We've come a long way since the cave paintings and petroglyphs of our prehistoric ancestors. The natural pigments and rudimentary tools used to make those ancient drawings and carvings have gone through many changes over the millennia, and this evolution shows no sign of ending. In fact, the pace at which new display graphics technology is being developed has resulted in commercially viable products that would have seemed far-fetched just a decade ago.
The latest high-tech displays rely on innovations such as electronic inks and papers and organic light-emitting diodes—things you may have thought could only exist as special effects in sci-fi movies. But these display systems are steadily coming of age, and major manufacturers are putting them to use in signage, industrial products, and consumer goods. Read on to discover more about these technologies and what unique opportunities they may have in store for you, whether your shop uses screen printing, wide-format inkjets, or other imaging methods.
Electronic paper at PARC
Xerox's Palo Alto Research Center (PARC), Palo Alto, CA, developed the technology for Gyricon, its electronic, reusable paper, in the 1970s. At the heart of a Gyricon sheet are bichromal balls (Figure 1), small spheres that are black on one side and white on the other (and have also been produced in other colors). Bob Street, a research fellow at PARC, explains that these bichromal balls are essentially embedded in a plastic sheet, and then the plastic sheet absorbs a liquid and swells. "The balls start out embedded in a hole, and that hole is made larger and filled with a small amount of liquid so they can move," he says.
The balls are electrically charged to be positive and negative at opposite poles. Applying voltage to the sheet's surface causes the spheres to rotate and show a color. Gyricon can be used to display text and pictures, and the technology is bistable—imagery remains on display until new voltage patterns are applied. But getting Gyricon to that point was a challenge.
"All of these methods, whether it's Gyricon spheres or electrophoretic particles, you want them to be bistable, but not too bistable, and you don't want them to relax too quickly," says Dave Biegelsen, a research fellow at PARC. "So the control of ions in liquids—whether electrophoretic or Gyricon—has always been a bit of a problem. It's only in these small increments over long periods of time that these things finally become stable technologies."Advertisement
The initial interest in Gyricon was its potential as a reusable and portable electronic paper. Biegelsen says researchers found early success with watches, calculators, and other products designed with large, seven-segment displays—though the intent was to boost the resolution. Gyricon media was made in a continuous-roll process in 2-ft-wide swaths, but Street says there was no obvious technical limit to making it bigger than that. "That made the signage part of it very attractive. You could boost the media very well," he notes.
In the beginning, Gyricon relied on voltage delivered via a fixed path of electrodes, a setup that Street says allowed users to make a limited number of fonts and characters. "Then the technology moved into essentially an arbitrary addressing of each pixel in the backplane—an active-matrix backplane. That allowed a more versatile, more complete set of images that could be displayed," he explains.
Another development was a process in which each bichromal ball was encapsulated in its own external, transparent sphere and held in a liquid, much like an egg sac. "You could, in principle, print those," Biegelsen says. "So you could have Gyricon ink if you wanted."
The Gyricon company incorporated about six years ago and took the lead on technical development. Some of that technology remains at PARC, but most was transferred to Gyricon LLC. Xerox Corp. terminated the operations of Gyricon LLC, its wholly owned subsidiary, at the end of 2005 and has since focused on licensing the intellectual property associated with its electronic paper. Re-imagable paper remains a part of ongoing projects at Xerox.
Research started at the MIT Media Lab led to the foundation of Cambridge, MA-based E Ink Corp. in 1997. E Ink's electronic-paper displays rely on microcapsules. Each microcapsule contains clear fluid, positively charged white pigment chips, and negatively charged black pigment chips. The electrical field you apply determines which pigment chips rise or fall. The microcapsules are smaller than 50 microns in size.Advertisement
Jennifer Haight, spokesperson for E Ink, says, "We coat them onto a thin film, so there are millions of them. When you apply the charge, you'll be able to see the characters that you're programming in."
E Ink sells neither its electronic ink, nor its finished electronic-paper product, E Ink Imaging Film, to the general public. Instead, the company sells its technology as a module to companies like Sony, Citizen, Lexar, and others (Figure 2).
E Ink's first product was a signage system called Immedia. It was updated by way of wireless computer, and E Ink targeted its sale to retail stores. From there, the company launched Ink in Motion, a preprogrammed sign that cycles through a series of different images. Such a product could be used for dynamic P-O-P displays, shelf talkers, wall mounted graphics, and other applications. Haight says Ink in Motion can be just about any size, but units are typically 5 x 7 in. or 8.5 x 11 in. E Ink sells Ink in Motion through a distributor.
