Method for producing solid composition, solid composition, and crosslinked rubber article

Abstract

Provided is a method for producing a solid composition, the method being capable of producing a solid composition substantially free from an emulsifier and excellent in crosslinking rate.　This method for producing a solid composition involves polymerizing monomers including TFE and PAVE in an aqueous dispersion containing substantially no water-soluble emulsifier and containing an aqueous medium and a first fluorine-containing polymer containing a TFE unit and a PAVE unit to obtain an aqueous dispersion containing a second fluorine-containing polymer, subjecting the aqueous dispersion containing the second fluorine-containing polymer to a stirring treatment, and collecting a solid obtained after the stirring treatment to obtain a solid composition, wherein: the proportion of the PAVE unit is 5-80 mol% with respect to the total of the TFE unit and the PAVE unit in the first fluorine-containing polymer; the proportion of units based on PAVE is 15-95 mol% with respect to the total of the TFE unit and the units based on PAVE in the second fluorine-containing polymer; and the content of the first fluorine-containing polymer is 0.01-4.0 mass% with respect to the total mass of the aqueous dispersion before starting the polymerization of the monomers.

Description

Method for producing solid composition, solid composition, crosslinked rubber article

[0001] The present invention relates to a method for producing a solid composition, the solid composition, and a crosslinked rubber article.

[0002] Crosslinked rubber articles obtained by crosslinking a composition containing a fluoropolymer are used in various industrial fields because they have excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. Examples of methods for producing such fluoropolymers include a method in which a fluorine-containing monomer is emulsion-polymerized in an aqueous medium using an emulsifier (see Patent Document 1).

[0003] International Publication No. 2022 / 052498

[0004] In the method for producing a fluorine-containing polymer disclosed in Patent Document 1, an emulsifier is used during polymerization, but if the emulsifier remains in a crosslinked rubber article produced using a composition containing a fluorine-containing polymer, it may have adverse effects such as contamination of the surrounding area, and therefore, recently, there has been a demand for a reduction in the amount of emulsifier. Furthermore, when producing crosslinked rubber articles, etc., a high crosslinking rate is required from the viewpoint of production efficiency. In other words, recently, there has been a demand for a fluorine-containing solid composition that is substantially free of emulsifier and has an excellent crosslinking rate.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a solid composition that is substantially free of an emulsifier and has an excellent crosslinking rate. Another object of the present invention is to provide the solid composition.

[0006] As a result of intensive investigations into the above-mentioned problems, the present inventors have found that a solid composition can be obtained without necessarily requiring an emulsifier or a component that reduces the crosslinking rate, by a method in which monomers are polymerized in an aqueous dispersion containing a predetermined first fluoropolymer and which is substantially free of an emulsifier, and then the resulting mixture is stirred to recover a solid composition, thereby arriving at the present invention.

[0007] That is, the inventors have found that the above problems can be solved by the following configuration: [1] A method for producing a solid composition, comprising polymerizing a monomer containing tetrafluoroethylene and perfluoro(alkyl vinyl ether) in an aqueous dispersion containing a first fluorine-containing polymer which is substantially free of a water-soluble emulsifier and contains units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and an aqueous medium, stirring the resulting aqueous dispersion containing a second fluorine-containing polymer, and recovering a solid obtained after the stirring treatment to obtain a solid composition, wherein the units based on perfluoro(alkyl vinyl ether) are 5 to 80 mol % relative to the total of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether) in the first fluorine-containing polymer, and the units based on perfluoro(alkyl vinyl ether) are 15 to 95 mol % relative to the total of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether) in the second fluorine-containing polymer,

[0023]

[0024] A method for producing a solid composition, wherein the content of the first fluorine-containing polymer is 0.01 to 4.0% by mass relative to the total mass of the aqueous dispersion before initiating polymerization of the monomers. [2] A method for producing a solid composition according to [1], wherein the solid composition has a storage modulus at 100°C of 300 kPa or more. [3] A method for producing a solid composition according to [1] or [2], wherein the solid composition does not contain an emulsifier, or, if the solid composition contains an emulsifier, the total content of the emulsifier is 500 ppb or less relative to the total mass of the solid composition. [4] A method for producing a solid composition according to any one of [1] to [3], wherein the total content of metals in the solid composition is 20 ppm by mass or less relative to the total mass of the solid composition. [5] The method for producing a solid composition according to any one of [1] to [4], wherein the second fluorine-containing polymer contains 35 to 80 mol% of units based on tetrafluoroethylene and 20 to 60 mol% of units based on perfluoro(alkyl vinyl ether), based on all units.[6] A method for producing a solid composition according to any one of [1] to [5], wherein the second fluorine-containing polymer contains at least one selected from the group consisting of a polymerizable unsaturated bond, a chlorine atom, a bromine atom, an iodine atom, and a nitrile group. [7] A method for producing a solid composition according to any one of [1] to [6], comprising a step of washing the solid composition. [8] A solid composition comprising a fluorine-containing polymer containing units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), the solid composition being substantially free of an emulsifier and satisfying Requirement X. Requirement X: In a mixture obtained by mixing the solid composition with water having a pH of 6 so that the amount of water is 5 times the mass of the solid composition, the pH of the mixture at 23°C 24 hours after the mixing is 4 or higher. [9] The solid composition according to [8], which is substantially free of a flocculant.

[10] A crosslinked rubber article obtained by crosslinking the solid composition according to [8] or [9].

[0008] According to the present invention, there is provided a method for producing a solid composition that is substantially free of emulsifiers and has an excellent crosslinking rate. Furthermore, according to the present invention, there are also provided the solid composition and a crosslinked rubber article obtained by crosslinking the solid composition.

[0009] The meanings of terms used in the present invention are as follows. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the upper and lower limits. In the numerical ranges described in this specification in stages, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the Examples. In this specification, each component may be used alone or in combination with two or more substances corresponding to the component. Herein, when two or more substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. A "unit" is a collective term for an atomic group derived from one molecule of the above-mentioned monomer, formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a portion of the above-mentioned atomic group. Hereinafter, a "unit based on a monomer" will also be simply referred to as a "unit." The content (mass % or mol %) of each unit relative to all units contained in the polymer is determined by analyzing the polymer by solid-state nuclear magnetic resonance spectroscopy (NMR), and usually, the content of each unit calculated from the amount of each monomer charged substantially coincides with the actual content of each unit.

[0010] [Method for producing a solid composition] The method for producing a solid composition of the present invention (hereinafter also referred to as "the present production method") comprises polymerizing a monomer containing tetrafluoroethylene (hereinafter also referred to as "TFE") and perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE") in an aqueous dispersion (hereinafter also referred to as "first aqueous dispersion") containing a first fluoropolymer which is substantially free of a water-soluble emulsifier and contains units based on TFE and units based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"), and an aqueous medium, stirring the resulting aqueous dispersion (hereinafter also referred to as "second aqueous dispersion") containing a second fluoropolymer, and recovering the solid matter obtained after the stirring treatment to obtain a solid composition, wherein the units based on PAVE in the first fluoropolymer account for 5 to 80 mol % of the total of the units based on TFE and the units based on PAVE, This is a method for producing a solid composition, wherein the second fluoropolymer contains 15 to 95 mol% of the PAVE-based units relative to the total of the TFE-based units and the PAVE-based units, and the content of the first fluoropolymer is 0.01 to 4.0 mass% based on the total mass of the aqueous dispersion before the initiation of polymerization of the monomers. This production method allows for the production of a solid composition that is substantially free of emulsifiers and has an excellent crosslinking rate. While the details of this are unclear, by carrying out polymerization in a first aqueous dispersion containing a predetermined amount of a predetermined first fluoropolymer, the first fluoropolymer functions as a polymerization site, allowing the monomers to be polymerized without the use of an emulsifier, resulting in a solid composition that is substantially free of emulsifiers. When an emulsifier is used during polymerization, a flocculant such as an acid is usually required to recover solids from the aqueous dispersion after polymerization. If such a flocculant remains in the solid composition, the crosslinking reaction is inhibited and the crosslinking rate is reduced. In this production method, since polymerization is carried out in a first aqueous dispersion that is substantially free of emulsifiers, a solid composition can be obtained by stirring. The solid composition thus obtained does not contain any components that inhibit crosslinking, and is therefore presumed to have an excellent crosslinking rate.In this specification, the step of polymerizing a monomer containing TFE and PAVE in a first aqueous dispersion to obtain a second aqueous dispersion containing a second fluoropolymer is also referred to as "step 1," and the step of subjecting the second aqueous dispersion to a stirring treatment and recovering a solid to obtain a solid composition is also referred to as "step 2." The monomer containing TFE and PAVE used in the step of obtaining the second aqueous dispersion containing the second fluoropolymer is also referred to as "specific monomer" hereinafter. Each step will be described below.

[0011] <Step 1> In step 1 of the present production method, polymerization is carried out in a first aqueous dispersion which is substantially free of a water-soluble emulsifier and which contains a first fluorine-containing polymer and an aqueous medium.

[0012] (First aqueous dispersion) - Emulsifier - The first aqueous dispersion does not use a water-soluble emulsifier and is substantially free of a water-soluble emulsifier. "Substantially free of a water-soluble emulsifier" means that the content of the water-soluble emulsifier in the first aqueous dispersion is 10 ppm by mass or less, preferably 100 ppb by mass or less, and more preferably 50 ppb by mass or less, relative to the total mass of the first aqueous dispersion. It is also preferable that the content is below the quantitation limit of the measurement method in the examples. An example of a lower limit is 1 ppb by mass. The content of the water-soluble emulsifier can be measured using a liquid chromatograph mass spectrometer. Specifically, the measurement methods described in paragraphs 0721 to 0732 of WO 2018 / 181904 can be mentioned, and the measurement method shown in the examples is preferred.

[0013] The water-soluble emulsifier means an emulsifier having a solubility of 100 mg or more in 1000 g of water at 25°C. Examples of the water-soluble emulsifier include water-soluble emulsifiers containing fluorine atoms and emulsifiers not containing fluorine atoms. Note that neither the first fluorine-containing polymer nor the second fluorine-containing polymer described below falls under the category of emulsifiers. The water-soluble emulsifier may be either ionic or nonionic.

[0014] Examples of the emulsifier having fluorine atoms include anionic fluorine-containing emulsifiers, such as emulsifiers containing fluorine atoms whose total carbon number excluding the anionic group is 20 or less, and fluorine-containing emulsifiers whose anionic moiety has a molecular weight of 800 or less.

[0015] The fluorine-free emulsifier does not have a fluorine atom but has a hydrocarbon group such as an alkyl group. The hydrogen atom of the hydrocarbon group of the fluorine-free emulsifier may be substituted with a halogen atom other than a fluorine atom. Examples of the fluorine-free emulsifier include ionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0016] Ionic hydrocarbon emulsifiers include anionic hydrocarbon emulsifiers, which have a negatively charged hydrophilic moiety, such as a carboxylic acid group, a sulfonic acid group, a sulfate group, a phosphonic acid group, or a phosphate group, and a hydrocarbon moiety, such as an alkyl group, as a hydrophobic moiety. Examples of anionic hydrocarbon emulsifiers include the highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10, linear alkyl polyethersulfonate sodium supplied by BASF as the Avanel® S series, sodium dodecyl sulfate, and the sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobelSurfaceChemistry LLC.

[0017] Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity in water without dissociating into ions and have a hydrocarbon group such as an alkyl group as the hydrophobic moiety. Examples of the hydrophilic moiety of nonionic hydrocarbon emulsifiers include water-soluble functional groups such as polyethylene oxide chains obtained by polymerization of ethylene oxide. Examples of nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, for example, block copolymers having polyethylene oxide and polypropylene oxide. Examples of nonionic hydrocarbon emulsifiers include the emulsifiers described in paragraphs

[0043] to

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

[0018] The emulsifier with fluorine atom and the emulsifier without fluorine atom can contain silicon atom.The emulsifier containing silicon atom can include siloxane emulsifier.The siloxane emulsifier can include the emulsifier described in U.S. Patent No. 6,841,616 (Wille et al.) and U.S. Patent No. 7,977,438 (Brothers et al.).

