The Development of Paper Gloss in Hot Calendering and Brushing

Abstract

In bleached, white top and coated packaging paper and board, paper gloss is a desirable property, whereas in printing papers print gloss is most desirable. One section of this paper deals with gloss development of uncoated paper and board and another section deals with coated paper. A final section addresses print gloss. The enhanced effect of hot calendering on paper gloss and print gloss, as compared to “air leak” smoothness, is illustrated. This enhancement is due to a thermal softening concentrated at the outermost layer of the paper in contact with the highly polished hot steel roll acting preferentially on the topographical irregularities up to a few microns. Brushing of coated papers produces some densification of the outermost coating layer, thereby filling the surface voids. Brushing improves both paper gloss and print gloss, as well as the gloss uniformity with no significant effect on the ‘fair leak” smoothness.