Process Improvement for the Narrow Web Printer
Changes in flexographic printing are happening faster than ever. Press speeds are getting faster and faster, and new plate and sleeve technologies facilitate vastly improved print quality. Additionally, the market is increasingly demanding shorter print runs to reduce working capital and allow for more rapid changes in label and packaging graphics, as well as short-term promotions.
While some are able to make capital investments in newer press and materials technologies, many are trying to improve quality and maximize efficiency of existing equipment to remain competitive. One simple way to maximize quality and efficiency is to evaluate the plate mounting tapes used in the printing process, and to ensure that the right tapes are being used for the application.
Being aware of the capabilities of plate mounting tapes, as well as working closely with your suppliers, can help to ensure that proper tapes are being used to maximize both processes and quality. Two key criteria are essential for evaluating plate mounting tapes: adhesives and foams; let’s take a closer look.
Plate Mounting Tape Adhesives
Without a doubt, one of the most important components of plate mounting tapes for narrow-web is the adhesive. The efficiency and process repeatability of mounting and demounting flexographic printing plates can make the difference between being profitable by prolonging the useful life of plates, or ruining plates and having to buy new ones. The adhesive can be the distinguishing factor between having to clean adhesive and foam residue off every cylinder when the job is stripped, or having the tape remove cleanly with little to 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 siliconized liner. This ideal, however, has been difficult for many narrow-web printers to realize.
On a daily basis, most narrow-web printers contend with printing plate edge lifting because of the use of thicker plates on narrow 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 extremely difficult to create an SOP (standard operating procedure) that is efficient and repeatable. In fact, with so many materials and variables in such a process, repeatability is virtually impossible.
When process replication and repeatability in unachievable, process efficiency is impossible. To achieve repeatability and efficiency, the printer must choose a proper plate mounting tape specifically engineered with today’s printing technologies and processes in mind. When selecting a plate mounting tape, be sure to select one that has a plate-side adhesive that is made for the plate material and thickness being used. If an incorrect tape is selected, prevalent edge lifting can occur with thicker plates, or torn or stretched plates with thin plates.
Additionally, be sure to choose an adhesive that is designed to bond to the cylinder or sleeves material being used. Using the wrong “open-side” adhesive can mean either bubbling or labor-intensive clean up.
Plate Mounting Tape Foams
While tape manufacturers are able to help narrow-web printers maximize their process efficiencies with adhesives specifically engineered for the narrow-web plate mounting and de-mounting processes, equally important is foam backing of the tapes. High print quality is directly associated with the quality of the foam used in plate mounting tapes, which serve as plate cushioning or support mediums. Industry suppliers strive to engineer the most technologically 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, a hard foam should be used to promote proper ink density and distribution. 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 density transfer, and pin holing will occur. Conversely, using a hard foam to print a screen or process area will lead to a number of print defects such as dot gain, slurring, or haloing to name a few. A thorough understanding of foam hardness levels and how they affect print quality is essential for producing high-quality products every time.
In trying to ensure the proper use of plate mounting tapes, the most important factor is good communication with plate mounting tape manufacturer.
(800) 426-2181; www.tesatape.com
About the Author
Joe Prunier is market manager – Print & Web Processing at tesa tape, inc. tesa tape manufactures a broad line of tapes designed for specific printing applications. tesa tape representatives can give you advice if you simply tell them about your press, plates, and artwork, to enable them to make a recommendation of the right tape that will improve your print quality, and make your process more efficient and profitable.