Curing inks and coatings with ultraviolet (UV) radiation has long been SOP for many printers, especially those producing packaging and labels. But, as well established as it is, conventional UV curing has had persistent drawbacks: high operating temperatures and energy requirements; ozone emissions; safety concerns about skin and eye exposure; and regulatory issues stemming from the presence of mercury in standard UV lamps.
Although conventional UV curing remains the norm for most kinds of printing, an alternative to it is making rapid technical advancements and is starting to attract the kind of attention that leads to mainstream adoption. This is curing with UV radiation generated by light emitting diodes, or UV LED for short. Its proponents say the technology works well with all printing processes and may even become the curing method of choice in some applications that now belong to conventional UV.
On October 28 and 29, more than 200 users and sellers of UV LED solutions came together in Rome, NY, for a conference on its progress in printing and other industrial market segments. The event, the first of its kind, was hosted by RadTech International, a trade association that promotes the use and development of UV and EB (electron beam) curing systems. The conference also featured a tour of the Smart Lighting Energy Research Center (ERC) at nearby Rensselaer Polytechnic Institute, an incubator for LED and other advanced illumination technologies.
The general focus was on UV LED for print and packaging, but also noted was its increasing importance in non-print uses such as outdoor displays, plastic cards, automotive interiors, wallpaper, flooring, furniture and fixtures, plumbing, and ceiling tiles. Research from RadTech indicates that sales in some of these UV and EB applications are growing by as much as 7% annually.
The scientific difference between UV radiation from LEDs and conventional, mercury-based lamps is in wavelength. The spectral output of UV LED lies in a narrow band of wavelengths from about 355 to 415 nanometers, just below and slightly overlapping with the spectrum of visible light. (Wavelengths from conventional UV units are more broadly distributed and produce more types of UV radiation.)
With their microchip-like arrays of miniaturized diodes, UV-emitting LED units bear little resemblance to the designs of the mercury-using arc lamps and microwave lamps that are the fixtures of conventional UV. As one conference speaker, Jennifer Heathcote (Phoseon Technology), put it, “the construction and operation of a UV LED curing system has more in common with a smart phone and a tablet” than with either of the conventional sources.
In practical terms, said Heathcote and other experts, UV LED systems set themselves apart from the other methods by being longer lived; more consistent in UV output; more energy efficient; simpler to work with because of their fast on/off operation; cooler in curing and therefore easier on heat-sensitive substrates; and free of ozone and mercury (the latter coming under increasing regulatory pressure, especially in Europe).
As an emerging technology, UV LED has had to deal with technical hurdles and market resistance. A panel of representatives from UV LED solutions vendors, moderated by WhatTheyThink, discussed the extent to which the problems and objections have been set aside.
Because of technical progress, they said, no longer valid are claims that UV LED curing units are underpowered or that they are too costly to use. The panelists noted that UV LED has been successfully installed on inkjet, flexo, screen, and offset printing systems and that with the help of ongoing R&D, the units will continue to become less expensive and more capable.
According to a speaker in another part of the program, there are now more than 60 suppliers of UV LED sources to meet a growing range of applications and processes. Remaining an issue, however, is the still-limited supply of inks, coatings, and adhesives that have been formulated to work with UV LED systems, which have different curing characteristics from those of conventional systems.
There also has been an uneven response to the technology from the press manufacturers. According to speaker Dene Taylor (Specialty Papers & Films Inc.), inkjet suppliers have led the way by offering more than 20 UV flatbed and roll-to-roll devices with LED curing. Offset press manufacturers, on the other hand, have been more reluctant to adopt it because of their heavy investments in traditional UV technologies and their concerns about the availability of compatible inks.
But, the conferees were unanimous in seeing a bright long-term future for UV LED as the technology comes fully into its own. “In less than 10 years, nearly all UV curing will be UV LED based,” Heathcote declared.
Institutions outside the industry are taking notice. RadTech put on the conference with the help of a grant from the New York State Energy Research and Development Authority (NYSERDA), a state agency that promotes clean and efficient energy use. And, the ERC at Rensselaer Polytechnic isn’t the only academic center in the state with a focus on UV LED. The subject also is covered in non-credit, credit, and advanced certificate courses presented by the Radiation Curing Program (RCP) at the SUNY College of Environmental Science and Forestry in Syracuse.
RadTech’s next major event for UV/EB will be RadTech 2016 in Chicago. Earlier this year, it launched UV+EB Technology, a quarterly magazine available free to qualified subscribers in print and digital editions. Issues can be examined here.
Another helpful information resource is the UV LED Curing Community, an online forum that lets market participants share their knowledge of UV LED curing technologies, applications, and chemistry.