Method for producing fluoroelastomer, aqueous dispersion, and solid composition

Abstract

A method for producing a fluoroelastomer is provided by which a fluoropolymer having excellent dispersion stability in water can be efficiently produced using an aqueous medium having a reduced environmental burden and without essentially requiring an emulsifier.　The method for producing a fluoroelastomer comprises polymerizing monomers including TFE and PAVE in an aqueous dispersion that contains substantially no water-soluble emulsifier and comprises an aqueous medium and a first fluoropolymer, which includes TFE units and PAVE units, thereby producing a second fluoropolymer. In the first fluoropolymer, the proportion of the PAVE units to the sum of the TFE units and the PAVE units is 20-95 mol%. In the second fluoropolymer, the proportion of PAVE units to the sum of TFE units and the PAVE units is 20-95 mol%. Before initiation of the polymerization of the monomers, the content of the first fluoropolymer is 0.01-4.0 mass% with respect to the mass of the whole aqueous dispersion.

Description

Method for producing fluorine-containing elastomer, aqueous dispersion, and solid composition

[0001] The present invention relates to a method for producing a fluorine-containing elastomer, an aqueous dispersion, and a solid composition.

[0002] Fluorine-containing elastomers are used in various industrial fields because of their excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. Examples of methods for producing fluorine-containing elastomers include a method of emulsion polymerization of a fluorine-containing monomer in an aqueous medium using an emulsifier (see Patent Document 1).

[0003] International Publication No. 2022 / 052498

[0004] The method for producing a fluorine-containing elastomer disclosed in Patent Document 1 uses an aqueous medium, which has a small environmental impact, but when a large amount of an emulsifier, which is an essential component, remains in the aqueous dispersion obtained by polymerization, it becomes necessary to remove the emulsifier depending on the application. In addition, the resulting fluorine-containing elastomer is also required to have excellent aqueous dispersion stability.

[0005] An object of the present invention is to provide a method for producing a fluorine-containing elastomer, which can efficiently produce a fluorine-containing elastomer having excellent aqueous dispersion stability using an aqueous medium with a small environmental load and without requiring an emulsifier. Another object of the present invention is to provide an aqueous dispersion and a solid composition.

[0006] As a result of extensive research, the present inventors have found that the above problems can be solved by the following configuration. [1] A method for producing a fluorine-containing elastomer, comprising polymerizing a monomer containing tetrafluoroethylene and perfluoro(alkyl vinyl ether) in an aqueous dispersion containing a first fluorine-containing polymer which is substantially free of a water-soluble emulsifier and contains units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and an aqueous medium, to produce a second fluorine-containing polymer, wherein the units based on perfluoro(alkyl vinyl ether) are 20 to 95 mol % relative to the total of the units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether) in the first fluorine-containing polymer, the units based on perfluoro(alkyl vinyl ether) are 20 to 95 mol % relative to the total of the units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether) in the second fluorine-containing polymer, and the content of the first fluorine-containing polymer is 0.01 to 4.0 mass % relative to the total mass of the aqueous dispersion before starting polymerization of the monomers. [2] The method for producing a fluorine-containing elastomer according to [1], wherein the monomers consist solely of tetrafluoroethylene and perfluoro(alkyl vinyl ether), or contain tetrafluoroethylene and perfluoro(alkyl vinyl ether) and at least one monomer selected from the group consisting of a monomer having two or more polymerizable unsaturated bonds, a monomer having one or more atoms of at least one kind selected from the group consisting of chlorine atoms, bromine atoms, and iodine atoms, and a monomer having a nitrile group. [3] The method for producing a fluorine-containing elastomer according to [1] or [2], wherein the amount of the monomer used is 1 to 80 parts by mass per 100 parts by mass of the aqueous medium used. [4] The method for producing a fluorine-containing elastomer according to any one of [1] to [3], wherein the monomers are polymerized in the presence of a polymerization initiator.[5] An aqueous dispersion comprising an aqueous medium and particles containing a fluorine-containing polymer, wherein the particles have an average particle size of 1 μm or less, the particles contain units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and the fluorine-containing polymer has at least one of a chlorine atom, a bromine atom, an iodine atom, and a nitrile group at at least one of its terminals and side chains, and the content of an emulsifier is 100 ppm by mass or less relative to the total mass of the aqueous dispersion. [6] The aqueous dispersion according to [5], wherein the particles consist solely of units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), or contain units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether) and at least one unit selected from the group consisting of units based on a monomer having two or more polymerizable unsaturated bonds, units based on a monomer having one or more atoms of at least one kind selected from the group consisting of chlorine atoms, bromine atoms, and iodine atoms, and units based on a monomer having a nitrile group. [7] A solid composition comprising a fluorine-containing polymer, wherein the solid composition contains units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), the solid composition is substantially free of an emulsifier, and has a storage modulus G' of 200 to 1200 kPa. [8] The solid composition according to [7], wherein the fluorine-containing polymer has at least one of a chlorine atom, a bromine atom, an iodine atom, and a nitrile group at at least one of its terminals and side chains. [9] A crosslinked rubber article obtained by crosslinking the solid composition according to [8].

