Variations in calcium ion concentration and pH influencing coating colour rheology, dewatering and immobilization

• Interparticle interactions in a coating colour are largely influeced by electrolyte concentration and suspension pH. The degree of interaction is reflected in the rheological and dewatering properties of the colour as well as in the structural properties of the immobilized coating layer. In the present study an attempt is made to correlate the degree of interparticle interaction created within coating colours by variation in calcium ion concentration and pH with the atomic absorption spectroscopy were applied to gain further information about the degree of interaction. Results showed that coating colours of a mix of calcium carbonate and clay exhibit a pronounced elastic character. The elastic response increased with calcium ino concentration. This is due to calcium calcium ions binding to the dispersing agent, making it less effective. A further cauce is the decrease in the thickness on the diffuse layer of counter ions surrounding the pigment particles. A pH-reducation further strenghened the created intrinsic three-dimensional network structure. An increase in calcium ion concentration resulted in a reduced water retention, slightly pronounced by a higher pH. The immobilization solids content as did also a lower pH. Characterization of coated layers drawn down on polyester film confirmed that a combination of a high calcium ion concentration and a reduction of pH results in a pronounced pigment interaction, reflected in a thicker layer with lower density and higher roughness.

Nyckelord

Coating colors

rheology

calcium ion

ph

dewatering

immobilization

structure

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