2-phenylimidazole-phosphoric acid salt as an accelerator for...

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate

Reexamination Certificate

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C528S094000, C528S112000, C548S377100

Reexamination Certificate




The present invention relates to latent curing agents and accelerators for epoxy resins, especially one-component epoxy compositions. “Latent” curing agents are those curatives that in a formulated system remain inactive under normal ambient conditions but react readily with epoxy resin at elevated temperatures. “Accelerators” are those materials that accelerate the reaction between epoxy resin and a curing agent. “One component” epoxy compositions are typically a blend of epoxy resin, curing agent and accelerator as well as additives and fillers.
Current one-component epoxy compositions may contain an acid anhydride as a latent curing agent. These compositions offer excellent shelf life but require very high temperature to cure. Accelerators such as imidazoles can be used with acid anhydrides to increase reactivity, however such accelerators adversely affect shelf stability of compositions.
There is a need for a one-component 100% solids epoxy composition which is cured by acid anhydride and offers a good balance of low-temperature cure and shelf stability.
U.S. Pat. No. 3,329,652 discloses curing polyepoxides with acid anhydrides using imidazole salts as activators for the acid anhydride.
U.S. Pat. Nos. 3,356,645 and 3,418,333 disclose curing polyepoxides with imidazole salts.
U.S. Pat. No. 3,746,686 discloses curable epoxy resin compositions comprising a polyepoxide and a salt of a polycarboxylic acid or anhydride and an imidazole.
U.S. Pat. No. 3,755,253 discloses catalyzing the diaminodiphenylsulfone cure of polyepoxides with an imidazole salt.
T. Kamon, et al, “Curing of Epoxy Resins. VI. Curing of Epoxy resins with Acid Salts of Imidazoles”, Shikizai Kyokaishi (1977), 50 (1), pp 2-7 discloses the study of the curing of epoxy resins with alkyl carboxylic acid and phosphoric acid salts of some imidazoles.
JP 58083023 describes a latent epoxy hardener prepared by placing 2-hepta-decylimidazoline in water, adding orthophosphoric acid, mixing for 10 minutes, filtering and drying in vacuo. “Epoxy Dispersion In Adhesive Applications”, Adhesives Age, May 1995, pages 34-37, discloses the use of 2-methylimidazole and dicyandiamide in water-based epoxy compositions.
The present invention is directed to 2-phenylimidazole phosphate salt and its use as an accelerator for acid anhydride latent curing agents in one-component heat curable epoxy compositions. The salt is the reaction product of 2-phenylimidazole and phosphoric acid.
The reaction of 2-phenylimidazole with phosphoric acid, especially in equimolar amounts, affords the dihydrogen phosphate salt, or biphosphate salt, of the following structure A
The invention provides:
an accelerator for acid anhydride latent curatives in heat cured epoxy compositions; and
one-component 100% solids epoxy compositions comprising 2-phenylimidazole phosphate salt, acid anhydride and an epoxy resin which offer a good balance of low-temperature cure and extended shelf stability.

patent: 3329652 (1967-07-01), Christie
patent: 3356645 (1967-12-01), Warren
patent: 3631150 (1971-12-01), Green
patent: 3632427 (1972-01-01), Green
patent: 4788076 (1988-11-01), Weiss
patent: 5508328 (1996-04-01), Olson
patent: 5534565 (1996-07-01), Zupancic et al.
Sawa et al., Abstract of JP 2053777, Feb. 1990.*
Kazushi, Abstract of JP 59020371, Feb. 1984.*
Lee & Neville, Handbook of Epoxy Resins, McGraw-Hill pp. 12-2, 12-12, 1967*
T. Kamon, et al., “Curing of Epoxy Resins,” Shikizai Kyokaishi (1977), 50(1), 2-7, Chemical Abstracts 86:172311.
N. Sawa, et al., “Preparation of 1-Benzylimidazoles as Epoxy Resin Hardeners,” Japan Kokai Tokkyo Koho, 6 pp., Chemical Abstracts 113:78398.
European Search Report, 01125886.0-21-2, dated Mar. 7, 2002.
European Search Report, 01125885.2-1202, dated Mar. 8, 2002.


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