Pigments in the paint industry
Pigments are insoluble in dispersion media (water, organic solvents, olives, etc.) highly dispersed substances that have a number of valuable physical, chemical and technological properties. Due to these properties pigments are used to obtain decorative and protective coatings for various purposes.
Pigments are substances that have the ability to transfer their color to other bodies or substances. Pigments can be colored (colored, chromatic) or gray, black, white (uncolored, achromatic). Dyestuffs also include dyes, but they are mostly used to dye fibers, fabrics, etc. Dyes dissolve selectively in organic media and water.
In the paint industry pigments are used in the manufacture of enamels, paints, primers, fillers and some other pigmented materials. Some pigments can also be used in other industries, such as pharmaceutical, paper, etc.
All pigments are divided into two broad groups: inorganic and organic.
Inorganic pigments are the most widely used in the paint industry.
Role of inorganic pigments in coatings industry
Inorganic pigments are not only added to coatings but also for their optical and decorative properties. Using pigments you can regulate important insulating, deformation and strength properties, anti-corrosive properties etc. In addition, it is possible to obtain special coatings, i.e. with specific properties, such as antifouling, heat-resistant, electrical insulation, antifriction, glow-in-the-dark, flame-retardant, etc.
o a greater extent the properties of pigmented paintwork materials depend on the film-forming substance and the pigments themselves. And structural features of coatings are determined by physical and chemical interaction of surface of pigment particles with polymeric phase of paintwork material. Such interaction often results in decreased mobility of macromolecules near the surface of particles, increased glass transition temperature of polymer, and changes in relaxation periods. The introduction of pigments into a paint system can have a very strong effect on it and on the process of forming a protective and decorative coating. For example, by accelerating the curing of the paint material or by slowing it down. In the first and in the second case, the structure of the three-dimensional polymer mesh that is formed changes.
The introduction of pigments to the paint system also changes all the deformation and strength characteristics of the coating: tensile strength, modulus of elasticity, wear resistance, etc. These indicators can both decrease and increase.
The protective properties of the coating largely depend on the structure of the paint material, therefore the introduction of pigments changes them. Water absorption and water permeability of the coating depends on the structure of the film-forming agent near the pigment particles. If the structure is loosened - the access of water to the surface of the painted product is facilitated, i.e. the paint coating has low protective properties and increased water permeability. If compacted layers of the film-forming agent are formed, the coating will be characterized by increased protective properties.
An interesting fact: pigmented coatings often have higher protective properties than non-pigmented coatings, because the corrosive agents, during diffusion to the protected surface, travel a longer distance.
With introduction of pigments into the paint system the adhesion strength of the coating slightly increases as well (due to the increase of the deformation and strength properties). Anodic processes on the base metal are also suppressed.
We can conclude that the properties of paintwork material and finished protective coatings are determined by their constituent parts, pigments in particular.
Classification of inorganic pigments
Inorganic pigments can be classified according to various indicators: color, purpose, production methods, chemical composition. But none of these classifications can be called optimal, because one group includes pigments with different properties.
The double classification of inorganic pigments is most often used, i.e. according to two attributes: chemical composition and color.