• As coverage levels increase and coated papers become a requirement, inkjet systems face significant challenges with drying their output.
• Although the productivity of inkjet systems has begun to rival web offset systems for certain run lengths, the issue of ink coverage can also impact speed.
• Longer drying systems are often better because the air, heat, and low humidity will have more time to act on the paper and allow it to dry.

By Jim Hamilton

Introduction

System vendors and paper mills are working diligently to create effective strategies for inkjet printing jobs that require glossy finishes and high coverage levels. These solutions can be distilled into two categories:

• Inkjet-treated papers
• Advanced inks and drying systems

Last week’s article discussed the pros and cons of inkjet-treated papers. This piece, the second in our two-part series, addresses advanced inks and drying systems.

High-speed color inkjet printing systems are particularly strong at printing applications like transactional documents, direct mail, and books on uncoated substrates at relatively low coverage levels. As coverage levels increase and coated papers become a requirement, inkjet systems face significant challenges with drying their output. Large quantities of water-based inks do not absorb easily into coated papers, resulting in mottled output and generally poor results. As discussed in my previous blog, one solution is to pre-treat the substrate with a solution that allows the water-based inks to adhere efficiently. That strategy results in higher paper costs and a requirement for printers with offset and inkjet systems to stock two types of paper. The vendors of inkjet printing systems have worked with the paper mills to test and promote treated papers, but some are also exploring advanced inks and drying systems that enable users to achieve strong results on standard offset stocks. The idea is that these advanced inks and drying systems will allow users to print at high coverage on just about any coated paper.

What is it About Production Inkjet?

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 the case with inkjet. Print service providers on 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 that must be laid down to achieve good-looking results. In addition, the energy consumption costs of the drying units on some of high-end inkjet systems can add significantly to the cost of a project. If variable data is not part of the job, it then becomes counterproductive to use a digital printing technology on something that offset printing excels at—making a lot of copies of the same thing. This inkjet coverage/paper cost equation is a real issue, and it is at the center of the argument about whether pre-treated papers make the most sense versus sophisticated inks and drying systems.

Another important factor to note about inkjet printing systems is that they all 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. For those who are cost-conscious, there’s a paper profile setting with a name like “Good.” If you aren’t too picky about print quality, this setting will work fine and will not cost you as much in consumables. For those who require higher quality levels, there are ways to adjust print resolution, droplet size, and UCR/GCR techniques to increase color gamut and hold finer detail. These higher quality profiles are generally given names like “Better” or “Best.” It all comes down to the amount of ink you want to use. If your system has sophisticated inks and dryers, you should be paying very close attention to this.

Speed is a factor that is extremely relevant in the commercial printing market. Inkjet systems are getting faster and faster, so their productivity has begun to rival web offset systems for certain run lengths. At the same time, however, the issue of ink coverage can also impact speed. Maybe you have to run the system at a slower speed because you need the high-resolution setting to take advantage of smaller droplet size so that you have better control over the volume of ink consumed. Maybe you have to slow the system down because the dryers 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.

Did you ever wonder why some production inkjet document printing systems are as long as freight trains? It comes back to the issues around drying. There are of course a lot of components in these systems when you consider the imaging heads, the dryers, and the required transport systems, but the length of these systems also gives the paper time to dry. Simply put, the longer that air, heat, and low humidity have time to act on the paper, the quicker it will dry. The system may even require an extended segment to put some humidity back into the paper to keep it dimensionally stable. As a result, it is often the case that longer drying systems are better.

It should be noted that Konica Minolta has worked to address the issue of high coverage and coated papers in a different way than other vendors of document printing systems. For its AccurioJet KM-1 product, Konica Minolta uses UV inks instead of water-based ones. This method avoids the use of treated inkjet papers since UV inks tend to dry well on a range of substrates. Although UV inks are employed by a wide range of large format printing systems because of their ability to print on unusual substrates (e.g., glass, metal, wood, and plastic), they are rarely used for document printing systems. The same cost concerns for ink and drying apply equally to the UV and water-based systems using advanced inks and dryers.

The Bottom Line

In summary, here are the top pros and cons for advanced inks and drying systems:

• PRO: Strong results for higher-coverage applications on a wide range of paper stocks
• PRO: The convenience and flexibility associated of stocking a single paper type for offset and inkjet technologies
• CON: Increased cost of the ink and electricity consumption
• CON: Some speed reductions for higher-coverage jobs or coated paper stocks

The success of high-productivity inkjet systems will depend on economically viable solutions, particularly in the commercial print market where printing on coated papers is a given. The decision about which method is preferable—inkjet-treated papers or advanced inks and drying systems—will generally come down to the requirements of the individual print service provider. In time, we should start to see if one method will prove more successful than the other. Although most paper mills and some system providers are opting for treated papers, other system providers are hedging their bets by offering both: systems that require inkjet-treated papers for many applications and systems with advanced inks and dryers that can handle a range of papers.

The inkjet market is currently undergoing a new evolution. Ultimately, the market will decide whether a single strategy or perhaps a combination of strategies will succeed in the long run. In the meantime, it will be important to focus on the overall costs of paper, ink, and power consumption, as well as the implications that these have on workflow and productivity.

Jim Hamilton is a well-known industry analyst who serves as Consultant Emeritus for a number of Keypoint Intelligence – InfoTrends’ consulting services. He supports areas including production digital printing, wide format signage, labels & packaging, functional & industrial printing, production workflow & variable data tools, document outsourcing, digital marketing & media, and customer communications.