RU2824595C1 - Method of producing fluoropolymer composition - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present invention relates to a method of producing a fluoropolymer-containing fluoropolymer composition. Method comprises polymerisation of a fluoromonomer in a reactor in the presence of a fluorine-containing surfactant, a polymerisation initiator and an aqueous medium for preparing an aqueous dispersion containing a fluoropolymer; then removing from the reactor the fluoromonomer remaining in the reactor, or extracting the aqueous dispersion from the reactor and placing it in a container different from the reactor; adding a radical generator to the aqueous dispersion; and thermal treatment of the aqueous dispersion containing the radical generator to obtain a fluoropolymer composition.

EFFECT: method enables to obtain a fluoropolymer composition with reduced content of a fluorine-containing surfactant with high efficiency, used in polymerisation of fluoromonomer, as well as content of fluorine-containing compound obtained during polymerisation of fluoromonomer.

15 cl, 8 tbl, 6 ex

Description

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

[0001] The present invention relates to a method for producing a fluoropolymer composition.

LEVEL OF TECHNOLOGY

[0002] A known method for producing a fluoropolymer is a method comprising emulsion polymerization of a fluoromonomer. An aqueous dispersion of a fluoropolymer obtained by emulsion polymerization contains components other than the fluoropolymer, such as a surfactant used in the emulsion polymerization. Various studies have been conducted on methods for reducing or removing such components other than the fluoropolymer.

[0003]

Patent Document 1 discloses a method for reducing the content of a fluoroethercarboxylic acid or a salt thereof having the formula: in an aqueous dispersion of a fluoropolymer.

[R ¹ -OL-COO ^- ]Y ⁺

Where:

R ¹ - a linear, branched or cyclic, partially or fully fluorinated aliphatic group, optionally containing an ether bond;

L is a branched, partially or fully fluorinated alkylene group, optionally containing an ether linkage; and

Y ⁺ is a hydrogen, ammonium or alkali metal cation;

and this method contains:

adding a stabilizer to an aqueous dispersion of a fluoropolymer to form a stabilized aqueous dispersion of a fluoropolymer;

heating the stabilized aqueous dispersion of the fluoropolymer to decarboxylate the fluoroethercarboxylic acid or a salt thereof to produce a fluoroether by-product; and

removing at least a portion of the fluoroether byproduct.

PRIOR ART

PATENT DOCUMENTS

[0004] Patent Document 1: Japanese Patent Application No. 2014-237842.

ESSENCE OF THE INVENTION

PROBLEM SOLVED BY THE INVENTION

[0005] The objective of the present invention is to provide a production method that makes it possible to obtain a fluoropolymer composition with a reduced content of a fluorine-containing surfactant used in the polymerization of a fluoromonomer, as well as a content of a fluorine-containing compound obtained in the polymerization of a fluoromonomer.

MEANS TO SOLVE THE PROBLEM

[0006] The present invention provides a method for producing a fluoropolymer composition comprising a fluoropolymer comprising polymerizing a fluoromonomer in a reactor in the presence of a fluorosurfactant, a polymerization initiator, and an aqueous medium to prepare an aqueous dispersion containing the fluoropolymer; then removing from the reactor the fluoromonomer remaining in the reactor, or extracting the aqueous dispersion from the reactor and placing it in a container different from the reactor; adding a radical generator to the aqueous dispersion; and heat treating the aqueous dispersion containing the radical generator to obtain the fluoropolymer composition.

[0007] In the production method of the present invention, the heat treatment temperature is preferably equal to or higher than the decomposition temperature of the radical generator.

In the production method according to the present invention, the radical generator is preferably a water-soluble radical generator.

In the production method according to the present invention, the radical generator is preferably an inorganic peroxide.

In the production method of the present invention, the content of the fluoropolymer in the aqueous dispersion to be heat treated is preferably 1 mass% or more.

In the production method of the present invention, the fluoropolymer composition is preferably an aqueous dispersion or powder.

In the production method according to the present invention, it is preferable that after obtaining an aqueous dispersion in the form of a fluoropolymer composition by heat treatment, the aqueous dispersion is cooled.

In the production method according to the present invention, it is preferable that after obtaining an aqueous dispersion in the form of a fluoropolymer composition by heat treatment, the aqueous dispersion is concentrated.

In the production method according to the present invention, it is preferable that after obtaining an aqueous dispersion in the form of a fluoropolymer composition by heat treatment, the fluoropolymer in the aqueous dispersion is agglomerated, and optionally the agglomerate is dried.

In the production method of the present invention, the fluorine-containing surfactant is preferably an anionic fluorine-containing surfactant represented by the following general formula (N ⁰ ):

X ⁿ⁰ -Rf ⁿ⁰ -Y ⁰ (N ⁰ )

where X ⁿ⁰ is H, Cl or F; Rf ⁿ⁰ is a linear, branched or cyclic alkylene group having 3-20 carbon atoms in which some or all of the H are replaced by F; the alkylene group optionally contains one or more ether linkages in which some of the H are optionally replaced by Cl; and Y ⁰ is an anionic group.

In the production method of the present invention, an aqueous dispersion obtained by polymerizing a fluoromonomer preferably contains a water-soluble fluorine-containing compound with a molecular weight of 1000 g/mol or less, and a fluoropolymer composition having a reduced content of the water-soluble fluorine-containing compound is obtained by heat treatment.

In the production method of the present invention, the water-soluble fluorine-containing compound is preferably a compound represented by the general formula (1):

General formula (1): [X-Rf-A ^- ] _i M ⁱ⁺

where X is H, Cl, Br, F or I; Rf is a linear or branched, partially or fully fluorinated aliphatic group, or a linear or branched, partially fluorinated or fully fluorinated aliphatic group interrupted by at least one oxygen atom; A ^- is an acidic group; M ⁱ⁺ is a cation having valence i; and i is an integer from 1 to 3.

In the production method of the present invention, the water-soluble fluorine-containing compound is preferably a compound represented by the general formula (2):

General formula (2): [C _n-1 F _2n-1 COO ^- ]M ⁺

where n is an integer from 9 to 12 and M ⁺ represents a cation.

In the production method of the present invention, the water-soluble fluorine-containing compound is preferably a compound represented by the general formula (3):

General formula (3): [R ¹ -OL-CO ₂ ^- ]M ⁺

where R ¹ is a linear or branched, partially or fully fluorinated aliphatic group, or a linear or branched, partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; L is a linear or branched non-fluorinated, partially or fully fluorinated alkylene group; and M ⁺ is a cation.

In the production method of the present invention, the fluoropolymer is preferably at least one fluoropolymer selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene/fluoroalkyl vinyl ether copolymer, tetrafluoroethylene/fluoroalkyl allyl ether copolymer, tetrafluoroethylene/hexafluoropropylene copolymer, ethylene/tetrafluoroethylene copolymer, ethylene/tetrafluoroethylene/hexafluoropropylene copolymer, polychlorotrifluoroethylene, chlorotrifluoroethylene/tetrafluoroethylene copolymer, ethylene/chlorotrifluoroethylene copolymer, polyvinyl fluoride, polyvinylidene fluoride, vinylidene fluoride/tetrafluoroethylene copolymer, fluoromonomer/vinyl ether copolymer, fluoromonomer polymer represented by the general formula (150): CF ₂ =CF-O-(CF ₂ CFY ¹⁵¹ -O) _n -(CFY ¹⁵² ) _m -A ¹⁵¹ ,

where Y ¹⁵¹ represents a fluorine atom, a chlorine atom, a -SO ₂ F group or a perfluoroalkyl group optionally containing an ether oxygen and a -SO ₂ F group; n represents an integer from 0 to 3; n Y ¹⁵¹ groups are the same or different; Y ¹⁵² represents a fluorine atom, a chlorine atom or a -SO ₂ F group; m represents an integer from 1 to 5; m Y ¹⁵² groups are the same or different; A ¹⁵¹ represents -SO ₂ X ¹⁵¹ , -COZ ¹⁵¹ or -POZ ¹⁵² Z ¹⁵³ ; X ¹⁵¹ represents F, Cl, Br, I, -OR ¹⁵¹ or -NR ¹⁵² R ¹⁵³ ; Z ¹⁵¹ , Z ¹⁵² and Z ¹⁵³ are the same or different and independently represent -NR ¹⁵⁴ R ¹⁵⁵ or -OR ¹⁵⁶ ; and R ¹⁵¹ , R ¹⁵² , R ¹⁵³ , R ¹⁵⁴ , R ¹⁵⁵ and R ¹⁵⁶ are the same or different and independently represent H, ammonium, an alkali metal or an alkyl group, an aryl group or a sulfonyl-containing group optionally containing a fluorine atom; and a fluoroelastomer.

BENEFICIAL EFFECTS OF THE INVENTION

[0008] The present invention can provide a production method that makes it possible to obtain a fluoropolymer composition with a reduced content of a fluorosurfactant used in the polymerization of a fluoromonomer, as well as a content of a fluorocompound obtained in the polymerization of a fluoromonomer.

DESCRIPTION OF IMPLEMENTATION OPTIONS

[0009] Specific embodiments of the present invention will be described in detail below, but the present invention is not limited thereto.

[0010] The present invention relates to a method for producing a fluoropolymer composition containing at least a fluoropolymer. In the production method of the present invention, the fluoropolymer composition is produced by polymerizing a fluoromonomer in a reactor in the presence of a fluorosurfactant, a polymerization initiator and an aqueous medium to prepare an aqueous dispersion containing the fluoropolymer; then removing the fluoromonomer remaining in the reactor from the reactor or extracting the aqueous dispersion from the reactor and placing it in a container different from the reactor; adding a radical generator to the aqueous dispersion; and heat treating the aqueous dispersion containing the radical generator.

[0011] An aqueous dispersion obtained by polymerizing a fluoromonomer may contain, in addition to the fluoropolymer, a fluorine-containing surfactant and a fluorine-containing compound obtained by polymerizing the fluoromonomer. In the production method of the present invention, an aqueous dispersion is prepared by polymerizing a fluoromonomer and then removing the fluoromonomer remaining in the reactor from the reactor, or the aqueous dispersion is removed from the reactor and then placed in a container different from the reactor used in the polymerization, whereby the polymerization reaction of the fluoromonomer is stopped sufficiently, and then a radical generator is added to the aqueous dispersion, and the aqueous dispersion is subjected to a heat treatment. Thus, after the polymerization reaction of the fluoromonomer is completed, a radical generator is added to the aqueous dispersion, then the aqueous dispersion is subjected to heat treatment, as a result of which the fluorine-containing surfactant and the fluorine-containing compound are decomposed in the aqueous dispersion, which makes it possible to obtain a fluoropolymer composition in which the content of the fluorine-containing surfactant and the content of the fluorine-containing compound are reduced.

[0012] In the production method of the present invention, a fluoromonomer is first polymerized in a reactor in the presence of a fluorine-containing surfactant, a polymerization initiator, and an aqueous medium to prepare an aqueous dispersion containing the fluoropolymer.

[0013] The polymerization of a fluoromonomer can be performed by loading a reactor with a fluoromonomer, a fluorine-containing surfactant, a polymerization initiator, an aqueous medium and optionally other additives, stirring the contents of the reactor, maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of a polymerization initiator to initiate a polymerization reaction. After the initiation of the polymerization reaction, a fluoromonomer, a polymerization initiator, a fluorine-containing surfactant and a chain transfer agent may be further added depending on the purpose. The polymerization method of the fluoromonomer is not limited, and may be an emulsion polymerization method or a suspension polymerization method, and is preferably an emulsion polymerization method.

[0014] Fluorinated surfactant

The fluorine-containing surfactant used in the polymerization of the fluoromonomer is not limited as long as it is a surfactant containing at least one fluorine atom, and conventionally known fluorine-containing surfactants can be used.

[0015] Examples of the fluorine-containing surfactant include anionic fluorine-containing surfactants. The anionic fluorine-containing surfactant may be, for example, a fluorine atom-containing surfactant having 20 or less carbon atoms in the portion excluding the anionic group.

[0016] The fluorine-containing surfactant may be a fluorine-containing surfactant in which the molecular weight of the anionic functional group is 1000 or less.

"Anionic functional group" means a part of a fluorosurfactant other than a cation. For example, in the case of F( _CF2 ) _n1COOM represented by the following formula (I), the anionic functional group is the part "F( _CF2 ) _n1COO ".

[0017] Examples of the fluorosurfactant also include fluorosurfactants having a LogPOW value of 3.5 or less. LogPOW is a partition coefficient between 1-octanol and water, and is represented by the expression LogP, where P is the ratio between the concentration of the fluorosurfactant in octanol and the concentration of the fluorosurfactant in water in a phase-separated octanol/water (1:1) mixture containing the fluorosurfactant.

The LogPOW value is obtained by performing HPLC on standard substances with known octanol/water partition coefficients (heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid) under the following conditions: column: TOSOH ODS-120T (φ4.6 mm × 250 mm, manufactured by Tosoh Corporation), elution solvent: acetonitrile/0.6 wt% _HClO4 solution =1/1 (vol), flow rate: 1.0 mL/min, sample volume: 300 μL, column temperature: 40°C, detection light: UV 210 nm; plotting a calibration curve between each elution time and the known octanol/water partition coefficients, and calculating the HPLC elution time of the sample liquid based on this calibration curve.

[0018] Specific examples of the fluorosurfactant include those disclosed in U.S. Patent Application Nos. 2007/0015864, 2007/0015865, 2007/0015866, 2007/0276103, 2007/0117914, 2007/142541, 2008/0015319, U.S. Patent Nos. 3,250,808, 3,271,341, Japanese Patent Application No. 2003-119204, International Patent Application Nos. WO 2005/042593, WO 2008/060461, WO 2007/046377, Japanese Patent Application No. 2007-119526, International Patent Application Nos. WO 2007/046482 and WO 2007/046345, U.S. Patent Application No. 2014/0228531, and International Patent Application Nos. WO 2013/189824 and WO 2013/189826.

[0019] The anionic fluorine-containing surfactant may be a compound represented by the following general formula (N ⁰ ):

X ⁿ⁰ -Rf ⁿ⁰ -Y ⁰ (N ⁰ )

where X ⁿ⁰ is H, Cl or F; Rf ⁿ⁰ is a linear, branched or cyclic alkylene group having 3-20 carbon atoms in which some or all of the H are replaced by F; the alkylene group optionally contains one or more ether linkages in which some of the H are optionally replaced by Cl; and Y ⁰ is an anionic group.

The anionic group ^Y0 may be -COOM, _-SO2M , or _-SO3M , and may be -COOM or _-SO3M .

M is H, a metal atom, NR ⁷ ₄ , an optionally substituted imidazolium, an optionally substituted pyridinium, or an optionally substituted phosphonium, and R ⁷ is H or an organic group.

Examples of a metal atom include the alkali metals (Group 1) and alkaline earth metals (Group 2), such as Na, K, or Li.

R ⁷ may be H or a C _1-10 organic group, H or a C _1-4 organic group, or H or a C _1-4 alkyl group.

