Digital printing - a problem for paper recycling

Differences between the various deinking processes are surprisingly high

Early morning in London and the Swiss newspaper NZZ is already available at the bookstall; Johannesburg, and the business community can buy a copy of the Financial Times the same day as their European counterparts; on an airplane the flight attendant hands out the afternoon edition of a color business journal; mass mailings and catalogs, bank statements and invoices, all these print products have in common digital delivery of the data to the printing press, saving time, cutting costs and increasing circulation.

But there is a downside - these products also have in common problems in removing the applied inks during the paper recycling process. Even small amounts of some of these products can seriously endanger the process of paper recycling.

Digital printing technologies are gaining a growing share of the market. In the near future, many of these printed products will end up in the recovered paper collection from households and offices, becoming part of the raw material to be recycled by papermakers. But the deinkability of some digital prints could turn out to be a threat to today's paper recycling systems: although some of these prints deink quite easily, others lead to severe problems, which may endanger the entire deinking process. A series of tests performed by scientists of the French Centre Technique du Papier (CTP) in Grenoble has also shown that all waterbased inks lead to severe deinking difficulties.

How digital affects deinking

For the first time scientists at CTP have systematically tested how different digital printing processes affect the deinking process. The results were recently presented at a workshop organised by CTP and the International Association of the Deinking Industry (INGEDE) in Grenoble. But only a few providers of digital printing equipment could be persuaded to take part in the workshop - for many of them recycling was not on the agenda.

Differences between processes currently on the market turned out to be surprisingly high. Particularly poor results were observed with liquid toner processes such as the one used by Indigo, which claims market leadership in digital color printing systems. These printers use a fast drying, so-called electro-ink. 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 at 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. The result is a high number of clearly visible dirt specks in the recycled paper. "This is really a threat to the deinking industry", Carré states. Even the third generation of these inks was not acceptable in terms of deinkability, he found. Indigo's Digital Offset Color presses print on a wide range of substrates - from coated and uncoated papers to transparencies, labels and plastic stocks. Substrates for speciality printing include PVC, polyester and polycarbonate. But Indigo, owned by Hewlett-Packard, has not looked into the deinkability of its paper products lately, says a spokesman at its European headquarters in Maastricht. Indigo's research department in Israel was unavailable for comment.

Some toners are a real threat to the deinking industry

"We had no idea that deinkability might be a problem", says Oliver Bauer, spokesman of Bosch Druck, a major German printer in central Bavaria. In January, to the plaudits of local politicians, it opened a new Indigo press, printing up to 2,000 four-colored A3- pages per hour. Bauer was surprised to hear that it contributes to an as-yet unresolved disposal problem. Other printers may also be surprised to learn the position of the German Environmental Authority (UBA): the German "Kreislaufwirtschaftsgesetz", a law managing waste and recycling issues, includes provisions to oblige producers to label products that might oppose the aim of the law: achieving a maximum possible degree of recycling. This means that digital print products, if they prove to endanger the recycling process, have to be marked like cigarettes with clearly visible warnings, such as: "Do not put into the waste paper collection." It would also mean printers being responsible for an adequate disposal of their products. Customers such as the major publishers, who are very concerned about the environmental compatibility of their print products, will not be happy about placing this kind of label on the cover of their products, especially when they tend to declare "100% totally chlorine-free (TCF) paper," or similar, to underline their efforts in sustainability.

Another threat, according to Carré, is "Elcography", a filmless and plateless print technology developed by the Canadian company Elcorsy. Since 1995, Elcorsy has cooperated with the Japanese company Toyo Ink. A digital press was recently supplied to Japan. After several prototypes, a beta test installation was planned for the first half of 2002. This first customer press will be used to print magazines and books. What is special about this development? According to Elcorsy, its digital press prints standard paper grades from the reel in a width of 45.5 cm at a speed of 2 m/second and a price of about three cents per page. A "page" is here defined as A3-sized, printed on one side with process colors (CMYK). With these aspects, speed and price, Elcorsy claims to offer an interesting prospect for printing small newspaper circulations.

