Method for producing solid composition, solid composition, 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

[Technical Field]

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

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

[0003] [Patent Document 1] International Publication No. 2022 / 052498 Summary of the Invention [Problem to be solved by the invention]

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

[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 completing the present invention.

[0007] That is, the inventors have found that the above problems can be solved by the following configuration. [1] 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, A method for producing a solid composition, comprising polymerizing a monomer containing tetrafluoroethylene and a perfluoro(alkyl vinyl ether), stirring the resulting aqueous dispersion containing a second fluorine-containing polymer, and recovering a solid obtained after the stirring, the first fluorine-containing polymer contains 5 to 80 mol % of units based on perfluoro(alkyl vinyl ether) relative to the total of units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), the second fluorine-containing polymer contains 15 to 95 mol % of the units based on perfluoro(alkyl vinyl ether) relative to the total of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether), A method for producing a solid composition, wherein 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 start of polymerization of the monomers. [2] The method for producing a solid composition according to [1], wherein the storage modulus of the solid composition at 100°C is 300 kPa or more. [3] The solid composition does not contain an emulsifier, 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. A method for producing the solid composition according to [1] or [2]. [4] The 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 mass ppm or less, based on 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 the units based on tetrafluoroethylene and 20 to 60 mol% of the units based on perfluoro(alkyl vinyl ether), based on all units. [6] The 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 the 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 a unit based on tetrafluoroethylene and a unit based on perfluoro(alkyl vinyl ether), Substantially free of emulsifiers A solid composition that meets requirement X. Requirement X: In a mixed liquid obtained by mixing the above solid composition with water having a pH of 6 so that the mass of the water is 5 times the mass of the above solid composition, the pH of the mixed liquid at 23°C 24 hours after 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]. [Effects of the Invention]

[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. DETAILED DESCRIPTION OF THE INVENTION

[0009] The terms used in the present invention have the following meanings. A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In the numerical ranges described in stages in this specification, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. In this specification, each component may be a single substance corresponding to the component, or two or more substances may be used in combination. When two or more substances are used in combination for each component, the content of the component refers to the total content of the substances used in combination, unless otherwise specified. As used herein, a combination of two or more preferred embodiments is a more preferred embodiment. The term "unit" refers collectively to an atomic group derived from one molecule of the monomer formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a part of the 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 of producing solid composition] The method for producing a solid composition of the present invention (hereinafter also referred to as "the present production method") comprises dissolving in an aqueous dispersion (hereinafter also referred to as "first aqueous dispersion") a first fluorine-containing polymer which is substantially free of a water-soluble emulsifier and which contains units based on tetrafluoroethylene (hereinafter also referred to as "TFE") and units based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"), and an aqueous medium, A method for producing a solid composition, comprising polymerizing a monomer containing TFE and PAVE, subjecting the obtained aqueous dispersion containing a second fluorine-containing polymer (hereinafter also referred to as "second aqueous dispersion") to a stirring treatment, and recovering a solid matter obtained after the stirring treatment to obtain a solid composition, comprising: the first fluorinated polymer contains 5 to 80 mol % of the PAVE-based units relative to the total of the TFE-based units and the PAVE-based units, the second fluorinated polymer contains 15 to 95 mol% of the PAVE-based units relative to the total of the TFE-based units and the PAVE-based units, In the method for producing a solid composition, 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 start of polymerization of the monomers. This production method allows the production of a solid composition that is substantially free of emulsifiers and has an excellent crosslinking rate. While the details of why this is the case are unclear, it is believed that by polymerizing in a first aqueous dispersion containing a predetermined amount of a specific first fluoropolymer, the first fluoropolymer functions as a polymerization site, allowing the monomers to polymerize 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 the solid from the aqueous dispersion after polymerization. If such a flocculant remains in the solid composition, the crosslinking reaction is inhibited and the crosslinking rate decreases. As described above, this production method involves polymerization in a first aqueous dispersion that is substantially free of emulsifiers, and thus a solid composition can be obtained by stirring. It is believed that the solid composition obtained in this manner also has an excellent crosslinking rate because it does not contain any components that inhibit crosslinking. 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 hereinafter also referred to as "specific monomer." Each step will be described below.

[0011] <Process 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 water-soluble emulsifiers" means that the content of water-soluble emulsifiers in the first aqueous dispersion is 10 mass ppm or less, preferably 100 mass ppb or less, and more preferably 50 mass ppb 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. The lower limit can be 1 mass ppb. The content of the water-soluble emulsifier can be measured using a liquid chromatograph mass spectrometer. Specifically, the measurement method described in paragraphs 0721 to 0732 of WO 2018 / 181904 can be used, and the measurement method described in the Examples is preferred.

[0013] The water-soluble emulsifier means an emulsifier whose solubility in 1000 g of water at 25°C is 100 mg or more. 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 a fluorine atom include anionic fluorine-containing emulsifiers. Examples of the anionic fluorine-containing emulsifier include emulsifiers containing fluorine atoms in which the total number of carbon atoms in the moiety excluding the anionic group is 20 or less, and fluorine-containing emulsifiers in which the molecular weight of the anionic moiety is 800 or less.

[0015] The fluorine-free emulsifier does not have a fluorine atom but has a hydrocarbon group such as an alkyl group. It is also possible to substitute a hydrogen atom of the hydrocarbon group of the fluorine-free emulsifier with a halogen atom other than a fluorine atom. The emulsifiers having no fluorine atoms include ionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

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

[0017] A nonionic hydrocarbon emulsifier is an emulsifier that exhibits surface activity in water without dissociating into ions and has a hydrocarbon group such as an alkyl group as a hydrophobic portion. The hydrophilic portion of the nonionic hydrocarbon emulsifier includes a water-soluble functional group such as a polyethylene oxide chain obtained from the polymerization of ethylene oxide. Nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, such as block copolymers having polyethylene oxide and polypropylene oxide. Examples of nonionic hydrocarbon emulsifiers include 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 may contain silicon atom.The emulsifier containing silicon atom includes siloxane emulsifier.The siloxane emulsifier includes 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] The first aqueous dispersion preferably does not substantially contain an emulsifier represented by any of formulae (S1) to (S4). When no emulsifier is used in producing the first fluorinated polymer 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-(CF2) n1 -COOM (S1) F-(CF2) n1 -COOM (S2) H-(CF2) n2 -SO3M (S3) F-(CF2) n2 -SO3M (S4) In formulas (S1) to (S4), n1 is an integer from 3 to 19, n2 is an integer from 4 to 20, Each M is independently a hydrogen atom, Na, K, or NH4.

