Learn about the realities of UV-ink compatibility and the obstacles manufacturers face in developing all-purpose UV formulations. Also find out how new exposure guidelines for a potentially hazardous UV-ink additive may impact your business.
By Tom Keegan
It's the P-O-P printer's dream--a single UV ink that works for all P-O-P substrates, requires no additives, presents no post-printing application concerns, and simplifies ink purchasing and inventory management. The concept always has been appealing to screen printers, but how realistic is a true, all-purpose UV ink? The all-purpose-ink concept became popular in the mid 1980s when the great conversion from solvent-based inks to more production-friendly UV formulations began. And like all popular ideas of the past, this all-purpose concept is coming into vogue once again in the form of new UV inks that are compatible with multiple P-O-P substrates. The rebirth of these inks comes with some changes, however. First and foremost is that the new formulations work well on a wider selection of materials than their predecessors. But manufacturers are wary of creating expectations that the inks can't meet, and most have decided that the term "all-purpose" is a little too ambitious. So the new UV inks are described as "multipurpose" formulations. Today's multipurpose inks have overcome many limitations that existed in earlier all-purpose varieties, due primarily to the fact that a greater assortment of chemical components are now available to ink manufacturers. These components allow multipurpose UV inks to provide performance capabilities that were not available in the past. Inks are now formulated with oligomers, monomers, and initiators that provide faster, stronger, and better adhesion to a broader range of substrates than ever. But even with these improved ingredients, UV inks still have limitations. Flexibility Consider the resin type employed in the ink. Epoxy and acrylic resins are known to form more rigid films. Urethane resins usually are considered to be soft and flexible. In reality, all of these resins are available in a wide spectrum of hardnesses, from flexible to rigid. But resins and monomers cannot be both rigid and flexible at the same time. This would defy the laws of physics. Ink manufacturers have to choose ink components that provide the proper rigidity to match the application for which the ink and substrate are intended. If the job involves producing double-sided prints on styrene, then the cured ink film should be more rigid. If the application concerns printing on polyethylene banners, a more flexible ink film is desirable. Adhesion Adhesion always is a major concern when evaluating any ink line. Important differences exist in the adhesion characteristics of various multipurpose UV inks on the market today. Most will adhere well to a variety of styrene, paper, and vinyl substrates. The most difficult substrates on which to print these inks are those in the plastic family known as polyolefins, specifically polyethylene and polypropylene. In P-O-P printing, treated polyethylene usually is found in the form of banner substrates. Polypropylene is most often seen molded into a fluted substrate for use in rigid displays or signs (other polyolefin materials also are used to produce fluted substrates). If these difficult substrates are part of your product mix, you'll need to thoroughly evaluate any multipurpose UV ink for acceptable adhesion on the materials before you use the ink in production. End use The significant differences in properties and performance characteristics of P-O-P substrates require different properties from UV inks to ensure effective and durable prints. Normally, printers are careful to check for ink adhesion when printing and curing inks. If a failure does occur, it usually surfaces during post-print processing in the form of ink chipping off when diecutting, bending, folding, sewing, etc. These problems sometimes occur because the ink was unable to form a proper adhesive bond with the substrate. But more likely, the ink film was too inflexible for the substrate. The environment in which the printed material will be displayed also influences the performance demands on the ink. Is the application a short-term indoor display where durability is a lesser concern? Or is the graphic intended for long-term outdoor use? In this situation, you not only have to consider the adhesion and rigidity of the ink film after printing, but also must determine if exposure to the elements will change these characteristics and allow the print to deteriorate before the promotion ends. A matter of preference Some printers have no interest in finding one ink that works well on multiple materials. They prefer to use inks that are tuned for specific substrates, giving them the piece of mind that they are getting the best possible performance characteristics with each application they print. Of course, this leads to the need to stock and keep track of multiple ink lines, which is the primary factor that drives other printers to use multipurpose formulations. Although the multipurpose ink's performance may not be optimized for any one application, it performs well enough on all their applications and simplifies ink management enough to justify its use. For most printers, however, the optimal solution to ink selection is somewhere in between. Today's multipurpose UV inks are a viable tool for many printers to reduce the total number of inks that they must inventory. For example, if a printer currently is printing one UV ink for vinyl banner, another for poly-ethylene banner, another for fluted polypropylene, and yet another for styrene and card stock, his total ink inventory (including leftovers from previous print runs) can get out of hand pretty fast. By selecting one UV multipurpose ink for the majority of these applications, and one or two complementary inks to round out the collection and address difficult substrates, all P-O-P applications can be satisfied and inventory control can be simplified. If you've been thinking about taking the plunge into multipurpose UV inks, remember to thoroughly assess the performance of the inks in all facets of production, including post-print processing. Make sure to test the inks for all the substrates and applications you typically print. Finally, single out any materials for which the multipurpose formulation is inadequate, then attempt to find the smallest number of additional ink lines that will allow you to satisfy jobs on these difficult substrates. Don't be afraid to get assistance from the ink supplier's technical-support staff, who can help guide you to formulations for all your needs. Tom Keegan is director of products and technical services for screen-ink manufacturer Nazdar, Shawnee, KS. He is responsible for developing and coordinating market studies that drive the company's product research and development efforts. With Nazdar for more than 14 years, he previously has served as the company's director of product development, director of technical/customer service, and director of product management. Keegan holds a bachelor's degree in biology with a minor in chemistry and is a frequent speaker at industry functions.
Did you enjoy this article? Click here to subscribe to the magazine.