Electrographic inks

The printing process is also novel. Elcorsy works with a new technology, electrographic inks. When the ink is manufactured, electrolytic salts are mixed into a pigmented polymer aqueous solution. This process ensures that the ink can later be broken down by electrolysis into different sized drops that are then transferred to the paper web where they quickly dry. Because the inks are water-based rather than oil-based, strike-through is practically impossible. However, deinking by conventional processes cannot be done. Instead, special catalytic agents are used to get the ink to flocculate and thus separate from the pulp. "The corresponding deinking has not yet been developed to production maturity", admits Pierre Castegnier, the inventor of Elcography. "We do not know how CTP did this study of deinkability of Elcography prints." Elcorsy, Castegnier says, has developed five ways of deinking paper. One of them is by immersion in water, flocculation and sedimentation. The ink is composed of a water-soluble resin, pigments, water and salts. The polymer in the printed ink images tends to dissolve in water and to flocculate in the presence of metal ions, a technique routinely used in the wastewater industry. The polymer PAAM, according to Castegnier, is biodegradable and used also as a humidity retention agent in agriculture. "A more thorough study would need to be done to imply that Elcography is a threat to the deinking industry", Castegnier says. "More important, we routinely send Elcography printed paper waste to a well-known Canadian paper recycler and they have not mentioned any problems over a three year period." The Kruger deinking plant, he says, takes four tonnes per week of Elcography paper. "We are also working on ways of making the water-soluble polymer hydrophobic. This would mean conventional deinking would stay the same."

Dry toners do it better

Dry toners, as they are applied for digital four color printing processes from Xeikon and Xerox, create fewer problems. The resulting brightness and residual ink are sufficient to lead to 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 than the contamination found when testing conventional office waste on an industrial deinking line. "Too high," Carré judges. 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. Frank Jacobs, Product Line Manager Color Engines at Xeikon, cannot provide any information regarding the deinkability or whether Xeikon has made its own investigations.

Tests of newspapers digitally printed electro-photographically using dry toner by Océ technology delivered positive results, says Carré. Océ's machines print Swiss newspapers in London, the Financial Times in South Africa and will print for the German daily Süddeutsche Zeitung in New York and Australia. 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 play a part, but an investigation into different toners has yet to be carried out. Gerd Goldmann of Océ Printing Systems Germany admits that in the past nobody had thought about the deinking problem. The aim instead had been to improve the adhesion of the toner to the paper, the opposite aim to deinkability. Previously unaware of the results of CTP's investigations, Goldmann was one of only two representatives of digital print manufacturers joining the workshop in Grenoble. Now, Océ wants to build on this advantage - Goldmann intensified the cooperation with CTP and wants to "continue the dialogue with the deinking industry".

Inkjet inks are hard to remove

The deinkability of inkjet prints varies. Black inks contain many finely distributed pigments that can neither be deinked nor discolored. As little as 10% of print products with these inks mixed with other recovered paper is enough to spoil the deinkability of the whole mixture. Among the dye-based black inks only a few can be discolored efficiently. Yellow and blue inks cannot be bleached at all - they leave an even shade in the deinked pulp.

Inkjets are not only used in the office. To make mass mailings more attractive by personalization, increasing volumes of direct mail, bills, statements and manuals are printed at a breathtaking speed of more than 2,000 pages/minute with inkjet printers. According to Laurent Mathieu of Scitex Digital Printing's Paris office, the ink is 95% water, but how to later remove the remaining 5% is not a question the company has considered.

The amount of recovered paper is constantly rising, thus requiring urgent cooperation between paper manufacturers, publishers, ink manufacturers and machinery developers, reckons INGEDE's Erwin Krauthauf. He believes the first workshop dealing with digital printing gave "reason to hope that a lot more can be done in the future (in this area)".

In Europe newsprint is on average made of more than 65% recovered paper - in Germany almost entirely from recovered paper, says Krauthauf. He sees enormous potential for a further increase in the use of recovered paper in other graphic papers, mainly in higher grade magazine papers. Here the utilization rate in Europe is still less than 8%. But to achieve an (also politically desirable) increase, the quality of the recovered paper must not decrease any further, says Krauthauf.

This requires a recyclingfriendly coordination of both the paper and the processes and products used, particularly in terms of inks and adhesives. To this end, INGEDE has developed a series of test and evaluation procedures. These "INGEDE Methods" can be downloaded from the association's website (www.ingede.com).

CTP is currently organizing a research project, sponsored by INGEDE and ADEME, with the aim of "focussing ink developers to consider possible effects on the deinking process when looking for new ink formulations", says Krauthauf. INGEDE and CTP hope that more ink and printing machine suppliers, printers, or chemical suppliers will find it useful and necessary to participate in the project, which starts later this year.

Axel Fischer is a science writer and film producer in Munich, Germany. He also does the public relations for INGEDE.