Method for producing fluorine-containing polymer

Abstract

A method for producing a fluorine-containing polymer includes a step for polymerizing a specific monomer in an aqueous dispersion containing a first fluorine-containing polymer and an aqueous medium to produce a second fluorine-containing polymer. The first fluorine-containing polymer contains a structural unit based on VdF and a structural unit based on at least one substance selected from the group consisting of HFP, fluorine-containing vinyl ether, CTFE, TFE, and fluorine-containing allyl ether. The fluorine-containing polymer has a Tg of -20°C or higher, a total heat of fusion of 40 J / g or less in the region of 100°C or higher as measured by DSC, a content of 100 mass ppm or less of fluorine-containing emulsifier, and a concentration of 10 mass ppm or less of sulfate ions.

Description

Method for producing fluorine-containing polymer

[0001] The present disclosure relates to a method for producing a fluorine-containing polymer.

[0002] Fluorine-containing polymers such as ethylene / tetrafluoroethylene copolymers are used in various industrial fields because of their excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc.

[0003] For example, Patent Document 1 describes a method for producing a copolymer of a fluorinated olefin and a hydrocarbon olefin, which comprises substantially emulsifier-free aqueous emulsion polymerization of the fluorinated olefin and the hydrocarbon olefin, and copolymerizing the fluorinated olefin and the hydrocarbon olefin in the presence of fluoropolymer particles.

[0004] Special Publication No. 2006-504844

[0005] The method for producing a fluoropolymer disclosed in Patent Document 1 has a small environmental impact in that emulsion polymerization is carried out substantially without using an emulsifier, but does not focus on the heat resistance of the resulting fluoropolymer. Therefore, there is a demand for a method for producing a fluoropolymer having excellent heat resistance.

[0006] The present disclosure has been made in view of the above circumstances, and an object of one embodiment of the present invention is to provide a method for producing a fluoropolymer having excellent heat resistance.

[0007] The present disclosure includes the following aspects: [1] A method for producing a second fluorine-containing polymer different from the first fluorine-containing polymer by polymerizing a monomer containing a fluorine-containing monomer in an aqueous dispersion containing a first fluorine-containing polymer and an aqueous medium, wherein the first fluorine-containing polymer contains a structural unit based on vinylidene fluoride and a structural unit based on at least one selected from the group consisting of hexafluoropropene, a fluorine-containing vinyl ether, chlorotrifluoroethylene, tetrafluoroethylene, and a fluorine-containing allyl ether, and has a glass transition temperature of −20° C. or higher, and in differential scanning calorimetry, does not exhibit an endothermic peak in a region of 100° C. or higher, or the total heat of fusion in a region of 100° C. or higher is 40 J / g or lower, and before starting polymerization of the monomers, the aqueous dispersion does not contain a fluorine-containing emulsifier, or the content of the fluorine-containing emulsifier is 100 ppm by mass or lower relative to the total mass of the aqueous dispersion, A method for producing a fluoropolymer, wherein the aqueous dispersion does not contain sulfate ions or the concentration of sulfate ions is 10 ppm by mass or less relative to the total mass of the aqueous medium in the aqueous dispersion before initiating polymerization of the monomers. [2] A method for producing a fluoropolymer according to [1], wherein the content of the first fluoropolymer is 0.01 to 4.0% by mass relative to the total mass of the aqueous dispersion before initiating polymerization of the monomers. [3] A method for producing a fluoropolymer according to [1] or [2], wherein the fluorine-containing monomer comprises at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropene, and vinylidene fluoride. [4] A method for producing a fluoropolymer according to any one of [1] to [3], wherein the monomer comprises ethylene. [5] A method for producing a fluoropolymer according to any one of [1] to [4], wherein the monomer is polymerized in the presence of a polymerization initiator X represented by the following formula (X): １ -O-OH...Formula (X) In formula (X), R １is an alkyl group having 1 to 7 carbon atoms. [6] A fluoropolymer composition comprising a first fluoropolymer and a second fluoropolymer different from the first fluoropolymer, wherein the first fluoropolymer comprises structural units based on vinylidene fluoride and structural units based on at least one selected from the group consisting of hexafluoropropene, a fluorinated vinyl ether, chlorotrifluoroethylene, tetrafluoroethylene, and a fluorinated allyl ether, and has a glass transition temperature of -20°C or higher, and in differential scanning calorimetry, has no endothermic peak in a region of 100°C or higher, or has a total heat of fusion in a region of 100°C or higher of 40 J / g or lower, the second fluoropolymer comprises at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropene, and vinylidene fluoride, the fluoropolymer composition does not contain a fluorinated emulsifier, or the content of the fluorinated emulsifier is 100 ppb by mass or less relative to the total mass of the first fluoropolymer and the second fluoropolymer, The fluoropolymer composition according to [6], which is an aqueous dispersion containing an aqueous medium, is a fluoropolymer composition having a sulfate ion concentration of 100 ppb by mass or less relative to the total mass of the first fluoropolymer and the second fluoropolymer.

[0008] According to one embodiment of the present invention, there is provided a fluoropolymer having excellent heat resistance.

[0009] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, in numerical ranges described in this specification, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, when multiple substances corresponding to each component are present in the composition, the amount of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0010] In the present disclosure, "before initiating polymerization of the specific monomer" means immediately before the initiation of polymerization of the specific monomer. Here, examples of "initiation of polymerization" include the time when the specific monomer and the polymerization initiator are brought into the reactor after the temperature inside the reactor is raised to the polymerization temperature or higher, and the time when the temperature inside the reactor is raised to the polymerization temperature or higher after the temperature inside the reactor is raised to the polymerization temperature or higher.

[0011] [Method for producing a fluorine-containing polymer] The method for producing a fluorine-containing polymer of the present disclosure comprises a step of polymerizing a monomer containing a fluorine-containing monomer (hereinafter also referred to as a "specific monomer") in an aqueous dispersion containing a first fluorine-containing polymer and an aqueous medium to produce a second fluorine-containing polymer different from the first fluorine-containing polymer. The first fluorine-containing polymer comprises structural units based on vinylidene fluoride and structural units based on at least one selected from the group consisting of hexafluoropropene, fluorine-containing vinyl ether, chlorotrifluoroethylene, tetrafluoroethylene, and fluorine-containing allyl ether, and has a glass transition temperature of -20°C or higher, and in differential scanning calorimetry, either does not exhibit an endothermic peak in the region of 100°C or higher, or the total heat of fusion in the region of 100°C or higher is 40 J / g or lower. Before starting polymerization of the specific monomer, the aqueous dispersion does not contain a fluorine-containing emulsifier, or the content of the fluorine-containing emulsifier is 100 ppm by mass or lower, relative to the total mass of the aqueous dispersion. Before the start of polymerization of the specific monomer, the aqueous dispersion does not contain sulfate ions, or the concentration of sulfate ions is 10 ppm by mass or less relative to the total mass of the aqueous medium in the aqueous dispersion.

[0012] The method for producing a fluorinated polymer of the present disclosure involves producing a second fluorinated polymer in the presence of a first fluorinated polymer containing a structural unit based on vinylidene fluoride and a structural unit based on at least one selected from the group consisting of hexafluoropropene, a fluorinated vinyl ether, chlorotrifluoroethylene, tetrafluoroethylene, and a fluorinated allyl ether.

[0013] According to the method for producing a fluoropolymer of the present disclosure, a fluoropolymer having excellent heat resistance can be produced which does not contain a fluorinated emulsifier or in which the content of the fluorinated emulsifier is 100 ppm by mass or less relative to the total mass of the aqueous dispersion.

[0014] In particular, a fluoropolymer excellent in heat resistance can be obtained when the first fluoropolymer has a glass transition temperature of −20° C. or higher, and in differential scanning calorimetry, there is no endothermic peak in the region of 100° C. or higher, or the total heat of fusion in the region of 100° C. or higher is 40 J / g or lower, and the aqueous dispersion does not contain sulfate ions or the concentration of sulfate ions is 10 ppm by mass or lower relative to the total mass of the aqueous medium in the aqueous dispersion before the start of monomer polymerization.

[0015] In contrast, in the production method described in Patent Document 1, the concentration of sulfate ions in the aqueous dispersion is high before the start of polymerization of the monomers, and therefore a fluoropolymer having excellent heat resistance cannot be obtained.

[0016] <First Fluorine-Containing Polymer> The first fluorine-containing polymer contains a structural unit based on vinylidene fluoride (hereinafter also referred to as "VdF"), and a structural unit based on at least one selected from the group consisting of hexafluoropropene (hereinafter also referred to as "HFP"), fluorine-containing vinyl ether, chlorotrifluoroethylene (hereinafter also referred to as "CTFE"), tetrafluoroethylene (hereinafter also referred to as "TFE"), and fluorine-containing allyl ether. Hereinafter, the structural unit based on at least one selected from the group consisting of HFP, fluorine-containing vinyl ether, CTFE, TFE, and fluorine-containing allyl ether will also be referred to as "structural unit T".

[0017] In the first fluorine-containing polymer, the content of structural units based on VdF is preferably from 30 to 70 mol %, more preferably from 30 to 65 mol %, based on the total amount of the first fluorine-containing polymer.

[0018] The fluorine-containing vinyl ether is preferably a compound represented by the following formula (1), from the viewpoint of excellent polymerization reactivity in producing the first fluorine-containing polymer and of enabling the second fluorine-containing polymer to be produced more efficiently:

[0019] CX １１ X １２ =CX １３ -O-(CX １４ X １５ ) ｍ１ -L １ - (CX１６ X １７ ) ｎ１ -A １ …(1)

[0020] In formula (1), X １１ , X １２ , X １３ , X １４ , X １５ , X １６ , and X １７ are each independently a hydrogen atom, a fluorine atom, or a fluoroalkyl group, and X １１ ~X １７ At least one of m is a fluorine atom or a fluoroalkyl group; １ is an integer from 1 to 10, and n １ is an integer from 0 to 10, and L １ is a single bond or a divalent linking group, １ is a hydrogen atom, a fluorine atom, or an ionic functional group.

[0021] X １１ , X １２ , X １３ , X １４ , X １５ , X １６ , and X １７ When X is a fluoroalkyl group, it preferably has 1 to 5 carbon atoms. １１ , X １２ , X １３ , X １４ , X １５ , X １６ , and X １７ is preferably a fluorine atom.

[0022] m １ is preferably 1 to 6, more preferably 1 to 3. １ is preferably 0.

[0023] L １ The divalent linking group represented by the following formula (I) is an alkylene group, —CH═CH—, —C≡C—, —O—, —S—, —CO—, —COO—, —OCO—, —CONR １１ -, -NR １２ CO- and combinations thereof are preferred. １When the divalent linking group represented by R is an alkylene group, it preferably has 1 to 5 carbon atoms. １１ and R １２ are each independently a hydrogen atom or an alkyl group. １１ and R １２ When is an alkyl group, it preferably has 1 to 5 carbon atoms.

