The role of barium sulfate, mica powder and kaolin in powder coatings
Fillers in powder coatings can not only reduce costs, but also play a great role in improving the performance of coating products. Such as improving the wear resistance and scratch resistance of the coating, reducing the sagging of the coating during melt leveling, improving corrosion resistance, and improving moisture resistance.
When selecting fillers for powder coatings, factors such as density, dispersion performance, particle size distribution, and purity need to be considered. Generally speaking, the higher the density, the lower the coverage of the powder coating; the dispersion of large particles is better than that of small particles; the filler is chemically inert and can avoid reacting with certain components of the powder formula such as pigments; the color of the filler should be as white as possible. The filler powder materials commonly used in powder coatings are mainly calcium carbonate, barium sulfate, talc, mica powder, kaolin, silica, wollastonite, etc.
Application of barium sulfate in powder coatings
Barium sulfate used as a pigment in coatings is of two types: natural and synthetic. The natural product is called barite powder, and the synthetic product is called precipitated barium sulfate.
In powder coatings, precipitated barium sulfate can enhance the leveling and gloss retention of powder coatings, and has good compatibility with all pigments. It can make powder coatings achieve ideal coating thickness and high powder coating rate in the spraying process.
Barite powder filler is mainly used in industrial primers and automotive intermediate coatings that require high coating strength, high filling power and high chemical inertness, and is also used in topcoats that require higher gloss. In latex paint, due to the high refractive index of barite (1.637), fine barite powder can have the function of translucent white pigment and can replace part of titanium dioxide in coatings.
Ultrafine barium sulfate has the characteristics of large filling amount, good brightness, good leveling, strong gloss retention and good compatibility with all pigments. It is the most ideal filler for powder coatings.
Application of mica powder in powder coatings
Mica powder is a complex silicate composition, the particles are scaly, heat resistance, acid and alkali resistance are excellent, and it affects the melt fluidity of powder coatings. It is generally used in temperature-resistant and insulating powder coatings and can be used as a filler for texture powder.
Application of Kaolin in Powder Coatings
Kaolin can improve thixotropy and anti-sedimentation properties. Calcined clay has no effect on rheological properties, but it can have matting effect, increase hiding power and increase whiteness like untreated clay, which are similar to talcum powder.
Kaolin generally has high water absorption and is not suitable for improving the thixotropy of coatings and preparing hydrophobic coatings. The particle size of kaolin products is between 0.2 and 1 μm. Kaolin with large particle size has low water absorption and good matting effect. Kaolin with small particle size (less than 1 μm) can be used for semi-gloss coatings and interior coatings.
Kaolin is also called hydrated aluminum silicate. According to different processing methods, kaolin can be divided into calcined kaolin and washed kaolin. Generally speaking, the oil absorption, opacity, porosity, hardness and whiteness of calcined kaolin are higher than those of washed kaolin, but the price is also higher than that of washed kaolin.