Surface tension studies of levelling additives in powder coatings

In powder coatings, melt surface tension plays a decisive role in the film formation. The surface tension is controlled and adjusted by adding levelli ng additives to powder coating formulations. The influence of additive prop erties like molecular weight and chemical structures (homopolymeric and cop olymeric polyacrylates and polyestermodified polysiloxanes) on surface tens ion of a typical powder coating binder (DER 664 UE, an epoxy resin) is stud ied by means of axisymmetric drop shape analysis in a temperature range fro m 138 to 184 degrees C. The high accuracy of the method allows small differ ences in surface tension values to be distinguished. It is shown that all a dditives considerably decrease the surface tension of the epoxy resin. In a ddition, notable differences in the effect of the two groups of additives ( acrylates and siloxanes) were found. Consequently, differences are expected in levelling and wetting of powder coatings formulated with polyacrylate o r polysiloxane additives. Moreover, viscosity measurements have been perfor med in order to investigate whether these additives also affect the viscosi ty of the epoxy resin. (C) 2000 Elsevier Science S.A. All rights reserved.