[0024] L １ is preferably a single bond.

[0025] A １ The ionic functional group represented by is —SO ３ M, -OSO ３ M, -B(OH) ２ , -P(=O)(OM) ２ , -OP(O)(OM) ２ or -COOM is preferred. M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ When a plurality of M's are present, the plurality of M's may be the same or different from each other.

[0026] R Ｍ１ and R Ｍ２ are each independently a hydrogen atom or a substituent, and R Ｍ１ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ１ may be the same or different from each other, R Ｍ２ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ２ may be the same or different from each other.

[0027] A １ is preferably a hydrogen atom or a fluorine atom, more preferably a fluorine atom.

[0028] Among them, the fluorine-containing vinyl ether is preferably a compound represented by the following formula (1A): CF ２ =CF-O-R ｆ１ ...(1A) In formula (1A), R ｆ１ represents a fluoroalkyl group having 1 to 10 carbon atoms. ｆ１From the viewpoint of superior polymerization reactivity, the number of carbon atoms is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The fluoroalkyl group may be linear or branched. The fluoroalkyl group is preferably a perfluoroalkyl group.

[0029] The fluorine-containing vinyl ether is preferably a perfluoroalkyl vinyl ether (hereinafter also referred to as "PAVE").

[0030] Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"). Of these, from the viewpoint of more efficient production of the second fluorinated polymer, PMVE or PPVE is preferred as PAVE, and PMVE is more preferred.

[0031] The fluorine-containing allyl ether is preferably a compound represented by the following formula (2), from the viewpoint of excellent polymerization reactivity in producing the first fluorine-containing polymer and enabling more efficient production of the second fluorine-containing polymer:

[0032] CX ２１ X ２２ =CX ２３ (CX ２４ X ２５ )-O-(CX ２６ X ２７ ) ｍ２ -L ２ - (CX ２８ X ２９ ) ｎ２ -A ２ …(2)

[0033] In formula (2), X ２１ , X ２２ , X ２３ , X ２４ , X ２５ , X ２６ , X ２７ , X ２８ , and X ２９ are each independently a hydrogen atom, a fluorine atom, or a fluoroalkyl group, and X ２１ ~X２９ At least one of m is a fluorine atom or a fluoroalkyl group; ２ is an integer from 1 to 10, and n ２ is an integer from 0 to 10, and L ２ is a single bond or a divalent linking group, ２ is a hydrogen atom, a fluorine atom, or an ionic functional group.

[0034] X ２１ , X ２２ , X ２３ , X ２４ , X ２５ , X ２６ , X ２７ , X ２８ , and X ２９ When X is a fluoroalkyl group, it preferably has 1 to 5 carbon atoms. ２１ , X ２２ , X ２３ , X ２４ , X ２５ , X ２６ , X ２７ , X ２８ , and X ２９ is preferably a fluorine atom.

[0035] m ２ is preferably 1 to 6, more preferably 1 to 3. ２ is preferably 0.

[0036] L ２ The divalent linking group represented by the following formula (I) is an alkylene group, —CH═CH—, —C≡C—, —O—, —S—, —CO—, —COO—, —OCO—, —CONR １１ -, -NR １２ CO- and combinations thereof are preferred. ２ When the divalent linking group represented by R is an alkylene group, it preferably has 1 to 5 carbon atoms. １１ and R １２ are each independently a hydrogen atom or an alkyl group. １１ and R １２ When is an alkyl group, it preferably has 1 to 5 carbon atoms.

[0037] L ２ is preferably a single bond.

[0038] A ２ The ionic functional group represented by is —SO ３ M, -OSO ３ M, -B(OH) ２ , -P(=O)(OM) ２ , -OP(O)(OM) ２ or -COOM is preferred. M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ When a plurality of M's are present, the plurality of M's may be the same or different from each other.

[0039] R Ｍ１ and R Ｍ２ are each independently a hydrogen atom or a substituent, and R Ｍ１ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ１ may be the same or different from each other, R Ｍ２ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ２ may be the same or different from each other.

[0040] A ２ is preferably a hydrogen atom or a fluorine atom, more preferably a fluorine atom.

[0041] Among these, the fluorine-containing allyl ether is preferably a compound represented by the following formula (2A): CF ２ =CF-CF ２ O-R ｆ２ ...(2A) In formula (2A), R ｆ２ represents a fluoroalkyl group having 1 to 10 carbon atoms. ｆ２ From the viewpoint of superior polymerization reactivity, the number of carbon atoms is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The fluoroalkyl group may be linear or branched. The fluoroalkyl group is preferably a perfluoroalkyl group.

[0042] The fluorine-containing allyl ether is preferably a perfluoroalkyl allyl ether.

[0043] Specific examples of perfluoroalkyl allyl ethers include perfluoro(methyl allyl ether), perfluoro(ethyl allyl ether), and perfluoro(propyl allyl ether).

[0044] Among these, from the viewpoint of heat resistance, the structural unit T is preferably a structural unit based on at least one selected from the group consisting of HFP and TFE. That is, the first fluorine-containing polymer preferably contains a structural unit based on VdF and a structural unit based on at least one selected from the group consisting of HFP and TFE. The first fluorine-containing polymer more preferably contains a structural unit based on VdF and a structural unit based on HFP, or contains a structural unit based on VdF, a structural unit based on HFP, and a structural unit based on TFE.

[0045] In the first fluorine-containing polymer, the total content of the structural unit T is preferably from 30 to 70 mol %, more preferably from 35 to 70 mol %, based on the total amount of the first fluorine-containing polymer.

[0046] The first fluorine-containing polymer may contain other structural units in addition to the structural units based on VdF and the structural unit T. From the viewpoint of more efficient production of the second fluorine-containing polymer, it is preferable that the first fluorine-containing polymer is substantially free of other structural units. "Substantially free of other structural units" means that the content of other structural units is 0.01 mol% or less based on the total amount of the first fluorine-containing polymer. The content of other structural units is more preferably 0 mol%.

[0047] The content of each structural unit contained in the polymer is １９ It is calculated by F-NMR analysis and infrared absorption spectrum analysis.

[0048] The glass transition temperature (hereinafter also referred to as "Tg") of the first fluoropolymer is -20°C or higher. When the Tg of the first fluoropolymer is -20°C or higher, aggregation of the second polymer is suppressed. From the viewpoint of further suppressing aggregation of the second polymer, the Tg of the first fluoropolymer is preferably -18°C or higher, more preferably -10°C or higher. From the viewpoint of improving the polymerization rate of the first fluoropolymer, the Tg of the first fluoropolymer is preferably 0°C or lower, more preferably -5°C or lower.

[0049] The Tg of the first fluoropolymer is measured by differential scanning calorimetry (DSC). For example, the Tg is measured using a differential scanning calorimeter DSC (DSC-204 F1 manufactured by NETZSCH). Specifically, 5 mg of a sample for measurement is weighed out and placed in an aluminum sample pan, cooled to -50°C in a nitrogen atmosphere, and then heated to 200°C at a rate of 10°C / min. The Tg is estimated from the inflection point observed during the heating operation.

[0050] As a method for adjusting the Tg of the first fluoropolymer within the above range, for example, a method of adjusting the type and amount of the monomer used in producing the first fluoropolymer can be mentioned.

[0051] The first fluorine-containing polymer has no endothermic peak in a region of 100°C or higher in differential scanning calorimetry (DSC), or has a total heat of fusion in a region of 100°C or higher of 40 J / g or less.

[0052] The total heat of fusion of the first fluoropolymer in the temperature range of 100° C. or higher is measured by the following method.

[0053] The heat of fusion in the range of 100°C or higher is measured using a differential scanning calorimeter DSC (DSC-204 F1 manufactured by NETZSCH). Specifically, 5 mg of a sample for measurement is weighed into an aluminum sample pan, cooled to -50°C under a nitrogen atmosphere, and then heated to 200°C at a rate of 10°C / min. During the temperature rise, the portion that deviates from the baseline in the range of 100°C to 200°C is identified as an endothermic peak. Based on the area of ​​the endothermic peak, the heat of fusion (J / g) is calculated using software provided with the instrument. If two or more endothermic peaks are present, the total value is calculated.

[0054] If there is no endothermic peak in the region of 100° C. or above, or the total heat of fusion in the region of 100° C. or above is 40 J / g or less, the resulting fluoropolymer (i.e., the mixture of the first fluoropolymer and the second fluoropolymer) is less likely to aggregate. The total heat of fusion in the region of 100° C. or above is preferably 20 J / g or less, and it is more preferable that there is no endothermic peak in the region of 100° C. or above.

[0055] A method for setting the heat of fusion of the first fluorinated polymer in the region of 100°C or higher within the above range can be exemplified by a method of adjusting the content of the VdF-based structural unit and the total content of the structural unit T within an appropriate range.

[0056] The first fluorine-containing polymer is preferably dispersed in the aqueous dispersion in the form of particles. The average particle size of the first fluorine-containing polymer is preferably from 1 to 200 nm, more preferably from 10 to 150 nm, and even more preferably from 30 to 120 nm, from the viewpoint of more efficiently producing the second fluorine-containing polymer.

[0057] The average particle size of the first fluoropolymer is determined by measuring the particle size distribution by a laser diffraction / scattering method, determining a cumulative curve with the total volume of the particle population set to 100%, and measuring the particle size (D50) at the point on the cumulative curve where the cumulative volume is 50%.

[0058] The first fluorine-containing polymer can be produced, for example, by polymerizing a monomer such as VdF in a polymerization solvent in the presence of a polymerization initiator. This results in a dispersion of the first fluorine-containing polymer dispersed in particulate form in the polymerization solvent. The polymerization solvent does not contain a fluorine-containing emulsifier, or the content of the fluorine-containing emulsifier is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, more preferably 25 mass ppm or less, even more preferably 5 mass ppm or less, still more preferably 1 mass ppm or less, particularly preferably 500 mass ppb or less, and extremely preferably 100 mass ppb or less, relative to the total mass of the polymerization solvent. The lower limit is 0 mass ppb. Further, the polymerization solvent does not contain any emulsifier other than the fluorine-containing emulsifier, or the content of the emulsifier other than the fluorine-containing emulsifier is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, more preferably 25 mass ppm or less, still more preferably 5 mass ppm or less, still more preferably 1 mass ppm or less, particularly preferably 500 mass ppb or less, and extremely preferably 100 mass ppb or less, relative to the total mass of the polymerization solvent. The lower limit is 0 mass ppb. Details of the fluorine-containing emulsifier and the emulsifier other than the fluorine-containing emulsifier will be described later.