[0022] -First fluoropolymer- 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 of enabling more efficient production of the second fluoropolymer. CF2=CF-OR f1 (1) In formula (1), R f1 represents a perfluoroalkyl group having 1 to 10 carbon atoms. f1 The number of carbon atoms in the alkyl group is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3, in terms of better polymerization reactivity. 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 PMVE or PPVE are preferred, with PMVE being more preferred, from the viewpoint of enabling more efficient production of the second fluorine-containing polymer.

[0025] In the first fluoropolymer, the TFE units account for 20 to 95 mol%, preferably 40 to 85 mol%, and from the viewpoint of more efficient production of the second fluoropolymer, more preferably 50 to 75 mol%, and even more preferably 60 to 70 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") In the first fluorine-containing polymer, the PAVE units are present in an amount of 5 to 80 mol%, preferably 15 to 60 mol%, and from the viewpoint of more efficient production of the second fluorine-containing polymer, more preferably 25 to 55 mol%, even more preferably 30 to 40 mol%, based on the total amount of TFE units and PAVE units. When PMVE units or PPVE units are used as PAVE units, the suitable amount to be used is similar. The total content of TFE units and PAVE units in the first fluorine-containing polymer 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 fluorine-containing polymer.

[0026] The first fluorine-containing polymer may contain units based on monomers other than TFE and PAVE, and it is also preferable that the first fluorine-containing polymer is substantially free of units based on other monomers, in order to enable more efficient production of the second fluorine-containing polymer. Substantially free of units derived from other monomers means that the content of units derived from 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 start of polymerization of the specific monomer, the content of the first fluoropolymer is 0.01 to 4.0 mass% relative to the total mass of the first aqueous dispersion, and from the viewpoint of more efficiently producing the second fluoropolymer, it is preferably 0.01 to 1.0 mass%, more preferably 0.01 to 0.8 mass%. In this specification, "before the start of polymerization of the specific monomer" means immediately before the polymerization initiation point. Here, "the time of initiation of polymerization" includes 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 temperature inside the reactor is raised to the polymerization temperature or higher, and the time when the temperature inside the reactor is raised to the polymerization temperature or higher after the specific monomer (when a polymerization initiator is used, the polymerization initiator and the specific monomer) are made to coexist in the reactor.

[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 solid content concentration is calculated by the following formula. "Solid content concentration (mass%) = 100 × mass (g) of heated residue of first aqueous dispersion / mass (2.0 g) of first aqueous dispersion"

[0029] The first fluorine-containing polymer is preferably produced by polymerizing monomers containing TFE and PAVE in an aqueous medium in the presence of a polymerization initiator, thereby obtaining 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 fluoropolymer are dispersed, may be used as the first aqueous dispersion as is, or the first fluoropolymer may be dispersed in another aqueous medium after solvent substitution, and the resulting dispersion 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 further 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 with 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 used for polymerizing a specific monomer after being subjected to a purification treatment to reduce or inactivate the polymerization initiator and its decomposition products. 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 having desired physical properties can be easily obtained. Examples of purification methods include a heat treatment method and a method of passing the solution through an ion exchange resin (preferably an anion exchange resin). The purification process may be carried out 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. If the average particle diameter of the anion exchange resin is within the above range, clogging is unlikely 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, first, the anion exchange resin is placed in a sieve shaker, and the particle size distribution is measured by sieving. Then, the diameter of the sieve opening corresponding to a cumulative residue of 50% by mass is determined, and this is taken as the average particle diameter. The anion exchange resin may be a gel type or a macroporous type. The matrix structure of the resin may be acrylic or styrene-based. 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 hydroxide ion is preferred 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 60 to 99.9 mass %, more preferably 96 to 99.9 mass %, and even more preferably 98 to 99.9 mass %, based on the total mass of the first aqueous dispersion.

[0035] -Other ingredients- The first aqueous dispersion may contain other components in addition to the first fluorine-containing 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 pH adjusters include inorganic salts and ammonia. Specific examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium bicarbonate and sodium carbonate. More preferred specific examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate. 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 relative to 100 parts by mass of the aqueous medium.

[0036] (Specific monomer) The specific monomer is a monomer including 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 monomers 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 the 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 better polymerization reactivity. BO preferably contains a fluorine atom, since this reduces the compression set of the crosslinked rubber article at high temperatures.

