Fundamental Studies of Linting in Offset Printing of Newsprint

Abstract

Linting is the removal of material from the surface of uncoated grades of paper during offset printing. Excessive linting reduces image quality and can reduce press productivity. In this paper, web-fed and sheet-fed linting trials have been used to investigate the effect of important press and paper variables on linting. Two of the most important printing parameters affecting linting were the take-off angle from the nip and the printing tone. From analysis of the effects of take-off angle and printing tone, two forces were identified as being especially important to linting: a film flow force in the nip and a tack force from the splitting of the ink film. A simple model was presented that could qualitatively explain why printing press speed, printing pressure and ink tack all had smaller effects on linting than would be expected from consideration of tack force alone. Laboratory printing tack tests and other measurements of paper properties were compared with lint measured in the sheet-fed trials. The tack force measured in laboratory printing was found to be lower for improved newsprint compared to newsprint, while the lint in both sheet-fed and web-fed trials was higher for the improved newsprint. Differences in the film flow in the nip were suggested to be responsible for both effects. The improved newsprint was also found to have a lower surface strength, as measured by delamination.