[0059] In the method for producing a fluoropolymer of the present disclosure, a specific monomer is polymerized in an aqueous dispersion containing a first fluoropolymer and an aqueous medium (hereinafter also referred to as "aqueous dispersion A"). After obtaining a dispersion of the first fluoropolymer, the dispersion of the first fluoropolymer may be used as aqueous dispersion A as is. Another aqueous medium may be added to the dispersion of the first fluoropolymer, and the resulting mixture may be used as aqueous dispersion A. Alternatively, the first fluoropolymer may be dispersed in another aqueous medium by solvent substitution, and the resulting mixture may be used as aqueous dispersion A. Alternatively, after obtaining a dispersion of the first fluoropolymer, the dispersion may be heated to remove a portion of the polymerization solvent, and the resulting dispersion may be used as aqueous dispersion A. As described below, it is preferable that sulfate ions have been removed from aqueous dispersion A by a sulfate ion removal means such as an anion exchange resin. Alternatively, ammonium ions may have been removed from aqueous dispersion A by an ammonium ion removal means such as a cation exchange resin.

[0060] The polymerization initiator used in the production of the first fluorine-containing polymer is preferably a water-soluble polymerization initiator, more preferably a persulfate such as ammonium persulfate, sodium persulfate or potassium persulfate; a peroxide such as disuccinic acid peroxide; or an azo compound such as azobisisobutylamidine dihydrochloride, still more preferably a persulfate, and particularly preferably ammonium persulfate.

[0061] The polymerization solvent may be water or a mixed solvent of water and a water-soluble organic solvent, such as tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, or tripropylene glycol.

[0062] <Aqueous medium> The aqueous medium contained in aqueous dispersion A may be the polymerization solvent used in producing the first fluoropolymer. Specific examples of the aqueous medium contained in aqueous dispersion A are the same as the specific examples of the polymerization solvent used in producing the first fluoropolymer. The content of the aqueous medium is preferably 60.0 to 99.9 mass%, more preferably 96.0 to 99.9 mass%, and even more preferably 98.0 to 99.9 mass%, based on the total mass of aqueous dispersion A.

[0063] The aqueous dispersion A does not contain a fluorine-containing emulsifier, or the content of the fluorine-containing emulsifier is 100 mass ppm or less, preferably 50 mass ppm or less, more preferably 25 mass ppm or less, even more preferably 5 mass ppm or less, still more preferably 1 mass ppm or less, particularly preferably 500 mass ppb or less, and extremely preferably 100 mass ppb or less, relative to the total mass of the aqueous dispersion A. The lower limit is 0 mass ppb. Examples of the fluorine-containing emulsifier include anionic fluorine-containing surfactants. Examples of the anionic fluorine-containing surfactant include surfactants containing fluorine atoms whose total carbon number excluding anionic groups is 20 or less. Examples of the fluorine-containing emulsifiers whose total carbon number excluding anionic groups is 20 or less include fluorine-containing surfactants whose anionic moiety has a molecular weight of 800 or less. The above-mentioned "anionic moiety" refers to the moiety excluding the cation of the fluorine-containing surfactant.

[0064] <Other Components> The aqueous dispersion A may contain other components in addition to the first fluorinated polymer and the aqueous medium. Specific examples of the other components that the aqueous dispersion A may contain include a chain transfer agent, an emulsifier other than the fluorinated emulsifier, a pH adjuster, and a wax.

[0065] In the present disclosure, an emulsifier is a compound that has a hydrophilic portion and a hydrophobic portion.

[0066] Examples of the emulsifier include a hydrocarbon-containing surfactant, a fluorine-containing emulsifier, and a polymer emulsifier. Neither the first fluorine-containing polymer nor the second fluorine-containing polymer falls under the category of an emulsifier. The emulsifier may be either ionic or nonionic.

[0067] The hydrocarbon-containing surfactant is a surfactant that contains a hydrocarbon group. More specifically, as long as the hydrocarbon-containing surfactant contains a hydrocarbon group, it may contain substitution with halogen atoms such as fluorine atoms and chlorine atoms. In the hydrocarbon-containing surfactant, it is preferred that 75% or more of the atoms or monovalent groups bonded to the carbon atoms of the hydrocarbon group are hydrogen atoms, more preferably 85% or more, and even more preferably 95% or more.

[0068] The hydrocarbon-containing surfactant can be exemplified by hydrocarbon surfactant and siloxane surfactant.Hydrocarbon surfactant means the surfactant that does not contain silicon atom, and 100% of the atoms or monovalent groups that bond to the carbon atom of hydrocarbon group are hydrogen atoms, so it does not contain halogen atoms such as chlorine atom and fluorine atom.Siloxane surfactant means the hydrocarbon-containing surfactant that has a hydrophobic group and contains a siloxane skeleton that contains many siloxane units.

[0069] Examples of hydrocarbon surfactants include anionic hydrocarbon surfactants. Anionic hydrocarbon surfactants refer to hydrocarbon surfactants having a negatively charged hydrophilic portion such as a carboxylic acid group, sulfonic acid group, sulfate group, phosphonic acid group, or phosphate group, and a hydrocarbon portion such as an alkyl group as a hydrophobic portion. An example of an anionic hydrocarbon surfactant is the highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10. Another example of an anionic hydrocarbon surfactant is the linear alkyl polyethersulfonate sodium salt supplied by BASF as part of the Avanel® S series.

[0070] Anionic hydrocarbon surfactants also include sodium dodecyl sulfate.

[0071] Another example of an anionic hydrocarbon surfactant is the sulfosuccinate surfactant Lankropol® K8300, available from Akzo Nobel Surface Chemistry LLC.

[0072] Hydrocarbon surfactants also include nonionic hydrocarbon surfactants.Nonionic hydrocarbon surfactants do not have charged groups, but have a hydrophobic portion that is often a long-chain hydrocarbon.The hydrophilic portion of nonionic hydrocarbon surfactants includes water-soluble functional groups such as polyethylene oxide chains obtained from the polymerization of ethylene oxide.Nonionic hydrocarbon surfactants include block copolymers with various types of polyalkylene oxide blocks, for example, polyethylene oxide and polypropylene oxide.

[0073] Examples of nonionic hydrocarbon surfactants include surfactants described in paragraphs

[0043] to

[0052] of JP-A No. 2016-537499.

[0074] Siloxane surfactants include those described in US Pat. Nos. 6,841,616 (Wille et al.) and 7,977,438 (Brothers et al.).

[0075] Examples of polymeric emulsifiers include water-soluble polymers obtained by polymerizing a monomer having a fluorine atom or a monomer not having a fluorine atom. Furthermore, examples of polymeric emulsifiers made of a polymer obtained by polymerizing a monomer having a fluorine atom or a monomer not having a fluorine atom include polymers having a hydrophilic group in the side chain. Examples of such polymeric emulsifiers include polymers containing structural units based on a compound having a site reactive in polymerization and a hydrophilic group. Furthermore, examples of polymers that do not originally have a hydrophilic group include polymers obtained by polymerizing structural units based on a compound having a group that can become a hydrophilic group and then post-treating the polymer, such as by hydrolysis.

[0076] Specific examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane.

[0077] Specific examples of pH adjusters include inorganic salts. Specific examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate; and carbonates such as sodium bicarbonate and sodium carbonate. More preferred specific examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate.

[0078] Specific examples of wax include Paraffin Wax-155 and Paraffin Wax-150 (both manufactured by Nippon Seiro Co., Ltd.).

[0079] When aqueous dispersion A contains a chain transfer agent, the content of the chain transfer agent is preferably 0.1 to 5.0 parts by mass per 100 parts by mass of the aqueous medium. Furthermore, the amount of the chain transfer agent used is preferably 0.1 to 20.0 parts by mass, more preferably 0.1 to 15.0 parts by mass, and even more preferably 0.1 to 10.0 parts by mass per 100 parts by mass of the specific monomer described below. When aqueous dispersion A contains an emulsifier other than a fluorinated emulsifier, the content of the emulsifier other than a fluorinated emulsifier is preferably 0.01 to 5.0 parts by mass per 100 parts by mass of the aqueous medium. When aqueous dispersion A contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium. When aqueous dispersion A contains a wax, the content of the wax is preferably 1 to 10 parts by mass per 100 parts by mass of the aqueous medium.

[0080] Before starting the polymerization of the specific monomer, the aqueous dispersion A does not contain fluoride ions, or the fluoride ion concentration is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, even more preferably 1 mass ppm or less, particularly preferably 500 mass ppb or less, and extremely preferably 100 mass ppb or less, relative to the total mass of the aqueous medium of the aqueous dispersion A. When the fluoride ion concentration is within the above range, the polymerization stability is excellent. One example of a method for adjusting the fluoride ion concentration to the above value is a method of removing fluoride ions using an anion exchange resin during the production of the first fluorine-containing polymer. Here, fluoride ions may be generated by the reaction between a polymerization initiator (e.g., ammonium persulfate) and a fluorine-containing monomer, and may be contained in the aqueous dispersion containing the first fluorine-containing polymer.

[0081] Before the start of polymerization of the specific monomer, the aqueous dispersion A does not contain sulfate ions, or the concentration of sulfate ions is preferably 10 ppm by mass or less, more preferably 5 ppm by mass or less, still more preferably 1 ppm by mass or less, and particularly preferably 0.1 ppm by mass or less, relative to the total mass of the aqueous medium in the aqueous dispersion A. When the concentration of sulfate ions is within the above range, a fluoropolymer having excellent heat resistance can be obtained.

[0082] An example of a method for adjusting the sulfate ion concentration within the above range is a method of removing sulfate ions using an anion exchange resin during the production of the first fluoropolymer. Here, the sulfate ions are derived, for example, from the polymerization initiator (particularly ammonium persulfate) used during the production of the first fluoropolymer, and may be contained in the aqueous dispersion containing the first fluoropolymer. It is presumed that by making the content of sulfate ions 10 ppm by mass or less (particularly 5 ppm by mass or less), it is possible to suppress the formation of terminal groups with low heat resistance in the second fluoropolymer, and as a result, a fluoropolymer (i.e., a mixture of the first fluoropolymer and the second fluoropolymer) with excellent heat resistance can be obtained.

[0083] Before the start of polymerization of the specific monomer, the concentration of ammonium ions is preferably 20 ppm by mass or less, more preferably 10 ppm by mass or less, relative to the total mass of the aqueous medium in the aqueous dispersion A, from the viewpoint of suppressing aggregation of the second fluorinated polymer. The lower limit may be 0 ppm by mass.

[0084] An example of a method for adjusting the ammonium ion concentration to the above value is a method of removing ammonium ions using a cation exchange resin during the production of the first fluoropolymer. Here, the ammonium ions are derived, for example, from the initiator (particularly ammonium persulfate) used during the production of the first fluoropolymer, and may be contained in the aqueous dispersion containing the first fluoropolymer. It is presumed that when the ammonium ion content is 20 ppm by mass or less, the ionic strength in the aqueous medium decreases, resulting in an improvement in the production efficiency of the second fluoropolymer.

[0085] The concentrations of fluoride ions, sulfate ions, and ammonium ions are measured using ion chromatography. Aqueous dispersion A is freeze-aggregated and then filtered, and the resulting aqueous medium is analyzed by ion chromatography. The analysis by ion chromatography is performed using an ion chromatograph ICS-5000 (manufactured by Thermo Fisher Scientific). A Dionex IonPac AS-19 separation column and a Dionex IonPac AG-19 guard column are used, and potassium hydroxide is used as the eluent.

