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FLEXO Magazine : February 2009
TECHNOLOGIES & TECHNIQUES D:: III :z: a. cC D:: ø o >< III .... ... D:: III Z Z - ø III III - Controlling Color on the Web You Need to Think Ink By Bill Pope and Bob Loescher G etting up to color is one thing. But staying within color tolerance is another. There are a lot of reasons for why color might start to shift during a run. But most of the time it comes down to one thing-ink. For the most part, if you can control the ink, you can keep color under control. Since UV inks are typically color stable, this article will focus on solvent- based and water-based inks. SOLVING SOLVENTS Let's start off with solvent-based inks. This is probably the easiest of them because you don't have a number of things to maintain. With solvent-based inks, the solvent flashes off and the ink system gets higher in viscosity. As it gets less fluid, the color gets darker, and the ink starts printing dirtier. The quality of the laydown, in this case, is primarily based on the viscosity. To get the viscosity down, you only add to it what you've lost. I don't believe in adding any type of solids to the system if you are not losing solids. Otherwise, when you do adjust the viscosity, you are changing the percentage of color in the system. Once you have proper color, you just want to replace what's being lost, in this case, solvents. Many wide web print- ers are still running two-rolled metering systems; they are not running doctor blades. In this case, viscosity greatly affects color. The hydraulic force of the ink itself will open up that two-roll metering nip and flood the anilox, which then floods the plate. Here viscosity really makes a huge difference. If you change your viscosity by five seconds, at 300fpm you are going to lose control of your color. FLEXO 2009 www.f I exog ra p hy.o rg FEBRUARY
Sustainable Winter 2009