Method for producing a fluoropolymer composition

Abstract

Provided is a method for producing a fluoropolymer composition that produces a fluoropolymer composition containing a fluoropolymer, wherein: an aqueous dispersion containing a fluoropolymer is prepared by polymerizing a fluoromonomer in the presence of a fluorine-containing surfactant, a polymerization initiator, and an aqueous medium in a reactor; after the aqueous dispersion has been prepared, the fluoromonomer remaining in the reactor is removed from the reactor or the aqueous dispersion in the reactor is recovered and housed in a container other than the reactor; a radical generator is added to the aqueous dispersion; and a fluoropolymer composition is obtained by heat treatment of the aqueous dispersion containing the radical generator.

Description

[Technical field]

[0001] The present disclosure relates to a method for making a fluoropolymer composition. [Background technology]

[0002] As a method for producing a fluoropolymer, a method of emulsion polymerization of a fluoromonomer is known. The 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 methods for reducing or removing such components other than the fluoropolymer have been studied.

[0003] Patent Document 1 discloses a method for reducing the fluoroether carboxylic acid or salt content of an aqueous fluoropolymer dispersion, the method comprising the steps of: [R 1 -OL-COO - ]Y + (In the formula, R 1 is a partially or fully fluorinated linear, branched or cyclic aliphatic group which may contain an ether bond; L is a partially or fully fluorinated branched alkylene group which may contain an ether bond; Y + is a hydrogen, ammonium or alkali metal cation) and a fluoroether carboxylic acid or salt having the formula: adding a stabilizer to the aqueous fluoropolymer dispersion to form a stabilized aqueous fluoropolymer dispersion; heating the stabilized aqueous fluoropolymer dispersion to decarboxylate the fluoroether carboxylic acid or salt to form a fluoroether by-product; removing at least a portion of the fluoroether by-products; and The method is described, which includes: [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-237842 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure aims to provide a production method capable of producing a fluoropolymer composition having a reduced content of fluorine-containing surfactant used in polymerizing a fluoromonomer and a reduced content of fluorine-containing compounds generated by polymerization of the fluoromonomer. [Means for solving the problem]

[0006] According to the present disclosure, a method for producing a fluoropolymer composition containing a fluoropolymer is provided, which comprises: polymerizing a fluoromonomer in a reactor in the presence of a fluorine-containing surfactant, a polymerization initiator and an aqueous medium to prepare an aqueous dispersion containing a fluoropolymer; after preparing the aqueous dispersion, either removing the fluoromonomer remaining in the reactor from the reactor, or recovering the aqueous dispersion in the reactor and storing 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 a fluoropolymer composition.

[0007] In the production method according to the present disclosure, the temperature of the heat treatment is preferably equal to or higher than the decomposition temperature of the radical generator. In the production method of the present disclosure, the radical generator is preferably a water-soluble radical generator. In the production method of the present disclosure, the radical generator is preferably an inorganic peroxide. In the production method of the present disclosure, the content of the fluoropolymer in the aqueous dispersion to be subjected to the heat treatment is preferably 1% by mass or more. In the manufacturing method of the present disclosure, the fluoropolymer composition is preferably an aqueous dispersion or a powder. In the production method of the present disclosure, after obtaining an aqueous dispersion as the fluoropolymer composition by the heat treatment, it is preferable to cool the aqueous dispersion. In the production method of the present disclosure, after obtaining an aqueous dispersion as the fluoropolymer composition by the heat treatment, it is preferable to concentrate the aqueous dispersion. In the production method of the present disclosure, it is preferable to obtain an aqueous dispersion as the fluoropolymer composition by the heat treatment, and then aggregate the fluoropolymer in the aqueous dispersion, and optionally dry the aggregate. In the production method according to the present disclosure, the fluorine-containing surfactant is represented by the following general formula (N 0 ): X n0 -Rf n0 -Y 0 (N 0 ) (In the formula, X n0 is H, Cl or F. n0 Y is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H's are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H's may be substituted with Cl. 0 is an anionic group. In the production method of the present disclosure, it is preferable that 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 that the 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 disclosure, the water-soluble fluorine-containing compound is preferably a compound represented by general formula (1). General formula (1): [X-Rf-A - ] i M i+ (wherein 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 or fully fluorinated aliphatic group interrupted by at least one oxygen atom; A - is the acid group, M i+ represents a cation having a valence i, where i is an integer from 1 to 3. In the production method of the present disclosure, the water-soluble fluorine-containing compound is preferably a compound represented by general formula (2). General formula (2):[C n-1 F 2n-1 COO - ]M + (In the formula, n is an integer of 9 to 12; M + represents a cation.) In the production method of the present disclosure, the water-soluble fluorine-containing compound is preferably a compound represented by general formula (3). General formula (3):[R 1 -OL-CO2 - ]M + (In the formula, R 1 represents 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 represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; M + represents a cation.) In the manufacturing method of the present disclosure, the fluoropolymer is 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 ester copolymer, and a copolymer represented by the general formula (150): CF2=CF-O-(CF2CFY 151 -O) n -(CFY 152 ) m -A 151 (In the formula, Y 151 represents a fluorine atom, a chlorine atom, a -SO2F group, or a perfluoroalkyl group. The perfluoroalkyl group may contain an etheric oxygen and a -SO2F group. n represents an integer of 0 to 3. n Y 151 may be the same or different. Y 152 represents a fluorine atom, a chlorine atom, or a -SO2F group. m represents an integer of 1 to 5. m Y 152 may be the same or different. A 151 -SO2X 151 , -COZ 151 or -POZ 152 Z 153 Represents X. 151 F, Cl, Br, I, -OR 151 or -NR 152 R 153 Represents Z. 151 , Z 152 and Z 153 are the same or different, -NR 154 R 155 -OR 156 Represents R 151 , R 152 , R 153 , R154 , R 155 and R 156 are the same or different and represent H, ammonium, an alkali metal, an alkyl group which may contain a fluorine atom, an aryl group, or a sulfonyl-containing group.) and fluororubbers. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a production method capable of producing a fluoropolymer composition having a reduced content of the fluorine-containing surfactant used in polymerizing the fluoromonomer and a reduced content of the fluorine-containing compound generated by the polymerization of the fluoromonomer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0010] The present disclosure relates to the method for producing fluoropolymer composition, which produces fluoropolymer composition containing at least fluoropolymer.In the production method of the present disclosure, in a reactor, in the presence of fluorine-containing surfactant, polymerization initiator and aqueous medium, fluoromonomer is polymerized to prepare the aqueous dispersion containing fluoropolymer, and after preparing the aqueous dispersion, either remove the fluoromonomer remaining in the reactor from the reactor, or collect the aqueous dispersion in the reactor and store it in a container different from the reactor used for polymerization, add radical generator to the aqueous dispersion, and heat-treat the aqueous dispersion containing radical generator to obtain fluoropolymer composition.

[0011] The aqueous dispersion obtained by polymerizing fluoromonomer may contain, in addition to fluoropolymer, fluorosurfactant and fluorine-containing compound produced by polymerization of fluoromonomer.In the manufacturing method of the present disclosure, prepare an aqueous dispersion by polymerization of fluoromonomer, remove the fluoromonomer remaining in the reactor from the reactor, or collect the aqueous dispersion in the reactor and store it in a container different from the reactor used for polymerization, and then add a radical generator to the aqueous dispersion and perform heat treatment.In this way, after stopping the polymerization reaction of fluoromonomer, add a radical generator to the aqueous dispersion and perform heat treatment, so that the fluorosurfactant and fluorine-containing compound are decomposed in the aqueous dispersion, and a fluoropolymer composition with reduced content of fluorosurfactant and fluorine-containing compound can be produced.

[0012] In the production method of the present disclosure, first, a fluoromonomer is 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 a fluoropolymer.

[0013] The polymerization of fluoromonomer can be carried out by charging a reactor with fluoromonomer, fluorine-containing surfactant, polymerization initiator, aqueous medium and other additives as necessary, stirring the contents of the reactor, and maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of polymerization initiator to start the polymerization reaction.After the polymerization reaction starts, fluoromonomer, polymerization initiator, fluorine-containing surfactant, chain transfer agent, etc. may be added according to the purpose.The polymerization method of fluoromonomer is not particularly limited, and may be emulsion polymerization method or suspension polymerization method, but emulsion polymerization method is preferred.

[0014] (Fluorine-containing surfactant) The fluorine-containing surfactant used in the polymerization of the fluoromonomer is not particularly limited as long as it is a surfactant containing at least one fluorine atom, and any conventionally known fluorine-containing surfactant can be used.

[0015] The fluorine-containing surfactant may be an anionic fluorine-containing surfactant, etc. The anionic fluorine-containing surfactant may be, for example, a surfactant containing fluorine atoms having a total carbon number of 20 or less excluding the anionic group.

[0016] The above-mentioned fluorine-containing surfactant may also be a surfactant containing fluorine in the anionic moiety having a molecular weight of 1,000 or less. The above-mentioned "anionic portion" means the portion of the above-mentioned fluorine-containing surfactant excluding the cation. For example, F(CF2) represented by the formula (I) described below n1 In the case of COOM, "F(CF2) n1 The "COO" part.

[0017] The above-mentioned fluorosurfactant also includes a fluorosurfactant having a LogPOW of 3.5 or less. The LogPOW is a partition coefficient between 1-octanol and water, and is expressed as LogP [wherein P represents the ratio of the fluorosurfactant concentration in octanol to the fluorosurfactant concentration in water when a 1:1 octanol / water mixture containing the fluorosurfactant undergoes phase separation]. The LogPOW is calculated from the HPLC elution time of the sample solution using a calibration curve of each elution time and the known octanol / water partition coefficient, which is prepared by performing HPLC on standard substances (heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid) having known octanol / water partition coefficients under the following conditions: column: TOSOH ODS-120T column (φ4.6 mm×250 mm, manufactured by Tosoh Corporation), eluent: acetonitrile / 0.6% by mass HClO4 water=1 / 1 (vol / vol%), flow rate: 1.0 ml / min, sample amount: 300 μL, column temperature: 40° C., and detection light: UV 210 nm.

[0018] Specific examples of the fluorine-containing surfactant include those described in U.S. Patent Application Publication No. 2007 / 0015864, U.S. Patent Application Publication No. 2007 / 0015865, U.S. Patent Application Publication No. 2007 / 0015866, U.S. Patent Application Publication No. 2007 / 0276103, U.S. Patent Application Publication No. 2007 / 0117914, U.S. Patent Application Publication No. 2007 / 142541, U.S. Patent Application Publication No. 2008 / 0015319, U.S. Patent No. 3,250,808, and the like. No. 3,271,341, JP 2003-119204 A, WO 2005 / 042593 A, WO 2008 / 060461 A, WO 2007 / 046377 A, JP 2007-119526 A, WO 2007 / 046482 A, WO 2007 / 046345 A, U.S. Patent Application Publication No. 2014 / 0228531 A, WO 2013 / 189824 A, and WO 2013 / 189826 A can be mentioned.

[0019] The anionic fluorine-containing surfactant may be a surfactant represented by the following general formula (N 0 ): X n0 -Rf n0 -Y 0 (N 0 ) (In the formula, X n0 is H, Cl or F. n0 Y is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H's are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H's may be substituted with Cl. 0 is an anionic group. Y 0 The anionic group may be -COOM, -SO2M, or -SO3M, and may be -COOM or -SO3M. M is H, a metal atom, or NR 7 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent, R 7is H or an organic group. The metal atom includes alkali metals (Group 1), alkaline earth metals (Group 2), etc., such as Na, K, or Li. R 7 As the 1-10 may be an organic group of H or C 1-4 may be an organic group of H or C 1-4 The alkyl group may be: M is H, a metal atom or NR 7 4, H, an alkali metal (group 1), an alkaline earth metal (group 2) or NR 7 4, which may be H, Na, K, Li or NH4. Above Rf n0 may be one in which 50% or more of H is substituted with fluorine.