[0086] Before the start of polymerization of the specific monomer, the content of the first fluoropolymer is preferably 0.01 to 4.0% by mass, more preferably 0.05 to 3.0% by mass, and even more preferably 0.1 to 2.0% by mass, relative to the total mass of the aqueous dispersion A. When the content of the first fluoropolymer is 0.01% by mass or more, the polymerization stability (productivity) is excellent. When the content of the first fluoropolymer is 4.0% by mass or less, the heat resistance of the resulting fluoropolymer (i.e., a mixture of the first fluoropolymer and the second fluoropolymer) is excellent.

[0087] Before starting polymerization of the specific monomer, the aqueous dispersion A does not contain a fluorine-containing emulsifier, or the content of the fluorine-containing emulsifier is 100 ppm by mass or less, preferably 50 ppm by mass or less, more preferably 25 ppm by mass or less, and even more preferably 5 ppm by mass or less, relative to the total mass of the aqueous dispersion A. In the method for producing a fluorine-containing polymer of the present disclosure, the second fluorine-containing polymer can be produced efficiently even if the aqueous dispersion does not contain a fluorine-containing emulsifier or if the content of the fluorine-containing emulsifier is 100 ppm by mass or less. The lower limit is 0 ppb by mass. In addition, in the method for producing a fluorine-containing polymer of the present disclosure, the second fluorine-containing polymer can be produced efficiently even if the aqueous dispersion A does not contain an emulsifier or if the content of the emulsifier is 100 ppm by mass or less. The lower limit is 0 ppb by mass.

[0088] <Specific Monomer> The specific monomer includes a fluorine-containing monomer.

[0089] The fluorine-containing monomer preferably contains at least one selected from the group consisting of TFE, CTFE, HFP, and VdF (hereinafter also referred to as "specific fluorine-containing monomer"), more preferably contains TFE, and even more preferably is TFE. Two or more types of fluorine-containing monomers may be used in combination.

[0090] When the fluorine-containing monomer does not contain other monomers described below, the amount of the fluorine-containing monomer used is preferably 97 to 100 mass%, more preferably 98 to 100 mass%, and even more preferably 99 to 100 mass%, relative to the amount of the specific monomer used. When the fluorine-containing monomer contains other monomers described below, the amount of the fluorine-containing monomer used may be 10.0 mol% or more but less than 100.0 mol%, more preferably 30.0 to 70.0 mol%, and even more preferably 40.0 to 60.0 mol%, relative to the amount of the specific monomer used. The amount of the fluorine-containing monomer used may be 90.0 to 99.9 mol%, and when melt-moldability is important, 95.0 to 99.0 mol% is preferred.

[0091] The specific monomer may also contain a fluorine-containing monomer other than the specific fluorine-containing monomer (hereinafter also referred to as "other fluorine-containing monomer"). Specific examples of the other fluorine-containing monomer include fluoroalkylethylene (hereinafter also referred to as "FAE") and PAVE. Two or more types of the other fluorine-containing monomer may be used in combination. Examples of FAE include compounds represented by the following formula: CZ ２ =CX(CF ２ ) ｍ Y (3) In formula (3), X, Y, and Z each independently represent a hydrogen atom or a fluorine atom, and m represents an integer of 2 to 6. Specific examples of FAE include CH ２ =CH(CF ２ ) ２ F (hereinafter also referred to as "PFEE"), CH ２ =CH(CF ２ ) ３ F, CH ２ =CH(CF ２ ) ４ F (hereinafter also referred to as "PFBE"), CH ２ =CF(CF２ ) ３ H, CH ２ =CF(CF ２ ) ４ H is exemplified, with PFEE or PFBE being preferred. Specific examples of PAVE are as described above. When another fluorine-containing monomer is used, the amount of the other fluorine-containing monomer used is preferably 0.1 to 30.0 mol %, more preferably 0.1 to 10.0 mol %, and even more preferably 0.5 to 5.0 mol %, relative to the amount of the specific monomer used.

[0092] The specific monomer may contain a monomer other than the fluorine-containing monomer (hereinafter also referred to as "other monomer"). Specific examples of the other monomer include ethylene, propylene, vinyl chloride, and vinylidene chloride. Among them, the other monomer preferably contains ethylene, and more preferably is ethylene. Two or more types of other monomers may be used in combination. The amount of the other monomer used is preferably 10.0 to 70.0 mol%, more preferably 20.0 to 60.0 mol%, and even more preferably 30.0 to 50.0 mol%, relative to the amount of the specific monomer used. The specific monomer may contain the specific fluorine-containing monomer, another fluorine-containing monomer, and another monomer.

[0093] The amount of the specific monomer used is preferably 1 to 50 parts by mass, more preferably 1 to 40 parts by mass, and even more preferably 1 to 30 parts by mass, per 100 parts by mass of the aqueous medium contained in the aqueous dispersion A.

[0094] <Polymerization initiator> In the method for producing a fluoropolymer of the present disclosure, it is preferable to polymerize the specific monomer in the presence of a polymerization initiator.

[0095] From the viewpoint of heat resistance, it is preferable to polymerize the specific monomer in the presence of a polymerization initiator X represented by the following formula (X): １ -O-OH...Formula (X) In formula (X), R １ is an alkyl group having 1 to 7 carbon atoms. １ The alkyl group represented by the formula (I) may be either linear or branched, preferably branched. The alkyl group preferably has 1 to 5 carbon atoms, more preferably 3 to 5 carbon atoms.

[0096] Examples of the polymerization initiator X include tert-butyl hydroperoxide and 1,1,3,3-tetramethylbutyl hydroperoxide.

[0097] It is also preferable to polymerize the specific monomer in the presence of a polymerization initiator Y that does not have a hydrophilic group and has a molecular weight of 200 or less.

[0098] Examples of hydrophilic groups that the polymerization initiator Y does not have include a hydroxyl group and an ionic functional group. The ionic functional group may be either a cationic functional group or an anionic functional group. Specific examples of the ionic functional group include a carboxylic acid group (-COO － ), sulfonic acid group (—SO ３ － ), sulfate group (-SO ４ ２－ ), a phosphonic acid group (—PO ３ ２－ ) and a phosphate group (-PO ４ ３－ ) and other anionic functional groups. The hydrophilic group is preferably a monovalent group.

[0099] The molecular weight of the polymerization initiator Y is 200 or less, preferably 190 or less, and more preferably 180 or less. The lower limit is preferably 50 or more, more preferably 100 or more, and even more preferably 120 or more.

[0100] The polymerization initiator Y is preferably a compound represented by formula (Y).

[0101] R ３ -CO-O-O-R ４ ...Formula (Y) In formula (Y), R ３ and R ４ are each independently an alkyl group having 1 to 5 carbon atoms. ３ and R ４ The alkyl group represented by R may be either a linear or branched chain, and is preferably a branched chain. ３ and R ４ The number of carbon atoms in the alkyl group represented by R is 1 to 5, preferably 2 to 5, more preferably 3 to 5, still more preferably 4 or 5, and particularly preferably 4. ３ and R ４The alkyl group represented by the formula (I) is preferably a methyl group, a propyl group, a butyl group or a dimethylpropyl group, more preferably a methyl group, an isopropyl group, a tert-butyl group or a 1,1-dimethylpropyl group.

[0102] Examples of the polymerization initiator Y include tert-butyl peroxypivalate (hereinafter also referred to as "PBPV"), tert-butyl peroxyisobutyrate (Luperox 80, tert-butyl perisobutyrate), tert-amyl peroxypivalate (Luperox 554), and tert-butyl peroxyacetate (Luperox 7, tert-butyl peracetate), with PBPV being preferred. Two or more types of polymerization initiator Y may be used in combination.

[0103] The polymerization initiator may also be a persulfate such as ammonium persulfate or potassium persulfate; or a water-soluble organic peroxide such as disuccinic acid peroxide, bisglutaric acid peroxide, or tert-butyl hydroperoxide (hereinafter also referred to as "TBHP"). The polymerization initiator may also be a water-soluble redox catalyst. Preferred water-soluble redox catalysts include a combination of an oxidizing agent such as bromic acid or a salt thereof, chloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, or hydrogen peroxide, with a reducing agent such as sulfurous acid or a salt thereof, hydrogen sulfite or a salt thereof, thiosulfuric acid or a salt thereof, an organic acid, or an inorganic salt. Preferred persulfates include potassium persulfate and ammonium persulfate. Preferred sulfites include sodium sulfite. Examples of inorganic salts include combinations of sulfate anions, sulfite anions, and chloride anions with metal ions. Preferred metal ions are transition metals, including manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver ions, with iron ions being particularly preferred. The inorganic salt is preferably iron (II) sulfate.

[0104] The amount of the polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, per 100 parts by mass of the specific monomer used.

[0105] <Other Components> When polymerizing the specific monomer, components other than those described above (hereinafter also referred to as "other components") may be further used. A specific example of the other component is a reducing agent. The amount of the other component used is preferably 0.1 to 2 parts by mass per 100 parts by mass of the specific monomer used.

[0106] <Steps> In the method for producing a fluoropolymer of the present disclosure, the specific monomer is polymerized in the aqueous dispersion A to produce a second fluoropolymer different from the first fluoropolymer.

[0107] The specific monomer is added to the reaction system (i.e., polymerization reaction vessel) by a conventional method. For example, the specific monomer may be added to the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer may be dissolved in an aqueous medium, and the resulting solution may be added to the reaction system continuously or intermittently. When a polymerization initiator is used, the polymerization initiator may be added to the reaction system all at once or in portions.

[0108] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. In the case of batch processing, the polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 700 minutes.

[0109] In the method for producing a fluoropolymer of the present disclosure, a specific monomer is polymerized in the presence of a first fluoropolymer to produce a second fluoropolymer, and therefore particles containing the first and second fluoropolymers are thought to be produced. That is, according to the method for producing a fluoropolymer of the present disclosure, it is presumed that the second fluoropolymer is obtained in the form of particles containing the first and second fluoropolymers. In this case, the method for producing a fluoropolymer of the present disclosure provides an aqueous dispersion in which particles containing the first and second fluoropolymers are dispersed in the aqueous medium.

[0110] The first fluorine-containing polymer and the second fluorine-containing polymer may exist separately in the aqueous dispersion, but are preferably present in the form of particles containing the first fluorine-containing polymer and the second fluorine-containing polymer. In this case, from the viewpoint of dispersion stability, the average particle size of the particles in the liquid is preferably 500 nm or less, more preferably 450 nm or less, and even more preferably 400 nm or less. Also, from the viewpoint of aggregation, the average particle size of the particles in the liquid is preferably 50 nm or more, more preferably 80 nm or more, and even more preferably 100 nm or more.

