Silicates as paint fillers
Silicates are the most diverse group of paint fillers. This group includes: natural calcium silicate (wollastonite), aluminum-sodium-potassium-magnesium (calcined clays and bentonite), magnesium (asbestos and talc), aluminum-calcium-sodium (labradorite), aluminum silicates (precipitated silicate, kaolin), aluminum-potassium (mica). In production of paintwork materials the most popular are mica, talc and kaolin.
Mica is potassium aluminosilicate. Its color is white or slightly tinted with iron impurities. The distinctive feature of mica as a filler of paintwork materials is the lamellar shape of its particles, which does not change even in the process of heavy grinding.
Mica, like calcium carbonate, can be obtained naturally and synthetically. Synthetic mica can withstand high thermal stresses without changing its structure, i.e. without breaking. Synthetic mica is often used as a filler in heat-resistant paints. It is mica that gives the paints thermal and corrosion resistance and resistance to ultraviolet radiation and mechanical damage. Synthetic mica is produced by melting a mixture of silicon dioxide, aluminum and magnesium oxides, silicofluoride of potassium and orthoclase (a type of feldspar) in electric furnaces at 1370 ° C. Natural mica is produced by dry or wet milling of potassium mica (muscovite).
When mica is used as a filler for paintwork materials, paints, etc. do not form dense, hard-to-mix sediments during long-term storage. Thanks to mica, paintwork materials adhere better to the surface to be protected, the adhesion of the coating to the substrate, the elasticity of the protective layer and the resistance to atmospheric corrosion are improved. Mica is often used as a filler in water-based paints and electrical insulation coatings.
Talc is a magnesium silicate, a soft white powder, a little greasy to the touch. Talc particles can have a needle or fibrous structure. Talc often contains iron, calcium or aluminum oxides, which either color it a little or give it a grayish hue. Talc is obtained by crushing talcumagnesite or talcite with subsequent classification. If micronized talc is needed, additional processing in jet mills is carried out.
Talc has found wide application in paint and varnish industry as it is well wetted and forms dispersions with film-forming substances. It is chemically inert and gives structural viscosity to paintwork materials. Paint on the basis of talc is characterized by high scratch and abrasion resistance and weather resistance.
Kaolin is a white powder with lamellar particle shape. Hydrated aluminum silicate, i.e. kaolin, is characterized by amphiphilicity. Kaolin is well wetted by non-polar organic liquids and water. The process of kaolin production as a paint filler includes several stages: crushing and thorough grinding, beneficiation and classification.
Kaolin is a component of many compositions: fillers and fillers, oil and water based paints. As well as semi-matte and matte anticorrosive protective layers.