Latent catalysts for epoxy curing systems

Abstract

The invention relates to epoxy resin compositions. More specifically, the invention is a composition suitable to cure an epoxy resin, preferably in a solvent, incorporating a cross-linking compound of a polycarboxylic acid anhydride or a copolymer of styrene and hydroxystyrene. Also, the invention relates to an epoxy resin composition comprising an inhibitor effective to extend the gel time of the composition at curing temperatures from 150° C. to 170° C., and a cross-linking compound as described.

What is claimed is:  
     
         1 . An epoxy resin composition comprising 
 a) a polyepoxide,    b) a cure inhibitor which is boric acid, a Lewis acid derivative of boron, an alkyl borane, a mineral acid having a nucleophilicity value “n” of greater than zero and less than 2.5 or an organic acid having a pKa value of 1 or more, but not more than 3, or a mixture of two or more thereof, and    c) more than 30 parts per 100 parts of polyepoxide, of at least one cross-linker.    
     
     
         2 . The epoxy resin according to  claim 1  including d) a solvent.  
     
     
         3 . The epoxy resin composition according to  claim 1  wherein the cross-linker is an anhydride of a polycarboxylic acid.  
     
     
         4 . The epoxy resin composition according to  claim 1  where in the cross-linker is a copolymer, containing optionally substituted styrene units of the formula  
       
         
           
           
               
               
           
         
       
       and optionally substituted hydroxystyrene units of the formula  
       
         
           
           
               
               
           
         
       
       in a ratio of 1:1 to 50:1, and wherein the total number of the said monomer units is from 3 to 10,000, m″ is from 0 to 5, each R 2  independently is C 1-3  alkyl or a halogen, and each m independently is from 0 to 4.  
     
     
         5 . The epoxy resin composition according to  claim 1  which also comprises a bifunctional chain extension compound.  
     
     
         6 . The epoxy resin composition according to  claim 5  wherein the bifunctional chain extension compound is bisphenol A, or tetrabromobisphenol A.  
     
     
         7 . The epoxy resin composition according to any one of the preceding claims, which also comprises a catalytic amount of a catalyst for accelerating the reaction of the polyepoxide with the cross-linker.  
     
     
         8 . The epoxy resin composition according to  claim 7 , wherein the catalyst is a heterocyclic nitrogen compound, an amine, a phosphine, an ammonium compound, a phosphonium compound, an arsonium compound or a sulfonium compound.  
     
     
         9 . The epoxy resin composition according to  claim 8 , wherein the catalyst is an imidazole of Formula 19, or a benzimidazole of Formula 20 
       
         
           
           
               
               
           
         
       
       wherein each R 11  independently is hydrogen, halogen, or an organic radical.  
     
     
         10 . The epoxy resin composition according to  claim 9 , wherein each R 11  independently is a hydrocarbyl radical or a substituted hydrocarbyl radical.  
     
     
         11 . The epoxy resin composition according to  claim 10 , wherein each R 11  independently is a C 1 -C 5  hydrocarbyl radical substituted with an ester, ether, amide, imide, amino, halogen, or mercapto group.  
     
     
         12 . The epoxy resin composition according to any one of  claims 1  to  11 , wherein the cross-linker includes a carboxylic acid anhydride according to Formula 12, or Formula 13 
       
         
           
           
               
               
           
         
       
       where p is from 1 to 100.  
     
     
         13 . The epoxy resin composition according to any one of  claims 1  to  11 , wherein the cross-linker includes phthalic anhydride, terphthalic anhydride, succinic anhydride, an alkyl-substituted anhydride, an alkenyl-substituted anhydride, succinic anhydride, tartaric acid anhydride, or a polyanhydride containing units of the formula  
       
         
           
           
               
               
           
         
       
       or units of the formula  
       
         
           
           
               
               
           
         
       
       where the ratio of k to 1 units is from 1:1 to 50:1, the total number of monomer units k and 1 is from 3 to 10,000, R 6  is hydrogen, C 1-3  allyl, or R 6 A; 
 R 6 A is:  
                     
 Q 3  is C 1-30  carbonyl, or methylene optionally substituted with one or two substituents of Formula R 6 A;  
 W is —OH, or —COOH;  
 m″ is from 0 to 5; and  
 R 2A  is from C 1-30  alkyl, halogen or hydrogen.  
 
     
     
         14 . An epoxy resin composition according any one of the preceding claims having a dielectric constant of 4.30, or less.  
     
     
         15 . An epoxy resin composition according to any one of the preceding claims having a dielectric dissipation factor of less than 0.010.  
     
     
         16 . A fiber reinforced composite article comprising a matrix including an epoxy resin according to any one of the preceding claims.  
     
     
         17 . The fiber reinforced composite article of  claim 16 , which is a laminate or a prepreg for an electric circuit.  
     
     
         18 . An electric circuit component having an insulating coating of the epoxy resin according to any one of claims  1  through  13 .  
     
     
         19 . A process of producing a coated article, comprising coating the article with an epoxy resin according to any one of claims  1  through  13 , and heating the coated article to cure the epoxy resin.  
     
     
         20 . A composition useful for curing a polyepoxide resin comprising: 
 a) a cross-linker capable of curing with a polyepoxide at elevated temperatures; and    b) a cure inhibitor which is boric acid, a Lewis acid derivative of boron, an alkyl borane, trimethoxyboroxine, a mineral acid having a nucleophilicity value “n” of greater than zero and less than 2.5, or an organic acid having a pKa value of 1 or more, but not more than 3, or a mixture of two or more thereof.    
     
     
         21 . A composition according to  claim 20  wherein the cross-linker is an anhydride of a polycarboxylic acid.  
     
     
         22 . A composition according to  claim 20  wherein the cross-linker is a copolymer of styrene and/or hydroxystyrene.  
     
     
         23 . A composition according to  claim 20  which further comprises: a bifunctional chain extender compound capable of reacting with a polyepoxide at elevated temperatures.  
     
     
         24 . A composition according to  claim 23 , which further comprises a catalytic amount of a catalyst for accelerating the reaction of the polyepoxide with the cross-linker and/or the bifunctional chain extender.  
     
     
         25 . A composition useful to cure a polyepoxide resin according to any one of  claims 20  to  24 , which further comprises a hydroxy-functional cross-linker having a functionality of 2.2 or more.