[0111] The average particle size of particles in the liquid is measured using a dynamic light scattering particle size distribution analyzer DLS (product name "SZ-100", manufactured by Horiba, Ltd.). D50 is calculated from the average particle size calculated by analyzing the acquired autocorrelation function using the monodisperse cumulant method. D50 is the average particle size of particles in the liquid.

[0112] The average particle size of the particles after drying is preferably 500 nm or less, more preferably 450 nm or less, and even more preferably 400 nm or less from the viewpoint of dispersion stability, and is preferably 50 nm or more, more preferably 80 nm or more, and even more preferably 100 nm or more from the viewpoint of aggregation.

[0113] The dried particles are photographed using a scanning electron microscope (product name "JSM-IT200", manufactured by JEOL Ltd.) Ten particles are selected from the obtained SEM image, and the particle diameters are measured, and the arithmetic mean value is used.

[0114] <Second Fluorine-Containing Polymer> The second fluorine-containing polymer obtained by the method for producing a fluorine-containing polymer of the present disclosure is a fluorine-containing polymer containing at least a structural unit based on the above-mentioned fluorine-containing monomer. The second fluorine-containing polymer may contain a structural unit based on the above-mentioned other monomer in addition to the structural unit based on the above-mentioned fluorine-containing monomer. The second fluorine-containing polymer preferably contains a structural unit based on the above-mentioned specific fluorine-containing monomer, and more preferably contains a structural unit based on TFE. The second fluorine-containing polymer preferably contains at least one selected from the group consisting of a polymer of TFE (hereinafter also referred to as "PTFE"), a copolymer of TFE and ethylene (hereinafter also referred to as "ETFE"), a copolymer of TFE and PAVE (hereinafter also referred to as "PFA"), a copolymer of TFE and HFP (hereinafter also referred to as "FEP"), and a copolymer of TFE and propylene, and more preferably contains at least one selected from the group consisting of PTFE and ETFE.

[0115] When the second fluorine-containing polymer contains PTFE, the content of structural units based on TFE contained in the second fluorine-containing polymer is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, based on all structural units constituting the second fluorine-containing polymer. The content of structural units based on TFE contained in the second fluorine-containing polymer is preferably 99 to 100 mass%, more preferably 99.9 to 100 mass%, and even more preferably 99.99 to 100 mass%, based on all structural units constituting the second fluorine-containing polymer.

[0116] ETFE contains structural units based on TFE and structural units based on ethylene. In ETFE, the proportion of structural units based on ethylene to the total of structural units based on TFE and structural units based on ethylene is preferably 20 to 70 mol%, more preferably 25 to 60 mol%, and even more preferably 35 to 55 mol%. The proportion of the total of structural units based on TFE and structural units based on ethylene to all structural units constituting ETFE is preferably 80 mol% or more, more preferably 85 mol% or more, and even more preferably 90 mol% or more, and is preferably 100 mol% or less, more preferably 99.5 mol% or less, and even more preferably 99 mol% or less.

[0117] The fluoropolymer obtained by the method for producing a fluoropolymer of the present disclosure (i.e., a mixture of the first fluoropolymer and the second fluoropolymer) is preferably crystalline. In the present disclosure, "crystalline" means that the heat of fusion in differential scanning calorimetry is 5 J / g or more.

[0118] Specifically, the heat of fusion is measured by the following method.

[0119] The heat of fusion is measured using a differential scanning calorimeter (DSC) (DSC-204 F1 manufactured by NETZSCH). Specifically, 10 mg of a sample for measurement is weighed into an aluminum sample pan, cooled to -50°C under a nitrogen atmosphere, and then heated to 370°C at a rate of 10°C / min. During the temperature rise, the portion that deviates from the baseline is identified as an endothermic peak. Based on the area of ​​the endothermic peak, the heat of fusion (J / g) is calculated using software attached to the instrument.

[0120] The heat of fusion of the second fluorine-containing polymer is preferably 30 J / g or more, more preferably 50 J / g or more. The upper limit of the heat of fusion of the second fluorine-containing polymer is, for example, 200 J / g.

[0121] [Fluoropolymer composition] The fluoropolymer composition of the present disclosure is a fluoropolymer composition comprising a first fluoropolymer and a second fluoropolymer different from the first fluoropolymer, wherein the first fluoropolymer comprises a structural unit based on VdF and a structural unit based on at least one selected from the group consisting of HFP, a fluorinated vinyl ether, CTFE, TFE and a fluorinated allyl ether, and has a glass transition temperature of -20°C or higher, and in differential scanning calorimetry, does not have an endothermic peak in the region of 100°C or higher, or has an endothermic peak in the region of 100°C or higher. the second fluoropolymer contains at least one member selected from the group consisting of TFE, CTFE, HFP and VdF; the fluoropolymer composition does not contain a fluorinated emulsifier or the content of the fluorinated emulsifier is 100 ppb by mass or less relative to the total mass of the first fluoropolymer and the second fluoropolymer; and the fluoropolymer composition does not contain sulfate ions or the concentration of sulfate ions is 100 ppb by mass or less relative to the total mass of the first fluoropolymer and the second fluoropolymer.

[0122] Preferred embodiments of the first fluorine-containing polymer and the second fluorine-containing polymer are as described above.

[0123] The fluorine-containing polymer composition does not contain a fluorine-containing emulsifier, or the content of the fluorine-containing emulsifier is 100 ppb by mass or less, preferably 25 ppb by mass or less, and more preferably 10 ppb by mass or less, relative to the total mass of the first fluorine-containing polymer and the second fluorine-containing polymer. Also, the fluorine-containing polymer composition does not contain an emulsifier, or the content of the fluorine-containing emulsifier is preferably 100 ppb by mass or less, more preferably 25 ppb by mass or less, and even more preferably 10 ppb by mass or less, relative to the total mass of the first fluorine-containing polymer and the second fluorine-containing polymer.

[0124] The fluoropolymer composition does not contain sulfate ions, or the concentration of sulfate ions is 100 ppb by mass or less, preferably 25 ppb by mass or less, more preferably 10 ppb by mass or less, relative to the total mass of the first fluoropolymer and the second fluoropolymer.

[0125] In the fluoropolymer composition, the content of the second fluoropolymer is preferably from 95 to 99.9 mass%, more preferably from 96 to 99.8 mass%, and even more preferably from 97 to 99.7 mass%, based on the total amount of the first fluoropolymer and the second fluoropolymer.

[0126] The content of structural units based on VdF is preferably from 0.1 to 2.5 mol %, more preferably from 0.2 to 2.0 mol %, and even more preferably from 0.3 to 2.0 mol %, based on the total amount of all structural units of the first fluorine-containing polymer and the second fluorine-containing polymer.

[0127] As described above, the second fluorine-containing polymer preferably contains at least one selected from the group consisting of PTFE, ETFE, PFA, FEP, and copolymers of TFE and propylene, and more preferably contains at least one selected from the group consisting of PTFE and ETFE.

[0128] When the second fluorine-containing polymer contains PTFE, the content of structural units based on TFE is preferably from 97.0 to 99.9 mol%, more preferably from 98.5 to 99.9 mol%, and even more preferably from 99.0 to 99.9 mol%, based on the total amount of all structural units of the first fluorine-containing polymer and the second fluorine-containing polymer.

[0129] When the second fluorine-containing polymer contains ETFE, the content of structural units based on TFE is preferably from 30.0 to 70.9 mol%, more preferably from 40.0 to 65.0 mol%, and even more preferably from 45.0 to 60.0 mol%, relative to the total amount of all structural units of the first fluorine-containing polymer and the second fluorine-containing polymer.

[0130] When the second fluorine-containing polymer contains PFA, the content of structural units based on TFE is preferably from 90.0 to 99.5 mol%, more preferably from 93.0 to 99.0 mol%, and even more preferably from 95.0 to 98.5 mol%, relative to the total amount of all structural units of the first fluorine-containing polymer and the second fluorine-containing polymer.

[0131] When the second fluorine-containing polymer contains FEP, the content of structural units based on TFE is preferably 80.0 to 99.0 mol%, more preferably 85.0 to 99.0 mol%, and even more preferably 90.0 to 98.5 mol%, based on the total amount of all structural units of the first fluorine-containing polymer and the second fluorine-containing polymer.

[0132] The form of the fluoropolymer composition is not particularly limited, and may be a solid or a liquid. That is, the fluoropolymer composition may be a solid composition or an aqueous dispersion.

[0133] The fluoropolymer composition is, in one form, an aqueous dispersion containing an aqueous medium. When the fluoropolymer composition is an aqueous dispersion, specific examples of the aqueous medium are the same as specific examples of the polymerization solvent used in producing the first fluoropolymer.

[0134] When the fluoropolymer composition is an aqueous dispersion, the solids concentration is, for example, 5 to 80 mass %. When the fluoropolymer composition is an aqueous dispersion, the fluoropolymer composition can be made into a solid composition by aggregating (for example, freeze-aggregating).

[0135] When the fluoropolymer composition is a solid composition, the heat of fusion of the fluoropolymer composition is preferably 5 J / g or more, more preferably 15 J / g or more, and even more preferably 30 J / g or more. The upper limit of the heat of fusion of the fluoropolymer composition is, for example, 200 J / g.

[0136] The present disclosure will be described in detail below with reference to examples. Examples 1 to 6 are working examples, and Examples 7 to 10 are comparative examples. However, the present disclosure is not limited to these examples.

[0137] [Measurement] Various measurement methods are as follows.

[0138] <Glass transition temperature (Tg)> Tg was measured using a differential scanning calorimeter DSC (DSC-204 F1 manufactured by NETZSCH). Specifically, 5 mg of a sample for measurement was weighed out and placed in an aluminum sample pan, cooled to −50° C. in a nitrogen atmosphere, and then heated to 200° C. at a rate of 10° C. / min. Tg was estimated from the inflection point observed during the heating operation.

[0139] <Total Heat of Fusion in the 100°C or Higher Range Measured by DSC> The heat of fusion in the 100°C or higher range was measured using a differential scanning calorimeter DSC (DSC-204 F1 manufactured by NETZSCH). Specifically, 5 mg of a sample for measurement was weighed into an aluminum sample pan, cooled to -50°C under a nitrogen atmosphere, and then heated to 200°C at a rate of 10°C / min. During the temperature rise, the portion that deviated from the baseline in the range of 100 to 200°C was identified as an endothermic peak. Based on the area of ​​the endothermic peak, the heat of fusion (J / g) was calculated using the software provided with the instrument. When two or more endothermic peaks were present, the total value was calculated. When no endothermic peak was present, "-" was entered in Table 1.

[0140] <Proportion of each unit in the polymer> The proportion of each unit in the polymer is １９ F-NMR analysis, １ It was determined by H-NMR analysis and infrared absorption spectrum analysis.

[0141] <Sulfate Ion Concentration> The sulfate ion concentration relative to the total mass of the aqueous medium in the aqueous dispersion was measured as follows. The aqueous dispersion was freeze-aggregated and then filtered, and the resulting aqueous medium was analyzed by ion chromatography. The ion chromatography analysis was performed using an ion chromatograph ICS-5000 (manufactured by Thermo Fisher Scientific). A Dionex IonPac AS-19 separation column, a Dionex IonPac AG-19 guard column, and KOH were used as the eluent.

