Effect of Fiber Properties on LWC Paper Structure and Printability, 1999 International Mechanical Pulping Conference Proceedings

Tiina Hallamaa, Annikki Heikkurinen & Ulla Forsström

The Finnish Pulp and Paper Research Institute, KCL

The effect of long fiber properties (fiber wall thickness and flexibility) on paper structure and printability was investigated by making pilot LWC papers from mechanical pulps with different long fiber properties but similar fractional compositions. The long fiber properties were varied by mixing a fine groundwood pulp with long TMP fibers corresponding to three different refining levels (unrefined, refined and highly refined). The properties of these papers were compared to those of conventional GW-based LWC paper and to a paper with a larger chemical pulp content. Base paper roughness was strongly affected by the fiber wall thickness of the long fibers: the thicker the fiber walls, the rougher the base paper surface. It was found that after coating and heatset printing the smoothest paper was that with largest content of chemical pulp, and the second smoothest were the highly refined TMP and GW papers. Long, thin-walled and flexible mechanical pulp fibers did not increase printed roughness compared to the GW reference and gave 16% higher tensile index and 23% higher tear index for the base paper. Wetting experiments under the environmental scanning electron microscope (ESEM) showed that the test papers had expanded to varying degrees during wetting, which could explain the difference between the roughening tendencies of mechanical and chemical pulp fibers in the paper.