Patent ID: 7468403

Claim:
A method of purifying an aqueous fluoropolymer emulsion comprising; purifying an aqueous fluoropolymer emulsion by a specific technique of concentration wherein the aqueous fluoropolymer emulsion comprises a fluoropolymer and a fluorine-containing surfactant, said specific technique of concentration is the concentration by phase separation, said concentration by phase separation is carried out for removing said fluorine-containing surfactant, and wherein said concentration by phase separation has a separation/removal step comprising; heating said emulsion in the presence of 15 to 40 parts by mass of the nonionic surfactant per 100 parts by mass of the fluoropolymer to thereby cause separation into an aqueous phase and a concentrated phase, followed by removing said aqueous phase to obtain said concentrated phase, said concentration by phase separation is carried out twice or more times, and said concentration by phase separation in the N-th time run (N being an integer of 2 or more) further has, prior to the separation/removal step, a water addition step comprising; adding water to the concentrated phase obtained by the separation/removal step in the concentration by phase separation in the (N−1)th time run (N being the same as above) to thereby obtain a diluted emulsion.