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FLEXO Magazine : January 2010
www.flexography.org JANUARY 2010 FLEXO 41 resolution optics, which allows WKA to produce plates at up to 4,000dpi resolution. The Best Choice 4,000 project was driven not only by WKA's desire to deliver practical benefits to its customers, but also to create something that strengthens partnerships with suppli- ers and provides them with market-leading products. The project, which largely entailed reproducing items that cannot be achieved in the normal resolution range, had three main objectives: • Increase sleeve quality • Achieve better reproducibility • Establish an even better process during sleeve manufacturing The lasered point on the sleeve is made up of significantly smaller pixels, using recently available high-resolution optics, which engraves im- age details with up to three times more pixels than standard resolutions. The laser point, which draws the pixels, is also much finer and falls to 6.35μ (versus 10μ). As WKA results show, this means that the smallest printing point of 45μ in diam- eter is now comprised of 40 laser points (or pixels), instead of the former 16. The high-resolution point, made up of several finer beams, makes for much sharper drawing. Creating such a simple yet highly effective technical foun- dation has a huge impact on the quality of sleeves and print- ing plates, which in turn ensures top-end flexible packaging: • The outlines of the objects are sharper in the stroke area on the plate and, therefore, also on the printed image. Plus the typeface is cleaner and the reproduction offers sharper edges. • The high resolution produces exact print screen points, ensuring the imagers are more stabile. • The greater definition of the high-resolution point leads to more drawing on the sleeve as well as in the print work. • The additional drawing elements ensure better definition of the points printed in the middle tone, and a better- defined point up close. The imaging standard in flexible packaging ranges today from a 42 to 48 (107 to 122lpi) printing screen, although WKA sometimes already goes higher---up to a 54 (137lpi) or even a 60 (152lpi) printing screen. And because demand is so high, tests have already been carried out with an interpolated higher resolution. However, the results offer no comparison with those produced using genuine 4,000dpi from the high- resolution solution. From the Best Choice project, WKA wanted to have at least a 48 (122lpi) printing screen, but ideally would like to move up to the 54 (137lpi) printing screen as standard. This would put the company in a far stronger position, especially with print results often being held against gravure standards. Manufacturing round printing plates has made it possible to print packaging that otherwise would have required gra- vure. For example, sleeves were always an advantage, with very small images and image motifs (inside the packaging), and this is enhanced further with high resolution. IN DAILY PRACTICE The project highlighted many wide-ranging benefits deliv- ered by the high-resolution solution: • The high-resolution points are more durable in the wash- ing process and more stable in printing; e.g., the quality of the drawing in lighter areas is much better with high resolution. • Where you go to the limits in the imager area (where you obtain structures due to grid angling), the printed result is denser and smoother with high resolution. • Moiré, grid patterns or grid phenomena previously ob- served can be eliminated. • Better handling of the printing plate; e.g., the cleaning behavior, print-run stability and reliable repeatability. WKA witnessed a number of other benefits using the high- er-resolution solution that were not anticipated before the Best Choice project began---higher sleeve durability, for example, due to the fact that the high-resolution point is more stable, and the point is better embedded. And in certain areas, faulty plates and repetitions have almost been eliminated. When the high-resolution optics were used in daily produc- tion, WKA reported even more advantages. The company was experiencing difficulties with one particular assignment, where the print work was unclean (especially in the lighter area) because of faulty developed points, and a run in the motif was unsatisfactory. In contrast, renewed imaging with the high-resolution optics delivered the desired smoothness in the run and eliminated the stripe pattern. Another excellent example of the high-resolution optics in action is the printing of carrier bags. They were printed at high speed during the Best Choice project with a 48 (122lpi) printing screen, but when the high-resolution optics were Udo Linke shows one of the sleeves produced with the high-resolution imager. Even at 107lpi, the dots created with the new optics at 4,000dpi are signifi- cantly rounder (right) than those of 2540 dpi (left). PLANTS & PROCESSES
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