or CSS-1h. 12. TB-100. The asphalt emulsion used in the slurry mix may be SS-1. SS-1h. allowing its use for rut-filling and is maintains a friction resistant surface throughout the service life. It can be applied at greater thicknesses than conventional slurry seals. The cationic asphalt emulsion often provides better asphalt adhesion to the aggregate. asphalt emulsion. 12-10 Slurry seal: A slurry seal is a homogeneous mixture of well-graded fine aggregate. Slurry seal is usually applied in a thickness of 3 to 6 mm. takes advantages of polymer modified asphalt emulsions. TB-114. The Slurry comes directly from a traveling mixing plant into an attached spreader box that spreads the slurry by a squeegee-type action as shown in Fig. Microsurfacing: A new slurry technique. Portland cement or fly ash. A careful mix design (ISSA TB-139. water and mineral fillers applied to a pavement as a surface treatment. respectively). Cutback asphalts have been used in the past for this purpose but asphalt emulsion is now preferred due to environmental and safety (fire hazard) concerns associated with cutback asphalt. The machine used for production of slurry seal is a self-contained. The polymer modified asphalt emulsion (2–4 % polymer by weight of asphalt) improves chip retention and enhances pavement durability (Sect. TB-09. HFMS or CMS asphalt emulsion could be used (ASTM D977 and D2397 for anionic and cationic emulsions. The aggregate is immediately rolled with a pneumatic roller and a light brooming may be necessary to remove any excess aggregate. limestone dust. HFRS or CRS is usually used. microsurfacing. continuous-flow mixing unit. In these tests. viscosity. ductility. 12. A distillation or evaporation test is used to recover the asphalt (emulsion residue) from the emulsion. but are not designed to correlate the binder performance for each application [21]. 12-11 Schematic diagram of a typical microsurfacing paver. During the residue recovery process. These include particle charge.3. The most common tests run on the recovered residue include penetration.2 Asphalt Emulsion Tests Standard tests and procedures for testing asphalt emulsions are specified in ASTM D244 and AASHTO T59. to confirm a designed polymer level in the modified asphalt). A minor difference in the temperature and length of the distillation would cause variation in the polymer morphology. storage stability. 12. but rather an emulsion containing dispersed latex particles in the aqueous 317 .g. Courtesy Akzo Nobel Asphalt Applications Inc.12. excess heat applied to the polymer modified asphalt emulsion causes formation of macroscopic polymer globules that are as large as a few mm in diameter. softening point.3 Paving with Asphalt Emulsion Fig. (e. which explains the poor reproducibility reported by the AEMA Materials Committee Round Robin Studies on emulsion residue characterization [22]. These tests are meant to be used as a quality control tool. elastic recovery and torsion recovery.3. demulsibility and others.3 Polymer Honeycomb Structure in Cured Asphalt Emulsion Modified asphalt emulsion with latex is not just an emulsion of polymer-modified asphalt. the asphalt emulsion is subjected to a maximum of as high as 260 °C for the distillation method or 167 °C for the evaporation. especially (b) and (c) demonstrate the honeycomb structures of the SBR polymer formed around asphalt particles. 12-12 Cured Asphalt Emulsion Right: Latex particles transform to a continuous polymer film surrounding asphalt particles. Some latex polymers are also adhering on the aggregate surface as seen in (c).318 12 Applications for Asphalt Modification phase. the flexible polymer-cement complex creates these honeycomb structures. not in the asphalt. and thus act as “spot welding” of asphalt particles to ensure maximum binding power. Menisci of water containing latex particles (and Portland cement particles for microsurfacing) form among asphalt particles when water starts to evaporate from the asphalt emulsion. Fig. . It is important to realize that the latex polymers should remain in the aqueous phase. In contrast. Here. SEM. To form the finest honeycomb structure the asphalt emulsion should not break (coalesce) during the process. 12-13. These photographs. Since Portland cement particles also remain in the aqueous phase. and transform to a continuous polymer film during the curing process. The treatment with OsO4 makes the SBR polymer insoluble to the organic solvent and also improves the contrast for the scanning electron microscope. as schematically shown in Fig. Scanning electron microscope observation of the microsurfacing pavement confirmed the presence of the polymer honeycomb structure [22]. observation. a sample of the freshly applied pavement sample was treated with OsO4 and the asphalt was extracted with MEK (methyl ethyl ketone) solvent. 12-12. promoting early strength development. The majorities of latex particles migrate together with water and accumulate in the menisci. Asphalt Asphalt Latex Film Latex Latex Modified Emulsion Left: Schematic illustration of latex modified asphalt emulsion showing that latex particles remain in the aqueous phase. The SBR latex for asphalt modification is designed to create a polymer film without coagulum formation. the honeycombs made only with Portland cement would also be very brittle and this would be the case when the polymer is present in the asphalt phase. which cures to form the honeycomb structure. A series of SEM photographs of the fractured surface were taken and shown in Fig. as shown in the right side of Figure 12-12. Advantages of this flexible honeycomb structure with SBR latex will be discussed later in the emulsion residue characterization. which are placed on the microscope slide glass. spontaneous formation of the polymer network was observed as shown in Fig. As seen in Fig. provides a sufficient amount of residue samples within 3–5 h for the Superpave binder characterization [22].4 Asphalt Emulsion Residue Characterization The need for an appropriate residue recovery procedure for asphalt emulsion has been recognized in both Europe and the US. When the emulsion is placed on sand particles. An optical microscope observation simulating chip seal was also conducted using SBR latex modified CRS-2 emulsion [23]. An example of estimating the rutting resistance temperature. 12-15. Tr (temperature at G*/sin(δ ) = 1 kPa) of microsurfacing emulsion residue is shown in Fig. Do these honeycombs strong enough to maintain their structure under repeated poundings by heavy weight truck tires running at above 100 km h–1 throughout the lifetime of the pavement? Pavement samples were taken from Texas State Highway 84 near Waco. which dries the emulsion at ambient temperature.3. A typ- 319 . This highway was treated with the microsurfacing in 1998.3 Paving with Asphalt Emulsion (b) 5µ µm (a) 25µ µm (a) (b) (c) (c) µm 10µ Fig. 12-14. 12-13 A series of scanning electron microscope photographs of the cured microsurfacing specimen demonstrating (a) and (b) SBR poly- 1µm mer honeycomb formed around asphalt particles.12. 12. 12-16. the honeycomb structure with the SBR latex polymer-cement complex is flexible enough to withstand repeated stresses after three years service at the highway condition. The forced airflow drying method. (c) Some polymers also adhere on the aggregate surface. Samples were taken from the wheel path as well as the shoulder of the pavement. The formulation used for this study is the same but without the aggregate and 10 g water. The value of Tr showed a rapid increase to 76 °C within the first 3 days of curing when 3 % of the . 12-14 Photomicrograph demonstrating spontaneous formation of polymer network upon curing of the CRS-2 asphalt emulsion modified with 3 % cationic SBR latex. Fig. paved in 1998. Fig. 10 g water and 1 g Portland cement. the unmodified asphalt emulsion was made with a PG64 asphalt and the rutting resistance temperature increased slightly from 66 °C to 68 °C after one month. 12-15 Latex Polymer Network 50µm ical microsurfacing formulation consists of 100 g aggregates. and samples taken in 2001.320 12 Applications for Asphalt Modification 5µm SEM photographs of microsurfacing pavement taken under the wheel path. 12-16. Texas State Highway 84 near Waco. This increase in Tr is mostly due to stiffening of the asphalt as the phase angle of the residue increases from 82° to 88° at Tr. 12 g of 65 % asphalt emulsion containing 3 % latex polymer. As seen in Fig. The sample with Portland cement shows a gradual increase in Tr to 71 °C within three weeks. 12-17. [24.12.3 Paving with Asphalt Emulsion SBR latex is also present in the mix. 12-16. as seen in Fig.5 Application Tests for Chip Seal and Microsurfacing Microsurfacing: Jones et al. surfactant and aggregates were used to eliminate all other variables 321 . and so simulating pavement temperature during the daytime. which maintains elasticity of the residue as seen with the low measured phase angle. Two PG grade improvement can be observed with the polymer-cement system. the emulsion was dried one day under the forced airflow. Two PG grades improvement in the rutting resistance was achieved after two weeks of curing. 25] analyzed the performance of seven polymer-modified asphalt emulsions for microsurfacing application. The European Standard for emulsions of pure and polymer modified bitumen including a residue recovery procedure and characterization of the recovered residue is currently under preparation. Two different latex polymer levels of 3 and 5 % were studied. demonstrating the rut filling capability of the microsurfacing system. and transferred into an oven at 60 °C. 12-16 The rutting resistance temperature. 12. Tr. of microsurfacing emulsion. confirming that SBR modified asphalt binder maintains the elasticity. The objective of their studies was to examine effects of different polymers on microsurfacing performance. cement and 3 % SBR latex. an accelerated curing test was also designed. Differences in the phase angle of these three samples are also summarized in Fig. The phase angle at Tr remained nearly constant at 77–78° throughout the curing. Three PG grades improvement (from PG64 of the unmodified asphalt) with 3 % latex polymer takes only 10 days of curing. Here.3. Fig. emulsion plus cement and emulsion. To evaluate potential benefits on performance during its lifetime. The same asphalt. Fig. 12-18 The authors concluded that SBR latex continues to perform well in virtually all the laboratory tests to which it has been subjected. LWT. Wet Abrasion Loss. Fig. g/ft2 322 The wet track abrasion test and loaded wheel test of cured microsurfacing specimen prepared with five different polymers reported by Jones [23.12 Applications for Asphalt Modification Accelerated curing of the microsurfacing residues at 60 °C after drying under forced airflow for one day. WTAT. 12-18. These conclusions. Results of the Wet Track Abrasion Test. can now be understood in the light of the formation of the polymer honeycomb structure providing excellent rutting resistance of the asphalt emulsion residue. especially LWT results. tended on average to outperform the solid polymers. % from the mix design. and Loaded Wheel Test. They also recognized that the materials which were received as latices. 24]. This is demonstrated in Figs 12-13 to 12-16]. are reproduced in Fig. . 12-17 60 15 40 10 20 5 N eo pr en e EV A SB S N at ur al 0 SB R 0 Wheel Track Deformation. [30] demonstrated a statistically significant relationship between a country’s economical development and its road infrastructure (Fig. Chip retention. Marchal et al. BASF developed a so-called eco-efficiency analysis. In comparison. 27]. and several attempts were reported in the literature to develop a laboratory procedure to simulate the field experience. A cold mix plant. min. % 80 Fig. and the percentage of retained chips is recorded as a function of curing time. as an internal decision making tool. ACTE) appears to be the most successful [26. The sample is subjected to the shearing action of a horizontal steam-hose.4 Eco-efficiency Analysis Chip seal: Loose chips from a freshly paved road are the major safety concern for chip seal operation. to help in evaluating products and processes for 323 .12. on average. 12-19. access to 27-lane meters of paved road. A modified fretting test (also know as the abrasion cohesion test Esso. education and employment opportunities. In this test. and approximately 50 % chip retention is considered to be strong enough to be open to traffic.4 Eco-efficiency Analysis Recent study by Queiroz et al. Use of a specially designed brush appears to reduce a problem of chip build-up around the steam-hose [29]. An example of the test results is shown in Fig. [27] report that the maximum chip retention does not exceed 80 % even with a fully cured asphalt emulsion. requires less initial capital investment and lower energy consumption than a hot mix plant. a known amount of CRS-2 asphalt emulsion and aggregates are spread on a roofing felt. and then rolled with a 30 kg rubber roller. 12-19 Results of modified fretting test demonstrating advantages of the early chip retention with cationic SBR latex modified emulsion. 60 Latex Modified 40 Unmodified 20 0 0 30 60 90 120 Curing time. which is attached to a Hobart sun and planet mixer. A well-developed and well-maintained highway system is credited for improvements in access to goods and services. it is only 16-lane centimeters for people in China! Improvement in cold mix technology to provide durable pavements would result in significant impact on the well being of people living in these developing countries. 12-20). For developed countries. using asphalt emulsion. which demonstrates early cohesion development with the latex modified asphalt emulsion [28]. environmental focus has shifted from pollution prevention to sustainable development. A person living in Australia has. 12. 31. refinery process. The eco-efficiency analysis was applied to compare three different paving methods of hot mix.76 exists between a country’s economical wellbeing and road infrastructure. chemical additives and aggregate production. 12-20 PGNP = GNP/Capita in $ and paved roads in km/million inhabitants are plotted for 98 countries [30]. cradle-to-grave evaluation) from raw material acquisition through production. The study integrates environmental impact analysis and economical consideration. For asphalt emulsion based paving. Here. this analysis includes not just for production of the asphalt emulsion and paving operations. 32]. which evaluates environmental aspects and potential impacts throughout a product’s life cycle (e. a 10-year life for the thin (4 cm) hot mix overlay and a 13-year life for the polymer modified hot mix overlay.g. The main goal of the eco-efficiency analysis is “To offer customers the best possible alternatives with the least environmental impact at the best cost”..324 12 Applications for Asphalt Modification A linear correlation with R2 = 0. Fig. sustainable development. The eco-efficiency analysis takes equal account of both the ecological and economic aspects and compares pros and cons of each choice. It has been realized that preventive maintenance of existing roadways is the most financially effective use of available resources [3. The base study assumes a 7-year life for the microsurfacing treatment (8–12 mm thick). The environmental impact analysis is based on the life-cycle analysis [34]. use and disposal. . polymer modified hot mix and asphalt emulsion based microsurfacing [33]. it starts from the crude oil production. 12-22 Eco-efficiency portfolio combines environmental impact with costs of treatments. all costs and environmental impacts were averaged over 0. Energy 1. Here. energy consumption. Results demonstrate that microsurfacing is more “Eco-Efficient” than hot mix overlays. the overall conclusion is that microsurfacing provides a better balance between cost-effectiveness and environmental impact than does a thin hot mix overlay as shown with the eco-efficiency portfolio of the preventive maintenance in Fig. Modified hot-mix asphalt Hot-mix asphalt Low eco-efficiency 1. The thicker hot mix layer let to a greater use of natural resources. recycling operation. When all factors were considered. emission. 12-21. microsurfacing had a lower environmental “footprint” as shown in Fig.0 Costs (relative) 0.00 Potential health effects Risk potential Fig. potential health effects. Cold-mix microsurfacing Hot-mix asphalt Modified hot-mix asphalt These environmental impacts were weighed according to how surveys said the public viewed their relative importance. as well as higher energy consumption and emission involved in its manufacture and transportation. When this result is combined with the annual costs of the treatments.2 325 .0 Fig.00 0.8 1. 12-21 Environmental profiles for microsurfacing and thin hot mix overlays.8 1.50 Raw material Emissions 0.5 Concluding Remarks It also includes waste production. These environmental impacts are classified into five parameters: raw materials consumption. 12-22.2 High eco-efficiency Environmental impact Cold-mix microsurfacing 1. and transportation and distribution of all these activities. and risk of accident and misuse.12. Microsurfacing has a lower environmental “footprint” than two other alternative treatments. Special Bitumens and Bitumens with Additives in Pavement Applications. J. Y. American Chemical Society.fr . Drs Alan James and Julia Wates of Akzo Nobel Surface Chemistry LLC.5 Concluding Remarks Asphalt roads account nearly 95 % (3 300 000 km) of the paved roads in the US Addition of as little as 2–3 % of polymers in the asphalt improves rutting resistance. Manual Series No. Construction of Hot Mix Asphalt Pavements. J. Recent studies [33] on eco-efficiency analysis clearly demonstrate economical and ecological advantages of the asphalt emulsion based microsurfacing for preventive maintenance. Asphalt Paving Technol. September 1997. P. T. Kandhal. 2nd Edition. The Asphalt 2 3 4 5 Handbook. Laboratoire central des Ponts et Chaussées.. H. World Road Association. Acknowledgement The author is grateful to Glynn Holleran of Valley Slurry Seal Co. PA. Jeremy Kissock of BASF New Zealand and Mike Taylor of BASF Corporation for their valuable comments and advice. slurry seal and microsurfacing applications. L. Bordeaux. 2nd edn. KY. Symposium of World Road Bitumen Emulsion Producers. 1975–1999. Hancock. Latex. D. Dr. 1996. The latex can be used for both hot mix and emulsion based paving. 1843. Assoc. S. Presented to the 7 8 9 10 Rubber Division. 32–69. R. Pavlovich..piarc.326 12 Applications for Asphalt Modification each year of the life of the treatment. 68A. F. Assoc. Thompson. King. Epps. Additives in Asphalt. T. A. Per Redelius of AB NYNÄS Petroleum. 4 (MS-4). November 21. 6 S. D. G. NAPA Research and Education Foundation Textbook. P. L. which are predominantly used for preventive maintenance. September 1999. Asphalt Paving Technol. D. 1982. Lee. King. www. Manual Series No. References 1 The Asphalt Institute. E. Brown. The study also suggests that future improvement in microsurfacing techniques could lead to additional cost and environmental advantages [33]. 12. UK Patent No. C. Commercial availability of the cationic form makes SBR latex ideal for chip seal. Lexington. and prevents premature fatigue and cold fracture crack formation. W. Asphalt Institute. Philadelphia. 55. 9952. Epps. Hot Mix Asphalt Materials. Mixture Design and Construction. Use of Modified Bituminous Binders. because it is an aqueous dispersion. 22. Shuler.icpc. 75th Historical Review and Index of Journals. Roberts. 1958. R. is the ideal polymer for modification of an asphalt emulsion. F. J. 1999. Hagman. Kennedy. Kandhal. World Road Association (PIARC) Technical Committee Flexible Roads (C8). A. 121–135. N. Proc. 67. Brûlé. pp. Evaluation of Polymer Modified Chip Seal Coats. R. Horvath. A Description of the Cohesive Breaking of Emulsions for Chip Seals. Asphalt Paving Technol. Symp. 1999. A. Record 1455. State-of-the-practice Design. Herr. J. 1999. 185–194. KY. 136–150. Brûlé. 19–49. National Economic Development and Prosperity Related to Paved Road Infrastructure. Construction and Performance of Microsurfacing. Bahia. AEMA Recommended Performance Guidelines. Maryland. Sharma. Esso Abrasion Cohesion Test. 1988. Asphalt Emulsion. 327 . KY. AEMA/ISSA Proc. 1989. P. L. Jones. Asphalt Emulsion Technology. AEMA/ARRA Annual Meeting. Wittlinger. Pavement Preventive Maintenance: Description. M. R. A. Washington. A. Heckmann. Lexington. National Research Council. D. Association of Asphalt Paving Technologist. 2000. Asphalt Paving Technol. 57. 41–64. Wates. K. L. ASTM STP 1349. James. Barnat. 68. Tanguy. H. Comparison of Environmental Implications of Asphalt and Steel-Reinforced Concrete Pavements. Asphalt Emulsion Manufactures Association. A.W. Asphalt Institute. J. C. Effectiveness. ASTM STP 1349. J. Symp. Flexible Pavement Rehabilitation and Maintenance. Annapolis. R. Comparison of Emulsion Residues Recovered by the Forced Air- 23 24 25 26 27 28 29 30 31 32 33 34 flow and RTFO Drying. H. Feb. DC. Paving Asphalt Polymer Blends: Relationships Between Composition. M. Symp.E. 545–575. D. Brion. Lok. R. FHWA-SA-94-051. 1991. Hislop. Strategic Highway Research Program (SHRP-A-369). 1988. P. Record 1626. 1994. Julien. Proc. Takamura. Takamura. Bahia. pp. J. K. R. 1 (SP-1). Arand. February. Symp. 64–88. The Structure of Polymer Modified Binders and Corresponding Asphalt Mixtures. B. A. D. Asphalt Containing Conventional and PolymerModified Bitumens in High and Low Temperature Conditions. Akzo Nobel internal results. U. C. Lexington. Y. Federal Highway Administration. 1–17. 105–113. Coyne. and Treatments. H. Marrakesh. J. Anderson. W. Polymer Network Formation in the Emulsion Residue Recovered by Forced Air Drying. K. Zhai. C. Transportation Res. Y. AEMA Annual Meeting. I. Takamura. ASTM Symp. Rubber Chemistry Technol. B. Wegan. 67. Int. H. Grangel. C. AEMA/ISSA Proc. Harder. Bitumen Emulsion Testing: Towards a Better Understanding of Emulsion Behavior. Cai. Sept. Ng. Syed. Flexible Pavement Rehabilitation and Maintenance. J. Christensen. Effectiveness of Highway Maintenance Treatments Used in Texas. W. E. Classification of Asphalt Binders into Single and Complex Binders. Polymer Modification of Paving Asphalt Binders. Assoc. 2nd edn. 346–355. 1998. 1994. M. 2000. Marchal. J. 1988. Hendrickson. 1998. Jones. pp. E. Binder Characterization and Evaluation Volume 3: Physical Characterization. Queiroz. J. Nov. S. PIARC XIXth World Road Congress. Asphalt Institute Manual Series No. Washington.P. L. Mamlouk. K. 1999. Haas. Hassan. pp. Asphalt Emulsion Technology. ISSA Annual Meeting. Freeman. 2001. Structure and Properties. Asphalt Paving Technol. 2nd edn. 1999. Predictive Capabilities for Maintenance Products. DC 1994. L. A Basic Asphalt Emulsion Manual. Cornet. Smitn.G. Transportation Res. D. 1999. V. 1994. W. Antle. Zaniewski. D. Lewandowski. R. Boussad. T. O. A. Superpave 12 13 14 15 16 17 18 19 20 21 22 Series No. B.References 11 Superpave Binder Manual. Button. 19. Int. 57. 1990. 447–480. the need of shorter construction time together with cost reduction. the diversification of building materials suitable for specific applications. known as dry mortar mixes guarantee defined and consistent performance of construction materials.Polymer Dispersions and Their Industrial Applications. As a practical consequence.1 Introduction The building/construction industry is the main industry for redispersible powders. increasing labor costs. The aggregates and the mineral binders were then mixed together by hand in the appropriate ratio and were gauged with water in order to obtain the fresh mortar ready to apply. Over the years the usage of dry mortar technology has been developed dramatically and modernized the way mortars are being used on a job-site. The job-site mix mortar technology is not able to meet adequately all these requirements. During the 1950s and 1960s both in Western Europe and the US. polymer modified building materials that needed only the addition of water before application. First there was a replacement of the job-site mixed mortars by premixed and pre-packed dry mix mortars. which can be seen nowadays in the whole world. which are more and more applied with machines. As a consequence the two-pack systems (mortar + dispersion) as well as 329 . These materials. like shortage of skilled workmen. Several reasons. the development of the modern construction and building chemical industry in the countries of the West from the 1960s onwards was influenced mainly by two important trends. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. 