3M Wall Decorating Film IJ86E is one of those rare films optimized for UV-curable printing. Used primarily for wall applications, the 6-mil film has a thin coating to make it as durable and vibrant as possible for UV-curable printing. Most manufacturers, including 3M, have tweaked their formulas to make their films as universal as possible.

Back in the day (“the day” being two years or so ago) flatbed UV-curable printing was the hot ticket. Boards, boards and more boards became the rallying cry as this segment of our industry would reap the benefits of cutting out the film/vinyl middleman for board printing.

Though exciting and quite profitable, the flatbed honeymoon wore off rather quickly. Board printing became more of a commodity. For color-critical work and the old standbys—banners, posters, vehicle wraps and most other printing—it was back to the aqueous and solvent roll printers.

OPTIMUS PRIME

Once hybrid (flatbed with roll-to-roll capability) and dedicated roll UV-curable printers began appearing on the scene, the emphasis naturally shifted and demand for roll materials compatible with the ink technology grew. Material manufacturers scrambled to “optimize” media solely for UV-curable inks.

Optimization usually meant a thin urethane-based top coat that provided better adhesion to the material. It also meant a corona treatment, though this was and still is a fairly rare solution since the treatment’s shelf life is quite short.

“In some high-volume shops you’ll see corona treatment as part of their production workflow. Otherwise, there’s not a lot of it about,” says Mike White, wide-format manager for Agfa. “A corona treatment is a way of electrically changing the surface of the substrate temporarily, whereas adding a coating or primer on it is a permanent change.”

When the hybrid printers made their debut, a smattering of optimized substrates also began to appear. These optimized materials helped bridge the gap when UV-curable transitioned to becoming a well-rounded production tool.

“Initially, we created products that were better for UV-curable inks than uncoated films. At that time, media manufacturers weren’t paying as much attention to Dyne levels on the raw material (Dyne level measures the wettability/adhesion of the surface). As long as the Dyne level is higher than about 30, UV-curable inks will bond well to the surface,” explains Jeff Leto, product manager for LexJet, Sarasota, Fla. “Now, film manufacturers are providing universal materials that meet that Dyne level threshold, so there are fewer roll materials that require some type of coating to optimize the ink adhesion to the surface.”

Leto adds that the ink formulations and ink delivery methods of the latest printer generation have improved significantly. The inks are more flexible, and thus form a more durable bond to a wider variety of surfaces.

Agfa’s Anapurna M series running roll-to-roll media. The feed and exit tables are on wheels and easily detached and rolled away. For boards, the tables roll into place and have quick-clamps to attach them back in register. Now, with most media “optimized” for UV-curable printing, the biggest factor is the ink.

Most films available for UV-curable printing are also compatible with solvent. Excluding vinyl, which solvent inks are able to bite into for a durable print, solvent and UV-curable films typically have a coating to make them receptive to solvent inks or the compatibility is built into the formula. UV-curable inks are not an issue with these cross-compatible films.

Arlon’s product line, for instance, doesn’t differentiate between ink technologies; the universal compatibility formula is built into the company’s line of films. Those formulas have been modified slightly over the years to keep up with new ink technologies. The difference is in the profiles used for each type of printer.

“Once UV-curable ink overcame the brittleness issue, it was pretty simple for us. We deal with UV in screen printing, and at one time you had to come at it with a very flexible vinyl to keep it from cracking. As the inks became more flexible, the base material didn’t matter as much, so the ink technology change has been a boon for our formulas because we didn’t have to go to extremes,” explains Chuck Bules, technical services manager for Arlon, Santa Ana, Calif. “Now, the most important thing about working with UV-curable inks is post-printing fabrication. You can die-cut without worrying about fracture and you can take off transfer tape without taking the ink off. With laminates, you tend to trap air with the more coarse topography of a UV-printed piece, so a softer, more pliable adhesive is preferred. Even if you use a laminate that’s not as soft, you can add a little bit of heat, maybe 105 degrees or so, to soften both the vinyl and the adhesive and allow them to make better contact.”

This banking machine was printed with a UV-curing printer and wrapped with Arlon DPF 4560GTX 3-mil Calendered Air Egress film and Series 3220 Cast laminate. Arlon’s films are compatible with all ink sets—aqueous, solvent and UV-curable. The formulas have changed slightly over the years to keep up with the latest ink technology.

THINK INK

Still, you’ll find a film here and there that’s labeled only for UV-curable printing, such as 3M’s new non-PVC 6-mil wall graphics film. More often than not, however, films labeled for UV-curable printing usually mean that they’re just not compatible with solvent-based inks as opposed to being specifically optimized for UV-curable inks.

“While surface modification may be needed for some materials in order to achieve adequate UV ink adhesion, the more important challenge is providing a consistent product with a very clean and uniform surface. Piezo printers are arguably the world’s best defect detector as they readily highlight any product inconsistencies,” says Mike Kesti, laboratory manager for 3M, St. Paul, Minn.

Kesti adds that most of the innovation, as far as ink receptivity goes, is on the ink formulation side, as opposed to the media side. He says that 3M and other UV-curable ink manufacturers are continually developing UV inks that have improved adhesion to a wider range of substrates and are more flexible so that they can be stretched and used in more demanding applications such as vehicle wraps. 

At this point, the best UV inks (such as 3M’s LF-200 UV inks for the Mimaki UJV-160 and 3M’s 2800 UV inks for the EFI Vutek’s QS printers) have generally caught up with just about anything a film manufacturer can throw at it.

Now, it’s a question of getting the ink to bond to extremely slick surfaces, like polystyrene, and to make the ink flexible enough for vehicle wraps, accelerating the adoption of these high performance inks and maintaining their performance at faster and faster printer speeds.

UV-curable inks from INX Digital and other ink manufacturers are now engineered to be as universal or specific as needed, depending on the shop and its workflow. Advances in ink technology have effectively solved the film optimization issue.

So, the real issue is not so much films optimized for UV-curable printing, but inks optimized for different printers and different applications. INX Digital, for instance, provides ink sets for specific printers, as well as three base inks: Rigid INX for rigid substrates, Multi-Flex INX for hybrid applications and Flex INX for roll-to-roll materials. From those three base formulations, INX Digital provides a variety of inks for different applications.

“Let’s say you’re running an HP 5300 in billboard mode, there’s an ink with a delay-cure formula for that application and printer type,” says Karla Witte, VP of business development for INX Digital. “There has been quite a difference in thinking lately. The idea that one ink would work optimally for all applications is simply not the case. We make inks for the end use, and that provides quite a bit more than one hybrid formula.”

INX Digital’s base hybrid formula, Multi-FlexINX, is for the shop that’s constantly switching between flatbed and roll-to-roll mode. As mentioned, however, from this base formula there are variations depending on the shop’s workflow.

“It’s expensive to change the inks, which is why you have to compromise to some degree when you’re regularly transitioning between rigid and roll-to-roll materials,” says Witte. “That’s the ink business these days, but it’s worked out well because when we hear from customers who have an idea to bring something new to the marketplace, first we’ll see if there’s something in our line that can be used for it, or make adjustments to the ink for that particular application.”