Latex binder for nonwoven fibers and article made therewith

Abstract

The invention relates to a latex that may be utilized as a binder for nonwoven applications to form a permeable sublayer of personal hygiene articles. The latex is prepared by a process including the steps of (1) polymerizing a monomer mixture comprising styrene, itaconic acid, surfactant and water soluble free radical initiator to form a seed; (2) sequentially adding equal increments of a monomer mixture of styrene, butadiene and acrylic acid to the seed under emulsion polymerization conditions to form a styrene-butadiene-acrylic acid copolymer; and then (3) neutralizing the styrene-butadiene-acrylic acid copolymer to a pH of about 4.5 to 7 to form the latex.

What is claimed:  
     
         1 . A latex which is particularly beneficial for utilization as a binder for nonwoven applications made by the process which comprises the steps of: 
 (1) polymerizing a monomer mixture comprising styrene, itaconic acid, surfactant and water soluble free radical initiator to form a seed;    (2) adding a monomer mixture of styrene, butadiene and chain transfer agent and reacting the mixture to between 40-95% conversion;    (3) sequentially adding equal increments of a monomer mixture of styrene, butadiene, acrylic acid and optional functional monomers, in the presence of a chain transfer agent to (2) under emulsion polymerization conditions and reacting to more than 99% conversion; and then    (4) neutralizing the copolymer from (3) to a pH of about 4.5 to 7 to form the latex.    
     
     
         2 . The latex of  claim 1  wherein the monomer mixture includes about 20-80 wt % styrene.  
     
     
         3 . The latex of  claim 1  wherein the monomer mixture also includes about 0.5-2.5 wt % itaconic acid, about 20-80 wt % butadiene and about 6-10 wt % acrylic acid.  
     
     
         4 . The latex of  claim 3  wherein the monomer mixture includes 8 wt %. acrylic acid.  
     
     
         5 . The latex of  claim 3  wherein the monomer mixture includes 2 wt % itaconic acid.  
     
     
         6 . The latex of  claim 1  wherein the monomer mixture includes about 0.05-2.0 wt % surfactant.  
     
     
         7 . The latex of  claim 1  wherein the copolymer is neutralized by addition of a base selected from potassium hydroxide, sodium bicarbonate, and ammonium hydroxide, sodium hydroxide.  
     
     
         8 . A method for making a composite useful as a personal hygiene article which comprises: 
 (1) treating a nonwoven fabric with a latex binder to form a permeable sublayer, the latex prepared by a process which comprises the steps of: 
 (a) polymerizing a monomer mixture comprising styrene, itaconic acid, surfactant and water soluble free radical initiator to form a seed;  
 (b) adding a monomer mixture of styrene, butadiene and chain transfer agent and reacting the mixture to between 40-95% conversion;  
 (c) sequentially adding equal increments of a monomer mixture of styrene, butadiene, acrylic acid and optional functional monomers, in the presence of a chain transfer agent to (b) under emulsion polymerization conditions and reacting to more than 99% conversion; and then  
 (d) neutralizing the copolymer from (c) to a pH of about 4.5 to 7 to form the latex;  
   (2) providing at least one fluid permeable top sheet layer and at least one substantially fluid impermeable backsheet layer; and    (3) interposing the sublayer material between the topsheet layer and backsheet layer.    
     
     
         9 . The method of  claim 8  wherein the permeable sublayer of the personal hygiene article is a web comprised of randomly arranged nonwoven fibers having an open structure and high loft.  
     
     
         10 . The method of  claim 9  wherein the web is formed by carding.  
     
     
         11 . The method of  claim 9  wherein the fibers are selected from natural textile fibers, artificial organic textile fibers, vinyl resin fibers and mixtures thereof.  
     
     
         12 . The method of  claim 9  wherein the fibers are selected from polyolefins, polyesters, acrylics, and polyamides.  
     
     
         13 . The method of  claim 12  wherein the polyolefin fibers include polypropylene, polyethylene, polybutene and their copolymers.  
     
     
         14 . The method of  claim 12  wherein the polyester fibers include any long synthetic polymer composed of at least 85% by weight of an ester of a dihydric alcohol and terephthalic acid.  
     
     
         15 . The method of  claim 12  wherein the acrylic fibers include any fiber forming substance containing a long chain synthetic polymer composed of at least 85% by weight acrylonitrile units —CH 2  CH(CN)—.  
     
     
         16 . The method of  claim 9  wherein the fibers are graphite fibers.  
     
     
         17 . The method of  claim 9  wherein the fibers are of a length of about 0.25 to 2 inches and about 1.2-15 denier.  
     
     
         18 . The method of  claim 8  wherein the latex binder is applied on the fiber mat is about 15-40 wt %.