3-527-60058-2 (Electronic) 13 Applications of Redispersible Powders Hermann Lutz and Christoph Hahner 13. there was a fast growing demand in the construction industry for new building materials and technologies. In the past up until to the 1950s mortars were exclusively used and applied as jobsite mixed mortars. where the mineral binder (mostly cement) and the aggregates (mostly silica sand) were transported separately to the job-site. KGaA ISBNs: 3-527-30286-7 (Hardback). but especially in Germany. The invention of redispersible powders enabled the industry for the first time to produce pre-packed. Secondly mortars started to be modified with polymer binders in order to improve the product quality and to meet the requirements of the modern building industry. the request for new materials and an increased demand for better quality of constructions were supporting a movement towards dry mix mortar technology. 13-1 Over 90 % of all industrial manufactured polymer dispersions are produced by emulsion polymerization. Tg. which are being used for applications in the building/construction industry. pre-mixed and pre-packed dry mix mortars. – very flexible. – no saponification. vinyl chloride. Spray-dried polymer particle. of –93 °C. The resulting emulsion will fulfill the functionality of a polymeric dispersion binder. The colloid protects the polymer particles from film forming during the spray drying process . Redispersible powders are manufactured by spray drying an emulsion (Fig. – ideal for co-polymerization with vinyl acetate. – very hydrophobic.2 Manufacturing of Redispersible Powders A redispersible powder is by definition a polymer in a powdered form that can be redispersed by adding water to it. – UV-resistant (no yellowing). versatic acid esters. The most important monomers. ethylene. are vinyl acetate. 13-1). To guarantee the performance of a redispersible powder in its final application a protective colloid is added to the emulsion before the spraying process. – very low glass transition temperature. and – good adhesion to most of the substrates. Fig. 13. Especially the use of ethylene as a co-monomer offers some extraordinary advantages: – environmentally safe. normally within a cementitious or gypsum based system. which are modified with redispersible powders.330 13 Applications of Redispersible Powders ready to use products (liquid or paste) were substituted by one-pack systems. styrene and acrylics. 13.2 Manufacturing of Redispersible Powders and is also responsible for that the powder will redisperse in water again (Figs 13-2 and 13-3). dispersion particle concentration particle concentration 100 69 % ppm 80 weight distribution curve 69 ppm 60 40 20 0 0 2 4 1 6 1 10 particle size (diameter) redispersion particle concentration particle concentration 100 92 % ppm 80 weight distribution curve 92 ppm 60 40 20 0 0 2 4 6 1 1 10 particle size (diameter) Fig. 13-2 Dispersion/redispersion – comparison of particle size distribution. spray drying adding water drying dispersion Fig. 13-3 protective colloid The spray-dry process. redispersible powder redispersion 331 332 13 Applications of Redispersible Powders Over the years poly vinyl alcohol (abbreviated PVOH or PVAl) proofed to be the most preferred protective colloid for that purpose. In a cementitious environment PVOH will be partly saponified and also absorbed of fine particles within a mortar, i.e. cement and fillers. This results in a film forming of the dispersed polymer and finally the polymer film is not redispersible any more. Since the polymer film (acting as a binder) is distributed throughout the cement matrix it improves dramatically the adhesion, abrasion resistance, flexural strength, flexibility, water impermeability/water repellency (hydrophobicity) and workability of a cementitious system. 13.3 Dry Mortar Technology The invention of redispersible powders by Wacker-Chemie in 1953 made for the first time the production of polymer modified dry mix mortars possible, which are nowadays referred to as one pack or one component system (“bagged” materials). New construction methods and building materials, which had the need for more safety, reliability, durability, efficiency and economy, have been achieved by using modern methods like the dry mix mortar technology. As a consequence worldwide the “jobsite mix technology” and the modification of mortars with liquid polymers on jobsites were and are substituted by polymer modified dry mix mortars. The product characteristics are very well adapted to the requirements of modern construction technologies, materials and climates. Pre-mixed and pre-packed dry mix mortars not only increase significantly the production performance and the productivity on construction sites, but guarantee also that high and constant quality binder, aggregates, and additives are being mixed exactly in the same ratio, thus ensuring a consistent high quality level within dry mix mortars. Furthermore, dry mix mortars offer solutions to specific problems that are precisely tailored to certain types of construction/material specifications. Especially in the USA, the legal aspect of a reliable, properly conducted construction job is very important to each manufacturer of construction materials. The use of redispersible powders and therefore also the use of polymer modified powdered mortars is already for many decades standard in the construction industry in Europe and North America (predominantly in the USA). Other marketplaces all over the world like South America, Asia, Africa and Australia are in the process following that example. More and more environmental reasons ask also for the usage of dry mortars, since the recycling of buckets becomes more and more an issue. Dry mortars are also easy to store, transport and do not require biocides. Typically dry mortar mixes contain the components listed in Tab. 13-1 and are defined according to German standard DIN 18557. The application areas of dry mix mortars are: – ceramic tile adhesive, – tile grouts, – E.I.F.S. (exterior insulation and finish systems)/E.T.I.C.S. (exterior thermal insulation compounds), 13.4 Markets and Application Areas of Redispersible Powders Tab. 13-1 Dry mortar mixes. Mineral binders Portland cement (OPC) High Alumina Cement (HAC) Special cement Hydrated lime Gypsum, anhydrite Aggregates fillers Polymer binder Additives Silica sand Redispersible powder Cellulose ether Hydrated lime Dolomite sand Marble sand Lightweight fillers Special and functional fillers Pigment Defoamer Air-entraining agent Retarder Accelerator Thickener Hydrophobing agents Plasticizers – – – – – – – – – – – self-leveling over- and underlayments, screeds, stucco, skim coat, topcoat/finish coat, patch and repair mortar, adhesive mortars (for all kind of substrates), crack isolation membrane, powder paints, gypsum based compounds (joint fillers), waterproof membranes/sealant slurry, pool decking, and stamped concrete. The following paragraphs will describe the most important and most developed application areas for redispersible powders as they are ceramic tile adhesives/ tile grouts, thermal insulation systems (E.I.F.S.), self-leveling underlayments, patch and repair mortars, as well as water proof membranes (sealant slurries). 13.4 Markets and Application Areas of Redispersible Powders To meet today’s technical requirements, almost all dry mix mortars require polymer modification. Many cementitious mortars contain cellulose ethers as an additive to improve water retention and workability. However, after setting and drying they will adhere poorly or not at all to most of the substrates used in modern construction technology such as polystyrene panels, fiber panels, wood panels, closed and non-absorbent substrates or old tiles. In addition, cementitious mortars are very hard, brittle and inflexible materials, whereas for many applications flexible and deformable cementitious materials are essential. As a consequence for almost all applications in modern construction, the modification of cementitious mortars with polymers is a must. In dry mix mortars the mineral binder, cement, and the polymer binder, redispersible powder, are ideal partners. The combination of both in a dry mix mortar 333 334 13 Applications of Redispersible Powders provides outstanding synergistic properties and characteristics, which cannot be achieved by either of the binders alone. 13.4.1 Adhesives for Ceramic Tiles Ceramic tiles as well as natural stone were previously installed exclusively by using the thick bed mortar technique. Silica sand and cement were mixed together on the job-site, in order to produce a simple cement mortar with a cement/sand ratio of approximately 1:4 to 1:5. In some countries only cement is still used in order to set tiles. After having applied (“buttered”) the mortar at a thickness of 15 to 30 mm (0.6 to 1.2 inch) on the reverse side of the water-soaked or pre-wet tile, the tile is pressed into the pre-wet surface. The tiles have to be tapped to ensure uniformity and flatness of the tile surface, thus obtaining a final mortar bed of 10 to 25 mm (0.4 to 0.8 inch). This procedure causes not only compaction of the mortar, but leads in addition to the migration of the fine cement particles into the porous back side of the tiles and the porous substrate as well. This process assures the mechanical fixing of the tile in the mortar bed. This type of mortar has no slip resistance. Therefore tiling of a vertical substrate has to be started at the bottom and distance splinters become necessary. The described procedure shows very clearly that the thick bed method is a very time, cost and material consuming process. More significantly, there are technical restrictions using this technique. One of the examples is that only small, porous tiles can be applied over porous, solid and strong mineral surfaces. The application of tiles over wood would be almost impossible, since a mortar without any polymer modification would not only be not flexible enough to withstand the movement of a wood substrate over an extended period of time, it would also have no sufficient adhesion to the substrate. Consequently severe damage could occur and therefore the thin bed mortar technique has replaced the thick bed mortar technique in most industrial countries. It started in the USA in the early 1950s by adding a polymeric binder in form of a liquid latex dispersion to a job-site mixed mortar (see Chapter 8). Nowadays dry mix mortars modified with redispersible powders dominate this market segment more and more. After gauging the polymer modified dry mix mortar with water, it can be applied with a notched trowel, producing a ribbed mortar bed of uniform thickness. Due to the good water retention capacity of the thin bed mortar, neither the tiles nor the substrate have to be pre-wet. The tiles are pressed into the thin layered mortar with a slightly twisting movement of the tile. An anti-sag ceramic tile adhesive allows installing tiles on vertical substrates without using distance splinters between the tiles. The tile installer can also start from the top of the wall instead of the bottom. The mortar bed, which fixes the tiles, has a thickness of approximately 2 to 4 mm (up to 0.25 inch). Since this method clearly uses less material, it is more cost effective, can be used more universally; its execution is clearly simpler, faster and safer. The clear advantages of dry mix mortars modified with redispersible powders, which apply also for tile grouts, are: 13.4 Markets and Application Areas of Redispersible Powders – good workability, fast and easy to use, creamy consistency, – good water retention, which results in a long open time and good adjustability even at high temperatures, and – substantial anti-sag properties, if required. As far as the formulations for ceramic tile adhesives go there is a high variety of mortars offered in the market place in order to meet all the specific requirements. A major difference, for example, between Europe and the United States is the usage of wood as a substrate in the USA. Differences in the formulation are also determined by requirements of specifications or application circumstances like interior or exterior, wall tile or floor tile, vitrified tile or more porous tile, fast setting or regular setting, flexible or even highly flexible. The availability of certain raw materials i.e. silica sand determines very often how a formulation will perform. The two most important specifications worldwide are the European Norms “EN” and the American Standards ANSI 118.1-1999. The biggest difference between the two standards is the principal test setup. The European Standards require mostly tensile bond adhesion testing where else the American Standard uses shear bond testing. The other difference is clearly the storage conditions for the specimen before testing. A listing of both standards is shown in Tab. 13-2. Tab. 13-2 EN and ANSI standards for CTAs. European standards EN 12004 Definitions and specifications EN 1308 Anti-sag EN 1347 Wetting capability (coverage) EN 1346 Open time EN 1348 Tensile adhesion testing, including heat and freeze-thaw storage EN 1324 Shear-strength for mastics EN 12002 Deformability of cementitious CTA US standards ANSI A 118.4 ANSI A 118.11 Specifications for Latex Portland cement mortar Specifications for EGP (exterior glue plywood) Latex–Portland cement mortar Cement-based standard tile adhesives can be classified in very simple (low quality) tile adhesives, which do not contain any polymeric binder. They do not meet European or American Standards. Such tile adhesives, providing a pure mechanical fixation can only be used for fixing small, very porous tiles. The substrate is supposed to be dimensionally stable, sound and solid as well as not showing any shrinkage or movement. If exposed to higher temperature or frost, there is a higher risk of failure. Non-modified mortars show for the most part no long-term performance. Simple tile adhesives have already a polymer modification of 1 to 1.5 % of a redispersible powder (calculated on total formulation). Such tile adhesives meet some parts of the mentioned national standards, but usually fulfill not all requirements. Only the usage of tiles with a medium porosity and small size could result in acceptable results with these types of adhesives. 335 336 13 Applications of Redispersible Powders Standard ceramic tile adhesives of good quality need approximately 1.5 to 3 % of redispersible powder on total dry mix. They meet the new European Norm for tile adhesives (mostly only C1 level) and pass also the ANSI specification 118.4 and 118.11. Larger formatted tiles can be applied with these materials over porous or less porous, dimensionally stable substrates. They are suitable for interior as well as exterior application. For standard applications these modified mortars provide higher quality security and a certain long-term stability, very much depending on the factors like climate conditions, weight traffic etc. Finally flexible (5 to 8 % of redispersible powder) and very flexible ceramic tile mortars with a polymer modification beyond 8 % up to even 25 %, guarantee the best performance over all, very good adhesion on all types of substrates with all types and sizes of tiles. These adhesives are used more universally and offer a much greater application variety, safety, as well as long-term durability and reliability. Nowadays these mortars are more and more used to fix the very popular highly vitrified tiles (water absorption <0.1 %) and natural stone tiles (like marble) in any format. The substrate can be non-porous and inorganic as well as wood. Even if the substrate still shows to a certain degree of shrinkage or expansion, including other types of movements or vibrations, these quality adhesives could be used to set tiles in a safe and durable way. Typical application examples for flexible ceramic tile mortars are: – floor heat system within the substrate, – to heat exposed surfaces, like i.e. tiles on a porch exposed to sunlight, – tiles over tiles, – over gypsum boards, – over backer boards, – over wood, – on water proof membranes, – on thermal and sound insulation panels, and – on light-weight concrete blocks. Tests conducted by international research and test institutes have proved that it is of high importance that cementitious adhesives provide a sufficient deformability and a certain degree of plasticity [1–4]. Only in that way, long-term durability and functionality can be guaranteed. Adhesive mortars have to be able to absorb stresses that occur between two materials as tiles and substrate in order to prevent damages. Typical damages are cracking or even delaminating of the tiles. Irreversible differential movement, such as shrinkage causes always stress between tile and substrate (fresh concrete is always likely to shrink). Reversible movements of the substrate like vibrations and thermal movements due to heat or cold are also sources of stress between substrate, adhesive and tile. The different modulus of elasticity of tiles and substrate is also enhancing the stress within a ceramic tile mortar (Fig. 13-4). European Norm EN 1348 addresses this issue in a heat test as well as in a freeze/ thaw test. Shear stress between substrate and tile normally concentrates in the peripheral zones of a tile. That means, the bigger the tile the higher the flexibility of the adhesive has to be in order to avoid cracking or delaminating of the tile. The flexibility (deformation capability) of a ceramic tile adhesive depends on the polymer/cement ratio. It is one of the two most important ratios to be determined in a ceramic 13.4 Markets and Application Areas of Redispersible Powders tiles tiles deformable adhesive mortar substrate eg. concrete substrate eg. concrete initial dimension initial dimension shrinkage of substrate eg. shrinkage of concrete expansion of tiles eg. thermal expansion tiles tiles rigid, non-deformable adhesive mortar substratre eg. concrete initial dimension Fig. 13-4 substrate eg. concrete initial dimension The stress between substrate and tile. tile mortar (the other one is the water/cement ratio). The German test DIN 18156/3, as well as EN 12002, measures the flexibility of ceramic tile adhesives. As a result of these tests it can clearly be shown, that the higher the polymer/cement ratio the higher the flexibility of a mortar system (Fig. 13-5). Fig. 13-5 The flexibility of ceramic tile adhesives. It is very important to mention that the deformation capability of a given cementitious system also depends to a large extent on the degree of hydration of the cement. Consequently, the flexibility of different adhesives can only be compared at identical 337 13 Applications of Redispersible Powders degrees of hydration of the cement. Unfortunately this is very often not considered within the storage conditions of different standards, that deal with the testing of flexibility (Fig. 13-6). 16.0 14.0 12.0 Flexion/deformation [mm] 338 10.0 8.0 6.0 4.0 2.0 0.0 50% Portland Cement 40% Portland Cement 35% Portland Cement 30% Portland Cement Traverse deformation test according to EN 12002 - 5% polymer modification at different cement levels standard conditions Fig. 13-6 water storage (full hydration) 7d sc/ 14d in water/ 21d sc EN 12002 results on flexibility. The relative humidity of approximately 95 % at the beginning is not kept constant during storage and is not sufficient for a full hydration of the cement. Over the time cementitious adhesives will reach their full hydration thus resulting in sometimes very low flexibility of the mortar. For example, the use of additives and/or polymers with a strong retardation effect on the cement will cause an incomplete hydration of the cement and will lead temporarily to a higher polymer-to-cement ratio. The flexibility measured at this point will not reflect the real flexibility of the system after full hydration of the cement phase. After complete hydration of the cement, “soft” polymers (lower glass transition temperature, Tg) will perform at an appropriate dosage level better compared to polymers with a higher Tg, especially if used and tested at lower temperatures (Fig. 13-7). (The glass transition temperature describes the flexibility of a polymer. The “rule of thumb” is the lower the Tg the higher the flexibility. Tg is determined from the ratio of different monomers and their individual Tg in a polymer, by use of the Fox equation [5]). The adhesion of tiles to the substrate is certainly as important for a ceramic tile adhesive as the flexibility. The European Norm uses a “pull off test” to determine the adhesion, where as the US standard ANSI 118.1 – 1999 prefers the shear bond test. A simple ceramic tile mortar with no polymer modification will fail in the adhesion test especially after heat aging or over wood (ANSI 118.11 – 1999). The same mortar modified with only 2 % of redispersible powder will pass both tests. With the pull-off it can be demonstrated that a ceramic tile adhesive without polymer or with a low polymer level will only be able to pass. there will be no mechanical anchoring like described earlier for porous tiles. 13-7 Flexibility at lower temperatures. An adhesive formulation that considers these two important components at the right amount is very likely to pass all international standards. only provides the adhesion. water absorption) should contain at least 6 % of redispersible powder and the cement content should be limited to 30 to 35 %.4 Markets and Application Areas of Redispersible Powders Fig. it can be demonstrated that only a sufficient amount of redispersible powder provides a significant adhesion on critical substrates like PVC. A ceramic tile adhesive that performs very well over almost all substrates. test.13. In addition. wood or tiles (Fig. 339 . if wall tiles (very porous. In this case. A sufficient high polymer modification of the ceramic tile adhesive is necessary especially when non-porous. high absorptive tiles) are used. 13-8). highly vitrified tiles (low to no water absorption) are used. in this case. with all types of tiles (size. This is. besides the outlined reasons for sufficient flexibility. However. in an adhesive formulation has more to be considered than only the polymer and cement level. another important factor for a higher polymer modification. The redispersible powder (chemical bonding). .340 13 Applications of Redispersible Powders Fig. Therefore. for example. a low tendency for staining. are very similar to ceramic tile adhesives in their formulations. abrasion resistance and flexibility. Redispersible powders with a hydrophobic effect are normally used to achieve all requirements of a tile grout.4. They are expected to be water repellent (hydrophobic). because US manufacturers offer a much greater variety of colors. to have good adhesion to the substrate and the edges of the tile. cohesion strength. which are used to fill the joints in between the tiles.2 Tile Grouts Tile grouts. in Germany. The use of redispersible powder improves adhesion bond strength to all types of substrates. They reduce the risk of efflorescence as well as staining of the grout. The fields of ceramic tile mortars and tile grouts are certainly the most developed for redispersible powders in cementitious applications. the deformability (flexibility). sufficient hardness. 13-8 Adhesion of ceramic tile adhesives to different substrates. color consistency is of high importance as well. The standards in the US and Europe are summarized in Tab. the open time the wetting capability as well as the workability within dry mix mortars. In the USA the field of tile grouts is much more diversified than. 13-3. the cohesive and flexural strength. 13. organizations exist representing the E. offered in Germany were shipped to a construction site as ready to use systems (pasty consistency).I.3 Exterior Insulation and Finish Systems and Top Coats With the beginning of the 1970s exterior insulation and finish systems (E. less damages of facades and possible savings at the over all building costs.S.) The first oil crisis in Germany 1973 together with financial support of the government for homeowners had helped tremendously to promote the system. (E.I.F.I.F.I.F.7 * There Specification for standard cement grouts for tile installation Specifications for polymer modified cement grouts for tile installation is also a draft of “Tile grout mortars for tiles. the country with the most usage of E. Mistakes occurred by not meeting the polymer cement ratio according to the manufacturers’ requirement. that also emphasizing a positive environmental aspect of E. The abbreviation used in Europe is ETICS – exterior thermal insulation compounds. In both countries. However. The use of machines also promoted dry mix mortars modified with redispersible powders. is the United States. As a consequence more than 18 billion liters of oil were saved (approximately 113 million barrels).6 ANSI A 118.F. 13-3 EN and ANSI standards for tile grouts. In the early 1970s. resulting in damages and complaints. Between 1973 and 1993 approximately 300 million square meters of E.F. The technology used in both countries is predominantly based on the usage of polystyrene as an insulating material.F. is predominantly used in North America. reliability and control over the formulation out of production as well as time and cost savings of machine applicable systems.S.S. 341 .4 Markets and Application Areas of Redispersible Powders Tab.S) were used in Germany.13.I. in the past within the United States has been more for optical reason.S. the materials for E.I.S. After Germany. European standards* EN 12808-1 Determination of chemical resistance EN 12808-2 Determination of abrasion resistance EN 12808-3 Determination of flexural and compressive strength EN 12808-4 Determination of shrinkage EN 12808-5 Determination of water absorption EN 12002 Determination of deformability US standards ANSI A 118.I. They had to be mixed with cement before usage. Recently more and more the energy saving aspect of the system has become a more considered aspect for homeowners. healthier climate condition inside the house. definitions and requirements” 13. EIMA”. This also means considerably less CO2 was released into the atmosphere. The time and cost savings remain tremendous.F. The industry shifted almost completely to dry mix systems in order to avoid the mentioned problems. Some of the advantages of E.I.F. are saving energy.4.S.I.S. were applied on facades in Germany. In the US. industry and its interest: representative of Germany is the “Fachverband Waermedaemm-Verbundsysteme” and of the USA the “Exterior Insulation Manufacturer Association.S.F. the use of E. 342 13 Applications of Redispersible Powders has clearly set the trend over the last 5–10 years towards more and more usage of the dry mortar technology and. EPS-Board 4. Substrates might vary. – adhesion of cementitious materials on polystyrene.I. The principle layers of an E. and – flexural and compressive strength. 