Effect of Drying on Coated Paper Print Mottle

Many researchers have shown that among papermaking processes critical for coated paper print quality, drying is a key step. The objective of the present work is to investigate the potential for changing coated paper properties, especially its printability, by varying drying conditions, including through a new drying parameter. All current non-contact drying of coated paper occurs in an air environment. An experimental drying fluid, superheated steam, was used here at both stages of coated paper production, the base sheet and the coated sheet. The results for drying in superheated steam were compared to those with the conventional air drying fluid. Drying in superheated steam is of particular interest for materials such as paper and coatings for which the properties are affected by the glass transition of its polymer constituents. Paper coated and dried in the two drying fluids in a custom coating-drying facility developed at McGill University was printed on a Prufbau press using cyan heatset ink in multiple-nip printing configuration. Mottle, evaluated quantitatively as a function of the scale of print nonuniformity, was significantly affected by the drying variables tested. Coated paper drying conditions affected the severity of print mottle, not the scale. Drying in superheated steam led to a more mottled sheet if used for drying the base sheet but gave less print mottle when used just for the coated sheet.