1. The role of titanium dioxide in coatings
Coatings are mainly composed of four parts: film-forming substances, pigments, solvents and additives. The pigments in the coating have a certain hiding power. It can not only cover the original color of the coated object, but also give the coating a bright color. 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 integrated, can enhance the mechanical strength and adhesion of the coating film, prevent cracking or falling off, and can increase the thickness of the coating film, prevent the penetration of ultraviolet rays or moisture, and improve the coating. The anti-aging and durability properties of the film extend the service life of the film and the protected object.
In the pigment, the amount of white pigment is very large, and the performance requirements of the coating for the white pigment: ①Good whiteness; ②Good grinding and wettability; ③Good weather resistance; ④Good chemical stability; ⑤Small particle size, hiding power and loss High color power, good opacity and gloss.
Titanium dioxide is a kind of white pigment that is widely used in coatings. Its output accounts for more than 70% of inorganic pigments, and its 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. The paint made of titanium dioxide has bright colors, high hiding power, strong tinting power, low dosage, and many varieties. It protects the stability of the medium, and can enhance the mechanical strength and adhesion of the paint film, prevent cracks, and prevent ultraviolet rays. It penetrates with water and prolongs the life of the paint film. The color matching of almost every pattern in the colorful pattern paint is inseparable from titanium dioxide.
Different types of coatings for different purposes have different requirements for titanium dioxide. For example, powder coatings require the use of rutile titanium dioxide with good dispersibility. Anatase titanium dioxide has low decoloring power and strong photochemical activity. When used in powder coatings, 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 color reducing power, and is very suitable for indoor powder coatings. In addition to good dispersibility, hiding power and color reducing power, titanium dioxide for outdoor powder coatings also requires good weatherability. Therefore, titanium powder for outdoor powder coatings is generally a rutile titanium dioxide produced by chlorination.
2. Analysis of the impact of main quality fluctuations of titanium dioxide on coatings
1 whiteness
Titanium dioxide is used as a white pigment for coatings. Its whiteness is very important and is one of the key quality indicators required by coatings. The poor whiteness of titanium dioxide will directly affect the appearance of the coating film. The main factor affecting the whiteness of titanium dioxide is the type and content of harmful impurities, because titanium dioxide is very sensitive to impurities, especially rutile titanium dioxide.
Therefore, even a small amount of impurities will have a significant impact on the whiteness of titanium dioxide. The whiteness of the titanium dioxide produced by the chloride process is often better than that produced by the sulfuric acid process. This is because the raw material titanium tetrachloride used in the production of titanium dioxide by the chloride process has been distilled and purified, and its own impurity content is less, while the sulfuric acid process uses The raw materials have high impurity content, which can only be removed by washing and bleaching techniques.
2 hiding power
The hiding power is the surface area of ??the coated object per square centimeter. When it is completely covered, the same area is painted. The greater the hiding power of the titanium dioxide used, the thinner the coating film can be, and the less the amount of paint required, The smaller the amount of titanium dioxide needed, if the hiding power of the titanium dioxide decreases, in order to achieve the same covering effect, the amount of titanium dioxide required increases, the production cost will increase, and the increase in the amount of titanium dioxide will cause the titanium dioxide in the coating It is difficult to disperse uniformly, and aggregation occurs, which will also affect the covering effect of the coating.
3 weather resistance
coatings require high weather resistance of titanium dioxide, especially for outdoor surface coatings, which require high weather resistance or ultra-high weather resistance. Using titanium dioxide with low weather resistance, the coating film will have problems such as fading, discoloration, chalking, cracking, and peeling. The crystal structure of rutile titanium dioxide is tighter than that of anatase titanium dioxide, and its photochemical activity is low. Therefore, the weather resistance is much higher than that of anatase titanium dioxide. Therefore, the titanium dioxide used for coatings is basically rutile titanium dioxide. The main method to improve the weather resistance of titanium dioxide is to perform inorganic surface treatment, that is, to coat one or more layers of inorganic oxides or hydrated oxides on the surface of titanium dioxide particles.
4 dispersion
Titanium dioxide is ultra-fine particles with large specific surface area and high surface energy. It is easy to aggregate between particles and is difficult to stably disperse in coatings. The poor dispersion of titanium dioxide will directly affect its optical properties such as color reduction, hiding power and surface gloss in the coating, and also affect the storage stability, fluidity, leveling, coating durability, and corrosion resistance of the coating. Application properties such as electrical conductivity and conductivity will also affect the production cost of coatings, 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 equipment is large.
The demand for titanium dioxide has been rising this year, especially for the titanium dioxide used in the lithium-ion aviation industry, which still has to rely on imports. As the downstream of titanium dioxide, coatings are affected by the environmental storm, and a large number of small and medium-sized enterprises have been shut down. In the future, the amount of titanium dioxide in the coatings market will also decrease.