“Our customers want a low price but high quality. Curtain coating technology allows us to meet these requirements,” says Shu Jinming, Vice General Manager, Ji’an Group Co, Ltd. The Chinese mill has successfully reduced the need for virgin pulp in its coated white top liner production.
There were two options when the Ji’an Group was making a decision about the coating technology for its new Valmet*-supplied coated board production line PM3 . Option 1 was to go for traditional blade coating with two or three blade coating stations. The three-ply base board would consist of a top ply of bleached kraft pulp, an under top of DIP and a bottom ply of OCC. Coating would be applied on white top base board.
However, option 2 presented a tempting alternative: Valmet’s novel multiply OptiLayer curtain coating. It would mean creating a totally new grade, curtain coated liner board for the Chinese market with no, or significantly less, virgin fibers in the base board because white chemical pulp would not be needed in the top ply. The brown base board would be coated with blade coating, two-layer curtain coating and again with blade coating.
Curtain coating turns brown white
The coating process and new grade was developed through successful cooperation between the Ji’an Group, Valmet and Styron, a leading chemical supplier for the paper industry. A number of coating trials were run with both white and brown base board. Blade coating revealed a clear difference between the two bases. Whereas the white base board produced smooth and uniform brightness after coating, the surface of the brown base board showed clear mottling of brightness. In other words, the brown base partly showed through the coating layer made solely by blade coating.
With Valmet’s multiply OptiLayer curtain coating technology Ji’an has been able to create a totally new grade, curtain coated liner board for the Chinese market that benefits both the mill and its customers.
The simultaneous application of the two-layer curtain coating layers resulted in excellent and even coverage of the brown base board. And better yet, this curtain coated brown board had the same superior physical and printing properties as standard coated white top linerboard. The mill quickly recognized the cost savings potential of curtain coating, provided the amount of virgin fiber could be significantly reduced.
“The blade technology would have made it very difficult for us to be competitive in the market, since the biggest challenge in producing coated liner is its fiber cost. Being able to offer our customers a better price will be our core advantage when competing with our competitors in the future,” points out Shu Junming. “Curtain coating technology will give us a cost saving advantage and also a wider selection of furnish. We will be able to supply a low-cost, high-quality product to the market.”
Clear cost savings achieved
Today, curtain coating is an integral part of the Valmet-supplied containerboard line that started up at the Ji’an mill in November 2011. The 7.25-m-we PM3 is the world’s fastest coated board machine with a design speed of 1,200 m/min. The mill has been able to optimize raw material costs and thereby reach clear savings in production costs.
“The cost saving is estimated to be 200 RMB per produced paper tonne compared to conventional grade,” says Wen Xuefeng, Mill Manager at Ji’an.
High physical and printing properties
Coating coverage as well as other physical and printing properties, such as brightness uniformity, smoothness and gloss, are on a high level with the curtain coating. The coating weight is approximately 30 grams in total.
“The appearance of the curtain coated board made from AOCC and OCC is the same as that of white top coated liner made from bleached pulp when the coating formula has been adjusted correctly,” Xuefeng adds
The introduction of curtain coating involved a lot of close cooperation between Ji’an’s Technical Manager Li Congding (left) and Mill Manager Wen Xuefeng with Valmet’s Project Manager Wenwei Liu.
