Sean Milmo, Ink World European Editor09.09.05
The priority for paper makers has been the supply of papers which satisfy the printers’ requirements for low costs through minimum wastage of paper and downtime.
Recently, however, paper companies have been devoting more effort to finding out more about the relationship between the surface of paper and inks.
The arrival of digital printing, with its need for papers with specific properties, forced the paper makers to channel more resources into studying the interplay between inks and their products.
As they have begun to focus on the efficiency of paper as a substrate for ink, the paper companies have also been trying to do more to bridge the gap between the paper and ink sectors.
Ink and paper companies in Europe have for a long time stood aloof from each other. Now the wariness has been replaced by a desire to work much closer together, particularly in the development of new papers and inks.
Slow growth in the paper and printing markets in Europe and pressure on costs have forced the two groups to cooperate more to boost efficiency and provide more effective solutions for printers’ needs.
This new tendency towards collaboration is not just confined to the paper and ink segments but has spread throughout the printing supply chain.
As a result this spirit of partnership also involves chemical producers, some of which supply both the paper and ink sectors, printing equipment manufacturers and the printers themselves.
“The future lies in working more closely together down the chain,” said Erik Ohls, director of the technical market group at UPM-Kymmene, the Finnish-based paper maker. “Printing is now so complex and done at such high speeds that no one can be the master of everything in the process,” he added. “Everyone at each production stage needs to help one another.”
Even companies making chemicals for the paper industry are setting up research links with printers rather than relying on their paper-making customers to find out about printers’ needs.
Raisio, a Finnish group making latex coatings for the paper sector, is creating a joint research and development centre with Hansa Print, a Finnish commercial printer. The unit, comprising a pilot printing plant, will be available to ink and paper companies and others in the printing sector. One aim is the development of latex binders which raise the effectiveness of inks.
“We are creating this center to find out primarily what the printers want, but we expect it to be used as well by research consortia which will include ink makers,” said Eero Sarkki, head of Raisio’s latex business. “With the evolution of so many different printing technologies requiring different coating systems, no one can stand alone any more.”
For paper companies, research on the interaction between their papers and ink is increasingly becoming a key to the success of their products.
“There used to be a time when paper companies and ink producers would develop products quite separately from each other,” Mr. Ohls said. “There would be no discussions between the two about how well the paper works with the ink and vice versa. We did not worry about each other at all.
“Now there has been a complete change,” he said. “In my 25 years in the paper industry, I don’t think paper and ink companies have ever cooperated so closely together.”
There is a feeling, nonetheless, that both sides need to do even more to get to know each other, especially about the technologies driving the two sectors.
“The level of cooperation between the two could be even better,” said Lars Gaedda, vice president, research and development, at M-real Corporation, one of Europe’s leading suppliers of office, magazine and consumer packaging papers.
“Paper makers have to understand more about the chemistry of inks and the ink producers the chemistry of paper surfaces,” he said. “But at least we are both going more and more in the right direction.”
A priority for paper manufacturers at the moment is the development of papers with surfaces which advance the runnability of papers through presses at a time of high speed printing. But increased runnability must not be obtained at the expense of the aesthetic quality of the printed page.
Raising the efficiency of ink performance has been helped by advances in electron microscopsy, spectrometry and other analytical tools for studying the topography of the printing surface.
A lot of attention has been paid to the way inks set and dry on the surface of papers. This is often related to the number, size and shape of the pores in the surface, which can be determined by the degree of roughness of the paper.
A well-established method for measuring roughness has been through the use of air flow from a pressurized cylinder applied to the surface of the paper. But it has a limited capacity to provide a detailed topographic picture of the paper surface.
Scanning and microscopic equipment have been able to give much more data on the surface distribution of coatings and on the depth and shape of voids and depressions in the paper.
“Equipment like atomic force microscopes enables us to discover much more detail about surface structures,” said Mr. Gaedda. “We can now find out more about both the physics and chemistry. We know more, for example, about the polar structures in paper and the chemistry relating to the behavior of solvents and the pigments in the inks on the paper.”
The Swedish Pulp and Paper Research Institute, Stockholm, Sweden, has used a photometric stereo method to build up three-dimensional images of paper surfaces.
It can be applied to non-printed areas of paper to predict the quality of printing by gravure or flexography. With gravure it can even identify where missing dots might occur.
With the use of an electromagnetic technology, the influence of the size and number of pores in paper coatings on the setting of inks can be monitored. Studies in the U.K. show the importance of relating the number and size of pores to the ink setting rate in order to achieve high print gloss.
Fast setting rates can lower the level of print gloss. An optimal setting rate leaves all the ink pigment on the surface with sufficient resin to enhance gloss.
Paper companies have been spending relatively large sums on research into new papers for digital printing to ensure that they have the proper structure and surfaces for both laser toners and ink jet inks.
Color toners and ink jet inks often have their own paper requirements which can be as different as those between offset and digital printing. Furthermore, the paper needs of different digital printing machines can vary.
Since its creation two years ago through the merger of Metsa-Serla, MoDo and Zanders, M-real has been aiming to build a strong position in the digital paper market and has set up R&D partnerships with OEMs in the digital sector. These have close ties with ink producers and formulators.
The company has set up a research center in Germany comprising laser and ink jet machines, including those for large-format printing, so that the development of new paper keeps pace with technological advances.
With the growth of personalized direct mail, paper makers have been producing high-grade coated papers for digital printing. However a lot of work has gone into the development of both standard and specialist grades of uncoated paper for digital equipment.
The use of toner adhesion aids on uncoated papers has helped raise the resolution of laser printed images fourfold to around 1,200 dots per inch. Similar levels have been reached with ink jet inks on uncoated papers, but until recently they did not provide the same optical density or image permanence. Now new surface treatment technologies, such as the use of sizing in the starch and of cationic resins in the paper production process, enable ink jet printing to reach the same quality standards as laser printing.
Outside the digital sector, similar efforts are being made to raise the quality of printing on uncoated paper to that of coated paper. This is usually being done through innovations in the manufacturing process, particularly at the calendering stage.
SCA launched last year a new uncoated paper, called offline multinip calendered (OMC) paper, which the Swedish-based company claims obtains the same quality as lightweight coated (LWC) paper in heatset web offset printing.
“We can now genuinely talk of a replacement for LWC,” said Wolfgang Kuehnel, head of customer technical service at SCA Graphic Laakirchen, Austria. “We’ve got there by the careful selection of filler plus the use of environmentally friendly bleaching techniques and minimizing the loss of whiteness during the production process.”
A high level of print gloss is achieved through careful compression and glazing of the paper during calendering.
“The paper is only compressed to a limited extent,” said Mr. Kuehnel. “Compression is concentrated on the area where the interaction occurs between the printing inks and the paper. Together with the high glossiness (of the paper), this achieves a print gloss that couldn’t previously be attained using uncoated paper.”
Innovations in paper making can be a slow procedure, especially as paper mills are becoming larger to benefit from economies of scale. Current research is pointing to radical changes in the components of paper but they could take many years to be realized.
“The development of new paper structures and surfaces to improve print quality is a continuous, evolutionary process,” said Mr. Gaedda. “There are some ideas in research on the use of smaller fibers to provide a much smoother surface on the paper but that is a technological revolution which is only a long-term prospect.”