Method for producing aqueous dispersion liquid of fluoropolymer, aqueous dispersion liquid of fluoropolymer, and coating material composition

Abstract

Provided is a method for producing an aqueous dispersion liquid of a fluoropolymer, with which a fluoropolymer-containing aqueous dispersion liquid is produced, the method comprising polymerizing a fluoromonomer in the presence of a fluorine-containing surfactant, a polymerization initiator, and an aqueous medium in a reactor to prepare an aqueous dispersion liquid containing a fluoropolymer, heat treating this aqueous dispersion liquid, adding a non-ionic surfactant to the heat-treated aqueous dispersion liquid, bringing the non-ionic surfactant-containing aqueous dispersion liquid into contact with an ion exchange resin, and concentrating the aqueous dispersion liquid obtained following the contact with the ion exchange resin.

Description

Method for producing aqueous fluoropolymer dispersion, aqueous fluoropolymer dispersion and coating composition

[0001] The present disclosure relates to a method for producing an aqueous fluoropolymer dispersion, an aqueous fluoropolymer dispersion, and a coating composition.

[0002] Patent Document 1 describes a method for decomposing fluorinated carboxylic acids, which comprises treating at least one fluorinated carboxylic acid selected from fluorinated carboxylic acids, salts thereof, and precursors thereof with hot water in a sealed container in the presence of peroxodisulfate ions.

[0003] JP 2008-285449 A

[0004] An object of the present disclosure is to provide a method for producing an aqueous fluoropolymer dispersion in which the content of a fluorine-containing compound having a hydrophilic group with 7 or fewer carbon atoms is reduced. Another object of the present disclosure is to provide an aqueous fluoropolymer dispersion in which the content of a fluorine-containing compound having a hydrophilic group with 7 or fewer carbon atoms is reduced.

[0005] According to the present disclosure, there is provided a method for producing an aqueous fluoropolymer dispersion containing a fluoropolymer, the method comprising the steps of 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, subjecting the aqueous dispersion to a heat treatment, adding a nonionic surfactant to the heat-treated aqueous dispersion, contacting the aqueous dispersion containing the nonionic surfactant with an ion exchange resin, and concentrating the aqueous dispersion obtained after contact with the ion exchange resin.

[0006] According to the present disclosure, it is possible to provide a method for producing an aqueous fluoropolymer dispersion in which the content of a fluorine-containing compound having a hydrophilic group with not more than 7 carbon atoms is reduced. Furthermore, according to the present disclosure, it is possible to provide an aqueous fluoropolymer dispersion in which the content of a fluorine-containing compound having a hydrophilic group with not more than 7 carbon atoms is reduced.

[0007] Before specifically describing the present disclosure, some terms used in the present disclosure will be defined or explained.

[0008] In the present disclosure, fluororesins are partially crystalline fluoropolymers, or fluoroplastics. Fluororesins have a melting point and are thermoplastic, but may be melt-processable or non-melt-processable.

[0009] In the present disclosure, melt-processable means that the polymer can be melted and processed using conventional processing equipment such as an extruder, an injection molding machine, etc. Therefore, melt-processable fluororesins usually have a melt flow rate of 0.01 to 500 g / 10 min, as measured by the measurement method described below.

[0010] In this disclosure, fluororubber refers to an amorphous fluoropolymer. "Amorphous" means that the magnitude of the melting peak (ΔH) appearing in differential scanning calorimetry (DSC) (heating rate 10°C / min) or differential thermal analysis (DTA) (heating rate 10°C / min) of the fluoropolymer is 4.5 J / g or less. Fluororubber exhibits elastomeric properties through crosslinking. Elastomeric properties refer to the ability of a polymer to be stretched and to retain its original length when the force required to stretch the polymer is no longer applied.

[0011] The monomer that provides a crosslinking site is a monomer (cure site monomer) having a crosslinkable group that provides a crosslinking site to the fluoropolymer for forming a crosslink with a curing agent.

[0012] In the present disclosure, polytetrafluoroethylene [PTFE] is preferably a fluoropolymer having a content of tetrafluoroethylene units relative to all polymer units of 99 mol % or more.

[0013] In the present disclosure, both the fluororesin (excluding polytetrafluoroethylene) and the fluororubber are preferably fluoropolymers having a tetrafluoroethylene unit content of less than 99 mol% relative to all polymerized units.

[0014] In the present disclosure, the content of each monomer constituting the fluoropolymer can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0015] In the present disclosure, the term "organic group" refers to a group containing one or more carbon atoms or a group formed by removing one hydrogen atom from an organic compound. Examples of the "organic group" include an alkyl group which may have one or more substituents, an alkenyl group which may have one or more substituents, an alkynyl group which may have one or more substituents, a cycloalkyl group which may have one or more substituents, a cycloalkenyl group which may have one or more substituents, a cycloalkadienyl group which may have one or more substituents, an aryl group which may have one or more substituents, an aralkyl group which may have one or more substituents, a non-aromatic heterocyclic group which may have one or more substituents, a heteroaryl group which may have one or more substituents, a cyano group, a formyl group, RaO-, RaCO-, and RaSO. ２ -, RaCOO-, RaNRaCO-, RaCONRa-, RaOCO-, RaOSO ２ -, and RaNRbSO ２ - (In these formulas, Ra is independently an alkyl group which may have one or more substituents, an alkenyl group which may have one or more substituents, an alkynyl group which may have one or more substituents, a cycloalkyl group which may have one or more substituents, a cycloalkenyl group which may have one or more substituents, a cycloalkadienyl group which may have one or more substituents, an aryl group which may have one or more substituents, an aralkyl group which may have one or more substituents, a non-aromatic heterocyclic group which may have one or more substituents, or a heteroaryl group which may have one or more substituents; and Rb is independently H or an alkyl group which may have one or more substituents). As the organic group, an alkyl group which may have one or more substituents is preferred.

[0016] In the present disclosure, the term "substituent" refers to a substitutable group. Examples of the "substituent" include an aliphatic group, an aromatic group, a heterocyclic group, an acyl group, an acyloxy group, an acylamino group, an aliphatic oxy group, an aromatic oxy group, a heterocyclic oxy group, an aliphatic oxycarbonyl group, an aromatic oxycarbonyl group, a heterocyclic oxycarbonyl group, a carbamoyl group, an aliphatic sulfonyl group, an aromatic sulfonyl group, a heterocyclic sulfonyl group, an aliphatic sulfonyloxy group, an aromatic sulfonyloxy group, a heterocyclic sulfonyloxy group, a sulfamoyl group, an aliphatic sulfonamido group, an aromatic sulfonamido group, a heterocyclic sulfonamido group, an amino group, and an aliphatic amino group. groups, aromatic amino groups, heterocyclic amino groups, aliphatic oxycarbonylamino groups, aromatic oxycarbonylamino groups, heterocyclic oxycarbonylamino groups, aliphatic sulfinyl groups, aromatic sulfinyl groups, aliphatic thio groups, aromatic thio groups, hydroxy groups, cyano groups, sulfo groups, carboxy groups, aliphatic oxyamino groups, aromatic oxyamino groups, carbamoylamino groups, sulfamoylamino groups, halogen atoms, sulfamoylcarbamoyl groups, carbamoylsulfamoyl groups, dialiphatic oxyphosphinyl groups, and diaromatic oxyphosphinyl groups.

[0017] The aliphatic group may be saturated or unsaturated and may have a hydroxy group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aliphatic group include alkyl groups having a total of 1 to 8, preferably 1 to 4, carbon atoms, such as a methyl group, an ethyl group, a vinyl group, a cyclohexyl group, and a carbamoylmethyl group.

[0018] The aromatic group may have, for example, a nitro group, a halogen atom, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aromatic group include aryl groups having 6 to 12 carbon atoms, preferably 6 to 10 carbon atoms in total, such as a phenyl group, a 4-nitrophenyl group, a 4-acetylaminophenyl group, and a 4-methanesulfonylphenyl group.

[0019] The heterocyclic group may have a halogen atom, a hydroxy group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the heterocyclic group include 5- or 6-membered heterocycles having a total of 2 to 12, preferably 2 to 10, carbon atoms, such as a 2-tetrahydrofuryl group and a 2-pyrimidyl group.

[0020] The acyl group may have an aliphatic carbonyl group, an arylcarbonyl group, a heterocyclic carbonyl group, a hydroxy group, a halogen atom, an aromatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the acyl group include acyl groups having a total of 2 to 8, preferably 2 to 4, carbon atoms, such as an acetyl group, a propanoyl group, a benzoyl group, and a 3-pyridinecarbonyl group.

[0021] The acylamino group may have an aliphatic group, an aromatic group, a heterocyclic group, etc., such as an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc. Examples of the acylamino group include acylamino groups having a total of 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, and alkylcarbonylamino groups having a total of 2 to 8 carbon atoms, such as an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc.

[0022] The aliphatic oxycarbonyl group may be saturated or unsaturated and may have a hydroxy group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aliphatic oxycarbonyl group include alkoxycarbonyl groups having a total of 2 to 8, preferably 2 to 4, carbon atoms, such as a methoxycarbonyl group, an ethoxycarbonyl group, and a (t)-butoxycarbonyl group.

[0023] The carbamoyl group may have an aliphatic group, an aromatic group, a heterocyclic group, etc. Examples of the carbamoyl group include an unsubstituted carbamoyl group, an alkylcarbamoyl group having a total of 2 to 9 carbon atoms, preferably an unsubstituted carbamoyl group, or an alkylcarbamoyl group having a total of 2 to 5 carbon atoms, such as an N-methylcarbamoyl group, an N,N-dimethylcarbamoyl group, or an N-phenylcarbamoyl group.

[0024] The aliphatic sulfonyl group may be saturated or unsaturated and may have a hydroxy group, an aromatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aliphatic sulfonyl group include alkylsulfonyl groups having a total of 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, such as a methanesulfonyl group.

[0025] The aromatic sulfonyl group may have a hydroxy group, an aliphatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, etc. Examples of the aromatic sulfonyl group include arylsulfonyl groups having a total of 6 to 10 carbon atoms, such as a benzenesulfonyl group.

[0026] The amino group may have an aliphatic group, an aromatic group, a heterocyclic group, or the like.

[0027] The acylamino group may have, for example, an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc. Examples of the acylamino group include acylamino groups having a total of 2 to 12 carbon atoms, preferably 2 to 8 carbon atoms, and more preferably alkylcarbonylamino groups having a total of 2 to 8 carbon atoms, such as an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propanoylamino group, etc.

[0028] The aliphatic sulfonamide group, aromatic sulfonamide group, and heterocyclic sulfonamide group may be, for example, a methanesulfonamide group, a benzenesulfonamide group, or a 2-pyridinesulfonamide group.

[0029] The sulfamoyl group may have an aliphatic group, an aromatic group, a heterocyclic group, etc. Examples of the sulfamoyl group include a sulfamoyl group, an alkylsulfamoyl group having 1 to 9 carbon atoms in total, a dialkylsulfamoyl group having 2 to 10 carbon atoms in total, an arylsulfamoyl group having 7 to 13 carbon atoms in total, and a heterocyclic sulfamoyl group having 2 to 12 carbon atoms in total, more preferably a sulfamoyl group, an alkylsulfamoyl group having 1 to 7 carbon atoms in total, a dialkylsulfamoyl group having 3 to 6 carbon atoms in total, an arylsulfamoyl group having 6 to 11 carbon atoms in total, and a heterocyclic sulfamoyl group having 2 to 10 carbon atoms in total, such as a sulfamoyl group, a methylsulfamoyl group, an N,N-dimethylsulfamoyl group, a phenylsulfamoyl group, and a 4-pyridine sulfamoyl group.

[0030] The aliphatic oxy group may be saturated or unsaturated and may have a methoxy group, an ethoxy group, an i-propyloxy group, a cyclohexyloxy group, a methoxyethoxy group, etc. Examples of the aliphatic oxy group include alkoxy groups having a total of 1 to 8, preferably 1 to 6, carbon atoms, such as a methoxy group, an ethoxy group, an i-propyloxy group, a cyclohexyloxy group, and a methoxyethoxy group.

[0031] The aromatic amino group and heterocyclic amino group may have an aliphatic group, an aliphatic oxy group, a halogen atom, a carbamoyl group, a heterocyclic group fused with the aryl group, or an aliphatic oxycarbonyl group, preferably an aliphatic group having 1 to 4 carbon atoms in total, an aliphatic oxy group having 1 to 4 carbon atoms in total, a halogen atom, a carbamoyl group having 1 to 4 carbon atoms in total, a nitro group, or an aliphatic oxycarbonyl group having 2 to 4 carbon atoms in total.

[0032] The aliphatic thio group may be saturated or unsaturated and includes alkylthio groups having a total of 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, such as a methylthio group, an ethylthio group, a carbamoylmethylthio group, and a t-butylthio group.

[0033] The carbamoylamino group may have an aliphatic group, an aryl group, a heterocyclic group, etc. Examples of the carbamoylamino group include a carbamoylamino group, an alkylcarbamoylamino group having a total of 2 to 9 carbon atoms, a dialkylcarbamoylamino group having a total of 3 to 10 carbon atoms, an arylcarbamoylamino group having a total of 7 to 13 carbon atoms, and a heterocyclic carbamoylamino group having a total of 3 to 12 carbon atoms, preferably a carbamoylamino group, an alkylcarbamoylamino group having a total of 2 to 7 carbon atoms, a dialkylcarbamoylamino group having a total of 3 to 6 carbon atoms, an arylcarbamoylamino group having a total of 7 to 11 carbon atoms, and a heterocyclic carbamoylamino group having a total of 3 to 10 carbon atoms, such as a carbamoylamino group, a methylcarbamoylamino group, an N,N-dimethylcarbamoylamino group, a phenylcarbamoylamino group, and a 4-pyridinecarbamoylamino group.

[0034] In this disclosure, ranges expressed by endpoints include all numbers subsumed within that range (eg, 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0035] In this disclosure, the term "at least 1" includes all numbers greater than or equal to 1 (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).

[0036] Specific embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0037] 1. Method for producing aqueous fluoropolymer dispersion An aqueous dispersion obtained by polymerizing a fluoromonomer may contain, in addition to the fluoropolymer, a fluorine-containing compound having a hydrophilic group. The fluorine-containing compound having a hydrophilic group includes a fluorine-containing surfactant added during polymerization and a fluorine-containing compound having a hydrophilic group produced by polymerization of the fluoromonomer.

[0038] In the production method of the present disclosure, after preparing an aqueous dispersion, the obtained aqueous dispersion is subjected to a heat treatment, and further, a nonionic surfactant is added to the heat-treated aqueous dispersion, thereby contacting the aqueous dispersion with an ion exchange resin while maintaining the content of the nonionic surfactant in the aqueous dispersion at a certain level or higher, and then concentrating the aqueous dispersion. It has been found that by using such a production method, an aqueous dispersion can be produced in which the content of a fluorine-containing compound having a hydrophilic group is surprisingly reduced, even when compared with conventional methods of subjecting an aqueous dispersion to ion exchange treatment or conventional methods of concentrating an aqueous dispersion by phase separation.

[0039] That is, the production method of the present disclosure is a production method for an aqueous fluoropolymer dispersion for producing an aqueous fluoropolymer dispersion containing a fluoropolymer, and includes the steps of 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, heat-treating the aqueous dispersion, adding a nonionic surfactant to the heat-treated aqueous dispersion, contacting the aqueous dispersion containing the nonionic surfactant with an ion exchange resin, and concentrating the aqueous dispersion obtained after contact with the ion exchange resin.

[0040] By using the production method of the present disclosure, it is possible to reduce the content of fluorine-containing compounds having a hydrophilic group having 7 or less carbon atoms in the aqueous fluoropolymer dispersion. Furthermore, by using the production method of the present disclosure, it is possible to reduce not only the content of fluorine-containing compounds having a hydrophilic group having 7 or less carbon atoms but also the content of fluorine-containing compounds having a hydrophilic group in the aqueous fluoropolymer dispersion.

[0041] Each step and the materials used in each step will be described in detail below.

[0042] (Fluoromonomer Polymerization) 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.

[0043] 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 required, 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 start of the polymerization reaction, fluoromonomer, polymerization initiator, fluorine-containing surfactant, chain transfer agent, etc. may be added additionally depending on the purpose.The polymerization method of fluoromonomer is not particularly limited, but emulsion polymerization method is preferred.

[0044] (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.

[0045] Examples of the fluorine-containing surfactant include anionic fluorine-containing surfactants, etc. The anionic fluorine-containing surfactant may be, for example, a surfactant containing fluorine atoms and having a total carbon number of 20 or less excluding the anionic group.

[0046] The fluorine-containing surfactant may also be a surfactant containing fluorine, the molecular weight of the anionic moiety of which is 1,000 or less. The "anionic moiety" means the part of the fluorine-containing surfactant excluding the cation. For example, F(CF) represented by the formula (I) below may be used. ２ ) ｎ１ In the case of COOM, "F(CF ２ ) ｎ１ This is the "COO" part.

[0047] The fluorine-containing surfactant also includes a fluorine-containing surfactant having a Log POW of 3.5 or less. The Log POW is the partition coefficient between 1-octanol and water, and is expressed as Log P [where P represents the ratio of the fluorine-containing surfactant concentration in octanol to the fluorine-containing surfactant concentration in water when a 1:1 octanol / water mixture containing the fluorine-containing surfactant undergoes phase separation]. The Log POW can be measured using a column: TOSOH ODS-120T column (φ4.6 mm×250 mm, manufactured by Tosoh Corporation), an eluent: acetonitrile / 0.6% by mass HClO ４ HPLC is performed on standard substances (heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid) with known octanol / water partition coefficients under conditions of 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. A calibration curve is prepared between each elution time and the known octanol / water partition coefficient, and the elution time is calculated from the HPLC elution time of the sample solution based on this calibration curve.

[0048] Specific examples of the fluorine-containing surfactants include those described in U.S. Patent Application Publication Nos. 2007 / 0015864, 2007 / 0015865, 2007 / 0015866, 2007 / 0276103, 2007 / 0117914, 2007 / 142541, 2008 / 0015319, and U.S. Pat. No. 3,250,808. , U.S. Patent No. 3,271,341, JP 2003-119204 A, WO 2005 / 042593, WO 2008 / 060461, WO 2007 / 046377, JP 2007-119526 A, WO 2007 / 046482, WO 2007 / 046345, U.S. Patent Application Publication No. 2014 / 0228531, WO 2013 / 189824, and those described in WO 2013 / 189826, and the like.

[0049] The anionic fluorine-containing surfactant may be a compound represented by the following general formula (N ０ ): Xｎ０ -Rf ｎ０ -Y ０ (N ０ ) (wherein, 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 atoms are substituted with F, and the alkylene group may contain one or more ether bonds, and some of the H atoms may be substituted with Cl. ０ is an anionic group. ０ The anionic group is -COOM, -SO ２ M or -SO ３ M, -COOM or -SO ３ M. M may be H, a metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７ is 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. ７ As the group, H or C １－１０ and may be an organic group of the formula: １－４ and may be an organic group of the formula: １－４ M may be H, a metal atom, or an alkyl group of the formula NR ７ ４ may be H, an alkali metal (Group 1), an alkaline earth metal (Group 2), or NR ７ ４ may be H, Na, K, Li or NH ４ The above Rf ｎ０ may be one in which 50% or more of H is substituted with fluorine.

[0050] The general formula (N ０ The compound represented by the following general formula (N １ ): X ｎ０ -(CF ２ ) ｍ１ -Y ０(N １ ) (wherein, X ｎ０ is H, Cl, and F, m1 is an integer from 3 to 15, and Y ０ is as defined above), a compound represented by the following general formula (N ２ ): Rf ｎ１ -O-(CF(CF ３ )CF ２ O) ｍ２ CFX ｎ１ -Y ０ (N ２ ) (wherein, 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 CF ３ and Y ０ is as defined above), a compound represented by the following general formula (N ３ ): Rf ｎ２ (CH ２ ) ｍ３ -(Rf ｎ３ ) ｑ -Y ０ (N ３ ) (wherein, 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, and 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 CF ２ -Y ０ (N ４ ) (wherein, 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; Y ｎ１ and Y ｎ２ are the same or different and are H or F, p is 0 or 1, and Y ０is as defined above.) and a compound represented by the general formula (N ５ ): (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 fully fluorinated alkyl group having 1 to 6 carbon atoms, which may contain an ether linkage. ｎ５ is a linear or branched partially or fully 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 wherein the total number of carbon atoms is 18 or less.

[0051] The general formula (N ０ ) More specifically, the compounds represented by the formula (I) below include perfluorocarboxylic acids (I), ω-H perfluorocarboxylic acids (II), perfluoroether carboxylic acids (III), perfluoroalkyl alkylene carboxylic acids (IV), perfluoroalkoxy fluorocarboxylic acids (V), perfluoroalkyl sulfonic acids (VI), ω-H perfluoro sulfonic acids (VII), perfluoroalkyl alkylene sulfonic acids (VIII), alkyl alkylene carboxylic acids (IX), fluorocarboxylic acids (X), alkoxy fluorosulfonic acids (XI), alkoxy fluorosulfonic acids (XI), and the like.

[0052] The perfluorocarboxylic acid (I) is represented by the following general formula (I): F(CF ２ ) ｎ１COOM (I) (wherein n1 is an integer of 3 to 14, and M is H, a metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７ is H or an organic group.

[0053] The ω-H perfluorocarboxylic acid (II) is represented by the following general formula (II): H(CF ２ ) ｎ２ COOM (II) (wherein n2 is an integer of 4 to 15, and M is as defined above).

[0054] The perfluoroethercarboxylic acid (III) is a compound represented by the following general formula (III): １ -O-(CF(CF ３ )CF ２ O) ｎ３ CF (CF ３ ) COOM (III) (wherein, 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.

[0055] The perfluoroalkyl alkylene carboxylic acid (IV) is represented by the following general formula (IV): ２ (CH ２ ) ｎ４ Rf ３ COOM (IV) (wherein, 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.

[0056] The alkoxyfluorocarboxylic acid (V) is represented by the following general formula (V): Rf ４ -O-CY １ Y ２ CF ２ -COOM (V) (wherein, Rf４ is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain ether bonds and / or chlorine atoms; Y １ and Y ２ are the same or different and are H or F, and M is as defined above.

[0057] The perfluoroalkylsulfonic acid (VI) is represented by the following general formula (VI): F(CF ２ ) ｎ５ SO ３ M (VI) (wherein n5 is an integer of 3 to 14, and M is as defined above).

[0058] The ω-H perfluorosulfonic acid (VII) is represented by the following general formula (VII): H(CF ２ ) ｎ６ SO ３ M (VII) (wherein n6 is an integer of 4 to 14, and M is as defined above).

[0059] The perfluoroalkyl alkylene sulfonic acid (VIII) is a compound represented by the following general formula (VIII): ５ (CH ２ ) ｎ７ SO ３ M (VIII) (wherein, 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.

[0060] The alkyl alkylene carboxylic acid (IX) is represented by the following general formula (IX): ６ (CH ２ ) ｎ８ COOM (IX) (wherein, Rf ６ is a linear or branched partially or fully 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.

[0061] The fluorocarboxylic acid (X) is represented by the following general formula (X): ７ -O-Rf ８ -O-CF ２ -COOM (X) (wherein, 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, and 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.

[0062] The alkoxyfluorosulfonic acid (XI) is represented by the following general formula (XI): Rf ９ -O-CY １ Y ２ CF ２ -SO ３ M (XI) (wherein, 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.

[0063] The compound (XII) is represented by the following general formula (XII): (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 fully 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. ０ is -COOM, -SO ２ M or -SO ３ M, and -SO ３M or COOM (wherein M is as defined above). Examples of L include a single bond, a partially or fully fluorinated alkylene group having 1 to 10 carbon atoms which may contain an ether bond.

[0064] The compound (XIII) has the following general formula (XIII): １１ -O-(CF ２ CF (CF ３ ) O) ｎ９ (CF ２ O) ｎ１０ CF ２ COOM (XIII) (wherein, Rf １１ is 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. ２ ClO(CF ２ CF (CF ３ ) O) ｎ９ (CF ２ O) ｎ１０ CF ２ COONH ４ (a mixture having an average molecular weight of 750, wherein n9 and n10 are defined above).

[0065] As mentioned above, examples of the anionic fluorine-containing surfactant include carboxylic acid surfactants and sulfonic acid surfactants.

[0066] The fluorine-containing surfactant may be one type of fluorine-containing surfactant or a mixture containing two or more types of fluorine-containing surfactants.

[0067] The fluorine-containing surfactant preferably has a methylene group (—CH ２ -), and more preferably, does not have a C-H bond. ２ By using a fluorine-containing surfactant having no - or C--H bond, the polymerization of the fluoromonomer can be smoothly carried out in the presence of an aqueous medium.

[0068] The number of H atoms in the hydrophobic group of the fluorine-containing surfactant is preferably 0 or 1, more preferably 0. By using a fluorine-containing surfactant having a small number of H atoms bonded to the 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 even more preferably 6 to 12. The hydrophobic group usually constitutes the above-mentioned "portion excluding the anionic group" of the molecular structure of the fluorine-containing surfactant. As the hydrophilic group, Y ０ Examples of the anionic group include the groups exemplified above for the anionic group of the formula (I). The fluorine-containing surfactant may be a saturated fluorinated surfactant in which all of the carbon atoms bonded to the hydrophobic group have been substituted with fluorine atoms.

[0069] 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 CF ２ -Y ０ (N ４ ) (wherein, Rf ｎ４ is a linear or branched or fully fluorinated alkyl group having 1 to 12 carbon atoms, which may contain an ether linkage (provided that -CH ２ -), 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 ): (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 alkyl group having 1 to 6 carbon atoms, which may contain an ether bond, or a fully fluorinated alkyl group (provided that -CH ２ -), except that X ｎ３ and Xｎ４ Both of Rf cannot be H. ｎ５ is a linear or branched or fully fluorinated alkylene group having 1 to 3 carbon atoms, which may contain an ether bond (provided that -CH ２ -), L is a linking group, and Y ０ is as defined above, where X ｎ２ , X ｎ３ , X ｎ４ and Rf ｎ５ wherein the total number of carbon atoms is 18 or less.

[0070] 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), general formula (X): Rf ７ -O-Rf ８ -O-CF ２ -COOM (wherein, Rf ７ is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, which may contain ether bonds and / or chlorine atoms (provided that -CH ２ -), and Rf ８ is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms (provided that -CH ２ Fluorocarboxylic acid (X) represented by general formula (XI): Rf ９ -O-CY １ FCF ２ -SO ３ M (wherein, Rf ９is 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 (provided that -CH ２ -), and Y １ is H or F, and M is as defined above.), an alkoxyfluorosulfonic acid (XI) represented by the general formula (XII): (In the formula, X １ , X ２ and X ３ may be the same or different and are H, F and straight or branched chain alkyl groups having 1 to 6 carbon atoms which may contain ether bonds or fully fluorinated alkyl groups (provided that -CH ２ -), except 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 (XII) represented by the general formula (XIII): Rf １１ -O-(CF ２ CF (CF ３ ) O) ｎ９ (CF ２ O) ｎ１０ CF ２ COOM (where Rf １１ represents a fluoroalkyl group having 1 to 5 carbon atoms and containing chlorine (wherein -CH ２ n9 is an integer of 0 to 3, n10 is an integer of 0 to 3, and M is as defined above. The use of these fluorine-containing surfactants allows the polymerization of fluoromonomers to proceed smoothly in the presence of an aqueous medium.

[0071] Examples of the fluorine-containing surfactant include compounds represented by the following formula: F(CF ２ ) ７ COOM, F(CF ２ ) ５COOM, H(CF ２ ), ６ COOM, H(CF ２ ), ７ COOM, CF ３ O(CF ２ ), ３ OCHFCF ２ COOM, C ３ F ７ OCF(CF ３ ),CF ２ OCF(CF ３ ),COOM, CF ３ CF ２ CF ２ OCF(CF ３ ),COOM, CF ３ CF ２ OCF ２ CF ２ OCF ２ COOM, C ２ F ５ OCF(CF ３ ),CF ２ OCF(CF ３ ),COOM, CF ３ OCF(CF ３ ),CF ２ OCF(CF ３ ),COOM, CF ２ ClCF ２ CF ２ OCF(CF ３ ),CF ２ OCF ２ COOM, CF ２ ClCF ２ CF ２ OCF ２ CF(CF ３ ),OCF ２ COOM, CF ２ ClCF(CF ３ ),OCF(CF ３ ),CF ２ OCF ２ COOM, CF ２ ClCF(CF ３ ),OCF ２ CF(CF ３ ),OCF ２ COOM, (In each formula, M is H, a metal atom, NR ７４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium. ７ is H or an organic group.

[0072] In the production method of the present disclosure, a fluorosurfactant having 7 or less carbon atoms can be particularly preferably used as the fluorosurfactant used in the polymerization of the fluoromonomer. By using a fluorosurfactant having 7 or less carbon atoms, the polymerization of the fluoromonomer can proceed smoothly, and the content of fluorine-containing compounds having a hydrophilic group having 7 or less carbon atoms, such as a fluorosurfactant having 7 or less carbon atoms, can be efficiently removed from the aqueous fluoropolymer dispersion by heat treatment, ion exchange treatment, and concentration treatment after polymerization.

[0073] Examples of the fluorine-containing surfactant having 7 or less carbon atoms include those compounds represented by the above-mentioned general formulas (I) to (XIII) having 7 or less carbon atoms. That is, examples of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms include the following compounds:

[0074] The perfluorocarboxylic acid (I) having 7 or less carbon atoms is represented by the following general formula (I): F(CF ２ ) ｎ１ COOM (I) (wherein n1 is an integer of 3 to 6, and M is H, a metal atom, or NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７ is H or an organic group.

[0075] The ω-H perfluorocarboxylic acid (II) having 7 or less carbon atoms is represented by the following general formula (II): H(CF ２ ) ｎ２ COOM (II) (wherein n2 is an integer of 4 to 6, and M is as defined above).

[0076] The perfluoroethercarboxylic acid (III) having 7 or less carbon atoms is represented by the following general formula (III): １-O-(CF(CF ３ )CF ２ O) ｎ３ CF (CF ３ ) COOM (III) (wherein, Rf １ is a trifluoromethyl group, n3 is 1, and M is as defined above.

[0077] The perfluoroalkyl alkylene carboxylic acid (IV) having 7 or less carbon atoms is represented by the following general formula (IV): ２ (CH ２ ) ｎ４ Rf ３ COOM (IV) (wherein, Rf ２ is a perfluoroalkyl group having 1 to 4 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 Rf ２ , Rf ３ and n4 are combined so that the total number of carbon atoms is 6 or less, and M is as defined above.

[0078] The alkoxyfluorocarboxylic acid (V) having 7 or less carbon atoms is represented by the following general formula (V): ４ -O-CY １ Y ２ CF ２ -COOM (V) (wherein, Rf ４ is a linear or branched partially or fully fluorinated alkyl group having 1 to 4 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.

[0079] The perfluoroalkylsulfonic acid (VI) having 7 or less carbon atoms is represented by the following general formula (VI): F(CF ２ ) ｎ５ SO ３ M (VI) (wherein n5 is an integer of 3 to 7, and M is as defined above).

