Development and Production Experience of the Multilayer Curtain-Coated Linerboard of Ji’an PM3, PaperCon 2013

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The Ji’an PM3 is the first linerboard machine in China to utilize multilayer curtain coating technology. Since the successful start-up at the end of 2011, further development work has been carried out to optimize running conditions, coating formulations and the base paper, in order to provide a product with satisfactory quality and lower cost-to-manufacture. The key challenges include designing the base board structure for the desired mechanical strength, designing the surface properties for subsequent coating operations, optimizing the high-speed running of the curtain coater to enhance production efficiency, minimizing the amount of titanium dioxide in the coating color, and balancing the coated board properties to make them suitable for both offset and flexo printing. The pilot and millscale results show that curtain coating has a major positive impact on brightness, while smoothness is improved mainly by the blade coating and calendering conditions. Optimization of base board properties and the blade + curtain + blade concept has resulted in the successful use of 100% recycled fiber to produce base board, while the final coated board meets market requirements for both offset and flexo printing in terms of its optical, mechanical and printability properties. Machine runnability is excellent at the current speed of 1000 m/min, and titanium dioxide has been eliminated totally in the coating formulations without affecting the coating coverage. A significant improvement in the total cost of coated white liner production has been achieved, compared to the conventional concept of using virgin fiber in the top ply. Future development will focus on combining low cost with further quality improvements to make it suitable for a wider range of end-use applications, including frozen food packaging and folding boxboard.