Method for producing fluoropolymer

A method for producing a fluoropolymer, comprising:

• polymerizing a fluoromonomer in an aqueous medium in the presence of a surfactant to provide a fluoropolymer, and
• drying the fluoropolymer obtained in the polymerization at 155° C. or higher while air is circulated in a drying furnace,
• wherein the fluoropolymer is polytetrafluoroethylene or modified polytetrafluoroethylene having modifying monomer units in a range of 0.00001 to 1% by mass,
• the surfactant is a carboxylic acid-based hydrocarbon-containing surfactant represented by the following formula (A):
• R—COO-M (A)
• wherein R is a non-halogenated alkyl group free from halogen atoms or a non-halogenated alkylene group free from halogen atoms, each of which optionally contains an ether bond;
• M is H, a metal atom, NR114, imidazolium optionally having a substituent, pyridinium optionally having a substituent, or phosphonium optionally having a substituent;
• and R11 is the same or different and is H or an organic group having 1 to 10 carbon atoms,
• in the polymerization, a redox initiator as a polymerization initiator is added to the aqueous medium, wherein an oxidizing agent for the redox initiator is selected from the group consisting of organic peroxides, permanganic acid, permanganates, manganese triacetate (C6H9MnO6), cerium (IV) salts, bromic acid and salts of bromic acid,
• in the polymerization, the carboxylic acid-based hydrocarbon-containing surfactant at the initial stage of polymerization is in an amount of 90 ppm or more based on the aqueous medium,
• the polymerization provides a fluoropolymer aqueous dispersion, and
• the fluoropolymer aqueous dispersion is substantially free from a compound represented by the following formula (3), and contains greater than 20 ppm of a compound represented by the following formula (4) based on the fluoropolymer,
• (H—(CF2)8—SO3)qM2 Formula (3)
• wherein M2 is H, a metal atom, NR114, imidazolium optionally having a substituent, pyridinium optionally having a substituent, or phosphonium optionally having a substituent;
• q is 1 or 2;
• and R11 is the same or different and is H or an organic group having 1 to 10 carbon atoms,
• (H—(CF2)7—COO)pM1 Formula (4)
• wherein M1 is H, a metal atom, NR54, imidazolium optionally having a substituent, pyridinium optionally having a substituent, or phosphonium optionally having a substituent;
• and p is 1 or 2;
• and R5 is the same or different and is H or an organic group having 1 to 10 carbon atoms.