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FLEXO Magazine : March 2009
TECHNOLOGIES & TECHNIQUES easier. After all, ink systems are chemistry. They are a sophisticated blend of solvents, amines, resins, pigments and so on. I have never met many press operators with a chemistry degree. The last thing we need is to be creating work off ink during set up while the press sits idle. The best way to achieve acceptable color match is to proof the inks before we go to press. This can easily be done in the ink room with the use of a handheld proofer system. We can correlate the proofer rolls to match that of the standardized anilox inventory. Now that we have standard- ized volumes on press, the ink technicians will have a consistent target to shoot for. Depending on the ink system being run- UV, solvent or water-based-we can de- termine the proper set of proofer rolls for predictable color matching. UV inks are loo-percent solids; what goes on the web stays on the web. UV inks will correlate one to one with the press rolls. Solvent and water-based inks have high percentages of vehicles and evaporants that flash off in the drying process. This needs to be taken into consideration when select- ing the proper proofer rolls. Typically you will see proofer rolls with a lo-percent to 3o-percent increase in volume over press anilox to obtain proper color match with thinner ink film print- ing. It will always be easier to err on the high side and extend then it would be to have to build color. Always consult with your ink and proofer roll supplier when determining the proper proofing systems. They have well defined processes to support the selection or proofer roll engravings and color matching guidelines. FIGURE 4. Handheld proofing system. - FIGURE 3. Banded polymer layout. PHOTOPOLYMER AND BACKING MATERIALS As with any good flexo reproduction process, the selection of plate type and backing is very crucial. Both of these elements can directly affect SID, contrast and dot gain. There are a wide variety of photopolymer and backing materials available. The newer digi- tal plate materials are harder in durometer and offer increased line-screen capabilities for higher definition printing. This makes the selection of backing material even more important than ever. When choosing the proper combination of plate and backing you must first consider the type of work being done. The cushion backing can come in a variety of densities. The re- production required will determine the correct density and plate Typically for high-line screen process printing a harder duro meter plate will be used with a lower density backing. This way, the dot structure will have rigid support and the backing will absorb the shock of the printing impression. MARCH 2009 www.flexography.org FLEXO
Sustainable Winter 2009