[0080] The ω-H perfluorosulfonic acid (VII) having 7 or less carbon atoms is represented by the following general formula (VII): H(CF ２ ) ｎ６ SO ３ M (VII) (wherein n6 is an integer of 4 to 7, and M is as defined above).

[0081] The perfluoroalkyl alkylene sulfonic acid (VIII) having 7 or less carbon atoms is represented by the following general formula (VIII): ５ (CH ２ ) ｎ７ SO ３ M (VIII) (wherein, Rf ５ is a perfluoroalkyl group having 1 to 4 carbon atoms, n7 is an integer of 1 to 3, and M is as defined above.

[0082] The alkyl alkylene carboxylic acid (IX) having 7 or less carbon atoms is represented by the following general formula (IX): ６ (CH ２ ) ｎ８ COOM (IX) (wherein, Rf ６ is a linear or branched partially or fully fluorinated alkyl group having 1 to 4 carbon atoms which may contain an ether bond, n8 is an integer from 1 to 3, and M is as defined above.

[0083] The fluorocarboxylic acid (X) having 7 or less carbon atoms is represented by the following general formula (X): ７ -O-Rf ８ -O-CF ２ -COOM (X) (wherein, Rf ７ is a linear or branched partially or fully fluorinated alkyl group having 1 to 2 carbon atoms, which may contain an ether bond and / or a chlorine atom, and Rf ８ is a linear or branched, partially or fully fluorinated alkyl group having 1 to 3 carbon atoms, and M is as defined above.

[0084] The alkoxyfluorosulfonic acid (XI) having 7 or less carbon atoms is represented by the following general formula (XI): Rf ９-O-CY １ Y ２ CF ２ -SO ３ M (XI) (wherein, Rf ９ is a linear or branched alkyl group having 1 to 5 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.

[0085] The compound (XII) having 7 or less carbon atoms is represented by the following general formula (XII): (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 fully fluorinated alkyl groups having 1 to 3 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. ０ is -COOM, -SO ２ M or -SO ３ M, and -SO ３ M or COOM (wherein M is as defined above). Examples of L include a single bond, a partially or fully fluorinated alkylene group having 1 to 4 carbon atoms which may contain an ether bond. However, X １ , X ２ , X ３ , Rf １０ , L and Y ０ The total number of carbon atoms is 7 or less.

[0086] The compound (XIII) having 7 or less carbon atoms is represented by the following general formula (XIII): １１ -O-(CF ２ CF (CF ３ ) O) ｎ９ (CF ２ O) ｎ１０ CF ２ COOM (XIII) (wherein, Rf１１ is a fluoroalkyl group containing chlorine and having 1 to 2 carbon atoms, n9 is an integer of 0 to 1, n10 is an integer of 0 to 1, and M is as defined above.

[0087] As the fluorine-containing surfactant having 7 or less carbon atoms, at least one selected from the group consisting of compounds represented by general formula (I), general formula (III), general formula (IX) and general formula (X) is preferred, and at least one selected from the group consisting of compounds represented by general formula (I) and general formula (III) is more preferred.

[0088] Examples of fluorine-containing surfactants having 7 or less carbon atoms include compounds represented by the following formulas. The fluorine-containing surfactant having 7 or less carbon atoms may be a mixture of these compounds. F(CF ２ ) ５ COOM, C.F. ３ CF ２ CF ２ OCF (CF ３ ) COOM, C.F. ３ CF ２ OCF ２ CF ２ OCF ２ COOM, C.F. ３ OCF (CF ３ )CF ２ OCF (CF ３ ) COOM, (In each formula, M is H, metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium. ７ is H or an organic group.

[0089] 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, and more preferably 5% by mass or less, and even more preferably 1% by mass or less, relative to the aqueous medium.

[0090] (Polymerization initiator) The polymerization initiator used for the polymerization of 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 target fluoropolymer, and the reaction rate.

[0091] As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

[0092] 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. Also usable are di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluorooctanoyl) 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 include di[perfluoro(or fluorochloro)acyl]peroxides such as di(ω-chlorohexafluorobutyryl)peroxide, di(ω-chlorodecafluorohexanoyl)peroxide, di(ω-chlorotetradecafluorooctanoyl)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.

[0093] The water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as ammonium salts, potassium salts, or sodium salts of persulfuric acid, perboric acid, perchloric acid, perphosphoric acid, or percarbonate; organic peroxides such as disuccinic acid peroxide or diglutaric acid peroxide; t-butyl permaleate; t-butyl hydroperoxide; etc. A reducing agent such as a sulfite may also be contained, and the amount used may be 0.1 to 20 times the amount of the peroxide.

[0094] 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 oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and cerium ammonium nitrate. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of 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 redox initiator combination. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0095] Examples of the redox initiator include potassium permanganate / oxalic acid, potassium permanganate / ammonium oxalate, ammonium persulfate / bisulfite / iron sulfate, manganese triacetate / oxalic acid, cerium ammonium nitrate / oxalic acid, and bromate / bisulfite, with potassium permanganate / oxalic acid being preferred. When using a redox initiator, either an oxidizing agent or a reducing agent may be charged into a polymerization vessel in advance, 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 vessel and then continuously add potassium permanganate thereto.

[0096] The amount of polymerization initiator to be added is not particularly limited, but may be added all at once, stepwise, or continuously at the beginning of polymerization in an amount (for example, several ppm relative to water concentration) that does not significantly decrease the polymerization rate. The upper limit is a range in which the reaction temperature can be increased while removing heat from the equipment using the heat of polymerization reaction, and a more preferred upper limit is a range in which the heat of polymerization reaction can be removed from the equipment.

[0097] The radical concentration during polymerization of fluoromonomers can be adjusted by adding a decomposer. Examples of decomposers include sulfites, bisulfites, bromates, diimines, oxalic acid, copper salts, and iron salts. Examples of sulfites include sodium sulfite and ammonium sulfite. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate. The amount of decomposer added is in the range of 25 to 300% by mass relative to the amount of oxidizing agent combined as a polymerization initiator (redox initiator). The amount of decomposer added is preferably 25 to 150% by mass, more preferably 50 to 100% by mass. The decomposer is preferably added after 5% by mass of the total fluoromonomer consumed in the polymerization reaction has been polymerized, and more preferably after 10% by mass has been polymerized. The amount of decomposer added is preferably an amount equivalent to 0.1 to 20 ppm by mass of the aqueous medium used, and more preferably an amount equivalent to 3 to 10 ppm by mass.

[0098] (Aqueous medium) The aqueous medium used for the polymerization of the fluoromonomer is a reaction medium for polymerization, 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 an ether or a ketone, and / or a fluorine-containing organic solvent having a boiling point of 40° C. or less.

[0099] 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, and an aqueous medium containing only water is more preferred, because it allows the polymerization of the fluoromonomer to proceed smoothly and also prevents a decrease in the efficiency of removing the fluorine-containing compound having a hydrophilic group.

[0100] 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 fluorine-containing compound having a hydrophilic group.

[0101] (Fluoromonomer) The fluoromonomer used in polymerization has at least one fluorine atom and at least one double bond.As the fluoromonomer, 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, 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 is a linear or branched fluoroalkyl group having 1 to 12 carbon atoms), a fluorinated vinyl heterocyclic compound, and a monomer that provides a crosslinking site.

[0102] The fluoroalkyl vinyl ether [FAVE] is, for example, a compound represented by the general formula (110): CF ２ =CF-ORf １１１ (wherein, Rf １１１ represents a perfluoroorganic group.) A fluoromonomer represented by general formula (120): CF ２ =CF-OCH ２ -Rf １２１ (wherein, Rf １２１ is a perfluoroalkyl group having 1 to 5 carbon atoms), a fluoromonomer represented by the general formula (130): CF２ = CFOCF ２ ORf １３１ (wherein, 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.) Fluoromonomers represented by general formula (140): CF ２ = CFO (CF ２ CF (Y １４１ ) O) ｍ (CF ２ ) ｎ F (wherein, 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.) and a fluoromonomer represented by the general formula (150): CF ２ =CF-O-(CF ２ CFY １５１ -O) ｎ -(CFY １５２ ) ｍ -A １５１ (In the formula, Y １５１ represents a fluorine atom, a chlorine atom, -SO ２ It represents a F group or a perfluoroalkyl group. The perfluoroalkyl group is an etheric oxygen and -SO ２ The group n may contain an F group. n represents an integer of 0 to 3. １５１ may be the same or different. １５２ represents a fluorine atom, a chlorine atom, or —SO ２ represents an F group, and m represents an integer of 1 to 5. １５２ may be the same or different. １５１ is -SO ２ X １５１ , -COZ １５１ or -POZ １５２ Z １５３ represents. １５１ is F, Cl, Br, I, -OR １５１ or -NR １５２ R １５３ Represents Z. １５１ , Z １５２ and Z １５３are the same or different and represent -NR １５４ R １５５ Or -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.

[0103] In the present disclosure, the term "perfluoroorganic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoroorganic group may have an ether oxygen atom.

[0104] The fluoromonomer represented by the general formula (110) is Rf １１１ is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5.

[0105] Examples of the perfluoroorganic group in the general formula (110) include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group. 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, Rf １１１ is of the following formula:

[0106]

[0107] (wherein m represents 0 or an integer of 1 to 4), Rf １１１ is of the following formula:

[0108]

[0109] (wherein n represents an integer of 1 to 4).

[0110] Among the fluoromonomers represented by the general formula (110), those represented by the general formula (160): CF ２ =CF-ORf １６１ (wherein, 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.

[0111] The fluoroalkyl vinyl ether is preferably at least one selected from the group consisting of fluoromonomers represented by the general formulae (160), (130) and (140).

[0112] The fluoromonomer represented by the general formula (160) is generally called perfluoro(alkyl vinyl ether). As the fluoromonomer represented by the general formula (160), at least one selected from the group consisting of perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether) is preferred, and at least one selected from the group consisting of perfluoro(methyl vinyl ether) and perfluoro(propyl vinyl ether) is more preferred.

[0113] The fluoromonomer represented by the general formula (130) is CF ２ = CFOCF ２ OCF ３ , C.F. ２ = CFOCF ２ OCF ２ CF ３ and C.F. ２ = CFOCF ２ OCF ２ CF ２ OCF ３ At least one selected from the group consisting of:

[0114] The fluoromonomer represented by the general formula (140) is CF ２ = CFOCF ２ CF (CF ３ ) O(CF ２ ) ３ F, CF ２= CFO (CF ２ CF (CF ３ ) O) ２ (CF ２ ) ３ F and CF ２ = CFO (CF ２ CF (CF ３ ) O) ２ (CF ２ ) ２ At least one selected from the group consisting of F is preferred.

[0115] The fluoromonomer represented by the general formula (150) is CF ２ = CFOCF ２ CF ２ SO ２ F, CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ SO ２ F, CF ２ = CFOCF ２ CF (CF ２ CF ２ SO ２ F) OCF ２ CF ２ SO ２ F and CF ２ = CFOCF ２ CF (SO ２ F) ２ At least one selected from the group consisting of:

[0116] 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 linear perfluoroalkyl group. １０１ The number of carbon atoms of the fluoromonomer represented by the general formula (100) is preferably 1 to 6. ２ =CFCF ３ , C.H. ２ =CFCF ２ CF ３ , C.H. ２ =CFCF ２ CF ２CF ３ , C.H. ２ =CFCF ２ CF ２ CF ２ H, CH ２ =CFCF ２ CF ２ CF ２ CF ３ , CHF=CHCF ３ (E form), CHF=CHCF ３ (Z-isomer), among which CH ２ =CFCF ３ Preferred is 2,3,3,3-tetrafluoropropylene represented by the following formula:

[0117] The fluoroalkylethylene includes fluoroalkyl ethylenes represented by the general formula (170): CH ２ =CH-(CF ２ ) ｎ -X １７１ (In the formula, X １７１ is H or F, and n is an integer of 3 to 10.) is preferred, and CH ２ =CH-C ４ F ９ and C.H. ２ =CH-C ６ F １３ At least one selected from the group consisting of:

[0118] The fluoroalkyl allyl ether is, for example, a compound represented by the general formula (180): CF ２ =CF-CF ２ -ORf １１１ (wherein, Rf １１１ represents a perfluoroorganic group.

[0119] Rf of general formula (180) １１１ is Rf in general formula (110). １１１ Rf is the same as １１１ As the fluoroalkyl aryl ether represented by the general formula (180), a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms is preferred. ２ =CF-CF ２-O-CF ３ , C.F. ２ =CF-CF ２ -O-C ２ F ５ , C.F. ２ =CF-CF ２ -O-C ３ F ７ and C.F. ２ =CF-CF ２ -O-C ４ F ９ At least one selected from the group consisting of CF ２ =CF-CF ２ -O-C ２ F ５ , C.F. ２ =CF-CF ２ -O-C ３ F ７ and C.F. ２ =CF-CF ２ -O-C ４ F ９ More preferably, at least one selected from the group consisting of CF ２ =CF-CF ２ -O-CF ２ CF ２ CF ３ is more preferred.

[0120] The fluorinated vinyl heterocycle may be a heterocyclic compound represented by the general formula (230): (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 is.

[0121] (In the formula, Z ２３１ and Z ２３２ are independently F or a fluorinated alkyl group having 1 to 3 carbon atoms.

[0122] The monomer that provides the crosslinking site is represented by the general formula (180): CX １８１ ２ =CX １８２ -R ｆ１８１ CHR １８１ X １８３ (In the formula, X １８１ and X １８２ are independently a hydrogen atom, a fluorine atom, or CH ３ , R ｆ １８１ represents a fluoroalkylene group, a perfluoroalkylene group, a fluoro(poly)oxyalkylene group or a perfluoro(poly)oxyalkylene group, R １８１ is a hydrogen atom or CH ３ , X １８３ is an iodine atom or a bromine atom, a fluoromonomer represented by 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 CH ３ , 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.) A fluoromonomer represented by the general formula (200): CF ２ = CFO (CF ２ CF (CF ３ ) O) ｍ (CF ２ ) ｎ -X ２０１ (wherein m is an integer of 0 to 5, n is an integer of 1 to 3, X ２０１ represents a cyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or —CH ２ I) and a fluoromonomer represented by the general formula (210): CH ２ =CFCF ２ O(CF(CF ３ )CF ２ O) ｍ (CF (CF ３ )) ｎ -X ２１１(wherein m is an integer of 0 to 5, n is an integer of 1 to 3, X ２１１ represents a cyano group, a carboxyl group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or —CH ２ OH.) and a fluoromonomer represented by the 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 represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. ２２１ -(Q) is a linear or branched alkylene group having 1 to 18 carbon atoms, a cycloalkylene group having 3 to 18 carbon atoms, or an at least partially fluorinated alkylene or oxyalkylene group having 1 to 10 carbon atoms, which may contain an oxygen atom; ｐ -CF ２ O-(CF ２ CF ２ O) ｍ (CF ２ O) ｎ -CF ２ -(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.

[0123] X １８３ and X １９３ is preferably an iodine atom. ｆ １８１ and R ｆ １９１ is preferably a perfluoroalkylene group having 1 to 5 carbon atoms. １８１ is preferably a hydrogen atom. ２０１represents a cyano group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or —CH ２ Preferably, X is I. ２１１ represents a cyano group, an alkoxycarbonyl group, an iodine atom, a bromine atom, or —CH ２ It is preferably OH.

[0124] The monomer that provides the crosslinking site is CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ C.N., C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ COOH, C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CH ２ I, CF ２ = CFOCF ２ CF ２ CH ２ I, CH ２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ ) CN, CH ２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ ) COOH, CH ２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ ) CH ２ OH, CH ２ = CHCF ２ CF ２ I, CH ２ =CH(CF ２ ) ２ CH=CH ２ , C.H. ２ =CH(CF ２ ) ６ CH=CH ２and C.F. ２ = CFO (CF ２ ) ５ CN, and CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CN and CF ２ = CFOCF ２ CF ２ CH ２ I is more preferred.

[0125] In the polymerization, the fluoromonomer and a fluorine-free monomer may be polymerized. Examples of the fluorine-free monomer include hydrocarbon-based monomers reactive with the fluoromonomer. Examples of the hydrocarbon-based 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 hydroxybenzo ... vinyl esters such as vinyl hydroxypropioate, 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 acid 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.

[0126] The above-mentioned fluorine-free monomer may also be a functional group-containing hydrocarbon monomer (excluding the monomer that provides a crosslinking site).Examples of the above-mentioned 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 methylolacrylamide; fluorine-free monomers having a nitrile group such as acrylonitrile and methacrylonitrile.

[0127] In the above polymerization, one or more of the above fluoromonomers are polymerized to obtain particles of the desired fluoropolymer.

[0128] (Chain Transfer Agent) In the production method of the present disclosure, the fluoromonomer can be polymerized in the presence of a chain transfer agent. The use of a chain transfer agent can adjust the polymerization rate and molecular weight. Examples of the chain transfer agent include esters such as dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate, and dimethyl succinate, as well as isopentane, methane, ethane, propane, methanol, isopropanol, acetone, various mercaptans, various halogenated hydrocarbons such as carbon tetrachloride, and cyclohexane.

[0129] Bromine compounds or iodine compounds may be used as chain transfer agents. The polymerization method using a bromine compound or an iodine compound may, for example, be a method of polymerizing a fluoromonomer in an aqueous medium in the presence of a bromine compound or an iodine compound in a substantially oxygen-free state (iodine transfer polymerization method). Representative examples of the bromine compound or iodine compound to be used include, for example, compounds represented by the general formula: R ａ I ｘ Br ｙ (wherein x and y are each an integer of 0 to 2 and satisfy 1≦x+y≦2; 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.

[0130] Examples of bromine compounds or iodine compounds include 1,3-diiodoperfluoropropane, 2-iodoperfluoropropane, 1,3-diiodo-2-chloroperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoethane, 1,3-diiodo-n-propane, CF ２ Br ２ , BrCF ２ CF ２ Br, CF ３ CFBrCF ２ Br, CFClBr ２ , BrCF ２ CFClBr, CFBrClCFClBr, BrCF ２ CF ２ CF ２ Br, BrCF ２ CFBrOCF ３, 1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 1-bromo-4-iodoperfluorobutane, 2-bromo-3-iodoperfluorobutane, 3-bromo-4-iodoperfluorobutene-1, 2-bromo-4-iodoperfluorobutene-1, monoiodomonobromo-substituted benzene, diiodomonobromo-substituted benzene, and (2-iodoethyl) and (2-bromoethyl) substituted benzenes, and these compounds may be used alone or in combination with each other.

[0131] 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.

[0132] 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 fluoromonomer supplied. The amount of chain transfer agent used is preferably an amount that is completely consumed during the polymerization of the fluoromonomer and does not remain in the aqueous dispersion containing the fluoropolymer, so as not to reduce the removal efficiency of the fluorine-containing compound having a hydrophilic group 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 fluoromonomer supplied.

[0133] The chain transfer agent may be added all at once to the reaction vessel before the initiation of polymerization, may be added all at once after the initiation of polymerization, may be added in multiple divided portions during the polymerization, or may be added continuously during the polymerization.

[0134] (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, etc. may be used.

[0135] Preferred stabilizing aids include paraffin wax, fluorine-based oil, fluorine-based solvent, and silicone oil. The stabilizing aids may be used alone or in combination of two or more. Paraffin wax is more preferred as the stabilizing aid. Paraffin wax may be liquid, semi-solid, or solid at room temperature, but saturated hydrocarbons having 12 or more carbon atoms are preferred. The melting point of the paraffin wax is generally preferably 40 to 65°C, more preferably 50 to 65°C.

[0136] The amount of the stabilizing aid used is preferably 0.1 to 12% by mass, more preferably 0.1 to 8% by mass, based on the mass of the aqueous medium used. It is desirable that the stabilizing aid is sufficiently hydrophobic so that it is completely separated from the aqueous dispersion after polymerization and does not become a contaminating component.

[0137] (Polymerization conditions) Polymerization of fluoromonomers 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 target fluoropolymer, the reaction rate, etc.

[0138] (Aqueous dispersion obtained by polymerization) An aqueous dispersion containing a fluoropolymer is obtained by polymerization of a fluoromonomer. The content of the fluoropolymer in the aqueous dispersion after polymerization is usually 8 to 50 mass % based on the aqueous dispersion.

[0139] The aqueous dispersion obtained by polymerizing a fluoromonomer usually contains, in addition to the fluoropolymer, the fluorine-containing surfactant used in polymerizing the fluoromonomer. Furthermore, the aqueous dispersion obtained by polymerizing a fluoromonomer may contain, in addition to the fluoropolymer, a fluorine-containing compound having a hydrophilic group produced by polymerization of the fluoromonomer. In the present disclosure, the fluorine-containing compound having a hydrophilic group includes the fluorine-containing surfactant added during polymerization and the fluorine-containing compound having a hydrophilic group produced by polymerization of the fluoromonomer.

[0140] In the present disclosure, the hydrophilic group possessed by the fluorine-containing compound is preferably an anionic group such as an acid group, for example, —NH ２ , -PO ３ M, -OPO ３ M, -SO ３ M, -OSO ３ Examples of the hydrophilic group include -M and -COOM (in each formula, M represents a cation). ３ M or -COOM is preferred, and -COOM is more preferred.

[0141] A typical compound as the fluorine-containing compound having a hydrophilic group in the aqueous dispersion obtained by polymerization is a fluorine-containing compound having a hydrophilic group with a molecular weight of 1000 g / mol or less. According to the production method of the present disclosure, an aqueous fluoropolymer dispersion can be produced in which the content of the fluorine-containing compound having a hydrophilic group with a molecular weight of 1000 g / mol or less is reduced.

[0142] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a fluorine-containing surfactant added during polymerization. The fluorine-containing surfactant added during polymerization is as described above for the fluorine-containing surfactant used in polymerization of a fluoromonomer.

[0143] The content of the fluorine-containing surfactant in the aqueous dispersion obtained by polymerization may be 10 ppm by mass or more, 100 ppm by mass or more, or 1000 ppm by mass or more, and may be 10% by mass or less, 5% by mass or less, or 1% by mass or less, relative to the fluoropolymer in the aqueous dispersion.

[0144] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a fluorine-containing surfactant having 7 or less carbon atoms added during polymerization. The fluorine-containing surfactant having 7 or less carbon atoms added during polymerization is as described above for the fluorine-containing surfactant used in polymerization of a fluoromonomer.

[0145] The content of the fluorine-containing surfactant having 7 or less carbon atoms in the aqueous dispersion obtained by polymerization may be 10 ppm by mass or more, 100 ppm by mass or more, or 1000 ppm by mass or more, or 10% by mass or less, 5% by mass or less, or 1% by mass or less, relative to the fluoropolymer in the aqueous dispersion.

[0146] The content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion obtained by polymerization (the total content of the fluorine-containing surfactant added during polymerization and the content of the fluorine-containing compound having a hydrophilic group produced by polymerization of the fluoromonomer) may be 10 ppm by mass or more, 100 ppm by mass or more, or 1000 ppm by mass or more, or 10% by mass or less, 5% by mass or less, or 1% by mass or less, relative to the fluoropolymer in the aqueous dispersion.

[0147] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a compound represented by the following general formula (1): － ] ｉ M ｉ＋ (Wherein, X represents H, Cl, Br, F or I; Rf 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; A－ is an acid group, M ｉ＋ represents a cation having a valence i, where i is an integer from 1 to 3.

[0148] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a compound represented by the following general formula (2): General formula (2): [C ｎ－１ F ２ｎ－１ COO － ]M ＋ (wherein n is an integer of 9 to 14, M ＋ represents a cation.)

[0149] It is known that compounds represented by general formula (2) (perfluoroalkanoic acids) are formed during polymerization when perfluoro(alkyl vinyl ether) or the like is used as a fluoromonomer (see WO 2019 / 161153).

[0150] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a compound represented by the following general formula (3): General formula (3): [R １ -O-L-CO ２ － ]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 linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; ＋ represents a cation.)

[0151] In one embodiment of the aqueous dispersion obtained by polymerization, the fluorine-containing compound having a hydrophilic group contains a compound represented by general formula (4). General formula (4): [H—(CF ２ ) ｍ CO ２ － ]M ＋ (wherein m is an integer of 3 to 19, M ＋ represents a cation.)

[0152] (Removal of fluoromonomer or recovery of aqueous dispersion) In the manufacturing method of the present disclosure, after preparing aqueous dispersion by polymerization, before carrying out heat treatment of aqueous dispersion, (a) can carry out at least one of the following operations: (a) remove the fluoromonomer remaining in reactor from reactor, and (b) recover the aqueous dispersion in reactor and store it in the container different from reactor.In particular, if the method of removing fluoromonomer in reactor is used, it can carry out subsequent process in the same reactor that is used in polymerization, and the productivity of aqueous fluoropolymer dispersion is improved, so it is preferred.

[0153] 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 stopped smoothly.

[0154] The method for 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 fluoromonomer may be removed from the reactor by venting until the pressure in the reactor reaches normal pressure, or the fluoromonomer may be removed from the reactor by reducing the pressure in the reactor to less than 0.0 MPaG, or the fluoromonomer in the reactor may be replaced with an inert gas such as nitrogen gas by supplying an inert gas into the reactor. Alternatively, the entire amount of the fluoromonomer in the reactor may be reacted and converted into a fluoropolymer, thereby removing the fluoromonomer from the reactor. The removal of the fluoromonomer remaining in the reactor from the reactor can be carried out to the extent that the polymerization reaction of the fluoromonomer is sufficiently stopped, so that a small amount of the fluoromonomer may remain in the reactor. The removed fluoromonomer can be recovered by known means. The recovered fluoromonomer may be reused to produce a fluoropolymer.

[0155] As a method for removing the fluoromonomer from the reactor, a method is also suitable in which, after preparing the aqueous dispersion, stirring of the contents of the reactor is stopped if 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.

[0156] When the polymerization of fluoromonomer is carried out at a temperature higher than room temperature, the reactor may be cooled before or after removing the fluoromonomer from the reactor.When removing the fluoromonomer from the reactor by means of evacuation or nitrogen substitution, there is a possibility that unreacted fluoromonomer, particularly in liquid form, remains in the reactor, but by cooling the reactor, the progress of the reaction of the unreacted fluoromonomer can be sufficiently suppressed.

[0157] The method for 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 content of the reactor may be stopped if 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 content of the reactor may be stopped if desired, and the aqueous dispersion may be supplied from the reactor to another container via a pipe connecting the reactor and another container.

[0158] To terminate the polymerization reaction of the fluoromonomer, a polymerization terminator (radical scavenger) may be added.

[0159] As the polymerization terminator, a compound that does not have the ability to re-initiate after addition or chain transfer to a free radical in the polymerization system is used. Specifically, a compound that easily undergoes a chain transfer reaction with a primary radical or a propagating radical to generate a stable radical that does not subsequently react with a monomer, or a compound that easily undergoes an addition reaction with a primary radical or a propagating radical to generate a stable radical, is used. The activity of what is generally called a chain transfer agent is characterized by the chain transfer constant and the re-initiation efficiency, and among chain transfer agents, those with a re-initiation efficiency of almost 0% are called polymerization terminators. Examples of polymerization terminators include aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and cupric chloride (CuCl ２ ) is preferred. Examples of aromatic hydroxy compounds include unsubstituted phenol, polyhydric phenol, salicylic acid, m- or p-salicylic acid, gallic acid, naphthol, etc. Examples of the unsubstituted phenol include o-, m-, or p-nitrophenol, o-, m-, or p-aminophenol, p-nitrosophenol, etc. Examples of polyhydric phenols include catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, naphthresorcinol, etc. Examples of aromatic amines include o-, m-, or p-phenylenediamine, benzidine, etc. Examples of the quinone compounds include hydroquinone, o-, m-, or p-benzoquinone, 1,4-naphthoquinone, alizarin, etc. Examples of thiocyanates include ammonium thiocyanate (NH ４ Examples of the polymerization terminator include potassium thiocyanate (KSCN), sodium thiocyanate (NaSCN), etc. Among these, quinone compounds are preferred, and hydroquinone is more preferred.

[0160] In one embodiment of the production method of the present disclosure, an aqueous dispersion containing a fluoropolymer is prepared, an inert gas is supplied into a reactor, and the aqueous dispersion in the reactor is subjected to a heat treatment. In this case, it is also a preferred embodiment that the radical generator described below is not added to the aqueous dispersion.

[0161] (Radical Generator) In one embodiment of the production method of the present disclosure, after preparing an aqueous dispersion by polymerization, a radical generator is added to the aqueous dispersion before subjecting the aqueous dispersion to heat treatment. In one embodiment of the production method of the present disclosure, after performing at least one of the operations (a) and (b), a radical generator is added to the aqueous dispersion before subjecting the aqueous dispersion to heat treatment. By adding the radical generator, the content of the fluorine-containing compound having a hydrophilic group can be further reduced.

[0162] 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.

[0163] The radical generator is not particularly limited as long as it is a compound that can decompose at the temperature during heat treatment to generate radicals. As the radical generator, a water-soluble radical generator is preferred because it can easily diffuse radicals in the aqueous dispersion.

[0164] 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.

[0165] The inorganic peroxide is preferably a water-soluble inorganic peroxide. Examples of the inorganic peroxide include hydrogen peroxide, perchlorates, perborates, perphosphates, percarbonates, and persulfates, with persulfates being preferred. The persulfates are preferably at least one selected from the group consisting of ammonium persulfate, sodium persulfate, and potassium persulfate, with ammonium persulfate being more preferred.

[0166] 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.

[0167] The radical generator may be a combination of an oxidizing agent and a reducing agent. By using a combination of an oxidizing agent and a reducing agent, 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.

[0168] Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, and cerium ammonium nitrate. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of 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 copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0169] 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, and bromate / bisulfite, 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.

[0170] The amount of the radical generator added is preferably 0.0001 times by mole or more, more preferably 0.001 times by mole or more, even more preferably 0.01 times by mole or more, and is preferably 1000 times by mole or less, more preferably 500 times by mole or less, and even more preferably 100 times by mole or less, relative to the number of moles of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion, since this can further improve the efficiency of removing the fluorine-containing compound having a hydrophilic group.

[0171] The content of the radical generator in the aqueous dispersion to be subjected to heat treatment is preferably 0.0001 times by mole or more, more preferably 0.001 times by mole or more, even more preferably 0.01 times by mole or more, and preferably 1000 times by mole or less, more preferably 500 times by mole or less, and even more preferably 100 times by mole or less, relative to the number of moles of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion, because this can further improve the efficiency of removing the fluorine-containing compound having a hydrophilic group.

[0172] The content of the radical generator in the aqueous dispersion to be subjected to heat treatment means, in the case where the aqueous dispersion is heated for the heat treatment after the radical generator is added to the aqueous dispersion, the content of the radical generator in the aqueous dispersion at the time when the temperature of the aqueous dispersion reaches the temperature for the heat treatment.

[0173] Furthermore, the content of the radical generator in the aqueous dispersion to be subjected to the heat treatment refers to the content of the radical generator in the aqueous dispersion at the time when the addition of the radical generator is completed, in the case where the aqueous dispersion is heated to a temperature for the heat treatment and then the radical generator is added to the aqueous dispersion.

