Lithographic offset ink rheology related to sensory descriptions of appearance and handling

Lithographic offset inks are pigment dispersions that behave as pseudoplastic, thixotropic fluids. Printers, who use these fluids in offset printing, judge some aspects of ink quality using a set of practiced visual and tactile perceptions that are referred to collectively as the “ink body.” Measurements of ink flow behavior are routinely performed to validate offset ink quality, but the measurements usually have been restricted to a small number of readings, such as a viscosity and a yield value. These measures, although suitable to provide some level of flow description of the ink, do not sufficiently represent perceptions of the fluid properties. A sequence of tests was developed to correspond more closely to an evaluation of ink body observable through sensory interaction with the fluid by sight and touch. Offset inks with a wide range of different body characteristics were rated by a sensory panel on a scorecard. Measurements in the test sequence were then used to predict the sensory panel ratings according to an algorithm obtained by partial least squares (PLS) regression analysis. Overall, the broader rheological description provides a better representation of the flow properties of offset printing ink. The test is suitable for practical use in a manufacturing environment for quality assurance.