Comparison of SGW and TMP as Fiber Raw Material for Film Coated LWC, 1999 Coating Conference Proceedings

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Jaana Ahlroos, Stora Enso Research
Johan Grön, Valmet Corporation

For paper machine lines with on-line coating, productivity is often as important as quality. Film coating is gaining ground in these applications, due to good runnability. To further improve paper and print quality in film coating, the base paper needs optimization. It is known that among the most important factors influencing the paper and print quality of coated paper, are the base paper properties. In this work, SGW (stone groundwood) and TMP (thermo-mechanical pulp) have been compared as the mechanical fiber raw material in film coated LWC paper. The effect of the sheet structure and surface properties of the base paper on paper and print quality has been studied. Variations in base sheet structure were created by varying the type of mechanical pulp, filler content and pre-calendering. The study showed that closing the paper structure and the paper surface prevents the coating from penetrating into the base sheet. This gives better coverage, which means improved coated surface properties and a better print result. The evenness in the printed image can also be improved. Closing the base paper structure can be done by means of lowering the freeness level, increasing the filler content or by pre-calendering.