Process for improving water-whitening resistance of pressure sensitive adhesives

Abstract

Pressure sensitive adhesive compositions having enhanced resistance to water-whitening comprising an aqueous emulsion polymer are disclosed. The polymer comprises the polymerization reaction product of a polymerizable aqueous emulsion comprising: (i) at least one hydrophobic alkyl acrylate or alkyl methacrylate ester of an alcohol, (ii) at least about 1 wt. % of at least one hydrophilic monomer, (iii) at least about 5 wt. % of at least one partially hydrophilic alkyl acrylate or alkyl methacrylate ester of an alcohol, and (iv) a water-soluble or water-dispersible polymerizable surfactant selected from compounds having a terminal allyl amine moiety, substituted phenyl compounds having at least one alkenyl substituent, polyoxyalkylene-1-(allyloxymethyl) alkyl ether sulfate salts, or mixtures thereof, and the average particle size of the polymer is less than or equal to 200 nm. Also disclosed are processes for preparing same.

1 . A process for preparing a pressure sensitive adhesive having enhanced resistance to water-whitening comprising: 
 (a) contacting water, an effective amount of a water-soluble or water-dispersible polymerizable surfactant selected from compounds having a terminal allyl amine moiety, substituted phenyl compounds having at least one alkenyl substituent, polyoxyalkylene-1-(allyloxymethyl) alkyl ether sulfate salts, or mixtures thereof, and an initial amount of polymerization initiator to form a mixture;    (b) continuously adding monomers and, optionally, additional water to said mixture and polymerizing the resultant emulsion to form a latex emulsion, wherein additional polymerization initiator is added during the polymerization of said emulsion, and wherein said monomers comprise: (i) at least one hydrophobic alkyl acrylate or alkyl methacrylate ester of an alcohol, (ii) at least about 1 wt. % of at least one hydrophilic monomer, (iii) at least about 5 wt. % of at least one partially hydrophilic alkyl acrylate or alkyl methacrylate ester of an alcohol, and (iv) a water-soluble or water-dispersible polymerizable surfactant selected from compounds having a terminal allyl amine moiety, substituted phenyl compounds having at least one alkenyl substituent, polyoxyalkylene-1-(allyloxymethyl) alkyl ether sulfate salts, or mixtures thereof, wherein the wt. % of monomers (i), (ii) and (iii) are based on the total weight of monomers (i), (ii) and (iii); and    (c) adjusting the pH of said latex emulsion with a suitable base to a pH of about 6.5 to about 9;    wherein said effective amount of water-soluble or water-dispersible polymerizable surfactant in said mixture is that amount necessary to produce said pressure sensitive adhesive having an average particle size of less than or equal to 200 nm.    
     
     
         2 . The process of claim.  1  wherein the amount of monomer (i) is about 70 to about 90 wt. %.  
     
     
         3 . The process of  claim 2  wherein the amount of monomer (i) is about 75 to about 85 wt. %.  
     
     
         4 . The process of  claim 1  wherein the amount of monomer (ii) is about 2 to about 10 wt. %.  
     
     
         5 . The process of  claim 4  wherein the amount of monomer (ii) is about 4 to about 8 wt. %.  
     
     
         6 . The process of  claim 1  wherein the amount of monomer (iii) is about 5 to about 20 wt. %.  
     
     
         7 . The process of  claim 6  wherein the amount of monomer (iii) is about 5 to about 18 wt. %.  
     
     
         8 . The process of  claim 1  wherein said pressure sensitive adhesive has an average particle size of less than or equal to 100 nm.  
     
     
         9 . The process of  claim 1  wherein said monomer (i) is at least one hydrophobic alkyl acrylate or alkyl methacrylate ester of an alcohol wherein the alkyl portion contains at least 4 carbon atoms.  
     
     
         10 . The process of  claim 9  wherein said monomer (i) is selected from isooctyl acrylate, 4-methyl-2-pentyl acrylate, 2-methylbutyl acrylate, isoamyl acrylate, sec-butyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isodecyl methacrylate, isononyl acrylate, isodecyl acrylate, or mixtures thereof.  
     
     
         11 . The process of  claim 9  wherein said monomer (i) is selected from n-butyl acrylate, 2-ethylhexyl acrylate, or mixtures thereof.  
     
     
         12 . The process of  claim 1  wherein said monomer (ii) is selected from a monoolefinic monocarboxylic acid, a monoolefinic dicarboxylic acid, or mixtures thereof.  
     
     
         13 . The process of  claim 12  wherein said monomer (ii) is selected from acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, crotonic acid, or mixtures thereof.  
     
     
         14 . The process of  claim 13  wherein said monomer (ii) is selected from acrylic acid, methacrylic acid, or mixtures thereof.  
     