M may be H, a metal atom, or NR ⁷ ₄ , may be H, an alkali metal (Group 1), alkaline earth metal (Group 2), or NR ⁷ ₄ , and may be H, Na, K, Li, or NH ₄ .

In the Rf ⁿ⁰ group, 50% or more of the H atoms can be replaced by fluorine atoms.

[0020] Examples of the compound represented by the general formula (N ⁰ ) include compounds represented by the following general formula (N ¹ ):

X ⁿ⁰ -(CF ₂ ) _m1 -Y ⁰ (N ¹ )

where X ⁿ⁰ is H, Cl, or F; m1 is an integer from 3 to 15; and Y ⁰ is defined above; a compound represented by the following general formula (N ² ):

Rf ⁿ¹ -O-(CF(CF ₃ )CF ₂ O) _m2 CFX ⁿ¹ -Y ⁰ (N ² )

where Rf ⁿ¹ is a perfluoroalkyl group having 1-5 carbon atoms; m2 is an integer from 0 to 3, X ⁿ¹ is F or CF ₃ , and Y ⁰ is defined above); a compound represented by the following general formula (N ³ ):

Rf ⁿ² (CH ₂ ) _m3 -(Rf ⁿ³ ) _q -Y ⁰ (N ³ )

where Rf ⁿ² is a partially or fully fluorinated alkyl group having 1-13 carbon atoms and optionally containing an ether bond and/or a chlorine atom, m3 is an integer from 1 to 3, Rf ⁿ³ is a linear or branched perfluoroalkylene group having 1-3 carbon atoms, q is 0 or 1, and Y ⁰ is defined above; a compound represented by the following general formula (N ⁴ ):

Rf ⁿ⁴ -O-(CY ⁿ¹ Y ⁿ² ) _p CF ₂ -Y ⁰ (N ⁴ )

where Rf ⁿ⁴ is a linear or branched, partially or fully fluorinated alkyl group having 1-12 carbon atoms and optionally containing an ether linkage, Y ⁿ¹ and Y ⁿ² are the same or different from each other and are independently H or F, p is 0 or 1, and Y ⁰ is defined above; and a compound represented by the following general formula (N ⁵ ):

where X ⁿ² , X ⁿ³ and X ⁿ⁴ may be the same or different from each other and are independently H, F or a linear or branched, partially or fully fluorinated alkyl group having 1-6 carbon atoms and optionally containing an ether bond; Rf ⁿ⁵ is a linear or branched, partially or fully fluorinated alkylene group having 1-3 carbon atoms and optionally containing an ether bond; L is a linking group; and Y ⁰ is defined above, with the proviso that the total number of carbon atoms in X ⁿ² , X ⁿ³ , X ⁿ⁴ and Rf ⁿ⁵ is 18 or less.

[0021] More specific examples of the compound represented by the above general formula (N ⁰ ) include a perfluorocarboxylic acid (I) represented by the following general formula (I), ω-H-perfluorocarboxylic acid (II) represented by the following general formula (II), perfluoroethercarboxylic acid (III) represented by the following general formula (III), perfluoroalkylalkylenecarboxylic acid (IV) represented by the following general formula (IV), perfluoroalkoxyfluorocarboxylic acid (V) represented by the following general formula (V), perfluoroalkylsulfonic acid (VI) represented by the following general formula (VI), ω-H perfluorosulfonic acid (VII) represented by the following general formula (VII), perfluoroalkylalkylenesulfonic acid (VIII) represented by the following general formula (VIII), alkylalkylenecarboxylic acid (IX) represented by the following general formula (IX), fluorocarboxylic acid (X) represented by the following general formula (X), an alkoxyfluorosulfonic acid (XI) represented by the following general formula (XI), a compound (XII) represented by the following general formula (XII), and a compound (XIII) represented by the following general formula (XIII).

[0022] Perfluorocarboxylic acid (I) is represented by the following general formula (I):

F( _CF2 ) _n1COOM (I)

where n1 is an integer from 3 to 14, M is H, a metal atom, NR ⁷ ₄ , an optionally substituted imidazolium, an optionally substituted pyridinium, or an optionally substituted phosphonium, and R ⁷ is H or an organic group.

[0023] ω-H perfluorocarboxylic acid (II) is represented by the following general formula (II):

H( _CF2 ) _n2COOM (II)

where n2 is an integer from 4 to 15 and M is defined above.

[0024] Perfluoroethercarboxylic acid (III) is represented by the following general formula (III):

Rf ¹ -O-(CF(CF ₃ )CF ₂ O) _n3 CF(CF ₃ )COOM (III)

where Rf ¹ is a perfluoroalkyl group having 1-5 carbon atoms, n3 is an integer from 0 to 3, and M is defined above.

[0025] Perfluoroalkylalkylenecarboxylic acid (IV) is represented by the following general formula (IV):

Rf ² (CH ₂ ) _n4 Rf ³ COOM (IV)

where Rf ² is a perfluoroalkyl group having 1-5 carbon atoms, Rf ³ is a linear or branched perfluoroalkylene group having 1-3 carbon atoms, n4 is an integer from 1 to 3, and M is defined above.

[0026] Alkoxyfluorocarboxylic acid (V) is represented by the following general formula (V):

Rf ⁴ -O-CY ¹ Y ² CF ₂ -COOM (V)

where Rf ⁴ is a linear or branched, partially or fully fluorinated alkyl group having 1-12 carbon atoms and optionally containing an ether linkage and/or a chlorine atom; Y ¹ and Y ² are the same or different from each other and represent independently H or F; and M is defined above.

[0027] Perfluoroalkyl sulfonic acid (VI) is represented by the following general formula (VI):

F( _CF2 ) _n5SO3M ( _VI )

where n5 is an integer from 3 to 14 and M is defined above.

[0028] ω-H perfluorosulfonic acid (VII) is represented by the following general formula (VII):

H( _CF2 ) _n6SO3M ( _VII )

where n6 is an integer from 4 to 14 and M is defined above.

[0029] Perfluoroalkylalkylene sulfonic acid (VIII) is represented by the following general formula (VIII):

Rf ⁵ (CH ₂ ) _n7 SO ₃ M (VIII)

where Rf ⁵ is a perfluoroalkyl group having 1-13 carbon atoms, n7 is an integer from 1 to 3, and M is defined above.

[0030] Alkylalkylenecarboxylic acid (IX) is represented by the following general formula (IX):

Rf ⁶ (CH ₂ ) _n8 COOM (IX)

where Rf ⁶ is a linear or branched, partially or fully fluorinated alkyl group having 1-13 carbon atoms and optionally containing an ether linkage, n8 is an integer from 1 to 3, and M is defined above.

[0031] Fluorocarboxylic acid (X) is represented by the following general formula (X):

Rf ⁷ -O-Rf ⁸ -O-CF ₂ -COOM (X)

where Rf ⁷ is a linear or branched, partially or fully fluorinated alkyl group having 1-6 carbon atoms and optionally containing an ether bond and/or a chlorine atom; Rf ⁸ is a linear or branched, partially or fully fluorinated alkyl group having 1-6 carbon atoms; and M is defined above.

[0032] Alkoxyfluorosulfonic acid (XI) is represented by the following general formula (XI):

Rf ⁹ -O-CY ¹ Y ² CF ₂ -SO ₃ M (XI)

where Rf ⁹ is a linear or branched, partially or fully fluorinated alkyl group having 1-12 carbon atoms and optionally containing an ether linkage and optionally containing chlorine; Y ¹ and Y ² are the same or different from each other and represent independently H or F; and M is defined above.

[0033] Compound (XII) is represented by the following general formula (XII):

where X ¹ , X ² and X ³ are the same or different from each other and represent independently H, F or a linear or branched, partially or fully fluorinated alkyl group having 1-6 carbon atoms and optionally containing an ether linkage; Rf ¹⁰ is a perfluoroalkylene group having 1-3 carbon atoms; L is a linking group; and Y ⁰ is an anionic group.

Y ⁰ may be -COOM, -SO ₂ M, or -SO ₃ M, and may be -SO ₃ M or COOM, where M is defined above.

Examples of the L group include a single bond, and a partially or fully fluorinated alkylene group having 1 to 10 carbon atoms and optionally containing an ether bond.

[0034] Compound (XIII) is represented by the following general formula (XIII):

Rf ¹¹ -O-(CF ₂ CF(CF ₃ )O) _n9 (CF ₂ O) _n10 CF ₂ COOM (XIII)

where Rf ¹¹ is a fluoroalkyl group having 1-5 carbon atoms containing chlorine, n9 is an integer from 0 to 3, _n10 is an integer from 0 to 3, and M is defined above. Examples of compound (XIII) include _CF2ClO ( _CF2CF ( _CF3 )O) _n9 ( _CF2O ) _n10CF2COONH4 (a mixture having an average molecular weight of 750, where n9 and n10 _are defined above).

[0035] As described above, examples of the anionic fluorine-containing surfactant include a carboxylic acid-based surfactant and a sulfonic acid-based surfactant.

[0036] The fluorine-containing surfactant may be a single fluorine-containing surfactant, or may be a mixture containing two or more fluorine-containing surfactants.

[0037] The fluorine-containing surfactant preferably does not have a methylene group (-CH ₂ -), and more preferably does not have a CH bond. The use of a fluorine-containing surfactant that does not have a methylene group (-CH ₂ -) or a CH bond within the molecule allows the fluoromonomer to be smoothly polymerized in the presence of an aqueous medium.

[0038] The number of H atoms that the hydrophobic group of the fluorosurfactant has is preferably 0 or 1, and more preferably 0. Using a fluorosurfactant in which the number of H atoms bonded to the carbon atoms constituting the hydrophobic group is small makes it possible to smoothly polymerize the fluoromonomer in the presence of an aqueous medium. The number of carbon atoms in the hydrophobic group of the fluorosurfactant having a hydrophobic group and a hydrophilic group is preferably 1 to 50, more preferably 3 to 20, and still more preferably 6 to 12. The hydrophobic group usually constitutes the above-described "portion except for the anionic group" in the molecular structure of the fluorosurfactant. Examples of the hydrophilic group include groups illustrated as the anionic group Y ⁰ . The fluorosurfactant may be a saturated fluorinated surfactant in which all carbon atoms attached to the hydrophobic group are replaced by fluorine atoms.

[0039] Examples of the fluorine-containing surfactants among the above-described anionic fluorine-containing surfactants include compounds represented by the general formula (N ¹ ), compounds represented by the general formula (N ² ), and compounds represented by the general formula (N ⁴ ):

Rf ⁿ⁴ -O-(CY ⁿ¹ F) _p CF ₂ -Y ⁰ (N ⁴ )

where Rf ⁿ⁴ is a linear or branched, partially or fully fluorinated alkyl group having 1-12 carbon atoms and optionally containing an ether linkage (provided that those having a -CH ₂ - group are excluded), Y ⁿ¹ is H or F, p is 0 or 1, and Y ⁰ is defined above; and compounds represented by the general formula (N ⁵ ):

where X ⁿ² , X ⁿ³ and X ⁿ⁴ may be the same or different from each other and are independently H, F or a linear or branched, partially or fully fluorinated alkyl group containing from 1 to 6 carbon atoms and optionally containing an ether linkage (except for those containing a -CH ₂ - group), provided that X ⁿ³ and X ⁿ⁴ are not simultaneously H; Rf ⁿ⁵ is a linear or branched, partially or fully fluorinated alkylene group containing from 1 to 3 carbon atoms and optionally containing an ether linkage (provided that groups containing -CH ₂ - are excluded); L is a linking group; and Y ⁰ is defined above, with the proviso that the total number of carbon atoms in X ⁿ² , X ⁿ³ , X ⁿ⁴ and Rf ⁿ⁵ is 18 or less.

[0040] Among the above-described anionic fluorine-containing surfactants, the fluorine-containing surfactant is preferably at least one selected from the group consisting of a perfluorocarboxylic acid (I) represented by the general formula (I), an ω-H perfluorocarboxylic acid (II) represented by the general formula (II), a perfluoroethercarboxylic acid (III) represented by the general formula (III), a perfluoroalkylalkylenecarboxylic acid (IV) represented by the general formula (IV), a perfluoroalkoxyfluorocarboxylic acid (V) represented by the general formula (V), a perfluoroalkylsulfonic acid (VI) represented by the general formula (VI), an ω-H perfluorosulfonic acid (VII) represented by the general formula (VII), a perfluoroalkylalkylenesulfonic acid (VIII) represented by the general formula (VIII), and a fluorocarboxylic acid (X) represented by the general formula (X): Rf ⁷ -O-Rf ⁸ -O- _CF2 -COOM

where Rf ⁷ is a linear or branched, partially or fully fluorinated alkyl group having 1-6 carbon atoms and optionally containing an ether linkage and/or a chlorine atom (provided that groups containing -CH ₂ - are excluded); Rf ⁸ is a linear or branched, partially or fully fluorinated alkyl group having 1-6 carbon atoms (provided that groups containing -CH ₂ - are excluded); and M is defined above, an alkoxyfluorosulfonic acid (XI) represented by the general formula (XI): Rf ⁹ -O-CY ¹ FCF ₂ -SO ₃ M

where Rf ⁹ is a linear or branched, partially or fully fluorinated alkyl group having 1-12 carbon atoms and optionally containing chlorine and optionally containing an ether linkage (provided that groups containing -CH ₂ - are excluded), Y ¹ is H or F, and M is defined above, a compound (XII) represented by the general formula (XII):

where X ¹ , X ² and X ³ are the same or different from each other and are independently H, F or a linear or branched, partially or fully fluorinated alkyl group having 1-6 carbon atoms and optionally containing an ether linkage (provided that groups containing -CH ₂ - are excluded), with the proviso that X ² and X ³ are not simultaneously a hydrogen atom, Rf ¹⁰ is a perfluoroalkylene group having 1-3 carbon atoms, L is a linking group and Y ⁰ is an anionic group, and

compound (XIII), represented by the general formula (XIII): Rf ¹¹ -O-(CF ₂ CF(CF ₃ )O) _n9 (CF ₂ O) _n10 CF ₂ COOM

where Rf ¹¹ is a fluoroalkyl group having 1-5 carbon atoms containing chlorine (provided that groups containing -CH ₂ - are excluded), n9 is an integer from 0 to 3, n10 is an integer from 0 to 3, and M is defined above. The use of such a fluorine-containing surfactant allows the fluoromonomer to polymerize smoothly in the presence of an aqueous medium.

[0041] Examples of the fluorine-containing surfactant include compounds represented by the following formulas. The fluorine-containing surfactant may be a mixture of these compounds.

