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The chemical bond theory is one of the important mechanisms underlying the adhesion of paint coatings; it refers to the chemical reactions that occur at the interface between the paint and the substrate, resulting in strong interaction forces such as covalent bonds, thereby enabling a firm bond. This type of bond has the highest strength and best durability, and is particularly common in thermosetting coatings. The formation of chemical bonds requires a reaction between the functional groups in the coating and the surface functional groups on the substrate; for example, coatings containing hydroxyl or carboxyl groups can form chemical bonds with the surface of metal oxides ； Silane coupling agents are often used as primers to promote chemical bonding between resins and glass, metal, or plastics ； Isocyanate-based coatings can react with active hydrogen on metal or rubber surfaces to form chemical bonds. Due to the extremely thin interface layer, chemical bonds are difficult to detect directly, but experiments have confirmed their existence and their significant role in enhancing bond strength. However, the formation of chemical bonds is not universal; specific chemical reaction conditions must be met, and the number of chemical bonds per unit area is much lower than that of intermolecular forces. Therefore, actual adhesion is often the result of a combination of chemical bonds, mechanical connections, and secondary forces.