[0020] The above general formula (N 0 The compound represented by the following general formula (N 1 ): X n0 -(CF2) m1 -Y 0 (N 1 ) (In the formula, X n0 is H, Cl, or F; m1 is an integer of 3 to 15; Y 0 is defined above.) a compound represented by the following general formula (N 2 ): Rf n1 -O-(CF(CF3)CF2O) m2 CFX n1 -Y 0 (N 2 ) (In the formula, Rf n1 is a perfluoroalkyl group having 1 to 5 carbon atoms, m2 is an integer of 0 to 3, and X n1 is F or CF3, and Y 0 is defined above.) a compound represented by the following general formula (N 3 ): Rf n2 (CH2) m3 -(Rf n3 )q -Y 0 (N 3 ) (In the formula, Rf n2 is a partially or fully fluorinated alkyl group having 1 to 13 carbon atoms, which may contain an ether bond and / or a chlorine atom, m3 is an integer of 1 to 3, Rf n3 is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, q is 0 or 1, and Y 0 is as defined above, a compound represented by the following general formula (N 4 ): Rf n4 -O-(CY n1 Y n2 ) p CF2-Y 0 (N 4 ) (In the formula, Rf n4 is a linear or branched, partially or completely fluorinated alkyl group having 1 to 12 carbon atoms, which may contain an ether bond; Y n1 and Y n2 are the same or different and are H or F, p is 0 or 1, and Y 0 is as defined above.) and a compound represented by the general formula (N 5 ): [ka] (In the formula, X n2 , X n3 and X n4 Rf may be the same or different and are H, F, or a linear or branched partially or completely fluorinated alkyl group having 1 to 6 carbon atoms, which may contain an ether bond. n5 is a linear or branched, partially or completely fluorinated alkylene group having 1 to 3 carbon atoms, which may contain an ether bond; L is a linking group; Y 0 is as defined above, where X n2 , X n3 , X n4 and Rf n5 The total number of carbon atoms is 18 or less.

[0021] The above general formula (N 0 More specifically, the compound represented by the formula (I) is a perfluorocarboxylic acid (I), a ω-H perfluorocarboxylic acid (II), a perfluoroether carboxylic acid (III), a perfluoroalkyl alkylene carboxylic acid (IV), a perfluoroalkoxy fluorocarboxylic acid (V), a perfluoroalkyl sulfonic acid (VI), a ω-H perfluoro sulfonic acid (VII), a perfluoroalkyl alkylene sulfonic acid (VIII), a perfluoroalkyl alkylene sulfonic acid (IX), a fluorocarboxylic acid (X), a fluorocarboxylic acid (X), a alkoxy fluoro sulfonic acid (XI), a compound (XII), a compound (XIII), and the like.

[0022] The perfluorocarboxylic acid (I) is represented by the following general formula (I): F(CF2) n1 COOM (I) (In the formula, n1 is an integer of 3 to 14, and M is H, a metal atom, or NR 7 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent, R 7 is H or an organic group.

[0023] The ω-H perfluorocarboxylic acid (II) is represented by the following general formula (II): H(CF2) n2 COOM (II) (wherein n2 is an integer of 4 to 15, and M is as defined above).

[0024] The perfluoroether carboxylic acid (III) is represented by the following general formula (III): Rf 1 -O-(CF(CF3)CF2O) n3 CF(CF3)COOM (III) (In the formula, Rf 1 is a perfluoroalkyl group having 1 to 5 carbon atoms, n3 is an integer of 0 to 3, and M is as defined above.

[0025] The perfluoroalkyl alkylene carboxylic acid (IV) is represented by the following general formula (IV): Rf 2 (CH2) n4 Rf 3 COOM (IV) (In the formula, Rf 2 is a perfluoroalkyl group having 1 to 5 carbon atoms, and Rf 3 is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, n4 is an integer of 1 to 3, and M is as defined above.

[0026] The alkoxyfluorocarboxylic acid (V) is represented by the following general formula (V): Rf 4 -O-CY 1 Y 2 CF2-COOM (V) (In the formula, Rf 4 is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain an ether bond and / or a chlorine atom; Y 1 and Y 2 are the same or different and are H or F, and M is as defined above.

[0027] The perfluoroalkylsulfonic acid (VI) is represented by the following general formula (VI): F(CF2) n5 SO3M (VI) (wherein n5 is an integer of 3 to 14, and M is as defined above).

[0028] The above ω-H perfluorosulfonic acid (VII) is represented by the following general formula (VII): H(CF2) n6 SO3M (VII) (wherein n6 is an integer of 4 to 14, and M is as defined above).

[0029] The perfluoroalkyl alkylene sulfonic acid (VIII) is represented by the following general formula (VIII): Rf 5 (CH2) n7 SO3M (VIII) (In the formula, Rf 5 is a perfluoroalkyl group having 1 to 13 carbon atoms, n7 is an integer of 1 to 3, and M is as defined above.

[0030] The alkyl alkylene carboxylic acid (IX) is represented by the following general formula (IX): Rf 6 (CH2) n8 COOM (IX) (In the formula, Rf 6 is a linear or branched partially or completely fluorinated alkyl group having 1 to 13 carbon atoms which may contain an ether bond, n8 is an integer from 1 to 3, and M is as defined above.

[0031] The fluorocarboxylic acid (X) is represented by the following general formula (X): Rf 7 -O-Rf 8 -O-CF2-COOM (X) (In the formula, Rf 7 is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, which may contain an ether bond and / or a chlorine atom; Rf 8 is a linear or branched, partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, and M is as defined above.

[0032] The alkoxyfluorosulfonic acid (XI) is represented by the following general formula (XI): Rf 9 -O-CY 1 Y 2 CF2-SO3M (XI) (In the formula, Rf 9 is a linear or branched alkyl group having 1 to 12 carbon atoms, which may contain an ether bond, and which may contain chlorine, and which is partially or completely fluorinated; Y 1 and Y 2 are the same or different and are H or F, and M is as defined above.

[0033] The compound (XII) is represented by the following general formula (XII): [ka] (In the formula, X 1 , X 2 and X 3 Rf may be the same or different and are H, F and linear or branched partially or completely fluorinated alkyl groups having 1 to 6 carbon atoms, which may contain ether bonds; 10 is a perfluoroalkylene group having 1 to 3 carbon atoms, L is a linking group, and Y 0 is an anionic group. Y 0 may be -COOM, -SO2M, or -SO3M, or may be -SO3M or COOM, where M is as defined above. Examples of L include a single bond, and a partially or fully fluorinated alkylene group having 1 to 10 carbon atoms which may contain an ether bond.

[0034] The compound (XIII) is represented by the following general formula (XIII): Rf 11 -O-(CF2CF(CF3)O) n9 (CF2O) n10 CF2COOM (XIII) (In the formula, Rf 11is a fluoroalkyl group containing chlorine and having 1 to 5 carbon atoms, n9 is an integer of 0 to 3, n10 is an integer of 0 to 3, and M is as defined above.) Compound (XIII) is represented by CF2ClO(CF2CF(CF3)O) n9 (CF2O) n10 CF2COONH4 (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 carboxylic acid surfactants and sulfonic acid surfactants.

[0036] The fluorine-containing surfactant may be one type of fluorine-containing surfactant or a mixture containing two or more types of fluorine-containing surfactants.

[0037] The fluorine-containing surfactant preferably has no methylene group (-CH2-), more preferably no C-H bond. By using a fluorine-containing surfactant that does not have a methylene group (-CH2-) or a C-H bond in the molecule, the polymerization of the fluoromonomer in the presence of an aqueous medium can be smoothly carried out.

[0038] The number of H atoms in the hydrophobic group of the fluorine-containing surfactant is preferably 0 or 1, and more preferably 0. By using a fluorine-containing surfactant having a small number of H atoms bonded to carbon atoms constituting the hydrophobic group, the polymerization of the fluoromonomer can be smoothly carried out in the presence of an aqueous medium. The number of carbon atoms in the hydrophobic group of the fluorine-containing surfactant having a hydrophobic group and a hydrophilic group is preferably 1 to 50, more preferably 3 to 20, and further preferably 6 to 12. The hydrophobic group usually constitutes the above-mentioned "part excluding the anionic group" in the molecular structure of the fluorine-containing surfactant. As the hydrophilic group, Y 0 The fluorine-containing surfactant may be a saturated fluorinated surfactant in which all of the carbon atoms bonded to the hydrophobic group are substituted with fluorine atoms.

[0039] As the fluorine-containing surfactant, among the above-mentioned anionic fluorine-containing surfactants, those represented by the general formula (N 1 ), a compound represented by the general formula (N 2 ), a compound represented by the general formula (N 4 ): Rf n4 -O-(CY n1 F) p CF2-Y 0 (N 4 ) (In the formula, Rf n4 is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain an ether bond (excluding those having -CH2-), and Y n1 is H or F, p is 0 or 1, and Y 0 is as defined above.) and a compound represented by the general formula (N 5 ): [ka] (In the formula, X n2 , X n3 and X n4 may be the same or different and are H, F, or a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, which may contain an ether bond (excluding those having -CH2-), provided that X n3 and X n4 Both Rf and Rf cannot be H. n5 is a linear or branched alkylene group having 1 to 3 carbon atoms, which may contain an ether bond, or a fully fluorinated alkylene group (excluding those having -CH2-), L is a linking group, Y 0 is as defined above, where X n2 , X n3 , X n4 and Rf n5 The total number of carbon atoms is 18 or less.

[0040] As the fluorine-containing surfactant, among the above-mentioned anionic fluorine-containing surfactants, perfluorocarboxylic acid (I) represented by general formula (I), ω-H perfluorocarboxylic acid (II) represented by general formula (II), perfluoroether carboxylic acid (III) represented by general formula (III), perfluoroalkyl alkylene carboxylic acid (IV) represented by general formula (IV), perfluoroalkoxy fluorocarboxylic acid (V) represented by general formula (V), perfluoroalkyl sulfonic acid (VI) represented by general formula (VII), ω-H perfluoro sulfonic acid (VII) represented by general formula (VII), perfluoroalkyl alkylene sulfonic acid (VIII) represented by general formula (VIII), perfluoroalkyl alkylene sulfonic acid (VIII) represented by general formula (X): Rf 7 -O-Rf 8 -O-CF2-COOM (In the formula, Rf 7 is a linear or branched partially or completely fluorinated alkyl group having 1 to 6 carbon atoms, which may contain an ether bond and / or a chlorine atom (excluding those having -CH2-), 8 is a linear or branched, partially or completely fluorinated alkyl group having 1 to 6 carbon atoms (excluding those having -CH2-), and M is as defined above. 9 -O-CY 1 FCF2-SO3M (In the formula, Rf 9 is a linear or branched alkyl group having 1 to 12 carbon atoms which may contain an ether bond and which is partially or completely fluorinated and may contain chlorine (excluding those having -CH2-), 1 is H or F, and M is as defined above.) an alkoxyfluorosulfonic acid (XI) represented by the general formula (XII): [ka] (In the formula, X 1 , X 2 and X 3may be the same or different and are H, F, and linear or branched alkyl groups having 1 to 6 carbon atoms, which may contain an ether bond, or fully fluorinated alkyl groups (excluding those having -CH2-), provided that X 2 and X 3 Both of Rf 10 is a perfluoroalkylene group having 1 to 3 carbon atoms, L is a linking group, and Y 0 is an anionic group. and a compound represented by the general formula (XIII): Rf 11 -O-(CF2CF(CF3)O) n9 (CF2O) n10 CF2COOM (In the formula, Rf 11 is a fluoroalkyl group having 1 to 5 carbon atoms containing chlorine (excluding those having -CH2-), n9 is an integer of 0 to 3, n10 is an integer of 0 to 3, and M is as defined above.) is more preferred. By using these fluorine-containing surfactants, the polymerization of fluoromonomers can be smoothly carried out in the presence of an aqueous medium.

[0041] The fluorine-containing surfactant may be a compound represented by the following formula: The fluorine-containing surfactant may be a mixture of these compounds. F(CF2)7COOM, F(CF2)5COOM, H(CF2)6COOM, H(CF2)7COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, C2F5OCF(CF3)CF2OCF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, [ka] (In each formula, M is H, metal atom, NR 7 4. An imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent.