[0007] According to the present invention, there is provided a method for producing a fluorine-containing elastomer, which can efficiently produce a fluorine-containing elastomer having excellent aqueous dispersion stability using an aqueous medium with a small environmental load and without requiring an emulsifier. Another object of the present invention is to provide an aqueous dispersion and a solid composition.

[0008] The meanings of terms used in the present invention are as follows. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the upper and lower limits. In the numerical ranges described in this specification in stages, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the Examples. In this specification, each component may be used alone or in combination with two or more substances corresponding to the component. Herein, when two or more substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. A "unit" is a collective term for an atomic group derived from one molecule of the above-mentioned monomer, formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a portion of the above-mentioned atomic group. Hereinafter, a "unit based on a monomer" will also be simply referred to as a "unit." The content (mass % or mol %) of each unit relative to the total units contained in a 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. A "fluoroelastomer" is an elastic fluorocopolymer having no melting point and exhibiting a storage modulus G' of 80 or more at 100°C and 50 cpm measured in accordance with ASTM D6204, and is distinguished from a fluororesin.

[0009] [Method for producing a fluorine-containing elastomer] The method for producing a fluorine-containing elastomer of the present invention (hereinafter also referred to as "the present production method") is a method for producing a fluorine-containing elastomer, which comprises polymerizing a monomer containing tetrafluoroethylene and perfluoro(alkyl vinyl ether) (hereinafter also referred to as "specific monomer") in an aqueous dispersion (hereinafter also referred to as "first aqueous dispersion") containing a first fluorine-containing polymer which is substantially free of an emulsifier and contains units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and an aqueous medium, to produce a second fluorine-containing polymer, wherein the first fluorine-containing polymer contains 20 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), and the second fluorine-containing polymer contains 20 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), In this method for producing a fluorine-containing elastomer, 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.

[0010] The reason why a fluorine-containing elastomer excellent in aqueous dispersion stability was efficiently produced by this production method without requiring an emulsifier is presumably that the use of an aqueous dispersion containing a predetermined amount of a first fluorine-containing polymer having a predetermined ratio of each unit allowed the first fluorine-containing polymer to function as a good polymerization site for the second fluorine-containing polymer when polymerizing the raw material monomers for the second fluorine-containing polymer, thereby achieving the desired effect. According to this production method, even when no emulsifier is used, a fluorine-containing elastomer having physical properties equivalent to or superior to those of a fluorine-containing elastomer produced using an emulsifier can be obtained.

[0011] <First Aqueous Dispersion> In the present production method, a first aqueous dispersion is used which is substantially free of a water-soluble emulsifier and contains a first fluorine-containing polymer and an aqueous medium.

[0012] (Emulsifier) ​​The first aqueous dispersion is substantially free of a water-soluble emulsifier. "Substantially free of a water-soluble emulsifier" means that the content of the water-soluble emulsifier in the first aqueous dispersion is 10 mass ppm or less, preferably 100 mass ppb or less, 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. An example of a lower limit is 1 mass ppb. The content of the water-soluble emulsifier can be measured using a liquid chromatograph mass spectrometer. Specifically, the measurement methods described in paragraphs 0721 to 0732 of WO 2018 / 181904 are mentioned, and the measurement methods shown in the examples are preferred.