13-9. In the US there are different authorities (regional and city codes) like the “American Society for Testing and Materials – ASTM”. Substrate 2. The testing of such systems is very severe.F. the “Building Officials and Code Administrators – BOCA”. system needs even a technical approval granted by testing institutes according to the “European Organization for Technical Approval. – water absorption. system are shown in Fig. EPS-Adhesive 3.F. as well as in the US several technical tests are conducted in order to prove the performance of E. therefore. Right on top of the substrate the insulation board is glued with an adhesive. Normally one will find concrete/brick as a substrate. EOTA”. under different test conditions.F. In Europe. . So far this level of warranty is not yet achieved in the US.S. Some of the most important types of tests conducted on an E. towards redispersible powders/polymers. Most of the tests are still very much depending on the country (Europe). system are: – stability and flammability. – insulation properties. Because of the use of redispersible powders. In the US it is normally plywood. In addition sometimes mechanical fasteners are use as well.I. has reached such a high level of reliability and quality consistency that manufacturers in Germany normally allow a 30-year warranty for their systems. Top Coat/Finish Fig.I. Information on test procedures is also available through EIMA. More specific information can be gathered through the different organizations. 1.I.I. In Europe the entire E. system. the application of E.F. the “International Conference of Building Officials – ICBO” and the “Southern Building Code Congress – SBCC”.S. – impact resistance.F.I. Base Coat 5. 13-9 The principle structure of an E.F. Normally the cement content in US systems is higher than in Europe. – low dirt pick up.) The addition of organic polymeric binders in form of redispersible powders to mineral plasters and stuccos can significantly enhance certain properties. Here we find probably the biggest difference between. flexibility). – good drying characteristic (high water vapor permeability). meaning a crack free base coat. (Finish or topcoats can also be named render. they can be considered equivalent. For that purpose the polymer-to-cement ratio should be as high as possible. This has to do with the fact that the preference in Europe is towards more flexible system where else in the US a hard surface appearance of the base coat is preferred by contractors. as with Germany. In order to meet these requirements the preferred redispersible powders used in topcoats are vinyl acetate/ethylene copolymers. – very low flammability. for example in thickness of the coating depending on the technology used. Top/finish coats must meet certain critical physical and technical requirements. – low water absorption or water repellency (hydrophobicity).4 Markets and Application Areas of Redispersible Powders 85 % of the insulation material used in Germany is Extruded Polystyrene “EPS”. The functionality of the base coat is protection and reinforcement of the EPS panel.13. this results in a higher polymer-to-cement ratio in European systems compared to US systems. for example. plaster or stucco. – the modulus of elasticity of the top coat should be lower than the modulus of elasticity of the substrate (layer below). such as adhesion to the substrate. topcoats are cement based as well. In Europe. low water absorption (hydrophobic effect by using special redispersible powders) and long-term durability. Normally slight differences apply. – mechanical stability (high impact resistance). The integrity of the base coat. mechanical resistance. Besides adhesion. Assuming the polymer content is very similar. Certainly as important as the base coat is the topcoat for the entire system. Germany and the United States. As far as the use of redispersible powder is concerned. The EPS adhesive is normally the same material as the base coat. is a precondition for good technical performance. These include: – good adhesion to the substrate (tensile adhesion strength). cement free systems that are very often ready to use and based on emulsion technology. water absorption or deformation capability (flexibility) is tested. In the US cementitious topcoats are almost not used at all. Especially when it comes to flammability vinyl 343 . the right polymer modification becomes also very important when impact resistance. – resistance to weathering. They are synthetic. – low susceptibility to cracking (good relaxation properties. The base coat has an important functionality within the entire system. The right modification of the base coat with at least 3 to 6 % redispersible powder will finally guarantee good performance values and as a consequence contribute to an excellent weather stability of the entire system. Without polymer modification there would be no adhesion of the EPS to the substrate and no adhesion of the base coat to the EPS panel. This is one of the main differences between Europe and US . F. pigments and additives. the capillary water absorption is reduced. forming a film that coats the pores without actually blocking them [6–8]. wetting agents and sometimes even surfactants. The addition of approximately 0. Because of the mentioned adhesion of the polymer to the cement pores the adhesion as well as the flexural strength and toughness of the material is improved also. 13-10 and demonstrate the formation of the polymer film within the cement matrix. of course. .F. perform the worst in this respect. aggregates (fillers like silica sand). hydrophobic agents. Thus a permanent effect is achieved throughout the mortar.S.I. industry as well as to topcoat manufacturers is certainly the hydrophobicity of their base coats and/or topcoats. Tab.I. Figure 13-11 shows the capillary water absorption of test specimen after up to 6 years outdoor exposure at different polymer levels. Because the pores (capillaries) are coated with a water repellent polymer film with good adhesion to the cement. the polymeric binder in the form of a redispersible powder is very quickly redispersed.I. such as cellulose ethers. lightweight fillers. Scanning electron micrographs are shown in Fig. 13-4 Specifications for topcoats. Then the polymer particles accumulate mainly in the pores.S based on acrylics and acrylates. The SEM technology was also used to demonstrate that the redispersible powders continue to fulfil their functionality over an extended period of time. fibers. This is also shown by experiments to determine physical factors such as water absorption and water vapor permeability on defined test specimen after long-term exposure to outdoor weathering conditions. German-US standards DIN 18555/ASTM C 109 DIN 18555-6/* DIN 52617/ASTM C 413 DIN 52615/ASTM E 96 DIN 18555/ASTM C 231 DIN/EN 196/ASTM C 580 * ASTM Compressive strength Tensile bond adhesion Water absorption Water-vapor permeability Air content Flexural strength E 2134-01 for E.344 13 Applications of Redispersible Powders chloride containing systems perform the best closely followed by vinyl acetate ethylene containing polymers. If the amount of redispersible powder stays within 3 to 6 % there is no loss of water vapor permeability.F. thickener.S. One aspect that is very important to the E. Mineral topcoats are composed of lime and cement as mineral binders. What is the mechanism behind a hydrophobic effect achieved by using a hydrophobic redispersible powder? When water is added to the dry mix topcoat. like styrene acrylics.5 to 2 % special hydrophobic redispersible powders to dry mortars additionally imparts uniform water repellency throughout without effecting the water vapor permeability. This. starch ethers. With the exception of any mineral binder this list applies also to synthetic topcoat which are almost exclusively used in the US. depends also very much on the hydrophobicity of the used redispersible powder. Table 13-4 shows some of the specifications for topcoats in Europe (Germany) and the US. Topcoats/E. 5 1 0.5% percentage redispersible powder on total formulation 21 days standard conditions Fig.4 Markets and Application Areas of Redispersible Powders Fig.0% 3. smooth and solid substrate in order to apply all kind of flooring materials like carpets.5 3 2.long term exposure 4 water absorption coefficient according to DIN 52617 3. 345 . 13.5 0 0. even for large areas.4. PVC.0% 3.13. tiles etc. wood parquet. On a given uneven substrate (i.5% 1. screed or surface to be refurbished). Self-leveling underlayments should be applicable in an easy and efficient manner. self-leveling mortars have to provide a suitable.e. 13-11 1 year outdoor exposure 6 years outdoor exposure Long-term performance of cementitious topcoats. 13-10 SEM of polymer film in cement matrix. Capillary water absorption of mineral topcoat .5 2 1.4 Self-leveling Underlayments The area of self-leveling underlayments (SLU) is out of a technical perspective probably the most complex one if it comes to applications of redispersible powders.0% 2. The technical requirement of a SLU reaches from very simple to highly sophisticated products. Depending on the dosage of the redispersible powder. still leads to severe and serious damage in the building industry.346 13 Applications of Redispersible Powders Therefore. provide low shrinkage. improves the flexural strength. The redispersible powder increases the adhesion to all kind of substrates. Polymer modification is absolutely necessary within this technology. The shorter the setting/drying time. unfortunately. the more complicated and expensive the formulation becomes. and. which are always applied by machines (mixing and pumping in one set up). allowing putting down the floor above the SLU in a certain time frame. high alumina cement (HAC) and gypsum (anhydrite). Self-leveling compounds (underlayments and screeds) are based on special hydraulic binders like Portland cement (OPC). In the past. elasticity and the abrasion resistance. self-leveling/troweling mortars and underlayments). In Ger- . However. They vary in thickness from a very thin layer of 1–10 mm (1/25–2/5 inch) (feather finish. the thicker the mortar is applied. Normally this is a question of the requirement of a specific job. self-leveling and self-smoothing properties. the techniques and the application is very well known for many years. it should perform fast setting/drying. 2. This becomes especially than very interesting.5 Patch and Repair Mortars Concrete is a very versatile.4. The set time (“walk over time”) of these materials changes from normal/regular setting to very fast setting products. when the SLU is also used as a wearing surface in an overlayment application. The cost of the repair of concrete structures has dramatically increased over the last 30 years in all industrial countries. Figure 13-12 shows the results of an abrasion test for a self-leveling compound with and without modification with a redispersible powder. SLUs are polymer modified by 1–10 % of redispersible powder calculated on total formulation. since the requirements are very sophisticated. saving time and thus the floor surface can be applied after only a few hours. high compressive strength and abrasion resistance. the abrasion resistance can be reduced significantly. According to their use and the specific requirements. So far there are no standards on self-leveling underlayments (SLU) in Europe or the U. Standard products are normally modified between 2 and 4 %. decreases the internal stresses (reduced crack formation and high abrasion resistance). Special powder grades will also support the self-leveling and self-flowing characteristics of the mortar. the SLU material has to have very good flow characteristics. in many cases.S. long-lasting and durable building and construction material if it is applied according to the state of the art. The SLU material should adhere to all kind of substrates.5 inch) for self-leveling screeds. up to 60 mm (approx. in order to achieve fast curing and drying by avoiding excessive shrinkage or expansion. and even today. 13. highly modified mortars are mainly used for refurbishment of wooden floorings with self-leveling compounds. repeated disregard of the fundamental principles of concrete and structural concrete application has lead. In addition. causes splitting of the concrete on top of the steel reinforcement. Once the alkaline environment of the steel reinforcing no longer exists. due to its volume increase. Acidic carbon dioxide (CO2) from the atmosphere and other aggressive media (such as SO2. many approximately 20 % of the cost of the volume of structural concrete work is attributed to the repair and maintenance of existing buildings and structures.4 Markets and Application Areas of Redispersible Powders Fig. 13-12 Abrasion resistance with and without redispersible powder. The degradation of structural concrete is caused by corrosion of the steel reinforcement due to chemical processes. which often occur over a long period of time. acid rain) neutralizes the alkalinity of the concrete. the steel starts to corrode and.13. A secondary cause of corrosion is the penetration of free chloride ions into the concrete. One of the main reasons is the carbonation of concrete. 347 . leading to chloride ion attack on the steel. parking decks. which are part of a “concrete rehabilitation system” (typical applications: repair work and rehabilitation of bridges. – abrasion resistance. – flexural strength. three main fundamental requirements of a concrete rehabilitation system must be fulfilled simultaneously: – restoration of the corrosion protection of the steel reinforcement (alkaline environment). – sufficient flexibility to reduce the risk of crack formation. tunnels. – durability. Usually. Typical applications are patching mortars for walls. i. cement-based mortars are used for indoor and outdoor applications. – easy to apply. voids. with namely patching mortars/compounds – repair and reconstruction of damaged reinforced and load-bearing concrete structures. in order to maintain and reconstitute their structural stability. for filling small holes. – flexibility (lower modulus of elasticity than substrate). – good adhesion to all construction substrates. and – water repellence for outdoor applications.348 13 Applications of Redispersible Powders In the construction industry concrete repair work can be classified in two types: – concrete repair. cracks and cavities in order to restore the original dimension. floors. whereas gypsumbased products are only used for some specific indoor applications (cosmetic repair). This is done in stages with different kind of mortars. To be able to guarantee the durable and reliable repair of structural concrete.e. – restoration and re-profiling of the concrete structure including its load-bearing functions. – low shrinkage. To meet the required technical criteria. if exposed to direct wear/load. – high durability and abrasion/wear resistance. and – water repellent effect by using special grades of hydrophobic redispersible powders. which does not contain steel reinforcement and which does not have load-bearing functions. These mortars must have the following characteristics: – good workability. Patching mortars are used to repair defective or damaged areas of mineral surfaces without taking on a load bearing function. ceilings. etc). and . etc. Patching mortars for re-profiling and cosmetic repair are mainly based on dry mix mortars and are not part of an entire repair or rehabilitation system. these patching mortars are applied as a polymer modified pre-packed dry mix mortar. – adhesion to all kind of substrates. The repair is normally done for aesthetic reasons (cosmetic repair work) only. Polymer modification with redispersible powder will – depending on the dosage – improve the: – workability of the mortar. – wetting capability of the substrate. steps of staircases. 13-14 shows the improvement in flexural strength of a typical reprofiling mortar applied by hand with and without different grades of redispersible powder. SO2.07 3 Tensile adhesion [N/mm2 ] 2.). is demonstrated in Fig. polymer modified cement concrete (PCC) mortars.13. salts. The flexural strength of the mortar is already significantly improved by adding only 2 % of redispersible powder without affecting the compressive strength too much. 13-13. which can be applied by hand. and – protection and finish coat (dispersion paints. are usually used for the rehabilitation of concrete structures. with and without applying a cementitious primer. The improvement of adhesion to concrete and steel.4 Markets and Application Areas of Redispersible Powders – restoration of the durability of the whole construction (protection against weathering and environmental damage caused by CO2. crack over bridging paints. using a polymer modified reprofiling mortar. in a wet or even a dry spraying process. Tensile bond adhesion after 28 d standard conditions polymer/cement ratio = 0. Fig. etc.5 2 1. 349 . – fine stopper or smoothing mortar (polymer modified cement based mortar containing fine aggregate). 13-13 with primer Adhesion to concrete and steel with and without primer. – restoration and re-profiling mortar (polymer modified cement based mortar). Different kind of mortars with different characteristics and functions are used as the components for concrete rehabilitation systems: – primer and adhesion promoter for the reinforced steel (polymer modified cementitious slurry or epoxy based coating materials). etc.5 0 over concrete over steel without primer Fig. Today.5 1 0. Cl2. cementitious waterproofing sealing slurries. – adhesion promoter slurry (primer or key-coat) for the concrete to be repaired (polymer modified cement based slurry).). cementitious waterproofing sealing slurries and bituminous waterproofing systems are used for that type of application.6 Waterproof Membranes Water in liquid or in vapor form is the most destructive weathering element for building constructions. Typically metal and plastic films. Despite this extremely short mixing and almost no slake time. which are materials to prevent surface. below-grade waterproofing materials.4. Above-grade waterproofing materials. Within this process the water is mixed with the dry mortar only in the jet. functionality and usage throughout its lifetime. could be categorized into: .and ground water or water under hydrostatic pressure from entering into a structure. masonry. Waterproofing and damp-proofing techniques are used to preserve a structure’s integrity. Almost the same improvements are obtained by applying the repair mortar through a dry shotcrete process. For preventing all possible water intrusions. 13. 13-14 redispersible powder 1 hand applied redispersible powder 2 redispersible powder 3 Flexural strength improvement by use of redispersible powders. the exterior of a building has to be protected form top to bottom with waterproofing materials. Exterior parts of a building could be classified in roof coating. After that the mixed mortar is immediately sprayed onto the surface. the redispersible powder redisperses quickly and completely enough in order to improve the tensile adhesion strength and the flexural strength in almost the same magnitude compared to a conventional application by hand.13 Applications of Redispersible Powders Flexural strength of repair systems modified with different redispersible powders and applied by different techniques 14 12 Flexural Strength [N/mm2 ] 350 10 8 6 4 2 0 shotcrete spray applied no polymer Fig. and natural stone structures. which prevent water intrusion into exposed structure elements. like concrete. rainwater and surface water.e. which are known as waterproofing membranes or sealant slurries.e. on balconies and porches (as a waterproofing layer to be tiled over). all kinds of paints. plasters). i. Some of the waterproofing materials are used to protect against the detrimental action of aggressive substances like salts and acids transported by the water. according to the German standard DIN 18195. Apart from protecting the exterior of building constructions.e. It is applied for the protection against penetration of water. seepage water). Further typical applications are the sealing and waterproofing of basement walls. Cementitious waterproofing membranes have been successfully used for more than 40 years in Europe for protection of a wide range of building structures and structural components. flexible. cementitious waterproofing membranes are often used as a protective surface-coating system for structural concrete (i. i. as well as the transport of humidity in the form of water vapor will avoid unnecessary repairs to building’s exterior or its damage or even destruction (deterioration). low hydrostatic pressure (soil dampness) or in combination with appropriate engineering even high hydrostatic pressure. Cementitious membranes (slurries) are used to waterproof wet rooms and water tanks. plastic waterproofing foils and metal tapes for interior and exterior applications. and – flashings. – mineral topcoats (renders. In addition. Traditional sealing and waterproofing systems. swimming pools. there is a multiplicity of waterproofing materials for interior use. acids. i. and due to their excellent weathering resistance they are also used for exterior surface protection. Different types of materials can be used in order to seal and protect the surface of buildings or its structural components against the intrusion of dampness and water.4 Markets and Application Areas of Redispersible Powders – decorative and finishing barrier systems. – damp-proofing materials. leakage will occur.13. include bituminous materials. walls and floors. chlorides and free carbon dioxide in order to avoid corrosion of the reinforcing metal and can provide a protective layer to a building against aggressive chemicals (sulfates. protection of reinforced structural concrete within new structures as well as for concrete structures after restoration). which reduce or prevent water vapor transmission through building materials and are not subjected to weathering or water pressure (water vapor barrier foils).e. materials or systems installed to direct water entering through the wall cladding back to the exterior like metal foils in walls to prevent capillary water uptake. The structures were either exposed to periodically or longterm wettings (surface water. Adequately controlling groundwater. dispersions (paintable waterproofing membranes) and mineral binders like cement. in bathrooms. in waste-water drains). Especially in the case of a tile application these slurries can also act as crack isolation membranes. Some of the advantages of cement-based waterproofing membranes are: 351 . All waterproofing has to be part of a whole system and must interact integrally to reach complete effectiveness and to prevent water infiltration. Nowadays products for that purpose are based on reactive resins like epoxy and/or polyurethane. In case one of these system parts fails or does not perform with all other protection systems. rigid waterproof membranes. which are stable. which are to a certain extend capable to over-bridge small cracks (up to approx. Simple. sulfate ions and carbon dioxide or other aggressive materials. In addition to the traditional. crack formation and on substrates difficult to be coated like wood. 1 mm) in the substrate. In contrast to other systems. steel. thickening agents and rheological additives in combination with the polymeric binder. they are diffusion and chemically resistant against chloride. sound and solid. which are polymer-modified. two different systems of cementitious waterproofing membranes or slurries are available: 1. good load-carrying capacity. Flexible and highly flexible waterproofing cementitious slurries are used on substrates still undergoing shrinkage. Thus far these flexible cement based waterproofing. Their physical properties are also less temperature dependent compared to bitumen based materials. aerated light weight blocks and gypsum. Today. good scratch resistance. 