Abstract
In powder coatings, melt surface tension plays a decisive role in the film formation. The surface tension is controlled and adjusted by adding levelling additives to powder coating formulations. The influence of additive properties like molecular weight and chemical structures (homopolymeric and copolymeric polyacrylates and polyestermodified polysiloxanes) on surface tension of a typical powder coating binder (DER 664 UE, an epoxy resin) is studied by means of axisymmetric drop shape analysis in a temperature range from 138 to 184°C. The high accuracy of the method allows small differences in surface tension values to be distinguished. It is shown that all additives considerably decrease the surface tension of the epoxy resin. In addition, 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 or polysiloxane additives. Moreover, viscosity measurements have been performed in order to investigate whether these additives also affect the viscosity of the epoxy resin.
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