[0013] A water-soluble emulsifier means an emulsifier having a solubility of 100 mg or more in 1000 g of water at 25°C. Examples of the water-soluble emulsifier include water-soluble hydrocarbon-containing surfactants, fluorine-containing emulsifiers, and polymer emulsifiers. Neither the first fluorine-containing polymer described below nor the second fluorine-containing polymer described below falls under the category of water-soluble emulsifiers. The water-soluble emulsifier may be either ionic or nonionic.

[0014] Hydrocarbon-containing surfactant is a surfactant that contains hydrocarbon.More specifically, at least some of the monovalent substituents on carbon atom are hydrogen atoms, and can also be substituted with halogen atoms such as fluorine atoms and chlorine atoms.In hydrocarbon-containing surfactant, preferably 75% or more of the monovalent substituents that substitute on carbon atom are hydrogen atoms, more preferably 85% or more are hydrogen atoms, and even more preferably 95% or more are hydrogen atoms.

[0015] The hydrocarbon-containing surfactant can be exemplified by hydrocarbon surfactant and siloxane surfactant.Hydrocarbon surfactant means a surfactant that does not contain silicon atom, and 100% of the monovalent substituents that are substituted on carbon atoms are hydrogen atoms, so it does not contain halogen atoms such as chlorine atoms and fluorine atoms.Siloxane surfactant means a hydrocarbon-containing surfactant that has a hydrophobic group and contains a siloxane skeleton that contains many siloxane units.

[0016] Examples of hydrocarbon surfactants include anionic hydrocarbon surfactants. Anionic hydrocarbon surfactants refer to hydrocarbon surfactants having a negatively charged hydrophilic portion, such as a carboxylic acid group, 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. An example of an anionic hydrocarbon surfactant is a highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10. Another example of an anionic hydrocarbon surfactant is a linear alkyl polyethersulfonate sodium salt supplied by BASF as part of the Avanel® S series.

[0017] Anionic hydrocarbon surfactants also include sodium dodecyl sulfate.

[0018] Another example of an anionic hydrocarbon surfactant is the sulfosuccinate surfactant Lankropol® K8300, available from AkzoNobelSurfaceChemistry LLC.

[0019] Hydrocarbon surfactants also include nonionic hydrocarbon surfactants.Nonionic hydrocarbon surfactants do not have charged groups, but have a hydrophobic portion that is often a long-chain hydrocarbon.The hydrophilic portion of nonionic hydrocarbon surfactants includes water-soluble functional groups such as polyethylene oxide chains obtained from the polymerization of ethylene oxide.Nonionic hydrocarbon surfactants include block copolymers with various types of polyalkylene oxide blocks, for example, polyethylene oxide and polypropylene oxide.

[0020] Examples of nonionic hydrocarbon surfactants include surfactants described in paragraphs

[0043] to

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

[0021] Siloxane surfactants include those described in US Pat. Nos. 6,841,616 (Wille et al.) and 7,977,438 (Brothers et al.).

[0022] The fluorine-containing emulsifier may be an anionic fluorine-containing surfactant. Examples of the anionic fluorine-containing surfactant include surfactants containing fluorine atoms whose total carbon number excluding the anionic group is 20 or less, and surfactants containing fluorine atoms whose anionic moiety has a molecular weight of 800 or less. The "anionic moiety" refers to the moiety excluding the cation of the fluorine-containing surfactant.

[0023] The polymer emulsifier may be a water-soluble polymer having a hydrophilic group in its side chain. Such a polymer emulsifier may be, for example, a polymer containing a unit based on a compound having a site capable of polymerization reaction and a hydrophilic group. In addition, even if the polymer does not originally have a hydrophilic group, a polymer containing a unit based on a compound having a group that can become a hydrophilic group may be subjected to post-treatment such as hydrolysis.

[0024] It is preferred that the first aqueous dispersion is substantially free of an emulsifier represented by any of formulae (S1) to (S4). When no emulsifier is used in producing the first fluoropolymer contained in the first aqueous dispersion, the amount of the compound represented by any of formulae (S1) to (S4) generated can be suppressed, making it easy to adjust the content of these compounds.

