The fillers commonly used in coatings include calcium carbonate (heavy calcium, light calcium), barite powder (barium sulfate), talc, kaolin (porcelain soil), porous powdered quartz (silica), white carbon black, precipitated barium sulfate, Mica powder, wollastonite, bentonite, etc.
Calcium carbonate
Calcium carbonate is the main filler (extender pigment) for paint
Classification of calcium carbonate for coatings
Classified by characteristics According to characteristics, calcium carbonate for coatings is mainly divided into light calcium carbonate and heavy calcium carbonate. Light calcium carbonate and heavy calcium carbonate. Light calcium carbonate (precipitated calcium carbonate) is divided into ordinary precipitated calcium carbonate, fine calcium carbonate, ultrafine calcium carbonate, and activated calcium carbonate; heavy calcium carbonate (natural product) is divided into heavy calcium carbonate, heavy fine calcium carbonate, and heavy calcium carbonate Active calcium carbonate.
Classified by crystal form. Precipitating calcium carbonate changes the process and controls the crystallization to obtain cubic crystals, needle crystals, spindle crystals, chain crystals and other fine calcium carbonate crystals.
Classified by crystal particle size Precipitated calcium carbonate can be divided into: fine calcium carbonate (average particle size 44～60um); medium calcium carbonate (average particle size 15～44um); fine calcium carbonate (average particle size 1～15um) ); Superfine calcium carbonate (0.1～1um); Superfine calcium carbonate (<0.1um).
Heavy calcium carbonate products are divided into single fly powder (200 mesh fineness), double fly powder (325 mesh fineness) and four fly powder (400 mesh fineness) according to the powder fineness. Calcium carbonate (1250 mesh fineness).
Application of calcium carbonate in coatings
Calcium carbonate is an important filler in paint production. Calcium carbonate plays the role of filling the framework and substrate (steel plate, wood) in the paint film, and enhances the deposition and permeability of the paint film. Especially used in metal anti-rust primer, it forms hydrogen bond with metal surface to increase the adhesion of paint film, and can absorb hydrogen ions to prevent the corrosion tendency of metal to form micro battery. In addition, calcium carbonate has good weatherability, has abrasion resistance, low electrolyte content, pH stabilization effect, and can improve corrosion resistance and paint rheology. Coarse calcium carbonate is limited to putty, filling compound, metal primer and other products, which require high pigment content, fluidity and rough surface; medium calcium carbonate is used in architectural coatings and indoor matt or semi-finished products. On light paint; fine-grained calcium carbonate is mainly precipitated calcium carbonate, which is used in printing inks.
Heavy calcium can be used in various internal and external coatings, and is suitable for use in water-based coatings. Due to its poor acid resistance, it hinders its application in external coatings. In general coatings, the amount of heavy calcium added is 10% to 35%, and the content in various relief coatings is as high as 50%.
In the coating industry, heavy calcium is used in addition to increase, and is mainly used to partially replace titanium dioxide (generally 10% to 20%, 30% in large quantities) and color pigments, replace light calcium and precipitated barium sulfate, and prevent corrosion And partly replace anti-rust pigments.
When heavy calcium is used in interior architectural paint, it can be used alone or in combination with talc. Compared with talcum powder, calcium carbonate can reduce the pulverization rate, improve the color retention of light-colored paints and increase the anti-fungal properties.
Compared with heavy calcium, light calcium has a small particle size and a narrow particle size distribution range, high oil absorption and brightness. Light calcium can be used where a large matting effect is required. It is more common to mix light calcium and heavy calcium in semi-gloss, matt paint and matt latex paint.