Лако-красочные материалы — производство

Among the large group of sulfates, barium sulfate (BaSO4) is the predominant filler in coatings. Two types of barium sulfate are used in coatings: natural (barite) and synthetic (blanc fixe). Barite, a naturally occurring crystalline mineral, is the source for natural barium sulfate extender, which is often contaminated with color — producing impurities that are chemically bleached to get brighter grades. Blanc fixe (precipitated BaSO4) is a very fine (0.5 to 4 pm) heavy powder comprised of BaSO4 crystals having a rhombic struc­ture. Due to high chemical purity, it is brighter than barite.

High density, high chemical inertness, low oil absorption value, and stability to light and heat are some of the most important features of this extender. With the highest refractive index (1.64) of the fillers, it exhibits a weak pigmentary property that is synergistic to opa­cifying pigments. Due to its low oil absorption value, high loading compositions are possible without affecting consistency; therefore, it is used in fillers and stoppers. It is used in industrial primers that require good filling power and fineness of particle size along with good sanding properties and hold-out. High density of these extenders is an important consideration, as they are prone to quick settling. For coatings requiring high gloss, blanc fixe with a very low particle size and narrow distribution (30 to 60 nm) is frequently recommended, though it is more expensive than general grades.