[0025] H-(CF ２ ) ｎ１ -COOM (S1) F-(CF ２ ) ｎ１ -COOM (S2) H-(CF ２ ) ｎ２ -SO ３ M (S3) F-(CF ２ ) ｎ２ -SO ３ M (S4) In formulas (S1) to (S4), n1 is an integer of 3 to 19, n2 is an integer of 4 to 20, and each M is independently a hydrogen atom, Na, K, or NH ４ is.

[0026] (First Fluorine-Containing Polymer) The first fluorine-containing polymer 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"). 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, thereby solubilizing the specific monomer even in the absence of an emulsifier and facilitating polymerization of the specific monomer. It is also presumed that the first fluorine-containing polymer contributes to the dispersion stabilization of particles, etc., described below, in the aqueous dispersion.

[0027] The PAVE is preferably a monomer represented by formula (1) from the viewpoint of excellent polymerization reactivity in producing the first fluoropolymer and enabling more efficient production of the second fluoropolymer. ２ =CF-O-R ｆ１ (1) In formula (1), R ｆ１ represents a perfluoroalkyl group having 1 to 10 carbon atoms. ｆ１ From the viewpoint of better polymerization reactivity, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The perfluoroalkyl group may be linear or branched.

[0028] Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"), and from the viewpoint of enabling more efficient production of the second fluorinated polymer, PMVE and PPVE are preferred, with PMVE being more preferred.

[0029] The content of PAVE units in the first fluoropolymer relative to the total of TFE units and PAVE units is 20 to 95 mol%, preferably 20 to 60 mol%, and from the viewpoint of more efficient production of the second fluoropolymer, more preferably 25 to 60 mol%, even more preferably 25 to 55 mol%. The total content of TFE units and PAVE units in the first fluoropolymer relative to all units of the first fluoropolymer is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, even more preferably 99.9 to 100.0 mol%.

[0030] The first fluorine-containing polymer may contain units based on monomers other than TFE and PAVE, but from the viewpoint of more efficiently producing the second fluorine-containing polymer, it may be substantially free of units based on other monomers. "Substantially free of units based on other monomers" means that the content of units based on other monomers is 0.01 mol % or less, preferably 0 mol %, based on the total units of the first fluorine-containing polymer.

[0031] Before the start of polymerization of the monomers to be used in polymerization of the second fluoropolymer, 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 enabling the second fluoropolymer to be produced more efficiently, it is preferably 0.01 to 0.6 mass%, more preferably 0.01 to 0.5 mass%.

[0032] In this specification, "before initiating polymerization of the monomers used in the polymerization of the second fluoropolymer" means immediately before the start of polymerization. Here, "the start of polymerization" includes the time when the monomers and the polymerization initiator 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 monomers and the polymerization initiator are made to coexist in the reactor. Note that the first aqueous dispersion before the start of polymerization of the monomers used in the polymerization of the second fluoropolymer does not contain the monomers and polymerization initiator used in the polymerization of the second fluoropolymer.

[0033] The content (solids concentration) of the first fluoropolymer can be measured, for example, by the following method. The content (solids concentration) of the first fluoropolymer in the first aqueous dispersion is determined by heating 2.0 g of the first aqueous dispersion at 170°C for 20 minutes, weighing the mass of the residue, and calculating the solids concentration using the following formula: "Solids concentration (mass %) = 100 × heating residue of first aqueous dispersion (g) / mass of first aqueous dispersion (2.0 g)"

[0034] The method for producing the first fluorine-containing polymer is preferably a method of polymerizing monomers containing TFE and PAVE in an aqueous medium in the presence of a polymerization initiator.This results in the first fluorine-containing polymer dispersed in the aqueous medium in the form of particles.The aqueous medium thus obtained in which the particles of the first fluorine-containing polymer are dispersed may be used as the first aqueous dispersion as is, or another aqueous medium may be added and used as the first aqueous dispersion.Furthermore, the first fluorine-containing polymer may be dispersed in another aqueous medium by solvent substitution, and this may be used as the first aqueous dispersion.

[0035] The polymerization initiator used in the production of the first fluorine-containing polymer is preferably a water-soluble polymerization initiator, more preferably a persulfate such as ammonium persulfate, sodium persulfate or potassium persulfate, or an organic polymerization initiator such as disuccinic acid peroxide or azobisisobutylamidine dihydrochloride, still more preferably a persulfate, and particularly preferably ammonium persulfate. Examples of the aqueous medium used in the production of the first fluorine-containing polymer include water and a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0036] 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.

