Acrylic pressure-sensitive adhesives with aziridine crosslinking agents

Abstract

A pre-adhesive composition is described comprising an acid-functional (meth)acrylate copolymer and an aziridine crosslinking agent, which when crosslinked provides a pressure-sensitive adhesive and pressure-sensitive adhesive articles.

1 . A method of preparing a pressure sensitive adhesive comprising combining;
 (a) a acid functional (meth)acrylate copolymer comprising
 i. 85 to 99 parts by weight of an (meth)acrylic acid ester of non-tertiary alcohol; 
 ii. 1 to 15 parts by weight of an acid functional monomer; 
 iii. 0 to 10 parts by weight of a second, non-acid functional, polar monomer; 
 iv. 0 to 5 parts vinyl monomer; 
 wherein i to iv is 100 parts by weight total monomer; with 
   (b) an aziridine crosslinking agent of the formula:   
       
         
           
           
               
               
           
         
         wherein 
         each R 3  is independently H or a C 1 -C 4  alkyl group, 
         z is 0, 1 or 2; 
         R 4  is a divalent alkylene, optionally substituted by one or more catenary ester groups, urea groups and/or urethane groups, and 
         R 6  is a monovalent alkyl or aryl group; and
 (c) heating the mixture to effect crosslinking. 
 
       
     
     
         2 . The method of  claim 1 , wherein said crosslinking agent is of the formula: 
       
         
           
           
               
               
           
         
       
       wherein
 each R 3  is independently H or a C 1 -C 4  alkyl group, 
 R 7  is a divalent alkylene, 
 X 1  is —NR 3 — or —O—, 
 R 6  is a monovalent alkyl or aryl group, and 
 z is 0, 1 or 2. 
 
     
     
         3 . The method of  claim 1 , wherein said crosslinking agent is of the formula: 
       
         
           
           
               
               
           
         
       
       where
 R 2  is H, or CH 3 ; 
 each R 3  is independently H or a C 1 -C 4  alkyl group, 
 z is 0, 1 or 2; 
 R 7  is a divalent alkylene, 
 X 1  is —NR 3 — or —O—, and 
 R 6  is a monovalent alkyl or aryl group. 
 
     
     
         4 . The method of  claim 1 , wherein said crosslinking agent is of the formula: 
       
         
           
           
               
               
           
         
       
       where
 R 2  is H, or CH 3 ; 
 each R 3  is independently H or a C 1 -C 4  alkyl group, 
 z is 0, 1 or 2; 
 X 1  is —NR 3 — or —O—, and 
 R 6  is a monovalent alkyl or aryl group. 
 
     
     
         5 . The method of  claim 1  wherein the acid-functional (meth)acrylate copolymer comprises:
 i. 85 to 99 parts by weight of an (meth)acrylic acid ester of non-tertiary alcohol;   ii. 1 to 15 parts by weight of an acid functional ethylenically unsaturated monomer;   iii. 0 to 10 parts by weight of a non-acid functional, ethylenically unsaturated polar monomer;   iv. 0 to 5 parts vinyl monomer; and   v. 0 to 5 parts of a multifunctional (meth)acrylate;   based on 100 parts by weight total monomer.   
     
     
         6 . The method of  claim 1  comprising 0.005 to 5.0 parts by weight of an aziridine crosslinking agent, relative to 100 parts of the copolymer. 
     
     
         7 . The method of  claim 1  wherein said non-acid functional, ethylenically unsaturated polar monomer is selected from 2-hydroxyethyl (meth)acrylate; N-vinylpyrrolidone; N-vinylcaprolactam; acrylamide; t-butyl acrylamide; dimethylamino ethyl acrylamide; N-octyl acrylamide; poly(alkoxyalkyl) (meth)acrylates; poly(vinyl methyl ether); and mixtures thereof. 
     
     
         8 . The method of  claim 1  wherein said copolymer comprises 1 to 5 parts by weight of acrylic acid and 1 to 5 parts by weight of a non-acid functional, ethylenically unsaturated polar monomer. 
     
     
         9 . The method of  claim 1  wherein said composition is an aqueous emulsion. 
     
     
         10 . The method of  claim 9  wherein said emulsion comprises:
 (a) 30 to about 70 weight percent, based on the total weight of the emulsion, of the composition of  claim 1 , and   (b)  30  to  70  weight percent of an aqueous phase comprising a surfactant, based on the total weight of the emulsion.   
     
     
         11 . The method of  claim 10  wherein said emulsion has a pH of >4. 
     
     
         12 . The method of  claim 1  wherein the acid functional monomer is selected from acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, oleic acid, β-carboxyethyl (meth)acrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, vinyl phosphonic acid, and mixtures thereof. 
     
     
         13 . The method of  claim 1  comprising 1 to 5 parts of a vinyl monomer selected from vinyl esters, styrene, substituted styrene, vinyl halide, vinyl propionate, and mixtures thereof. 
     
     
         14 . The method of  claim 1  wherein said non-tertiary alcohol of said (meth)acrylic acid ester of non-tertiary alcohol is selected from 2-octanol or dihydrocitronellol. 
     
     
         15 . The method of  claim 1  wherein said composition comprises a syrup polymer comprising:
 a) first component solute polymer comprising:
 i. 85 to 99 parts by weight of an (meth)acrylic acid ester of non-tertiary alcohol; 
 ii. 1 to 15 parts by weight of an acid functional monomer; 
 iii. 0 to 10 parts by weight of a second, non-acid functional, polar monomer; 
 iv. 0 to 5 parts vinyl monomer, and 
   b) a second component comprising at least one free-radically polymerizable solvent monomer, and   c) an aziridine crosslinking agent of the formula;   
       
         
           
           
               
               
           
         
         wherein 
         each R 3  is independently H or a C 1 -C 4  alkyl group, 
         z is 0, 1 or 2; 
         R 4  is a divalent alkylene, optionally substituted by one or more catenary ester groups, urea groups and/or urethane groups, and 
         R 6  is a monovalent alkyl or aryl group. 
       
     
     
         16 . Compounds of the formulas: 
       
         
           
           
               
               
           
         
       
       where
 R 2  is H, or CH 3 ; 
 each R 3  is independently H or a C 1 -C 4  alkyl group, 
 R 8  is a monovalent alkyl group an aryl group; and 
 z is 0, 1 or 2; or 
 
       
         
           
           
               
               
           
         
       
       where
 R 2  is H, or CH 3 ; 
 each R 3  is independently H or a C 1 -C 4  alkyl group, 
 R 9  is a monovalent alkyl or aryl group, and 
 z is 0, 1 or 2.