"It's not a static sign," Haight explains. With a color overlay, like a clear transparency with color printed on it, you effectively have a color sign. They're designed to be throwaways, although certainly not to the extent paper is. They run on two AA batteries."
E Ink shifted its focus almost solely to high-resolution displays when Sony signed on as a customer. The company's other area of interest is segmented displays, which Haight describes as simple, small-scale signage products. They can be found in watches, calculator displays, and the Lexar JumpDrive Mercury, which is pictured in Figure 2. Products such as the JumpDrive Mercury benefit from the bistable E Ink technology. The JumpDrive Mercury is a portable USB drive that is powered only when connected to a PC. Its E Ink segmented display indicates changes in available space, and the display continues to show the device's current status, even when the drive is disconnected from the PC.
The displays E Ink sells to Sony support four levels of grayscale and resolution of about 190 points/in. The high-res displays use thin-film transistors (TFTs), which essentially are current-carrying devices fabricated of thin films of silicon deposited on glass. Sony used the high-res displays in an e-book reader it developed in 2004, called LIBRIé. The Sony Reader, a model developed for the American market, may be available this year.Advertisement
E Ink's future focus includes color displays (Figure 3). Haight says the company hopes to sell color units either at the end of 2007 or early in 2008. The company currently overlays a color filter array on its E Ink Imaging Film—the same way LCD displays use color—but Haight says E Ink's researchers may be working on ways to use color inks. Flexible displays are also on the agenda.
"Because [our displays] are made on a plastic film, they're inherently flexible," Haight explains. "The problem has been that the electronics that marry with them are not flexible. Currently, there is no thin-film transistor in mass production that is flexible, which has really been a stumbling block to have an e-book reader that you could roll up or fold. If you wanted high resolution, that's not possible. TFTs currently are made mostly on glass."
Even though graphics and industrial printers aren't able to print E Ink's microcapsules or buy its finished films, opportunities exist to print on accessory items and components used in products that employ E Ink's technology. E Ink also sells a prototype kit that gives product designers access to the technology. The kit may be useful to shops that are exploring high-tech OEM projects to pair with their printing capabilities. The kit includes an active-matrix display made of E Ink's imaging film and the hardware and software necessary to produce a fully functional portable device.
Another take on electronic paper
"The simplest analogy: We can do television on paper," says Michael Feldman, president of Quantum Paper, Bloomfield Hills, MI. The company has developed two types of electronic paper: a static display (Figure 4) and an addressable, dynamic display. Both are flexible and rollable—but not foldable, and Feldman notes that their current draw is similar to static electricity. Neither display is bistable.
"The static display ranges from about 12-18 layers, depending on the artwork that is printed on top of the lamp," Feldman explains. "The foundation layers are a series of compounds and inks where we lay out a circuit that patterns the areas for illumination, and we can put an emitting ink on top of the lamp itself to create a wide gamut of color. In the instance of a dynamic display, we create a very fine printed matrix of addressable pixels. We essentially pixelate a piece of paper."
The technology is scalable, from shelf displays to billboards. According to Feldman, large displays are easier to make than small ones. "We can get very good resolution on a billboard with a much lower pixel density than what would be required for a cell phone," he says. "The density is a function of the application. We can achieve resolution comparable to high-definition TV on a piece of paper. That would require a gravure press to achieve the resolution, but that resolution isn't a requirement in many applications."
Quantum Paper's technology can be applied to a variety of substrates—cardboard, static cling, plastic, cloth, glass, and more. But Feldman says the company's present focus is on developing paper-based substrates. "Paper offers the most advantages and the most upside right now, so that's our priority. On a practical level, there is a minimum thickness, but we're using 100-lb cover stock," he says.
Quantum Paper's products are printed primarily by rotary screen and flexo. In fact, Quantum licenses its technology to printers, typically in the litho industry, whose annual revenues range from $20-300 million. Those who license the technology commit to put in place either an automated rotary screen line that Quantum has manufactured to its specs or a flexo system.
"We want to be confident that the printers have the resources and capabilities to make a commitment. We want a material commitment from them that they're going to make this a significant portion of their business," Feldman says. "It's our premise that if Quantum Paper products can, in a couple of years, be 20% of their gross revenue, then the profitability of Quantum Paper will far exceed the profitability of the rest of the business."
