The main factors of pigments influencing the properties of coatings

Pigment is an important part of coating The most important role of pigment is to cover and give the coating color In addition, it can protect and improve the application performance and mechanical properties of coating When choosing pigments, coating manufacturers should pay attention to the following aspects of pigment performance: (1) the size of pigment particles the average particle size of most pigments is 0.01-1.0um, but the particle size of physical pigments and a small number of other pigments is large, the single particle size can reach 100um, and the average particle size can reach 50um The size of the particles directly affects the hiding power and coloring power of the pigment The smaller the size of the particles is, the larger the dispersion is, the larger the area of the reflected light is, and the larger the hiding power is For most pigments, the most effective particle size is half the wavelength of visible light Coloring power is the ability of one pigment to mix with another to form a strong or weak color The smaller the particles, the greater the coloring power (2) Shape of pigment particle shape of pigment particle mainly affects the fluidity, storage and durability of paint Pigments mainly exist in three shapes: ① nodular particles, similar to spherical particles, such as titanium dioxide, lithopone, etc.; ⑦ needle particles, such as some zinc white and talcum powder, etc., have reinforcing effects on needle pigments, which can improve the mechanical properties of coatings; ③ flat particles, such as gold pigments, also have reinforcing effects on coatings, and some flat pigments are strong Strong orientation, parallel to the coating surface, thus reducing the permeability of gas and water, with good corrosion resistance and special appearance (3) Surface area of pigment particles the specific surface area of a particle is defined as the surface area of a unit mass pigment It is inversely proportional to the particle size When the mass of pigment particles remains constant, the particle size is reduced by half and the surface area is doubled The specific surface area of pigment particles is usually measured by penetration method (measuring the flow of gas through the pigment particle layer) or adsorption method (measuring the amount of gas or liquid adsorbed by the pigment sample) (4) The surface treatment of raw material particles can be properly treated, and the surface of pigment particles can be modified or completely replaced by new surfaces The purpose of surface treatment is as follows: ① the existence of surfactant should control supersaturation, solubilization, nucleation, growth and phase transformation, so as to affect the formation of pigment; ② the existence of polyphosphate, silicon dihydrogen, lead or its hydroxide on inorganic pigment particles can keep the shape of particles, so as to prevent the formation of pores in the process of calcination; ③ none The existence of organic coating on the surface of organic pigment particles can improve the wetting effect, increase the dispersion and stability of pigment, and thus improve the rheological property of paint; ④ the light, weather, acid and alkali resistance and solvent resistance can also be improved by surface treatment (5) Particle size distribution of pigment particles pigment is a kind of solid particles No matter what the manufacturing process, it can not be a particle size composition, but there is a certain distribution range When the particle frequency is used to plot the particle size distribution, the particle size distribution is non normal and left skew That is to say, the probability of occurrence of small particles is more than that of large particles, and there is a peak value That is to say, the probability of occurrence of particles under a certain particle size is the largest On both sides of the peak value, the faster the curve declines, the better