HYDROCEROL® – The right Chemical Foaming Agents for your ApplicationNeil Whelan, Anne Witte, Thomas Holzberg 1. Introduction Picture 1: Clariant Masterbatches is recognised world-wide as Foaming and nucleating agents are available as both, powders and various sizes of the leader in color and additive solutions for the granules. plastics industry. The family of HYDROCEROL® chemical foaming and nucleating agents is a key component of Clariant’s comprehensive product line. Foaming thermoplastics with HYDROCEROL® masterbatches adds excellent toughness and rigidity, enabling the design of more functional, complex parts. Aesthetics and processability can also be enhanced. HYDROCEROL® concentrates are specified world-wide to reduce weight, improve performance, and optimise costs in products ranging from business machine housings and medical packaging to material handling systems, automotive parts and window profiles. With superior technology, global presence and customer commitment second to none, Clariant is your partner in achieving leadership in your market. 1. Foaming Agents Foaming agents are used to produce foamed products for thermoplastic polymers. Several types of thermoplastic resins such as PVC, PE, PP, PS, ABS and TPE are foamed commercially. Foaming agents can be either a physical gas or a chemical that decomposes in a polymer melt during processing, and releases a gas. In both cases the gas has to be homogeneously dispersed and dissolved in the polymer melt under pressure in the extruder. When the melt exits the die, the pressure drops and the gas expands the melt, creating a cellular structure in the polymer. 0.1. Chemical Foaming Agents Chemical substances that decompose or react by the influence of heat are called chemical foaming agents. Solid organic and inorganic substances are used as chemical foaming agents. The solid residues react as nucleation centres. This leads to a finer cell structure and a better solubility of the gas in the polymer melt. Requirements to an ideal chemical foaming agent are: • Decomposition reaction has to be in a defined temperature range, according to the requirements of the used polymer • Avoid very fast reaction (explosion) by decomposition of the chemical foaming agent and prevention of a heat build – up or burning • Easy mixing and uniform dispersion of the chemical foaming agent in the polymer • High gas yield and feasibility of the chemical foaming agent • Approved for food-contact applications • Chemical foaming agents should not be corrosive for tools and melt exposed surfaces. • Low influence on the mechanical properties • No discoloration and plate out of the effects The variety of demanded properties leads to the fact that no chemical foaming agent can satisfy all of these properties. Therefore certain processes often require individual foaming agent formulations. 1 140 – 165 120 – N 150 2 C . 2 H 2 O 0.4´OBSH Oxybis(benzolsulfonylhydrazide) 5-Phenyltetrazole 5 .0.1. Already at 120°C the evolution of gas begins. citric acid and its salts are used as endothermic chemical foaming agents. H 110 – 140 120 – N 3 C 140 2 ) O .PT p-Toluylensulfonyl. O 2 H 240 – 250 190 – N . Exothermic Chemical Foaming Agents After the activation energy for the decomposition is achieved. The reaction stops if the melt temperature of the polymers drops below the reaction temperature.1.220 150 – s C 300 e O s . a 155 . which generate heat during decomposition • Endothermic chemical foaming agents.TSH hydrazide Decompositio Gas yield M n temp.Chemical foaming agents are divided by their enthalpy of reaction into two groups: • Exothermic chemical foaming agents. the reaction needs no more external energy. Endothermic Chemical Foaming Agents For the decomposition of endothermic chemical foaming agents energy is needed during the whole reaction time.TSS semicarbazide p-Toluylensulfonyl. Substances like sodium bicarbonate. The energy excess has to be removed by intense cooling. 2 . which absorb heat during the decomposition 0. 2 210 2 O 215 .0. [°C] [ml/g] a i n 205 – 215 280 – N 320 2 g . Important exothermic chemical foaming agents are: Description Short Structural formula Azodicarbonamide ADC Modified ADC 4.235 120 – N ( 140 2 N . The evolution is slow and homogenous. the temperature of the melt causes the decomposition reaction of the CFA. 3 . Gaseous components are generated and dissolved in the polymer melt by the extrusion pressure. PETG TPE. profile and tube. Foam extrusion is used for the manufacture of cast film. Applications HYDROCEROL® foaming and nucleating agents can be used for foaming most thermoplastics: • • • • • • • • PP. This cellular structure results in density reductions of 15 to 30% in films and sheets and 20 to 40% in pipes. sheet. the foaming agent masterbatch (or powder) is either mixed or fed together with the polymer. Picture 2: Extruded Profile (PS. The wide variety of applications for foamed extrusion products ranges from decorative ribbons through thermoformed