Method for producing aqueous polytetrafluoroethylene dispersion

1. A method for producing an aqueous dispersion containing non-melt-processable polytetrafluoroethylene particles, the method comprising

polymerizing tetrafluoroethylene in an aqueous medium in the presence of perfluoro hexanoic acid or its salt,

wherein tetrafluoroethylene is polymerized further in the presence of a nonionic surfactant (2),

wherein the nonionic surfactant (2) is a fluorine-free nonionic surfactant.

2. A method for producing an aqueous dispersion containing non-melt-processable polytetrafluoroethylene particles, the method comprising

polymerizing tetrafluoroethylene in an aqueous medium in the presence of perfluoro hexanoic acid or its salt,

wherein tetrafluoroethylene is polymerized further in the presence of fluoropolyether acid having a molecular weight of at least 800 g/mol or its salt (1), and

wherein the amount of the fluoropolyether acid or its salt (1) is 10 to 100 ppm based on the amount of the aqueous medium.

3. The method according to claim 2 ,

wherein the fluoropolyether acid or its salt (1) has at least one repeated structure selected from the group consisting of repeated structures represented by the formulae (1a) to (1d):

(—CFCF 3 —CF 2 —O—) n   (1a);

(—CF 2 —CF 2 —CF 2 —O—) n   (1b);

(—CF 2 —CF 2 —O—) n —(—CF 2 —O—) m   (1c); and

(—CF 2 —CFCF 3 —O—) n —(—CF 2 —O—) m   (1d),

 wherein m and n each represent an integer of 1 or more.

4. The method according to claim 2 ,

wherein the fluoropolyether acid or its salt (1) is a carboxylic acid or its salt, and has repeated structures represented by the formulae (1a):

(—CFCF 3 —CF 2 —O—) n   (1a);

wherein n represent an integer of 1 or more.

5. A method for producing an aqueous dispersion containing non-melt-processable polytetrafluoroethylene particles, the method comprising

polymerizing tetrafluoroethylene in an aqueous medium in the presence of perfluoro hexanoic acid or its salt,

wherein tetrafluoroethylene is polymerized further in the presence of a comonomer (3) having a monomer reactivity ratio of 0.1 to 8,

the amount of the comonomer (3) is 0.001 to 0.01% by mass based on the net amount of the produced polytetrafluoroethylene.

6. The method according to claim 5 ,

wherein the comonomer (3) is at least one selected from the group consisting of comonomers represented by the formulae (3a) to (3d):

CH 2 ═CH—Rf 1   (3a),

wherein Rf 1 represents a C1-C10 perfluoroalkyl group;

CF 2 ═CF—O—Rf 2   (3b),

wherein Rf 2 represents a C1-C2 perfluoroalkyl group;

CF 2 ═CF—O—(CF 2 ) n CF═CF 2   (3c),

wherein n represents 1 or 2;

wherein X 3 and X 4 each represent F, Cl, or a methoxy group, and Y is represented by the formula Y1 or Y2; and

wherein Z and Z′ each represent F or a C1-C3 fluorinated alkyl group.

7. A method for producing an aqueous dispersion containing non-melt-processable polytetrafluoroethylene particles, the method comprising

polymerizing tetrafluoroethylene in an aqueous medium in the presence of perfluoro hexanoic acid or its salt,

wherein tetrafluoroethylene is polymerized further in the presence of a reactive emulsifier (4),

wherein the reactive emulsifier (4) is at least one selected from the group consisting of compounds represented by the formulae (4a) to (4e):

CF 2 ═CF—(CF 2 ) n1 —Y 3   (4a),

wherein n1 represents an integer of 1 to 10, Y 3 represents —SO 3 M 1 or —COOM 1 , M 1 represents H, NH 4 , or an alkali metal;

CF 2 ═CF—(CF 2 C(CF 3 )F) n2 —Y 3   (4b),

wherein n2 represents an integer of 1 to 5, and Y 3 is as defined above;

CF 2 ═CF—O—(CFX 1 ) n3 —Y 3   (4c),

wherein X 1 represents F or CF 3 , n3 represents an integer of 1 to 10, and Y 3 is as defined above;

CF 2 ═CF—O—(CF 2 CFX 1 O) n4 —CF 2 CF 2 —Y 4   (4d),

wherein n4 represents an integer of 1 to 10, Y 4 represents —SO 3 M 2 or —COOM 2 , M 2 represents NH 4 or an alkali metal, and X 1 is as defined above; and

CX 2 2 ═CFCF 2 —O—(CF(CF 3 )CF 2 O) n5 —CF(CF 3 )—Y 3   (4e),

wherein X 2 s are the same as one another and represent F or H, n5 represents an integer of 0 or 1 to 10, and Y 3 is as defined above.