Titanium dioxide itself has strong photochemical activity, and is prone to inactivation, yellowing, powdering, etc. under the sun, especially ultraviolet rays. A layer of inorganic material is wrapped on the surface of the titanium dioxide, which not only gets rid of the above defects, but also improves the characteristics of the titanium dioxide product. Based on the research and operation, we have learned that the use of many inorganic substances to solve the coated titanium dioxide can significantly improve the powdering resistance and color retention of titanium dioxide, and many researches have been carried out on inorganic treatment agents. The most important category is the hydrated oxides or hydroxides of inorganic metals.

Aluminum and silicon are the two most important surface treatment agents. At this stage, titanium dioxide manufactured abroad is basically coated with these two or one of them.

1. Aluminum package

The method is to add soluble aluminum salts such as aluminum sulfate and sodium metaaluminate to the titanium dioxide slurry, and acid or alkali neutralizes to pH=9-10 under well-balanced mixing, so that the aluminum is deposited on the surface of the titanium dioxide particles with aluminum hydroxide. Precipitated, the coated aluminum oxide is approximately stored in the form of oxypore boehmite, and the others are stored in the form of amorphous hydrosol.

The key to this coating method is to have a fast mixing rate to avoid excessively high or low acid values, because the aluminum oxide hydrate produced in the reaction is evenly wrapped on the surface of the titanium dioxide particles in a deposition manner to produce a layer of film , And the tightness of the film is related to the rate of neutralization. If the neutralization rate is too fast, a sponge-like film will be produced; conversely, if the neutralization rate is slow, a symmetrical and tight film will be produced on the surface of the particles. . A suitable neutralization rate can be selected according to the requirements. Products with a sponge film are mainly used in water-based paints such as latex paint because of their high hiding power; while products with a dense film are mainly used in vehicles, walls, etc., which are often exposed to the sun because of their good weather resistance. The surface of the object.

Alumina coating technology has a unique problem, which is the poor filtration properties of the slurry, mainly due to the weak hydrogen bonds in the hydrated alumina. In addition, the amount of soluble salt is also an influencing factor. It can be improved by adding flocculants such as magnesium sulfate, zinc sulfate, and aluminum sulfate to carry out flocculation and deposition under acidic conditions.

2. Silicon wrap

The method is to add water glass to the titanium dioxide slurry, and then add acid to neutralize it, so that the silicon is deposited on the surface of the titanium dioxide particles in the form of silicic acid, and then a layer of uniformly indeterminate silicon oxide hydrate surface layer is produced. membrane. There must be good agitation in all the wrapping links to prevent part of the acid value from being uneven.

The titanium dioxide coated by the silicon coating method can improve the hydrophilicity of the color paste, improve the water dispersibility, increase the hiding power of the color paste, and improve its anti-chalking properties.

3. Iron parcel

The method is to add a small amount of titanium dioxide powder to boiling water under rapid mixing, and then slowly drop the solution into it until a sol is produced. Because the sol itself can be used as a color paste in cosmetics, and it can absorb ultraviolet rays. After adding titanium dioxide, its ability to absorb ultraviolet rays is stronger. Therefore, the titanium dioxide manufactured by the iron coating method can reduce the photochemical activity of the product, and the product can be used in sunscreen cosmetics.

4. Silicon and aluminum composite package

In order to improve the actual effect of the coating solution, two or more coating agents can be used to carry out composite surface coating. The more commonly used composite coating methods include inorganic composite coating and inorganic-organic composite coating. Among them, inorganic composite coating products include silicon-aluminum composite coating, silicon-zinc composite coating, and silicon-zirconium composite coating.

Titanium dioxide coated with aluminum oxide can reflect ultraviolet rays and enhance the anti-pulverization properties of the coating, while titanium dioxide coated with silicon has better hydrophilicity. If the compound of aluminum and silicon (you can also put silicon and then add aluminum) is used to wrap the surface of the particles one by one, the product will have the advantage of two coating methods: silicon alone and aluminum alone at the same time. In the case of silicon-aluminum composite coating, different mass ratios of aluminum oxide and silicon dioxide can achieve different practical effects.

The silicon-aluminum composite coating has a coating order problem. When manufacturing color pastes with high weather resistance, it is usually coated with aluminum first and then silicon. When applied to water-based coatings, it is coated with silicon first and then aluminum. The manufacturing method of this kind of products is to add the aluminum salt solution to the titanium dioxide system with sodium silicate at the corresponding temperature, and adjust the value to the left and right to develop the coating. Sodium silicate solution can also be added to the aluminum salt solution.

5. Mixed packages

Mixed coating is also called mixed co-precipitation coating, which refers to the neutralization method to deposit two or more coating agents on the surface of titanium dioxide particles at the same time under the same acidic or alkaline conditions.