Aqueous fluoropolymer dispersion

Abstract

Provided is an aqueous fluoropolymer dispersion containing: a polymer (I) having a hydrophilic group; a fluoropolymer; a non-ionic surfactant (a) having an HLB of more than 8; and an aqueous medium, wherein no fluorine-containing surfactant is substantially included, the content of the fluoropolymer is 40-70 mass% relative to the aqueous fluoropolymer dispersion, the content of the non-ionic surfactant (a) is 4.0-12 mass% relative to the fluoropolymer, and the height of foam of the aqueous fluoropolymer dispersion produced in a foaming test is no more than 140 mm.

Description

Fluoropolymer aqueous dispersion

[0001] The present disclosure relates to aqueous fluoropolymer dispersions.

[0002] Patent Document 1 describes a composition containing polytetrafluoroethylene, a polymer (I) containing polymerized units (I) based on a monomer represented by general formula (I), a nonionic surfactant, and an aqueous medium, wherein the content of the polytetrafluoroethylene in the composition is 10% by mass or more relative to the composition, and the content of the nonionic surfactant in the composition is 1.0% by mass or more relative to the polytetrafluoroethylene. １ X ３ =CX ２ R (-CZ １ Z ２ -A ０ ) ｍ (I) (wherein, X １ and X ３ are each independently F, Cl, H or CF ３ and X ２ is H, F, an alkyl group or a fluorine-containing alkyl group; A ０ is an anionic group; R is a linking group; Z １ and Z ２ are each independently H, F, an alkyl group or a fluorine-containing alkyl group; and m is an integer of 1 or more.

[0003] International Publication No. 2021 / 045227

[0004] An object of the present disclosure is to provide an aqueous fluoropolymer dispersion that is less likely to foam.

[0005] According to the present disclosure, there is provided an aqueous fluoropolymer dispersion containing a polymer (I) having a hydrophilic group, a fluoropolymer, a nonionic surfactant (a) having an HLB of more than 8, and an aqueous medium, wherein the aqueous fluoropolymer dispersion is substantially free of a fluorine-containing surfactant, the content of the fluoropolymer is 40% by mass or more and 70% by mass or less, and the content of the nonionic surfactant (a) is 4.0% by mass or more and 12% by mass or less, based on the fluoropolymer, and the height of bubbles produced by the aqueous fluoropolymer dispersion in a foamability test is 140 mm or less.

[0006] According to the present disclosure, an aqueous fluoropolymer dispersion that is less likely to foam can be provided.

[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] In the present disclosure, perfluororubber (perfluoroelastomer) is a fluoropolymer having a perfluoromonomer unit content of 90 mol% or more, preferably 91 mol% or more, relative to all polymerized units, a glass transition temperature of 20°C or less, a melting peak (ΔH) magnitude of 4.5 J / g or less, and a fluorine atom concentration of 71 mass% or more, preferably 71.5 mass% or more. In the present disclosure, the fluorine atom concentration in the fluoropolymer is determined by calculation of the concentration (mass%) of fluorine atoms in the fluoropolymer from the type and content of each monomer constituting the fluoropolymer.

[0012] In the present disclosure, a perfluoromonomer is a monomer that does not contain a carbon atom-hydrogen atom bond in the molecule. The perfluoromonomer may be a monomer containing carbon atoms and fluorine atoms, or a monomer in which some of the fluorine atoms bonded to carbon atoms have been substituted with chlorine atoms, or may contain nitrogen atoms, oxygen atoms, sulfur atoms, phosphorus atoms, boron atoms, or silicon atoms in addition to carbon atoms. The perfluoromonomer is preferably a monomer in which all hydrogen atoms have been substituted with fluorine atoms. The perfluoromonomer does not include monomers that provide crosslinking sites.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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. The organic group is preferably an alkyl group which may have one or more substituents.

[0018] 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.).

[0019] 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.).

[0020] Specific embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0021] Aqueous fluoropolymer dispersions containing a high concentration of fluoropolymer can be used for various applications in the form of an aqueous dispersion. When an aqueous fluoropolymer dispersion contains a fluoropolymer at a high concentration, the dispersion stability of the fluoropolymer in the aqueous fluoropolymer dispersion is likely to be impaired. Therefore, as described in Patent Document 1, a technique is known for improving the dispersion stability of the fluoropolymer by using a polymer (I) containing polymerized units (I) and a nonionic surfactant in an aqueous fluoropolymer dispersion.

[0022] However, it has now been found that when such an aqueous fluoropolymer dispersion is stirred, foaming may occur, which may cause a problem of reducing the quality of the final product when it is applied to various uses.A means for suppressing foaming of an aqueous fluoropolymer dispersion containing a high concentration of fluoropolymer and containing a polymer having a hydrophilic group and a nonionic surfactant has not yet been investigated.

[0023] The first aqueous fluoropolymer dispersion of the present disclosure is an aqueous fluoropolymer dispersion containing a polymer (I) having a hydrophilic group, a fluoropolymer, a nonionic surfactant (a) having an HLB of more than 8, and an aqueous medium, and is substantially free of a fluorine-containing surfactant, the content of the fluoropolymer is 40% by mass or more and 70% by mass or less, based on the aqueous fluoropolymer dispersion, the content of the nonionic surfactant (a) is 4.0% by mass or more and 12% by mass or less, based on the fluoropolymer, and the height of bubbles produced by the aqueous fluoropolymer dispersion in a foamability test is 140 mm or less.

[0024] The first aqueous fluoropolymer dispersion of the present disclosure has the above-mentioned configuration, and therefore, despite containing a high concentration of fluoropolymer, the dispersion stability of the fluoropolymer is high and the dispersion is less likely to foam. Therefore, even when the aqueous fluoropolymer dispersion is applied to various applications, problems caused by foaming of the aqueous dispersion are less likely to occur, and high-quality products can be produced.

[0025] The second aqueous fluoropolymer dispersion of the present disclosure is a fluoropolymer aqueous dispersion containing a polymer (I) having a hydrophilic group, a fluoropolymer, a nonionic surfactant (a) having an HLB of more than 8, a nonionic surfactant (b) having an HLB of 8 or less, and an aqueous medium, wherein the aqueous fluoropolymer dispersion is substantially free of a fluorine-containing surfactant, the content of the fluoropolymer is 40% by mass or more and 70% by mass or less, and the content of the nonionic surfactant (a) is 4.0% by mass or more and 12% by mass or less, based on the fluoropolymer.

[0026] The second aqueous fluoropolymer dispersion of the present disclosure has the above-mentioned configuration, and therefore, despite containing a high concentration of fluoropolymer, the dispersion stability of the fluoropolymer is high and the dispersion is less likely to foam. Therefore, even when the aqueous fluoropolymer dispersion is applied to various applications, problems caused by foaming of the aqueous dispersion are less likely to occur, and high-quality products can be produced.

[0027] The first and second aqueous fluoropolymer dispersions of the present disclosure (hereinafter, both may be simply referred to as aqueous fluoropolymer dispersions) will be described in detail below.

[0028] (Aqueous Fluoropolymer Dispersion) In one embodiment, the aqueous fluoropolymer dispersion can be characterized by a foam height produced by a foaming test of 140 mm or less.

[0029] The foam height is an index of the foaming power of the aqueous fluoropolymer dispersion. If the foam height generated in the foaming test is 140 mm or less, when the aqueous fluoropolymer dispersion is used in various applications, foam is unlikely to be generated or the generated foam is likely to disappear, so that problems caused by foaming of the aqueous dispersion are unlikely to occur and high-quality products can be produced.

[0030] The height of the foam is preferably 120 mm or less, more preferably 100 mm or less, and even more preferably 70 mm or less.

[0031] The foam height of the aqueous dispersion can be specified by adjusting the fluoropolymer content in the aqueous dispersion to 55% by mass, conducting a foamability test by the Ross-Miles method in accordance with JIS K3362, dropping the aqueous fluoropolymer dispersion with the fluoropolymer content adjusted to 55% by mass to generate foam, and measuring the foam height immediately after dropping.

[0032] In one embodiment, the fluoropolymer content of the aqueous fluoropolymer dispersion is 40% by mass or more and 70% by mass or less, preferably 45% by mass or more, more preferably 55% by mass or more, and preferably 67% by mass or less, more preferably 65% ​​by mass or less, based on the aqueous fluoropolymer dispersion.

[0033] The fluoropolymer content (P mass %) in the aqueous fluoropolymer dispersion 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: P = [Z / X] × 100 (mass %).

[0034] In one embodiment, the content of the nonionic surfactant (a) in the aqueous fluoropolymer dispersion is 4.0% by mass or more and 12% by mass or less, preferably 5.0% by mass or more, more preferably 5.5% by mass or more, and preferably 10% by mass or less, more preferably 8.0% by mass or less, based on the fluoropolymer.

[0035] The content (N mass %) of the nonionic surfactant (a) is a value calculated from the heating residue (Y g) obtained by heating about 1 g (X g) of a sample at 110°C for 30 minutes, and the heating residue (Z g) obtained by further heating the obtained heating residue (Y g) at 300°C for 30 minutes, according to the formula: N = [(Y - Z) / X] x 100 (mass %).

[0036] In one embodiment, the content of polymer (I) in the aqueous fluoropolymer dispersion is preferably 0.1 ppm by mass or more, more preferably 0.5 ppm by mass or more, even more preferably 10.0 ppm by mass or more, and preferably 2000 ppm by mass or less, more preferably 1500 ppm by mass or less, even more preferably less than 1000 ppm by mass, still more preferably 500 ppm by mass or less, and particularly preferably 250 ppm by mass or less, based on the aqueous dispersion.

[0037] In one embodiment, the content of polymer (I) in the aqueous fluoropolymer dispersion is, relative to the fluoropolymer, preferably 0.001% by mass or more, more preferably 0.005% by mass or more, even more preferably 0.01% by mass or more, particularly preferably 0.05% by mass or more, and most preferably 0.10% by mass or more, and is preferably 10% by mass or less, more preferably 5.0% by mass or less, even more preferably 2.0% by mass or less, particularly preferably 1.0% by mass or less, and most preferably 0.50% by mass or less.

[0038] The content of polymer (I) in the polymer dispersion can be determined by solid-state NMR measurement or melt NMR measurement. When polymer (I) contains a carbonyl group, it can also be determined by a Fourier transform infrared spectrometer. Further, the content of polymer (I) in the polymer dispersion can be determined by solid-state NMR measurement or melt NMR measurement. Furthermore, the content of polymer (I) in the polymer dispersion can be determined by a Fourier transform infrared spectrometer. Further, the content of polymer (I) in the polymer dispersion can be determined by a Fourier transform infrared spectrometer. Further, the content of polymer (I) in the polymer dispersion can be determined by a Fourier transform infrared spectrometer. Methods for measuring the content of each polymer are described in JP-A-2012 / 082707, JP-A-2012 / 082703, JP-A-2012 / 082451, JP-A-2006 / 135825, JP-A-2004 / 067588, JP-A-2009 / 068528, JP-A-2004-075978, JP-A-2001-226436, JP-A-1992 / 017635, JP-A-2014 / 069165, JP-A-11-181009, etc. As a method for measuring the content of polymer (I), the measurement methods for each polymer described therein can be used.

[0039] In one embodiment, the aqueous fluoropolymer dispersion is substantially free of fluorinated surfactants.

[0040] In the present disclosure, "substantially free of fluorine-containing surfactant" means that the content of fluorine-containing surfactant in the aqueous dispersion is 10 ppm by mass or less, preferably 1 ppm by mass or less, more preferably 100 ppb by mass or less, even more preferably 10 ppb by mass or less, still more preferably 1 ppb by mass or less, and particularly preferably below the detection limit of the fluorine-containing surfactant as measured by liquid chromatography-mass spectrometry (LC / MS).

