The role of titanium dioxide in coatings

Titanium dioxide is an important white pigment, which can be divided into plate titanium type, anatase titanium type and rutile type. The plate titanium type is very unstable. Compared with traditional white pigments such as lead white, zinc white and lithopone, titanium dioxide has many excellent properties, such as high refractive index, strong achromatic power, great hiding power and harmless, and is called a good white pigment. It is used in coatings, plastics, chemical fiber, ceramics and other industries. The amount of coating is large, accounting for 57% of the total amount of titanium dioxide. How can titanium dioxide be used in coatings?

1、 The role of titanium dioxide in coatings

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

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

Titanium dioxide is a kind of white pigment 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, which is mostly consumed by the coating industry. The paint made of titanium dioxide has bright colors, high hiding power, strong tinting power, low consumption and many varieties. It can protect the stability of the medium, enhance the mechanical strength and adhesion of the paint film, prevent cracks, prevent ultraviolet ray and water penetration, and extend the life of the paint film. The color matching of almost every pattern in the colorful pattern paint can not be separated from titanium dioxide.

Different kinds of coatings with different uses have different requirements for titanium dioxide, for example, powder coatings require rutile titanium dioxide with good dispersion. Anatase titanium dioxide has low achromatic power and strong photochemical activity. When used in powder coatings, the film is prone to yellowing. The rutile titanium dioxide produced by sulfuric acid method has the advantages of moderate price, good dispersion, good hiding power and achromatic power, and is very suitable for indoor powder coatings. In addition to good dispersibility, hiding power and achromatic power, titanium dioxide used for outdoor powder coatings should also have good weatherability. Therefore, rutile titanium dioxide produced by general chlorination method is used for outdoor powder coatings.

2、 Analysis of the influence of the main quality fluctuation of titanium dioxide on the coating

1 Whiteness

As a white pigment of coatings, the whiteness of titanium dioxide is very important, which is one of the key quality indicators required by coatings. The poor whiteness of titanium dioxide will directly affect the appearance of coatings. The main factor affecting the whiteness of titanium dioxide is the 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 titanium dioxide produced by the chlorination process is often better than that produced by the sulfuric acid process. This is because the titanium tetrachloride used as the raw material for the production of titanium dioxide by the chlorination process has been distilled and purified, and its own impurity content is low, while the impurity content of the raw material used by the sulfuric acid process is high, and the impurities can only be removed by washing, bleaching and other processes.

2 Covering force

The hiding power is the surface area of each square centimeter of the object to be coated. When the object is completely covered and the same area is coated, the greater the hiding power of the titanium dioxide used, the thinner the coating film will be. The less the amount of paint required, the less the amount of titanium dioxide required. If the hiding power of titanium dioxide decreases, and the amount of titanium dioxide required to achieve the same covering effect increases, the production cost will increase, and the amount of titanium dioxide will increase, It will cause the titanium dioxide to be difficult to disperse evenly in the coating, and will also affect the covering effect of the coating.

3 Weather resistance

The coating has high requirements for the weather resistance of titanium dioxide, especially for outdoor surface coating, which requires high weather resistance or ultra-high weather resistance. When titanium dioxide with low weather resistance is used, the film will suffer from fading, discoloration, chalking, cracking, peeling and other problems. The crystal structure of rutile type titanium dioxide is more compact than that of anatase type titanium dioxide, with low photochemical activity, so the weather resistance is also much higher than that of anatase type titanium dioxide. Therefore, the titanium dioxide used for coating is basically rutile type titanium dioxide. The main way to improve the weather resistance of titanium dioxide is to conduct inorganic surface treatment, that is, coating one or more layers of inorganic oxides or hydrated oxides on the surface of titanium dioxide particles.

4 Dispersion

Titanium dioxide is an ultra-fine particle with large specific surface area and high surface energy. It is easy to gather among particles and difficult to disperse stably in the coating. The poor dispersivity of titanium dioxide will directly affect its optical properties such as achromatic power, hiding power and surface gloss in the coating, and also affect the storage stability, fluidity, leveling, coating durability, corrosion resistance and conductivity of the coating. 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 in the coating manufacturing process, And the loss of instruments and equipment is large.

The demand for titanium dioxide has been rising this year, especially for titanium dioxide used in the lithium battery industry, which still needs to be imported. As the downstream of titanium dioxide, a large number of small and medium-sized enterprises have been shut down due to the impact of environmental storm. In the future, the amount of titanium dioxide used in the coating market will also decrease.