Volume 89 Issue 31 | pp. 42-44
Issue Date: August 1, 2011

Rethinking Deinking

Climb in digital printing puts pressure on paper recycling
Department: Science & Technology | Collection: Green Chemistry
News Channels: Environmental SCENE
Keywords: ink, printing, deinking, paper, recycling
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Raw Material
A diverse mix of wastepaper awaits deinking at FutureMark Paper’s mill in Alsip, Ill., where it will be recycled into paper for magazines such as the one you’re reading.
Credit: Steve Smith/FutureMark Paper
Waste paper awaits deinking at FutureMark Paper’s mill in Aslip, Ill., where it will be recycled into paper for magazines
 
Raw Material
A diverse mix of wastepaper awaits deinking at FutureMark Paper’s mill in Alsip, Ill., where it will be recycled into paper for magazines such as the one you’re reading.
Credit: Steve Smith/FutureMark Paper

Wire-tied bales of paper stack nearly to the ceiling of FutureMark Paper’s recycled paper mill in suburban Chicago. A closer look at the bales’ innards reveals a diverse mix of cast-off office paper, newspaper, colorful catalogs, and glossy magazine pages.

Paper recyclers have long dealt with this hodgepodge of paper types. But in recent years, they have faced a new challenge: ink from digital printing presses. Changes in the way some paper is printed have mills concerned that they could be forced to alter how they scrub recovered paper of unwanted ink.

New ink and old ink don’t always mix. Many high-volume digital printing presses rely on water-based inks while conventional analog printing presses use oily inks. In their deinking processes, paper recyclers take advantage of analog inks’ hydrophobicity. But such processes don’t work with all digital inks. So the hunt is on for new ways to deink paper—and for new digital inks that will work with today’s deinking chemistry.

Recyclers’ concerns are still mostly about the future. That’s because analog methods such as offset printing still dominate the newspaper and magazine printing industry, the source of most recycled paper. “By some estimates, more than 95% of the 50 to 60 trillion commercial printed pages are still being printed using analog printing processes, largely offset,” says Tom Baratz, a senior consultant for Newton, Mass.-based Lyra Research, which keeps track of the digital printing industry.

But digital methods are gaining ground. “Digital print penetration is growing steadily each year,” Baratz says. Such printing methods offer more flexibility and customization than those that currently dominate large-scale commercial printing, he says. Ink-jet and toner-based methods are among the digital printing technologies fighting to take high-volume market share away from the analog goliaths.

The book printing industry offers an early sign that digital is beginning to chip away at those goliaths, according to Eric G. Hanson, director of Hewlett-Packard’s Printing & Content Delivery Lab in Palo Alto, Calif. He points to CPI, Europe’s largest producer of black-and-white books, which recently began using digital printing presses from Hewlett-Packard (HP) to cost-effectively produce relatively small quantities, or “runs,” of up to 3,000 books. The company expects the market for short-run books to grow 8–10% per year. “Not every book is a best seller,” explains CPI chairman Pierre-François Catté.

Commercial deinking plants typically use a combination of mechanical action and chemistry to detach ink from paper fibers, according to Andreas M. Faul, managing director of the International Association of the Deinking Industry (INGEDE), whose members include 32 deinking mills in Europe and one in Pakistan. In most plants, he says, recovered paper is agitated in water with soap, typically one that is fatty acid-based, under alkaline conditions. The soap and the basic conditions swell the papers’ fibers and dislodge the attached ink. When air is bubbled through the pulp-water slurry, the soap creates foam at the slurry’s surface. Dislodged hydrophobic ink particles tend to get swept up and stuck in this foam, which is then skimmed from the slurry. The deinking process is repeated several times until the pulp reaches the desired brightness.

This chemistry was developed to remove offset and other analog printing inks from newspapers and magazines, says Samuel Schabel, who heads the department of paper technology and mechanical process engineering at Germany’s Technische Universität Darmstadt. It also happens to work well for most toner-based prints, such as those made by laser printers. But it doesn’t work nearly as well for the water-based inks used in some high-end ink-jet presses. Rather than migrate to the foam, these water-based inks remain in the water, which recirculates repeatedly in commercial deinking plants. As a consequence, Schabel explains, the inclusion of even relatively small amounts of ink-jet prints in paper recycling streams can darken a plant’s recirculating water and decrease the brightness of the recycled pulp.

Recyclers have also voiced complaints about prints from HP’s high-volume liquid electrophotography presses, which are sold under the name Indigo. The liquid toner used by such presses is difficult to remove by conventional deinking processes and can leave specks in the recycled paper, Schabel says. Last fall, an office-paper recycling plant in Germany had to discard seven 20-ton reels of freshly recycled paper after accepting an unusually large amount of raw material from Indigo-printed photo books.

As high-volume ink-jet printing, as well as HP’s Indigo, begins to take hold in on-demand book printing, custom mailings, and other niche markets, “recycling mills can’t avoid these prints,” Faul says.

That worries Wouter Peddemors, who looks after FutureMark Paper’s deinking operation. “There’s no method for sorting paper by its ink,” he says.

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Lab Scale
Ng’s team at HP uses a miniature version of the giant deinking cell used in a paper recycling plant to test novel deinking chemistries
Credit: Hewlett-Packard
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Lab Scale
Ng’s team at HP uses a miniature version of the giant deinking cell used in a paper recycling plant to test novel deinking chemistries
Credit: Hewlett-Packard

Digital printers are responding to deinkers’ concerns. Earlier this year, INGEDE and the Digital Print Deinking Alliance—whose members include large-scale ink-jet makers HP, Ricoh’s InfoPrint Solutions, Kodak, and Océ Printing Systems—announced that they would collaborate to improve the removal of ink-jet inks from recovered paper. Among the solutions the two associations will explore are optimizing the mills’ deinking processes, tweaking inks, treating freshly printed images to ease ink removal later, and even changing the characteristics of paper.

