Hiding power and titanium dioxide particle size has a direct relationship, generally speaking, in coating system with high pigment volume concentration, larger particle size of titanium dioxide pigment coverage is higher in low pigment volume concentration of the coating system, titanium dioxide pigment particle size smaller high covering power.
Seen from the optics, pigments for light reflection and absorption can cause hidden and bleaching, white pigment in the whole range of visible light, almost equal strength reflects all wavelengths of visible light, so scattering is huge, can absorb very little. Increase the opacity, hiding power and tinting strength of main direction is improving the scattering power of titanium dioxide, followed by reducing the absorptive capacity of the titanium dioxide. Increase the scattering power of titanium dioxide was the primary means to make titanium dioxide particle size and particle size distribution in line with requirements and has a good dispersion. Reduced absorptive capacity mainly depends on impurities removal can produce as much as possible in the processing of color and improve the purity of titanium dioxide can reduce the absorption of light.
Second, the lack of transparency
What opacity refers to the pigment particles of light radiation-proof capability. In fact, it is covering the same thing. As for titanium dioxide, opacity depends on its refractive index and grain size distribution, is the essence of optical refractive index difference between the resulting titanium dioxide with the surrounding medium.
In more than half a wavelength range of visible light, titanium dioxide particle size finer the grain structure is more smooth and greater dispersion, opacity, the greater and greater coverage. But there is a certain limit. When the average particle size of 0.2 microns, and opacity of the highest, greatest covering power; when the average particle size of less than half the wavelength of visible light, is because of the transparency of Crystal light coverage decreased. It can be seen that particles larger than small is good.