Organo-tin compounds as latent catalysts for epoxy VPI resins

Organo-tin compounds (e.g., trialkyl- and triaryltin halides, acetates, hydroxides, and related compounds) have been found to be extremely effective latent catalysts for vacuum pressure impregnation epoxy formulations. Fast gel times at elevated temperatures combined with long storage life-times at ambient make it possible to use these organo-tin compounds in formulating low viscosity solventless impregnating resins and potting compounds. Very low power factor values (<0.3% at 150°C) are found with some of these impregnants, after cure, indicating possible uses in high voltage insulation applications. Epoxy/organo-tin complexes, possibly via “inner oxonium salt” formation, are postulated to explain the unusual cure characteristics displayed by cycloaliphatic epoxy resin formulations containing these compounds