The influence of paper surface energy on multicolor offset print mottling

Abstract

An evaluation of a series of commercial uncoated, semimatte, and glossy coated woodfree papers for the multicolor sheet-fed offset press is presented. This study is aimed at better understanding of mutual influences of surface free energy, paper surface roughness, and fountain solution on print mottling occurring in full-scale printing conditions. Each paper has unique structure in terms of surface roughness, porosity, and surface energy that are the result of manufacturing technology. At the point of contact of liquid with paper, the surface dynamic process of liquid absorption by paper occurs, involving phenomena such as wetting, penetration, diffusion, and swelling. Mottling of colored surface printed by cyan, magenta, yellow, and black inks copied the surface roughness of coated paper. Mottling in the second, third, and fourth printing units showed deviation from mottling in the first printing unit, depending on surface free energy of paper and on the frequency of paper-surface wetting by fountain solution before and after printing.