[0174] The content of the radical generator can be calculated based on the amount of radical generator added, the half-life of the radical generator and the time from the time of addition, and the temperature for the heat treatment.

[0175] When the amount of radical generator added is relatively large, the fluoropolymer in the aqueous dispersion may be partially or entirely precipitated by the heat treatment. Since the fluoropolymer precipitation by the heat treatment can be suppressed and the aqueous fluoropolymer dispersion can be produced with high productivity without impairing the removal efficiency of the fluorine-containing compound having a hydrophilic group, the amount of radical generator added is preferably 50 molar times or less, more preferably 25 molar times or less, and even more preferably 10 molar times or less, relative to the number of moles of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion.

[0176] The method for 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.

[0177] 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 polymerizing the fluoromonomer, the temperature reached by cooling the aqueous dispersion after polymerizing the fluoromonomer, or the temperature of the heat treatment. That is, after adding the radical generator to the aqueous dispersion, the aqueous dispersion may be heated for the heat treatment, or the aqueous dispersion may be heated to a temperature for the heat treatment and then the radical generator may be added to the aqueous dispersion.

[0178] (Heat Treatment) In the production method of the present disclosure, the aqueous dispersion obtained by polymerization or the aqueous dispersion to which a radical generator has been added (aqueous dispersion containing a radical generator) is subjected to heat treatment. By subjecting the aqueous dispersion to heat treatment before contacting the aqueous dispersion with an ion exchange resin, the content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion can be surprisingly reduced.

[0179] The aqueous dispersion to be subjected to heat treatment preferably contains substantially no nonionic surfactant. The content of the nonionic surfactant in the aqueous dispersion to be subjected to heat treatment may be less than 1 mass% relative to the fluoropolymer in the aqueous dispersion, and may be 0 to 0.5 mass%. The content of the nonionic surfactant in the aqueous dispersion to be subjected to heat treatment is preferably less than 1 mass%, more preferably 0.5 mass% or less, and even more preferably 0.1 mass% or less. It is particularly preferable that the aqueous dispersion to be subjected to heat treatment does not contain a nonionic surfactant.

[0180] Before the heat treatment, the content of the fluoropolymer in the aqueous dispersion may be adjusted by a known method such as concentration or dilution.

[0181] 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 aqueous fluoropolymer dispersion can be produced with high productivity without impairing the removal efficiency of the fluorine-containing compound having a hydrophilic group. 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.

[0182] The content of the fluorine-containing surfactant added during polymerization in the aqueous dispersion to be subjected to heat treatment may be 10 ppm by mass or more, 100 ppm by mass or more, or 1000 ppm by mass or more, or 10% by mass or less, 5% by mass or less, or 1% by mass or less, relative to the mass of the fluoropolymer in the aqueous dispersion.

[0183] The content of the fluorine-containing surfactant having 7 or less carbon atoms in the aqueous dispersion to be subjected to heat treatment may be 10 ppm by mass or more, 100 ppm by mass or more, or 1000 ppm by mass or more, and may be 10% by mass or less, 5% by mass or less, or 1% by mass or less, relative to the fluoropolymer in the aqueous dispersion.

[0184] The content of the fluorine-containing compound having a hydrophilic group produced by polymerization of a fluoromonomer in the aqueous dispersion to be subjected to heat treatment is preferably 1 ppb by mass or more, more preferably 10 ppb by mass or more, and preferably 1000 ppm by mass or less, more preferably 500 ppm by mass or less, and still more preferably 50 ppm by mass or less, relative to the mass of the fluoropolymer in the aqueous dispersion.

[0185] The content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion to be subjected to heat treatment (the total content of the fluorine-containing surfactant added during polymerization and the content of the fluorine-containing compound having a hydrophilic group produced by polymerization of the fluoromonomer) may be 10 ppm by mass or more, 100 ppm by mass or more, or 1000 ppm by mass or more, and may be 10% by mass or less, 5% by mass or less, or 1% by mass or less, relative to the fluoropolymer in the aqueous dispersion.

[0186] The temperature of the heat treatment 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, and preferably 120° C. or lower, more preferably 110° C. or lower, even more preferably 100° C. or lower, particularly preferably 90° C. or lower, because this can further improve the efficiency of removing the fluorine-containing compound having a hydrophilic group. When the heat treatment is performed on an aqueous dispersion containing an added radical generator, the heat treatment temperature is preferably equal to or higher than the temperature at which the radical generator decomposes to generate radicals (decomposition temperature).

[0187] When the temperature of the heat treatment is relatively high, the fluoropolymer in the aqueous dispersion may be partially or entirely precipitated by the heat treatment. The temperature of the heat treatment is preferably 95° C. or less, more preferably 90° C. or less, and even more preferably 85° C. or less, because this can suppress the fluoropolymer precipitation due to the heat treatment and can produce the aqueous fluoropolymer dispersion with high productivity without impairing the removal efficiency of the fluorine-containing compound having a hydrophilic group.

[0188] In the heat treatment of aqueous dispersion, if aqueous dispersion can be maintained at a desired temperature or higher, it is not necessary to heat aqueous dispersion.For example, when the temperature of fluoromonomer polymerization is sufficiently high, and the temperature of the obtained aqueous dispersion is also sufficiently high, heat treatment can be started before the obtained aqueous dispersion is cooled.However, since it can suppress the precipitation of fluoropolymer due to heat treatment, and can produce fluoropolymer aqueous dispersion with high productivity without impairing the removal efficiency of fluorine-containing compounds having hydrophilic groups, it is preferable to cool the aqueous dispersion before and after removing fluoromonomer from reactor or recovering the aqueous dispersion in reactor, and heat this aqueous dispersion to the above-mentioned temperature range, and maintain this temperature for a certain period.The temperature of the aqueous dispersion to be subjected to heat treatment can be, for example, 30 ° C or less.

[0189] When the heat treatment is performed while heating the aqueous dispersion, the heating means is not particularly limited. For example, the aqueous dispersion may be heated by placing a container containing the aqueous dispersion in a thermostatic bath, or the aqueous dispersion may be placed in a container equipped with a heater and heated by the heater.

[0190] The pressure of the heat treatment is not particularly limited and may be atmospheric 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 atmospheric pressure.

[0191] The heat treatment time 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, even more preferably 600 minutes or less, since this can further improve the efficiency of removing the fluorine-containing compound having a hydrophilic group.

[0192] The heat treatment may be carried out while stirring the aqueous dispersion.

[0193] (Addition of nonionic surfactant to heat-treated aqueous dispersion) In the production method of the present disclosure, a nonionic surfactant is added to the heat-treated aqueous dispersion. By adding a nonionic surfactant, the dispersibility of the fluoropolymer in the heat-treated aqueous dispersion can be improved, and the dispersibility of the fluoropolymer can be maintained even during the ion exchange treatment. As a result, the content of fluorine-containing compounds having hydrophilic groups in the aqueous dispersion can be surprisingly reduced, and an aqueous dispersion with excellent dispersion stability can be produced. In one embodiment of the production method of the present disclosure, an aqueous dispersion not containing a nonionic surfactant is heat-treated, and then a nonionic surfactant is added to the heat-treated aqueous dispersion.

[0194] Nonionic surfactants typically contain no charged groups and have a hydrophobic portion that is a long hydrocarbon chain. The hydrophilic portion of the nonionic surfactant contains water-soluble functional groups, such as ethylene ether chains derived from polymerization with ethylene oxide.

[0195] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkyl esters, sorbitan alkyl esters, polyoxyethylene sorbitan alkyl esters, glycerol esters, and derivatives thereof.

[0196] Specific examples of polyoxyethylene alkyl ethers include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, and polyoxyethylene behenyl ether.

[0197] Specific examples of polyoxyethylene alkylphenyl ethers include polyoxyethylene nonylphenyl ether and polyoxyethylene octylphenyl ether.

[0198] Specific examples of polyoxyethylene alkyl esters include polyethylene glycol monolaurate, polyethylene glycol monooleate, and polyethylene glycol monostearate.

[0199] Specific examples of sorbitan alkyl esters include polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, and polyoxyethylene sorbitan monooleate.

[0200] Specific examples of polyoxyethylene sorbitan alkyl esters include polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, and polyoxyethylene sorbitan monostearate.

[0201] Specific examples of glycerol esters include glycerol monomyristate, glycerol monostearate, and glycerol monooleate.

[0202] Specific examples of the above derivatives include polyoxyethylene alkylamines, polyoxyethylene alkylphenyl-formaldehyde condensates, polyoxyethylene alkyl ether phosphates, and the like.

[0203] The ethers and esters may have an HLB value of 10-18.

[0204] Examples of nonionic surfactants include Triton (registered trademark) X series (X15, X45, X100, etc.), Tergitol (registered trademark) 15-S series, Tergitol (registered trademark) TMN series (TMN-6, TMN-10, TMN-100X, etc.), and Tergitol (registered trademark) L series, all manufactured by The Dow Chemical Company; and Pluronic (registered trademark) R series (31R1, 17R2, 10R5, 25R4 (m to 22, n to 23) and Iconol (registered trademark) TDA series (TDA-6, TDA-9, TDA-10), all manufactured by BASF.

[0205] The nonionic surfactant is preferably a nonionic surfactant that does not contain fluorine. Examples thereof include ether-type nonionic surfactants such as polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, and polyoxyethylene alkylene alkyl ether; polyoxyethylene derivatives such as ethylene oxide / propylene oxide block copolymers; ester-type nonionic surfactants such as sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, and polyoxyethylene fatty acid ester; and amine-based nonionic surfactants such as polyoxyethylene alkylamine and alkylalkanolamide.

[0206] In the above nonionic surfactants, the hydrophobic group may be any of an alkylphenol group, a linear alkyl group, and a branched alkyl group.

[0207] The nonionic surfactant is preferably a nonionic surfactant represented by general formula (i): ６ -O-A １ -H (i) (wherein, R ６ is a linear or branched primary or secondary alkyl group having 8 to 18 carbon atoms, and A １ is a polyoxyalkylene chain.

[0208] In general formula (i), R ６ The number of carbon atoms in R is preferably 10 to 16, and more preferably 12 to 16. ６ When the carbon number of R is 18 or less, the aqueous dispersion tends to have excellent sedimentation stability. ６ If the carbon number of R exceeds 18, the flow temperature is high and it is difficult to handle. ６ If the number of carbon atoms is less than 8, the surface tension of the aqueous dispersion increases, and the permeability and wettability tend to decrease.

[0209] A １The polyoxyalkylene chain of A may be composed of oxyethylene and oxypropylene. It is a polyoxyalkylene chain having an average repeat number of 5 to 20 oxyethylene groups and an average repeat number of 0 to 2 oxypropylene groups, and is a hydrophilic group. The number of oxyethylene units may include either a broad or narrow unimodal distribution as is usually provided, or a broader or bimodal distribution obtained by blending. When the average repeat number of oxypropylene groups is greater than 0, the oxyethylene groups and oxypropylene groups in the polyoxyalkylene chain may be arranged in a block or random configuration. From the viewpoint of the viscosity and sedimentation stability of the aqueous dispersion, a polyoxyalkylene chain having an average repeat number of 7 to 12 oxyethylene groups and an average repeat number of 0 to 2 oxypropylene groups is preferred. In particular, A １ When the number of oxypropylene groups is 0.5 to 1.5 on average, low foaming properties are favorable, and this is preferred.

[0210] More preferably, R ６ is (R')(R'')HC-, where R' and R'' are the same or different straight, branched, or cyclic alkyl groups having a total of at least 5, preferably 7 to 17, carbon atoms. Preferably, at least one of R' or R'' is a branched or cyclic hydrocarbon group.

[0211] Specific examples of the polyoxyethylene alkyl ether include C １３ H ２７ -O-(C ２ H ４ O) ｎ -H, C １２ H ２５ -O-(C ２ H ４ O) ｎ -H, C １０ H ２１ CH (CH ３ ) CH ２ -O-(C ２ H ４ O) ｎ -H, C １３ H ２７ -O-(C ２ H ４ O) ｎ-(CH(CH ３ ) CH ２ O) -H,C １６ H ３３ -O-(C ２ H ４ O) ｎ -H, HC(C ５ H １１ ) (C ７ H １５ )—O—(C ２ H ４ O) ｎ —H (in each formula, n is an integer of 1 or more). Commercially available polyoxyethylene alkyl ethers include, for example, the Genapol X series (manufactured by Clariant) such as Genapol X080 (trade name), the Noigen TDS series (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) such as Noigen TDS-80 (trade name), the Leocol TD series (manufactured by Lion Chemical Industries, Ltd.) such as Leocol TD-90 (trade name), the Lionol (registered trademark) TD series (manufactured by Lion Chemical Industries, Ltd.), the T-Det A series (manufactured by Harcros Chemicals) such as T-Det A138 (trade name), and the Tergitol (registered trademark) 15-S series (manufactured by The Dow Chemical Company).

[0212] Also preferred is an ethoxylate of 2,6,8-trimethyl-4-nonanol having an average of about 4 to about 18 ethylene oxide units, an ethoxylate of 2,6,8-trimethyl-4-nonanol having an average of about 6 to about 12 ethylene oxide units, or a mixture thereof. Nonionic surfactants of this type are also commercially available, for example, under the trade names TERGITOL TMN-6, TERGITOL TMN-10, and TERGITOL TMN-100X (all trade names, manufactured by The Dow Chemical Company).

[0213] The hydrophobic group of the nonionic surfactant may be any of an alkylphenol group, a linear alkyl group, and a branched alkyl group. For example, the nonionic surfactant may be a nonionic surfactant represented by the general formula (ii): ７ -C ６ H ４ -O-A ２ -H (ii) (wherein, R７ is a linear or branched alkyl group having 4 to 12 carbon atoms, and A ２ is a polyoxyalkylene chain.) Specific examples of the nonionic surfactant include Triton (registered trademark) X-100 (trade name, manufactured by The Dow Chemical Company).

[0214] A ２ The polyoxyalkylene chain of A may be composed of oxyethylene and oxypropylene. It is a polyoxyalkylene chain having an average repeat number of 5 to 20 oxyethylene groups and an average repeat number of 0 to 2 oxypropylene groups, and is a hydrophilic group. The number of oxyethylene units may include either a broad or narrow unimodal distribution as is usually provided, or a broader or bimodal distribution obtained by blending. When the average repeat number of oxypropylene groups is greater than 0, the oxyethylene groups and oxypropylene groups in the polyoxyalkylene chain may be arranged in a block or random configuration. From the viewpoint of the viscosity and sedimentation stability of the aqueous dispersion, a polyoxyalkylene chain having an average repeat number of 7 to 12 oxyethylene groups and an average repeat number of 0 to 2 oxypropylene groups is preferred. In particular, A ２ When the number of oxypropylene groups is 0.5 to 1.5 on average, low foaming properties are favorable, and this is preferred.

[0215] More preferably, R ７ is a primary or secondary alkyl group, more preferably (R')(R")HC-, where R' and R" are the same or different straight, branched, or cyclic alkyl groups having a total of at least 5, preferably 7 to 17 carbon atoms. Preferably, at least one of R' or R" is a branched or cyclic hydrocarbon group.

[0216] The nonionic surfactant also includes polyol compounds. Specific examples include those described in International Publication No. 2011 / 014715. Typical examples of polyol compounds include compounds having one or more sugar units as polyol units. The sugar units may be modified to contain at least one long chain. Suitable polyol compounds containing at least one long chain moiety include, for example, alkyl glycosides, modified alkyl glycosides, sugar esters, and combinations thereof. Sugars include, but are not limited to, monosaccharides, oligosaccharides, and sorbitan. Monosaccharides include pentoses and hexoses. Typical examples of monosaccharides include ribose, glucose, galactose, mannose, fructose, arabinose, and xylose. Oligosaccharides include oligomers of 2 to 10 identical or different monosaccharides. Examples of oligosaccharides include, but are not limited to, sucrose, maltose, lactose, raffinose, and isomaltose.

[0217] Typically, sugars suitable for use as polyol compounds include cyclic compounds containing a five-membered ring with four carbon atoms and one heteroatom (typically oxygen or sulfur, but preferably oxygen), or a six-membered ring with five carbon atoms and one heteroatom, preferably oxygen, as described above. These further contain at least two or at least three hydroxy groups (—OH groups) attached to the carbon ring atoms. Typically, the sugars are modified in that one or more of the hydrogen atoms of the hydroxy groups (and / or hydroxyalkyl groups) attached to the carbon ring atoms are replaced with a long-chain residue such that an ether or ester bond is created between the long-chain residue and the sugar moiety. Sugar-based polyols may contain one sugar unit or multiple sugar units. One sugar unit or multiple sugar units may be modified with a long-chain moiety as described above. Specific examples of sugar-based polyol compounds include glycosides, sugar esters, sorbitan esters, and mixtures and combinations thereof.

[0218] A preferred class of polyol compounds are the alkyl or modified alkyl glucosides. These classes of surfactants contain at least one glucose moiety. (wherein x represents 0, 1, 2, 3, 4, or 5; R １ and R ２ independently represent H or a long chain unit containing at least 6 carbon atoms, with the proviso that R １ and R ２ and at least one of R is not H. １ and R ２ Typical examples of alkyl polyglucosides include fatty alcohol residues. Examples of fatty alcohols include hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol (lauryl alcohol), tetradecanol, hexadecanol (cetyl alcohol), heptadecanol, octadecanol (stearyl alcohol), eicosanoic acid, and combinations thereof. While the above formula represents a specific example of an alkyl polyglucoside showing glucose in the pyranose form, it is understood that other sugars or sugars of the same sugar but in different enantiomeric or diastereomeric forms may also be used. Alkyl glucosides can be obtained, for example, by the acid-catalyzed reaction of glucose, starch, or n-butyl glucoside with aliphatic alcohols, which typically results in a mixture of various alkyl glucosides (Alkylpolygylcoside, Rompp, Lexikon Chemie, Version 2.0, Stuttgart / New York, George Thieme Verlag, 1999). Examples of aliphatic alcohols include hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol (lauryl alcohol), tetradecanol, hexadecanol (cetyl alcohol), heptadecanol, octadecanol (stearyl alcohol), eicosanoic acid, and combinations thereof. Alkyl glucosides are also commercially available from Cognis GmbH, Dusseldorf, Germany under the trade names GLUCOPON or DISPONIL.

[0219] Other nonionic surfactants include difunctional block copolymers supplied by BASF as part of the Pluronic® R series, and tridecyl alcohol alkoxylates supplied by BASF as part of the Iconol® TDA series.

[0220] The nonionic surfactant is preferably at least one selected from the group consisting of nonionic surfactants represented by general formula (i) and nonionic surfactants represented by general formula (ii), and more preferably a nonionic surfactant represented by general formula (i).

[0221] The nonionic surfactant preferably does not contain an aromatic moiety.

[0222] Nonionic surfactants include, among others, ethoxylates of 2,6,8-trimethyl-4-nonanol having an average of about 4 to about 18 ethylene oxide units, ethoxylates of 2,6,8-trimethyl-4-nonanol having an average of about 6 to about 12 ethylene oxide units, C １３ H ２７ -O-(C ２ H ４ O) ｎ -H, C １２ H ２５ -O-(C ２ H ４ O) ｎ -H, C １０ H ２１ CH (CH ３ ) CH ２ -O-(C ２ H ４ O) ｎ -H, C １３ H ２７ -O-(C ２ H ４ O) ｎ -(CH(CH ３ ) CH ２ O) -H,C １６ H ３３ -O-(C ２ H ４ O) ｎ -H, HC(C ５ H １１ ) (C７ H １５ )—O—(C ２ H ４ O) ｎ At least one selected from the group consisting of —H (wherein n is an integer of 1 or more) is preferred.

[0223] In one embodiment of the manufacturing method of the present disclosure, a nonionic surfactant is added to the heat-treated aqueous dispersion to prepare an aqueous dispersion in which the content of the nonionic surfactant in the aqueous dispersion is 5% by mass or more relative to the fluoropolymer. The content of the nonionic surfactant in the aqueous dispersion to which the nonionic surfactant has been added is more preferably 7% by mass or more, even more preferably 9% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0224] The content of the nonionic surfactant is a value calculated from the heating residue (Yg) obtained by heating about 1 g (Xg) of a sample at 110°C for 30 minutes, and the heating residue (Zg) obtained by further heating the obtained heating residue (Yg) at 300°C for 30 minutes, according to the formula: N = [(Y-Z) / Z] x 100 (mass%).

[0225] In the production method of the present disclosure, it is also preferable to cool the aqueous dispersion to less than 50° C. after the heat treatment and before contacting the aqueous dispersion with the ion exchange resin. By sufficiently cooling the aqueous dispersion before contacting the aqueous dispersion with the ion exchange resin, it is possible to suppress turbidity of the aqueous dispersion when a nonionic surfactant is added, and to further improve the effect of reducing the content of the fluorine-containing compound having a hydrophilic group by contacting the aqueous dispersion with the ion exchange resin.

[0226] (Ion Exchange Treatment) In the production method of the present disclosure, a nonionic surfactant is added to an aqueous dispersion, and then the aqueous dispersion containing the nonionic surfactant is brought into contact with an ion exchange resin. By bringing the heat-treated aqueous dispersion containing the nonionic surfactant into contact with the ion exchange resin, the content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion can be surprisingly reduced.

[0227] As the ion exchange resin, an anion exchange resin can be suitably used. ＋ R １ R ２ R ３ X － (In the formula, R １ , R ２ and R ３ are the same or different and are a hydrogen atom or an organic group, and R １ , R ２ and R ３ At least one of the groups is an organic group having 3 or more carbon atoms. X represents a counter ion. ４ R ５ (In the formula, R ４ and R ５ are the same or different and are a hydrogen atom or an organic group, and R ４ and R ５ At least one of the groups is an organic group having two or more carbon atoms.

[0228] In general formula (A1), R １ , R ２ and R ３ are the same or different and each represents a hydrogen atom or an organic group. １ , R ２ and R ３ may all be organic groups, or one may be a hydrogen atom and two may be organic groups. Furthermore, two may be hydrogen atoms and one may be an organic group. The organic group has one or more carbon atoms. The organic group preferably has two or more carbon atoms. １ , R ２ and R ３ is a preferred embodiment in which the group is an organic group having two or more carbon atoms.

[0229] In general formula (A1), R １ , R ２ and R ３ At least one of R is an organic group having 3 or more carbon atoms. １ , R ２ and R ３Among R, one may be an organic group having 3 or more carbon atoms, and two may be a hydrogen atom or an organic group having 1 or 2 carbon atoms. Alternatively, two may be organic groups having 3 or more carbon atoms, and one may be a hydrogen atom or an organic group having 1 or 2 carbon atoms. １ , R ２ and R ３ All of the groups may be organic groups having 3 or more carbon atoms.

[0230] R １ , R ２ and R ３ In the formula (I), the number of carbon atoms in the organic group is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. The number of carbon atoms in the organic group may be 5 or less.

[0231] In general formula (A1), R １ , R ２ and R ３ At least one of the groups is preferably an organic group having a carbon number of 4 or more. By adopting such a structure, the specific fluorine-containing compound can be removed more efficiently.

[0232] R １ , R ２ and R ３ The organic group in is preferably an alkyl group, an alkanol group, or an alkenyl group, more preferably an alkyl group or an alkanol group, and even more preferably an alkyl group.

[0233] In the present disclosure, the term "alkyl group" is a general term for a group remaining after removing one hydrogen atom from an aliphatic saturated hydrocarbon, and includes a linear or branched alkyl group having one or more carbon atoms, or a cyclic alkyl group having three or more carbon atoms.

[0234] In addition, in the present disclosure, the term "alkanol group" is a general term for the group remaining after removing one hydrogen atom from an alkanol, and includes linear or branched alkanol groups having one or more carbon atoms and cyclic alkanol groups having three or more carbon atoms.

[0235] R １ , R ２ and R ３ are the same or different and are alkyl groups having 2 or more carbon atoms or alkanol groups having 1 or more carbon atoms, R１ , R ２ and R ３ At least one of these is preferably an alkyl group having 3 or more carbon atoms.

[0236] R １ , R ２ and R ３ are the same or different and are alkyl groups having 2 or more carbon atoms or alkanol groups having 2 or more carbon atoms, R １ , R ２ and R ３ In one of the more preferred embodiments, at least one of the groups is an alkyl group having 3 or more carbon atoms.

[0237] R １ , R ２ and R ３ are the same or different and are an alkyl group having 2 or more carbon atoms or an alkanol group having 1 or more carbon atoms; R １ , R ２ and R ３ In one preferred embodiment, at least one of the groups is an alkyl group having 4 or more carbon atoms.

[0238] Also, R １ , R ２ and R ３ are the same or different and are alkyl groups having 2 or more carbon atoms or alkanol groups having 2 or more carbon atoms, R １ , R ２ and R ３ In one preferred embodiment, at least one of the groups is an alkyl group having 4 or more carbon atoms.

[0239] The number of carbon atoms in the alkyl group is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. The number of carbon atoms in the alkyl group may be 5 or less.

[0240] The alkanol group preferably has 10 or less carbon atoms, more preferably 8 or less carbon atoms, and even more preferably 6 or less carbon atoms. The alkanol group may have 5 or less carbon atoms.

[0241] In the general formula (A1), X is a counter ion. Examples of X include Cl, OH, Br, I, and NO. ３ , S.O. ４ and the like, and Cl or OH is preferable.４ In the case of a divalent anion such as the above, one counter ion is coordinated to two molecules of the repeating units of general formula (A1).

[0242] In general formula (A2), R ４ and R ５ are the same or different and are a hydrogen atom or an organic group, and R ４ and R ５ At least one of R is an organic group having two or more carbon atoms. ４ and R ５ may all be organic groups, or one may be a hydrogen atom and the other an organic group.

[0243] In general formula (A2), R ４ and R ５ At least one of the groups is an organic group having two or more carbon atoms.

[0244] R ４ and R ５ Among R, one may be an organic group having 2 or more carbon atoms, and the other may be a hydrogen atom or an organic group having 1 carbon atom. ４ and R ５ may both be organic groups having two or more carbon atoms.

[0245] R ４ and R ５ At least one of the groups may be an organic group having 3 or more carbon atoms, or may be an organic group having 4 or more carbon atoms.

[0246] Also, R ４ and R ５ It is also preferred that is an organic group having two or more carbon atoms.

[0247] R ４ and R ５ In the formula (I), the number of carbon atoms in the organic group is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. The number of carbon atoms in the organic group may be 5 or less.

[0248] The above R ４ and R ５ The organic group in is preferably an alkyl group, an alkanol group, or an alkenyl group, more preferably an alkyl group or an alkanol group, and even more preferably an alkyl group.

[0249] R ４ and R ５ are the same or different and are alkyl groups or alkanol groups, and ４ and R ５ In one of the more preferred embodiments, at least one of the groups is an alkyl group having two or more carbon atoms or an alkanol group having two or more carbon atoms.

[0250] The number of carbon atoms in the alkyl group is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. The number of carbon atoms in the alkyl group may be 5 or less.

[0251] The number of carbon atoms in the alkanol group is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. The number of carbon atoms in the alkanol group may be 5 or less.

[0252] The anion exchange resin is preferably one in which a group represented by general formula (A1) or a group represented by general formula (A2) is bonded to a resin matrix. Examples of the anion exchange resin include a resin matrix made of a styrene-based or acrylic polymer to which a group represented by general formula (A1) or a group represented by general formula (A2) is bonded. The styrene-based or acrylic polymer used as the resin matrix is ​​not limited, and for example, a resin matrix used in a known anion exchange resin can be used. From the viewpoint of the removal efficiency of fluorine-containing compounds having a hydrophilic group, the anion exchange resin is preferably one in which the resin matrix is ​​styrene-based.

[0253] The basicity of the anion exchange resin can be varied depending on the type of polymer backbone and / or ion exchange group.

[0254] The anion exchange resin preferably has a pore diameter of 1 to 5,000 Å. From the viewpoint of removal efficiency, the pore diameter is preferably 50 Å or more, more preferably 100 Å or more, and even more preferably 150 Å or more. It may also be 200 Å or more, or 250 Å or more. It may also be 1,000 Å or less. The pore diameter can be calculated, for example, by measuring the specific surface area and total pore volume by gas adsorption method.

[0255] From the viewpoint of removal efficiency, the anion exchange resin preferably has a total exchange capacity of 0.1 eq / L-resin or more, more preferably 0.3 eq / L-resin or more, even more preferably 0.5 eq / L-resin or more, and particularly preferably 0.7 eq / L-resin or more. The upper limit is preferably 5.0 eq / L-resin or less, more preferably 2.0 eq / L-resin or less, and particularly preferably 1.5 eq / L-resin or less.

[0256] The water content of the anion exchange resin is preferably 20% by mass or more, more preferably 30 to 70% by mass, and even more preferably 35 to 65% by mass. When the water content of the anion exchange resin is 30% by mass or more, the fluorine-containing compound can be efficiently removed. Furthermore, the fluorine-containing compound easily diffuses within the anion exchange resin particles. When the water content of the anion exchange resin is 70% by mass or less, a decrease in the strength of the anion exchange resin particles due to insufficient cross-linking can be suppressed.

[0257] The moisture content of an anion exchange resin can be measured by the following method. First, 10 mL of a sample in the standard form is accurately weighed out using a measuring cylinder, the resin is wrapped in a cloth and centrifuged to remove any adhering moisture, and the mass of the resin is then quickly measured. Next, the resin is dried in a thermostatic oven at 105°C for 4 hours, and then allowed to cool in a desiccator for 30 minutes. The mass of the dried resin is then weighed and the moisture content is calculated using the following formula: Moisture content (mass%) = (mass of resin before drying (g) - mass of resin after drying (g)) / mass of resin before drying (g) x 100

[0258] Anion exchange resins are usually spherical. The average particle size of the anion exchange resin is preferably 0.1 to 5 mm, more preferably 0.2 to 2 mm, and particularly preferably 0.3 to 1.5 mm. If the average particle size of the anion exchange resin falls within the above range, the packed column of the anion exchange resin is less likely to clog. The average particle size is a value determined by a sieving method. Specifically, the anion exchange resin is first placed in a sieve shaker, and the particle size distribution is measured by sieving. Then, the diameter of the sieve opening corresponding to a total of 50% of the residual classification is determined, and this is taken as the average particle size.

[0259] As the anion exchange resin, a commercially available product may be used, for example, PFA694E, A592E manufactured by Purolite Co., Ltd.

[0260] Furthermore, a resin having an ion exchange group (excluding the group represented by the general formula (A1) and the group represented by the general formula (A2)) can also be used as the anion exchange resin. Such anion exchange resins include resins having at least one ion exchange group selected from the group consisting of an amino group and a quaternary ammonium group (excluding the group represented by the general formula (A1) and the group represented by the general formula (A2)). Such anion exchange resins include resins having an ion exchange group represented by the following general formula (B1): -N ＋ (CH ３ ) ３ X － (wherein X represents a counter ion), or a group represented by the following general formula (B2): ＋ (CH ３ ) ２ (C ２ H ４ OH)X － (wherein X represents a counter ion) is preferred. X in general formulas (B1) and (B2) is preferably Cl, OH, Br, I, NO ３ , S.O. ４ and the like, and Cl or OH is preferable. ４ In the case of a divalent anion such as the above, one counter ion is coordinated to two molecules of the repeating units of general formula (A1).

