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FLEXO Magazine : September 2013
or having the tape remove cleanly with no required cleaning. The adhesive requirements are simple: bond to the sleeves/ cylinders and plates as securely as possible during printing to completely eliminate any possibility of plate edge lifting or bubbling; and when the job is done, remove as easily as a sili- conized liner. This ideal, however, has been difficult for many narrow web printers to realize. On a daily basis, most narrow web printers contend with plate edge lifting because of the use of thicker plates on nar- row diameter cylinders, or damaged printing plates because the adhesion to the plate is so high, they either stretch or tear during demounting. To overcome edge lifting, printers have used primers, magic markers, edge sealers and tapes. Additionally, many printers have used adhesion blockers (such as talc, chalk, soap or shellac) to make removal easy enough so as not to destroy the plates. All of these techniques, however, make it impossible to create a Standard Op- erating Procedure (SOP) that is efficient and repeatable. In fact, with so many variables in such a process, repeatabil- ity is virtually impossible. When process replication and repeatability is unachiev- able, process efficiency is impossible. To achieve repeatability and ef- ficiency, the printer must choose a proper platemounting tape specifically engineered with today ’s printing tech- nologies and processes in mind. When selecting a platemounting tape, be sure to select one that has a plate-side adhe- sive that is made for the plate material and thickness being used. If an incorrect tape is selected, edge lifting can occur with thicker plates, or torn or stretched plates with thin plates. Additionally, be sure to choose an adhesive that is de- signed to bond to the cylinder or sleeve material being used. Using the wrong “ open-side” adhesive can mean either bubbling or labor-intensive clean up. Platemounting FoamS While proper tape adhesives play an important role in optimizing narrow web printing processes, equally important is the foam inner core of the tape. High quality print is directly associated with the quality of the foam core used in plate- mounting tapes. The foam serves as a plate cushioning and support medium. Industry suppliers strive to engineer the most technologi- cally advanced press, plate, and ink formulations to promote the highest print quality from today ’s plate technology. If, however, the wrong foam is used, the print quality can suffer greatly. When evaluating foam, it is important to understand how hardness levels of foams correlate to specific types of printing. For example, for printing dense solid material, hard foam should be used to promote proper ink density and distribu- tion. For printing fine screens with high line screen plates, softer tapes provide the best cushioning effect to act as a “ shock absorber.” This shock absorbing effect mitigates dot gain and any bouncing in the cylinders that can show as banding or gear marks in the print. Using the wrong foam hardness can, however, have a disastrous effect on print quality; as an example, using a soft foam to print a solid area will not allow for sufficient ink densi- ty transfer, and pinholing will occur. Conversely, using a hard foam to print a screen or process area will lead to a number 64 FLEXO september 2013 www.flexography.org