Characterization and Moldability Analysis of Epoxy Reaction Injection Molding Resins

The interest in extending the Reaction Injection Molding (RIM) process to non-urethane resins has generated need for a greater understanding of the molding behavior of these fast-cure systems. Epoxy, for example, is recognized as a candidate for commercial RIM, but its lower reaction rate and high heat of reaction render it more difficult to mold than polyurethane. The kinetics and rheology of such a resin must therefore be well characterized in order to undertstand the molding process and evaluate its feasibility. A method of fully characterizing an epoxy molding system by combining adiabatic reactor studies, infra-red spectrometry, and viscometer data is therefore described. This provides time-temperature-conversion-viscosity correlations which can be directly utilized in computer studies designed to minimize actual molding times while avoiding a damaging exotherm during cure. The particular system studied is a low viscosity liquid epoxy cured with aminoethylpiperazine and was foundto be moldable over specific temperature ranges. Conducting an analysis of this type on a prospective resin can help determine the value of further investment in experimentation, material development, molding equipment, and tooling.