3 to 6 % of redispersible powder. movements or dimensional changes like shrinkage. non-polymer modified cement based slurries are still used for the protection against surface water. Standard or rigid mineral waterproofing slurries. even if exposed permanently. They are used for mineral substrates. in principle. Cement-based waterproofing slurries are easy to use. and much higher water vapor permeability compared to most of the other systems. polymers are added in form of liquid dispersions on the job-site or in form of a redispersible powder already mixed in the dry mix mortar. excellent resistance against long term weathering. provide an excellent workability and make sure that there is no need for a post watertreatment of the applied slurry. but they are not suitable to seal against water under hydrostatic pressure. and the extremely low deformability or flexibility of these non modified systems. Consequently there are no problems with blistering since water vapor passes through the membrane. In order to improve the poor adhesion. developments in the late 1970s led in Europe to flexible waterproofing slurries. vibrations. sealing slurries have been mainly used as two-component systems (liquid dispersion/emulsion added to the . the redispersible powder. The use of special additives in the dry mix mortars like water retention agents. cementitious waterproofing slurries can even be used on damp and wet mineral surfaces.352 13 Applications of Redispersible Powders – – – – – excellent resistance against water. pre-packed dry mix mortars containing approx. movements. 2. The flexibility of such products strongly depends on the polymer/cement ratio and certainly also on the flexibility of the polymer itself. Flexible and highly flexible cementitious waterproofing slurries (as two-component or one-component systems). There should be no risk for crack formation. the poor water tightness. stresses. Due to their high polymer content (up to 25–40 % on total formulation). non toxic. provide a fully bound and monolithic surface without joints and can be easily applied on substrates with complex surface shapes. in modern construction technique more and more the one-component. consistently. excellent results. job-site mix technology and job-site modification of mortars with liquid polymers is being replaced all over the world. – stuccos. adhesion to various substrates. Dry mix mortars modified with redispersible powders provide a significantly improved productivity on the construction site. modified with high dosages of special redispersible powders are used. As a consequence. more efficient and safer handling and processing of the product. This eliminates onsite mixing errors and ensures. These one-component. rapid. efficiently and economically to apply. – patch and repair mortars. 13. But due to the many disadvantages of modifying mortars with liquid dispersions on a job-site. premixed polymermodified dry mix mortars are offering advantages as they were already discussed within this chapter.13. skim-coats and finishing renders. that are modified with redispersible powders have been successfully used for many decades all over the world. Dry mix mortars. and – powder paints. – waterproofing sealing slurries (membranes). – self-leveling under. – tile grout mortars. The most typical applications are: – ceramic tile adhesives. They allow a high degree of rationalization coupled with an easy.and overlayments.5 Summary The need for new construction methods and building materials. – mortars for the thermal insulation systems. flexibility and deformability of 353 . flexible cementitious slurries. Redispersible powders make the production of complete pre-manufactured high quality mortars (“bagged mortars”) possible. The combination of the mineral binder with a polymeric binder in the form of an redispersible powder in dry mix mortars guarantees outstanding synergistic properties and characteristics. The modification of dry mix mortars with dry polymers in the form of redispersible powders also significantly improves the technical performance of the mortars. which cannot be achieved by either of the binders alone. mainly based on cement but also on gypsum. reliably.5 Summary pre-packed dry mix). – joint compounds. that are safely. The quality of the workmanship is consistent on a high level thus improving the warranty status of a construction job dramatically. The sufficient modification of mineral dry mix mortars by redispersible powders will improve workability. promotes modern technologies like the “dry mix mortar technology”. Especially since product characteristics can be specifically designed for modern construction requirements and climate conditions by using dry mix mortars. “Ermittlung des Verformungsverhaltens von Duennbettmoerteln bzw. Bull. abrasion resistance. Gravenhage. 0314 Oslo 3. J. flexural and cohesive strength and the long-term durability. 8 1971.. Schulze. 23. Phys. Tonindustrie-Zeitung 1985.. density (impermeability). 5. 1. possible. Projekte E 3593. J. 1956.J. Manufacturers. Schweizer Baublatt 1988. . Beton 1991. References 1 Research report No. contractors. Het vermijden van Schade aan gelijmd Wandtegelwerk”. 5 6 7 8 methode for proving av even tile aoverfore relative bewegelser mellom underlag og fliser (flexksibilitet)” von BYGGFORSK. Trondheim 04/08/1992. Netherlands. Vereinigung von Systembouwers. Netherlands). 4 Rapport “Lim for keramiske fliser. 3 Research report B II 5 – 800177-118. 109. Postboks 123 Blindern. Klebstoffen fuer keramische Fliesen”. 31. which become more and more popular with all kinds of construction materials. 95. 44. 232. 13 of “Vereinigung von Systembouwers van de Werkgroep SA 5. 2 Publications of G. 211. applicators and end-users (“Do it yourself” market) all benefit significantly from dry mix mortars modified with redispersible powders. Wesseling (TNO Institute. K. Soc. Norwegisches Bauforschungsinstitut. Technische Universitaet Hannover. Am. Schulze. That technology almost exclusively makes machine applications. in Tonindustrie Zeitung No. Adler. Forskningsveien 3 b.354 13 Applications of Redispersible Powders the mortars. 698. March 1975. Dr.. Fox T. August 1979 von Prof.. Tegels. Kirtschig. Nevertheless. In addition to toughening of thermoplastic matrices. Toughening. polymeric impact modifiers and process aids provide some of the most unique and valued performance and processing enhancements [2. melt strength. and polyesters. and they have evolved over that time into a broad array of product offerings. dispersion and surface quality. aesthetics. processing. the compounded annual growth rate (CAGR) of plastics was about 7–8 % between 1992 and 1997. polymer morphology. Processing aids are mainly applied to a PVC compound for fusion promotion. These additives have been around for many years. This is primarily due to the fact that plastics continue to replace traditional materials such as metals. The successful application of plastic materials has substantially enabled the incorporation of additives to the resins. accounted for more than half of the plastics consumption in the segment. PVC poly(vinyl chloride). Emulsion polymerization is commercially attractive because of the low manufacturing cost and ease of isolation for the resulting latex products. which enables scientists to design proper polymer composition. Weier 14. achieving CAGR of 9 % [1]. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. Ultra 355 .Polymer Dispersions and Their Industrial Applications. polymer structure. The first polymeric additives produced using emulsion polymerization technology were core-shell impact modifiers made of methacrylate–butadiene–styrene (MBS). 3]. rheology control. In a very dynamic market such as building and construction. wood. polycarbonate. which were introduced in 1956. core-shell impact modifiers were also applied to fracture toughening of thermoset resins such as epoxy and unsaturated polyesters [6–11]. 3-527-60058-2 (Electronic) 14 Applications for Modification of Plastic Materials Chuen-Shyong Chou and Jane E. the application has been extended to polyolefin and many engineering resins such as nylon. and polymer molecular weight/ molecular weight distribution. and minerals. KGaA ISBNs: 3-527-30286-7 (Hardback). and economics are the major performance attributes. A key reason is the versatility of emulsion polymerization. Amongst the numerous additives used. In the same period of time. 5]. The additives were originally aimed at improvements in PVC processing capability and toughness.1 Introduction The global plastics industry is growing rapidly with an annual average rate of 4–6 %. These were followed by all-acrylic process aids and acrylic impact modifiers [4. and increase productivity. more uniform cell structures with less rupture and lower foam density can be achieved. In addition to PVC. It is possible to control the morphology of the system with layers. In addition to impact modifiers and processing aids.356 14 Applications for Modification of Plastic Materials high molecular weight processing aids are critical components in foamed PVC. improving heat distortion temperature (HDT). and has a different molecular weight distribution. lobes or isolated domains of specific composition. – Various polymer morphologies with different molecular structures and molecular weights can be achieved with a multiple-stage process. 14. and latex particles. however. The polymer molecular weight can be controlled with appropriate initiator and reaction conditions. – Because the molecular weight is very high in the absence of chain-transfer agents. micelles. The core polymer is based on a low glass transition temperature (Tg) rubber and is surrounded by a hard polymeric shell (high Tg material). Several possible polymerization loci can be present simultaneously including the aqueous phase. broadening the thermoforming window. These polymeric modifiers offer some unique properties and many of the developments are also tied closely to emulsion polymerization technology. molecular weight is easily controlled by the addition of chain-transfer agents. and allows for additional control of the properties. the technology is extremely complicated. With the help of the processing aid. The core rubber is made in the first stage of the emulsion polymerization. improve surface quality. enhancing compatibility in polymer alloys. A core-shell impact modifier is probably the best model to illustrate the utility of emulsion polymerization technology. – An emulsion polymerization can easily achieve a relatively high conversion of monomer to polymer. The major advantages include: – The rate of polymerization is usually considerably greater than in a bulk process. . polymeric processing aids are becoming popular in other thermoplastics for certain limited applications. Emulsion polymerization techniques are in wide commercial use because of their many advantages. controlling light diffusion and optical properties. Lubricating type processing aids prevent the melt plastic from sticking to metal surface. Although the process appears straightforward. particle-water interface. and improving the plastic and cellulose composites processing. the process is not without its drawbacks.2 Emulsion Polymerization and Isolation Technology A comprehensive description of emulsion polymerization chemistry can be found in books written by Gilbert [12] and Lovell and El-Aasser [13] and Blackley [14]. a number of polymeric modifiers have been promoted for controlling gloss. – The polymer usually has a considerably higher average molecular weight than that from a solution polymerization or bulk process. monomer droplets. hence any problems with residual monomer are minimized and monomer consumption is maximized. It also affects the powder storage stability such as compacting tendencies. followed by filtration of the aqueous phase and final drying of the resulting wet-cake. Ultra high molecular weight polymers can only be achieved by an emulsion polymerization process. and styrene-acrylonitrile (SAN) copolymers. Spray drying involves injecting the emulsion with hot air and forcing it rapidly through a rotating nozzle. Products with a wide range of weight average molecular weights. The monomers used. A much cleaner product can be produced in this manner. the polymer molecular weight. Polymeric processing aids are generally high Tg copolymers and contain a large fraction of methyl methacrylate (MMA) or styrene-acrylonitrile. Although highly efficient. such as emulsifier and inorganic salts.1 Isolation Technology Free-flow powders.14. thus requiring less water removal. to evaporate the water quickly [74]. and the internal structure of the rubber core affect the impact performance. polystyrene. Isolation of the emulsion is therefore an important part of commercial processes. The shell of the particles. The shell polymer provides ease of isolation and/or handling and facilitates dispersion and interaction with the matrix. granules or pellets are the common product forms used in the plastic industry. occasionally referred to as the outer or hard stage. The references shown in Tab.2. consists of a polymer that is chemically grafted onto the core.1 provide additional details on the emulsion polymerization process for specific type of polymeric modifiers. from about 100 000 g mol–1 to over 6 000 000 g mol–1. 357 . are commercially available. It is typically made with monomers such as butyl acrylate (BA) and/or butadiene (Bd). Typical commercial examples of polymers used in the outer stage are poly(methyl methacrylate). a full range of technology has been developed around controlled coagulation of the emulsion. this method results in the retention of non-volatile elements added during the polymerization.2 Emulsion Polymerization and Isolation Technology and serves as the part of the modifier that promotes impact. The product form can have a significant effect on its ease of handling. 14. 14. The polymeric processing aids can be grouped by their specific function and/or application. The three most common approaches to isolation are contrasted below: Feed Residence time in dryer Powder particle size (µm) Spray dryer Fluid-bed dryer Flash dryer Emulsion 5–100 s 10–500 Wet cake 1–300 min 10–3000 Wet cake 1–5s 10–300 Spray drying is an attractive approach as long as the polymer solids content is high. which might affect the resin. Details of these methodologies have been published extensively [75–78]. To this end. compounding and incorporation into the matrix. BA. prevent polymer melt from sticking to hot surface. improve melt strength in polyolefin and engineering resins. 157–183 Melt rheology modifiers Methacrylate-based polymer Lower melt viscosity in PVC and ABS. The first commercial processing aid product was introduced by the Rohm and Haas Company for processing rigid PVC in the 1950s [4]. reduce melt fracture. EA. provide good cell uniformity. EVA Promote PVC fusion. 144 HDT modifiers α-Methylstyrene/ AN. Processing aids were developed to enhance melt processing. SAN/MMA Promote PVC fusion. epoxy and other thermoset resins. assist mold release. 60–62. 146 PVOH processing AIDS MMA/NVP/ methacrylic acid Enable melt processing. Sty Reduce surface gloss. improve mixing and homogeneity in ABS/SAN blend 63–70. BMA PVC processing aids MMA/Sty. reduce downtime. SAN. improve surface quality and throughput 54–59 Foamed PVC processing aids MMA/BMA. SAN Promote PVC fusion. 122. maintain rigidity and barrier properties of the polymer 71–73 Acrylic impact Modifiers BA//MMA. diffuse light in polycarbonate 154–155 14. BA/MMA. 14-1 Polymeric modifiers classified by function. epoxy and other thermoset resins. MMA INCREASE service temperature. BA SAN/MMA.3 Processing Aids Many plastic materials have limited applications due to either undesirable physical properties or poor processing capability. EA. This unique . Bd/Sty//MMA/Sty Toughen PVC. weatherable 115–118. improve surface quality.358 14 Applications for Modification of Plastic Materials Tab. and improve surface quality 15–53 Lubricating processing aids BA/Sty/MMA. engineering resins. increase process flexibility 51. increase throughput. improve melt elasticity and strength. Type General Composition Function/Application Refs General purpose MMA/BA.. clear or opaque application 130–134. 2-EHA/MMA Toughen PVC. engineering resins. 141. 123 MBS impact modifiers Bd//MMA/Sty. and provide better product quality [79]. reduce foam density. improve melt strength and grain retention 147–153 Flatting agent/ light diffuser MMA. The composition and the polymer structure of the processing aid affects the compatibility with PVC and alters properties such as fusion promotion and lubrication. Point “B” refers to the beginning of melting. and elasticity. to the mechanical properties of the final product are related to the homogeneity of the polymer melt during the conversion process. On the other hand. Similar development efforts have been applied to other thermoplastic materials and polymer blends since the 1980s. and. the molecular weight and molecular weight distribution play the major role in controlling the melt rheology. 14. lubrication. increasing dispersibility. Processing aids help to increase cohesion and homogeneity of the melt. and enhancing the overall balance of properties. This has led to the ability to get equal performance from lower levels of process aid. The most common processing aids are methyl methacrylate based polymers. Although processing aids are generally added to PVC and other thermoplastics in small quantity (0. rigid PVC is not processable due to its inherent particulate structure. mainly related to the fusion and melt rheology during processing [3]. polymer architecture. melt strength. melt extensibility.1 Processing Aids for PVC In a thermoplastic resin. which help to create and transfer localized shear heat to melt the PVC during fusion process. The torque observed at 359 . which consists of a mixing head with two rolls. Figure 14-1 shows the PVC fusion process as reflected in the curve of fusion torque vs. Unlike the majority of other thermoplastic resins. melt rheology modification. time. The melt temperature in each stage can also be recorded. The function and performance of a specific type of processing aid is affected by the chemical composition.5–5 %). improving efficiency. 5]. followed by the appearance of the fusion peak. PMMA based polymers have a high glass transition temperature (Tg) and are also extremely compatible with PVC [80. polymer molecular weight. 81]. Improving melt rheology. materials that disperse more rapidly with greater clarity. Each processing aid may provide more than one function. Processing aids offer several benefits to a PVC formulation. Fusion promotion and melt homogeneity The most common approach to characterize the PVC fusion process employs the Brabender® Plasticorder or Haake Rheometer. as well as the proposed mechanism are well documented [3.3 Processing Aids technology was well acknowledged and led to the surge of the PVC industry. in the case of clear applications.3. Point “A” is referred as the “compaction” peak and corresponds to compression and densification of the powder. It requires a long processing time at high temperatures which leads to thermal degradation.14. (especially melt strength versus viscosity) have been the major goals of new processing aid development [82]. The difference in time between A and C is called “fusion time”. they dramatically alter the processing characteristics without a substantial effect on other application properties. Processing aids can be classified by functions such as fusion promotion. and the matrix type. Point “C” occurs as PVC fuses into melt. and dispersion promotion. The history and development of processing aids for PVC. The fusion curve is strongly influenced by the formulation type. the smoothness of rolling bank in the roll mill can provide a rough estimate. As the heating and shearing continue. free of pinholes. and loses its integrity. which is referred as the equilibrium torque. and has no air streak and melt fracture. PVC is not completely melted at this stage and the majority of melt is in the form of sub-microscopic particles. 14-1 Torque rheometry of a PVC compound. crumbles. A C Torque 360 D E B Time Fig. and homogeneous. 180 °C processing temperature. The unmodified PVC film tears. With only 2 % acrylic processing aid in a tin-stabilized PVC (K-value = 61) at 180 °C. The equilibrium torque can be interpreted as a rough estimate of melt viscosity. .14 Applications for Modification of Plastic Materials point “C” is called the “fusion torque”. smooth. This technique provides the level of gelation and is related to the fusion of the PVC specimen [83]. The difference in time between A and E is called the “degradation time”. and the rolling bank is also smooth. and does not correlate well with good melt homogeneity. A Differential Scanning Calorimetry (DSC) method can help to assess the degree of PVC fusion. and loading level. However. shear rate. torque versus time. The PVC melt homogeneity can be examined under a transmission electron microscope. Faster fusion time does not indicate complete breakdown of the PVC particulate structure. the sheet is strong. dehydrochlorination and cross-linking of PVC chains can occur. In contrast. processing temperature. The resulting sheets of both processes are shown in Fig. The fusion continues to occur as the torque drops down to an approximately constant value at point “D”. producing the torque increase at point “E”. a non-homogeneous melt on the roll and a badly fractured rolling bank can be observed when no processing aid is added. the stock on the roll is clear. With processing aid. 14-2. While the extruder output rate is stabilized. The acrylic copolymers that are typically used as processing aids are generally compatible with PVC. Fig. Die swell is another method for measuring melt elasticity. extensibility. The sheet (A) is hazy and has no film integrity. and with their long chains. Extensibility describes the PVC melt’s ability to undergo large elongation or stretching deformation without rupture.3 Processing Aids A tin-stabilized PVC (K = 61) formulation was processed at 180 °C for 4 min. Melt elasticity is an important factor in establishing melt stability as the melt enters and pro- 361 . 14-3. Increased rupture stress and extensibility helps the PVC become far more resistant to rupture-induced defects. (A) Without the addition of processing aid.14. it tends to return to its original form after external force is removed. Therefore. and elasticity defines the “toughness” of a melt. and elasticity Melt strength is a phenomenon reflecting both elasticity and elongational viscosity. measuring the melt strength quantitatively is usually difficult. Without polymeric processing aid. elongation. The Gottfert Rheotens is a device that uses a gear-like strain gauge – instrumental “puller” to draw a fully fused melt from a right-angled (vertical drop) extruder. the rheological properties of the PVC melt can be recorded quantitatively. The sheet (B) is clear. This behavior is commonly observed as the swelling of an extrudate as it exits the die. the geared take-off accelerates until the melt (extrudate) breaks. strong and has a smooth surface. A combination of tensile strength. interact to produce a stiffer and more elastic melt. PVC would not withstand high stress or extension. 14-2 Melt strength. As predicted. Elasticity is related to the tendency to return to its original state when stresses are removed. the extrudate weight is dependent upon the concentration of processing aid. The degree of swelling is related to the polymer recoverable strain or elasticity and is normally expressed as swell ratio (extrudate diameter/die exit diameter) or by the comparison of the weight of a fixed length of extrudate. Although the practical effects of melt strength are abundantly clear to the processor. (B) With 2 phr of Paraloid K-125. When a polymer is deformed. It is difficult to separate these rheological properties. the die swell is related to the polymer molecular weight. As shown in Fig. The higher die entry pressure observed when processing aid is present is also a good indicator of higher melt elasticity [79]. 87]. 1. The effect of processing aid level on the surface quality of a PVC foam rod is shown in Fig. Especially in injection molding.5 phr Advastab TM-181. On the other hand. it has been demonstrated that a low level of standard acrylic processing aid does not have a noticeable effect on melt viscosity [44. a low density foam with fine cell structure and good surface quality can be achieved.5 million 2. a combination of multi-function processing aids can balance the melt rheology and melt homogeneity.2 phr OP Wax.14 Applications for Modification of Plastic Materials 50 Extrudate W eight (g) 362 A B C D 45 : : : : Mw Mw Mw Mw = = = = 1. 