Is Inkjet in Your Future?

What will your in-plant operation look like two years from now? How about five years? One technology that may be finding a home on your shop floor is inkjet printing. It may already be present in the form of monochrome addressing systems or wide-format devices. But if the hopes and dreams of leading equipment providers play out, full-color inkjet presses may also coexist alongside offset and EP (electrophotographic) systems.

So what will these systems look like? A lot like they do right now, only better. High-speed, full-color inkjet today is at roughly the same stage of development as EP color toner was about 10 years ago: partially ready for prime time but with the caveat that buyers of these systems are pioneers on the leading edge of an emerging technology.

The presses from the big players are all continuous-feed models and feature speeds from 225 to 650 feet per minute and print widths up to 30˝.

InfoPrint, Kodak, Screen and Océ all have numerous installations in a range of print facilities. HP has a handful of its big inkjet systems installed, while Kodak and Xerox either offer new systems today or are readying them for the market. All require minimum monthly volumes of at least 10-15 million impressions before the economics begin to work, so they are not for everybody. With one or two exceptions, there are no cut-sheet production inkjet systems available.

As these systems evolve, new algorithms will focus on the subtleties of drop size and placement, improved print quality, amount of ink used, color accuracy, and the range of papers available. Further under the hood will be print speeds, head durability, use of additional colors and increasingly powerful servers. We can expect a long battle for dominance as the different technologies evolve. And it all starts with the print head.

The print head is the core of every inkjet system. Highly engineered and manufactured to exacting specifications, arrays of heads fire ink droplets at fast-moving paper from banks of tiny nozzles. There are two primary technologies, continuous inkjet and drop-on-demand, with the latter employing three different techniques for putting ink on paper.

Continuous Ink-jet

CIJ technology is used primarily by Kodak, initially with monochrome heads for addressing applications and on hybrid offset/inkjet systems, then on the company's VX and VT lines of high-speed four-color printers.

CIJ heads fire a steady stream of electrically charged ink droplets at the paper. Text and images are created by deflecting unwanted drops into a gutter and then to a waste container. While capable of high speeds, CIJ has traditionally been unable to achieve the image quality of other technologies.

That's changed dramatically with Kodak's proprietary STREAM technology, used in the company's new Prosper S10 print heads and the 5000XL Prosper press. STREAM sends an electrical pulse to heaters surrounding each nozzle opening in the head. The emerging ink is broken into a continuous stream of fine droplets. Drops not required are deflected and re-circulated to the ink supply.

With much smaller drop sizes and superior drop control than older CIJ systems, STREAM can deliver near offset quality printing on a variety of substrates, including some coated glossy stocks. This sets it apart from other inkjet systems, and appeals to print providers seeking high speed (up to 650 feet per minute), a 24.5˝ print width, excellent print quality up to 175 lpi, and monthly print volumes of up to 120 million A4 impressions.

Kodak officially launched the Prosper 5000XL at IPEX in May, but has been announcing orders since the fall of 2009. The press, however, will not be generally available until the middle of 2011. About half of the orders already announced will be monochrome machines. These are destined for book manufacturers, where throughput speed and high print quality appeal to publishers looking to take advantage of the new supply chain economics offered by high-speed inkjet technology. The balance will be full-color models for transactional, direct mail and transpromo applications.

Drop on Demand

As the term implies, these heads fire ink droplets only when needed, aiming them at specific spots on the media to create an image. Although initially used in an enormous range of low-speed printers, drop-on-demand heads can also run very –quickly. Three markedly different technologies use DOD heads

Thermal inkjet (TIJ) is the most common technology, primarily because of its use in millions of desktop printers in homes, small offices and schools, as well as in most wide-format printers and in commercial applications such as addressing systems and engineering plotters. Thermal heads are less expensive than those in CIJ or piezoelectric systems but have to be replaced more often, typically when changing ink.

TIJ works by sending a pulse of electrical current through a small chamber containing the ink. The heat from the pulse causes an explosion of steam, creating a bubble that displaces ink in the chamber, firing a droplet of ink through a nozzle onto the surface of the media.

HP, the leading advocate for TIJ, uses the technology in the majority of its desktop and wide-format printers, and has extended it into commercial print with its big T-300 and the recently announced "duplex-in-a-box" T-200 inkjet web presses. Both machines use the same kind of industrial-strength heads as some of HP's wide-format systems. HP says the heads at customer sites are proving more reliable than anticipated, delivering better uptime and requiring fewer replacements.

Print quality is not quite as good as some samples from the Kodak Prosper, but are more than satisfactory for the applications for which these devices are intended. That spans most types of direct mail, transactional/transpromo documents, and many types of publishing, including books with numerous color photos and illustrations such as textbooks, cookbooks, how-to guides, etc.

While there are differences between HP's TIJ and offset output, the economics of the new publishing models this technology offers outweigh any differences in print quality. The only real critique is that TIJ cannot yet print on a coated stock at high speed. While a limitation for some applications, it is not a show stopper. And given that HP has more than a little experience spraying ink onto coated surfaces, one imagines we may not have to wait too long.

For the moment, HP requires the use of specially treated papers, or use of a "bonding agent" that limits ink penetration into the page, minimizes dot gain and helps ensure ink adhesion. HP's big T-300, which prints up to 30˝ wide at 400 feet per minute, is available now while the 20˝ T-200 should be available in early 2011.

Piezoelectric: A Proven Solution

Piezoelectric heads have been a mainstay of inkjet printing for a quarter of a century. The word piezo comes from a Greek term meaning to squeeze or press. There's an ink-filled chamber behind each nozzle. When voltage is applied to piezoelectric material in the chamber, the material changes shape. This creates a pressure pulse in the ink that squeezes a droplet through the nozzle.

Piezo heads can accommodate a wider variety of inks than TIJ or CIJ heads, and although piezo heads are more expensive, they tend to be substantially more durable, capable of thousands (rather than hundreds) of hours of use.

InfoPrint, Océ and Screen all use piezo heads in their high-speed inkjet presses, as does Kodak in its VL series. In each, the print quality is perfectly acceptable for many transactional/transpromo jobs, as well as direct mail and publishing applications like textbooks, cookbooks and others requiring color photos and illustrations. In reviewing the samples available, Océ's JetStream family—the widest range of piezoelectric inkjet systems available—seems to have a slight edge on quality at the moment, on a par with HP's T-300. Systems from all these companies are available now, with new models likely to continue raising the bar on quality and productivity. Both InfoPrint and Océ offer MICR inks for security and check printing.

Each vendor using piezo heads has a list of approved papers for use with their respective devices, although the InfoPrint 500 uses ink with characteristics that limit penetration into the substrate, broadening the potential range of papers available.

A Compact Approach

Taking a different approach than vendors of the big iron is RISO. Intended for office and light production use, RISO's ComColor machines are compact, inexpensive, quiet and use sheets of paper rather than large rolls. Capable of up to 150 pages per minute, they are finding homes in small print shops, some transactional service bureaus (where they may serve as backups for bigger inkjet systems) and in-plants where low-cost color printing is required. MICR capability is available through a third party.

What's most interesting is that none of these machines are the game-changers pundits would have you believe. It will be a machine-generation or two—when cut-sheet models come to market that compete directly with EP systems, and offer inkjet economics at lower print volumes (i.e. under 2 million/month)—before the shape of the –market will truly change. And vendors are silent on plans for cut-sheet inkjet. For the next five years, inkjet systems will take work from both offset and EP presses, but will ultimately coexist rather than replace or dominate. IPG