Over the past decade, we have seen how high-speed production color inkjet systems have revolutionized the document printing market. What is less visible is the important role that paper has played in the suitability of inkjet technology for various print applications. Ink coverage, paper type, and running cost are key factors that ultimately determine whether inkjet is the most appropriate and effective method to use, and they also play a role in the future growth potential for inkjet.
Inkjet in Low Coverage Applications on Uncoated Papers
Inkjet has been part of the mailing landscape for decades in applications like addressing, coding, and personalization. These highly productive printheads are typically narrow and low-resolution, and primarily suited to monochrome printing via imprinting units mounted on mailing and finishing lines. As printhead technology has improved, full-page color inkjet systems were developed that had a particular sweet spot for mailers in transactional applications. Direct mailers and book printers also benefited from these systems. The common thread between these applications is that they are often printed using relatively low ink coverage on uncoated papers. Uncoated papers easily absorb the water-based inks that are most commonly used by the high-speed cut-sheet and roll-fed inkjet systems on the market today. In addition, at lower coverage levels, it is relatively easy to dry the resulting output without causing ripples or warps in the paper. For transactional mailers, this ability was nothing short of revolutionary. It enabled them to eliminate the two-step process of printing variable monochrome data onto pre-printed offset color shells with logos and other design elements. We saw transactional printers make this change virtually overnight. Direct mailers who worked with pre-printed shells were the next to benefit, and yet they often had promotional work that required higher coverage on coated papers. Was it possible for inkjet to address this as well?
Coated Papers and Higher Coverage
The coated surfaces of matte and glossy papers used in promotional applications present a more substantial challenge for inkjet because the surface does not readily absorb the ink. This is not a major issue for oil-based offset inks that adhere well to the paper’s surface, but without proper precautions, water-based inkjet inks may bead up on the surface of a coated paper and fail to adhere well, leaving a mottled appearance. This problem becomes even more significant for inkjet at the higher coverage levels that are common with promotional pieces using many graphics, photos, and design elements.
Inkjet system providers use two main strategies to address this challenge:
•Inkjet-treated papers: These papers have been treated with a solution that allows the inkjet inks to adhere well to the paper. These treatments are generally applied at the paper mill, but they can also be applied at a separate location or even at the printing site. Inkjet-treated papers provide print service providers (PSPs) with some assurance that the stocks will perform well for the applications that they print on their high-speed production color inkjet systems. This certainly appeals to PSPs, but the challenge is that adding a pre-treatment increases the cost of the paper and generally forces the PSP to stock two classes of paper: one for their offset presses and one for their inkjet systems. This is not ideal, but it does address the problem.
•Advanced inks and drying systems: These systems enable users to achieve strong results on standard offset paper stocks. The idea is that these advanced ink and drying systems will allow users to print at high coverage on just about any coated paper. While this addresses the issue, it also adds cost. In general, much of the cost of inkjet printing is built into the inks. Developing an all-purpose ink for multiple paper types adds to the cost. On top of that, more ink is consumed at higher coverage. This makes it extremely important for PSPs using inkjet to understand the costs associated with ink consumption.
One of the things that differentiates offset printing from production inkjet is the cost of ink. Offset inks are relatively inexpensive, but this is not so with inkjet. Today, PSPs at the front lines are learning the hard way that using an inexpensive paper on an inkjet project can be financially disastrous in the long run because of the amount of ink required to achieve a good-looking result. Furthermore, the energy consumption costs of the drying units on some of the high-end inkjet systems can add significantly to the cost of a project. If variable data isn’t part of the job, it may then become counterproductive to use digital print technology. Why not just use offset instead? It is extremely cost-effective at making a lot of copies of the same thing. If that’s what you’re doing, it could be the best solution.
The interplay between area coverage and paper cost is central to the success and future growth of inkjet. It is also at the center of the argument about whether pre-treated papers make the most sense versus sophisticated inks and drying systems. We are in an evolutionary time when it comes to inkjet technology. The market will ultimately decide whether a single strategy or perhaps a combination of strategies will succeed in the long run. In the meantime, keep your focus on the overall costs of paper, ink, and power consumption, and assess the implications that these have on workflow and productivity.
Paper Profiles, Speed, and Drying
Three other factors are also worth considering:
•Paper profiles: All inkjet printing systems offer paper profiles that are designed to achieve the best result with a given paper. There are often slight variations of these profiles related to output quality and ink consumption. If you are cost-conscious, there is a paper profile setting with a name like “Good.” If you aren’t overly concerned with print quality, this setting will work fine and will not cost you as much in consumables. If you want higher quality levels, there are ways to adjust print resolution, droplet size, halftoning, and ink usage to increase color gamut and hold finer detail. These higher quality profiles are generally called something like “Better” or “Best.” It all comes down to the amount of ink you want to use to achieve the results you need.
•Speed: Inkjet systems are getting so fast that their productivity rivals web offset presses for certain run lengths— yet the issue of ink coverage can impact speed as well. You may need to run the system at a slower speed to take advantage of a high-resolution setting and smaller droplet size so that you have better control over the volume of ink consumed. You may need to slow the system down because the dryers will need more time to dry the ink at high coverage. Neither of these options is particularly appealing to someone who has paid millions of dollars for a high-speed system.
•Drying: Did you ever notice how long some production inkjet document printing systems are? This has a lot to do with drying. There are a lot of components in these systems when you consider the imaging heads, the dryers, and the required transport systems, but one of the things that helps is giving the paper some extra “travel time” to dry. In short, the longer that the air, heat, and low humidity of the dryers have time to act on the paper, the better it will dry. The system may even need an extended segment to put some humidity back into the paper to keep it dimensionally stable. As is often the case with dryers, longer is usually better.
Recommendations for Mailers
Mailers who own or are considering the purchase of a high-speed color inkjet system should look carefully at their application mix and overall paper use. Cost calculations for your system should be closely tracked and include the impact of ink consumption, energy use, paper type and cost, operator cost, paper waste, overhead, and required consumables such as inkjet paper treatments. It is also worth looking at your customers’ requirements for turnaround time, personalization, and just-in-time manufacturing. These advantages of digital print can have an important impact on customer satisfaction that goes beyond the raw cost calculations. Whatever you do, your decisions about paper use will be critical to the success of inkjet in your facility.
Jim Hamilton of Green Harbor Publications (www.greenharbor.com) is an industry analyst, market researcher, writer, and public speaker. For many years he was Group Director in charge of InfoTrends’ Production Digital Printing & Publishing consulting services. He has a BA in German from Amherst College and a Master’s in Printing Technology from the Rochester Institute of Technology.
This article originally appeared in the November/December, 2020 issue of Mailing Systems Technology.