0.5 million 3. Melt viscosity Many thermoplastic resins have excellent physical properties and high service temperature. an ultra high molecular weight processing aid with Mw = 8 × 106 is about 30 % more effective in terms of foam density. As shown in Fig.5 million 6 million 40 35 30 25 0 1 2 3 4 Processing Aid Level (phr) 5 6 Fig. With the help of a proper processing aid. poor surface structure. the cell structure of an extruded foam is more uniform with lower rupture tendencies [86. One of the more recent advances in processing aids has been the development of ultra high molecular weight materials specifically designed for use in PVC foam applications [84. 85]. 14-5. it is a major challenge for any material to fill thin walls. 14-3 Effect of Processing Aid Molecular Weight and Concentration on Extrudate Weight. which are often accompanied by high melt viscosity. The PVC melt can withstand great extension before it breaks [88]. However. Rigid PVC compounds . and gas containment can be low (blow out). ceeds through the die in extrusion. PVC formulation was based on 100 phr PVC (K = 57). and surface quality compared with a similar processing aid with the Mw = 6 × 106. long flow paths. and/or complex shapes. High melt viscosity makes processing more difficult and often decreases productivity as well as product quality. 14-4. Most high molecular weight processing aids increase the melt viscosity.5 phr ALDO MS and 0. Without a proper processing aid. the foam can have large cells. cell uniformity. Therefore. 89]. 14.5 Good 4.3 Processing Aids Processing Aid Level (phr) Processing Aid Molecular Weight (x106) Foam Density (g/cc) Surface Quality 6 6.38 Excellent Fig. The melt viscosity can also be measured by many modern analytical rheometric instruments including capillary rheometers. 14-5 Effect of processing aid level on the surface quality of free foam rods.5 6. (B) 3 phr.5 8. tin stabilizer (TM-950F). A qualitative assessment of the effect of major melt rheology properties on selected conversion processes is shown in Tab. As mentioned earlier. (D) 5 phr. and azodicarbonamide as blowing agent.0 0. Effect of melt rheology on conversion process The processing of polymeric materials such as plastics is characterized by a wide variety of distinct methods or techniques.5 0.37 Excellent tin stabilizer (TM-950F). equilibrium torque as measured in a Haake Rheometer can serve as a rough estimate of melt viscosity provided a proper control is used. based on a free foam formulation with PVC (K = 62). Many appliance parts. (E) 6 phr. business equipment. (C) 4 phr.5 0. (A) 2 phr. and azodicarbonamide as blowing agent and different level of Paraloid K-400 as processing aid. 14-4 Effect of processing aid molecular weight on PVC foam extrusion. (A) 4. Each technique has a different set of melt rheology requirements that are dictated by the processing mechanism and the equipment design. The formulation is based on PVC (K = 62). electronic enclosures are made from PVC compounds formulated with processing aids and impact modifiers. 14-2. (B) (C) (D) (E) have successfully met the challenge. 363 . Fig. and minimize delays in fusion. However. high melt strength. Compared with conventional processing aids. the haze can be corrected with proper adjustment of refractive index [92]. 14-3. and lubricating. Tab. help to reduce melt fracture and shear stress and improve surface quality and do not affect the clarity of the matrix polymer. enhanced blush physical properties Reduced jetting Can reduce flow lengths if too high Lubrication Lubricants are used to prevent plastic melt from sticking to metal surfaces during processing. improve melt homogeneity.364 14 Applications for Modification of Plastic Materials Qualitative assessment of major melt rheological properties versus selected conversion processes. A number of disadvantages are associated with non-polymeric lubricants including plate-out. such as Paraloid K-175. clarity. this family of processing aids is less compatible with the matrix polymers. Therefore. The commercial lubricant processing aids for PVC. 91] were developed to help metal release. The performance attributes of different types of processing aids are shown in Tab. significant haze is developed due to the immiscibility with the resin. reduce plate-out. Lubricating processing aids combine both lubricants and processing aid functions. General purpose processing aids provide a balance of melt strength and melt viscosity. An optimum balance of efficiency and clarity can be achieved using selected polymers such as Paraloid K-120ND and K-130D (Rohm and Haas). migration. and delay fusion. Processing aid type Commercially available processing aids can be divided into four types – general purpose. enhanced parison sag physical properties Uniform wall thickness Bi-orientation Reduced melt fracture at high output rates Extrusion Uniform melt Higher takeflow. . They help to promote PVC fusion and have excellent dispersibility under low shear conditions. enhanced off speeds physical Foam density properties Higher takeoff speeds Reduced melt fracture Surface finish Foam cell structure Injection molding Uniform melt Reduce gate flow. Lubricating processing aids [90. but can give flow lines Can generate air bubbles if too high Can reduce output if too high Blowmolding Uniform melt Reduced flow. 14-2 Melt homogeneity Calendaring Smooth rolling bank Uniform thickness Melt strength Melt extensibility Melt elasticity Melt viscosity Higher takeoff speeds Better thermoformability Higher takeoff speeds Bi-orientation Deep draw thermoforming Reduced melt fracture. high efficient. the combination of different types of processing aids could provide the converters with optimum processing. These processing aids provide low foam density. melt strength processing aids are mainly used in PVC foam applications. melt homogeneity. or K-130D. profile extrusion. Historically. as well as the productivity. calendered or extruded sheet. even in a highly filled system such as pipe formulation. Metablen P710 (Atofina/Mitsubishi Rayon). Hot metal release/lub. and a consistent processing. is commonly applied to applications such as blow-molded containers. The combination of a lubricating processing aid such as Paraloid K-175 with other types of processing aids. high surface quality. and provides better surface quality dimensional control in the finished product. high-flow injection-molded parts. The most common high-efficient processing aids are Paraloid K125 (Rohm and Haas). The recommended processing aids are Paraloid K-400/K415/K-435 (Rohm and Haas). melt fracture. Metablen P530 (Atofina/Mitsubishi Rayon). Kane Ace PA101 (Kanegafuchi). foam core pile. and hot metal release affects the aesthetics. As mentioned in the previous section. High efficiency processing aids produce even higher melt strength than the general purpose type. It is very common that a PVC compound is formulated with more than one type of processing aid. siding. Metablen P501(Atofina/Mitsubishi Rayon) and Barorapid 3F(Barlocher). The balance of melt rheology. Processing Aid Type General purpose High efficiency High melt strength Lubricating Molecular weight (Mw × 106) Melt homogeneity Melt strength (increase) Melt elasticity (increase) Melt extensibility Melt viscosity (increase) Fusion time Dispersion (under low shear) Clarity in PVC Stress whitening resist. 14-3 Processing aid type versus performance attributes. an optimal level of Paraloid K-130D with 365 . such as Paraloid K-120ND. and foam sheet. Polymeric lubricants that improve melt processing. K-125. and Vinuran 3833 (BASF). In addition to higher melt strength. The common lubricating processing aids include Paraloid K-175 (Rohm and Haas). Kane Ace PA-40 (Kanegafuchi).14. Vestiform R315 (Huls). As shown in Fig. 1–3 ++++ ++ ++ ++ + + ++++ +++ ++++ + 3–5 ++++ +++ +++ +++ +++ ++ ++ +++ ++++ + 6+ ++++ ++++ ++++ ++ +++ +++ + ++ NA + <1 ++ + + + + + ++++ ++++ ++++ ++++ + = least. Vestiform R450 (Huls). and process efficiency are defined as lubricating processing aids. etc. A proper level of each ingredient is critical and can affect the product quality. Metablen P550/P551 (Atofina/Mitsubishi Rayon). ++++ = greatest Kane Ace PA-20/30 (Kanegafuchi). Baroropid 10F/20F/30F (Barlocher).3 Processing Aids Tab. 14-6. and Vinuran 3833 (BASF). hot metal release. including profile. conduit. This type of processing aid improves melt homogeneity and processing rate. This is attributed to their higher polymer molecular weight. pipe fittings. 3. and ABS/SAN blends [63–70]. The use of high molecular weight polymers as processing aids for PVOH enables a smooth melt processing without compromising the rigidity and barrier properties [71–73]. The film thickness is approximately 0. However. Addition of an extremely low level of fluorocarbon processing aid reduces melt viscosity and eliminates melt fracture in a film extrusion of linear low density polyethylene [94]. also known as PVDC. 14-6 Effect of processing aid on flow lines and air marks of calendered sheet. polycarbonate. is another thermoplastic with excellent barrier properties but poor processability upon heat and shear stress. 14. (C) 1. polyesters.5 mm. Acrylic based additives reduce the thermal degradation and preserve the majority of important properties [95].5 phr Paraloid K-130D and 0. PET.25 phr Paraloid K-175.25 phr Paraloid K-175.2 Processing Aids for Other Resins The use of processing aids to improve melt processing behaviors in resins other than PVC has increased in the recent years. PVDC is significantly less stable than PVC and would normally degrade rapidly at the temperature required for processing. Methacrylate based polymers are reported to enhance the mill-processing of polyethylene. The higher alkyl methacrylates based processing aids improve the melt strength of polypropylene and are useful in thermoforming operations to produce containers and appliance housings. Some of the polymeric processing aids are manufactured by emulsion polymerization but some of them are not. PVOH.5 phr Paraloid K-130D and 0. Clear and rigid PVC formulation (A) 1. can be increased substantially by the addition of a low level of processing aid [69]. especially multilayer film and sheet.366 14 Applications for Modification of Plastic Materials K-175 helps to improve optical clarity as well as to eliminate flow-line and air marks in a rigid clear PVC calendered sheet. . Poly(vinylidene chloride). Acrylic processing aids were found to improve melt strength and melt homogeneity in thermoplastics such as polyolefins. Poly(vinyl alcohol).5 phr Paraloid K-125 and 0. (B) 1.75 phr Paraloid K-175. Lower molecular weight methacrylate based processing aids were applied as rheology modifiers in ABS to lower melt viscosity and to facilitate melt processing [93]. The melt strength and melt viscosity of aromatic polyesters such as poly(ethylene terephthalate). (A) (B) (C) Fig. is used in packaging applications. due to its high strength and barrier properties. and thus high energy absorption. this soft. the rubber core can be designed to optimize impact performance. and even those commonly thought to have relatively high ductility. which can lead to large tradeoffs in other mechanical properties. in the range of tens to hundreds of nanometers. by physical aging or through high stresses or flaws introduced into the material. while at the same time avoid plasticizing or softening the polymer. Improved flexibility in formulating and processing is provided by using an additive approach. a blend containing the discrete rubber domains may be created “in-reactor” through chemical process modifications during the manufacture of the base polymer matrix material. or stages. storage and handling. rubbery phase ideally exists as discrete domains dispersed within the plastic to enable the impact energy absorption. This ability to produce and control the optimal blend morphology and final domain size of the rubbery phase is extremely important in achieving good impact resistance in the resulting plastic material. such as polycarbonate. In some cases. in which the characteristics of the final blend are produced by formulating and adding the desired type and amount of modifying additives just prior to or during the final melt processing step. low Tg polymers having ideal elastomeric properties for impact modification. Emulsion polymerization methods can produce very high molecular weight. and the extra process steps introduce additional complexity and cost into the process. or toughness. or “core-shell” emulsion graft copolymers was an important milestone in impact modifier technology [96. Using core-shell technology. The development of multiple-stage. and therefore the desired material modifications may also vary. may become embrittled at very cold temperatures. such as tensile or flexural modulus. can also be designed to enhance the processing and dispersion attributes of 367 . Particles of highly uniform particle size. while a higher Tg outer stage eliminates the tackiness normally associated with rubbery polymers and so allows for easier isolation. may be synthesized. while the continuous glassy phase dominates the surface hardness and other mechanical properties. The key to improving the impact resistance of a plastic is to enable the polymer to absorb larger amounts of mechanical energy. Another limitation to the in-situ approach is that a typical manufactured polymer resin may be used in a wide variety of downstream applications. each with its own unique performance requirements. Often it is difficult to properly control the desired blend morphology. without undergoing catastrophic failure due to fracture.14.4 Impact Modifiers 14. Many plastics suffer from inherent brittleness. refers to the ability of a material to withstand high rates of applied loads. softer polymer phase into the plastic. emulsion technology provides an ideal method for meeting the requirements for such an additive system. The most common solution to this dilemma is the introduction of a second. The outer stage. In the final processed material. Through the use of standard crosslinking techniques. 97].4 Impact Modifiers Impact resistance. particle size is permanently set so that the original emulsion particle is preserved during the plastic melt processing step. In the case of impact modifiers. Impact energy is normalized and reported in units of energy per area or length of crack. The optimal rubber domain particle size for impact resistance is therefore based on a balance of these competitive effects. most typically in the case where the shell polymer composition is chosen based on its compatibility with the matrix polymer. Most commonly. Virtually all of the emulsion-made impact modifiers for PVC applications are of the core-shell variety. over 25 million tons (50 billion lb) of PVC were produced worldwide [109. the energy absorption mechanism may occur via multiple crazing or cracking. PVC is a unique polymer in that. it can be modified by various additives to provide a tremendous range of properties. in which case the actual energy. the particle size and distribution of the rubbery modifier must be carefully controlled. AtoFina. ranging from soft and flexible to rigid and tough.1 Impact Modifiers for PVC Poly(vinyl chloride) (PVC) is the largest and most important resin for the application of emulsion-based impact modifiers. as specified by ASTM D256 or ISO 179 protocols. Small particles are thought to be effective due to the larger total number of particles distributed in the matrix. in which the drop height (and therefore potential energy) of the weight is increased until material failure is observed [108]. with the largest commercial producers being Rohm and Haas. The dart may be instrumented. The pendulum hammer falls and strikes the sample to initiate fracture at the notch. while the neat resin is virtually useless. within the rubber domains during the impact event. In addition to composition. testing is done using a notched Izod or Charpy pendulum impact test. which promotes improved mixing to form the optimal dispersed-phase blend morphology. In 1999. load and elongation properties of the material may be measured as the dart punctures the material. or voiding. Kaneka and Mitsubishi Rayon. In some matrix systems. Recent work in understanding impact mechanisms has focused on the possible role of cavitation. and varies depending on the nature of the matrix resin system being modified [106. Another common impact test method involves the use of a dropped weight or dart to impact a flat surface or sheet of processed plastic material. 110]. and the resulting shorter interparticle distances [99–101]. which allows for stress release and increased deformation of the adjacent matrix [103–105]. for example.368 14 Applications for Modification of Plastic Materials the additive. PVC is an inherently tough polymer. The thin sections or ligaments of matrix between the particles are more susceptible to induced shear deformation and drawing than a thicker part or section. Impact specifications and test methods vary according to application. A more basic drop test is the Gardner test. It is well known that impact performance is highly dependent on particle size [98]. Larger particles are thought to be more conducive to this cavitation mechanism. and mounted onto a pendulum-type impact tester. but is .4. 107]. 14. The total energy absorbed in the fracture is measured from the loss in potential energy of the pendulum. Specimens are prepared by cutting a small initial notch into a bar of the plastic material to be tested. in which case large particles may be favored due to their ability to initiate and arrest the growth of these localized fractures [102]. 14-7 Influence of temperature and core-shell modifier addition on the impact performance of PVC. flaw or other site of potential high stress concentration. which tend to occur when a load is applied at the interface of materials having different moduli [101]. In this way. 600 400 200 0 0 1 2 3 4 5 6 7 Impact Modifier Level in PVC (phr) Fig. 1200 Notched Izod Impact Energy (J/m) 0. and largely negates the negative effects of lower temperatures or sharper notches in the test specimen. along with the potential for embrittlement at sub-ambient use temperatures. as shown in Figs 14-7 and 14-8. Notch or crack sensitivity refers to the inability of a material to resist fracture in the presence of a notch. the neat resin. 369 . lead to most PVC applications requiring some form impact modification. In a typical impact experiment. It is now generally accepted that the primary source of energy dissipation occurs in the matrix resin itself. This feature. large amounts of energy are absorbed through an increase in elongation of the material at moderate load levels (Fig. In the case of PVC.25 mm notch radius 1000 800 23 C.4 Impact Modifiers characterized as notch sensitive [111]. Various mechanisms have been proposed to explain the effectiveness of rubber domains in improving the toughness of plastic resins [106]. 113. 20 C.14. which is intrinsically ductile. 114]. and plastic flow or deformation occurs in preference to crack initiation and/or propagation [101. The primary role of the rubbery domains is to provide multiple sites of highly localized stress concentrations. rather than in the rubber domains [98–112]. crack. the inclusion of a moderate amount of impact modifier produces an almost tenfold increase in impact energy absorption vs. 14-9). the localized stresses can exceed the yield stress of the material. The energy absorbed is calculated from the area under the stressstrain curve. so that for the . Notched Izod Impact Energy (J/m) 370 0.50 mm Notch Radius 1. heat distortion resistance. Unmodified Yield point Load Elongation Impact Modified PVC Fig. Pipe. all manufactured via profile or sheet extrusion. vinyl siding. allowing the polymer to yield and undergo extensive elongation. attributes which are aided by the use of high molecular weight PVC resins. The impact modifier lowers the yield stress of the polymer. with K values typically greater than 65. and window profiles. These applications are generally formulated to be opaque. unplasticized PVC is used extensively in the building and construction markets. Core-shell impact modifiers reduce the notch sensitivity. At smaller notch radii (sharper notch). and white or light pastel in color. Examples of some formulations are shown in Tab.30 mm Notch Radius 2000 1500 1000 500 0 0 1 2 3 4 Impact Modifier Level (phr) 5 6 7 Fig. 14-4. and intrinsic toughness. Building products often require a high degree of rigidity.14 Applications for Modification of Plastic Materials 2500 20 C. PVC building products Rigid. 14-8 Notch sensitivity of PVC.25 mm Notch Radius 0. the PVC specimen is embrittled. 14-9 Effect of impact modification on the macroscopic tensile properties of a polymer such as PVC. represent the largest building product markets. 0 1.8 1.15 8.0 0. A hard stage or shell is polymerized around the rubber core to allow for isolation of the emulsions into non-compacting. The shell polymer. There are also examples of acrylic modifiers containing small amounts of non-weatherable.0 5. Poly(butyl acrylate). 371 . with a Tg of approximately –45 °C. 14-4 Examples of PVC formulations for building products (parts per hundred resin). 14-11). free flowing powders. aid Acrylic impact modifier Siding capstock Window profile Pipe 100.2 1. this is usually achieved through the use of a poly(methyl methacrylate) based shell composition.2 – – 0.5 – – 1. In weatherable PVC applications. such as butadiene. which typically makes up 70 to 90 % of the total modifier. is most commonly used commercially. additives can generally be designed without consideration to refractive index and particle size. Optimal impact performance for all-acrylic modifiers in PVC building products is attained through the use of particles with diameters in the 80–300 nm range. leading to poorer impact (Fig. 14-10). is generally not highly crosslinked.0 0.0 0. The rubbery core. A modifier with insufficient amounts of PVC-compatible materials in the shell will result in poorer dispersion of the modifier (Fig. which may enhance the rubbery features of the core at the expense of small tradeoffs in weatherability [117. as well as to provide various performance properties.14.0 100. K-67 Tin stabilizer Calcium stearate Paraffin wax 165 °F Polyethylene wax Bisamide wax Oxidized polyethylene wax Titanium dioxide Calcium carbonate Process aid (K-120 type) Lubricating proc.0 1. PVC.0 purpose of optical properties. unlike the rubbery core. is crosslinked through the addition of small amounts of multifunctional monomers during the free radical acrylate polymerization. 118]. Acrylic impact modifiers have a rubbery core based on low Tg acrylates with moderately long side chains.2 1.1 – – 8.0 100.0 0. This requirement is well met through the use of all-acrylic polymer compositions.1 9. The key distinguishing feature of impact modifiers used in building products is weatherability.0 5. 116]. The shell plays a critical role in impact modification by enabling easier mixing and dispersion of the modifier into the polymer matrix. so that the resulting crosslinked core contains less than 5 % extractable polymer. which combines a suitably high Tg with excellent miscibility in PVC [119–121].0 – 4.4 Impact Modifiers Tab.5 – 3. allowing the final modified PVC parts to retain color and mechanical properties after extensive exposure to UV radiation. providing good elastomeric properties at reasonable cost.4 0. so that the shell polymer chains are free to mix and interact with the surrounding matrix on the molecular level.2 1.0 1.0 1. but very low Tg monomers.5 5.7 0.0 3. which contain no residual unsaturated sites susceptible to UV degradation [115. 000 Modifier shell effects on dispersion in PVC.0 mm x 50. 14-10 shell with poor PVC miscibility. 14-11 The shell can further be designed around desired rheological and secondary properties.000 x 50.14 Applications for Modification of Plastic Materials 1.) Impact performance of the two modifiers compared in Fig. 14-10. while the larger white and black particles are voids and inorganic fillers. Modifier B has a more miscible shell. degree of grafting. and composition can alter processing and rheology properties such as viscosity.0 µm 1. The all-acrylic modifier particles are the small white particles in the micrographs. die swell and PVC fu- . melt strength. Better compatibility and dispersion of the modifier in the PVC results in superior impact efficiency. produces large agglomerates and there are significant areas of unmodified matrix. 