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FLEXO Magazine : May 2012
Here is a scenario that involves a very absorbent substrate (See Figure 4): • Absorbent substrate ink = “dives” into substrate • Ink “dives” into substrate = want a lot of ink • Want a lot of ink = high volume anilox roller • High volume anilox roller = thick ink film thickness • Thick ink film thickness = more dot gain • More dot gain = lower LPI graphics • Lower LPI graphics = larger size images • Larger size images = farther view- ing distance • Farther viewing distance = registra- tion is not as critical A heavier ink film thickness might cause the press to run slower because more time or heat is needed to dry the ink. A heavier ink film thickness can re- sult in dot bridging or dirty print, which is very common in flexo (See Figure 5 and Figure 6). All the images were printed on a two-roll system with reverse angle doc- tor blade. The blade material was thin steel and lamella tipped. Print results can be quite different with a plastic or composite doctor blade. This is where flexographic decisions must be made carefully because a different inking system configuration can result in dif- ferent printing characteristics. NASCAR drivers spend time running trials with their cars to get the best per- formance for each track they race on. They tune the cars to the tracks. Printers and graphics teams must do the same tuning on their racetrack: the substrate. All decisions begin with the substrate and a good printer must stay in tune with it. Ink metering configurations will need changing—and testing. n About the Author: Kern Cox is an instructor at Clemson University in the Sonoco Institute of Packaging Design and Graphics. Kern regularly con- ducts industry education workshops and seminars related to all the major printing processes. He also coordinates product testing and R&D projects re- lated to printing and packaging. Kern has more than 15 years experience in the printing industry. The Sonoco Institute at Clemson University is a state-of-the-art facility with 21st century printing and packaging resources. It can be found at www.sonocoinstitute. com. Kern can be contacted at kernc@ clemson.edu or 864-238-4705. Editor ’s Note: Next month, FLEXO presents its annual Anilox Roll & Doctor Blade Selection Guide. Both print deck components and the critical compatibility between them will be profiled in depth. Figure 6: Mid volume anilox (3.0 BCM) allows for good ink coverage on solids. This particular substrate allows for clean halftones at higher graphics LPI because of ink absorption. www.flexography.org May 2012 FLEXO 51