The organic light-emitting diode (OLED) was discovered in the 1970s by Dr. Ching Tang, a scientist at Eastman Kodak Co., who found organic materials that glowed in response to electrical currents. Since then, several companies have developed the technology further, helping it to evolve from its original green color to polychromatic displays and onward to full color.
Ghassan Jabbour, a professor of chemical and materials engineering at Arizona State University, describes OLEDs as simple devices consisting of multilayered structures sandwiched between two electrodes. Jabbour researches organic and hybrid optoelectronics, including OLED technology, and has participated in printing OLEDs on paper, plastic, textiles, glass, and silicon (Figure 5). He says OLEDs are grouped in two camps: small molecule (OLEDs) and polymer organic (PLEDs).
"You can inkjet print polymers, and you can screen print them," he explains. "On the other hand, we were also able to screen print molecules by putting them in polymer hosts. Both versions can be printed if one knows what to do with them. You can print them and make very nice displays."
Jabbour says displays can be quickly made using screen printing or roll-to-roll printing (offset), but the resolution will not be as high as what can be attained when using vacuum thermal evaporation (VTE). We'll discuss VTE a little later.
"You print organics like any ink, and then you print or deposit electrodes," he says. "There is no curing. You let it dry, and that's it."
Environment is a major consideration when screen or inkjet printing OLEDs. Jabbour says printing and encapsulating displays in open air is fine for the purpose of demonstration, but an inert environment around the print-ing area—such as one produced by nitrogen—is necessary to ensure a display's longevity.
Janice Mahon, vice president of technology commercialization for Universal Display Corp. (UCD), Ewing, NJ, says a number of different organic molecules are used to build OLEDs—and several types of OLEDs are made (Figure 6). She explains that the molecules either naturally occur as a crystalline materials or naturally occur in a polymer precursor, typically some type of monomer.
"In the case of small-molecule or crystalline OLED materials, they're usually deposited using conventional vacuum thermal evaporation," Mahon says. "They're put in a crucible or boat. That boat is heated up, and those materials then evaporate or sublime. They then recondense on a substrate that is positioned upside down in side the vacuum chamber."
OLED displays are either passive matrix or active matrix. A passive-matrix display emits lights by conducting energy through columns and rows of anodes and cathodes. Thin films of organic materials are sandwiched between the anodes and cathodes. Application of electrical current causes the pixels in the two-dimensional array to emit light. Pixels become brighter as more current is applied. MP3 players, cell phones, and other portable electronics are popular candidates for passive-matrix OLEDs.
Active-matrix OLEDs use thin-film transistors to continuously control the flow of current through each pixel in a display. The active-matrix OLED is designed to use less power than passive displays, which makes the technology a better choice for portable devices in which battery power must be conserved. Active-matrix OLEDs also have been used in the production of prototype televisions and other types of larger displays.
White, phosphorescent, transparent/top-emitting, and flexible OLEDs are other technologies UCD develops. White OLEDs have the potential to produce 200 lumens/W, which Mahon says exceeds what conventional fluorescent tubes can provide. These OLEDs can be used in displays and have potential uses in illuminating frontlit and backlit graphics. This technology also is of interest to the US Department of Energy's solid-state lighting initiative.
Phosphorescent OLEDs, she explains, use metallo-organic molecules and offer a great deal of power efficiency. For instance, a display that would normally consume 1 watt of power could consume just watt. "It also has a dramatic impact as you get to larger and larger displays, where heat dissipation becomes more of an issue," she says.
Transparent and top-emitting OLEDs share a similar method of construction. Transparent OLEDs emit light from the top and bottom. The use of a transparent anode, cathode, and substrate makes that possible. The use of an opaque substrate makes what would be a transparent OLED a top-emitting display instead.
"The concept of having a transparent display is one of those wild kinds of technologies," Mahon says. "The thought of being able to have displays integrated directly into a windshield or window for signage and advertising is tremendous."
The materials that drive the displays described here have yet to become completely accessible to graphics and industrial printers. But as the development of these technologies continues, printing companies will likely be among those who reap rewards from the ability to produce portable and addressable signage, promotional displays, and much more. In the mean time, we can look to the systems described here as bold and revolutionary signs of things to come.
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