Process for reducing the amount of fluorinated surfactant in aqueous fluoropolymer dispersions

Abstract

The present invention provides a process of reducing the amount of fluorinated emulsifier in an aqueous fluoropolymer dispersion by contacting the aqueous fluoropolymer dispersion with an anion exchange resin in a non-fixed resin bed, the process comprising: (a) mixing the aqueous fluoropolymer dispersion with an effective amount of a surfactant so as to stabilize the fluoropolymer dispersion while being contacted with the anion exchange resin; (b) contacting the aqueous fluoropolymer dispersion with an anion exchange resin by agitating the aqueous fluoropolymer dispersion with an effective amount of anion exchange resin for a time of less than 4 hours to reduce the amount of fluorinated emulsifier in the aqueous fluoropolymer dispersion to a desired level; and (c) separating the anion exchange resin from the aqueous fluoropolymer dispersion.

1 . A composition comprising an aqueous fluoropolymer dispersion produced by a process comprising: 
 a. mixing the aqueous fluoropolymer dispersion with an effective amount of a surfactant so as to stabilize the fluoropolymer dispersion while being contacted with the anion exchange resin;    b. contacting the aqueous fluoropolymer dispersion with an anion exchange resin by agitating the aqueous fluoropolymer dispersion with an anion exchange resin for a time of less than 4 hours; and    c. separating the anion exchange resin from the aqueous fluoropolymer dispersion.    
     
     
         2 . Composition according to  claim 1  wherein the time is between 5 minutes and 2 hours.  
     
     
         3 . Composition according to  claim 1  wherein the surfactant to stabilize the fluoropolymer dispersion is a non-ionic surfactant  
     
     
         4 . Composition according to  claim 1  wherein the anion exchange resin is added in an amount corresponding to a volume ratio of anion exchange resin to fluoropolymer dispersion of at least 15:85.  
     
     
         5 . Composition according to  claim 1  wherein the surfactant to stabilize the fluoropolymer dispersion is used in an amount of 1 to 5% by weight relative to the total amount of solids in said aqueous fluoropolymer dispersion.  
     
     
         6 . Composition according to  claim 1  wherein the fluoropolymer comprises a fluoropolymer selected from the group consisting of polytetrafluoroethylene, modified polytetrafluoroethylene and thermoplastic melt processible fluoropolymers.  
     
     
         7 . Composition according to  claim 1  wherein the fluorinated emulsifier is a perfluoroalkanoic acid or salt thereof.  
     
     
         8 . Composition comprising an aqueous fluoropolymer dispersion produced by a process comprising: 
 (a) mixing the aqueous fluoropolymer dispersion with an effective amount of a surfactant so as to stabilize the fluoropolymer dispersion while being contacted with the anion exchange resin;    (b) contacting the aqueous fluoropolymer dispersion with the anion exchange resin by agitating the aqueous fluoropolymer dispersion with an effective amount of anion exchange resin and for a time sufficient to reduce the amount of fluorinated emulsifier in the aqueous dispersion to a desired level;    (c) separating the anion exchange resin from the fluoropolymer dispersion; and    (d) re-using in step (b) at least once the anion exchange resin separated in step (c) without having been regenerated.    
     
     
         9 . Composition according to  claim 8  wherein the anion exchange resin in step (b) is used in a volume ratio with respect to the aqueous fluoropolymer dispersion of at least 15:85.  
     
     
         10 . Composition according to  claim 9  wherein the volume ratio is between 15:85 and 50:50.  
     
     
         11 . Composition according to  claim 8  wherein the anion exchange resin is re-used to an extent of between 10% and 90% of the anion exchange resins capacity.  
     
     
         12 . Composition according to  claim 8  wherein the surfactant to stabilize the aqueous fluoropolymer dispersion is a non-ionic surfactant.  
     
     
         13 . A kit for reducing the amount of anionic surfactant in an aqueous fluoropolymer dispersion comprising: 
 a. an aqueous fluoropolymer dispersion containing from 0.5 to 15 percent by weight based on the weight of solids in the fluoropolymer dispersion of a non-ionic surfactant, wherein the aqueous fluoropolymer dispersion is in fluid contact with;    b. an anion exchange resin capable of being agitated so as to reduce the amount of fluorinated emulsifier in the aqueous dispersion.    
     
     
         14 . Kit according to  claim 13  wherein the non-ionic surfactant is represented by a formula R 1 —O—[CH 2 CH 2 O] n —[R 2 O] m R 3 , wherein R 1  represents an aromatic or aliphatic hydrocarbon group having at least 8 carbon atoms, R 2  represents an alkylene having 3 carbon atoms, R 3  represents hydrogen or a C 1 -C 3  alkyl group, n has a value of 0 to 40, m has a value of 0 to 40 and the sum of n+m being at least 2.  
     
     
         15 . Kit according to  claim 13  wherein the anion exchange resin present in an amount corresponding to a volume ratio of anion exchange resin to fluoropolymer dispersion of at least 15:85.  
     
     
         16 . Kit according to  claim 13  wherein the non-ionic surfactant is present in an amount of 1 to 5% by weight relative to the total amount of solids in the aqueous fluoropolymer dispersion.  
     
     
         17 . Kit according to  claim 13  wherein the fluoropolymer comprises a fluoropolymer selected from the group consisting of polytetrafluoroethylene, modified polytetrafluoroethylene and thermoplastic melt processible fluoropolymers.  
     
     
         18 . Kit according to  claim 1  wherein the fluorinated emulsifier is a perfluoroalkanoic acid or salt thereof.  
     
     
         19 . Kit according to  claim 19  wherein the non-ionic surfactant is represented by a formula:  
       
         
           
           
               
               
           
         
       
       wherein R is an alkyl group of 4 to 20 carbon atoms and r represents a value of 4 to 20.