Ambient-temperature-stable, one-part curable epoxy adhesive

A one-part curable epoxy sheet comprised of a composition in the shape of a sheet, said composition comprising a mixture of

• A. epoxy resin capable of being cured to a cured epoxy resin when exposed to an activated latent curative system;
• B. a latent curative system in an amount sufficient to cure said epoxy resin comprising (a) at least one epoxy resin miscible first curative comprising a latent hardener, selected from dicyandiamide and its derivatives, contained substantially as a core within a multiplicity of ambient-temperature-stable, impermeable microcapsules having capsule walls comprised of a thermoplastic polymeric material and (b) at least one epoxy resin latent second curative comprising a latent accelerator, which is a metal imidazolate compound of the formula:
• MLm
• wherein
• M is a metal selected from the group of Ag(I), Cu(I), Cu(II), Cd(II), Zn(II), Hg(II), Ni(II) and Co(II),
• L is an imidazolate of the formula
• wherein R1, R2, and R3 are selected from a hydrogen atom, an alkyl radical or aryl radical and m is the valence of M, in an amount sufficient when activated to cure said epoxy resin admixed uniformly within said curable epoxy resin, wherein the microcapsule walls isolate the first curative from the second curative, admixed uniformly within said curable epoxy resin;
• C. sufficient particulate thermoplastic polymeric material having a melt flow temperature that exceeds ambient temperature and the ability to be at least partially melt blended into the epoxy resin to at least regionally plasticize the cured epoxy resin, wherein up to all of the total weight of said particulate thermoplastic polymeric material may be provided by the thermoplastic polymeric material of said microcapsule walls.

A method of making a cured epoxy composition comprising the steps of

• A. providing a one-part curable epoxy composition comprising a mixture of (a) epoxy resin capable of being cured to a cured epoxy resin when exposed to an activated latent curative system;
• (b) a latent curative system in an amount sufficient to cure said epoxy resin comprising (i) at least one epoxy resin miscible first curative comprising a latent hardener, selected from dicyandiamide and its derivatives, contained substantially as a core within a multiplicity of ambient-temperature-stable, impermeable microcapsules having capsule walls comprised of a thermoplastic polymeric material and (ii) at least one epoxy resin latent second curative comprising a latent accelerator, which is a metal imidazolate compound of the formula:
• MLm
• wherein
• M is a metal selected from the group of Ag(I), Cu(I), Cu(II), Cd(II), Zn(II), Hg(II), Ni(II) and Co(II),
• L is an imidazolate of the formula
• wherein R1, R2, and R3 are selected from a hydrogen atom, an alkyl radical or aryl radical and m is the valence of M,
• in an amount sufficient when activated to cure said epoxy resin admixed uniformly within said curable epoxy resin, wherein the microcapsule walls isolate the first curative from the second curative, admixed uniformly within said curable epoxy resin;
• and (c) sufficient particulate thermoplastic polymeric material having a melt flow temperature that exceeds ambient temperature and the ability to be at least partially melt blended into the epoxy resin to at least regionally plasticize the cured epoxy resin, wherein up to all of the total weight of said particulate thermoplastic polymeric material may be provided by the thermoplastic polymeric material of said microcapsule walls;
• and
• B. heating said mixture at least to the melt flow temperature of said polymeric material.