Aqueous fluororesin dispersion and method for producing the same

Abstract

The present invention provides an aqueous fluororesin dispersion comprising a melt-processable fluororesin which is low in fluorinated surfactant concentration and excellent in dispersion stability even when the concentration of the melt-processable fluororesin is high. The present invention is related to an aqueous fluororesin dispersion comprising a melt-processable fluororesin particle dispersed in an aqueous medium, wherein a concentration of the melt-processable fluororesin is 55 to 75% by mass relative to the aqueous fluororesin dispersion, and a fluorinated surfactant content in the aqueous fluororesin dispersion is not higher than a level corresponding to 100 ppm of the melt-processable fluororesin.

1 . An aqueous fluororesin dispersion comprising a melt-processable fluororesin particle dispersed in an aqueous medium,
 wherein a concentration of the melt-processable fluororesin is 55 to 75% by mass relative to the aqueous fluororesin dispersion, and   a fluorinated surfactant content in the aqueous fluororesin dispersion is not higher than a level corresponding to 100 ppm of the melt-processable fluororesin.   
   
   
       2 . The aqueous fluororesin dispersion according to  claim 1 ,
 which has an electric conductivity of not lower than 10 μS/cm.   
   
   
       3 . The aqueous fluororesin dispersion according to  claim 1 ,
 wherein the melt-processable fluororesin particle has an average primary particle diameter of 10 to 400 nm.   
   
   
       4 . The aqueous fluororesin dispersion according to  claim 1   which is obtained from a raw aqueous fluororesin dispersion by a treatment with an ion exchange resin and a concentration by phase separation.   
   
   
       5 . The aqueous fluororesin dispersion according to  claim 4 ,
 wherein the concentration by phase separation is carried out in the presence of an electrolyte and/or a nonfluorinated anionic emulsifier.   
   
   
       6 . The aqueous fluororesin dispersion according to  claim 5 ,
 wherein the electrolyte is at least one selected from the group consisting of sulfuric acid, succinic acid, carbonic acid, and salts thereof.   
   
   
       7 . The aqueous fluororesin dispersion according to  claim 5 ,
 wherein the nonfluorinated anionic emulsifier is one such that a 0.1% (by mass) aqueous solution thereof has a surface tension of not higher than 60 mN/m.   
   
   
       8 . A method for producing the aqueous fluororesin dispersion according to  claim 1 ,
 wherein a raw aqueous fluororesin dispersion comprising a melt-processable fluororesin particle dispersed in an aqueous medium is subjected to a treatment in contact with an ion exchange resin and a concentration by phase separation in the presence of an electrolyte and/or a nonfluorinated anionic emulsifier to thereby obtain the aqueous fluororesin dispersion.   
   
   
       9 . The method for producing the aqueous fluororesin dispersion according to  claim 8 ,
 wherein the raw aqueous fluororesin dispersion is brought into contact with the ion exchange resin,   and then, after the step of adding the electrolyte and/or the nonfluorinated anionic emulsifier, the concentration by phase separation is carried out.   
   
   
       10 . The method for producing the aqueous fluororesin dispersion according to  claim 9 ,
 wherein the electrolyte and/or nonfluorinated anionic emulsifier is added in an amount corresponding to 10 to 10000 ppm of the melt-processable fluororesin.   
   
   
       11 . The method for producing the aqueous fluororesin dispersion according to  claim 8 ,
 wherein the concentration by phase separation is carried out in the presence of the electrolyte in an amount corresponding to 10 to 10000 ppm of the melt-processable fluororesin and/or the nonfluorinated anionic emulsifier in an amount corresponding to 10 to 10000 ppm of the melt-processable fluororesin.