F( _CF2 ) _7COOM ,

F( _CF2 ) _5COOM ,

H( _CF2 ) _6COOM ,

H( _CF2 ) _7COOM ,

CF ₃ O(CF ₂ ) ₃ OCHFCF ₂ COOM,

C ₃ F ₇ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COOM,

CF ₃ CF ₂ CF ₂ OCF(CF ₃ )COOM,

CF ₃ CF ₂ OCF ₂ CF ₂ OCF ₂ COOM,

C ₂ F ₅ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COOM,

CF ₃ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COOM,

CF ₂ ClCF ₂ CF ₂ OCF(CF ₃ )CF ₂ OCF ₂ COOM,

CF ₂ ClCF ₂ CF ₂ OCF ₂ CF(CF ₃ )OCF ₂ COOM,

CF ₂ ClCF(CF ₃ )OCF(CF ₃ )CF ₂ OCF ₂ COOM, and

CF ₂ ClCF(CF ₃ )OCF ₂ CF(CF ₃ )OCF ₂ COOM,

where M is H, a metal atom, NR ⁷ ₄ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium.

[0042] The amount of the fluorine-containing surfactant added is preferably 10 ppm to 10 mass%, more preferably 100 ppm or more, and even more preferably 300 ppm or more, and more preferably 5 mass% or less, and still more preferably 1 mass% or less, based on the mass of the aqueous medium.

[0043] Polymerization initiator

The polymerization initiator used in the polymerization of the fluoromonomer is not limited as long as it can generate radicals in a specific polymerization temperature range, and known oil-soluble and/or water-soluble polymerization initiators can be used. The polymerization initiator can also be combined with a reducing agent and the like to form a redox agent and initiate polymerization. The concentration of the polymerization initiator is appropriately determined according to the type of monomer, the molecular weight of the target fluoropolymer, and the reaction rate.

[0044] The polymerization initiator may be an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator.

[0045] The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, and representative examples thereof include a dialkyl peroxycarbonate such as diisopropyl peroxydicarbonate and di-sec-butyl peroxydicarbonate; a peroxyester such as tert-butyl peroxyisobutyrate and tert-butyl peroxypivalate; and also a dialkyl peroxide such as di-tert-butyl peroxide, and a di[perfluoro(or fluorochloro)acyl]peroxide such as di(ω-hydro-dodecafluorohexanoyl) peroxide, di(ω-hydro-tetradecafluoroheptanoyl) peroxide, di(ω-hydrohexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, di(ω-chloro-hexafluorobutyryl) peroxide, di(ω-chloro-decafluorohexanoyl) peroxide, di(ω-chloro-tetradecafluorooctanoyl) peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl peroxide, ω-chloro-hexafluorobutyryl-ω-chlorodecafluorohexanoyl peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl peroxide, di(dichloropentafluorobutanoyl) peroxide, di(trichlorooctafluorohexanoyl) peroxide, di(tetrachloroundecafluorooctanoyl) peroxide, di(pentachlorotetradecafluorodecanoyl) peroxide and di(undecachlorothoriacontafluorodocosanoyl) peroxide.

[0046] The water-soluble radical polymerization initiator may be a known water-soluble peroxide, and examples include ammonium salts, potassium salts and sodium salts of persulfuric acid, perboric acid, perchloric acid, perphosphoric acid and percarbonic acid, organic peroxides such as disuccinic acid peroxide and diglutaric acid peroxide and the like, tert-butyl permaleate and tert-butyl hydroperoxide. A reducing agent such as sulfite may be contained together, and the amount thereof may be 0.1 to 20 times the amount of the peroxide.

[0047] For example, when the polymerization is performed at a low temperature of 30°C or lower, the polymerization initiator used is preferably a redox initiator obtained by combining an oxidizing agent and a reducing agent. Examples of the oxidizing agent include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and ammonium cerium nitrate. Examples of the reducing agent include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of the persulfates include ammonium persulfate and potassium persulfate. Examples of the sulfites include sodium sulfite and ammonium sulfite. In order to increase the decomposition rate of the initiator, the combination of the redox initiator also preferably contains a copper salt or an iron salt. An example of the copper salt is copper (II) sulfate, and an example of the iron salt is iron (II) sulfate.

[0048] Examples of the oxidation-reduction initiator include potassium permanganate/oxalic acid, ammonium persulfate/bisulfite/ferrous sulfate, manganese triacetate/oxalic acid, ammonium cerium nitrate/oxalic acid, and bromate/bisulfite, and potassium permanganate/oxalic acid is preferable. In the case of using the oxidation-reduction initiator, either the oxidizing agent or the reducing agent may be introduced into the polymerization tank in advance, and then the other may be added continuously or intermittently to initiate the polymerization. For example, when using potassium permanganate/oxalic acid, oxalic acid is preferably charged into the polymerization tank, and then potassium permanganate is continuously added thereto.

[0049] The amount of the polymerization initiator added is not limited, and the polymerization initiator is added in an amount that does not significantly reduce the polymerization rate (for example, in a concentration of several parts per million in water) or more immediately at the initial stage of polymerization, or can be added sequentially or continuously. The upper limit is within a range in which an increase in the reaction temperature is allowed when the heat of the polymerization reaction is removed through the surface of the device, and more preferably the upper limit is within a range in which the heat of the polymerization reaction can be removed through the surface of the device.

[0050] By adding a decomposer during the polymerization of a fluoromonomer, it is possible to control the concentration of radicals during the polymerization. Examples of the decomposer include sulfites, bisulfites, bromates, diimines, oxalic acid, copper salts and iron salts. Examples of sulfites include sodium sulfite and ammonium sulfite. The copper salt may be copper (II) sulfate, and the iron salt may be iron (II) sulfate. The amount of the decomposer added is in the range of 25-300 mass % based on the mass of the oxidizing agent as a polymerization initiator (redox initiator). The amount of the decomposer added is preferably 25-150 mass %, and more preferably 50-100 mass %. The decomposer is preferably added after polymerization of 5 mass % of the total fluoromonomer consumed in the polymerization reaction, and is more preferably added after polymerization of 10 mass %. The amount of the decomposer added is preferably 0.1-20 parts by weight (ppm) per million and more preferably 3-10 ppm by weight of the aqueous medium used.

[0051] Aquatic environment

An aqueous medium for use in polymerization of a fluoromonomer is a reaction medium in which polymerization is performed, and means a liquid containing water. The aqueous medium is not limited as long as it contains water, and may be an aqueous medium containing water and, for example, a fluorine-free organic solvent such as an ether or a ketone, and/or a fluorine-containing organic solvent having a boiling point of 40°C or lower.

[0052] The aqueous medium preferably contains only water, or contains only water and an organic solvent not containing fluorine, and more preferably contains only water, since the polymerization of the fluoromonomer can proceed smoothly and the deterioration in the efficiency of removing the fluorine-containing surfactant and the fluorine-containing compound by heat treatment after preparing the aqueous dispersion can be suppressed.

[0053] The water content in the aqueous medium is preferably 90% or more, more preferably 95% or more, even more preferably 99.0% or more, even more preferably 99.5 or more, and particularly preferably 99.9% or more, and may be 100% by weight of the aqueous medium, since the polymerization of the fluoromonomer can proceed smoothly, and the deterioration in the efficiency of removing the fluorine-containing surfactant and the fluorine-containing compound by heat treatment after preparing the aqueous dispersion can be suppressed.

[0054] Fluoromonomer

A fluoromonomer for use in polymerization has at least one fluorine atom and at least one double bond. The fluoromonomer is preferably at least one monomer selected from the group consisting of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), vinyl fluoride, vinylidene fluoride (VdF), trifluoroethylene, fluoroalkyl vinyl ether, fluoroalkylethylene, fluoroalkyl allyl ether, trifluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, hexafluoroisobutene, a fluoromonomer represented by the general formula (100): CHX ¹⁰¹ = CX ¹⁰² Rf ¹⁰¹ , where one of X ¹⁰¹ and X ¹⁰² is H, the other is F, and Rf ¹⁰¹ is a linear or branched fluoroalkyl group containing from 1 to 12 carbon atoms, a fluorinated vinyl heterocyclic compound and a monomer that provides a crosslinking site.

[0055] The fluoroalkyl vinyl ether (FAVE) is preferably, for example, at least one selected from the group consisting of:

fluoromonomer represented by the general formula (110): CF ₂ =CF-ORf ¹¹¹

where Rf ¹¹¹ represents a perfluoroorganic group;

fluoromonomer represented by the general formula (120): CF ₂ =CF-OCH ₂ -Rf ¹²¹

where Rf ¹²¹ is a perfluoroalkyl group having 1-5 carbon atoms;

fluoromonomer represented by the general formula (130): CF ₂ =CFOCF ₂ ORf ¹³¹

where Rf ¹³¹ is a linear or branched perfluoroalkyl group having 1-6 carbon atoms, a cyclic perfluoroalkyl group having 5-6 carbon atoms, or a linear or branched perfluorooxyalkyl group having 2-6 carbon atoms and containing 1-3 oxygen atoms;

fluoromonomer represented by the general formula (140): CF ₂ =CFO(CF ₂ CF(Y ¹⁴¹ )O) _m (CF ₂ ) _n F

where Y ¹⁴¹ represents a fluorine atom or a trifluoromethyl group; m is an integer from 1 to 4; and n is an integer from 1 to 4; and

fluoromonomer represented by the general formula (150): CF ₂ =CF-O-(CF ₂ CFY ¹⁵¹ -O) _n -(CFY ¹⁵² ) _m -A ¹⁵¹

where Y ¹⁵¹ represents a fluorine atom, a chlorine atom, a -SO ₂ F group or a perfluoroalkyl group optionally containing an ether oxygen and a -SO ₂ F group; n represents an integer from 0 to 3; n Y ¹⁵¹ groups are the same or different; Y ¹⁵² represents a fluorine atom, a chlorine atom or a -SO ₂ F group; m represents an integer from 1 to 5; m Y ¹⁵² groups are the same or different; A ¹⁵¹ represents -SO ₂ X ¹⁵¹ , -COZ ¹⁵¹ or -POZ ¹⁵² Z ¹⁵³ ; X ¹⁵¹ represents F, Cl, Br, I, -OR ¹⁵¹ or -NR ¹⁵² R ¹⁵³ ; Z ¹⁵¹ , Z ¹⁵² and Z ¹⁵³ are the same or different and independently represent -NR ¹⁵⁴ R ¹⁵⁵ or -OR ¹⁵⁶ ; and R ¹⁵¹ , R ¹⁵² , R ¹⁵³ , R ¹⁵⁴ , R ¹⁵⁵ and R ¹⁵⁶ are the same or different and independently represent H, ammonium, an alkali metal or an alkyl group, an aryl group or a sulfonyl-containing group optionally containing a fluorine atom.

[0056] As used herein, the term "perfluoroorganic group" means an organic group in which all hydrogen atoms bonded to carbon atoms are replaced by fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0057] An example of a fluoromonomer represented by the general formula (110) is a fluoromonomer in which Rf ¹¹¹ is a perfluoroalkyl group having 1 to 10 carbon atoms. The perfluoroalkyl group preferably has 1 to 5 carbon atoms.

[0058] Examples of the perfluoroorganic group in the general formula (110) include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

Examples of the fluoromonomer represented by the general formula (110) also include monomers represented by the general formula (110) in which Rf ¹¹¹ is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms; monomers in which Rf ¹¹¹ is a group represented by the following formula:

[0059]

[0060] where m is an integer of 0 or 1-4; and also ethers in which Rf ¹¹¹ is a group represented by the following formula:

[0061]

[0062] where n is an integer from 1 to 4.

[0063] Of these, the fluoromonomer represented by the general formula (110) is preferably a fluoromonomer represented by the general formula (160): CF ₂ =CF-ORf ¹⁶¹

wherein Rf ¹⁶¹ is a perfluoroalkyl group having 1-10 carbon atoms. Rf ¹⁶¹ is preferably a perfluoroalkyl group having 1-5 carbon atoms.

[0064] The fluoroalkyl vinyl ether is preferably at least one selected from the group consisting of fluoromonomers represented by the general formulas (160), (130) and (140).

[0065] The fluoromonomer represented by the general formula (160) is preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether) and perfluoro(propyl vinyl ether), and more preferably is at least one selected from the group consisting of perfluoro(methyl vinyl ether) and perfluoro(propyl vinyl ether).

[0066] The fluoromonomer represented by the general formula (130) is preferably at least one monomer selected from the group consisting of CF ₂ =CFOCF ₂ OCF ₃ , CF ₂ =CFOCF ₂ OCF ₂ CF ₃ and CF ₂ =CFOCF ₂ OCF ₂ CF ₂ OCF ₃ .

[0067] The fluoromonomer represented by the general formula (140) is preferably at least one monomer selected from the group consisting of CF ₂ =CFOCF ₂ CF(CF ₃ )O(CF ₂ ) ₃ F, CF ₂ =CFO(CF ₂ CF(CF ₃ )O) ₂ (CF ₂ ) ₃ F, and CF ₂ =CFO(CF ₂ CF(CF ₃ )O) ₂ (CF ₂ ) ₂ F.

[0068] The fluoromonomer represented by the general formula (150) is preferably at least one monomer selected from the group consisting of CF ₂ =CFOCF ₂ CF ₂ SO ₂ F, CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ SO ₂ F, CF ₂ =CFOCF ₂ CF(CF ₂ CF ₂ SO ₂ F)OCF ₂ CF ₂ SO ₂ F, and CF ₂ =CFOCF ₂ CF(SO ₂ F) ₂ .

[0069] The fluoromonomer represented by the general formula (100) is preferably a fluoromonomer in which Rf ¹⁰¹ is a linear fluoroalkyl group, and more preferably a fluoromonomer in which Rf ¹⁰¹ is a linear perfluoroalkyl group. Rf ¹⁰¹ preferably has 1 to 6 carbon atoms. Examples of the fluoromonomer represented by the general formula (100) include _{CH2 = CFCF3} , _CH2 =CFCF2CF3 _{, CH2 = CFCF2CF2CF3 , CH2 = CFCF2CF2CF2H} , _{CH2 = CFCF2CF2CF2CF3} , CHF= _CHCF3 (E-isomer) and CHF= _CHCF3 (Z _- isomer), and particularly _2,3,3,3 -tetrafluoropropylene represented by _the formula _CH2 = _CFCF3 is preferable.

[0070] The fluoroalkylethylene is preferably a fluoroalkylethylene represented by the general formula (170): CH ₂ =CH-(CF ₂ ) _n -X ¹⁷¹

where X ¹⁷¹ is H or F, and n is an integer from 3 to 10, and more preferably at least one selected from the group consisting of CH ₂ =CH-C ₄ F ₉ and CH ₂ =CH-C ₆ F ₁₃ .

[0071] An example of a fluoroalkyl allyl ether is a fluoromonomer represented by the general formula (180): CF ₂ =CF-CF ₂ -ORf ¹¹¹

where Rf ¹¹¹ represents a perfluoroorganic group.

