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FLEXO Magazine : January 2012
With a brief pre-pro, your crew can anticipate problems, adjust inks and settings to accommodate changes, and alert one another to specific settings before commencing a job. It also offers opportunity for more experienced personnel to ex- plain why items are worth noting and to clarify steps to take. SPEED, FLOW & CONTROL The current trend of higher press speeds means every min- ute of downtime equals missed production, and where every minute running product out of spec equals that much more to throw away. As press speed increases, so does the threat of potential pitfalls. Issues not seen before will eventually confront operators. They may see ink flinging or misting—which is rare at lower press speeds. Or, the laydown of the ink may be poor. The likely cause (ink drying too fast) is counterintuitive. One would think that the faster the press runs, the faster ink should dry. This is not necessarily true. The dynamics of ink change at faster press speeds. The inks must fill the anilox cells within the very short duration between the wiping and control of the doctor blades—less than one hundredth of a second at 1200 fpm— and must completely evacuate from those cells and transfer to the plate. Operators are accustomed to higher viscosities printing out stronger and denser, but lower ink viscosity allows better filling and evacuation of the anilox cells, most particu- larly high line count, low volume rolls. This, too, is counterintuitive and an experienced, trained staff will be mindful. Crews need to watch for variations in color density as press speed changes. On start-up, presses, as well as the rolls, plates, cushion back and the inks, are relatively cool and the color densities are bound to change. The ovens and the mechanical processes—the doctor blade contact points, the compression/ rebound of the plate material, and ink recirculation—not only build heat but take some time to reach a state of equilibrium www.flexography.org january 2012 FLEXO 9 www.nag-detroit.com 586.486.1110 North American Graphics is YOUR source for Kodak Flexcel NX Ask about our Print Performance GUARANTEE Flexcel NX DigiCap plates to 60 inches #1SourceBook_NAG_Ad.indd 1-2 11/4/11 5:58:31 PM Knowledgeable press crews hold the key to consistent and repeatable ink laydown. Problems like mottling (top photo, right), can be avoided.