[0019] The emulsifier having a fluorine atom and the emulsifier not having a fluorine atom may be a polymer emulsifier. Examples of the polymer emulsifier include a water-soluble polymer having a hydrophilic group in a side chain. Examples of such a polymer emulsifier include a polymer containing a unit based on a compound having a site capable of reacting by polymerization and a hydrophilic group. Further examples include polymers obtained by subjecting a polymer based on a compound having a group that can become a hydrophilic group, even if it does not have hydrophilicity during polymerization, to post-treatment such as hydrolysis.

[0020] It is preferable that the first aqueous dispersion is substantially free of an emulsifier represented by any of formulae (S1) to (S4). When no emulsifier is used in producing the first fluoropolymer contained in the first aqueous dispersion, the amount of the compound represented by any of formulae (S1) to (S4) generated can be suppressed, making it easier to adjust the content of these compounds.

[0021] H-(CF ２ ) ｎ１ -COOM (S1) F-(CF ２ ) ｎ１ -COOM (S2) H-(CF２ ) ｎ２ -SO ３ M (S3) F-(CF ２ ) ｎ２ -SO ３ M (S4) In formulas (S1) to (S4), n1 is an integer of 3 to 19, n2 is an integer of 4 to 20, and each M is independently a hydrogen atom, Na, K, or NH ４ is.

[0022] -First Fluorine-Containing Polymer-The first fluorine-containing polymer contains units based on TFE and units based on PAVE. It is presumed that the first fluorine-containing polymer adsorbs and incorporates the specific monomer at the hydrophobic portion during polymerization of the specific monomer described below, solubilizes the specific monomer even when the first aqueous dispersion does not contain an emulsifier, and facilitates the progress of polymerization of the specific monomer. It is also presumed that the first fluorine-containing polymer contributes to dispersion stabilization in the first aqueous dispersion.

[0023] The PAVE is preferably a monomer represented by formula (1) from the viewpoint of excellent polymerization reactivity in producing the first fluoropolymer and enabling more efficient production of the second fluoropolymer. ２ =CF-O-R ｆ１ (1) In formula (1), R ｆ１ represents a perfluoroalkyl group having 1 to 10 carbon atoms. ｆ１ From the viewpoint of better polymerization reactivity, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The perfluoroalkyl group may be linear or branched.

[0024] Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"), and from the viewpoint of enabling more efficient production of the second fluorinated polymer, PMVE or PPVE is preferred, and PMVE is more preferred.

[0025] In the first fluoropolymer, the content of TFE units is 20 to 95 mol%, preferably 40 to 85 mol%, based on the total of units based on TFE (also referred to as "TFE units") and units based on PAVE (also referred to as "PAVE units"), and from the viewpoint of more efficient production of the second fluoropolymer, it is more preferably 50 to 75 mol%, and even more preferably 60 to 70 mol%. In the first fluoropolymer, the content of PAVE units is 5 to 80 mol%, preferably 15 to 60 mol%, based on the total of TFE units and PAVE units, and from the viewpoint of more efficient production of the second fluoropolymer, it is more preferably 25 to 55 mol%, and even more preferably 30 to 40 mol%. When PMVE units or PPVE units are used as PAVE units, the preferred amount used is similar. The total content of TFE units and PAVE units in the first fluoropolymer is preferably from 99.0 to 100.0 mol%, more preferably from 99.5 to 100.0 mol%, and even more preferably from 99.9 to 100.0 mol%, based on all units of the first fluoropolymer.

[0026] The first fluorine-containing polymer may contain units based on monomers other than TFE and PAVE, and from the viewpoint of enabling more efficient production of the second fluorine-containing polymer, it is also preferable that it is substantially free of units based on other monomers. "Substantially free of units based on other monomers" means that the content of units based on other monomers is 0.01 mol % or less, and preferably 0 mol %, based on the total units of the first fluorine-containing polymer.

[0027] Before the polymerization of the specific monomer is initiated, the content of the first fluorine-containing polymer is 0.01 to 4.0% by mass, based on the total mass of the first aqueous dispersion, and from the viewpoint of more efficient production of the second fluorine-containing polymer, it is preferably 0.01 to 1.0% by mass, more preferably 0.01 to 0.8% by mass. In this specification, "before the polymerization of the specific monomer is initiated" means immediately before the start of polymerization. Here, examples of "start of polymerization" include the time when the specific monomer (when a polymerization initiator is used, the polymerization initiator and the specific monomer) are made to coexist in the reactor after the reactor is heated to a temperature equal to or higher than the polymerization temperature, and the time when the specific monomer (when a polymerization initiator is used, the polymerization initiator and the specific monomer) are made to coexist in the reactor after the reactor is heated to a temperature equal to or higher than the polymerization temperature.

[0028] The content (solids concentration) of the first fluoropolymer in the first aqueous dispersion can be measured, for example, by the following method. 2.0 g of the first aqueous dispersion is heated at 170°C for 20 minutes, and then the mass of the residue is weighed and the solids concentration is calculated by the following formula: "Solids concentration (mass %) = 100 × mass (g) of heated residue of first aqueous dispersion / mass (2.0 g) of first aqueous dispersion"

[0029] As a method for producing the first fluorine-containing polymer, a method of polymerizing monomers containing TFE and PAVE in an aqueous medium in the presence of a polymerization initiator is preferred. This gives the first fluorine-containing polymer dispersed in the aqueous medium in the form of particles. The aqueous medium thus obtained in which the particles of the first fluorine-containing polymer are dispersed may be used as is as the first aqueous dispersion. Alternatively, the solvent may be replaced, and the first fluorine-containing polymer may be dispersed in another aqueous medium, which may be used as the first aqueous dispersion.

[0030] The polymerization initiator used for polymerizing the first fluorine-containing polymer is preferably a water-soluble polymerization initiator. Among water-soluble polymerization initiators, persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate, or organic polymerization initiators such as disuccinic acid peroxide and azobisisobutylamidine dihydrochloride are more preferred, persulfates are still more preferred, and among persulfates, ammonium persulfate is particularly preferred.

[0031] The aqueous medium used in producing the first fluorinated polymer includes water and a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0032] It is preferable that the first fluorine-containing polymer is produced substantially free of emulsifiers. The emulsifiers (types of emulsifiers, definition of "substantially free") are as described above.

[0033] The first aqueous dispersion containing the first fluoropolymer is preferably subjected to a purification treatment to reduce or inactivate the polymerization initiator and its decomposition products before use in the polymerization of a specific monomer. By removing the polymerization initiator and its decomposition products that may be contained in the first aqueous dispersion containing the first fluoropolymer through the purification treatment, a solid composition with desired physical properties is easily obtained. Examples of purification methods include a heat treatment method and a method of passing the dispersion through an ion exchange resin (preferably an anion exchange resin). The purification treatment may be performed multiple times. From the viewpoint of removal efficiency, the total exchange capacity of the anion exchange resin is preferably 0.1 eq / L-resin or more, more preferably 0.3 eq / L-resin or more, even more preferably 0.5 eq / L-resin or more, and particularly preferably 0.7 eq / L-resin or more. The total exchange capacity of the anion exchange resin may be 20 eq / L-resin or less. The anion exchange resin is preferably spherical. The average particle diameter of the anion exchange resin is preferably 0.1 to 5 mm, more preferably 0.2 to 2 mm, and even more preferably 0.3 to 1.5 mm. When the average particle diameter of the anion exchange resin is within the above range, clogging is less likely to occur when the anion exchange resin is packed. The average particle diameter of the anion exchange resin is a value determined by a sieving method. Specifically, the anion exchange resin is first placed in a sieve shaker and the particle size distribution is measured by sieving. The diameter of the sieve opening corresponding to a cumulative 50% by mass of the residual fraction is then determined, and this is taken as the average particle diameter. The anion exchange resin may be of a gel type or a macroporous type. The resin matrix structure may be acrylic or styrene-based. Furthermore, the functional group in the anion exchange resin may be either strongly basic or weakly basic, but strongly basic is preferred from the viewpoint of impurity adsorption efficiency. The counter anion of the anion exchange resin may be a chloride ion or a hydroxide ion, but is preferably a hydroxide ion from the viewpoint of further reducing the impurity concentration in the aqueous dispersion.

[0034] -Aqueous medium- Specific examples of the aqueous medium contained in the first aqueous dispersion include the aqueous medium used in the production of the first fluorine-containing polymer described above. Before the start of polymerization of the specific monomer, the content of the aqueous medium is preferably from 60 to 99.9 mass%, more preferably from 96 to 99.9 mass%, and even more preferably from 98 to 99.9 mass%, based on the total mass of the first aqueous dispersion.

[0035] -Other Components- The first aqueous dispersion may contain components other than the first fluorinated polymer and the aqueous medium. Specific examples of the other components include a reducing agent, a pH adjuster, and a chain transfer agent, which will be described later. Specific examples of the pH adjuster include inorganic salts and ammonia. Specific examples of the inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium hydrogen carbonate and sodium carbonate. More preferred specific examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate. When the first aqueous dispersion contains a pH adjuster, the content of the pH adjuster is preferably 0.004 to 3.0 parts by mass per 100 parts by mass of the aqueous medium.

[0036] (Specific Monomer) The specific monomer is a monomer containing TFE and PAVE. Preferred embodiments of TFE and PAVE as the specific monomer are the same as the preferred embodiments of TFE and PAVE in the first fluorine-containing polymer described above. The total amount of TFE and PAVE used is preferably 80 to 100 mol%, more preferably 90 to 100 mol%, and even more preferably 95 to 100 mol%, based on the amount of the specific monomer used.

[0037] The specific monomer may contain a monomer other than TFE and PAVE (hereinafter also referred to as "other monomer"). Specific examples of the other monomer include a monomer having two or more polymerizable unsaturated bonds (hereinafter also referred to as "BO"), a monomer having one or more atoms of at least one kind selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom (hereinafter also referred to as "R Ｈａｌ "), a monomer having a nitrile group (hereinafter referred to as "R ＣＮ"), and a compound represented by formula (6) described below (hereinafter also referred to as "POAVE").

[0038] BO is a monomer having two or more polymerizable unsaturated bonds. Examples of the polymerizable unsaturated bond include a carbon atom-carbon atom double bond (C═C) and a carbon atom-carbon atom triple bond (C≡C). The number of polymerizable unsaturated bonds that BO has is preferably 2 to 6, more preferably 2 or 3, and even more preferably 2, in terms of superior polymerization reactivity. BO preferably contains a fluorine atom in terms of reducing the compression set of a crosslinked rubber article at high temperatures.

[0039] BO is preferably a monomer represented by formula (2) in view of better releasability of the crosslinked rubber article. ２１ R ２２ =CR ２３ -) ａ１ R ２４ (2) In formula (2), R ２１ , R ２２ , and R ２３ each independently represents a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group; a1 represents an integer of 2 to 6; R ２４ represents an a1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of an a1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms. ２１ , multiple R ２２ and multiple R ２３ may be the same or different, and are particularly preferably the same. a1 is preferably 2 or 3, and particularly preferably 2. In view of better polymerization reactivity of BO, R ２１ , R ２２ , and R ２３ is preferably a fluorine atom or a hydrogen atom, and R ２１ , R ２２ , and R ２３ are more preferably all fluorine atoms or all hydrogen atoms, and in view of better mold releasability of the crosslinked rubber article, R ２１ , R ２２, and R ２３ It is particularly preferred that all of R are fluorine atoms. ２４ R may be linear, branched, or cyclic, preferably linear or branched, and particularly preferably linear. ２４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5. ２４ Although R may or may not have an etheric oxygen atom, it is preferable that R has an etheric oxygen atom in view of better crosslinking reactivity and rubber physical properties. ２４ The number of etheric oxygen atoms in R is preferably 1 to 6, more preferably 1 to 3, and particularly preferably 1 or 2. ２４ The etheric oxygen atom in R ２４ It is preferred that the nucleotide sequence is located at the end of the nucleotide sequence.

