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FLEXO Magazine : February 2009
..-\.t- '.,.--" , What is ::: TEST? TEST is a joint effort between the FFTA and complying educational institutions to expand technical skills required by a continually advancing flexographic process, bringing state- of-the-art professional development solutions to the flexographic industry. . TEST Technical Tidbit: Each month TEST will feature a technical tidbit from one of our part- ners.lfyou have a question you would like to be put to TEST send it to: email@example.com Our question goes to our friends at Dunwoody College of Technology Dea r TEST, I have been a narrow web flexographic press operator for the past 17 years and have recently changed jobs to the platemaking department. I currently manufacture analog flexographic printing print plates for our pressroom using a solvent-wash system. Upon my transition, I have encountered multiple problems with the stability of the relief of our flexographic print- ing plates. The plate manufacturer recommends that I do a back exposure step test. However, I have absolutely no idea what this means or how it is done! Could you please provide for me an explanation of the back exposure test and possibly provide a procedure for performing this test? Sincerely Mr. Platemaker Dear Mr. Platemaker, The primary reasons we perform a back exposure on a flexographic printing plate is to fully attach the floor layer of the plate to the polyester backing and establish the relief depth. During the back exposure, the polymer is cured to form a solid in a progressive migratory manner. The longer the exposure or the more UV-A energy absorbed, the thicker the floor becomes. Variables that can affect proper exposure include differences in UV sensitivity for the photopolymer, and UV energy output, especially as the UV lamps age. Back-exposure tests should be conducted regularly to establish the rate of cure for particular combinations of photopolymer materials and exposure equipment. To perform this test, we start by exposing a sample of the plate material through the polyes- ter backing sheet on the exposure equipment. It usually works best by exposing a strip 12in. long and 3in. wide. Using a marker, measure and mark all of the steps and exposure times you wish to test leaving both ends of the strip with zero exposure. Please note, the exposure times should be stepped according to the plate material and the equipment manufacturer's recommendations. The resulting thickness steps produced in the plate material are recorded and charted to form a back-exposure guide for the particular material and machine. :1- .. TEST About our TEST Partner: The Dunwoody College of Technology Graphics and Print- ing Technologies program is a two-year course offering three program tracks-Design, Prepress, and Press. Regardless of the track that students choose, all classes incorporate state- of-the-art equipment in conjunction with hands-on learning. Dunwoody received the Harper Flexo College of the Year award in 2002, 2003, and 2006. Dunwoody College of Technology, an FFTA Educational partner since 1999. ..... Founding Sponsors Ron&Katherine Harper <f]HARPEJr
Sustainable Winter 2009