1200 10 % Modifier Notched Izod Impact Energy (J/m) 372 Modifier A (poor dispersion) Modifier B (good dispersion) 960 720 480 240 0 14 16 18 20 22 24 Impact Test Temperature (C. containing a Fig. Shell molecular weight. Fig. resulting in more uniform dispersion in the PVC resin. Modifier A. which can be obtained through the use of many standard emulsion synthesis techniques. 14-5. These are an example of in-situ impact modification. 14-5 Commonly used commercial weatherable impact modifiers. dictate that somewhat low- 373 . which are commonly manufactured by extrusion. pre-set particle morphology. Alternatives to emulsion-based additives include linear (non-graft) polymers such as ethylene vinyl acetate and chlorinated polyethylene. levels and morphology. lower performance applications.14. 123]. Tab. injection molding and blow molding. is also key to achieving optimal performance of the impact modifier. These systems provide excellent impact properties without the need for a separate hard shell or additive step. PVC Durables and packaging Core-shell impact modifiers are commonly used in PVC packaging applications. Manufacturer Trade name Product Description Rohm and Haas Paraloid Atofina Durastrength Kaneka Kane Ace KM-334 KM-355 KM-377 KM-350 D-200 D-200L D-300 FM-10 FM-20 FM-22 FM-25 General purpose all-acrylic High efficiency Impact and low gloss Low temperature PVC fusion Weatherable with Bd content Impact and low gloss High efficiency General purpose all-acrylic High efficiency Highest efficiency Impact and rheology Weatherable core-shell impact modifiers are highly efficient. Final performance properties such as surface gloss. several manufacturers provide pre-toughened PVC resins or concentrates. 122. part shrinkage and thermal stability can also be controlled through the use of appropriate design of the outer shell. along with final property needs such as flexibility. Processing requirements. Unlike PVC building products. Optimal morphology and impact performance must be achieved through very careful control of the processing and formulation conditions [124–126]. where the rubber polymer is introduced and grafted into the matrix during the PVC polymerization [127–129]. The corresponding disadvantage to the formulator and processor is the lack of flexibility in adjusting the additive types. The disadvantage of these non-core shell additives is the absence of a well-defined.4 Impact Modifiers sion promotion [115. including interior ducts and appliance housings. as in some types of PVC pipes. such as films. and are therefore the most commonly used impact modifiers for PVC building products. A well defined core-shell morphology. packaging and durable applications are often made by calendering. Examples of current commercially available modifiers are shown in Tab. sheets and clear bottles. requiring only 4–8 parts in most formulations. as well as some PVC durable items. In Europe. The latter polymer is a popular choice for low cost. Appropriate amounts of styrene can be incorporated into the core and shell of the modifier to adjust the modifier refractive index.5 – – 0.1 – – 1. complete breakdown of the modifier powder particles and complete dispersion back to the emulsion particle size scale are necessary to avoid haze and optical inhomogeneities cause by gels. 14-6.374 14 Applications for Modification of Plastic Materials er molecular weight PVC resins are used. Polybutadiene is economical.0 0.2 – 0.0 20.0 10.0 1. PVC.0 1. and also through the use of added multifunctional cross-linkers.0 – 0. Tab.2 – – 30.2 0. K-57-58 Tin stabilizer Calcium stearate Paraffin wax 165 °F Glycerol monostearate Montan ester wax Saturated ester wax Titanium dioxide Calcium carbonate Process aid Lubricating proc.6 0. it is often necessary to add higher levels of impact modifier. Since lower molecular weight resins have intrinsically lower toughness. Methyl methacrylate and styrene-acrylonitrile are common compositions that provide good processing and miscibility with the PVC. has an extremely low Tg of approximately –80 °C. leading to higher potential impact performance than all-acrylic compositions.2 – – – 1.4 1. Note that. but are useful only in opaque applications. which can be achieved through refractive index matching of the modifier composition with the PVC matrix [130]. Many packaging applications require high transparency. Crosslinking of the Bd or Bd/Sty core is controlled through process-induced self-crosslinking of Bd.5 5. typically in the K-50 to K-65 range.0 – – – – 1.0 1.0 2.6 0.0 – – 12.0 – 100.06 Because weatherability is often not an important requirement.0 – – 100. Examples of some formulations are shown in Tab. core-shell modifiers in this area are usually based on butadiene rubbers. Stress whitening is also a .0 1. The role of the shell is analogous to the case of all-acrylic modifiers. such as divinylbenzene. 14-6 Examples of non-weatherable PVC formulations (parts per hundred resin).5 0. and superior elastomeric properties. Core-shell modifiers based on a butadiene homopolymer core result in the highest impact efficiency. although the molecular structure and composition must be tailored for different processing requirements and secondary properties. in addition to the impact modifier. the combinations of lubricants in these formulations differ from those associated with building products. In transparent applications. at the expense of some embrittlement of the p-Bd rubber and resulting lower impact efficiency. aid Bd-based impact modifier MBS clear impact modifier Heat distortion additive Blue toner PVC electrical box Bottle Clear film 100. 133]. Rayon Metablen Kaneka Kane Ace BTA-730 BTA-833 BTA-715 BTA-753 BTA-751 C-201 C-132 C-223 B-52 B-51 B-22 Clear film and sheet Clear bottles Low crease whitening High efficiency. impact modifiers must also meet specific FDA toxicity and organoleptic requirements. The higher processing temperatures of engineering resins require the addition of significant levels of heat stabilizers and antioxidants to acrylic or butadiene based emulsion rubbers [132.14.4 Impact Modifiers common occurrence in transparent films. the general approach of adding a second phase of rubbery material is common to most cases. opaque. injection molding Clear film and sheet. both emulsion and non-emulsion based. Although the toughening mechanisms. is used commercially. Resins other than PVC are usually compounded as pellets. Antioxidants and heat stabilizers are often added to Bd-based modifiers to prevent undue degradation of the modifiers during the high temperature drying and melt processing operations. creating a challenge for proper impact modifier dispersion and adhesion.2 Engineering Resins Engineering resins offer superior performance in various mechanical. such as polycarbonate. and associated applications. These polymers range from those that are considered inherently tough. and can be minimized by proper design of the modifier for adhesion and void resistance [131]. Tab. The most widely used emulsion based additives are the all-acrylic or MBS coreshell polymers. which lessens the advantages in powder properties provided by emulsion polymer isolation techniques.4. and encompass a wide variety of compositions and applications. a much broader range of rubber technologies. nylon. 14-7 Commonly used commercial non-weatherable impact modifiers. In contrast to PVC. bottles Low Crease whitening High efficiency opaque High efficiency opaque Low crease whitening Clear film and sheet. Manufacturer Trade name Product Description Rohm and Haas Paraloid Atofina/Mitsubishi. bottles 14. morphologies and optimal particle size for impact modification are specific to each type of matrix. 14-7. to the more brittle polystyrene and SAN [106]. and polyethylene terephthalate. Some examples of commercially available Bd-based impact modifiers. Common approaches to this problem 375 . In food packaging applications. rather than powders. are shown in Tab. thermal and aesthetic properties. Methacrylate-based shell compositions are generally not highly miscible with the various engineering resin compositions. opaque High efficiency. 14 Applications for Modification of Plastic Materials include the incorporation of functional polymers in the shell. can be used at levels from 10 to 30 % to efficiently increase impact resistance [2. Unlike most other engineering resins. 800 Notched Izod Impact Energy (J/m ) 376 640 23 C 480 0C 320 160 0 0 2 4 6 8 10 12 % Acrylic Core-Shell Modifier in Polycarbonate Impact behavior of polycarbonate modified with a core-shell impact modifier. 137]. In the case of PET. 135]. offered by General Electric under the trade name Xenoy. but the use of hydroxy-containing compositions can aid in allowing the use of core-shell type additives for effective toughening [134] (Fig. which is an inherently tougher resin created by copolymerizing PET and cyclohexanedimethanol [2]. which may be emulsion-based. PBT (polybutylene terephthalate) is traditionally toughened using ABS resins. Transparent PET applications require index refraction matching. or a third compatibilizing polymer. polycarbonate has some miscibility with PMMA. Fig. 14-12 PET (polyethylene terephthalate) has poor affinity for traditional shell compositions. the additive systems also compete with PETG. available from Eastman Chemical. Core-shell emulsion polymers. which can be compatibilized with PBT through the use of GMA (glycidyl methacrylate). PC-PBT blends. Common examples of toughened engineering resins include polycarbonate and polyesters. 14-13). An example of impact modified PC-PBT blend morphology . 136. to promote compatibility or chemical reactions between the modifier shell and resin. imposing another constraint on the design of these emulsion additives [134. are commonly used in many automotive applications and can be effectively toughened by core-shell modifiers. 14-12). and traditional core-shell modifiers can significantly enhance the impact performance (Fig. 14-13 Impact behavior of a PET resin modified with a core-shell impact modifier. 14-14). Emulsion polymerization can be used to synthesize Bd or Bd-S rubber seeds. PC. 1 µm 377 . fol- Fig.14.94 IV C-PET) Fig. ABS (Acrylonitrile-butadiene-styrene) is one of the oldest engineering resins. (Fig. 50 % PC and 10 % core-shell modifier.000 X patible with. in this case. The coreshell modifier tends to reside in the polymer phase it is most com20. clearly shows that the core-shell impact modifier prefers to exclusively reside in the more compatible PC phase.4 Impact Modifiers 10 Dynatup Drop Dart Energy (J) 8 6 -10 C 4 2 0 0 2 4 6 8 10 12 % Acrylic Core-Shell Modifier in PET (0. The blend contains 40 % PBT. 14-14 Morphology of impact modified two-phase PC–PBT blend. Core-shell polymers can be created by minimizing and carefully controlling the SAN polymerization to create the desired morphology. Impact modification of nylons is generally achieved through the incorporation of reactive groups in the rubber [139.378 14 Applications for Modification of Plastic Materials lowed by additional polymerization of styrene and acrylonitrile to form an in-situ impact modified resin. the conditions and compositions must be carefully controlled to prevent undesired increases in melt viscosity. and further encapsulated by a PMMA based outer stage. PMMA. Alternatively. 140]. commonly known as Plexiglas®. soft acrylate shell. Since these compositions react with the nylon during the melt processing. . 144]. the composition can be blended with additional SAN polymer to produce the desired blend ratios and properties [138]. surrounded by an inner. While core-shell modifiers have been applied successfully to these systems [141. These ABS polymers can be used as additives to modify SAN and other resin matrices. The role of the inner hard core is to provide refractive index matching and improved stiffness retention to the overall matrix. the most common commercial approach is the use of olefin-based elastomers grafted with functional monomers as maleic anhydride. 142]. methacrylate based inner core. Additional studies have demonstrated the effectiveness of a large number of alternative multilayer designs in improving the toughness and balance of properties in impact modified PMMA [145]. Acknowledgment The authors wish to thank the Rohm and Haas Company for their support. provides an interesting example of the application of emulsion synthesis to design multi-layer core-shell impact modifiers [143. A common three-stage polymer used to impact modify commercial PMMA resins contains a hard. 4. 465. Praze 1981. Chichester. . L. K. P. Wiersma. S.). 1992). 13. 4. V.027. R. C. Flatau (to Chemische Werke Huels AG). NY. 1986. K. A. J.206. T. Hatzman. Backderf.179. Tuzuki. Wilson. Compd. 4. 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Sci.892. Higashitani. Stabenow. R. Elsevier. Aradt. Graham. 1990). Chem. C. 25(4). 1986. Polym. J. Strella. 1977. 1410–1437. A. Impact Test and Service Performance of Thermoplastics. Vinyl Technol. 1990. Colloid Interface Sci. US Pat. A. J. 5. 3. 1988. 89796a. R. J. US Pat. Sci. D. 107. Gaymans.-C. in: Antioxidants in Thermoplastic Polymer Additives. Sherratt. Tech. Y. A. 60/166337 (1985). American Chemical Society. Young. J. 2(2). J. T. J. Kunststoffe 1995.-C. 104. Abstr. US Pat. H. 6. Watanabe. 5. Kushida. M. 1994. 62/39650 (1987). J.275 (Feb. P. W. Hiltner. J. J.536. 1993) J. McDonald. Washington.) Marcel Dekker. S.1225. Davis. 1994) M. Japanese Pat. 1994. 4. A. 869. D. US Pat. 1988. Yamada. 71. Berard. 5. Rubber Composites. Dekkers.). J. Ann.278. London. in: Toughening Agents for Engineering Polymers in Rubber Toughened Engineering Plastics. 85. US Pat. W. 5. . T. V. Tago. 1998. Naka. 1984. A. Hobbs.963.Chapman and Hall. J. E.237. 5. M. A. 1165136b. R. Keskkula.004 (Aug.846. Kushida. Lovell. Shah. S.657 (Dec. 107. J. 4. Williams. 11.174. US Pat. US Pat. Y. Mater. 1969). 27(9). Sci. 5. N. A. in Rubber Toughened Engineering Plastics. Wu (to Rohm and Haas). and Appl.835 (1976) to Rohm and Haas. Paul.198 (Jan. E.793. M. 5. Polymer (1989). US Pat. A. Y. US Pat. R.031. M. S. London. 4. Ranson (to Reichhold). M. 4. Burford. S. J. Watkins. R. Chem. J. J.869 (1989) to Huls. Yoshihara. Dekkers.382 References 122 US Pat. Nees-Brand. J. 1994) M. 1990). Grohman (to GE). K. 395. T.1219.670. N. Soc. Sci. 23. 3623. 3. Hagiwara. Science and Engineering. B.402 (1974) to Rohm and Haas. D.324. Hertz (to Union Carbide). Kinloch (eds) Advances in Chemistry Series 233. 5. Eng. Theory and Practice. Grohman (to GE). 8. Mater. US Pat. Lutz (ed. 1988. P. US Pat. Ohtsuka.509 (1987) to Kaneka. 1996. 62/596655 (1987). Riew. Hobbs. Tech. 30. Plast. Paolino. 17. Eng. C. 24324n. S. May 1967. N.. Siegmann. 1998) J. 1993. 1986.967 (1995) to Rohm and Haas. 4. Amagi.585 (Feb.798. NY.622 (October 16. 117. 452. J. K.358 (1979) to DuPont. M. Aoyanage. Collyer (ed. H. Japanese Pat. M. E. 1989. J.427. Meyer. J. Plast.).548 (1985) to Huls. US Pat. Japanese Pat. K. Vinyl Add. J.461 (June 28. Wu (to Rohm and Haas). Chapman and Hall. Conf. US Pat. Multiphase Toughening Particle Technology in Toughened Plastics I. Schuijer. Chem. 24(11). Kobayashi.164. Mater. H. Whittle. 11. Proc. Borggreve. Saunders. A. S. 1987. 3. US Pat. Polym. 23. J. US Pat.434 (1992) to Rohm and Haas.391. Abstr. 1995) M. Abstr. LeBlanc. P.232.300 (1977) to Rohm and Haas. 21. J. P. 142 R. 23. Chem. V. Collyer (ed. Watkins. Grohman (to GE).086.991 (1993) to Huls. R.409. US Pat. Gaymans in: Toughened 143 144 145 146 147 148 149 150 151 152 153 154 155 Polyamides. N. 1987.047 (2000) to Rohm and 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 Haas. A. DC. US Pat. 4. H.971. Sci. condoms. flexible products normally associated with this process are gloves. the article is removed from the former. such as car body parts or toys. “form” or “former”. Andrew Lanham. The coated former is then heated to dry and cure the polymer as necessary. with the very minor exception of the use of some high modulus synthetic emulsion polymer as a reinforcing material for catheters. One example of this is the use of curing agents to produce elastomeric properties. KGaA ISBNs: 3-527-30286-7 (Hardback). The area is dominated by the use of natural rubber for gloves and condoms. Matching the strength. balloons. being particularly useful as a method for coating irregularly shaped items. is dipped with an appropriate dwell time into a liquid containing the polymer. tear resistance and dipping characteristics of natural rubber has provided a formidable challenge to the synthetic polymer chemist. at least in concept. UK 15. The idea of producing a thin coating by dipping an article into a liquid coating material is well established. Balloons and catheters remain the domain of natural rubber. In another guise. perhaps complex. Harlow. catheters and feeder teats and soothers for babies. This book is concerned with synthetic emulsion polymers. The various types of synthetic polymer used for dipping are discussed in the next section. The polymers from which they are made often include additives to produce the desired physical properties. a simple one. modulus. whose shape it retains. thinwalled articles from natural or synthetic polymers. shapes. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. a suitable shape. called in the industry a “mold”. Finally. and it has to be said that at the start of the 21st century their use in the production of dipped goods is relatively limited. the dipping technique can be used to produce flexible. In the dipping process. where the final article exhibits the ability to recover its original dimensions after the removal of an applied stress. The thin walled. Synthoner Ltd. The dipping process therefore provides the means to make seamless thin-walled items with predetermined. and Karen Spenceley. 3-527-60058-2 (Electronic) 15 Applications for Dipped Goods Robert Groves.Polymer Dispersions and Their Industrial Applications. 383 .1 Introduction The dipping process is. as described in the next section. The protective glove market can be subdivided as follows. – to produce skin-contact items that are completely free of proteins. unsupported industrial and fabric supported gloves.2 Polymers Used by the Dipping Industry Although natural rubber dominates the dipping sector. no synthetic aqueous emulsion polymer is used. It is in the area of hand protection that synthetic emulsion polymers have made inroads into the dominance of natural rubber. 8 g per piece) Unsupported Household Industrial Fabric-supported (approx. The reasons have been associated with specific technical benefits. Disposable Medical Surgical Examination Light industrial (approx. – with the correct polymer design. synthetic polymers can offer significant technical benefits for some applications. Currently. – to make gloves which have a lower surface electrical resistance than natural rubber. and applying a polymer coating to the fabric by dipping. 30 g per piece) (20 to 100 g per piece) (Fabric glove coated with 30–80 g polymer) Disposable and unsupported gloves consist of a film of a chosen polymer with a thickness appropriate to the end use. 12 g per piece) (approx. the alternative to natural rubber is provided by polyurethane dipped from organic solvent. Fabric-supported gloves are made by pulling a woven fabric “liner” on to a former. Synthetic polymers have found their main use in light industrial. . 15. a useful property in gloves that are used in electronic assembly because of the reduced risk of damaging sensitive components by static electricity. 8 g per piece) (approx.384 15 Applications for Dipped Goods For condoms. but it is believed that currently some 12 % of the estimated 400 000 dry tonne worldwide market for polymeric gloves (excluding household gloves) is with synthetic emulsion polymers. while about 15 % uses non-aqueous synthetic products. where an alternative material to natural rubber is desirable because of potential protein allergy problems. Accurate market figures are difficult to obtain. The main benefits for synthetics that have so far emerged are: – the ability to produce gloves with a much higher degree of resistance to non-polar organic solvents than is possible with natural rubber. to achieve greater mechanical protection (puncture and abrasion resistance) than is possible with natural rubber. Polyurethane and styrene-butadiene-styrene block copolymers dissolved in organic solvent have been used to produce gloves and. Nitrile also has a significantly lower surface electrical resistivity than natural rubber. acrylonitrile and a third monomer that contains a carboxylic acid group (usually methacrylic acid). for the producers of dipped articles. also condoms.15. the polymer must be provided in a liquid form.3 Principles of Dipping Several synthetic polymers are used by the glove industry. Some attempts have been made to convert polymers that have been synthesized in organic solvent into aqueous emulsions suitable for dipping. So far these attempts have been largely unsuccessful at the commercial scale. in which the polymerization reaction and the formation of an aqueous emulsion occur simultaneously. Heat treatment causes the plastisol to gel and the plasticizer to dissolve in the polymer. and therefore finds use in gloves for use in areas where static electricity might be a problem. the ratio of the three monomers can also be used by the polymer chemist as an important tool in tailoring the final product properties. However. resistance to oils and fats and excellent light and ozone resistance. A former of the desired shape is dipped into a liquid mix 385 . In this process. giving the final flexible composition. Gloves made from this polymer are known as polychloroprene or “Neoprene” (Neoprene is a trademark of E I DuPont de Nemours and Co). These polymers are: – Copolymers of butadiene. which is a dispersion of the polymer in an organic liquid. reaction temperature and control of the polymer molecular weight are important in order to obtain the desired final glove properties. most of which is a plasticizer for the polymer. Nitrile and polychloroprene latices are made by the industrial process of emulsion polymerization. safety and environmental reasons. 15. Clearly. The particular advantages of this polymer are resistance to many solvents and excellent mechanical protection (abrasion and puncture resistance). For poly(vinyl chloride) the liquid is a plastisol. Gloves made from this copolymer are often termed “nitrile”. – Homopolymers of 2-chloro-1. in the case of polyurethane. for dipping. In the case of the nitrile latex.3-butadiene (“chloroprene”). because of the cost involved in the multistage process and because the relatively large quantity of surfactant added to achieve emulsification increases the difficulty of controlled gellation during the dipping process.3 Principles of Dipping The basic concept of producing a coating or a thin-walled article by the dipping process is straightforward. a water-borne polymer system is often highly desirable for health. Gloves made from this composition are commonly termed “vinyl”. The key attributes of this material are a similar stress-strain response (“feel”) to natural rubber. There are only two commercially important water-borne polymers currently used by the dipping industry and both are used to manufacture hand-protection articles. The thickness of the deposit can be controlled by the concentration and drying of the coagulant solution and the colloidal stability and total solids of the dispersion. Blackley [2] and Lanham and Eidam [3]. The first is simply by adjusting the viscosity and solids content of the liquid. in order to produce the desired wall thickness in the final article. In addition. 15. This method has been used mainly in the production of thicker items. refinements and modifications have to be added to the basic principles to yield a viable. For the manufacture of condoms.4. the mix or coag- . which must be provided as a colloidal dispersion. Further information on the dipping process has been published by various authors. thus enhancing the amount of mix deposited. Finally the thin. Straight dipping usually yields thin films. A third method used to control deposition on to the former is to use additives in the mix that cause destabilization and/or a viscosity increase at elevated temperature. There are several ways in which the deposition of the mix can be controlled. is to provide the shape of the desired final product. flexible film is removed from the former to yield the desired product. Deposition of the mix is therefore facilitated if a hot former is used. the following notes are necessarily directed towards this area. The coagulant causes a localized destabilization and viscosity rise in the dispersion at the surface of the former. such as an aqueous solution of calcium nitrate. The process continues by heating the coated former to solidify. 