[0040] Of the monomers represented by formula (2), specific examples of suitable monomers include the monomers represented by formula (3) and the monomers represented by formula (4).

[0041] (CF ２ =CF-) ２ R ３１ (3) In formula (3), R ３１ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms.

[0042] (CH ２ =CH-) ２ R ４１ (4) In formula (4), R ４１ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms.

[0043] Specific examples of the monomer represented by formula (3) include CF ２ = CFO (CF ２ ) ２ OCF = CF ２ , C.F. ２ = CFO (CF２ ) ３ OCF = CF ２ , CF ２ = CFO(CF ２ ) ４ OCF = CF ２ , CF ２ = CFO(CF ２ ) ６ OCF = CF ２、 CF ２ = CFO(CF ２ ) ８ OCF = CF ２ , CF ２ = CFO(CF ２ ) ２ OCF(CF ３ )CF ２ OCF = CF ２ , CF ２ = CFO(CF ２ ) ２ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , CF ２ = CFO CF ２ O(CF ２ CF ２ O) ２ CF = CF ２ , CF ２ = CFO(CF ２ O) ３ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , CF ２ = CFO CF ２ CF(CF ３ )O(CF ２ ) ２ OCF(CF ３ )CF ２ OCF = CF ２ , and, CF ２ = CFO CF ２ CF ２ O(CF ２ O) ２ CF ２ CF ２ OCF = CF ２Among the monomers represented by formula (3), a more preferred specific example of the monomer is CF ２ = CFO (CF ２ ) ３ OCF = CF ２ (hereinafter also referred to as "C3DVE"), and CF ２ = CFO (CF ２ ) ４ OCF = CF ２ (hereinafter, also referred to as "C4DVE"). Specific examples of the monomer represented by formula (4) include CH ２ =CH(CF ２ ) ２ CH=CH ２ , C.H. ２ =CH(CF ２ ) ４ CH=CH ２ , and C.H. ２ =CH(CF ２ ) ６ CH=CH ２ Among the monomers represented by formula (4), specific examples of more preferred monomers include CH ２ =CH(CF ２ ) ６ CH=CH ２ (hereinafter also referred to as "C6DV"). Among them, C3DVE or C4DVE is preferable for BO.

[0044] R Ｈａｌ Specific examples of more suitable monomers include a monomer having a bromine atom and a monomer having an iodine atom. Specific examples of the monomer having a bromine atom include CF ２ = CFOCF ２ CF ２ CF ２ OCF ２ CF ２Br, bromotrifluoroethylene, 4-bromo-3,3,4,4-tetrafluorobutene-1 (BTFB), vinyl bromide, 1-bromo-2,2-difluoroethylene, perfluoroallyl bromide, 4-bromo-1,1,2-trifluorobutene-1, 4-bromo-1,1,3,3,4,4-hexafluorobutene, 4-bromo-3-chloro-1,1,3,4,4-pentafluorobutene, 6-bromo-5,5,6,6-tetrafluorohexene, and 4-bromoperfluorobutene-1,3,3-difluoroallyl bromide. Also included are 2-bromo-perfluoroethyl perfluorovinyl ether and CF ２ Br-R ｆ -O-CF=CF ２ (R ｆ is a perfluoroalkylene group), for example, CF ２ BrCF ２ O-CF=CF ２ , ROCF = CFBr, and ROCBr = CF ２ (R is a lower alkyl group or a fluoroalkyl group), specifically, ３ OCF = CFBr and CF ３ CH ２ Specific examples of the monomer having an iodine atom include the monomer represented by the formula: CHR=CH-Z-CH ２ CHR-I (wherein R is —H or —CH ３ Z is a linear or branched C alkyl group optionally containing one or more ethereal oxygen atoms; １ ~C １８ iodinated olefins of the formula I(CH) as disclosed in U.S. Pat. No. 5,717,036, which are (per)fluoroalkylene groups or (per)fluoropolyoxyalkylene groups as disclosed in U.S. Pat. No. 5,674,959. ２ CF ２ CF ２ ) ｎ OCF = CF ２ and ICH ２ CF ２ O[CF(CF ３ )CF ２ O]ｎ CF = CF ２ (wherein n = 1 to 3) and the like. Also included are iodoethylene, 4-iodo-3,3,4,4-tetrafluorobutene-1 (ITFB), 3-chloro-4-iodo-3,4,4-trifluorobutene, 2-iodo-1,1,2,2-tetrafluoro-1-(vinyloxy)ethane, 2-iodo-1-(perfluorovinyloxy)-1,1,-2,2-tetrafluoroethylene, 1,1,2,3,3,3-hexafluoro-2-iodo-1-(perfluorovinyloxy)propane, 2-iodoethyl vinyl ether, 3,3,4,5,5,5-hexafluoro-4-iodopentene, and iodotrifluoroethylene, as disclosed in U.S. Pat. No. 4,694,045. Also included are allyl iodide and 2-iodo-perfluoroethyl perfluorovinyl ether.

[0045] R ＣＮ From the viewpoint of polymerization reactivity, it is preferable that the copolymer has a polymerizable unsaturated bond, and more preferably has one polymerizable unsaturated bond. Specific examples of the polymerizable unsaturated bond include a carbon-carbon double bond (C═C) and a carbon-carbon triple bond (C≡C).

[0046] R ＣＮ is preferably a monomer represented by the following formula (5) in view of the superior mold releasability and heat resistance of the solid composition: ５１ R ５２ =CR ５３ -R ５４ -CN (5) In formula (5), R ５１ , R ５２ , and R ５３ each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R ５４ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms. ＣＮ From the viewpoint of excellent polymerization reactivity of R ５１ , R ５２ , and R ５３is preferably a fluorine atom or a hydrogen atom, and R ５１ , R ５２ , and R ５３ It is more preferred that all of R are fluorine atoms or all of R are hydrogen atoms, and in view of the superior mold releasability and heat resistance of the crosslinked rubber article, ５１ , R ５２ , and R ５３ It is particularly preferred that all of R are fluorine atoms. ５４ R may be linear, branched, or cyclic, and is preferably linear or branched. ５４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5. ５４ R may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in order to obtain better rubber properties. ５４ The number of etheric oxygen atoms in the formula (5) is preferably 1 to 3, and particularly preferably 1 or 2. Specific examples of the monomer represented by formula (5) include CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CN (hereinafter also referred to as "8CNVE"), CF ２ = CFO (CF ２ ) ５ CN (hereinafter also referred to as "MV5CN"), CF ２ = CFOCF ２ CF ２ CF ２ OCF (CF ３ ) CN and CF ２ = CFO (CF ２ ) ３ CN is exemplified, and 8CNVE or MV5CN is preferred in that the solid composition has better mold releasability and heat resistance.

[0047] POAVE is a compound represented by formula (6): CF ２ =CF(OCF ２ CF ２ ) ｎ -(OCF ２ ) ｍ -ORｆ２ (6) In formula (6), R ｆ２ represents a perfluoroalkyl group having 1 to 4 carbon atoms, n represents an integer of 0 to 3, m represents an integer of 0 to 4, and n+m represents an integer of 1 to 7.

[0048] R ｆ２ In the formula, the perfluoroalkyl group may be linear or branched. ｆ２ The number of carbon atoms in is preferably 1 to 3. When n is 0, m is preferably 1 or 2. When n is 1, m is preferably an integer of 2 to 4. When n is 2 or 3, m is preferably 0. n is preferably an integer of 1 to 3. R ｆ２ When the number of carbon atoms, n, and m are within the above ranges, the low-temperature properties of the crosslinked rubber article are excellent, and the productivity of the solid composition is improved.

[0049] Specific examples of POAVE include the following. The abbreviation for the compound is given in parentheses after the formula. CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ４ -OCF ３ (C9PEVE), CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ２ -OCF ３ (C7PEVE), CF ２ =CF-(OCF ２ CF ２ ) ２ -OCF ２ CF ３ (EEAVE), CF ２ =CF-(OCF ２ CF ２ ) ３ -OCF ２ CF ３ (EEEAVE), CF ２ =CF-OCF ２ -OCF ３ , C.F. ２ =CF-OCF ２ -OCF ２ -OCF ３As the POAVE, C9PEVE, C7PEVE, EEAVE, or EEEAVE is preferred in terms of superior low-temperature properties of crosslinked rubber articles and productivity of solid compositions. These compounds can be produced from the corresponding alcohols by the method described in WO 00 / 056694.

[0050] The amount of the other monomer used is preferably 0 to 20 mol %, more preferably 0 to 10 mol %, and even more preferably 0 to 5 mol %, based on the amount of the specific monomer used.

[0051] The specific monomer consists of only TFE and PAVE, or contains TFE and PAVE and BO, R Ｈａｌ , and R ＣＮ It is preferable that the polymer contains at least one monomer selected from the group consisting of:

[0052] (Polymerization Initiator) In step 1 of the present production method, the specific monomer is preferably polymerized in the presence of a polymerization initiator. The polymerization initiator is preferably an oil-soluble radical initiator, a water-soluble radical initiator, or a water-soluble redox catalyst. Specific examples of oil-soluble radical initiators include oil-soluble organic peroxides such as tert-butyl peroxypivalate and diisopropyl peroxydicarbonate. Specific examples of water-soluble radical initiators include persulfates such as ammonium persulfate and potassium persulfate, and water-soluble organic peroxides such as disuccinic acid peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide. The water-soluble redox catalyst is preferably 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. The persulfate is preferably potassium persulfate or ammonium persulfate. The sulfite salt is preferably sodium sulfite. The inorganic salt may be a combination of a sulfate anion, a sulfite anion, or a chloride anion with a metal ion. The metal ion is preferably a transition metal, such as manganese, iron, cobalt, nickel, copper, zinc, cerium, or silver ion, with iron ion being preferred. The inorganic salt is preferably iron (II) sulfate. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator, and from the viewpoint of more efficient production of the fluorine-containing polymer, a water-soluble radical initiator is more preferred, and a persulfate or a water-soluble organic peroxide is even more preferred. Two or more polymerization initiators may be used in combination.

[0053] 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.

[0054] (Chain Transfer Agent) In step 1 of the present production process, it is also preferable that the specific monomer is polymerized in the presence of a chain transfer agent. Specific examples of the chain transfer agent include chain transfer agents having an iodine atom, ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane, and chain transfer agents having an iodine atom are preferred. By polymerizing the specific monomer using a chain transfer agent having an iodine atom, a fluorine-containing polymer having an iodine atom at its terminal can be produced.

[0055] The chain transfer agent having an iodine atom is preferably a compound represented by formula (I): (R ｆ ) - (X) ２ (I) In formula (I), R ｆ is a fluoroalkylene group having 1 to 16 carbon atoms or an aromatic ring group, and X is an iodine atom or a bromine atom, and at least one of X is an iodine atom. ｆ The fluoroalkylene group of R may be linear or branched. ｆ Preferably, X is a perfluoroalkylene group. Preferably, all of X are iodine atoms.