[0072] Rf ¹¹¹ in the general formula (180) is the same as Rf ¹¹¹ in the general formula (110). Rf ¹¹¹ is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. The fluoroalkyl allyl ether represented _by the general formula (180) is preferably at least one ether selected from the group consisting of _CF2 =CF- _CF2 -O- _CF3 , _CF2 = _CF - _CF2 - _OC2F5 , _CF2 =CF- _CF2 - _OC3F7 and _CF2 =CF- _{CF2 - OC4F9} , more preferably at least one ether selected from the group consisting of _CF2 =CF- _CF2 - _{OC2F5 , CF2} =CF- _{CF2 - OC3F7} and _CF2 =CF- _CF2 - _OC4F9 , and still more preferably is _CF2 =CF- _CF2 - _{O - CF2CF2CF3 .}

[0073] An example of a fluorinated vinyl heterocyclic compound is a fluorinated vinyl heterocyclic compound represented by the general formula (230):

where each of X ²³¹ and X ²³² independently represents F, Cl or a methoxy group, and Y ²³¹ corresponds to the formula Y ²³² or Y ²³³ :

[0074]

where each of Z ²³¹ and Z ²³² independently represents F or a fluorinated alkyl group having 1-3 carbon atoms.

[0075] The monomer that provides the crosslinking site is preferably at least one monomer selected from the group consisting of:

fluoromonomer represented by the general formula (180): CX ¹⁸¹ ₂ =CX ¹⁸² -R _f ¹⁸¹ CHR ¹⁸¹ X ¹⁸³

wherein each of X ¹⁸¹ and X ¹⁸² independently represents H, F or CH ₃ ; R _f ¹⁸¹ represents a fluoroalkylene group, a perfluoroalkylene group, a fluoro(poly)oxyalkylene group or a perfluoro(poly)oxyalkylene group; R ¹⁸¹ represents a hydrogen atom or CH ₃ ; and X ¹⁸³ represents an iodine atom or a bromine atom;

fluoromonomer represented by the general formula (190): CX ¹⁹¹ ₂ =CX ¹⁹² -R _f ¹⁹¹ X ¹⁹³

wherein each of X ¹⁹¹ and X ¹⁹² independently represents H, F or CH ₃ ; R _f ¹⁹¹ represents a fluoroalkylene group, a perfluoroalkylene group, a fluoro(poly)oxyalkylene group or a perfluoro(poly)oxyalkylene group; and X ¹⁹³ represents an iodine atom or a bromine atom;

fluoromonomer represented by the general formula (200): CF ₂ =CFO(CF ₂ CF(CF ₃ )O) _m (CF ₂ ) _n -X ²⁰¹

where m is an integer from 0 to 5; n is an integer from 1 to 3; and X ²⁰¹ represents a cyano group, a carboxy group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or - CH ₂ I; and

fluoromonomer represented by the general formula (210): CH ₂ =CFCF ₂ O(CF(CF ₃ )CF ₂ O) _m (CF(CF ₃ )) _n -X ²¹¹

where m is an integer from 0 to 5; n is an integer from 1 to 3; and X ²¹¹ represents a cyano group, a carboxy group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or - CH ₂ OH; and

monomer represented by the general formula (220): CR ²²¹ R ²²² =CR ²²³ -Z ²²¹ -CR ²²⁴ =CR ²²⁵ R ²²⁶

wherein ^R221 , ^R222 , ^R223 , ^R224 , ^R225 and ^R226 are the same or different and represent independently a hydrogen atom or an alkyl group having 1-5 carbon atoms; and ^Z221 represents a linear or branched alkylene group having 1-18 carbon atoms and optionally having an oxygen atom, a cycloalkylene group having 3-18 carbon atoms and an at least partially fluorinated alkylene or oxyalkylene group having 1-10 carbon atoms, or a (per)fluoropolyoxyalkylene group represented by the formula:

-(Q) _p -CF ₂ O-(CF ₂ CF ₂ O) _m (CF ₂ O) _n -CF ₂ -(Q) _p -

where Q is an alkylene or oxyalkylene group; p is 0 or 1; and m/n is 0.2-5, having a molecular weight of 500-10000.

[0076] Preferably, each of X ¹⁸³ and X ¹⁹³ independently represents an iodine atom. Preferably, each of R _f ¹⁸¹ and R _f ¹⁹¹ independently represents a perfluoroalkylene group having 1 to 5 carbon atoms. Preferably, R ¹⁸¹ represents a hydrogen atom. Preferably, X ²⁰¹ represents a cyano group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or —CH ₂ I. Preferably, X ²¹¹ represents a cyano group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or —CH ₂ OH.

[0077] Preferably, the monomer that provides the crosslinking site is at least one selected from the group consisting of CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ CN, CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ COOH, CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ CH ₂ I, CF ₂ =CFOCF ₂ CF ₂ CH ₂ I, CH ₂ =CFCF ₂ OCF(CF ₃ )CF ₂ OCF(CF ₃ )CN, CH ₂ =CFCF ₂ OCF(CF ₃ )CF ₂ OCF(CF ₃ )COOH, CH ₂ =CFCF ₂ OCF(CF ₃ )CF ₂ OCF(CF ₃ )CH ₂ OH, CH ₂ =CHCF ₂ CF ₂ I, CH ₂ =CH(CF ₂ ) ₂ CH=CH ₂ , CH ₂ =CH(CF ₂ ) ₆ CH=CH ₂ and CF ₂ =CFO(CF ₂ ) ₅ CN, and more preferably, it is at least one selected from the group consisting of CF ₂ =CFOCF ₂ CF(CF ₃ )OCF ₂ CF ₂ CN and CF ₂ =CFOCF ₂ CF ₂ CH ₂ I.

[0078] In polymerization, the fluoromonomer may be polymerized with a non-fluorine monomer. An example of a non-fluorine monomer is a hydrocarbon monomer that can react with the fluoromonomer. Examples of the hydrocarbon monomer include alkenes such as ethylene, propylene, butylene, and isobutylene; alkyl vinyl ethers such as ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether, and cyclohexyl vinyl ether; vinyl esters such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl isobutyrate, vinyl valerate, vinyl pivalate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl versatate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl benzoate, vinyl p-tert-butyl benzoate, vinyl cyclohexanecarboxylate, monochlorovinyl acetate, vinyl adipate, vinyl acrylate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl cinnamate, vinyl undecylenate, vinyl hydroxyacetate, vinyl hydroxypropionate, vinyl hydroxybutyrate, vinyl hydroxyvalerate, vinyl hydroxyisobutyrate and vinyl hydroxycyclohexanecarboxylate; alkyl allyl ethers such as ethyl allyl ether, propyl allyl ether, butyl allyl ether, isobutyl allyl ether and cyclohexyl allyl ether; alkyl allyl ethers such as ethyl allyl ether, propyl allyl ether, butyl allyl ether, isobutyl allyl ether and cyclohexyl allyl ether; and (meth)acrylic esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate and vinyl methacrylate.

[0079] The fluorine-free monomer may also be a hydrocarbon monomer having a functional group (provided that a monomer that provides a crosslinking site is excluded). Examples of the hydrocarbon monomer having a functional group include hydroxyalkyl vinyl ethers such as hydroxyethyl vinyl ether, hydroxypropyl vinyl ether, hydroxybutyl vinyl ether, hydroxyisobutyl vinyl ether and hydroxycyclohexyl vinyl ether; fluorine-free monomers having a carboxyl group such as acrylic acid, methacrylic acid, itaconic acid, succinic acid, succinic anhydride, fumaric acid, fumaric anhydride, crotonic acid, maleic acid, maleic anhydride and perfluorobutenoic acid; fluorine-free monomers having a sulfo group such as vinyl sulfonic acid; fluorine-free monomers having a glycidyl group, such as glycidyl vinyl ether and glycidyl allyl ether; fluorine-free monomers having an amino group, such as aminoalkyl vinyl ether and aminoalkyl allyl ether; fluorine-free monomers having an amide group, such as (meth)acrylamide and methylolacrylamide; and fluorine-free monomers with a nitrile group, such as acrylonitrile and methacrylonitrile.

[0080] In the polymerization, the desired fluoropolymer particles can be obtained by polymerizing one, two or more of the above-mentioned fluoromonomers.

[0081] Chain Transfer Agent

In the production method of the present invention, the fluoromonomer can also be polymerized in the presence of a chain transfer agent. The use of a chain transfer agent makes it possible to control the polymerization rate and the molecular weight. Examples of the chain transfer agent include esters such as dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate and dimethyl succinate, as well as isopentane, methane, ethane, propane, methanol, isopropanol, acetone, various mercaptans, various halogenated hydrocarbons such as carbon tetrachloride, and cyclohexane.

[0082] The chain transfer agent may be a bromine compound or an iodine compound. An example of a polymerization method involving a bromine compound or an iodine compound is a method in which a fluoromonomer is polymerized in an aqueous medium substantially in the absence of oxygen and in the presence of a bromine compound or an iodine compound (iodine transfer polymerization). Representative examples of the bromine compound or iodine compound used include compounds represented by the following general formula:

R ^a I _x B r _y

where x and y are integers from 0 to 2 satisfying the condition 1≤x+y≤2, and R ^a is a saturated or unsaturated fluorocarbon or chlorofluorocarbon group having 1-16 carbon atoms, or a hydrocarbon group having 1-3 carbon atoms and optionally containing an oxygen atom. When using an iodine compound or a bromine compound, an iodine atom or a bromine atom is introduced into the polymer and serves as a crosslinking point.

[0083] Examples of the iodine compound or the bromine compound include 1,3-diiodoperfluoropropane, 2-iodoperfluoropropane, 1,3-diiodo-2-chloroperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoethane, 1,3-diiodo-n-propane, CF ₂ Br ₂ , BrCF ₂ CF ₂ Br, CF ₃ CFBrCF ₂ Br, CFClBr ₂ , BrCF ₂ CFClBr, CFBrClCFClBr, BrCF ₂ CF ₂ CF ₂ Br, BrCF ₂ CFBrOCF ₃ , 1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 1-bromo-4-iodoperfluorobutane, 2-bromo-3-iodoperfluorobutane, 3-bromo-4-iodoperfluorobutene-1,2-bromo-4-iodoperfluorobutene-1, as well as the product of monoiodo- and monobromosubstitution, the product of diiodine- and monobromosubstitution and the product of (2-iodoethyl)- and (2-bromoethyl)-substitution of benzene, and these compounds can be used individually or can also be mutually combined.

[0084] Of these, it is preferable to use 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane and 2-iodoperfluoropropane from the viewpoint of polymerization reactivity, crosslinkability, easy availability, etc.

[0085] The amount of the chain transfer agent used is usually 1 to 50,000 ppm, and preferably 1 to 20,000 ppm, based on the total amount of the supplied fluoromonomer. The amount of the chain transfer agent used is preferably such that it is completely absorbed during the polymerization of the fluoromonomer and does not remain in the aqueous dispersion containing the fluoropolymer, so as not to deteriorate the removal efficiency of the fluorosurfactant and the fluorocompound in the heat treatment after the preparation of the aqueous dispersion as much as possible. Accordingly, the amount of the chain transfer agent used is more preferably 10,000 ppm or less, more preferably 5,000 ppm or less, still more preferably 1,000 ppm or less, particularly preferably 500 ppm or less, and most preferably 200 ppm. per million or less based on the total amount of fluoromonomer supplied.

[0086] The chain transfer agent may be added to the reactor all at once before initiation of the polymerization, may be added all at once after initiation of the polymerization, may be added in several portions during the polymerization, or may be added continuously during the polymerization.

[0087] Other additives

In the polymerization of the fluoromonomer, additives such as buffers, pH adjusters, stabilizing additives, and dispersion stabilizers may be used. In the polymerization of the fluoromonomer, radical scavengers and decomposers may be added to control the polymerization rate and molecular weight. In addition, fluorine-free anionic surfactants, fluorine-free nonionic surfactants, fluorine-free cationic surfactants, etc. may be used in the polymerization of the fluoromonomer.

[0088] The stabilizing additive is preferably paraffin wax, fluorine-containing oil, fluorine-containing solvent, silicone oil, etc. One stabilizing additive may be used singly or two or more of them may be used in combination. The stabilizing additive is more preferably paraffin wax. The paraffin wax may be in the form of a liquid, semi-solid, or solid at room temperature, and is preferably a saturated hydrocarbon containing 12 or more carbon atoms. Generally, the melting point of the paraffin wax is preferably 40 to 65°C, and more preferably 50 to 65°C.

[0089] The amount of the stabilizing additive used is preferably 0.1-12% by mass, and more preferably 0.1-8% by mass, based on the mass of the aqueous medium used. It is desirable that the stabilizing additive be sufficiently hydrophobic so that it is completely separated from the aqueous dispersion after polymerization and does not serve as a polluting component.

[0090] Polymerization conditions

The fluoromonomer can be polymerized under normal pressure and temperature. Generally, the polymerization temperature is 5-120°C, and the polymerization pressure is 0.05-10 MPa g. The polymerization temperature and polymerization pressure are appropriately determined according to, for example, the type of monomer, the molecular weight of the target fluoropolymer, and the reaction rate.

[0091] Water dispersion

Polymerization of the fluoromonomer results in an aqueous dispersion containing the fluoropolymer. The content of the fluoropolymer in the aqueous dispersion after polymerization is typically 8-50 wt.% by weight of the aqueous dispersion.

[0092] An aqueous dispersion obtained by polymerizing a fluoromonomer generally contains, in addition to a fluoropolymer, a fluorosurfactant used in polymerizing the fluoromonomer. Furthermore, the aqueous dispersion obtained by polymerizing a fluoromonomer may contain, in addition to a fluoropolymer, a fluorocompound obtained by polymerizing the fluoromonomer. In the present invention, the fluorocompound is a compound that is not added during polymerization of the fluoromonomer, such as a compound having a structure similar to that of the fluorosurfactant but having a different number of carbon atoms.

[0093] A typical fluorine-containing compound in the aqueous dispersion is a water-soluble fluorine-containing compound having a molecular weight of 1,000 g/mol or less. The production method of the present invention makes it possible to produce a fluoropolymer composition in which the content of a water-soluble fluorine-containing compound having a molecular weight of 1,000 g/mol or less in an aqueous dispersion obtained by polymerizing a fluoromonomer is reduced. The molecular weight of the fluorine-containing compound may be, for example, 800 g/mol or less.

[0094] The aqueous dispersion in one embodiment comprises a compound represented by the following general formula (1) in the form of a water-soluble fluorine-containing compound:

general formula (1): [X-Rf-A ^- ] _i M ⁱ⁺

where X is H, Cl, Br, F or I; Rf is a linear or branched, partially or fully fluorinated aliphatic group or a linear or branched, partially fluorinated or fully fluorinated aliphatic group interrupted by at least one oxygen atom; A ^- is an acidic group; M ⁱ⁺ is a cation having valence i; and i is an integer from 1 to 3.

[0095] The aqueous dispersion in one embodiment comprises a compound represented by the following general formula (2) in the form of a water-soluble fluorine-containing compound:

General formula (2): [C _n-1 F _2n-1 COO ^- ]M ⁺

where n is an integer from 9 to 12 and M ⁺ is a cation.

[0096] It is known that a compound represented by the general formula (2) (perfluoroalkanoic acid) is formed during polymerization when a perfluoroalkyl vinyl ether or the like is used as a modifying monomer (see patent document WO 2019/161153).

