Improved prediction of offset ink setting rates based on experimental data and filtration equations

The setting rates of inks on paper influence the printing operation and the quality of the final product. Although much work has been reported on the effect of the coating structure on setting rates, much less work has been done understanding the ink parameters, especially the influence of emulsification. A series of four papers were tested with three inks. The inks were characterized in terms of printing properties, rheology, and their filtration behavior. The filtration rate is used to obtain a permeability value of the ink filtercake. The value of the maximum tack was determined to be more dependent on the smoothness of the paper tested than on the type of ink. The dynamics and magnitude of the tack test were dependent on the ink viscosity, but viscosity alone does not explain the results. The measured ink filtercake permeabilities are different between the ink types by a factor of 2. The setting rate is found to be primarily a function of the viscosity of the oil used in the ink, rather than a function of the pigment and resin system.