[0056] Specific examples of the compound represented by formula (I) include 1,2-diiodoperfluoroethane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane (hereinafter also referred to as "C4DI"), 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,3-diiodo-2-chloroperfluoropropane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoperfluoropropane, 1,3-diiodoper ...4-diiodoperfluorobutane (hereinafter also referred to as "C4DI"), 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,3-diiodoperfluoropropane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorobutane, 1,5-diiodoperfluoropentane, 1,12-diiodoperfluorododecane, 1,16 Examples of the compound represented by formula (I) include iodoethane, 1,3-diiodo-n-propane, (2-iodoethyl)-substituted benzene, 1-iodo-4-bromoperfluorobutane, 1-iodo-6-bromoperfluorohexane, 1-iodo-8-bromoperfluoroctane, 1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 2-bromo-3-iodoperfluorobutane, 3-bromo-4-iodoperfluorobutene-1, 2-bromo-4-iodoperfluorobutene-1, monoiodomonobromo-substituted benzene, and diiodomonobromo-substituted benzene. C4DI is preferred as the compound represented by formula (I).

[0057] The amount of the chain transfer agent used is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.1 to 1 part by mass, per 100 parts by mass of the specific monomer used.

[0058] In view of the superior crosslinkability of the resulting solid composition, the present production method is preferably carried out in such a manner that the specific monomer is BO, R Ｈａｌ , and R ＣＮ or the first aqueous dispersion preferably contains a chain transfer agent containing an iodine atom.

[0059] (Means) Step 1 is a step of polymerizing the specific monomer in the first aqueous dispersion to obtain a second aqueous dispersion containing a second fluorine-containing polymer. 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 becomes 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. When a component other than those mentioned above (for example, a chain transfer agent) is used, the other component may be added to the reaction system all at once or in portions.

[0060] 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.

[0061] The polymerization of the specific monomer is preferably carried out in the substantial absence of an emulsifier. Examples of the emulsifier include the emulsifiers described above. "Substantially no emulsifier is present" refers to an environment in which the content of the emulsifier is 0.03 ppm by mass or less, preferably 0.02 ppm by mass or less, and more preferably 0 ppm by mass, relative to the total mass of the aqueous medium contained in the first aqueous dispersion.

[0062] (Second Fluorine-Containing Polymer) A second fluorine-containing polymer is produced by step 1 of the present production method. The second fluorine-containing polymer contains units based on a specific monomer. In the second fluorine-containing polymer, the TFE units are 5 to 85 mol%, preferably 40 to 80 mol%, based on the total of the TFE units and PAVE units. From the viewpoint of more efficient production of the second fluorine-containing polymer, the TFE units are 5 to 85 mol%, preferably 40 to 80 mol%, and from the viewpoint of more efficient production of the second fluorine-containing polymer, more preferably 50 to 75 mol%, and even more preferably 60 to 70 mol%. In the second fluorine-containing polymer, the PAVE units are 15 to 95 mol%, preferably 20 to 60 mol%, based on the total of the TFE units and PAVE units. From the viewpoint of more efficient production of the second fluorine-containing polymer, the PAVE units are 25 to 50 mol%, and even more preferably 30 to 40 mol%. When PMVE units or PPVE units are used as the PAVE units, the suitable amounts used are similar. The total content of TFE units and PAVE units in the second fluorine-containing polymer is preferably from 80 to 100 mol %, more preferably from 90 to 100 mol %, and even more preferably from 95 to 100 mol %, based on all units of the second fluorine-containing polymer.

[0063] The second fluorine-containing polymer contains TFE units and PAVE units, and preferably further contains units based on other monomers. Examples of units based on other monomers include units based on other monomers in the specific monomers described above. The TFE units, relative to all units in the second fluorine-containing polymer, are preferably 35 to 80 mol%, more preferably 47 to 75 mol%, and even more preferably 59 to 70 mol%. The PAVE units, relative to all units in the second fluorine-containing polymer, are preferably 20 to 60 mol%, more preferably 25 to 50 mol%, and even more preferably 30 to 40 mol%. The units based on other monomers, relative to all units in the second fluorine-containing polymer, are preferably 0.01 to 5 mol%, more preferably 0.05 to 3 mol%, and even more preferably 0.10 to 1 mol%.

[0064] The second fluorine-containing polymer preferably contains at least one selected from the group consisting of a polymerizable unsaturated bond, a chlorine atom, a bromine atom, an iodine atom, and a nitrile group, and more preferably contains at least one selected from the group consisting of a polymerizable unsaturated bond, an iodine atom, and a nitrile group, in order to provide a solid composition with better crosslinkability. In particular, it is preferable that the second fluorine-containing polymer contains at least one selected from the above at at least one of its terminals and side chains.

[0065] In step 1, the second fluorine-containing polymer is produced, and a second aqueous dispersion in which particles containing the second fluorine-containing polymer are dispersed in an aqueous medium is obtained.

[0066] (Second aqueous dispersion) The second aqueous dispersion is an aqueous dispersion containing the second fluorine-containing polymer obtained in step 1. In other words, the second aqueous dispersion is an aqueous dispersion in which particles containing a fluorine-containing polymer (hereinafter also referred to as "specific particles") are dispersed in an aqueous medium, and the fluorine-containing polymer contains a second fluorine-containing polymer. The specific particles may or may not contain the first fluorine-containing polymer. The second aqueous dispersion may contain the first fluorine-containing polymer dispersed in the form of particles.

[0067] -Specific particles- A suitable embodiment of the fluorine-containing polymer contained in the specific particles is the same as that of the second fluorine-containing polymer described above. The content of the specific particles in the second aqueous dispersion is preferably 1 to 50 mass %, more preferably 10 to 40 mass %, and even more preferably 15 to 30 mass %, relative to the total mass of the second aqueous dispersion, from the viewpoint of dispersion stability of the specific particles. The content of the specific particles in the second aqueous dispersion (solid content concentration) can be measured, for example, by the following method. 2.0 g of the second aqueous dispersion is heated at 170°C for 20 minutes, and then the mass of the residue is weighed, and the solid content concentration is calculated by the following formula: "Solid content concentration (mass %) = 100 × mass (g) of heated residue of second aqueous dispersion / mass (2.0 g) of second aqueous dispersion"

[0068] The average particle size of the specific particles is preferably 1 μm or less, and from the viewpoint of dispersion stability of the specific particles, it is more preferably 500 nm or less, and even more preferably 400 nm or less. From the viewpoint of recovery efficiency in step 2 described below, the average particle size of the specific particles is preferably 50 nm or more, more preferably 60 nm or more, and even more preferably 80 nm or more. The average particle size of the specific particles is a particle size calculated by analyzing an autocorrelation function obtained by dynamic light scattering using a monodisperse cumulant method.

[0069] -Aqueous medium- Specific examples of the aqueous medium contained in the second aqueous dispersion are the same as the specific examples of the aqueous medium contained in the first aqueous dispersion described above. The content of the aqueous medium is preferably 50 to 99 mass%, more preferably 60 to 99 mass%, and even more preferably 70 to 99 mass%, relative to the total mass of the second aqueous dispersion, from the viewpoint of dispersion stability of the specific particles.

[0070] -Emulsifier- The content of the emulsifier in the second aqueous dispersion is preferably 100 mass ppm or less, more preferably 75 mass ppm or less, even more preferably 50 mass ppm or less, even more preferably 1 mass ppm or less, and particularly preferably 25 mass ppb or less, relative to the total mass of the second aqueous dispersion, in order to achieve better effects of the present invention. It is also preferable that the content be below the quantitation limit of the measurement method in the examples. An example of a lower limit is 1 mass ppb. It is preferable that no emulsifier is used in the second aqueous dispersion. The content of the emulsifier can be measured by the same method as for the first aqueous dispersion described above. Specific examples of the emulsifier are as described above. The emulsifier in the second aqueous dispersion may or may not be water-soluble.

[0071] <Step 2> In step 2 of the present production method, the second aqueous dispersion obtained in step 1 is subjected to a stirring treatment, and the solid matter is collected to obtain a solid composition.

[0072] (Stirring Treatment) Specific methods for the stirring treatment include, for example, a method using a stirring device that rotates a stirring shaft equipped with stirring blades. Specific examples of the shape of the stirring blades include paddle blades, inclined paddle blades, propeller blades, disk blades, three-bladed swept blades, anchor blades, turbine blades, and disk turbine blades, with paddle blades or disk turbine blades being preferred in terms of excellent stirring efficiency. The number of the stirring blades is preferably 1 to 10, more preferably 2 to 4. Specific examples of the shape of the vessel used in the stirring treatment include cylindrical, conical, elliptical, rectangular, and pyramidal shapes, with cylindrical being preferred in terms of mixability and fluidity. The stirring device may be provided with a baffle.

[0073] The stirring time is preferably 0.1 to 24 hours, more preferably 0.1 to 12 hours, and even more preferably 0.1 to 6 hours. The peripheral speed of stirring is preferably 2 to 50 m / s, more preferably 3 to 30 m / s, and even more preferably 5 to 30 m / s. The peripheral speed may be constant during stirring or may change during stirring. It is also preferable that the peripheral speed is faster than the peripheral speed in step 1. The peripheral speed of stirring represents the speed of the blade at the tip of the stirring blade. The temperature of the aqueous dispersion during stirring treatment is preferably 10 to 90°C, more preferably 10 to 80°C, and even more preferably 15 to 70°C.

[0074] (Solid matter) The solid matter is a solid matter obtained by the stirring treatment, and includes a fluorine-containing polymer. In this specification, the term "solid matter" refers to a solid that is not stably dispersed in an aqueous medium, and a dispersoid stably dispersed in an aqueous medium is considered not to be a solid matter even if it is a solid that is insoluble in the aqueous medium. For example, among the insoluble components (e.g., specific particles) contained in the second aqueous dispersion after stirring, the dispersoid stably dispersed in the aqueous medium is not included in the solid matter, and sediment, floating matter, etc. are included in the solid matter. Examples of the solid matter include agglomerates of specific particles. Examples of the stably dispersed dispersoid include dispersoids that pass through Type 5A filter paper specified in JIS P 3801 [Filter paper (for chemical analysis)].

[0075] The solid matter is recovered to obtain the solid composition of the present invention. Specific examples of the method for recovering the solid matter include filtration and centrifugation, with filtration being preferred.

[0076] <Washing> The present production method preferably further comprises a step of washing the recovered solid composition (hereinafter also referred to as "step 3"). Step 3 makes it possible to remove components other than the fluoropolymer contained in the solid composition (for example, emulsifiers, monomers, polymerization initiators, and reaction products thereof), making it easier to obtain crosslinked rubber articles with desired physical properties. Examples of the washing liquid in the washing step include the above-mentioned aqueous media, with water being preferred and ultrapure water being more preferred because it has a low content of impurities that may cause crosslinking inhibition.

[0077] Specific examples of washing methods include a method in which the solid composition is immersed in a washing solution and stirred, and a method in which the solid composition is showered with a washing solution. Washing and dehydration of the solid composition may be repeated multiple times. Specific examples of dehydration methods include squeezing and centrifugation. The amount of washing solution used in the washing step is preferably 1 to 20 times, more preferably 1 to 10 times, and even more preferably 1 to 5 times the total mass of the solid composition. The temperature of the washing solution used in the washing step is preferably 5 to 80°C, more preferably 10 to 70°C, and more preferably 20 to 60°C.