[0261] The anion exchange resin is preferably one in which an ion exchange group (excluding the group represented by the general formula (A1) and the group represented by the general formula (A2)) is bonded to a resin matrix, and examples of the resin matrix include styrene-based or acrylic polymers. The styrene-based or acrylic polymer used as the resin matrix is ​​not limited, and for example, a resin matrix used in a known anion exchange resin can be used. From the viewpoint of the removal efficiency of fluorine-containing compounds having a hydrophilic group, it is preferable that the resin matrix of the anion exchange resin B is styrene-based.

[0262] The resin having an ion exchange group (excluding the group represented by the general formula (A1) and the group represented by the general formula (A2)) may be weakly basic or strongly basic. A strongly basic anion exchange resin is preferred. The basicity of the anion exchange resin can be varied depending on the type of polymer skeleton and / or ion exchange group.

[0263] The resin having an ion exchange group (excluding the group represented by the general formula (A1) and the group represented by the general formula (A2)) preferably has a pore diameter of 1 to 5,000 Å. From the viewpoint of removal efficiency, the pore diameter is preferably 50 Å or more, more preferably 100 Å or more, and even more preferably 150 Å or more. It may also be 200 Å or more, or 250 Å or more. It may also be 1,000 Å or less. The pore diameter can be calculated, for example, by measuring the specific surface area and the total pore volume by a gas adsorption method.

[0264] From the viewpoint of removal efficiency, the resin having ion exchange groups (excluding the groups represented by the general formula (A1) and the groups represented by the general formula (A2)) preferably has a total exchange capacity of 0.1 eq / L-resin or more. More preferably, it is 0.3 eq / L-resin or more, even more preferably 0.5 eq / L-resin or more, and particularly preferably 0.7 eq / L-resin or more. Furthermore, the larger the total exchange capacity, the better, but for example, the upper limit is preferably 5.0 eq / L-resin, more preferably 2.0 eq / L-resin or less, and particularly preferably 1.5 eq / L-resin or less.

[0265] The water content of the resin having an ion exchange group (excluding the group represented by the general formula (A1) and the group represented by the general formula (A2)) is preferably 20% by mass or more, more preferably 30 to 70% by mass, and even more preferably 35 to 65% by mass.

[0266] Resins having ion exchange groups (excluding the groups represented by the general formula (A1) and the groups represented by the general formula (A2)) are usually spherical. The average particle size of resins having ion exchange groups (excluding the groups represented by the general formula (A1) and the groups represented by the general formula (A2)) is preferably 0.1 to 5 mm, more preferably 0.2 to 2 mm, and particularly preferably 0.3 to 1.5 mm. If the average particle size is within the above range, the packed column of the anion exchange resin is less likely to clog. The average particle size is a value determined by a sieving method. Specifically, first, the anion exchange resin is placed in a sieve shaker and the particle size distribution is measured by sieving. Then, the diameter of the sieve opening corresponding to 50% of the total residual classification is determined and this is taken as the average particle size.

[0267] As the resin having an ion exchange group (excluding the group represented by the general formula (A1) and the group represented by the general formula (A2)), a commercially available product may be used, and examples thereof include the Diaion (trademark) SA series manufactured by Mitsubishi Chemical Corporation, A400, A300, etc. manufactured by Purolite Co., Ltd., the Amberlite (trademark) series manufactured by DuPont, and the Amberjet (trademark) series such as IRA4002OH.

[0268] The ion exchange resin is preferably at least one selected from the group consisting of a resin in which a group represented by general formula (B1) is bonded to a styrene-based polymer and a resin in which a group represented by general formula (B2) is bonded to a styrene-based polymer. Of these, OH is preferred as X in general formulas (B1) and (B2).

[0269] The pH of the aqueous dispersion obtained by adding the nonionic surfactant is usually less than 7, and the temperature is less than 35° C. In the production method of the present disclosure, after adding the nonionic surfactant to the aqueous dispersion, and before carrying out the ion exchange treatment, it is preferable to adjust the pH of the aqueous dispersion containing the nonionic surfactant to 7 or more, and to adjust the temperature of the aqueous dispersion containing the nonionic surfactant to 35° C. or more. By adjusting the pH and temperature of the aqueous dispersion before carrying out the ion exchange treatment, the content of the fluorine-containing compound having a hydrophilic group in the finally obtained aqueous dispersion can be surprisingly reduced.

[0270] The pH of the aqueous dispersion to be subjected to the ion exchange treatment is preferably 7 or more, more preferably 8 or more, even more preferably 9 or more, and preferably 14 or less, more preferably 13 or less, even more preferably 12 or less.

[0271] The pH can be adjusted by adding an alkali such as ammonia to the aqueous dispersion.

[0272] The temperature of the aqueous dispersion to be subjected to the ion exchange treatment is preferably 35° C. or higher, more preferably 37° C. or higher, and even more preferably 39° C. or higher, and is preferably lower than the cloud point of the nonionic surfactant, and more preferably lower than a temperature 10° C. lower than the cloud point of the nonionic surfactant. The temperature of the aqueous dispersion to be subjected to the ion exchange treatment may be, for example, 50° C. or lower, or 45° C. or lower.

[0273] In the production method of the present disclosure, it is preferable to maintain the temperature of the aqueous dispersion at 35° C. or higher during the ion exchange treatment. The temperature of the aqueous dispersion during the ion exchange treatment is preferably 37° C. or higher, more preferably 39° C. or higher, and is preferably lower than the cloud point of the nonionic surfactant, more preferably lower than a temperature 10° C. lower than the cloud point of the nonionic surfactant. The temperature of the aqueous dispersion during the ion exchange treatment may be, for example, 50° C. or lower, or 45° C. or lower.

[0274] In the production method of the present disclosure, the pH of the aqueous dispersion may change during the ion exchange treatment. When the ion exchange treatment is repeated, it is preferable to check the pH of the aqueous dispersion each time the ion exchange treatment is started, and if the pH is below 7, to adjust the pH to 7 or higher. The pH of the aqueous dispersion before each ion exchange treatment is preferably 8 or higher, more preferably 9 or higher, and preferably 14 or lower, more preferably 13 or lower, and even more preferably 12 or lower.

[0275] The pressure when the aqueous dispersion is brought into contact with the ion exchange resin is not particularly limited, but may be, for example, 0.1 to 10 atmospheres, and the contact can be carried out at normal pressure (about 1 atmosphere).

[0276] The time for contacting the aqueous dispersion with the ion exchange resin is not particularly limited, and may be from 0.1 seconds to 100 hours, from 1 second to 50 hours, or from 1 second to 10 hours.

[0277] The amount of ion exchange resin to be contacted with the aqueous dispersion is preferably 10,000 g or less, preferably 0.1 g or more, more preferably 1 g or more, even more preferably 5 g or more, still more preferably 10 g or more, and particularly preferably 100 g or more, relative to 1,000 g of the fluoropolymer in the aqueous dispersion.

[0278] After the aqueous dispersion is brought into contact with the ion exchange resin, the aqueous dispersion and the ion exchange resin are separated, and the aqueous dispersion can be recovered.

[0279] The aqueous dispersion may be contacted with the ion exchange resin in a batch or flow manner.

[0280] The number of times that the aqueous dispersion is contacted with the ion exchange resin may be one time or two or more times. By repeating the contact of the aqueous dispersion with the ion exchange resin two or more times, the content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion can be further reduced. The number of times that the aqueous dispersion is contacted with the ion exchange resin may be 10 or less.

[0281] The aqueous dispersion can be contacted with the ion exchange resin by a conventional method. For example, the method can be carried out by adding the ion exchange resin to the aqueous dispersion and stirring, or by a column method in which the aqueous dispersion is passed through a column packed with an ion exchange resin. The packed column used in the column method can be any of a moving type, a fixed bed type, or a fluidized bed type.

[0282] When the method of adding an ion exchange resin to an aqueous dispersion and stirring is used, the aqueous dispersion is contacted with the ion exchange resin, and then the ion exchange resin and the aqueous dispersion are separated. The method for separating the ion exchange resin and the aqueous dispersion is not limited, and for example, a method such as filtration can be used.

[0283] (Addition of nonionic surfactant to aqueous dispersion subjected to ion exchange treatment) In one embodiment of the production method of the present disclosure, a nonionic surfactant is added to the aqueous dispersion obtained after contact with the ion exchange resin. By adding the nonionic surfactant, the dispersibility of the fluoropolymer in the aqueous dispersion subjected to ion exchange treatment can be improved, and the concentration of the aqueous dispersion can be smoothly promoted. As a result, the content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion can be surprisingly reduced, and an aqueous dispersion with excellent dispersion stability can be produced.

[0284] Examples of the nonionic surfactant to be added to the aqueous dispersion obtained after contact with the ion exchange resin include the nonionic surfactant to be added to the heat-treated aqueous dispersion. Those that can be suitably used as the nonionic surfactant to be added to the heat-treated aqueous dispersion can also be suitably used as the nonionic surfactant to be added to the aqueous dispersion obtained after contact with the ion exchange resin.

[0285] By adding a nonionic surfactant to the ion-exchanged aqueous dispersion, it is preferable to prepare an aqueous dispersion in which the content of the nonionic surfactant in the aqueous dispersion is 1 to 40 mass % relative to the fluoropolymer. The content of the nonionic surfactant in the ion-exchanged aqueous dispersion is more preferably 5 mass % or more and more preferably 30 mass % or less.

[0286] (Concentration Treatment) In the production method of the present disclosure, the aqueous dispersion obtained after contact with the ion exchange resin is concentrated.

[0287] Concentration methods include phase separation concentration, electrophoresis, ion exchanger method, membrane concentration, etc. Phase separation concentration, ion exchanger method, and membrane concentration can be carried out under conventionally known treatment conditions, and are not particularly limited, but can be carried out by the methods described in WO 2004 / 050719, JP-A 2002-532583, and JP-A 55-120630.

[0288] The concentration method is preferably a method in which the aqueous dispersion is separated into two or more phases and the concentrated phase is recovered, preferably concentration by phase separation or electrophoresis, and more preferably concentration by phase separation. Phase separation concentration can be carried out, for example, by heating the aqueous dispersion to cause phase separation into a fluoropolymer-free phase (supernatant phase) and a fluoropolymer-containing phase (concentrated phase), removing the fluoropolymer-free phase, and recovering the fluoropolymer-containing phase (concentrated phase).

[0289] The recovered fluoropolymer-containing phase (concentrated phase) contains the fluoropolymer, the nonionic surfactant, and the aqueous medium, as well as the fluorine-containing compound having a hydrophilic group in a content reduced compared to before concentration.

[0290] The temperature for the phase separation concentration can be selected based on the cloud point of the nonionic surfactant contained in the aqueous dispersion, and is preferably at least 10°C lower than the cloud point of the nonionic surfactant, and is preferably at most 10°C higher than the cloud point of the nonionic surfactant.

[0291] In the production method of the present disclosure, it is also preferable to repeatedly carry out concentration by phase separation. By repeatedly carrying out concentration by phase separation, the content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion can be easily reduced to a desired content.

[0292] The number of repetitions is not particularly limited, but is preferably 2 or more, more preferably 3 or more. The upper limit of the number of repetitions is not limited, but may be, for example, 10 or less. By repeatedly performing the phase separation concentration, the content of the fluorine-containing compound having a hydrophilic group can be further reduced.

[0293] When the phase separation concentration is performed two or more times, the first phase separation concentration is preferably performed by heating at a temperature at least 10°C lower than the cloud point of the nonionic surfactant and then allowing to stand, resulting in separation into an upper supernatant phase and a concentrated phase. The second or subsequent phase separation concentration is preferably performed by heating at a temperature at least 10°C lower than the cloud point of the nonionic surfactant and then allowing to stand, resulting in separation into an upper supernatant phase and a concentrated phase.

[0294] When the phase separation concentration is repeated multiple times, except for the final phase separation concentration, the phase separation concentration can be stopped when the solids concentration of the fluoropolymer in the aqueous dispersion reaches 48 to 52 mass%, an aqueous medium can be added to the concentrated aqueous dispersion, and then the phase separation concentration can be repeated. By stopping the phase separation concentration when the solids concentration of the fluoropolymer reaches the above range, each phase separation concentration can be completed in a short time without decreasing the removal efficiency of the fluorine-containing compound having a hydrophilic group in each phase separation concentration, and as a result, the total time required for the phase separation concentration can be shortened.

[0295] The pH of the aqueous dispersion to be concentrated is preferably 4.0 to 12.0, more preferably 7.0 or higher, even more preferably 8.0 or higher, and particularly preferably 9.0 or higher. By adjusting the pH of the aqueous dispersion within the above range, it is possible to increase both the rate at which the concentration of the fluoropolymer in the aqueous dispersion is increased and the rate at which the fluorine-containing compound having a hydrophilic group in the aqueous dispersion is removed, and the concentration of the fluoropolymer in the finally obtained aqueous dispersion becomes high.

[0296] The fluoropolymer content in the aqueous fluoropolymer dispersion obtained by concentration is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, and preferably 70% by mass or less, more preferably 68% by mass or less, and even more preferably 67% by mass or less, relative to the aqueous dispersion. The higher the fluoropolymer content in the aqueous fluoropolymer dispersion, the easier it is to maintain a high fluoropolymer content, even when various additives are added to the aqueous fluoropolymer dispersion.

[0297] The fluoropolymer content in the aqueous dispersion can be determined by measuring the solids concentration of the aqueous dispersion and the content of the nonionic surfactant in the aqueous dispersion, and subtracting the content of the nonionic surfactant from the solids concentration of the aqueous dispersion. The solids concentration of the aqueous dispersion is a value calculated from the heating residue (Zg) obtained by heating about 1 g (Xg) of a sample at 110°C for 30 minutes and then at 300°C for 30 minutes according to the formula: P = Z / X x 100 (mass%).

[0298] (Treatment of concentrated aqueous dispersion) In the manufacturing method of the present disclosure, nonionic surfactant can be added to concentrated aqueous dispersion.In particular, when aqueous dispersion is concentrated by phase separation concentration, the content of nonionic surfactant in the obtained aqueous dispersion may be reduced, but by adding nonionic surfactant to concentrated aqueous dispersion, the dispersibility of fluoropolymer in concentrated aqueous dispersion can be improved.

[0299] As the nonionic surfactant to be added to the concentrated aqueous dispersion, it is preferable to add two types of nonionic surfactants with different hydrophilicity. HLB can be used as an index representing the difference in hydrophilicity, and for example, it is preferable to include a nonionic surfactant with an HLB of 13.00 or more but less than 13.50 and a nonionic surfactant with an HLB of 13.50 or more but 15.00 or less (preferably 14.50 or less, more preferably 14.00 or less). Adding nonionic surfactants with different HLBs can also suppress foaming without adding an antifoaming agent.

[0300] By adding a nonionic surfactant to the concentrated aqueous dispersion, it is preferable to prepare an aqueous dispersion in which the content of the nonionic surfactant in the aqueous dispersion is 4.0 to 12.0 mass% relative to the fluoropolymer. The content of the nonionic surfactant in the aqueous dispersion is more preferably 4.5 mass% or more, even more preferably 5.0 mass% or more, more preferably 10 mass% or less, even more preferably 8.0 mass% or less, and still more preferably 7.0 mass% or less.

[0301] In the manufacturing method of the present disclosure, a viscosity modifier can be added to the concentrated aqueous dispersion.

[0302] As the viscosity modifier, a non-fluorine-containing anionic surfactant can be suitably used. The non-fluorine-containing anionic surfactant typically has a hydrophilic portion such as a carboxylate, sulfonate, or sulfate, and a hydrophobic portion which is a long-chain hydrocarbon portion such as an alkyl.

[0303] Examples of the fluorine-free anionic surfactant include alkyl sulfates such as lauryl sulfate, alkylaryl sulfonic acids such as dodecylbenzenesulfonic acid, alkyl sulfosuccinates, and salts thereof. The fluorine-free anionic surfactant may be composed of one or more of these compounds in combination.

[0304] The sulfosuccinic acid alkyl ester and its salts may be monoesters, but are preferably diesters.

[0305] Examples of sulfosuccinic acid alkyl esters and salts thereof include sulfosuccinic acid alkyl esters represented by the general formula: R ２１ -OCOCH(SO ３ A ２１ ) CH ２ COO-R ２２ (In the formula, R ２１ and R ２２ are the same or different and represent an alkyl group having 4 to 12 carbon atoms; A ２１ is an alkali metal, alkaline earth metal or NH ４ and alkyl sulfosuccinates represented by the following formula (I):

[0306] R ２１ and R ２２Examples of the alkyl group include linear or branched alkyl groups such as n-butyl, iso-butyl, sec-butyl, n-pentyl, iso-pentyl, neopentyl, tert-pentyl, n-hexyl, iso-hexyl, tert-hexyl, n-heptyl, iso-heptyl, tert-heptyl, n-octyl, iso-octyl, tert-octyl, n-nonyl, iso-nonyl, tert-nonyl, n-decyl, and 2-ethylhexyl.

[0307] A ２１ Examples include Na, NH ４ Examples of the alkyl sulfosuccinate include di-n-octyl sulfosuccinate and di-2-ethylhexyl sulfosuccinate.

[0308] The fluorine-free anionic surfactant may have an acid group. The acid group is preferably selected from the group consisting of a carboxyl group, a sulfate group, a sulfonic acid group, a phosphate group, and salts thereof, and more preferably selected from the group consisting of a carboxyl group, a sulfate group, a sulfonic acid group, and salts thereof.

[0309] The fluorine-free anionic surfactant may further have, in addition to the acid group, other groups such as a polyoxyalkylene group having an oxyalkylene group having 2 to 4 carbon atoms, an amino group, etc. The amino group is not protonated.

[0310] As the fluorine-free anionic surfactant, an anionic hydrocarbon surfactant having a hydrocarbon as the main chain is preferred. Examples of hydrocarbons include those having a saturated or unsaturated aliphatic chain having 6 to 40 carbon atoms, preferably 8 to 20 carbon atoms. The saturated or unsaturated aliphatic chain may be either a straight chain or a branched chain, or may have a cyclic structure. The hydrocarbon may be aromatic or may have an aromatic group. The hydrocarbon may have a heteroatom such as oxygen, nitrogen, or sulfur.

[0311] Examples of fluorine-free anionic surfactants include alkyl sulfonic acids such as lauryl sulfonic acid and salts thereof; alkylaryl sulfates and salts thereof; aliphatic (carboxylic) acids such as lauric acid and salts thereof; alkyl phosphates, alkylaryl phosphates, and salts thereof; and the like. Among these, preferred are those selected from the group consisting of sulfonic acids, carboxylic acids, and salts thereof, and more preferred are aliphatic carboxylic acids or salts thereof. Examples of the aliphatic carboxylic acids or salts thereof include saturated or unsaturated aliphatic carboxylic acids having 9 to 13 carbon atoms, in which the terminal H may be replaced with —OH, or salts thereof. Preferred examples of the aliphatic carboxylic acids or salts thereof include monocarboxylic acids, and preferred examples of the monocarboxylic acids include decanoic acid, undecanoic acid, undecenoic acid, lauric acid, and hydroxydodecanoic acid.

[0312] The fluorine-free anionic surfactant is preferably at least one selected from the group consisting of alkyl sulfosuccinates and salts thereof, alkyl sulfates and salts thereof, and monocarboxylic acids and salts thereof, more preferably at least one selected from the group consisting of dioctyl sulfosuccinate, lauryl sulfate, decanoic acid and salts thereof, and even more preferably at least one selected from the group consisting of dioctyl sulfosuccinate, ammonium dioctyl sulfosuccinate, ammonium lauryl sulfate, and ammonium decanoate.

[0313] By adding a viscosity modifier to the concentrated aqueous dispersion, it is preferable to prepare an aqueous dispersion in which the content of the viscosity modifier in the aqueous dispersion is 10 to 5000 ppm by mass relative to the fluoropolymer. The content of the viscosity modifier in the aqueous dispersion is more preferably 50 ppm by mass or more, even more preferably 100 ppm by mass or more, more preferably 4000 ppm by mass or less, and even more preferably 3000 ppm by mass or less.

[0314] In the production method of the present disclosure, a pH adjuster such as aqueous ammonia may be added to the concentrated aqueous dispersion in order to adjust the pH of the aqueous dispersion. The pH of the aqueous dispersion is preferably 8 to 13, more preferably 9 to 12, and even more preferably 9 to 11.

[0315] The pH can be measured at 25° C. in accordance with JIS K6893.

[0316] In the production method of the present disclosure, a preservative can be added to the concentrated aqueous dispersion. By adding a preservative to the aqueous dispersion, spoilage and bacterial growth of the aqueous dispersion can be suppressed while suppressing precipitation of the fluoropolymer, even when the aqueous dispersion is stored for a long period of time.

[0317] Examples of preservatives include isothiazolones, azoles, pronopol, chlorothalonil, methylsulfonyltetrachloropyrrolidin, carbentazim, fluorophorbet, sodium diacetate, and diiodomethyl-paratolylsulfone.

[0318] By adding a preservative to the concentrated aqueous dispersion, it is preferable to prepare an aqueous dispersion in which the content of the preservative in the aqueous dispersion is 0.01 to 0.5% by mass relative to the fluoropolymer. The content of the preservative in the aqueous dispersion is more preferably 0.05% by mass or more and more preferably 0.2% by mass or less.

[0319] In the manufacturing method of the present disclosure, a water-soluble polymer may be added to the concentrated aqueous dispersion. Examples of the water-soluble polymer compound include methyl cellulose, alumina sol, polyvinyl alcohol, carboxylated vinyl polymer, polyethylene oxide (dispersion stabilizer), polyethylene glycol (dispersion stabilizer), polyvinylpyrrolidone (dispersion stabilizer), phenol resin, urea resin, epoxy resin, melamine resin, polyester resin, polyether resin, acrylic silicone resin, silicone resin, silicone polyester resin, and polyurethane resin.

[0320] 2. Aqueous Fluoropolymer Dispersion According to the production method of the present disclosure, an aqueous fluoropolymer dispersion can be obtained in which the content of a fluorine-containing compound having a hydrophilic group having 7 or fewer carbon atoms is reduced. According to the present disclosure, there is provided an aqueous fluoropolymer dispersion containing a fluoropolymer, a nonionic surfactant, and a fluorine-containing compound having a hydrophilic group having 7 or fewer carbon atoms, wherein the fluoropolymer content is 50 to 70 mass% relative to the aqueous fluoropolymer dispersion, the nonionic surfactant content is 4.0 to 12 mass% relative to the fluoropolymer, and the content of the fluorine-containing compound having a hydrophilic group having 7 or fewer carbon atoms is more than 0 ppb by mass and less than 300 ppb by mass relative to the aqueous fluoropolymer dispersion.

[0321] The aqueous fluoropolymer dispersion of the present disclosure contains a fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms. The content of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms in the aqueous dispersion is more than 0 ppb by mass and less than 300 ppb by mass, relative to the aqueous dispersion. A preferred upper limit of the content of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms in the aqueous dispersion is 280 ppb by mass or less, 260 ppb by mass or less, 240 ppb by mass or less, 220 ppb by mass or less, 200 ppb by mass or less, 180 ppb by mass or less, 160 ppb by mass or less, or 140 ppb by mass or less. The preferred lower limit of the content of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms in the aqueous dispersion is 0.1 ppb by mass or more, 1 ppb by mass or more, 5 ppb by mass or more, 10 ppb by mass or more, 20 ppb by mass or more, 30 ppb by mass or more, 40 ppb by mass or more, or 50 ppb by mass or more.

[0322] Examples of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms include those described above as the fluorine-containing surfactants having 7 or less carbon atoms used in the polymerization of fluoromonomers. That is, in one embodiment of the aqueous dispersion, the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms contains at least a fluorine-containing surfactant having 7 or less carbon atoms.

[0323] Furthermore, according to the production method of the present disclosure, it is possible to reduce not only the content of fluorine-containing compounds having a hydrophilic group having 7 or less carbon atoms but also the content of fluorine-containing compounds having a hydrophilic group in the aqueous fluoropolymer dispersion.

[0324] In one embodiment of the fluoropolymer aqueous dispersion, it contains a fluorine-containing compound having a hydrophilic group. The content of the fluorine-containing compound having a hydrophilic group in the aqueous dispersion is more than 0 mass ppb and less than 300 mass ppb relative to the aqueous dispersion. The preferred upper limit of the content of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms in the aqueous dispersion is 280 mass ppb or less, 260 mass ppb or less, 240 mass ppb or less, 220 mass ppb or less, 200 mass ppb or less, 180 mass ppb or less, 160 mass ppb or less, or 140 mass ppb or less. The preferred lower limit of the content of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms in the aqueous dispersion is 0.1 mass ppb or more, 1 mass ppb or more, 5 mass ppb or more, 10 mass ppb or more, 20 mass ppb or more, 30 mass ppb or more, 40 mass ppb or more, or 50 mass ppb or more.

[0325] As the fluorine-containing compound having a hydrophilic group, the fluorine-containing surfactants mentioned above for use in the polymerization of fluoromonomers can be mentioned.That is, in one embodiment of the aqueous dispersion, the fluorine-containing compound having a hydrophilic group contains at least a fluorine-containing surfactant.As the fluorine-containing surfactant, a typical compound is a fluorine-containing surfactant having a molecular weight of 1000 g / mol or less, preferably 800 g / mol or less.

[0326] In one embodiment of the fluoropolymer aqueous dispersion, the dispersion is substantially free of a compound represented by the following general formula (1) as a fluorine-containing compound having a hydrophilic group: － ] ｉ M ｉ＋ (Wherein, X represents H, Cl, Br, F or I; Rf 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; A － is an acid group, M ｉ＋represents a cation having a valence i, where i is an integer from 1 to 3.

[0327] In one embodiment of the fluoropolymer aqueous dispersion, the dispersion is substantially free of a compound represented by the following general formula (2) as a fluorine-containing compound having a hydrophilic group. ｎ－１ F ２ｎ－１ COO － ]M ＋ (wherein n is an integer of 9 to 14, M ＋ represents a cation.)

[0328] The compound represented by general formula (2) (perfluoroalkanoic acid) is known to be formed during polymerization when perfluoroalkyl vinyl ether or the like is used as a modified monomer (see WO 2019 / 161153).

[0329] In one embodiment of the fluoropolymer aqueous dispersion, the dispersion is substantially free of a compound represented by the following general formula (3) as a fluorine-containing compound having a hydrophilic group. １ -O-L-CO ２ － ]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 linear or branched non-fluorinated, partially fluorinated or fully fluorinated alkylene group; ＋ represents a cation.)

[0330] In one embodiment of the fluoropolymer aqueous dispersion, the dispersion is substantially free of a compound represented by general formula (4) as a fluorine-containing compound having a hydrophilic group. ２ ) ｍ CO ２ － ]M ＋ (wherein m is an integer of 3 to 19, M ＋ represents a cation.)

[0331] In the present disclosure, "substantially free of any of the compounds represented by general formulas (1) to (4)" means that the content of any of the compounds represented by general formulas (1) to (4) in the aqueous fluoropolymer dispersion is 50 mass ppb or less. The content of any of the compounds represented by general formulas (1) to (4) in the aqueous fluoropolymer dispersion is preferably 35 mass ppb or less, more preferably 25 mass ppb or less, even more preferably 10 mass ppb or less, still more preferably 1 mass ppb or less, and particularly preferably below the detection limit for fluorinated surfactants as measured by liquid chromatography-mass spectrometry (LC / MS).

[0332] The content of the fluorine-containing compound having a hydrophilic group in the aqueous fluoropolymer dispersion can be quantified by known methods. For example, it can be quantified by LC / MS analysis. First, methanol is added to the aqueous fluoropolymer dispersion, extraction is performed, and the resulting extract is analyzed by LC / MS. To further improve the extraction efficiency, treatments such as Soxhlet extraction and ultrasonic treatment may be performed. The resulting extract is appropriately concentrated with a nitrogen purge, and the fluorine-containing compound having a hydrophilic group in the concentrated extract is measured by LC / MS. Molecular weight information is extracted from the obtained LC / MS spectrum, and a match with the structural formula of the candidate fluorine-containing compound having a hydrophilic group is confirmed. Thereafter, aqueous solutions containing five or more levels of the confirmed fluorine-containing compound having a hydrophilic group are prepared, and LC / MS analysis of the aqueous solutions with each content is performed. The relationship between the content and the area area relative to the content is plotted, and a calibration curve is drawn. Then, using the calibration curve, the area area of ​​the LC / MS chromatogram of the fluorine-containing compound having a hydrophilic group in the extract can be converted to the content of the fluorine-containing compound having a hydrophilic group. The resulting extract can be concentrated by purging with nitrogen, which allows the lower limit of quantitation of the measurement method to be lowered.

[0333] The fluoropolymer contained in the aqueous fluoropolymer dispersion of the present disclosure will be described later.

[0334] The content of the fluoropolymer in the aqueous fluoropolymer dispersion is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 57% by mass or more, still more preferably 60% by mass or more, and preferably 70% by mass or less, more preferably 68% by mass or less, still more preferably 67% by mass or less, and still more preferably 65% ​​by mass or less, based on the aqueous dispersion.

[0335] Examples of the nonionic surfactant include those that can be used in the production method of the present disclosure. The content of the nonionic surfactant in the aqueous fluoropolymer dispersion is 4.0 to 12% by mass, more preferably 4.5% by mass or more, even more preferably 5.0% by mass or more, more preferably 10% by mass or less, even more preferably 8.0% by mass or less, and still more preferably 7.0% by mass or less, based on the fluoropolymer.

[0336] The aqueous fluoropolymer dispersion of the present disclosure also preferably contains a fluorine-free anionic surfactant. Examples of the fluorine-free anionic surfactant include those that can be used in the production method of the present disclosure. The content of the fluorine-free anionic surfactant in the aqueous fluoropolymer dispersion is preferably 10 to 5,000 ppm by mass, more preferably 50 ppm by mass or more, even more preferably 100 ppm by mass or more, more preferably 4,000 ppm by mass or less, and even more preferably 3,000 ppm by mass or less, based on the fluoropolymer.

[0337] The viscosity of the aqueous fluoropolymer dispersion of the present disclosure is preferably 2.0 mPa·s or more, more preferably 5.0 mPa·s or more, even more preferably 10.0 mPa·s or more, particularly preferably 15.0 mPa·s or more, and is preferably 100 mPa·s or less, more preferably 80 mPa·s or less, even more preferably 70 mPa·s or less, and still more preferably 60 mPa·s or less.

[0338] The viscosity of the aqueous dispersion is measured using a B-type rotational viscometer (manufactured by Toki Sangyo Co., Ltd., rotor No. 2) at a rotation speed of 60 rpm, a measurement time of 120 seconds, and at 25°C.

