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 the 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, large hiding power, harmless and so on. It is used in coatings, plastics, chemical fiber, ceramics and other industries. The amount of coating is very large, accounting for about 57% of the total amount of titanium dioxide. So how can titanium dioxide be applied to coatings?
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1、 Role of titanium dioxide in coatings
The coating is mainly composed of film-forming material, pigment, solvent and additives. The pigment in the coating has a certain hiding power. It can not only cover the original color of the coated object, but also give the film bright color to realize the decorative effect of lighting and beautification. At the same time, the pigment and the curing agent and substrate are closely integrated, and can enhance the mechanical strength and adhesion of the coating, prevent cracking or falling off, and enhance the thickness of the coating, prevent the penetration of ultraviolet or moisture, improve the aging and durability of the coating, and prolong the service life of the coating and the protected object.
In the pigment, the amount of white pigment is very large, and the performance requirements of the coating for white pigment are as follows: 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 gloss.
Titanium dioxide is a 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 titanium dioxide in the world 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 coloring power, low dosage and many varieties, which can protect the stability of the medium, enhance the mechanical strength and adhesion of the paint film, prevent cracks, prevent the penetration of ultraviolet and moisture, and prolong the service life of the paint film. The color matching of almost every pattern in the colorful pattern paint is inseparable from titanium dioxide.
Different kinds of coatings for different purposes 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. Rutile titanium dioxide produced by sulfuric ACID method has the advantages of moderate price, good dispersion, good hiding power and achromatic power. It is very suitable for indoor powder coating. Titanium dioxide for outdoor powder coating not only requires good dispersion, covering power and achromatic power, but also requires good weather resistance. Therefore, titanium powder for outdoor powder coating is generally rutile titanium dioxide produced by chlorination method.
2、 Influence of main quality fluctuation of titanium dioxide on Coatings
1 whiteness
As the white pigment of the coating, the whiteness of titanium dioxide is very important and is one of the key quality indicators required by the coating. The poor whiteness of titanium dioxide will directly affect the appearance of the coating. 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 titanium dioxide produced by the chlorination 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 chlorination process has been distilled and purified, and its impurity content is low. However, the impurity content of the raw material used by the sulfuric acid process is high, so the impurities can only be removed by washing and bleaching.
2. Covering force
The covering power is the surface area of the coated object per square centimeter. When it is completely covered, apply the same area. The greater the covering power of titanium dioxide used, the thinner the film can be. The less the amount of paint required, the less the amount of titanium dioxide required. If the covering power of titanium dioxide decreases, the amount of titanium dioxide required increases to achieve the same covering effect, The production cost will increase and the amount of titanium dioxide will increase, which will make it difficult for titanium dioxide to disperse evenly in the coating and aggregate, which will also affect the covering effect of the coating.
3 weather resistance
Coatings have high requirements for the weather resistance of titanium dioxide, especially for outdoor surface coatings, which require titanium dioxide with high or ultra-high weather resistance. When titanium dioxide with low weather resistance is used, the coating will have problems such as fading, discoloration, chalking, cracking and peeling. The crystal structure of rutile titanium dioxide is more compact than that of anatase titanium dioxide, and the photochemical activity is low. Therefore, the weather resistance is much higher than that of anatase titanium dioxide. Therefore, the titanium dioxide for coating is basically rutile titanium dioxide. The main method to improve the weather resistance of titanium dioxide is 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 aggregate between particles and is difficult to disperse stably in the coating. The poor dispersion of titanium dioxide will directly affect its optical properties such as achromatic power, covering power and surface gloss in the coating, as well as its application properties such as storage stability, fluidity, leveling, coating durability, anti-corrosion and conductivity. In addition, it will also affect the production cost of the coating because of the high energy consumption of grinding and dispersion, It accounts for most of the total energy consumption in the coating manufacturing process, and the loss of instruments and equipment is large.
This year, the demand for titanium dioxide has been rising, especially for titanium dioxide used in lithium battery aviation 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 in the coating market will also be reduced.
