Anilox technology for today’s high print quality environment: The impact of the cell Depth-to-Opening ratioson ink release By: David Lanska Narrow Web Sales Manager Stork Cellramic, Inc. 8399 North 87th Street / PO Box 241370 Milwaukee, WI 53224-9031 ph: 414-357-0260 fax: 414-357-0267 E mail: [email protected] For the label printer, color density and dot gain are two of the most critical factors in the success of a print job. In order to achieve the print quality and graphic impact demanded by print buyers, changes have to be made on-press and in press components. Doctor blades have become standard in most operations. Higher line screen plates are used with high pigment-load, fast drying inks. To prevent dot dipping and muddy plates, higher linecount anilox rolls are specified. As anilox linecount increases, however, the challenge of achieving color strength becomes greater. One of the most common ways to strengthen ink densities is to specify that anilox rolls be produced to ever-higher cell volumes. To achieve these volumes, anilox manufacturers have to engrave deeper. While the depth of an engraved anilox cell significantly affects the ink carrying capacity of the cell, the actual delivered volume may not always benefit from the added depth. By pushing the envelope of depth-to-opening ratios, we decided to try to answer several questions: 05). We would run the tests on a common narrow web press at a local print shop that routinely runs process print jobs at various plate screens up to 200 lines. and 464 centipoise with pH of 9. we had the plates designed with separations of 133 and 150 line screen values. Our goal was to keep as many variables constant as possible. TEST CONDITIONS Plates To gain as much information as possible from a limited number of press runs.04 – 9. Inks We ran most of the trials with one of three viscosities of water based process magenta ink (148. changing only one with each press run. and 204 centipoise with pH of 8.95). . (88. We would run tests with different viscosities of ink on both paper and film substrates. 164. We also decided to perform a subexperiment testing the inks on a set of reverse plates. 328. we developed a set of test parameters using banded anilox rolls.92-8. We also ran a limited number of trials with three viscosities of water based PMS 072 blue.- What is the effect on printed ink density as Depth-to-Opening ratios are increased ? At what D-to-O do we fail to get increased ink density ? How is dot gain affected as D-to-O ratios are increased ? Do D-to-O results vary with viscosity of the ink ? Is the density curve constant for D-to-O ratios at different line counts ? Do we get different results on paper than we get on film ? - With these questions in mind. Our “Flex-odyssey” had 24% 32% 40% 48% 52% 40 30 20 10 0 begun. The second was a 500 LPI engraved to the same set of D-to-O ratios. The ratios we decided on were 24%. The first was a 300 LPI engraved to five specified D-toO ratios. a 900 LPI again with the same set of ratios. we added a sixth band to each roll. This “control” band would also be at 52%. 32%. To insure even impression. 48% and 52%. Anilox Cell Depths: 40 30 20 18 11 10 6 0 25 15 8 30 18 10 36 21 12 39 23 13 300 LPI 500 LPI 900 LPI 24% 32% 40% 48% 52% Depth to Opening Ratio We ran a total of 16 different trials 60 50 marking the gear side of the sample and indicating anilox line count and ink viscosity for the given test. . If both 52% bands were getting similar density readings. 40%. We were then ready for the analysis phase. The third.Anilox Rolls We made up three banded anilox rolls. we would be confident that our impression was consistent from one end of the roll to the other. we hoped to ascertain the point at-which we fail to gain added solid ink density by engraving deeper. we took densitometer readings in the 100% coverage areas in each test band using a manually adjusted densitometer that was calibrated prior to taking our measurements. To even out any error. These readings were then averaged and graphed. 20% and 50% screen values on the 133 line separations. By going well beyond the “optimum” range. we established our D-to-O tests to find the apex of the curve. The D-to-O ratios for our tests ranged from 24% (falling on the low end of this range) to 52% (nearly twice what was considered the maximum acceptable D-to-O). we took a total of 10 readings across three repeats for every band. Because there were visible imperfections including dot bridging and gear marks. the readings were taken in areas of the samples where defects were minimal.ANALYSIS Because the primary focus of our testing was solid ink density. We applied the average standard deviation of the readings to the graph as an indication of the statistical error from the print process. Because of commonly held beliefs that there is an “optimum” range of D-to-O ratios between 23% and 33%. we expected to see the densitometer readings rise in a curve similar to the cell depths. as well as the evaluation process. . (which also had been calibrated). (Readings on the reverse plate trials were done for solid ink density only). Because there was some variation in the averaged solid density readings between the two densitometers. 20%. We took an entirely new set of density readings at Fox Valley Technical College using an automatic densitometer. we decided to use the automatic densitometer for all solid and screen value measurements for this study. but then plateau at some point. We continued our measurements by taking readings on 1%. EXPECTED RESULTS For solid ink density. and at 10%. and 50% on the 150 line separations. We also felt that higher viscosity inks would lay down heavier than their lower viscosity counterparts. . we also expected to see a dot gain increase coinciding with the progression of increased cell depth of the higher D-to-O engraved bands. we expected to see higher solid density on trials run on paper than those on film. Although it seemed fairly obvious based on the absorption characteristics of the two substrates.50 45 40 35 30 25 20 15 10 5 0 24% 32% 40% 48% 52% Expected Solid Ink Density Trend We also expected to experience the disadvantages purported to occur when going beyond the so-called “optimum” range: • • • • Rough cell walls Inconsistent and unpredictable engravings Poor ink release efficiency Difficulty cleaning the cells. Based on earlier published results from the testing conducted by FTROP. Because we would be applying a thicker film of ink with the higher D-to-O ratios. we considered it logical to expect more gain. What we found surprising was our solid ink densities did not plateau with any of the anilox line count / ink viscosity combinations tested on either