Mounting tapes, the unsung heroes of the flexographic printing process, can make or break the quality of a print job. Careful selection of plates and cylinders, while immensely important to the final product, can be negated if the chosen mounting tape does not meet the requirements of the print job.
With so many tape choices available, spanning the spectrum of soft to hard and with several combinations of adhesives, selecting the right mounting tape may appear to be a daunting task, but some reference points and a little bit of experimentation can help guide the process.
The Density Issue
Typically, the most pressing issue in selecting a mounting tape is determining how hard or dense the tape should be. Many mounting tape suppliers offer a range of hardnesses that can include variations such as very soft, medium-soft, medium, medium-hard, hard, and more.
According to Joe Prunier, marketing manager for print and web processing at tesa tape, harder tapes are generally best when printing solids, and softer tapes are better when printing high-resolution screens or process work. This is because images created for four-color separations are really arrays of very tiny dots that must be placed accurately onto the substrate to achieve the desired color. Too hard a tape creates resistance on the plate and the dots will be larger than they should be, creating color shifts in the final product.
“If there’s too much resistance and you squeeze that dot too much, it makes it bigger than it should be, which creates dot gain,” Prunier explains. “Dot gain completely changes the color characteristic. A color can come in too vivid or be too dark.”
Yet on the other hand, when printing a solid color or an opaque white, a harder tape is needed because the coverage needs to be as dense as possible, and the resistance increases the color density.
Scott Johnston, a corporate account manager at Anderson & Vreeland, explains that as press speeds are increasing, so is the usage of harder tapes.
“Generally, harder plate materials these days mean faster presses and we’re recommending firmer plate mount tapes.”
Find Your Fit
While some general guidelines can help converters determine which tape will help deliver the best results, finding the right mounting tape isn’t a one-size-fits-all situation. There are many variables at play, and according to Paul Teachout, vice president of sales and marketing at Nilpeter, it sometimes makes the most sense to find the tape solution that provides the best middle ground.
Teachout explains that many converters are running combination work, and instead of creating potential hang ups by working with several different tapes, they are selecting one tape and plate combination that best serves the given circumstance.
Thinking as a converter, Teachout says, “If I’m going to optimize my process I might compromise a little on this end and a little on that end, but at the end of the day, what works best for us is choosing a plate material and a combination tape that fits 90 percent of my work and streamlines my supply chain and my manufacturing process.”
According to Bill Enright, application engineer with Mark Andy Print Products, both the quantity and quality of available tapes has increased in recent years. Because of this, he says printers and converters who may have been using a specific type of tape over a number of years may be best served by trying some new combinations to see if they can improve their results. Tapes are improving, he notes, and the manufacturers’ goal is to improve the process for converters, so exploring new product offerings can often lead to better results.
“There have been a lot of advancements in mounting tapes and adhesive systems,” Enright relates. “They’re not all created equal and converters should try some of the different variations to find out what’s going to give them the best performance.”
Stick To It
When it comes to plate mounting tapes, a common converter complaint is plate lift—when the plate is pulled away from the mounting tape or the roll to which it is attached. Enright finds all too often that the cause is plate rolls or the plates themselves not being properly cleaned.
Enright says using general purpose shop rags for cleaning can be detrimental. This is because when rags are sent out to be cleaned, they get mixed in with rags from other locations and can be returned with unwanted oils lingering in the fibers. When used for cleaning, these oils can wind up on a roll and interfere with tape adhesion.
“When I go into a print shop and they have a problem, the first thing I like to do is load up one of these shop rags with alcohol and squeeze it out over a white surface and show them the discoloration,” Enright says. “This stuff comes out black. You can show them that what they’re using for cleaning is a contaminated surface to begin with.”
Prunier agrees, noting that dirty plates or rollers are highly detrimental to mounting tapes because the tapes are designed to stick to just one surface. So, if a mylar or polyurethane surface has dirt, soap, or another foreign substance on it, the tape will be rendered ineffective.
To properly clean the surface, Prunier says a paper towel will work fine and can be used in conjunction with isopropyl alcohol or a makeup solvent.
“Just take simple, benign, cheap, widely-available materials and make sure that what’s on the back of your plate is not inhibiting the material from working the way it was designed to,” he says.
Because there are so many variables and options to choose from, Prunier recommends using tape suppliers as a resource, explaining that the proper advice can be just a phone call away.
“View the people who provide the tape as a value added resource,” he says.
Cory Francer is an Analyst with NAPCO Research, where he leads the team’s coverage of the dynamic and growing packaging market. Cory also is the former editor-in-chief of Packaging Impressions and is still an active contributor to its print magazines, blogs, and events. With a decade of experience as a professional journalist and editor, Cory brings an eye for storytelling to his packaging research, providing compelling insight into the industry's most pressing business issues. He is an active participant in many of the industry's associations and has played an essential role in the development of the annual Digital Packaging Summit. Cory can be reached at cfrancer@napco.com