The film-forming substance of anti-corrosion coating has chemical stability in the corrosive medium, and its standard is related to the composition and chemical structure of the film-forming substance. It mainly depends on whether it is easy to react with the corrosive medium or decompose into small molecules in the medium under dry film conditions.
Whether it is considered from the perspective of anti-electrochemical corrosion or pure isolation, the shielding effect of anti-corrosion coatings is very important, and the shielding property of the paint film depends on the structure of the film forming pores and coating pinholes. The transmission speed of water, oxygen and ions to the paint film is different. The penetration rate of water is much greater than that of ions. Oxygen transmission is more complicated and has a great relationship with temperature. Water and oxygen can form corrosive electricity on the metal surface after passing through the paint film. There are fewer ions penetrating the paint film, and their direct effect on the substrate metal can be ignored, but it will increase the conductivity of the paint film.
When the molecules in the film-forming structure have more functional groups, the structure of the latex paint film has fewer pores, and can react with each other during the film-forming process to form a net-like three-dimensional structure with high cross-link density, thereby enhancing the corrosion resistance of the coating. The physical and mechanical properties of the paint film greatly affect the anti-corrosion effect of anti-corrosion coatings. They are related to the molecular weight, chain links, and side genes of the membrane-forming material. The influence of pigments and fillers in the paint coloring pigments play a role in coloring, body pigments are used to adjust the mechanical properties of the paint film or paint fluidity. For anti-corrosion coatings, in addition to the above two pigments, pigments for the purpose of anti-corrosion are added: one is anti-rust pigments that use their chemical properties to inhibit metal corrosion; the other is flake pigments, which are improved by physical action The shielding of the coating. Antirust pigments can be divided into three basic pigments: basic pigments, soluble pigments and metal powder pigments.
Alkaline pigments react with oily film-forming materials to form metal soaps, such as red lead, lead monoxide, lead cyanamide, basic lead chromate, calcium leadate, and basic lead sulfate. After the metal soap comes into contact with water, its decomposition products can play a role in corrosion inhibition. In addition, the paint film improves the shielding effect on the environment when generating metal soap. The alkaline pigment keeps the interface between the paint film and the metal slightly alkaline, and also plays a role in corrosion protection. Soluble pigments, perchloroethylene paints are usually chromate pigments. These pigments dissolve chromate ions after contact with moisture. Chromate ion has a strong oxidation effect, which can passivate the metal surface and thus play a role in corrosion protection.