Process for forming solid pressure sensitive adhesive polymer microspheres

Abstract

In forming pressure sensitive adhesive microspheres by copolymerizing a non-ionic monomer of an alkyl acrylate or alkyl methacrylate ester of a non-tertiary alcohol and an ionic monomer copolymerizable with said non-ionic monomer, non-free radically polymerizable acid is present during the polymerization to promote formation of solid rather than hollow microspheres and to reduce residual unconverted ionic monomer. These microspheres exhibit reduced adhesive transfer in downstream use as a repositionable pressure sensitive adhesive. A water soluble initiator is optionally added to the polymerization mixture after achieving about 90% conversion of the non-ionic monomer to further reduce residual unconverted ionic monomer.

1 . A process for preparing solid polymeric pressure sensitive adhesive microspheres comprising: 
 (a) contacting a polymerizable aqueous emulsion of at least one non-ionic monomer of an alkyl acrylate or alkyl methacrylate ester of a non-tertiary alcohol and at least one ionic monomer copolymerizable with said non-ionic monomer and at least one non-free radically polymerizable acid; and    (b) polymerizing the emulsion to form an aqueous suspension of said solid polymeric pressure sensitive adhesive microspheres;    wherein said non-free radically polymerizable acid is contacted with said polymerizable aqueous emulsion prior to achieving about 95% conversion of said non-ionic monomer.    
     
     
         2 . The process of  claim 1  wherein the alkyl group of said non-ionic monomer has from 4 to about 14 carbon atoms.  
     
     
         3 . The process of  claim 2  wherein said non-ionic monomer is selected from 2-ethyl hexyl acrylate or n-butyl acrylate.  
     
     
         4 . The process of  claim 1  wherein said ionic monomer is an alkali metal, ammonium or amine salt of an acid selected from a monoolefinic monocarboxylic acid, a monoolefinic dicarboxylic acid or mixtures thereof.  
     
     
         5 . The process of  claim 4  wherein said ionic monomer is an alkali metal, ammonium or amine salt of acrylic acid.  
     
     
         6 . The process of  claim 5  wherein said ionic monomer is ammonium acrylate or sodium acrylate.  
     
     
         7 . The process of  claim 4  wherein said ionic monomer is produced in situ by reaction of an acid selected from a monoolefinic monocarboxylic acid, a monoolefinic dicarboxylic acid or mixtures thereof with a compound selected from an alkali metal hydroxide, ammonium hydroxide or an amine, and wherein said non-free radically polymerizable acid is contacted with said polymerizable aqueous emulsion after formation of said ionic monomer.  
     
     
         8 . The process of  claim 1  wherein said non-free radically polymerizable acid is selected from acetic acid, hexanoic acid, phenyl undecanoic acid, stearic acid, hydrochloric acid, sulfuric acid or mixtures thereof.  
     
     
         9 . (canceled)  
     
     
         10 . The process of  claim 1  wherein an oil soluble, low water soluble initiator is added to said polymerizable aqueous emulsion and polymerization initiated after said non-free radically polymerizable acid is contacted with said polymerizable aqueous emulsion.  
     
     
         11 . The process of  claim 1  wherein an oil soluble, low water soluble initiator is added to said polymerizable aqueous emulsion and polymerization initiated before said non-free radically polymerizable acid is contacted with said polymerizable aqueous emulsion.  
     
     
         12 . The process of  claim 1  further comprising adding a water soluble initiator to the polymerization mixture after achieving about 90% conversion of said non-ionic monomer.  
     
     
         13 . The solid polymeric pressure sensitive adhesive microspheres produced by the process of any of claims  1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11  or  12 .  
     
     
         14 - 27 . (canceled)