HP chemist Hou T. Ng and his team are already looking for solutions. In their lab in a basement of HP’s labyrinth research facility, Ng’s band of chemists and engineers are rethinking the deinking of HP’s digital prints. Ng points to a 55-gal blue drum filled with a mishmash of shredded papers of different ilk. “The paper that comes into a recycling plant is very diverse,” he explains. “Newsprint, magazines, office paper, photos—these different kinds of paper are not all printed with the same inks.” But the process used to remove those inks is a one-size-fits-all solution, he says.

Ng’s colleagues Manoj K. Bhattacharyya, Laurie S. Mittelstadt, and Wenjia Zhang invited C&EN to see the modified deinking chemistry that the team developed. They demonstrated that their neutral, surfactant-enabled chemistry readily deinks HP’s ink-jet and even its Indigo prints. First the researchers chopped ink-stained, image-ridden pages and mixed the paper pieces with warm water containing small amounts of two surfactants, sodium dodecyl sulfate and a polyethylene glycol ether, at neutral pH rather than the alkaline conditions used in most commercial deinking plants. Bhattacharyya then mashed the mixture in an industrial kitchen mixer and transferred it to a miniature version of the giant deinking cell used in a paper recycling plant. Within minutes, dirty foam appeared at the surface of the agitated water-pulp slurry. Zhang siphoned it off into buckets. Then, using a vacuum-assisted machine that resembles a tortilla press, she fashioned the white slurry into sheets of paper. Only the tiniest flecks of ink were perceptible in the finished paper.

Still, it’s not yet clear whether this chemistry will see adoption in commercial deinking mills. “In a lab you can only test the behavior of a printed product in an idealized deinking process,” says INGEDE’s Faul. “To see whether it might work in the real world, you must go to the pilot scale.”

What’s more, Faul says, mill owners have been perfecting their deinking chemistry for decades, doing all they can to boost their recycled-paper yields. As a result, he argues, they would prefer a change in digital inks themselves to a change in deinking chemistry.

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Digital Press
European book printer CPI uses Hewlett Packard’s ink-jet press to produce short-run books.
Credit: Hewlett-Packard
Hou T. Ng in his lab at HP.
 
Digital Press
European book printer CPI uses Hewlett Packard’s ink-jet press to produce short-run books.
Credit: Hewlett-Packard

That’s got some companies rethinking ink. Xerox recently introduced a high-volume commercial ink-jet printer that uses solid, waterless ink made of a mix of engineered low-molecular-weight waxes and resins. Several things make Xerox’s ink-jet prints readily deinkable in existing deinking plants, says Don Titterington, the company’s vice president of printhead and ink R&D. For starters, “the ink isn’t soluble in water,” he explains. And because pixels of ink are attached to the paper via mechanical rather than chemical means, “the ink comes off of the paper in fairly large particles.” As a result, Xerox’s lighter-than-water ink particles readily float up to the foam at conventional deinking mills, he says. The firm hopes the printing press will find use in printing books, direct mail, and statements from retirement funds or credit card companies, for example.

Fujifilm has also developed ink-jet presses that use inks that can be readily removed during recycling.

In addition to changes in ink or deinking, there is a third possibility, some in the industry say: Paper itself could use a rethink. “When you think about deinking, paper is as big a factor as ink,” says Nils Miller, a senior scientist in HP’s imaging and printing group. “But papermaking is both an art and a science.” In addition to recycled or virgin fibers, most paper contains fillers, such as chalk or clay, that can affect deinkability. But each paper company has its own recipe, he notes. “Normally, a paper company will decide how to formulate paper based on cost, what happens to be available, or what they’ve used before. They don’t think about what the formulation means for deinking.”

That may soon start to change, Miller suggests. Paper products that can be more easily deinked—and thus recycled—could be marketed as a greener, more environmentally friendly alternative to current papers. “That could be a competitive advantage,” he says.

Indeed, the European Union has proposed that future labels measuring the environmental friendliness of printed products take recyclability—and deinkability in particular—into account, Faul says. That may force paper mills and printer manufacturers alike to ensure that all paper can be stripped of its ink. “We have no choice,” Faul explains. “We must extend the life cycle of our precious paper-fiber resources.”  

Printing MethodsConventional (analog)Digital

Major markets: newspapers, magazines, most books

Offset lithography: Image is transferred to a printing plate using solvent-based inks. The image is then transferred to a rubber blanket and finally to paper.

Gravure: Image is engraved into a metal cylinder. The recesses are filled with a water- or solvent-based ink, which is then pressed onto paper.

Flexography: Raised image is created on flexible polymer plate. Resulting relief plate is rolled through water-based ink and then transferred first to a series of metal cylinders and finally to paper.

Major markets: short-run book printing, direct mail, packaging, photo products

Ink-jet: Image is created by jetting droplets of water-based or waterless ink onto paper.

Liquid electrophotography: Image is produced by scanning a laser beam across a photoconductor-coated drum to selectively remove charge. Liquid toner particles are transferred to discharged areas on the drum, then to a rubber blanket, and finally to paper.

Laser: Image is produced by scanning a laser beam across a drum coated with organic photoconductor to selectively remove charge. Charged areas attract dry toner particles, which are then fused onto paper.

 
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