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FLEXO Magazine : October 2009
www.flexography.org OCTOBER 2009 FLEXO 31 Expert + Supplier Sleeves and Rotary Screen pn STORK PRINTS AMERICA, INC 3201 ROTARY DRIVE CHARLOTTE, NC 28269 – USA P 704.598.7171 + F 704.596.0858 firstname.lastname@example.org Rotary Screen Integration Units (RSI's): A complete portfolio of rotary screen print units with up to 36" width and 28" repeat. Ultimate quality results with our unique screen material for our rotary screen units or other rotary screen heads already on the market. RotaMesh® & RotaPlate®. Sleeves: A complete portfolio of sleeves for both flexo and gravure applications. Seamless OptiFlex® ITR blanks. Custom and specialty applications. + + + unfortunately can't be quantified. The post exposure phase of platemaking finishes the cross linking of the photopolymer, or more simply put provides thorough curing of the material. This is something that can't be measured, so determining how much energy required is too little, enough, or too much is a challenge. A good approach to this would be to adhere to your supplier 's recommendation of dosage and when the main exposure (imaging) lamps begin to drop in intensity, increase the dosage for the post exposure so that the total energy received by the plate remains the same. With respect to the detack process, it is not quantified by measurement, but rather qualified by how dry the plate feels after it's exposed to the UVC energy. A plate that has been given just enough UVC energy and one that has been given an excessively high dose will feel the same. However, the plate given the high dosage will be more prone to crack- ing and lose much of its long-term durability. A good way to determine the correct level of energy needed it is to do a step exposure starting with a small dose and increasing the dos- age in small increments until the plate feels adequately dry. In addition, FIRST recommends measuring other properties after the plate is finished. This is not the best time to find dots that are not at full height or washed off the plate, nor is it good to find the plate is still tacky because it was assumed that the lamps are fine. Since FIRST recommends that all finished plate dots be at full height, optimizing and maintaining proper exposure provides some additional insurance of overall plate quality. Measuring small tone value areas on a plate accurately and consistently with a micrometer is difficult. The spring tension or pneumatic pressure on the measurement foot can depress the relatively small total surface area of those dots, yielding an erroneously low reading. This is particularly true with respect to digital plates, the dots of which are rounded at the print surface. Plates with images that utilize specialized screening techniques or FM screening in highlight areas and vignettes to prevent printing of hard edges are also suscep- tible to measuring below full height because of the removal of some dots or the distant spacing between them. If exposures are correct and the other attributes measure in accordance with FIRST, it is likely that the dots will in fact be at full height. In summary, the specifications and tolerances for photo- polymer printing plates have remained largely unchanged since the Premier Edition of FIRST in 1997. Digital imaging of photopolymer brought relief specs to the industry with the Third Edition in 2003. FIRST 4.0 has greatly expanded on methods, tools, and documentation for process control; and specific to platemaking, has given us the first lesson in a new language and a new tool to speak it. So yes, FIRST 4.0 really is different. ABOUT THE AUTHOR: Tom Cassano is an applications devel- opment specialist for MacDermid Printing Solutions. He has been in the industry for 22 years and is a member of the FTA Awards Committee. TECHNOLOGIES & TECHNIQUES
Sustainable Fall 2009