packaging to profiles for picture frames and foam core pipes. Extrusion In the extrusion of chemically foamed products. HDPE. profiles and boards. During processing.1. The pressure gradient between the extrusion pressure and the ambient pressure at the die exit causes a cellular structure to form within the extrudate – in much the same way uncorking a bottle of champagne causes the wine to foam. ABS PVC PET. TPU. LDPE PS. blown film.Advantages of endothermic chemical foaming agents: • • • • Shorter machine cycle times compared to exothermic CFA´s Food contact approved No discoloration and odour Convenient temperature control 1. Also a better workability (sawing) and higher output of the laminated profile is reachable. TPR PC PA and most polymer blends The foaming of thermoplastic resins offers the following advantages: • • • • • • • weight reduction raw material saving thermal and acoustic insulation elimination of warpage and sink marks increase in wall stiffness (sandwicheffect) surface textures as a design . PVC) A weight reduction up to 30% is to achieve.tool processing aid 0. For example: for a 30% weight reduction.Most conventional extruders can be used for foaming. This delayed foaming is referred to as a “halo“ and it indicates that there is no foaming or expansion occurring in the die or extruder. During the cooling process of the foamed melt. it is very important to select the proper resin grade. this may result in a poor adhesion of the two layers. The resin selection is key because the foam layer has better flow characteristics (lower apparent viscosity) compared to the solid layer of the same resin. If the layers differ too much in viscosity. Co-extruded foam products are produced with a foamed inner layer. The use of melt pumps can improve the extrusion process in the following ways: • the melt flow is stabilized • the pressure in the barrel can be increased • less shear stress An optimum foam quality will be achieved when the melt exiting the die is free of bubbles and the foaming starts after the die. decorative ribbons or packaging tapes. The use of screen packs is not absolutely necessary in foam extrusion as impurities. For the outer layer.g. unfoamed outer layers. a “softer“ resin is recommended. PS) Thermoforming without any problems. and solid. if the following requirements are fulfilled: • the melt temperature must be high enough to ensure a complete decomposition of the foaming agent • the pressure of the melt must be kept high enough to keep the gas dissolved in the polymer melt until the melt exits the extrusion die. If screen packs are used. it is important that they are not too fine. In this case. Picture 4: No-pressure pipe (PVC) CO-Extrusion for a better surface. This will compensate the expected expansion.roll is too short: the time for the foam-formation is too short • the distance between die and the chill-roll is too short: the foam structure will be crushed • the haul-off speed is too high to produce a thinner film: the foam bubbles are highly stretched and as a result the density of the foamed film may increase.15%. by 50% weight 4 . Picture 3: Food trays (PE. Higher output compare to the compact pipe. the weight reduction has to be considered. the following problems may commonly be encountered: • the distance between the die and the chill . Chemical foamed or nucleated (Direct gassing) with a weight reduction of min. this can result in a pressure drop and possible prefoaming. e. gels. or additive agglomerates are usually not visible. while a resin that is somewhat harder is recommended for the inner. When adjusting the die gap. Sometimes this type of orientation is desired. the gap should be reduced by 30% compared to a solid sheet of the same thickness. Otherwise. foamed layer. PS and PET. such as PP. The use of a shut-off nozzle is advantageous to prevent drooling and premature foaming. 0. The tooling strength for foam injection molds need not to be as high as for solid injection molds as the internal pressure is lower. particularly in thick-wall parts. Steel/chromium alloys (approx. HYDROCEROL® PEX formulations are available for most common packaging resins. which generate heat during the decomposition. Density reductions between 15 to 30% are usual in standard monolayer as well as in coextruded (e.15% weight 5 . reduction of appr. Some particulars have also to be considered in the design of molds for foamed parts. If a shut-off nozzle is not available it is helpful to keep the barrel/nozzle pushed against the mold without retraction during plasticizing. A-B-A) applications.reduction. enabling a thermoforming without surface defects.1. 20% cycle time and 10 . 