[0039] BO is preferably a monomer represented by formula (2) in that the crosslinked rubber article has better releasability. (CR 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 from each other, and are particularly preferably the same from each other. a1 is preferably 2 or 3, and 2 is particularly preferred. Because of the superior polymerization reactivity of BO, 21 , R 22 , and R 23 is preferably a fluorine atom or a hydrogen atom, and R 21 , R 22 , and R 23 It is more preferable that all of R are fluorine atoms or all are hydrogen atoms, and in view of better mold releasability of the crosslinked rubber article, 21 , R 22 , and R 23 It is particularly preferred that all of are fluorine atoms. R 24 R may be linear, branched, or cyclic, preferably linear or branched, and particularly preferably linear. 24 The number of carbon atoms is preferably 2 to 8, more preferably 3 to 7, further preferably 3 to 6, and particularly preferably 3 to 5. R 24 may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in view of better crosslinking reactivity and rubber physical properties. R 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] (CF2=CF-)2R 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] (CH2=CH-)2R 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 CF2=CFO(CF2)2OCF=CF2, CF2=CFO(CF2)3OCF=CF2, CF2=CFO(CF2)4OCF=CF2, and CF2=CFO(CF2)6OCF=CF 2、 CF2=CFO(CF2)8OCF=CF2, CF2=CFO(CF2)2OCF(CF3)CF2OCF=CF2, CF2=CFO(CF2)2O(CF(CF3)CF2O)2CF=CF2, CF2=CFOCF2O(CF2CF2O)2CF=CF2, CF2 =CFO(CF2O)3O(CF(CF3)CF2O)2CF=CF2, CF2=CFOCF2CF(CF3)O(CF2)2OCF(CF3)CF2OCF=CF2, and CF2=CFOCF2CF2O(CF2O)2CF2CF2OCF=CF2. Among the monomers represented by formula (3), specific examples of more suitable monomers include CF2=CFO(CF2)3OCF=CF2 (hereinafter also referred to as "C3DVE") and CF2=CFO(CF2)4OCF=CF2 (hereinafter also referred to as "C4DVE"). Specific examples of the monomer represented by formula (4) include CH2=CH(CF2)2CH=CH2, CH2=CH(CF2)4CH=CH2, and CH2=CH(CF2)6CH=CH2. Among the monomers represented by formula (4), a more preferred specific example of the monomer is CH2=CH(CF2)6CH=CH2 (hereinafter also referred to as "C6DV"). Among these, 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 monomers having a bromine atom include CF2=CFOCF2CF2CF2OCF2CF2Br, 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, 2-bromo-perfluoroethyl perfluorovinyl ether and CF2Br-R f -O-CF=CF2(R f fluorinated compounds such as CFBrCFO-CF=CF, ROCF=CFBr, and ROCBr=CF (R is a lower alkyl group or a fluoroalkyl group), specifically CHOCF=CFBr and CFCHOCF=CFBr. Specific examples of the monomer having an iodine atom include a monomer of the formula: CHR=CH-Z-CHCHR-I (wherein R is -H or -CH; Z is a linear or branched C-C alkyl group optionally containing one or more ethereal oxygen atoms). 18Included are iodinated olefins of the formula I(CHCFCF) 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. n OCF = CF2 and ICH2CF2O [CF(CF3)CF2O] n Examples of unsaturated ethers include CF═CF2 (where n=1 to 3). Other examples include 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. Other examples include 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 that the solid composition has better mold releasability and heat resistance. CR 51 R 52 =CR 53 -R 54 -CN (5) In formula (5), R 51 , R 52 , and R 53each 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. R CN Because of its excellent polymerization reactivity, R 51 , R 52 , and R 53 is preferably a fluorine atom or a hydrogen atom, and R 51 , R 52 , and R 53 It is more preferable 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 are fluorine atoms. R 54 R may be linear, branched, or cyclic, and is preferably linear or branched. 54 The number of carbon atoms is preferably 2 to 8, more preferably 3 to 7, further preferably 3 to 6, and particularly preferably 3 to 5. R 54 may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in view of better rubber properties. R 54 The number of etheric oxygen atoms in is preferably 1 to 3, and particularly preferably 1 or 2. Specific examples of the monomer represented by formula (5) include CF2=CFOCF2CF(CF3)OCF2CF2CN (hereinafter also referred to as "8CNVE"), CF2=CFO(CF2)5CN (hereinafter also referred to as "MV5CN"), CF2=CFOCF2CF2CF2OCF(CF3)CN, and CF2=CFO(CF2)3CN, of which 8CNVE or MV5CN are preferred in terms of better mold releasability and heat resistance of the solid composition.

[0047] POAVE is a compound represented by formula (6). CF2=CF(OCF2CF2)n -(OCF2) m -OR f2 (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 (R), the perfluoroalkyl group may be linear or branched. f2 The number of carbon atoms 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 description in parentheses after the formula is the abbreviation for the compound. CF2=CF-OCF2CF2-(OCF2)4-OCF3(C9PEVE), CF2=CF-OCF2CF2-(OCF2)2-OCF3(C7PEVE), CF2=CF-(OCF2CF2)2-OCF2CF3(EEAVE), CF2=CF-(OCF2CF2)3-OCF2CF3(EEEAVE), CF2=CF-OCF2-OCF3, CF2=CF-OCF2-OCF2-OCF3 As POAVE, C9PEVE, C7PEVE, EEAVE, or EEEAVE is preferred in terms of better low-temperature properties of crosslinked rubber articles and productivity of solid compositions. These compounds can be produced using the corresponding alcohols as starting materials 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 oxidation-reduction catalyst. Specific examples of oil-soluble radical initiators include oil-soluble organic peroxides such as tert-butyl peroxypivalate and diisopropyl peroxydicarbonate. Specific examples of the water-soluble radical initiator include persulfates such as ammonium persulfate and potassium persulfate, disuccinic acid peroxide, bisglutaric acid peroxide, and water-soluble organic peroxides such as tert-butyl hydroperoxide. The water-soluble oxidation-reduction catalyst is preferably a combination of an oxidizing agent such as bromic acid or its salts, chloric acid or its salts, persulfuric acid or its salts, permanganic acid or its salts, or hydrogen peroxide, and a reducing agent such as sulfurous acid or its salts, hydrogen sulfite or its salts, thiosulfuric acid or its salts, organic acids, or inorganic salts. Potassium persulfate or ammonium persulfate is preferred as the persulfate. Sodium sulfite is preferred as the sulfite. Examples of inorganic salts include combinations of sulfate anions, sulfite anions, or chloride anions with metal ions. Transition metal ions are preferred, including manganese, iron, cobalt, nickel, copper, zinc, cerium, and silver ions, with iron ions being preferred. Iron (II) sulfate is preferred as the inorganic salt. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator, more preferably a water-soluble radical initiator from the viewpoint of more efficient production of the fluorine-containing polymer, and further preferably a persulfate or a water-soluble organic peroxide. Two or more types of 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, relative to 100 parts by mass of the amount of the specific monomer used.

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

[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, X is an iodine atom or a bromine atom, and at least one X is an iodine atom. R f The fluoroalkylene group of R may be linear or branched. f As the alkyl group, a perfluoroalkylene group is preferred. It is preferable that all of X's 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, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,5-diiodoperfluoropropane, 1,6-di Examples of iodoethane 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, monoiodo-monobromo-substituted benzene, and diiodo-monobromo-substituted benzene. The compound represented by formula (I) is preferably C4DI.

