Those of us used to traditional offset and digital printing rarely give the concept of white ink a second thought. After all, “white” is typically synonymous with the color of paper, so when we want something to be white, we design it with the absence of any color. (Tellingly, in Adobe InDesign, we select the color swatch labeled “Paper.”) There are situations, however, when—oxymoronic as it may seem—we need to specify the color white.

Two applications of white ink: (left) white, et al. on Plexiglass, and (right) on black Sintra. (Images courtesy Océ Display Graphics Systems)

Getting It White

Although offset shops are no strangers to white inks, printers with digital devices have long found printing white to be a challenge, if not impossible, until quite recently. A large part of the reason will not be a surprise to anyone who has ever painted a room: white ink requires a high degree of opacity, especially if it is being printed over a non-white color or on a non-white substrate. Achieving this opacity in turn requires a thick ink—but a thick ink can play havoc with inkjet printheads. As a result, not just any wide-format device can print white; the hardware has to be specifically designed to handle it. Most wide-format equipment manufacturers have introduced new models capable of handling white ink, and many also offer special “white ink kits.” Models in Océ’s Arizona series handle white, HP offers a White Ink Kit for its HP Scitex FB series of flatbed presses, several EFI Rastek and Vutek models can print white, Roland DGA has begun adding white ink options for its inkjets, and Epson has an aqueous white ink, to name just a handful of vendors.

“Formulating a successful white ink solution presents several unique engineering challenges,” says Jeff Edwards, International Product Marketing Manager for Océ Display Graphics Systems. “The most appropriate pigment material for white is titanium dioxide, which is very heavy compared to the pigments used in colored inks and doesn’t like to stay suspended in a fluid. The result is myriad processes to agitate the ink to ensure the particles remain evenly distributed throughout the fluid, particularly during idle time.”

Titanium dioxide (TiO₂) has long been used the primary pigment in white spot inks for offset, gravure, flexo, and screen printing.

White ink not only needs to be opaque enough to cover non-white substrates, but also translucent enough to work effectively in backlit applications.

(Is there such a thing as white toner for electrostatic devices? Yes, but it is not widespread.)

One of the major drivers for white ink development has been the advent of UV-curable flatbed printing systems for printing on both rigid and backlit substrates. However, says Edwards, “there is a significant difference in the quality of ink and the implementation between the different manufacturers. Some use larger white ink droplets than CMYK in order to achieve the coverage and ink film thickness they need; others are incapable of printing in the same manner as they do with CMYK and as a result can really only perform flood coating with white ink under/over the printed area and are not capable of high quality images in white ink.”

Ink quality then is one issue which affects the shop attempting to print white ink, and a related issue is speed and cost. Some white inks may require more than one pass to opaquely cover the substrate, which can affect job throughput and turnaround time, as well as the overall rate of ink consumption. If you have to use twice as much white ink, you’re going to go through it twice as fast.

“With white ink, the ‘devil is in the details,’” says Edwards.

Shades of White

While “traditional” (if that’s the word to use) white ink is opaque and often TiO₂-based, Epson’s UltraChrome HDR White Ink takes a unique approach, utilizing “an all-new Organic Hollow Resin Particle Technology, which forces light to randomly scatter, producing the illusion of seeing the color white.” This ink technology is part of the company’s Stylus Pro WT7900 system which is designed for, among other applications, proofing and prototyping gravure- and flexo-printed jobs that will use white ink.

The White Stuff

As white ink formulation and performance have improved, applications for it have proliferated, both on rollfed and flatbed printers, although the latter is where most of the action has been. Some of the top new uses for white ink are on transparent films, where “paper” and “white” are not synonymous. White inks are thus often used in backlit applications, especially those in which the image is viewed from the unprinted side of the media, such as point-of-purchase and other types of retail advertising displays. Some wide-format printers can print in layers, with the white layer sandwiched between two colored layers (one envisions a very thin, Technicolor Oreo) on the same side of the substrate. “This is achieved by printing color data on two separate layers with a white flood fill printed as a diffusing layer between them,” says Edwards. The advantage of this is that it allows the graphic to be lit from either side, enabling users to rely on ambient light and turn off the lightbox, saving energy.

Opportunities for Printers—Or, No More Bad White Puns

One of the important aspects of any shop looking to offer or expand wide-format printing capabilities is to carve out unique niches and applications, and these niches and applications are often aided and abetted by new technology. “Technology,” though, doesn’t always mean advances in hardware. New ink formulations like white inks seem low-tech, but a lot of engineering “technology” goes into them.

White inks can serve several useful purposes for shops that employ them. Not only can they be used—as described above—to provide unique types of transparent and backlit applications, and used by themselves on non-white substrates, they can also serve as “base coats” on non-white substrates on top of which other colors can be overprinted without risking show-through. (Again, the analogy of painting a room is apt here, as we often use a white primer coat, especially when we want to paint a lighter color over a darker one. Anyone who has ever tried to paint a blue room yellow knows how this works...or sometimes doesn’t.)

Still, investigating and developing white ink applications is an excellent way to carve out a unique product niche. As is also the case in small-format printing, coming up with new types of products is a way to provide added value for current customers—and appeal to new ones.

“More than 90% of our customers choose to equip their flatbed printers with white ink printing capability,” says Océ’s Edwards. “They prove every day that the ability to print on unusual or even exotic media and objects opens a huge range of possibilities.”

That 90% figure says several important things, the most crucial of which is that having the capability to print white is becoming a basic capability of today’s wide-format printer. So even as it opens the door to new possibilities, like so many once-cutting-edge things in the printing industry, it may soon become a basic necessity.