Durst Rho

Think Ink: Hybrid UV-Aqueous Inkjet Technology

Ray Work, Ph.D., heads Work Associates, a consultant firm specializing in inkjet printing technologies, applications and markets. He worked for more than 28 years in research, research management, business development and business management with DuPont. Dr. Work holds a Ph.D. in physical inorganic chemistry from the University of New Orleans. He can be reached via e-mail at workassociates@comcast.net, or visit his Web site www.workassoc.com.

Over the past few years in wide format graphics we have seen movement toward the development of greener ink solutions like low-VOC eco-solvents, HP's “Latex” inks, and more durable ink solutions like UV-LED cure systems. But all of the current approaches leave room for further improvement. Whether the challenge is physical durability, adhesion, color gamut, gloss and gloss uniformity or environmental friendliness—each of the currently available ink solutions has certain shortcomings.

Now a different approach is beginning to be exploited that moves the technology forward to what promises to be a new level of performance: hybrid UV-aqueous inkjet ink technology. Here we will discuss the nature of this technology, how it relates to current UV-cure systems and aqueous ink technologies, and then explore anticipated improvements this technology is expected to deliver in printing systems which are now becoming available.

What is this New Technology?

This new technology—developed by Sun Chemical’s SunJet division and launched last year—is called "Aquacure." Sun Chemical is a member of the DIC Group which is one of the largest ink companies in the world. Sun often partners with print equipment manufacturers to design inks specifically for their equipment.

Last fall grand-format printer maker Durst announced the first market launch of the Rho WT 250 HS, a flatbed printer using hybrid UV-aqueous technology—a technology Durst calls "Durst Water Technology." Then, at the recent drupa trade fair in Europe held in early June this year, Durst rolled out the Rhotex 500, a five-meter-wide roll-fed soft signage and fabric printer which also employs the "Functional Aqueous Inks," as Durst terms them.

Also at that drupa event, EFI unveiled a new technology it calls AquaEndure technology. Like the Durst solution, EFI's AquaEndure technology is a water-based ink set that offers the benefits and durability of UV-cure technology. The company says AquaEndure technology has a further advantage because the ink can be cured using a low-temperature UV-LED curing system. EFI says AquaEndure will be used across many of its platforms and segments in the future.

SunJet's Aquacure technology evolved from an established product line of water-based UV-curable flexographic inks offered by Sun Chemical. The ink is 60-90 percent water with a very low level of co-solvent humectants (non-toxic organic chemicals that keep the inkjet nozzles from drying out too quickly). The co-solvent humectants used are similar to those used in water-based wide format pigmented inks, or in HP “Latex” inks. And the photo initiators, sensitizers, resins and monomers in Aquacure inks are similar to those used in conventional UV-curable inks, with additives to help the wetting of the substrates. The result is a low-odor, low-solids ink that produces a desirably thin film on the substrate similar in performance to offset or flexographic printing inks.

How is it Cured?

The curing of this new water-based ink is accomplished using a two-step process. First, the ink is heated immediately after printing to remove the water and “pin” the ink droplets onto the substrate's surface to prevent the drops from combining or reticulating which would degrade the image quality.

When all the water is evaporated, the thin ink film layer coalesces in a similar manner to HP's “Latex” inks. Once dry the coalesced film of ink is then cured using UV cure lamps, or electron beam radiation. In a flatbed system the two stages are done in-line. If the ink is not dry before UV irradiation then a robust ink film will not be produced.

What are the Benefits?

This technology promises performance that is the closest to flexographic or offset printing of any inkjet printing system to date. It provides a thin highly pigmented, cured ink layer with high color gamut and gloss. Much better color can be achieved than with regular UV ink since it forms a thinner layer. With a thinner ink layer and fewer solids comes easier UV curing. With only 10-40 percent solids, the cost of manufacturing the inks should be much lower than with traditional UV inks which are nearly 100 percent solids. Since the dried ink is chemically crosslinked it offers the potential of higher durability compared to “Latex” ink which is not chemically crosslinked but only forms a film when heated.

Conclusions

Kudos to Sun Chemical for developing what I believe has the potential to become the next big thing in inkjet inks—and kudos to Durst and EFI for introducing printing systems for hybrid UV-aqueous technology. This bodes well for the future of wide format inkjet printing by eliminating some of the shortcomings of the ink systems in use today with a much more environmentally desirable ink chemistry.