[0078] [Solid composition] A solid composition can be obtained by this production method. The solid composition of the present invention (hereinafter also referred to as "the solid composition") contains a fluoropolymer containing TFE units and PAVE units, is substantially free of emulsifiers, and satisfies requirement X described below. In this specification, the term "solid composition" means a composition having a solid content mass of 99% by mass or more. The solid content mass is calculated by the following method based on the masses before and after heating. After heating 2.0 g of the solid composition at 170°C for 20 minutes, the mass of the residue is weighed and the solid content mass is calculated by the following formula: Solid content mass (mass %) = 100 × (mass of residue) / (mass of solid composition)

[0079] <Fluoropolymer> The fluoropolymer contained in the present solid composition contains TFE units and PAVE units. Details of the TFE units and PAVE units are the same as those of the TFE units and PAVE units in the first fluoropolymer described above, respectively, and preferred embodiments are also the same. The fluoropolymer contained in the present solid composition preferably contains a second fluoropolymer, and more preferably is the second fluoropolymer. That is, preferred embodiments of the fluoropolymer contained in the present solid composition are the same as those of the second fluoropolymer described above. The present solid composition may or may not contain the first fluoropolymer. In this specification, when there is only one type of fluoropolymer, "all units of the fluoropolymer" means all units contained in that one type of fluoropolymer. In addition, when there are two or more types of fluoropolymers contained in the specific particles, "all units of the fluoropolymer" means all units contained in the two or more types of fluoropolymers.

[0080] The fluorine-containing polymer contained in the present solid composition may contain units based on other monomers than TFE units and PAVE units, for example, units based on other monomers in the above-mentioned specific monomers.

[0081] The fluorine-containing polymer contained in the present solid composition preferably contains at least one selected from the group consisting of a polymerizable unsaturated bond, a chlorine atom, a bromine atom, an iodine atom, and a nitrile group, in terms of having better crosslinkability, and more preferably contains at least one selected from the group consisting of a polymerizable unsaturated bond, an iodine atom, and a nitrile group. In particular, it is preferable that at least one selected from the above is contained in at least one of the terminal and side chain of the fluorine-containing polymer. By using the above-mentioned other monomers in addition to TFE and PAVE as the specific monomer, any one of a polymerizable unsaturated bond, a chlorine atom, a bromine atom, an iodine atom, and a nitrile group can be introduced into the side chain or terminal of the fluorine-containing polymer. Furthermore, by polymerizing the specific monomer using a chain transfer agent having an iodine atom, an iodine atom can be introduced into the terminal of the fluorine-containing polymer. When the fluorine-containing polymer contained in the specific particles has iodine atoms, the proportion of iodine atoms is preferably from 0.01 to 5.00 mass%, more preferably from 0.01 to 2.00 mass%, and still more preferably from 0.01 to 1.00 mass%, relative to the total mass of the fluorine-containing polymer.

[0082] The content of the fluorine-containing polymer is preferably from 99.0 to 100 mass %, more preferably from 99.5 to 100 mass %, and even more preferably from 99.8 to 100 mass %, based on the total mass of the solid composition.

[0083] <Emulsifier> The solid composition is substantially free of emulsifiers. The phrase "the solid composition is substantially free of emulsifiers" means that no emulsifiers are used in the production process of the solid composition, and the solid composition does not contain any emulsifiers. Alternatively, if the solid composition contains any emulsifiers, the total content of emulsifiers is 500 ppb or less relative to the total mass of the solid composition. When the solid composition contains an emulsifier, the total content of emulsifiers is preferably 250 ppb by mass or less, more preferably 100 ppb by mass or less, and even more preferably 50 ppb by mass or less, relative to the total mass of the solid composition. It is also preferably below the quantitation limit of the measurement method in the examples. Examples of lower limits include more than 0 ppb by mass. Note that, in the above, the number of types of emulsifiers contained in the solid composition refers to the number of types of emulsifiers whose content exceeds the quantitation limit, and emulsifiers whose content is below the quantitation limit are not counted. Specifically, when the contents of emulsifier X, emulsifier Y, and emulsifier Z in a solid composition are measured, if the contents of emulsifier X and emulsifier Y are all above the quantitation limit and the content of emulsifier Z is below the quantitation limit, this means that the solid composition contains two emulsifiers, emulsifier X and emulsifier Y. The emulsifier contents can be measured by the method for measuring the emulsifier contents in the above-mentioned method for producing a solid composition. The emulsifiers that can be contained in the solid composition are as described above.

[0084] It is preferred that the solid composition is substantially free of a compound (emulsifier) ​​represented by any one of formulas (S1) to (S4). When no emulsifier is used in producing the first fluoropolymer contained in the first aqueous dispersion, the amount of the compound represented by any one of formulas (S1) to (S4) generated can be suppressed, making it easier to adjust the content of these compounds.

[0085] H-(CF ２ ) ｎ１ -COOM (S1) F-(CF ２ ) ｎ１ -COOM (S2) H-(CF ２ ) ｎ２ -SO ３ M (S3) F-(CF ２ ) ｎ２ -SO ３M (S4) In formulas (S1) to (S4), n1 is an integer of 3 to 19, n2 is an integer of 4 to 20, and each M is independently a hydrogen atom, Na, K, or NH ４ In the solid composition of the present invention, the total content of the compounds represented by any one of formulas (S1) to (S4) is preferably 25 mass ppb or less, more preferably 20 mass ppb or less, relative to the total mass of the solid composition. It is also preferably below the quantitation limit of the measurement method in the examples. The lower limit may be more than 0 mass ppb.

[0086] <Requirement X> The solid composition of the present invention satisfies requirement X. When requirement X is satisfied, the solid composition has a low content of components that inhibit crosslinking, and the effects of the present invention are excellent. Requirement X: In a mixed liquid obtained by mixing the solid composition with water having a pH of 6 so that the mass of the water is 5 times the mass of the solid composition, the pH of the mixed liquid at 23°C 24 hours after mixing is 4 or more.

[0087] The pH of the mixed solution at 23°C 24 hours after mixing is 4 or more, more preferably 5 or more. The pH is preferably 12 or less, more preferably 10 or less. The pH of the mixed solution is measured after mixing the solid composition with water and allowing to stand at 23°C for 24 hours. The pH can be measured using a known pH meter. An example of a method for obtaining a solid composition that satisfies the above requirement X is a method in which the stirring treatment conditions are adjusted without using a flocculant.

[0088] <Flocculant> In the present production method, the aqueous dispersion is subjected to a stirring treatment, and solids in the aqueous dispersion are recovered to obtain a solid composition, so acid flocculation, base flocculation, and flocculation using a coagulant are not performed. In other words, the solid composition does not contain residues of the flocculant used in acid flocculation, base flocculation, and flocculation using a coagulant, so the above-mentioned requirement X can be satisfied. In the case of acid flocculation, a method of adding a solution containing an acid is adopted, and examples of the acid to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, and nitric acid is also adopted. In the case of base flocculation, a method of adding a solution containing a base is adopted, and examples of the base include sodium hydroxide, potassium hydroxide, and ammonium carbonate. For flocculation using a coagulant, known coagulants are used, and known examples of known coagulants include aluminum salts, calcium salts, magnesium salts, and ammonium salts. Specifically, ammonium carbonate, aluminum sulfate, and compounds of the general formula M'Al(SO ４ ) ２ ・12H ２ Examples of suitable flocculants include alum, calcium nitrate, and magnesium sulfate represented by the formula: ##STR00001## where M' is a monovalent cation other than lithium. The solid composition of the present invention is substantially free of flocculants. The phrase "solid composition is substantially free of flocculants" means that no flocculants are used in the production process of the solid composition, and the solid composition does not contain an emulsifier. Alternatively, if the solid composition contains the flocculants, the total content of the flocculants is 25 ppb by mass or less, based on the total mass of the solid composition. If the solid composition contains a flocculant, the total content of the flocculants is preferably 25 ppb by mass or less, and more preferably 20 ppb by mass or less, based on the total mass of the solid composition. The lower limit can be greater than 0 ppb by mass.

[0089] <Storage Modulus> The storage modulus G' of the solid composition at 100°C and 50 cpm is preferably 300 kPa or more, more preferably 350 kPa or more. From the viewpoint of moldability of crosslinked rubber articles, the storage modulus G' is preferably 850 kPa or less, more preferably 800 kPa or less. The storage modulus G' at 100°C and 50 cpm is a value measured in accordance with ASTM D5289 and ASTM D6204, and detailed measurement conditions are as shown in the Examples. An example of a method for adjusting the storage modulus is a method of adjusting the amount and order of use of each of the above-mentioned monomers.

[0090] The solid composition is also preferably a fluorine-containing elastomer. A "fluorine-containing elastomer" is an elastic fluorine-containing polymer having no melting point and exhibiting a storage modulus G' of 80 or more at 100°C and 50 cpm as measured in accordance with ASTM D6204, and is distinguished from a fluororesin.

[0091] <Metal Content> The total metal content of the solid composition is preferably 50 ppm by mass or less, more preferably 20 ppm by mass or less, and even more preferably 10 ppm by mass or less, relative to the total mass of the solid composition, in order to reduce surrounding contamination during use. It is also preferable that the metal content is equal to or less than the measurement limit of the measurement method described in the Examples below. The lower limit can be 0.1 ppm by mass. The metal content is the total content of 29 metal elements (Fe, Na, K, Li, Be, Mg, Al, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Mo, Ag, Cd, In, Sn, Cs, Ba, Pb, and Bi) measured by an absolute calibration curve method using an inductively coupled plasma mass spectrometer. The metal content of the solid composition can be measured by ashing the solid composition, dissolving the resulting ash in acid, and measuring the metal content in the resulting solution using an inductively coupled plasma mass spectrometer. Detailed measurement conditions are as shown in the Examples. The solid composition produced by this production method does not require the use of a metal-containing flocculant during recovery, and the metal content can be easily adjusted to the above range.

[0092] [Use] The present production method is preferably used for producing crosslinked rubber articles, that is, the solid composition obtained by the present production method is preferably used for producing crosslinked rubber articles.

[0093] Specific examples of the crosslinked rubber article include sealing materials and cushioning materials such as rings, packings, oil seals, gaskets, diaphragms, and sheets. Other examples include sealing materials for semiconductor devices, oil drilling components, electric wire coating materials, heat-resistant and chemical-resistant sealing materials, heat-resistant and oil-resistant sealing materials, corrosion-resistant rubber coating materials, urea-resistant grease sealing materials, rubber coating materials, adhesive rubbers, hoses, tubes, calendar sheets (rolls), sponges, rubber rolls, heat-dissipating sheets, solution-crosslinked products, rubber sponges, bearing seals, linings, insulating sheets for automobiles, insulating sheets for electronic devices, rubber bands, packings / valves, fenders, fibers / nonwoven fabrics, board sealing materials, rubber gloves, stators for uniaxial eccentric screw pumps, parts for urea SCR systems, vibration isolators, vibration dampers, and sealants.

[0094] The cross-sectional shapes of the above rings, packings and seals are not particularly limited, and examples thereof include O-shaped, square, and ferrule shapes, and may also include irregular shapes such as D-shaped, X-shaped, Y-shaped, L-shaped, T-shaped, and V-shaped.

[0095] Examples of fields in which fluororubber articles are used include semiconductor-related, food and beverage manufacturing equipment, pharmaceutical manufacturing equipment, medical parts, chemical transport equipment, nuclear power plant equipment, iron plate processing equipment, general industry, electricity, fuel cells, electronic components, optical equipment components, space equipment components, petrochemical plant equipment, equipment components for exploring and mining energy resources such as oil and gas, oil refining, oil transport equipment components, automobiles, aircraft, space / rockets, ships, chemical industries such as chemical plants, chemicals such as pharmaceuticals, photography such as developing machines, printing machines, painting equipment, analytical equipment, analytical / physical and chemical machinery such as meters, and food equipment for food plants and household goods.