13% Cr) are often the preferred mold material due to their longevity and cost/performance. fine cell structure smooth surface reduction in cycle times rapid degassing-leading to time reduction in the downstream processing operations (e. HYDROCEROL® PEX Series The HYDROCEROL® PEX Series is specially designed for Packaging EXtrusion applications where the thermoforming characteristics of the finished film are a key issue. PE. Picture 5: Containers + Boxes (HDPE/PP) In addition to the reduction/avoidance of sink marks and warping. PEX Series foaming agents produce an especially fine-celled foam structure. Endothermic products are characterised by the fact that they consume energy during decomposition. Injection Molding Endothermic foaming agents have proven to be especially useful in foam injection molding.g. compared to exothermic products. When designing the cooling channels they must provide sufficient cooling to avoid post-expansion. The gates and runners should be designed to achieve a quick and uniform filling of the mold. It is important that the mold is vented at the end of the flow path and that the size is sufficient to withstand the high injection speeds.g. which leads to the following benefits in the process: • • • • • • • uniform. coating) no discoloration In principle CFAs can be processed on almost any commonly available injection molding machine. creating the typical structure. that includes solid skin and cellular core. The mold cavity needs to be filled at high speed to ensure that the dispersed gas bubbles create the necessary expansion after injection. Density reductions of 5 to 10 % can occur with the use of these products. At the nozzle the temperature can be reduced by 10 . Typical examples are injection molded automotive. ITP Series foaming agents will produce a micro-cellular foam with no adverse influence on surface appearance. Direct Gassing Physically blown foams of low density are manufactured by the direct gassing method.1. No holding pressure is applied for foam injection molding to avoid foam compression except when thicker outer skins are desired. It is obvious that thicker walls favor the formation of foam. In these cases a holding pressure similar to molding solid parts should be used. The weight reduction greatly depends on the part geometry. Sink marks and warpage are caused by material shrinkage during cooling. finecelled foam structure. structural foam parts display a mat surface finish.20% to increase the back pressure. electronic and appliance housings. In some cases it is recommended that an accumulator is employed. 0. HYDROCEROL® ITP Series The HYDROCEROL® ITP Series is designed for use in thin-wall parts requiring the elimination or reduction of sink marks and warpage. Reduction of warping and15 . Picture 7: Housings (PS. etc.20% weight. 6 .When setting the cylinder temperature the melt temperature in the feed section must be lower than the decomposition temperature of the CFA to avoid gas losses through the material hopper.) Easy filling of parts with a long flow path. ABS. Picture 6: Wine corks (EVA/PE/TPE) The Production is only possible with CFA. In the compression zone the melt temperature should be sufficiently high to generate the maximum gas yield. A small amount of special CFA formulations will reduce these significantly. Defined diffusion and de-corking properties The injection pressure must be high enough to obtain a high injection rate. Glossy surfaces can only be achieved using optimum process parameters and specially formulated masterbatches that provide an excellent dispersion of the CFA in the melt. The main reason why CFAs are used is to achieve part weight reduction which in turn saves material cost. by a weight reduction up to 50%. They often appear in parts with ribs and bosses. leading to lower resin consumption. Typically. Using our active nucleating agents gives a more regular. The expansion pressure presses the melt against the cold wall of the mold. Inactive nucleators include solid materials with fine particle size such as talc. polymers must be capable of supporting cell growth and cell stability. An increased melt strength enables the processor to achieve lower foam densities. calcium carbonate and silica. insulation and gasketing. Lighter weight thermoplastic foams with densities down to 15 kg/m3 can only be produced in a so called direct gassed extrusion process with physical foaming agents. such polymers as polyethyleneterephthalate (PET). fine celled foams will expand more rapidly than coarser foams. there are different ways to increase the melt strength: • with GPPS a higher melt strength can be obtained by adding HIPS or EPDM • the melt strength of LDPE can be raised by adding LLDPE • the foamability of standard PP can be improved by adding high melt strength PP The direct gassed extrusion of virgin resins without any additional additives delivers a rather coarse foam structure. To achieve a fine and uniform cell structure the addition of a so-called nucleating agent is necessary. a high melt strength avoids bursting of cell walls thus improving the foamability of a resin. As the expansion of the foamable melt is a diffusion controlled process. These materials function as nucleators by providing an interruption in the system when the