Multilayer curtain coating boosts profits in manufacturing of coated board

摘要

Manufacturers of coated board are under continuous cost pressures. The high price of bleached pulps as well as of recycled fibers challenges the economics of coated board production. Multilayer curtain coating eliminates the process bottlenecks associated with contour coating that is traditionally done using the air knife application. Furthermore, the unequalled coverage of curtain coating combined with its engineered multi-layer structure opens up whole new possibilities to optimize the base sheet composition in coated boards. Significant financial gains are achieved by partially or wholly eliminating the need for bleached and de-inked pulps. Using all unbleached recycled furnish in the base sheet, and coating with multilayer curtain enables production of a product similar to conventional coated white top liner or white lined chipboard (WLC). Reduced raw material cost combined with better machine efficiency results in better profit margins with the new concept. Metso's OptiLayer curtain coater is a multilayer slide-die curtain coater. It provides good coverage and as there is more than one coating layer, tailor-made properties can be achieved using different functionalities in the different layers. Cost optimization is the primary driver of multilayer coating: lower-cost coating can be used for the bulk of the coating, while the expensive ingredients important for the surface properties or opacity can be concentrated in the right layers. There are no speed limitations, nozzle clogging or coating reclaim challenges with the curtain coater and coating solids can be kept high. In the curtain coater, coating losses are minimized, as basically all the coating pumped to the coating station is applied to the sheet. The first machine producing coated white top liner with OptiLayer started up at Dong II Ansan mill in South Korea in December 2008. The target of the rebuild was to develop a grade approaching low basis weight coated white lined chipboard grades without using any white fibers and the target has been achieved very well. The next two projects currently under delivery include a brand new production line for high smoothness and high brightness coated whitetop liner in China, and a rebuild of a white lined chipboard machine in Mexico. Both projects employ multilayer curtain coating to reduce or eliminate the need for white fibers..