The rate of ink setting on coated papers influences the final product quality as well as press operation. Much of the past work has focused on the influence of coating layer structure on ink setting rates: fine pores have been found to set ink more rapidly than large pores. Little has been reported on the influence of ink composition on ink setting. Various models, based on different physical pictures of setting, have been proposed to describe the rate of ink setting, but a careful testing of these models has not been reported in the literature.;A novel experimental procedure was designed to characterize the rheological behavior of inks as oils are pulled into porous substrate. Also, a simple method was developed to measure the rate of oil removal from an ink into a porous material. Two alkyl resins were dispersed in mineral and linseed oils. Various ink-oil mixtures were also used. A composite ceramic plate was used to simulate a porous layer similar to a paper coating. The measured absorption rate and the change in viscosity were compared to various models in the literature. The existing models could not predict both the absorption rate and the observed rheology change. A modified filtercake model that accounted for dissolved resin in the oil phase predicted both types of data for both the resin-oil and the ink-oil systems.;The effect of ink setting on the leveling of an ink film after the printing event was examined through dynamic print gloss. The gloss of a freshly printed sample was measured with a custom made laboratory device with a cyan offset ink that was diluted with a small quantity of mineral oil. The leveling of an ink film on a porous substrate was modeled, with different descriptions of the ink setting process. These model predictions were compared with the dynamics of print gloss measured on slow and fast setting papers. The filtercake model gave better predictions than other models for parameters within the expected range.
展开▼
