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FLEXO Magazine : February 2009
TECHNOLOGIES & TECHNIQUES Once you are at a steady speed and state of color on the press and are running at the desired speed, there should be no ad- justments that are about pigment. It should all be about viscos- ity and pH. When your inks are drying appropriately, and your viscosity and pH are inline, you should not have to do anything else until you add fresh inks. In that case, you may have to make the same adjustments you did when you got up to color the first time. MANY MEASUREMENTS To measure and control color on press, there are two paths: densitometry and colorimetry. Densitometry is based on the complimentary filters of the process colors cyan, magenta, and yellow and is the original method of "color measurement." However, density is not color. Advancements in instrument de- sign have allowed for cost-effective solutions to measure color as the human eye sees it-colorimetrically. Here, the reflectance of the color across the visual spectrum is measured and values are calculated that define color in terms of lightness, hue, and chromaticity. This is a much more accurate way of measuring color, however, it can be very complicated to interpret the numbers at press-side and make decisions on what to do. Therefore, a common approach is to use both methods to- gether: verify the color with colorimetry, then determine the corresponding densitometric value(s). Then, for process control on press, operators can use densitometry and react to values that follow a simpler scale (higher or lower values compared to the target) and have an easier time of making adjustments. The main caveat, however, is that the ink formulation cannot change-there can be no introduction of components (pigments, etc.) that change the color of the ink. The risk you run is having the same density value(s), but having a different color. This even goes for changing to a new batch of the same formulation. If so, verify again with colorimetry, then control with densitometry. Finally, it's also fine to control the process with just colorimetry- it's just more complicated and requires a good understanding of color in three-dimensions.. ABOUT THE AUTHOR: Bob Loescher is technical seroice rep- resentative at Water Ink Technologies. He has 29 years in flexo print- ing and related industries. He has seroed 11 years in his current role. Loescher also spent eight years working with acrylic resins supporting the water-based flexo ink industry at BF Goodrich. He has two years' experience in prepress/graphic arts at Pinnacle Graphics, and eight years as press operator/production superoisor for a wide web converter. Bill Pope is technical director of the FT A. Winner of the PIt, 2008 Technical Innovation Award X-celerate your produdivity 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-elusive 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. -FLEX Distributed in North America by: 33, BROOK STREET CT 06110 WEST HARTFORD USA U.S.A. Tel: 860 2322323 Fax: 860 2330162 www.matik.com ø OMET Innovation With Passion Lecco - Italy www.omet.it
Sustainable Winter 2009