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Saturday, July 19, 2008

Bisphenol A Epoxy Adhesive

The bisphenol A. Epoxy adhesives stick to most things, and are probably the most versatile of all high strength adhesives. Since the time the early nineteen forties when the commercial importance of epoxy resins became recognized in Switzerland and the USA, an enormous number of patents has been taken out relating to their composition and use; while most of these patents do not deal specifically with adhesive use, many embrace it in a general way. Also numerous papers and three or four books have been published on the subject of epoxy resins and their applications.

Among the early patent are those of Trey Fretes, and Ciba of Switzerland, and Devoe & Reynolds and Shell of USA. Some of these describe use as adhesives while others relate to methods of preparing the resin and hardening it, the glycidyl compounds themselves having been described some years earlier.

Preparation of the Glycidyl Compounds

By reacting epichlorohydrin with a substance having a molecular structure containing replaceable hydrogen atoms such as hydroxyl group, a glycidyl ether R-O-CH2 -CH-O-CH 2 may be obtained, the glycidyl compounds of bisphenol A are the outstanding examples. The molecular structure of this is commonly represented as complete formula that is shown aromatic structure.

The monomeric diglycidyl ether, for which the value of n is 0, is of lower viscosity than higher members of the series, although if sufficiently pure it may be a crystalline solid. As the value of n increases the resin becomes progressively, a more viscose liquid, a solid of low softening point, and a solid of high softening point. The special advantage of a liquid (solvenless) adhesive needs no emphasing; nevertheless, the solid polymers also make useful adhesives, they are in fact together but they are in fact tougher but have lower hot-strengths.