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

[0043] (Polymerization initiator) The polymerization initiator used for the polymerization of the fluoromonomer is not particularly limited as long as it can generate radicals within the polymerization temperature range, and known oil-soluble and / or water-soluble polymerization initiators can be used. Furthermore, it can also be combined with a reducing agent or the like to initiate polymerization as a redox. The concentration of the polymerization initiator is appropriately determined depending on the type of monomer, the molecular weight of the desired fluoropolymer, and the reaction rate.

[0044] As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

[0045] The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, for example, dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and disec-butyl peroxydicarbonate, peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate, dialkyl peroxides such as di-t-butyl peroxide, and the like. In addition, di(ω-hydro-dodecafluorohexanoyl) peroxide, di(ω-hydro-tetradecafluoroheptanoyl) peroxide, di(ω-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, di(ω-chloro Representative examples of perfluoro(or fluorochloro)acyl]peroxides include di(ω-hexafluorobutyryl) peroxide, di(ω-chloro-decafluorohexanoyl) peroxide, di(ω-chloro-tetradecafluorooctanoyl) peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl) peroxide, di(trichlorooctafluorohexanoyl) peroxide, di(tetrachloroundecafluorooctanoyl) peroxide, di(pentachlorotetradecafluorodecanoyl) peroxide, and di(undecachlorodotriacontafluorodocosanoyl) peroxide.

[0046] The water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as 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, t-butyl permaleate, t-butyl hydroperoxide, etc. A reducing agent such as sulfites may also be contained, and the amount used may be 0.1 to 20 times that of the peroxide.

[0047] For example, when polymerization is carried out at a low temperature of 30°C or less, it is preferable to use a redox initiator that combines an oxidizing agent and a reducing agent as the polymerization initiator. Examples of the oxidizing agent include persulfates, organic peroxides, potassium permanganate, manganese triacetate, cerium ammonium nitrate, etc. Examples of the reducing agent include sulfites, bisulfites, bromates, diimines, oxalic acid, etc. 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, it is also preferable to add a copper salt or an iron salt to the combination of the redox initiator. Examples of the copper salt include copper(II) sulfate, and examples of the iron salt include iron(II) sulfate.

[0048] Examples of the redox initiator include potassium permanganate / oxalic acid, ammonium persulfate / bisulfite / iron sulfate, manganese triacetate / oxalic acid, cerium ammonium nitrate / oxalic acid, bromate / bisulfite, and the like, with potassium permanganate / oxalic acid being preferred. When using a redox initiator, either an oxidizing agent or a reducing agent may be charged in advance into a polymerization tank, and then the other may be added continuously or intermittently to initiate polymerization. For example, when potassium permanganate / oxalic acid is used, it is preferred to charge oxalic acid into a polymerization tank and continuously add potassium permanganate thereto.

[0049] The amount of polymerization initiator to be added is not particularly limited, but may be added all at once, stepwise, or continuously in an amount (for example, several ppm relative to water concentration) at least at which the polymerization rate does not drop significantly. The upper limit is a range in which the reaction temperature may be increased while removing heat from the equipment side by the polymerization reaction heat, and a more preferable upper limit is a range in which the polymerization reaction heat can be removed from the equipment side.

[0050] When the fluoromonomer is polymerized, the radical concentration during polymerization can be adjusted by adding a decomposer. Examples of the decomposer include sulfite, bisulfite, bromate, diimine, oxalic acid, copper salt, and iron salt. Examples of the sulfite include sodium sulfite and ammonium sulfite. Examples of the copper salt include copper (II) sulfate, and examples of the iron salt include iron (II) sulfate. The amount of the decomposer added is in the range of 25 to 300 mass% based on the amount of the oxidizing agent combined as the polymerization initiator (redox initiator). The amount of the decomposer added is preferably 25 to 150 mass%, more preferably 50 to 100 mass%. In addition, it is preferable to add the decomposer after 5 mass% of the total fluoromonomer consumed in the polymerization reaction is polymerized, and more preferably after 10 mass% is polymerized. The amount of the decomposer added is preferably an amount equivalent to 0.1 to 20 mass ppm of the mass of the aqueous medium used, and more preferably an amount equivalent to 3 to 10 mass ppm.

[0051] (aqueous medium) The aqueous medium used in the polymerization of fluoromonomers is a reaction medium in which polymerization is carried out, and refers to a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and, for example, a fluorine-free organic solvent such as ether or ketone, and / or a fluorine-containing organic solvent having a boiling point of 40° C. or less.

[0052] As the aqueous medium, an aqueous medium containing only water or an aqueous medium containing only water and a fluorine-free organic solvent is preferred, since it allows the polymerization of the fluoromonomer to proceed smoothly and also prevents a decrease in the efficiency of removing the fluorine-containing surfactant and the fluorine-containing compound due to heat treatment after the preparation of the aqueous dispersion, and an aqueous medium containing only water is more preferred.

[0053] The content of water in the aqueous medium is preferably 90% or more, more preferably 95% or more, even more preferably 99.0% or more, still more preferably 99.5% or more, particularly preferably 99.9% or more, and may be 100%, based on the mass of the aqueous medium, because this allows the polymerization of the fluoromonomer to proceed smoothly and also prevents a decrease in the efficiency of removing the fluorinated surfactant and the fluorinated compound due to heat treatment after the preparation of the aqueous dispersion.

[0054] (Fluoromonomer) The fluoromonomer used in the polymerization has at least one fluorine atom and at least one double bond. Examples of the fluoromonomer include tetrafluoroethylene [TFE], hexafluoropropylene [HFP], chlorotrifluoroethylene [CTFE], vinyl fluoride, vinylidene fluoride [VdF], trifluoroethylene, fluoroalkyl vinyl ether, fluoroalkyl ethylene, fluoroalkyl allyl ether, trifluoropropylene, pentafluoropropylene, trifluorobutene, tetrafluoroisobutene, hexafluoroisobutene, and the general formula (100): CHX 101 =CX 102 Rf 101 (In the formula, X 101 and X 102 is H on one side and F on the other side, and Rf 101 At least one selected from the group consisting of a fluoromonomer represented by (wherein is a straight-chain or branched fluoroalkyl group having 1 to 12 carbon atoms), a fluorinated vinyl heterocyclic compound, and a monomer that provides a crosslinking site is preferred.

[0055] Examples of the fluoroalkyl vinyl ether [FAVE] include: General formula (110): CF2=CF-ORf 111 (In the formula, Rf 111 represents a perfluoro organic group; General formula (120): CF2=CF-OCH2-Rf 121 (In the formula, Rf 121 is a perfluoroalkyl group having 1 to 5 carbon atoms), General formula (130): CF2=CFOCF2ORf 131 (In the formula, Rf 131 is a linear or branched perfluoroalkyl group having 1 to 6 carbon atoms, a cyclic perfluoroalkyl group having 5 to 6 carbon atoms, or a linear or branched perfluorooxyalkyl group having 2 to 6 carbon atoms and containing 1 to 3 oxygen atoms, General formula (140): CF2=CFO(CF2CF(Y 141 )O) m (CF2) n F (In the formula, Y 141 represents a fluorine atom or a trifluoromethyl group; m is an integer of 1 to 4; and n is an integer of 1 to 4. General formula (150): CF2=CF-O-(CF2CFY 151 -O) n -(CFY 152 ) m -A 151 (In the formula, Y 151 represents a fluorine atom, a chlorine atom, a -SO2F group, or a perfluoroalkyl group. The perfluoroalkyl group may contain an etheric oxygen and a -SO2F group. n represents an integer of 0 to 3. n Y 151 may be the same or different. Y 152 represents a fluorine atom, a chlorine atom, or a -SO2F group. m represents an integer of 1 to 5. m Y 152 may be the same or different. A 151-SO2X 151 , -COZ 151 or -POZ 152 Z 153 Represents X. 151 F, Cl, Br, I, -OR 151 or -NR 152 R 153 Represents Z. 151 , Z 152 and Z 153 are the same or different, -NR 154 R 155 -OR 156 Represents R 151 , R 152 , R 153 , R 154 , R 155 and R 156 are the same or different and represent H, ammonium, an alkali metal, an alkyl group which may contain a fluorine atom, an aryl group, or a sulfonyl-containing group. At least one selected from the group consisting of:

[0056] In the present disclosure, the "perfluoro organic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. The perfluoro organic group may have an ether oxygen.

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

[0058] Examples of the perfluoro organic 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. The fluoromonomer represented by the general formula (110) further includes a fluoromonomer represented by the general formula (110) in which Rf 111 is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, Rf111 is the following formula:

[0059] [ka]

[0060] (wherein m represents 0 or an integer of 1 to 4), Rf 111 is the following formula:

[0061] [ka]

[0062] (wherein n represents an integer of 1 to 4).

[0063] Among the fluoromonomers represented by the general formula (110), General formula (160): CF2=CF-ORf 161 (In the formula, Rf 161 Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms. 161 is preferably a perfluoroalkyl group having 1 to 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 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 at least one selected from the group consisting of perfluoro(methyl vinyl ether) and perfluoro(propyl vinyl ether).

[0066] The fluoromonomer represented by general formula (130) is preferably at least one selected from the group consisting of CF2=CFOCF2OCF3, CF2=CFOCF2OCF2CF3 and CF2=CFOCF2OCF2CF2OCF3.

[0067] The fluoromonomer represented by general formula (140) is preferably at least one selected from the group consisting of CF2=CFOCF2CF(CF3)O(CF2)3F, CF2=CFO(CF2CF(CF3)O)2(CF2)3F, and CF2=CFO(CF2CF(CF3)O)2(CF2)2F.

[0068] The fluoromonomer represented by general formula (150) is preferably at least one selected from the group consisting of CF2=CFOCF2CF2SO2F, CF2=CFOCF2CF(CF3)OCF2CF2SO2F, CF2=CFOCF2CF(CF2CF2SO2F)OCF2CF2SO2F and CF2=CFOCF2CF(SO2F)2.

[0069] The fluoromonomer represented by the general formula (100) is Rf 101 is a linear fluoroalkyl group, and Rf 101 More preferred is a fluoromonomer in which Rf is a straight-chain perfluoroalkyl group. 101 The number of carbon atoms in the formula (100) is preferably 1 to 6. Examples of the fluoromonomer represented by the formula (100) include CH2=CFCF3, CH2=CFCF2CF3, CH2=CFCF2CF2CF3, CH2=CFCF2CF2CF2H, CH2=CFCF2CF2CF2CF3, CHF=CHCF3 (E form), CHF=CHCF3 (Z form), and the like. Of these, 2,3,3,3-tetrafluoropropylene represented by CH2=CFCF3 is preferred.

[0070] The fluoroalkyl ethylenes include: General formula (170): CH2=CH-(CF2) n -X 171 (In the formula, X 171is H or F, and n is an integer of 3 to 10. Fluoroalkylethylenes represented by the formula: CH2=CH-C4F9 and CH2=CH-C6F 13 At least one selected from the group consisting of:

[0071] Examples of the fluoroalkyl allyl ether include General formula (180): CF2=CF-CF2-ORf 111 (In the formula, Rf 111 represents a perfluoro organic group.

[0072] Rf of general formula (180) 111 is Rf in general formula (110). 111 is the same as Rf 111 is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. As the fluoroalkyl allyl ether represented by the general formula (180), at least one selected from the group consisting of CF2=CF-CF2-O-CF3, CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9 is preferable, at least one selected from the group consisting of CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9 is more preferable, and CF2=CF-CF2-O-CF2CF2CF3 is even more preferable.

[0073] The fluorinated vinyl heterocycle may be represented by the general formula (230): [ka] (In the formula, X 231 and X 232 are independently F, Cl, a methoxy group or a fluorinated methoxy group; Y 231 is the formula Y 232 or formula Y 233 It is.

