Components of Coatings

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Coatings mainly consist of four parts: film-forming substances, pigments, solvents, and additives.

As the foundation of coatings, film-forming substances play a decisive role in the properties of both the coatings themselves and the formed films. They have the function of binding other components in the coatings to form films. There are many types of substances that can be used as film-forming materials; in the modern coating industry, resins are mainly used. Resins are organic substances existing in an amorphous state, usually referring to high-molecular polymers. In the past, natural resins were used as film-forming substances in coatings; nowadays, synthetic resins are widely applied, such as alkyd resins, acrylic resins, chlorinated rubber resins, and epoxy resins.

Pigments are a main component of colored coatings (pigmented paints). Pigments impart color to the films and enable the films to cover the surface of the coated objects, thereby fulfilling their decorative and protective functions. Some pigments can also provide properties such as improving the mechanical performance of the films, enhancing the durability of the films, and offering corrosion resistance, electrical conductivity, flame retardancy, etc.
Pigments can be classified according to different criteria:
By source: natural pigments and synthetic pigments;
By chemical composition: inorganic pigments and organic pigments;
By function in coatings: coloring pigments, extender pigments, and special-effect pigments.
Inorganic pigments are the most widely used in coatings, synthetic pigments are also widely applied, and currently, organic pigments are developing rapidly.

Solvents can dissolve or disperse the film-forming substances in coatings into a uniform liquid state, facilitating application and film formation. After application, they can volatilize from the films into the atmosphere. In principle, solvents do not constitute the films and should not remain in the films.
Many chemicals, including water, inorganic compounds, and organic compounds, can be used as solvent components in coatings. In some modern coatings, certain compounds have been developed and applied—these compounds can not only dissolve or disperse film-forming substances into a liquid state but also chemically react with film-forming substances during the application and film-forming process to form new substances that remain in the films. Such compounds are called reactive activators or reactive diluents. Some solvents are added during the manufacturing of coatings, while others are added during the coating application process.

Additives are also known as auxiliary material components of coatings, but they cannot form films independently. However, after the coatings form films, they can exist as a component of the films. The role of additives is to improve the performance of coatings or films in a specific aspect.
Different types of coatings require additives with different functions; even coatings of the same type may need different additives due to differences in their intended use, application method, or performance requirements. A single coating can use multiple types of additives to exert their respective effects (e.g., defoamers, wetting agents, anti-sagging agents, anti-settling agents, driers, plasticizers, mildew inhibitors, etc.).