As digital printing platforms take on larger shares of commercial printing, toner production gets serious.

By Noel Ward, Digital Printing Editor — Graphic Arts Online

Some of the magic in digital printing is the stuff that actually makes the words and pictures on a page. With offset printing, ink generally is not specifically developed for the particular platform (with some exceptions, like Heidelberg Saphira inks for Anicolor or Presstek DI inks). On the whole, offset ink gets loaded into the press, and after color adjustment, you’re good to go. It’s different with digital presses. Each flavor of print engine is developed with a specific toner chemistry. Though they may have colorants in common, the chemistry for that toner that pops off the photoconductor and fuses onto the paper is a long way from the ink used in an offset press.

 

Most of the companies that make electrophotographic (EP) presses persist in calling their toner “dry ink,” even though it’s really a minutely milled plastic powder that’s highly engineered and manufactured under tightly controlled conditions. Chemical and material science, plus a side course in physics, are all part of making it work in the fandango of heat and light inside a modern digital press. With a couple of exceptions, toner is produced as blocks or sheets of a plastic or polyester in each of the four process colors. These are pulverized using a number of different processes until the particle sizes, depending on vendor, range from roughly 4 to 15 microns. By comparison, a particle of talcum powder is about 10 microns and the diameter of a human hair is about 70 microns. This explains why toner so eagerly embeds itself on your clothes when you load printers, and can be hard to wash off your hands.

Is it ink or is it toner?

One of the exceptions is HP Indigo, which grinds the particles even finer, to just 1–2 microns, and mixes them with a liquid carrier to create an electrically charged viscous paste that at a casual glance looks very much like offset ink in consistency. Benny Landa, creator of the Indigo press, once told me that if the toner particles used in the company’s ElectroInk were not suspended in the liquid or paste, they would just float around the room. Well, maybe. But think of the dust you see in the sunlight coming through your window and you get the idea of how fine 1 micron is.

This tiny particle size is instrumental in providing a consistent gloss, sharp image edges and thin image layers that map well to the surface of a page. The result is a uniform finish on a wide variety of substrates. Since ElectroInk possesses some of the rheological characteristics of liquid or paste offset inks, many printers feel Indigo prints have a look and feel that’s closer to offset printing than those other digital presses. While it looks like ink, it functions fundamentally like all electrophotographic toners: taking on an electrical charge to be attracted to an image with an opposite charge. ElectroInk drys to a tack on a warm cylinder before transferring under pressure to the paper. (Dry toners are generally fused with heated fuser rolls.)

A major development is chemical toner. First introduced in the 1990s, it has recently begun to come into significant distribution, though it is still much less common than conventional pulverized toner. Long-term, though, it will likely become the most common type of toner for most electrophotographic printing applications as it offers several advantages over conventional toner. It’s somewhat less expensive to manufacture, and because it is “grown” in a controlled process, the particles have a much more uniform structure and size—more spherical than the random-sized, rough-edged shards typical of pulverized toner.

“The uniformity helps improve print quality, especially in color images,” says Mary Fromm, worldwide toner VP at Xerox in Webster, NY. “Because it can be imbued with favorable properties for charging, image transfer and fusing, chemical toner can also impact equipment design, performance and energy consumption.”

One of the more visible examples today is EA (Emulsion Aggregation) toner developed by Fuji Xerox and Xerox, which is used in a number of the company’s latest digital color copiers and printers. The DocuColor 700, launched last year at drupa, uses it, as do the latest models of the Nuvera 144 and 288 monochrome presses.

As a rule, chemical and conventional toner are not compatible with each other, and a copier or printer is typically engineered to use one or the other. “This is part of the product development decision process,” says Fromm, “and it’s often decided fairly early on, depending on the objectives for the product.”

For example, Xerox’s iGen3 and iGen4 presses were designed from the ground up to use conventional toner, so we’re unlikely to see an EA toner version of either box. On the other hand, the Nuvera 144 and 288 were introduced with conventional toner but were designed in a way that allowed for a different configuration of the machines to use EA toner.

I can see clearly now

Whether chemical or conventional, dry or liquid, toner is a critical part of image quality in digital printing, and every vendor offers technologies that differentiate them from their competitors.

One of the more interesting forms of toner these days is the clear toner offered by Kodak on its NexPress line. The clear toner—which looks like a white powder—goes in the fifth imaging station on the NexPress. Initially this was offered as a way to put a spot or flood matte or gloss on a page, much like varnish on an offset press. It was intended to add eye-appeal and made mail pieces less prone to rub-off when being abused by mailing machinery. A second step, running pages through the offline NexGlosser, reheats the clear toner yielding a hard gloss that looks much like a lamination, which can take substantial punishment in the mail stream and still look great.

Kodak has taken this process a step further with Intelligent Dimensional Coating, which uses a specialized fifth toner station to add texture to an image, building up a clear toner with a larger particle size that lets it rise above the surface of the page, not unlike old-style offset thermography. Kodak’s Intelligent Dimensional Coating adds visual interest, better tactility, and can make images jump off the page. [The technique was used on the March 2009 GAM cover.]

“The effect is achieved by building up a layer of clear toner, which is comprised of larger particles than pigmented toner,” explains Chuck Hura, toner guru and worldwide product manager, digital printing solutions at Kodak. Hura showed me a guide Kodak provides for designers to use when creating documents using Adobe Creative Suite so they can more easily achieve the look and feel they seek. A little time in Illustrator, Photoshop and InDesign gets the file ready so the special toner and the NexPress can work their magic. According to Kodak, all new NexPress systems are shipping with this (previously optional) fifth toner station, and use of clear toner and Intelligent Dimensional Coating is growing among NexPress owners.

