by Cassandra Balentine
Digital printing technology brings many advantages to the evolving corrugated print space, including the ability to print short run lengths and easily change designs.
There are two ways corrugated is digitally printed to—direct and indirect.
The direct printing method is just what it sounds like, directly printing onto the substrate—in this case corrugated material—with a digital print device. “Direct-to-board corrugated printing is an optimal process to maximize the efficiencies and advantages of digital printing. Direct printing is applied to the board after it is corrugated, which allows for reduced lead times, printing on demand, and last-minute changes to reflect customers’ requests, and therefore, quick turnaround times,” explain Phil Jackman, global product manager–digital, and James Gould, product manager of Streamline Inks, Sun Chemical.
Indirect is digitally preprinting the top liner of a corrugated box before it is fed into the corrugator to become a board. Jackman and Gould comment that this process is more suited to printing higher volume jobs that are usually lower value. “There is considerably more printed work committed to stock—as a work in progress—in this process, which poses a risk of obsolescence if designs need to change.”
While both are effective methods of utilizing digital print technologies for corrugated jobs, this article focuses on direct digital printing to corrugated. Looking at the advantages as well as limitations direct printing offers in the corrugated space.
Direct Digital Benefits
Direct digital printing brings similar advantages over analog to every segment it touches. Corrugated is no exception.
Speed to market tops the list of advantages for direct digital even when compared with indirect digital printing. Lloyd Kent, VP sales and operations, Kento North America, explains that this is because many indirect printing processes have multiple components needed to form the final product. Some of these components are outsourced, with applicable lead times. Others that are in house can be affected by scheduling limitations, which can cause additional chaos in production.
Manufacturers and other users are able to easily modify images while reducing makeready time with direct digital corrugated printing, bringing better versatility, flexibility, and more opportunities to increase profit, shares Brigette Wyatt, business development manager, Kao Collins Corporation.
Jim Wegemer, the former national accounts director for INX International Ink Co. who recently retired after a 50-year career in the industry, adds that users can eliminate the need to carry printed inventory on the floor. “You can update your image at the last minute with simple software changes so there is no need to redo prepress and produce new printing plates.”
“The ability to use inkjet drop on demand technology for high-quality printing with integrated variable data means that direct to corrugated material printing can be as high quality and flexible as short-run labeling. Depending on the demands of the individual customer and their chosen material the technology behind inkjet printing on an industrial scale is literally scalable to the requirements of the industry,” share John Corrall, chairman, and Nadina Using, sales and marketing, Industrial Inkjet Ltd.
The fact that the printheads do not need to make contact with the media is also an advantage.
“With direct print using digital, you don’t make contact with the corrugated board so there is no possibility of crushing the board, which can occur with flexography,” explains Pedro J. Martínez, CEO, AFFORD.
Martínez adds that as a non-contact printing system, substrates are able to change without many adjustments.
Press manufacturers incorporate equipment to find imperfections in corrugated boards. “When these flaws are detected, the printheads raise, allowing the flawed board to pass under it safely. This minimizes damage to the printheads,” shares Wyatt.
Just as direct digital printing for corrugated brings many benefits, there are challenges to consider.
Wyatt sums these up as ink cost and maintenance of equipment.
“Although it is getting much better, with some large solid print areas it is harder to produce a high-quality print with single-pass digital printing and no visible banding lines,” adds Wegemer.
Martínez sees economy and printing consistency as the major limitations for digital printing. He admits that progress has been made in the last few years with ink formulations that are consistent and robust, but being cost competitive in long runs is still far off.
Another limitation is the space and overall infrastructure in an existing plant. “The producible sheet size of many digital single-pass printers—most are 125 to 190 feet long—takes up massive space that usually isn’t available,” offers Kent.
Further, there is the tipping point to consider. “You reach a point where a larger print job becomes more cost effective to do in a flexographic format. The cost of flexographic printing plates and job set up are spread out over a greater number of printed corrugated sheets,” adds Wegemer.
A majority of digital printers for corrugated do not currently die cut inline. Therefore, Wegemer says printed sheets should be taken to a second equipment center for die cutting. “There are discussions and concepts being reviewed in this area, but this is not yet accomplished on a commercial basis,” says Wegemer.
Direct digital printing is also limited by the amount of warp that can exist with the corrugated board.