substrate – even at 52% D-to-O. We actually would have 2 1.8 1.7 1.3 Manual Auto Solid Ink Density Readings Between Densitometers . but when the error bars based on standard deviation of the readings were added.6 1.9 1. the solid ink density readings showed a clear trend toward higher ink densities as D-to-O increased.4 1.ACTUAL RESULTS Solid Ink Density As expected. The more ink the cells carried. The actual density readings did not always follow a nice clean progression.5 1. the best-fit curves indicated the variations were within statistical expectations of normal process variation. the more we put down. While the efficiency of ink release may have decreased somewhat as depth increased (which was not proven by these trials). . Our results for solid ink density at different viscosities also conformed to expectations. Because multi-hit pulsed laser technology was employed for these test rolls. we only had one sample that provided the curve expected.5 1.55 1. we believe these issues may be indicative of attempting to force a non-pulsed (continuous wave) laser beyond its’ capabilities. the greater carrying capacity of the cells at higher D-to-O ratios clearly overcame any reduced transfer efficiency that may have occurred. we found negligible difference in the cell structure between the various D-to-O ratios all the way to 52% on each test roll. regardless of D-to-O ratio. The higher the viscosity. Because the rolls were quickly attended to.1. the anilox roll in use was cleaned with a standard press-wash and a cloth.35 1.4 1.3 1. Between each press run. Many of the graphs had dips or peaks and produced conflicting trends. It was no surprise that solid ink densities on paper were higher than on film or that they followed a very similar curve. As for the rough cell walls and engraving difficulties said to occur when engraving beyond 33% D-to-O. (Note: Each plate had both 133 and 150 line separations so each press run resulted in readings for two sets of samples). (Similar results were also obtained on the reverse plate trials). Out of the 18 different samples on 9 different press runs with screened plates. Dot Gain Our dot gain results were much more surprising. the higher the ink density readings.45 Ink Density 1. we did not experience difficulties cleaning any of the bands on any press run.25 900 MV FILM 24 32 40 48 52 900 MV PAPER Depth-to-Opening had to engrave deeper yet in order to find the apex of the curve.6 1. we found 17 different ways NOT to get a clean. In our case. straightforward dot gain curve. even though our readings did not present one. Other factors appear to have influenced our densitometer readings including such things as ink rheology (flow characteristics). . Our inconclusive results simply indicate a more dynamic and complicated relationship between the many variables at play. (As mentioned earlier. surface tension of the substrates. We were not deterred by these results and took our cue from Thomas Edison who was once asked about the many failed attempts in the process of inventing the light bulb. I’ve just found 10.) It is important to note that a relationship between dot gain and D-to-O may well exist.000 ways that won’t work”. our testing proved inconclusive on the question of dot gain.Consequently. and striations from gear marks and/or web stretch. we tried to stay away from areas of defect when taking our readings. He responded: “I have not failed. some dot bridging. we can conclude that some other variable(s) appear to have had greater effect on dot gain than D-to-O. pushing the . Even where dot bridging was negligible. as the amount and severity of dot bridging occurrences were much higher with the 500 LPI engravings than with the 900’s. From our testing. we believe it is possible to get even higher solid densities beyond 52%. We suspect the primary contributor to dot bridging was dot dipping. (on samples run with 133 and 150 line separations inked by 900 LPI engravings). As a rule of thumb. the industry appears to be adopting a 5:1 ratio. More recently. We did not find the point of diminishing returns for ink density. we still saw conflicting gain curves. dot dipping. we have traditionally recommended maintaining a 4:1 ratio of anilox linecount to plate screen. While we might suspect the latter. From a practical standpoint. The dot bridging experienced with many of the screen values may have been caused by the specific combination of ink rheology and substrate. we dismissed that conclusion noting the conflicting dot gain curves in the traditionally acceptable range of D-to-O ratios between 24% and 32%. or the unintended result of pushing the D-to-O ratios too far.CONCLUSIONS Many factors appear to have combined to produce inconclusive results for dot gain. Because we were able to achieve greater solid ink densities even as high as 52% D-to-O. Our 500 LPI engravings fell below the 4:1 ratio on both the 150 and 133 line separations. and there is a lot more to learn about how cell depth affects print results. What is clear is that achieving greater solid ink density can be accomplished in a variety of ways including. and analyze over 6000 densitometer readings.D-to-O beyond traditional norms presents an option for those who may be struggling to achieve an extremely high solid ink density. log. The results achieved were based on the test parameters described earlier with the tests conducted in a production environment. We can also state with absolute certainty (based on the testing conducted over the last several months) that it takes a bloody long time to take. press speeds. David provides numerous . but not limited to choice of substrate and ink viscosity. support. or perhaps even heavy coating weights for a given job. Inc. We cannot say that we would get the same results with other types of inks. substrates. as that goes beyond the scope of this testing. etc. which appears to have the greatest direct bearing on solid ink density. and the use of their facilities: CL & D Graphics Environmental Inks and Coatings Fox Valley Technical College Biography: David Lanska is the Narrow Web Sales Manager for Stork Cellramic. Pushing anilox D-to-O ratios beyond traditional norms is the approach. So our odyssey continues… I would like to gratefully acknowledge our partners in this project for their time. He has been involved with the flexographic industry for over 20 years. He is an award-winning author.com.training seminars and anilox audits across the US and Canada. David holds an MBA from Concordia University Wisconsin. having been one of the first recipients of the Flexo Magazine Annual Author’s Awards. . by fax at 414-357-0267.Lanska@stork. or by e-mail at David. He can be reached by phone at 414-357-0260.