[0142] <Average particle size of particles in liquid> The raw material liquid was degassed for 5 minutes at room temperature (25°C), pressurized with nitrogen to 0.2 MPaG, and then purged to atmospheric pressure to obtain a sample for measurement. The particle size of the obtained sample was measured using a dynamic light scattering particle size distribution analyzer DLS (product name "SZ-100", manufactured by Horiba, Ltd.). D50 was calculated from the average particle size calculated by analyzing the obtained autocorrelation function using the monodisperse cumulant method. D50 was taken as the average particle size of the particles in the liquid.

[0143] <Average particle size of dried particles> The dried particles were photographed using a scanning electron microscope (product name "JSM-IT200", manufactured by JEOL Ltd.) Ten particles were selected from the obtained SEM image, and the particle sizes were measured, and the arithmetic average value was used.

[0144] [Example 1] (Production of Raw Material Liquid A) Distilled water (717 g), HFP (42 g), and VdF (4.5 g) were charged into a 1.0 L stainless steel pressure reactor and heated to 90°C while stirring at 500 rpm. The pressure inside the reactor at 90°C was 1.98 MPaG. Next, an aqueous ammonium persulfate solution (3.6% by mass, 5 mL) was added to initiate polymerization. As the polymerization started, the pressure inside the reactor decreased, and when the pressure reached 1.81 MPaG, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 96 minutes. After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated raw material liquid A.

[0145] (Production of Raw Material Liquid B) To the above raw material liquid A (712 g) was added a cation exchange resin (trade name "Diaion SK1BH", manufactured by Mitsubishi Chemical Corporation) (28.4 g). 60 minutes after the start of stirring, the raw material liquid and the cation exchange resin were separated by filtration. To a part (690 g) of the filtered raw material liquid was added an anion exchange resin (trade name "Diaion SA10AOH", manufactured by Mitsubishi Chemical Corporation) (20 g). 60 minutes after the start of stirring, the raw material liquid and the anion exchange resin were separated by filtration to obtain raw material liquid B. Raw material liquid B is a dispersion of particles of the first fluoropolymer in an aqueous medium. The particles of the first fluoropolymer in raw material liquid B had an average particle size of 114 nm. The composition of the first fluoropolymer is as shown in Table 1.

[0146] (Production of second fluoropolymer) A 1.0 L stainless steel pressure reactor was charged with raw material liquid B (600 g) and wax (28 g) to obtain aqueous dispersion A. The content of the first fluoropolymer was 0.75 mass% based on the total mass of aqueous dispersion A. Aqueous dispersion A did not contain a fluorinated emulsifier or any emulsifier other than the fluorinated emulsifier. The concentration of sulfate ions in aqueous dispersion A was less than 0.1 ppm by mass based on the total mass of the aqueous medium in the aqueous dispersion.

[0147] The aqueous dispersion A was degassed under vacuum and then heated to 70°C. After completion of the temperature increase, TFE was introduced into the reactor until the internal pressure reached 1.4 MPaG. An aqueous disuccinic acid peroxide (DSAP) solution (0.56 mass%, 11 mL) was added to initiate polymerization. TFE was continuously added so as to prevent a decrease in pressure as the polymerization progressed (i.e., so as to maintain an internal pressure of 1.4 MPaG). After 292 minutes, when 80 g of TFE had been consumed, the reactor was cooled and the gas was purged to terminate the polymerization reaction. A dispersion containing a fluoropolymer was obtained. After completion of the polymerization reaction, almost no coagulum was observed in the dispersion containing the fluoropolymer. The fluoropolymer had an average particle size of 301 nm.

[0148] In the dispersion containing the fluoropolymer, the solids concentration of the fluoropolymer was 10.1 mass %.

[0149] The dispersion containing the fluoropolymer was freeze-aggregated, filtered, and dried. The dried fluoropolymer had an average particle size of 238 nm. The composition of the fluoropolymer was confirmed by NMR to be TFE / VdF / HFP=99.3 / 0.3 / 0.4 (molar ratio).

[0150] [Example 2] (Production of Raw Material Solution A) Distilled water (717 g), HFP (42 g), VdF (39 g), and TFE (2.6 g) were charged into a 1.0 L stainless steel pressure reactor and heated to 90°C while stirring at 500 rpm. The pressure inside the reactor when it reached 90°C was 1.90 MPaG. Next, an aqueous ammonium persulfate solution (3.6% by mass, 5 mL) was added to initiate polymerization. As the polymerization started, the pressure inside the reactor decreased, and when the pressure reached 1.76 MPaG, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 37 minutes. After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated raw material solution A.

[0151] (Production of Raw Material Liquid B) To the above raw material liquid A (712 g) was added a cation exchange resin (trade name "Diaion SK1BH", manufactured by Mitsubishi Chemical Corporation) (28.4 g). 60 minutes after the start of stirring, the raw material liquid and the cation exchange resin were separated by filtration. To a part (690 g) of the filtered raw material liquid was added an anion exchange resin (trade name "Diaion SA10AOH", manufactured by Mitsubishi Chemical Corporation) (20 g). 60 minutes after the start of stirring, the raw material liquid and the anion exchange resin were separated by filtration to obtain raw material liquid B. Raw material liquid B is a dispersion of particles of the first fluoropolymer in an aqueous medium. The particles of the first fluoropolymer in raw material liquid B had an average particle diameter of 120 nm. The composition of the first fluoropolymer is as shown in Table 1.

[0152] (Production of second fluoropolymer) A 1.0 L stainless steel pressure reactor was charged with raw material liquid B (600 g) and wax (28 g) to obtain aqueous dispersion A. The content of the first fluoropolymer was 0.82 mass% based on the total mass of aqueous dispersion A. Aqueous dispersion A did not contain a fluorinated emulsifier or any emulsifier other than the fluorinated emulsifier. The concentration of sulfate ions in aqueous dispersion A was less than 0.1 ppm by mass based on the total mass of the aqueous medium in the aqueous dispersion.

[0153] The aqueous dispersion A was degassed under vacuum and then heated to 70°C. After completion of the temperature increase, TFE was introduced into the reactor until the internal pressure reached 1.4 MPaG. An aqueous disuccinic acid peroxide (DSAP) solution (0.56 mass%, 11 mL) was added to initiate polymerization. TFE was continuously added so as to prevent a decrease in pressure as the polymerization progressed (i.e., so as to maintain an internal pressure of 1.4 MPaG). After 280 minutes, when 80 g of TFE had been consumed, the reactor was cooled and the gas was purged to terminate the polymerization reaction. A dispersion containing a fluoropolymer was obtained. After completion of the polymerization reaction, almost no coagulum was observed in the dispersion containing the fluoropolymer. The fluoropolymer had an average particle size of 278 nm.

[0154] In the dispersion containing the fluoropolymer, the solids concentration of the fluoropolymer was 10.3 mass %.

[0155] The dispersion containing the fluoropolymer was freeze-aggregated, filtered, and dried. The dried fluoropolymer had an average particle size of 225 nm. The composition of the fluoropolymer was confirmed by NMR to be TFE / VdF / HFP=99.4 / 0.4 / 0.2 (molar ratio).

[0156] [Example 3] (Production of Raw Material Solution A) Distilled water (717 g), HFP (42 g), and VdF (4.5 g) were charged into a 1.0 L stainless steel pressure reactor and heated to 90°C while stirring at 500 rpm. The pressure inside the reactor at 90°C was 1.90 MPaG. Next, an aqueous ammonium persulfate solution (3.6% by mass, 5 mL) was added to initiate polymerization. As the polymerization started, the pressure inside the reactor decreased, and when the pressure reached 1.80 MPaG, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 97 minutes. After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated raw material solution A.

[0157] (Production of Raw Material Liquid B) To the above raw material liquid A (712 g) was added a cation exchange resin (trade name "Diaion SK1BH", manufactured by Mitsubishi Chemical Corporation) (28.4 g). 60 minutes after the start of stirring, the raw material liquid and the cation exchange resin were separated by filtration. To a part (690 g) of the filtered raw material liquid was added an anion exchange resin (trade name "Diaion SA10AOH", manufactured by Mitsubishi Chemical Corporation) (20 g). 60 minutes after the start of stirring, the raw material liquid and the anion exchange resin were separated by filtration to obtain raw material liquid B. Raw material liquid B is a dispersion of particles of the first fluoropolymer in an aqueous medium. The particles of the first fluoropolymer in raw material liquid B had an average particle size of 117 nm. The composition of the first fluoropolymer is as shown in Table 1.

[0158] (Production of second fluoropolymer) The above-mentioned raw material liquid B was used as aqueous dispersion A. The content of the first fluoropolymer was 0.72% by mass based on the total mass of aqueous dispersion A. Aqueous dispersion A did not contain a fluorinated emulsifier and no emulsifier other than the fluorinated emulsifier. The concentration of sulfate ions in aqueous dispersion A was 1.3 ppm by mass based on the total mass of the aqueous medium in the aqueous dispersion.

[0159] A 1.0 L stainless steel pressure reactor was charged with raw material solution B (600 g), perfluorobutylethylene (PFBE, 0.73 g), and t-butyl methyl ether (0.51 g), and the temperature was raised to 70 ° C. while stirring at 260 rpm. TFE was injected into the reactor until the pressure reached 1.8 MPaG, and then 2 mL of an isododecane solution of PBPV (trade name "Marukasol", manufactured by Maruzen Oil Co., Ltd., 40% by mass) was added to initiate polymerization. To prevent the pressure from decreasing as the polymerization progressed (i.e., to maintain an internal pressure of 1.8 MPaG), a mixed gas of TFE and ethylene (TFE:ethylene = 54:46 (molar ratio)) was continuously added, and 3.2 g of PFBE was added in four installments. After 229 minutes, when 80 g of a mixed gas of TFE and ethylene (TFE:ethylene=54:46 (molar ratio)) had been consumed, the reactor was cooled and the gas was purged to terminate the polymerization reaction. A dispersion containing a fluoropolymer was obtained. After completion of the polymerization reaction, almost no coagulum was found in the dispersion containing the fluoropolymer. The fluoropolymer had an average particle size of 234 nm.

[0160] In the dispersion containing the fluoropolymer, the solids concentration of the fluoropolymer was 10.3 mass %.

[0161] The dispersion containing the fluoropolymer was freeze-aggregated, filtered, and dried. The dried fluoropolymer had an average particle size of 164 nm. The composition of the fluoropolymer was confirmed by NMR to be TFE / ethylene / PFBE / VdF / HFP=54.8 / 43.5 / 0.8 / 0.5 / 0.4 (molar ratio).