[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, relative to 100 parts by mass of the amount 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 above-mentioned specific monomer in the above-mentioned first aqueous dispersion to obtain a second aqueous dispersion containing a second fluorine-containing polymer. The specific monomer is introduced into the reaction system (i.e., polymerization reaction vessel) by a conventional method. For example, the specific monomer may be introduced into the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer may be dissolved in an aqueous medium, and the resulting solution may be introduced into 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 other components (e.g., chain transfer agents) are used, the other components may be added to the reaction system all at once or in portions.

[0060] The polymerization temperature is preferably from 10 to 95°C, more preferably from 15 to 90°C. The polymerization pressure is preferably from 0.5 to 4.0 MPaG, more preferably from 0.6 to 3.5 MPaG. In the case of batch processing, the polymerization time is preferably from 90 to 1,000 minutes, more preferably from 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. "Emulsifier is substantially absent" means an environment in which the content of emulsifier is 0.03 mass ppm or less relative to the total mass of the aqueous medium contained in the first aqueous dispersion, preferably 0.02 mass ppm or less, and more preferably 0 mass ppm.

[0062] (Second fluoropolymer) A second fluorine-containing polymer is produced in 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 account for 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%, based on the total of the TFE units and PAVE units. In the second fluorine-containing polymer, the PAVE units are present in an amount of 15 to 95 mol%, preferably 20 to 60 mol%, and from the viewpoint of more efficient production of the second fluorine-containing polymer, more preferably 25 to 50 mol%, even more preferably 30 to 40 mol%, based on the total amount of TFE units and PAVE units. When PMVE units or PPVE units are used as PAVE units, the suitable amount to be used is 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 also preferably contains units based on other monomers, such as those in the above-mentioned specific monomers. In the second fluorine-containing polymer, the TFE units preferably account for 35 to 80 mol %, more preferably 47 to 75 mol %, and even more preferably 59 to 70 mol %, based on all units. In the second fluorine-containing polymer, the amount of PAVE units relative to all units is preferably from 20 to 60 mol %, more preferably from 25 to 50 mol %, and even more preferably from 30 to 40 mol %. In the second fluorine-containing polymer, the amount of units based on other monomers relative to all units is preferably from 0.01 to 5 mol %, more preferably from 0.05 to 3 mol %, and even more preferably from 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 that the crosslinkability of the solid composition is more excellent. In particular, it is preferred that the second fluorine-containing polymer contains at least one type selected from the above at least at its terminal and side chain.

[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 fluoropolymer obtained in step 1. In other words, the second aqueous dispersion is an aqueous dispersion in which particles containing a fluoropolymer (hereinafter also referred to as "specific particles") are dispersed in an aqueous medium, and the fluoropolymer contains the second fluoropolymer. 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 preferred embodiment of the fluorine-containing polymer contained in the specific particles is the same as 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 (solid content) of the specific particles in the second aqueous dispersion 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 heating 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, is more preferably 500 nm or less, and even more preferably 400 nm or less. 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, from the viewpoint of recovery efficiency in step 2 described below. The average particle size of the specific particles is a particle size calculated by analyzing the autocorrelation function obtained by dynamic light scattering using the 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 %, based on 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 obtain a more excellent effect of the present invention. It is also preferable that the content be less than the quantitation limit of the measurement method in the examples. The lower limit can be 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 that 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] <Process 2> In step 2 of this 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] (Mixing process) A specific example of the stirring method is 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, disc blades, three-bladed swept-back blades, anchor blades, turbine blades, and disc turbine blades, and paddle blades or disc turbine blades are preferred because of their excellent stirring efficiency. The number of the stirring blades is preferably 1 to 10, and more preferably 2 to 4. Specific examples of the shape of the vessel used in the stirring treatment include a cylindrical shape, a conical shape, an elliptical cylindrical shape, a rectangular cylindrical shape, and a pyramidal shape, with a cylindrical shape being preferred from the standpoint of mixability and fluidity. The stirring device may be provided with a baffle plate.

[0073] The stirring time is preferably from 0.1 to 24 hours, more preferably from 0.1 to 12 hours, and even more preferably from 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 vary during stirring. The peripheral speed is also preferably faster than the peripheral speed in step 1. The peripheral speed of stirring refers to the speed of the impeller at the tip of the impeller. The temperature of the aqueous dispersion during the stirring treatment is preferably from 10 to 90°C, more preferably from 10 to 80°C, and even more preferably from 15 to 70°C.

[0074] (solids) The solid matter is a solid matter obtained by the above stirring treatment, and contains 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, while the precipitates and floating matter are included in the solid matter. Examples of the solid matter include agglomerates of specific particles. The stably dispersed dispersoid is, for example, a dispersoid that passes through a type 5A filter paper specified in JIS P 3801 (filter paper (for chemical analysis)).

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

[0076] <Cleaning> Preferably, the present production method 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 fluorine-containing polymer 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. The washing liquid in the washing step may be the aqueous medium described above, with water being preferred, and ultrapure water being more preferred since it contains a small amount of impurities that may cause crosslinking inhibition.

[0077] Specific examples of the washing method include a method of immersing the solid composition in a washing solution and stirring it, and a method of showering the solid composition with a washing solution. Washing and dehydration of the solid composition may be repeated multiple times. Specific examples of the dehydration method include squeezing and centrifugation. The amount of the washing liquid 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 liquid in the washing step is preferably 5 to 80°C, more preferably 10 to 70°C, and even more preferably 20 to 60°C.