[0041] The content of the fluorine-containing surfactant can be measured, for example, by adding methanol to the aqueous dispersion, extracting, and subjecting the obtained extract to LC / MS analysis. To further increase the extraction efficiency, treatments such as Soxhlet extraction and ultrasonic treatment may be performed. Molecular weight information is extracted from the obtained LC / MS spectrum, and its agreement with the structural formula of the candidate fluorine-containing surfactant is confirmed. Then, aqueous solutions containing five or more levels of the identified fluorine-containing surfactant are prepared, and LC / MS analysis is performed on the aqueous solutions containing each level. The relationship between the content and the area relative to the content is plotted, and a calibration curve is drawn. Using the calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing surfactant in the extract can be converted to the content of the fluorine-containing surfactant.

[0042] (Nonionic surfactant (b)) In one embodiment, the aqueous fluoropolymer dispersion contains a nonionic surfactant (b) having an HLB of 8 or less. The nonionic surfactant (b) having an HLB of 8 or less reduces the foaming power of the aqueous fluoropolymer dispersion and suppresses foaming when the aqueous fluoropolymer dispersion is stirred. When a nonionic surfactant with a high HLB is used, it is difficult to suppress foaming when the aqueous fluoropolymer dispersion is stirred.

[0043] The HLB value of the nonionic surfactant (b) is 8 or less, and preferably 1 or more.

[0044] In the present disclosure, the HLB of the nonionic surfactant (b) is a value defined by the Griffin method using the following calculation formula: HLB value = 20 × [sum of chemical formula weights of hydrophilic moieties] / molecular weight

[0045] The nonionic surfactant (b) is preferably at least one selected from the group consisting of acetylene diol surfactants and alkane diol surfactants.

[0046] Acetylene diol surfactants are surfactants that have a carbon-carbon triple bond in the molecule. Examples of acetylene diol surfactants include acetylene diol surfactants (which have both an acetylene bond and two hydroxyl groups in the same molecule) and surfactants in which an alkylene oxide unit is added to an acetylene diol.

[0047] As the acetylene diol surfactant, a compound represented by the general formula (11) and a compound represented by the general formula (12) are preferred.

[0048]

[0049] (In the formula, R １ and R ２ each independently represents an alkyl group having 3 to 9 carbon atoms; R ３ and R ４ each independently represents an alkylene group having 1 to 4 carbon atoms, m and n are integers, and the sum of m and n is 2 to 50.

[0050] Commercially available acetylenic diol surfactants may be used, such as Dynol (registered trademark) 607, Surfynol (registered trademark) 104E, 104H, and 420 (all manufactured by Nissin Chemical Industry Co., Ltd.).

[0051] Examples of alkanediol surfactants include surfactants having one alkylene group and two hydroxyl groups in the same molecule.

[0052] Examples of the alkanediol surfactant include a compound represented by the general formula (13) and a compound represented by the general formula (14).

[0053] HO-R ５ -OH (13) (wherein, R５ represents a linear or branched alkylene group having 1 to 200 carbon atoms.

[0054] HO-R ６ -OH (14) (wherein, R ６ represents a linear or branched polyoxyalkylene group having 1 to 200 carbon atoms.

[0055] Commercially available alkanediol surfactants may be used, such as Surfynol (registered trademark) AD01 (manufactured by Nissin Chemical Industry Co., Ltd.).

[0056] In one embodiment, the surface tension of a 0.1% aqueous solution of the nonionic surfactant (b) is 40 mN / m or less.

[0057] In the present disclosure, the surface tension of the nonionic surfactant (b) can be measured by the Wilhelmy method at 25°C.

[0058] In one embodiment, the content of the nonionic surfactant (b) is 0.2 mass% or more and 10 mass% or less, preferably 0.3 mass% or more, more preferably 0.5 mass% or more, and preferably 8.0 mass% or less, more preferably 5.0 mass% or less, based on the fluoropolymer aqueous dispersion.

[0059] The content of the nonionic surfactant (b) can be calculated from the amount of the nonionic surfactant (b) used in preparing the aqueous dispersion.

[0060] (Nonionic surfactant (a)) In one embodiment, the aqueous fluoropolymer dispersion contains a nonionic surfactant (a) having an HLB of more than 8. By using the nonionic surfactant (a), the dispersion stability of the aqueous fluoropolymer dispersion can be improved. Furthermore, the nonionic surfactant (a) smoothly promotes concentration when the aqueous fluoropolymer dispersion is concentrated by a phase separation concentration method, so that the aqueous fluoropolymer dispersion containing the nonionic surfactant (a) is easy to produce. It is usually difficult to obtain an aqueous dispersion having a fluoropolymer content of, for example, 40 mass% or more by concentrating the aqueous fluoropolymer dispersion by a phase separation concentration method using a nonionic surfactant (b) having an HLB of 8 or less instead of the nonionic surfactant (a). Therefore, the aqueous fluoropolymer dispersion containing the nonionic surfactant (a) and the nonionic surfactant (b) is easy to produce, has high dispersion stability of the fluoropolymer, and is less likely to foam, despite containing a high concentration of the fluoropolymer.

[0061] Nonionic surfactants (a) typically contain no charged groups and have a hydrophobic portion that is a long hydrocarbon chain, while the hydrophilic portion of the nonionic surfactant (a) contains a water-soluble functional group, such as an ethylene ether chain derived from polymerization with ethylene oxide.

[0062] The HLB value of the nonionic surfactant (a) is greater than 8, preferably 10 or greater, and preferably 18 or less.

[0063] In the present disclosure, the HLB of the nonionic surfactant (a) is a value defined by the Griffin method using the following calculation formula: HLB value = 20 × [sum of chemical formula weights of hydrophilic moieties] / molecular weight

[0064] The nonionic surfactant (a) 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 １is a polyoxyalkylene chain.

[0065] 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.

[0066] A １ 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 １ When the number of oxypropylene groups is 0.5 to 1.5 on average, low foaming properties are favorable, and this is preferred.

[0067] 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.

[0068] Specific examples of the polyoxyethylene alkyl ether include C １３ H ２７ -O-(C ２ H４ 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).

[0069] Also preferred is the nonionic surfactant (a) 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).

[0070] The hydrophobic group of the nonionic surfactant (a) may be any of an alkylphenol group, a linear alkyl group, and a branched alkyl group. For example, the nonionic surfactant (a) may be a surfactant represented by the general formula (ii): ７ -C ６ H ４ -O-A ２ -H (ii) (wherein, R ７ 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 (a) include Triton (registered trademark) X-100 (trade name, manufactured by The Dow Chemical Company).

[0071] A ２The 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.

[0072] 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.

[0073] Other examples of the nonionic surfactant (a) include difunctional block copolymers supplied by BASF as the Pluronic® R series and tridecyl alcohol alkoxylates supplied by BASF as the Iconol® TDA series.

[0074] The nonionic surfactant (a) 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).

[0075] The nonionic surfactant (a) preferably does not contain an aromatic moiety.

[0076] (Aqueous medium) In one embodiment, the fluoropolymer aqueous dispersion contains an aqueous medium. The aqueous medium is not particularly limited as long as it contains water, and may contain water and, for example, a fluorine-free organic solvent such as ether or ketone, and / or a fluorine-containing organic solvent having a boiling point of 40°C or lower. The aqueous medium is preferably an aqueous medium containing only water, or an aqueous medium containing only water and a fluorine-free organic solvent, and more preferably an aqueous medium containing only water. That is, the aqueous medium is preferably water.

[0077] (Polymer (I) having a hydrophilic group) In one embodiment, the aqueous fluoropolymer dispersion contains a polymer (I) having a hydrophilic group. By using the polymer (I) having a hydrophilic group, the dispersion stability of the aqueous fluoropolymer dispersion can be improved.

[0078] The polymer (I) is a polymer having one or more hydrophilic groups in the molecule. The hydrophilic groups are preferably ionic groups, and more preferably anionic groups.

[0079] In the present disclosure, anionic groups include anionic groups such as sulfate groups, carboxylate groups, and acid groups such as —COOH, —COONH ４ The anionic group includes a functional group that provides an anionic group such as an acid-base group, such as a sulfate group, a carboxylate group, a phosphate group, a phosphonate group, a sulfonate group, or a -C(CF ３ ) ２ OM (wherein 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.

[0080] The ion exchange capacity of the polymer (I) is, in order of preference, 0.80 meq / g or more, 1.50 meq / g or more, 1.75 meq / g or more, 2.00 meq / g or more, 2.20 meq / g or more, more than 2.20 meq / g, 2.50 meq / g or more, 2.60 meq / g or more, 3.00 meq / g or more, and 3.50 meq / g or more. The ion exchange capacity is the content of ionic groups (anionic groups) in the polymer (I) and is calculated from the composition of the polymer (I).

[0081] In polymer (I), the ionic (anionic) groups are typically distributed along the polymer backbone. The polymer (I) comprises a polymer backbone with recurring side chains attached to the backbone, which preferably carry ionic groups.

[0082] Preferably, polymer (I) comprises ionizable groups having a pKa of less than 10, more preferably less than 7. The ionizable groups of polymer (I) are preferably selected from the group consisting of sulfonate, carboxylate, phosphonate, and phosphate.

[0083] The terms "sulfonate, carboxylate, phosphonate, and phosphate" are intended to refer to the respective salts or the respective acids capable of forming salts. When salts are used, the salts are preferably alkali metal or ammonium salts. Preferred ionic groups are carboxylate and sulfonate groups.

[0084] The polymer (I) preferably has an ion exchange ratio (IXR) of 53 or less. The IXR is defined as the number of carbon atoms in the polymer backbone relative to the ionic group. ２ F) is not considered an ionizable group for purposes of determining IXR.

[0085] IXR is preferably 0.5 or more, more preferably 1 or more, even more preferably 3 or more, even more preferably 4 or more, particularly preferably 5 or more, and particularly preferably 8 or more. IXR is more preferably 43 or less, more preferably 33 or less, and particularly preferably 23 or less.

[0086] The polymer (I) is preferably water-soluble. Water-soluble means the property of being easily dissolved or dispersed in an aqueous medium. The particle size of the water-soluble polymer (I) cannot be measured by dynamic light scattering (DLS), for example, or the particle size is 10 nm or less.

[0087] The number average molecular weight of the polymer (I) is 0.1 × 10 ４ More than 0.2 × 10 ４ More preferably, 0.3 × 10 ４ More preferably, 0.4 × 10 ４ More preferably, 0.5 × 10 ４ More preferably, 1.0 x 10 ４ More preferably, 3.0 × 10 ４ More particularly, 3.1 × 10 ４ More than 75.0×10 is most preferable. ４ Preferably, 50.0 x 10 ４ More preferably, 40.0 x 10 ４ More preferably, 30.0 x 10 ４ The following is particularly preferred: 20.0 x 10 ４ The following are particularly preferred. The number average molecular weight and weight average molecular weight are values ​​calculated by gel permeation chromatography (GPC) using monodisperse polystyrene as a standard. When measurement by GPC is not possible, the number average molecular weight of polymer (I) can be determined from the correlation between the number average molecular weight calculated from the number of terminal groups obtained by NMR, FT-IR, etc. and the melt flow rate. The melt flow rate can be measured in accordance with JIS K 7210.

[0088] The lower limit of the weight average molecular weight of the polymer (I) is, in order of preference, 0.2 × 10 ４ That's it, 0.4 x 10 ４ That's it, 0.6 x 10 ４ That's it, 0.8 x 10 ４ That's it, 1.0 x 10 ４ That's it, 2.0 x 10 ４ That's it, 5.0 x 10 ４ That's it, 10.0 x 10４ That's it, 15.0 x 10 ４ That's it, 20.0 x 10 ４ That's it, 25.0 x 10 ４ The upper limit of the weight average molecular weight of the polymer (I) is preferably 150.0×10 ４ Below, 100.0 x 10 ４ Below, 60.0 x 10 ４ Below, 50.0 x 10 ４ Below, 40.0 x 10 ４ The following is the result.

