PAPER INK INTERACTIONS. Impact of oil-binder interaction on pore structure in paper coating as studied by internal reflectance Part 1 : implications of pore volume loss for print drying

Abstract The absorption of liquid into a pore network structure depends on porosity, pore size distribution, surface free energy of the involved phases, and external pressure. In the case of ink setting on coated paper, significant decrease of accessible pore volume can take place due to swelling of latex binder particles when contacted with the vehicle of oil-based ink. The reduction in pore network connectivity can be detected by an optical retlectance measurement procedure based on the refractive index differences between the coating components and the surrounding medium present in the interparticle pores. In this study, GCC mode l coatings with latices displaying differing oil uptake and swelling characteristics were exposed to liquid supersource imbibition without external pressure. Effects of both linseed oil and minerat oil were studied. In the case of free liquid propagation, i.e. in coatings with low content of binders, a linearly increasing trend of logarithmic retlectance gradient in the coating thickness is observed as a function of time, indicating deceleration of the wetting front propagation in consequence of the establishment of the flow resistive viscous factors at long timescales, and the subsequent approach of the saturation point at the wetting front. In contrast, in the case of restricted propagation, due to high binder content of swelling Iatex particles, a deviation of the logarithmic retlectance gradient from the linear trend is observed as saturation is approached. However, the relationship between spatial logarithmic retlectance gradient and liquid uptake per unit cross-sectional porosity continues to follow linear trends irrespective of the binder if the porosity is corrected for the loss due to swelling, thus enabling the effect of the binder on the structure to be studied in isolation.