[0097] The aqueous dispersion in one embodiment comprises a compound represented by the following general formula (3) in the form of a water-soluble fluorine-containing compound:

general formula (3): [R ¹ -OL-CO ₂ ^- ]M ⁺

where R ¹ is a linear or branched, partially or fully fluorinated aliphatic group or a linear or branched, partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; L is a linear or branched non-fluorinated, partially or fully fluorinated alkylene group; and M ⁺ is a cation.

[0098] The aqueous dispersion in one embodiment comprises a compound represented by the general formula (4) in the form of a water-soluble fluorine-containing compound:

general formula (4): [H-(CF ₂ ) _m CO ₂ ^- ]M ⁺

where m is an integer from 3 to 19 and M ⁺ represents a cation.

[0099] Fluoropolymer

A fluoropolymer, such as fluororubber or fluoroelastomer, is produced by polymerizing a fluoromonomer.

[0100] Examples of the fluororubber include polytetrafluoroethylene (PTFE), TFE/FAVE copolymer (PFA), TFE/fluoroalkyl allyl ether copolymer, TFE/HFP copolymer (FEP), ethylene (Et)/TFE copolymer (ETFE), Et/TFE/HFP copolymer, polychlorotrifluoroethylene (PCTFE), CTFE/TFE copolymer, Et/CTFE copolymer, polyvinyl fluoride (PVF), polyvinylidene fluoride (PVdF), VdF/TFE copolymer, fluoromonomer/vinyl ether copolymer, and a polymer of a fluoromonomer represented by the general formula (150).

[0101] In particular, the fluororubber is preferably at least one selected from the group consisting of PTFE, PFA and FEP, since the effects provided by the production method of the present invention are thereby improved.

[0102] The PTFE may be homo-PTFE or modified PTFE. The modified PTFE comprises a block of TFE and a block of a modifying monomer capable of copolymerizing with TFE. The PTFE may be high molecular weight PTFE that is not melt processable and capable of fibrillation, or low molecular weight PTFE that is melt processable and not capable of fibrillation.

[0103] The modifying monomer is not limited as long as it can be copolymerized with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene (HFP); chlorofluoroolefins such as CTFE; hydrogen-containing fluoroolefins such as trifluoroethylene and VdF; fluoroalkyl vinyl ether (FAVE); fluoroalkyl allyl ether; perfluoroalkylethylene; ethylene; and a fluorovinyl ether having a nitrile group. One modifying monomer may be used, or multiple modified monomers may be used.

[0104] The fluoroelastomer may be a partially fluorinated elastomer or a perfluoroelastomer.

[0105] Examples of the partially fluorinated elastomer include a VdF-based fluoroelastomer, a TFE/propylene (Pr)-based fluoroelastomer, a TFE/propylene/VdF-based fluoroelastomer, an ethylene/HFP-based fluoroelastomer, an ethylene/HFP/VdF-based fluoroelastomer, an ethylene/HFP/TFE-based fluoroelastomer, and an ethylene/HFP/FAVE-based elastomer. In particular, at least one elastomer selected from the group consisting of a VdF-based fluoroelastomer and a TFE/propylene-based fluoroelastomer is preferable.

[0106] Specific examples of the VdF-based fluoroelastomer include a VdF/HFP-based elastomer, a VdF/HFP/TFE-based elastomer, a VdF/CTFE-based elastomer, a VdF/CTFE/TFE-based elastomer, a VdF/fluoromonomer represented by the general formula (100)-based elastomer, a VdF/fluoromonomer represented by the general formula (100)/TFE-based elastomer, a VdF/perfluoromethyl vinyl ether (PMVE)-based elastomer, a VdF/PMVE/TFE-based elastomer, and a VdF/PMVE/TFE/HFP-based elastomer. The VdF/fluoromonomer-based elastomer represented by the general formula (100) is preferably a VdF/ _CH2 = _CFCF3- based elastomer, and the VdF/fluoromonomer-based elastomer represented by the general formula (100)/TFE-based elastomer is preferably a VdF/TFE/ _CH2 = _CFCF3 -based elastomer.

[0107] The perfluoroelastomer is preferably at least one selected from the group consisting of TFE-containing perfluoroelastomers, such as a TFE/fluoromonomer copolymer represented by the general formula (110), (130) or (140), and a TFE/fluoromonomer copolymer represented by the general formula (110), (130) or (140)/monomer that provides a crosslinking site.

[0108] The aqueous dispersion in one embodiment comprises, as a fluoropolymer, a fluoropolymer having a fluoroalkyl vinyl ether block.

[0109] An aqueous dispersion containing a fluoropolymer having a fluoroalkyl vinyl ether block can be prepared by polymerizing a fluoroalkyl vinyl ether as a fluoromonomer. When a fluoroalkyl vinyl ether is used as a fluoromonomer, a compound represented by the general formula (2) (perfluoroalkanoic acid) can be obtained during the polymerization of the fluoromonomer. The aqueous dispersion containing a fluoropolymer having a fluoroalkyl vinyl ether block can contain the compound represented by the general formula (2) as a water-soluble fluorine-containing compound.

[0110] The content of the fluoroalkyl vinyl ether block in the fluoropolymer is preferably 0.0000001-30 mol%, more preferably 0.000001 mol% or more, and still more preferably 0.00001 mol% or more, and preferably 25 mol% or less, more preferably 20 mol% or less, and particularly preferably 8 mol% or less, based on the amount of all polymerization blocks constituting the fluoropolymer.

[0111] Examples of fluoropolymers having such a polymerization block include:

fluororubbers such as fluoroalkyl vinyl ether modified PTFE (FAVE) and TFE/FAVE copolymer (PFA);

partially fluorinated elastomers such as ethylene/HFP/FAVE based elastomer, VdF/PMVE based elastomer, VdF/PMVE/TFE based elastomer and VdF/PMVE/TFE/HFP based elastomer;

as well as perfluoroelastomers.

[0112] The aqueous dispersion in one embodiment comprises low molecular weight PTFE as the fluoropolymer.

[0113] Low molecular weight PTFE is usually produced by polymerization including polymerization conditions for obtaining low molecular weight PTFE, or can be produced by reducing the molecular weight of high molecular weight PTFE obtained by polymerization by a known method (such as thermal decomposition or radiation decomposition). In the production method of the present invention, an aqueous dispersion containing low molecular weight PTFE can be prepared by polymerization including polymerization conditions for obtaining low molecular weight PTFE.

[0114] In the present invention, high-molecular PTFE refers to PTFE that is not melt-processable and is capable of fibrillation. On the other hand, low-molecular PTFE refers to PTFE that is melt-processable and is not fibrillated.

[0115] The term "non-melt processable" means the property that the melt flow rate cannot be measured at a temperature above the crystalline melting point in accordance with ASTM D 1238 and D 2116.

[0116] The presence or absence of fibrillation ability can be determined by "paste extrusion", which is a representative method for forming "high molecular weight PTFE powder", which is a powder made of a TFE polymer. Generally, high molecular weight PTFE can be extruded in the form of a paste because it is capable of fibrillation. When the unfired molded product obtained by paste extrusion exhibits essentially no strength or elongation, such as when it exhibits 0% elongation and breaks when stretched, it can be regarded as incapable of fibrillation.

[0117] The high molecular weight PTFE described above preferably has a standard specific gravity (SSG) of 2.130-2.280. The standard specific gravity is measured by the water displacement method in accordance with ASTM D 792, using a sample formed in accordance with ASTM D 489589. In the present invention, “high molecular weight” means that the standard specific gravity is within the above-mentioned range.

[0118] Low molecular weight PTFE has a melt viscosity of 1× ¹⁰² to 7× ¹⁰⁵ Pa×s at 380°C. In the present invention, “low molecular weight” means that the melt viscosity is within the above-mentioned range.

[0119] Fluoromonomer removal or aqueous dispersion recovery

After the aqueous dispersion is prepared, the fluoromonomer remaining in the reactor is removed from the reactor. Alternatively, after the aqueous dispersion is prepared, the aqueous dispersion is removed from the reactor and placed in a container different from the reactor. Preferably, a method of removing the fluoromonomer from the reactor is used because subsequent steps can be performed in the same reactor that was used in the polymerization, and thus the productivity of the fluoropolymer composition is increased.

[0120] After preparing the aqueous dispersion, it is preferable to stop stirring the contents of the reactor and then remove the fluoromonomer or extract the aqueous dispersion, because subsequent operations become easy or the polymerization of the fluoromonomer can be smoothly completed.

[0121] The method for removing the fluoromonomer from the reactor is not limited. After preparing the aqueous dispersion, the fluoromonomer can be removed from the reactor by stopping, if desired, stirring the contents of the reactor and releasing the gas until the pressure in the reactor reaches normal, the fluoromonomer can be removed from the reactor by reducing the pressure in the reactor below 0.0 MPa manom, or the fluoromonomer in the reactor can be replaced with an inert gas such as nitrogen gas by feeding the inert gas into the reactor. In addition, the fluoromonomer can be removed from the reactor by reacting all of the fluoromonomer in the reactor to convert it into a fluoropolymer. As long as the removal of the fluoromonomer remaining in the reactor from the reactor can be carried out to such a degree that the polymerization reaction of the fluoromonomer is sufficiently stopped, a small amount of the fluoromonomer may remain in the reactor. The removed fluoromonomer can be recovered by a known means. The recovered fluoromonomer can be reused for the production of fluoropolymer.

[0122] A preferred method for removing the fluoromonomer from the reactor may be a method comprising, after preparing the aqueous dispersion, stopping the stirring of the reactor contents, if desired, reducing the pressure inside the reactor below 0.0 MPa gage, and then feeding an inert gas into the reactor. Reducing the pressure in the reactor and feeding the inert gas may be repeated multiple times.

[0123] When a fluoromonomer is polymerized at a temperature higher than normal, the reactor may be cooled before removing the fluoromonomer from the reactor or after removing the fluoromonomer from the reactor. When the fluoromonomer is removed from the reactor by, for example, releasing gas or purging with nitrogen, unreacted fluoromonomer, especially in liquid form, may remain in the reactor, and thus cooling the reactor can sufficiently suppress the reaction progress of the unreacted fluoromonomer.

[0124] The method for extracting the aqueous dispersion from the reactor and placing it in a container different from the reactor used in the polymerization is not limited. For example, after preparing the aqueous dispersion, if desired, stirring of the contents of the reactor can be stopped, the reactor can be opened, and the aqueous dispersion in the reactor can be poured into another container, or after preparing the aqueous dispersion, stirring of the contents of the reactor can be stopped if desired, and the aqueous dispersion can be fed from the reactor to another container through a pipe that connects the reactor and the other container.

[0125] To complete the polymerization reaction of the fluoromonomer, a polymerization chain terminator (radical scavenger) may be added.

[0126] A polymerization chain terminator may be a compound that does not have the ability to be reinitiated after addition or chain transfer to a free radical in a polymerization system. Specifically, a compound that readily undergoes a chain transfer reaction with a primary radical or a growing radical and then forms a stable radical that does not react with a monomer, or a compound that readily undergoes an addition reaction with a primary radical or a growing radical to form a stable radical is used. The activity of what is commonly referred to as a chain transfer agent is characterized by a chain transfer constant and a reinitiation efficiency, and among chain transfer agents, those that have nearly 0% reinitiation efficiency are called polymerization chain terminators. The polymerization chain terminator is preferably at least one compound selected from the group consisting of aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates and copper chloride ( _CuCl2 ). Examples of aromatic hydroxy compounds include unsubstituted phenols, polyhydric phenols, salicylic acid, m- or p-salicylic acid, gallic acid and naphthol. Examples of unsubstituted phenols include o-, m- or p-nitrophenol, o-, m- or p-aminophenol and p-nitrosophenol. Examples of polyhydric phenols include catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol and naphtresorcinol. Examples of aromatic amines include o-, m-, or p-phenylenediamine and benzidine. Examples of quinone compounds include hydroquinone, o-, m-, or p-benzoquinone, 1,4-naphthoquinone, and alizarin. Examples of thiocyanates include ammonium thiocyanate (NH ₄ SCN), potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN). In particular, the polymerization chain terminator is preferably a quinone compound, and more preferably hydroquinone.

[0127] Radical Generator

After the fluoromonomer remaining in the reactor is removed from the reactor, a radical generator is added to the aqueous dispersion. The aqueous dispersion to which the radical generator is added may be an aqueous dispersion remaining in the reactor or an aqueous dispersion removed from the reactor and placed in another container.

[0128] The content of the fluoropolymer in the aqueous dispersion can be adjusted before adding the radical generator. The content of the fluoropolymer can be adjusted by a known method such as concentration or dilution.

[0129] The content of the fluoropolymer in the aqueous dispersion immediately before adding the radical generator is preferably 1 mass% or more based on the mass of the aqueous dispersion, because the fluoropolymer composition can be produced with high productivity without reducing the efficiency of removing the fluorosurfactant and the fluorocompound. The lower limit of the content of the fluoropolymer is, in order of preference, 10 mass% or more, 15 mass% or more, 20 mass% or more, 25 mass% or more, and 30 mass% or more. The upper limit of the content of the fluoropolymer is preferably 60 mass% or less, more preferably 55 mass% or less, and still more preferably 50 mass% or less.

[0130] The content of the fluoropolymer in the aqueous dispersion to be heat treated is preferably 1 mass% or more, more preferably 5 mass% or more, and still more preferably 10 mass% or more, based on the weight of the aqueous dispersion, because the fluoropolymer composition can be produced with high productivity without reducing the efficiency of removing the fluorosurfactant and the fluorocompound. The upper limit of the content of the fluoropolymer is preferably 60 mass% or less, more preferably 55 mass% or less, and still more preferably 50 mass% or less. The aqueous dispersion to be heat treated is an aqueous dispersion to which a radical generator is added (an aqueous dispersion containing a radical generator).

[0131] The content of the fluorosurfactant in the aqueous dispersion immediately before adding the radical generator or the content of the fluorosurfactant in the aqueous dispersion to be heat treated is preferably 500 ppm or more, and more preferably 1000 ppm or more, and preferably 10 mass% or less, more preferably 5 mass% or less, and even more preferably 1 mass% or less, based on the mass of the fluoropolymer in the aqueous dispersion.

[0132] The content of the fluorine-containing compound in the aqueous dispersion immediately before adding the radical generator or the content of the fluorine-containing compound in the aqueous dispersion to be heat treated is preferably 500 ppm or more, and more preferably 1000 ppm or more, and preferably 1.0 mass% or less, more preferably 0.1 mass% or less, and even more preferably 0.01 mass% or less, based on the mass of the fluoropolymer in the aqueous dispersion.

[0133] The total content of the fluorine-containing surfactant and the fluorine-containing compound in the aqueous dispersion immediately before adding the radical generator or the total content of the fluorine-containing surfactant and the fluorine-containing compound in the aqueous dispersion to be heat treated is preferably 500 ppm or more, and more preferably 1000 ppm or more, and preferably 10 mass% or less, more preferably 5 mass% or less, and even more preferably 1 mass% or less, based on the mass of the fluoropolymer in the aqueous dispersion.

[0134] The radical generator is not limited as long as it is a compound that can generate radicals by decomposition at a heat treatment temperature. The radical generator is preferably a water-soluble radical generator since the radicals can easily diffuse into an aqueous dispersion.