15. including Carl [1]. In this process. good control over the temperatures of the dipping mix and former is necessary. This section describes some of the methodology used in achieving practical systems. for example to make gloves or balloons. Obviously. Coagulant dipping is the method most often used to deposit thicker films in a single dip. however. the former is dipped into the liquid mix. the mold or former is first dipped into a coagulant liquid. commercial dipping process. Heat sensitizing additives that have been used with natural rubber include polyvinylmethyl ether and polypropylene glycol. This process is called simple or straight dipping and is the method usually employed for making condoms from natural rubber latex. Since at present the only significant use of synthetic emulsion polymers is with nitrile and polychloroprene latices for glove manufacture. The process is arranged so that on withdrawal.4 Dipping Synthetic Polymer Emulsions in Practice Inevitably. dry and cure the deposited mix.386 15 Applications for Dipped Goods that contains the material of which the final product is to be made. with this system especially. and is applicable to both solution and dispersion mixes. for example babies’ teats. a thin deposit of the mix is left on the former.1 Former Design Obviously the main requirement of a former for unsupported glove production. the final film is normally built up by two or more separate dips. After partial drying of the coagulant. specific left and right hand formers are used. The production of fabric supported gloves requires special formers. 15-1) should be such that air bubbles are not entrained on the former surface as it enters the mix. The formers should be easy to clean. Of the many materials tried. the same former shape is used for both left and right hands. where only the fabric liner should contact the dipping mix.15. (center) for fabric supported gloves (hand specific) and (right) for industrial unsupported gloves (hand specific). 387 . The design of the former (Fig. Since these gloves are relatively difficult to stretch. otherwise an irregular or incomplete deposit results. the former is often designed with a moveable joint at the base of the thumb (or even a detachable thumb) to ease the task of removing the final product. For thin disposable gloves. Clearly. since it accepts coagulant readily and its micro-roughness helps to limit length-direction shrinkage of the drying polymer film. For thicker gloves and thin surgical gloves. The design should also minimize the tendency for the thin film to shrink in the length direction of the former during drying. Fig. unglazed porcelain is favored for formers for unsupported glove manufacture. many of the features required by formers for unsupported gloves are unnecessary for fabric supported work. 15-1 Former designs for (left) thin multi-purpose gloves (ambidextrous).4 Dipping Synthetic Polymer Emulsions in Practice ulant must easily wet the former. 15-1 and the various additives are discussed below.0 0. Tab. but this value will vary according to the particular grade of latex being used.0. It is added in dilute form.0 0. For both polychloroprene and nitrile polymers the zinc oxide.5–2.4. In this case it is reasonably certain that the mechanism is one of interaction of zinc cations with the carboxyl groups present in the nitrile copolymer [5].0 0–0.5 Trace 0–0. A typical pH for a dipping mix would be approximately 9.388 15 Applications for Dipped Goods 15. Some ac- . potassium hydroxide) is normally added to the latex first.4 Antioxidant is normally included in the latex by the polymer manufacturer. together with the other accelerators.0 parts.5–5. Levels of ZnO used with nitrile polymers are in the range 0. 15-1. However. also activates the sulfur vulcanization. the sulfur curing is thought to be of less significance than the effect conferred by the interactions between zinc cations and carboxyl groups [3]. such as aqueous ammonia.5–5. it is usual to use several additives to achieve the desired performance. A fugitive alkali. In nitrile compounds. It is used in fairly large quantities (5–10 parts per hundred of dry polymer) in polychloroprene compounds as a cross-linking agent. for carboxylated nitrile products.5–2.5 0. can be used but gives a greater tendency for skin formation on the mix surface. The zinc oxide also reduces the colloidal stability of the mix and so influences the amount deposited on the former during coagulant dipping.0 0. since concentrations above 5 % can cause the latex to flocculate. reportedly functioning by acting as a hydrochloric acid acceptor [4]. as it tends to stabilize the compound to the addition of the other components. zinc oxide is also found to act as a curing agent. A typical mix for producing a glove is shown in Tab. The alkali (in the example of Tab. Zinc oxide is an interesting ingredient. Ingredient Parts active per hundred dry rubber Carboxylated nitrile rubber Antioxidant dispersion Potassium hydroxide solution Zinc oxide dispersion Sulfur dispersion Accelerator dispersion Titanium dioxide dispersion Pigments Thickeners 100 0–1. but if not it can be added to the mix by the compounder.2 Mix Design Although the mix consists mainly of the polymer dispersion. The alkali also affects the pick-up on to the former and hence the final polymer film thickness. having a profound effect on the physical properties of the final film. 15-1 Typical latex-based formulation for dipped gloves. Chemical Type Benzothiazoles 2-Mercaptobenzothiazole 2. although conclusive evidence for human carcinogenicity is scant.15. This issue is discussed in detail by Estlander et al. 15-2 Commonly used accelerators for nitrile and neoprene latices. [6]. thiazoles and carbamates were used. is added as an opacifying agent. because its high refractive index gives it a high opacifying efficiency and it can therefore be used in relatively small quantities with minimal impact on the physical properties of the product. but their use has declined because of problems with skin allergies. Table 15-3 lists a few of the thickener materials that have been used in dipping compounds.2-Dithiobisbenzothiozole-2-sulfenamide Benzothiazolesulfenamides N-Cyclohexylbenzothiazole-2-sulfenamide N-t-Butylbenzothiazole-2-sulfenamide 2-Morpholinothiobenzothiazole N-Dicyclohexylbenzothiazole-2-sulfenamide Dithiocarbamates Tetramethylthiuram monosulfide Tetramethylthiuram disulfide Zinc diethyldithiocarbamate Amines Diphenylguanidine Di-o-tolylguanidine Common abbreviation MBT MBTS CBS TBBS MBS TMTM TMTD ZDEC DPG DOTG The choice of accelerator depends on the curing profile and final properties desired. since these materials can give rise to discoloration in the presence of trace amounts of copper. despite its expense. A thickener is often used to control the mix viscosity. It also enhances the color imparted by the pigment. accelerators such as thiurams. in the form of an aqueous dispersion. as discussed recently by Loadman [7]. Previously. Care has to be exercised in the use of dithiocarbamates. Titanium dioxide. In addition to the problems of contact dermatitis. N-nitrosamines are believed to be carcinogenic. Titanium dioxide is used. Tab. which in turn affects pick-up on to the former. Dithiocarbamates and thiuram sulfides have the potential to decompose to give N-nitrosamine precursors [3]. 15-2. it may be necessary to consider the formation of N-nitrosamines by accelerators. 389 .4 Dipping Synthetic Polymer Emulsions in Practice celerators that are commonly used to increase the rate of sulfur curing are listed in Tab. PvOH usually gives a thixotropic rheology. The aqueous coagulant solution is usually held at high temperature (about 60 °C). Thickeners for dipping compounds. their relatively low cost.4. They usually give a pseudoplastic rheology.390 15 Applications for Dipped Goods Tab. Casein also acts as a colloid stabilizer. 15. This is an inert powder. low toxicity and low environmental impact. The advantages of these materials include their efficiency in coagulating anionic emulsion polymers. A surfactant is often added to the coagulant solution to ensure adequate wetting of the former. Casein Unsupported gloves Expensive. 15-3. 15. It is susceptible to infection problems. A technique sometimes employed is to dissolve the coagulant in a mixture of water and alcohol. but of course the use of alcohol raises problems from a health. safety and environmental standpoint. Polyvinyl alcohol Fabric supported gloves Solutions of PvOH can be difficult to prepare. Chemical type Used in Comments Polyacrylates Unsupported. alcoholic coagulant is used at a lower temperature than the aqueous type.3 Coagulant The usual coagulants employed for glove dipping are calcium salts that are soluble in water. Materials to discourage foaming in the mix or the formation of a thin film of wet mix between the fingers of a glove (“webbing”) can also be added. The main advantages are an improved drying rate and improved wetting of the former. which reduces the adhesion between the final dipped film and the former. to accelerate its rate of drying on the former surface.4. Additional surfactant may be added to adjust the colloidal stability and thus the thickness or quality of the dipped film. becoming effective on raising their pH. Other additives are also frequently employed in the dipping mix. . Because of its faster drying rate. thus making the removal of the finished glove easier. In the following sections. for example talc or calcium carbonate. in particular calcium nitrate and calcium chloride.4 The Dipping Process Many aspects of the dipping process can be adjusted to suit the particular type of glove being produced. heavier weight gloves Polyacrylates are often supplied as an emulsion. some process details are given for each of the three main types of gloves that are made using synthetic latex. It is quite common for the coagulant solution also to contain 1 to 5 % of a parting aid. for example electronics. the for- 391 . Cleaning is followed by a thorough rinse with clean water. formers are taken out of the process for a more extensive cleaning.4 Dipping Synthetic Polymer Emulsions in Practice Disposable gloves These products are often referred to as thin gloves and find use mainly in the healthcare sector. where their primary function is to prevent transfer of infectious agents between medical workers and patients. carrying the formers in and out of the liquid. individual or pairs of formers are attached at intervals to an endless chain that moves at constant speed. the coagulant-coated former comes into contact with the latex and the polymer deposit starts to build up on the former surface. The next step is to dip the former into the coagulant solution. However. 15-2 Stripping Coagulant Bath Latex Bath Beading Drying & Vulcanisation Leaching Anti-tack Bath Continuous dipping process. A secondary function can be to provide protection against pharmaceutical preparations. At stations where dipping occurs. The coagulant picked up by the former is dried before the next step. Disposable gloves are also used in industrial applications. the concentration being monitored by specific gravity. enabling the formers to visit each processing station in turn. Former Cleaning Fig. In this central step of the process. the track bends downwards then upwards. perhaps with sulfuric or chromic acid. A schematic diagram of the process is given in Fig. by ultrasonic treatment or a suitable combination of these methods. This operation gives high volume output for relatively low cost. by brush scrubbing. The process starts with cleaning of the formers. The solution strength is typically in the range 10–25 % by weight. Here. an essential step without which poor quality films will result. the process is rather inflexible and is best suited to large runs of one type of glove. increasing in thickness with dwell time in the latex bath. The most usual manufacturing process for disposable gloves is the continuous or chain process.15. where the purpose of the glove is to prevent assembly workers contaminating clean items. Entry and exit is therefore not vertical. such as silicon wafers or disk drive surfaces. As required. 15-2 and the various steps are explained below. Cleaning is accomplished by passing the formers through a bath of mineral acid or alkali containing surfactant. At the following station. re-dried. Long leaching times are preferred from a technical standpoint.392 15 Applications for Dipped Goods mer temperature. in which teams of three or four workers line each side of the chain to pull off and briefly check the gloves for holes. Occasionally compressed air jets are used to assist with the stripping process. making them difficult to strip. since high leach water temperatures can promote excessive length direction shrinkage of synthetic latices. Following beading. Undercured gloves tend to have low tensile strength and high elongation. giving a marked reduction in surface tack that makes the gloves easier to don. Sophisticated cure ovens will allow the curing to be phased. The tack of the polymer at this stage of processing is sufficient for the bead to be held in place. clean water. the glove is leached. The polymer at the cuff of the glove is then rolled on to itself by the action of mechanical rollers or brushes. capable of being used on multiple occasions. find use in both industrial and domestic situations. space and cost constraints and is normally of the order of 5–10 min. A slightly cooler temperature may be programmed for the final oven stage. However. a washing process carried out by immersing the glove in warm (40–50 °C). On leaving the latex dip tank. For the curing of disposable gloves. The glove is then dipped into an anti-tack compound. to avoid ungelled latex on the outside of the film flowing to the bottom of the former. The penultimate stage of the process is drying and vulcanization. which improves comfort by absorbing perspiration. Care must be exercised in the leaching process. a process known as “beading”. defect-free film. by tumbling in heated ovens. to achieve the maximum removal of water-soluble materials. forming a firm. The removal of the glove from the former (“stripping”). Finally. QC tested and packed. The chlorine reacts with the surface layer of polymer molecules. is the only fully manual part of the process. in practice. the formers are lifted to the horizontal and rotated. Following tumbling. gloves are usually chlorinated by immersion in an aqueous dilute chlorine solution (a technique also used for natural rubber disposable gloves). The purpose of applying this material is to reduce the rubber-rubber friction when the glove is ultimately peeled from the former. The purpose of the bead is to give the cuff of the thin glove adequate tear-resistance. . The latex layer continues to consolidate after removal from the latex bath. which may be a silicone emulsion or a slurry of calcium carbonate. Unsupported heavier weight gloves Thicker walled gloves. the gloves may be washed. leach duration is limited by time. and to prevent the interior surfaces of the glove sticking together on storage. gelled coating. approximately 20 min at 120 °C is required. They are often made with a lining of small fibers (“floc lined”). thus easing its removal. Disposable gloves can be further dried offline. speed and smoothness of former entry and exit are important factors in the production of an even. for example to bring the temperature gradually to around 120 °C to avoid blistering. Incomplete drying can lead to problems of glove surfaces sticking to one another on storage. to make glove removal easier. recent concern over protein allergy has led to the increased use of sophisticated synthetic polymers in this area also. the critical factors of entry and exit rate and former temperature have to be 393 . Within limits. the formers are usually inverted to achieve a more uniform distribution of the solution over the surface. outlined as follows.15. the formers enter and leave the coagulant at right angles to the solution surface. However. the time spent at each station can be independently varied. but they are more commonly produced by the batch process. The process again begins with the cleaning of formers. As for thin gloves. The coagulant solution is of a higher concentration and dip times are much longer than those used for disposable gloves. the former is dipped into the latex bath. Jigs to which perhaps 20 or 30 formers are fixed are moved sequentially on guide rails from station to station. Fig. 15-3 Former Cleaning Coagulant Bath Stripping Chlorination Bath Latex Bath Leaching Bath Drying & Vulcanisation Flock Adhesive Flocking Booth Batch dipping process. The various steps in this process are described below and the similarities and differences in the production conditions compared to those used for disposable gloves are highlighted. only moving in the vertical plane. [6]. These standards cover areas such as resistance to chemical penetration. With the batch process. Operations such as dipping into a liquid bath are achieved using hydraulic equipment. A schematic diagram of the batch process for thicker unsupported gloves is given in Fig. puncture resistance and abrasion resistance. After drying the coagulant. where the speed of movement round the track is constant. 15-3. so more control is possible than with the continuous process. Further information on protective gloves is given in the book edited by Mellström et al.4 Dipping Synthetic Polymer Emulsions in Practice Industrial gloves will probably be destined for use as protective equipment and will therefore be required to meet specific safety standards. using similar methods to those employed in the thin glove process. After withdrawal from the coagulant. Household gloves are normally made from natural rubber and have been regarded as price-driven commodity items. Heavier weight gloves may be made by the continuous process in a similar manner to that described above. The most common coagulant solution is aqueous calcium nitrate at 30–40 % by weight. They are primarily used where a high degree of mechanical protection. Curing times of up to 45 min are quite usual. The fibers are made airborne by compressed air or electrostatic methods in a booth. it is common to use an adhesive that is based on the main glove polymer. After stripping. When the polymer film has gelled sufficiently it is leached in warm. For heavier gloves. While the cut and sewn type predominates . but not immersed in it. since it can be used to encourage an orientation of the fibers perpendicular to the glove surface. the latex mix viscosity and the latex stabilizing system. The drying and curing of heavy gloves is slower than for disposable gloves. or they are knitted in one piece. In addition. and thicker gloves certainly require more time than disposable ones. industrial gloves tend to need a higher degree of crosslinking to give chemical resistance. If the gloves are to be flock lined. Flock contacts. To achieve a good bond. The best manufacturing units use both former design and machine layout to ease this process. into which the gloves are moved. The liners are formed by cutting and sewing the chosen fabric into the desired shape. but also of the coagulant strength and temperature. The construction is based on a textile “liner” which has been coated with a polymeric layer. the next step is the application of a flock adhesive. and adheres to. The flock normally consists of cotton fibers. The electrostatic method is useful in this regard. As well as having more water to evaporate. The liner fabric gives a benefit in user comfort and may be made from cotton. Typical leach conditions used for heavier weight gloves are 10 to 15 min with water temperature in the range 45–70 °C.394 15 Applications for Dipped Goods optimized to produce an even polymer film. again by dipping. Note that film thickness is not only a function of dwell time in the latex. the drying rate of heavy gloves has to be limited to prevent escaping water vapor “ballooning” the glove. it can be a fairly demanding one. The chlorination step is similar to that employed with thin gloves. for thicker gloves especially. the gloves may be chlorinated or given a further heat treatment before being inspected and packed. The adhesive should form a good bond with both the glove polymer and the flock fibers and should not be coagulated by any residual coagulant that might be on the polymer surface at this stage of the process. one side may be chlorinated on machine and the other off-line. nylon or even Kevlar. the wet adhesive and conditions are adjusted so that the fibers are wetted by the adhesive. is required. Fabric-supported gloves Fabric-supported or coated fabric gloves are a small but important part of the market. clean water. polyester. since highly cross-linked polymers can offer significant resistance to the manipulation required for removal from the former. Stripping is a manual process and. combined with water and chemical resistance. It is advisable to use as long a leach time as practicable. This stage is essential to remove surfactants and coagulant that would otherwise result in surface tack on the finished gloves. For thicker gloves. dwell times in the latex bath may be in excess of 2 min and for very heavy gloves a second dip may be employed. The use of a heat-sensitized dipping compound is complicated by the difficulty of achieving a controlled temperature at the liner surface and the difficulty of controlling the mix viscosity close to the liner in the presence of a hot former. 15.5 The Testing of Synthetic Gloves An increasing number of standards concerned with the performance of gloves are becoming available. As there are many types of supported glove and production methods vary.15. including: International USA UK France Germany Europe Former USSR International Standard Organization American National Standards Institute American Society for Testing and Materials British Standards Institution Association Française de Normalization Deutsches Institut für Normung European Standards State Committee for Standards (ISO) (ANSI) (ASTM) (BSI) (NF) (DIN) (EN) (GOST) Note that various professional organizations have also developed standards which can be useful for glove testing. a significant amount of the coagulant may be absorbed into the liner. If a coagulant method is chosen. that the key issue is to control the application of the polymer coating. no attempt will be made to describe their manufacture here in any detail. In addition to fabric design. The dipping of supported gloves is carried out successfully by only a few companies worldwide and the technology is generally proprietary. however. 15. lower labor cost and increased comfort. compound surface energy and the depth and duration of dipping are some of the factors that can be used to achieve a successful over-dip. The presence of a fabric liner creates some practical problems in the dipping process. be used.1 Non-safety-critical Gloves There is a number of standards specifying the general performance of polymeric materials which might be used in the manufacture of gloves. the knitted liner is finding increasing popularity because of the reduced material wastage. compound low-shear viscosity. the coagulant and straight dipping methods are the most favored. They come from a variety of sources (regulatory bodies). both the 395 .5. For example.5 The Testing of Synthetic Gloves because of its ease of production. With the correct control of latex compound rheology. It can be said. of course. requiring removal from the finished glove by thorough washing. so that good coverage and good adhesion are achieved but without excessive penetration of fabric liner by the mix. In general. straight dipping can. This standard refers to general methods for testing elastomeric materials. 15-4. rather than protect the worker. and for gloves designed to give protection against electrical hazards. Gloves that are used in electronic assembly are designed primarily to protect the product under manufacture.396 15 Applications for Dipped Goods ASTM and BSI have issued methods for testing the physical properties of rubbers and the effects on rubbers of accelerated aging. Gloves meeting these requirements carry the CE mark. Some standards relating to glove material cleanliness and to the testing of static electrical properties of materials are available and used in this area. one means of minimizing the risk of these hazards actually causing harm. referred to above. These hazards include physical damage. Tests specified include tensile strength and elongation (before and after aging).2 Safety-critical Gloves The hand is perhaps exposed to more hazards than any other part of the body. The general tests relating to the physical properties of glove materials. which sets out specifications aimed at assisting in the achievement of performance consistency. which allows them to be marketed throughout all European Community countries. 15. Clearly. biological and radioactive hazards. There are many standards that specify tests and performance for protective gloves. chemical contact and contact with biological agents. The European Union has detailed a number of requirements for protective glove manufacturers in the Personal Protective Equipment Directive 89/686/EEC. is to select an appropriate glove. Particular standards dealing with surgical and examination gloves exist.5. may be used. chemical. some of which are material specific. The ASTM has issued a standard for household or beautician’s gloves. 