Titanium dioxide is an important white pigment, which can be divided into plate titanium type, anatase type and rutile type, plate titanium type is very unstable. Compared with traditional white pigments such as lead white, zinc white, zinc barium white, titanium dioxide has a variety of excellent properties such as high refractive index, strong achromatic power, large hiding power, and harmlessness, and is known as a good white pigment. Used in coatings, plastics, chemical fibers, ceramics and other industries. Among them, the amount of paint is very large, accounting for about 57% of the total amount of titanium dioxide. So how is titanium dioxide applied to coatings?

First, the role of titanium dioxide in coatings

The coating is mainly composed of four parts, such as film-forming substances, pigments, solvents and additives, and the pigments in the paint have a certain hiding power, which can not only cover the original color of the painted object, but also give the coating film a bright color, and realize the decorative effect of lighting and beautification. At the same time, the pigment is closely combined with the curing agent and the substrate, and is integrated, which can enhance the mechanical strength and adhesion of the coating film, prevent cracking or falling off, and can enhance the thickness of the coating film, prevent the penetration of ultraviolet rays or moisture, improve the anti-aging and durability of the coating film, and extend the service life of the coating film and the protected object.

Among the pigments, the amount of white pigment is very large, and the performance requirements of the coating for white pigment: (1) good whiteness; (2) Good grinding and wettability; (3) Good weather resistance; (4) Good chemical stability; (5) Small particle size, high hiding power and achromatic power, good opacity and gloss.

Titanium dioxide is a white pigment used in coatings, its output accounts for more than 70% of inorganic pigments, and the consumption accounts for 95.5% of the total consumption of white pigments. At present, about 60% of the world's titanium dioxide is used to manufacture various coatings, especially rutile titanium dioxide, most of which is consumed by the coating industry. Coatings made of titanium dioxide, bright color, high hiding power, strong coloring power, saving dosage, many varieties, protect the stability of the medium, and can enhance the mechanical strength and adhesion of the paint film, prevent cracks, prevent ultraviolet rays and moisture penetration, prolong the life of the paint film, and the color matching of almost every pattern in the colorful pattern paint is inseparable from titanium dioxide.

Different kinds of coatings for different uses have different requirements for titanium dioxide, such as powder coatings require rutile titanium dioxide with good dispersion. Anatase titanium dioxide has low achromatic power, strong photochemical activity, used in powder coatings, and the coating film is prone to yellowing. The rutile titanium dioxide produced by the sulfuric acid method has the advantages of moderate price, good dispersion, good hiding power and achromatic power, etc., and is very suitable for indoor powder coating. In addition to good dispersion, hiding power and color elimination power, titanium dioxide for outdoor powder coating also requires good weathering, so the rutile titanium dioxide produced by the general chlorination method of titanium powder for outdoor powder coating.

Second, the impact of the main quality fluctuation of titanium dioxide on the coating

1 whiteness

Titanium dioxide as a white pigment of the coating, its whiteness is very important, is one of the key quality indicators of the coating requirements, titanium dioxide whiteness is poor, will directly affect the appearance of the coating film. The main factor affecting the whiteness of titanium dioxide is the type of harmful impurities, because titanium dioxide is very sensitive to impurities, especially rutile titanium dioxide.

Therefore, even trace impurities will have a significant impact on the whiteness of titanium dioxide. The whiteness of titanium dioxide produced by the chlorination process is often better than that produced by the sulfuric acid process, because the raw material titanium tetrachloride used in the chlorination process to produce titanium dioxide has been distilled and purified, and the impurity content of the raw materials used in the sulfuric acid process is high, and the impurities can only be removed by washing and bleaching and other process technologies.

2 Hiding power

The hiding force is the surface area of the coated object per square centimeter, when it is completely covered, the same area is coated, the larger the hiding force of the titanium dioxide used, the thinner the coating film, the smaller the amount of paint required, the less amount of titanium dioxide is required, if the hiding power of titanium dioxide is reduced, in order to achieve the same covering effect, the amount of titanium dioxide required increases, then the production cost will increase, and the amount of titanium dioxide increases, which will lead to titanium dioxide in the coating is difficult to disperse evenly, and the aggregation will also affect the covering effect of the coating.

3. Weather resistance

Coatings have high requirements for the weather resistance of titanium dioxide, especially surface coatings for outdoor use, which require high weather resistance or ultra-high weather resistance titanium dioxide. Using titanium dioxide with low weather resistance, the coating film will appear fading, discoloration, chalking, cracking, peeling and other problems. The crystal structure of rutile titanium dioxide is tighter than that of anatase titanium dioxide, and the photochemical activity is low, so the weather resistance is much higher than that of anatase titanium dioxide, so the titanium dioxide used for coating is basically rutile titanium dioxide. The main way to improve the weather resistance of titanium dioxide is to treat it inorganically, that is, to coat the surface of titanium dioxide particles with one or more layers of inorganic oxides or hydrated oxides.

4. Dispersion

Titanium dioxide is an ultrafine particle with a large specific surface area, high surface energy, easy aggregation between particles, and it is difficult to disperse stably in the coating. Poor dispersion of titanium dioxide will directly affect its optical properties such as achromaticity, hiding power and surface gloss in the coating, but also affect the storage stability, fluidity, leveling, coating durability, corrosion resistance and conductivity of the coating and other application performance, in addition, it will also affect the production cost of the coating, because the energy consumption of grinding and dispersion operations is high, accounting for most of the total energy consumption of the coating manufacturing process, and the loss of instruments and equipment is large.

This year, the demand for titanium dioxide has been rising, especially titanium dioxide used in the lithium aviation industry, which still needs to rely on imports. As the downstream of titanium dioxide, coatings were affected by the environmental protection storm, and a large number of small and medium-sized enterprises were shut down. In the future, the amount of titanium dioxide in the coating market will also be reduced.