Background: The Challenges of Developing a One-Package Epoxy Resin

Epoxy resins are widely used as electric insulating materials and as part of molded products, adhesives and coatings. In addition to adhesion for metal, glass and ceramics, epoxy resins provide superior chemical resistance, resistance to elevated temperatures and excellent electrical insulation characteristics as well as low moisture absorption and rigidity.

Most epoxy resins utilize curing agents such as aromatic or aliphatic amines, amides, polyamides or acid anhydride. Often, the epoxy resin and curing agent form a two-part system in which the two components are stored separately and mixed in the correct quantities just prior to use.

Obviously, a one-package epoxy resin system would have considerable advantages over two part systems. Besides being more convenient, a one-package system would also permit continuous use over extended periods of time. The problem, however, is that a one-package epoxy resin requires a so-called latent curing agents, i.e., one that does not react with epoxy resins at room temperature but reacts with the epoxy resin when heated.

Among the compounds that have been proposed as a latent curing agent are dicyanodiamide (DICY) combined with epoxy resins. Unfortunately, although these compounds offer excellent storage stability, they must be heated for long periods at temperatures of at least 180ºC. In contrast, the use of conventional accelerators tends to impair storage stability. Until Ajicure, no compound offered the ideal combination of a long pot life and a short cure time.