Titanium dioxide is an important white pigment, which can be divided into plate titanium type, anatase titanium type, and rutile type. Plate titanium type is very unstable. Compared with traditional white pigments such as lead white, zinc white, and lithopone, titanium dioxide powder has various excellent properties such as high refractive index, strong fading power, large covering power, and harmlessness, making it a very good white pigment. Applied in industries such as coatings, plastics, chemical fibers, ceramics, etc. The amount of coating used is large, accounting for approximately 57% of the total amount of titanium dioxide. So how can titanium dioxide be applied to coatings?
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 degree of covering power, which not only covers the original color of the object being coated, but also gives the coating a bright color, achieving a decorative effect of brightening and beautification. 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.
In pigments, the amount of white pigment is large, and the performance requirements for white pigments are as follows: ① good whiteness; ② Good grinding wettability; ③ Good weather resistance; ④ Good chemical stability; ⑤ Small particle size, high hiding and fading power, good opacity and glossiness.
Titanium dioxide is a commonly used white pigment in coatings, accounting for over 70% of the production of inorganic pigments and 95.5% of the total consumption of white pigments. Currently, 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. Coatings made of titanium dioxide have bright colors, high covering power, strong coloring power, low dosage, and a wide range of varieties. They protect the stability of the medium, enhance the mechanical strength and adhesion of the paint film, prevent cracks, prevent UV and water penetration, and extend the lifespan of the paint film. Almost every pattern in colorful pattern coatings cannot be matched without titanium dioxide.
Different types and uses of coatings have different requirements for titanium dioxide, such as powder coatings that require the use of well dispersed rutile type titanium dioxide. Acute titanium dioxide has low fading 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 dispersibility, good covering power and fading power, and is very suitable for indoor powder coatings. In addition to good dispersibility, covering power, and fading power, titanium dioxide used for outdoor powder coatings also needs to have good weather resistance. Therefore, rutile type titanium dioxide produced by chlorination method is commonly used for outdoor powder coatings.
2、 Analysis of the Influence of Main Quality Fluctuations of Titanium Dioxide on Coatings
1 whiteness
Titanium dioxide, as a white pigment in coatings, its whiteness is crucial and one of the key quality indicators required for coatings. Poor whiteness of titanium dioxide directly affects the appearance of the coating film. The main factor affecting the whiteness of titanium dioxide is the type and content of harmful impurities, as titanium dioxide is very sensitive to impurities, especially rutile type titanium dioxide.
So, even trace impurities can 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 used in the chlorination process for producing titanium dioxide, titanium tetrachloride, has been distilled and purified, with low impurity content. However, the raw material used in the sulfuric acid process has a high impurity content, and can only be removed through processes such as washing and bleaching.
2 Covering force
The covering power is the surface area of the object to be coated per square centimeter. When the same area is fully covered, the greater the covering power of the titanium dioxide used, the thinner the coating film. The less paint required, the less titanium dioxide required. If the covering power of the 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 used will increase, It will cause titanium dioxide powder to be difficult to disperse evenly in the coating, leading to aggregation, 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 or ultra-high weather resistance of titanium dioxide. When using titanium dioxide with low weather resistance, the coating may experience problems such as fading, discoloration, pulverization, cracking, and peeling. The crystal structure of rutile type titanium dioxide is more compact than that of anatase type titanium dioxide, with lower photochemical activity, and therefore much higher weather resistance than anatase type titanium dioxide. Therefore, almost all titanium dioxide used in coatings is rutile type titanium dioxide. The main method to improve the weather resistance of titanium dioxide is to perform inorganic surface treatment, which involves coating one or more layers of inorganic oxides or hydrated oxides on the surface of titanium dioxide particles.
4 Dispersibility
Titanium dioxide is a ultrafine particle with a large specific surface area and high surface energy. It is prone to aggregation between particles and is difficult to disperse stably in coatings. The poor dispersibility of titanium dioxide powder directly affects its optical properties such as fading power, covering power, and surface glossiness in coatings. It also affects the storage stability, fluidity, leveling, coating durability, corrosion resistance, and conductivity of coatings. In addition, it also affects the production cost of coatings, as grinding and dispersion operations require high energy consumption, accounting for the majority 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 continuously increasing this year, especially for titanium dioxide used in the lithium electric aviation industry, which still relies on imports. As the downstream of titanium dioxide, coatings have been affected by the environmental storm and a large number of small and medium-sized enterprises have been shut down. In the future, the usage of titanium dioxide in the paint market will also decrease.
