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FLEXO Magazine : October 2013
mum compression, 1-mm. per second, 10-Hz. data collection rate). The critical angle was found to lie be- tween 72 degree and 74 degree shoulder angles (See Figure 3). The 72 degree angle dot did not fail at all, whereas the 74 degree dot and all those with steeper shoulder angles always failed. Among the group of dots that failed under compression, there was a clear relationship between the onset of failure and the shoulder angle (See Figure 4). The steepest shouldered dots failed at the lowest compression levels, with decreases in shoulder angle allowing the dot to absorb progressively more compression before failing. While this trend is in itself not surprising, this is the first instance we have seen where dot compression response behavior has been quantified in a coherent manner. AnALYZing resuLts Although this model system is simplis- tic in many ways, it has given research- ers the ability to visualize and quantify phenomena that are directly relevant to flexographic printing. We have quanti- fied the significant impact of shoulder angle on dot deformation and force generation, both of which are major contributors to print gain. Studies indi- cate that steeper dot shoulders reduce the rate of print surface increase with compression, which obviously causes gain through mechanical means. All other things being equal, this should mean that steeper shoulders are a highly desirable trait. However, there is a limit to how far this logic can be extended, because at some point the dot simply becomes unstable to compression and fails to behave as a dot, ruining its ability to create the desired halftone image. In their model system, researchers found this “critical angle” to be between 72 degrees and 74 degrees, and that beyond this critical angle, the onset of dot failure occurs at lower compression levels with increasing shoulder angle. Dot compression studies have also helped explain the favorable print be- havior of plates made with LUX plate- making technology. A print characteris- tic of plates made by LUX is an increase in “impression latitude” on press, such that changes in dot compression have less effect on dot gain (See Figure 5). These model compression studies suggest that this favorable print behav- ior is due to the steep shoulder angle of the LUX-produced dots (shown in Image 5), which causes a decrease in the rate of gain with compression. Perhaps more importantly, the model dot system has yielded insight that enhances plate and platemaking technology development, suggesting design targets for even better gain performance and highlight dot stability in future generations of products. n About the Author: Dr. Timothy Gotsick is the vice president of technology for MacDermid Printing Solutions. He pos- sesses a PhD in organic chemistry from the University of Tennessee. He has been with MacDermid for 10 years. image 4 Figure 3 Figure 4 Figure 5 image 5 www.flexography.org OCTOBER 2013 FLeXo 63 62 FLeXo OCTOBER 2013 www.flexography.org 1-888-478-0998 No Plate Lifting No Plate Mounting Perfect Registration Every time. Discover Your New Media Source for Seamless Imaging Photopolymer Sleeves Laser Engravable Elastomers