“With contact printing you can physically hold the warped board down while it is printed. With direct digital printing, the board is held down by a vacuum and there are limits to this. If you have a corrugated board that has higher warp, you can sometimes run this on a digital printer by increasing your gap—the distance between the corrugated surface and the printhead. However, with digital printing the greater the gap between the corrugated surface and the printhead, the lower your print quality will be. Flat corrugated board is important to digital printing,” explains Wegemer.
Direct to board corrugated printing historically presented difficulties due to print pressures, which can crush the flutes. “Of course, inkjet printing is non-contact so it overcomes this main issue, but direct digital printing still has challenges arising from the substrate due to its inherent lack of uniformity. Variations in thickness, sheets not being perfectly flat, curled edges, and variations in absorbency all pose some challenges,” share Jackman and Gould.
Martínez agrees, noting that packaging materials often lack surface flatness, which is a challenge for digital printing due to the high risk of damaging the printheads.
Corrall and Using believe environmental factors may impact the longevity of system parts with aqueous-based digital printing to corrugated. Increasing uptime, controlling maintenance time and costs, and automating where possible is imperative.
Many single-pass printers have a limited lifetime, which Kent feels corrugated converters have a hard time digesting and rightfully so. “Buying a robust corrugated machine with digital that is upgradeable addresses this issue and makes the purchase much safer and more palatable.”
When integrating inkjet into production lines, Corrall and Using feel there are specific concerns that should be taken in account, particularly in places in the line where allowances and flexibility of expectation should be topics of discussion. Areas of concern must be managed and safeguards put in place. Inkjet printing relies essentially on the ink droplet landing where it needs to go. Having the correct hardware and printheads to ensure system safety and avoid printhead strike is essential. “The environment matters and the entire solution—ink, ink system, and printhead work with each other to account for the environmental factors at play.”
Also consider the location and point of print. “Understand whether the printing will take place pre- or post- crease cut, before folding, after filling, top down, or sideways. The possibilities are almost endless as are the options that can be provided for them. Integration onto wide format production lines is increasingly possible with growing print widths and single-pass printing at much higher speeds than multi-pass and increasing production capability can more than improve a companies’ return on investment in some cases,” share Corrall and Using.
As much of corrugated is food and ecommerce related—sometimes both—the ability to print onto a preassembled product is essential in some sectors, creating a need for a full-color solution integrated directly onto the end of the packaging line, they comment.
While direct digital has great potential, it hasn’t yet made major inroads in terms of market penetration.
Wyatt says based on his company’s internal research, that very little corrugated printing is currently done digitally, estimating that it is maybe two percent digital versus 98 traditional printing.
Kent feels that the representation of direct digital print onto corrugated is practically a “rounding error.” He explains that digital transformation has been slowed by many factors with the cost of ink being a primary reason. As ink costs continue to come down he predicts new technologies such as hybrid printing will be considered and advanced workflow systems will help the transformation gain steam. “It already is but the pace is destined to pick up substantially,” he admits.
Wegemer adds that digital printing directly onto corrugated board continues to grow significantly every year, but admits it is still small overall compared to flexographic/lithographic printing on corrugated. “It is difficult to give an exact percentage, but of all the corrugated board that is printed it is likely that less than five percent of the total square feet printed is done with digital printers.”
Martínez expects a larger proportion of digital printing equipment to emerge in the coming years, with special focus on applications of smaller size, such as paper bags and small boxes popular in retail. “There will also be an increase in high-productivity digital equipment, due to the better and more consistent output of these devices.”
Wegemer admits that it may be some time before we see significant improvements in the speeds that corrugated digital printing is capable of. “The percentage of digital printing for overall corrugated could double in the next five years, but it would still be well less than ten percent of all printed corrugated.”
Wyatt also expects digital printing for corrugated applications to increase in the coming years. “The growth in small businesses will increase the number of short-run jobs, making digital printing more desirable.”
Kent adds that there is no “why not” when it comes to investing in this technology, since direct digital for corrugated will be a must sooner than later. “We know others will soon incorporate converting solutions into their machines and it is likely many corrugated packaging manufacturers will look to add digital print to existing analog machines.”
Jackman and Gould point out that direct digital printing to corrugated is mostly decentralized, meaning the printing machines are often smaller but situated closer to the customer. “There are significantly more digital printers serving this application area—with hundreds, or even thousands of digital presses in current use,” they note.
