Effect of coating structure on print gloss after sheet-fed offset printing

Print gloss is highly determined by the surface and pore structure of the printing substrate. The relations between print gloss and coating topography, ink amount and setting rate have been studied after full-scale sheet-fed offset printing of commercially and pilot manufactured fine papers. It was found that micro roughness, but not macro roughness was smoothened by the ink film. Thus, macro roughness determines print gloss to a large extent and features in the size range of 0.05-0.25 mm were found to be highly detrimental. Papers coatings with high amounts of large pigments normally have a matt appearance. Print gloss of such papers appears to be determined not only by macro roughness but also by ink amount, while ink amount only has a slight impact on print gloss of smooth papers. Print gloss increment due to ink amount was found to increase in the order gloss<silk<matt. It was also confirmed that high setting rates reduced print gloss, most likely. due to reduced leveling of the ink film split pattern. Ink setting rate increased with decreasing pore size.