Key Strategies: Digital Paper Selection and Optimization

Printers are living in an unprecedented world of substrate flexibility. The restrictions that once limited the types of papers that could successfully run on digital presses are no longer presenting the same obstacles they did in digital’s early days. But in an industry driven by print quality, speed, and application performance, printers who strategically select and optimize the substrates they use in digital printing will be at a distinct advantage.

Whether the technology in question is electrophotography or inkjet, the variances in the print processes, end-use application, and quality requirements will impact how a paper performs. But finding the right paper for the job does not have to be a guessing game for printers, as numerous resources are at their fingertips to ensure that they and their customers will be satisfied with the result.

According to Dave Bell, senior solution consultant for Ricoh USA, that typically starts with consulting with the digital printing press OEM. By describing the application and its performance requirements, the internal experts at digital press supplier companies can provide the guidance that will drive the success of the job.

“I give them what the red flags are, what they should be looking for, and where they might have performance issues,” Bell says. “It could be nothing more than using a less optimal substrate. They have the right press, they have the right inks, and they printed it well. But they missed one key point, the substrate, that was important to the customer.”

Determining Decision Factors

While selecting a substrate to use for a job is among the earliest steps of the production process, printers should start by thinking about the end use of an application and how it is going to be handled long after it comes off the press. Jennifer Pennington, director of product management and OEM partnerships for Kodak, explains that — especially with production inkjet — working backwards by answering questions such as “what is your end application?” and “what are your quality goals?” can help determine the right paper to use.

Pennington adds that printers will commonly ask if they can use their standard offset stocks when producing a new job on an inkjet device. And while the answer is often ‘yes,’ Pennington notes that papers designed specifically for inkjet will deliver superior results.

“Offset printing is a paste and inkjet inks are water,” Pennington says. “So, inherently, the absorption characteristics of those papers are completely different. To have the best quality, adjust the surface of that paper so it can hold that ink and dissipate the water in a way that doesn’t disrupt the fiber underneath.”

When selecting a paper for production inkjet printing, a key decision point for print service providers is whether to go with a coated or an uncoated sheet. Because inkjet inks are liquid, they are absorbed into the fibers of the paper, rather than sitting on the substrate’s surface. The deeper the ink penetrates into the paper, the more it may show through the other side while limiting opacity on the printed surface.

Scott Silsbee, who manages Canon Solutions America’s Media Lab in Boca Raton, Florida, explains that coated paper will typically hold the ink closer to the surface, resulting in a higher color gamut and more vivid printing. Coated paper will typically cost more than a comparable uncoated counterpart, but in an application where high quality graphics or ink density is needed, it tends to be the best choice. However, he adds that coating is not a requirement for inkjet printing and, in certain applications, uncoated paper can be a great option when cost-effective, high-speed printing is desirable.

“Generally coated papers aren’t used as much in the transactional market,” Silsbee says. “That’s more of an economy of scale because they want to print as cheaply as they can to get the bill or statement out in front of the customers to have remittance for payment or to have a general statement.”

Advancements in the presses themselves have also led to increased substrate versatility. For example, UV-LED curing on many inkjet presses is an emerging tool that provides instantly dried ink, eliminating the need for any pretreatment of the paper for the printing process. The Konica Minolta KM-1e is a cutsheet color inkjet system utilizing UV-LED, and as Keith Miller, president and CEO of Strategic Factory — a printing and marketing company based in Owings Mills, Maryland — explains, installing the press has led to increased efficiency and higher quality in its offset and digital print applications.

“You don’t need any pretreated paper and you don’t need any additional curing on the paper other than what the press does while printing,” Miller says. “We can literally run any paper and many other substrates we want on this press. There’s zero makeready, no plates, and minimal setup. So that’s been a massive advancement.”

Other key technological advancements that have opened the doors to increased substrate versatility are in inkjet inks themselves. SCREEN, for example, has launched its SC inks, which are available on its TruePress Jet 520HD series continuous feed inkjet press. They provide printers the ability to print on standard and non-premium offset coated papers and eliminate the need for pretreating.

According to Aron Allenson, SCREEN Americas’ product manager for the TruePress Jet 520 series, engineering the SC inks was a key initiative for SCREEN, as it allows customers to take the guesswork out of paper selection for high-speed inkjet printing. He explains that the inks are jetted in a highly precise manner and, once they make contact with the substrate, dry almost instantly. In addition to allowing printers to utilize a variety of offset stocks in the inkjet process, Allenson says SC inks perform well on glossy stocks, even with limited absorption properties, due to how quickly these inks dry.

“We want you to be able to not be constrained,” Allenson notes. “We want printers to be able to take any paper they want, and be able to run it without any hoops to jump through or special setups or things like that.”

Toner and Contending with Heat

While all digital printing processes involve applying heat to the substrate, electrophotographic (EP) or toner-based printing processes are more heat intensive than inkjet. Because of the heat generated during the fusing of toner to the substrate, printers using EP in their shops should be mindful of the paper they are sending through this equipment.

