Modeling absorption and rheological changes as suspensions are applied to porous substrates

Abstract

During the application of a suspension to a porous substrate, some components of the suspension can penetrate the substrate and change the properties of the suspension. During offset printing, a pigmented ink contacts porous paper and absorption of the oil from the ink by the paper influences the final product quality and press operations. Although various models have been presented in the literature to describe these processes, a quantitative comparison of models is lacking.Commercial cyan ink was diluted with mineral oil to generate various pigment and resin concentrations in the oil base. A porous ceramic plate with pores of approximately one micron in the top layer was used to simulate the porous layer of a paper-coating layer. The absorption rate of the ink-oil mixture into the plate was characterized gravimetrically. The viscosity change of the mixture after contact with the ceramic plate was characterized by a controlled stress rheometer. Three different models described in the literature were developed further to predict absorption rates and the rate of increasing viscosity. Next, the predictions of these models were compared to the experiments.A filtercake based model predicts the absorption rate at various concentrations of oil and ink. The increase in viscosity due to absorption is predicted qualitatively using various models. A modified filtercake model is proposed that predicts the absorption rates and viscosity increases of these systems within expected accuracy.