Inorganic Coatings of High-Weather TiO2
Titanium dioxide is the white pigment with the best performance, known as the "king of white pigments", and is widely used in coatings, paints, plastics, inks, chemical fibers, rubber and other industries. However, the untreated titanium dioxide pigment has photochemical activity, and under visible light, especially under ultraviolet irradiation, it can degrade the surrounding organic matter, and it is easy to produce light loss, yellowing, chalking and other phenomena, so weather resistance has become a very important application index of titanium dioxide. Therefore, it is of great significance to study the surface treatment of titanium dioxide to improve the quality of titanium dioxide and prepare high value-added titanium dioxide.
In order to improve the weather resistance of titanium dioxide pigments, titanium dioxide is usually treated with an inorganic surface coating to isolate titanium dioxide from the surrounding organic matter to improve its weather resistance and dispersion. Before the coating, the titanium dioxide particles should be dispersed in water, so that the particles to be wrapped can reach the best dispersion state, and have the most suitable viscosity, so that a complete film layer can be precipitated on the surface of each particle, and the dispersant added to the titanium dioxide slurry can significantly improve the dispersion effect of titanium dioxide.
The preparation process of high weather-resistant titanium dioxide is as follows: the crude rutile titanium dioxide that has been crushed to a certain fineness (less than 0.15% of the residue of 45μm sieve) is added to water, dispersants such as sodium hexametaphosphate and sodium silicate are added, and the pH value is adjusted by caustic soda 9~11. The above slurry is ground with a sand mill to disperse the titanium dioxide particles that are clustered together, and then enter the coating equipment to heat the above slurry to a certain temperature. Under the condition of good stirring, the coating agent is added to adjust the pH value of the system, so that the coating agent is deposited on the surface of titanium dioxide. And cured for a certain period of time, a layer of inorganic coating on the surface of titanium dioxide is completed. If several layers of inorganic oxides are to be coated, the slurry temperature and pH value are adjusted again, and the second substance is added to the coating.
After the surface of titanium dioxide is coated with inorganic oxide protective film, its surface properties have undergone fundamental changes, not only with new surface properties, but also with new physical and chemical properties.
The inorganic coating elements used for high weather-resistant titanium dioxide are mainly aluminum and silicon. The surface coating process can be divided into the following three types:
1. Silica coating;
2. Aluminum oxide coating;
3. Silicon-aluminum composite coating
