HOT SOFT CALENDERING - EFFECT ON SURFACE FINISH AND PRINTABILITY OF PAPER

Paper mills are under continual pressure. Customers demand products with better printability, runnability, and uniformity. Investors want to minimize raw-material costs and run the paper machine at capacity while producing the most profitable grades of paper. The community calls for increased use of recycled fibers. A hot soft calender can help the papermaker satisfy all these demands. This article recounts the experience of a European mill that installed a hot soft calender to produce new grades of high-gloss wood-free paper. The authors review the reasons for the mill's decision to purchase the on-line machine and the problems encountered during the first months of operation. The focus then shifts to results of pilot-plant trials documenting the effects of hot soft calendering on coated-paper properties. The tests were designed to show how sheet formation and precalendering interact to affect bulk, smoothness, gloss, and printing uniformity of hot-soft-calendered glossy coated paper. The mill used the results to optimize operation of the hot soft calender.