[0074] [ka] (In the formula, Z 231 and Z 232 are independently F or a fluorinated alkyl group having 1 to 3 carbon atoms.

[0075] Examples of monomers that provide crosslinking sites include: General formula (180):CX 181 2=CX 182 -R f 181 CHR 181 X 183 (In the formula, X 181 and X 182 are independently a hydrogen atom, a fluorine atom, or CH3, R f 181 represents a fluoroalkylene group, a perfluoroalkylene group, a fluoro(poly)oxyalkylene group or a perfluoro(poly)oxyalkylene group; R 181 is a hydrogen atom or CH3, X 183 is an iodine atom or a bromine atom. General formula (190):CX 191 2=CX 192 -R f 191 X 193 (In the formula, X 191 and X 192 are independently a hydrogen atom, a fluorine atom, or CH3, R f 191 represents a fluoroalkylene group, a perfluoroalkylene group, a fluoropolyoxyalkylene group or a perfluoropolyoxyalkylene group; X 193 is an iodine atom or a bromine atom. General formula (200): CF2=CFO(CF2CF(CF3)O) m (CF2) n -X 201 (In the formula, m is an integer of 0 to 5, n is an integer of 1 to 3, X 201is a cyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CHI; and General formula (210): CH2=CFCF2O(CF(CF3)CF2O) m (CF(CF3)) n -X 211 (In the formula, m is an integer of 0 to 5, n is an integer of 1 to 3, X 211 is a cyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CHOH; General formula (220):CR 221 R 222 =CR 223 -Z 221 -CR 224 =CR 225 R 226 (In the formula, R 221 , R 222 , R 223 , R 224 , R 225 and R 226 are the same or different and each is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. 221 represents a linear or branched alkylene group having 1 to 18 carbon atoms, a cycloalkylene group having 3 to 18 carbon atoms, an at least partially fluorinated alkylene group or oxyalkylene group having 1 to 10 carbon atoms, which may have an oxygen atom, or -(Q) p -CF2O-(CF2CF2O) m (CF2O) n -CF2-(Q) p - (wherein Q is an alkylene group or an oxyalkylene group, p is 0 or 1, and m / n is 0.2 to 5), and is a (per)fluoropolyoxyalkylene group having a molecular weight of 500 to 10,000. At least one selected from the group consisting of:

[0076] X 183 and X 193is preferably an iodine atom. f 181 and R f 191 R is preferably a perfluoroalkylene group having 1 to 5 carbon atoms. 181 is preferably a hydrogen atom. 201 is preferably a cyano group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CH2I. 211 is preferably a cyano group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or -CHOH.

[0077] Monomers that provide crosslinking sites include CF2=CFOCF2CF(CF3)OCF2CF2CN, CF2=CFOCF2CF(CF3)OCF2CF2COOH, CF2=CFOCF2CF(CF3)OCF2CF2CH2I, CF2=CFOCF2CF2CH2I, CH2=CFCF2OCF(CF3)CF2OCF(CF3)CN, CH2=CFCF2OCF(CF3)CF2OCF(CF3)COOH, CH2=CFCF2OC At least one selected from the group consisting of F(CF3)CF2OCF(CF3)CH2OH, CH2=CHCF2CF2I, CH2=CH(CF2)2CH=CH2, CH2=CH(CF2)6CH=CH2 and CF2=CFO(CF2)5CN is preferred, and at least one selected from the group consisting of CF2=CFOCF2CF(CF3)OCF2CF2CN and CF2=CFOCF2CF2CH2I is more preferred.

[0078] In the polymerization, the fluoromonomer and a non-fluorine-containing monomer may be polymerized. Examples of the non-fluorine-containing monomer include hydrocarbon monomers reactive 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 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 para-t-butylbenzoate, vinyl cyclohexanecarboxylate, vinyl monochloroacetate, vinyl adipate, vinyl acrylate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl cinnamate, vinyl undecylenate, vinyl hydroxyacetate, vinyl hyaluronate ... vinyl esters such as 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 esters such as ethyl allyl ester, propyl allyl ester, butyl allyl ester, isobutyl allyl ester, and cyclohexyl allyl ester; 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 functional group-containing hydrocarbon monomer (excluding the monomer that provides a crosslinking site). Examples of the functional group-containing hydrocarbon monomer 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 methylol acrylamide; fluorine-free monomers having a nitrile group such as acrylonitrile and methacrylonitrile.

[0080] In the above polymerization, one or more of the above fluoromonomers can be polymerized to obtain particles of the desired fluoropolymer.

[0081] (Chain transfer agent) In the manufacturing method of the present disclosure, the fluoromonomer can be polymerized in the presence of a chain transfer agent. The polymerization rate and molecular weight can be adjusted by using the chain transfer agent. 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] Bromine compounds or iodine compounds may be used as chain transfer agents. Examples of polymerization methods using bromine compounds or iodine compounds include a method of polymerizing a fluoromonomer in an aqueous medium in the presence of a bromine compound or iodine compound in a substantially oxygen-free state (iodine transfer polymerization method). Representative examples of the bromine compounds or iodine compounds used include, for example, compounds represented by the general formula: R a I x Br y (In the formula, x and y are each an integer of 0 to 2, and 1≦x+y≦2 is satisfied; R a is a saturated or unsaturated fluorohydrocarbon group or chlorofluorohydrocarbon group having 1 to 16 carbon atoms, or a hydrocarbon group having 1 to 3 carbon atoms, which may contain an oxygen atom). By using a bromine compound or an iodine compound, iodine or bromine is introduced into the polymer and functions as a crosslinking point.

[0083] Examples of the bromine compound or iodine 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, CF2Br2, BrCF2CF2Br, CF3CFBrCF2Br, CFClBr2, BrCF2 Examples of the iodoperfluoroalkyl group include CFClBr, CFBrClCFClBr, BrCF2CF2CF2Br, BrCF2CFBrOCF3, 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, monoiodomonobromo-substituted benzene, diiodomonobromo-substituted benzene, and (2-iodoethyl) and (2-bromoethyl)-substituted benzene. These compounds may be used alone or in combination with each other.

[0084] Among these, it is preferable to use 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, and 2-iodoperfluoropropane in terms of polymerization reactivity, crosslinking reactivity, availability, and the like.

[0085] The amount of chain transfer agent used is usually 1 to 50,000 mass ppm, preferably 1 to 20,000 mass ppm, based on the total amount of fluoromonomers supplied. The amount of chain transfer agent used is preferably an amount that is completely consumed during polymerization of fluoromonomers and does not remain in the aqueous dispersion containing fluoropolymer, so as not to reduce the efficiency of removing fluorine-containing surfactants and fluorine-containing compounds by heat treatment after preparing the aqueous dispersion as much as possible. Therefore, the amount of chain transfer agent used is more preferably 10,000 mass ppm or less, even more preferably 5,000 mass ppm or less, still more preferably 1,000 mass ppm or less, particularly preferably 500 mass ppm or less, and most preferably 200 mass ppm or less, based on the total amount of fluoromonomers supplied.

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

[0087] (Other additives) In the polymerization of fluoromonomers, additives such as buffers, pH adjusters, stabilizing aids, and dispersion stabilizers can be used. In addition, in the polymerization of fluoromonomers, radical scavengers and decomposers can be added to adjust the polymerization rate and molecular weight. In addition, in the polymerization of fluoromonomers, fluorine-free anionic surfactants, fluorine-free nonionic surfactants, fluorine-free cationic surfactants, and the like can be used.

[0088] As the stabilizing aid, paraffin wax, fluorine-based oil, fluorine-based solvent, silicone oil, etc. are preferable. The stabilizing aid may be used alone or in combination of two or more. As the stabilizing aid, paraffin wax is more preferable. The paraffin wax may be liquid, semi-solid, or solid at room temperature, but is preferably a saturated hydrocarbon having 12 or more carbon atoms. The melting point of the paraffin wax is usually preferably 40 to 65°C, more preferably 50 to 65°C.

[0089] The amount of the stabilizing aid used is preferably 0.1 to 12 mass %, more preferably 0.1 to 8 mass %, based on the mass of the aqueous medium used. It is desirable that the stabilizing aid is sufficiently hydrophobic and completely separated from the aqueous dispersion after polymerization so as not to become a contaminating component.

[0090] (Polymerization conditions) The polymerization of the fluoromonomer can be carried out under normal pressure and temperature. Usually, the polymerization temperature is 5 to 120°C, and the polymerization pressure is 0.05 to 10 MPaG. The polymerization temperature and polymerization pressure are appropriately determined depending on the type of monomer, the molecular weight of the desired fluoropolymer, the reaction rate, etc.

[0091] (aqueous dispersion) By polymerization of the fluoromonomer, an aqueous dispersion containing a fluoropolymer is obtained. The content of the fluoropolymer in the aqueous dispersion after polymerization is usually 8 to 50 mass % relative to the aqueous dispersion.

[0092] The aqueous dispersion obtained by polymerizing a fluoromonomer usually contains, in addition to the fluoropolymer, the fluorine-containing surfactant used in polymerizing the fluoromonomer. Also, the aqueous dispersion obtained by polymerizing a fluoromonomer may contain, in addition to the fluoropolymer, a fluorine-containing compound generated by polymerization of the fluoromonomer. In this disclosure, the fluorine-containing compound is a compound that is not added during polymerization of the fluoromonomer, and includes, for example, a compound that has a structure similar to that of the fluorine-containing surfactant but has a different carbon number.

[0093] As the fluorine-containing compound in the aqueous dispersion, a typical compound is a water-soluble fluorine-containing compound having a molecular weight of 1000 g / mol or less. According to the manufacturing method of the present disclosure, a fluoropolymer composition can be manufactured in which the content of the water-soluble fluorine-containing compound having a molecular weight of 1000 g / mol or less in the aqueous dispersion obtained by polymerization of a fluoromonomer is reduced. The molecular weight of the fluorine-containing compound may be, for example, 800 g / mol or less.

[0094] In one embodiment of the aqueous dispersion, the water-soluble fluorine-containing compound is a compound represented by the following general formula (1). General formula (1): [X-Rf-A - ] i M i+ (wherein 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 or fully fluorinated aliphatic group interrupted by at least one oxygen atom; A - is the acid group, M i+ represents a cation having a valence i, where i is an integer from 1 to 3.

[0095] In one embodiment of the aqueous dispersion, the water-soluble fluorine-containing compound is a compound represented by the following general formula (2). General formula (2):[C n-1 F 2n-1 COO - ]M + (In the formula, n is an integer of 9 to 12; M + represents a cation.)

[0096] It is known that compounds represented by general formula (2) (perfluoroalkanoic acids) are formed during polymerization when perfluoroalkyl vinyl ethers or the like are used as modified monomers (see WO 2019 / 161153).

[0097] In one embodiment of the aqueous dispersion, the water-soluble fluorine-containing compound is a compound represented by the following general formula (3). General formula (3):[R 1 -OL-CO2 - ]M + (In the formula, R 1represents 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 represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; M + represents a cation.)

[0098] In one embodiment of the aqueous dispersion, the water-soluble fluorine-containing compound contains a compound represented by the general formula (4): General formula (4):[H-(CF2) m CO2 - ]M + (In the formula, m is an integer of 3 to 19, M + represents a cation.)

[0099] (Fluoropolymer) Fluoropolymers such as fluororesins and fluororubbers can be obtained by polymerization of fluoromonomers.

[0100] Examples of fluororesins 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 ester copolymer, and polymers of fluoromonomers represented by general formula (150).

[0101] Among them, the fluororesin is preferably at least one selected from the group consisting of PTFE, PFA, and FEP, since the effects of the production method of the present disclosure are greatly exhibited.

[0102] The PTFE may be homo-PTFE or modified PTFE. The modified PTFE contains a TFE unit and a modified monomer unit based on a modified monomer copolymerizable with TFE. The PTFE may be a high molecular weight PTFE that is non-melt processable and fibrillating, or a low molecular weight PTFE that is melt processable and not fibrillating.