For the most part however, advancements in digital press technology have made this a substantially smaller concern than in the past. For example, James Quan, manager of the Xeikon Innovation Center in Itasca, Illinois, shares that much of the work that needs to be done to prepare a paper substrate for Xeikon’s dry toner process is done automatically by the press. This includes a conditioning section that removes excess moisture from the paper, which leads to better fusing results, and automatic speed controls that determine the optimum speed range based on the paper’s specifications.

“As you define and create the print media file or the script for that material, part of the data you’re entering is the weight of that paper and within that weight range it will only permit certain speeds,” Quan says. “It’s sort of built into the technology that for these weights of paper, you can only run at specific speeds in order to maximize the quality of the output.”

Beyond automation aspects of toner-based presses, mechanical advancements have also created more flexibility for printers. Heidelberg, which has established a footprint in the digital world with its series of Versafire presses, has implemented oil-less belt fusing, which not only reduces the heat needed in applying toner to a substrate, thereby improving system reliability, but improves print quality as well.

Dan Maurer, VP of digital print for Heidelberg USA, explains the combination of oil-less fusing and toner formulations that melt at lower temperatures have reduced many of the heat-related issues that were once a concern when printing with toner. Prior to oil-less fusing, Maurer explains that oil was needed to release the paper from the fuser, which could also result in streaks in the print.

“Now we have eliminated the No. 1 cause of streaks in a toner-based press,” he adds. “The performance in terms of giving good image quality for a commercial printer immediately gets tremendously better, but we also get the benefits of reduced gloss, wider substrate range, and significantly improved reliability.”

HP Indigo, which offers liquid electrophotographic (LEP) digital presses to the commercial, label, and packaging segments, uses its distinct technology to maximize substrate versatility. In an email, Eli Mahal, head of labels and packaging marketing for HP Indigo, says that the advantages of the LEP process extend to heat sensitive substrates beyond paper.

“Unlike inkjet, HP Indigo LEP technology dries the ink on a blanket and transfers a thin ink layer in perfect registration without damaging the media properties,” Mahal writes. “This unique capability is extremely important in wine stock, and thin and heat-sensitive media commonly used in the flexible packaging and shrink sleeve industry.”

Strategies for Optimization

Digital press manufacturers and paper suppliers have invested heavily in research and development initiatives that have resulted in today’s substrate flexibility. But, there are still steps that commercial printers can take in house to maximize the results they can achieve with digital printing. Among the most important precautions a printer can take is in paper storage, particularly as it pertains to moisture and humidity.

Xerox, which offers both toner-based and inkjet equipment, has invested beyond its technology and into its training and support staff. Beth Barrese, inkjet media specialist for Xerox, says that when a new press is installed, the training that goes along with getting staff members up to speed on the technology also includes education on proper paper storage.

“Because Xerox is so keenly aware of how paper can impact performance, we’ve invested in the personnel and technology to evaluate — on behalf of our customers — some of the paper attributes and how those run in our printers,” Barrese says. “Most of our training information for customers will include things like best storage practices. So, when our customers, especially in the production environment, install a new machine, we’ll go in and deliver training. Although it’s a small piece of it, we do talk about how to get the best out of your paper, and that’s usually storage and handling.”

Beyond the printing considerations that go into paper selection, finishing and converting processes should play a role in how printers decide on substrates. Maurer explains that for many applications, inkjet or toner is not the only consumable that gets applied to the paper, and the reaction between paper and adhesives for example, should be considered when making a substrate decision.

“With some digital inkjet presses on the market, if you’re gluing for a mailer or a carton and you’re coming around the backside of it and you’re applying a water-based glue, if that substrate is porous, it could absorb that water through the board or through the substrate and potentially reactivate the inkjet ink or the aqueous coating on the other side,” he says. “So you have to be aware of that as well when you’re working with your substrates.”

Maurer adds that this problem does not exist with toner machines or UV inkjet.

Investing in high-end converting, or having paper converted externally can also be advantageous for substrate consistency. Barrese explains that a strong converting process can result in more predictable performance due to the optimization that occurs before the paper is run through a digital press.

“It’s worth it to invest in quality converting,” she says. “If a customer is buying folio-sized sheets and using their own guillotine cutter to create sheets of various sizes, that may not be the most effective long term. It might be valuable to have a mill convert for you or pay a high-quality converter. And then you get a consistent size and dust-free edges. They might wrap it in a vapor barrier like a ream wrapper.”

While the versatility of today’s digital presses has lifted many restrictions on the substrates that can be run successfully, it is important that printers adopting digital understand how to optimize the press, ink or toner, and substrate to achieve the best performance on press and in its end use application. Digital has leveled the playing field across commercial printing, so companies that maximize their efficiency and results will remain ahead of the competition.

“Before getting into inkjet, it’s important to seek out education on what can and can’t be done,” Pennington says. “We [Kodak Prosper] can do almost everything with the right set of parameters. You have to have the right paper, you have to have the right ink settings, and you have to have the right drying to achieve true production speed.”