[0339] The aqueous fluoropolymer dispersion of the present disclosure also preferably contains a preservative. Examples of the preservative include those that can be used in the production method of the present disclosure. The content of the preservative in the aqueous fluoropolymer dispersion is preferably 0.01 to 0.5% by mass, more preferably 0.05% by mass or more, and more preferably 0.2% by mass or less, based on the fluoropolymer.

[0340] The pH of the aqueous fluoropolymer dispersion of the present disclosure is preferably 8-13, more preferably 9-12, and even more preferably 9-11.

[0341] The pH can be measured at 25° C. in accordance with JIS K6893.

[0342] The aqueous fluoropolymer dispersion of the present disclosure may contain other components. Examples of the other components include water-soluble polymer compounds. Examples of the water-soluble polymer compounds include methyl cellulose, alumina sol, polyvinyl alcohol, carboxylated vinyl polymer, polyethylene oxide (dispersion stabilizer), polyethylene glycol (dispersion stabilizer), polyvinylpyrrolidone (dispersion stabilizer), phenol resin, urea resin, epoxy resin, melamine resin, polyester resin, polyether resin, acrylic silicone resin, silicone resin, silicone polyester resin, and polyurethane resin.

[0343] The aqueous fluoropolymer dispersion of the present disclosure can be used as an aqueous coating material by blending it with known compounding agents such as pigments, thickeners, dispersants, antifoaming agents, antifreezing agents, and film-forming aids, or by further combining it with other polymer compounds.

[0344] Next, the fluoropolymer in the aqueous dispersion obtained by the production method of the present disclosure and the fluoropolymer in the aqueous dispersion of the present disclosure will be described in more detail.

[0345] (Fluoropolymer) Fluoropolymers such as fluororesins and fluororubbers can be obtained by polymerization of fluoromonomers.

[0346] Examples of the fluoropolymer include a TFE polymer in which the monomer having the largest molar fraction in the polymer (hereinafter referred to as the "most abundant monomer") is TFE, a VDF polymer in which the most abundant monomer is VDF, and a CTFE polymer in which the most abundant monomer is CTFE.

[0347] Preferably, the fluoropolymer has an ion exchange ratio (IXR) greater than 53. Preferred fluoropolymers have no ionic groups or a limited number of ionic groups resulting in an ion exchange ratio greater than about 100. Preferred fluoropolymers have an ion exchange ratio of 1000 or greater, more preferably 2000 or greater, and even more preferably 5000 or greater.

[0348] The TFE polymer may suitably be a TFE homopolymer or a copolymer comprising (1) TFE, (2) one or more fluorine-containing monomers other than TFE having 2 to 8 carbon atoms, particularly VDF, HFP, or CTFE, and (3) other monomers. Examples of the (3) other monomers include fluoro(alkyl vinyl ethers) having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms; fluorodioxole; perfluoroalkylethylene; ω-hydroperfluoroolefin, etc.

[0349] The TFE polymer may also be a copolymer of TFE and one or more fluorine-free monomers. Examples of the fluorine-free monomers include alkenes such as ethylene and propylene; vinyl esters; and vinyl ethers. The TFE polymer may also be a copolymer of TFE and one or more fluorine-containing monomers having 2 to 8 carbon atoms and one or more fluorine-free monomers.

[0350] The VDF polymer may suitably be a VDF homopolymer [PVDF] or a copolymer of (1) VDF, (2) one or more fluoroolefins other than VDF having 2 to 8 carbon atoms, particularly TFE, HFP, or CTFE, and (3) a perfluoro(alkyl vinyl ether) having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms.

[0351] The CTFE polymer may suitably be a CTFE homopolymer or a copolymer consisting of (1) CTFE, (2) one or more fluoroolefins other than CTFE having 2 to 8 carbon atoms, particularly TFE or HFP, and (3) a perfluoro(alkyl vinyl ether) having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms.

[0352] The CTFE polymer may also be a copolymer of CTFE with one or more non-fluorine-containing monomers, and the non-fluorine-containing monomers include alkenes such as ethylene and propylene; vinyl esters; and vinyl ethers.

[0353] The fluoropolymers may be glassy, ​​plastic or elastomeric. They may be amorphous or partially crystalline and may be subject to compression sintering, melt processing or non-melt processing.

[0354] In the production method of the present disclosure, it is preferable to produce a fluororesin as the fluoropolymer. The aqueous fluoropolymer dispersion of the present disclosure preferably contains a fluororesin as the fluoropolymer.

[0355] In the production method of the present disclosure, for example, (I) a tetrafluoroethylene polymer [TFE polymer (PTFE)] can be suitably produced as a non-melt-processable fluororesin, and (II) an ethylene / TFE copolymer [ETFE], a TFE / HFP copolymer [FEP], a TFE / perfluoro(alkyl vinyl ether) copolymer [PFA, MFA, etc.], a TFE / perfluoroallyl ether copolymer, a TFE / VDF copolymer, or an electrolyte polymer precursor can be suitably produced as a melt-processable fluororesin.

[0356] The fluoropolymer is preferably a fluororesin, and particularly, a fluororesin having a fluorine substitution rate of 50% or more as calculated by the following formula is more preferred, a fluororesin having a fluorine substitution rate of more than 50% is even more preferred, a fluororesin having a fluorine substitution rate of 55% or more is even more preferred, a fluororesin having a fluorine substitution rate of 60% or more is even more preferred, a fluororesin having a fluorine substitution rate of 75% or more is still more preferred, a fluororesin having a fluorine substitution rate of 80% or more is particularly preferred, and a fluororesin having a fluorine substitution rate of 90 to 100%, i.e., a perfluororesin, is most preferred. (Formula) Fluorine substitution rate (%) = (number of fluorine atoms bonded to carbon atoms constituting the fluoropolymer) / ((number of hydrogen atoms bonded to carbon atoms constituting the fluoropolymer) + (number of fluorine atoms and chlorine atoms bonded to carbon atoms constituting the fluoropolymer)) × 100

[0357] The perfluororesin is more preferably a fluororesin having a fluorine substitution rate of 95 to 100%, further preferably polytetrafluoroethylene (PTFE), FEP or PFA, still more preferably PTFE or PFA, and particularly preferably PTFE.

[0358] The fluoropolymer may have a core-shell structure. Examples of fluoropolymers having a core-shell structure include modified PTFE particles containing a core of high molecular weight PTFE and a shell of lower molecular weight PTFE or modified PTFE. Examples of such modified PTFE include the PTFE described in JP-A-2005-527652.

[0359] The core-shell structure may have the following structures: Core: TFE homopolymer Shell: TFE homopolymer Core: Modified PTFE Shell: TFE homopolymer Core: Modified PTFE Shell: Modified PTFE Core: TFE homopolymer Shell: Modified PTFE Core: Low molecular weight PTFE Shell: High molecular weight PTFE Core: High molecular weight PTFE Shell: Low molecular weight PTFE

[0360] In the fluoropolymer having the core-shell structure, the lower limit of the core ratio is preferably 0.5% by mass, more preferably 1.0% by mass, even more preferably 2.0% by mass, even more preferably 3.0% by mass, particularly preferably 5.0% by mass, and most preferably 10.0% by mass. The upper limit of the core ratio is preferably 99.5% by mass, more preferably 99.0% by mass, even more preferably 98.0% by mass, even more preferably 97.0% by mass, particularly preferably 95.0% by mass, and most preferably 90.0% by mass.

[0361] In the fluoropolymer having the core-shell structure, the lower limit of the shell ratio is preferably 0.5% by mass, more preferably 1.0% by mass, even more preferably 2.0% by mass, even more preferably 3.0% by mass, particularly preferably 5.0% by mass, and most preferably 10.0% by mass. The upper limit of the shell ratio is preferably 99.5% by mass, more preferably 99.0% by mass, even more preferably 98.0% by mass, even more preferably 97.0% by mass, particularly preferably 95.0% by mass, and most preferably 90.0% by mass.

[0362] In the fluoropolymer having the core-shell structure, the core or the shell can be configured to have two or more layers. For example, it may be a fluoropolymer having a three-layer structure with a core center portion of modified PTFE, a core outer layer portion of TFE homopolymer, and a shell of modified PTFE.

[0363] The fluoropolymer having the core-shell structure also includes a particle of the fluoropolymer having multiple cores.

[0364] The above-mentioned (I) non-melt-processible fluororesin and (II) melt-processible fluororesin, which are preferably produced by the production method of the present disclosure, are preferably produced in the following manner.

[0365] (I) Non-melt-processable fluororesin In the production method of the present disclosure, the polymerization of TFE is usually carried out at a polymerization temperature of 10 to 150 ° C and a polymerization pressure of 0.05 to 5 MPaG. For example, the polymerization temperature is more preferably 30 ° C or higher, and even more preferably 50 ° C or higher. Also, it is more preferably 120 ° C or lower, and even more preferably 100 ° C or lower. Also, the polymerization pressure is more preferably 0.3 MPaG or higher, and even more preferably 0.5 MPaG or higher, and also more preferably 5.0 MPaG or lower, and even more preferably 3.0 MPaG or lower. In particular, from the viewpoint of improving the yield of fluoropolymer, it is preferably 1.0 MPaG or higher, more preferably 1.2 MPaG or higher, more preferably 1.5 MPaG or higher, and even more preferably 2.0 MPaG or higher.

[0366] In one embodiment, the polymerization is carried out by charging pure water into a pressure-resistant reactor equipped with a stirrer, deoxidizing, then charging TFE, adjusting the temperature to a predetermined value, and adding a polymerization initiator to initiate the reaction. If the pressure decreases as the reaction proceeds, additional TFE is continuously or intermittently supplied to maintain the initial pressure. When a predetermined amount of TFE has been supplied, the supply is stopped, the TFE in the reactor is purged, and the temperature is returned to room temperature to terminate the reaction. Additional TFE may be continuously or intermittently supplied to prevent the pressure from decreasing.

[0367] In the production of above-mentioned TFE polymer (PTFE), also can use various known modified monomers together.In this disclosure, above-mentioned TFE polymer is not only TFE homopolymer, but also the concept of TFE and modified monomer copolymer, which is non-melt processable (hereinafter referred to as "modified PTFE").

[0368] The modifying monomer is not particularly limited as long as it can be copolymerized with TFE, and includes fluoromonomers and non-fluoromonomers. The modifying monomer used may be one type or multiple types.

[0369] The non-fluoromonomer is not particularly limited and may be a monomer represented by the general formula: ２ =CR Ｑ１ -LR Ｑ２ (In the formula, R Ｑ１represents a hydrogen atom or an alkyl group. L represents a single bond, -CO-O-*, -O-CO-* or -O-. * represents R Ｑ２ represents the bonding position with Ｑ２ represents a hydrogen atom, an alkyl group or a nitrile group.

[0370] Examples of non-fluoromonomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, vinyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, ethyl vinyl ether, cyclohexyl vinyl ether, etc. Of these, butyl methacrylate, vinyl acetate, and acrylic acid are preferred as non-fluoromonomers.

[0371] Examples of fluoromonomers include perfluoroolefins such as hexafluoropropylene (HFP); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF); perhaloolefins such as chlorotrifluoroethylene; perfluorovinyl ethers; (perfluoroalkyl)ethylenes; and perfluoroallyl ethers.

[0372] The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorovinyl ethers represented by the general formula (A): CF ２ ═CF-ORf (A) (wherein Rf represents a perfluoroorganic group). In the present disclosure, the term "perfluoroorganic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0373] Examples of the perfluorovinyl ether include perfluoro(alkyl vinyl ether) [PAVE], which is represented by general formula (A) and in which Rf is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5.

[0374] Examples of the perfluoroalkyl group in the PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

[0375] The perfluorovinyl ether further includes those in which Rf in the general formula (A) is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and those in which Rf ... the following formula:

[0376]

[0377] (wherein m represents 0 or an integer of 1 to 4), and Rf is a group represented by the following formula:

[0378] CF ３ CF ２ CF ２ -(O-CF(CF ３ )-CF ２ ) ｎ - (wherein n represents an integer of 1 to 4).

[0379] Hydrogen-containing fluoroolefins include CH ２ =CF ２ , CFH=CH ２ , CFH=CF ２ , C.H. ２ =CFCF ３ , C.H. ２ = CHCF ３ , CHF=CHCF ３ (E form), CHF=CHCF ３ (Z-isomer), etc.

[0380] The (perfluoroalkyl)ethylene (PFAE) is not particularly limited, and examples thereof include (perfluorobutyl)ethylene (PFBE) and (perfluorohexyl)ethylene.

[0381] Examples of perfluoroallyl ethers include those represented by the general formula: CF ２ =CF-CF ２Examples of the fluoromonomer include those represented by —ORf (wherein Rf represents a perfluoroorganic group).

[0382] Rf in the above general formula is the same as Rf in general formula (A). Rf is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. Examples of perfluoroallyl ethers include CF ２ =CF-CF ２ -O-CF ３ , C.F. ２ =CF-CF ２ -O-C ２ F ５ , C.F. ２ =CF-CF ２ -O-C ３ F ７ , and CF ２ =CF-CF ２ -O-C ４ F ９ At least one selected from the group consisting of CF ２ =CF-CF ２ -O-C ２ F ５ , C.F. ２ =CF-CF ２ -O-C ３ F ７ , and CF ２ =CF-CF ２ -O-C ４ F ９ More preferably, at least one selected from the group consisting of CF ２ =CF-CF ２ -O-CF ２ CF ２ CF ３ is more preferred.

[0383] A preferred example of the modifying monomer is the modified monomer (3) having a monomer reactivity ratio of 0.1 to 8. The presence of the modified monomer (3) makes it possible to obtain PTFE particles having a small particle size and an aqueous dispersion having high dispersion stability.

[0384] Here, the monomer reactivity ratio in copolymerization with TFE is the value obtained by dividing the rate constant of the reaction of the growing radical with TFE when the growing radical is less than the repeating unit based on TFE by the rate constant of the reaction of the growing radical with modified monomer.The lower this value, the higher the reactivity of the modified monomer with TFE.The monomer reactivity ratio can be calculated by copolymerizing TFE with modified monomer, determining the composition in the produced polymer immediately after the start, and using the Feynman-Ross equation.

[0385] The copolymerization was carried out in a 6.0L stainless steel autoclave using 3600g of deionized and degassed water, 1000 mass ppm of ammonium perfluorooctanoate relative to the water, and 100g of paraffin wax at a pressure of 0.78 MPaG and a temperature of 70 ° C. 0.05g, 0.1g, 0.2g, 0.5g, and 1.0g of modified monomer were added to the reactor, respectively, and 0.072g of ammonium persulfate (20 mass ppm relative to water) was added. TFE was continuously supplied to maintain the polymerization pressure at 0.78 MPaG. When the amount of TFE charged reached 1000g, stirring was stopped and the reactor was depressurized until atmospheric pressure was reached. After cooling, the paraffin wax was separated to obtain an aqueous dispersion containing the resulting polymer. The aqueous dispersion was stirred to coagulate the resulting polymer, and then dried at 150 ° C. The composition of the resulting polymer is calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0386] The modified monomer (3) having a monomer reactivity ratio of 0.1 to 8 is preferably at least one selected from the group consisting of modified monomers represented by formulas (3a) to (3d): CH ２ =CH-Rf １ (3a) (wherein, Rf １ is a perfluoroalkyl group having 1 to 10 carbon atoms.) CF ２ ═CF—O—Rf ２ (3b) (wherein, Rf ２ is a perfluoroalkyl group having 1 to 2 carbon atoms.) CF ２ =CF-O-(CF ２ )ｎ CF = CF ２ (3c) (Wherein, n is 1 or 2.)

[0387] (In the formula, X ３ and X ４ is F, Cl or a methoxy group, and Y is of formula Y1 or Y2.

[0388] (In formula Y2, Z and Z′ are F or a fluorinated alkyl group having 1 to 3 carbon atoms.)

[0389] The content of the modified monomer (3) unit is preferably in the range of 0.00001 to 1.0% by mass relative to the total polymerized units of PTFE. The lower limit is more preferably 0.0001% by mass, more preferably 0.0005% by mass, even more preferably 0.001% by mass, and even more preferably 0.005% by mass. The upper limit is, in order of preference, 0.90% by mass, 0.50% by mass, 0.40% by mass, 0.30% by mass, 0.20% by mass, 0.15% by mass, 0.10% by mass, 0.08% by mass, 0.05% by mass, and 0.01% by mass.

[0390] As the above-mentioned modified monomer, because it can obtain the aqueous dispersion of the average primary particle diameter of primary particle is small, the aspect ratio of primary particle is small, and excellent stability, it is preferred to be selected from the group consisting of hexafluoropropylene, chlorotrifluoroethylene, vinylidene fluoride, perfluoro(alkyl vinyl ether), (perfluoroalkyl)ethylene, ethylene, and the modified monomer of the functional group and hydrophilic group that can react by radical polymerization.By using the above-mentioned modified monomer, it can obtain the aqueous dispersion of PTFE that has the average primary particle diameter smaller, the aspect ratio of primary particle is small, and excellent dispersion stability.In addition, it can obtain the aqueous dispersion of less uncoagulated polymer.

[0391] From the viewpoint of reactivity with TFE, the modified monomer preferably contains at least one selected from the group consisting of hexafluoropropylene, perfluoro(alkyl vinyl ether), and (perfluoroalkyl)ethylene. More preferably, it contains at least one selected from the group consisting of hexafluoropropylene, perfluoro(methyl vinyl ether), perfluoro(propyl vinyl ether), (perfluorobutyl)ethylene, (perfluorohexyl)ethylene, and (perfluorooctyl)ethylene. The total amount of the hexafluoropropylene unit, perfluoro(alkyl vinyl ether) unit, and (perfluoroalkyl)ethylene unit is preferably in the range of 0.00001 to 1% by mass relative to the total polymerization units of PTFE. The lower limit of the total amount is more preferably 0.0001% by mass, more preferably 0.0005% by mass, even more preferably 0.001% by mass, and even more preferably 0.005% by mass. The upper limits are, in order of preference, 0.80 mass%, 0.70 mass%, 0.50 mass%, 0.40 mass%, 0.30 mass%, 0.20 mass%, 0.15 mass%, 0.10 mass%, 0.08 mass%, 0.05 mass%, and 0.01 mass%.

[0392] The modified monomer preferably includes a modified monomer having a functional group capable of reacting by radical polymerization and a hydrophilic group (hereinafter referred to as "modified monomer (A)").

[0393] By making the above-mentioned modified monomer (A) exist, it is possible to obtain the PTFE particles with small primary particle diameter, and obtain the aqueous dispersion with high dispersion stability.In addition, it is also possible to reduce the amount of uncoagulated polymer.Furthermore, it is possible to reduce the aspect ratio of primary particle.

[0394] The amount of the modified monomer (A) used is preferably more than the amount corresponding to 0.1 ppm by mass of the aqueous medium, more preferably more than 0.5 ppm by mass, even more preferably more than 1.0 ppm by mass, even more preferably 5 ppm by mass or more, and particularly preferably 10 ppm by mass or more. If the amount of the modified monomer (A) used is too small, the average primary particle diameter of the resulting PTFE may not be small. The amount of the modified monomer (A) used may be within the above range, but the upper limit can be, for example, 5000 ppm by mass. In addition, in the above production method, the modified monomer (A) may be added to the system during the reaction to improve the stability of the aqueous dispersion during or after the reaction.

[0395] The modified monomer (A) is highly water-soluble, so even if unreacted modified monomer (A) remains in the aqueous dispersion, it can be easily removed in the concentration step or the coagulation and washing steps.

[0396] The above-mentioned modified monomer (A) is incorporated into the produced polymer during the polymerization process, but since the concentration of the modified monomer (A) itself in the polymerization system is low and the amount incorporated into the polymer is small, there are no problems such as a decrease in the heat resistance of PTFE or coloration after baking.

[0397] The hydrophilic group in the modified monomer (A) is, for example, —NH ２ , -PO ３ M, -OPO ３ M, -SO ３ M, -OSO ３ M, -COOM (in each formula, M is H, a metal atom, NR ７ｙ ４ , optionally substituted imidazolium, optionally substituted pyridinium or optionally substituted phosphonium, R ７ｙ are H or organic groups and may be the same or different. Any two of them may be bonded to each other to form a ring.) Among the above hydrophilic groups, -SO ３ M or -COOM is preferred. ７ｙ The organic group in R is preferably an alkyl group. ７ｙAs the group, H or C １－１０ is preferably an organic group represented by the formula: １－４ More preferred are organic groups represented by the formula: １－４ The metal atom is preferably a monovalent or divalent metal atom, such as an alkali metal (Group 1) or an alkaline earth metal (Group 2), and more preferably Na, K, or Li.

[0398] Examples of the "functional group capable of reacting by radical polymerization" in the modifying monomer (A) include groups having an ethylenically unsaturated bond, such as a vinyl group and an allyl group. The group having an ethylenically unsaturated bond is a group represented by the following formula: CX ｅ X ｇ =CX ｆ R- (wherein, X ｅ , X ｆ and X ｇ are each independently F, Cl, H, or CF ３ , C.F. ２ H, C.F.H. ２ , or CH ３ and R is a linking group. The linking group of R can be represented by the formula: ａ Preferably, the linking group is -CH=CH ２ , -CF=CH ２、 -CH=CF ２、 -CF = CF ２ , -CH ２ -CH=CH ２ , -CF ２ -CF=CH ２ , -CF ２ -CF = CF ２ , -(C=O)-CH=CH ２ , -(C=O)-CF=CH ２ , -(C=O)-CH=CF ２ , -(C=O)-CF=CF ２ , -(C=O)-C(CH ３ ) = CH ２ , -(C=O)-C(CF ３ ) = CH ２ , -(C=O)-C(CH ３ ) = CF ２ , -(C=O)-C(CF ３ ) = CF ２, —O—CH ２ -CH=CH ２ , —O—CF ２ -CF=CH ２ , —O—CH ２ -CH=CF ２ , —O—CF ２ -CF = CF ２ Examples of groups having an unsaturated bond include the following.

[0399] The modified monomer (A) has a functional group that can react by radical polymerization, so when used in the polymerization, it is assumed that it will react with the fluorine-containing monomer at the initial stage of the polymerization reaction, and form particles that have hydrophilic groups derived from the modified monomer (A) and have high stability.Therefore, it is thought that when polymerization is carried out in the presence of the modified monomer (A), the number of particles will increase.

[0400] The polymerization may be carried out in the presence of one type of the modifying monomer (A), or in the presence of two or more types thereof.

[0401] In the polymerization, a compound having an unsaturated bond can be used as the modifying monomer (A).

[0402] The modifying monomer (A) is a compound represented by the general formula (4): ｉ X ｋ =CX ｊ R ａ - (CZ １ Z ２ ) ｋ -Y ３ (4) (wherein, X ｉ , X ｊ and X ｋ are each independently F, Cl, H or CF ３ and Y ３ is a hydrophilic group; R ａ is a linking group; Z １ and Z ２ are each independently H, F or CF ３ and k is 0 or 1. Examples of the hydrophilic group include —NH ２ , -PO ３ M, -OPO ３ M, -SO ３ M, -OSO３ M, -COOM (in each formula, M is H, a metal atom, NR ７ｙ ４ , optionally substituted imidazolium, optionally substituted pyridinium or optionally substituted phosphonium, R ７ｙ are H or organic groups and may be the same or different. Any two of them may be bonded to each other to form a ring.) Among the above hydrophilic groups, -SO ３ M or -COOM is preferred. ７ｙ The organic group in R is preferably an alkyl group. ７ｙ As the group, H or C １－１０ is preferably an organic group represented by the formula: １－４ More preferred are organic groups represented by the formula: １－４ The alkyl group represented by the formula (I) is more preferred. Examples of the metal atom include monovalent and divalent metal atoms, such as alkali metals (Group 1) and alkaline earth metals (Group 2), with Na, K, or Li being preferred. By using the modified monomer (A), an aqueous dispersion having a smaller average primary particle size and better stability can be obtained. Furthermore, the aspect ratio of the primary particles can be made smaller.

[0403] The above R ａ is a linking group. In the present disclosure, a "linking group" refers to a divalent linking group. The linking group may be a single bond and preferably contains at least one carbon atom. The number of carbon atoms may be 2 or more, 4 or more, 8 or more, 10 or more, or 20 or more. There is no upper limit, but it may be, for example, 100 or less, or 50 or less. The linking group may have a linear or branched, cyclic or acyclic structure, saturated or unsaturated, substituted or unsubstituted, and may optionally contain one or more heteroatoms selected from the group consisting of sulfur, oxygen, and nitrogen, and may optionally contain one or more functional groups selected from the group consisting of ester, amide, sulfonamide, carbonyl, carbonate, urethane, urea, and carbamate. The linking group may not contain carbon atoms, but may contain a catenary heteroatom such as oxygen, sulfur, or nitrogen.

[0404] The above R ａ is preferably a catenary heteroatom such as oxygen, sulfur, or nitrogen, or a divalent organic group. ａ When R is a divalent organic group, the hydrogen atom bonded to the carbon atom may be replaced with a halogen other than fluorine, such as chlorine, and the group may or may not contain a double bond. ａ may be either linear or branched, and may be either cyclic or acyclic. ａ R may contain functional groups (e.g., esters, ethers, ketones, amines, halides, etc.). ａ R may also be a non-fluorinated divalent organic group, or a partially fluorinated or perfluorinated divalent organic group. ａ Examples of the hydrocarbon group include a hydrocarbon group in which no fluorine atoms are bonded to a carbon atom, a hydrocarbon group in which some of the hydrogen atoms bonded to a carbon atom are substituted with fluorine atoms, a hydrocarbon group in which all of the hydrogen atoms bonded to a carbon atom are substituted with fluorine atoms, -(C=O)-, -(C=O)-O-, or a hydrocarbon group containing an ether bond, which may contain an oxygen atom, a double bond, or a functional group.

[0405] R ａ is preferably -(C=O)-, -(C=O)-O-, or a hydrocarbon group having 1 to 100 carbon atoms which may contain an ether bond and may contain a carbonyl group, and in the hydrocarbon group, some or all of the hydrogen atoms bonded to the carbon atoms may be substituted with fluorine. ａ is preferably —(CH ２ ) ａ -, - (CF ２ ) ａ -, -O-(CF ２ ) ａ -, - (CF ２ ) ａ -O-(CF ２ ) ｂ -, -O(CF ２ ) ａ -O-(CF ２ ) ｂ -, - (CF ２ ) ａ-[O-(CF ２ ) ｂ ] ｃ -、-O(CF ２ ) ａ -[O-(CF ２ ) ｂ ] ｃ -、-[(CF ２ ) ａ -O] ｂ -[(CF ２ ) ｃ -O] ｄ -、-O[(CF ２ ) ａ -O] ｂ -[(CF ２ ) ｃ -O] ｄ -、-O-[CF ２ CF(CF ３ )O] ａ -(CF ２ ) ｂ -、-(C=O)-、-(C=O)-O-、-(C=O)-(CH ２ ) ａ -、-(C=O)-(CF ２ ) ａ -、-(C=O)-O-(CH ２ ) ａ -、-(C=O)-O-(CF ２ ) ａ -、-(C=O)-[(CH ２ ) ａ -O] ｂ -、-(C=O)-[(CF ２ ) ａ -O] ｂ -、-(C=O)-O[(CH ２ ) ａ -O] ｂ -、-(C=O)-O[(CF ２ ) ａ -O] ｂ -、-(C=O)-O[(CH ２ ) ａ -O] ｂ -(CH ２ ) ｃ -、-(C=O)-O[(CF ２ ) ａ -O] ｂ -(CF ２ ) ｃ-, -(C=O)-(CH ２ ) ａ -O-(CH ２ ) ｂ -, -(C=O)-(CF ２ ) ａ -O-(CF ２ ) ｂ -, -(C=O)-O-(CH ２ ) ａ -O-(CH ２ ) ｂ -, -(C=O)-O-(CF ２ ) ａ -O-(CF ２ ) ｂ -, -(C=O)-OC ６ H ４ - and at least one selected from combinations thereof. In the formula, a, b, c, and d are independently at least 1. a, b, c, and d may independently be 2 or more, 3 or more, 4 or more, 10 or more, or 20 or more. The upper limits of a, b, c, and d are, for example, 100.

[0406] R ａ A specific example of a suitable group is —CF ２ —O—, —CF ２ -O-CF ２ -, -CF ２ -O-CH ２ -, -CF ２ -O-CH ２ CF ２ -, -CF ２ -O-CF ２ CF ２ -, -CF ２ -O-CF ２ CH ２ -, -CF ２ -O-CF ２ CF ２ CH ２ -, -CF ２ -O-CF(CF ３ ) -, -CF ２ -O-CF(CF ３ )CF ２ -, -CF ２ -O-CF(CF ３ )CF ２-O-, -CF ２ -O-CF(CF ３ )CH ２ -, -(C=O)-, -(C=O)-O-, -(C=O)-(CH ２ )-, -(C=O)-(CF ２ )-, -(C=O)-O-(CH ２ )-, -(C=O)-O-(CF ２ )-, -(C=O)-[(CH ２ ) ２ -O] ｎ -, -(C=O)-[(CF ２ ) ２ -O] ｎ -, -(C=O)-O[(CH ２ ) ２ [[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​-O-CF(CF ３ ) -, -CF ２ -O-CF(CF ３ )CF ２ -, -CF ２ -O-CF(CF ３ )CF ２ -O-, -(C=O)-, -(C=O)-O-, -(C=O)-(CH ２ )-,-(C=O)-O-(CH ２ )-,-(C=O)-O[(CH ２ ) ２ -O] ｎ -, -(C=O)-O[(CH ２ ) ２ -O] ｎ - (CH ２ )-,-(C=O)-(CH ２ ) ２ -O-(CH ２ )-, or -(C=O)-O-C ６ H ４ In the above formula, n is an integer of 1 to 10.

