Class H solventless encapsulants — Unsaturated polyester development and evaluation

This paper examines the technical data accumulation in the development of an Unsaturated Polyester for Class H applications in ballast transformers and stators. The data has been developed over a period of four years and the varnish capability per ASTM D 2307 has been carried out to where actual testing substantiates the validity of extrapolation of the Arrhenius equation.¹ Additional methods for establishing the Thermal Index such as weight loss and Helical Coil Bond Strength will be considered. Although this is nothing new it does offer insight to the definite thermal improvements being incorporated in unsaturated polyesters and that laboratory screening can aid the resin chemist.