[0078] [Solid composition] This manufacturing method results in a solid composition. The solid composition of the present invention (hereinafter also referred to as "the present solid composition") contains a fluoropolymer containing TFE units and PAVE units, is substantially free of an emulsifier, and satisfies the requirement X described below. In this specification, the term "solid composition" refers to a composition having a solid content of 99% by mass or more. The solid content is calculated by the following method based on the mass before and after heating. 2.0 g of the solid composition is heated at 170°C for 20 minutes, and then the mass of the residue is weighed and the solid content mass is calculated using the following formula. Solid content mass (mass%) = 100 × (mass of residue) / (mass of solid composition)

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

[0080] The fluorine-containing polymer contained in the present solid composition may contain units based on other monomers than TFE units and PAVE units, such as 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, 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 obtain more excellent crosslinkability. In particular, it is preferable that the fluorine-containing polymer contains at least one selected from the above at at least one of its terminals and side chains. By using the above-mentioned other monomers as the specific monomers in addition to TFE and PAVE, any 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 end of the fluorine-containing polymer. In addition, by polymerizing the specific monomers using a chain transfer agent having an iodine atom, an iodine atom can be introduced into the end 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 even more preferably from 0.01 to 1.00 mass %, based on 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 manufacturing process of the solid composition, and the solid composition does not contain any emulsifiers, or if the solid composition contains any of the above-mentioned emulsifiers, the total content of the emulsifiers is 500 ppb or less based on the total mass of the solid composition. When the solid composition contains an emulsifier, the total content of the emulsifier is preferably 250 mass ppb or less, more preferably 100 mass ppb or less, and even more preferably 50 mass ppb or less, based on 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. In the above, the number of types of emulsifiers contained in the solid composition is 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 both above the quantitation limit and the content of emulsifier Z is below the quantitation limit, this means that the solid composition contains two types of emulsifiers, emulsifier X and emulsifier Y. The content of the emulsifier can be measured by the method for measuring the content of the emulsifier in the method for producing the solid composition described above. The emulsifiers that the solid composition may contain are as described above.

[0084] The solid composition is preferably substantially free of a compound (emulsifier) ​​represented by any one of formulas (S1) to (S4). When no emulsifier is used in producing the first fluorinated polymer 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-(CF2) n1 -COOM (S1) F-(CF2) n1 -COOM (S2) H-(CF2) n2 -SO3M (S3) F-(CF2) n2 -SO3M (S4) In formulas (S1) to (S4), n1 is an integer from 3 to 19, n2 is an integer from 4 to 20, Each M is independently a hydrogen atom, Na, K, or NH4. 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, based on 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 mixture obtained by mixing a 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 mixture at 23°C 24 hours after mixing is 4 or higher.

[0087] The pH of the mixture at 23° C. 24 hours after mixing is 4 or higher, and more preferably 5 or higher. The pH is preferably 12 or lower, and more preferably 10 or lower. The pH of the mixture is measured after mixing the solid composition with water and then leaving the mixture to stand for 24 hours at 23° C. 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 conditions are adjusted without using a flocculant.

[0088] <Flocculant> In this production method, the aqueous dispersion is subjected to a stirring treatment, and the solid matter in the aqueous dispersion is recovered to obtain a solid composition, so that acid coagulation, base coagulation, and coagulation using a coagulant are not performed. In other words, the solid composition does not contain residues of the coagulant used in acid coagulation, base coagulation, and coagulation using a coagulant, so the above-mentioned requirement X can be satisfied. In the case of acid coagulation, a method of adding a solution containing an acid is employed, and examples of the acid to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, and hydrofluoric acid, and examples of the acid to be added include nitric acid. For base coagulation, a method of adding a solution containing a base is employed, and examples of the base include sodium hydroxide, potassium hydroxide, and ammonium carbonate. For aggregation using a coagulant, known coagulants are used, including aluminum salts, calcium salts, magnesium salts, and ammonium salts. Specific examples include ammonium carbonate, aluminum sulfate, alum represented by the general formula M'Al(SO4)2·12H2O (where M' is a monovalent cation other than lithium), calcium nitrate, and magnesium sulfate. The solid compositions of the present invention are substantially free of flocculants. The phrase "the solid composition is substantially free of a flocculant" means that no flocculant is used in the production process of the solid composition, and the solid composition does not contain an emulsifier, or, if the solid composition contains the above-mentioned flocculant, the total content of the flocculant is 25 ppb by mass or less based on the total mass of the solid composition. When the solid composition contains a flocculant, the total content of the flocculant is preferably 25 ppb by mass or less, more preferably 20 ppb by mass or less, based on the total mass of the solid composition. The lower limit may be more 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 the detailed measurement conditions are as shown in the examples. An example of a method for adjusting the storage modulus is to adjust 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 that has no melting point and exhibits 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 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, based on the total mass of the solid composition, in order to reduce surrounding contamination during use. It is also preferable that the total metal content is below 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 the 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 and then dissolving the resulting ash in an acid to obtain a solution, which is then measured 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 fall within the above range.

[0092] [Application] The present production method is preferably used for producing a crosslinked rubber article, i.e. the solid composition obtained by the present production method is preferably used for producing a crosslinked rubber article.

[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, circuit 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] Fields in which fluororubber articles are used include, for example, semiconductor-related fields, food and beverage manufacturing equipment, pharmaceutical manufacturing equipment, medical parts, chemical transport equipment, nuclear power plant equipment, steel 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 and rockets, ships, chemical industries such as chemical plants, pharmaceuticals and other chemicals, photography such as developing machines, printing machines, painting equipment, analytical equipment, analytical and physicochemical machinery such as meters, and food equipment for food plants and household goods.

[0096] In the semiconductor-related fields, the present invention can be used, for example, in 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, the present invention can be used in 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 Examples 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 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 treatment equipment (e.g., 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. In the above-mentioned semiconductor-related fields, the present invention can be used, for example, 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 conveying equipment, etc. More specifically, the present invention can be used in 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 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 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 treatment equipment (e.g., 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 the semiconductor manufacturing process. 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 articles can be produced by crosslinking the solid compositions of the present invention. Examples of the crosslinking method include a method in which a crosslinking agent is added and then kneaded or molded. Specific examples of the crosslinking agent include organic peroxides, polyols, amines, and triazines, with organic peroxides being preferred in terms of the productivity, heat resistance, and chemical resistance of 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. [Example]

[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 measuring device (ELSZ, manufactured by Otsuka Electronics Co., Ltd.) with the aqueous dispersion of each example described below as a sample.

