PROCESS FOR REMOVING FLUORINATED EMULSIFIER FROM FLUOROPOLMER DISPERSIONS USING AN ANION-EXCHANGE RESIN AND A pH-DEPENDENT SURFACTANT AND FLUOROPOLYMER DISPERSIONS CONTAINING A pH-DEPENDENT SURFACTANT

Abstract

A process of reducing the amount of fluorinated emulsifiers in fluoropolymer dispersions by contacting the fluoropolymer dispersion with an anion exchange resin in the presence of a pH-dependent surfactant, and fluoropolymer dispersions containing the pH-dependent surfactant and uses thereof.

1 . A process of reducing the amount of fluorinated emulsifier in a fluoropolymer dispersion, the process comprising contacting the fluoropolymer dispersion with an anion exchange resin in the presence of a pH-dependent surfactant to remove at least a portion of the fluorinated emulsifier wherein the dispersion is contacted with the anion exchange resin at a pH at which the pH-dependent surfactant is in the non-ionic form. 
     
     
         2 . The process according to  claim 1  wherein the pH-dependent surfactant has a reduced surface activity in its cationic form compared to its non-ionic form. 
     
     
         3 . The process according to  claim 1  wherein the pH-dependent surfactant, in its non-ionic form, is an amine. 
     
     
         4 . The process according to  claim 1  wherein the pH-dependent surfactant in its non-ionic form is a tertiary amine with at least one of the three residues linked to the N-atom being a polyoxy alkyl residue and the remaining residues being a non-polar carbohydrate. 
     
     
         5 . The process according to  claim 1  wherein the pH-dependent surfactant in its non-ionic form is a tertiary amine with one of the three residues linked to the N-atom being a polyoxy alkyl and the remaining residue(s) being a linear or branched alkyl. 
     
     
         6 . The process according to  claim 1  wherein the pH-dependent surfactant in its non-ionic form corresponds to the general formula 
       
         
           
           
               
               
           
         
       
       with m and n being independent of each other an integer from 1 to 15 and R being a branched, saturated or non-saturated, linear or cyclic alkyl, alkylamine, polyamine alkyl, alkyloxy or polyoxy alkyl residue. 
     
     
         7 . The process according to  claim 1  wherein the fluoropolymer dispersion prior to being contacted with the anion exchange resin comprises at least about 0.02% by weight based on the solid content of the dispersion of the fluorinated emulsifier. 
     
     
         8 . The process according to  claim 1  wherein the fluorinated emulsifier is a perfluorinated carboxylic acid. 
     
     
         9 . The process according to  claim 1  wherein the fluorinated emulsifier corresponds to the general formula:
   [R f -O-L-COO] i X i+     
       wherein L represents a linear partially or fully fluorinated alkylene group or an aliphatic hydrocarbon group R f  represents a linear partially or fully fluorinated aliphatic group or a linear partially or fully fluorinated aliphatic group interrupted with one or more oxygen atoms, X i+ represents a cation having the valence i and i is 1, 2 or 3. 
     
     
         10 . An aqueous fluoropolymer dispersion comprising:
 i) from about 5% to about 70% by weight based on the weight of the dispersion of a fluoropolymer, and
 ii) at least about 0.02% by weight based on the solid content of the dispersion of a pH-dependent surfactant, the pH-dependent surfactant having depending on the pH of the dispersion either a cationic or a non-ionic form and wherein the pH-depedent surfactant is capable in its non-ionic form of stabilising the dispersion. 
   
     
     
         11 . The aqueous fluoropolymer dispersion according to  claim 10  further comprising less than about 0.02% by weight based on the weight of the solid content of the dispersion of a fluorinated emulsifier. 
     
     
         12 . Process of preparing a composition containing a coagulated fluoropolymer said process comprising:
 i) providing an aqueous fluoropolymer dispersion containing:
 a) from about 5% to about 70% by weight based on the weight of the dispersion of a fluoropolymer, and 
 b) at least about 0.02% by weight based on the solid content of the dispersion of a pH-dependent surfactant wherein the pH-dependent surfactant has, depending on the pH of the dispersion, either a cationic or a non-ionic form and is capable in its non-ionic form of stabilising the dispersion; 
   ii) reducing the pH of the dispersion to a level at which the pH-dependent surfactant is in its cationic form,
 iii) coagulating the dispersion. 
   
     
     
         13 . The process according to  claim 12 , wherein the dispersion further comprises less than about 0.02% by weight based on the solid content of the dispersion of a fluorinated emulsifier. 
     
     
         14 . The process according to  claim 12  further comprising adding one or more coating ingredients to the dispersion before carrying out iii). 
     
     
         15 . A coated substrate comprising a coagulated fluoropolymer obtainable by the process according to  claim 12 . 
     
     
         16 - 17 . (canceled)