Coating film formation mainly includes coating adhesion and coating drying.
A Coating Adhesion
The first step of adhesion between steel strip substrate and coating is the wetting of coating on the surface of substrate. The wetting of coating can replace the air and water previously adsorbed on the surface of steel strip substrate. At the same time, the volatilization of solvent on the surface of substrate plays a role of dissolution or swelling. If the solubility parameters of coating film-forming resin and the surface of substrate are selected properly, it will be able to replace the air and water previously adsorbed on the surface of steel strip substrate. It is very important for the good adhesion of the coating to form an intermixing layer between the substrate surface and the coating film.
B Coating Drying
The coating adherence construction is only the first step of coating film formation in the coating process of color coated sheet, and the process of solid continuous film formation should be continued to complete the whole coating film formation process. This process from "wet film" to "dry film" is often referred to as "drying" or "curing". This drying and curing process is the core of the coating film forming process. Coatings with different forms and compositions have their own film-forming mechanism, which is determined by the properties of film-forming substances used in coatings. Usually we divide the film formation of coatings into two categories: solid and field.
(1) Non-transforming type. Generally refers to the physical film formation mode, that is, mainly depends on the volatilization of solvents or other dispersing media in the film, and the film viscosity gradually increases to form a solid film. For example: acrylic paint, chlorinated rubber paint, ethylene paint and so on.
(2) Conversion type. Generally speaking, chemical reaction occurs in the process of film formation, and coating mainly depends on chemical reaction to form film. This kind of film-forming material is the process of film-forming material in coatings, which is called polymer after construction. It can be said that it is a special way of polymer synthesis. It completely follows the reaction mechanism of polymer synthesis. For example: alkyd coatings, epoxy coatings, polyurethane coatings, phenolic coatings and so on. However, most of the modern coatings are not formed by a single way, but by a variety of ways to eventually film, coil coating is a typical way to rely on a variety of ways to eventually film.