[0135] Examples of the radical generator include organic peroxides, inorganic peroxides, organic azo compounds, and combinations of oxidizing and reducing agents, preferably at least one selected from the group consisting of inorganic peroxides, organic peroxides, and combinations of oxidizing and reducing agents.

[0136] The inorganic peroxide is preferably a water-soluble inorganic peroxide. Examples of the inorganic peroxide include hydrogen peroxide, perchlorates, perborates, perphosphates, percarbonates and persulfates, and persulfate is preferred. The persulfate is preferably at least one selected from the group consisting of ammonium persulfate, sodium persulfate and potassium persulfate, and is more preferably ammonium persulfate.

[0137] The organic peroxide is preferably a water-soluble organic peroxide. Examples of the organic peroxide include peroxydicarbonates such as disuccinic acid peroxide and diglutaric acid peroxide.

[0138] The radical generator may be a combination of an oxidizing agent and a reducing agent. Using a combination of an oxidizing agent and a reducing agent makes it possible to generate radicals from the radical generator through a redox reaction between the oxidizing agent and the reducing agent, and thus the temperature during the heat treatment can be reduced.

[0139] Examples of the oxidizing agent include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and ammonium cerium nitrate. Examples of the reducing agent include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of the persulfate include ammonium persulfate and potassium persulfate. Examples of the sulfites include sodium sulfite and ammonium sulfite. In order to increase the decomposition rate of the oxidizing agent, a copper salt or an iron salt is also preferably added. An example of a copper salt is copper (II) sulfate, and an example of an iron salt is iron (II) sulfate.

[0140] Examples of a combination of an oxidizing agent and a reducing agent include potassium permanganate/oxalic acid, ammonium persulfate/bisulfite/ferrous sulfate, manganese triacetate/oxalic acid, ammonium cerium nitrate/oxalic acid, and bromate/bisulfite, and potassium permanganate/oxalic acid is preferred. In the case of using a combination of an oxidizing agent and a reducing agent, either the oxidizing agent or the reducing agent may be introduced into the polymerization tank in advance, and then the other one may be added continuously or intermittently.

[0141] From the viewpoint of improving the efficiency of removing the fluorine-containing surfactant and the fluorine-containing compound, the amount of the radical generator added is preferably 0.0001 mol or more, more preferably 0.001 mol or more, and even more preferably 0.01 mol or more, and preferably 1000 mol or less, more preferably 500 mol or less, and even more preferably 100 mol or less per mole of the fluorine-containing surfactant in the aqueous dispersion.

[0142] When the amount of the added radical generator is relatively large, the fluoropolymer in the aqueous dispersion may partially or completely precipitate as a result of the heat treatment. Accordingly, when producing an aqueous dispersion in which the fluoropolymer is dispersed in an aqueous medium as a fluoropolymer composition obtained by the heat treatment, it is necessary to select an upper limit on the amount of the added radical generator. When producing an aqueous dispersion as a fluoropolymer composition obtained by the heat treatment, the amount of the added radical generator is preferably 50 mol or less, more preferably 25 mol or less, and still more preferably 10 mol or less per mol of the fluorosurfactant in the aqueous dispersion, because the precipitation of the fluoropolymer can be suppressed without deteriorating the removal efficiency of the fluorosurfactant and the fluorocompound.

[0143] The method for adding the radical generator is not limited. The radical generator can be added as is to the aqueous dispersion, or a solution containing the radical generator can be prepared and added to the aqueous dispersion. The radical generator can be added while stirring the aqueous dispersion, or the aqueous dispersion can be stirred after adding the radical generator.

[0144] The temperature of the aqueous dispersion to which the radical generator is added is not limited, and it may be the temperature of the aqueous dispersion after polymerization of the fluoromonomer, may be the temperature after cooling the aqueous dispersion after polymerization of the fluoromonomer, or may be the temperature of the heat treatment. That is, after the radical generator is added to the aqueous dispersion, the aqueous dispersion may be heated for the heat treatment, or the radical generator may be added to the aqueous dispersion after the aqueous dispersion is heated to the temperature of the heat treatment.

[0145] Heat treatment

After adding the radical generator to the aqueous dispersion to obtain an aqueous dispersion containing the radical generator, thermal treatment of the aqueous dispersion containing the radical generator is performed.

[0146] The temperature of the heat treatment is not limited as long as it is at least a temperature at which the radical generator decomposes to form radicals (decomposition temperature) or higher, and is preferably 35°C or higher, more preferably 40°C or higher, even more preferably 45°C or higher, and particularly preferably 50°C or higher, and preferably 120°C or lower, more preferably 110°C or lower, even more preferably 100°C or lower, and particularly preferably 90°C or lower.

[0147] When the heat treatment temperature is relatively high, the fluoropolymer in the aqueous dispersion may partially or completely precipitate due to the heat treatment. Accordingly, when producing an aqueous dispersion in which the fluoropolymer is dispersed in an aqueous medium as a fluoropolymer composition obtained by heat treatment, it is necessary to select an upper limit of the heat treatment temperature. When producing an aqueous dispersion as a fluoropolymer composition obtained by heat treatment, the heat treatment temperature is preferably 95°C or lower, more preferably 90°C or lower, and still more preferably 85°C or lower, since it is possible to suppress the precipitation of the fluoropolymer without deteriorating the removal efficiency of the fluorosurfactant and the fluorocompound.

[0148] When thermally treating an aqueous dispersion, it is not always necessary to heat the aqueous dispersion if the aqueous dispersion can be maintained at a desired temperature or higher. For example, when the temperature at which the fluoromonomer is polymerized is sufficiently high and the temperature of the resulting aqueous dispersion is also sufficiently high, the thermal treatment can be initiated by adding a radical generator to the aqueous dispersion before cooling the resulting aqueous dispersion. On the other hand, for example, when producing an aqueous dispersion as a fluoropolymer composition by suppressing the precipitation of a fluoropolymer without deteriorating the efficiency of removing a fluorosurfactant and a fluorocompound, the amount of the radical generator added and the temperature of the heat treatment must be strictly controlled, and therefore it is preferable that the aqueous dispersion is cooled before or after removing the fluoromonomer from the reactor or withdrawing the aqueous dispersion from the reactor, the radical generator is added to the cooled aqueous dispersion to prepare an aqueous dispersion containing the radical generator, the aqueous dispersion is heated to the above-mentioned temperature range, and this temperature is maintained for a certain period of time. The temperature of the aqueous dispersion immediately before adding the radical generator may be, for example, 30°C or lower.

[0149] The heating means when performing the heat treatment by heating the aqueous dispersion is not limited. For example, a container containing the aqueous dispersion may be placed in a vessel with a constant temperature and heated, or the aqueous dispersion may be placed in a container provided with a heater and heated by the heater.

[0150] The pressure during the heat treatment is not limited, and may be normal pressure. For example, when the temperature during the heat treatment is relatively high and it is necessary to suppress the boiling of the aqueous dispersion, the pressure during the heat treatment may exceed normal pressure.

[0151] The heat treatment time is not limited if the generated radicals sufficiently act on the components contained in the aqueous dispersion, and is preferably 15 minutes or more, more preferably 30 minutes or more, and even more preferably 60 minutes or more, and preferably 1200 minutes or less, more preferably 900 minutes or less, and even more preferably 600 minutes or less.

[0152] The heat treatment can be performed while stirring the aqueous dispersion. Radicals are formed by decomposing the radical generator during the heat treatment, and when a combination of an oxidizing agent and a reducing agent is used as the radical generator, radicals are formed by thermal decomposition of the radical generator and also by an oxidation-reduction reaction.

[0153] Fluoropolymer composition

After the aqueous dispersion containing the radical generator is subjected to thermal treatment, a fluoropolymer composition is obtained. The fluoropolymer composition can be cooled after thermal treatment.

[0154] The form of the fluoropolymer composition is not limited, and it may be an aqueous dispersion (heat-treated aqueous dispersion), powder, thick suspension, gel, and the like. An aqueous dispersion is preferable from the viewpoint of its excellent workability. In the aqueous dispersion, the fluoropolymer particles are preferably dispersed in an aqueous medium. Regardless of the form of the fluoropolymer composition, the content of the fluorine-containing surfactant used in the polymerization of the fluoromonomer and the content of the fluorine-containing compound obtained in the polymerization of the fluoromonomer are reduced in the fluoropolymer composition obtained by the production method of the present invention, and the purity of the fluoropolymer is extremely high.

[0155] The content of the fluorosurfactant in the fluoropolymer composition is preferably less than 500 ppm and more preferably 300 ppm or less by weight of the fluoropolymer.

[0156] The content of the fluorine-containing compound in the fluoropolymer composition is preferably less than 500 ppm by weight of the fluoropolymer.

[0157] The total content of the fluorine-containing surfactant and the fluorine-containing compound in the fluoropolymer composition is preferably less than 500 ppm and more preferably 300 ppm or less by weight of the fluoropolymer.

[0158] The content of the fluorine-containing surfactant and the content of the fluorine-containing compound obtained by polymerizing the fluoromonomer in an aqueous dispersion or in a fluoropolymer composition can be measured by liquid chromatography with mass spectrometry (LC/MS/MS).

First, methanol is added to the composition to perform extraction, and the resulting extract is subjected to LC/MS/MS analysis. To further improve the extraction efficiency, Soxhlet extraction, ultrasonic treatment, etc. can be performed.

Molecular weight information is extracted from the obtained LC/MS/MS spectrum to confirm the structural formula match of the candidate fluorosurfactant.

Thereafter, aqueous solutions with five or more different levels of the confirmed fluorosurfactant and fluorocompound are prepared, and LC/MS/MS analysis of these aqueous solutions with the corresponding levels of content is performed, and a relationship between the content level and the area corresponding to that content level is plotted to obtain a calibration curve.

Then, using this calibration curve, the area of the LC/MS/MS chromatogram of the fluorosurfactant and fluorocompound in the extract can be converted into the content of the fluorosurfactant and fluorocompound.

[0159] Additional processing

The fluoropolymer composition obtained by heat treatment can be brought into contact with an adsorbent. The form of the fluoropolymer composition in this case is preferably an aqueous dispersion.

[0160] When the fluoropolymer composition obtained by heat treatment is an aqueous dispersion, the fluoropolymer composition can be diluted or concentrated by known methods.

[0161] Examples of the concentration method include a phase separation concentration method, an electroconcentration method, an electrophoresis method, an ion exchange method, and a membrane concentration method. The phase separation concentration method, the ion exchange method, and the membrane concentration method can be carried out under generally known processing conditions by the methods disclosed in Patent Document WO 2004/050719, National Publication of International Patent Application No. 2002-532583, and Japanese Patent Application Laid-off No. 55-120630.

[0162] When the fluoropolymer composition is recovered as a slurry or a wet polymer after heat treatment, powder, resin, crumb, etc. of the fluoropolymer can be obtained by drying the slurry or the wet polymer. When the fluoropolymer composition obtained by heat treatment is an aqueous dispersion, powder, etc. can be obtained by agglomerating the fluoropolymer and optionally drying the agglomerate.

[0163] The method for agglomerating the fluoropolymer is not limited. For example, the aqueous dispersion is diluted with water to a polymer concentration of 5-20% by weight, the pH value is optionally adjusted to neutral or alkaline, and then the aqueous dispersion is stirred more vigorously than during the polymerization of the fluoromonomer in a container equipped with a stirrer. The fluoropolymer can be agglomerated by adding a water-soluble organic compound such as methanol or acetone, an inorganic salt such as potassium nitrate or ammonium carbonate, or an inorganic acid such as hydrochloric acid, sulfuric acid or nitric acid as a coagulating agent to the aqueous dispersion and stirring the mixture. After the fluoropolymer is agglomerated, the agglomerated fluoropolymer can be recovered as a wet polymer.

[0164] The thick suspension or wet polymer can be dried.

[0165] When the fluoropolymer is a melt-processable fluoropolymer, the powder of the fluoropolymer composition obtained by drying can be formed into pellets by melt extrusion.

[0166] The fluoropolymer composition obtained above can be used in various applications.

[0167] A fluoropolymer composition (powder) containing PTFE as a fluoropolymer is preferable for molding, and suitable applications include tubes and the like for hydraulic systems and fuel systems of aircraft and automobiles, flexible hoses for chemical liquids, steam and the like, and coatings for electrical wires.

[0168] A fluoropolymer composition (aqueous dispersion) containing PTFE as a fluoropolymer is preferably mixed with a nonionic surfactant to stabilize and further concentrate the aqueous dispersion, and then further mixed, depending on its purpose, with an organic or inorganic filler to form a composition, and is used in a variety of applications. The composition, when applied to a metal or ceramic substrate, can provide a coating surface having non-stickiness, low friction coefficient and excellent gloss, smoothness, abrasion resistance, weather resistance and heat resistance, which is suitable for coating rollers, kitchen utensils, etc., and for impregnating glass fabric, etc.

[0169] An organosol can also be prepared from a fluoropolymer composition (aqueous dispersion) containing PTFE as a fluoropolymer. The organosol may contain PTFE and an organic solvent, examples of the organic solvent include ether-based solvents, ketone-based solvents, alcohol-based solvents, amide-based solvents, ester-based solvents, aliphatic hydrocarbon-based solvents, aromatic hydrocarbon-based solvents, and halogenated hydrocarbon-based solvents, and N-methyl-2-pyrrolidone and dimethylacetamide are suitable. The organosol can be prepared by a method described in, for example, patent document WO 2012/002038.

[0170] A fluoropolymer composition containing PTFE as a fluoropolymer is also preferably used as a processing aid. When used as a processing aid, an aqueous dispersion or fine powder is mixed with a base polymer, etc. to improve the melt strength of the base polymer during melt processing and to improve the mechanical strength, electrical properties, non-flammability, anti-drip properties during combustion, and slipperiness of the resulting polymer.

[0171] A fluoropolymer composition containing PTFE as a fluoropolymer is also preferably used as a binder for batteries or in dust-proof applications.

[0172] A fluoropolymer composition containing PTFE as a fluoropolymer is also preferably combined with a resin other than PTFE and used as a processing aid. The fluoropolymer composition is suitable as a starting material for PTFE disclosed in, for example, Japanese Laid-Open Patent Application No. 11-49912, U.S. Patent No. 5,804,654, Japanese Laid-Open Patent Application No. 11-29679, and Japanese Laid-Open Patent Application No. 2003-2980. The processing aid containing the fluoropolymer composition is not inferior to the processing aids disclosed in these publications.

[0173] The fluoropolymer composition containing PTFE as a fluoropolymer is also preferably mixed with an aqueous dispersion of a melt-processable fluororesin, so that the components coagulate to form a co-coagulated powder. This powder is suitable as a processing aid.

[0174] Examples of the melt-processable fluororesin include FEP, PFA, TFE/fluoroalkyl allyl ether copolymers, ETFE, and ethylene/TFE/HFP copolymers (EFEP), and in particular PFA, TFE/fluoroalkyl allyl ether copolymers, and FEP are preferred.

