Investigation of the effects on paint quality of Sivas talc used in water borne paints

Talc is a functional filler commonly used in paint industry. Although having reach talc deposits in our country a final micronized talc product required by paint industry with the specification of fine particle size and more important with high opacity cannot be produced. Therefore, imported talc products are preferred to supply the high quality talc demand of domestic paint industry. The performance of talc in paint depends on its structural properties like particle morphology, particle size distribution, oil absorption. In spite of having chemically and mineralogical high quality of talc raw material in Sivas – Zara, reach and important talc deposits of Turkey, it is seen that ground talc products from this region are not in accordance with the required properties compared to import talc products. The weakness of Sivas talc in paint applications were opened to discussion through the morphological, physical and surface properties of talc as a functional filler in terms of the paint quality (opacity, etc.) and was tried to be improved with experimental studies. The performances of talc products produced at different grinding conditions effecting its morphology were compared with the performances of imported three merchant talc samples in paint. In the first step, talc raw material was ground and grinding parameters were determined by considering the lowest aver. Particle size (d50) for each conventional ball mill and agitated ball mill. Paint production was realized according to an industrial water-based paint receipe by using merchant talc samples and the talc samples produced at grinding experiments. The amount of talc in each receipe kept constant (5%) and opacity was measured for each paint produced by talc samples. Talc samples obtained from grinding were characterized (particle size, oil absorption, etc.) by considering paint results and surface properties like contact angle, zeta potential, surface energy, etc. have been determined on selected samples to question the relationship between particle size and opacity. Also, the differences at particle morphology (aspect ratio, roundness, etc.) were determined by using SEM images and AFM analysis of ground talc samples. Finally, it was shown with the experiments that the dispersion and settling behaviours of talc particles in paint suspension differed due to change at their surface properties depending on the change at their morphology after grinding. This behaviour was evaluated according to classical DLVO theory with the attractive and repulsive forces effective on particles in suspension and was determined that specially the attractive forces (EDL) were dominant on talc behaviour in paint. It was also seen on AFM analysis that the characteristics plane and edge surfaces of talc were changed due to grinding and the behaviour of talc in suspension was also changed depending on this change. This was explained by the help of (Kynch) settling theory.