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Printer Technology: Looking Under the Hood

Ken Mergentime is the former executive editor of Sign & Digital Graphics and WRAPS magazines.

The rapid pace of technological development and innovation in the area of wide-format digital printers has dramatically changed the landscape of print possibilities for the sign and commercial graphics industry. From ultra-high resolutions and ever increasing production speeds to the ever-widening range of printable substrates—the technology that enables these feats has become the backbone of this progress.

The end-goal, of course, has always been increased quality and productivity. Here we present perspectives on today's printer technologies, from some industry members who are directly involved in printer manufacturing. We will look at what they feel are some of today's most important technological developments, and then drill down into three specific technology areas: printheads, LED UV-cure technology and media transport systems.

Most Important Technologies

There are obviously different opinions as to which technology introduced to wide-format printing in the last five years might be the most important—the answer really depends on who you ask. And with the advent of so many technologies—true grayscale printing, latex ink technology, hybrid inks, multi-drop capabilities, etc.—it's instructive to consider a few perspectives.

Deborah Hutcheson, director of marketing, Agfa Graphics North America, takes a bit of a holistic view. "Wide-format technology advancements can be characterized as a process of evolution rather then one of revolution," she says. "We continue to see steady progress in printhead technology, UV ink curing technology, image processing techniques and media transport automation."

On the other hand, Joseph J. Ryan, director of business development for Ricoh Printing Systems America, points specifically to the availability of white ink to the industry as important. Opaque white ink, he says, is now being widely used in a variety of sign and graphic applications.

"White tends to have a physically large pigment size, which made it a bit harder to work with in the past, but that has changed," he says. "You need that white opacity for many different digital sign applications such as backlits, which benefit hugely from white ink. If you want to print onto a dark surface, you have to put down a white undercoat; so white ink has done a lot to broaden both the colors of substrates and the colors of inks people are using."

This development has also helped put wide-format inkjet on a more equal footing with screen printing.

Andrew Oransky, vice president of sales and marketing, Roland DGA, Irvine, California, believes the emergence of LED curing systems for UV-cure printers was the biggest game-changer of the last five years.

"LED-based UV-cure technology has solved a lot of problems that earlier UV-cure printer technology was plagued with," he says, pointing to the disadvantages of traditional curing lamps such as the requisite high heat, high energy consumption and relatively short lamp life.

"When ink formulators and lamp manufacturers came together to develop effective LED curing systems, all these problems were solved," Oransky says.

Mark Goodearl, senior ink product manager, EFI Inkjet Solutions, agrees. "Production speed of LED-based UV-curing inkjet is the most significant development because it eliminated so many of the challenges that come with other solvent and even traditional UV," he says. "Even with the advent and growth of latex, LED-UV printing has emerged as higher-volume, low-energy production system for businesses that have grown their output volumes and still need to print onto a broad range of substrates."

Printhead Technology

The printhead is the most complex and crucial part of any inkjet printer. It's safe to say that more research and development has gone into improving printheads than any other part of a printer—and today's printheads are more sophisticated, versatile and complex than ever before.

"The most important recent development for printheads," says Ricoh's Ryan, "is the availability of page-wide arrays—very long arrays of linear printheads, such as the SAMBA printhead developed by Dimatix." Similar in concept to HP's Page-wide array printhead technology, this design allows a much wider print swath in a single pass with guaranteed perfect nozzle alignment, he says. "Historically, if you wanted to print across a 12" or 17" path, you’d be using smaller printheads, with around one thousand nozzles each, and you would have to have their orifices stitched together." Eliminating the stitching process—and the slight misalignments that can arise from it—results in much higher speeds with higher quality printing, he says.

"At Agfa we feel that several printhead developments are key," Hutcheson says. "Higher nozzle densities, the use of finer droplets, higher jetting frequencies, variable drop capability which improves gray scale, higher jetting robustness (for greater reliability) and wider ink compatibility are all important." These developments have helped her company deliver UV inkjet systems with higher productivity, higher image quality and improved system reliability, she adds.

Ryan says that with the ability to produce multiple drop sizes from a single printhead one can achieve very high resolution with tiny drops, while at the same time affording faster printing because larger drops can also be laid down on areas where needed. To achieve a larger drop size from a printhead nozzle with a relatively small native drop size, several droplets are ejected from the printhead nozzle in rapid succession, and then the drops merge in mid-flight before reaching the media surface as a larger single drop.

Hutcheson says that looking forward, "Agfa sees printhead technology continuing to evolve and improve productivity, quality, jetting robustness. We see the future technology offering a broader ink scope, a lower cost per nozzle and page wide arrays for single pass printing." 

LED UV-Cure Technology

As noted above, LED-based UV-cure technology is having a powerful influence on the industry, but how does it differ from conventional UV-cure print technology? They differ both in the lamps used and in the ink formulations.

EFI's Goodearl says that unlike the conventional wide-spectrum arc and mercury vapor lamps typically used in UV-cure systems, LED lamps produce a much narrower spectrum of light. The LED-UV inks are formulated with a set of special light-reactive monomers that can respond to the narrower band of LED light.

