Paper Surface Properties Versus Stress During Drying, 1991 International Paper Physics Conference Proceedings

At PFI there has been developed and built a laboratory instrument in which a test sheet can dry out while controlling the drying stress. By the instrument the drying stress (drying force) can be varied simultaneously and differently in both directions of the test sheet (x- and y-direction). By varying the drying stress in the sheet, the sheet dries either restrained, under shrinkage or by straining it at a chosen level of dry content. This instrument has been used to evaluate the relationship between different degrees of shrinkage and the surface properties of the sheets. Several works have presented the relationship between drying stress, or shrinkage, and the mechanical properties of paper (paper strength etc.). Less attention has been given to investigate how shrinkage of paper influences the surface properties.

The results presented in this paper, show a clear relationship between surface properties and the magnitude of the shrinkage. Surface properties in this work are evaluated by standard measuring methods as Bendtsen Roughness, Parker-Print-Surface, and Paper Gloss. Although the results presented are based on a rather small population of observations, the relationship is clearly established. For some surface properties the differences can even be identified after soft calendering of the sheet. The results also show that a moderate straining of a test sheet gives, in some cases, a smoother sheet surface.