[0175] The aqueous dispersion also preferably contains a melt-processable fluororesin. Examples of the melt-processable fluororesin include FEP, PFA, TFE/fluoroalkyl allyl ether copolymers, ETFE, and EFEP. The aqueous dispersion containing the melt-processable fluororesin can be used as a coating material. The melt-processable fluororesin ensures sufficient melting of the PTFE particles, thereby improving the film-forming ability and imparting gloss to the resulting film.

[0176] The fluorine-free resin to which the juice coagulated powder is added may be in the form of powder, granules, or emulsion. The addition is preferably carried out by applying a shear force in a known manner such as extrusion mixing or roller mixing, from the viewpoint of sufficiently mixing each resin.

[0177] A fluoropolymer composition containing PTFE as a fluoropolymer is also preferably used as a dust suppressant. The dust suppressant can be used in a method for suppressing dust of a dust-generating substance by fibrillating PTFE by mixing with the dust-generating substance and applying a compression-shear action to the mixture at a temperature of 20 to 200°C, such as the method disclosed in Japanese Patent Nos. 2827152 or 2538783. The fluoropolymer composition can be suitably used, for example, in the dust suppressant composition described in International Patent Application WO 2007/004250, and can also be suitably used in the dust control method described in International Patent Application WO 2007/000812.

[0178] The dust suppressant is suitably used for suppressing dust in the fields of building materials, soil stabilizers, curing materials, fertilizers, landfills for ash and hazardous substances, explosion-proof equipment, cosmetics, and pet excrement sand such as cat sand.

[0179] A fluoropolymer composition (aqueous dispersion) containing PTFE as a fluoropolymer is also preferably used as a raw material for producing PTFE fiber by a dispersion spinning method. The dispersion spinning method is a method in which an aqueous dispersion of PTFE and an aqueous dispersion of a matrix polymer are mixed, the mixture is extruded to form an intermediate fiber structure, and then the intermediate fiber structure is calcined to decompose the matrix polymer and sinter PTFE particles, thereby providing PTFE fibers.

[0180] A fluoropolymer composition (powder) containing PTFE as a fluoropolymer has stretchability and is not melt-processable, and is useful as a starting material for a stretchable body (porous body). When the stretchable body of the present invention is a film (a stretched PTFE film or a porous PTFE film), the stretched body can be formed by stretching PTFE in a known manner. Stretching makes it possible to easily form fibrils of high-molecular PTFE, thereby obtaining a porous body (film) of PTFE including knots and fibers. Preferably, stretching the paste extrudate in the form of a sheet or rod in the extrusion direction can provide a uniaxially stretched film. Further stretching in the transverse direction using, for example, a tenter can provide a biaxially stretched film. It is also preferable to perform pre-sintering before stretching.

[0181] This expanded PTFE body is a porous body having high porosity, and can be suitably used as a filter material for various microfiltration filters such as air filters and chemical filters, and a support member for polymer electrolyte films. The expanded body is also used as a material for articles used in the fields of textiles, medicine, electrochemistry, sealants, air filters, ventilation/internal pressure regulation, liquid filters and consumer goods, etc. The following are examples of specific applications.

[0182] Electrochemical Region

Examples of applications in this area include prepregs for dielectric materials, EMI shielding materials, and thermally conductive materials. More specifically, examples include printed circuit boards, EMI shielding materials, thermally conductive materials, and insulating materials.

[0183] Sealant Area

Examples of applications in this area include gaskets, packings, pump diaphragms, pump tubes and aircraft sealants.

[0184] Air Filter Area

Examples of applications in this field include ULPA filters (for semiconductor manufacturing), HEPA filters (for hospitals and semiconductor manufacturing), cylinder filters with replaceable filter element (for industry), bag filters (for industry), heat-resistant bag filters (for exhaust gas cleaning), heat-resistant pleated filters (for exhaust gas cleaning), SINBRAN filters (for industry), catalytic filters (for exhaust gas cleaning), desiccant filters (for hard drive encapsulation), desiccant vent filters (for hard drive encapsulation), vent filters (e.g. for hard drive encapsulation), purifier filters, general purpose felt laminates, GT replaceable filter element filters (for GT replaceable elements), and cooling filters (for electronic device housings).

[0185] Ventilation/internal pressure regulation area

Examples of applications in this field include freeze-drying materials such as freeze-drying vessels, automotive ventilation materials for electronic circuits and lamps, vessel-related applications such as vessel covers, protective ventilation for electronic devices including small devices such as tablet terminals and mobile phone terminals, and ventilation for medical treatment.

[0186] Liquid Filter Area

Examples of applications in this field include semiconductor liquid filters (for semiconductor manufacturing), hydrophilic PTFE filters (for semiconductor manufacturing), chemical filters (for chemical liquid processing), pure water line filters (for pure water production), and backwash liquid filters (for industrial wastewater treatment).

[0187] Consumer goods area

Examples of applications in this area include clothing, cable guides (motorcycle traction cables), motorcycle clothing, molded liners (medical supports), filters for cleaning agents, bagpipes (musical instruments), cables (e.g. signal cables for guitars), and strings (for stringed instruments).

[0188] Textile area

Examples of applications in this area include PTFE fibers (fibrous materials), machine threads (textiles), weaving yarns (textiles) and ropes.

[0189] Medical field

Examples of applications in this area include implants (stretchable products), artificial blood vessels, catheters, general surgery (tissue reinforcement materials), head and neck products (dura mater alternatives), oral health (tissue regeneration), and orthopedics (bandages).

[0190] A fluoropolymer composition containing low molecular weight PTFE as a fluoropolymer is suitably used as an additive for improving lubricity and surface texture of a coating in the production of plastics, inks, cosmetics, coating materials, lubricants, office equipment parts and toners (see, for example, Japanese Patent Application Laid-off No. 10-147617).

[0191] Thus, a fluoropolymer composition containing FEP as a fluoropolymer can be used in the production of a variety of molded articles such as coatings for electric wires, foam coatings for electric wires and cables, etc., tubes, films, sheets and fibers.

[0192] A fluoropolymer composition containing a TFE/FAVE (PFA) copolymer or a TFE/fluoroalkyl allyl ether copolymer as a fluoropolymer can be suitably used in, for example, sheets, films, packages, round blanks, square blanks, pipes, tubes, round tanks, square tanks, tanks, semiconductor wafer carriers, semiconductor wafer boxes, measuring cylinders, filter housings, flow meters, pumps, valves, taps, connectors, nuts, electric wires and heat-resistant electric wires. Among these, tubes, pipes, tanks, connectors and the like for use in various chemical reaction devices, semiconductor manufacturing devices and acidic or alkaline chemical supply devices and the like, each of which requires chemical impermeability, are preferable.

[0193] A fluoropolymer composition (aqueous dispersion) containing a TFE/FAVE (PFA) copolymer or a TFE/fluoroalkyl allyl ether copolymer as a fluoropolymer can also be suitably mixed with a nonionic surfactant and optionally a polyethersulfone, a polyamideimide and/or a polyimide and a metal powder that are dissolved or dispersed in an organic solvent, and thus a primer composition can be obtained. This primer composition can be used in a method of applying a fluororesin to a metal surface. The method includes applying a primer composition to a metal surface, applying a fluoropolymer composition to the obtained primer layer, and baking the fluoropolymer composition layer together with the primer layer.

[0194] The form of the fluoropolymer composition containing the fluoroelastomer as the fluoropolymer is preferably a gum or crumb. The fluoropolymer composition in the form of the gum, crumb, etc. can be mixed with an additive such as a curing agent and a filler to be processed into a fluoroelastomer composition.

[0195] Examples of the curing agent include polyhydric alcohols, polyamines, organic peroxides, organotin compounds, bis(aminophenol)tetramine, or bis(thioaminophenol).

[0196] The fluoroelastomer composition can be formed and crosslinked to obtain a molded article of the fluoroelastomer. The article molded of the fluoroelastomer is suitable for seals, gaskets, coatings of electric wires, hoses, pipes, laminated products, accessories, etc., in particular, parts of devices for the production of semiconductors, automobile parts, etc.

[0197] While embodiments have been described above, it will be understood that various changes in form and detail may be made without departing from the spirit and scope of the claims.

EXAMPLES

[0198] Next, embodiments of the present invention will be described with reference to Examples, but the present invention is not limited to these Examples.

[0199] The various numerical values in the Examples were measured in the following ways.

[0200] Concentration of solids in aqueous dispersion

One gram of the aqueous dispersion was dried in an air dryer at 150°C for 60 min, and the percentage value of the ratio of the mass of the dried residue to the mass (1 g) of the aqueous dispersion was used as the solids concentration.

[0201] Melt viscosity

The melt viscosity was measured by maintaining 2 g of a sample preheated at 380°C for 5 min at that temperature under a load of 0.7 MPa in accordance with ASTM D 1238 using a flow meter (manufactured by Shimadzu Corporation) and a 2φ-8L die.

[0202] Standard Specific Gravity (SSG)

Using a specimen formed in accordance with ASTM D 4895-89, SSG was measured by the water displacement method in accordance with ASTM D 792.

[0203] Modifying monomer block content (PTFE)

The content of PPVE block in PTFE was determined based on infrared absorption by preparing a thin film disk by pressing PTFE powder and performing FT-IR measurement in which the ratio of light absorption at 995 cm ^-1 / light absorption at 935 cm ^-1 was multiplied by 0.14.

[0204] PPVE Block Contents (PFA)

The PPVE block content of PFA was determined by ¹⁹ F-NMR analysis.

[0205] Peak Temperature

The peak temperature was measured using a TG/DTA (thermogravimetric differential thermal analyzer) by accurately weighing approximately 10 mg of PTFE powder, which had not previously been heated to 300°C or higher, and storing it in a specialized aluminum pan. A differential thermal curve (DTA) was obtained by heating the aluminum pan at a rate of 10°C/min over a temperature range of 25°C to 600°C in air, and the temperature corresponding to the maximum value of the obtained differential thermal curve was considered as the peak temperature.

[0206] Melting point

The melting point was measured using a differential scanning calorimeter (DSC). A 10 mg sample was weighed, heated from 140°C to 360°C at a rate of 10°C/min, held at 360°C for 1 min, then cooled to 140°C at a rate of 10°C/min, held at 140°C for 1 min, and again heated to 380°C at a rate of 10°C/min. The peak melting temperature (Tm) of the melting curve obtained during the second heating was considered as the melting temperature.

[0207] Melt Flow Rate (MFR)

Using a melt index apparatus equipped with a corrosion-resistant cylinder, die and piston (manufactured by Toyo Seiki Seisaku-sho, Ltd.) conforming to ASTM D 1238-95, 5 g of the sample was placed and held for 5 min in the cylinder at a temperature of 372±1°C, and then extruded through the die opening under a load (piston and weight) of 5 kg, and the extrusion rate (g/10 min) of the melt at this time was determined as MFR.

[0208] Measurement of perfluorohexanoic acid, perfluoroundecanoic acid and perfluoroethercarboxylic acid A in the extract

1. Calibration curves of perfluorohexanoic acid, perfluoroundecanoic acid and perfluoroethercarboxylic acid A

Five concentration levels of methanol standard solutions of perfluorohexanoic acid, perfluoroundecanoic acid and perfluoroethercarboxylic acid A with known concentrations from 1 ng/mL to 100 ng/mL were prepared and measurements were performed using a liquid chromatograph with a mass spectrometer (Waters, LC-MS ACQUITY UPLC/TQD). First-order fitting was used to generate calibration curves from sample concentrations and their peak integrals.

[0209] LC-MS instrument configuration and measurement conditions

[Table 1]

LC Block Equipment Acquity UPLC by Waters Column Acquity UPLC BEH C18 1.7mm (2.1x50mm) by Waters Mobile phase A _CH3CN In 20 mM _{CH3COONH4 / H2O} 0 → 1.5 min A:B=10:90 1.5 → 8.5 min A:B=10:90 → A:B=90:10 Linear gradient 8.5 → 10 min A:B=90:10 Flow rate 0.4 ml/min Column temperature 40°C Injected sample quantity: 5 µl MS Block Equipment TQ Detector Measurement mode MRM (Multiple Reaction Monitoring) Ionization method Electrospray ionization, negative mode

[0210] MRM Measurement Parameters

[Table 2]

Compound Precursor Product Perfluorohexanoic acid 313 269 Perfluoroundecanoic acid 563 519 Perfluoroethercarboxylic acid A 395 351

[0211] 2. Perfluorohexanoic acid content in the extract

Perfluorohexanoic acid was measured using a liquid chromatograph with a mass spectrometer. The extract was appropriately diluted with methanol to obtain a measurement solution so that the amount of perfluorohexanoic acid in the measurement solution was within the calibration curve. Regarding the measurement solution, the peak area of perfluorohexanoic acid was determined using the MRM method, and the content of perfluorohexanoic acid was determined from the calibration curve.

[0212] 3. Perfluoroundecanoic acid content in the extract

Perfluoroundecanoic acid was measured using a liquid chromatograph with a mass spectrometer. The extract was appropriately diluted with methanol to obtain a measurement solution so that the amount of perfluoroundecanoic acid in the measurement solution was within the calibration curve. Regarding the measurement solution, the peak area of perfluoroundecanoic acid was determined using the MRM method, and the content of perfluoroundecanoic acid was determined from the calibration curve.

[0213] 4. Content of perfluoroethercarboxylic acid A in the extract

Perfluoroethercarboxylic acid A was measured using a liquid chromatograph with a mass spectrometer. The extract was appropriately diluted with methanol to obtain a measurement solution so that the amount of perfluoroethercarboxylic acid A in the measurement solution was within the calibration curve. Regarding the measurement solution, the peak area of perfluoroethercarboxylic acid A was determined using the MRM method, and the content of perfluoroethercarboxylic acid A was determined from the calibration curve.

[0214] Production Example 1

An aqueous PTFE dispersion 1 was obtained in the same manner as in Example 7 of patent document WO 2009/020187, except that the amount of ammonium perfluorohexanoate was changed from 1.7 g to 2.0 g.

[0215] The PTFE aqueous dispersion 1 was taken out of the reactor into the air and cooled to obtain a PTFE aqueous dispersion 2. Various physical properties of the obtained PTFE aqueous dispersion 2 were measured. The results are shown in Table 3.

[0216] Nitric acid was added to the obtained PTFE aqueous dispersion 2, the mixture was subjected to high shear to coagulate, the obtained wet powder was dried, and thus PTFE powder was obtained. Various physical properties of the obtained PTFE powder were measured. The results are shown in Table 3. Accordingly, it was found that the obtained PTFE powder was low molecular weight PTFE.

[0217] [Table 3]

Production example 1 Concentration of solids wt.% 20.4 Melt viscosity Pa⋅s 1.6×10 ⁴ Peak temperature (°C) 329

[0218] Synthesis Example 1

A 1 L autoclave was purged with nitrogen, charged with 16.5 g of dehydrated tetramethylurea and 220 g of diethylene glycol dimethyl ether, and cooled. Then, 38.5 g of carbonyl fluoride were added, followed by 100 g of hexafluoropropylene oxide, and the mixture was stirred. Then, 38.5 g of carbonyl fluoride and 100 g of hexafluoropropylene oxide were further added. Then, the same amounts of carbonyl fluoride and hexafluoropropylene oxide were further added. After completion of the reaction, the reaction mixture was taken out and separated, and thus the reaction product in the lower phase was obtained.

