Kaolin in Paint Applications
Kaolin is a functional extender that offers more than simply cost reduction of paint formulations. Properties that can be modified by careful choice of kaolin extender are;
Opacity is generated by the difference between the refractive index of a material and the medium surrounding it. TiO2 has a high refractive index compared to most paint ingredients and hence gives high opacity. Most extenders have refractive indices similar to the paint binder and therefore can exert only a limited efect on opacity. However, selecting a fine particle size kaolin such as Supreme™ can increase the efficiency of the TiO2 by improving the spacing of the TiO2 particles. Platy hydrous kaolin is more effective in increasing opacity than talc or calcium carbonate with an equivalent spherical diameter.
Fine kaolin has less effect on gloss than coarse kaolin. This means that depending on the gloss required, a suitable kaolin can be selected. Compared to calcium carbonate and talc with an equivalent spherical diameter, coarse hydrous kaolin gives the lowest gloss at 85°. Matting efficiency is also superior.
The effect that the choice of extender has on the fiinal paint colour is a function of the extender colour. Hydrous kaolin becomes less white as particle size increases, so to minimise the effect on colour a fine hydrous kaolin should be selected.
Gel strength can be increased by the use of hydrous kaolin, improving the in can appearance of paint.
High low shear viscosity is indicative of the levelling and flow behaviour of paint and can indicate the sag resistance of paint, important post application properties. Paints formulated with hydrous kaolin shows significantly higher low shear visocsity than those formulated with talc or calcium carbonate.
Solvent based gloss paints for many years contained minimal mineral extender, mainly because of the effect on the gloss. The innovative Polsperse™ 10 changed this by offering paint makers the possibility to extend TiO2 in solvent based gloss paints, using the spacing that fine hydrous kaolins give. In addition, the equipment used to produce Polsperse 10 predisperses the hydrous kaolin allowing the paint maker to use high speed dissolvers rather than bead mills traditionally associated with this type of paint – cutting processing time and increasing efficiency.
Product Related Literature
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