Effect of latex on surface structure and wetting of pigment coatings

Abstract

The amount and type of latex binder has a significant effect on both the structure and chemical properties of pigment coatings, which affects critical surface properties, e.g., gloss, ink setting rate via liquid absorption, and spreading properties. Increased knowledge is required for improved optimization in practical applications of pigment coating layers. To this end, the effect of binder amount for two different styrene–butadiene latices in kaolin pigment coatings on a base paper was studied, by measuring the surface topography, surface chemistry, and liquid absorption of these coatings. The topography was thoroughly analyzed from nanometer to millimeter length scales by atomic force microscopy (AFM), confocal optical microscopy (COM), and X-ray tomography. The area fractions of latex and pigments on the surface of the coating were determined from AFM phase contrast images, and the contact angles for pure latex and kaolin fractions were determined by using the Cassie equation. An explicit value for the effective surface area of the coatings was determined from the topographic data, which was used for determining the Wenzel correction for the contact angles. Work of adhesion and surface energy components were determined for the samples using three different methods (Owens–Wendt, Wu, vOCG). The latex was found to be evenly distributed over the surfaces, based on AFM phase imaging and ToF–SIMS mapping. The latex binder amount significantly affected the wetting behavior and interfacial properties of the coating layer. The results of this fundamental study can be used for optimization of functional properties of pigment coating systems by regulation of the amount and properties of their latex binder.