Titanium dioxide is a widely used white pigment with high optical and chemical stability. Paints incorporating titanium dioxide exhibit vibrant colors, strong tinting strength, excellent hiding power, and enhanced mechanical strength and adhesion of the paint film. Titanium dioxide also blocks UV and moisture penetration to a certain extent, slowing down the aging of the paint film. Therefore, improving the sustainable development of the titanium dioxide industry is urgent. Coating is an essential step in the post-processing of titanium dioxide, effectively enhancing key properties such as hiding power, dispersibility, stability, and weather resistance in coatings, making it a highly cost-effective solution for product enhancement.
Overview of Titanium Dioxide Coating Modification Technologies
Currently, there are numerous known titanium dioxide surface coating technologies. For example, a relatively uniform coating can improve titanium dioxide’s weather resistance to a certain extent, while a porous and loose coating can enhance the hiding power of titanium dioxide surface coatings. As for titanium dioxide products that can simultaneously meet these characteristics, how to adjust the relationship between these properties to achieve the best performance of titanium dioxide is one of the issues that my country still needs to continue to study.
There are two types of titanium dioxide coating technologies: organic coating and inorganic coating. Organic coating agents generally use silicones, polyols, organic amines, etc. Inorganic coating technologies include alumina coating, silicon-aluminum oxide composite coating, and silicon oxide coating. These two modification technologies need to be used simultaneously and have clear sequence standards. In the normal operation process, the first step is to perform inorganic coating modification, and the second step is to modify the organic coating.
The role of titanium dioxide inorganic coating technology in improving performance
- Alumina coated titanium dioxide
Coating titanium dioxide on the surface of titanium dioxide with alumina is one of the common means in industry to improve the dispersion stability of titanium dioxide water-based systems. Among them, the microstructure of the aluminum oxide coating layer on the surface of titanium dioxide has a direct impact on the surface properties of the particles, such as the hydroxyl density, surface free energy, surface potential, and steric hindrance, and thus affects its dispersion stability in the aqueous system. By regulating the coating process factors, the microstructure of the aluminum oxide coating layer can be regulated and optimized.
- Zirconium dioxide coated titanium dioxide
Titanium dioxide has a certain photocatalytic activity and can absorb ultraviolet light to generate active groups, causing the surrounding organic medium to degrade and reducing the service life of the product. Zirconium dioxide has a high refractive index and extremely weak absorption capacity for ultraviolet light. Therefore, coating the surface of titanium dioxide particles with continuous and dense zirconium dioxide can not only reduce the absorption of ultraviolet light, but also hinder the direct contact between the active groups and the surrounding medium and the external environment, thereby improving the light resistance of titanium dioxide.
- Silica coated titanium dioxide
The silica coating layer on the surface of titanium dioxide can hinder its direct contact with the surrounding medium and the external environment, thereby improving the weather resistance of titanium dioxide. The microstructure of the silica coating on the surface of titanium dioxide directly determines the area of titanium dioxide particles exposed to the external environment or surrounding medium, which in turn affects its weather resistance.
- Aluminum phosphate coated titanium dioxide
When titanium dioxide is used in industries such as papermaking and exterior wall coatings, it needs to have both high light resistance and excellent dispersion stability. At present, the practical application requirements are mainly achieved by inorganic-organic composite coating of titanium dioxide. Developing a product that can simultaneously meet the requirements of light resistance and dispersion stability through a single inorganic coating can significantly reduce the cost of subsequent organic coating. Aluminum-based materials, as good electron acceptors, can annihilate the photogenerated electrons generated by titanium dioxide absorbing ultraviolet light, inhibit the generation of active groups, and improve light resistance; while the introduction of phosphate groups can adjust the surface potential of titanium dioxide particles and improve dispersion stability. Therefore, coating the surface of titanium dioxide with aluminum phosphate can simultaneously improve the light resistance and dispersion stability of titanium dioxide.
The Enhanced Effect of Organic Coating Technology on Titanium Dioxide
The primary function of organic coating agents is to enhance the various properties of titanium dioxide in organic matter. This action works by altering the surface properties of titanium dioxide. There are two primary methods for bonding titanium dioxide particles to organic coatings: chemical adsorption, which occurs through a reaction between the hydroxyl groups on the titanium dioxide particle surface and the organic coating agent. Physical adsorption, in which the organic coating agent physically manifests itself as a surface adsorption effect, consists of two components: lipophilic and hydrophilic.
