On the combined use of scratch tests and CLA profilometry for the characterization of polyester powder coatings: influence of scratch load and speed

The prediction of the mechanical properties of polyester powder coatings is of paramount importance, asthey have to undergo a wide variety of forces and deformations during their service life. Determine theresponse of polymeric coatings to the actual loading conditions can be, however, very troublesome astheir properties are function of the material physical state, rate-dependence and yield and breakbehaviour. Further, the characterization of soft, contaminated organic surfaces such as polymers canoften cause severe problems with reliability and imaging accuracy due to instrumental artefacts.This is therefore the context in which this paper investigates the capability of multiple parametersscratch tests joined with non-contact CLA profilometry and FE-SEM to detect the scratch response ofpolyester powder coatings for protective and decorative outdoor applications. Scratch tests with bluntcontact geometry were used to evaluate the response of polyester coatings baked at different time–temperature programs and, so, at different stages of their curing process. In particular, being suchcoatings highly non-linear in their response tomechanical stress or strain, the influence from scratch load and speed was carefully taken into account. Analytical evaluations of the experimental results led to goodcorrelations between the extent of the deformed zone after scratch, scratch parameters and curingoperational settings. This allows mapping the scratch response of the polyester topcoats to broad rangesof both scratch parameters and curing conditions.