Nano-Mechanical Properties and Topography of Thermosetting Acrylic Powder Coatings

By D.C. Andrei, J.L. Keddie, J.N. Hay, B.J. Briscoe, D. Parsonage

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 to 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 (about 100 µm in diameter) are randomly distributed at the surface. The nano-mechanical properties within these pits are similar to the bulk of the coating.