[0407] -R in general formula (4) ａ - (CZ １ Z ２ ) ｋ - is -CF ２ -O-CF ２ -, -CF ２ -O-CF(CF ３ ) -, -CF ２ -O-C(CF ３ ) ２ -, -CF ２ -O-CF ２ -CF ２ -, -CF ２ -O-CF ２ -CF (CF ３ ) -, -CF ２ -O-CF ２ -C(CF ３ ) ２ -, -CF ２ -O-CF ２ CF ２ -CF ２ -, -CF ２ -O-CF ２ CF ２ -CF (CF３ )-、-CF ２ -O-CF ２ CF ２ -C(CF ３ ) ２ -、-CF ２ -O-CF(CF ３ )-CF ２ -、-CF ２ -O-CF(CF ３ )-CF(CF ３ )-、-CF ２ -O-CF(CF ３ )-C(CF ３ ) ２ -、-CF ２ -O-CF(CF ３ )CF ２ -CF ２ -、-CF ２ -O-CF(CF ３ )CF ２ -CF(CF ３ )-、-CF ２ -O-CF(CF ３ )CF ２ -C(CF ３ ) ２ -、-CF ２ -O-CF(CF ３ )CF ２ -O-CF ２ -、-CF ２ -O-CF(CF ３ )CF ２ -O-CF(CF ３ )-、-CF ２ -O-CF(CF ３ )CF ２ -O-C(CF ３ ) ２ -、-(C=O)-、-(C=O)-O-、-(C=O)-(CH ２ )-、-(C=O)-(CF ２ )-、-(C=O)-O-(CH ２ )-、-(C=O)-O-(CF ２ )-、-(C=O)-[(CH ２ ) ２ -O] ｎ -(CH ２ )-、-(C=O)-[(CF ２ ) ２ -O]ｎ -(CF ２ )-、-(C=O)-[(CH ２ ) ２ -O] ｎ -(CH ２ )-(CH ２ )-、-(C=O)-[(CF ２ ) ２ -O] ｎ -(CF ２ )-(CF ２ )-、-(C=O)-O[(CH ２ ) ２ -O] ｎ -(CF ２ )-、-(C=O)-O[(CH ２ ) ２ -O] ｎ -(CH ２ )-(CH ２ )-、-(C=O)-O[(CF ２ ) ２ -O] ｎ -(CF ２ )-、-(C=O)-O[(CF ２ ) ２ -O] ｎ -(CF ２ )-(CF ２ )-、-(C=O)-(CH ２ ) ２ -O-(CH ２ )-(CH ２ )-、-(C=O)-(CF ２ ) ２ -O-(CF ２ )-(CF ２ )-、-(C=O)-O-(CH ２ ) ２ -O-(CH ２ )-(CH ２ )-、-(C=O)-O-(CF ２ ) ２ -O-(CF ２ )-(CF ２ )-、-(C=O)-O-(CH ２ ) ２ -O-(CH ２ )-C(CF ３ ) ２ -、-(C=O)-O-(CF ２ ) ２ -O-(CF２ )-C(CF ３ ) ２ - or -(C=O)-O-C ６ H ４ -C(CF ３ ) ２ - is preferred, and -CF ２ -O-CF(CF ３ ) -, -CF ２ -O-CF ２ -CF (CF ３ ) -, -CF ２ -O-CF ２ CF ２ -CF (CF ３ ) -, -CF ２ -O-CF(CF ３ )-CF(CF ３ ) -, -CF ２ -O-CF(CF ３ )CF ２ -CF (CF ３ ) -, -CF ２ -O-CF(CF ３ )CF ２ -O-CF(CF ３ )-, -(C=O)-, -(C=O)-O-(CH ２ )-,-(C=O)-O-(CH ２ )-(CH ２ )-,-(C=O)-O[(CH ２ ) ２ -O] ｎ - (CH ２ )-(CH ２ )-,-(C=O)-O-(CH ２ ) ２ -O-(CH ２ )-C(CF ３ ) ２ - or -(C=O)-O-C ６ H ４ -C(CF ３ ) ２ In the above formula, n is an integer of 1 to 10.

[0408] Specific examples of the compound represented by formula (4) include: (In the formula, X ｊ and Y ３ is the same as above. n is an integer of 1 to 10.

[0409] R ａ As the general formula (r1): -(C=O) ｈ -(O) ｉ -CF ２ -O-(CX ６ ２ ) ｅ -{O-CF(CF ３ ) ｆ -(O) ｇ - (r1) (wherein, X ６ are each independently H, F or CF ３ wherein e is an integer of 0 to 3, f is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, and i is 0 or 1), and a divalent group represented by the general formula (r2): -(C=O) ｈ -(O) ｉ -CF ２ -O-(CX ７ ２ ) ｅ -(O) ｇ - (r2) (wherein, X ７ are each independently H, F or CF ３ wherein e is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, and i is 0 or 1.) is also preferred.

[0410] -R in general formula (4) ａ - (CZ １ Z ２ ) ｋ - may also be represented by the following formula (t1): -(C=O) ｈ -(O) ｉ -CF ２ -O-(CX ６ ２ ) ｅ -{O-CF(CF ３ ) ｆ -(O) ｇ -CZ １ Z ２ - (t1) (wherein, X ６ are each independently H, F or CF ３ wherein e is an integer of 0 to 3, f is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, i is 0 or 1, and Z １and Z ２ are each independently F or CF ３ In formula (t1), a divalent group represented by １ and Z ２ is one F and the other CF ３ In addition, in the general formula (4), -R ａ - (CZ １ Z ２ ) ｋ - is the following formula (t2): -(C=O) ｈ -(O) ｉ -CF ２ -O-(CX ７ ２ ) ｅ -(O) ｇ -CZ １ Z ２ - (t2) (wherein, X ７ are each independently H, F or CF ３ wherein e is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, i is 0 or 1, and Z １ and Z ２ are each independently F or CF ３ In formula (t2), a divalent group represented by １ and Z ２ is one F and the other CF ３ It is more preferable that:

[0411] The compound represented by the general formula (4) is a compound having a hydrophilic group (Y ３ ) except for the above, it is also preferable that the compound has a C—F bond and does not have a C—H bond. ｉ , X ｊ , and X ｋ All of the are F and R ａ is preferably a perfluoroalkylene group having one or more carbon atoms, and the perfluoroalkylene group may be either linear or branched, may be either cyclic or acyclic, and may contain at least one catenary heteroatom. The number of carbon atoms in the perfluoroalkylene group may be 2 to 20, or may be 4 to 18.

[0412] The compound represented by the general formula (4) may be partially fluorinated. That is, the compound represented by the general formula (4) may have a hydrophilic group (Y ３ ), it is also preferred that the alkyl group has at least one hydrogen atom bonded to a carbon atom and at least one fluorine atom bonded to a carbon atom.

[0413] The compound represented by general formula (4) is also preferably a compound represented by the following formula (4a): CF ２ ═CF—O—Rf ０ -Y ３ (4a) (wherein, Y ３ is a hydrophilic group, and Rf ０ is a perfluorinated divalent linking group which may be linear or branched, cyclic or acyclic in structure, saturated or unsaturated, substituted or unsubstituted, and which optionally contains one or more heteroatoms selected from the group consisting of sulfur, oxygen, and nitrogen.

[0414] The compound represented by general formula (4) is also preferably a compound represented by the following formula (4b): CH ２ =CH-O-Rf ０ -Y ３ (4b) (wherein, Y ３ is a hydrophilic group, and Rf ０ is a perfluorinated divalent linking group defined by formula (4a).

[0415] In the general formula (4), Y ３ Ha-OSO ３ One of the preferred embodiments is Y. ３ Ga-OSO ３ When M is a compound represented by general formula (4), CF ２ =CF(OCF ２ CF ２ CH ２ OSO ３ M), CF ２ =CF(O(CF ２ ) ４ CH ２ OSO ３ M), CF ２ =CF(OCF ２ CF (CF ３ ) CH２ OSO ３ M), CF ２ =CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ CH ２ OSO ３ M), CH ２ =CH((CF ２ ) ４ CH ２ OSO ３ M), CF ２ =CF(OCF ２ CF ２ SO ２ N (CH ３ ) CH ２ CH ２ OSO ３ M), CH ２ =CH(CF ２ CF ２ CH ２ OSO ３ M), CF ２ =CF(OCF ２ CF ２ CF ２ CF ２ SO ２ N (CH ３ ) CH ２ CH ２ OSO ３ In the above formula, M is the same as above.

[0416] In the general formula (4), Y ３ Ha-SO ３ M is also a preferred embodiment. ３ Ga-SO ３ When M is a compound represented by general formula (4), CF ２ =CF(OCF ２ CF ２ SO ３ M), CF ２ =CF(O(CF ２ ) ４ SO ３ M), CF ２ =CF(OCF ２ CF (CF ３ ) SO ３ M), CF ２=CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ SO ３ M), CH ２ =CH(CF ２ CF ２ SO ３ M), CF ２ =CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ CF ２ CF ２ SO ３ M), CH ２ =CH((CF ２ ) ４ SO ３ M), CH ２ =CH((CF ２ ) ３ SO ３ In the above formula, M is the same as above.

[0417] In the general formula (4), Y ３ It is also a preferred embodiment that Y is -COOM. ３ is -COOM, the compound represented by general formula (4) is CF ２ =CF(OCF ２ CF ２ COOM), C.F. ２ =CF(OCF ２ CF ２ CF ２ COOM), C.F. ２ =CF(O(CF ２ ) ５ COOM), C.F. ２ =CF(OCF ２ CF (CF ３ ) COOM), CF ２ =CF(OCF ２ CF (CF ３ ) O(CF ２ ) ｎ COOM) (n is greater than 1), CH ２ =CH(CF ２ CF ２ COOM), CH ２ =CH((CF ２) ４ COOM), CH ２ =CH((CF ２ ) ３ COOM), C.F. ２ =CF(OCF ２ CF ２ SO ２ NR'CH ２ COOM), C.F. ２ =CF(O(CF ２ ) ４ SO ２ NR'CH ２ COOM), C.F. ２ =CF(OCF ２ CF (CF ３ ) SO ２ NR'CH ２ COOM), C.F. ２ =CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ SO ２ NR'CH ２ COOM), CH ２ =CH(CF ２ CF ２ SO ２ NR'CH ２ COOM), C.F. ２ =CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ CF ２ CF ２ SO ２ NR'CH ２ COOM), CH ２ =CH((CF ２ ) ４ SO ２ NR'CH ２ COOM), CH ２ =CH((CF ２ ) ３ SO ２ NR'CH ２ In the above formula, R' is H or C １－４ is an alkyl group, and M is the same as above.

[0418] In the general formula (4), Y ３ Ha-OPO３ M or -OP(O)(OM) ２ It is also a preferred embodiment that ３ Ga-OPO ３ M or -OP(O)(OM) ２ In this case, the compound represented by the general formula (4) is CF ２ =CF(OCF ２ CF ２ CH ２ OP (O) (OM) ２ ), CF ２ =CF(O(CF ２ ) ４ CH ２ OP (O) (OM) ２ ), CF ２ =CF(OCF ２ CF (CF ３ ) CH ２ OP (O) (OM) ２ ), CF ２ =CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ CH ２ OP (O) (OM) ２ ), CF ２ =CF(OCF ２ CF ２ SO ２ N (CH ３ ) CH ２ CH ２ OP (O) (OM) ２ ), CF ２ =CF(OCF ２ CF ２ CF ２ CF ２ SO ２ N (CH ３ ) CH ２ CH ２ OP (O) (OM) ２ ), C.H. ２ =CH(CF ２ CF ２ CH ２ OP (O) (OM) ２ , C.H. ２ =CH((CF ２ ) ４ CH ２ OP (O) (OM)２ ), C.H. ２ =CH((CF ２ ) ３ CH ２ OP (O) (OM) ２ In the above formula, M is the same as above.

[0419] In the general formula (4), Y ３ Ha-PO ３ M or -P(O)(OM) ２ It is also a preferred embodiment that ３ Ga-PO ３ M or -P(O)(OM) ２ In this case, the compound represented by the general formula (4) is CF ２ =CF(OCF ２ CF ２ P(O)(OM) ２ ), CF ２ =CF(O(CF ２ ) ４ P(O)(OM) ２ ), CF ２ =CF(OCF ２ CF (CF ３ ) P (O) (OM) ２ ), CF ２ =CF(OCF ２ CF (CF ３ ) OCF ２ CF ２ P(O)(OM) ２ ), C.H. ２ =CH(CF ２ CF ２ P(O)(OM) ２ ), C.H. ２ =CH((CF ２ ) ４ P(O)(OM) ２ ), C.H. ２ =CH((CF ２ ) ３ P(O)(OM) ２ ) and the like, in which M is the same as above.

[0420] The compound represented by the general formula (4) includes a compound represented by the general formula (5): CX ２ =CY(-CZ ２ -O-Rf-Y ３) (5) (In the formula, X is the same or different and is -H or -F; Y is -H, -F, an alkyl group or a fluorine-containing alkyl group; Z is the same or different and is -H, -F, an alkyl group or a fluorine-containing alkyl group. Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms or a fluorine-containing alkylene group having 2 to 100 carbon atoms and an ether bond. Y ３ is the same as above.), a compound represented by general formula (6): CX ２ =CY(-O-Rf-Y ３ ) (6) (In the formula, X is the same or different and is -H or -F, Y is -H, -F, an alkyl group or a fluorine-containing alkyl group, and Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms or a fluorine-containing alkylene group having an ether bond and having 2 to 100 carbon atoms. Y ３ is the same as above.) and a compound represented by general formula (7): CX ２ =CY(-Rf-Y ３ ) (7) (In the formula, X is the same or different and is -H or -F, Y is -H, -F, an alkyl group or a fluorine-containing alkyl group, and Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms or a fluorine-containing alkylene group having an ether bond and having 2 to 100 carbon atoms. Y ３ is the same as above.) The fluorine-containing alkylene group having 2 to 100 carbon atoms and an ether bond is an alkylene group that does not contain a structure in which an oxygen atom is at the terminal and contains an ether bond between carbon atoms.

[0421] In general formula (5), X is -H or -F. Both Xs may be -F, or at least one X may be -H. For example, one X may be -F and the other may be -H, or both Xs may be -H.

[0422] In general formula (5), Y is -H, -F, an alkyl group or a fluorine-containing alkyl group. The alkyl group is an alkyl group that does not contain a fluorine atom, and may have one or more carbon atoms. The alkyl group preferably has six or fewer carbon atoms, more preferably four or fewer carbon atoms, and even more preferably three or fewer carbon atoms. The fluorine-containing alkyl group is an alkyl group that contains at least one fluorine atom, and may have one or more carbon atoms. The fluorine-containing alkyl group preferably has six or fewer carbon atoms, more preferably four or fewer carbon atoms, and even more preferably three or fewer carbon atoms. Y may be -H, -F or -CF ３ is preferred, and —F is more preferred.

[0423] In general formula (5), Z's may be the same or different and are -H, -F, an alkyl group, or a fluoroalkyl group. The alkyl group is an alkyl group that does not contain a fluorine atom, and may have one or more carbon atoms. The alkyl group preferably has six or fewer carbon atoms, more preferably four or fewer carbon atoms, and even more preferably three or fewer carbon atoms. The fluorine-containing alkyl group is an alkyl group that contains at least one fluorine atom, and may have one or more carbon atoms. The fluorine-containing alkyl group preferably has six or fewer carbon atoms, more preferably four or fewer carbon atoms, and even more preferably three or fewer carbon atoms. The Z's may be -H, -F, or -CF ３ is preferred, and —F is more preferred.

[0424] In general formula (5), it is preferable that at least one of X, Y, and Z contains a fluorine atom. For example, X may be —H, and Y and Z may be —F.

[0425] In general formula (5), Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms, or a fluorine-containing alkylene group having 2 to 100 carbon atoms and an ether bond. The number of carbon atoms in the fluorine-containing alkylene group is preferably 2 or more. Also, the number of carbon atoms is preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less. Examples of the fluorine-containing alkylene group include -CF ２ -, -CH ２ CF ２ -, -CF ２ CF ２ -, -CF ２ CH ２ -, -CF２ CF ２ CH ２ -, -CF(CF ３ ) -, -CF(CF ３ )CF ２ -, -CF(CF ３ ) CH ２ The fluorine-containing alkylene group is preferably a perfluoroalkylene group.

[0426] The number of carbon atoms of the fluorine-containing alkylene group having an ether bond is preferably 3 or more. The number of carbon atoms of the fluorine-containing alkylene group having an ether bond is preferably 60 or less, more preferably 30 or less, and even more preferably 12 or less. Examples of the fluorine-containing alkylene group having an ether bond include those represented by the following formula: (In the formula, Z １ is F or CF ３ ;Z ２ and Z ３ are H or F; Z ４ is H, F or CF ３ ; p1+q1+r1 is an integer of 1 to 10; s1 is 0 or 1; t1 is an integer of 0 to 5). Specific examples of the fluorine-containing alkylene group having an ether bond include -CF(CF ３ )CF ２ -O-CF(CF ３ )-,-(CF(CF ３ )CF ２ -O) ｎ -CF (CF ３ )-(wherein n is an integer from 1 to 10), -CF(CF ３ )CF ２ -O-CF(CF ３ ) CH ２ -, -(CF(CF ３ )CF ２ -O) ｎ -CF (CF ３ ) CH ２ - (wherein n is an integer of 1 to 10), -CH ２ CF ２ CF ２ O-CH ２ CF ２ CH ２ -, -CF ２ CF２ CF ２ O-CF ２ CF ２ -, -CF ２ CF ２ CF ２ O-CF ２ CF ２ CH ２ -, -CF ２ CF ２ O-CF ２ -, -CF ２ CF ２ O-CF ２ CH ２ The fluorine-containing alkylene group having an ether bond is preferably a perfluoroalkylene group.

[0427] In the general formula (5), Y ３ is -COOM, -SO ３ M or -OSO ３ M (M is H, metal atom, NR ７ｙ ４ , optionally substituted imidazolium, optionally substituted pyridinium or optionally substituted phosphonium, R ７ｙ are H or organic groups, and may be the same or different. Any two of them may be bonded to each other to form a ring. ７ｙ The organic group in R is preferably an alkyl group. ７ｙ As the group, H or C １－１０ is preferably an organic group represented by the formula: １－４ More preferred are organic groups represented by the formula: １－４ The metal atom includes alkali metals (Group 1) and alkaline earth metals (Group 2), and Na, K, or Li is preferred. M represents —H, a metal atom, or NR ７ ４ is preferred, and —H, an alkali metal (Group 1), an alkaline earth metal (Group 2), or NR ７ ４ is more preferred, and —H, —Na, —K, —Li or NH ４ is more preferred, and —H, —Na, —K or NH ４is even more preferred, -H, -Na or NH ４ is particularly preferred, and —H or —NH ４ The most preferred is the above Y ３ As the group, -COOM or -SO ３ M is preferred, and —COOM is more preferred.

[0428] The compound represented by general formula (5) is preferably a compound (5a) represented by general formula (5a): CH ２ =CF(-CF ２ -O-Rf-Y ３ ) (5a) (wherein Rf and Y ３ is the same as above.)

[0429] Specific examples of the compound represented by the general formula (5a) include compounds represented by the following formula:

[0430]

[0431] (In the formula, Z １ is F or CF ３ ;Z ２ and Z ３ are H or F; Z ４ is H, F or CF ３ p1+q1+r1 are integers of 0 to 10; s1 is 0 or 1; t1 is an integer of 0 to 5; Y ３ is the same as above. However, Z ３ and Z ４ are both H, then p1+q1+r1+s1 is not 0). More specifically, compounds represented by the following formula are exemplified:

[0432]

[0433] Among them,

[0434]

[0435] It is preferable that:

[0436] The compound represented by general formula (5a) includes compounds represented by formula (5a) ３ is preferably -COOM, and in particular CH ２ =CFCF ２ OCF (CF ３ ) COOM, and CH２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ )COOM (wherein M is as defined above), and CH ２ =CFCF ２ OCF (CF ３ ) COOM is more preferred.

[0437] The compound represented by general formula (5) is preferably a compound (5b) represented by general formula (5b): CX ２ ２ =CFCF ２ -O-(CF(CF ３ )CF ２ O) ｎ５ -CF (CF ３ )-Y ３ (5b) (where each X ２ are the same and represent F or H. n5 represents 0 or an integer of 1 to 10, Y ３ is the same as the above definition.)

[0438] In the formula (5b), n5 is preferably 0 or an integer of 1 to 5, more preferably 0, 1 or 2, and even more preferably 0 or 1, in terms of the stability of the resulting aqueous dispersion. ３ is preferably -COOM in that it provides adequate water solubility and stability of the aqueous dispersion, and M is preferably H or NH in that it is less likely to remain as an impurity and the heat resistance of the resulting molded article is improved. ４ It is preferable that:

[0439] Examples of the compound represented by the formula (5b) include CH ２ =CFCF ２ OCF (CF ３ ) COOM, C.H. ２ =CFCF ２ OCF (CF ３ )CF ２ OCF (CF ３ ) COOM (wherein M is as defined above).

[0440] Further, examples of the compound represented by the general formula (5) include a compound represented by the general formula (5c).

[0441] CF ２ =CFCF ２ -O-Rf-Y ３ (5c) (wherein Rf and Y ３ is the same as above)

[0442] More specifically, etc.

[0443] In general formula (6), X is -H or -F. Both Xs may be -F, or at least one X may be -H. For example, one X may be -F and the other may be -H, or both Xs may be -H.

[0444] In general formula (6), Y is -H, -F, an alkyl group or a fluorine-containing alkyl group. The alkyl group is an alkyl group that does not contain a fluorine atom, and may have one or more carbon atoms. The alkyl group preferably has six or fewer carbon atoms, more preferably four or fewer carbon atoms, and even more preferably three or fewer carbon atoms. The fluorine-containing alkyl group is an alkyl group that contains at least one fluorine atom, and may have one or more carbon atoms. The fluorine-containing alkyl group preferably has six or fewer carbon atoms, more preferably four or fewer carbon atoms, and even more preferably three or fewer carbon atoms. The Y may be -H, -F or -CF ３ is preferred, and —F is more preferred.

[0445] In general formula (6), it is preferable that at least one of X and Y contains a fluorine atom. For example, X may be —H, and Y and Z may be —F.

[0446] In general formula (6), Rf is a fluorine-containing alkylene group having 1 to 40 carbon atoms, or a fluorine-containing alkylene group having 2 to 100 carbon atoms and an ether bond. The number of carbon atoms in the fluorine-containing alkylene group is preferably 2 or more. The number of carbon atoms in the fluorine-containing alkylene group is preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less. Examples of the fluorine-containing alkylene group include -CF ２ -, -CH ２ CF ２ -, -CF２ CF ２ -, -CF ２ CH ２ -, -CF ２ CF ２ CH ２ -, -CF(CF ３ ) -, -CF(CF ３ )CF ２ -, -CF(CF ３ ) CH ２ The fluorine-containing alkylene group is preferably a perfluoroalkylene group.

[0447] In the above general formula (6), Y ３ is -COOM, -SO ３ M or -OSO ３ M (M is H, metal atom, NR ７ｙ ４ , optionally substituted imidazolium, optionally substituted pyridinium or optionally substituted phosphonium, R ７ｙ are H or organic groups, and may be the same or different. Any two of them may be bonded to each other to form a ring. ７ｙ The organic group in R is preferably an alkyl group. ７ｙ As the group, H or C １－１０ is preferably an organic group represented by the formula: １－４ More preferred are organic groups represented by the formula: １－４ The metal atom includes alkali metals (Group 1) and alkaline earth metals (Group 2), and Na, K, or Li is preferred. M represents —H, a metal atom, or NR ７ ４ is preferred, and —H, an alkali metal (Group 1), an alkaline earth metal (Group 2), or NR ７ ４ is more preferred, and —H, —Na, —K, —Li or NH ４ is more preferred, and —H, —Na, —K or NH ４ is even more preferred, -H, -Na or NH ４ is particularly preferred, and —H or —NH ４ The most preferred is the above Y ３As the group, -COOM or -SO ３ M is preferred, and —COOM is more preferred.

[0448] The compound represented by general formula (6) is preferably at least one selected from the group consisting of compounds represented by general formulas (6a), (6b), (6c), (6d), and (6e). ２ =CF-O-(CF ２ ) ｎ１ -Y ３ (6a) (wherein n1 represents an integer of 1 to 10, and Y ３ is the same as the definition above.) CF ２ =CF-O-(CF ２ C (CF ３ ) F) ｎ２ -Y ３ (6b) (wherein n2 represents an integer of 1 to 5, and Y ３ is the same as the definition above.) CF ２ =CF-O-(CFX １ ) ｎ３ -Y ３ (6c) (wherein, X １ is F or CF ３ n3 represents an integer of 1 to 10; Y ３ is the same as the definition above.) CF ２ =CF-O-(CF ２ CFX １ O) ｎ４ -(CF ２ ) ｎ６ -Y ３ (6d) (wherein n4 represents an integer of 1 to 10, n6 represents an integer of 1 to 3, and Y ３ and X １ is the same as the definition above.) CF ２ =CF-O-(CF ２ CF ２ CFX １ O) ｎ５ -CF ２ CF ２ CF ２ -Y ３ (6e) (wherein n5 represents an integer of 0 to 10, and Y ３ and X １ is the same as the above definition.)

[0449] In the formula (6a), n1 is preferably an integer of 5 or less, and more preferably an integer of 2 or less. ３ is preferable in that it can provide a suitable water solubility and stability of the aqueous dispersion. ３ M is preferably H or NH, in that M is unlikely to remain as an impurity and the heat resistance of the resulting molded article is improved. ４ It is preferable that:

[0450] Examples of the compound represented by the formula (6a) include CF ２ =CF-O-CF ２ COOM, C.F. ２ =CF(OCF ２ CF ２ COOM), C.F. ２ =CF(OCF ２ CF ２ CF ２ COOM), C.F. ２ =CF-O-CF ２ SO ３ M., C.F. ２ =CF(OCF ２ CF ２ SO ３ M), CF ２ =CF(OCF ２ CF ２ CF ２ SO ３ M) (wherein M is as defined above).

[0451] In the formula (6b), n2 is preferably an integer of 3 or less in terms of the stability of the resulting aqueous dispersion, and Y ３ is preferable in that it provides suitable water solubility and stability of the aqueous dispersion. ３ M is preferably H or NH, in that M is unlikely to remain as an impurity and the heat resistance of the resulting molded article is improved. ４ It is preferable that:

[0452] In the formula (6c), n3 is preferably an integer of 5 or less in terms of water solubility, and Y ３ is preferable in that it provides suitable water solubility and stability of the aqueous dispersion.３ M is preferably H or NH in that dispersion stability is improved. ４ It is preferable that:

[0453] In the formula (6d), the X １ In terms of the stability of the aqueous dispersion, -CF ３ In terms of water solubility, n4 is preferably an integer of 5 or less, and Y ３ is preferable to -COOM or -SO in that it provides suitable water solubility and stability of the aqueous dispersion. ３ Preferably, M is H or NH. ４ It is preferable that:

[0454] Examples of the compound represented by the formula (6d) include CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ COOM, C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ COOM, C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CF ２ COOM, C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ SO ３ M., C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ SO ３ M., C.F. ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CF ２ SO ３ M (wherein M is H, NH ４ or an alkali metal.

[0455] In the general formula (6e), n5 is preferably an integer of 5 or less in terms of water solubility, and Y ３ is preferable to -COOM or -SO in that it provides suitable water solubility and stability of the aqueous dispersion. ３ Preferably, M is H or NH. ４ It is preferable that:

[0456] Examples of the compound represented by general formula (6e) include CF ２ = CFOCF ２ CF ２ CF ２ COOM, C.F. ２ = CFOCF ２ CF ２ CF ２ SO ３ M (wherein M is H, NH ４ or an alkali metal.

[0457] In general formula (7), Rf is preferably a fluorine-containing alkylene group having 1 to 40 carbon atoms. In general formula (7), at least one of X and Y preferably contains a fluorine atom.

[0458] The compound represented by general formula (7) is represented by general formula (7a): CF ２ =CF-(CF ２ ) ｎ１ -Y ３ (7a) (wherein n1 represents an integer of 1 to 10, and Y ３ is the same as defined above.) and a compound represented by general formula (7b): CF ２ =CF-(CF ２ C (CF ３ ) F) ｎ２ -Y ３ (7b) (wherein n2 represents an integer of 1 to 5, and Y ３ is as defined above. ３ is -SO ３ M or -COOM is preferred, where M is H, a metal atom, NR ７ｙ ４, optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium. ７ｙ represents H or an organic group.

[0459] In the formula (7a), n1 is preferably an integer of 5 or less, and more preferably an integer of 2 or less. ３ is preferable in that it can provide a suitable water solubility and stability of the aqueous dispersion. ３ M is preferably H or NH, in that M is unlikely to remain as an impurity and the heat resistance of the resulting molded article is improved. ４ The compound represented by the formula (7a) is preferably, for example, CF ２ =CFCF ２ COOM, C.F. ２ =CFCF ２ SO ３ M (wherein M is as defined above).

[0460] In the formula (7b), n2 is preferably an integer of 3 or less in terms of the stability of the resulting aqueous dispersion, and Y ３ is preferable in that it provides suitable water solubility and stability of the aqueous dispersion. ３ M is preferably H or NH, in that M is unlikely to remain as an impurity and the heat resistance of the resulting molded article is improved. ４ It is preferable that:

[0461] The modified monomer preferably contains modified monomer (A), and preferably contains at least one selected from the group consisting of compounds represented by general formula (5a), general formula (5c), general formula (6a), general formula (6b), general formula (6c), and general formula (6d), and more preferably contains a compound represented by general formula (5a) or general formula (5c).

[0462] When using a modified monomer (A) as the modified monomer, the content of the modified monomer (A) unit is preferably in the range of 0.00001 to 1.0 mass% relative to the total polymerized units of the TFE polymer (PTFE).The lower limit is more preferably 0.0001 mass%, more preferably 0.0005 mass%, even more preferably 0.001 mass%, and even more preferably 0.005 mass%.The upper limit is, in order of preference, 0.90 mass%, 0.50 mass%, 0.40 mass%, 0.30 mass%, 0.20 mass%, 0.15 mass%, 0.10 mass%, 0.08 mass%, 0.05 mass%, and 0.01 mass%.

[0463] According to purpose, the aqueous dispersion of TFE polymer can also be preferably used as the composition that organic or inorganic filler is added to in various applications.By coating above-mentioned composition on the substrate that is made of metal or ceramic, it can make the coating surface that has non-adhesiveness and low friction coefficient, and has excellent gloss, smoothness, abrasion resistance, weather resistance and heat resistance, and is suitable for the coating of rolls, cooking utensils, etc., the impregnation processing of glass cloth, etc.

[0464] An organosol of a TFE polymer can also be prepared from the aqueous dispersion. The organosol can contain the TFE polymer and an organic solvent. Examples of the organic solvent include ether-based solvents, ketone-based solvents, alcohol-based solvents, amide-based solvents, ester-based solvents, aliphatic hydrocarbon-based solvents, aromatic hydrocarbon-based solvents, and halogenated hydrocarbon-based solvents. N-methyl-2-pyrrolidone, dimethylacetamide, and the like are preferably used. The organosol can be prepared, for example, by the method described in International Publication No. 2012 / 002038.

[0465] The aqueous dispersion of above-mentioned TFE polymer is also preferably used as processing aid.When used as processing aid, by mixing the aqueous dispersion with host polymer etc., it can improve the melt strength during the melt processing of host polymer, and can improve the mechanical strength, electrical properties, flame retardancy, anti-dripping property during burning and sliding property of the obtained polymer.

[0466] The aqueous dispersion of the TFE polymer is also preferably used as a binder for batteries and for dust prevention purposes.

[0467] The aqueous dispersion of the TFE polymer is also preferably used as a processing aid after being compounded with a resin other than the TFE polymer.The aqueous dispersion is suitable as a raw material for the PTFE described in, for example, 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 aqueous dispersion is in no way inferior to the processing aids described in the above publications.

[0468] The aqueous dispersion of above-mentioned TFE polymer can also be mixed with the aqueous dispersion of melt-processable fluororesin to be coagulated, and be made into coprecipitated powder.Above-mentioned coprecipitated powder is suitable as processing aid.

[0469] Examples of the melt-processable fluororesin include FEP, PFA, TFE / perfluoroallyl ether copolymer, ETFE, ethylene / TFE / HFP copolymer [EFEP], etc., with PFA or FEP being preferred.

