The size of organic
Pigment particles has a great influence on the color performance of coatings.
On the one hand, it affects the covering power and coloring power of the paint, within a certain range of pigment particle size, the covering power of the paint increases; when the pigment particles become small, the specific surface increases, and the coloring power of the paint increases. Pigment particle size also has an effect on the color light of the paint, usually the particle size is large, the particle size distribution is wide, the color light is dark; on the contrary, the color light is bright.
On the other hand, pigment particle size also affects the UV resistance of paint. When the particle becomes small, the specific surface area increases, the absorbed light energy increases, the degree of destruction also increases, so the paint fades faster. Pigment particle size is small, the gravity is small, the paint is not easy to stratify and precipitate; but the pigment with small particle size has large specific surface area, the surface energy increases so that the chance of flocculation and roughness of the paint increases, which is not conducive to grinding and dispersion.
Most organic pigments exist in crystal state, and the phenomenon of "homogeneous heterocrystal" is very common. Copper phthalocyanine crystal, common Q-type red blue (such as
Pigment Blue 15) poor stability, after specific
Solvent treatment is turned into a stable P-type green blue (such as 15:3);
Pigment Violet 19 (quinolone structure) has α, β and γ 3 kinds of crystal, α-type has no value, β-type for the purple-red, and γ-type for the blue red.
In the design of coating formulations, pay attention to the rational use of additives and solvents to prevent different crystal types from transforming under certain conditions, which will cause the coating to undergo chromatic drift and make it difficult to find the right color according to the standard plate.
Organic pigments are dispersed in solid state in the applied coating medium. Whether the pigments are easily dispersed or not, as well as the stability of the dispersed system directly affects the performance of the coating and the coating film. The dispersion performance of pigment in coating depends on many kinds of factors, such as the chemical structure of pigment, crystal type, surface treatment process and auxiliaries, the original particle size and particle size distribution of pigment before application; in addition, the grinding process of the coating and the performance of the grinding equipment itself, and the selection of dispersant will also affect the dispersion stability of pigment.
