Titanium dioxide performance and its function and application in coatings

October 30, 2018

Tddchem

7453

1. Classification and quality standards of pigment grade titanium dioxide

Titanium dioxide pigments are classified into two types, anatase and rutile. According to international practice, they are called R and A. The rutile and anatase types which are not post-treated are referred to as RI type and AI type, respectively; the post-treated rutile type and anatase type are referred to as R2, R3 and A2, respectively. Most of the commercially available rutile titanium dioxides are of the R2 and R3 types, of which the R2 type accounts for more than 70%. R2 and R3 accounted for 77% and 22% of the rutile titanium dioxide for coatings, respectively.

At present, the models used in China are different from international practices. There are only three types of pigment titanium dioxide, namely BA0101, BA0102 and BA0103. BA0101 and BA0102 are anatase, BA0103 is rutile, BA0101 is not post-treated, and BA0102 and BA0103 are post-treated. For the quality standards of pigment titanium dioxide in China, see GB/T1706-93.

There is a big gap between China's standards and foreign standards. In particular, there is only one model of rutile titanium dioxide, which makes many newly developed, introduced and special titanium dioxide varieties unable to be used in comparison with current standards in China. At the same time, China's production plants and users have only controlled and accepted product quality in accordance with national standards for a long time, instead of changing the process according to user needs to produce products that meet the different needs of customers. It is reported that China will soon introduce new standards.

Why do BA0102 anatase and BA0103 rutile titanium dioxides undergo post-coating treatment? The reason is that after the coating treatment, the titanium dioxide has a reduced water solubility, is not easy to coagulate, the oil absorption is reduced, and the whiteness, electrical resistivity, Achromatic power, hiding power, pigment grinding dispersibility, paint storage stability, paint film water resistance, light resistance, weather resistance and durability are all improved, thereby improving the quality of titanium dioxide.

In China, whether the sulfuric acid method or the chlorination method is adopted, the quality of rutile-type titanium dioxide prepared is lower than that of imported rutile-type titanium dioxide such as R-930 and R-902, mainly in low color-reducing power, low hiding power and weather resistance. Poor properties, poor oil dispersion, and high oil absorption. Therefore, domestic rutile titanium dioxide can still resist the competition of imported rutile titanium dioxide, and even import a large amount of rutile titanium dioxide every year.

2. Properties and uses of pigment grade titanium dioxide

Pigment-grade titanium dioxide has high refractive index, strong decolorizing power, large hiding power, good dispersibility, good whiteness, non-toxicity, stable physical and chemical properties, and excellent optical and electrical properties. Therefore, its use is very wide, paint, plastic (9170, -40.00, -0.43%), paper, chemical fiber, ink, rubber (11360, -165.00, -1.43%), cosmetics, etc. should use pigment-grade titanium dioxide. The largest amount is paint, accounting for about 57%. In particular, rutile titanium dioxide is mostly consumed by the coatings industry. With the rapid rise of China's automobile industry, construction industry and water-based coatings, the coatings industry not only needs more titanium dioxide in quantity, but also has higher quality requirements and more varieties.

The rutile type titanium dioxide has a refractive index of 2.76, and the anatase type titanium dioxide has a refractive index of 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, indicating that the amount of rutile titanium dioxide can be reduced by 25% to 30% if it has the same hiding power as anatase titanium dioxide. In addition, the rutile titanium dioxide has a compact structure, is relatively stable, has low photochemical activity, is resistant to ultraviolet light, is not easily powdered outdoors, and has better weather resistance and gloss than anatase titanium dioxide. Therefore, it is widely used in various high-grade ships, bridges, automobiles, construction and other outdoor coatings, which account for about 70% of the coatings, while the anatase titanium dioxide is easy to be powdered and easy to yellow. For indoor coatings or primers, the amount is only 30% of the titanium dioxide used in the coating.

3. The role of pigment grade titanium dioxide in coatings

The coating is a viscous suspension of binders, pigments, fillers, solvents and auxiliaries. It is coated on the surface of the object to form a tough coating film to protect and protect the object.

The pigment in the paint has a certain hiding power, which not only can cover the original color of the surface of the coated object, but also can impart a bright color to the coating film to achieve the beauty and decoration. At the same time, the pigment and the fixing agent are tightly combined and integrated into one body, which can enhance the mechanical strength and adhesion of the coating film, prevent cracks, increase the thickness of the coating film, prevent the penetration of ultraviolet rays and moisture, improve the aging resistance of the coating film, and prolong the film. Service life.

Regardless of solvent-based or water-based paints, if titanium dioxide is used, its effect is not only covering and decorating, but also important to improve the physicochemical properties of the coating, enhance chemical stability, and even improve hiding power, color reduction, and corrosion resistance. It is resistant to light and weather, enhances the mechanical strength and adhesion of the paint film, prevents cracks, prevents the transmission of ultraviolet rays and moisture, and delays aging and prolongs the life of the paint film. At the same time, it can also save materials and increase varieties.

Among the pigments, white pigments are the most widely used, and white paints and light paints are used. Therefore, white pigments are used in much more paints than other pigments. The white pigments commonly used in coatings are zinc white, zinc white, titanium white and the like. Since some synthetic resin coatings have a large degree of polymerization, if zinc white is added, the zinc white is alkaline, and the free fat in the coating tends to be thickened by acid resistance; if zinc white is added, the weather resistance is poor. However, the use of titanium white can improve the above disadvantages. Because the titanium white particles are fine and uniform, the photochemical stability is high. In terms of hiding power, the rutile titanium white is 7 times that of zinc white, 5.56 times that of zinc white, and the anatase titanium white is 5.57 times that of zinc white. In terms of color reduction, rutile titanium dioxide is 8.3 times that of zinc white, 6.25 times that of zinc white, and anatase titanium white is 6.4 times that of zinc white, which is 4.8 of zinc white. Times. In terms of use effect, 1t titanium white is equivalent to at least 4t zinc white; in terms of service life (referring to outdoor powder resistance), the coating using titanium white pigment is three times higher than the coating of zinc white pigment. Therefore, the use of titanium white can greatly reduce the amount of pigment in the entire coating, and at the same time the paint is bright, not easy to yellow, light, heat, abrasion, weathering, alkali, sulfur, and dilute acid. It is precisely because titanium white has superior performance than zinc white and zinc white, and it has become the best white pigment in the production of paint. The amount of titanium white accounts for more than 90% of the total pigment for coatings, and accounts for more than 95% of the white pigment for coatings. It accounts for 10% to 25% of the cost of coating raw materials.

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