Binder composition

Abstract

A binder composition is provided including a copolymer binder and a hydrophobically modified alkali soluble emulsion polymer. The binder composition is useful as a component of paper coating compositions. As provided is a coating process including the paper coating composition and a paper substrate coated with a paper coating including the binder composition.

We claim:  
     
         1 ) A binder composition consisting essentially of: 
 a) from 80 to 98 weight % of a copolymer binder comprising as polymerized units: 
 i) 98.5 to 70 weight % of at least one first monomer selected from the group consisting of C 2 -C 8  esters of methacrylic acid and acrylic acid;  
 ii) 1 to 30 weight % of at least one second monomer selected from the group consisting of styrene, acrylonitrile, and methyl methacrylate;  
 iii) 0.5 to 5 weight % of at least one third monomer selected from the group consisting of acrylic acid, methacrylic acid, acrylamide, methacrylamide, and 2-acrylamido-2-methylpropanesulfonic acid; wherein said copolymer binder is an emulsion polymer and has a glass transition temperature in the range of −35° C. to 0° C.; and  
   b) from 20 to 2 weight % of a hydrophobically modified alkali soluble emulsion.    
     
     
         2 ) The composition of  claim 1  further including sufficient surfactant to ensure stability of said binder composition.  
     
     
         3 ) The composition of  claim 1  wherein said at least one first monomer is selected from the group consisting of butyl acrylate, ethyl acrylate, and 2-ethyl hexyl acrylate.  
     
     
         4 ) The composition of  claim 1  wherein the average particle diameter of said copolymer binder is in the range of 0.10 μm to 0.50 μm.  
     
     
         5 ) A coating process comprising: 
 a) preparing a paper coating composition by admixing ingredients comprising 100 parts by dry weight pigment slurry; from 1.6 to 9.8 parts by dry weight copolymer binder comprising as polymerized units 98.5 to 70% of at least one first monomer selected from the group consisting of C 2 -C 8  esters of methacrylic acid and acrylic acid, 1 to 30% of at least one second monomer selected from the group consisting of styrene, acrylonitrile, and methyl methacrylate, 0.5 to 5% of at least one third monomer selected from the group consisting of acrylic acid, methacrylic acid, acrylamide, methacrylamide, and 2-acrylamido-2-methylpropanesulfonic acid; wherein said copolymer binder is an emulsion polymer and has a glass transition temperature in the range of −35° C. to 0° C.; and from 0.04 to 2.0 parts by dry weight hydrophobically modified alkali soluble emulsion;     wherein said paper coating composition has a pH in the range of 6 to 10;     and wherein said paper coating composition has a solids level in the range of 30 to 75 weight %;    b) applying said paper coating composition onto a paper substrate; and    c) drying said paper substrate coated with said paper coating composition.    
     
     
         6 ) The coating process of  claim 5  wherein said paper coating composition has a solids level in the range of 50 to 70 weight %.  
     
     
         7 ) The coating process of  claim 5  wherein the coating speed is greater than 600 meters per minute.  
     
     
         8 ) The coating process of  claim 5  wherein the dry weight of said paper coating composition on said paper substrate is in the range of 3 to 12 grams per square meter.  
     
     
         9 ) A paper substrate coated with a paper coating composition comprising: 
 a) 100 parts by weight pigment;    b) from 1.6 to 9.8 parts by weight copolymer binder comprising as polymerized units: 
 i) 98.5 to 70% first monomer selected from the group consisting of C 2 -C 8  esters of (meth)acrylic acid;  
 ii) 1 to 30% second monomer selected from the group consisting of styrene, acrylonitrile, and methyl methacrylate;  
 iii) 0.1 to 5% of at least one third monomer selected from the group consisting of acrylic acid, methacrylic acid, acrylamide, methacrylamide, and 2-acrylamido-2-methylpropanesulfonic acid;  
   wherein said copolymer binder is an emulsion polymer and has a glass transition temperature in the range of −35° C. to 0° C.; and    c) from 0.04 to 2.0 parts by weight hydrophobically modified alkali swellable emulsion polymer.    
     
     
         10 ) The paper substrate of  claim 10  wherein the coat weight of said paper coating composition is in the range of 3 to 12 grams per square meter.