US Patent 7238735 Process for producing aqueous dispersion of purified polytetrafluoroethylene

A process for producing an aqueous dispersion of purified polytetrafluoroethylene (PTFE), comprising passing a crude aqueous dispersion of PTFE comprising from 10 to 50 mass % of PTFE fine particles having an average particle diameter of from 0.1 to 0.5 μm, from 0.05 to 1.0 mass %, based on PTFE, of a fluorine-containing carboxylic acid salt (APFO) and from 2 to 20 mass %, based on PTFE, of a nonionic surfactant through a column packed with a weak basic AER 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 APFO concentration. The process can increase the absorption of APFO by the anion exchange resin, prevents agglomeration of PTFE during passage and makes it easy to elute the absorbed APFO.