[0162] [Example 4] (Production of Raw Material Solution A) Distilled water (717 g), HFP (42 g), and VdF (4.5 g) were charged into a 1.0 L stainless steel pressure reactor and heated to 90°C while stirring at 500 rpm. The pressure inside the reactor when it reached 90°C was 1.97 MPaG. Next, an aqueous ammonium persulfate solution (3.6% by mass, 5 mL) was added to initiate polymerization. As the polymerization started, the pressure inside the reactor decreased, and when the pressure reached 1.80 MPaG, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 95 minutes. After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated raw material solution A.

[0163] (Production of Raw Material Liquid B) To the above raw material liquid A (712 g) was added a cation exchange resin (trade name "Diaion SK1BH", manufactured by Mitsubishi Chemical Corporation) (28.4 g). 60 minutes after the start of stirring, the raw material liquid and the cation exchange resin were separated by filtration. To a part (690 g) of the filtered raw material liquid was added an anion exchange resin (trade name "Diaion SA10AOH", manufactured by Mitsubishi Chemical Corporation) (20 g). 60 minutes after the start of stirring, the raw material liquid and the anion exchange resin were separated by filtration to obtain raw material liquid B. Raw material liquid B is a dispersion of particles of the first fluoropolymer in an aqueous medium. The particles of the first fluoropolymer in raw material liquid B had an average particle size of 115 nm. The composition of the first fluoropolymer is as shown in Table 1.

[0164] (Production of second fluoropolymer) A 1.0 L stainless steel pressure reactor was charged with raw material liquid B (600 g), 16 g of t-butanol, and 5 g of methyl acetate to obtain aqueous dispersion A. The content of the first fluoropolymer was 0.82 mass% based on the total mass of aqueous dispersion A. Aqueous dispersion A did not contain a fluorinated emulsifier and no emulsifier other than the fluorinated emulsifier. The concentration of sulfate ions in aqueous dispersion A was 0.7 ppm by mass based on the total mass of the aqueous medium in the aqueous dispersion.

[0165] 0.73 g of PFBE was added to aqueous dispersion A, and after vacuum degassing, the temperature was raised to 50°C. After completion of the temperature increase, a mixed gas of TFE and ethylene (TFE:ethylene = 84:16 (molar ratio)) was introduced into the reactor until the internal pressure reached 1.8 MPaG. A t-butyl hydroperoxide aqueous solution (0.20 mass%, 8 mL) and a sodium sulfite aqueous solution (0.92 mass%, 13 mL) were added to initiate polymerization. As the polymerization progressed, a mixed gas of TFE and ethylene (TFE:ethylene = 54:46 (molar ratio)) was continuously added to prevent a decrease in pressure (i.e., to maintain an internal pressure of 1.8 MPaG), and 2.8 g of PFBE was added in four divided portions. During the polymerization, an aqueous t-butyl hydroperoxide solution (0.20 mass%) and an aqueous sodium sulfite solution (0.92 mass%) were intermittently added to the reactor at a rate of 1 mL / 10 min, respectively. After 355 minutes, the reactor was cooled and the raw material gas was purged to terminate the polymerization reaction. The amount of the mixed gas of TFE and ethylene (TFE:ethylene=54:46 (molar ratio)) consumed was 80 g. A dispersion containing a fluoropolymer was obtained. After the polymerization reaction was completed, almost no coagulum was observed in the dispersion containing the fluoropolymer. The fluoropolymer had an average particle size of 192 nm.

[0166] In the dispersion containing the fluoropolymer, the solids concentration of the fluoropolymer was 9.1 mass %.

[0167] The dispersion containing the fluoropolymer was freeze-aggregated, filtered, and dried. The dried fluoropolymer had an average particle size of 176 nm. The composition of the fluoropolymer was confirmed by NMR to be TFE / ethylene / PFBE / VdF / HFP=54.6 / 43.5 / 0.8 / 0.6 / 0.5 (molar ratio).

[0168] [Example 5] (Production of a second fluoropolymer) Ultrapure water (121 g), raw material solution B (475 g) from Example 1, PPVE (20 g), and t-BuOMe (0.5 g) were charged into a 1.0 L stainless steel pressure reactor to obtain aqueous dispersion A. Aqueous dispersion A was heated to 70°C while stirring at 260 rpm. TFE was injected into the reactor until the pressure reached 1.0 MPaG, and an aqueous solution of ammonium persulfate (APS) (1.9 mass%, 4 mL) was added to initiate polymerization. As the polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain the pressure constant. When 60 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 238 minutes. After the polymerization reaction was completed, almost no coagulum was observed in the dispersion containing the fluoropolymer. The fluoropolymer had an average particle size of 156 nm.

[0169] In the dispersion containing the fluoropolymer, the solids concentration of the fluoropolymer was 7.0 mass %.

[0170] The dispersion containing the fluoropolymer was freeze-aggregated, filtered, and dried. The dried fluoropolymer had an average particle size of 150 nm. The composition of the fluoropolymer was confirmed by NMR to be TFE / PPVE / VdF / HFP=98.0 / 1.0 / 0.4 / 0.6 (molar ratio).

[0171] [Example 6] Ultrapure water (149 g), raw material solution B (475 g) from Example 1, and t-BuOMe (0.5 g) were charged into a 1.0 L stainless steel pressure reactor to obtain aqueous dispersion A. Aqueous dispersion A was heated to 63°C while stirring at 260 rpm. Next, HFP (16 g) was charged, and TFE was injected until the reactor pressure reached 1.0 MPaG. An aqueous solution of ammonium persulfate (APS) (0.5% by mass, 5 mL) was added to initiate polymerization. As the polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain the pressure constant. When 100 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 560 minutes. After the polymerization reaction was completed, almost no coagulum was observed in the dispersion containing the fluoropolymer. The fluoropolymer had an average particle size of 198 nm.

[0172] In the dispersion containing the fluoropolymer, the solids concentration of the fluoropolymer was 15.0 mass %.

[0173] The dispersion containing the fluoropolymer was freeze-aggregated, filtered, and dried. The dried fluoropolymer had an average particle size of 192 nm. The composition of the fluoropolymer was confirmed by NMR to be TFE / HFP / VdF=94.9 / 4.8 / 0.3 (molar ratio).

[0174] [Example 7] (Production of Raw Material Liquid A) Distilled water (717 g), HFP (15 g), and VdF (7.2 g) were charged into a 1.0 L stainless steel pressure reactor and heated to 90°C while stirring at 500 rpm. The pressure inside the reactor at 90°C was 1.70 MPaG. Next, an aqueous ammonium persulfate solution (3.6% by mass, 5 mL) was added to initiate polymerization. As the polymerization started, the pressure inside the reactor decreased, and when the pressure reached 1.40 MPaG, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 9 minutes. After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated raw material liquid A.

[0175] (Production of Raw Material Liquid B) To the above raw material liquid A (712 g) was added a cation exchange resin (trade name "Diaion SK1BH", manufactured by Mitsubishi Chemical Corporation) (28.4 g). 60 minutes after the start of stirring, the raw material liquid and the cation exchange resin were separated by filtration. To a part (690 g) of the filtered raw material liquid was added an anion exchange resin (trade name "Diaion SA10AOH", manufactured by Mitsubishi Chemical Corporation) (20 g). 60 minutes after the start of stirring, the raw material liquid and the anion exchange resin were separated by filtration to obtain raw material liquid B. Raw material liquid B is a dispersion of particles of the first fluoropolymer in an aqueous medium. The particles of the first fluoropolymer in raw material liquid B had an average particle size of 105 nm. The composition of the first fluoropolymer is as shown in Table 1.

[0176] (Production of second fluoropolymer) A 1.0 L stainless steel pressure reactor was charged with raw material liquid B (600 g) and wax (28 g) to obtain aqueous dispersion A. The content of the first fluoropolymer was 0.75 mass% based on the total mass of aqueous dispersion A. Aqueous dispersion A did not contain a fluorinated emulsifier or any emulsifier other than the fluorinated emulsifier. The concentration of sulfate ions in aqueous dispersion A was less than 0.1 ppm by mass based on the total mass of the aqueous medium in the aqueous dispersion.

[0177] The aqueous dispersion A was degassed under vacuum and then heated to 70°C. After completion of the temperature increase, TFE was introduced into the reactor until the internal pressure reached 1.4 MPaG. An aqueous disuccinic acid peroxide (DSAP) solution (0.56 mass%, 11 mL) was added to initiate polymerization. TFE was continuously added so as to prevent a decrease in pressure as the polymerization progressed (i.e., so as to maintain an internal pressure of 1.4 MPaG). After 29 minutes, when 5 g of TFE had been consumed, the reactor was cooled and the gas was purged to terminate the polymerization reaction. After the polymerization reaction was completed, the reactor contained coagulum, and no dispersion containing a fluoropolymer was obtained.

[0178] [Example 8] (Production of Raw Material Solution A) Distilled water (717 g), HFP (32 g), and VdF (4.5 g) were charged into a 1.0 L stainless steel pressure reactor and heated to 90°C while stirring at 500 rpm. The pressure inside the reactor at 90°C was 1.84 MPaG. Next, an aqueous ammonium persulfate solution (3.6% by mass, 5 mL) was added to initiate polymerization. As the polymerization started, the pressure inside the reactor decreased, and when the pressure reached 1.52 MPaG, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 88 minutes. After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated raw material solution A.

[0179] (Production of Raw Material Liquid B) To the above raw material liquid A (712 g) was added a cation exchange resin (trade name "Diaion SK1BH", manufactured by Mitsubishi Chemical Corporation) (28.4 g). 60 minutes after the start of stirring, the raw material liquid and the cation exchange resin were separated by filtration. To a part (690 g) of the filtered raw material liquid was added an anion exchange resin (trade name "Diaion SA10AOH", manufactured by Mitsubishi Chemical Corporation) (20 g). 60 minutes after the start of stirring, the raw material liquid and the anion exchange resin were separated by filtration to obtain raw material liquid B. Raw material liquid B is a dispersion of particles of the first fluoropolymer in an aqueous medium. The particles of the first fluoropolymer in raw material liquid B had an average particle size of 122 nm. The composition of the first fluoropolymer is as shown in Table 1.

[0180] (Production of second fluoropolymer) A 1.0 L stainless steel pressure reactor was charged with raw material liquid B (600 g) and wax (28 g) to obtain aqueous dispersion A. The content of the first fluoropolymer was 0.74 mass% based on the total mass of aqueous dispersion A. Aqueous dispersion A did not contain a fluorinated emulsifier or any emulsifier other than the fluorinated emulsifier. The concentration of sulfate ions in aqueous dispersion A was less than 0.1 ppm by mass based on the total mass of the aqueous medium in the aqueous dispersion.

[0181] The aqueous dispersion A was degassed under vacuum and then heated to 70°C. After completion of the temperature increase, TFE was introduced into the reactor until the internal pressure reached 1.4 MPaG. An aqueous disuccinic acid peroxide (DSAP) solution (0.56 mass%, 11 mL) was added to initiate polymerization. TFE was continuously added so as to prevent a decrease in pressure as the polymerization progressed (i.e., so as to maintain an internal pressure of 1.4 MPaG). After 27 minutes, when 5 g of TFE had been consumed, the reactor was cooled and the gas was purged to terminate the polymerization reaction. After the polymerization reaction was completed, the reactor contained coagulum, and no dispersion containing a fluoropolymer was obtained.