[0103] The modified monomer is not particularly 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 ethers [FAVE], fluoroalkyl allyl ethers, perfluoroalkyl ethylene, ethylene, fluorine-containing vinyl ethers having a nitrile group, etc. The modified monomer used may be one type or multiple types.

[0104] The fluororubber may be a partially fluorinated rubber or a perfluororubber.

[0105] Examples of partially fluorinated rubber include VdF-based fluororubber, TFE / propylene (Pr)-based fluororubber, TFE / propylene / VdF-based fluororubber, ethylene / HFP-based fluororubber, ethylene / HFP / VdF-based fluororubber, ethylene / HFP / TFE-based fluororubber, ethylene / HFP / FAVE-based rubber, etc. Among these, at least one selected from the group consisting of VdF-based fluororubber and TFE / propylene-based fluororubber is preferred.

[0106] Specific examples of VdF-based fluororubbers include VdF / HFP-based rubber, VdF / HFP / TFE-based rubber, VdF / CTFE-based rubber, VdF / CTFE / TFE-based rubber, VdF / fluoromonomer-based rubber represented by general formula (100), VdF / fluoromonomer / TFE-based rubber represented by general formula (100), VdF / perfluoro(methyl vinyl ether) [PMVE]-based rubber, VdF / PMVE / TFE-based rubber, VdF / PMVE / TFE / HFP-based rubber, etc. As the VdF / fluoromonomer-based rubber represented by general formula (100), VdF / CH2=CFCF3-based rubber is preferred, and as the VdF / fluoromonomer / TFE-based rubber represented by general formula (100), VdF / TFE / CH2=CFCF3-based rubber is preferred.

[0107] The perfluororubber is preferably at least one selected from the group consisting of perfluororubbers containing TFE, for example, TFE / fluoromonomer copolymers represented by general formula (110), (130) or (140), and TFE / fluoromonomer represented by general formula (110), (130) or (140) / monomer copolymers providing crosslinking sites.

[0108] In one embodiment of the aqueous dispersion, the fluoropolymer contains a fluoropolymer that contains fluoroalkyl vinyl ether units.

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

[0110] The content of fluoroalkyl vinyl ether units in the fluoropolymer is preferably 0.0000001 to 30 mol%, more preferably 0.000001 mol% or more, even more preferably 0.00001 mol% or more, preferably 25 mol% or less, even more preferably 20 mol% or less, and particularly preferably 8 mol% or less, based on the total polymerized units constituting the fluoropolymer.

[0111] Examples of fluoropolymers containing such polymerized units include: Fluororesins such as PTFE modified with fluoroalkyl vinyl ether (FAVE) and TFE / FAVE copolymer (PFA); Partially fluorinated rubbers such as ethylene / HFP / FAVE rubber, VdF / PMVE rubber, VdF / PMVE / TFE rubber, VdF / PMVE / TFE / HFP rubber; Perfluororubber; etc.

[0112] In one embodiment of the aqueous dispersion, the fluoropolymer contains low molecular weight PTFE.

[0113] Low molecular weight PTFE can generally be produced by polymerization employing polymerization conditions for producing low molecular weight PTFE, or by reducing the molecular weight of high molecular weight PTFE obtained by polymerization using a known method (thermal decomposition, decomposition by radiation irradiation, etc.). In the production method of the present disclosure, an aqueous dispersion containing low molecular weight PTFE can be prepared by polymerization employing polymerization conditions for producing low molecular weight PTFE.

[0114] In this disclosure, high molecular weight PTFE refers to PTFE that is non-melt processable and fibrillating, whereas low molecular weight PTFE refers to PTFE that is melt processable and not fibrillating.

[0115] By non-melt processable it is meant that the melt flow rate cannot be measured above the crystallizing melting point according to ASTM D 1238 and D 2116.

[0116] The presence or absence of fibrillation properties can be judged by "paste extrusion," a typical method for molding "high molecular weight PTFE powder," a powder made from a TFE polymer. Paste extrusion is usually possible because high molecular weight PTFE has fibrillation properties. If the unsintered molded product obtained by paste extrusion has no substantial strength or elongation, for example, if it breaks when pulled with an elongation of 0%, it can be considered to have no fibrillation properties.

[0117] The high molecular weight PTFE preferably has a standard specific gravity (SSG) of 2.130 to 2.280. The standard specific gravity is measured by a water displacement method in accordance with ASTM D 792 using a sample molded in accordance with ASTM D4895 89. In the present disclosure, "high molecular weight" means that the standard specific gravity is within the above range.

[0118] Low molecular weight PTFE has a melt viscosity of 1×10 at 380℃. 2 ~7×10 5 In this disclosure, "low molecular weight" means that the melt viscosity is within the above range.

[0119] (Removal of fluoromonomers or recovery of aqueous dispersions) After preparing the aqueous dispersion, remove the fluoromonomer remaining in the reactor from the reactor. Alternatively, after preparing the aqueous dispersion, recover the aqueous dispersion in the reactor and store it in a container different from the reactor. If the method of removing the fluoromonomer in the reactor is used, the subsequent process can be carried out in the same reactor used in polymerization, and the productivity of the fluoropolymer composition is improved, which is preferable.

[0120] After preparing the aqueous dispersion, it is preferable to stop stirring the contents of the reactor before removing the fluoromonomer or recovering the aqueous dispersion, since this makes the subsequent operations easier and allows the polymerization of the fluoromonomer to be smoothly terminated.

[0121] The method of removing the fluoromonomer from the reactor is not particularly limited. After preparing the aqueous dispersion, if desired, the stirring of the contents of the reactor may be stopped, and the pressure in the reactor may be exhausted until normal pressure, so that the fluoromonomer is removed from the reactor, or the pressure in the reactor may be reduced to less than 0.0 MPaG, so that the fluoromonomer is removed from the reactor, or an inert gas such as nitrogen gas may be supplied into the reactor to replace the fluoromonomer in the reactor. In addition, the entire amount of the fluoromonomer in the reactor may be reacted to convert it into a fluoropolymer, so that the fluoromonomer is removed from the reactor. The removal of the fluoromonomer remaining in the reactor from the reactor may be performed to an extent that the polymerization reaction of the fluoromonomer is sufficiently stopped, and a small amount of the fluoromonomer may remain in the reactor. The removed fluoromonomer can be recovered by a known means. The recovered fluoromonomer may be reused to produce a fluoropolymer.

[0122] As a method for removing the fluoromonomer from the inside of the reactor, a method is also suitable in which, after preparing the aqueous dispersion, stirring of the contents of the reactor is stopped as desired, the pressure in the reactor is reduced to less than 0.0 MPaG, and then an inert gas is supplied into the reactor. The reduction in pressure in the reactor and the supply of the inert gas may be repeated several times.

[0123] When polymerization of fluoromonomer is carried out at a temperature higher than room temperature, the reactor may be cooled before or after removing fluoromonomer from the reactor. When removing fluoromonomer from the reactor by means of evacuation or nitrogen replacement, there is a possibility that unreacted fluoromonomer, particularly in liquid form, remains in the reactor, but by cooling the reactor, the progress of reaction of unreacted fluoromonomer can be sufficiently suppressed.

[0124] The method of recovering the aqueous dispersion in the reactor and storing it in a container different from the reactor used for polymerization is not particularly limited. For example, after preparing the aqueous dispersion, stirring of the contents of the reactor may be stopped as desired, the reactor may be opened, and the aqueous dispersion in the reactor may be poured into another container, or after preparing the aqueous dispersion, stirring of the contents of the reactor may be stopped as desired, and the aqueous dispersion may be supplied from the reactor to another container through a pipe connecting the reactor and the other container.

[0125] In order to terminate the polymerization reaction of the fluoromonomer, a polymerization terminator (radical scavenger) may be added.

[0126] As the polymerization terminator, a compound that does not have the ability to restart after addition or chain transfer to the free radical in the polymerization system is used. Specifically, a compound that easily undergoes a chain transfer reaction with a primary radical or a growing radical, and then generates a stable radical that does not react with a monomer, or a compound that easily undergoes an addition reaction with a primary radical or a growing radical to generate a stable radical is used. The activity of a chain transfer agent is generally characterized by the chain transfer constant and the restart efficiency, and among chain transfer agents, a chain transfer agent with a restart efficiency of almost 0% is called a polymerization terminator. As the polymerization terminator, at least one selected from the group consisting of aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and cupric chloride (CuCl2) is preferable. As the aromatic hydroxy compounds, unsubstituted phenols, polyhydric phenols, salicylic acid, m- or p-salicylic acid, gallic acid, naphthol, etc. can be mentioned. Examples of the unsubstituted phenol include o-, m-, or p-nitrophenol, o-, m-, or p-aminophenol, and p-nitrosophenol. Examples of the polyhydric phenol include catechol, resorcin, hydroquinone, pyrogallol, phloroglucin, and naphthresorcinol. Examples of the aromatic amine include o-, m-, or p-phenylenediamine, and benzidine. Examples of the quinone compound include hydroquinone, o-, m-, or p-benzoquinone, 1,4-naphthoquinone, and alizarin. Examples of the thiocyanate include ammonium thiocyanate (NH4SCN), potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN). Among these, the polymerization terminator is preferably a quinone compound, and more preferably hydroquinone.

[0127] (Radical generator) After removing the fluoromonomer remaining in the reactor from the reactor, a radical generator is added to the aqueous dispersion. The aqueous dispersion to which the radical generator is added may be the aqueous dispersion remaining in the reactor, or may be the aqueous dispersion recovered from the reactor and stored in a separate container.

[0128] Before adding the radical generator, the content of the fluoropolymer in the aqueous dispersion may 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% by mass or more based on the mass of the aqueous dispersion, since the fluoropolymer composition can be produced with high productivity without impairing the removal efficiency of the fluorine-containing surfactant and the fluorine-containing compound. The lower limit of the fluoropolymer content is, in order of preference, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, and 30% by mass or more. The upper limit of the fluoropolymer content is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less.

[0130] The content of the fluoropolymer in the aqueous dispersion to be subjected to the heat treatment is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, based on the mass of the aqueous dispersion, since the fluoropolymer composition can be produced with high productivity without impairing the removal efficiency of the fluorine-containing surfactant and the fluorine-containing compound. The upper limit of the fluoropolymer content is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. The aqueous dispersion to be subjected to the heat treatment is an aqueous dispersion to which a radical generator has been added (aqueous dispersion containing a radical generator).

[0131] The content of the fluorosurfactant in the aqueous dispersion immediately before the addition of the radical generator or the content of the fluorosurfactant in the aqueous dispersion to be subjected to heat treatment is preferably 500 ppm by mass or more, more preferably 1000 ppm by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by 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 the addition of the radical generator or the content of the fluorine-containing compound in the aqueous dispersion to be subjected to heat treatment is preferably 500 ppb by mass or more, more preferably 1000 ppb by mass or more, and preferably 1.0% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.01% by 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 the addition of the radical generator, or the total content of the fluorine-containing surfactant and the fluorine-containing compound in the aqueous dispersion to be subjected to heat treatment, is preferably 500 ppm by mass or more, more preferably 1000 ppm by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, based on the fluoropolymer in the aqueous dispersion.

[0134] The radical generator is not particularly limited as long as it is a compound that can be decomposed at the temperature during heat treatment to generate radicals. As the radical generator, a water-soluble radical generator is preferable because it can easily diffuse radicals in the aqueous dispersion.

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

[0136] The inorganic peroxide is preferably a water-soluble inorganic peroxide. The inorganic peroxide may be hydrogen peroxide, perchlorate, perborate, perphosphate, percarbonate, persulfate, etc., and is preferably a persulfate. The persulfate is preferably at least one selected from the group consisting of ammonium persulfate, sodium persulfate, and potassium persulfate, and more preferably ammonium persulfate.

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

[0138] As the radical generator, an oxidizing agent and a reducing agent can be used in combination. By using an oxidizing agent and a reducing agent in combination, radicals can be generated from the radical generator by a redox reaction between the oxidizing agent and the reducing agent, so that the temperature during heat treatment can be lowered.