[0089] The viscosity of an aqueous solution of polymer (I) is preferably 5.0 mPa.s or more, more preferably 8.0 mPa.s or more, even more preferably 10.0 mPa.s or more, particularly preferably 12.0 mPa.s or more, and most preferably 14.0 mPa.s or more, and is preferably 100.0 mPa.s or less, more preferably 50.0 mPa.s or less, even more preferably 25.0 mPa.s or less, and especially preferably 20.0 mPa.s or less.

[0090] The viscosity of the aqueous solution of polymer (I) can be determined by adjusting the content of polymer (I) in the aqueous solution to 33 mass % based on the aqueous solution, and measuring the viscosity of the obtained aqueous solution at 20°C using a tuning fork vibro viscometer (model number: SV-10) manufactured by A&D Co., Ltd.

[0091] The critical micelle concentration (CMC) of the polymer (I) is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less.

[0092] The critical micelle concentration of the polymer (I) can be determined by measuring the surface tension, for example, using a surface tensiometer CBVP-A3 manufactured by Kyowa Interface Science Co., Ltd.

[0093] The acid value of the polymer (I) is preferably 60 or more, more preferably 90 or more, even more preferably 120 or more, particularly preferably 150 or more, and most preferably 180 or more. The upper limit is not particularly limited, but is preferably 300 or less.

[0094] The acid value of the polymer (I) is determined by the amount of anionic groups other than the acid functional groups, such as —COOM and —SO ３ M, -OSO ３ M or -C(CF ３ ) ２ OM (M is a metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７ When the compound has a group (H or an organic group), these groups can be converted into acid groups and then measured by acid-base titration.

[0095] The polymer (I) is preferably a polymer containing polymerized units (I) based on the monomer (I) represented by the general formula (I): １ X ３ =CX ２ R (-CZ １ Z ２ -A ０ ) ｍ (I) (wherein, X １ and X ３ are each independently F, Cl, H or CF ３ and X ２ is H, F, an alkyl group or a fluorine-containing alkyl group; A ０ is an anionic group; R is a linking group; Z １ and Z ２ are each independently H, F, an alkyl group or a fluorine-containing alkyl group; and m is an integer of 1 or more.

[0096] R is a linking group. In the present disclosure, a "linking group" is an (m+1)-valent linking group, and when m is 1, it is a divalent linking group. The linking group may be a single bond and preferably contains at least one carbon atom, and 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.

[0097] The linking group may be linear or branched, cyclic or acyclic in 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 be a catenary heteroatom such as oxygen, sulfur, or nitrogen.

[0098] m is an integer of 1 or more, preferably 1 or 2, and more preferably 1. When m is an integer of 2 or more, Z １ , Z ２ and A ０ may be the same or different. Next, a preferred structure when m is 1 in general formula (I) will be described.

[0099] R is preferably a catenary heteroatom such as oxygen, sulfur, or nitrogen, or a divalent organic group.

[0100] When R is a divalent organic group, a hydrogen atom bonded to a carbon atom may be replaced with a halogen atom other than fluorine, such as chlorine, and may or may not contain a double bond. R may be either linear or branched, and may be cyclic or acyclic. R may also contain a functional group (e.g., ester, ether, ketone (keto group), amine, halide, etc.).

[0101] R may also be a non-fluorinated divalent organic group, or a partially fluorinated or perfluorinated divalent organic group.

[0102] R may be, for example, a hydrocarbon group in which no fluorine atoms are bonded to the carbon atoms, a hydrocarbon group in which some of the hydrogen atoms bonded to the carbon atoms are substituted with fluorine atoms, or a hydrocarbon group in which all of the hydrogen atoms bonded to the carbon atoms are substituted with fluorine atoms, and these may contain an oxygen atom, a double bond, or a functional group.

[0103] R is preferably a hydrocarbon group having 1 to 100 carbon atoms which may contain an ether bond or a keto group, and in the hydrocarbon group, some or all of the hydrogen atoms bonded to the carbon atoms may be substituted with fluorine.

[0104] R is preferably —(CH ２ ) ａ -, - (CF ２ ) ａ -, - (CF ２ ) ａ -O-, -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 -, -O[(CF ２ ) ａ -O] ｂ - [(CF ２ ) ｃ -O]ｄ -, -O-[CF ２ CF (CF ３ ) O] ａ -(CF ２ ) ｂ -, -O-(CF ２ ) ａ -O-[CF(CF ３ )CF ２ O] ｂ -, -O-[CF ２ CF (CF ３ ) O] ａ -(CF ２ ) ｂ -O-, -O-[CF ２ CF (CF ３ ) O] ａ -(CF ２ ) ｂ -O-[CF(CF ３ )CF ２ O] ｃ -, -[CF ２ CF (CF ３ ) O] ａ -, -[CF(CF ３ )CF ２ O] ａ -, - (CF ２ ) ａ -O-[CF(CF ３ )CF ２ O] ａ -, - (CF ２ ) ａ -O-[CF(CF ３ )CF ２ O] ａ -(CF ２ ) ｂ -, -[CF ２ CF (CF ３ )] ａ -CO-(CF ２ ) ｂ - 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 limit of a, b, c, and d is, for example, 100.

[0105] More preferably, R is —O—CF ２ -, -O-CF ２ CF ２ -, -O-CF ２ CF ２ —O—, —O—CF ２ CF ２ CF ２ -, -O-CF ２ CF ２ CF ２ —O—, —O—CF ２ CF (CF ３ ) -O-, -O-CF ２ CF ２ -O-CF(CF ３ )CF ２ —O—, —O—CF ２ CF (CF ３ )-O-CF ２ CF ２ —O— and —O—CF ２ CF (CF ３ )-O-CF ２ - At least one selected from the following.

[0106] R is a group represented by the general formula (r1): -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, and g is 0 or 1), and a divalent group represented by the general formula (r2): -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, and g is 0 or 1) is more preferred.

[0107] A specific example of a suitable R is —CF ２—O—, —CF ２ -O-CF ２ -, -CF ２ -O-CH ２ -, -CF ２ -O-CH ２ CF ２ -, -O-CF ２ -, -O-CF ２ CF ２ -, -O-CF ２ CF ２ CF ２ -, -O-CF ２ CF ２ CF ２ CF ２ -, -O-CF ２ CF (CF ３ )-O-CF ２ -, -O-CF ２ CF (CF ３ )-O-CF 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 )CF ２ -O-CF ２ -, -CF ２ -O-CF(CF ３ ) CH ２ Among these, R is preferably a perfluoroalkylene group which may contain an oxygen atom, specifically, —CF ２ —O—, —CF ２ -O-CF ２ -, -O-CF ２-, -O-CF ２ CF ２ -, -O-CF ２ CF (CF ３ )-O-CF ２ -, -O-CF ２ CF (CF ３ )-O-CF ２ CF ２ -, -CF ２ -O-CF ２ CF ２ -, -CF ２ -O-CF(CF ３ ) -, -CF ２ -O-CF(CF ３ )CF ２ - or -CF ２ -O-CF(CF ３ )CF ２ —O— is preferred.

[0108] -R-CZ of general formula (I) １ Z ２ - is a group represented by the general formula (s1): -CF ２ -O-(CX ６ ２ ) ｅ -{O-CF(CF ３ ) ｆ -(O) ｇ -CZ １ Z ２ - (s1) (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, and Z １ and Z ２ are each independently H, F, an alkyl group or a fluorine-containing alkyl group), and in formula (s1), Z １ and Z ２ is F or CF ３ is more preferred, one of which is F and the other is CF ３ It is more preferable that:

[0109] In addition, in the general formula (I), -R-CZ １ Z ２ - is a group represented by the general formula (s2): -CF ２-O-(CX ７ ２ ) ｅ -(O) ｇ -CZ １ Z ２ - (s2) (wherein, X ７ are each independently H, F or CF ３ where e is an integer of 0 to 3, g is 0 or 1, and Z １ and Z ２ are each independently H, F, an alkyl group or a fluorine-containing alkyl group), and in formula (s2), Z １ and Z ２ is F or CF ３ is more preferred, one of which is F and the other is CF ３ It is more preferable that:

[0110] -R-CZ of general formula (I) １ Z ２ - is -CF ２ -O-CF ２ -, -O-CF ２ CF ２ -, -O-CF ２ CF ２ CF ２ -, -O-CF ２ CF ２ CF ２ CF ２ -, -O-CF ２ CF (CF ３ )-O-CF ２ -, -O-CF ２ CF (CF ３ )-O-CF ２ CF ２ -, -O-CF ２ CF (CF ３ )-O-CF ２ CF ２ CF ２ -, -CF ２ -O-CF(CF ３ ) -, -CF ２ -O-C(CF ３ ) ２ -, -CF ２ -O-CF ２ -CF ２ -, -CF ２2009 ２ -CF(CF ３ )-、-CF ２ 2009 ２ -C(CF ３ ) ２ -、-CF ２ 2009 ２ CF ２ -CF ２ -、-CF ２ 2009 ２ CF ２ -CF(CF ３ )-、-CF ２ 2009 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 2009 ２ -、-CF ２ -O-CF(CF ３ )CF ２ -O-CF(CF ３ )-、または、-CF ２ -O-CF(CF ３ )CF ２ -O-C(CF ３ ) ２- is preferred, and -O-CF ２ CF ２ -, -O-CF ２ CF ２ CF ２ -, -O-CF ２ CF ２ CF ２ CF ２ -, -O-CF ２ CF (CF ３ )-O-CF ２ -, -O-CF ２ CF (CF ３ )-O-CF ２ CF ２ -, -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 ) - or -CF ２ -O-CF(CF ３ )CF ２ -O-CF(CF ３ )- is more preferred, and —O—CF ２ CF ２ -, -O-CF ２ CF (CF ３ )-O-CF ２ CF ２ - is more preferred.

[0111] It is also preferred that the polymer (I) is highly fluorinated. For example, the polymer (I) contains phosphate group moieties (e.g., CH ２ OP (O) (OM) ２ ) and sulfate group moieties (e.g., CH ２ OS (O) ２ anionic groups (A) such as ０), it is preferred that 80% or more, 90% or more, 95% or more, or 100% of the C—H bonds in polymer (I) are substituted with C—F bonds.

[0112] The monomer (I) and the polymer (I) contain an anionic group (A ０ ) except for the above, it is also preferable that the compound has a C—F bond and does not have a C—H bond. １ , X ２ , and X ３ is preferably F, and R is a perfluoroalkylene group having one or more carbon atoms, and the perfluoroalkylene group may be either linear or branched, may be 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.

[0113] The monomer (I) and the polymer (I) may be partially fluorinated. That is, the monomer (I) and the polymer (I) may have an anionic group (A ０ ), 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.

[0114] Anionic group (A ０ ) is -SO ２ M, -SO ３ M, -OSO ３ M, -COOM, -SO ２ NR'CH ２ COOM, -CH ２ OP (O) (OM) ２ , [-CH ２ O] ２ P(O)(OM), -CH ２ CH ２ OP (O) (OM) ２ , [-CH ２ CH ２ O] ２ P(O)(OM), -CH ２ CH ２ OSO ３ M, -P(O)(OM) ２ , -SO ２ NR'CH２ CH ２ OP (O) (OM) ２ , [-SO ２ NR'CH ２ CH ２ O] ２ P(O)(OM), -CH ２ OSO ３ M, -SO ２ NR'CH ２ CH ２ OSO ３ M, or -C(CF ３ ) ２ Among them, -SO ３ M, -OSO ３ M, -COOM, -P(O)(OM) ２ or -C(CF ３ ) ２ -OM is preferred, -COOM and -SO ３ M, -OSO ３ M, -P(O)(OM) ２ or -C(CF ３ ) ２ OM is more preferred, and —SO ３ M, -COOM or -P(O)(OM) ２ is more preferred, and —SO ３ M or -COOM is particularly preferred.