[0182] Example 9 (Production of Raw Material Solution A) Ultrapure water (740 g), sodium sulfite (88 mg), n-BMA (n-butyl methacrylate, 330 mg), iron(II) sulfate heptahydrate (11 mg), and sodium hydroxyethylethylenediaminetriacetate dihydrate (product name "Chilest HC", manufactured by Chelest Corporation) (17 mg) were charged into a 1.2 L stainless steel pressure reactor, and the temperature was raised to 60°C while stirring at 500 rpm. An aqueous ammonium persulfate solution (5.0 mass%, 3.8 mL) was added, and polymerization was carried out for 60 minutes. After completion of the polymerization reaction, the liquid was withdrawn. This liquid was designated raw material solution A.

[0183] (Production of Raw Material Solution B) To the raw material solution A (712 g), a cation exchange resin (trade name "Diaion SK1BH", manufactured by Mitsubishi Chemical Corporation) (28.4 g) was added. 60 minutes after the start of stirring, the raw material solution and the cation exchange resin were separated by filtration. To a portion (690 g) of the filtered raw material solution, an anion exchange resin (trade name "Diaion SA10AOH", manufactured by Mitsubishi Chemical Corporation) (20 g) was added. 60 minutes after the start of stirring, the raw material solution and the anion exchange resin were separated by filtration to obtain raw material solution B. Raw material solution B is a dispersion of particles of the first polymer in an aqueous medium. The particles of the first polymer in raw material solution B had an average particle diameter of 96 nm. The composition of the first polymer is as shown in Table 1.

[0184] (Production of Fluoropolymer) A 1.0 L stainless steel pressure reactor was charged with raw material liquid B (600 g) and wax (28 g) to obtain aqueous dispersion A. The content of the first polymer was 0.82 mass% based on the total mass of aqueous dispersion A. Aqueous dispersion A did not contain a fluorine-containing emulsifier or any emulsifier other than the fluorine-containing emulsifier. The concentration of sulfate ions in aqueous dispersion A was less than 0.1 ppm by mass based on the total mass of the aqueous medium in the aqueous dispersion.

[0185] The aqueous dispersion A was degassed under vacuum and then heated to 70°C. After completion of the temperature increase, TFE was introduced into the reactor until the internal pressure reached 1.4 MPaG. An aqueous disuccinic acid peroxide (DSAP) solution (0.56 mass%, 11 mL) was added to initiate polymerization. TFE was continuously added so as to prevent a decrease in pressure as the polymerization progressed (i.e., so as to maintain an internal pressure of 1.4 MPaG). After 357 minutes, when 80 g of TFE had been consumed, the reactor was cooled and the gas was purged to terminate the polymerization reaction. A dispersion containing a fluoropolymer was obtained. After completion of the polymerization reaction, almost no coagulum was observed in the dispersion containing the fluoropolymer. The fluoropolymer had an average particle size of 298 nm.

[0186] In the dispersion containing the fluoropolymer, the solids concentration of the fluoropolymer was 10.1 mass %.

[0187] The dispersion containing the fluoropolymer was freeze-aggregated, filtered, and dried. The dried fluoropolymer had an average particle size of 230 nm. The composition of the fluoropolymer was confirmed by NMR to be TFE / n-BMA=99.6 / 0.4 (molar ratio).

[0188] Example 10 (Preparation of Raw Material Solution A) Raw material solution A was obtained in the same manner as in Example 3.

[0189] After obtaining raw material liquid A, ion exchange treatment was not carried out, and raw material liquid A was used as raw material liquid B. Raw material liquid B is a dispersion of particles of the first fluoropolymer in an aqueous medium. In raw material liquid B, the particles of the first fluoropolymer had an average particle diameter of 128 nm. The composition of the first fluoropolymer is as shown in Table 1.

[0190] (Production of second fluoropolymer) The above-mentioned raw material liquid B was used as aqueous dispersion A. The content of the first fluoropolymer was 0.72% by mass based on the total mass of aqueous dispersion A. Aqueous dispersion A did not contain a fluorinated emulsifier and no emulsifier other than the fluorinated emulsifier. The concentration of sulfate ions in aqueous dispersion A was 280 ppm by mass based on the total mass of the aqueous medium in the aqueous dispersion.

[0191] A 1.0 L stainless steel pressure reactor was charged with raw material solution B (600 g), perfluorobutylethylene (PFBE, 0.73 g), and t-butyl methyl ether (0.51 g), and the temperature was raised to 70 ° C. while stirring at 260 rpm. TFE was injected into the reactor until the pressure reached 1.8 MPaG, and then 2 mL of an isododecane solution of PBPV (trade name "Marukasol", manufactured by Maruzen Oil Co., Ltd., 40% by mass) was added to initiate polymerization. To prevent the pressure from decreasing as the polymerization progressed (i.e., to maintain an internal pressure of 1.8 MPaG), a mixed gas of TFE and ethylene (TFE:ethylene = 54:46 (molar ratio)) was continuously added, and 3.2 g of PFBE was added in four installments. After 215 minutes, when 80 g of a mixed gas of TFE and ethylene (TFE:ethylene=54:46 (molar ratio)) had been consumed, the reactor was cooled and the gas was purged to terminate the polymerization reaction. A dispersion containing a fluoropolymer was obtained. After completion of the polymerization reaction, almost no coagulum was found in the dispersion containing the fluoropolymer. The fluoropolymer had an average particle size of 240 nm.

[0192] In the dispersion containing the fluoropolymer, the solids concentration of the fluoropolymer was 10.3 mass %.

[0193] The dispersion containing the fluoropolymer was freeze-aggregated, filtered, and dried. The dried fluoropolymer had an average particle size of 168 nm. The composition of the fluoropolymer was confirmed by NMR to be TFE / ethylene / PFBE / VdF / HFP=54.8 / 43.5 / 0.7 / 0.6 / 0.4 (molar ratio).

[0194] [Evaluation] <Heat of fusion and melting point> The heat of fusion and melting point of the obtained fluoropolymer were measured using a differential scanning calorimeter (product name "DSC-204 F1", manufactured by NETZSCH). Specifically, 5 mg of a sample for measurement was weighed out and placed in an aluminum sample pan, cooled to -50°C under a nitrogen atmosphere, and then heated to 370°C at a rate of 10°C / min. During the temperature increase, a portion that deviated from the baseline was identified as an endothermic peak. Based on the area of ​​the endothermic peak, the heat of fusion (J / g) was calculated using software attached to the device. The top of the endothermic peak during melting was taken as the melting point.

[0195] <5% Weight Loss Temperature> The 5% weight loss temperature of the obtained fluoropolymer was measured using a simultaneous differential thermal and thermogravimetric analyzer (product name "STA-2500", manufactured by NETZSCH). Specifically, 10 mg of a sample for measurement was weighed out and placed in an aluminum sample pan, and heated in an air atmosphere from 50°C to 500°C at a rate of 10°C / min. The temperature at which the change in weight due to heating indicated 95% by mass relative to the mass of the charged sample was defined as the 5% weight loss temperature.

[0196] <Coloration> The coloration of the obtained fluoropolymer was evaluated. A: Not colored. B: Colored.

[0197] In Examples 7 and 8, a dispersion containing a fluoropolymer could not be obtained, and therefore evaluation could not be carried out.

[0198]

[0199] As shown in Table 1, in Examples 1 to 6, the 5% weight loss temperature was higher than the melting point, indicating excellent heat resistance. In addition, in Examples 1 to 6, it was found that coloration was suppressed.

[0200] The disclosure of Japanese Patent Application No. 2024-099101, filed on June 19, 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. A method for producing a second fluorine-containing polymer different from the first fluorine-containing polymer by polymerizing a monomer containing a fluorine-containing monomer in an aqueous dispersion containing a first fluorine-containing polymer and an aqueous medium, wherein the first fluorine-containing polymer contains structural units based on vinylidene fluoride and structural units based on at least one selected from the group consisting of hexafluoropropene, a fluorine-containing vinyl ether, chlorotrifluoroethylene, tetrafluoroethylene, and a fluorine-containing allyl ether, and has a glass transition temperature of -20°C or higher, and in differential scanning calorimetry, does not exhibit an endothermic peak in a region of 100°C or higher, or the total heat of fusion in a region of 100°C or higher is 40 J / g or lower, and before starting polymerization of the monomers, the aqueous dispersion does not contain a fluorine-containing emulsifier, or the content of the fluorine-containing emulsifier is 100 ppm by mass or lower relative to the total mass of the aqueous dispersion, the aqueous dispersion does not contain sulfate ions, or the concentration of sulfate ions is 10 ppm by mass or less relative to the total mass of the aqueous medium in the aqueous dispersion, before polymerization of the monomers is initiated.

2. The method for producing a fluoropolymer according to claim 1, wherein the content of said first fluoropolymer is 0.01 to 4.0% by mass based on the total mass of said aqueous dispersion before the start of polymerization of said monomers.

3. A method for producing a fluorine-containing polymer according to claim 1 or 2, wherein the fluorine-containing monomer comprises at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropene, and vinylidene fluoride.

4. The method for producing a fluorine-containing polymer according to claim 1 or 2, wherein the monomer comprises ethylene.

5. The method for producing a fluorine-containing polymer according to claim 1 or 2, wherein the monomers are polymerized in the presence of a polymerization initiator X represented by the following formula (X): １ -O-OH...Formula (X) In formula (X), R １ is an alkyl group having 1 to 7 carbon atoms.

6. A fluoropolymer composition comprising a first fluoropolymer and a second fluoropolymer different from the first fluoropolymer, wherein the first fluoropolymer comprises structural units based on vinylidene fluoride and structural units based on at least one selected from the group consisting of hexafluoropropene, fluorinated vinyl ether, chlorotrifluoroethylene, tetrafluoroethylene, and fluorinated allyl ether, and has a glass transition temperature of -20°C or higher, and in differential scanning calorimetry, has no endothermic peak in a region of 100°C or higher, or has a total heat of fusion in a region of 100°C or higher of 40 J / g or lower, the second fluoropolymer comprises at least one selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropene, and vinylidene fluoride, and the fluoropolymer composition does not contain a fluorinated emulsifier, or the content of the fluorinated emulsifier is 100 ppb by mass or less based on the total mass of the first fluoropolymer and the second fluoropolymer, The fluoropolymer composition, wherein the fluoropolymer composition does not contain sulfate ions or has a sulfate ion concentration of 100 ppb by mass or less based on the total mass of the first fluoropolymer and the second fluoropolymer.

7. The fluorine-containing polymer composition according to claim 6, which is an aqueous dispersion containing an aqueous medium.

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