Press Release 2/2001
Digital Print Technologies:
A Nightmare for Paper Recycling?
Many digital printing inks can hardly be removed
On the airplane the flight attendant passes out the afternoon edition of a coloured business journal. In London a Swiss newspaper is available already early in the morning at the bookstall delivered no more by mail-plane through the night but transmitted via satellite and printed on the spot. Mass mailings try to catch more attention through personalisation. All these print products have one thing in common: Straight away the data reach the printing press digitally. But they also have in common that the applied inks often hardly can be removed during the paper recycling process. On the contrary, even small amounts of these products can seriously endanger the process of paper recycling.
For the first time scientists of the French Centre Technique du Papier (CTP) have put together systematically, how different digital printing processes affect the deinking process. The results have recently been presented during a workshop organised by CTP and INGEDE in Grenoble. But only a few providers of digital printing equipment could be convinced to take part in the workshop.
The differences between several processes that are currently on the market turned out to be surprisingly high. Particularly poor results were observed with liquid toner processes as the one used by Indigo: These printers use a fast drying so-called Electro-Ink (particular ink by Indigo). The toner is transferred from a drum to the electrostatically charged paper, where it is fused to form a polymer film. When the printed paper is dissolved in the beginning of the recycling process, these films result in large but very soft particles, found CTP scientist Bruno Carré. These particles can neither be removed by the usual screens nor through flotation, which is the common process to separate standard inks from the paper fibres. The result is a high amount of clearly visible dirt specks in the recycled paper. "This is really a threat to the deinking industry", Carré stated. Even the third generation of these inks was not acceptable in terms of deinkability.
Dry toners as they are applied for digital four colour printing processes by Xeikon and Xerox create less problems. The resulting brightness and residual ink are sufficient to lead to a good deinkability. But the number of dirt specks is still too high it is lower compared to other types of digital prints but still 10 to 100 times higher compared to the contamination found when testing conventional office waste on an industrial deinking line. "Too high", Carré judged, an additional dispersion step would be necessary to achieve acceptable results. Differences in the rating of particular processes were mainly caused by different fusion temperature or printing speed.
Positive results, according to Carré, delivered the tests with digitally printed newspapers by the Océ technology that electro photographically uses dry toner. Preliminary results show that the brightness after the recovered paper treatment is even better than with conventional offset printed newspapers. Here also, the chosen fusion temperature together with the printing speed could be the reason for the good results. The composition of the toner could also matter, but yet no investigation about different toners exists. Gerd Goldmann of Océ Printing Systems Germany admitted, that in the past nobody had thought about the deinking problem. The aim had rather been to improve the adhesion of the toner to the paper this being the opposite aim to deinkability. Goldmann promised to continue the dialogue with the deinking industry.
Inkjet inks can hardly be removed
The deinkability of inkjet prints lead to different results. Black inks contain more and more finely distributed pigments that can neither be deinked nor discoloured. Even ten per cent of print products with these inks among other recovered paper to recycle spoil the deinkability of the whole mixture. Among the dye based black inks only a few can be discoloured efficiently. Yellow and blue inks cannot be bleached at all they leave an even shade in the deinked pulp.
Inkjets are not only applied in the office. To make mass mailings more attractive by personalisation, ever rising volumes of direct mail, billings, statements and manuals are printed at a breathtaking speed of more than 2.000 pages per minute with inkjet printers. According to Laurent Mathieu of Scitex Digital Printing’s Paris Office, the ink consists of 95 per cent water but how the remaining five per cent can be removed later, about that also in his company nobody has ever thought of.
The amount of recovered paper rises continuously, which requires an early cooperation of paper manufacturers, publishers, ink manufacturers and machinery developers, stated INGEDE chairman Erwin Krauthauf. The first workshop dealing with digital printing gave "reason to hope that also here a lot more can be done in the future".
In Europe on average newsprint is made of more than 65 per cent recovered paper in Germany almost only from recovered paper, Krauthauf said. He saw an enormous potential for a further increase of the use of recovered paper in other graphic papers, however, mainly in higher grade magazine papers. Here the utilisation rate in Europe is still less than eight per cent. In order to succeed with the also politically desired increase, the recovered paper quality must not decrease any further, Krauthauf said. Particularly in terms of inks and adhesives, a recycling-friendly coordination of the utilised processes and products with the paper used has to be taken into account. For that, INGEDE develops a series of test and evaluation procedures. These "INGEDE Methods" can be downloaded from INGEDE's pages on the internet.
INGEDE is an association of leading European paper manufacturers founded in 1989. INGEDE aims at promoting utilisation of recovered graphic paper (newsprint, magazines and office paper) and improving the conditions for an extended use of recovered paper for the production of graphic and hygiene papers.
19 December, 2001
A (German) summary of the workshop with some illustrations can be found here. English summary will follow.