Combined use of scratch tests and CLA profilometry to characterize polyester powder coatings

The use of scratch tests at different stages of the curing process is of crucial importance in powder coatings as it can provide helpful information on formulating the base material, on setting curing operational parameters and, above all, on progressively establishing coating properties during baking. In particular, this paper deals with the use of sliding spherical contact geometry to characterize the scratch response of a clear polyester topcoat electrostatically sprayed onto metallic substrate and baked under different time-temperature programs in a convection oven. Friction force and penetration depth were on-line monitored during scratch tests. Following this, residual deformation patterns were analyzed by using a combination of non-contact CLA profilometry and FE-SEM. Analytical examination and simple mathematical simulation of the experimental results found good correlations between the size of the deformed area after scratch and curing operating parameters. This makes it possible to map the scratch response of the clear polyester topcoats to ranges of curing conditions.