[0139] Examples of the oxidizing agent include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and cerium ammonium 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. It is also preferable to add a copper salt or an iron salt to increase the decomposition rate of the oxidizing agent. Examples of the copper salt include copper(II) sulfate, and examples of the iron salt include iron(II) sulfate.

[0140] Examples of combinations of oxidizing agents and reducing agents include potassium permanganate / oxalic acid, ammonium persulfate / bisulfite / iron sulfate, manganese triacetate / oxalic acid, cerium ammonium nitrate / oxalic acid, bromate / bisulfite, etc., with potassium permanganate / oxalic acid being preferred. When using a combination of an oxidizing agent and a reducing agent, either the oxidizing agent or the reducing agent may be added to the aqueous dispersion in advance, and then the other 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 molar times or more, more preferably 0.001 molar times or more, even more preferably 0.01 molar times or more, and is preferably 1000 molar times or less, more preferably 500 molar times or less, and even more preferably 100 molar times or less, based on the number of moles of the fluorine-containing surfactant in the aqueous dispersion.

[0142] When the amount of radical generator added is relatively large, the fluoropolymer in the aqueous dispersion may be partially or entirely precipitated by heat treatment. Therefore, when obtaining an aqueous dispersion in which the fluoropolymer is dispersed in an aqueous medium as the fluoropolymer composition obtained by heat treatment, it is necessary to select the upper limit of the amount of radical generator added. The amount of radical generator added when obtaining an aqueous dispersion as the fluoropolymer composition obtained by heat treatment is preferably 50 molar times or less, more preferably 25 molar times or less, and even more preferably 10 molar times or less, based on the mole number of the fluoropolymer in the aqueous dispersion, since it can suppress the precipitation of the fluoropolymer without impairing the removal efficiency of the fluorosurfactant and the fluorine-containing compound.

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

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

[0145] (Heat treatment) A radical generator is added to an aqueous dispersion to prepare an aqueous dispersion containing the radical generator, and then the aqueous dispersion containing the radical generator is subjected to a heat treatment.

[0146] The temperature for the heat treatment is not particularly limited as long as it is equal to or higher than the temperature at which the radical generator decomposes to generate radicals (decomposition temperature), but is preferably 35°C or higher, more preferably 40°C or higher, even more preferably 45°C or higher, particularly preferably 50°C or higher, 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 temperature of heat treatment is relatively high, the fluoropolymer in the aqueous dispersion may be partially or entirely precipitated by heat treatment.Therefore, when obtaining an aqueous dispersion in which the fluoropolymer is dispersed in an aqueous medium as the fluoropolymer composition obtained by heat treatment, it is necessary to select the upper limit of the temperature of heat treatment.The temperature of heat treatment when obtaining an aqueous dispersion as the fluoropolymer composition obtained by heat treatment is preferably 95°C or less, more preferably 90°C or less, and even more preferably 85°C or less, since it can suppress the precipitation of the fluoropolymer without impairing the removal efficiency of the fluorine-containing surfactant and the fluorine-containing compound.

[0148] In the heat treatment of the aqueous dispersion, if the aqueous dispersion can be maintained at a desired temperature or higher, it is not necessary to heat the aqueous dispersion. For example, when the temperature for polymerizing the fluoromonomer is sufficiently high and the temperature of the resulting aqueous dispersion is also sufficiently high, the heat treatment can be started by adding a radical generator to the aqueous dispersion before the resulting aqueous dispersion is cooled. On the other hand, in the case of producing an aqueous dispersion as a fluoropolymer composition by suppressing precipitation of the fluoropolymer without impairing the removal efficiency of the fluorine-containing surfactant and the fluorine-containing compound, it is necessary to strictly control the amount of radical generator added and the temperature of the heat treatment. Therefore, it is preferable to cool the aqueous dispersion before and after removing the fluoromonomer from the reactor or recovering the aqueous dispersion in the reactor, add a radical generator to the cooled aqueous dispersion, prepare an aqueous dispersion containing the radical generator, heat the aqueous dispersion to the above temperature range, and maintain the temperature for a certain period of time. The temperature of the aqueous dispersion just before adding the radical generator may be, for example, 30° C. or less.

[0149] The heating means when performing the heat treatment while heating the aqueous dispersion is not particularly limited. For example, a container containing the aqueous dispersion may be placed in a thermostatic chamber and heated, or the aqueous dispersion may be contained in a container equipped with a heater and heated by the heater.

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

[0151] The heat treatment time is not particularly limited as long as it is a time that allows the generated radicals to act sufficiently on the components contained in the aqueous dispersion, but is preferably 15 minutes or more, more preferably 30 minutes or more, even more preferably 60 minutes or more, and is preferably 1200 minutes or less, more preferably 900 minutes or less, and even more preferably 600 minutes or less.

[0152] The heat treatment may be carried out while stirring the aqueous dispersion. Radicals are generated by decomposition of a radical generator by heat treatment, but when a combination of an oxidizing agent and a reducing agent is used as a radical generator, radicals are generated by thermal decomposition of the radical generator and also by a redox reaction.

[0153] (Fluoropolymer Composition) After the aqueous dispersion containing the radical generator is heat-treated, a fluoropolymer composition is obtained. The fluoropolymer composition after the heat treatment may be cooled.

[0154] The form of the fluoropolymer composition is not particularly limited, and may be an aqueous dispersion (aqueous dispersion subjected to heat treatment), a powder, a slurry, a gel, or the like. From the viewpoint of excellent handling, an aqueous dispersion is preferred. In an aqueous dispersion, it is preferred that fluoropolymer particles are dispersed in an aqueous medium. Regardless of the form of the fluoropolymer composition, the fluoropolymer composition obtained by the production method of the present disclosure has a reduced content of the fluorine-containing surfactant used in polymerizing the fluoromonomer and a reduced content of the fluorine-containing compound generated by the polymerization of the fluoromonomer, and has an extremely high purity of the fluoropolymer.

[0155] The content of the fluorine-containing surfactant in the fluoropolymer composition is preferably less than 500 ppm by mass, more preferably 300 ppm by mass or less, based on the mass of the fluoropolymer.

[0156] The content of the fluorine-containing compound in the fluoropolymer composition is preferably less than 500 ppb by mass based on the mass 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 by mass, more preferably 300 ppm by mass or less, based on the mass of the fluoropolymer.

[0158] The content of the fluorine-containing surfactant in the aqueous dispersion or the fluoropolymer composition and the content of the fluorine-containing compound produced by polymerization of the fluoromonomer can be measured by liquid chromatography-mass spectrometry (LC / MS / MS). First, methanol is added to the composition to perform extraction, and the resulting extract is analyzed by LC / MS / MS. To further increase the extraction efficiency, treatments such as Soxhlet extraction and ultrasonic treatment may be performed. Molecular weight information is extracted from the obtained LC / MS / MS spectrum, and its agreement with the structural formulas of candidate fluorine-containing surfactants and fluorine-containing compounds is confirmed. Then, aqueous solutions containing five or more levels of the confirmed fluorine-containing surfactant and fluorine-containing compound are prepared, and LC / MS / MS analysis is performed on the aqueous solutions containing each level of content. The relationship between the content and the area for each content is plotted, and a calibration curve is drawn. Then, using the calibration curve, the area of ​​the LC / MS / MS chromatogram of the fluorine-containing surfactant and the fluorine-containing compound in the extract can be converted into the content of the fluorine-containing surfactant and the fluorine-containing compound.

[0159] (Post-processing) The fluoropolymer composition obtained by the heat treatment may be contacted with an adsorbent. In this case, the fluoropolymer composition is preferably in the form of an aqueous dispersion.

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

[0161] Examples of the concentration method include a phase separation concentration method, an electric concentration method, an electrophoresis method, an ion exchange method, a membrane concentration method, etc. The phase separation concentration method, the ion exchange method, and the membrane concentration method can be carried out under conventionally known treatment conditions, and are not particularly limited, and can be carried out by the methods described in International Publication No. 2004 / 050719, JP-A-2002-532583, and JP-A-55-120630.

[0162] When the fluoropolymer composition is recovered as a slurry or wet polymer after heat treatment, the slurry or wet polymer can be dried to obtain fluoropolymer powder, gum, crumb, etc. When the fluoropolymer composition obtained by heat treatment is an aqueous dispersion, the fluoropolymer can be agglomerated and, optionally, the agglomerate can be dried to obtain powder, etc.

[0163] The method of aggregating the fluoropolymer is not particularly limited. For example, the aqueous dispersion is diluted with water to a polymer concentration of 5 to 20% by mass, and in some cases, the pH is adjusted to neutral or alkaline, and then the mixture is stirred in a container equipped with a stirrer with more vigor than during polymerization of the fluoromonomer. The fluoropolymer may be aggregated by adding water-soluble organic compounds such as methanol and acetone; inorganic salts such as potassium nitrate and ammonium carbonate; and inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid as coagulants to the aqueous dispersion and stirring the mixture. After aggregating the fluoropolymer, the aggregated fluoropolymer can be recovered as a wet polymer.

[0164] The slurry or wet polymer may be dried.

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

[0166] The fluoropolymer composition thus obtained can be used for various applications.

[0167] A fluoropolymer composition (powder) containing PTFE as a fluoropolymer is preferred for molding, and suitable applications include hydraulic and fuel system tubes for aircraft and automobiles, flexible hoses for chemicals, steam, etc., and wire coating applications.

[0168] A fluoropolymer composition (aqueous dispersion) containing PTFE as a fluoropolymer is preferably stabilized and further concentrated by adding a nonionic surfactant, and used in various applications as a composition with organic or inorganic fillers added according to the purpose. The above composition, when coated on a substrate made of metal or ceramic, can provide a coating surface with non-adhesiveness and a low coefficient of friction, and excellent gloss, smoothness, abrasion resistance, weather resistance, and heat resistance, and is suitable for painting rolls, cooking utensils, etc., and impregnation processing of glass cloth, etc.

[0169] An organosol can also be prepared from a fluoropolymer composition (aqueous dispersion) containing PTFE as a fluoropolymer. The organosol can contain PTFE and an organic solvent, and the organic solvent can be an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, an amide-based solvent, an ester-based solvent, an aliphatic hydrocarbon-based solvent, an aromatic hydrocarbon-based solvent, or a halogenated hydrocarbon-based solvent, and N-methyl-2-pyrrolidone, dimethylacetamide, or the like can be suitably used. The organosol can be prepared, for example, by the method described in International Publication No. 2012 / 002038.

[0170] The fluoropolymer composition containing PTFE as the fluoropolymer is also preferably used as a processing aid.When used as a processing aid, the above-mentioned aqueous dispersion or the above-mentioned fine powder can be mixed with a host polymer or the like to improve the melt strength during melt processing of the host polymer, and improve the mechanical strength, electrical properties, flame retardancy, anti-dripping property during combustion, and sliding property of the obtained polymer.

[0171] The fluoropolymer composition containing PTFE as the fluoropolymer is also preferably used as a binder for batteries and for dust prevention purposes.

[0172] The fluoropolymer composition containing PTFE as the fluoropolymer is also preferably used as a processing aid after compounding with a resin other than PTFE. The fluoropolymer composition is suitable as a raw material for PTFE, for example, as described in JP-A-11-49912, U.S. Pat. No. 5,804,654, JP-A-11-29679, and JP-A-2003-2980. The processing aid using the fluoropolymer composition is in no way inferior to the processing aids described in the above publications.

[0173] The fluoropolymer composition (aqueous dispersion) containing PTFE as fluoropolymer is also preferably mixed with the aqueous dispersion of melt-processable fluororesin and coagulated to form coagulated powder. The coagulated powder is suitable as a processing aid.

[0174] Examples of the melt-processable fluororesin include FEP, PFA, TFE / fluoroalkyl allyl ether copolymer, ETFE, ethylene / TFE / HFP copolymer [EFEP], and the like. Among these, PFA, TFE / fluoroalkyl allyl ether copolymer, and FEP are preferred.

