AN EXPERIMENTAL EVALUATION OF THE GOVERNING MOISTURE MOVEMENT PHENOMENA IN THE PAPER COATING PROCESS PART I: THEORETICAL ASPECTS

摘要

The most important issue when coating paper, is the modelling of the moisturernmovement in the coating process, since the water movement pattern is stronglyrnconnected to binder movement and the final structure of fibres and coating colour,rnwhich in turn affects the final printing properties of the paper. Therefore, we are nowrnstudying theoretically a novel laboratory method to determine the dynamic waterrnmovement in a hygroscopic porous media, I.e. the liquid movement in the paper coatingrnprocess. The experimentally determined physical properties yield information relevantrnto the mass and energy balances of a real paper coating process. We have also studiedrnthe widely used Lucas-Washburn capillary suction theory in combination with thernbuild-up of a filter-cake in the coating colour. The study shows, that the water loss fromrnthe coating colour into a hygroscopic material can be well explained by applying vapourrndiffusion into the base paper as the governing mass transfer mechanism.