[0037] It is preferable to carry out a purification treatment to reduce or inactivate the polymerization initiator and its decomposition products from an aqueous dispersion containing particles containing a first fluoropolymer, and then use the resulting dispersion in polymerization to obtain a second fluoropolymer. In the purification treatment, the polymerization initiator and its decomposition products that may be contained in the dispersion containing the first fluoropolymer are removed, making it easier to obtain a second fluoropolymer with desired physical properties. Examples of purification methods include heat treatment and a method of removal using an ion exchange resin (preferably an anion exchange resin). The purification treatment may be carried out multiple times.

[0038] (Aqueous medium) The aqueous dispersion used in the present production method contains an aqueous medium. The aqueous medium contained in the first aqueous dispersion may be the polymerization solvent used in producing the first fluoropolymer, as described above. Specific examples of the aqueous medium contained in the first aqueous dispersion are the same as the specific examples of the aqueous medium used in producing the first fluoropolymer described above. Before starting polymerization of the monomers used in polymerizing the second fluoropolymer, 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.

[0039] (Other Components) The first aqueous dispersion may contain components other than the first fluorinated polymer and the aqueous medium. Specific examples of other components that the first aqueous dispersion may contain include a chain transfer agent, a reducing agent, and a pH adjuster. Specific examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane. Furthermore, examples of chain transfer agents include compounds represented by formula (I) described below. Specific examples of reducing agents include sulfurous acid or its salts, hydrogen sulfite or its salts, thiosulfuric acid or its salts, sulfinic acid or its salts, organic acids, and inorganic salts. Specific examples include sodium formaldehyde sulfoxylate dihydrate and 2-hydroxy-2-sulfinate acetic acid disodium. 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 examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate. When the first aqueous dispersion contains a chain transfer agent, the content of the chain transfer agent is preferably 0.1 to 5 parts by mass per 100 parts by mass of the aqueous medium. Furthermore, the amount of the chain transfer agent used is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 15 parts by mass, and even more preferably 0.1 to 10 parts by mass per 100 parts by mass of the specific monomer described below. When the first aqueous dispersion contains a reducing agent, the content of the reducing agent is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium. When the first aqueous dispersion contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium.

[0040] The specific monomer is a monomer containing TFE and PAVE. The amount of TFE and PAVE used is preferably 80 to 100 mol %, more preferably 90 to 100 mol %, and still more preferably 95 to 100 mol %, based on the amount of the specific monomer used.

[0041] The specific monomer may contain a monomer other than TFE and PAVE (hereinafter also referred to as "other monomer"). Specific examples of the other monomer include a monomer having two or more polymerizable unsaturated bonds (hereinafter also referred to as "DV"), 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, a monomer having a nitrile group (hereinafter also referred to as "R ＣＮ "), and a unit based on the compound (6) described below (hereinafter also referred to as a "POAVE unit").

[0042] DV is a monomer having two or more polymerizable unsaturated bonds. Specific 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 in DV is preferably 2 to 6, more preferably 2 or 3, and even more preferably 2, in terms of superior polymerization reactivity. DV preferably further contains a fluorine atom in terms of reducing the compression set of the crosslinked rubber article at high temperatures.

[0043] DV is preferably a monomer represented by formula (2) in view of better releasability of the crosslinked rubber article. ２１ R ２２ =CR ２３ -) ａ１ R ２４ (2) In formula (2), R ２１ , R ２２ and R ２３ each independently represents a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group; a1 represents an integer of 2 to 6; R ２４ represents a monovalent 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 the perfluorohydrocarbon group. ２１ , multiple R ２２ and multiple R ２３ may be the same or different, and are particularly preferably the same. a1 is preferably 2 or 3, and particularly preferably 2. In terms of better polymerization reactivity of DV, R２１ , R ２２ , R ２３ is preferably a fluorine atom or a hydrogen atom, and R ２１ , R ２２ , R ２３ It is more preferred that all of R are fluorine atoms or all of R are hydrogen atoms, and in view of better mold releasability of the crosslinked rubber article, ２１ , R ２２ , R ２３ It is particularly preferred that all of R are fluorine atoms. ２４ R may be linear, branched, or cyclic, preferably linear or branched, and particularly preferably linear. ２４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, even more preferably 3 to 6, and particularly preferably 3 to 5. ２４ Although R may or may not have an etheric oxygen atom, it is preferable that R has an etheric oxygen atom in view of better crosslinking reactivity and rubber physical properties. ２４ The number of etheric oxygen atoms in R is preferably 1 to 6, more preferably 1 to 3, and particularly preferably 1 or 2. ２４ The etheric oxygen atom in R ２４ It is preferred that the nucleotide sequence is located at the end of the nucleotide sequence.