[0102] [Production of solid composition] <Production of raw material solution A> A 2.2 L stainless steel pressure reactor equipped with an anchor impeller was charged with ultrapure water (1130 g), 30 mass% aqueous ammonia (30 mg), PMVE (72 g), and TFE (14 g). The mixture was heated to 90 °C while stirring at 600 rpm. Next, 30 cc of ammonium persulfate (5.0 mass%) aqueous solution was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE was added to maintain a constant pressure. After 4 g of TFE was injected, the reactor was cooled and the polymerization reaction was terminated. 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 4 g of TFE and 0 g of PMVE. The total amounts of TFE and PMVE added were 18 g and 72 g, respectively. The remaining gas in the reactor was recovered, and the liquid was withdrawn. This liquid was designated as raw material liquid A. After freeze-coagulating the raw material liquid A, it was filtered off, and the resulting fluoropolymer 1A was analyzed by NMR, and as a result, it was found that the PAVE unit / TFE unit ratio was 34 / 66 (molar ratio).

[0103] <Production of raw material solution B> To 1000 g of HPR4002Cl (a styrene-based gel-type strongly basic anion exchange resin manufactured by DuPont), 2000 g of an 8% by mass aqueous solution of sodium hydroxide was added, 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® HPR650H (a cation exchange resin manufactured by DuPont) was added to the filtrate. 60 minutes after stirring began, the raw material solution and the ion exchange resin were separated by filtration to obtain 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 stainless steel pressure reactor having an internal volume of 2.2 L and equipped with an anchor impeller was charged with raw material liquid B (1000 g) and ultrapure water (175 g) to obtain aqueous dispersion 1-1. The content of fluoropolymer 1A was 0.4 mass% based on 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 heated to 80 °C while stirring at 600 rpm. TFE and PMVE were injected into the reactor until the reactor pressure reached 1.5 MPa [gauge], and an aqueous ammonium persulfate solution (20 ml of 1.0% by mass APS aqueous solution, 0.2 g of ammonium persulfate) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE / PMVE was injected at a molar ratio of 65 / 35 to maintain the pressure constant. After injecting 256 g of TFE and 217 g of PMVE, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 380 minutes. The total monomers added before the polymerization initiation were 14 g of TFE and 90 g of PMVE. The total amounts of the monomers added after the initiation of polymerization were 256 g for TFE and 217 g for PMVE, with the total amount of TFE added being 270 g and the total amount of PMVE added being 307 g.

[0105] The aqueous dispersion 1-1 described above did not substantially contain any water-soluble emulsifier. Specifically, the contents of emulsifier A and the compounds represented by formulae (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 formulae (S1) to (S4) were not produced from the components used in producing aqueous dispersion 1-1, and were not used, so they are not contained in aqueous dispersion 1-1. The solid content of aqueous dispersion 1-1 was measured, and an amount of aqueous dispersion 1-1 corresponding to 0.05 g of solid content 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 vigorously shaken until coagulation occurred. The solid content was removed, and the liquid phase was centrifuged at 4000 rpm for 1 hour, and the supernatant was extracted. Measurement was performed using the same method as the measurement method for <Emulsifier Content> described below, except for the sample preparation method. As a result, the content of the compound represented by any of formulas (S1) to (S4) in aqueous dispersion 1-1 was also below the quantitation limit.

[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 diameter 92.7 nm) containing a fluoropolymer were dispersed in an aqueous medium, and the solid concentration was 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 with eight blades attached at right angles and equidistantly spaced around the circumference of a disk, and the solid matter was then 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 1. The peripheral speed (m / s) of the stirring was the speed of the impeller at the tip of the impeller. The fluorine-containing polymer contained in the obtained solid composition 1 was analyzed by NMR, and as a result, it was found that the PAVE unit / TFE unit ratio was 34 / 66 (molar ratio).

[0107] <Production of raw material solution C> Except for appropriately changing the amounts of each component used, a fluoropolymer 1C was polymerized in the same procedure as in the production of raw material liquid A, and this liquid was designated as raw material liquid C. Raw material liquid C was freeze-aggregated and then filtered, and the resulting fluoropolymer 1C was analyzed by NMR, revealing that the PAVE unit / TFE unit ratio was 32 / 68.

[0108] <Production of raw material solution D> Raw material liquid D was produced in the same manner as 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 liquid D (1000 g) and ultrapure water (175 g) to obtain aqueous dispersion 1-2. The content of fluoropolymer 1C was 0.4 mass% based on the total mass of aqueous dispersion 1-2. Aqueous dispersion 1-2 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), perfluoro-1,4-diiodobutane (2.0 g), and TFE (14 g) were charged to aqueous dispersion 1-2 and heated to 80 °C while stirring at 600 rpm. TFE and PMVE were injected into the reactor until the reactor pressure reached 1.5 MPa [gauge], and an aqueous APS solution (0.5% by mass, 16 ml, 0.08 g of ammonium persulfate) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE / PMVE was injected at a molar ratio of 65 / 35 to maintain a constant pressure. After adding 256 g of TFE and 217 g of PMVE, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 290 min. The total monomers added before the polymerization initiation were 14 g of TFE and 72 g of PMVE. The total monomers added after the polymerization initiation 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. After recovering the gas remaining in the reactor, 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 diameter 140.3 nm) containing a fluoropolymer were dispersed in an aqueous medium, and the solid concentration was 28.6 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 as a result, it was found that the PAVE unit / TFE unit ratio was 35 / 65 (molar ratio).

