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FLEXO Magazine : October 2013
and fingerprint. We run an individual fingerprint for each set of variables (press, ink, substrate, etc.), so that when those variables change, we know what the printed piece is going to look like. FingerPrint FiLe When building a fingerprint file, it’s safe to only include the graphics, tables and linescreens that any press will print ef- fectively. But you’ll typically find with a good profile that not all portions will succeed. Why? It’s important when building a file to include linescreens higher than typically printed, reverse copy smaller than usual and highlight dots you typically can- not hold with the current process. When simply preparing for something like moving from one manufacturer’s polymer plate to another manufacturer’s polymer plate, fingerprinting to determine minimum dot, dot gain, line screen and registration is the standard practice. But when embracing new technologies like elastomer and ex- panded gamut, the goal is to build a fingerprint that reaches beyond the boundaries of what you’ve printed successfully in the past. With new technology, it’s good to know the threshold and sweet spot. It’s important not to take the safe route—If a print shop has never printed higher than 120 linescreen, it should put 133 and 150 on the fingerprint, so that at some point, the print will fail. By doing this, a printer can understand exactly where its limitations lie. The printer may find that printing a higher density or a finer linescreen is a real possibility when it hasn’t been before. Production conditions Don’t roll out the proverbial red carpet when fingerprinting. The goal is to print in the same environment and process a printer normally would. This will create an apples-to-apples comparison between the fingerprinting job and a typical job. When preparing for a fingerprinting job, take these steps into consideration: • Be mindful of what average printing conditions are and attempt to maintain them for every print job • Fingerprint with the same ink, density, pressure, speed and operators normally used • Mount the sleeves, bring the press up to speed, set im- pression, check density and pull sheets for evaluation A typical 1-color fingerprint should take less than 20 min- utes from start to finish. The goal is not to create a product that cannot be reproduced on a day-to-day basis; rather, the goal is to develop a process that offers the best quality and repeatability on re-runs and in matching proofs. Key components should be documented and recorded for future review. One option is to build a database for a print- ing process so future runs will be engraved and proofed with curves built from data collected in prior runs. By continuing to take readings from live production, a printer can later tweak the proofing and engraving curves. FingerPrint reAding After it is printed, it is important to precisely read the fingerprint and know what to look for. Here’s a breakdown of Carey Color’s process—remember, we are not always on the pressrun and not always capable of making density and impression changes while the sleeves are running: • Visually check for imperfections like streaking or band- ing, ink bridging and impression • Evaluate visual consistency of ink laydown and density • With a densitometer, measure dot gain in the following areas: 1 percent to 5 percent 25 percent 50 percent 75 percent Solids • Enter the readings into software that plots dot gain char- acterization curves. It’s important to take readings from four places across the sheet and then allow the software to determine an average At times, run several different sleeves made with different elastomer compounds. The purpose of this is to find the best printing combination. By making changes in compounds and anilox a printer is able to pick the material and durometer best suited. When fingerprinting for elastomer, include target areas with slight variations of dot height and shoulder angle. Include a target with a slight bump curve in the mid tone, push targets with the highest possible linescreen ruling and feature text and reverse text down to one point. Story and art: Carey Color Inc. 70 FLeXo OCTOBER 2013 www.flexography.org