紙の表面ラフニング機構に関する研究 （第１報） ラフニングに及ぼす面内内部応力の影響

Abstract

Surface roughening of paper is a phenomenon which occurs when paper becomes wet in contact with moisture, water or aqueous liquid, and adversely affects print quality. Release of internal stress of paper was reported as one of the causes for surface roughening of paper. It is generally recognized that internal stress of paper is created in a sheet during drying under tension, and it is released when the sheet is wetted. However, there is anisotropy of created internal stress ; in-plane stresses induced by drying tension and out-of-plane stresses. The contribution of in-plane internal stress to surface roughening was investigated. Machine-made sheets were subjected to cycles of calendering and soaking in water. In-plane internal stress of those samples was determined in terms of a rate of tensile stress relaxation to logarithmic time by Kubat's method. In-plane internal stress decreased remarkably by soaking, but did not change by calendering. Smoothness of the samples with intenser calendering conditions decreased more substantially by soaking in water. Reduction in smoothness of the samples after soaking depended on that before soaking, but not on the degree of reduction in internal stress. Consequently, release of in-plane internal stress could not be always a main cause for surface roughening on a printing-related smoothness scale, but may be responsible for deformation on a large scale.