In the coating dispersion system, the pigment is one of the very important components. The size , shape and surface characteristics of the particles all affect the dispersion characteristics of the pigment in the coating system, and ultimately affect the performance of the coating film. Studies have shown that for a given pigment and medium system, the relationship between light scattering intensity and particle size increases first and then decreases; pigments with different refractive indices have a critical particle size range for a given light wave, within this range Theoretical light scattering is strongest. The hiding power, coloring power, and brightness of the pigment are all related to the particle size of the pigment, as shown in the figure. Hiding power is the result of light scattering and absorption by pigments, mainly scattering, especially for white pigments. The relationship between the hiding power of the pigment and the particle size of the pigment varies with the refractive index of the pigment. The relationship between the high refractive index pigment and the particle size of the pigment is relatively large, and the change of the low refractive index pigment with the size of the pigment is relatively small, but there are suitable particle sizes. scope. For most pigments, the effective particle size is half the wavelength of visible light. Tinting strength is the ability of a pigment to form a strong or weak pigment after mixing with another pigment, and the relative tinting strength increases with the decrease of particle size.
The particle size distribution and shape also affect the optical properties of the pigment. The narrower the particle size distribution of the system, the higher the brightness, and the acicular particles have stronger tinting power than the non-acicular particles.
The weather resistance of the pigment is also related to the particle size. Experiments have shown that titanium dioxide with larger particle size has better weather resistance in different paint materials, while titanium dioxide with smaller particle size has poor weather resistance. This is because the pigment with smaller particle size has larger specific surface area and higher photoactivity. Pigments with smaller particle size can be surface modified to improve their weather resistance. Due to the requirements of self-cleaning performance, at present, people are studying nano-pigments with photocatalytic function, such as anatase titanium dioxide, etc., which are added to the exterior wall coating system. The principle is that nano-sized semiconductor catalysts have a higher surface area. Activity, the energy of excited electrons is high, so it has strong electron transfer ability, so as to realize the catalytic oxidation and decomposition of dirt, and achieve the purpose of cleaning. Of course, in actual application, the particle size of the pigment should depend on the specific conditions, and the influence of various aspects needs to be considered comprehensively.