     
         15 . The process of  claim 1  wherein said monomer (iii) is selected from methyl acrylate, methyl methacrylate, ethyl acrylate, or mixtures thereof.  
     
     
         16 . The process of  claim 15  wherein said monomer (iii) is selected from methyl acrylate, methyl methacrylate, or mixtures thereof.  
     
     
         17 . The process of  claim 1  wherein the total amount of water-soluble or water-dispersible polymerizable surfactant added in steps (a) and (b) is about 0.1 to about 5 wt. % of the total weight of monomers (i), (ii) and (iii) charged.  
     
     
         18 . The process of  claim 17  wherein the total amount of water-soluble or water-dispersible polymerizable surfactant added in steps (a) and (b) is about 0.5 to about 2 wt. % of the total weight of monomers (i), (ii) and (iii) charged.  
     
     
         19 . The process of  claim 17  wherein the amount of water-soluble or water-dispersible polymerizable surfactant in said mixture of step (a) is at least about 20 wt. % of the total amount of water-soluble or water-dispersible polymerizable surfactant added in steps (a) and (b).  
     
     
         20 . The process of  claim 1  wherein said polymerizable surfactant has a hydrophilic portion selected from a sulfonate allyl amine moiety, a sulfate allyl amine moiety, or a phosphate allyl amine moiety, and a hydrophobic portion selected from —R, or a group having the formula  
         RO—(CH 2 CH 2 O)n,—;  
       wherein R is an alkyl group or an alkyl-substituted phenyl group wherein the alkyl group has 1 to 20 carbon atoms, and n is an integer from 2 to 100.  
     
     
         21 . The process of  claim 20  wherein n is an integer from 2 to 15.  
     
     
         22 . The process of  claim 1  wherein said polymerizable surfactant is an allyl amine salt of an alkyl benzene sulfonate having the formula  
       
         
           
           
               
               
           
         
       
       wherein R 1  is an alkyl group having 1 to 20 carbon atoms, and X +  is selected from  + NH 3 ,  + NH 2 R 4 , or  + NHR 4 R 5 , wherein R 4  and R 5  are independently selected from C 1 -C 4  alkyl or hydroxyalkyl groups.  
     
     
         23 . The process of  claim 22  wherein said polymerizable surfactant is an allyl amine salt of dodecylbenzene sulfonate.  
     
     
         24 . The process of  claim 1  wherein said polymerizable surfactant is an allyl amine salt of an alkyl ether sulfate having the formula  
       
         
           
           
               
               
           
         
       
       wherein R 2  is an alkyl group having 1 to 20 carbon atoms, n is an integer from 2 to 100, and X +  is selected from  + NH 3 ,  + NH 2 R 4 , or  + NHR 4 R 5 , wherein R4 and R 5  are independently selected from C 1 -C 4  alkyl or hydroxyalkyl groups.  
     
     
         25 . The process of  claim 24  wherein n is an integer from 2 to 15.  
     
     
         26 . The process of  claim 25  wherein said polymerizable surfactant is an allyl amine salt of laureth sulfate.  
     
     
         27 . The process of  claim 1  wherein said polymerizable surfactant is an allyl amine salt of a phosphate ester having the formula  
       
         
           
           
               
               
           
         
       
       wherein R 3  is an alkyl or alkyl-substituted phenyl group wherein the alkyl group has 1 to 20 carbon atoms, n is an integer from 2 to 100, and X + is selected from  + NH 3 ,  + NH 2 R 4 , or  + NHR 4 R 5 , wherein R 4  and R 5  are independently selected from C 1 -C 4  alkyl or hydroxyalkyl groups.  
     
     
         28 . The process of  claim 27  wherein n is an integer from 2 to 15.  
     
     
         29 . The process of  claim 27  wherein said polymerizable surfactant is an allyl amine salt of nonylphenol ethoxylate (9 moles EO) phosphate ester.  
     
     
         30 . The process of  claim 1  wherein said polymerizable surfactant is an allyl amine salt of a sulfate having the formula  
         R 6 —SO 3   −+ X—CH 2 —CH═CH 2    
       wherein R 6  is an alkyl group having 6 to 20 carbon atoms, and X + is selected from  + NH 3 ,  + NH 2 R 4 , or  + NHR 4 R 5 , wherein R 4  and R 5  are independently selected from C 1 -C 4  alkyl or hydroxyalkyl groups.  
     
     
         31 . The process of  claim 30  wherein R 6  is an alkyl group having 10 to 18 carbon atoms.  
     
