About Epoxy Adhesive

Epoxyalkyl Ester Adhesives

Glycidyl compounds can be made by the reaction of epichlorohydrin with a substance other than an amino or hydroxyl compound, and the products of reaction with polycarboxylic acids or anhydrides known as epoxyalkyl ester are of some interest. These resins, wherein the important functional groups are epoxide, are quite unlike the polyester referred to.

In the development of the epoxyalkyl ester adhesives, Henkel and Cie of Germany have been prominent. Epoxyalkyl esters can be prepared by reacting a halide of a polybasic aromatic carboxylic acid with an epoxide compound containing a hydroxyl group such as glycidol, also by reacting a salt of such an acid, or the acid or anhydride itself in the presence of a catalyst with epichlorohydrin.

Epoxy Resin of Olefin

The epoxy resin of this class are the products f epoxidation effected by means of an oxygen-donating substance, referred to at the beginning of this section as the second method of producing epoxy resins.

These resins will be discussed only briefly because, although they have created considerable interest, they can not yet be said to have assumed importance as adhesives.

Epoxides of this class comprise both cycloaliphatic and aliphatic structures, examples are dicyclopentodiene dioxide (mp. 184oC), vinyl cyclohexene dioxide (a liquid), structures containing cyclohexene oxide rings (usually liquids), and epoxidised butadiene resins (usually liquids). In their development the Union Carbide Corporation of USA, Ciba of Switzerland and the Food Machinery Company of USA have been prominent.

Epoxidation of Olefin Compounds

From the results of adhesion tests it would appear that in their present state of development the room temperature strength of the cycloapipharic epoxides generally, is lower than that of the glycidyl ethers, even lower than that of those glycidyl system which incorporate a hardener that inevitable gives a brittle cured adhesive. The strength temperature relationship of the compounded illustrated above when cured with a 35/36 mixture of phthalic and tetrahydrophthalic anhydrides.

It is in the hot strength of these epoxides that most adhesives interest will probably develop. It has been reported that dicyclopentadiene dioxide cured with a maleic anhydride/polyol mixture gives the highest known service temperature properties, with a Deflection Temperature of 300oC. However, it will be noted that a Deflection Temperature of this order has been quoted for the glycidyl polyester of certain tris and tetrakis phenols.

Non Flammable epoxy Resin

The glycidyl ethers, the epoxides of olefines are capable of homopolymerization but the homopolymers are not attractive as adhesives. The range of interesting resins that the peracid method of epoxidation makes possible leads one to think that the future will inevitably bring a valuable range of adhesives, with perhaps the important extremes of high strength with flexibility at the other.

The normal bisphenol A glycidyl ethers are flammable, the degree depending on the curing agent. In an adhesive, flammability is usually not important because the mass of adhesive in any one area is small, and only partially exposed, but it is possible that there are applications where non flammability is important.