[0096] In the above-mentioned semiconductor-related fields, the present invention can be used in, for example, semiconductor manufacturing equipment, liquid crystal panel manufacturing equipment, plasma panel manufacturing equipment, plasma display panel manufacturing equipment, plasma addressed liquid crystal panel manufacturing equipment, organic electroluminescence (EL) panel manufacturing equipment, field emission display panel manufacturing equipment, solar cell substrate manufacturing equipment, semiconductor conveying equipment, etc. More specifically, examples of such equipment include chemical vapor deposition (CVD) equipment, gas control devices such as semiconductor gas control devices, dry etching equipment, wet etching equipment, plasma etching equipment, reactive ion etching equipment, reactive ion beam etching equipment, sputter etching equipment, ion beam etching equipment, oxidation diffusion equipment, sputtering equipment, ashing equipment, plasma ashing equipment, cleaning equipment, ion implantation equipment, plasma CVD equipment, exhaust equipment, exposure equipment, polishing equipment, film formation equipment, dry etching cleaning equipment, ultraviolet (UV) / ozone cleaning equipment, ion beam cleaning equipment, laser beam cleaning equipment, plasma cleaning equipment, gas etching cleaning equipment, extraction cleaning equipment, Soxhlet extraction cleaning equipment, high temperature and high pressure extraction cleaning equipment, microwave extraction cleaning equipment, supercritical extraction cleaning equipment, cleaning equipment using hydrofluoric acid, hydrochloric acid, sulfuric acid, ozone water, etc., steppers, coater developers, chemical mechanical polishing (CMP) equipment, excimer laser exposure machines, chemical liquid piping, gas piping, plasma processing equipment (for example, nitrogen trifluoride (NF ３) plasma treatment, oxygen plasma treatment, fluorine plasma treatment, etc.), heat treatment film formation equipment, wafer transport equipment, wafer cleaning equipment, silicon wafer cleaning equipment, silicon wafer processing equipment, low-pressure CVD (LPCVD) equipment, lamp annealing equipment, reflow equipment, etc. In the above-mentioned semiconductor-related fields, for example, the present invention can be used in semiconductor manufacturing equipment, organic electroluminescence (EL) panel manufacturing equipment, field emission display panel manufacturing equipment, plasma addressed liquid crystal panel manufacturing equipment, plasma display panel manufacturing equipment, liquid crystal panel manufacturing equipment, solar cell substrate manufacturing equipment, plasma panel manufacturing equipment, semiconductor transport equipment, etc. More specifically, reactive ion beam etching equipment, ion beam etching equipment, sputter etching equipment, plasma etching equipment, reactive ion etching equipment, dry etching equipment, wet etching equipment, chemical vapor deposition (CVD) equipment, gas control equipment such as semiconductor gas control equipment, oxidation diffusion equipment, sputtering equipment, plasma ashing equipment, ashing equipment, cleaning equipment, ion implantation equipment, plasma CVD equipment, exhaust equipment, exposure equipment, polishing equipment, film formation equipment, dry etching cleaning equipment, ultraviolet (UV) / ozone cleaning equipment, ion beam cleaning equipment, laser beam cleaning equipment, plasma cleaning equipment, gas etching Examples of such equipment include cleaning equipment, extraction cleaning equipment, Soxhlet extraction cleaning equipment, high-temperature and high-pressure extraction cleaning equipment, microwave extraction cleaning equipment, supercritical extraction cleaning equipment, cleaning equipment that uses hydrofluoric acid, hydrochloric acid, sulfuric acid, ozone water, etc., steppers, coater developers, chemical mechanical polishing (CMP) equipment, excimer laser exposure machines, chemical liquid piping, gas piping, plasma treatment equipment (for example, nitrogen trifluoride (NF3) plasma treatment, oxygen plasma treatment, fluorine plasma treatment, etc.), heat treatment film formation equipment, wafer transport equipment, wafer cleaning equipment, silicon wafer cleaning equipment, silicon wafer treatment equipment, low-pressure CVD (LPCVD) equipment, lamp annealing equipment, and reflow equipment.

[0097] Examples of uses in the semiconductor-related field include various sealing materials such as O-rings and gaskets for gate valves, quartz windows, chambers, chamber lits, gates, bell jars, couplings, and pumps; various sealing materials such as O-rings for resist developer and stripper solutions, hoses and tubes; linings and coatings for resist developer tanks, stripper tanks, wafer cleaning solution tanks, and wet etching tanks; pump diaphragms; rolls for transporting wafers; hose tubes for wafer cleaning solutions; sealants for clean facilities such as clean rooms; sealing materials for semiconductor manufacturing equipment and device storage facilities for wafers and the like; and diaphragms for transporting chemical solutions in semiconductor manufacturing processes. Examples of uses in the semiconductor-related field include hose tubes for wafer cleaning liquids, linings and coatings for resist developer tanks, stripper tanks, wafer cleaning liquid tanks, and wet etching tanks, pump diaphragms, rolls for transporting wafers, gate valves, quartz windows, chambers, chamber lits, gates, bell jars, couplings, various sealants such as O-rings and gaskets for pumps, various sealants such as O-rings for resist developer liquids and stripper liquids, hoses and tubes, sealants for clean facilities such as clean rooms, sealing materials for semiconductor manufacturing equipment and device storage facilities for wafers and the like, and diaphragms for transporting chemical liquids in semiconductor manufacturing processes.

[0098] The crosslinked rubber article can be produced by crosslinking the solid composition of the present invention. Examples of crosslinking methods include adding a crosslinking agent and kneading or molding the resulting mixture. Specific examples of crosslinking agents include organic peroxides, polyols, amines, and triazines. Organic peroxides are preferred because they provide excellent productivity, heat resistance, and chemical resistance to the crosslinked rubber article. Specific examples of organic peroxides include dialkyl peroxides, α,α'-bis(tert-butylperoxy)-p-diisopropylbenzene, α,α'-bis(tert-butylperoxy)-m-diisopropylbenzene, benzoyl peroxide, tert-butylperoxybenzene, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane. Specific examples of dialkyl peroxides include 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroxyperoxide, tert-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne, tert-butylperoxymaleic acid, and tert-butylperoxyisopropyl carbonate.

[0099] In the production of crosslinked rubber articles, other components besides the crosslinking agent may be used, such as catalysts, crosslinking aids, acid acceptors, fillers and reinforcing materials, scorch retarders, crown ethers, and mold release agents.

[0100] Examples of the molding method include injection molding, extrusion molding, coextrusion molding, blow molding, compression molding, inflation molding, transfer molding, and calendar molding.

[0101] The present invention will be described in detail below with reference to examples. Examples 1 to 3 are working examples, and Examples 4 and 5 are comparative examples. However, the present invention is not limited to these examples. The average particle size of particles in the aqueous dispersion was measured using a dynamic light scattering particle size analyzer (ELSZ, manufactured by Otsuka Electronics Co., Ltd.) using the aqueous dispersion of each example described below as a sample.

[0102] [Production of Solid Composition] <Production of Raw Material Solution A> Ultrapure water (1130 g), 30% by mass aqueous ammonia solution (30 mg), PMVE (72 g), and TFE (14 g) were charged into a 2.2 L stainless steel pressure reactor equipped with an anchor impeller, and the temperature was raised to 90°C while stirring at 600 rpm. Next, an aqueous ammonium persulfate solution (5.0% by mass, 30 cc) was added to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. When 4 g of TFE had been injected, the reactor was cooled and the polymerization reaction was terminated. The total amounts of monomers added before the initiation of polymerization were 14 g of TFE and 72 g of PMVE. The total amounts of monomers added after the initiation of polymerization were 4 g of TFE and 0 g of PMVE. The total amount of TFE added was 18 g, and the total amount of PMVE added was 72 g. The gas remaining in the reactor was collected, and then the liquid was withdrawn. This liquid was designated as raw material liquid A. Raw material liquid A was freeze-coagulated and then filtered to obtain a fluoropolymer 1A, which was analyzed by NMR and found to have a PAVE unit / TFE unit ratio of 34 / 66.

[0103] <Production of Raw Material Solution B> 2000 g of an 8% by mass aqueous sodium hydroxide solution was added to 1000 g of HPR4002Cl (a styrene-based gel-type strongly basic anion exchange resin manufactured by DuPont), and the mixture was stirred for 60 minutes to exchange the chloride ions in the resin for hydroxide ions. The total exchange capacity of the anion exchange resin was 1.25 eq / L-Resin, and the average diameter was 0.50 to 0.65 mm. The resulting anion exchange resin (200 g) was added to the raw material solution A, and stirring was initiated. 150 minutes after stirring began, the raw material solution and the ion exchange resin were separated by filtration. Next, 50 g of AmberLite (registered trademark) HPR650H (a cation exchange resin manufactured by DuPont) were added to the filtrate. 60 minutes after stirring began, the raw material solution and the ion exchange resin were separated by filtration, yielding raw material solution B. In raw material liquid B, particles of fluoropolymer 1A were dispersed in an aqueous medium, and the content of fluoropolymer 1A was 0.6% by mass relative to the total mass of raw material liquid B.

[0104] Example 1 A 2.2 L stainless steel pressure reactor equipped with an anchor impeller was charged with raw material solution B (1000 g) and ultrapure water (175 g) to obtain aqueous dispersion 1-1. The content of fluoropolymer 1A was 0.4 mass% relative to the total mass of aqueous dispersion 1-1. Perfluoro-1,4-diiodobutane (1.25 g), PMVE (90 g), and TFE (14 g) were charged to aqueous dispersion 1-1, and the temperature was raised to 80°C while stirring at 600 rpm. TFE and PMVE were injected until the pressure in the reactor reached 1.5 MPa [gauge], and an aqueous ammonium persulfate solution (20 ml of an aqueous 1.0 mass% APS solution, 0.2 g of ammonium persulfate) was added to initiate polymerization. As the polymerization started, the pressure inside the reactor decreased, so TFE / PMVE was injected at a molar ratio of 65 / 35 to maintain the pressure constant. When 256 g of TFE and 217 g of PMVE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 380 minutes. The total amounts of monomers added before the start of polymerization were 14 g of TFE and 90 g of PMVE. The total amounts of monomers added after the start of polymerization were 256 g of TFE and 217 g of PMVE. The total amount of TFE added was 270 g, and the total amount of PMVE added was 307 g.

[0105] The above-mentioned aqueous dispersion 1-1 did not substantially contain a water-soluble emulsifier. Specifically, the contents of emulsifier A and the compounds represented by formulas (S1) to (S4), which will be described later, were measured by the following method. Note that, in producing aqueous dispersion 1-1, emulsifiers other than emulsifier A and the compounds represented by formulas (S1) to (S4) were not produced from the components used in producing aqueous dispersion 1-1, nor were they used, and therefore are not contained in aqueous dispersion 1-1. The solids content of aqueous dispersion 1-1 was measured, and an amount of aqueous dispersion 1-1 corresponding to 0.05 g of solids was weighed into a 100 mL screw tube. Then, 40 g of water and methanol were added to the weighed aqueous dispersion 1-1 so that the water / methanol ratio was 50 / 50 by volume. The mixture was then shaken vigorously until coagulation occurred. The solids were removed, and the liquid phase was centrifuged at 4000 rpm for 1 hour, and the supernatant was extracted. Except for the sample preparation method, the measurement was performed in the same manner as the measurement method for <Emulsifier content> described below. As a result, the content of the compound represented by any one of Formulas (S1) to (S4) was also below the quantitation limit for Aqueous Dispersion 1-1.

[0106] After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated as aqueous dispersion 2-1. Aqueous dispersion 2-1 was a dispersion in which particles (average particle size 92.7 nm) containing a fluoropolymer were dispersed in an aqueous medium, and had a solids concentration of 20.5% by mass. The aqueous dispersion 2-1 was placed in a cylindrical tank and stirred at 5 m / s for 150 minutes using a disk turbine impeller having eight blades attached at right angles at equal intervals on the outer periphery of a disk, and the solid was then recovered by filtration. The recovered solid was washed with 2,000 g of ultrapure water at 40°C and dried to obtain a rubbery solid composition 1. The peripheral speed of the stirring (m / s) is the speed of the impeller at the tip of the stirring impeller. NMR analysis of the fluoropolymer contained in the obtained solid composition 1 revealed that the ratio of PAVE units to TFE units was 34 / 66 (molar ratio).

