Drying tension and shrinkage in paper and board: Part 2 A symmetric three-ply board

The hypothetical shrinkage and internal tension behaviour of a symmetric three-ply board was investigated by utilising results of drying shrinkage and tension in separate individual plies (Part I of this paper) and using a simulated internal dryness profile of such a multiply board during drying on a typical paper machine cylinder dryer train. In paperboard the top plies dry first and tend to shrink first and they also have higher shrinkage potential. During unrestrained drying the middle ply restrains the shrinkage of the top ply and this has an improving effect on the smoothness and tensile stiffness of the top layer. Experimental results and simulated internal dryness distributions show large differences in dryness and drying stress/shrinkage behaviour (between top and middle plies) throughout the drying process. Generally the differences were largest when the average board dryness was 75-80%.