30 January 2017 Digital Printing Technologies

Tough questions on paper

Paper companies have to decide whether to develop new grades to suit inkjet presses or hope that the technology will allow printers to use existing substrates.

Just as press suppliers converted their laser print customers into inkjet customers, so paper mills have been able to continue supplying the same papers to these users with little impact on quality. Because this was not the crucial factor.

As inkjet moves towards litho quality, towards four-colour printing with high ink coverage and to litho replacement applications, inkjet optimised papers are going to be needed. Or are they?

Some of the press suppliers are claiming to be able to print on standard offset papers, some require a pretreatment to achieve a surface for the ink to hold on to without unwanted penetration into the fibres of a paper, some are working with an ink that does the same job.

Other suppliers are hoping that inkjet optimised papers will become cost competitive with general papers and so will not need to invest in special inks or coatings.

But the low demand for papers like this is acting as a barrier to development of these papers. If demand remains relatively low, there will be little chance for paper mills to achieve a satisfactory return on investment from money spent on R&D. Some have rowed back on plans to develop inkjet specific papers and are investing instead in packaging grades for example.

Others hope that the papers that they currently offer will be suitable for inkjet printing. However, inkjet printing is not the same as offset litho. As printers have found, if two papers are suited to litho printing, there is no guarantee that both will be suited to inkjet printing. or perhaps that where they work with one press provider, they will not work with another press provider. The chemistry of an ink and with the surface of the paper can interact in unexpected ways.

For this reason much is made of the need to profile papers to ensure that they will work and why inkjet providers have extensive testing programmes. A brand name alone is no guarantee of suitability. For example, Canon bills its ImageStream as capable of printing on litho papers with no further preparation. However, in tests it found that the same paper produced at separate mills gives different results. The CutStar version of the paper runs well, the web offset version does not.

Litho printers have frequently complained when production of a paper is moved to a different mill because despite having the same specifications, it behaves in a completely different way on press. What is exasperating for offset litho when paper is made differently, could be disastrous for inkjet.

One key issue for the printer and technology provider is the amount of dust and other debris that comes off the web. Antistatic and web cleaning devices should be used at all times and care should also be taken to ensure that sensors are kept clean whether part of the press or part of a separate finishing line. Many a call out is unnecessary if the sensors which control cut off length, perforations and folder timing are kept clear of paper dust.

But there are paper makers that have seen the opportunity in paper for inkjet and have come up with papers that are specified to work on inkjet presses. At the forefront are Mitsubishi Paper Mills and CVG. In addition Mondi, Steinbeis, Felix Schoeller, Arctic Paper and UPM will all be at the Hunkeler Innovation Days to talk paper.

There are two key absentees from previous events: Sappi which seems to be concentrating on packaging opportunities and Ziegeler, whose collapse into bankruptcy showed that having an inkjet paper is not enough. Other mills, Bolloré among them, have been testing formulations to come up with a paper suitable for inkjet applications.

The task is to develop a paper that will work with the three inkjet technologies in use, piezo, continuous and thermal with predictable results. It makes much more commercial sense if a paper mill can produce a universal inkjet paper rather than papers specific to the different processes.

It is tied up in the amount of water that the paper is expected to cope with while retaining dimensional stability, preventing excessive ingress into the paper fibres while also enabling the pigments to grip the surface of the paper.

CVG, however, has demonstrated that it is possible to focus on developing papers for inkjet printing and succeed in doing so. It has papers which work with dye and pigment inks, which are suited to book publishing, transactional and direct mail applications, for continuous or drop on demand inkjet. “The different technologies makes a difference for the paper and the treatment,” says sales manager Felix van Boeckel. “Some machines are better for certain applications perhaps.”

The Dutch mill is relatively small so could not compete with the groups when producing coated woodfree papers. Consequently it had been early to seize the opportunity that inkjet seemed to present. It now has matt and silk effect papers, but no high gloss paper as the calcium carbonate coating needed is not compatible with the chemistry of the inks used.

“The choice of which paper to use will depend on the price a company wants to pay and how much colour is involved,” says van Boeckel. CVG’s papers are price competitive for an inkjet treated paper. And papers that are treated at the mill on an industrial scale are going to be cheaper than any paper that is coated at the print plant either inline or on standalone equipment where the printer has to invest in a coating line as well as the consumable.

“And our paper will give a better, more consistent result,” he adds. “On an uncoated paper, the mill treatment is designed to stop the ink spreading out, which also reduces the amount of ink that is needed.”

Mitsubishi Paper Mill’s Jetscript brand has been recognised a wide ranging set of papers for transactional, direct mail and publishing applications, tested and approved by the major inkjet press providers. It also makes proofing paper and high quality sheeted inkjet paper.

Its papers are recognised as probably delivering the best quality, but are also the most expensive and printers and their customers are not always prepared to pay the premium demanded.

Others papermakers with a similar background have been looking at the potential of adapting cut sheet inkjet papers for high speed inkjet use. None has yet come up with a paper that offers the quality needed at the price that printers consider affordable.

Mondi, in contrast, has come from the offset paper side so understands the requirement in terms of cost. It has a set if papers developed for varying degrees of ink absorption to run on high speed inkjet presses with the look and feel of conventional offset papers but without the hassle in running that can be associated with standard offset papers.

Its NeuJet silk paper has been approved by the majority of inkjet press providers. Mondi says the surface has been treated to hold colour on the top of the paper thus consuming less ink and enabling fast drying. It delivers, the company says, “full deep colours at highest printing speeds reaching offset capabilities”. Colour gamut is in excess of most other inkjet papers and reaching the extent of offset on coated papers.

The paper is available as a matte and matte premium grade while Mondi also offers 100% recycled papers and uncoated papers for inkjet printing.

Likewise ArjoWiggins Graphic has a range of recycled papers in its Cocoon and Cycles families that are suited to inkjet printing. “This inkjet portfolio complements the rest of our digital product offering. We see this product range as an innovative and alternative solution for printers and their corporate clients. These specially engineered, premium quality web inkjet papers are already creating profitable new markets in transpromo and direct mail, with increasing commercial print applications,” says Jean Charles Monange, sales and marketing director of ArjoWiggins Graphic.

The rate of increase in commercial print applications will be watched carefully by the paper industry. For mills timing will be crucial. While it is too soon to assess the impact of new latex styles of ink, it appears clear that running an inkjet press on a standard paper without any other treatment is not going to deliver the desired results.

Some kind of inkjet optimised paper is going to be needed. When offset litho first emerged, it became clear that existing letterpress papers were far from suitable. Mills will have learned the lesson from that experience.

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Mondi is one of the papermakers developing papers to suit the requirements of inkjet printing. Technology developers are divided in supporting this type of work or trying to find ways to print on standard offset papers.

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