[0115] 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.

[0116] The metal atom includes alkali metals (Group 1) and alkaline earth metals (Group 2), and is preferably Na, K or Li.

[0117] M is —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 ４is 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 is most preferred.

[0118] In the polymer (I), each polymer unit (I) may have a different anionic group or may have the same anionic group.

[0119] The monomer (I) is preferably a monomer (1) represented by the general formula (1). The polymer (I) is preferably a polymer (1) containing a polymerized unit (1) based on the monomer represented by the general formula (1). CX ２ =CY(-CZ ２ -O-Rf-A) (1) (In the formula, X is the same or different and represents -H or F; Y is -H, -F, an alkyl group or a fluorine-containing alkyl group; Z is the same or different and represents -H, -F, an alkyl group or a fluoroalkyl 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. A is -COOM, -SO ３ M, -OSO ３ M or -C(CF ３ ) ２ OM (M is -H, metal atom, -NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７ is H or an organic group.) However, at least one of X, Y, and Z contains a fluorine atom.)

[0120] The polymer (1) may be a homopolymer of the monomer (1) represented by the general formula (1), or may be a copolymer with other monomers.

[0121] 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 that contains an ether bond between carbon atoms.

[0122] In general formula (1), 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.

[0123] In general formula (1), 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.

[0124] In general formula (1), 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.

[0125] In general formula (1), 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.

[0126] In the general formula (1), 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.

[0127] 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, even more preferably 10 or less, particularly preferably 6 or less, and most preferably 3 or less. The fluorine-containing alkylene group includes, for example, —CF ２ -, -CH ２ CF ２ -, -CF ２ CF ２ -, -CF ２ CH ２ -, -CF ２ CF ２ CF 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.

[0128] 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, even more preferably 12 or less, particularly preferably 9 or less, and most preferably 6 or less. The fluorine-containing alkylene group having an ether bond is, for example, a group represented by the general 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; and t1 is an integer of 0 to 5).

[0129] Specific examples of the fluorine-containing alkylene group having an ether bond include —CF ２ CF (CF ３ ) OCF ２ -, -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 CF ２ CF ２ O-CF ２ -, -CF ２ CF ２ CF ２ O-CF ２ CF ２ -, -CF ２ CF ２ CF ２ O-CF ２ 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.

[0130] In the general formula (1), A is -COOM, -SO ３ M, -OSO ３ M or -C(CF ３ )２ OM (M is H, metal atom, NR ７ ４ , optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium, and R ７ is H or an organic group).

[0131] R ７ As the group, H or C １－１０ is preferably an organic group of the formula １－４ More preferred are organic groups of the formula: １－４ More preferred are alkyl groups of the formula:

[0132] The metal atom includes alkali metals (Group 1) and alkaline earth metals (Group 2), and is preferably Na, K or Li.

[0133] M is 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 is most preferred.

[0134] A is -COOM or -SO ３ M is preferred.

[0135] Examples of the monomer represented by the general formula (1) include a monomer represented by the general formula (1a): CX ２ =CFCF ２ -O-(CF(CF ３ )CF ２ O) ｎ５ -CF (CF ３ )-A (1a) (wherein each X is the same and represents F or H, n5 represents 0 or an integer of 1 to 10, and A is as defined above).

[0136] In general formula (1a), 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 that particles having a small primary particle size can be obtained.

[0137] The polymer (1) may be a homopolymer of the monomer represented by the general formula (1a) or a copolymer with other monomers.

[0138] The monomer (1) is preferably a monomer represented by the general formula (1A). The polymerized unit (1) is preferably a polymerized unit (1A) based on a monomer represented by the general formula (1A). CH ２ =CF(-CF ２ —O—Rf-A) (1A) (wherein Rf and A are the same as defined above.)

[0139] The polymer (1) may be a homopolymer of the monomer represented by the general formula (1A) or a copolymer with other monomers.

[0140] Specific examples of the monomer represented by formula (1A) include the monomer represented by the general formula:

[0141]

[0142] (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 0 to 10; s1 is 0 or 1; t1 is an integer of 0 to 5, provided that Z ３ and Z ４ are both H, then p1+q1+r1+s1 is not 0; A is the same as defined above). More specifically,

[0143]

[0144] Among them,

[0145]

[0146] It is preferable that:

[0147] In the monomer represented by the general formula (1A), A in the formula (1A) is preferably -COOM, and particularly preferably CH ２ =CFCF ２ OCF (CF ３ ) COOM, and CH ２ =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.

[0148] The monomer (I) is preferably a monomer (2) represented by the general formula (2). The polymer (I) is preferably a polymer (2) containing a polymer unit (2) based on the monomer represented by the general formula (2). CX ２ =CY(-O-Rf-A) (2) (In the formula, X's may be the same or different and each represent -H or F; Y represents -H, -F, an alkyl group or a fluorine-containing alkyl group; Rf represents a fluorine-containing alkylene group having 1 to 40 carbon atoms or a fluorine-containing alkylene group having 2 to 100 carbon atoms and having an ether bond or a keto group; and A is the same as defined above.)

[0149] The monomer (I) is preferably a monomer (3) represented by the general formula (3). The polymer (I) is preferably a polymer (3) containing a polymer unit (3) based on the monomer represented by the general formula (3). CX ２ =CY(-Rf-A) (3) (In the formula, X is the same or different and represents -H or F; Y 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; and A is the same as defined above.)

[0150] The polymer (I) may be a homopolymer consisting of only the polymerized unit (I), or may be a copolymer containing the polymerized unit (I) and a polymerized unit based on another monomer copolymerizable with the monomer represented by the general formula (I). From the viewpoint of solubility in an aqueous medium, a homopolymer consisting of only the polymerized unit (I) is preferred. The polymerized units (I) may be the same or different in each occurrence, and the polymer (I) may contain polymerized units (I) based on two or more different monomers represented by the general formula (I).

[0151] The polymer (I) usually has a terminal group. The terminal group is a terminal group generated during polymerization, and typical terminal groups are independently selected from hydrogen, iodine, bromine, linear or branched alkyl groups, and linear or branched fluoroalkyl groups, and may optionally contain at least one catenary heteroatom. The alkyl group or fluoroalkyl group preferably has 1 to 20 carbon atoms. These terminal groups are generally generated from the initiator or chain transfer agent used in forming the polymer (I) or during the chain transfer reaction.

[0152] In the polymer (I), the content of the polymerized units (I) relative to the total polymerized units is, in order of preference, 1.0 mol% or more, 3.0 mol% or more, 5.0 mol% or more, 10 mol% or more, 20 mol% or more, 30 mol% or more, 40 mol% or more, 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, and 90 mol% or more. The content of the polymerized units (I) is particularly preferably substantially 100 mol%, and the polymer (I) is most preferably composed only of the polymerized units (I).

[0153] In the polymer (I), the content of polymerization units based on other monomers copolymerizable with the monomer represented by general formula (I) is, in order of preference, 99.0 mol% or less, 97.0 mol% or less, 95.0 mol% or less, 90 mol% or less, 80 mol% or less, 70 mol% or less, 60 mol% or less, 50 mol% or less, 40 mol% or less, 30 mol% or less, 20 mol% or less, and 10 mol% or less, based on all polymerization units. It is particularly preferable that the content of polymerization units based on other monomers copolymerizable with the monomer represented by general formula (I) is substantially 0 mol%, and it is most preferable that the polymer (I) does not contain polymerization units based on other monomers.

[0154] The polymer (I) can be obtained by polymerizing the monomer (I) using a known method. Polymerizing the monomer (I) in an aqueous medium can produce a crude composition in which the polymer (I) is dispersed or dissolved in the aqueous medium. The crude composition thus obtained typically contains more than 1.0 mass% of dimers and trimers of the monomer (I) in total, relative to the mass of the polymer (I). The content of dimers and trimers in the crude composition can be determined by performing gel permeation chromatography (GPC) analysis of the crude composition and calculating the ratio (area percentage) of the total peak area of ​​the dimers and trimers to the total area of ​​each peak in the chromatogram obtained by GPC analysis.

[0155] Next, the dimer and trimer of the monomer (I) contained in the crude composition obtained by polymerization of the monomer (I) are removed from the crude composition. The means for removing the dimer and trimer is not particularly limited, but at least one means selected from the group consisting of ion exchange treatment, ultrafiltration, microfiltration, dialysis membrane treatment, liquid separation, and reprecipitation is preferred, at least one means selected from the group consisting of ion exchange treatment, ultrafiltration, microfiltration, and dialysis membrane treatment is more preferred, ion exchange treatment and ultrafiltration are even more preferred, and ultrafiltration is particularly preferred.

[0156] By carrying out such a removal treatment, not only the dimer and trimer of the monomer (I) can be removed, but also the initiator added during the polymerization of the monomer (I). Therefore, even when the obtained polymer (I) is used to polymerize a fluoromonomer, no initiator remains in the polymer (I), and therefore the influence of the initiator added during the polymerization of the monomer (I) can be reduced.

[0157] (Fluorine-containing surfactant) In one embodiment, the aqueous fluoropolymer dispersion is substantially free of a fluorine-containing surfactant. Examples of the fluorine-containing surfactant include anionic fluorine-containing surfactants. 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.

[0158] 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" refers to the portion 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.

[0159] 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.

[0160] The anionic fluorine-containing surfactant may be a compound represented by the following general formula (N ０ ): X ｎ０ -Rf ｎ０ -Y ０ (N ０ ) (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 ７is H or an organic group. The metal atom includes alkali metals (Group 1), alkaline earth metals (Group 2), etc., such as Na, K, or Li. 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.

[0161] 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, 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 ether bonds and / or chlorine atoms; Y ｎ１ and Y ｎ２ are the same or different and are H or F, p is 0 or 1, and Y ０ is as defined above.) and a compound represented by the general formula (N ５ ): (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.

[0162] 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.

[0163] The perfluorocarboxylic acid (I) is represented by the following general formula (I): F(CF ２ ) ｎ１ COOM (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.

[0164] 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).

[0165] The perfluoroethercarboxylic acid (III) is a compound represented by the following general formula (III): １ -O-(CF(CF ３ )CF ２ O) ｎ３CF (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.

[0166] 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.

[0167] The alkoxyfluorocarboxylic acid (V) is represented by the following general formula (V): Rf 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 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.

[0168] 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).

[0169] The ω-H perfluorosulfonic acid (VII) is represented by the following general formula (VII): H(CF ２ ) ｎ６ SO ３M (VII) (wherein n6 is an integer of 4 to 14, and M is as defined above).

[0170] 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.

[0171] 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.

[0172] 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.

[0173] 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 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; Y １ and Y ２ are the same or different and are H or F, and M is as defined above.

[0174] 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 ３ M or COOM (wherein M is as defined above). Examples of L include a single bond and a partially or fully fluorinated alkylene group having 1 to 10 carbon atoms which may contain an ether bond.

[0175] 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) ｎ１０CF ２ COONH ４ (a mixture having an average molecular weight of 750, wherein n9 and n10 are defined above).

[0176] As mentioned above, examples of the anionic fluorine-containing surfactant include carboxylic acid surfactants and sulfonic acid surfactants.

[0177] The fluorine-containing surfactant may be one type of fluorine-containing surfactant or a mixture containing two or more types of fluorine-containing surfactants.