[0044] 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).

[0045] (CF ２ =CF-) ２ R ３１ (3) In formula (3), R ３１ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of the perfluorohydrocarbon group.

[0046] (CH ２ =CH-) ２ R ４１ (4) In formula (4), R ４１represents 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 the perfluorohydrocarbon group.

[0047] Specific examples of the monomer represented by formula (3) include CF ２ = CFO (CF ２ ) ２ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ３ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ４ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ６ OCF = CF ２、 CF ２ = CFO (CF ２ ) ８ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ２ OCF (CF ３ )CF ２ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ２ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , C.F. ２ = CFOCF ２ O (CF ２ CF ２ O) ２ CF = CF ２ , C.F. ２ = CFO (CF ２ O) ３ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , C.F. ２ = CFOCF ２ CF (CF ３ ) O(CF ２ ) ２ OCF (CF３ )CF ２ OCF = CF ２ , C.F. ２ = CFOCF ２ CF ２ O (CF ２ O) ２ CF ２ CF ２ OCF = CF ２ Among the monomers represented by formula (3), a more preferred specific example of the monomer is CF ２ = CFO (CF ２ ) ３ OCF = CF ２ (hereinafter referred to as "C3DVE"), CF ２ = CFO (CF ２ ) ４ OCF = CF ２ (hereinafter, also referred to as "C4DVE"). Specific examples of the monomer represented by formula (4) include CH ２ =CH(CF ２ ) ２ CH=CH ２ , C.H. ２ =CH(CF ２ ) ４ CH=CH ２ , C.H. ２ =CH(CF ２ ) ６ CH=CH ２ Among the monomers represented by formula (4), specific examples of more preferred monomers include CH ２ =CH(CF ２ ) ６ CH=CH ２ (hereinafter also referred to as "C6DV"). Among them, the DV is preferably C3DVE or C4DVE.

[0048] Examples of the 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 include a monomer having a chlorine atom, a monomer having a bromine atom, and a monomer having an iodine atom. Specific examples of the monomer having a bromine atom include CF ２ = CFOCF ２ CF ２ CF ２ OCF２ CF ２ Br, 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, 4-bromoperfluorobutene-1,3,3-difluoroallyl bromide. Also, 2-bromo-perfluoroethyl perfluorovinyl ether, CF ２ Br-R ｆ -O-CF=CF ２ (R ｆ is a perfluoroalkylene group), for example, CF ２ BrCF ２ O-CF=CF ２ , ROCF=CFBr, ROCBr=CF ２ (wherein R is a lower alkyl group or a fluoroalkyl group), specifically, ３ OCF = CFBr or CF ３ CH ２ Specific examples of the monomer having an iodine atom include the monomer represented by the formula: CHR=CH-Z-CH ２ CHR-I (wherein each of the R's is independently —H or —CH ３ and Z is a linear or branched C １ ~C １８ iodinated olefins of the formula I(CH) as disclosed in U.S. Pat. No. 5,717,036, which are (per)fluoroalkylene groups or (per)fluoropolyoxyalkylene groups as disclosed in U.S. Pat. No. 5,674,959. ２ CF ２ CF ２ ) ｎ OCF = CF ２ and ICH ２ CF ２ O[CF(CF３ )CF ２ O] ｎ CF = CF ２ (wherein n = 1 to 3) and the like. Also included are iodoethylene, 4-iodo-3,3,4,4-tetrafluorobutene-1 (ITFB), 3-chloro-4-iodo-3,4,4-trifluorobutene, 2-iodo-1,1,2,2-tetrafluoro-1-(vinyloxy)ethane, 2-iodo-1-(perfluorovinyloxy)-1,1,-2,2-tetrafluoroethylene, 1,1,2,3,3,3-hexafluoro-2-iodo-1-(perfluorovinyloxy)propane, 2-iodoethyl vinyl ether, 3,3,4,5,5,5-hexafluoro-4-iodopentene, and iodotrifluoroethylene, as disclosed in U.S. Patent No. 4,694,045. Also included are allyl iodide and 2-iodo-perfluoroethyl perfluorovinyl ether. Specific examples of monomers having chlorine atoms include any of the above monomers in which the bromine or iodine atom is replaced with a chlorine atom. Additional examples include chlorotrifluoroethylene (CTFE), vinyl chloride, and vinylidene chloride.