[0219] 1000 ml of tetraglyme and CsF (75 g) were charged into a 6 L autoclave and the autoclave was purged with nitrogen. Then, the autoclave was cooled and 2100 g of the reaction product obtained above were charged into it, and hexafluoropropylene oxide was introduced into the autoclave to initiate the reaction. Eventually, 1510 g of hexafluoropropylene oxide was added. Then, the contents were taken out and separated into an upper phase and a lower phase using a separatory funnel. The upper phase had a mass of 1320 g and the lower phase had a mass of 3290 g. The lower phase was rectified.

[0220] Then, 1000 g of pure water were added to 1000 g of the product obtained by rectifying the lower phase to carry out hydrolysis. Then, the organic phase (lower phase) was recovered by liquid separation using a separatory funnel. The recovered organic phase (lower phase) was washed with a sulfuric acid solution. The washed organic phase was subjected to simple distillation to obtain a distillate. In addition, 500 g of the distillate obtained above was added dropwise to an aqueous solution obtained by mixing 76 g of a 28 wt % aqueous ammonia solution and 600 g of pure water. After completion of the dropwise addition, the pH was adjusted to 7 by adding 28 wt % aqueous ammonia solution. This mixture was freeze-dried, and thus a white solid A (perfluoroethercarboxylic acid A) was obtained.

[0221] Production Example 2

3580 g of deionized water and 7.56 g of the white solid A obtained in Synthesis Example 1 were added to a 6 L internal volume SUS reactor equipped with a stirrer. Then, the reactor contents were sucked off while heating to 70°C while purging the reactor with TFE to remove oxygen from the reactor, and its contents were stirred. After adding 0.5 g of ethane and 71 g of perfluoropropyl vinyl ether (PPVE) to the reactor, TFE was added until the pressure became 2.4 MPa g. Then, 306 mg of ammonium persulfate (APS) initiator dissolved in 20 g of deionized water was added to the reactor. After adding the initiator, the pressure decreased and polymerization initiation was observed. TFE was added to the reactor to maintain a constant pressure of 2.4 MPa g. After the polymerization was initiated, 108 mg of ammonium persulfate and 84 g of PPVE were continuously added. When the TFE consumption in the reaction reached approximately 1600 g, the TFE feeding and stirring were stopped, and the reaction was completed. After that, the reactor was evacuated until the pressure in the reactor reached normal pressure, and thus an aqueous dispersion of PFA 3 was obtained.

[0222] The aqueous dispersion of PFA 3 was taken out of the reactor into air and cooled to obtain an aqueous dispersion of PFA 4. Various physical properties of the obtained aqueous dispersion of PFA 4 were measured. The results are shown in Table 4.

[0223] The obtained aqueous dispersion of PFA 4 was stirred, coagulated and dried. Various physical properties of the obtained PFA powder were measured. The results are shown in Table 4.

[0224] [Table 4]

Production example 2 Concentration of solids wt.% 30.5 Contents of PPVE wt.% 6.5 MFR g/10 min 2.1 Melting point (°C) 295

[0225] Production Example 3

3580 g of deionized water, 160 g of paraffin, and 4.7 g of the white solid A obtained in Synthesis Example 1 as a fluorine-containing surfactant were added to a 6 L internal volume SUS steel reactor equipped with a stirrer. Then, the contents of the reactor were sucked off while heating to 70°C while purging the reactor with TFE to remove oxygen from the reactor, and the contents were stirred. Then, 6.5 g of PPVE was introduced with TFE into the reactor. Then, 50 mg of APS dissolved in 20 g of deionized water as an initiator was added to the reactor, and the pressure was adjusted to 1.5 MPa g. TFE was added so as to maintain a constant pressure of 1.5 MPa g. When the consumption of TFE in the reaction reached 1543 g, the feeding of TFE and stirring were stopped, and the reaction was completed. After this, the reactor was evacuated until the pressure in the reactor reached normal, and thus an aqueous dispersion of PTFE 5 was obtained.

[0226] The aqueous dispersion of PTFE 5 was taken out of the reactor into the air and cooled, the paraffin wax was removed, and thus an aqueous dispersion of PTFE 6 was obtained. Various physical properties of the obtained aqueous dispersion of PTFE 6 were measured. The results are shown in Table 5.

[0227] The obtained aqueous dispersion of PTFE 6 was coagulated, and the coagulated wet powder was dried. Various physical properties of the obtained PTFE powder were measured. The results are shown in Table 5.

[0228] [Table 5]

Production example 3 Concentration of solids wt.% 30.0 SSG - 2,163 Contents of PPVE wt.% 0.28

[0229] Comparative Example 1

14.7 g of the PTFE aqueous dispersion 2 obtained in Production Example 1 and 7.3 g of deionized water were added to a screw cap test tube having an internal volume of 100 ml, then 10 ml of methanol were added, and the mixture was vigorously shaken until it agglomerated, and then centrifuged at 4000 rpm for 1 hour to separate the polymer.

[0230] The obtained extract was analyzed. The measurement results are shown in Table 6.

[0231] Example 1

14.7 g of the PTFE aqueous dispersion 2 obtained in Production Example 1 and 7.3 g of an aqueous solution of ammonium persulfate with a concentration of 0.13 mass% as an inorganic peroxide were added to a screw cap test tube having an internal volume of 100 ml, and maintained at an internal temperature of 80°C for 3 hours. After the heat treatment, the mixture was cooled, and 10 ml of methanol was added. The subsequent operations were carried out in the same manner as in Comparative Example 1 to obtain an extract. The measurement results are shown in Table 6.

[0232] Example 2

The same operations as in Example 1 were carried out except that an aqueous solution of ammonium persulfate with a concentration of 1.3 wt% was used instead of an aqueous solution of ammonium persulfate with a concentration of 0.13 wt%. The measurement results are shown in Table 6.

[0233] [Table 6]

Comparative example 1 Example 1 Example 2 Perfluorohexanoic acid ppm/polymer 2.4×10 ³ 1.3×10 ³ 7.1×10 ¹

[0234] Comparative Example 2

10 g of the aqueous dispersion of PFA 4 obtained in Production Example 2 and 11 g of deionized water were added to a screw cap test tube having an internal volume of 100 ml, and the same operations as in Comparative Example 1 were carried out. The obtained extract was analyzed. The measurement results are shown in Table 7.

[0235] Example 3

10 g of the aqueous dispersion of PFA 4 obtained in Production Example 2 and 11 g of an aqueous solution of ammonium persulfate with a concentration of 0.11 mass% were added to a screw cap test tube having an internal volume of 100 ml, and maintained at an internal temperature of 80°C for 3 hours. After the heat treatment, the mixture was cooled, and 10 ml of methanol was added. The subsequent operations were carried out in the same manner as in Comparative Example 1 to obtain an extract. The measurement results are shown in Table 7.

[0236] Example 4

The same operations as in Example 3 were carried out except that an aqueous solution of ammonium persulfate with a concentration of 1.1 wt% was used instead of an aqueous solution of ammonium persulfate with a concentration of 0.11 wt%. The measurement results are shown in Table 7.

[0237] [Table 7]

Comparative example 2 Example 3 Example 4 Perfluoroundecanoic acid parts per billion/polymer 1.3×10 ³ 2.9×10 ² Perfluoroethercarboxylic acid A ppm/polymer 1.4×10 ³ 5.4×10 ² 3.1

[0238] Comparative Example 3

10.2 g of the PTFE 6 aqueous dispersion obtained in Production Example 3 and 2.7 g of deionized water were added to a screw cap test tube having an internal volume of 100 ml, and the same operations as in Comparative Example 1 were performed. The obtained extract was analyzed. The measurement results are shown in Table 8.

[0239] Example 5

10.2 g of the PTFE 6 aqueous dispersion obtained in Production Example 3 and 2.7 g of an aqueous solution of ammonium persulfate with a concentration of 0.11 mass% were added to a screw cap test tube having an internal volume of 100 ml, and maintained at an internal temperature of 80°C for 3 hours. After the heat treatment, the mixture was cooled, and 10 ml of methanol was added. The subsequent operations were carried out in the same manner as in Comparative Example 1 to obtain an extract. The measurement results are shown in Table 8.

[0240] Example 6

The same operations as in Example 5 were carried out except that an aqueous solution of ammonium persulfate with a concentration of 1.1 wt% was used instead of an aqueous solution of ammonium persulfate with a concentration of 0.11 wt%. The measurement results are shown in Table 8.

[0241] [Table 8]

Comparative example 3 Example 5 Example 6 Perfluoroethercarboxylic acid A ppm/polymer 6.1×10 ² 1.4×10 ² 0.8

Claims (29)

1. A method for producing a fluoropolymer-containing fluoropolymer composition, comprising: polymerizing a fluoromonomer in a reactor in the presence of a fluorine-containing surfactant, a polymerization initiator and an aqueous medium to obtain an aqueous dispersion containing a fluoropolymer; after the aqueous dispersion is prepared, removing from the reactor the fluoromonomer remaining in the reactor, or removing the aqueous dispersion from the reactor and placing it in a container different from the reactor; adding a radical generator to the aqueous dispersion; and subjecting an aqueous dispersion containing a radical generator to thermal treatment to obtain a fluoropolymer composition, where the heat treatment temperature is 35°C or higher and 120°C or lower. 2. The production method according to item 1, wherein the heat treatment temperature is equal to or higher than the decomposition temperature of the radical generator. 3. The method of production according to claim 1 or 2, wherein the radical generator is a water-soluble radical generator. 4. The production method according to claim 1 or 2, wherein the radical generator is an inorganic peroxide. 5. The production method according to claim 1 or 2, wherein the content of the fluoropolymer in the aqueous dispersion subjected to heat treatment is 1 wt.% or more. 6. The method of production according to claim 1 or 2, wherein the fluoropolymer composition is an aqueous dispersion or powder. 7. The method of production according to claim 1 or 2, comprising, after heat treatment to obtain an aqueous dispersion as a fluoropolymer composition, cooling the aqueous dispersion. 8. The method of production according to claim 1 or 2, comprising, after heat treatment to obtain an aqueous dispersion as a fluoropolymer composition, concentrating the aqueous dispersion. 9. The production method according to claim 1 or 2, comprising, after heat treatment to obtain an aqueous dispersion as a fluoropolymer composition, agglomerating the fluoropolymer in the aqueous dispersion and optionally drying the agglomerate. 10. The production method according to claim 1 or 2, wherein the fluorine-containing surfactant is an anionic fluorine-containing surfactant represented by the following general formula (N ⁰ ): X ⁿ⁰ -Rf ⁿ⁰ -Y ⁰ (N ⁰ ) where X ⁿ⁰ is H, Cl or F; Rf ⁿ⁰ is a linear, branched or cyclic alkylene group having 3-20 carbon atoms in which some or all of the H are replaced by F; the alkylene group optionally contains one or more ether linkages in which some of the H are optionally replaced by Cl; and Y ⁰ is an anionic group. 11. The production method according to claim 1 or 2, wherein the aqueous dispersion obtained by polymerizing the fluoromonomer contains a water-soluble fluorine-containing compound having a molecular weight of 1000 g/mol or less, and the fluoropolymer composition having a reduced content of the water-soluble fluorine-containing compound is obtained as a result of heat treatment. 12. The method of production according to claim 11, wherein the water-soluble fluorine-containing compound is a compound of the general formula (1): general formula (1): [X-Rf-A ^- ] _i M ⁱ⁺ where X is H, Cl, Br, F or I; Rf is a linear or branched, partially or fully fluorinated aliphatic group, or a linear or branched, partially fluorinated or fully fluorinated, aliphatic group interrupted by at least one oxygen atom; A ^- is an acidic group; M ⁱ⁺ is a cation having valence i; and i is an integer from 1 to 3. 13. The method of production according to claim 11, wherein the water-soluble fluorine-containing compound is a compound of the general formula (2): general formula (2): [C _n-1 F _2n-1 COO ^- ]M ⁺ where n is an integer from 9 to 12 and M ⁺ represents a cation. 14. The method of production according to claim 11, wherein the water-soluble fluorine-containing compound is a compound of the general formula (3): general formula (3): [R ¹ -OL-CO ₂ ^- ]M ⁺ where R ¹ is a linear or branched, partially or fully fluorinated aliphatic group, or a linear or branched, partially or fully fluorinated aliphatic group interrupted by at least one oxygen atom; L is a linear or branched non-fluorinated, partially or fully fluorinated alkylene group; and M ⁺ is a cation. 15. The production method according to claim 1 or 2, wherein the fluoropolymer is at least one fluoropolymer selected from the group consisting of polytetrafluoroethylene, a tetrafluoroethylene/fluoroalkyl vinyl ether copolymer, a tetrafluoroethylene/fluoroalkyl allyl ether copolymer, a tetrafluoroethylene/hexafluoropropylene copolymer, an ethylene/tetrafluoroethylene copolymer, an ethylene/tetrafluoroethylene/hexafluoropropylene copolymer, polychlorotrifluoroethylene, a chlorotrifluoroethylene/tetrafluoroethylene copolymer, an ethylene/chlorotrifluoroethylene copolymer, polyvinyl fluoride, polyvinylidene fluoride, a vinylidene fluoride/tetrafluoroethylene copolymer, a fluoromonomer/vinyl ether copolymer, a fluoromonomer polymer represented by the general formula (150): CF ₂ =CF-O-(CF ₂ CFY ¹⁵¹ -O) _n -(CFY ¹⁵² ) _m -A ¹⁵¹ , wherein Y ¹⁵¹ represents a fluorine atom, a chlorine atom, a -SO ₂ F group or a perfluoroalkyl group optionally containing an ether oxygen or a -SO ₂ F group; n represents an integer from 0 to 3; n Y ¹⁵¹ groups are the same or different; Y ¹⁵² represents a fluorine atom, a chlorine atom or a -SO ₂ F group; m represents an integer from 1 to 5; m Y ¹⁵² groups are the same or different; A ¹⁵¹ represents -SO ₂ X ¹⁵¹ , -COZ ¹⁵¹ or -POZ ¹⁵² Z ¹⁵³ ; X ¹⁵¹ represents F, Cl, Br, I, -OR ¹⁵¹ or -NR ¹⁵² R ¹⁵³ ; Z ¹⁵¹ , Z ¹⁵² and Z ¹⁵³ are the same or different and independently represent -NR ¹⁵⁴ R ¹⁵⁵ or -OR ¹⁵⁶ ; and R ¹⁵¹ , R ¹⁵² , R ¹⁵³ , R ¹⁵⁴ , R ¹⁵⁵ and R ¹⁵⁶ are the same or different and independently represent H, ammonium, an alkali metal or an alkyl group, an aryl group or a sulfonyl-containing group optionally containing a fluorine atom; and a fluoroelastomer.