Coating Pore Structure and Offset Printed Gloss, 1996 Coating Conference Proceedings

Printed gloss is influenced by paper gloss and ink absorptivity of the surface. When the coating pore size distribution is varied enough, absorptivity differences outweigh underlying paper gloss in effect on printed gloss. A series of discrete, isotropic, monodisperse, calcium carbonate pigments were synthesized in order to produce coatings with well defined pore size distributions. Average particle diameters ranged from 0.45 to 0.19 µm. Among laboratory coated papers, paper gloss increased and offset printed gloss decreased as particle size decreased. In other words, as particle size decreased absorptive forces carried printed gloss in reverse of paper gloss. The change in gloss due to printing, the snap, showed high negative correlation with the ink setting rate as measured by the Paper and Ink Stability Test. Both snap and ink setting rate correlated strongly with the coating pore size distribution as determined by mercury intrusion porosimetry. Increased total pore volume and decreased average pore diameter caused both faster ink setting and lower snap.