[0110] <Example 3> A 2.2 L stainless steel pressure reactor 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% based on 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 to aqueous dispersion 1-3 and heated to 80 °C while stirring at 600 rpm. TFE and PMVE were injected until the reactor pressure reached 1.5 MPa [gauge], and an aqueous APS solution (0.5% by mass, 16 ml, 0.08 g of ammonium persulfate) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE / PMVE was injected at a molar ratio of 65 / 35 to maintain the pressure constant. After 6 g of TFE had been added, perfluoro-1,4-diiodobutane (2.0 g) was injected. After 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 monomers added before the polymerization initiation were 14 g of TFE and 72 g of PMVE. The total amounts of the monomers added after the initiation of polymerization were 256 g for TFE and 217 g for PMVE, with the total amount of TFE added being 270 g and the total amount of PMVE added being 289 g. After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated as aqueous dispersion 2-3. Aqueous dispersion 2-3 was a dispersion in which particles (average particle diameter 96 nm) containing a fluoropolymer were dispersed in an aqueous medium, and the solid concentration was 27.6 mass%. The aqueous dispersion 2-3 was stirred with six turbine blades at 30 m / s for 150 minutes, and the solid matter was collected by filtration. The collected solid matter was washed with 2,000 g of ultrapure water at 25°C and dried to obtain a rubbery solid composition 3. The fluorine-containing polymer contained in the obtained solid composition 3 was analyzed by NMR, and as a result, it was found that the PAVE unit / TFE unit ratio was 34 / 65 (molar ratio).

[0111] <Example 4> A 2.2 L stainless steel pressure reactor equipped with an anchor impeller was degassed and then charged with ultrapure water (1004 g), a 30 wt% solution (80.1 g) of C2F5OCF2CF2OCF2COONH4 (emulsifier A) as a 30 wt% solution, and a 5 wt% aqueous solution (10.49 g) of disodium hydrogen phosphate dodecahydrate. The gas phase was then purged with nitrogen. While stirring at 600 rpm using an anchor impeller, PMVE (72 g) and TFE (14 g) were added under pressure, and the internal temperature was raised to 80 °C. Next, an aqueous solution of APS (1.0 wt%, 20 ml) was added to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE / PMVE (65 / 35 molar ratio) was added under pressure to maintain a constant pressure of 1.2 MPa [gauge]. After 160 g of TFE and 133 g of PMVE were injected, the reactor was cooled to terminate the polymerization reaction, which took 262 minutes. The gas remaining in the reactor was collected, and then the liquid was withdrawn. This liquid was designated as aqueous dispersion 4. Aqueous dispersion 4 was a dispersion in which particles (average particle diameter 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. The fluorine-containing polymer contained in the obtained solid composition 4 was analyzed by NMR, and as a result, it was found that the PAVE unit / TFE unit ratio was 35 / 65 (molar ratio).

[0112] <Example 5> After degassing a 2.2 L stainless steel pressure reactor equipped with an anchor impeller, ultrapure water (1004 g), a 30 wt% solution (80.1 g) of C2F5OCF2CF2OCF2COONH4 (emulsifier A) and a 5 wt% aqueous solution (10.49 g) of disodium hydrogen phosphate dodecahydrate were charged and the gas phase was replaced with nitrogen. While stirring at 600 rpm using an anchor impeller, PMVE (72 g) and TFE (14 g) were pressurized into the reactor, and the internal temperature was raised to 80 °C. Next, an aqueous solution of APS (1.0 wt%, 20 ml, ammonium persulfate 0.1 g) was added to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE / PMVE (65 / 35 molar ratio) was pressurized and maintained at a constant pressure of 1.2 MPa [gauge]. After 160 g of TFE and 133 g of PMVE were injected, the reactor was cooled to terminate the polymerization reaction, which took 280 minutes. The gas remaining in the reactor was collected, and then the liquid was withdrawn. This liquid was designated as aqueous dispersion 5. Aqueous dispersion 5 was a dispersion in which particles containing fluoropolymer 1G (average particle diameter 98.6 nm) were dispersed in an aqueous medium, and had a solids concentration of 20.1% by mass. The aqueous dispersion 5 was added to a nitric acid aqueous solution (3% by mass, 2,500 g) and stirred, and 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 fluorine-containing polymer 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] The 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 mixture at 23°C was measured using a benchtop 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 with a two-roll mill at 23° C. for 10 minutes. After kneading, the gap between the two roll mills 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 agent: TAIC-WH60, manufactured by Mitsubishi Chemical, triallyl isocyanurate 60% diluted with silica Crosslinking agent: Perhexa 25B, NOF Corp., 2,5-dimethyl-2.5-di(t-butylperoxy)hexane Release agent: Nonsal SN-1, NOF Corp., sodium stearate

[0116] [Table 1]

[0117] The obtained sheet for evaluating the crosslinking rate was cut into 10 g pieces to obtain cut sheets. 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 torque obtained was set to 0% and the maximum torque was set to 100%, and the processing time required to obtain a 50% torque value was defined as t 50 , the processing time at which the torque value is 90% is t 90 It was decided.

[0118] <Emulsifier content> (Preparing the 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 to obtain a pulverized powder. The freeze-pulverization conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 mins, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 0.25 g of the resulting ground powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours. The mixture was then centrifuged (5000 rpm, 5 minutes) to precipitate each fluoropolymer. The supernatant was used as the extract. The resulting extract was analyzed by LC / MS / MS. 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. LC / MS analysis of each aqueous solution was performed, and the relationship between the content and the area area was plotted to create a calibration curve. Using the calibration curve, the area area of ​​the LC / MS chromatogram of the fluorine-containing emulsifier and hydrocarbon emulsifier in the extract was converted to the content of the fluorine-containing emulsifier and hydrocarbon emulsifier.

[0119] [Table 2]

[0120] MRM measurement parameters are selected appropriately depending on the structure of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured. Literature values ​​for MRM parameters can be used, or they can be calculated using an LC-MS system. The specific procedure for determining MRM parameters using an LC-MS system is as follows: Using an LC / MS system (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 (where R is a hydrogen atom or an organic group having 1 to 10 carbon atoms, and may be the same or different), an optionally substituted imidazolium, an optionally substituted pyridinium, or an optionally substituted phosphonium. F-(CF2)n1-COOMS (S2) F-(CF2)n2-SO3MS (S4) Here, n1 is an integer from 3 to 17, and n2 is an integer from 4 to 12.

