The adhesion of the organic coating should include two aspects, one is the adhesion between the organic coating and the base metal surface, and the other is the cohesion of the organic coating itself. Both are integral to the protective effect of the coating. The higher the adhesion strength of the organic coating on the surface of the metal substrate, the better; the tough and dense paint film of the coating itself can play a good role in blocking external corrosion factors. The coating cannot be firmly attached to the surface of the substrate, and no complete coating can play a role; the coating itself has poor adhesion, and the film layer is easy to crack and lose its protective effect. These two factors together determine the adhesion of the coating and constitute a key factor in determining the protective effect of the coating.
There are many theories about coating adhesion. There are two basic factors that affect paint adhesion: the wettability of the paint to the substrate and the roughness of the substrate. The better the wettability of the coating to the metal substrate, the better the adhesion; a certain surface roughness acts as an anchor pattern in the coating.
There are many methods for testing the adhesion between coatings and substrates. Many institutions have formulated corresponding standards and prepared many instruments and tools for detecting adhesions. There are two main methods suitable for on-site inspection of adhesion: X or cross-cut method with tools and pull-off method. Both of these methods can be used in the laboratory and are more suitable for application on the construction site.
When testing the adhesion of anti-corrosion coatings, if the results of the scratch X method and the scratch method are not satisfactory, the pull-off method can be used as the main reference method.