15-5 and 15-6. physical dimensions and freedom from holes. . as well as protection from heat and cold. There are individual standards for assessing protection from mechanical. Some of the standards that have found use in the protective glove area are listed in Tabs. such as those mentioned in the preceding paragraph. 15-4 North American standard test methods. ASTM D120 E1 ASTM D412 ASTM D573 ASTM D624 ASTM D991 ASTM D1418 ASTM D3577 ASTM D3578 ASTM D4679 ASTM D5151 ASTM D5250 ASTM D5712 ASTM D6319 ASTM E595 Tab. BS/EN 368 BS/EN 369 BS/EN 374-1 BS/EN 374-2 BS/EN 374-3 BS/EN 388 BS/EN 407 BS/EN 420 BS/EN 421 BS/EN 455-1 BS/EN 455-2 BS/EN 464 BS/EN 511 BS 903 :A2 BS 903: A9 BS 903: C1 BS 2782: Part 2 BS 2782: Method 231A BS 7506:1 Protective Clothing for Use against Liquid Chemicals – penetration of liquids Protective Clothing for Use against Liquid Chemicals – permeation of liquids Protective Gloves against Chemicals and Microorganisms – terminology and performance requirements Protective Gloves against Chemicals and Microorganisms – determination of resistance to penetration Protective Gloves against Chemicals and Microorganisms – determination of resistance to permeation by chemicals Protective Gloves against Mechanical Risk Protective Gloves against Thermal Risks (heat and/or fire) General Requirements for Gloves Protective Gloves against Ionizing Radiation and Radioactive Contamination Medical Gloves for Single Use – specification for freedom from holes Medical Gloves for Single Use – specification for physical properties Protective Clothing – Protection against Liquid Chemicals – gas leak test Protective Gloves Against Cold Physical Testing of Rubber – determination of tensile stress–strain properties Methods of Testing Vulcanized Rubber – determination of abrasion resistance Methods of Testing Vulcanized Rubber – determination of surface resistivity Methods of Testing Plastics – electrical properties Methods of Testing Plastics – determination of surface resistivity Measurement in Electrostatics – guide to basic electrostatics 397 .15. 15-5 Standard Specification for Rubber Insulating Gloves Standard Test Methods for Vulcanized Rubber – tension Standard Test Method for Rubber – deterioration in an air oven Standard Test Method for Tear Strength of Conventional Vulcanized Rubber and Thermoplastic Elastomers Standard Test Method for Rubber Property – volume resistivity of electrically conductive and antistatic products Standard Practice for Rubber and Rubber Latices – nomenclature Standard Specification for Rubber Surgical Gloves Standard Specification for Rubber Examination Gloves Standard Specification for Rubber Household or Beautician Gloves Standard Test Method for Detection of Holes in Medical Gloves Standard Specification for Polyvinyl Chloride Gloves for Medical Application Standard Test Method for Analysis of Protein in Natural Rubber and its Products Standard Specification for Nitrile Examination Gloves for Medical Application Standard Test Method for Total Mass Loss from Outgassing in a Vacuum Environment European standard test methods.5 The Testing of Synthetic Gloves Tab. Vol. Wilmington. L Kanerva.D.). Rubber Conf. Chapman and Hall. Int. CRC Press. Delaware. Mellström. C. Polym. standards will be updated and others newly issued. Distler (ed. C. Calvert (ed. Florida. in: Protective Gloves for Occupational Use. . 1994. 1982. as new technologies evolve. M.D. Applied Science. K. D. Polymer Latices Science and Technology. UK. but are included to give the reader some idea of the breadth of standards available. Dupont De Nemours. Carl. 48. Wahlberg. E. Alzorriz. O. Blackley. Proc. 6 T Estlander. 580. 1999. 15-6 Professional standard test methods UK Dept of Health M. Loadman. UK. J. R. Clearly.). 2 D. 3 A. A. Manchester. London. Bratby. 1962. USA. References 1 J. G. E. USA. Germany. R Jolanki. Eidam. Weinheim. Maibach (eds). 1999. H. 5 L. Boca Raton. I. I. Lanham. in: Wäßrige Polymerdispersionen. Ibarra.. M. Int. WileyVCH. J. Neoprene Latex – Principles of Compounding and Processing. 1996. 4 D. 1997. 2nd edn. London.010 Institute of Environmental Sciences and Technology (USA) IES-RP-CC005. TSS/D/300. UK. 3. N. in: Polymer Latices and their Applications.398 15 Applications for Dipped Goods Tab. 7 M.2 Specification for non-sterile NR latex examination gloves Gloves and finger cots used in clean rooms and other controlled environments These lists are not intended to be exhaustive. 296 ff.. 293 applications tests 97 f. 136. 156 f. 285. 332.Polymer Dispersions and Their Industrial Applications.. 159 f. 303.. 313 ff. 395 ff.. 12. 240. 193 ff. 176 f... 168 ff.. 3-527-60058-2 (Electronic) Index a abrasion cohesion test Esso (ACTE) 323 abrasion resistance 115. 304 ff. 261. 275 ff. 183 – appearance 169 – basecoat 167 – clearcoat 167 – crosslinking 183 – electrocoat 167 – emulsion polymers 176 – formulation 168 – function of ingredients 168 – function 167 – layer 167 – main ingredients 168 – microgels 177 – miniemulsions 177 – performance 169 – primer 167 – standard tests 169 automotive leather 284. KGaA ISBNs: 3-527-30286-7 (Hardback). 210 ff... 294 average degree of polymerization 195 b back-coating of carpets 259. 237 f. 202 antifreeze agents 235 anti-sag 334 apparel leather 284... 358 acrylic esters 90.. 142 ff.... 132. 246 f. 335 ff. 228 ff. 339 adhesion level 210 adhesion-elongation 238 adhesive raw materials 192 adhesives 191 ff. 330. 154.. aqueous 1 aqueous flexo news ink 121 aqueous ink 104 aqueous phase analysis 57 asphalt binder 304 asphalt composition 310 asphalt consumption 301 asphalt emulsion 302.. 273 f.. 221 f.. 142. 321. 232. 114. 338 f. 355 adhesion 191 ff. Edited by Dieter Urban and Koichi Takamura Copyright © 2002 Wiley-VCH Verlag GmbH & Co. 334 agglomeration number 28 aggregates 332 aging resistance 299 American Standards (ANSI) 335 analytical ultracentrifuge 51 antifoam agents 6. 217. 151. – anionic 315 – application 314 – cationic 315 – cured 318 – ductility 317 – elastic recovery 317 – latex modified 318 – medium-setting 313 – modification 301 – penetration 317 – properties 309 – rapid-setting 313 – slow-setting 313 – softening point 317 – specification 304 – tests 317 – torsion recovery 317 automotive coating 163 ff. 249.. 90... 368. 240. 262 bally flexometer 297 barrier coatings 7 basecoat 173 ff. 108.. 287. 332 f. 332 accelerators 389 acorn structure 5 acrylates 90 acrylic adhesive 220 acrylic dispersions 6.. 299... 94 additives 78. 130 f. 147 f. 114 f. 344 399 . 291. 303 ff. 70. core-shell impact modifier 376 core-shell particle 71 corona discharge 118 corona-pretreated film 218 corrosion inhibitor 114 CPVP 126 cracking 336 crinkle resistance 116 critical micelle concentration (CMC) 19. 203 biodegradability 6 blistering 93 ff. chain entanglement 21 chain transfer 18 chain transfer agent 32. construction adhesives 224 construction industries 191 contaminants 36 conversion 22 conversion process 363 – melt rheology 363 conversion-time curve 23 core-shell modifiers 373 core-shell structure 4 f. – adhesive scrim coat 263 – pre-coat 263 – unitary backing 264 carpet production 255 carpet terminology 260 cement 333 cementitious topcoats 345 centrifugation 51 ceramic tile adhesives 238 ff. 178. 198 characterization 41 ff. 263 f. 94 f. coefficient of friction 116 colloid mill 313 color 65 concrete 242. ff. 273 f. 90. biocides 6. 113. 273 f. 127. – paints 127 – sole binder 90 – styrene-acrylate 96 f. 90. 256 ff. 346 ff. 90 carpet 253 carpet backcoating 259 carpet backing 253 carpet backing binders 253. 92 ff. 84 ff... 291. 167. 87 ff. 33. 220 . – co-binder thickeners 87 – pigments 86 – sheet-fed offset 86 coating layers 166 coating of carpets 261 coating support materials 205 coating weight of adhesives 207 co-binder 84. 97 – synthetic 90 f. 86. 135. – styrene-butadiene 95. – maintenance 347 – rehabilitation 349 – repair 347 f.400 Index bending beam rheometer 306. calender 85 f. 291. 21. 256. 253. butadiene-acrylonitrite copolymers 385 ff. 308 bimodal 5 binder 78... 332 ff. 27 critical PVC 126 critical surface tension 65 cross-linking 4. carboxylic acid 26 carboxymethylcellulose 88.. binding strength 87. 321 – application test 321 coagulant dipping 386 coagulants 390 coagulation 3 coagulum 37 coagulum grit 42 coating 205 coating color 81. 258 – carboxylated styrene-butadiene 256 – cold SB (styrene-butadiene) 256 – high solids styrene-butadiene latex (HSL) 256 – hot SB (styrene-butadiene) 256 – natural latex 256 carpet laminating 259. butyl acrylate 90 c calcium carbonate 86 f. 85. 256 ff. 9. 93 butadiene 9. 285. block resistance 116 board 92 branching 18 brightness 84. butadiene-styrene copolymers 11. capillary hydrodynamic fractionation 53 capillary water absorption 345 carboxylated styrene/butadiene (XSB) dispersions 6. 183 f. 332 – natural 90 f.. 90. chelating agent 34 chemical bonding 273 chemical reacting adhesives 192 chemical resistance 116 china clay 86 chip seal 316. 202 degradation time 360 delaminating 336 delamination resistance 221 density 43 diafiltration 58 dialysis 58 differential scanning calorimetry 60 dilatancy 45 dipped gloves 388 dipped goods 383 dipping 384 ff. – coalescing agent 129 – latex 128 film forming emulsion polymer 117 film morphology 70 film whitening 67 401 .C.T. 10 ethylene/vinyl acetate copolymers 6. extenders 132 extensibility 361 exterior decorative coating 146 ff. 202 film formation 128 f. 235 dispersion 1 dissolution 66 double-sided adhesive tapes 209 Dougherty-Krieger equation 47 dry adhesion 299 dry mix mortars 333. 330 ff.I.F. dynamic shear rheometry (DSR) 306 electric double layer 26 electrical tapes 208 electrocoat 170 ff. 330. direct print corrugated inks 119 disc centrifuge 53 dispersing aids 133. 137.. 114.I. – application tests 151 – formulation 150 f fastness 299 fatigue cracking 306 Fikentscher’s K-value 195. 16.I. 17.S.F.) 332 e E. 136. 20. 139 defoamer 6. electrokinetics 56 electrolytes 33 electrophoretic mobility 56 elongation at break 6. systems 342 e-coat 170 eco-efficiency analysis 323 efflux time 44 elastic modulus 62 elastic recovery 237 elasticity 6 elastomeric roof coatings 247 elastomeric wall coating 149 f. d decorative coatings 123 ff. 390 ff. – application tests 148 – exterior exposure testing 148 – formulations 147 – performance tests 147 – standard application tests 147 exterior insulation and finish systems (E. – forms 386 – mix design 388 – polymers 384 – practical aspects 386 – principles 385 – process 383. 63 elpo 170 embrittlement 299 emission measurement 230 – chamber method 230 emulsified asphalts 302 emulsifier coverage 55 emulsifiers 9 emulsion polymerization 3. 360 fillers 86. 352 dry mortar technology 332 – pre-mixed 332 – pre-packed 332 – redispersible powders 332 drying test 116 dwell time 212 dynamic light scattering 49 dynamic mechanical analysis 63 f.Index cup and plate inks 120 curtain coater 289 f.) 332 exterior insulation systems 341 exterior thermal insulation compounds (E. 90. 356 – at atmospheric pressure 16 – at high pressures 16 – mechanism 17 emulsion 1 emulsion polymers 15 – synthesis 15 emulsion vehicle 109 engineering resins 375 environmental impact 325 equipment 39 ethene 8.S. 393 – batch process 393 – continuous process 391 gloves 384. pseudoplastic 45 foam backing 257 foam impregnation 274 foaming 6 foaming behavior 48 fogging test 300 foil duct tapes 208 folding carton inks 118 food packaging 7 form 386 – dipping 386 form cleaning 391 – dipping 391 formulation 86 f. 338.. 288. 224. 227 f. 94. 357 gloss 65. Newtonian 45 flow. 60. induction period 21 industrial maintenance coatings 155 ff. 147 ff. 199 ff. 107. – application tests 156. 156 f. 236.. 336 – packaging 217 flexing endurance 297 flexographic 103 – ink formulation 107 – printing press 105 flexural strength 332 flocculation techniques 57 flock lining 394 floor-covering adhesives 224 flow behavior 44 flow curve 44 flow. 336. 263 f. 195.402 Index finish systems 341 finishing 287 finishing coats 287 flexibility 332. hydration 337 hydrodynamic particle diameter 50 hydrophobicity 332 i impact behavior 376 impact modification 370 impact modifiers 11. 93. 233. – dipping 391 – disposable 391 – fabric supported 394 – polymeric 391 – protective 396 – testing 395 – unsupported 392 gradient polymer elution chromatography 69 grain impregnation 287 gravure 103 – ink 106 – ink formulation 107 – printing press 106 – roll 206 Green Label certification 227 – of adhesives 227 green strength development 230 h heat distortion temperature (HDT) 356 heat resistance 116 heat sensitivity 33 Helio test 100 high float emulsions 314 hot light aging 300 hot mix asphalt 302 f. 178 . 152 f. 158 – formulation 157 – performance tests 156 – salt spray testing 158 inisurf 9 initiation 18 initiator 9. 330. 128... 239. 219. 245. 388 free radical 18 free-radical polymerization 25 freeze-thaw 116. 274. 249.. 245.. 336 – stability 48 functional monomers 26 furniture automotive 222 furniture leathers 295 fusion promotion 359 g gas chromatography 56 gas permeation 68 gel effect 21 gel fraction 67 gel permeation chromatography 69 glass transition temperature 1. 373. 112 gloss enamel 142 glossy film lamination 219 glove dipping 391.. 243. 150. 171. 372 impact resistance 367 impurities 35 f. 168.. 99. 31. 367. 203 f. 141. 391 ff. 338 – mortar 338 flexible 217.. 6. 375 – non-weatherable 375 – weatherable core shell 373 impact performance 369. 117 ff. 154. 70 intrinsic viscosity 69 isolation technology 356 f. 222 laser light scattering 49 latex 3 – definition 3 – paints 125 lawn and garden bag inks 118 layers 166 – automotive coatings 166 leather 283. 321 – application test 321 – pavement 320 Mie scattering 4 milk carton ink 120 milk carton wet rub 116 mineral topcoats 344 miniemulsions 177 403 .. – adhesion test 144 – application tests 142 – block resistance 145 – formulation 140 f. – waterproof 350 f. 177 microorganisms 6. j joint filling compositions 233 k kaolin clay 86.Index – half-life 31 – thermal decomposition 32 – thermally dissociating 31 initiator systems 30 – half-life 30 – peroxides 30 – persulfate 30 ink 93 – absorption 93 – additives 113 – color strength 114 – composition 106 – for films 117 – jet papers 81 – splitting 97 ff. 203 – protection against 203 microscopic characterization 68 microsurfacing 316. 291 – binder 291 – structure 283 leather articles 292 leather finishing 285 f.. 296 – test methods 296 leather industry 283 leather production 284 letterpress 103 life-cycle analysis 324 light-fastness 300 light transmission 49 liquid soaps 7 loaded wheel test (LWT) 322 loss modulus 63 low film forming temperature 112 low temperature cracking 306 lubrication 364 m manufactures 12 manufacturing processes 34 – batch 34 – continuous 34 – plug-flow continuous reactor 34 – semi-batch 35 Maron plot 55 masking tapes 209 mastic products 231 mechanical characterization 62 mechanical stability 48 medical diagnosis 7 melt homogeneity 359 melt rheology 363 melt strength 361 melt viscosity 362 membrane filtration techniques 58 membranes 350 f. metallic effect 186 metallic flog (MF) index 182 micellar nucleation 20 micelles 19 microgels 70. – freeze-thaw stability 142 – heat age stabilitiy 142 – interior flat coatings 140 – performance test 145 – print resistance test 145 – scrub test 144 – stability heat age test 142 – stain resistance test 144 – wall coatings enamels 140 interior enamels 140 internal surface area 3 interparticle crosslinking 67. 87 l laboratory reactors 15 laminating adhesives 217 f. in-line injection 311 interior decorative coating 139 ff. – rotogravure printing 93 – sheet-fed 85 f. 109. 81.. 210 ff. – web offset printing 93 offset test 99 oligomeric radicals 20 opacifying aids 134 – hollow sphere particles 134 – TiO2 134 opacity 82. 94 f. peel value 197 performance grading 304 f.. 313 peel resistance 229 – measurement 229 peel strength 196. 230 optical characterization 65 organic pigments 107 original equipment manufacturers (OEM) 164 – coatings 164 p P&I test 99 packaging tapes 208 paint formulations 125 paints 127 – binder 127 paper coating 76. 331 – dispersion/redispersion 331 particle surface 54 patch mortar 346 paving 303. permanent deformation 306 permanent paper label 203 permeability 7 permeation 66 pH 43 photon correlation spectroscopy 49 pick strength 93 – see binding strength pigments 82 ff. 86. paper machine 78 paper products 120 – inks 120 paper properties 78 paperboard coatings 75 particle morphology 70 particle size 48. 99 multiple wall bags 121 – inks 121 n natural adhesives 192 natural rubber latex 11. – application tests 275 – applications 268 – binders 273 – standard test methods 276 notch sensitivity 370 o OEM coatings 164 offset printing 82.. 93 open time 113. 94. – butadiene 24 – concentration 21 – diene 24 – fox equation 23 – functional 26 – major 23 – polymer design 25 – polymer properties 23 – vinyl monomer 24 mortar 239. 84 – coating colors 84 – coating techniques 84 paper gloss 84 paper industry 75 f. 85. 25 f. 202 – coat 288 – dispersion 108 – dispersion stability 104 – extender 132 – surface treatment 109 – volume content of paints (PVC) 125 f. 286 – migration 286 plastics production 10 . 93 ff.404 Index minimum film formation temperature (MFFT) 59. 132. plastic materials 355 – modification 355 plasticizer 201. 241 ff. 94 monomers 23. mottling 93. 348 ff. 303 needlepunched carpet 255 neoprene latex 303 newspapers 121 – inks 121 non-weatherable impact modifiers 375 non-weatherable PVC formulations 374 non-woven manufacturing systems 270 non-wovens 267 ff. 357 monomer 23 f. 128 model system 17 modified fretting 323 modifier shell effects 372 modulus of elasticity 336 moisture vapor transmission 247 molecular weight 69. 127. particle size distribution 52. 79. . 288. 175. 222 f. – effect 366 – for PVC 359 – for resins 366 – types 364 product resistance 116 propagation 18 propagation rate 21 propene 9 f. – composition 173 – formulations 152 f. 291 – leather-finishing 291 polyacrylates 11 polybutadiene dispersions 291 polychloroprene adhesives 225 poly-coated board 120 polyken probe tack 214 polymer characterization 68 polymer colloids 1 polymer compositions 129 – binder 129 – styrene-butadiene copolymers 129 polymer corporation 131 – acrylic copolymers 131 – specialty monomers 131 polymer design 25 polymer dispersion 2 f.. – polymers used 172 – requirements 172 – surfacer 172 primer coating 151 ff. 205. 41... 154 protective colloid 6. 191. pulp suspension 79 pump-in 311 PVC durables 373 PVC formulations 371 – for building products 371 405 . 207. – application tests 153 – marker stain resistance 153 – stain blocking 153 print bonding 274 printability 93 printability tests 99 printing 103 printing inks 103. 115 – tests 115 printing processes 92.. 179 ff. protective coatings 123. 9 protective films 209 protective gloves 384 pulp 77 ff. 217 f. 103 probe tack method 214 process aids 355 process conditions 37 – branching 37 – crosslinking 37 – monomer/polymer concentration 37 – number of particles 38 – temperature 38 processing aids 359 ff. 273 – characterization 41 – chemical bonding 273 – commercial importance 10 – definition 3 – manufactures 12 – names 2 – properties 3 – suppliers 13 – synthesis 15 polymer films 58 polymer isolation technology 357 polymer modified cement concrete (PCC) 349 polymer strength 6 polymer/cement ratio 337 – flexibility 337 polymeric impact modifiers 355 polymeric modifiers 358 – classification 358 – processing aids 358 polymeric gloves 397 – standard test 397 polymerizable surfactants 30 polymer-modified asphalt 309 polymer-modified mortars 241 polyolefins 10 polystyrene 10 polystyrene dispersions 7 polyurethane adhesives 223 polyurethane dispersions 7. 210 – test methods 210 pressurized aging vessel (PAV) 304 primer 172 f. 10 ff. 332 polyvinyl chloride 10 porosity 93 pre-mixed 332 pre-packed 332 pre-print corrugated inks 119 pressure sensitive adhesives 193. 172. 292 polyurethanes 110 polyvinyl acetate 90 polyvinyl alcohol 88 ff.. 170. 285.Index plywood on lumber shear test 232 polyacrylate dispersions 194. . 217. 21 raw hide production 285 raw materials 8 reactive monomers 9 recycling 10 redispersible powders 329. 204. 94. sub-floor mastics 231 . 80 – low molecular weight 80 – polymeric 80 slot-die coating 207 SLU 345.406 Index q quasielastic light scattering quick-stick 213 49 r raspberry structure 4. 129... 357 – emulsion polymerization 330 spray-dry process 331 spray dyeing 287 spray machine 289 spraying 289 stability 47 starch 79 ff. 90. 339 – adhesion 339 – building materials 329 – building/construction industry 329 – dry mix mortar technology 329 – premixed 329 – pre-packed 329 repair mortar 241. 347 – abrasion resistance 347 – surface 347 slurry seal 316 soap titration 55 solids content 42 solubility parameters 67 solution polymers 113 solution vehicles 112 solvent based ink 103 soy protein 90 f. 273 f. 236 f. 332. – production 237 – slurries 351 – tensile stress values 236 – types 235 seed polymer 39 seeded emulsion polymerization 20 seeded processes 29 selected conversion processes 364 self-adhesive articles 210 – labels 194. spray drying 330. 5 rate of polymerization 19. 86.. 256 ff. 210. 205 – products 199 – tapes 207 self-leveling underlayments (SLU) 345 serum separation techniques 57 shear strength 198.. 90 f. 256 ff. 88. rolling ball 215 roof coating 248 rosin fumarate ester 110 rosin fumarates 104 rotating thin film oven test (RTFOT) 304 rotogravure printing 82 f. static light scattering 51 steady shear viscosity profile 182 steam cracker products 8 storage modulus 63 storage stability 48 stress-strain measurements 62 styrene 10. 346. 216. 94 styrene-butadiene dispersions 6. 303 ff. styrene-butadiene rubber (SBR) latex 227. 350 residual volatiles 56 residue characterization 319 resin 104 – support 110 resinated pigments 109 resistance to flow 237 re-solubility 112 reverse gravure 205 re-wetting 116 rheology control agent 181 roll coating 289 f. 90. 229 – measurement 216 shear thinning 45 shear value 197 shoe upper leather 292 shotcrete process 350 silane-based coupling 235 size press 79 sizing agent 78. 99 rubber milk 3 rub-fastness 298 rub test – metal corrugator 116 rutting 306 s safety 40 – capacity limitation 40 – design pressure 40 – relief devices 40 sand 333 saturation 274 scale-up criteria 15 scrim coat 262 sealant 233 f. 96. 304 ff... 344 torque rheometry 360 toughness 63. 237 f. 296 ff. 350 waterproofing sealing 351 waterproofing system 350 water-soluble binders 185 – properties 185 water-soluble oligomers 4 wax emulsions 113 weatherability 374 weatherable impact modifiers 373 web consolidation 272 – chemical bonding 272 – mechanical bonding 272 – thermal bonding 272 web formation 271 – dry-laid 271 – spun-laid 271 – wet-laid 271 wet adhesion 299 407 . 213 tackifying resins 200 tack measurement method 214 tanning 283 tensile strength 63 termination 18 test methods 97 f... 159 f. 90. Zahn efflux cup 117 volatile organic compounds (VOC) 165.Index superpave binder specification 305 superpave performance grade 304 surface-active materials 27 surface print inks 118 surface sizing 76. 147. vinyl chloride 10 vinylidene chloride 7 viscosity 5 f.. 182 – dilatant 6 – pseudoplastic 5 – shear rate 5 – thixotropic 5 viscosity.. 132 f. 249. 65 tufted carpet 254 ff.. 79 ff. 250. 210 ff. 341.. 258 w wall coatings 139 wall mastics 231 water based ink 103 water impermeability 332 water loss of green concrete 248 water resistance 117 water uptake 67 water-borne binders 176 – aqueous polyurethane dispersions 179 – for automotive coating 179.. 368. u unitary coating 264 v vario gravure 206 vinyl acetate copolymers 6. 130. surface tension 43 surface tension of films 117 surface treatment 108. 133. thermoset coatings 183 thick bed mortar technique 334 thickeners 7. 235. 142 ff. 395 ff. 228 ff. 232. 141. 334.. 335 ff. 168 ff. 151. 84 ff.. 45. 156 f. 114 – physical properties 27 – structural influences on properties 28 surfmer 9 swelling 66 synthetic additives 78 synthetic adhesives 192 t tack 6.. 367 towel and tissue ink 122 traffic marking paints 158 ff. 390 – anionic 235 – dipping compounds 390 thickening 201 thin bed mortar technique 334 thixotropy 45 tile adhesives 240 – test methods 240 tile grouts 332.. 240. 160. 314 – of pigments 109 surfactant 27 ff. – ANSI Standards 341 – EN Standards 341 titanium dioxide 84. 261.. 195. – dry-through time 159 – formulation 160 – no-pick-up test 160 – retro-reflectance 160 transmission electron microscopy 70 transparency 6.. 202 top coats 288... 114 f... 86.. – application tests 159 f. 210. 147 f. 275 ff. 273 f. 11. 181 – rheology control agents (RCA) 181 – secondary acrylic dispersions 179 water-borne coatings 163 – applicaton properties 185 water-borne emulsion polymers 124 waterproofing membranes 244. 340 f. 221 f. 246 f.. 330 ff. 408 Index wet finishing 286 wet pick strength 94 ff. y 322 yellowing 94. 299 Young’s modulus 62 z zeta potential 56 Zosel tack measurement 215 . wet track abrasion test (WTAT) wetting 65 wetting agents 201 wetting aids 136 white-point temperature 60 workability 332 work of fracture 63 woven carpet 254 f.