[0121] [Table 3]

[0122] [Table 4]

[0123] (Quantitative determination of fluorine atom-containing emulsifiers and hydrocarbon emulsifiers contained in solid compositions) Specifically, five levels of methanol standard solutions of an emulsifier having fluorine atoms and a hydrocarbon emulsifier with known concentrations of 1 to 180 ng / g were prepared, and a was calculated using equation (A1-1) by using a first-order approximation from the respective sample concentrations and peak integral values. A=a×X (A1-1) A: Peak area of ​​each emulsifier, X: Concentration of each emulsifier (ng / g)

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

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

[0126] <Method for quantifying the compounds of formula (S1) and formula (S3) contained in a 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 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, followed by ultrasonic treatment at 50°C for 2 hours and centrifugation (5000 rpm, 5 minutes) to precipitate each fluoropolymer, and the supernatant was used as the extract. The resulting extract was measured by LC / MS / MS. 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. Five or more levels of methanol solution were prepared using aqueous solutions of fluorine-containing emulsifiers with known concentrations. LC / MS analysis of the methanol solutions with each concentration was performed, and the relationship between the content and the area against the content was plotted to create a calibration curve. Using this calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing emulsifier in the extract was converted to the content of the fluorine-containing emulsifier. 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 with the same carbon number (formula (S2)). 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 with the same carbon number (formula (S4)). The MRM parameters for formula (S1) and formula (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 using equations (A2-1) and (A2-1') based on the respective sample concentrations and peak integral values ​​using a linear approximation. 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] [Table 5]

[0128] [Table 6]

[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 by formula (A2-1) above, and a' in formula (A2-2') means a' calculated by formula (A2-1') above. XCm=ACm / a (A2-2) XCm: Content (ng / g) of the compound represented by formula (S1) with carbon number (n+1) in each extract ACm: Peak area of ​​the compound represented by formula (S1) with carbon number (n+1) in each extract XCm'=ACm' / a' (A2-2') XCm': Content (ng / g) of the compound represented by formula (S3) with carbon number n in each extract ACm': Peak area of ​​the compound represented by formula (S3) with carbon number n in each extract The limit of quantification in this measurement is 1 ng / g.

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

[0132] The content (ZCm') of formula (S3) in the solid matter relative to the total mass of the solid matter was calculated using the following formula (A2-4). ZCm'=XCm'×ρ1×La / W1 (A2-4) ZCm': Content of the compound represented by formula (S3) with carbon number n contained in the solid ρ1: Density of the extraction solvent (methanol in each example) La: Volume of extraction solvent (5 mL in each example) W1: Sample mass used for extraction (2.5 g of solid material in each example) The emulsifier content shown in each of Examples 1 to 5 indicates the total content of emulsifier A and the compounds represented by the above formulae (S1) to (S4) relative to the total mass of each solid composition. (Examples 1 to 3 do not use emulsifier A, and the total content of the compounds represented by the above formulae (S1) to (S4) is shown.)

[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 treatment with white sulfuric acid.Then, the solution was dissolved in dilute nitric acid, and the contents of 29 kinds of 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, Bi) were measured using an inductively coupled plasma mass spectrometer (Agilent Technologies, ICP-MS 7500cs) by the absolute calibration curve method, and the total contents thereof were calculated. In the table below, the metal content indicates the total content of the above 29 metal elements.

[0134] <Storage modulus G'> The measurement device used was a rubber processability analyzer "PREMIER RPA (manufactured by Alpha Technologies, die shape: D0380)." The solid composition obtained in each example was kneaded for 10 minutes at room temperature (23°C) using a two-roll mill 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 above-mentioned measurement device. The die temperature was previously set to 100°C. Next, the sample was held at 100°C for 2 minutes at a frequency of 30 cpm and an amplitude angle of 0.2°C, and then the amplitude angle was increased to 0.5°C 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] [Table 7]

[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 the production method for obtaining a solid composition by polymerization using an aqueous solution containing an emulsifier. The resulting solid composition contained an emulsifier, and the crosslinking rate of the resulting solid composition was poor.

[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 specification of the present invention.

Claims

1. In an aqueous dispersion comprising a first fluorine-containing polymer which is substantially free of a water-soluble emulsifier and which contains units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and an aqueous medium, A method for producing a solid composition, comprising polymerizing a monomer containing tetrafluoroethylene and a perfluoro(alkyl vinyl ether), stirring an aqueous dispersion containing the obtained second fluorine-containing polymer, and recovering a solid obtained after the stirring, the first fluorinated polymer contains 5 to 80 mol % of units based on perfluoro(alkyl vinyl ether) relative to the total of units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), the second fluorinated polymer contains 15 to 95 mol % of units based on perfluoro(alkyl vinyl ether) relative to the total of units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), before the start of polymerization of the monomers, the content of the first fluorinated polymer is 0.01 to 4.0% by mass relative to the total mass of the aqueous dispersion, The method for producing a solid composition, wherein the aqueous dispersion is substantially free of the water-soluble emulsifier means that the content of the water-soluble emulsifier is 10 ppm by mass or less relative to the total mass of the aqueous dispersion.

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

3. the solid composition does not contain an emulsifier, 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. A method for producing the solid composition according to claim 1 or 2.

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. 3. The method for producing a solid composition according to claim 1, wherein, relative to all units in the second fluorinated polymer, the units based on tetrafluoroethylene account for 35 to 80 mol % and the units based on perfluoro(alkyl vinyl ether) account for 20 to 60 mol %.

6. 3. 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, further 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 emulsifiers the content of the fluorine-containing polymer is 99.0% by mass or more based on the total mass of the solid composition, in the fluorine-containing polymer, the units based on perfluoro(alkyl vinyl ether) account for 15 to 95 mol % based on the total of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether), The solid composition being substantially free of the emulsifier means that the content of the emulsifier is 500 ppb or less based on the total mass of the solid composition; A solid composition that satisfies requirement X. 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 the mixing is 4 or higher.

9. Substantially free of flocculants The solid composition according to claim 8, wherein the solid composition is substantially free of the flocculant means that the content of the flocculant is 25 ppb by mass or less, based on the total mass of the solid composition.

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

11. A crosslinked rubber article as described in claim 10, which is obtained by crosslinking the solid composition using the solid composition and a crosslinking agent.

12. A crosslinked rubber article as described in claim 11, wherein the solid composition is crosslinked further using a filler or reinforcing material.

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