blowing agent comes out of solution to start a bubble. The melt strength characterizes the ability of a resin to keep thin melt films stable. Mixtures based on sodium bicarbonate and citric acid or ready to-use masterbatches are 7 . MDPE) are foamed to produce protective packaging. insulation and gasketing. cushioning.Foam extrusion with chemical foaming agents can achieve foam densities as low as 500 kg/m3. When manufacturing light weight forms. labels. Picture 9: Pipe insulation without and with nucleation. Depending on the type of resin. also act as nucleating agents. The foam structure is homogeneous and fine To produce a good. inactive (or passive) and active nucleators. clay. As a result. There are basically two types of nucleating agents. Recently. diatomaceous earth. Chemical foaming agents. The efficiency of these materials is effected by the shape and size of the particle. Polyethylenes (LDPE. low density. The number of nucleating sites also influences the rate of expansion. polypropylene and others have become commercially interesting and are showing promising growth opportunities. wire and cable jacketing. Several types of thermoplastic resins are foamed commercially by the direct gassing process. Picture 8: Pipe insulation HYDROCEROL act as nucleant. larger cells need longer to grow because the foaming agent must diffuse further through the polymer melt to the next growing cell. materials which generate gas upon decomposition. a nucleating site means a starting point from where the foam cells start growing. The nucleating agent provides nucleating sites where the physical foaming agent will come out of solution during foam expansion. closed celled foam structure in the direct gassing process. If a nucleating agent can provide a higher number of nucleating sites then more cells are formed and the average cell size will be smaller. Foamed polystyrene products include food containers. LLDPE. HYDROCEROL® NUC grades are also available as blends of active and inactive nucleating agents. the system can run out of control which leads to drastic variations in the foam quality and physical properties of the final product. 8 .or PS-based masterbatches. combining the advantages of both types.widely used as nucleating agents. For a similar foam quality the dosage of an inactive nucleant has to be 3 to 8 times higher than that of an active nucleant. corresponding with the resins most commonly used in physical foaming. The dosage of active nucleating agents directly effects the foam quality (cell/cm2) and the foam density (kg/m3). 1. The higher levels of inactive nucleants can be particularly disadvantageous if reclaimed materials are fed back into the process. The nucleation of direct gassed systems with chemical foaming agents is called “active nucleation“. such as talc. When using regrind which contains inactive nucleators. They are available as either active foam nucleators or as chemically inactive nucleating masterbatches. These special. As a result of the higher efficiency of active nucleators they can be used at significantly lower use levels versus inactive nucleators. HYDROCEROL Product Line Clariant provides a diverse and comprehensive range of chemical foaming and nucleating agents. HYDROCEROL® NUC Series The HYDROCEROL® NUC Series is designed to provide process-relevant nucleation solutions to specific application requirements. HYDROCEROL® NUC grades are typically supplied as PE. Clariant can custom-formulate additive masterbatches to meet the most stringent and demanding application requirements. The products listed on the following pages represent only a sampling of the comprehensive line of HYDROCEROL® additive masterbatches. Active nucleators are generally more efficient and provide smaller and more uniform cells versus inactive nucleators. patented products are supplied either as powders or as masterbatches. In addition. HYDROCER OL Grade EXTR IM DG PE PP PVC PS/ABS Eng. TP PO E. M PO M TP E TP E TP E TP E. Plastics Endothermic Foaming BIH Agents BIH 20 BIH 40 BIH 70 BM 40 BM 70 CF CF 20 E CF 20 P CF 40 E CF 40 S (Mod) CF 70 CLM 70 Compound Powder PE PE PE PE PE Powder PE PE-Copo PE PS PE PE Powder _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ TP E. PC PC/ AB S 9 . M PO M TP E. TP PO E. PO M _ _ _ _ _ _ _ _ _ _ _ HK 40 B CT 583 HDPE PS _ _ _ _ _ _ _ _ PE T. IM: Injection Molding.HK 70 HP 20 P HP 30 E HP 40 P PE PE-Copo PE PE-Copo _ _ _ _ _ _ _ _ Exothermic Foaming Agents AB 40 E 232 397 529 PE Powder Acrylate Acrylate _ _ _ _ _ _ EXTR: Extrusion.com Anne Witte Clariant Masterbatch GmbH & Co. Contact Do you want to know more about HYDROCEROL®? Please don´t hesitate to contact us: Neil Whelan Clariant Australia _: Neil. DG: Direct-Gassing (Nucleating _ Suggested _ May be used Agent) after testing 1. OHG Marketing HYDROCEROL _: Anne.com Thomas Holzberg Clariant Masterbatch GmbH & [email protected] 10 . OHG Technical Service HYDROCEROL _: [email protected]@clariant. Available Brochures: 11 .