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The digital printing market is undergoing an ultraviolet (UV) revolution. But it needs inks to do it.

UV inkjet technology has been around for many years in the cable and wire industry, but the application has been limited due to ink viscosity restrictions inherent with continuous inkjet print heads. During the past five years, however, new print heads based on Piezo technology have been developed and the result has been a dramatic increase in the range of ink viscosity.

“With the recent advent of new UV curable raw materials, inks can be developed which have improved handling and compatibility with a wide range of substrates,” says James Balcerski, Ph.D., market development manager for Sartomer Company, a global supplier of specialty chemicals used in manufacturing ink and coatings.

The Benefits
UV inks offer several key benefits for inkjet machines, according to industry experts. One of the most notable advantages is the instant dry feature that leaves the graphic completely cured. As a result, no solvents penetrate the substrate once it comes off the printer.

“There’s no need to worry about ink drying or ink penetrating the substrate and affecting things like adhesion,” says Anthony Carrozzella, a spokesperson for 3M’s Commercial Graphics division. “Because of instant drying there is less substrate dependence.”

Since UV inks don’t dry on the print head, they can eliminate some of the annoying problems associated with cleaning and purging the head to remove insoluble material. Theoretically, you can achieve greater print production rates with UV ink because you don’t have to wait on drying solvents or perform as much printer maintenance.

Carrozzella also notes that UV inks result in consistent images from substrate to substrate. And there are environmental advantages over solvent inks as UV boasts fewer emissions.

“The ideal UV curable inkjet inks will enable printed images to have water resistance, fade resistance, no volatile organic compounds (VOCs) and media independence,” says Stephen Emery, vice president of sales and marketing for American Ink Jet Corp., an ink manufacturer. “UV curable inks will allow a variety of uncoated media from roll feed to rigid substrates (formic, glass, etc.) to be imaged. This will expand the potential applications for printing of graphics. The requirement for lamination will also diminish.”

Sartomer’s Balcerski says these benefits make UV inks the choice for the new generation of presses utilizing one pass curing technology.

Three Approaches to UV Inks
There are three main approaches to UV inks: water-based, hot melt and low-viscosity versions.

Water-based
Water-based UV inkjet technology is attracting attention because it uses water as a diluent to produce lower viscosity. Water-based UV inks are formulated with UV-curable resin emulsions. But there are drawbacks with this technology. The system needs to get rid of the water before the UV lamp cures the ink.

“Getting rid of the water is difficult as you want to cure as quickly as possible to prevent undesirable dot gain, wicking or feathering into the substrate,” says Emery. “If water is present, then the ink will not adhere to the substrate. UV curable inks that are 100 percent solids will be the first product available.”

Hot melt
Hot melt jet inks are dependent upon a large viscosity drop that could occur with specialty ink jet formulations. But the jury is still out on this approach. There is a distinct topography with these inks and experts say they may or may not be subject to wear and abrasion or cracking with flexible substrates.

Low-Viscosity Version
There are also UV inks based on low-viscosity version of convention UV formulations. The low-viscosity UV curable inks are designed to work with the commercially available Piezo type print heads. The higher viscosity inks are for use with industrial type print heads such as the Spectra products.

“The advantages of low-viscosity versions are that we can bring UV curable inkjet inks to the wide format market versus the super wide (grand format) and new flatbeds,” says Emery. “Low viscosity for wide format and new applications will evolve over the next several years. Higher viscosity inks for the industrial markets and super wide format and flatbed printers. Also, there are other niche applications which will require modified UV ink formulas.”

The Vendors
3M has been making UV-curable inks for the screen printing market for many years under its Piezo Ink Jet Ink Series 2500UV line. Carrozzella says 3M will soon be introducing a more flexible ink that will be ideal for longer-term durable graphics, including fleet applications.

But 3M has plenty of competition in this market.

Following an extensive development program, SunJet has announced the joint launch of a new UV inkjet ink, formulated in close collaboration with printhead manufacturer, Xaar plc.

Crystal UFX UV ink jet ink is specifically designed for use in the Xaar XJ500 high performance print head. It combines the print head stability of a UV ink with reliable jetting to satisfy the demands of high speed fixed head and scanning print systems. After virtually instant cure of the ink film, these inks show good adhesion across a wide range of materials, with good flexibility and resistance properties. The ink is available in process colors (standard and light shades) and a custom spot color base system to provide a valuable color tool for the print designer.

American Ink Jet’s UV-Gold system provides the chromatic, highly saturated colors with super-fast dry times. Although this system is not waterproof, without lamination the UV-Gold system can withstand at least 100 days of intense sunshine with negligible fade. Tests by Wilhelm Imaging Research, Inc. have concluded that images printed with UV-Gold inks on UV Glossy Media will last 30 years to 35 years indoors without noticeable fading, making this combo ideal for permanent indoor application.

Sartomer recently released a family of polyester acrylate oligomers with a unique combination of properties that makes them well suited for UV inkjet. And many other vendors are developing products targeting this growing market.

The Challenges
Still, there are challenges to bringing UV ink to the mainstream. Cost is still a factor. UV curable inks are more costly tan conventional inks due to the specialty raw materials used in the formulations. In fact, UV inks can be up to two to three times the cost of conventional inks.

UV curable Inks also have some health and safety issues. It is well documented that exposure to some UV raw materials can result in some irritancy and sensitization.

“When buying a digital UV printer, the user should discuss with the manufacturer what health and safety provisions are incorporated into the printer,” says Vutek spokesperson Joe Lahut. “Some UV lamp systems generate ozone and this must be vented or neutralized. Inkjet printers generate a very small amount of mist that must also be removed from the printer enclosure. The user should have both mercury and UV ink spill kits available.”

Balcerski says the challenge for ink makers continues to be to develop inks that will meet the application viscosity requirements, adhesion and flexibility, cure speed, pigment stability, and health and safety restrictions. That, he adds, takes innovation because traditional products designed for the flexographic or screen print industries, will not satisfy all of these technical issues.

Collaboration is Key
Still, companies in this market are looking ahead to a bright future. Collaboration among vendors is one key to success. Inkjet manufacturers should work closely with UV lamp companies and chemical component manufacturers, says Balcerski, because this will allow the printer manufacturer or system integrator to focus on integration of the hardware and not waste time on selecting the UV Lamp source. The end result will be a shorter time to market for printers using UV curable inkjet, which will, in turn, benefit the ink companies.

Spectra, a developer and manufacturer of state-of-the-art piezoelectric inkjet printheads and related consumables, has a heavy hand in collaboration with American Ink Jet, Flint Ink, Durst, Inkware, Vutek, Inca and Sericol, for example.

“These relationships clearly point out the difference between traditional UV ink development and the inkjet market,” says Balcerski. “The successful evolution of UV inkjet technology will only occur with a close technical exchange among industry participants.”

Emery and others believe that as users realize the benefits of using UV inks they will gain a greater foothold in the market. One thing is for sure: the next two to four years will be critical for UV curable inks. Experts say much will depend on the printer technology. Several equipment manufacturers have recently introduced wide format inkjet printers that utilize UV inks. As these machines come to market, the demand for UV inkjet Inks will grow exponentially.

Check out part three of this series to learn more about UV printer technology.