The particle size of the pigment is about 0.2~100μm, and its shape can be spherical, scaly and rod-like. Generally, the commonly used pigments are fine powders of 0.2~10μm, which are insoluble in solvents, water and oils. Pigments can give the paint color and hiding power, improve the mechanical properties and durability of the coating; some can make the coating have anti-rust, anti-fouling, magnetic, conductive and other functions.
Pigments can be classified into inorganic pigments and organic pigments according to their composition; they can be divided into coloring pigments, extender pigments and functional pigments according to their performance. Coloring pigments are widely used and there are many varieties. The purpose of adding extender pigments is not for coloring and hiding power, but generally as fillers to improve the coloring effect of coloring pigments and reduce costs. Functional pigments, such as antirust pigments, matting pigments, antifouling pigments, electromagnetic wave attenuating pigments, etc., are developing rapidly and occupy an increasingly important position.
The performance of the coating is affected by the following properties of the pigment: ① the shape of the pigment; ② the particle size and distribution of the pigment; ③ the volume fraction of the pigment; ④ the dispersion effect of the pigment in the coating.
The pigment volume fraction (σ) and the critical pigment volume fraction (σcritical) have a significant impact on the properties of the coating, expressed as
The solid base material in the above formula refers to the non-volatile base material in the coating. Many properties of coatings and coating films gradually change with the % value. When σ% exceeds a certain value, these properties will change abruptly. This specific σ value is called critical pigment volume fraction σcritical. The σ criticality is an important parameter in the paint formulation, and its physical meaning is: when the σ criticality is reached, the pigment particles in the coating film are just surrounded and wetted by the resin base material in the paint; when the σ is lower than the σ critical value, The amount of base material is redundant in addition to surrounding and wetting the pigment; when the % in the formula is higher than % critical, the amount of base material in the coating film is not enough to surround and wet all the pigments, and some physical properties of the coating there will be drastic changes
