Process to prepare pressure-sensitive hybrid composite latex adhesives

Abstract

The invention is directed to an improvement in a process for preparing an aqueous emulsion of pressure-sensitive adhesive based upon acrylic esters having a good balance of adhesive and cohesive properties and to the resulting emulsion. In the basic process, a pressure-sensitive adhesive formulation comprised of at least one ester of acrylic or methacrylic acid is polymerized in the presence of water and an emulsifier thereby forming an emulsion polymerized pressure-sensitive adhesive. The improvement resides in effecting the polymerization of said pressure-sensitive adhesive formulation comprised of at least one ester of acrylic or methacrylic acid in the presence of from 5 to 30 percent by weight of a styrene containing polymer containing at least 80 percent by weight styrene.

What is claimed is:  
     
         1 . In a pressure-sensitive adhesive comprised of emulsion polymerized units of (a) from 60 to 95 percent by weight of at least one at least one C 6-12  alkyl acrylate; (b) from 0 to 10 percent by weight of ethylenically unsaturated compounds having a glass transition temperature of above 0° C. and contain no functional groups other than an ethylenically unsaturated group; (c) from 0 to 10 percent by weight of ethylenically unsaturated compound having at least one acid or acid anhydride group; and (d) from 0 to 20 percent by weight of further ethylenically unsaturated compounds, weight percentages based on the total weight of polymer, the improvement which comprises forming said pressure-sensitive adhesive by emulsion polymerization in the presence of a styrene containing polymer.  
     
     
         2 . The pressure-sensitive adhesive of  claim 1  wherein the group (a) monomer includes 2-ethylhexyl acrylate.  
     
     
         3 . The pressure-sensitive adhesive of  claim 2  wherein the group (b) monomer includes butyl acrylate or methyl methacrylate.  
     
     
         4 . The pressure-sensitive adhesive of  claim 1  wherein the pressure-sensitive adhesive is comprised of from 5 to 30 percent by weight styrene containing polymer based upon the combined weight of said pressure-sensitive adhesive and said styrene containing polymer and polystyrene is the styrene containing polymer.  
     
     
         5 . The pressure-sensitive adhesive of  claim 4  wherein the polystyrene is present in an amount from 10 to 20 percent by weight.  
     
     
         6 . The pressure-sensitive adhesive of  claim 5  wherein said aqueous pressure-sensitive adhesive has a Tg of from −45° C. to −75° C.  
     
     
         7 . In a process for producing a pressure-sensitive adhesive comprised of emulsion polymerized units of (a) from 60 to 95 percent by weight of at least one at least one C 6-12  alkyl acrylate; (b) from 0 to 10 percent by weight of ethylenically unsaturated compounds having a glass transition temperature of above 0° C. and contain no functional groups other than an ethylenically unsaturated group; (c) from 0 to 10 percent by weight of ethylenically unsaturated compound having at least one acid or acid anhydride group; and (d) from 0 to 20 percent by weight of further ethylenically unsaturated compounds, the weight percentages based on the total weight of polymer, the improvement which comprises forming said pressure-sensitive adhesive by emulsion polymerization in the presence of a styrene containing polymer.  
     
     
         8 . The process of  claim 7  wherein the styrene containing polymer is present in an amount from 5 to 30 percent by weight of the pressure-sensitive adhesive.  
     
     
         9 . The process of  claim 8  wherein said pressure-sensitive adhesive has a Tg of from −45° C. to −75° C.  
     
     
         10 . The process of  claim 9  wherein the pressure-sensitive adhesive is polymerized in the presence of a polystyrene latex as the styrene containing polymer.  
     
     
         11 . The process of  claim 10  wherein the pressure-sensitive adhesive includes polymerized units of least one ester of acrylic or methacrylic acid selected from the group consisting of a C 1  to C 8  alkyl acrylate or a C 1  to C 8  alkyl methacrylate.  
     
     
         12 . The process of  claim 11  wherein said C 1  to C 8  alkyl acrylate and C 1  to C 8  alkyl methacrylate is selected from the group consisting of methyl methacrylate and 2-ethylhexyl acrylate.