[0107] <Production of Raw Material Liquid C> A fluoropolymer 1C was polymerized in the same procedure as in the production of raw material liquid A, except that the amounts of each component were appropriately changed, and this liquid was used as raw material liquid C. Raw material liquid C was freeze-coagulated and then filtered off, and the resulting fluoropolymer 1C was analyzed by NMR, revealing that the ratio of PAVE units to TFE units was 32 / 68 (molar ratio).

[0108] <Production of Raw Material Liquid D> Raw material liquid D was produced in the same procedure as for raw material liquid B, except that raw material liquid C was used instead of raw material liquid A. Raw material liquid D contained particles of fluoropolymer 1C dispersed in an aqueous medium, and the content of fluoropolymer 1C was 0.6% by mass relative to the total mass of raw material liquid D.

[0109] Example 2 A 2.2 L stainless steel pressure reactor equipped with an anchor impeller was charged with raw material solution D (1000 g) and ultrapure water (175 g), to obtain aqueous dispersion 1-2. The content of fluoropolymer 1C was 0.4 mass% relative to the total mass of aqueous dispersion 1-2. Aqueous dispersion 1-2 did not substantially contain a water-soluble emulsifier. The emulsifier content was confirmed by the same method as for aqueous dispersion 1-1 described above. PMVE (72 g), perfluoro-1,4-diiodobutane (2.0 g), and TFE (14 g) were charged into aqueous dispersion 1-2, and the temperature was raised to 80°C while stirring at 600 rpm. TFE and PMVE were injected until the pressure in the reactor reached 1.5 MPa [gauge], and an aqueous APS solution (0.5 mass%, 16 ml, 0.08 g of ammonium persulfate) was added to initiate polymerization. Since the pressure inside the reactor decreased with the initiation of polymerization, TFE / PMVE was injected at a molar ratio of 65 / 35 to maintain the pressure constant. When 256 g of TFE and 217 g of PMVE had been added, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 290 minutes. The total amounts of monomers added before the initiation of polymerization were 14 g of TFE and 72 g of PMVE. The total amounts of monomers added after the initiation of polymerization were 256 g of TFE and 217 g of PMVE. The total amount of TFE added was 270 g, and the total amount of PMVE added was 289 g. The gas remaining in the reactor was recovered, and then the liquid was withdrawn. This liquid was designated as aqueous dispersion 2-2. Aqueous dispersion 2-2 was a dispersion in which particles (average particle size 140.3 nm) containing a fluoropolymer were dispersed in an aqueous medium, and had a solids concentration of 28.6% by mass. The aqueous dispersion 2-2 was stirred with a paddle blade at 10 m / s for 150 minutes, and then the solid matter was collected by filtration. The collected solid matter was washed with 2,000 g of ultrapure water at 40°C and dried to obtain a rubbery solid composition 2. The fluorine-containing polymer contained in the obtained solid composition 2 was analyzed by NMR, and the ratio of PAVE units to TFE units was found to be 35 / 65 (molar ratio).

[0110] Example 3 A stainless steel pressure reactor having an internal volume of 2.2 L equipped with an anchor impeller was charged with raw material liquid D (1000 g) and ultrapure water (175 g), to obtain aqueous dispersion 1-3. The content of fluoropolymer 1C was 0.4 mass% relative to the total mass of aqueous dispersion 1-3. Aqueous dispersion 1-3 did not substantially contain a water-soluble emulsifier. The content of the emulsifier was confirmed by the same method as for aqueous dispersion 1-1 described above. PMVE (72 g) and TFE (14 g) were charged into aqueous dispersion 1-3, and the temperature was raised to 80°C while stirring at 600 rpm. TFE and PMVE were injected until the pressure in the reactor reached 1.5 MPa [gauge], and an aqueous APS solution (0.5 mass%, 16 ml, 0.08 g of ammonium persulfate) was added to initiate polymerization. As the polymerization began, the pressure inside the reactor decreased, so TFE / PMVE was injected at a molar ratio of 65 / 35 to maintain a constant pressure. When 6 g of TFE had been added, perfluoro-1,4-diiodobutane (2.0 g) was injected. When 256 g of TFE and 217 g of PMVE had been added, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 290 minutes. The total amounts of monomers added before the start of polymerization were 14 g of TFE and 72 g of PMVE. The total amounts of monomers added after the start of polymerization were 256 g of TFE and 217 g of PMVE. The total amounts of TFE and PMVE added were 270 g and 289 g, respectively. The gas remaining in the reactor was recovered, and the liquid was withdrawn. This liquid was designated aqueous dispersion 2-3. Aqueous Dispersion 2-3 was a dispersion in which particles (average particle size 96 nm) containing a fluoropolymer were dispersed in an aqueous medium, and had a solids concentration of 27.6% by mass. Aqueous Dispersion 2-3 was stirred with six turbine blades at 30 m / s for 150 minutes, and then the solid matter was collected by filtration. The collected solid was washed with 2,000 g of ultrapure water at 25°C and dried to obtain a rubbery solid composition 3. The fluoropolymer contained in the obtained solid composition 3 was analyzed by NMR, and the ratio of PAVE units to TFE units was 34 / 65 (molar ratio).

[0111] <Example 4> A stainless steel pressure reactor with an internal volume of 2.2 L and equipped with an anchor blade was degassed, and then ultrapure water (1004 g), an emulsifier C ２ F ５ OCF２ CF ２ OCF ２ COONH ４ A 30% by mass solution (80.1 g) of (emulsifier A) and a 5% by mass aqueous solution (10.49 g) of disodium hydrogen phosphate dodecahydrate were charged, and the gas phase was replaced with nitrogen. While stirring at a speed of 600 rpm using an anchor blade, PMVE (72 g) and TFE (14 g) were injected into the vessel, and the internal temperature was then raised to 80 ° C. Next, an aqueous APS solution (1.0% by mass, 20 ml) was added to initiate polymerization. Since the pressure inside the reactor decreased with the start of polymerization, TFE / PMVE was injected at a molar ratio of 65 / 35, and the pressure was maintained constant at 1.2 MPa [gauge]. When 160 g of TFE and 133 g of PMVE were injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 262 minutes. The gas remaining in the reactor was recovered, and the liquid was withdrawn. This liquid was designated as aqueous dispersion 4. Aqueous Dispersion 4 was a dispersion in which particles (average particle size 84 nm) containing a fluoropolymer were dispersed in an aqueous medium, and had a solids concentration of 21.1% by mass. An aqueous aluminum sulfate solution (5%, 2,000 g) was added to the aqueous dispersion 4, and the aggregates were collected by filtration. The collected aggregates were washed with 2,000 g of ultrapure water at 40°C, and then the solids were collected by filtration. The collected solids were dried to obtain a rubbery solid composition 4. NMR analysis of the fluoropolymer contained in the obtained solid composition 4 showed that the ratio of PAVE units to TFE units was 35 / 65 (molar ratio).

[0112] <Example 5> A stainless steel pressure reactor with an internal volume of 2.2 L and equipped with an anchor blade was degassed, and then ultrapure water (1004 g), an emulsifier C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４A 30% by mass solution (80.1 g) of (emulsifier A) and a 5% by mass aqueous solution (10.49 g) of disodium hydrogen phosphate dodecahydrate were charged, and the gas phase was replaced with nitrogen. While stirring at a speed of 600 rpm using an anchor blade, PMVE (72 g) and TFE (14 g) were injected into the vessel, and the internal temperature was then raised to 80 ° C. Next, an aqueous APS solution (1.0% by mass, 20 ml, 0.1 g of ammonium persulfate) was added to initiate polymerization. Since the pressure inside the reactor decreased with the start of polymerization, TFE / PMVE was injected at a molar ratio of 65 / 35, and the pressure was maintained constant at 1.2 MPa [gauge]. When 160 g of TFE and 133 g of PMVE were injected, the reactor was cooled, and the polymerization reaction was terminated. The polymerization time was 280 minutes. The gas remaining in the reactor was recovered, and the liquid was then extracted. This liquid was named Aqueous Dispersion 5. Aqueous Dispersion 5 was a dispersion in which particles containing fluoropolymer 1G (average particle size 98.6 nm) were dispersed in an aqueous medium, and had a solid concentration of 20.1% by mass. The above-mentioned Aqueous Dispersion 5 was added to an aqueous nitric acid solution (3% by mass, 2,500 g) and stirred, and then the solid was collected by filtration. The collected solid was washed with 2,000 g of ultrapure water at 60°C and dried to obtain a rubbery solid composition 5. The fluoropolymer contained in the obtained solid composition 5 was analyzed by NMR, and as a result, it was found that the ratio of PAVE units to TFE units was 35 / 65 (molar ratio).

[0113] [Measurement and Evaluation Methods] Various measurement and evaluation methods are as follows.

[0114] <Requirement X> Each solid composition obtained in each example was weighed out in the amount shown in the table below, and mixed with the amount shown in the table below (5 times the mass of the solid composition) of water adjusted to 23°C and pH 6. After 24 hours, the pH of the mixed solution at 23°C was measured using a desktop pH meter (LAQUA, manufactured by HORIBA).

[0115] <Crosslinking rate t ５０ and t ９０> Using each solid composition obtained in each example, a composition for crosslinking rate evaluation having the composition shown in Table 1 below was blended and kneaded for 10 minutes at 23°C using two rolls. After kneading, the gap between the two rolls was adjusted to obtain a 3 mm thick sheet for crosslinking rate evaluation. In the table below, the components and abbreviations are as follows: CB: MT Carbon N990, manufactured by Vanderbilt Crosslinking aid: TAIC-WH60, manufactured by Mitsubishi Chemical, triallyl isocyanurate 60% silica diluted product Crosslinking agent: Perhexa 25B, manufactured by NOF Corp., 2,5-dimethyl-2.5-di(t-butylperoxy)hexane Mold release agent: Nonsal SN-1, manufactured by NOF Corp., sodium stearate

[0116]

[0117] The obtained crosslinking rate evaluation sheet was cut into 10 g pieces to obtain a cut sheet. The cut sheet was sandwiched between two polyester films (ALFA Technologies, PART #F0311-S, 130 mm x 130 mm x 24 μm) on both sides of the main surface to obtain a measurement sample. For the measurement sample, the torque (dNm) was measured under the following conditions: measurement device: PREMIER RPA (manufactured by Alpha Technologies), die shape: D0380, 150 °C, 12 minutes, 100 cpm, angle: 3.00 deg. The minimum value of the obtained torque was set to 0%, and the maximum value of the torque was set to 100%, and the processing time at which the torque value reached 50% was defined as t ５０ , the processing time at which the torque value reaches 90% is t ９０ It was decided.

[0118] <Emulsifier Content> (Preparation of Measurement Sample) The solid compositions obtained in each example described below were freeze-pulverized using a freeze-pulverizer Freezer Mill 6775 (manufactured by SPEX) under the following conditions. Before freeze-pulverization, 10% by mass of dibutylhydroxytoluene (BHT) was added to the solid composition in advance, based on the total mass of the solid composition, to obtain a pulverized powder. The freeze-pulverization conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 minutes, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 0.25 g of the obtained pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate each fluoropolymer. The supernatant was used as an extract. The obtained extract was subjected to LC / MS / MS analysis. The fluorine-containing emulsifier and hydrocarbon emulsifier in the extract were measured using a liquid chromatograph mass spectrometer. The measurement equipment configuration and LC-MS measurement conditions are shown in Table 1. Using aqueous solutions of fluorine-containing emulsifier and hydrocarbon emulsifier with known concentrations, aqueous solutions with five or more levels of content were prepared, and LC / MS analysis was performed on the aqueous solutions with each content. The relationship between the content and the area relative to the content was plotted to draw a calibration curve. Using the calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing emulsifier and hydrocarbon emulsifier in the extract was converted into the content of the fluorine-containing emulsifier and hydrocarbon emulsifier.

