Coating Terms

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Description
General name for micron-sized powder coating input materials, many of which are comprised of grinded natural minerals (baryte, calcite, talc, kaolin, mica) and some of which are obtained by synthetic methods (Blanc Fixe, lithopone). While main reason for using extenders is cost reduction, they can also be used to improve certain properties. For extenders used in pigmentless coatings, it is crucial that extenders are also colorless and have refractive indicis close to the binder’s refractive index in order for the transparent look not to be affected.
Although pigments and extenders are produced as primary particles, they form aggregates and agglomerates when they are in touch with each other in bulk phase. In dispersion stage, these pigment clusters are tried to break down to primary particles. If dispersed pigments are not stable, they form loosely combined units called flocculates. Since, the distinction between these three terms might not be clear, for a better understanding a schematic representation is given below.



See Also Aggregate, Agglomerate, Flocculate
Breaking down of pigment flocculates which are combined as agglomerates or aggregates, in a binder and solvent medium. Dispersion of pigments and extenders is performed using high-speed dispersers and wet mills.
Quartz powder which is obtained by grinding amorphous quartz is widely used in paint industry as matting additive. Furthermore, SiO2 based on diatomaceous earth is used for the same purpose. Moreover, pyrogenic silica obtained by burning of silicon tetrachloride (SiCl4) is used as rheology modifier in paints.