Patent ID: 8680209

Claim:
A method for producing a stabilized fluoropolymer which comprises producing said stabilized fluoropolymer by subjecting a treatment target substance containing a sulfonic-acid-derived-group-containing fluoropolymer to a fluorination treatment, wherein said sulfonic-acid-derived-group-containing fluoropolymer is a fluoropolymer containing —SO 3 M (in which M represents H, NR 1 R 2 R 3 R 4 or M 1 1/L ; R 1 , R 2 , R 3 and R 4 are the same or different and each represents H or an alkyl group containing 1 to 4 carbon atoms; and M 1 represents an L-valent metal), and said treatment target substance has a moisture content of not higher than 500 ppm by mass, said method comprising the steps of producing said sulfonic-acid-derived-group-containing fluoropolymer by emulsion polymerization, drying said sulfonic-acid-derived-group-containing fluoropolymer to produce said treatment target substance, and fluorinating said treatment target substance, wherein the sulfonic-acid-derived-group-containing fluoropolymer is a copolymer which is at least binary comprising an acid-derived group-containing perhalovinyl ether represented by the general formula (I): CF 2 ═CF—O—(CFY 2 ) m -A (I) (wherein Y 2 represents F, Cl, Br or I; m represents an integer of 1 to 5; when m is an integer of 2 to 5, m atoms of Y 2 are the same or different; A represents —SO 2 X or —COZ; X represents F, Cl, Br, I or —NR 5 R 6 and Z represents —NR 7 R 8 or —OR 9 ; R 5 , R 6 , R 7 and R 8 are the same or different and each represents H, an alkali metal element, an alkyl group or a sulfonyl-containing group and R 9 represents an alkyl group containing 1 to 4 carbon atoms) and a copolymerizable monomer with said acid-derived group-containing perhalovinyl ether, said copolymerizable monomer is an “other vinyl ether” other than said acid-derived group-containing perhalovinyl ether and an ethylenic monomer, and said copolymer comprises 5 to 40 mole percent of an acid-derived group-containing perhalovinyl ether unit derived from said acid-derived group-containing perhalovinyl ether, 60 to 95 mole percent of an ethylenic monomer unit derived from said ethylenic monomer and 0 to 5 mole percent of an “other vinyl ether unit” derived from said “other vinyl ether”.