     
         32 . The process of  claim 1  wherein said polymerizable surfactant is a substituted phenyl compound having the formula  
       
         
           
           
               
               
           
         
       
       wherein R 7  is an alkyl, alkenyl or aralkyl group containing 6 to 18 carbon atoms; R 8  is a hydrogen atom or an alkyl, alkenyl or aralkyl group containing 6 to 18 carbon atoms; R 9  is a hydrogen atom or a propenyl group; A is an unsubstituted or substituted alkylene group containing 2 to 4 carbon atoms; n is an integer of 1 to about 200; and M is an alkali metal, an ammonium ion, or an alkanolamine residue.  
     
     
         33 . The process of  claim 30  wherein said polymerizable surfactant is a substituted phenyl compound having the formula  
       
         
           
           
               
               
           
         
       
     
     
         34 . The process of  claim 33  wherein R 7  is alkyl, A is ethylene, and M is alkali metal or ammonium.  
     
     
         35 . The process of  claim 34  wherein R 7  is nonyl, n is about 10 to about 30, and M is ammonium.  
     
     
         36 . The process of  claim 1  wherein said polymerizable surfactant is a polyoxyalkylene-1-(allyloxymethyl) alkyl ether sulfate salt having the formula:  
       
         
           
           
               
               
           
         
       
       wherein R 10  is an alkyl group containing 8 to 30 carbon atoms; R 11  is hydrogen or methyl; A is an unsubstituted or substituted alkylene group having 2 to 4 carbon atoms; n is 0 or an integer of 1 to about 200; and M is an alkali metal, an ammonium ion, or an alkanolamine residue.  
     
     
         37 . The process of  claim 36  wherein said polymerizable surfactant is a polyoxyalkylene-1-(allyloxymethyl) alkyl ether sulfate salt having the formula:  
       
         
           
           
               
               
           
         
       
       wherein R 10  is an alkyl group containing 8 to 14 carbon atoms; and n is an integer of 1 to about 200.  
     
     
         38 . The process of  claim 1  wherein the total amount of said polymerization initiator added is about 0.01 to about 0.5 wt. % of the total weight of monomers (i), (ii) and (iii) charged.  
     
     
         39 . The process of  claim 1  further comprising the addition of a vinyl ester of a C 2  to C 12  carboxylic acid to said latex emulsion after the conversion of monomers (i), (ii) and (iii) is greater than 90%.  
     
     
         40 . The process of  claim 39  wherein said vinyl ester is added to said latex emulsion after the conversion of monomers (i), (ii) and (iii) is greater than 95%.  
     
     
         41 . The process of  claim 1  further comprising the addition of a vinyl ester of a C 2  to C 12  carboxylic acid to said latex emulsion after the addition of monomers is completed.  
     
     
         42 . A pressure sensitive adhesive composition having enhanced resistance to water-whitening comprising an aqueous emulsion polymer prepared according to the process of  claim 1 .  
     
     
         43 . A pressure sensitive adhesive composition having enhanced resistance to water-whitening comprising an aqueous emulsion polymer prepared according to the process of  claim 40 .  
     
     
         44 . A process for preparing a pressure sensitive adhesive having enhanced resistance to water-whitening comprising: 
 (a) contacting water, an effective amount of a water-soluble or water-dispersible polymerizable surfactant selected from compounds having a terminal allyl amine moiety, substituted phenyl compounds having at least one alkenyl substituent, polyoxyalkylene-1-(allyloxymethyl) alkyl ether sulfate salts, or mixtures thereof, and an initial amount of polymerization initiator to form a mixture;    (b) continuously adding monomers and, optionally, additional water to said mixture and polymerizing the resultant emulsion to form a latex emulsion, wherein additional polymerization initiator is added during the polymerization of said emulsion, and wherein said monomers comprise: (i) about 70 to about 90 wt. % of at least one hydrophobic alkyl acrylate ester selected from n-butyl acrylate, 2-ethylhexyl acrylate, or mixtures thereof, (ii) about 2 to about 10 wt. % of at least one hydrophilic monomer selected from acrylic acid, methacrylic acid, or mixtures thereof, (iii) about 5 to about 20 wt. % of methyl acrylate, and (iv) a water-soluble or water-dispersible polymerizable surfactant selected from compounds having a terminal allyl amine moiety, substituted phenyl compounds having at least one alkenyl substituent, polyoxyalkylene-1-(allyloxymethyl) alkyl ether sulfate salts, or mixtures thereof, wherein the wt. % of monomers (i), (ii) and (iii) are based on the total weight of monomers (i), (ii) and (iii); and    (c) adjusting the pH of said latex emulsion with a suitable base to a pH of about 6.5 to about 9;    wherein said effective amount of water-soluble or water-dispersible polymerizable surfactant in said mixture is that amount necessary to produce said pressure sensitive adhesive having an average particle size of less than or equal to 200 nm.