[0119]

[0120] The MRM measurement parameters are selected appropriately depending on the structures of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured. Literature values ​​can be used for the MRM parameters, or they can be calculated using an LC-MS instrument. The specific procedure for determining MRM parameters using an LC-MS instrument is as follows: Using an LC / MS instrument (Shimadzu Corporation, LCMS-8060NX), select product ion search, input the molecular weights of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured, and then perform precursor ion, precursor adjustment, voltage optimization, and product m / z optimization. The calculated MRM measurement parameters are used. As an example, the MRM measurement parameters for compounds (S2) and (S4), which are fluorine-containing emulsifiers, are shown in the table below. In formulas (S2) and (S4), MS represents a hydrogen atom, a metal atom, NR4 (wherein R may be the same or different and represents a hydrogen atom or an organic group having 1 to 10 carbon atoms), an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. F-(CF2)n1-COOMS (S2) F-(CF2)n2-SO3MS (S4) where n1 is an integer from 3 to 17 and n2 is an integer from 4 to 12.

[0121]

[0122]

[0123] (Quantitative Analysis of Fluorine-Containing Emulsifier and Hydrocarbon Emulsifier Contained in Solid Composition) Specifically, five levels of methanol standard solutions of fluorine-containing emulsifier and hydrocarbon emulsifier with known concentrations of 1 to 180 ng / g were prepared, and a was calculated from the sample concentration and peak integral value of each emulsifier using a first-order approximation according to formula (A1-1): A = a × X (A1-1), where A is the peak area of ​​each emulsifier and X is the concentration (ng / g) of each emulsifier.

[0124] Next, the amount of emulsifier contained in the extract was calculated using formula (A1-2). Note that a in formula (A1-2) means a obtained by the above formula (A1-1). XCm = ACm / a (A1-2) XCm: content (ng / g) of emulsifier in each extract ACm: peak area of ​​emulsifier in each extract The quantitation limit in this measurement is 1 ng / g.

[0125] The content of the emulsifier in the solid composition relative to the total mass of the solid composition (ZCm) was calculated using the following formula (A1-3): ZCm = XCm × ρ1 × La / W1 (A1-3) ZCm: content of the emulsifier contained in the solid composition ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid composition in each example)

[0126] <Method for Quantifying Formula (S1) and Formula (S3) Contained in Solid Composition> The solid compositions obtained in each example described below were freeze-pulverized using a freeze-pulverizer Freezer Mill 6775 (manufactured by SPEX) under the following conditions. Before freeze-pulverization, 10% by mass of dibutylhydroxytoluene (BHT) was added to the solid composition in advance, based on the total mass of the solid composition, to obtain a pulverized powder. The freeze-pulverization conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 minutes, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 2.5 g of the obtained pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate each fluoropolymer. The supernatant was used as the extract. The obtained extract was subjected to LC / MS / MS analysis. The fluorine-containing emulsifier in the extract was measured using a liquid chromatograph mass spectrometer. The measurement equipment configuration and LC-MS measurement conditions were as described above. Using aqueous solutions of emulsifiers containing fluorine atoms with known concentrations, methanol solutions with five or more different concentrations were prepared. LC / MS analysis of the methanol solutions with each concentration was performed, and the relationship between the content and the area relative to the content was plotted to draw a calibration curve. Using the calibration curve, the area of ​​the LC / MS chromatogram of the emulsifier containing fluorine atoms in the extract was converted to the content of the emulsifier containing fluorine atoms. The content of the compound represented by formula (S1) contained in each extract was determined by converting each compound in formula (S1) where n1 = 3 to 13 into a perfluorocarboxylic acid (formula (S2)) with the same carbon number. Furthermore, the content of the compound represented by formula (S3) contained in each extract was determined by converting each compound in formula (S3) where n2 = 4 to 10 into a perfluorosulfonic acid (formula (S4)) with the same carbon number. The MRM parameters for formulas (S1) and (S3) are shown in Tables 5 and 6. Specifically, five levels of methanol standard solutions of perfluorocarboxylic acid and perfluorosulfonic acid with known concentrations of 1 to 180 ng / g were first prepared, and a and a' were calculated from the respective sample concentrations and peak integral values ​​using linear approximation according to formulas (A2-1) and (A2-1').A = a × X (A2-1) A: peak area of ​​perfluorocarboxylic acid, X: concentration of perfluorocarboxylic acid (ng / g) A' = a' × X' (A2-1') A': peak area of ​​perfluorosulfonic acid, X': concentration of perfluorosulfonic acid (ng / g).

[0127]

[0128]

[0129] Specifically, first, the peak areas of the compounds represented by formula (S1) and formula (S3) contained in each of the extracts were determined using the liquid chromatograph mass spectrometer.

[0130] Next, the contents of the compound represented by formula (S1) and the compound represented by formula (S3) were calculated using formulas (A2-2) and (A2-2'), respectively. Note that a in formula (A2-2) means a calculated using formula (A2-1) above, and a' in formula (A2-2') means a' calculated using formula (A2-1') above. XCm ​​= ACm / a (A2-2) XCm: content (ng / g) of the compound represented by formula (S1) and having carbon number (n+1) in each extract ACm: peak area of ​​the compound represented by formula (S1) and having carbon number (n+1) in each extract XCm' = ACm' / a' (A2-2') XCm': content (ng / g) of the compound represented by formula (S3) and having carbon number n in each extract ACm': peak area of ​​the compound represented by formula (S3) and having carbon number n in each extract The quantitation limit in this measurement is 1 ng / g.

[0131] The content (ZCm) of the compound represented by formula (S1) in the solid relative to the total mass of the solid was calculated using the following formula (A2-3): ZCm = XCm × ρ1 × La / W1 (A2-3) ZCm: content of the compound represented by formula (S1) with carbon number (n+1) contained in the solid ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid in each example)

[0132] The content (ZCm') of the compound represented by formula (S3) in the solid material relative to the total mass of the solid material was calculated using the following formula (A2-4): ZCm' = XCm' × ρ1 × La / W1 (A2-4) ZCm': content of the compound represented by formula (S3) and having carbon number n contained in the solid material ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of sample used for extraction (2.5 g of solid material in each example) The emulsifier content listed in each of Examples 1 to 5 indicates the total content of emulsifier A and the compounds represented by the above formulas (S1) to (S4) relative to the total mass of each solid composition. (Examples 1 to 3 did not use emulsifier A, and the content essentially indicates the total content of the compounds represented by the above formulas (S1) to (S4).)

[0133] <Metal Content> Each solid composition obtained in each example was placed in a platinum crucible and incinerated in a high-temperature electric heating furnace, followed by a sulfuric acid white smoke treatment. The solid composition was then dissolved in dilute nitric acid, and the contents of 29 metal elements (Fe, Na, K, Li, Be, Mg, Al, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Mo, Ag, Cd, In, Sn, Cs, Ba, Pb, and Bi) were determined using an inductively coupled plasma mass spectrometer (ICP-MS 7500cs, manufactured by Agilent Technologies) by the absolute calibration curve method, and the total content was calculated. In the table below, the metal content indicates the total content of the 29 metal elements.

[0134] <Storage Modulus G'> A rubber processability analyzer "PREMIER RPA (manufactured by Alpha Technologies, die shape: D0380)" was used as the measuring device. The solid composition obtained in each example was kneaded for 10 minutes at room temperature (23°C) using two rolls to produce a sheet with a thickness of 3 mm. The thickness of the sheet was adjusted by adjusting the gap between the two rolls. The obtained sheet was cut to a weight of approximately 10 g to obtain a cut sheet. The cut sheet was sandwiched between two polyester films (ALFA Technologies PART#F0311-S, 130 mm x 130 mm x 24 μm) to obtain a measurement sample. The sample was placed on the die of the measuring device. The die temperature was previously set to 100°C. Next, the sample was held at 100°C for 2 minutes under conditions of 30 cpm frequency and 0.2°C amplitude angle, and then the amplitude angle was set to 0.5° and the frequency was increased to 10 cpm, 20 cpm, and 50 cpm to measure the storage modulus. The storage modulus at 50 cpm and 100°C was taken as the storage modulus G' (unit: kPa) of the sample.

[0135]

[0136] The evaluation results of Examples 1 to 3 showed that the production method of the present invention can produce a solid composition with an excellent crosslinking rate because it is substantially free of emulsifiers and flocculants that reduce the vulcanization rate. In Examples 4 and 5, a flocculant was used in obtaining a solid composition by polymerization using an aqueous solution containing an emulsifier, and the resulting solid composition contained an emulsifier, resulting in a poor crosslinking rate.

[0137] The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2023-222139, filed on December 28, 2023, are hereby incorporated by reference as the disclosure of the present invention.

Claims

1. A method for producing a solid composition, which comprises: in an aqueous dispersion containing a first fluorine-containing polymer that substantially does not contain a water-soluble emulsifier and contains a unit based on tetrafluoroethylene and a unit based on perfluoro(alkyl vinyl ether), and an aqueous medium, polymerizing a monomer containing tetrafluoroethylene and perfluoro(alkyl vinyl ether), subjecting the obtained aqueous dispersion containing a second fluorine-containing polymer to a stirring treatment, and recovering the solid matter obtained after the stirring treatment to obtain a solid composition, wherein the unit based on perfluoro(alkyl vinyl ether) is 5 to 80 mol% based on the total of the unit based on tetrafluoroethylene and the unit based on perfluoro(alkyl vinyl ether) in the first fluorine-containing polymer, the unit based on perfluoro(alkyl vinyl ether) is 15 to 95 mol% based on the total of the unit based on tetrafluoroethylene and the unit based on perfluoro(alkyl vinyl ether) in the second fluorine-containing polymer, and the content of the first fluorine-containing polymer is 0.01 to 4.0% by mass based on the total mass of the aqueous dispersion before the polymerization of the monomer is initiated.

2. The method for producing a solid composition according to claim 1, wherein the storage elastic modulus of the solid composition at 100 °C is 300 kPa or more.

3. The method for producing a solid composition according to claim 1 or 2, wherein the solid composition does not contain an emulsifier, or when the solid composition contains the emulsifier, the total content of the emulsifier is 500 ppb or less based on the total mass of the solid composition.

4. The method for producing a solid composition according to claim 1 or 2, wherein the total content of metals in the solid composition is 20 ppm by mass or less based on the total mass of the solid composition.

5. The method for producing a solid composition according to claim 1 or 2, wherein the unit based on tetrafluoroethylene is 35 to 80 mol% and the unit based on perfluoro(alkyl vinyl ether) is 20 to 60 mol% based on all units in the second fluorine-containing polymer.

6. The method for producing a solid composition according to claim 1 or 2, wherein the second fluorine-containing polymer contains at least one selected from the group consisting of a polymerizable unsaturated bond, a chlorine atom, a bromine atom, an iodine atom, and a nitrile group.

7. The method for producing a solid composition according to claim 1 or 2, comprising a step of washing the solid composition.

8. A solid composition comprising a fluorine-containing polymer containing units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), substantially free of an emulsifier, and satisfying requirement X. Requirement X: In a mixed solution obtained by mixing the solid composition and water at pH 6 such that the mass of the water is 5 times the mass of the solid composition, the pH of the mixed solution at 23 °C after 24 hours from the mixing is 4 or more.

9. The solid composition according to claim 8, substantially free of a flocculant.

10. A crosslinked rubber article obtained by crosslinking the solid composition according to claim 8 or 9.

Images