Structural epoxy resin adhesives containing chain-extended elastomeric tougheners capped with phenol, polyphenol or aminophenol compounds

Abstract

Structural adhesives are prepared from a chain extended elastomeric toughener that contains urethane and/or urea groups, and have terminal isocyanate groups that are capped with a phenol, a polyphenol or an aminophenol compound. The adhesives have very good storage stability and cure to form cured adhesives that have good lap shear and impact peel strengths.

1 . A one-part structural adhesive comprising:
 A) at least one epoxy resin;   B) a reactive elastomeric toughener containing capped isocyanate groups; and   C) one or more epoxy curing agents;   wherein the elastomeric toughener is formed by   a) reacting an excess of a polyisocyanate with a 300-3000 equivalent weight polyol or with a mixture of a 300-3000 equivalent weight polyol and a branching agent, to form an isocyanate-terminated prepolymer;   b) reacting the isocyanate-terminated prepolymer with a chain extender to produce a chain extended, isocyanate-terminated prepolymer, and   c) capping at least 90% of the terminal isocyanate groups of the chain extended, isocyanate- terminated prepolymer with a capping agent selected from a monophenol, a polyphenol or an aminophenol.   
     
     
         2 . The structural adhesive of  claim 1 , wherein the 300-3000 equivalent weight polyol is a polyether, a hydroxyl-terminated polybutadiene or a mixture of a polyether and a hydroxyl-terminated polybutadiene. 
     
     
         3 . The structural adhesive of  claim 2 , wherein the chain extender contains two phenolic hydroxyl groups. 
     
     
         4 . The structural adhesive of  claim 3  wherein the capping agent is a monophenol. 
     
     
         5 . The structural adhesive of  claim 3  wherein the capping agent is a polyphenol. 
     
     
         6 . The structural adhesive of  claim 3  wherein the capping agent is an aminophenol. 
     
     
         7 . The structural adhesive of  claim 2 , wherein the epoxy resin includes at least one diglycidyl ether of a polyhydric phenol. 
     
     
         8 . The structural adhesive of  claim 2 , which contains at least one epoxide-terminated liquid rubber. 
     
     
         9 . The structural adhesive of  claim 2 , further comprising a latent catalyst which becomes active only upon exposure to elevated temperatures. 
     
     
         10 . The structural adhesive of  claim 9  wherein the latent catalyst is 2,4,6-tris(dimethylaminomethyl)phenol integrated into a poly(p-vinylphenol) matrix or 2,4,6-tris(dimethylaminomethyl)phenol integrated into a novolac resin. 
     
     
         11 . The structural adhesive of  claim 2  wherein the curing agent includes one or more of a boron trichloride/amine complex, a boron trifluoride/amine complex, dicyandiamide, melamine, diallylmelamine, acetoguanamine and benzoguanamine, 3-amino-1,2,4-triazole, adipic dihydrazide, stearic dihydrazide, isophthalic dihydrazide, semicarbazide, cyanoacetamide, and diaminodiphenylsulphones. 
     
     
         12 . The structural adhesive of  claim 2  further comprising one or more of calcium carbonate, calcium oxide, talc, carbon black, textile fibers, glass particles or fibers, aramid pulp, boron fibers, carbon fibers, a mineral silicate, mica, powdered quartz, hydrated aluminum oxide, bentonite, wollastonite, kaolin, fumed silica, silica aerogel, a polyurea compound, a polyamide compound, or aluminum powder, iron powder or microballoons having an average particle size of up to 200 microns and density of up to 0.2 g/cc. 
     
     
         13 . A method comprising applying the structural adhesive  claim 1  to the surfaces of two members, and curing the structural adhesive to form an adhesive bond between the two members.