[0175] The aqueous dispersion preferably contains the melt-processable fluororesin. Examples of the melt-processable fluororesin include FEP, PFA, TFE / fluoroalkyl allyl ether copolymer, ETFE, and EFEP. The aqueous dispersion containing the melt-processable fluororesin can be used as a coating material. The melt-processable fluororesin can sufficiently fuse PTFE particles together, improving film-forming properties and providing gloss to the resulting coating.

[0176] The fluorine-free resin that the above-mentioned co-coagulation powder is added to can be in powder form, pellet form, or emulsion form.The above-mentioned addition is preferably carried out while applying shear force by known methods such as extrusion kneading, roll kneading, etc., in order to thoroughly mix each resin.

[0177] It is also preferable to use a fluoropolymer composition containing PTFE as a fluoropolymer as a dust suppression treatment. The dust suppression treatment can be used in a method of mixing with a dust-generating substance and subjecting the mixture to a compression-shear action at a temperature of 20 to 200°C to fibrillate PTFE and suppress the dust of the dust-generating substance, such as the method described in Japanese Patent No. 2827152 and Japanese Patent No. 2538783. The fluoropolymer composition can be suitably used in the dust suppression treatment composition described in International Publication No. 2007 / 004250, and can also be suitably used in the dust suppression treatment method described in International Publication No. 2007 / 000812.

[0178] The above-mentioned dust suppression treatment agent is suitably used for dust suppression treatment in the fields of building materials, soil stabilization materials, solidification materials, fertilizers, landfill disposal of incineration ash and harmful substances, explosion prevention, cosmetics, and sand for pet excretion, such as cat litter.

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

[0180] A fluoropolymer composition (powder) containing PTFE as a fluoropolymer has extensibility and non-melt processability, and is also useful as a raw material for an extruded body (porous body). When this extruded body is a film (PTFE extruded film or PTFE porous film), it can be extruded by a known PTFE extrusion method. By stretching, high molecular weight PTFE is easily fibrillated, and a PTFE porous body (membrane) consisting of nodes and fibers is obtained. Preferably, a uniaxially stretched film can be obtained by roll-stretching a sheet-like or rod-like paste extrudate in the extrusion direction. Furthermore, a biaxially stretched film can also be obtained by stretching in the width direction using a tenter or the like. It is also preferable to perform a semi-baking treatment before stretching.

[0181] This PTFE stretched body is a porous body with high porosity, and can be suitably used as a filter material for various precision filtration filters such as air filters and chemical filters, a support material for polymer electrolyte membranes, etc. It is also useful as a material for products used in the fields of textiles, medicine, electrochemicals, sealing materials, air filtration, ventilation / internal pressure adjustment, liquid filtration, general consumer goods, etc. Specific applications are exemplified below.

[0182] Electrochemical Field Dielectric material prepreg, EMI shielding material, heat transfer material, etc. More specifically, printed wiring board, electromagnetic shielding material, insulating heat transfer material, insulating material, etc.

[0183] Sealing materials field Gaskets, packing, pump diaphragms, pump tubes, aircraft sealing materials, etc.

[0184] Air Filtration Field ULPA filters (for semiconductor manufacturing), HEPA filters (for hospitals and semiconductor manufacturing), cylindrical cartridge filters (for industrial use), bag filters (for industrial use), heat-resistant bag filters (for exhaust gas treatment), heat-resistant pleated filters (for exhaust gas treatment), SINBRAN filters (for industrial use), catalyst filters (for exhaust gas treatment), adsorbent filters (for HDD installation), adsorbent vent filters (for HDD installation), vent filters (for HDD installation and others), vacuum cleaner filters (for vacuum cleaners), general-purpose multi-layer felt material, GT cartridge filters (for GT compatible products), cooling filters (for electronic equipment housings), etc.

[0185] Ventilation / internal pressure regulation field Freeze-drying materials such as freeze-drying containers, automotive ventilation materials for electronic circuits and lamps, container applications such as container caps, protective ventilation applications for electronic devices including small terminals such as tablet terminals and mobile phones, medical ventilation applications, etc.

[0186] Liquid Filtration Semiconductor liquid filtration filters (for semiconductor manufacturing), hydrophilic PTFE filters (for semiconductor manufacturing), chemical filters (for chemical liquid treatment), pure water production line filters (for pure water production), backwash type liquid filtration filters (for industrial wastewater treatment), etc.

[0187] General consumer goods field Clothing, cable guides (movable wires for motorcycles), motorcycle clothing, cast liners (medical supporters), vacuum cleaner filters, bagpipes (musical instruments), cables (signal cables for guitars, etc.), strings (for stringed instruments), etc.

[0188] Textiles PTFE fiber (textile material), sewing thread (textile), weaving thread (textile), rope, etc.

[0189] Medical field Internal implants (extended products), artificial blood vessels, catheters, general surgery (tissue reinforcement materials), head and neck products (dura substitutes), oral health (tissue regenerative medicine), orthopedics (bandages), etc.

[0190] Fluoropolymer compositions containing low molecular weight PTFE as a fluoropolymer are suitable as additives for improving, for example, the slipperiness and texture of coating surfaces in the production of plastics, inks, cosmetics, paints, greases, office automation equipment components, toners, and the like (see, for example, JP-A-10-147617).

[0191] Fluoropolymer compositions containing FEP as the fluoropolymer can be used to produce various molded articles such as covering materials for electric wires, foamed electric wires, cables, wires, etc., tubes, films, sheets, filaments, etc.

[0192] Fluoropolymer compositions containing a TFE / FAVE copolymer [PFA] or a TFE / fluoroalkyl allyl ether copolymer as the fluoropolymer can be suitably used, for example, for sheets, films, packings, round bars, square bars, pipes, tubes, round tanks, square tanks, tanks, wafer carriers, wafer boxes, beakers, filter housings, flow meters, pumps, valves, cocks, connectors, nuts, electric wires, heat-resistant electric wires, etc. Among these, they can be suitably used for tubes, pipes, tanks, connectors, etc. used in various chemical reaction equipment and semiconductor manufacturing equipment, which require impermeability to chemical solutions, and further in acidic or alkaline chemical solution supply equipment, etc.

[0193] A primer composition can also be obtained by adding a nonionic surfactant to a fluoropolymer composition (aqueous dispersion) containing a TFE / FAVE copolymer [PFA] or a TFE / fluoroalkyl allyl ether copolymer as a fluoropolymer, and dissolving or dispersing polyethersulfone, polyamideimide and / or polyimide, and metal powder in an organic solvent as required. This primer composition can also be used in a method for coating a metal surface with a fluororesin, which comprises applying the primer composition to a metal surface, applying a fluoropolymer composition onto the primer layer thus formed, and baking the fluoropolymer composition layer together with the primer layer.

[0194] The form of the fluoropolymer composition containing fluororubber as the fluoropolymer is preferably gum or crumb. A curing agent, a filler, etc. can be added to the fluoropolymer composition in the form of gum, crumb, etc., to process it into a fluororubber composition.

[0195] The curing agent may, for example, be a polyol, a polyamine, an organic peroxide, an organotin, a bis(aminophenol)tetraamine, or a bis(thioaminophenol).

[0196] The fluororubber composition can be molded and crosslinked to obtain a fluororubber molded article, which is suitable for use as a seal, a gasket, an electric wire coating, a hose, a tube, a laminate, an accessory, etc., and is particularly suitable for use as a part for semiconductor manufacturing equipment, an automobile part, etc.

[0197] Although the embodiments have been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims. EXAMPLES

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

[0199] The values ​​in the examples were measured by the following methods.

[0200] <Solid content concentration of aqueous dispersion> 1 g of the aqueous dispersion was dried in a blower dryer at 150° C. for 60 minutes, and the ratio of the mass of the heating residue to the mass (1 g) of the aqueous dispersion was expressed as a percentage and used.

[0201] <Melt viscosity> In accordance with ASTM D 1238, using a flow tester (manufactured by Shimadzu Corporation) and a 2Φ-8L die, 2 g of a sample preheated at 380 °C for 5 minutes was measured while maintaining the temperature at the above temperature under a load of 0.7 MPa.

[0202] <Standard Specific Gravity (SSG)> Using a sample molded in accordance with ASTM D4895-89, the measurement was carried out by the water displacement method in accordance with ASTM D-792.

[0203] <Content of Modified Monomer Unit (PTFE)> The content of the PPVE unit in PTFE was determined by multiplying the ratio of the absorbance at 995 cm -1 to the absorbance at 935 cm -1 by 0.14 from the infrared absorbance obtained by subjecting a thin film disk prepared by press molding PTFE powder to FT-IR measurement.

[0204] <Content of PPVE Unit (PFA)> The content of the PPVE unit in PFA was 19 determined by 19F-NMR analysis.

[0205] <Peak Temperature> Approximately 10 mg of PTFE powder without a heating history at a temperature of 300 °C or higher was precisely weighed, placed in a dedicated aluminum pan, and measured using a TG / DTA (simultaneous differential thermal and thermogravimetric analyzer). The peak temperature was determined as the temperature corresponding to the maximum value in the differential thermal (DTA) curve obtained by heating the aluminum pan from 25 °C to 600 °C at a rate of 10 °C / min in an air atmosphere.

[0206] <Melting Point> The measurement was carried out using a DSC (differential scanning calorimeter). 10 mg of the sample was weighed, heated from 140 °C to 360 °C at 10 °C / min, held at 360 °C for 1 minute, then cooled to 140 °C at 10 °C / min, held at 140 °C for 1 minute, and then heated again to 380 °C at 10 °C / min. The melting peak temperature (Tm) obtained from the melting curve during the second heating was taken as the melting point.

[0207] <Melt flow rate (MFR)> Using a melt indexer (manufactured by Toyo Seiki) equipped with a corrosion-resistant cylinder, die, and piston conforming to ASTM D1238-95, 5 g of the sample was filled into a cylinder maintained at 372±1°C and held for 5 minutes, after which it was extruded through the die orifice under a load of 5 kg (piston and weight), and the extrusion rate of the molten material at this time (g / 10 min) was calculated as the MFR.

[0208] <Measurement of the content of perfluorohexanoic acid, perfluoroundecanoic acid, and perfluoroether carboxylic acid A in the extract> 1. Calibration curves for perfluorohexanoic acid, perfluoroundecanoic acid, and perfluoroether carboxylic acid A Five levels of methanol standard solutions of perfluorohexanoic acid, perfluoroundecanoic acid, and perfluoroether carboxylic acid A with known concentrations of 1 ng / mL to 100 ng / mL were prepared and measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC / TQD). A calibration curve was created using a first-order approximation from each sample concentration and peak integral value.

[0209] Measurement equipment configuration and LC-MS measurement conditions [Table 1]

[0210] MRM measurement parameters [Table 2]

[0211] 2. Perfluorohexanoic acid content in the extract Perfluorohexanoic acid was measured using a liquid chromatograph mass spectrometer. The extract was appropriately diluted with methanol to prepare a measurement solution so that the amount of perfluorohexanoic acid in the measurement solution was within the calibration curve. The peak area of ​​perfluorohexanoic acid was determined using the MRM method for the measurement solution, 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 mass spectrometer. The extract was appropriately diluted with methanol to prepare a measurement solution so that the amount of perfluoroundecanoic acid in the measurement solution was within the calibration curve. The peak area of ​​perfluoroundecanoic acid was determined using the MRM method for the measurement solution, and the content of perfluoroundecanoic acid was determined from the calibration curve.

[0213] 4. Content of perfluoroether carboxylic acid A in the extract Perfluoroether carboxylic acid A was measured using a liquid chromatograph mass spectrometer. The extract was appropriately diluted with methanol to prepare a measurement solution so that the amount of perfluoroether carboxylic acid A in the measurement solution was within the calibration curve. The peak area of ​​perfluoroether carboxylic acid A in the measurement solution was determined using the MRM method, and the content of perfluoroether carboxylic acid A was determined from the calibration curve.

[0214] Manufacturing Example 1 A PTFE aqueous dispersion 1 was obtained in the same manner as in Example 7 of WO 2009 / 020187, except that the amount of ammonium perfluorohexanoate added was changed from 1.7 g to 2.0 g.

