Heat-curing epoxy resin composition containing non-aromatic ureas as accelerator

Abstract

The present invention relates to heat-curing epoxy resin compositions, which are characterized by high impact strength, good storage stability, and a low curing temperature. The epoxy resin compositions are suitable for use as a construction shell adhesive and for producing structural foams. They can already be cured in so-called bottom-baking conditions. Furthermore, it has been found that the use of an accelerator of the formula (Ia) or (Ib) results in an increase of the impact strength of heat-curing epoxy resin compositions.

1 . A heat-curing epoxy resin composition comprising
 a) at least one epoxy resin A having on average more than one epoxide group per molecule;   b) at least one epoxy-resin hardener B which is activated by elevated temperature and is an amine, amide, carboxylic anhydride or polyphenol; and   c) at least one accelerant C of the formula (Ia) or (Ib)   
       
         
           
           
               
               
           
         
         where R 1  is H or an n-valent aliphatic, cycloaliphatic or araliphatic radical; 
         R 2  and R 3    
         either 
         each independently of one another are an alkyl group or aralkyl group; 
         or 
         together are a divalent aliphatic radical having 3 to 20 C atoms which is part of an optionally substituted heterocyclic ring having 5 to 8; 
         R 1′  is an n′-valent aliphatic, cycloaliphatic or araliphatic radical; R 2′  is an alkyl group or aralkyl group or alkylene group; 
         R 3′  independently at each occurrence is H or an alkyl group or aralkyl group; and 
         n and n′ are each from 1 to 4. 
       
     
     
         2 . The heat-curing epoxy resin composition of  claim 1 , wherein the epoxy resin composition further comprises at least one toughness improver D. 
     
     
         3 . The heat-curing epoxy resin composition of  claim 1 , wherein n is 1 or 2. 
     
     
         4 . The heat-curing epoxy resin composition of  claim 1 , wherein R 1  is H and R 2  and R 3  are each a methyl, ethyl or propyl group. 
     
     
         5 . The heat-curing epoxy resin composition of  claim 1 , wherein R 1    alternatively   is an alkylene group having 4 to 10 carbon atoms;   or is   
       
         
           
           
               
               
           
         
         or 
         is a biuret or an isocyanurate of an aliphatic or araliphatic diisocyanate, following removal of the isocyanate groups; 
         or 
         is a xylylene group. 
       
     
     
         6 . The heat-curing epoxy resin composition of  claim 1 , wherein the hardener B is selected from the group consisting of diaminodiphenol sulfone, adipic dihydrazide, trimellitic anhydride derivatives, novolaks, and dicyandiamide. 
     
     
         7 . The heat-curing epoxy resin composition of  claim 1 , wherein the heat-curing epoxy resin composition is free from organic carboxylic acids. 
     
     
         8 . The heat-curing epoxy resin composition of  claim 2 , wherein the toughness improver D is selected from the group consisting of blocked polyurethane polymers, liquid rubbers, epoxy resin-modified liquid rubbers, and core-shell polymers. 
     
     
         9 . The heat-curing epoxy resin composition of  claim 2 , wherein the toughness improver D is a liquid rubber which is an acrylonitrile/butadiene copolymer terminated with carboxyl groups or (meth)acrylate groups or epoxide groups, or is a derivative thereof. 
     
     
         10 . The heat-curing epoxy resin composition of  claim 2 , wherein the toughness improver D is a blocked polyurethane polymer of the formula (II) 
       
         
           
           
               
               
           
         
         where 
         Y 1  is a linear or branched polyurethane polymer PU1 terminated with m+m′ isocyanate groups, following the removal of all of the terminal isocyanate groups; 
         Y 2  independently at each occurrence is a blocking group which is eliminated at a temperature above 100° C.; 
         Y 3  independently at each occurrence is a group of the formula (II′) 
       
       
         
           
           
               
               
           
         
         where R 4  is a radical of an aliphatic, cycloaliphatic, aromatic or araliphatic epoxide, containing a primary or secondary hydroxyl group following the removal of the hydroxide groups and epoxide groups; 
         p is 1, 2 or 3 and 
         m and m′ are each between 0 and 8, with the proviso that m+m′ is from 2 to 8. 
       
     
     
         11 . The heat-curing epoxy resin composition of  claim 9 , wherein Y 2  is a radical which is selected from the group consisting of 
       
         
           
           
               
               
           
         
         where 
         R 5 , R 6 , R 7 , and R 8  each independently of one another is an alkyl or cycloalkyl or aryl or aralkyl or arylalkyl group 
         or R 5  together with R 6 , or R 7  together with R 8 , form part of a 4- to 7-membered ring which if desired is substituted; 
         R 9 , R 9′  and R 10  each independently of one another is an alkyl or aralkyl or aryl or arylalkyl group or is an alkyloxy or aryloxy or aralkyloxy group; 
         R H  is an alkyl group, 
         R 12 , R 13 , and R 14  each independently of one another are an alkylene group having 2 to 5 C atoms, which optionally has double bonds or is substituted, or are a phenylene group or a hydrogenated phenylene group; 
         R 15 , R 16 , and R 17  each independently of one another are H or are an alkyl group or are an aryl group or an aralkyl group; and 
         R 18  is an aralkyl group or is a mono- or polycyclic substituted or unsubstituted aromatic group which optionally contains aromatic hydroxyl groups. 
       
     
     
         12 . The heat-curing epoxy resin composition of  claim 10 , wherein m is other than 0. 
     
     
         13 . The heat-curing epoxy resin composition of  claim 1 , wherein the epoxy resin composition comprises at least one chemical blowing agent. 
     
     
         14 . The heat-curing epoxy resin composition of  claim 1 , wherein that fraction of the epoxy resin A is 10%-85%. 
     
     
         15 . The heat-curing epoxy resin composition of  claim 1 , wherein the amount of the epoxy-resin hardener B which is activated by elevated temperature is 0.1%-30%. 
     
     
         16 . The heat-curing epoxy resin composition of  claim 1 , wherein the amount of the accelerant C is 0.01%-6.0%. 
     
     
         17 . The heat-curing epoxy resin composition of  claim 2 , wherein the fraction of the toughness improver D is 0.1%-50%. 
     
     
         18 . A one-component heat-curing adhesive comprising the heat-curing epoxy resin composition of  claim 1 . 
     
     
         19 . A coating comprising the heat-curing epoxy resin composition of  claim 1 . 
     
     
         20 . A method for increasing the impact toughness of heat-curing epoxy resin compositions comprising adding an accelerant of the formula (Ia) or (Ib) as in  claim 1  to a heat-curing epoxy resin composition. 
     
     
         21 . A method of adhesively bonding heat-stable materials, wherein these materials are contacted with a heat-curing epoxy resin composition of  claim 1  and the method comprises one or more steps of curing at a temperature of 100-220° C. 
     
     
         22 . The method of adhesive bonding of  claim 21 , wherein the materials are contacted with heat-curing epoxy resin composition, after adhesive bonding, the adhesively bonded materials are used at temperatures between 120° C. and −40° C. 
     
     
         23 . An adhesively bonded article obtained by a method of  claim 21 . 
     
     
         24 . The bonded article of  claim 23 , wherein the article is a vehicle or a component for installation in or on a vehicle. 
     
     
         25 . A structural foam for the reinforcement of cavities comprising the heat-curing epoxy resin composition of  claim 1 . 
     
     
         26 . A foamed article obtained by at least partially filling a cavity with a heat-curing composition of  claim 1  and heating the adhesively bonded materials to a temperature of 100-220° C. 
     
     
         27 . A vehicle or vehicle component comprising a foamed article of  claim 26 .