Wide format UV printing evolves to include the use of UV LED lamps to provide more efficient curing. In addition to energy savings, the low heat enables UV ink compatibility with a broader range of heat-sensitive substrate options.
Hiroshi Ono, group product manager, Roland DGA Corporation, explains that traditional UV lamps emit a broad spectrum of light. The shorter wavelength pins the ink or cures the surface, and the longer wavelength cures the ink from the inside. With this process, print providers experience exacting print quality because the ink is cured almost instantly.
UV LED lamps feature a more concentrated, narrow spectral emission in the longer wavelength. Because of this, they do not work as well with traditional UV inks. “The biggest hurdle for UV LED is that it omits a single wavelength with relatively lower dosage than other traditional lamps like mercury vapor technology. For this reason it is important for the ink to be well tuned to the lamp, as well as the speed of the print carriage,” says Ken Kisner, VP of business development/CTO, digital division ink technologies, INX Digital International Co.
New ink sets propel the adoption of UV LED curing. With it, print providers experience benefits such as safer printer operating, lower energy consumption, and broader substrate options. Technology advancements, new feature sets, and the role of UV LED lamps are important discussion points concerning UV LED.
There has been much in the way of developments regarding UV ink for the wide format space. The differences in the spectral output between traditional UV and UV LED demand ink set advancement.
Muslim Contractor, UV chemistry platform manager, Collins Ink Corporation, says UV LED curing allows heat sensitive materials to be printed. “The lower energy consumption and longer life of the LED lamps can reduce operating costs sufficiently to make LEDs a more cost-effective option, despite the higher initial costs,” he adds.
“LED UV printing results in less wasted ink; because with cool curing, you don’t create situations where heat warps substrates and creates printhead strikes,” adds Thomas Krumm, product marketing manager, EFI.
As previously noted, traditional UV bulbs emit a broader range of wavelengths and as such, the inks are designed to react to several wavelengths simultaneously. “UV LED lamps are tuned to a very specific and narrow wavelength, so LED curing inks need to be optimized to work with that specific wavelength,” says Rich Dunklee, global UV market segment manager, Nazdar Ink Technologies.
Chad Klostermann, inks and warranties marketing manager, 3M Commercial Graphics, agrees, adding that ink formulation changes are needed to address curing at lower wavelengths of light as well as with a little or no heat source. “With these changes, it is imperative to cure the ink completely—not just the ink’s surface—so a strong bond between the ink and its substrate is established, including heat-sensitive substrates that cannot tolerate traditional UV lights.
One notable trend is the development of UV inks formulated with specific applications in mind, such as metal, glass, corrugated, plastics, or ceramics. “This comes as no surprise since the traditional markets for flexographic, offset, gravure, and rotary screen always had application-specific formulas.”
Pedro J. Martinez, CEO, Afford Industrial S.A., adds that in the early days, formulators could use standard monomers and oligomers used for other printing methods. However, there was also a lack of knowledge regarding UV LED technologies. He explains that with more suited raw materials and extended knowledge of UV LED technology, ink manufacturers can produce specifically formulated products.
As UV LED printers emerge and ink sets mature, a trend towards UV LED is apparent.
“The biggest development in UV LED is the power of currently available LED lamps. The additional power allows for a more extensive and faster cure of the ink, which in turn provides the proper adhesion and abrasion resistance,” says Kisner.
Flexibility, adhesion to a broader range of substrates, and durability are all properties of UV ink that manufacturers continuously work to improve. “As new substrates emerge in the marketplace, ink companies need to react to provide ink that not only works with well-established brands, but also meets the performance requirements of emerging products,” says Dunklee.
Contractor explains that the challenge with LED curing is maintaining the speed of curing achievable with traditional UV lamps. LED ink development requires a deeper understanding of the LED system as the curing window is more specific than with traditional UV.
New inks that utilize raw materials developed for inkjet aim to improve major challenges of UV inkjet inks—flexibility, curing speed, and resistance to humidity. “Inkjet ink manufacturers have had the time to optimize formulations and the learning curve of the process improves the final product quality,” suggests Martinez.
Klostermann says broad-based ink solutions designed for many applications, substrates, and performance levels, create the best options for today’s customers and the graphics industry. “In the past, these robust solutions were solvent based. Today, UV ink development continues to strive for robust UV inks solutions that meet or exceed the standards set by solvent-based inks,” he explains.
Ruth Zach, marketing coordinator, Bordeaux Digital PrintInk, notes that while this new generation of inks address many challenges with better success, it is important to remember that surfaces still require pre-treatment in order for the ink to adhere well. “Also, chipping is still an issue, since printing on flexible substrates is more difficult to achieve with UV inks. Many ink manufacturers offer UV inks that adhere well to highly flexible substrates,” she explains. “These inks are formulated with extended elongation properties that solve the problem of chipping in most surfaces and further expand the possibilities for UV inks.”
In addition to ink enhancements, the development of UV LED heating lamps helps improve the final output of UV LED cured output.
The heat, or more accurately, the lack of heat generated by UV LED lamps makes them ideal for use with very heat-sensitive substrates like thin polycarbonate films. Traditional UV lamps are known to warp sensitive substrates.
Reduced energy requirements are an advantage of UV LED. “In very large operations with multiple UV printers, the heat generated by the lamps can have a significant impact on the utility costs needed to maintain the optimum electricity costs of running a LED lamp, making them attractive to operations looking to save on utility costs,” says Dunklee.
The biggest hurdle for UV LED is its single wavelength emission and relatively lower dosage than traditional lamps, which limits the photo initiators that may be used to cure the ink. “The lower power output is not as well suited for penetrating higher film builds,” admits Kisner. “For this reason, it is important for the ink to be well tuned to the lamp as well as the speed of the print carriage.”
“You develop the ink to work with the intensity and wavelength of the lamps on the printer. But, you can’t forget other aspects of printing,” warns Klostermann. For example, the amount of ink lay down and speed at which you run the printer are also important to generating the final graphic results and performance for a customer.
John Kaiser, product marketing manager, inkjet inks, graphic systems division, Fujifilm North America Corporation, says new UV LED ink technology relies on a longer UV wavelength for the cure.
The LED lamps providing this wavelength produce much less heat and last up to ten times longer than traditional UV mercury vapor lamps. Because of this, the LED technology shift advantage resides with the cure system and not the ink. “The photo initiators in traditional UV ink systems will not cure under this lamp technology and have not changed in response to the introduction of UV LED inks,” explains Kaiser.
Overall, LED UV lamps provide an advantage in terms of longevity, productivity, and total cost of ownership. Krumm notes that traditional UV lamps gradually deteriorate with use, while LED UV lamps provide an instant on, consistent cure that ensures high-quality printing while giving print providers high-quality output.
“In the end, users get more uptime, more consistency, and sometimes significant energy savings using UV LED inks and lamps,” adds Krumm. He points to a customer in Europe, that reportedly cut its energy usage by 75 percent by switching to UV LED.
The development of UV is of interest to many wide format print providers. In addition to the benefits traditional UV printing technology provides, the evolution into UV LED enables further benefits, including lower energy consumption, safer operation, and more media options. As manufacturers of traditional UV solutions begin to offer UV LED solutions, ink sets also evolve.