[0178] (Anionic hydrocarbon surfactant) In one embodiment, the aqueous fluoropolymer dispersion contains an anionic hydrocarbon surfactant. By using the anionic hydrocarbon surfactant, the dispersion stability of the aqueous fluoropolymer dispersion can be further improved.

[0179] The content of the anionic hydrocarbon surfactant in the aqueous fluoropolymer dispersion is preferably 10 to 5000 ppm by mass, more preferably 50 ppm by mass or more, and preferably 3000 ppm by mass or less, and more preferably 2000 ppm by mass or less, based on the fluoropolymer.

[0180] Furthermore, examples of anionic hydrocarbon surfactants that can be used include those described in International Publication Nos. 2013 / 146950 and 2013 / 146947. Examples include those having a saturated or unsaturated aliphatic chain containing 6 to 40 carbon atoms, preferably 8 to 20 carbon atoms, and more preferably 9 to 13 carbon atoms. The saturated or unsaturated aliphatic chain may be either a linear or 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.

[0181] Examples of anionic hydrocarbon surfactants include alkyl sulfonates, alkyl sulfates, alkylaryl sulfates, and salts thereof; aliphatic (carboxylic) acids and salts thereof; alkyl phosphates, alkylaryl phosphates, and salts thereof; and among these, alkyl sulfonates, alkyl sulfates, aliphatic carboxylic acids, and salts thereof are preferred.

[0182] Preferred alkyl sulfates or salts thereof include ammonium lauryl sulfate and sodium lauryl sulfate. Preferred aliphatic carboxylic acids or salts thereof include succinic acid, decanoic acid, undecanoic acid, undecenoic acid, lauric acid, hydrododecanoic acid, and salts thereof.

[0183] (Other Components) In one embodiment, the aqueous fluoropolymer dispersion contains other components, such as a preservative.

[0184] Examples of preservatives include isothiazolones, azoles, pronopol, chlorothalonil, methylsulfonyltetrachloropyrrolidin, carbentazim, fluorophorbet, sodium diacetate, and diiodomethyl-paratolylsulfone.

[0185] The content of the preservative in the aqueous fluoropolymer dispersion is preferably 0.01 to 0.5% by mass, more preferably 0.05 to 0.2% by mass, based on the fluoropolymer.

[0186] Other components include water-soluble polymer compounds, such as 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.

[0187] (Production Method) The aqueous fluoropolymer dispersion of the present disclosure can be produced by a production method for an aqueous fluoropolymer dispersion, for example, comprising the steps of: polymerizing a fluoromonomer in an aqueous medium substantially in the absence of a fluorine-containing surfactant and in the presence of a polymer (I) having a hydrophilic group, thereby preparing a polymerization dispersion containing a fluoropolymer, the polymer (I), and an aqueous medium; mixing the polymerization dispersion with a nonionic surfactant (a) to prepare a pre-concentration composition; concentrating the pre-concentration composition to prepare a concentrated composition; and adding the nonionic surfactant (b) to the concentrated composition to prepare the aqueous fluoropolymer dispersion.

[0188] (Preparation of Polymer Dispersion by Polymerization) In one embodiment of the production method, a polymer dispersion is prepared by polymerizing a fluoromonomer in an aqueous medium in the substantial absence of a fluorine-containing surfactant and in the presence of a polymer (I) having a hydrophilic group. The resulting polymer dispersion contains a fluoropolymer, the polymer (I), and an aqueous medium.

[0189] (Fluoromonomer) The fluoromonomer used in the manufacturing method of the present disclosure is preferably one that has 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 heterocycle, and a monomer that provides a crosslinking site.

[0190] Examples of the fluoroalkyl vinyl ether include those represented by the general formula (110): CF ２ =CF-ORf １１１ (wherein, Rf １１１ represents a perfluoroorganic group. Fluoromonomers represented by the following formula (I) are preferred.

[0191] 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.

[0192] The fluoromonomer represented by general formula (160) is preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether), and more preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether) and perfluoro(propyl vinyl ether).

[0193] 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 ２ CF ３ , C.H. ２ =CFCF ２ CF ２ CF ２H, 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:

[0194] 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 It is more preferable that the polymer is at least one selected from the group consisting of:

[0195] Examples of the fluoroalkyl allyl ether include those represented by the general formula (180): CF ２ =CF-CF ２ -ORf １１１ (wherein, Rf １１１ represents a perfluoroorganic group.

[0196] 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 F５ , 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 preferable.

[0197] 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.

[0198] (In the formula, Z ２３１ and Z ２３２ are independently F or a fluorinated alkyl group having 1 to 3 carbon atoms.

[0199] 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 ) OCF２ 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 ２ , and CF 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 It is more preferable that the compound is at least one selected from the group consisting of I.

[0200] In the polymerization, the fluoromonomer may be polymerized with a non-fluorine-containing monomer, such as a hydrocarbon-based monomer reactive with the fluoromonomer.

[0201] In the above polymerization, one or more of the above fluoromonomers are polymerized to obtain particles of the desired fluoropolymer.

[0202] (Polymerization) The polymerization of fluoromonomer is carried out substantially in the absence of a fluorine-containing surfactant (excluding compounds having a functional group capable of reacting by radical polymerization and a hydrophilic group). Conventionally, a fluorine-containing surfactant has been used for the polymerization of fluoromonomer in an aqueous medium, but according to the production method of the present disclosure, a fluoropolymer can be obtained even without using a fluorine-containing surfactant.

[0203] In the present disclosure, "substantially in the absence of a fluorinated surfactant" means that the amount of the fluorinated surfactant relative to the aqueous medium is 10 ppm by mass or less. The amount of the fluorinated surfactant relative to the aqueous medium is preferably 1 ppm by mass or less, more preferably 100 ppb by mass or less, even more preferably 10 ppb by mass or less, and still more preferably 1 ppb by mass or less.

[0204] The polymerization of the fluoromonomer is carried out in the presence of polymer (I). The amount of polymer (I) added in the polymerization is preferably more than 0.02 mass% and not more than 10 mass% relative to the aqueous medium, and the more preferred upper limit is not more than 1 mass%. By setting the amount of polymer (I) added within the above range, the polymerization of the fluoromonomer in the aqueous medium can be smoothly carried out. The amount of polymer (I) added is the total amount of polymer (I) added in the polymerization.

[0205] In the polymerization, the polymer (I) may be added all at once, or the polymer (I) may be added continuously. Continuous addition of the polymer (I) means, for example, adding the polymer (I) over time, without interruption, or in portions, rather than all at once. In the polymerization, an aqueous solution containing the polymer (I) and water may be prepared, and the aqueous solution may be added.

[0206] In the above polymerization, it is preferable to start adding polymer (I) before the solid content of the fluoropolymer formed in the aqueous medium reaches 0.5 mass%, and then continue to add polymer (I) continuously.The timing of starting adding polymer (I) is preferably before the solid content of the fluoropolymer reaches 0.3 mass%, more preferably before it reaches 0.2 mass%, even more preferably before it reaches 0.1 mass%, and particularly preferably at the same time as the start of polymerization.The above solid content is the content of the fluoropolymer relative to the total of the aqueous medium and the fluoropolymer.

[0207] In the above polymerization, if at least one polymer (I) is used, it is possible to efficiently produce a fluoropolymer. In addition, two or more compounds included in the polymer (I) may be used simultaneously, and other surfactant compounds other than the polymer (I) may be used simultaneously, as long as they are volatile or may remain in a molded product made of the fluoropolymer.

[0208] In the polymerization, a nucleating agent may be used. The amount of the nucleating agent added can be appropriately selected depending on the type of the nucleating agent. The amount of the nucleating agent added may be 5000 ppm by mass or less, preferably 1000 ppm by mass or less, more preferably 500 ppm by mass or less, even more preferably 100 ppm by mass or less, particularly preferably 50 ppm by mass or less, and most preferably 10 ppm by mass or less, relative to the aqueous medium.

[0209] In the above polymerization, it is preferable to add a nucleating agent to the aqueous medium before the start of polymerization or before the solid content of the fluoropolymer formed in the aqueous medium reaches 5.0 mass %. By adding the nucleating agent at the early stage of polymerization, an aqueous dispersion having a small average primary particle size and excellent stability can be obtained.

[0210] The amount of the nucleating agent added at the beginning of polymerization is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, still more preferably 0.05% by mass or more, and particularly preferably 0.1% by mass or more, based on the amount of the fluoropolymer to be obtained. The upper limit of the amount of the nucleating agent added at the beginning of polymerization is not limited, but is, for example, 2000% by mass.

[0211] The use of a nucleating agent results in a fluoropolymer having a smaller primary particle size compared to polymerization carried out in the absence of said nucleating agent.

[0212] Examples of the nucleating agent include dicarboxylic acids, perfluoropolyether (PFPE) acids or salts thereof, hydrocarbon-containing surfactants, etc. The nucleating agent preferably does not contain an aromatic ring and is preferably an aliphatic compound.

[0213] The nucleating agent is preferably added before or simultaneously with the addition of the polymerization initiator, but the particle size distribution can also be adjusted by adding it during the polymerization.

[0214] The amount of the dicarboxylic acid is preferably 1000 ppm by mass or less, more preferably 500 ppm by mass or less, and even more preferably 100 ppm by mass or less, relative to the aqueous medium.

[0215] The perfluoropolyether (PFPE) acid or salt thereof may have any chain structure in which oxygen atoms in the main chain of the molecule are separated by saturated fluorocarbon groups having 1 to 3 carbon atoms. Also, two or more types of fluorocarbon groups may be present in the molecule. A representative structure has a repeating unit represented by the following formula: (-CFCF ３ -CF ２ -O-) ｎ(VII) (-CF ２ -CF ２ -CF ２ -O-) ｎ (VIII) (-CF ２ -CF ２ -O-) ｎ -(-CF ２ -O-) ｍ (IX) (-CF ２ -CFCF ３ -O-)n-(-CF ２ -O-) ｍ (X)

[0216] These structures are described by Kasai in J. Appl. Polymer Sci. 57, 797 (1995). As disclosed therein, the PFPE acid or its salt may have a carboxylic acid group or its salt at one or both termini. The PFPE acid or its salt may also have a sulfonic acid or phosphonic acid group or their salt at one or both termini. The PFPE acid or its salt may also have a different group at each terminus. For monofunctional PFPEs, the other terminus of the molecule is usually perfluorinated but may contain a hydrogen or chlorine atom. The PFPE acid or its salt has at least two ether oxygens, preferably at least four ether oxygens, and even more preferably at least six ether oxygens. Preferably, at least one of the fluorocarbon groups separating the ether oxygens, more preferably at least two of such fluorocarbon groups, has two or three carbon atoms. Even more preferably, at least 50% of the fluorocarbon groups separating the ether oxygens have 2 or 3 carbon atoms. Also preferably, the PFPE acid or salt thereof has a total of at least 15 carbon atoms, for example, the preferred minimum value of n or n+m in the repeating unit structure is at least 5. Two or more of the PFPE acids or salts thereof having acid groups at one or both termini may be used in the manufacturing method of the present disclosure. The PFPE acid or salt thereof preferably has a number average molecular weight of less than 6,000 g / mol.

[0217] The amount of the hydrocarbon-containing surfactant added is preferably 40 ppm by mass or less, more preferably 30 ppm by mass or less, and even more preferably 20 ppm by mass or less, relative to the aqueous medium. It is estimated that the ppm amount of lipophilic nucleation sites present in the aqueous medium is less than the amount added. Therefore, the amount of lipophilic nucleation sites is less than the above-mentioned 40 ppm by mass, 30 ppm by mass, and 20 ppm by mass. Since the lipophilic nucleation sites are thought to exist as molecules, even a small amount of the hydrocarbon-containing surfactant can generate a large amount of lipophilic nucleation sites. Therefore, beneficial effects can be obtained by adding only about 1 ppm by mass of the hydrocarbon-containing surfactant to the aqueous medium. The preferred lower limit is 0.01 ppm by mass.

