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FLEXO Magazine : September 2010
Technologies & Techniques Troubleshooting Guide: Pinholes/Fisheyes By Peter Menzian The printing condition referred to as pinholing, also known as fisheyes, is essentially describing the ab- sence of good inklaydown, particularly in solid or solid/ reverse type coverage. It is most noticeable when printing dark colors like black, blue, red etc. Instead of a true solid and smooth layer of the printing ink, the printed image is allowing the paper/film to shine through the ink. It can have the appearance of an 80 to 90 percent shadow dot or screen. This, of course, is very undesirable as it forces the operator to add more pressure, which can create many other issues. Why does iT haPPen? Traditionally, the flexographic printing process was known for its ability to achieve good ink coverage. The original two-roll inking system, slow drying inks, hard tapes, and soft natural rubber plates provided a very high solid ink density. However, in order to compete with gravure or offset, the industry evolved and became more technically sophisticated. While the improvements dramatically enhanced the overall quality and consistency, some of those improvements helped to create the opportunity for pinholes. Today ’s presses are capable of printing at speeds in ex- cess of 2,000fpm, and the average production speed in wide web is between 1,200 and 1,600fpm. To run this fast, we need very fast drying inks, finely controlled ink metering (chamber blades), lower volume anilox rollers, etc. Consequently, in an ongoing effort to print faster and finer line screens, the ink film thickness applied today is a fraction of what it used to be. Less ink means the ink dries faster, and a fast drying ink will lead to pinholing. While this concept is somewhat general, it helps to under- stand why there is such a large concern about pinholing. A more specific reason for pinholing and a more common cause would be the anilox roller selection (see FLEXO August 2010, pages 86-100). All too often, an anilox roller is selected because a printer needs to print “combo images,” solid and fine type, or even screens on the same station—a perfect recipe for pinholing. The same holds true for the plate/tape package on the cylinder or sleeve. Plates have become thinner and harder over the years. All tape manufacturers have done a great job allowing us to select from a huge variety of tapes. Softer tapes are giving us the compressibility we need for high speed and to make up for the inaccuracy in the package. If that package becomes too soft: more pinholing. In other words, the softer the plate/ tape package, the more pinholing will occur. The reason is, the softer the impression, the more ink that stays on the plate. The left sample shows pinholing using a plate relief of .027in. The right shows no Pinholing using a plate relief: .022in. image courtesy DuPont Packaging graphics. 60 FLeXO sePTeMBer 2010 www.flexography.org X-celerate your productivity The all new X-Flex is designed to shrink your problems down •X-tremely reduced waste •X-tra short set up time •X-tremely compact footprint •X-tremely easy to adjust and operate •X-tra flexibility X-Flex platform redefines the market in narrow web printing technology. Reduce your costs and keep quality up, thanks to its X-clusive features: •Gearless Technology •Vision System – one-touch auto register control •X-tra short web path Let the X-Flex set a new benchmark for your company. ESP MATIK, INC. 33, BROOK STREET CT 06110 WEST HARTFORD USA U.S.A. Tel: 860 2322323 Fax: 860 2330162 www.matik.com Innovation With Passion Lecco – Italy www.omet.it Distributed in North America by: X-Flex Launch A4 + MATIK.qxd 22/1/08 4:19 pm Page 1 FLX_Sept2010_mech.indd 60 9/2/10 12:42 AM