Dec 11
8
Inkjet: De Trouble With Deink
By Richard Romano, Managing Editor, WhatTheyThink’s Going Green
If you have been to any industry event or read the trade press in the past two or three years, you know that inkjet printing is one of the hot topics (if not the hot topic) being bruited about today. However, for all of the advantages it holds for print providers, the impending growth of large-scale commercial inkjet printing has an environmental downside that researchers are busy trying to solve before inkjet volume swells. This problem was also the topic du jour at a brace of European conferences held in early November, the CTP’s Technical Conference on Deinking of Digital Prints in Grenoble and IMI’s 19th European Ink Jet Printing Conference in Lisbon.
The environmental problem—or, more correctly, the recycling problem—that inkjet poses is that of deinking (or de-inking, if you prefer that spelling) printed paper for recycling. We tend not to think about this, but when paper mills recycle paper, they have to get rid of the ink somehow.
With offset printing, which still accounts for between 90% and 95% of all paper recovered for recycling, the deinking process is not especially problematic, thanks to the fact that what makes the lithographic process work (the use of hydrophobic, or water-repellent, ink) also helps the deinking process because paper fibers are hydrophilic (water-absorbent). In one of the most common deinking processes, called froth flotation, recovered paper is mixed with water where it dissolves and is re-pulped into a slurry. Chemicals such as soaps or lye (NaOH) are used to swell the paper fibers and dislodge particles of ink and other matter. When ink is hydrophobic, that’s not especially troublesome, since the particles are easy to “shoo” off water-laden paper fibers. Air is then blown into the mixture to form bubbles containing the particulates, which can then be skimmed off. The process is repeated a few times and you’re left with clean white paper pulp.
Another, simpler method is called wash deinking in which dispersants are added to the slurry to shoo or “wash” the ink and other particles off the paper fibers and the slurry is then filtered to remove the particles. The deinking process that paper mills use has been developed for both offset and gravure inks.
Enter digital printing. Toner has presented its own problems over the years, especially so-called “liquid toners,” but inkjet is where the real trouble lies. Unlike offset and other commercial inks, inkjet inks are typically water-based. They are hard to remove with current deinking processes, can contaminate the entire recycling system, and irreparably stain the paper fibers. A fitting analogy is doing laundry and mixing bright colors with whites—we’ve all had a brand new red shirt turn white socks or underpants a lovely shade of pink (usually the day before gym class…). So a lot of research is being done to try to develop a deinking process that can handle inkjet. Compounding the problem is that the process will have to handle all kinds of printing inks. After all, getting consumers, recyclers, and/or paper mills to separate offset and digitally printed papers is not going to happen.
At present, inkjet accounts for a very small percentage of overall volume of reclaimed paper sent for recycling, but as WhatTheyThink and other industry publications have written at great length, that may very well change. A recent article in Printweek said:
Research body InfoTrends said it believed inkjet currently contributes around 7% of digital print volume in document printing, but the growth of production output is likely to increase the overall inkjet share to 13% by 2015. This could lead to a tenfold increase in the amount of inkjet print in the recycled waste stream, rising from 0.05% to 0.5% by 2015.
The article covered the two conferences cited earlier, pointing out that almost two dozen studies have been released examining how to improve the inkjet deinking process.
The DPDA-sponsored (the Digital Print Deinking Alliance) studies outlined how improvements can be made through changing deinking conditions; however, Fischer was sceptical about the feasibility of making changes to the current mill deinking model of flotation.
“Everything you do for inkjet will reduce the yield for offset,” he said, explaining that the current process has been developed for the hydrophobic ink properties of offset print, which makes up 90% of the waste stream going into these mills. Making changes to accommodate hydrophillic inkjet reduces the overall yield, and creates more waste because the fibres themselves are hydrophillic.
The paper industry has been focusing on the deinking process itself, but other efforts have been looking further upstream, such as developing inkjet inks that are more deinking friendly or substrate coatings that facilitate the deinking process.
Two organizations leading the way are INGEDE (founded in 1989 by European paper manufacturers as the International Association of the Deinking Industry) and the Digital Print Deinking Alliance (DPDA). Earlier this year, both of them signed a letter of collaboration and are jointly conducting more research on deinking processes. (The DPDA had some early success last year.) Still, progress has been slow.
Using recycled grades is one of the easiest and often most cost-effective means of “greening” the printing process. If inkjet volume does grow as substantially as many industry experts forecast, then making inkjet printing compatible with recycling processes is of paramount importance.
Richard Romano is managing editor of WhatTheyThink’s Going Green, and is a writer and analyst for the graphic communications industry.
