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FLEXO Magazine : October 2010
Technologies & Techniques Let’s Not Forget the Solids steps to Reduce Pinholing in solids with low Volume Anilox Rolls By Rich emmerling and Dan Reilly There has been a great deal of attention spent on how to ease the task of printing screens and dots. Advance- ments in practically all areas of prepress, press design and inks (to mention just a few) have helped to enhance flexo’s print quality. These have helped to address or improve difficult print quality obstacles that separated flexo printed products from competitive printing technologies. Flexo now has a better handle on how to control highlight dot gain, print smoother vignettes and print cleaner longer with less press stops. An area of common concern that I hear on a regular basis is, “how can the quantity of pinholes be reduced, and what is the cause of the trail edge void (straight line of pinholes found at the bottom of solids).” Not being able to control these areas can affect the printed quality of the fine elements in the print job. Flint Group’s Technical Team has worked together to help answer these questions. Over the years, we have worked to gain a better under- standing of how cushion tape modulus, plate durometer and plate surface tension can affect the task of printing smoother solids. The results of these tests have been documented and are well known throughout our industry. It is common knowl- edge that firmer cushion tapes can help to reduce pinholes, and softer plates on some substrates can do the same. How- ever, both can have the side effect of increasing dot gain and can reduce impression latitude on press. As far as the plate’s surface tension (a constantly debated subject), this is controlled by the plate manufacturer. The choice of the ink and the cushion tape, to adjust the compress- ibility of the system to withstand the mechanical pressure in the press, is a primary issue to be considered. The surface energy of a plate is determined by its raw material and is not altered significantly during the platemaking process. Microscopic images of solids areas screened and without surface screening printed with identical press conditions. images courtesy Flint group Flexographic Products. 12 FLeXO octoBeR 2010 www.flexography.org 0 5 10 15 20 1A 1B 2A 2B 3A 3B 4A 4B 5A 5B 6A TotalScore Different Ink Systems at two Viscosities Results of Blind Study trail edge evaluation pinholing evaluation • Two technical teams got together to gain an under- standing of the effect that variations within solvent ink systems have on printing smooth solids. • The print test was completed at Packaging Special- ties in Gainesville, GA using a PCMC wide web press. • Each sample was given two grades of one to five, with five being the highest. • Conclusion: To print smoother solids, use the ideal ink/ substrate combination, highest modulus cushion tape possible without increasing dot gain, reduce the plate thickness and utilize effective surface screening. Scores 5 4 3 2 1 very good result very bad result FLX_Oct10_mech.indd 12 10/15/10 12:31 AM
Sustainable Fall 2010