[0218] The hydrocarbon-containing surfactants include nonionic and cationic surfactants, including siloxane surfactants such as those disclosed in U.S. Pat. No. 7,897,682 (Brothers et al.) and U.S. Pat. No. 7,977,438 (Brothers et al.).

[0219] The hydrocarbon-containing surfactant is preferably a nonionic surfactant (e.g., a nonionic hydrocarbon surfactant). That is, the nucleating agent is preferably a nonionic surfactant. The nonionic surfactant preferably does not contain an aromatic moiety.

[0220] Examples of the nonionic surfactant include nonionic surfactants that can be contained in the aqueous fluoropolymer dispersion.

[0221] In the polymerization, a compound having a functional group capable of reacting by radical polymerization and a hydrophilic group may be used together with the polymer (I). As the compound having a functional group capable of reacting by radical polymerization and a hydrophilic group, the same compound as the modifying monomer (A) described below can be used.

[0222] In the polymerization, in addition to the polymer (I) and other surfactant compounds used as desired, additives for stabilizing each compound can be used, such as buffers, pH adjusters, stabilizing aids, and dispersion stabilizers.

[0223] 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.

[0224] 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.

[0225] The polymerization is carried out by charging an aqueous medium, the polymer (I), a monomer, and other additives as necessary into a polymerization reactor, stirring the contents of the reactor, maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of a polymerization initiator to initiate the polymerization reaction. After the polymerization reaction has started, additional monomers, polymerization initiators, chain transfer agents, polymer (I), etc. may be added depending on the purpose. The polymer (I) may also be added after the polymerization reaction has started.

[0226] 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 used, the molecular weight of the desired fluoropolymer, and the reaction rate.

[0227] The polymerization initiator 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.

[0228] As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

[0229] The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, and representative examples thereof include dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and disec-butyl peroxydicarbonate, peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate, and dialkyl peroxides such as di-t-butyl peroxide.

[0230] 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, perborate, 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.

[0231] 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 combination of redox initiators. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0232] 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.

[0233] 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.

[0234] In the above polymerization, known chain transfer agents, radical scavengers and decomposers may be added depending on the purpose to adjust the polymerization rate and molecular weight.

[0235] 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.

[0236] 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.

[0237] 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.

[0238] 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.

[0239] The amount of the chain transfer agent used is usually 1 to 50,000 ppm by mass, preferably 1 to 20,000 ppm by mass, based on the total amount of fluoromonomers supplied.

[0240] 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.

[0241] As the polymerization initiator, persulfates (e.g., ammonium persulfate), or organic peroxides such as disuccinic acid peroxide and diglutaric acid peroxide can be used alone or in the form of a mixture thereof. They may also be used in combination with a reducing agent such as sodium sulfite to form a redox system. Furthermore, during polymerization, a radical scavenger such as hydroquinone or catechol, or a peroxide decomposer such as ammonium sulfite, can be added to adjust the radical concentration in the system.

[0242] In the above polymerization, a fluoromonomer may be polymerized in an aqueous medium in the presence of polymer (I) to produce an aqueous dispersion of fluoropolymer particles, and the fluoromonomer may be seed-polymerized to the fluoropolymer particles in the aqueous dispersion of fluoropolymer particles to obtain a fluoropolymer.

[0243] The content of the fluoropolymer in the polymer dispersion (solid content concentration) is usually 10 to 50% by mass, more preferably 15% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less.

[0244] The fluoropolymer content in the polymer dispersion is a value obtained by drying 1 g of the polymer dispersion in a blower dryer at 150°C for 60 minutes, measuring the mass of the heating residue, and calculating the mass of the heating residue relative to the mass (1 g) of the polymer dispersion as a percentage.

[0245] (Preparation of Pre-Concentrated Composition) In one embodiment of the production method, a pre-concentrated composition is prepared by mixing a polymer dispersion obtained by polymerizing a fluoromonomer with a nonionic surfactant (a). The obtained pre-concentrated composition contains a fluoropolymer, a polymer (I), an aqueous medium, and a nonionic surfactant (a).

[0246] The content of the nonionic surfactant (a) in the composition before concentration is preferably 1.0% by mass or more, preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, based on the fluoropolymer. If the content of the nonionic surfactant (a) is too low, concentration may become difficult, and if the content of the nonionic surfactant (a) is too high, economic efficiency may be impaired.

[0247] The content of the fluoropolymer in the composition before concentration (solids concentration) is usually 8 to 50% by mass, preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less.

[0248] The pH of the pre-concentration composition is preferably 4.0 to 11.5, 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 pre-concentration composition to fall within the above range, the concentration rate can be further increased.

[0249] In one embodiment of the pre-concentration composition, it contains a fluorine-containing surfactant. Even when the pre-concentration composition contains a fluorine-containing surfactant, the fluorine-containing surfactant can be removed from the composition by concentrating it, thereby obtaining an aqueous fluoropolymer dispersion with a reduced fluorine-containing surfactant content.

[0250] In one embodiment of the pre-concentration composition, it is substantially free of a fluorine-containing surfactant.

[0251] In the present disclosure, the phrase "substantially free of fluorinated surfactant" means that the content of fluorinated surfactant in the pre-concentration composition is 10 ppm by mass or less, preferably 1 ppm by mass or less, more preferably 100 ppb by mass or less, even more preferably 10 ppb by mass or less, still more preferably 1 ppb by mass or less, and particularly preferably below the detection limit of the fluorinated surfactant as measured by liquid chromatography-mass spectrometry (LC / MS).

[0252] The content of the fluorine-containing surfactant in the pre-concentration composition can be measured by the same method as for the content of the fluorine-containing surfactant in the aqueous dispersion.

[0253] (Preparation of concentrated composition by concentration) In one embodiment of the production method, the concentrated composition is prepared by concentrating the pre-concentration composition. The resulting concentrated composition contains a fluoropolymer, a polymer (I), an aqueous medium, and a nonionic surfactant (a).

[0254] An aqueous medium such as water or alcohol may be added to the composition before or during the concentration of the pre-concentrated composition. The aqueous medium may be a single component such as water or alcohol, or a mixture of water and alcohol.

[0255] 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.

[0256] The concentration method is preferably concentration by phase separation, which can be carried out, for example, by heating the pre-concentration composition 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).

[0257] The recovered fluoropolymer-containing phase (concentrated phase) contains the fluoropolymer, polymer (I), an aqueous medium, and nonionic surfactant (a).

[0258] The temperature for the phase separation concentration can be selected based on the cloud point of the nonionic surfactant (a) contained in the pre-concentration composition, and is preferably at least 10°C lower than the cloud point of the nonionic surfactant (a) and preferably not higher than 10°C higher than the cloud point of the nonionic surfactant (a).

[0259] In the production method of the present disclosure, phase separation concentration may be repeated.

[0260] 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.

[0261] When the phase separation concentration is performed two or more times, the first phase separation concentration is preferably performed by heating at a temperature 10°C lower than the cloud point of the nonionic surfactant (a) or higher 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 10°C lower than the cloud point of the nonionic surfactant (a) or higher and then allowing to stand, resulting in separation into an upper supernatant phase and a concentrated phase.

[0262] (Addition of nonionic surfactant (b)) In one embodiment of the production method, the aqueous fluoropolymer dispersion is prepared by adding a nonionic surfactant (b) to the concentrated composition. This allows the aqueous fluoropolymer dispersion of the present disclosure to be obtained.

[0263] The concentrated composition may contain the nonionic surfactant (a) described above in addition to the nonionic surfactant (b). The concentrated composition may contain the hydrocarbon-based anionic surfactant described above in addition to the nonionic surfactant (b). Furthermore, the concentrated composition may contain other components such as the preservatives described above in addition to the nonionic surfactant (b).

[0264] A pH adjuster such as aqueous ammonia may be added to the concentrated composition for the purpose of adjusting the pH.

[0265] The pH of the aqueous fluoropolymer dispersion obtained by concentration is preferably 8 to 13, more preferably 9 to 12, and even more preferably 9 to 11.

[0266] The pH is a value measured at 25°C in accordance with JIS K6893.

[0267] Next, the fluoropolymer in the aqueous dispersion of the present disclosure and the fluoropolymer in the aqueous dispersion obtained by the manufacturing method of the present disclosure will be described in more detail.

[0268] (Fluoropolymer) As the fluoropolymer, a fluoropolymer (excluding the polymer (I)) is preferable.

[0269] 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.

[0270] 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.

[0271] In the production method of the present disclosure, for example, (I) as a non-melt-processable fluororesin, tetrafluoroethylene polymer [TFE polymer (PTFE)] is used, (II) as a melt-processable fluororesin, ethylene / TFE copolymer [ETFE], TFE / HFP copolymer [FEP], TFE / perfluoro(alkyl vinyl ether) copolymer [PFA, MFA, etc.], TFE / perfluoroallyl ether copolymer, TFE / VDF copolymer, electrolyte polymer precursor is used, and (III) as a fluororubber, TFE / pro Suitable examples of copolymers that can be produced include propylene copolymers, TFE / propylene / third monomer copolymers (wherein the third monomer is VDF, HFP, CTFE, a fluoroalkyl vinyl ether, or the like), copolymers of TFE and a fluoroalkyl vinyl ether; HFP / ethylene copolymers, HFP / ethylene / TFE copolymers; VDF / HFP copolymers, HFP / ethylene copolymers, VDF / TFE / HFP copolymers; and the fluorine-containing segmented polymers described in JP-B-61-49327.

[0272] 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

[0273] The perfluororesin is more preferably a fluororesin having a fluorine substitution rate of 95 to 100%, further preferably PTFE, FEP or PFA, and particularly preferably PTFE.

[0274] 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.

[0275] The above-mentioned (I) non-melt-processable fluororesin, (II) melt-processable fluororesin, and (III) fluororubber, which are suitably produced by the production method of the present disclosure, are preferably produced in the following manner.

[0276] (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.

[0277] 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.

[0278] In the production of PTFE, various known modified monomers can also be used in combination. In the present disclosure, PTFE is a concept that includes not only TFE homopolymer but also copolymer of TFE and modified monomer (hereinafter referred to as "modified PTFE").

[0279] 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.

[0280] 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.

[0281] 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.

[0282] 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.

[0283] 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.

[0284] 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:

[0285]

[0286] (wherein m represents 0 or an integer of 1 to 4), and Rf is a group represented by the following formula:

[0287] CF ３ CF ２ CF ２ -(O-CF(CF ３ )-CF ２ ) ｎ - (wherein n represents an integer of 1 to 4).

[0288] 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.

[0289] The (perfluoroalkyl)ethylene (PFAE) is not particularly limited, and examples thereof include (perfluorobutyl)ethylene (PFBE) and (perfluorohexyl)ethylene.

[0290] Examples of perfluoroallyl ethers include those represented by the general formula: CF ２ =CF-CF ２ Examples of the fluoromonomer include those represented by —ORf (wherein Rf represents a perfluoroorganic group).

[0291] 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 preferable.

[0292] From the viewpoint of reactivity with TFE, the modified monomer preferably comprises at least one selected from the group consisting of hexafluoropropylene, perfluoro(alkyl vinyl ether) and (perfluoroalkyl)ethylene.More preferably, it comprises 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.

[0293] In the production of the above-mentioned TFE polymer, polymer (I) can be used within the range of use in the production method of the present disclosure described above.The concentration of polymer (I) is not particularly limited as long as it is within the above-mentioned range.If the added amount is too large, needle-shaped particles with a large aspect ratio will be generated, and the aqueous dispersion will become gel-like, resulting in loss of stability.The lower limit of the amount of polymer (I) used is preferably 0.0001% by mass, more preferably 0.001% by mass, even more preferably 0.01% by mass, particularly preferably 0.02% by mass, based on the aqueous medium.The upper limit of the amount of polymer (I) used is preferably 10% by mass, more preferably 5% by mass, based on the aqueous medium.