[0470] The aqueous dispersion preferably contains the melt-processable fluororesin.The melt-processable fluororesin can be exemplified by FEP, PFA, TFE / perfluoroallyl ether copolymer, ETFE, EFEP, etc.The aqueous dispersion containing the melt-processable fluororesin can be used as coating material.The melt-processable fluororesin can sufficiently fuse the particles of the TFE polymer together, so that it can improve film-forming property and make the obtained coating film glossy.

[0471] The aqueous dispersion of the TFE polymer is also preferably used as a dust-suppressing treatment. The dust-suppressing treatment can be used in a method of mixing the TFE polymer with a dust-generating substance and subjecting the mixture to a compression-shear action at a temperature of 20 to 200°C to fibrillate the TFE polymer and suppress the dust of the dust-generating substance, such as the methods described in Japanese Patent No. 2827152 and Japanese Patent No. 2538783. The aqueous dispersion of the TFE polymer can be suitably used in the dust-suppressing treatment composition described in WO 2007 / 004250, for example, and can also be suitably used in the dust-suppressing treatment method described in WO 2007 / 000812.

[0472] The dust suppression treatment agent is suitable for use in the fields of building materials, soil stabilization materials, solidification materials, fertilizers, landfill disposal of incineration ash and hazardous substances, explosion prevention, cosmetics, and dust suppression treatment of sand for pet excretion, such as cat litter.

[0473] The aqueous dispersion of the TFE polymer is also preferably used as a raw material for obtaining TFE polymer fibers by the dispersion spinning method. The dispersion spinning method is a method in which the aqueous dispersion of the TFE polymer 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 TFE polymer particles, thereby obtaining TFE polymer fibers.

[0474] The manufacturing method of the present disclosure can also be used to manufacture low-molecular-weight PTFE. Low-molecular-weight PTFE can be manufactured by polymerization, or by lowering the molecular weight of high-molecular-weight PTFE obtained by polymerization using a known method (thermal decomposition, decomposition by irradiation, etc.).

[0475] Low-molecular-weight PTFE (also called PTFE micropowder) having a molecular weight of 600,000 or less has excellent chemical stability, extremely low surface energy, and is resistant to fibrillation. Therefore, it is suitable as an additive for improving the slipperiness and texture of coating surfaces in the production of plastics, inks, cosmetics, paints, greases, office automation equipment components, toners, etc. (see, for example, JP-A-10-147617).

[0476] Furthermore, low-molecular-weight PTFE may be obtained by polymerizing TFE or a monomer copolymerizable with TFE with TFE in the presence of a chain transfer agent. In this case, the chain transfer agent is preferably at least one selected from the group consisting of alkanes having 2 to 4 carbon atoms. Specifically, methane, ethane, propane, butane, and isobutane are more preferred, and ethane and propane are even more preferred. In this case, the amount of chain transfer agent is preferably 10 mass ppm or more or more than 10 mass ppm relative to the aqueous medium.

[0477] When the low-molecular-weight PTFE obtained by the above polymerization is used as a powder, the aqueous dispersion can be coagulated to form powder particles.

[0478] In this disclosure, high molecular weight PTFE refers to non-melt-processible and fibrillating PTFE, while low molecular weight PTFE refers to melt-processible and non-fibrillating PTFE.

[0479] The term "non-melt processable" means that the melt flow rate cannot be measured at a temperature higher than the crystallization melting point in accordance with ASTM D 1238 and D 2116.

[0480] The presence or absence of fibrillation properties can be determined by "paste extrusion," a typical method for molding "high molecular weight PTFE powder," which is 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 at 0% elongation, it can be considered to have no fibrillation properties.

[0481] 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 the water displacement method in accordance with ASTM D 792 using a sample molded in accordance with ASTM D 4895-89. In this disclosure, "high molecular weight" means that the standard specific gravity is within the above range.

[0482] The low-molecular-weight PTFE has a melt viscosity of 1×10 at 380° C. ２ ~7 x 10 ５ In the present disclosure, "low molecular weight" means that the melt viscosity is within the above range. The melt viscosity is measured in accordance with ASTM D 1238 using a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die, with a 2 g sample preheated at 380°C for 5 minutes, and maintained at the above temperature under a load of 0.7 MPa.

[0483] The melt viscosity of the high molecular weight PTFE is much higher than that of the low molecular weight PTFE, making it difficult to measure its melt viscosity accurately. On the other hand, although the melt viscosity of the low molecular weight PTFE can be measured, it is difficult to obtain a molded product from the low molecular weight PTFE that can be used to measure its standard gravity, making it difficult to measure its accurate standard gravity. Therefore, in this disclosure, standard specific gravity is used as an indicator of the molecular weight of the high molecular weight PTFE, and melt viscosity is used as an indicator of the molecular weight of the low molecular weight PTFE. Note that no measurement method is known that can directly determine the molecular weight of either the high molecular weight PTFE or the low molecular weight PTFE.

[0484] The high-molecular-weight PTFE preferably has a peak temperature of 333 to 347° C., more preferably 335 to 345° C. The low-molecular-weight PTFE preferably has a peak temperature of 322 to 333° C., more preferably 324 to 332° C. The peak temperature can be specified as the temperature corresponding to the maximum value that appears on a differential thermal (DTA) curve obtained by using a TG / DTA (thermogravimetric / differential thermal analyzer) to raise the temperature of PTFE that has not been heated to a temperature of 300° C. or higher at a rate of 10° C. / min.

[0485] The peak temperature of PTFE may be 322 to 347°C. When PTFE is high molecular weight PTFE, the upper limit of the peak temperature of PTFE may be 347°C or lower, 346°C or lower, 345°C or lower, 344°C or lower, 343°C or lower, 342°C or lower, 341°C or lower, or 340°C or lower. When PTFE is high molecular weight PTFE, the lower limit of the peak temperature of PTFE may be 333°C or higher or 335°C or higher. When PTFE is low molecular weight PTFE, the upper limit of the peak temperature of PTFE may be 333°C or lower or 332°C or lower. When PTFE is low molecular weight PTFE, the lower limit of the peak temperature of PTFE may be 322°C or higher or 324°C or higher.

[0486] The average primary particle diameter of the primary particles of low molecular weight PTFE is preferably 10-300 nm, more preferably 50 nm or more, even more preferably 100 nm or more, still more preferably 150 nm or more, and more preferably 250 nm or less.The relatively small average primary particle diameter of the primary particles can be obtained, for example, by adding a modified monomer to the polymerization system at the initial stage of TFE polymerization.

[0487] The average primary particle size of the primary particles of low-molecular-weight PTFE can be measured by dynamic light scattering. First, an aqueous dispersion of low-molecular-weight PTFE with a polymer solids concentration adjusted to about 1.0% by mass is prepared, and the average primary particle size can be measured using dynamic light scattering at a measurement temperature of 25°C, a refractive index of the solvent (water) of 1.3328, a viscosity of the solvent (water) of 0.8878 mPa s, and an accumulation number of 70. For example, an ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) can be used for the dynamic light scattering method.

[0488] The average primary particle diameter can also be measured by the following method. The dispersion is diluted with water to a solid content of 0.15% by mass, and the transmittance of 550 nm incident light per unit length of the diluted latex obtained and the number-average particle diameter determined by measuring the unidirectional diameter using a transmission electron microscope photograph are measured to prepare a calibration curve. Using this calibration curve, the average particle diameter can be calculated from the measured transmittance of 550 nm incident light of each sample.

[0489] The high-molecular-weight PTFE preferably exhibits at least one endothermic peak in the range of 333 to 347°C in a heat of fusion curve when PTFE that has not been heated to a temperature of 300°C or higher is heated at a rate of 10°C / min using a differential scanning calorimeter (DSC), and the heat of fusion between 290 and 350°C calculated from the heat of fusion curve is 52mJ / mg or more. The heat of fusion of PTFE is more preferably 55mJ / mg or more, and even more preferably 58mJ / mg or more.

[0490] (II) Melt-processable fluororesin (1) In the production method of the present disclosure, the polymerization of FEP is preferably carried out at a polymerization temperature of 10 to 150° C. and a polymerization pressure of 0.3 to 6.0 MPaG.

[0491] The monomer composition (mass %) of FEP is preferably TFE:HFP=(60-95):(5-40), more preferably (85-92):(8-15).

[0492] In addition to TFE and HFP, other monomers copolymerizable with these monomers may be polymerized to obtain a copolymer of TFE, HFP, and other monomers as FEP. Examples of the other monomers include the above-mentioned fluoromonomers (excluding TFE and HFP) and non-fluorine-containing monomers. One or more types of other monomers may be used. Perfluoro(alkyl vinyl ether) is preferred as the other monomer. The content of the other monomer units in FEP may be 0.1 to 2% by mass based on the total monomer units.

[0493] In the polymerization of the above-mentioned FEP, it is preferable to use cyclohexane, methanol, ethanol, propanol, ethane, propane, butane, pentane, hexane, carbon tetrachloride, chloroform, methylene chloride, methyl chloride, etc. as a chain transfer agent, and it is preferable to use ammonium carbonate, disodium hydrogen phosphate, etc. as a pH buffer.

[0494] (2) In the production method of the present disclosure, the polymerization of TFE / perfluoro(alkyl vinyl ether) copolymers such as PFA and MFA and TFE / perfluoroallyl ether copolymers is preferably carried out at a polymerization temperature of 10 to 100°C and a polymerization pressure of 0.3 to 6.0 MPaG.

[0495] The preferred monomer composition (mol %) of the TFE / perfluoro(alkyl vinyl ether) copolymer is TFE:perfluoro(alkyl vinyl ether)=(90-99.7):(0.3-10), more preferably (97-99):(1-3). The perfluoro(alkyl vinyl ether) is preferably a compound represented by the formula: CF ２ =CFORf ４ (wherein, Rf ４ is a perfluoroalkyl group having 1 to 6 carbon atoms).

[0496] In addition to TFE and perfluoro(alkyl vinyl ether), other monomers copolymerizable with these monomers may be polymerized to obtain a copolymer of TFE, perfluoro(alkyl vinyl ether), and other monomers as a TFE / perfluoro(alkyl vinyl ether) copolymer. Examples of the other monomers include the above-mentioned fluoromonomers (excluding TFE and perfluoro(alkyl vinyl ether)) and fluorine-free monomers. One or more types of other monomers may be used. The content of the other monomer units in the TFE / perfluoro(alkyl vinyl ether) copolymer may be 0.1 to 2 mass% based on the total monomer units.

[0497] The preferred monomer composition (mol %) of the TFE / perfluoroallyl ether copolymer is TFE:perfluoroallyl ether=(90-99.7):(0.3-10), more preferably (97-99):(1-3). The perfluoroallyl ether is a compound represented by the formula: CF ２ =CFCF ２ ORf ４ (wherein, Rf ４ is a perfluoroalkyl group having 1 to 6 carbon atoms).

[0498] In addition to TFE and perfluoroallyl ether, other monomers copolymerizable with these monomers may be polymerized to obtain a copolymer of TFE, perfluoroallyl ether, and other monomers as a TFE / perfluoroallyl ether copolymer. Examples of other monomers include the above-mentioned fluoromonomers (excluding TFE and perfluoroallyl ether) and fluorine-free monomers. One or more types of other monomers may be used. The content of other monomer units in the TFE / perfluoroallyl ether copolymer may be 0.1 to 2 mass% based on the total monomer units.

[0499] In the polymerization of the above-mentioned TFE / perfluoro(alkyl vinyl ether) copolymer and TFE / perfluoroallyl ether copolymer, it is preferable to use cyclohexane, methanol, ethanol, propanol, propane, butane, pentane, hexane, carbon tetrachloride, chloroform, methylene chloride, methyl chloride, methane, ethane, etc. as a chain transfer agent, and it is preferable to use ammonium carbonate, disodium hydrogen phosphate, etc. as a pH buffer.

[0500] Furthermore, a primer composition can be obtained by adding a nonionic surfactant to the aqueous dispersion of TFE / perfluoro(alkyl vinyl ether) copolymer such as PFA or MFA and TFE / perfluoroallyl ether copolymer, 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 the method for coating a metal surface with a fluororesin, which comprises applying this primer composition to a metal surface, applying a melt-processable fluororesin composition on the primer layer thus formed, and baking the melt-processable fluororesin composition layer together with the primer layer.

[0501] (3) In the production method of the present disclosure, the polymerization of ETFE is preferably carried out at a polymerization temperature of 10 to 100° C. and a polymerization pressure of 0.3 to 2.0 MPaG.

[0502] The preferred monomer composition (mol %) of ETFE is TFE:ethylene=(50 to 99):(50 to 1).

[0503] In addition to ethylene and TFE, other monomers that can be copolymerized with these monomers can also be polymerized to obtain the copolymer of ethylene, TFE and other monomers as ETFE.Other monomers can include the above-mentioned fluoromonomers (but excluding TFE) and non-fluorine-containing monomers (but excluding ethylene).As other monomers, one or more kinds can be used.

[0504] Other monomers include hexafluoropropylene, perfluorobutylethylene, perfluorohexylethylene, 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooct-1-ene, 2,3,3,4,4,5,5-heptafluoro-1-pentene (CH ２ =CFCF ２ CF ２ CF ２ H), 2-trifluoromethyl-3,3,3-trifluoropropene ((CF ３ ) ２ CF=CH ２ ) is preferred.

[0505] The content of other monomer units in ETFE may be 0 to 20% by mass based on the total monomer units. A preferred mass ratio is TFE:ethylene:other monomer=(63 to 94):(27 to 2):(1 to 10).

[0506] In the above polymerization of ETFE, it is preferable to use, as a chain transfer agent, cyclohexane, methanol, ethanol, propanol, ethane, propane, butane, pentane, hexane, carbon tetrachloride, chloroform, methylene chloride, methyl chloride, or the like.

[0507] (4) An electrolyte polymer precursor can also be produced using the production method of the present disclosure. In the production method of the present disclosure, the polymerization of the electrolyte polymer precursor is preferably carried out at a polymerization temperature of 10 to 100°C and a polymerization pressure of 0.1 to 2.0 MPaG. The electrolyte polymer precursor is a polymer having a -SO ２ X １５１ , -COZ １５１ or -POZ １５２ Z １５３ (X１５１ , Z １５１ , Z １５２ and Z １５３ The ion-exchange polymer is composed of a monomer containing a functional group represented by the formula (which will be described later), and can be converted into an ion-exchange polymer through hydrolysis treatment.

[0508] The monomer used for the electrolyte polymer precursor is represented by the general formula (150): CF ２ =CF-O-(CF ２ CFY １５１ -O) ｎ -(CFY １５２ ) ｍ -A １５１ (In the formula, Y １５１ represents a fluorine atom, a chlorine atom, -SO ２ It represents a F group or a perfluoroalkyl group. The perfluoroalkyl group is an etheric oxygen and -SO ２ The group n may contain an F group. n represents an integer of 0 to 3. １５１ may be the same or different. １５２ represents a fluorine atom, a chlorine atom, or —SO ２ represents an F group, and m represents an integer of 1 to 5. １５２ may be the same or different. １５１ is -SO ２ X １５１ , -COZ １５１ or -POZ １５２ Z １５３ represents. 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 represent -NR １５４ R １５５ Or -OR １５６ Represents R １５１ , R １５２ , R １５３ , R １５４ , R １５５ and R １５６are 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. ) Examples of the monomer used for the electrolyte polymer precursor include a compound containing two fluorosulfonyl groups described in WO 2007 / 013532, and -SO ２ Examples also include perfluoromonomers having an F group and a dioxolane ring. The preferred monomer composition (mol %) of the electrolyte polymer precursor is TFE:vinyl ether=(50 to 99):(50 to 1), more preferably TFE:vinyl ether=(50 to 93):(50 to 7).

[0509] The electrolyte polymer precursor may be modified with a third monomer in an amount of 0 to 20% by mass of the total monomers, such as CTFE, vinylidene fluoride, perfluoroalkyl vinyl ether, perfluorobutenyl vinyl ether, cyclic monomers such as perfluoro-2,2-dimethyl-1,3-dioxolane and perfluoro-2-methylene-4-methyl-1,3-dioxole, and polyfunctional monomers such as divinylbenzene.

[0510] The electrolyte polymer precursor thus obtained can be formed into a membrane, for example, and then subjected to hydrolysis with an alkaline solution and treatment with a mineral acid to form a polymer electrolyte membrane, which can be used in fuel cells, electrolysis devices, redox flow batteries, and the like. Alternatively, an electrolyte polymer dispersion can be obtained by subjecting the electrolyte polymer precursor to hydrolysis with an alkaline solution while maintaining its dispersed state. Subsequently, the electrolyte polymer precursor can be dissolved in, for example, a water / alcohol mixed solvent by heating to 120°C or higher in a pressure vessel to form a solution. The solution thus obtained can be used, for example, as a binder for electrodes, or can be combined with various additives and cast into a membrane, which can be used, for example, as an antifouling coating film or an organic actuator.

[0511] (5) TFE / VDF Copolymer In the production method of the present disclosure, the polymerization temperature for the TFE / VDF copolymer is not particularly limited and may be 0 to 100° C. The polymerization pressure is determined appropriately depending on other polymerization conditions such as the polymerization temperature, but may usually be 0 to 9.8 MPaG.

[0512] The preferred monomer composition (mol %) of the TFE / VDF copolymer is TFE:VDF=(5-90):(95-10). The TFE / VDF copolymer may also be modified with a third monomer within the range of 0-50 mol % of the total monomers. The preferred ratio is TFE:ethylene:third monomer=(30-85):(10-69.9):(0.1-10).

[0513] The third monomer may be a compound represented by the formula: CX １１ X １２ =CX １３ (CX １４ X １５ ) ｎ１１ X １６ (In the formula, X １１ ~X １６ are the same or different and represent H, F or Cl, and n11 represents an integer of 0 to 8, excluding TFE and VDF, or a monomer represented by the formula: CX ２１ X ２２ =CX ２３ -O(CX ２４ X ２５ ) ｎ２１ X ２６ (In the formula, X ２１ ~X ２６ are the same or different and represent H, F or Cl, and n21 represents an integer of 0 to 8.

[0514] The third monomer may also be a fluorine-free ethylenic monomer. In order to maintain heat resistance and chemical resistance, the fluorine-free ethylenic monomer is preferably selected from ethylenic monomers having 6 or less carbon atoms. Examples include ethylene, propylene, 1-butene, 2-butene, vinyl chloride, vinylidene chloride, alkyl vinyl ethers (methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, etc.), maleic acid, itaconic acid, 3-butenoic acid, 4-pentenoic acid vinyl sulfonic acid, acrylic acid, and methacrylic acid.

[0515] It is also preferred to coat the aqueous dispersion of the TFE / VDF copolymer on a porous substrate made of polyolefin resin and use it as a composite porous membrane.It is also preferred to disperse inorganic particles and / or organic particles in the aqueous dispersion, coat it on a porous substrate and use it as a composite porous membrane.The composite porous membrane obtained in this way can be used as a separator for lithium secondary batteries, etc.

[0516] The aqueous fluoropolymer dispersion of the present disclosure can be suitably used in coating compositions, and can be suitably used in liquid coating compositions.The coating composition of the present disclosure contains an aqueous fluoropolymer dispersion with a reduced content of fluorine-containing compounds having hydrophilic groups with 7 or less carbon atoms, and therefore provides a film with a large contact angle and a small friction coefficient.The reason for this is not clear, but it is presumed that the dispersion stability of the fluoropolymer particles in the coating composition is moderately low due to the inclusion of an aqueous fluoropolymer dispersion with a low content of fluorine-containing compounds having hydrophilic groups, and therefore, during film formation, the fluoropolymer particles are more likely to float to the surface of the film than other components, resulting in a high content of fluoropolymer on the film surface.

[0517] The coating composition of the present disclosure may contain other components in addition to the above-described aqueous fluoropolymer dispersion, such as a film-forming agent and a binder resin.

[0518] The coating composition of the present disclosure can be prepared by mixing the aqueous fluoropolymer dispersion of the present disclosure with other components. Alternatively, the aqueous fluoropolymer dispersion of the present disclosure and an aqueous medium may be mixed to prepare a coating composition with an adjusted solids concentration. Alternatively, the aqueous fluoropolymer dispersion of the present disclosure and a nonionic surfactant may be mixed to prepare a coating composition with an adjusted nonionic surfactant content. The coating composition of the present disclosure may have a different fluoropolymer content from the aqueous fluoropolymer dispersion of the present disclosure, or may have a different nonionic surfactant content from the aqueous fluoropolymer dispersion of the present disclosure.

[0519] In one embodiment, the coating composition of the present disclosure contains a fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms. The content of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms in the coating composition is more than 0 ppb by mass and less than 300 ppb by mass, relative to the coating composition. A preferred upper limit of the content of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms in the coating composition is 280 ppb by mass or less, 260 ppb by mass or less, 240 ppb by mass or less, 220 ppb by mass or less, 200 ppb by mass or less, 180 ppb by mass or less, 160 ppb by mass or less, or 140 ppb by mass or less. A preferred lower limit of the content of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms in the coating composition is 0.1 ppb by mass or more, 1 ppb by mass or more, 5 ppb by mass or more, 10 ppb by mass or more, 20 ppb by mass or more, 30 ppb by mass or more, 40 ppb by mass or more, or 50 ppb by mass or more.

[0520] Examples of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms include those described above as the fluorine-containing surfactants having 7 or less carbon atoms used in the polymerization of fluoromonomers. That is, in one embodiment of the coating composition, the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms contains at least a fluorine-containing surfactant having 7 or less carbon atoms.

[0521] In one embodiment, the coating composition of the present disclosure contains a fluorine-containing compound having a hydrophilic group. The content of the fluorine-containing compound having a hydrophilic group in the coating composition is more than 0 ppb by mass and less than 300 ppb by mass, based on the coating composition. The upper limit of the content of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms in the coating composition is preferably 280 ppb by mass or less, 260 ppb by mass or less, 240 ppb by mass or less, 220 ppb by mass or less, 200 ppb by mass or less, 180 ppb by mass or less, 160 ppb by mass or less, or 140 ppb by mass or less. The lower limit of the content of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms in the coating composition is preferably 0.1 ppb by mass or more, 1 ppb by mass or more, 5 ppb by mass or more, 10 ppb by mass or more, 20 ppb by mass or more, 30 ppb by mass or more, 40 ppb by mass or more, or 50 ppb by mass or more.

[0522] Examples of the fluorine-containing compound having a hydrophilic group include those fluorine-containing surfactants used in the polymerization of fluoromonomers, which are mentioned above.

[0523] <Film-forming agent> In one embodiment of the coating composition of the present disclosure, a film-forming agent is contained. When a film-forming agent is contained, the coating composition can suppress the occurrence of cracks when the resulting coating is dried, and the coating composition has excellent workability.

[0524] Examples of the film-forming agent include acrylic resins such as depolymerizable acrylic resins, urethane resins, polyethylene glycol, and polypropylene glycol.

[0525] When the coating composition of the present disclosure is applied, dried, and then baked, the depolymerizable acrylic resin gradually decomposes while maintaining its binding effect on the fluoropolymer, thereby preventing the occurrence of cracks.

[0526] In one embodiment of the coating composition of the present disclosure, a depolymerizable acrylic resin is contained in addition to PTFE. The depolymerizable acrylic resin preferably remains up to the temperature at which PTFE begins to melt (melting temperature), even if depolymerization begins below the melting point of PTFE, and decomposes and volatilizes at the baking (processing) temperature. For example, at the melting temperature of PTFE (usually 240-345°C), 5% or more, particularly 10% or more, at least 50%, and preferably at least 20%, remain, but at the baking (processing) temperature (usually a temperature above the melting temperature of PTFE and up to 415°C, preferably 360-400°C), only 10% or less, particularly 5% or less remain, and essentially none remain at the completion of baking. From this perspective, the depolymerization (decomposition) temperature of the depolymerizable acrylic resin is preferably about 200°C or higher but lower than the baking (processing) temperature. In particular, regardless of the type of resin, a depolymerizable acrylic resin that remains at about 25 to 50% in the temperature range of 300 to 320°C and at about 20 to 10% in the temperature range of 330 to 345°C is suitable in terms of the balance between the effect of preventing shrinkage cracking and the effect of preventing discoloration, and any depolymerizable acrylic resin that satisfies this condition can be used.

[0527] As described in "Polym. Eng. Soi., Vol. 6, p. 273 (1966)," "Plast. Massy., Vol. 75, p. 48 (1971)," and "Deterioration of Polymer Materials," Corona Publishing, p. 144 (1958), the more branches there are in the polymer chain, the weaker the C-C bond and C-H bond become, and the easier it is to undergo oxidative decomposition and depolymerization. Examples of depolymerizable acrylic resins include methacrylate resins, and specific examples thereof include those represented by the formula (8): CH ２ =C(CH ３Preferred examples include methacrylate homopolymers or copolymers essentially containing a methacrylate monomer represented by the formula: )COOR (wherein R is an alkyl or hydroxyalkyl group having 1 to 5 carbon atoms). Specific examples of methacrylate monomers that are preferably used include methyl methacrylate, ethyl methacrylate, propyl methacrylate, dimethylpropyl methacrylate, butyl methacrylate, and pentyl methacrylate. Of these, depolymerizable acrylic resins containing butyl methacrylate as a monomer are preferred because of their low glass transition temperature and good depolymerizability (decomposability).

[0528] Although there is no problem if a stable emulsion can be formed using a homopolymer, from the viewpoint of stabilizing the emulsion, a monomer having a carboxyl group or a hydroxyl group may be used as a comonomer as appropriate.

[0529] The depolymerizable acrylic resin can be used as fine particles (depolymerizable acrylic resin emulsion) produced by a method such as emulsion polymerization, and the average particle size is preferably 0.1 to 100 μm, particularly 0.2 to 1 μm. Particles with an average particle size of less than 0.1 μm tend to easily cause mud cracking, while particles with an average particle size of more than 100 μm tend to make coating difficult.

[0530] In the coating composition of the present disclosure, the content of the depolymerizable acrylic resin is preferably 5 to 25 parts, more preferably 7 to 20 parts, and even more preferably 10 to 15 parts per 100 parts of the fluoropolymer, from the viewpoints of film-forming properties and prevention of coloration of the coating.

[0531] The depolymerizable acrylic resin is preferably mixed with the other ingredients in the form of an emulsion.

[0532] <Binder Resin> In one embodiment of the coating composition of the present disclosure, a binder resin is contained. When a binder resin is contained, the coating composition can provide a film with excellent adhesion to the substrate. The binder resin has the effect of improving the film hardness and gloss of the resulting film.

[0533] Examples of binder resins include polyamideimide (PAI), polyimide (PI), polyethersulfone (PES), polyarylene sulfide (PAS), polyetherimide, polyetheretherketone, aromatic polyester, etc. The binder resins may be used alone or in combination of two or more.

[0534] PAI is a resin made of a polymer having an amide bond and an imide bond in its molecular structure. There are no particular limitations on the PAI. Examples of PAI include, but are not limited to, resins made of high-molecular-weight polymers obtained by various reactions, such as the reaction of an aromatic diamine having an amide bond in the molecule with an aromatic tetracarboxylic acid such as pyromellitic acid; the reaction of an aromatic tricarboxylic acid such as trimellitic anhydride with a diamine such as 4,4-diaminophenyl ether or a diisocyanate such as diphenylmethane diisocyanate; and the reaction of a dibasic acid having an aromatic imide ring in the molecule with a diamine. As PAI, those made of a polymer having an aromatic ring in the main chain are preferred because of their excellent heat resistance.

[0535] PI is a resin made of a polymer having an imide bond in its molecular structure. There are no particular limitations on the PI, but examples include resins made of high-molecular-weight polymers obtained by the reaction of aromatic tetracarboxylic anhydrides such as pyromellitic anhydride. As PI, those made of polymers having an aromatic ring in the main chain are preferred because of their excellent heat resistance.

[0536] PES is represented by the following general formula:

[0537]

[0538] The PES is not particularly limited, but examples thereof include a resin made of a polymer obtained by polycondensation of dichlorodiphenyl sulfone and bisphenol.

[0539] PAS is a resin made of a polymer having a repeating unit represented by the general formula -[Ar-S]- (wherein Ar represents an arylene group). The PAS is not particularly limited, but examples thereof include polyphenylene sulfide (PPS).

[0540] As the binder resin, at least one selected from the group consisting of PAI, PI, PES, and PPS is preferred, with PAI being more preferred, as it can provide a film with even better adhesion to the substrate. Furthermore, PES is preferred as the binder resin, as it can suppress coloration during baking and increase the degree of freedom in the color tone of the film. Using a combination of PAI and PES as the binder resin is also a preferred embodiment.

[0541] In the coating composition of the present disclosure, the content of the binder resin is preferably 5% by mass or more, more preferably 8% by mass or more, and preferably 15% by mass or less, more preferably 12% by mass or less, based on the coating composition. When the content of the binder resin is within the above range, a coating having even better adhesion to the substrate can be obtained.

[0542] In the coating composition of the present disclosure, the mass ratio of the fluoropolymer to the binder resin (fluoropolymer / binder resin) is preferably 90 / 10 to 50 / 50, more preferably 85 / 15 to 60 / 40, and even more preferably 80 / 20 to 70 / 30. When the mass ratio of the fluoropolymer to the binder resin is within the above range, a coating having even better adhesion to the substrate can be obtained.

[0543] The coating composition of the present disclosure may contain other components, such as preservatives, water-soluble polymer compounds, pigments, fillers, antifoaming agents, drying agents, thickeners, organic solvents, leveling agents, anti-cracking agents, dispersants, antifreezing agents, solid lubricants, anti-settling agents, moisture absorbers, surface conditioners, thixotropy-imparting agents, viscosity modifiers, anti-gelling agents, UV absorbers, HALS (light stabilizers), matting agents, plasticizers, anti-color separation agents, anti-skinning agents, anti-scratch agents, rust inhibitors, mildew inhibitors, antibacterial agents, antioxidants, flame retardants, anti-sagging agents, antistatic agents, silane coupling agents, various reinforcing agents, various extenders, conductive fillers, and colloidal silica.

[0544] The paint composition of the present disclosure contains a preservative, which makes it possible to inhibit spoilage and bacterial growth of the paint composition even when the paint composition is stored for a long period of time.

[0545] Examples of preservatives include isothiazolones, azoles, pronopol, chlorothalonil, methylsulfonyltetrachloropyrrolidin, carbentazim, fluorophorbet, sodium diacetate, and diiodomethyl-paratolylsulfone.

[0546] The content of the preservative in the coating composition of the present disclosure is preferably 0.01 to 0.5 mass %, more preferably 0.05 to 0.2 mass %, relative to the fluoropolymer.

[0547] Examples of the water-soluble polymer compound include methyl cellulose, alumina sol, polyvinyl alcohol, carboxylated vinyl polymer, polyethylene oxide (dispersion stabilizer), polyethylene glycol (dispersion stabilizer), polyvinylpyrrolidone (dispersion stabilizer), phenol resin, urea resin, epoxy resin, melamine resin, polyester resin, polyether resin, acrylic silicone resin, silicone resin, silicone polyester resin, and polyurethane resin.

