A Multiphase Mechanism for Setting and Gloss Development of Offset Ink, 2006 TAPPI Advanced Coating Fundamentals Symposium

Coatings that cause rapid offset ink-setting can limit ink gloss by retaining the ink split pattern. Published mechanisms do not explain ink leveling rate satisfactorily. Specifically, their underlying assumptions would require the ink film to release most of its solvent (oil) content in the first few seconds. To address this limitation, a new mechanism for the initial stage of offset ink-setting is proposed and compared to previous mechanisms. According to this new hypothesis, ink setting is based on non-equilibrium, sub-second time scale interactions among multiple chemical phases in the ink film. These interactions make ink viscosity dependent on rate of oil removal by the coating as well as on remaining oil content. This mechanism explains how ink leveling can be arrested in as little as 2 seconds while oil content is still high. It also provides tools for an ink-maker to make inks with less sensitivity to coating pore structure.