[0294] The polymer (I) may be added all at once to a 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 polymerization, or may be added continuously during polymerization.

[0295] In the production of the above-mentioned TFE polymer, as the polymerization initiator, persulfates (e.g., ammonium persulfate), organic peroxides such as disuccinic acid peroxide and diglutaric acid peroxide can be used alone or in the form of a mixture thereof.Also, they can be used in combination with a reducing agent such as sodium sulfite to form a redox system.Furthermore, during polymerization, a radical scavenger such as hydroquinone or catechol can be added, or a peroxide decomposer such as ammonium sulfite can be added, to adjust the radical concentration in the system.

[0296] As the redox polymerization initiator, it is preferable to use a redox initiator that combines an oxidizing agent and a reducing agent. 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 combination of redox initiators. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0297] 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.

[0298] In the production of the TFE polymer, known chain transfer agents can be used, including, for example, saturated hydrocarbons such as methane, ethane, propane, and butane; halogenated hydrocarbons such as chloromethane, dichloromethane, and difluoroethane; alcohols such as methanol, ethanol, and isopropanol; and hydrogen. However, those that are in a gaseous state at normal temperature and pressure are preferred.

[0299] The amount of the chain transfer agent used is usually 1 to 10,000 ppm by mass, preferably 1 to 5,000 ppm by mass, based on the total amount of TFE supplied.

[0300] In the production of the TFE polymer, a saturated hydrocarbon having 12 or more carbon atoms, which is substantially inert to the reaction and becomes liquid under the above reaction conditions, can also be used as a dispersion stabilizer for the reaction system in an amount of 2 to 10 parts by mass per 100 parts by mass of the aqueous medium. Furthermore, ammonium carbonate, ammonium phosphate, etc. can be added as a buffer for adjusting the pH during the reaction.

[0301] Upon completion of the TFE polymerization, a polymer dispersion having a solid content of 1.0 to 50% by mass and an average primary particle size of 50 to 500 nm can be obtained. The lower limit of the solid content is preferably 5% by mass, more preferably 8% by mass. The upper limit is not particularly limited, but may be 40% by mass or even 35% by mass. The lower limit of the average primary particle size is preferably 100 nm, more preferably 150 nm. The upper limit is preferably 400 nm, more preferably 350 nm. The average primary particle size can be measured by dynamic light scattering. The average primary particle size can be measured by preparing an aqueous dispersion having a solid content of approximately 1.0% by mass, using dynamic light scattering at 25°C, with a refractive index of 1.3328 for the solvent (water) and a viscosity of 0.8878 mPa·s, and measuring 70 times in total. For dynamic light scattering, an ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) can be used, for example.

[0302] The aqueous dispersion of TFE polymer can also be stabilized and further concentrated by adding nonionic surfactant, and can be used in various applications as the composition of adding organic or inorganic filler according to purpose.By coating the above-mentioned composition on the substrate made of metal or ceramic, it can make the coating surface of 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., and the impregnation processing of glass cloth, etc.

[0303] 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.

[0304] 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.

[0305] 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.

[0306] 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.

[0307] 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.

[0308] 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.

[0309] The fluoropolymer may be a low molecular weight PTFE.

[0310] 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).

[0311] Furthermore, a low-molecular-weight PTFE may be obtained by dispersing a polymerization initiator and polymer (I) in an aqueous medium in the presence of a chain transfer agent, and polymerizing TFE with TFE or a monomer copolymerizable with TFE. 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.

[0312] 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.

[0313] The fluoropolymer may be high molecular weight PTFE. 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.

[0314] 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.

[0315] 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.

[0316] 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.

[0317] 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.

[0318] 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.

[0319] 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.

[0320] 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.

[0321] The average primary particle diameter of the primary particles of low molecular weight PTFE is preferably 10 to 300 nm, more preferably 50 nm or more, even more preferably 100 nm or more, particularly preferably 150 nm or more, 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.

[0322] 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.

[0323] 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.

[0324] The fluoropolymer may be a TFE / HFP copolymer (FEP). The preferred monomer composition (mass %) of FEP is TFE:HFP=(60-95):(5-40), more preferably (85-92):(8-15).

[0325] 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 fluorine-containing monomers (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.

[0326] In the polymerization of FEP, the polymer (I) can be used within the range of use in the production method of the present disclosure, but is usually added in an amount of 0.0001 to 10% by mass relative to 100% by mass of the aqueous medium.

[0327] The fluoropolymer may be a TFE / perfluoro(alkyl vinyl ether) copolymer (PFA). 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) may be a compound represented by the formula: CF ２ =CFORf ４ (wherein, Rf ４ is a perfluoroalkyl group having 1 to 6 carbon atoms).

[0328] 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 fluorine-containing monomers (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.

[0329] In the production method of the present disclosure, when the fluoropolymer is coagulated, washed, dried, or the like, wastewater and off-gas are generated. The polymer (I), decomposition products and by-products produced from the polymer (I), residual monomers, and the like may be recovered and purified from the wastewater generated by the coagulation or washing and / or the off-gas generated by drying, thereby allowing the polymer (I), decomposition products and by-products produced from the polymer (I), residual monomers, and the like to be reused. The method for the recovery and purification is not particularly limited, but can be carried out by known methods. For example, the method described in JP-A-2011-520020, the method described in U.S. Patent Application Publication No. 2007 / 15937, U.S. Patent Application Publication No. 2007 / 25902, and U.S. Patent Application Publication No. 2007 / 27251, and specifically the following method may be used.

[0330] Examples of a method for recovering the polymer (I), decomposition products and by-products of the polymer (I), residual monomers, etc., from the wastewater include a method of contacting the wastewater with adsorption particles such as ion exchange resin, activated carbon, silica gel, clay, zeolite, etc., to adsorb the polymer (I), etc., and then separating the wastewater from the adsorption particles. Incineration of the adsorption particles having the polymer (I), etc., can prevent the release of the polymer (I), etc., into the environment.

[0331] Alternatively, the polymer (I) or the like can be recovered by desorbing and eluting it from ion exchange resin particles that have adsorbed the polymer (I) or the like using a known method. For example, when the ion exchange resin particles are anion exchange resin particles, the polymer (I) or the like can be eluted by contacting a mineral acid with the anion exchange resin. Subsequently, when a water-soluble organic solvent is added to the resulting eluate, the mixture usually separates into two phases. The lower phase containing the polymer (I) or the like can be recovered and neutralized to recover the polymer (I) or the like. Examples of the water-soluble organic solvent include polar solvents such as alcohols, ketones, and ethers.

[0332] Other methods for recovering the polymer (I) and the like from the ion exchange resin particles include a method using an ammonium salt and a water-soluble organic solvent, and a method using an alcohol and, if desired, an acid. In the latter method, an ester derivative of the polymer (I) and the like is produced, which can be easily separated from the alcohol by distillation.

[0333] If the wastewater contains fluoropolymer particles or other solids, it is preferable to remove them before contacting the wastewater with the adsorbent particles. Methods for removing the fluoropolymer particles and other solids include a method in which they are precipitated by adding an aluminum salt or the like, and then separating the wastewater from the precipitate, and electrocoagulation. Mechanical methods, such as crossflow filtration, depth filtration, and precoat filtration, may also be used for removal. From the viewpoint of productivity, the concentration of the unaggregated fluoropolymer in the wastewater is preferably low, more preferably less than 0.4% by mass, and particularly preferably less than 0.3% by mass.

[0334] Examples of a method for recovering the polymer (I) and the like from the off-gas include a method in which a scrubber is used to contact the off-gas with deionized water, an aqueous alkali solution, an organic solvent such as a glycol ether solvent, or the like to obtain a scrubber solution containing the polymer (I) and the like. When a highly concentrated aqueous alkali solution is used as the aqueous alkali solution, the scrubber solution can be recovered in a state in which the polymer (I) and the like are phase-separated, facilitating the recovery and reuse of the polymer (I) and the like. Examples of the alkali compound include alkali metal hydroxides and quaternary ammonium salts.

[0335] The scrubber solution containing the polymer (I) and the like may be concentrated using a reverse osmosis membrane or the like. The concentrated scrubber solution usually contains fluoride ions, but by further adding alumina after concentration to remove the fluoride ions, it is possible to facilitate the reuse of the polymer (I) and the like. Alternatively, the scrubber solution may be brought into contact with adsorbent particles to adsorb the polymer (I) and the like, and the polymer (I) and the like may be recovered by the method described above.

[0336] The polymer (I) and the like recovered by any of the above methods can be reused in the production of a fluoropolymer.

[0337] 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.

[0338] <1> According to a first aspect of the present disclosure, there is provided an aqueous fluoropolymer dispersion containing a polymer (I) having a hydrophilic group, a fluoropolymer, a nonionic surfactant (a) having an HLB of greater than 8, and an aqueous medium, wherein the aqueous fluoropolymer dispersion is substantially free of a fluorine-containing surfactant, the content of the fluoropolymer is 40% by mass or more and 70% by mass or less, based on the aqueous fluoropolymer dispersion, the content of the nonionic surfactant (a) is 4.0% by mass or more and 12% by mass or less, based on the fluoropolymer, and the foam height of the aqueous fluoropolymer dispersion generated in a foaming test is 140 mm or less. <2> According to a second aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to the first aspect, further containing a nonionic surfactant (b) having an HLB of 8 or less. <3> According to a third aspect of the present disclosure, there is provided an aqueous fluoropolymer dispersion containing a polymer (I) having a hydrophilic group, a fluoropolymer, a nonionic surfactant (a) having an HLB of more than 8, a nonionic surfactant (b) having an HLB of 8 or less, and an aqueous medium, wherein the aqueous fluoropolymer dispersion is substantially free of a fluorine-containing surfactant, the content of the fluoropolymer is 40% by mass or more and 70% by mass or less, based on the aqueous fluoropolymer dispersion, and the content of the nonionic surfactant (a) is 4.0% by mass or more and 12% by mass or less, based on the fluoropolymer. <4> According to a fourth aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to the second or third aspect, wherein the content of the nonionic surfactant (b) is 0.2% by mass or more and 10% by mass or less, based on the aqueous fluoropolymer dispersion. <5> According to a fifth aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to any of the second to fourth aspects, wherein the nonionic surfactant (b) is at least one selected from the group consisting of acetylene diol surfactants and alkane diol surfactants. <6> According to a sixth aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to any of the second to fifth aspects, wherein the surface tension of a 0.1% aqueous solution of the nonionic surfactant (b) is 40 mN / m or less.<7> According to a seventh aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to any one of the first to sixth aspects, wherein the nonionic surfactant (a) is at least one selected from the group consisting of nonionic surfactants represented by general formula (i) and nonionic surfactants represented by general formula (ii). 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. ７ -C ６ H ４ -O-A ２ -H (ii) (wherein, R ７ is a linear or branched alkyl group having 4 to 12 carbon atoms, and A ２ is a polyoxyalkylene chain.) <8> According to an eighth aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to any one of the first to seventh aspects, wherein the hydrophilic group of the polymer (I) is an ionic group, and the ion exchange capacity of the polymer (I) is 0.80 meq / g or more. <9> According to a ninth aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to any one of the first to eighth aspects, wherein the ion exchange rate of the polymer (I) is 53 or less. <10> According to a tenth aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to any one of the first to ninth aspects, wherein the polymer (I) is water-soluble. <11> According to an eleventh aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to any one of the first to ninth aspects, wherein the number average molecular weight of the polymer (I) is 0.1 x 10 ４ As described above, there is provided an aqueous fluoropolymer dispersion according to any one of the first to tenth aspects. <12> According to a twelfth aspect of the present disclosure, there is provided an aqueous fluoropolymer dispersion according to any one of the first to eleventh aspects, in which the polymer (I) contains polymerized units (I) based on the monomer (I) represented by general formula (I). CX １ X ３ =CX ２ R (-CZ １ Z ２ -A ０ ) ｍ(I) (wherein, X １ and X ３ are each independently F, Cl, H or CF ３ and X ２ is H, F, an alkyl group or a fluorine-containing alkyl group; A ０ is an anionic group; R is a linking group; Z １ and Z ２ are each independently H, F, an alkyl group or a fluorine-containing alkyl group; and m is an integer of 1 or more.) <13> According to a thirteenth aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to any one of the first to twelfth aspects, wherein the fluoropolymer is a perfluororesin. <14> According to a fourteenth aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to any one of the first to thirteenth aspects, wherein the fluoropolymer is polytetrafluoroethylene. <15> According to a fifteenth aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to any one of the first to fourteenth aspects, wherein the fluoropolymer is non-melt-processable polytetrafluoroethylene. <16> According to a sixteenth aspect of the present disclosure, there is provided the aqueous fluoropolymer dispersion according to any one of the first to fifteenth aspects, wherein the polymer (I) is a polymer containing polymerized units (1) based on a monomer represented by general formula (1) or a polymer containing polymerized units (2) based on a monomer represented by general formula (2), and the content of polymerized units (1) is 90 mol % or more based on all polymerized units and the content of polymerized units (2) is 90 mol % or more based on all polymerized units, the content of polymer (I) is 10.0 to 1000 ppm by mass relative to the aqueous fluoropolymer dispersion, the HLB of the nonionic surfactant (a) is 10 or more, and the content of the nonionic surfactant (a) is 4.0 mass % or more and 8.0 mass % or less based on the fluoropolymer, and the content of the nonionic surfactant (b) is 0.5 mass % or more and 5.0 mass % or less based on the aqueous fluoropolymer dispersion. CX ２ =CY(-CZ ２-O-Rf-A) (1) (In the formula, X is the same or different and represents -H or F; Y is -H, -F, an alkyl group or a fluorine-containing alkyl group; Z is the same or different and represents -H, -F, an alkyl group or a fluoroalkyl 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. A is -COOM or -SO ３ M (M is H or NH ４ ) where at least one of X, Y and Z contains a fluorine atom. ２ =CY(-O-Rf-A) (2) (wherein X may be the same or different and is -H or F; Y 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 having an ether bond or a keto group; A is -COOM or -SO ３ M (M is H or NH ４ )

