MD microstriations in paper: A two-sided shrinkage phenomenon?

We observed extremely small striations, highly oriented in the machine direction, 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. The MD microstriations were always worse on the paper side that was pressed against the wet felts in the last nip or two, but there was no correlation between the striations in the paper and the felt contact pattern. The mechanism appears to be an interaction between pressing and drying that leads to a different rate of shrinkage on each side of the paper during drying, causing a microscopic buckling.