This is in contrast to indirect digital printers, which tend to be centralized as they are aligned to the corrugation plants, meaning the print machines are larger, more productive, and serve many customers through distribution. They estimate that there are only a handful of indirect digital printers currently in operation.
“Sun Chemical expects the trend in direct corrugated digital printing to continue growing. Direct printing aligns with the efficient, optimized capabilities of inkjet and allows for the fast turnaround currently required. This type of printing provides a shorter process path after printing and thus can offer reduced lead times using newer technology to meet the demands of an ever-changing market. A concurrent trend in the market is the use of more paper substrates in packaging, revealing an industry wide—and often consumer driven—desire to increase use of sustainable materials wherever feasible,” share Jackman and Gould.
Compared to Analog
While digital print solutions for corrugated advance, it is up against very mature ink technologies.
“Traditional analog printing uses inks that are high(er) in viscosity, that are manually but precisely, pressed onto the board/paper. In contrast, direct digital printing uses inkjet technology, which utilizes a much lower viscosity ink, so that it can be ejected from the printhead. Thus, the inkjet drop placement accuracy and amount of absorbency—which is typically more with a lower viscosity ink—can strongly influence the image quality that can be achieved,” say Jackman and Gould.
When it comes to ink adhesion and spread, Kent explains that traditional flexographic printing utilizes specific anilox rolls, inks, and printing plates that need to be optimized and specified for the liners being used. “If a plant runs a variety of liners they will get varying results, some good and some bad.”
With the proliferation of digital ink suppliers, a lot of attention is now being paid to the single-pass segment. “Ink recipes are being perfected to meet many requirements, most notable print quality. Along with this, some flexographic ink companies work with these digital suppliers to formulate primers and overprint varnishes (OPVs) that work well with digital inks,” offers Kent.
He adds that almost 100 percent of direct digital single-pass printers utilize a primer to control the printed dots once they hit the liner. “In some cases, a primer is not needed but in most, the primer controls the dot gain, absorption, and protects the print from the abrasive converting process that will ensue. The correct volume of primer applied will also control the absorption on highly porous materials. Having the ability to control the amount of primer on various substrates allows for prints on coated and uncoated virgin, or recycled liners. Without a primer this flexibility is non-existent, and results are variable and unpredictable.”
It is important to note that single-pass digital printing results vary depending on the ink technology used.
“Water-based digital inks for corrugated typically require a primer or bonding agent, and an overprint coating to protect the print. UV LED, or even conventional UV ink technology, typically requires a primer but does not need an overprint coating to protect the print,” explains Wegemer.
Jackman and Gould agree, pointing out a variety of substrates are used in corrugated printing—white, brown, coated and uncoated, etc.—and these low viscosity inkjet inks would perform quite differently across the range. It is therefore common to use a primer in digital print systems. “This is mostly to harmonize the substrate variances to some extent and to give a more consistent drop spread/dot gain. Adhesion poses much less of a challenge.”
“Where UV inkjet inks give amazing vibrancy of pigment, for a long time aqueous inks could not compete and essentially looked like watercolor images. Improvements in ink options, using hybrid water- or latex-based inks for inkjet printing ensures a vibrancy of color that matches UV inks and provides good adhesion. Line speed and dryer location can manage ink absorption and spread. Improvements in inks can now accommodate coated corrugated providing improved gloss levels on par with label stock and allowing for a photo finish. Even on very absorbent stocks that typically suffer from excessive ink bleed there are now jettable primers to ensure the color print is sharp and crisp. By reducing ink spread and absorption they also save on color ink usage—and in fact more than pay for themselves,” add Corrall and Using.
Martínez believes AFFORD can reach similar, if not better, levels of adhesion on corrugated boards than with traditional printing methods, achieving prints with excellent adhesion and very high scuff and scratch resistance.
“Formulations are even custom tailored for specific corrugated stock,” says Wyatt. “This optimizes the image quality while maintaining printing performance.”
Kent stresses that ink spread and adhesion should not be an issue in single-pass digital print. “Utilizing a primer matched to the digital ink assures this but another layer of protection is provided with an application of OPV after the digital print. The OPV is used many times for aesthetics, glossy or satin, but it does provide a robust layer of protection over the print.”
Direct digital printing to corrugated is a small but growing part of the overall market segment. While there are still challenges to iron out, the potential is there—especially when considering a hybrid approach.
Nov2023, Industrial Print Magazine