The Correlation Between Coating Penetration and Coating Properties, 2006 Coating & Graphic Arts Conference

The quality of a coating layer, and the efficiency of the coating, depends to a large part on the penetration of the coating into the paper. Rheology and coating solids are known to influence the final product quality, but the mechanisms are not clear. Coating rheology has been correlated with final coating void fraction, but its influence on coating penetration has not been reported. The influence of pigment shape on coating penetration has not been well documented because an economical method to measure coating penetration has not been presented.

The relationship between coating color rheology, pigment type, and coating penetration is reported here. Coatings that contain different pigments and additives are characterized in terms of viscous and elastic properties and applied to paper. Coating penetration is characterized using a confocal laser scanning microscopy (CLSM) in conjunction with image analysis.

The results indicate that both elasticity and viscosity prevent the coating penetration for pigments with a moderate shape factor. This relationship must be related to the flow rate into a pore. Kaolin pigments with a high shape factor have less penetration than the low shape factor pigment and do not depend on coating rheology. The results suggest that high shape factor pigments can block pores preventing pigment penetration.