As we all know, paint generally consists of four basic components: film-forming substances (resins, emulsions), pigments (including body pigments), solvents and additives (auxiliaries). Among them, pigments in paints mainly play the role of giving color to the coating and providing hiding power. Pigments can be divided into coloring pigments and body pigments. The former is mainly responsible for color performance, while body pigments are also called fillers, which are mainly used to improve the thickness and functionality of the coating. Non-metallic mineral powders are mostly used as fillers in paints.
Calcium carbonate powder is the most commonly used non-metallic mineral powder filler. Thanks to its extremely high cost performance, this “most commonly used” is unparalleled. Calcium carbonate has the advantages of fineness, uniformity, high whiteness, and good optical properties. Adding it to water-based paints can greatly improve the reinforcement, transparency, thixotropy, and leveling of the system, and significantly improve the stain resistance, scrub resistance, and adhesion of the paint, and has an anti-sedimentation effect.
According to the different production processes and performance, it can be divided into heavy calcium carbonate, light calcium carbonate, and nano calcium carbonate.
Heavy calcium carbonate
Heavy calcium carbonate has become the most important filler in the coating industry due to its cheapness, easy availability, good whiteness, low oil absorption, moderate specific gravity, good dispersibility and other advantages. It is of great help in reducing costs and is widely used in latex paint, waterproof paint, light anti-corrosion industrial paint, floor paint, wood paint and powder coating and other coating segments. However, heavy calcium carbonate produced by processing different raw ores has differences in purity, particle density, bulk density, etc., so its hiding power, washability, glossiness, processing fluidity and stability in coatings are different.
Xu Yonghua, Gan Kunxiu and others compared the application of different heavy calcium carbonates in latex paint, inorganic coatings and polyester powder coatings and found that the heavy calcium carbonate produced from large calcite as the raw material in interior wall latex paint has better contrast ratio and washability than the heavy calcium carbonate produced from small calcite and dolomite; the heavy calcium carbonate produced from dolomite as the raw material in inorganic interior wall coatings has poor stability and is not suitable for use in inorganic interior wall coatings, while the heavy calcium carbonate produced from calcite as the raw material has better stability in inorganic interior wall coatings. In polyester powder coatings, the heavy calcium carbonate produced from dolomite as the raw material has significantly better processability, paint film gloss, paint film whiteness and contrast ratio than the small calcite and large calcite products of the same specifications.
Light calcium carbonate
Light calcium carbonate is characterized by low density and fine particles, but poor stability. Due to its excellent suspension and dry film hiding power, it was widely used in latex paint in the early years. It can effectively improve the storage suspension and dry hiding power of the paint. However, if the process is not well controlled during the production of light calcium carbonate, it is often easy to cause excessive free calcium ions, which can easily cause emulsion demulsification and affect the stability of the paint. Therefore, after calcined kaolin was put on the market, the application of light calcium carbonate in architectural coatings has become less and less; in addition, due to its high oil absorption and poor fluidity, light calcium carbonate is also used in sand-textured powder coating products.
With the continuous enrichment of modifier types and the continuous development of modification equipment, more and more modified calcium carbonate products are used in the coatings industry to improve the functionality of the products.