The Effect of Drying Conditions on Paper Curl

Abstract: The aim of this study was to further increase the understanding on the mechanisms that influence the development and magnitude of curl after drying. We focused both on the immediate curl measured immediately after drying, and on the process-induced curl measured after conditioning. Both experimental studies and modeling have been conducted.



First, the question was whether a steam-heated cylinder could be used to influence the process-induced curl. An inhomogeneous two-ply paperboard was used in the investigation. To identify those mechanisms that primarily influence the curl, four complementary trials were carried out in which the evaporation, free shrinkage, moisture gradients and conditioning were investigated.



Secondly, the goal was to establish how the immediate and process-induced curl depended on the development of a moisture gradient during drying. To eliminate the influence of the structure on curl, a homogeneous paperboard was used.



Thirdly, the goal was specifically to identify and clarify the mechanism that influences the magnitude of the immediate curl. In order to do so, a mathematical model was developed. Drying stress, elastic modulus and the thickness of the respective plies in the two-ply laminate were used as input data