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Coating is a material that can be applied to the surface of objects using specific application methods; upon curing, it forms a continuous coating layer that serves to protect, decorate, and provide other special functions for the object being coated. Coatings are composed of film-forming substances, pigments, fillers, solvents, additives, etc.; these components may vary slightly depending on the required performance characteristics. For example, varnishes contain no pigments or fillers, while powder coatings contain no solvents. Composition of coatings: 1. Main film-forming substances: These are primarily oils and resins – materials that, when applied to a surface, can dry and form a film. They are the key substances that enable the coating to adhere firmly to the surface being coated, forming a continuous film. In the coating industry, synthetic resins such as alkyd resins and acrylic resins are commonly used as raw materials, and they constitute the main components of coatings. 2. Secondary film-forming substances: Pigments, fillers, and dyes are considered secondary film-forming substances. Pigments are fine powdery substances that enable coatings to exhibit various colors and provide coverage; they also help adjust the viscosity of coatings, increase the thickness of the paint film, enhance mechanical strength and fillability, and improve the durability and wear resistance of the paint film. Based on the properties of the pigments, they can be further divided into inorganic pigments, organic pigments, and extender pigments. Pigments have coloring power and covering power. Fillers have a filling function. Dyes have coloring power but no covering power. 3. Film-forming aids: Additives. They are used in small amounts in coatings, but can significantly improve the performance of these coatings, such as dispersants, levelers, defoamers, thickeners, etc. 4. Volatile substances: Solvents are substances capable of dissolving other substances to form a homogeneous liquid solution. They have a significant impact on the viscosity, gloss, leveling properties, wetting ability, and adhesion of coatings. For example, diluents such as cyclohexane and xylene facilitate the proper dissolution of the film-forming substances, allowing for the adjustment of the appropriate viscosity and ensuring the achievement of properties such as flow, wetting, drying, and curing of the coating. Solvents are divided into organic solvents and inorganic solvents.