Influence of Ink Properties on Transfer During Printing.

Previously, ink transferred during printing was divided into that immobilized by the paper during the dwell time and that which splits from the remainder. The latter portion might be called the free ink split. The relation of the free ink transferred during printing to the rheological properties of the ink has now been explored. The fraction of the free ink film which split to the stock has been correlated with the rheological functions: plastic viscosity, yield value, and Inkometer readings; however, no systematic effects due to vehicle or pigment were apparent. The shortness of ink expressed as the ratio of yield value to plastic viscosity provided inverse linear correlations with the film splitting behavior. Separate correlations were obtained for each vehicle system. Effects of vehicle viscosity, vehicle polarity and adsorbed moisture at the pigment-vehicle interface were found. A mechanism of film splitting is described which qualitatively explains the influence of ink shortness. The ink film passes through a region of no shear just prior to splitting; consequently, the critical step in splitting appears to occur at or near zero rates of shear.