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Overview

Printing digitally has many advantages such as reducing overprint, accuracy, no storage costs and many more.

But some digital printing processes also have disadvantages compared to conventional offset and gravure printing: They lack good deinkability in the paper mill. Even small amounts of these undeinkable prints can have a big effect in the mixture that a paper mill processes every day.

INGEDE tries to inform all members of the paper chain about these problems. INGEDE also tries to cooperate with printer manufacturers to provide them with the necessary background in order to contribute to the development of better deinkable printed products. INGEDE also frequently participates in conferences, organizes seminars and has set up the Digital Round Table as a constructive cooperation.

INGEDE Actions in digital print deinking

Publications dealing with digital print deinking

Digital Round Table dealing with digital print deinking

How it began: INGEDE/CTP Workshop in 2001

Paper recycling and deinking: The basic facts are simple

Deinking is the key process in paper recycling. Hydrophobic (water-repellent) ink particles are separated from hydrophilic (water-wettable) fibers. This process has been developed for offset and gravure inks which are roughly more than 95 % in the current recovered paper mixture.

Different printing processes can neither be sorted apart manually than automatically. This is what happens with the household collection: Board, plastic, dirt and other impurities and unwanted papers are removed.

In the paper mill, the sorted recovered paper is dissolved in water in a long drum or in a pulper. Screens separate large contaminants. During the pulping, chemicals like caustic soda (NaOH) and soap are added to make the fibres swell and support detachment of ink particles.

During the flotation process, air is blown throw the mixture of about 1 % fibres and 99 % water. The bubbles take hydrophobic (water-repellent) ink particles with them and bring them to the surface where they are skimmed off. This is repeated in several consecutive steps to remove as many ink particles as possible, achieving the desired brightness.

Current waterbased inks create problems as they cannot be removed in this process and accumulate in the system. Closing the water-loops is the major environmental achievement of the paper industrie in the last two decades, at least in Europe. Here dyes and ink particles too small to be removed have no other exit than the fibers: They stain them just as red socks dye the underwear in the washing machine. This is not only the case for inkjet inks but also for undeinkable flexo inks that the paper mills have been struggling for more than 20 years.

Solution for inkjet: to create a precipitation

One way to solve this problem has already been demonstrated by HP: The Web Press which was presented at drupa used an experimental ink system where a ‘bonding agent’ led to a precipitation of a special pigmented ink on to of the paper fiber network rather than bleeding into it. The windfall profit is perfect deinkability. As it looks now, pigmented inks provide the chance for a solution that matches the deinking process, for dyes this is improbable. Unfortunately, the samples presented at drupa were only experimental and the bonding agent technology now is only offered as an option. HP also looks at other ways to improve the deinkability. Other ink and inkjet suppliers also look for better deinkable inks.

Current inkjet: Even small amounts can create problems. It is unlikely that e. g. waterbased inkjet printed newspaper will be evenly distributed among the total paper collection, so mere percentages are irrelevant. If only one neighbourhood is supplied with an inkjet printed newspaper, the household collection from here will not only be useless for recycling but a significant problem if it mixes with other, originally deinkable paper. The same would be true for a high-volume transpromo mailing. Already the paper industry has problems with a variety of small contaminations, e. g. from SOHO inkjet printers, leading to a rising background of brightness problems in the mills.

Left: Sample of an waterbased inkjet printed newspaper from drupa 2008 with one drop of water

Right: Inkjet prints lare like a sponge full of ink – they bleed into the circulation water of the paper mill (click pictures to enlarge)

Recent developments comfirm that it is possible to develop inkjet printing systems that are good deinkable (see below).

For completely different reasons, current liquid toner (Indigo) prints fail to pass INGEDE's deinkability test. They leave large, visible dirt specks (photo composition showing the size of the specks below) resulting from the very flexible ink film that peels off the paper. In general, in a mill it requires additional energy and leads to significant fiber losses to reduce the number of dirt specks coming into the recycling process from various sources. INGEDE discusses this with HP.

Dry toners for about 20 years have been good deinkable at least for production size printers. It was just the old slow SOHO printers which, at low speeds, literally ironed the toner resin into the fiber network, attaching pigment particles firmly to the fibers from which they were difficult to remove. This has improved dramatically with the speed of the printers. And the output of today’s dry toner production printers is mostly even better deinkable than offset newspapers.

After HP at drupa 2008 claimed liquid toner to be as good deinkable as dry toners, INGEDE ran additional tests with the same test file on paper from the same reel showing that this is not the case (see also INGEDE Press Release).

This chart shows the results of a comparative deinking study: The number of specks found according to INGEDE Method 11 is much higher for liquid toner than for dry toner samples – no matter which lab pulper used.

INGEDE Method 11 has been developed to compare the deinkability of different printed products and to rate the challenge a printed product means to a standard deinking plant. It simulates the two important steps of deinking – detachment of the ink from the fibers and ink removal from the system. It does not simulate the full process in a deinking plant. This would not make sense as a deinking plant includes several steps to cope with present impurities such as a disperser to reduce dirt specks. The presence of these units cannot be taken as an excuse to challenge them so they cannot be included into the evaluation of the deinkability of a print product.

Finally: Intense cooperation with IJ printer manufacturers to find solutions

Since the first workshop in 2001 INGEDE has tried to get in contact with inkjet manufacturers in order to cooperate in terms of recyclability/deinkability. Despite many efforts at many occasions like the NIP conferences and a multitude of personal e-mails, it took until spring 2008, after INGEDE had published another press release about problems in deinking inkjet.

In April 2008 representatives of Kodak Versamark, HP Inkjet and Océ Inkjet followed an invitation of INGEDE for a round table discussion, and as a result formed the Digital Print Deinking Alliance (DPDA) which is very much appreciated by INGEDE. Finally, the printer industry becomes aware of its responsibility for the total life cycle of the printed product. It is not sustainable (and not compatible with all the green claims being made) to place the costs of coping with the environmental disadvantages of a new product on somebody else’s shoulders rather than taking product responsibility.

INGEDE has always seeked the cooperation of all members of the paper chain. That is our business. Now there finally is an intense cooperation between INGEDE and DPDA to improve understanding and to find solutions. And was just a matter of time until inkjet printed products become deinkable.

At the IPEX 2010 fair in Birmingham, two new inkjet printing systems were presented, using different approaches to achieve "good deinkability" according to the ERPC deinkability scores. For details see INGEDE's press release. These developments are an acknowledgment for the consistent dialogue of the paper industry with the digital printer manufacturers which INGEDE leads for a couple of years now. They also show that it is actually possible to design inkjet prints in a way that they work well in the existing system of paper recycling.

Summary of the 2001 Workshop and more publications

INGEDE's press release about deinkable inkjet inks at IPEX 2010

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