UV - It's Good ... But Be Careful

UV inks are a great addition to the world of flexographic printing, but knowing the simple do's and don'ts will keep converters' blood pressure under control.

AHHH, ULTRAVIOLET (UV) flexographic printing … it's great! The use of UV materials in general, is making the printing market a bit more rewarding for some, as long as they are used correctly in particular applications. For instance, there are different rules for medical applications than for food applications. packagePRINTING spoke with some experts in the field to find out what printers need to know to incorporate UV flexographic printing in their arsenal.

You are what you eat

In the October issue of packagePRINTING, there was an in-depth discussion on UV and Electron Beam (EB) inks, and how RadTech is working with the Food and Drug Administration (FDA) to get UV/EB inks approved for use in direct contact with food. Until that happens, though, printers are still running UV inks in food packaging, but not in direct contact with food stuffs—there's usually a layer of some other material between the packaging and the food. Even though this makes it safe for the consumer, there are rules and regulations a printer must follow.

Zubair Khan, director technical development—energy curable products for Environmental Inks and Coatings, stresses the importance of monitoring extractables when running UV inks or coatings for indirect contact with food packaging and being wary of different ink products that are offered throughout the industry. "Printers have to be careful about the low-extractable products being offered by some companies. Unless printers have tight control over their processes, ensuring the highest degree of cure and repeatable print reproduction using low-extractable products, they should not venture into this area of food packaging using UV technology," he said. He offered cationic UV inks as a still-popular technology for indirect contact with food applications due to their advantage of post curing, which results in a high degree of cure.

In medical applications, Khan warns printers strongly about the use of UV. "UV inks or coatings are not recommended for any applications that may result in incidental contact with skin, body fluids, labels for blood bags, or indirect contact with medication," he said.

Unraveling the mystery

Bob Waddington, general manager, UVitec Printing Ink, understands the ins and outs of UV flexographic printing, but knows many printers still shy away from the technology because of common misconceptions about the printing process. He offered a list of these untruths:

• False: The wash-up solutions, as well as the curing units, are unsafe. "UV ink is a 100 percent solid ink, meaning they are virtually free of VOCs. The inks should be used with the normal amount of care that would be used for any ink product. The chemicals used for wash up of the press and work area are on par with other industrial chemicals," Waddington said.

• False: UV flexo inks are too expensive. "While UV flexo inks are generally of higher cost than their conventional counterparts, the energy-curable products will provide more mileage," said Waddington.

• False: The benefits simply don't outweigh the negatives. "Each printer and each application will be the judge of the viability of energy curing," said Waddington. "From an environmental, production, and performance level, energy curing brings money to the bottom line."

Some general do's and don'ts

Some of those in the UV flexographic industry have offered some simple do's and don'ts of running UV flexo. According to Jim Flynn, printing technology, Gallus Inc., it's important to have a spotless pressroom. "UV flexo attracts the dust, and the goal is to keep the process pure and impurities out." Flynn suggests using a stickyback lint roller when cleaning the flexoplates or removing dust, because chemicals and excess rubbing can damage and reduce the life of the flexo plate.

Flynn also wants printers to set their goals higher. "Using higher screen counts with UV flexo and better graphics can produce outstanding results. Take advantage of the lower dot gains and better coverage to achieve better results than you have seen before."

Terry Trexler, product manager, Gallus Inc., said to always check the dyne level of the substrate, at speed, for good ink adhesion. "The dyne level can change as the substrate is moving, so it's important to conduct this test at operational speed."

As many "do's" there are in flexographic printing, there are that many—if not more—"don'ts." Flynn said one of the more important issues for a printer to keep in mind is to not run the UV lamps on high intensity unless absolutely necessary. "Excess light energy can enter the web and cause problems that are otherwise avoidable. This practice also saves on energy as well as extends the life of the bulbs," he said.

Another important "don't" Flynn stresses is to not use silicone anywhere near the press, especially with combination printing. "Spray silicone can travel in the air and contaminate the ink, leading to laydown problems on the press," he said. A third important factor to keep in mind when printing with UV is to watch the pressure on doctor blades. "Don't use too much pressure. Excess pressure can lead to premature wear," Trexler said.

by Megan Wolf

Assistant Editor