Patent ID: 7238735

Claim:
A process for producing an aqueous dispersion of purified polytetrafluoroethylene, which comprises passing a crude aqueous dispersion of polytetrafluoroethylene comprising from 10 to 50 mass % of polytetrafluoroethylene fine particles having an average particle diameter of from 0.1 to 0.5 μm, from 0.05 to 1.0 mass %, based on polytetrafluoroethylene, of a fluorine-containing carboxylic acid salt represented by the formula (1) and from 2 to 20 mass %, based on polytetrafluoroethylene, of a nonionic surfactant represented by the formula (2) and/or the formula (3) through a column packed with a weak basic anion exchange resin upward at a linear velocity of 0.1 to 2 mm/sec with a contact time of 0.2 to 4 hours to reduce the content of the fluorine-containing carboxylic acid salt: formula (1): R 1 —COOX (wherein R 1 is a C 5-9 alkyl group having fluorine atoms instead of from 90 to 100% of the hydrogen atoms (which may contain from 1 to 2 ether oxygen atoms), and X is an ammonium ion); formula (2): R 2 —O—A—H (wherein R 2 is a C 8-18 alkyl group, and A is a polyoxyalkylene chain consisting of from 5 to 20 oxyethylene groups and from 0 to 2 oxypropylene groups); and formula (3): R 3 —C 6 H4—O—B—H (wherein R 3 is a C 4-12 alkyl group, and B is a polyoxyalkylene chain consisting of from 5 to 20 oxyethylene groups).