MD Microstriations in paper: a two-sided shrinkage phenomenon?

Very small striations, highly oriented in the machine direction (MD), were observed on one side of finished paper from various paper machines. Observations and measurements of this previously unreported roughening showed it to adversely affect coating and printing quality. Other observations showed the MD microstriations were always worse on the paper side that was pressed against the wet felts in the last nip or two. However, we could find no correlation between the striations in the paper and the felt contact pattern and, therefore, feel the mechanisms involved in this particular roughening are not directly caused by embossing from the felt. Several other roughening mechanisms are discussed. We currently think that the most viable mechanism appears to be an interaction between pressing and drying which leads to a different shrinkage on each side of the paper. The differential shrinkage in turn causes a microscale buckling which appears worse on one side.