[0548] As the pigment, various conventionally known pigments can be used, such as titanium oxide, carbon black, red iron oxide, extender pigments, etc. In the coating composition of the present disclosure, the content of the pigment is preferably 0.1 to 20.0% by mass, and more preferably 1 to 10% by mass, relative to the coating composition.

[0549] Examples of the filler include inorganic fillers, diamond, fluorinated diamond, and carbon black.

[0550] Examples of inorganic fillers include pigments, mica particles, mica particles coated with pigments, titanium-coated mica, inorganic nitrides, carbides, borides and oxides of zirconium, tantalum, titanium, tungsten, silicon, aluminum or beryllium (specifically, aluminum oxide, silicon carbide, zirconium oxide, zirconium carbide, etc.), metal flakes, metal powder, clay, talc, tourmaline, jade, germanium, corundum, silica stone, chrysoberyl, topaz, beryl, garnet, quartz, garnet, barium sulfate, glass, and the like.

[0551] The inorganic filler provides the function of improving abrasion resistance, and mica is preferred in terms of aesthetic appearance. The particle size of the mica particles is 10 to 100 μm, preferably 15 to 50 μm. If the particle size is less than 10 μm, the abrasion resistance and brilliance tend to decrease, and if it exceeds 100 μm, the non-stickiness tends to decrease. The mica particles coated with a pigment are, for example, TiO ２ Fe ２ O ３ The pigment can be obtained by adhering the above pigment to the mica particles by a sintering deposition method or the like.

[0552] Examples of metal flakes include flakes of titanium, zirconium, aluminum, zinc, antimony, tin, iron, nickel, etc., but titanium and zirconium are preferred from the viewpoint of rust resistance. The size of the flakes can be within the range of sizes normally used in paints.

[0553] Examples of metal powders include powders of gold, silver, copper, platinum, and stainless steel.

[0554] As the defoaming agent, various aqueous defoaming agents can be used, and examples thereof include lower alcohols such as methanol, ethanol, butanol, etc.; higher alcohols such as amyl alcohol, polypropylene glycol and derivatives thereof; oils and fats such as oleic acid, tall oil, mineral oil, soap, etc.; surfactants such as sorbitan fatty acid esters, polyethylene glycol fatty acid esters, Pluronic (registered trademark) type nonionic surfactants, etc.; and silicone surfactants such as siloxanes, silicone resins, etc., which can be used alone or in combination. Representative commercially available defoaming agents include B-series products such as Adekanate B and Adekanate B1068 (manufactured by Asahi Denka Kogyo Co., Ltd.); SN Deformer series products such as Formaster DL, Nopco NXZ, and SN Deformer 113, 325, 308, and 368; Dehydran 1293 and Dehydran 1513 (manufactured by San Nopco Ltd.); Flonone SB-110N, SB-210, 510, and 551, and Aqualene 800 and 805. , Aqualene 1488 (manufactured by Kyoeisha Chemical Co., Ltd.); Surfynol 104E, 440 (acetylene-based defoamers manufactured by Air Products Co., Ltd.); KS-607A (manufactured by Shin-Etsu Chemical Co., Ltd.); FS Antifoam (manufactured by Dow Corning Corporation); BYK-020, 031, 073, W (manufactured by BYK-Chemie); Dehydran 981 (manufactured by Henkel Hakusui Chemical Co., Ltd.); Epan-410, 710, 720 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.); Tego Foamex series (manufactured by Tego Goldschmidt); Foamrex-747, TY-10, EP series (manufactured by Nicca Chemical Co., Ltd.). The content of the defoamer in the coating composition is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass.

[0555] An example of the desiccant is cobalt oxide.

[0556] Examples of thickeners include methyl cellulose, polyvinyl alcohol, carboxylated vinyl polymers, etc. In the coating composition of the present disclosure, the content of the thickener is preferably 0.1 to 20% by mass, and more preferably 0.5 to 10% by mass.

[0557] The organic solvent is preferably a high-boiling polyhydric alcohol, which can prevent mud cracks from occurring when the coating composition of the present disclosure is applied and then dried.

[0558] A high-boiling polyhydric alcohol (hereinafter referred to as "polyhydric alcohol") has two or more hydroxyl groups and a boiling point of 100°C or higher. Polyhydric alcohols containing nitrogen atoms are not preferred because they cause discoloration due to thermal decomposition during baking. Preferably, the boiling point is at or above the drying temperature of the coating composition, more preferably at or above 150°C, and particularly at or above 200°C. The preferred number of hydroxyl groups in a polyhydric alcohol is 2 to 3. Substances with one or no hydroxyl group and a boiling point of 100°C or higher have poor hydrophilicity, making uniform mixing difficult. Many polyhydric alcohols with four or more hydroxyl groups are solid at room temperature, making it difficult to expect mud crack prevention effects.

[0559] The polyhydric alcohol must be completely evaporated or decomposed and vaporized by heating during the baking process described below. Therefore, it is preferable that the boiling point or thermal decomposition temperature is equal to or lower than the melting temperature of the fluoropolymer contained in the coating composition, preferably 340°C or lower.

[0560] Suitable polyhydric alcohols include, for example, one or more of ethylene glycol (boiling point: 198°C), 1,2-propanediol (boiling point: 188°C), 1,3-propanediol (boiling point: 214°C), 1,2-butanediol (boiling point: 190°C), 1,3-butanediol (boiling point: 208°C), 1,4-butanediol (boiling point: 229°C), 1,5-pentanediol (boiling point: 242°C), 2-butene-1,4-diol (boiling point: 235°C), glycerin (boiling point: 290°C), 2-ethyl-2-hydroxymethyl-1,3-propanediol (boiling point: 295°C), and 1,2,6-hexanetriol (boiling point: 178°C under 5 mmHg pressure). Of these, glycerin is preferred.

[0561] In the coating composition of the present disclosure, the content of the polyhydric alcohol is generally 5 to 18 mass %, preferably 7 to 15 mass %, and particularly preferably 7 to 12 mass %, relative to the fluoropolymer. By keeping the content of the polyhydric alcohol within the above range, it is possible to prevent the occurrence of mud cracks while preventing discoloration of the resulting coating.

[0562] If necessary, organic solvents other than the high-boiling polyhydric alcohols may be blended within a range that does not impair the effects of the present disclosure. Examples of such organic solvents include aromatic hydrocarbon solvents such as toluene and xylene, aliphatic hydrocarbon solvents having 9 to 11 carbon atoms, and aliphatic hydrocarbon solvents having 10 to 12 carbon atoms.

[0563] By using the coating composition of the present disclosure, a film can be obtained. The film obtained from the coating composition of the present disclosure has excellent water and oil repellency and low friction.

[0564] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0565] <1> According to a first aspect of the present disclosure, there is provided a method for producing an aqueous fluoropolymer dispersion containing a fluoropolymer, comprising the steps of: 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; heat-treating the aqueous dispersion; adding a nonionic surfactant to the heat-treated aqueous dispersion; contacting the aqueous dispersion containing the nonionic surfactant with an ion exchange resin; and concentrating the aqueous dispersion obtained after contact with the ion exchange resin. <2> According to a second aspect of the present disclosure, there is provided a method according to the first aspect, wherein, after preparing an aqueous dispersion by polymerization and before heat-treating the aqueous dispersion, at least one of the following operations is carried out: (a) removing the fluoromonomer remaining in the reactor from the reactor; and (b) recovering the aqueous dispersion in the reactor and storing it in a container different from the reactor. <3> According to a third aspect of the present disclosure, there is provided a production method according to the second aspect, in which a radical generator is added to the aqueous dispersion after performing at least one of the operations (a) and (b) and before heat-treating the aqueous dispersion. <4> According to a fourth aspect of the present disclosure, there is provided a production method according to any of the first to third aspects, in which an aqueous dispersion containing a radical generator is prepared by adding a radical generator to the aqueous dispersion after preparing the aqueous dispersion by polymerization and before heat-treating the aqueous dispersion. <5> According to a fifth aspect of the present disclosure, there is provided a production method according to any of the first to fourth aspects, in which the heat treatment temperature is 50°C or higher. <6> According to a sixth aspect of the present disclosure, there is provided a production method according to the fifth aspect, in which the aqueous dispersion is cooled to less than 50°C after heat-treating and before contacting the aqueous dispersion with an ion exchange resin. <7> According to a seventh aspect of the present disclosure, there is provided a production method according to any one of the first to sixth aspects, in which an aqueous dispersion is prepared in which the content of the nonionic surfactant in the aqueous dispersion is 5 mass % or more relative to the fluoropolymer by adding a nonionic surfactant to the heat-treated aqueous dispersion.<8> According to an eighth aspect of the present disclosure, there is provided a production method according to any one of the first to seventh aspects, wherein the nonionic surfactant is represented by general formula (i): R. ６ -O-A １ -H (i) (wherein, R ６ is a linear or branched primary or secondary alkyl group having 8 to 18 carbon atoms, and A １ is a polyoxyalkylene chain.) <9> According to a ninth aspect of the present disclosure, there is provided a production method according to any one of the first to eighth aspects, in which contact of the aqueous dispersion with the ion exchange resin is repeated two or more times. <10> According to a tenth aspect of the present disclosure, there is provided a production method according to any one of the first to ninth aspects, in which the aqueous dispersion is concentrated by a method of separating the aqueous dispersion into two or more phases and recovering the concentrated phase. <11> According to an eleventh aspect of the present disclosure, there is provided a production method according to any one of the first to tenth aspects, in which a nonionic surfactant is added to the concentrated aqueous dispersion. <12> According to a twelfth aspect of the present disclosure, there is provided an aqueous fluoropolymer dispersion comprising a fluoropolymer, a nonionic surfactant, and a fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms, wherein the fluoropolymer content is 50 to 70 mass% relative to the aqueous fluoropolymer dispersion, the nonionic surfactant content is 4.0 to 12 mass% relative to the fluoropolymer, and the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms is more than 0 ppb by mass and less than 300 ppb by mass relative to the aqueous fluoropolymer dispersion. <13> According to a thirteenth aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to the twelfth aspect, wherein the nonionic surfactant is represented by general formula (i): ６ -O-A １ -H (i) (wherein, R ６ is a linear or branched primary or secondary alkyl group having 8 to 18 carbon atoms, and A １is a polyoxyalkylene chain.) <14> According to a fourteenth aspect of the present disclosure, there is provided an aqueous fluoropolymer dispersion according to the twelfth or thirteenth aspect, in which the fluoropolymer contains a perfluoro(alkyl vinyl ether) unit. <15> According to a fifteenth aspect of the present disclosure, there is provided an aqueous fluoropolymer dispersion according to the fourteenth aspect, in which the fluoropolymer is substantially free of a fluorine-containing compound having a hydrophilic group represented by general formula (2). General formula (2): [C ｎ－１ F ２ｎ－１ COO － ]M ＋ (wherein n is an integer of 9 to 14, M ＋ represents a cation.) <16> According to a sixteenth aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to any one of the twelfth to fifteenth aspects, wherein the fluoropolymer is polytetrafluoroethylene. <17> According to a seventeenth aspect of the present disclosure, there is provided a coating composition containing the aqueous fluoropolymer dispersion according to any one of the twelfth to sixteenth aspects.

[0566] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0567] The values ​​in the examples were measured by the following methods.

[0568] (1) Solid content concentration (P) Approximately 1 g (X g) of a sample was placed in an aluminum cup with a diameter of 5 cm, heated at 110°C for 30 minutes, and further heated at 300°C for 30 minutes. Based on the heating residue (Z g), P was determined using the formula: P = Z / X × 100 (mass%).

[0569] (2) Average primary particle size The PTFE aqueous dispersion was diluted with water to a solid content of 0.15% by mass, and the transmittance of the 550 nm incident light per unit length of the diluted aqueous dispersion was measured, and the number-based average primary particle size was determined by measuring the unidirectional diameter using a transmission electron microscope photograph, to create a calibration curve. Using this calibration curve, the average primary particle size was determined from the measured transmittance of the 550 nm incident light of each sample.

[0570] (3) pH Using a glass electrode (manufactured by Horiba, Ltd.), the pH at 25° C. was measured in accordance with JIS K6893.

[0571] (4) Standard Specific Gravity (SSG) Using a sample molded in accordance with ASTM D4895-89, it was measured by the water displacement method in accordance with ASTM D-792.

[0572] (5) Content of modified monomer The perfluoro(propyl vinyl ether) (PPVE) content was determined by press-molding PTFE powder to prepare a thin film disk, measuring the infrared absorbance of the thin film disk by FT-IR, and determining the content of perfluoro(propyl vinyl ether) (PPVE) at 995 cm －１ Absorbance at / 935 cm －１ The absorbance ratio was calculated by multiplying the absorbance ratio at 0.14.

[0573] (6) Nonionic surfactant content (N) Approximately 1 g (X g) of a sample was placed in an aluminum cup with a diameter of 5 cm and heated at 110°C for 30 minutes to obtain the heating residue (Y g). The heating residue (Y g) was then heated at 300°C for 30 minutes to obtain the heating residue (Z g). The amount calculated from the formula: N = [(Y - Z) / Z] x 100 (mass%) minus the amount of stabilizer was used to determine the nonionic surfactant content. The stabilizer was calculated based on the amount added during preparation.

[0574] (7) Viscosity The viscosity was measured at 25° C. using a B-type rotational viscometer (manufactured by Toki Sangyo Co., Ltd., rotor No. 2) at a rotation speed of 60 rpm for a measurement time of 120 seconds.

[0575] (8) Measurement of the content of fluorine-containing compounds having a hydrophilic group having 7 or less carbon atoms 5.0 g of the aqueous dispersion was weighed, 10 g of methanol was added, and the mixture was poured into a cylindrical filter paper. Soxhlet extraction was performed so that the total amount of methanol used as the extraction solvent became 150 g, and the resulting extract was made up to volume with methanol to 250 ml, thereby obtaining an extract containing fluorine-containing compounds having a hydrophilic group having 7 or less carbon atoms.

[0576] Five levels of methanol standard solutions of fluorine-containing compounds having a hydrophilic group with 7 or less carbon atoms at known concentrations of 0.1 to 100 ng / mL were prepared, and measurements were carried out using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC / TQD). A calibration curve was created using a first-order approximation from the respective sample concentrations and peak integral values.

[0577] The content of fluorine-containing compounds having a hydrophilic group with a carbon number of 7 or less was measured using a liquid chromatograph mass spectrometer. The peak area of ​​the fluorine-containing compounds having a hydrophilic group with a carbon number of 7 or less was determined for the extract by MRM, and the content of the fluorine-containing compounds having a hydrophilic group with a carbon number of 7 or less contained in the aqueous dispersion was determined. The quantitation limit was 10 ppb by mass.

[0578] (9) Measurement of the content of the fluorine-containing compound having a hydrophilic group represented by general formula (2) 5.0 g of the aqueous dispersion was weighed, 10 g of methanol was added, and the mixture was poured into a cylindrical filter paper, followed by Soxhlet extraction so that the total amount of methanol used as the extraction solvent became 150 g, and the resulting extract was adjusted to a constant volume of 250 ml with methanol to obtain an extract containing a fluorine-containing compound having a hydrophilic group represented by general formula (2). ｎ－１ F ２ｎ－１ COO － ]M ＋ (wherein n is an integer of 9 to 14, M ＋ represents a cation.)

[0579] Calibration curve Five levels of methanol standard solutions of perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), perfluorododecanoic acid (PFDoDA), perfluorotridecanoic acid (PFTrDA), and perfluorotetradecanoic acid (PFTeDA) with known concentrations of 0.1 to 50 ng / mL were prepared, and measurements were performed 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.

[0580] The content of the fluorine-containing compound having a hydrophilic group represented by general formula (2) was measured using a liquid chromatograph mass spectrometer. The peak area of ​​the fluorine-containing compound having a hydrophilic group represented by general formula (2) was determined for the extract by MRM, and the content of the fluorine-containing compound having a hydrophilic group represented by general formula (2) contained in the aqueous dispersion was determined. The quantitation limit was 10 ppb by mass.

[0581] Measurement equipment configuration and LC-MS measurement conditions

[0582] MRM measurement parameters

[0583] The average molecular structures of the surfactants used in the examples and comparative examples are shown below. Surfactant (a): C １３ H ２７ O (CH ２ CH ２ O) ８ H (average number of methyl groups per molecule: 4.0), HLB: 13.30, cloud point: 60°C Surfactant (b): C １３ H ２７ O (CH ２ CH ２ O) １０ H (average number of methyl groups per molecule: 4.0), HLB: 13.80, cloud point: 71°C

[0584] Synthesis Example 1 A white solid A was obtained by the method described in Synthesis Example 1 of WO 2021 / 045228. The obtained white solid A was a fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms.

[0585] Production Example 1: 3,580 g of deionized water, 160 g of paraffin wax, and 4.7 g of the white solid A obtained in Synthesis Example 1 as a fluorine-containing surfactant were placed in a 6 L stainless steel reactor equipped with a stirrer. The contents of the reactor were then heated to 70°C while being aspirated and simultaneously purged with TFE to remove oxygen from the reactor, and the contents were stirred. 6.5 g of PPVE was injected into the reactor using TFE. 50 mg of APS dissolved in 20 g of deionized water was injected into the reactor as an initiator, and the pressure was adjusted to 1.5 MPaG. TFE was added to maintain a constant pressure of 1.5 MPaG. When the amount of TFE consumed in the reaction reached 1,543 g, the supply of TFE was stopped, stirring was stopped, and the reaction was terminated.

[0586] Thereafter, the reactor was evacuated until the pressure inside it reached atmospheric pressure, and then the pressure was further reduced to −0.01 MPaG. Nitrogen was then introduced into the reactor to return it to atmospheric pressure (0.00 MPaG), and an aqueous PTFE dispersion 1-1 was obtained.

[0587] The PTFE aqueous dispersion 1-1 was taken out of the reactor into the atmosphere and cooled, and the paraffin wax was removed to obtain a PTFE aqueous dispersion 1-2. The resulting PTFE aqueous dispersion 1-2 had a solids concentration of 30.0 mass% and an average primary particle diameter of 270 nm.

[0588] The resulting PTFE aqueous dispersion 1-2 was diluted with deionized water to a solids concentration of approximately 10% by mass, coagulated under high-speed stirring conditions, and the coagulated wet powder was dried for 18 hours at 150° C. The resulting PTFE powder had a standard specific gravity of 2.163 and a PPVE content of 0.28% by mass.

[0589] Comparative Example 1 A PTFE aqueous dispersion C-1 was prepared by adding a surfactant (a) as a nonionic surfactant to the PTFE aqueous dispersion 1-2 obtained in Production Example 1 in an amount of 10 parts by mass relative to 100 parts by mass of PTFE. A strongly basic anion exchange resin was added to the PTFE aqueous dispersion C-1 in an amount of 60 parts by mass relative to 100 parts by mass of PTFE, and the mixture was gently stirred for 180 minutes, after which the anion exchange resin was separated by filtration to obtain a PTFE aqueous dispersion C-2.

[0590] Furthermore, the anion exchange resin was again added to the PTFE aqueous dispersion C-2, and after gentle stirring for 180 minutes, the anion exchange resin was separated by filtration to obtain a PTFE aqueous dispersion C-3.

[0591] To the resulting PTFE aqueous dispersion C-3, surfactant (a) was added in an amount of 16 parts by mass relative to 100 parts by mass of PTFE, and the mixture was maintained at 63°C for 3 hours to separate into an upper supernatant phase and a concentrated phase. Only the concentrated phase was collected to obtain PTFE aqueous dispersion C-4.

[0592] The resulting PTFE aqueous dispersion C-4 had a solids concentration of 69.1% by mass and a nonionic surfactant content of 2.7% by mass relative to PTFE.

[0593] To the resulting PTFE aqueous dispersion C-4, surfactant (b) was added so that the concentration was 5.0% by mass relative to PTFE, ammonium lauryl sulfate was added at 500 ppm relative to PTFE, an isothiazolone-based preservative was added at 1000 ppm relative to PTFE, and aqueous ammonia was added so that the pH was 9.5. Further, deionized water was added so that the solids content was 63% by mass, yielding PTFE aqueous dispersion C-5. The resulting PTFE aqueous dispersion C-5 had a solids concentration of 62.9% by mass, a nonionic surfactant content of 5.0% by mass relative to PTFE, a pH of 9.5, and a viscosity of 26.8 mPa s.

[0594] The content of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms, such as the fluorine-containing surfactant synthesized in Synthesis Example 1, was 560 ppb by mass relative to the aqueous dispersion.

[0595] The content of the fluorine-containing compound having a hydrophilic group represented by general formula (2) was below the limit of quantitation (10 ppb by mass) in all cases.

[0596] The entire amount of PTFE aqueous dispersion 1-2 obtained in Production Example 1 was transferred to a heat treatment container. The mixture was heated to 80°C in 30 minutes in an air atmosphere in the heat treatment container, and 2.6 g of ammonium persulfate (1.0 moles relative to the number of moles of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms in the aqueous dispersion) dissolved in 40 g of deionized water was added as a radical generator, followed by holding for 3 hours to obtain PTFE aqueous dispersion 1-3.

[0597] Except for using PTFE aqueous dispersion 1-3 instead of PTFE aqueous dispersion 1-2 obtained in Production Example 1, the same procedure as in Comparative Example 1 was repeated, except that a nonionic surfactant was added, the mixture was brought into contact with an anion exchange resin twice, and concentration by phase separation was carried out, and only the concentrated phase was recovered, thereby obtaining PTFE aqueous dispersion 1-4.

[0598] The resulting PTFE aqueous dispersion 1-4 had a solids concentration of 70.2% by mass and a nonionic surfactant content of 2.6% by mass relative to PTFE.

[0599] To the resulting PTFE aqueous dispersion 1-4, surfactant (b), ammonium lauryl sulfate, an isothiazolone-based preservative, and aqueous ammonia were added, as in Comparative Example 1. Deionized water was then added so that the solids content was 63% by mass, yielding PTFE aqueous dispersion 1-5. The resulting PTFE aqueous dispersion 1-5 had a solids concentration of 63.0% by mass, a nonionic surfactant content of 5.0% by mass relative to PTFE, a pH of 9.6, and a viscosity of 26.2 mPa s.

[0600] The content of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms, such as the fluorine-containing surfactant synthesized in Synthesis Example 1, was 110 ppb by mass relative to the aqueous dispersion.

[0601] The content of the fluorine-containing compound having a hydrophilic group represented by general formula (2) in which the carbon number n is 9 to 14 was below the limit of quantitation (10 ppb by mass) in all cases.

[0602] Example 2 To the PTFE aqueous dispersion 1-4 obtained in Example 1, surfactant (a) and deionized water were added so that the ratio of nonionic surfactant to PTFE and the ratio of water to PTFE were the same as those before the phase separation concentration in Example 1, and the mixture was maintained at 61°C for 3 hours to separate into a supernatant phase and a concentrated phase. Only the concentrated phase was recovered to obtain PTFE aqueous dispersion 2-1.

[0603] The resulting PTFE aqueous dispersion 2-1 had a solids concentration of 71.5% by mass and a nonionic surfactant content of 2.4% by mass relative to PTFE.

[0604] To the resulting PTFE aqueous dispersion 2-1, surfactant (b), ammonium lauryl sulfate, an isothiazolone preservative, and aqueous ammonia were added, as in Comparative Example 1. Deionized water was then added so that the solids content was 63% by mass, yielding PTFE aqueous dispersion 2-2. The resulting PTFE aqueous dispersion 2-2 had a solids concentration of 62.9% by mass, a nonionic surfactant content of 5.1% by mass relative to PTFE, a pH of 9.5, and a viscosity of 26.0 mPa s.

[0605] The content of the fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms, such as the fluorine-containing surfactant synthesized in Synthesis Example 1, was 52 ppb by mass relative to the aqueous dispersion.

[0606] The content of the fluorine-containing compound having a hydrophilic group represented by general formula (2) in which the carbon number n is 9 to 14 was below the limit of quantitation (10 ppb by mass) in all cases.

[0607] Next, embodiments of the coating compositions containing the aqueous PTFE dispersions obtained in the above Examples and Comparative Examples will be described with reference to Examples.

[0608] The values ​​in the examples were measured by the following methods: <Contact angle> The contact angles with water and n-cetane were measured using a contact angle meter CA-DT model manufactured by Kyowa Interface Science Co., Ltd.

[0609] <Coefficient of Friction> Using a surface property tester HEIDON Type 38 manufactured by Shinto Scientific Co., Ltd., the static and dynamic coefficients of friction were measured when a ball indenter was pressed against the surface with a load of 1 kg and moved at a speed of 600 mm / min.

[0610] In Comparative Example 2 and Examples 3 and 4, the following materials were used.

[0611] Polyamideimide resin aqueous dispersion: Aqueous dispersion of polyamideimide resin varnish prepared by the method described in Production Example 1 of WO 2016 / 147790

[0612] 50% by mass aqueous solution of nonionic surfactant: 50% by mass aqueous solution of polyoxyethylene alkyl ether

[0613] Carbon black pigment mill base (solid content: 20% by mass): A water-based black pigment paste prepared by grinding commercially available carbon black pigment (average particle size: 100 nm or less) together with a nonionic surfactant and water using a sand mill and glass beads as dispersion media.

[0614] Thickener: methyl cellulose Leveling agent: acetylene glycol Depolymerizable acrylic resin emulsion: butyl methacrylate resin, average particle size 0.3 μm, butyl methacrylate resin content 40 mass% Hydrocarbon solvent: mixture of C10 to C12 aliphatic saturated hydrocarbons

[0615] Comparative Example 2 The following components were mixed by stirring to obtain a primer composition P-1. PTFE aqueous dispersion C-5 40.0 parts Polyamideimide resin aqueous dispersion 39.0 parts 50% by weight aqueous solution of nonionic surfactant 8.0 parts Carbon black pigment mill base (solid content: 20% by weight) 3.6 parts Thickener 7.0 parts Leveling agent 1.0 part Water 1.4 parts

[0616] Furthermore, the following components were stirred and mixed to obtain a top coat composition T-1: PTFE aqueous dispersion C-5 70.0 parts Depolymerizable acrylic resin emulsion 12.6 parts 50% by mass aqueous solution of nonionic surfactant 7.9 parts Glycerin 3.1 parts Hydrocarbon solvent 1.3 parts Water 5.1 parts

[0617] Next, primer composition P-1 was applied to an aluminum substrate and dried at 100°C for 20 minutes. Subsequently, top coat composition T-1 was applied to the primer coating, dried at 100°C for 20 minutes, and then heated at 380°C for 20 minutes to obtain a coating. The contact angle and friction coefficient of this coating were measured. The results are shown in Table 3.

[0618] Example 3 A coating was obtained in the same manner as in Comparative Example 2, except that a primer composition P-2 and a top coat composition T-2 were obtained by using PTFE aqueous dispersion 1-5 instead of PTFE aqueous dispersion C-5. The contact angle and friction coefficient of this coating were measured. The results are shown in Table 3.

[0619] Example 4 A coating was obtained in the same manner as in Comparative Example 2, except that a primer composition P-3 and a top coat composition T-3 were obtained by using the PTFE aqueous dispersion 2-2 instead of the PTFE aqueous dispersion C-5. The contact angle and friction coefficient of this coating were measured. The results are shown in Table 3.

[0620]

Claims

1. A method for producing an aqueous fluoropolymer dispersion containing a fluoropolymer, 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; The aqueous dispersion is subjected to a heat treatment, A nonionic surfactant is added to the heat-treated aqueous dispersion, Contacting an aqueous dispersion containing a nonionic surfactant with an ion exchange resin; Concentrating the aqueous dispersion obtained after contact with the ion exchange resin Manufacturing method.

2. The method according to claim 1, wherein after preparing an aqueous dispersion by polymerization, before subjecting the aqueous dispersion to heat treatment, at least one of the following operations is carried out: (a) removing the fluoromonomer remaining in the reactor from the reactor; and (b) recovering the aqueous dispersion in the reactor and storing it in a container other than the reactor.

3. 3. The method according to claim 2, wherein after carrying out at least one of the operations (a) and (b), a radical generator is added to the aqueous dispersion before the aqueous dispersion is subjected to a heat treatment.

4. 3. The method according to claim 1, further comprising the step of adding a radical generator to the aqueous dispersion before subjecting the aqueous dispersion to a heat treatment after preparing the aqueous dispersion by polymerization, thereby preparing the aqueous dispersion containing the radical generator.

5. 3. The method according to claim 1, wherein the heat treatment is performed at a temperature of 50° C. or higher.

6. 6. The process according to claim 5, wherein after the heat treatment, the aqueous dispersion is cooled to less than 50° C. before contacting the aqueous dispersion with the ion exchange resin.

7. 3. The method according to claim 1 or 2, wherein a nonionic surfactant is added to the heat-treated aqueous dispersion to prepare an aqueous dispersion having a nonionic surfactant content of 5 mass% or more relative to the fluoropolymer.

8. 3. The method according to claim 1, wherein the nonionic surfactant is represented by general formula (i): R ６ -O-A １ -H (i) (In the formula, R ６ is a linear or branched primary or secondary alkyl group having 8 to 18 carbon atoms; A １ is a polyoxyalkylene chain.

9. 3. The method according to claim 1, wherein the contact of the aqueous dispersion with the ion exchange resin is repeated two or more times.

10. 3. The process according to claim 1, wherein the aqueous dispersion is concentrated by separating the aqueous dispersion into two or more phases and recovering the concentrated phase.

11. 3. The method according to claim 1 or 2, wherein a nonionic surfactant is added to the concentrated aqueous dispersion.

12. 1. An aqueous fluoropolymer dispersion comprising: The composition contains a fluoropolymer, a nonionic surfactant, and a fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms, The content of the fluoropolymer is 50 to 70% by mass based on the aqueous fluoropolymer dispersion, The content of the nonionic surfactant is 4.0 to 12% by mass based on the fluoropolymer, The content of a fluorine-containing compound having a hydrophilic group having 7 or less carbon atoms is more than 0 ppb by mass and less than 300 ppb by mass based on the aqueous fluoropolymer dispersion. Aqueous fluoropolymer dispersions.

13. The aqueous fluoropolymer dispersion according to claim 12, wherein the nonionic surfactant is represented by general formula (i): R ６ -O-A １ -H (i) (In the formula, R ６ is a linear or branched primary or secondary alkyl group having 8 to 18 carbon atoms; A １ is a polyoxyalkylene chain.

14. 14. The aqueous fluoropolymer dispersion according to claim 12 or 13, wherein the fluoropolymer contains perfluoro(alkyl vinyl ether) units.

15. The aqueous fluoropolymer dispersion according to claim 14, which is substantially free of a fluorine-containing compound having a hydrophilic group represented by formula (2). General formula (2): [C ｎ－１ F ２ｎ－１ COO － ] ＋ (wherein n is an integer from 9 to 14; M ＋ represents a cation.)

16. 14. The aqueous fluoropolymer dispersion according to claim 12 or 13, wherein the fluoropolymer is polytetrafluoroethylene.

17. A coating composition comprising the aqueous fluoropolymer dispersion according to claim 12 or 13.