Structural epoxy resins containing core-shell rubbers

Abstract

Core-shell rubbers are incorporated into epoxy adhesives. The adhesives are structural type adhesives that contain an epoxy resin and a toughener, and may contain a liquid rubber in addition to the core-shell rubber. The adhesives have good modulus and tensile strength, which are obtained without loss of elongation and adhesive properties.

What is claimed is: 
     
         1 . A structural adhesive, comprising:
 A) at least one particulate core-shell rubber;   B) a reactive toughener that has isocyanate groups that are blocked or capped with a phenolic compound, an aminophenolic compound, a primary or secondary aliphatic or cycloaliphatic amine, a benzyl alcohol, an aromatic amine, a benzyl amine or a thiol;   C) at least one non-rubber-modified epoxy resin; and   D) one or more epoxy curing agents,   
       wherein the structural adhesive is curable at a temperature of 80° C. or higher. 
     
     
         2 . The structural adhesive of  claim 1 , wherein the core-shell rubber particles have a rubbery core portion that has a T g  of −50° C. or below. 
     
     
         3 . The structural adhesive of  claim 2 , wherein the rubber core portion constitutes from 50 to 95 weight percent of the core-shell rubber particles. 
     
     
         4 . The method of  claim 3 , which contains at least 2 weight percent of the core-shell rubber. 
     
     
         5 . The method of  claim 4 , which contains at least 3 weight percent of the core-shell rubber. 
     
     
         6 . The method of  claim 5 , which contains up to 12 weight percent of the core-shell rubber. 
     
     
         7 . The structural adhesive of  claim 6 , further comprising a rubber-modified epoxy resin. 
     
     
         8 . The structural adhesive of  claim 7 , wherein the total rubber content of the structural adhesive is from 2.5 to 30 weight percent. 
     
     
         9 . The structural adhesive of  claim 8 , wherein the total rubber content of the structural adhesive is from 5 to 20 weight percent. 
     
     
         10 . The structural adhesive of  claim 8  which contains at least 8 weight percent of the reactive toughener. 
     
     
         11 . The structural adhesive of  claim 11  which contains at least 12 weight percent of the reactive toughener. 
     
     
         12 . The structural adhesive of  claim 1 , wherein the reactive tougher corresponds to the formula: 
       
         
           
           
               
               
           
         
       
       wherein m is 1 or 2, n is 2 to 6, R 1  is an n-valent radical of an elastomeric prepolymer after the removal of the terminal isocyanate, amino or hydroxyl group(s), the elastomeric prepolymer being soluble or dispersible in epoxy resin, W and X are independently —O— or —NR 3 —, at least one of W and X being —NR 3 —, R 2  is an m+1-valent radical of a polyphenol or aminophenol after the removal of a phenolic hydroxyl group when X is —O— and of the amino group when X is —NR 3 —, and R 3  is hydrogen, a C 1  to C 6  alkyl or phenyl. 
     
     
         13 . The structural adhesive of  claim 1 , wherein the reactive tougher corresponds to at least one of formula II or formula III: 
       
         
           
           
               
               
           
         
       
       wherein R 8  is independently in each occurrence a C 2-20  m-valent alkyl moiety; R 9  is independently in each occurrence a polyether chain; R 10  is independently in each occurrence an alkylene, cycloalkylene or mixed alkylene and cycloalkylene moiety, optionally containing one or more oxygen or sulfur atoms; R 11  is a direct bond or an alkylene, carbonyl, oxygen, carboxyloxy, or amido moiety; R 12  is independently in each occurrence an alkyl, alkenyl, alkoxy, aryloxy or aryloxy moiety with the proviso that if s=1, then q=0; X′ is 0 or —NR 13  with the proviso that X′ is O where s is 1; and that where s is 0, X′ is O in at least one occurrence; R 13  is independently in each occurrence hydrogen or alkyl; t is independently in each occurrence a number of about 1 to about 6; u is independently in each occurrence a number of 1 or greater; o is independently in each occurrence 0 or 1 if s is 0 and 0 if s is 1; s is independently in each occurrence 0, or 1; and q is independently in each occurrence a number of from 0 to 1. 
     
     
         14 . The structural adhesive of  claim 1 , wherein the reactive tougher corresponds to the formula: 
       
         
           
           
               
               
           
         
       
       wherein R 14  is the elastomeric prepolymer residue after removal of isocyanate groups, said residue having a valence of t+v=2 to 6 with t=1 to 6 and v=0 to 5, X″ is the residue of the primary or secondary aliphatic, cycloaliphatic, heteroaromatic and/or araliphatic amine, a thiol and/or an alkyl amide after removal of an amine or thiol hydrogen and Y″ is the residue of the phenol and/or the polyphenol after removal of a phenolic hydrogen. 
     
     
         15 . A structural adhesive, comprising:
 A) at least 10 weight percent, based on the weight of the adhesive, of one or more liquid rubber-modified epoxy resins;   B) at least 2 weight percent, based on the weight of the adhesive, of at least one core-shell rubber in the form of particles having at least one rubbery core portion and at least one shell portion that has a T g  of at least 50° C., the rubbery core constituting from 50 to 95% of the weight of the core-shell rubber particles;   C) at least 8 weight percent, based on the weight of the adhesive, of a reactive toughener that has isocyanate groups that are blocked or capped with a phenolic compound, an aminophenolic compound, a primary or secondary aliphatic or cycloaliphatic amine, a benzyl alcohol, an aromatic amine, a benzyl amine or a thiol;   D) at least one non-rubber-modified epoxy resin; and   E) one or more epoxy curing agents,   
       wherein the structural adhesive has a total rubber content of from 8 to 30% by weight and is curable at a temperature of 80° C. or higher. 
     
     
         16 . The structural adhesive of  claim 15 , wherein the core-shell rubber particles have a rubbery core portion that has a T g  of −50° C. or below. 
     
     
         17 . The structural adhesive of  claim 16 , wherein the rubber core portion constitutes from 60 to 90 weight percent of the core-shell rubber particles. 
     
     
         18 . The structural adhesive of  claim 16 , wherein the total rubber content of the structural adhesive is from 10 to 20 weight percent. 
     
     
         19 . The structural adhesive of  claim 18  which contains at least 12 weight percent of the reactive toughener. 
     
     
         20 . The structural adhesive of  claim 16  which contains at least 2.5% of the core-shell rubber, at least 10 weight percent of the reactive toughener and which has a total rubber content of at least 10 weight percent.