Abstract
Epoxy resins are generally two-component thermosetting resins composed of a hardener and a curing accelerator which are mixed at the time of use. However, it is inconvenient to weigh and mix the two-component resins just before use. Therefore, one-component resins which contain epoxides and hardeners are required. Acid hydrazide and dicyandiamide are typical hardeners that are used for the one-component epoxy resins. Both of them are solid dispersion type latent hardener based on their insolubility in the epoxy resin. In these systems, solid dispersion technique is needed, and they can not be used in the sealing and adhesion of the gap smaller than the particle size of the hardener. Hence, a hardener which can exhibit the latency in homogeneous system is required. We found that a phosphate synthesized from a phosphoric acid ester with an organic base can be used as a thermal latent hardener for epoxy resins. Because the reaction of the phosphate with epoxy resins was initiated by heating, the phosphate gave long pot life even in the homogeneous composition. It was suggested that the curing proceeded with an anionic polymerization mechanism initiated by a phenoxide anion generated by the reaction of the phosphate with an epoxy group.