Hot flashes

Whether the toner is conventional or chemical, most digital presses are cut-sheet devices that print one sheet of paper at a time. The electrophotographic process puts heat and pressure to melt the powdered plastic and bond it to the page. But as print speed increases, the paper simply can’t spend enough time in the fuser for a proper bond. Enter flash fusing using heat and light energy and a different type of toner. (See TechWatch, December 2007 GAM.)

The toner is still pulverized plastic powder, but with chemicals and additives that let it melt suddenly and almost instantaneously when exposed to specific types and temperatures of light. “The toner is actually designed a bit differently,” says Xerox’s Fromm. “It has an ingredient that absorbs the infrared fuser light, and that’s what makes it melt.” This bonds it to the paper, enabling substantially higher print speeds than can be achieved with pressure fusing and at substantially lower energy costs.

“This is a much more paper-friendly fusing process,” notes Guy Broadhurst, VP new technology at the production printing systems division of Océ North America, Boca Raton, FL. The company’s VarioStream 9000 and ColorStream 10000 continuous feed printers use infrared lamps and toner with lower melting point to fuse pages running at up over 850 pages per minute. “The toner is not only easier to produce, but the fusing process assures better penetration of toner into the paper, while reducing the amount of power and heat required,” notes Broadhurst.

Xerox uses a similar technology on its monochrome 650 and 1300 devices and 490/980 continuous-color feed presses. “There’s no contact between the fuser and the paper, and while the page does heat up for an instant, only the toner is affected and moisture isn’t driven out of the paper,” notes Fromm. “This is important for a variety of finishing and binding operations.”

Punch Graphix claims it was the first to implement polyester-based shape-modified toners in high-speed digital color printing. It’s FA toner gives more vivid colors and a wider application range, and is FDA-approved for indirect food contact. Any Xeikon engine with an X-800 front end and equipped with FA toner is Pantone-licensed. Five predefined spot color FA toners for use in the fifth station of a Xeikon presses are red, green, blue, orange and extra magenta. Xeikon also custom blends toners.

Toner in light-duty machines

Last fall, Canon introduced a light-duty imagePRESS C1+with clear toner for short runs and proofing. The 14 page-per-minute imagePRESS handles coated and textured stocks. The clear toner can also be used as a security feature, printing watermarks. The imagePRESS Server Q2v2 is offered for high-end users.

Konica Minolta bizhub PRO C65hc departs from standard four-color toner sets with a High Chroma toner, built around an extended color gamut. (See p.31.) This lets it reproduce more of the sRGB color gamut so output is much closer to that displayed on sRGB monitors. Konica Minolta says High Chroma technology was specifically developed to support the sRGB criteria for cross-media communication. Konica Minolta says it is aiming its BizHub PRO C65hc at in-plants, print-for-pay retailers and “forward thinking commercial printers looking to confidently migrate to a digital workflow from offset with a cost-effective solution.” The bizhub PRO C65hc has acquired Pantone color approval and licensing. And Konica Minolta says the bizhub PRO C65hc greatly exceeds offset print results using the industry standard delta E 2000 testing methodology. When compared with other printers in the same category, the Konica Minolta bizhub PRO C65hc has one of the largest PMS gamuts.

PRINT 09 advances

Toner developments were a key part of the news at PRINT 09. Xerox announced a new low-gloss toner for its DocuColor 7002/8002, which also feature an in-line spectrophotometer and Automated Color Quality Suite (ACS), compatible with digital front ends from EFI, Creo and the Xerox FreeFlow Print Server. The choice of servers, low-gloss toner and full ACQS capabilities make it the strongest product offering in its class, says Xerox. The first one went into Kings College in Wilkes-Barre, PA.

HP announced new white inks for its Indigo 5000 and 5500. These expand the machine’s ability to handle packaging and unique creative work.

MGI showed its DP60 Pro digital color press, which uses high-definition, oil-free toners. The company also showed its JetVarnish inkjet coating system, compatible with its DP60 Pro toner, as well as offset inks and other toners.

Xerox showed its iGen4 Automated Packaging Solution. Stora Enso, which optimized substrates for it and integrated the materials handling system, has sold it in Europe since its launch last year. Because the iGen4 APS is designed for short-run packaging, Xerox has applied for FDA approval of the toner in food packaging uses. The automated, inline system handles production of complex folding cartons—including variable-data—with little intervention, Xerox says. Components include the iGen4 press, Epic CTi-635 varnishing unit, and a Kama diecutter that can also apply foil—all compatible with the underlying toner.

Xeikon ran its 8000 inline with toner-compatible UV coating, lamination and supergloss coating. Xeikon also had a “label area,” with numerous samples to demonstrate the capabilities of its Xeikon 3300 digital label press.

Just one part of the system

Broadhurst, Fromm and Hura all point out that, as highly developed and as vital it is, toner is just one component of very complex systems. Almost all toners are designed, engineered and produced to match the operating characteristics of specific families of digital presses. While they may share a multitude of characteristics with other toners from the same vendor, they are anything but interchangeable, and have to work reliably with a long list of substrates that may pass though a given press. Many modern presses automatically adjust to accommodate different papers, yet how the toner in that press works over a range of papers and fusing temperatures is an essential element of print quality.

The more you understand about toner, it becomes clear that even though it as a consumable product, toner is anything but a mere commodity.