Improvement of Dimensional Stability of Paper in a Drying Process (Third Report)

Abstract

It is important to understand how paper is dried and shrunk in a drying process for improvement of the dimensional stability. The cross-directional shrinkage profiles were measured under several restraint forces like vacuum and fabric restraints in the commercial paper machine. The magnitude of shrinkage was affected more significantly by fabric restraint than by vacuum restraint. The cross-directional stretch and hygro-expansion profiles of the dried paper were also measured. These were shown to be non-uniform in the cross machine direction and the highest values were found to occur at the front and back edges. By using paper rolls of newsprint taken from the middle and edge of the paper machines, printing tests by a tower type offset press were conducted and the register error socalled“fan-out”, was evaluated. In the paper from the edge there occurred a higher register error than that in the paper from the middle because of the elongation difference due to water absorption in the printing process. Also, in the paper from the edge, there was found to occur a difference in the register error between the front and the back due to unsymmetrical stability in the cross machine direction.For improvement of non-uniform dimensional stability at the edge, reducing open draw length in the dryer section and reducing evaporation at the edge in the open draw section must be effective.