Surface coating properties of different shape and size pigment blends

The effect of different shape and size of pigments in blends on latex coating surface properties was investigated. Two pigment blends were compared. Both blends were made of plate-like kaolin pigment but with different size prismatic precipitated calcium carbonate at different volume ratios. All coatings were applied on absorbent as well as non-absorbent substrates. Surface coating properties investigated include surface morphology, surface chemistry and surface energy. Surface morphology was characterized by measuring gloss and roughness, surface chemistry was characterized by X-ray Photoelectron Spectroscopy and surface energy was estimated by Kaelable approach.It was found that all surface coating properties were affected by pigment shape and size but with different extents. Pigment blend with coarse PCC particles produces lower gloss and higher roughness than pigment blend with fine PCC particles. While the coating gloss was mostly affected by the pigment size, the coating roughness was mostly affected by the substrate absorbency.Amount of both latex and pigments at the coating surface was affected by the pigment blend ratio and the pigment size and shape selected. Pigment size is playing a major role in determining surface chemical content. X-ray Photoelectron Spectroscopy (XPS) results revealed that decreasing the PCC particle size caused the latex content at the surface to increase and the pigment content (kaolin + PCC) to decrease for the different substrates investigated.Pigment blends with coarse PCC particles show a higher surface energy than that of fine PCC particles for all coatings investigated. These results agree with the roughness increase as a result of increasing PCC particle size.The systematic decrease of surface energy and increase of surface chemistry as a result of changing pigment blend ratio for the coatings applied over absorbent and non-absorbent substrates were modeled in a set of empirical equations.