The application of water to the surface of a paper or board web (in printing, coating, surface sizing etc.) causes a decrease in MD tension and a rapid increase in web width. Both processes have complex time-dependences whose details have direct practical relevance. For example, in color offset printing the amount of CD expansion between printing units determines fan-out and other misregister problems.
No single traditional measurement can predict the amount of expansion or reveal its causes. We use KCL Vesikko and supplementary paper transmittance analysis to study the CD expansion and sorption dynamics for different papers and experimental conditions. With a new sorption model we can predict the experimentally observed movements of water inside paper.