Nano-mechanical properties and topography of thermosetting acrylic powder coatings

Both nano-scratching and nano-indentation techniques have been used to evaluate the mechanical properties of the surface of acrylic coatings, with and without added pigment. The coatings were formed from thermosetting, acrylic powders. Both types of coatings--clear and pigmented--do not exhibit any significant differences in their hardness with an increase in baking time from 7-15 min. According to the scratching profiles, the deformation induced at the surface is virtually elastic. Introducing the pigment causes a slight increase in the elastic modulus but no significant variation in hardness. In all coatings, the computed hardness and the elastic modulus values are higher near the surface (perhaps as a result of tip geometry effects), but these readily reach plateau values that are consistent with other work available in the literature. A long-range surface profiler, which provided two-dimensional and three-dimensional topographical maps of the coating surfaces, reveals undulations in the surface with a wavelength on the order of 2-4 mm. Moreover, the topography of the pigmented coating is significantly smoother than that of the clear coating in which shallow pits (approx100 mu m in diameter) are randomly distributed at the surface. The nano-mechanical properties within these pits are similar to the bulk of the coating. Substrate: steel.