[0339] Next, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.

[0340] The values ​​in the examples were measured by the following methods.

[0341] <PTFE solids concentration (content) in aqueous dispersion> The PTFE solids concentration (P mass %) in the aqueous dispersion was calculated from the formula: P = [Z / X] × 100 (mass %), using the heating residue (Yg) obtained by placing about 1 g (X g) of a sample in an aluminum cup having a diameter of 5 cm and heating it at 110°C for 30 minutes, and the heating residue (Z g) obtained by further heating the obtained heating residue (Y g) at 300°C for 30 minutes.

[0342] <Nonionic surfactant content> The content (N mass%) of the nonionic surfactant (a) relative to PTFE in the aqueous dispersion obtained in Production Example 1 was calculated from the formula: N = [(Y-Z) / Z] x 100 (mass%), using the heating residue (Yg) obtained by placing about 1 g (Xg) of the sample in an aluminum cup with a diameter of 5 cm and heating it at 110°C for 30 minutes, and the heating residue (Zg) obtained by heating the obtained heating residue (Yg) at 300°C for 30 minutes. The content of the nonionic surfactant (b) was calculated from the amount of nonionic surfactant (b) used in preparing the aqueous dispersion.

[0343] <Surface Tension> A 0.1% aqueous solution was prepared at 25° C., and the surface tension of the resulting aqueous solution was measured by the Wilhelmy method.

[0344] <Foam Height> The PTFE content in the aqueous dispersion was adjusted to 55% by mass, and a foamability test was carried out by the Ross-Miles method in accordance with JIS K3362, to measure the foam height immediately after the aqueous PTFE dispersion was added dropwise.

[0345] The nonionic surfactants used in the examples are as follows:

[0346] Nonionic surfactants (a) having an HLB of more than 8: Nonionic surfactant (a1): Noigen TDS-80 (HLB: 13) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Nonionic surfactant (a2): TERGITOL TMN6 (HLB: 13) manufactured by The Dow Company

[0347] Nonionic surfactants (b) having an HLB of 8 or less Nonionic surfactant (b1): Dynol 607 manufactured by EVONIK (surface tension of 0.1% aqueous solution: 27 mN / m, HLB: 8) Nonionic surfactant (b2): Surfynol 104E manufactured by EVONIK (surface tension of 0.1% aqueous solution: 33 mN / m, HLB: 4) Nonionic surfactant (b3): ​​Surfynol AD01 manufactured by EVONIK (surface tension of 0.1% aqueous solution: 36 mN / m, HLB: 3)

[0348] Production Example 1 A PTFE aqueous dispersion 1 was obtained by the method described in Example 4 of WO 2021 / 045227. The obtained PTFE aqueous dispersion 1 had a solids concentration of 60.3% by mass and a nonionic surfactant (a1) content of 5.5% by mass relative to PTFE. Other components, such as the content of the polymer (I) having a hydrophilic group (concentration of polymer D) and the content of the fluorine-containing surfactant, were the same as those of the PTFE aqueous dispersion 4-1 described in Example 4 of WO 2021 / 045227.

[0349] Examples 1 to 4 Deionized water and a nonionic surfactant shown in Table 1 were added to PTFE aqueous dispersion 1, and a foaming test was carried out. The results are shown in Table 1. The content of the nonionic surfactant shown in Table 1 is the content of the nonionic surfactant added to PTFE aqueous dispersion 1, and does not include the content of nonionic surfactant (a1).

[0350] Comparative Example 1 Deionized water was added to PTFE aqueous dispersion 1, and a foaming test was carried out. The results are shown in Table 1.

[0351] Comparative Example 2 Deionized water and nonionic surfactant (a2) were added to PTFE aqueous dispersion 1, and a foaming test was carried out. The results are shown in Table 1.

[0352]

Claims

1. An aqueous fluoropolymer dispersion comprising a polymer (I) having a hydrophilic group, a fluoropolymer, a nonionic surfactant (a) having an HLB of more than 8, and an aqueous medium, said aqueous fluoropolymer dispersion being substantially free of a fluorine-containing surfactant, said fluoropolymer content being 40% by mass or more and 70% by mass or less, based on said aqueous fluoropolymer dispersion, said nonionic surfactant (a) content being 4.0% by mass or more and 12% by mass or less, based on said fluoropolymer, and said aqueous fluoropolymer dispersion having a foaming test bubble height of 140 mm or less.

2. The aqueous fluoropolymer dispersion according to claim 1, further comprising a nonionic surfactant (b) having an HLB of 8 or less.

3. An aqueous fluoropolymer dispersion comprising: a polymer (I) having a hydrophilic group; a fluoropolymer; a nonionic surfactant (a) having an HLB of more than 8; a nonionic surfactant (b) having an HLB of 8 or less; and an aqueous medium, wherein the aqueous fluoropolymer dispersion is substantially free of a fluorine-containing surfactant, the content of the fluoropolymer is 40% by mass or more and 70% by mass or less, based on the aqueous fluoropolymer dispersion, and the content of the nonionic surfactant (a) is 4.0% by mass or more and 12% by mass or less, based on the fluoropolymer.

4. The aqueous fluoropolymer dispersion according to claim 2 or 3, wherein the content of the nonionic surfactant (b) is 0.2% by mass or more and 10% by mass or less based on the aqueous fluoropolymer dispersion.

5. The aqueous fluoropolymer dispersion according to any one of claims 2 to 4, wherein the nonionic surfactant (b) is at least one selected from the group consisting of acetylene diol surfactants and alkane diol surfactants.

6. The aqueous fluoropolymer dispersion according to any one of claims 2 to 5, wherein the surface tension of a 0.1% aqueous solution of the nonionic surfactant (b) is 40 mN / m or less.

7. The aqueous fluoropolymer dispersion according to any one of claims 1 to 6, wherein the nonionic surfactant (a) is at least one selected from the group consisting of nonionic surfactants represented by general formula (i) and nonionic surfactants represented by general formula (ii). 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; A １ is a polyoxyalkylene chain. ７ -C ６ H ４ -O-A ２ -H (ii) (wherein, R ７ is a linear or branched alkyl group having 4 to 12 carbon atoms; A ２ is a polyoxyalkylene chain.

8. The aqueous fluoropolymer dispersion according to any one of claims 1 to 7, wherein the hydrophilic group of the polymer (I) is an ionic group, and the ion exchange capacity of the polymer (I) is 0.80 meq / g or more.

9. The aqueous fluoropolymer dispersion according to any one of claims 1 to 8, wherein the ion exchange rate of the polymer (I) is 53 or less.

10. The aqueous fluoropolymer dispersion according to any one of claims 1 to 9, wherein the polymer (I) is water-soluble.

11. The number average molecular weight of the polymer (I) is 0.1 x 10 ４ The aqueous fluoropolymer dispersion according to any one of claims 1 to 10.

12. The aqueous fluoropolymer dispersion according to any one of claims 1 to 11, wherein the polymer (I) contains polymerized units (I) based on the monomer (I) represented by the general formula (I). CX １ X ３ = C.X. ２ R (-CZ １ Z ２ -A ０ ) ｍ (I) (wherein, X １ and X ３ are each independently F, Cl, H or CF ３ and X ２ is H, F, an alkyl group or a fluorine-containing alkyl group; A ０ is an anionic group; R is a linking group; Z １ and Z ２ are each independently H, F, an alkyl group or a fluorine-containing alkyl group; and m is an integer of 1 or more.

13. The aqueous fluoropolymer dispersion according to any one of claims 1 to 12, wherein the fluoropolymer is a perfluororesin.

14. The aqueous fluoropolymer dispersion according to any one of claims 1 to 13, wherein the fluoropolymer is polytetrafluoroethylene.

15. The aqueous fluoropolymer dispersion according to any one of claims 1 to 14, wherein the fluoropolymer is a non-melt-processable polytetrafluoroethylene.

16. The aqueous fluoropolymer dispersion according to any one of claims 1 to 15, wherein the polymer (I) is a polymer containing polymerized units (1) based on a monomer represented by general formula (1) or a polymer containing polymerized units (2) based on a monomer represented by general formula (2), the content of the polymerized units (1) is 90 mol% or more based on the total polymerized units, the content of the polymerized units (2) is 90 mol% or more based on the total polymerized units, the content of the polymer (I) is 10.0 to 1000 mass ppm based on the aqueous fluoropolymer dispersion, the HLB of the nonionic surfactant (a) is 10 or more, the content of the nonionic surfactant (a) is 4.0 mass% or more and 8.0 mass% or less based on the fluoropolymer, and the content of the nonionic surfactant (b) is 0.5 mass% or more and 5.0 mass% or less based on the aqueous fluoropolymer dispersion. CX ２ = CY (-CZ ２ -O-Rf-A) (1) (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 fluoroalkyl 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. A is -COOM or -SO ３ M (M is H or NH ４ ) where at least one of X, Y and Z contains a fluorine atom. ２ ═CY(—O—Rf-A) (2) (wherein X is the same or different and is —H or F; Y 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 an ether bond or a keto group having 2 to 100 carbon atoms. A is —COOM or —SO ３ M (M is H or NH ４ )

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