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FLEXO Magazine : January 2008
TECHNOLOGIES-& IMAGE 5 At left is the ablated mask, with light area representing intended halftone dot. At right is the resulting dot using patent-pending plate technology, virtually the same size dot as the ablated digital mask Figure 5. lymerization of the photopolymer at the plate surface, which in turn creates the nubby dot profile (See Figure 3). The rounded profile creates many challenges for flexo printers. The balance between solids and halftones is difficult to man- age with impression settings, as digital plates are less tolerant of over-impression. The rounded profile of the dot creates a cutback of strokes and halftone dots, leading some to believe that they print with less gain. However, imaging clarity is compro- mised, particularly in small type and fine detail. As impression is added to digital plates, the ink rolls easily beyond the in- .;J B5E.2 1.2 : 56 000000 WD.20, 9mm 1.2, 0 v x 1.20 300um '" i: l \ \' \ \ \ \ B5E.2 11: 33 000000 WD18, 9mm 1.2, O V xl.20 300um IMAGE 6 Both images show 102 line screen images at 120X. The image at top shows 7% no-bump "nubby" conventional digital dots, while the bottom image shows "flat-topped" patent-pending plate technology with a true 2% dot. Figure 7. - ECHNIQUES tended dot size, and dot gain is difficult to manage. Particularly on direct-printed corrugated, the rounded dot profile makes it impossible to print without fluting of halftones. Still, the digital workflow offers benefits, such as the elimina- tion of film negatives, less opportunity for contamination during plate-making, and improved plate-making efficiencies. The chal- lenge became how to improve the dot profile-how to achieve the flat-topped dot. Incorporating some of the technology discussed above for optimized analog plates, in combination with patent-pending techniques that permit complete polymerization of the intended image areas, a totally new digital plate has been created. This is a flat-topped dot (see Figure 4), on a true digital plate (with no separate mask and no lamination required). This new dot structure makes individual halftone dots more responsive, as they transfer some of the compression to the bevel, instead of all of the compression occurring at the face. The relief depth of the plates is enhanced, by 30 percent to 50 percent over conventional digital. The plate surface represents ex- actly what the laser ablated, and permits control of dot gain with- out bump curves (see Figures 5, 6 and 7). Dot gain is minimized, and can be easily managed with normal cutback curves. These unique digital plates are available in .045, .067, .090, .107, .125, .155, and even in .250 caliper materials, and can be made from any commercially available digital sheet photopolymer material. Testing has been done from 45-line screen to well over 200-line conventional screening, proving this plate suitable for brown-box shipping containers or litho-like wide-web applications.. ABOUT THE AUTHOR: David Price is the sales manager at PRPJIexo in Indianapolis, IN. He's been involved in flexo prepress and platemaking, and the corrugated industry for the past 34 years, largely at PRPJIexo. Ned Wier, PRPJIexo director of research, invented both patented IlExSpect" and patent-pending IlDigital ExSpect" technology. Contact email@example.com or visit their website at www.prpflexo. com for more information. IMAGE 7 The top half of this image shows the actual print of a UPC code from patent-pending digital plates, compared to a film positive ofthe same image for comparison. The UPC was printed with .155 plates on .120 foam, with 280 line screen anilox rolls at 5.7 bcm. The print is crisp and clean, showing almost no gain, yet good ink density. JANUARY 2008 www. f I exog ra p hy.o rg Figure 6 FLEXO