[0215] The PTFE aqueous dispersion 1 was taken out from the reactor into the atmosphere 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, and coagulation was caused by applying strong mechanical shearing force, and the obtained wet powder was dried to obtain PTFE powder. Various physical properties of the obtained PTFE powder were measured. The results are shown in Table 3. From this, it can be seen that the obtained PTFE powder is low molecular weight PTFE.

[0217] [Table 3]

[0218] Synthesis Example 1 After replacing the atmosphere in a 1L autoclave with nitrogen, 16.5g of dehydrated tetramethylurea and 220g of diethylene glycol dimethyl ether were charged and cooled. 38.5g of carbonyl fluoride was charged, and then 100g of hexafluoropropylene oxide was introduced and stirred. Then, 38.5g of carbonyl fluoride and 100g of hexafluoropropylene oxide were additionally charged. Then, the same amount of carbonyl fluoride and hexafluoropropylene oxide were further charged. After the reaction was completed, the reaction mixture was taken out and separated to obtain the reaction product in the lower phase.

[0219] A 6L autoclave was charged with 1000ml of tetraglyme and 75g of CsF, and the atmosphere in the autoclave was replaced with nitrogen. The autoclave was then cooled, and 2100g of the reaction product obtained above was charged, and hexafluoropropylene oxide was introduced into the autoclave to initiate the reaction. Finally, 1510g of hexafluoropropylene oxide was charged. The contents were then extracted, and the upper and lower phases were separated using a separatory funnel. The upper phase was 1320g, and the lower phase was 3290g. The lower phase was rectified.

[0220] Next, 1000 g of pure water was added to 1000 g of the product obtained by rectification of the lower phase to carry out hydrolysis. After that, the organic phase (lower phase) was collected by separation using a separatory funnel. The collected organic phase (lower phase) was washed with sulfuric acid water. The washed organic phase was subjected to simple distillation to obtain a distillate. Furthermore, 500 g of the distillate obtained above was added dropwise to an aqueous solution obtained by mixing 76 g of 28 mass% aqueous ammonia solution and 600 g of pure water. After completion of the dropwise addition, a 28 mass% aqueous ammonia solution was added to adjust the pH to 7. This was freeze-dried to obtain a white solid A (perfluoroether carboxylic acid A).

[0221] Manufacturing Example 2 In a 6L SUS reactor equipped with a stirrer, 3580g of deionized water and 7.56g of the white solid A obtained in Synthesis Example 1 were placed. The contents of the reactor were then heated to 70°C, while being aspirated and purged with TFE to remove oxygen from the reactor, and the contents were stirred. 0.5g of ethane and 71g of perfluoropropyl vinyl ether (PPVE) were added to the reactor, and then TFE was added until the pressure reached 2.4MPaG. 306mg of ammonium persulfate (APS) initiator dissolved in 20g of deionized water was injected into the reactor. After the injection of the initiator, a drop in pressure occurred and the start of polymerization was observed. TFE was added to the reactor to keep the pressure constant at 2.4MPaG. After the start of polymerization, 108mg of ammonium persulfate and 84g of PPVE were continuously added. When the amount of TFE consumed in the reaction reached about 1600g, the supply of TFE was stopped, the stirring was stopped, and the reaction was terminated. Thereafter, the pressure inside the reactor was evacuated until it reached normal pressure, and PFA aqueous dispersion 3 was obtained.

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

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

[0224] [Table 4]

[0225] Production Example 3 In a 6L SUS reactor equipped with a stirrer, 3580g of deionized water, 160g of paraffin wax, and 4.7g of the white solid A obtained in Synthesis Example 1 as a fluorine-containing surfactant were placed. The contents of the reactor were then heated to 70°C while being aspirated, and purged with TFE at the same time to remove oxygen from the reactor, and the contents were stirred. 6.5g of PPVE was pressurized into the reactor with TFE. 50mg of APS dissolved in 20g of deionized water was injected into the reactor as an initiator, and the pressure was set to 1.5MPaG. TFE was added so that the pressure was constant at 1.5MPaG. When the amount of TFE consumed in the reaction reached 1543g, the supply of TFE was stopped, the stirring was stopped, and the reaction was terminated. Thereafter, the reactor was vented until the pressure in the reactor reached normal pressure, and PTFE aqueous dispersion 5 was obtained.

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

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

[0228] [Table 5]

[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 placed in a screw tube having an internal volume of 100 ml, 10 ml of methanol was added, and the mixture was thoroughly shaken until flocculation occurred, and then centrifuged at 4,000 rpm for 1 hour to separate the polymer.

[0230] The resulting extract was analyzed, and the 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% by mass as an inorganic peroxide were placed in a screw tube with an internal volume of 100 ml, and the tube was kept at an internal temperature of 80° C. for 3 hours. After the heat treatment, the tube was cooled and 10 ml of methanol was added. The subsequent operations were the same as those in Comparative Example 1 to obtain an extract. The measurement results are shown in Table 6.

[0232] Example 2 The same operation as in Example 1 was carried out, except that an aqueous solution of ammonium persulfate having a concentration of 1.3% by mass was used instead of the aqueous solution of ammonium persulfate having a concentration of 0.13% by mass. The measurement results are shown in Table 6.

[0233] [Table 6]

[0234] Comparative Example 2 10 g of the PFA aqueous dispersion 4 obtained in Production Example 2 and 11 g of deionized water were placed in a 100 ml screw tube, and the same procedure as in Comparative Example 1 was carried out. The obtained extract was analyzed. The measurement results are shown in Table 7.

[0235] Example 3 10 g of the PFA aqueous dispersion 4 obtained in Production Example 2 and 11 g of an aqueous solution of ammonium persulfate with a concentration of 0.11% by mass were placed in a screw tube with an internal volume of 100 ml, and the tube was kept at an internal temperature of 80° C. for 3 hours. After the heat treatment, the tube was cooled, and 10 ml of methanol was added. The subsequent operations were the same as in Comparative Example 1, and an extract was obtained. The measurement results are shown in Table 7.

[0236] Example 4 The same operation as in Example 3 was carried out, except that an aqueous solution of ammonium persulfate having a concentration of 1.1% by mass was used instead of the aqueous solution of ammonium persulfate having a concentration of 0.11% by mass. The measurement results are shown in Table 7.

[0237] [Table 7]

[0238] Comparative Example 3 10.2 g of the PTFE aqueous dispersion 6 obtained in Production Example 3 and 2.7 g of deionized water were placed in a 100 ml screw tube, and the same operation as in Comparative Example 1 was carried out. The obtained extract was analyzed. The measurement results are shown in Table 8.

[0239] Example 5 10.2 g of the PTFE aqueous dispersion 6 obtained in Production Example 3 and 2.7 g of an aqueous solution of ammonium persulfate with a concentration of 0.11% by mass were placed in a screw tube with an internal volume of 100 ml, and the tube was kept at an internal temperature of 80° C. for 3 hours. After the heat treatment, the tube was cooled, and 10 ml of methanol was added. The subsequent operations were the same as those in Comparative Example 1, and an extract was obtained. The measurement results are shown in Table 8.

[0240] Example 6 The same operation as in Example 5 was carried out, except that an aqueous solution of ammonium persulfate having a concentration of 1.1% by mass was used instead of the aqueous solution of ammonium persulfate having a concentration of 0.11% by mass. The measurement results are shown in Table 8.

[0241] [Table 8]

Claims

1. A method for producing a fluoropolymer composition comprising the steps of: A fluoromonomer is 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 a fluoropolymer; After preparing the aqueous dispersion, the pressure in the reactor is reduced to less than 0.0 MPaG, or an inert gas is supplied into the reactor to replace the fluoromonomer in the reactor with an inert gas, thereby removing the fluoromonomer remaining in the reactor from the reactor, or the aqueous dispersion in the reactor is recovered and stored in a container different from the reactor; adding a radical generator to the aqueous dispersion; The aqueous dispersion containing the radical generator is subjected to a heat treatment at a temperature at which the radical generator is decomposed to generate radicals. A method for producing a fluoropolymer composition, comprising the steps of: the amount of the radical generator added is 0.0001 mole or more relative to the number of moles of the fluorine-containing surfactant in the aqueous dispersion, The fluorine-containing surfactant is represented by the following general formula (N ０ ): X ｎ０ -Rf ｎ０ -Y ０ (N ０ ) (In the formula, X ｎ０ is H, Cl or F. ｎ０ is a linear, branched or cyclic alkylene group having 3 to 20 carbon atoms, in which some or all of the H's are replaced by F, and the alkylene group may contain one or more ether bonds, and some of the H's may be replaced by Cl. ０ is an anionic group; The aqueous dispersion obtained by polymerizing the fluoromonomer contains a water-soluble fluorine-containing compound having a molecular weight of 1,000 g / mol or less, and the heat treatment is carried out to obtain the fluoropolymer composition in which the content of the water-soluble fluorine-containing compound is reduced.

2. The method according to claim 1 , wherein the radical generator is a water-soluble radical generator.

3. 3. The method according to claim 1, wherein the radical generator is an inorganic peroxide.

4. The method according to any one of claims 1 to 3, wherein the content of the fluoropolymer in the aqueous dispersion to be subjected to the heat treatment is 1 mass % or more.

5. The method according to any one of claims 1 to 4, wherein the fluoropolymer composition is in the form of an aqueous dispersion or a powder.

6. The method according to any one of claims 1 to 5, wherein after the aqueous dispersion is obtained as the fluoropolymer composition by the heat treatment, the aqueous dispersion is cooled.

7. The method according to any one of claims 1 to 6, wherein after the heat treatment is performed to obtain an aqueous dispersion as the fluoropolymer composition, the aqueous dispersion is concentrated.

8. The manufacturing method according to any one of claims 1 to 7, wherein the heat treatment is carried out to obtain an aqueous dispersion as the fluoropolymer composition, and then the fluoropolymer in the aqueous dispersion is coagulated, and the coagulated product is optionally dried.

9. The method according to any one of claims 1 to 8, wherein the water-soluble fluorine-containing compound is a compound represented by general formula (1): General formula (1): [X-Rf-A － ] ｉ M ｉ＋ (wherein 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 or fully fluorinated aliphatic group interrupted by at least one oxygen atom; A － is an acid group, M ｉ＋ represents a cation having a valence i, where i is an integer from 1 to 3.

10. The method according to any one of claims 1 to 8, wherein the water-soluble fluorine-containing compound is a compound represented by general formula (2): General formula (2): [C ｎ－１ F ２ｎ－１ COO － ] ＋ (wherein n is an integer from 9 to 12; M ＋ represents a cation.)

11. The method according to any one of claims 1 to 8, wherein the water-soluble fluorine-containing compound is a compound represented by general formula (3): General formula (3): [R １ -O-L-CO ２ － ] ＋ (In the formula, R １ represents 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 represents a linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; M ＋ represents a cation.)

12. The fluoropolymer is 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 ester copolymer, and general formula (150): CF ２ =CF-O-(CF ２ CFY １５１ -O) ｎ - (CFY １５２ ) ｍ -A １５１ (In the formula, Y １５１ is a fluorine atom, a chlorine atom, -SO ２ The perfluoroalkyl group is an ether-type oxygen group or a -SO ２ F group. n represents an integer of 0 to 3. １５１ may be the same or different. １５２ is a fluorine atom, a chlorine atom or -SO ２ F group. m represents an integer of 1 to 5. １５２ may be the same or different. A １５１ is -SO ２ X １５１ , -COZ １５１ Or -POZ １５２ Z １５３ Represents: X １５１ is F, Cl, Br, I, -OR １５１ Or -NR １５２ R １５３ Represents Z. １５１ , Z １５２ and Z １５３ are the same or different and each represents -NR １５４ R １５５ Or -OR １５６ Represents １５１ , R １５２ , R １５３ , R １５４ , R １５５ and R １５６ and each of the groups represented by the formula (I) and (II) may be the same or different and represent H, ammonium, an alkali metal, an alkyl group which may contain a fluorine atom, an aryl group, or a sulfonyl-containing group.

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