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FLEXO Magazine : January 2009
TECHNOLOGIES & TECHNIQUES Sleeves Understanding Variables (Part II) Cushion By Rich Emmerling and Bill Bower Editor’s Note: This article expands upon principles explained in FLEXO’s May 2008 issue, page 56. T he majority of flexo plates used today are mounted using traditional cushion tape mounted to either composite sleeves or steel plate cylinders. There are several sticky- back manufacturers in the industry, each with a variety of cush- ion tape selections. Many of the recent print quality improve- ments can be attributed to advancements in these cushion tapes. As we all know, a compressible layer is necessary in order to print demanding graphics, but they are an expensive consumable item. However, many printers have converted to a different ap- proach by using cushion/compressible sleeves and mounting the plates to these sleeves by using a thin, non-compressible, lower cost transfer tape. Cushion sleeves decrease costs by eliminating the need for the expensive cushion tapes while the cushion layer on the sleeve helps reduce press/plate bounce, which will allow for faster press speeds. Cushion sleeves improve consistency by using a more rugged cushion layer (as compared to cushion tapes). This cushion layer is less likely to break down during long pressruns, which ensures consistent print quality from the beginning to the end of the run, and from run to run of fre- quently repeating jobs. The thickness of the cushion layer is thicker than the standard 15 to 20mm cushion tapes, which allows for wider impression latitude on press. The relatively hard, yet highly compressible surface of the print enhancement sleeve enables the printing of halftone images and solids on the same print deck. In addition, customers using compressible sleeves should expect to see better print quality and longer life from their photopolymer plates. 28 FLEXO JANUARY 2009 Many questions arise when considering this approach. To mention a few: What is the right cushion level? What is the ideal plate thickness and durometer? Can I achieve equivalent or ever better results with the compressible sleeves as compared to cur- rently used cushion tapes? To answer these questions we ran a statistically designed experiment where we varied plate and cushion durometer. The purpose of this experiment was to document the effect that two different plates and three different cushion sleeves had on solid ink density and dot gain as well as to provide guidance to our customers on the ideal plate and cushion sleeve construc- tion for the flexible packaging industry. EXPERIMENT DESIGN The total experiment consisted of 14 trials. These trials con- sisted of a basic experiment of 12 press runs which represented a full factorial design to estimate the effects of Flint Group ny- loflex® plates (ACT D and ACE D) at 0.045in. with three Rotec cushion sleeves (No. 1 - low; No. 2 - medium; and No. 3 - high durometer), and two un-replicated trials consisting of the ACT D and ACE D on typical stickyback tapes. Estimates of internal error were obtained from the available replicates. Trials were run in random order. Press Conditions Substrate: Polypropylene Ink: Solvent based Press speed: 1,000fpm www. f le xography. org FLEXIBLE PACKAGING
End of Year 2008