Performance of Titanium Dioxide & Its Function and Application in Coatings
Titanium dioxide pigments are divided into two types: anatase type and rutile type. According to international practice, they are called R type and A type respectively. The rutile type and anatase type without post-treatment are called RI type and AI type respectively; the rutile type and anatase type after the post-treatment are called R2, R3 and A2 type respectively. At present, most of the rutile titanium dioxides on the market belong to R2 and R3 types, of which R2 type accounts for more than 70% of sales. R2 and R3 account for 77% and 22% of rutile titanium dioxide for coatings, respectively.
Performance and use of pigment grade titanium dioxide
Pigment-based titanium dioxide has high refractive index, strong achromatic power, large hiding power, good dispersibility, good whiteness, non-toxic, stable physical and chemical properties, and excellent optical and electrical properties, so it has a wide range of uses , Paint, plastic, paper, chemical fiber, ink, rubber, cosmetics, etc. all use pigment-grade titanium dioxide. Among them, the largest amount is paint, accounting for about 57%. In particular, rutile titanium dioxide is mostly consumed by the coating industry. With the rapid rise of China’s automobile industry, construction industry and water-based coatings, the coating industry not only needs more titanium dioxide in quantity, but also has higher quality requirements and more varieties.
The refractive index of rutile titanium dioxide is 2.76, and the refractive index of anatase titanium dioxide is 2.55. The hiding power is determined by the difference between the refractive index of the pigment and the refractive index of the medium, and their relative values can be calculated according to the formula. The reflection coefficient of rutile titanium dioxide is 25% to 30% higher than that of anatase titanium dioxide, which means that if it produces the same hiding power as anatase titanium dioxide, the amount of rutile titanium dioxide can be reduced by 25% to 30%. In addition, rutile titanium dioxide has a compact structure, relatively stable, low photochemical activity, resistance to ultraviolet light, is not easy to pulverize outdoors, and has better weather resistance and gloss than anatase titanium dioxide. Therefore, it is widely used in various outdoor coatings with high weather resistance for high-grade ships, bridges, automobiles, buildings, etc., which accounts for about 70% of the coatings. Anatase titanium dioxide is easy to pulverize and yellow, so it is generally only used For indoor coatings or primers, the amount only accounts for 30% of the titanium dioxide used in coatings.
The role of pigment grade titanium dioxide in coatings
Coatings are viscous suspensions composed of base materials, pigments, fillers, solvents and additives. It is coated on the surface of the object to form a tough coating film, which plays a role of decoration and protection on the object.
Regardless of solvent-based or water-based coatings, if titanium dioxide is used, its role is not only to cover and decorate, but also to improve the physical and chemical properties of the coating, enhance chemical stability, and even improve hiding power, color reducing power, and corrosion resistance., Light resistance, weather resistance, enhance the mechanical strength and adhesion of the paint film, prevent cracks, prevent the penetration of ultraviolet rays and moisture, thereby delaying aging and extending the life of the paint film. At the same time, it can save materials and increase varieties.
Regardless of solvent-based or water-based coatings, if titanium dioxide is used, its role is not only to cover and decorate, but also to improve the physical and chemical properties of the coating, enhance chemical stability, and even improve hiding power, color reduction power, and corrosion resistance. , Light resistance, weather resistance, enhance the mechanical strength and adhesion of the paint film, prevent cracks, prevent the penetration of ultraviolet rays and moisture, thereby delaying aging and extending the life of the paint film. At the same time, it can save materials and increase varieties.
Among the pigments, white pigments are the most widely used. Both white paints and light-colored paints use it. Therefore, the amount of white pigments used in paint production is much more than other pigments. The white pigments commonly used in coatings include zinc white, lithopone, titanium white and so on. Because some synthetic resin coatings have a high degree of polymerization, if zinc white is added, the zinc white will have a tendency to thicken due to its alkalinity and anti-acid effect with the free fat in the coating; if zinc white is added, the weather resistance will be poor. But the use of titanium dioxide can improve the above shortcomings. Because the titanium dioxide particles are small and uniform, and the photochemical stability is high, in terms of hiding power, rutile titanium dioxide is 7 times that of zinc white and 5.56 times that of lithopone, and anatase titanium dioxide is 5.57 times that of zinc white. Lithopone is 4.3 times; in terms of decoloring power, rutile titanium dioxide is 8.3 times that of zinc white and 6.25 times that of lithopone. Anatase type titanium dioxide is 6.4 times that of zinc white and 4.8 times that of lithopone. Times. In terms of use effect, 1t of titanium dioxide is at least equivalent to 4t of lithopone; in terms of service life (referring to outdoor chalking resistance), the coating with titanium white as a pigment is 3 times higher than that with lithopone as a pigment. Therefore, the use of titanium dioxide can greatly reduce the amount of pigments in the entire coating, and the coatings made are bright in color, not easy to yellow, light resistance, heat resistance, abrasion resistance, weather resistance, alkali resistance, sulfur resistance, and dilute acid resistance. It is precisely because titanium white has superior performance than zinc white and lithopone, it has become the best white pigment indispensable in paint production. The amount of titanium dioxide accounts for more than 90% of the total amount of pigments used in coatings, and more than 95% of the total amount of white pigments used in coatings. It accounts for 10% to 25% of the cost of coating raw materials.
Article source: China Powder Network