SMALL-SCALE TOPOGRAPHICAL VARIATIONS OF NEWSPRINT SURFACES AND THEIR EFFECTS ON PRINTING INK TRANSFER DISTRIBUTION

Theoretically, it is desirable to have uniform ink coverage on the pri nted areas of paper. In practice, the ink distribution on printed surf aces may vary considerably, depending on local topographical variation s. in a study focusing on commercially printed newsprint paper, the de tailed topographical paper surface variation was measured and related to ink distribution, using SEM measuring techniques, Local surface var iations of individual, stiff, mechanical fibres were measured, and sho wn to affect the ink distribution strongly. Local peaks on the fibre s urface, and the bottom of interfibre voids are commonly free of ink, e specially for offset printing; it appears that ink spreading in interf ibre capillaries is of minor importance. Ink on surfaces not having be en in contact with the offset blanket is rarely seen. Capillary spread ing of ink into interfibre voids is typical, however, of flexographic printing.