The Covering Effect of Titanium Dioxide in Coatings

Hiding power is an important property of a paint that measures its ability to hide the underlying color. In practical applications, the hiding power of a paint is evaluated by applying the paint to a black and white substrate and then measuring the ratio of reflected light using a spectrophotometer. This ratio is called the contrast ratio, which reflects the effect of the paint on covering the base color. The higher the contrast ratio, the stronger the hiding power of the paint. The improvement of hiding power mainly depends on the light scattering mechanism. In coatings, the presence of pigment particles causes light to scatter as it passes through the interface between the pigment and the resin. Since the refractive index of the pigment particles is often different from the refractive index of the resin, this difference in refractive index causes light to be refracted, reflected, or scattered at the interface. The refractive index of rutile titanium dioxide is higher than that of anatase titanium dioxide, so rutile titanium dioxide can provide better hiding power in coatings, which is one of the reasons why it is widely used in the coatings industry. In addition, the size and distribution of pigment particles will also affect the degree of light scattering and thus the hiding power. Pigment particles with moderate particle size and even distribution can scatter light more effectively and enhance the hiding effect. Therefore, when designing coating formulations, selecting the appropriate pigment type and adjusting the dispersion state of the pigment are key factors to improve hiding power. 

In coatings, the hiding power of the coating film is not only affected by the refractive index of the pigment, but also by the thickness of the coating film. As a white pigment with high refractive index, titanium dioxide has very strong light scattering ability. When the particle size of titanium dioxide is close to half the wavelength of the incident light, approximately between 0.2 and 0.3 microns, it can achieve the best light scattering effect. This is because in this case, the incident light will be diffracted near the pigment particles, and its scattering cross section will increase to 4 to 5 times the actual geometric cross section of the particles, thereby significantly improving the hiding power. In order to achieve the best hiding performance, coating manufacturers will carefully select the type of titanium dioxide (such as rutile), adjust its particle size distribution, and ensure that the pigment particles are evenly dispersed in the coating film. Such optimization not only improves the hiding power of the coating, but also helps improve the gloss and durability of the coating to meet the needs of different application scenarios.

The agglomeration effect of titanium dioxide particles can have a negative impact on light scattering efficiency. In order to reduce agglomeration, dispersants are often added to coating formulations to improve the dispersion of titanium dioxide particles in the coating matrix. The role of dispersants is to reduce the attraction between pigment particles and prevent them from agglomerating. Well-dispersed titanium dioxide particles can provide more scattering centers, thereby enhancing the hiding power of the coating. In addition, the pH value, viscosity and grinding process of the coating will also affect the dispersion state of titanium dioxide particles. During the coating preparation process, it is crucial to control the dispersion quality of titanium dioxide. Poor dispersion not only reduces hiding power but also affects other properties of the coating film, such as gloss, color consistency and durability. Therefore, coating manufacturers must carefully design formulas and processes to ensure optimal dispersion of titanium dioxide to achieve high-performance coating products. Our company can develop and produce titanium dioxide that meets various industry specifications according to user needs, and hopes to cooperate with domestic and foreign customers for mutual benefit and win-win results.