Non-fibrous fillers for epoxy resin formulations

Non-reinforcing fillers are commonly used in epoxy resin formulations to reduce shrinkage, improve thermal shock resistance, dissipate heat, impart flame retardancy and lower costs. Because of the numerous types of fillers available and the lack of systematic comparisons of the effect of these fillers on properties of representative epoxy formulations, selection of the optimum filler for a given application may involve considerable guess-work. The principal objective of this study is to provide comparative data illustrating the effect of 19 fillers on the electrical properties, shrinkage, thermal shock resistance, water resistance, viscosity and stability of two typical epoxy resin formulations. A flexibilized anhydride cured epoxy system of the type used for electrical encapsulations and a general purpose, rigid, aliphatic amine cured epoxy system were selected as the binders for this study. Filler loadings were equated on a volume concentration basis because of the wide difference in densities of the fillers studied and the more direct relationship of properties such as shrinkage, thermal shock resistance, viscosity and cost per manufactured unit to volume concentration rather than weight concentration.