However, "unlike with standard UV lamps, there is no warm up period required for LED-based cure lamps," Goodearl says. "As a result, LED lamps last longer."

The other main benefit, he says is the elimination of the high heat that conventional UV cure lamps produce (upwards of 200 degrees). "LED lamps cure at about 80 degrees Fahrenheit, which is much cooler than both the heat generated by conventional UV lamps and the heat required to dry prints on latex printers. This creates tremendous energy savings." In addition, he points out that it also means that users can print onto heat-sensitive substrates such as corrugated board and very thin films that can warp, curl or melt due to high heat.

Jay Roberts, product manager of UV printers for Roland DGA, points out additional ink  differences. "These inks are dramatically different in both chemical make-up and functionality," he says. "Conventional UV-curable inks tend to be more aggressive, bonding to a slightly greater surface area. However, UV-LED inks have an added bonding agent. While UV-LED inks do not have any negative effects upon materials, they do tend to bond less aggressively to substrates unless a stronger chemical bonding agent is used in the formula," Roberts says.

Digital UV inks have been evolving since their introduction to the market in 2005, gradually improving in adhesion, flexibility and durability. The problem has been that when you improve adhesion, flexibility is often lost—great for printing onto rigid substrates, but this industry demands a huge range of substrates.

Goodearl says that his company has been working on the flexibility issue as well. "A few years after EFI established an LED production printer, we addressed one of the remaining challenges with LED. Working with 3M we developed an ink formulation that doesn’t have as hard a cure and won’t crack when stretched or 'silver' when laminated," he says. "Now LED-UV printer users can create fleet and vehicle graphics and other applications that require greater flexibility."

"No digital UV ink can meet every demand placed upon it," Roberts says. "Instead these inks tend to be 'middle-of-the-road,' providing the best results for the most widely-used substrates. We have yet to develop formulations that meet all of the requirements equally."

Roberts notes that in the screen printing industry, where UV-cure technology have been in place for many decades, there are 47 different "flavors" of UV-curable screen printing ink, each designed to meet different application requirements.

Roland has four of these UV ink "flavors" for digital printing.  The company developed a "traditional" UV ink (ECO-UV) to satisfy the majority of requirements, then added additional formulations (ECO-UV 2 and ECO-UV 3) designed to adhere well to PE (polyethylene), PP (polypropylene) and PVC (polyvinyl chloride) substrate families. "As these inks were evolving," Roberts says, "we also introduced our ECO-UV S ink, a truly flexible ink, much more flexible than existing formulations."

EFI's Goodearl notes that initially a big barrier to LED’s growth was its slower production speeds. "Reaching full production levels with LED was the initial spark in the chain of events that will likely see the entire UV space in inkjet imaging migrate to LED at some point in the future."

Additionally, Goodearl points out that in April of last year the European Union released EU directive 2009/125/EC which established a ban on mercury-containing lamps in the European Union. "This includes HID (high-intensity discharge) mercury vapor lamps often used in conventional UV-curing inkjet printers. While the EU eventually decided to postpone the ban until September of 2018 in Europe, the prospect of a ban is certainly a motivating factor for wider adoption of LED-based curing systems."

Media Transport Technology

Another crucial area of printer technology has been the evolution of media transport technologies. It has become especially important with the larger high-speed flatbed presses where rigid substrates are involved; and also in the area of production-grade inkjet textile printers.

"In the new 'normal' for today’s print environment," says Chris Guyett, sales operations and marketing communications manager for Durst Image Technology, Rochester, New York, "maximizing print volume and production efficiently, needs to be the top of the list of operational concerns for print service providers. With higher print speeds and automation workflows, media handling and transport have become integral to today’s printing systems."

Guyett says that older media transport systems worked by simple motors, electronic circuit boards and often required manual corrections by the operator during printing. However, newer transport systems function with a combination of mechatronics and software, he says. "Constant and consistent sensory measurement of the state of the media (weight, roll diameter, width, thickness, tension, etc.), where the calculation of these measurements and then constant controlling of the right parameters allow the transporting of even difficult and dimensionally unstable medias in a reliable and consistent way."

Becky McConnell, associate product marketing manager, FUJIFILM North America, Graphic Systems Division, explains the advantage of automated sheet-loading systems. "Fully automatic load and offload reduces handling time significantly," she says. "It allows high-production print providers to maximize the efficiency of their machines."

The Inca Onset presses sold by Fujifilm use the Hostert sheet-loading system, McConnell says. A pallet full of sheeting is placed at the loader end and a single sheet is picked up with a vacuum apparatus (equipped with a tapper and air-jetter). The grippers then pull the sheet onto a lay table for registration. The offload system then pulls the sheet from the lay table to the printer's bed and the table vacuum is engaged to draw down the sheet. Once printing is complete, the offload system then uses vacuum grippers to pull the sheet off the bed and onto the off-load pallet for stacking.

This kind of auto load/unload system guarantees that the printer's high print speeds are not hindered in any way.

"As throughput on high production presses continues to grow," McConnell says, "attention will continue to focus on media transport and handling systems. In the future, I would expect that high-production press manufacturers and distributors will increasingly partner with finishing solution providers to create a seamless manufacturing process for high throughput wide-format printing."