TESTING COATINGS FOR ADHESION TO SUBSTRATE

摘要

The objective of painting is to make the coating adhere to the substrate. Except in rare cases like the "strippable" coatings, adhesion should be quite good. This promotes resistance to chipping on impact or flaking on bending. Strictly speaking, the binder material within the coating formulation has two functions. It has to adhere the whole film to the substrate (an interface adhesion), and it has to adhere the pigment particles together or encapsulate them so they do not fall out of the film (cohesion). If the substrate has previously been coated (e.g., with a primer), the interface bond is particularly important. Testing for adhesion is fraught with complications because the physical failure may be cohesive within the coating film or the substrate or may be an actual adhesive failure in the interface, whether the interface is with the basic metal substrate or with a primer (or other previously applied) coating. It is not enough to say it fails; how it fails must also be recorded.