[0049] R ＣＮ From the viewpoint of polymerization reactivity, it is preferable that the copolymer has a polymerizable unsaturated bond, and it is particularly preferable that the copolymer 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).

[0050] R ＣＮ is preferably a monomer represented by the following formula (5) from the viewpoint of better mold releasability and heat resistance.

[0051] CR ５１ R ５２ =CR ５３ -R ５４ -CN (5) In formula (5), R ５１ , R ５２ and R ５３ each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R ５４represents 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 the perfluorohydrocarbon group. ＣＮ From the viewpoint of excellent polymerization reactivity of R ５１ , R ５２ , R ５３ is preferably a fluorine atom or a hydrogen atom, and R ５１ , R ５２ , R ５３ It is more preferred that all of R are fluorine atoms or all of R are hydrogen atoms, and in view of the superior mold releasability and heat resistance of the crosslinked rubber article, ５１ , R ５２ , R ５３ It is particularly preferred that all of R are fluorine atoms. ５４ R may be linear, branched, or cyclic, and is preferably linear or branched. ５４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, even more preferably 3 to 6, and particularly preferably 3 to 5. ５４ R may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in order to obtain better rubber properties. ５４ The number of etheric oxygen atoms in the formula (5) is preferably 1 to 3, and particularly preferably 1 or 2. Specific examples of the monomer represented by formula (5) include CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CN (hereinafter also referred to as "8CNVE"), CF ２ = CFO (CF ２ ) ５ CN (hereinafter also referred to as "MV5CN"), CF ２ = CFOCF ２ CF ２ CF ２ OCF (CF ３ ) CN, CF ２ = CFO (CF ２ ) ３ CN, and 8CNVE and MV5CN are preferred in terms of superior mold releasability and heat resistance.

[0052] The POAVE unit is a unit based on compound (6). ２ =CF(OCF ２ CF ２ ) ｎ -(OCF ２ ) ｍ -OR ｆ２ (6) However, R ｆ２ is a perfluoroalkyl group having 1 to 4 carbon atoms, n is an integer of 0 to 3, m is an integer of 0 to 4, and n+m is an integer of 1 to 7.

[0053] R ｆ２ In the formula (R), the perfluoroalkyl group may be linear or branched. ｆ２ The number of carbon atoms in is preferably 1 to 3. When n is 0, m is preferably 3 or 4. 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 fluoroelastomer when made into a crosslinked rubber article are further improved, and the productivity of the fluoroelastomer is improved.

[0054] Specific examples of compound (6) include the following. The abbreviation for the compound is given in parentheses after the formula: CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ４ -OCF ３ (C9PEVE), CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ２ -OCF ３ (C7PEVE), CF ２ =CF-(OCF ２ CF ２ ) ２ -OCF ２ CF ３ (EEAVE), CF ２ =CF-(OCF ２ CF ２ ) ３ -OCF２ CF ３ (EEEAVE), CF ２ =CF-OCF ２ -OCF ３ , C.F. ２ =CF-OCF ２ -OCF ２ -OCF ３ As compound (6), C9PEVE, C7PEVE, EEAVE, or EEEAVE is preferred from the viewpoints of further improving the low-temperature properties when the fluoroelastomer is made into a crosslinked rubber article and improving the productivity of the fluoroelastomer. These compounds can be produced from the corresponding alcohols as raw materials by the method described in WO 00 / 56694.

[0055] The amount of the other monomer used is preferably 0 to 90 mol %, more preferably 0 to 80 mol %, and even more preferably 0 to 70 mol %, based on the amount of the specific monomer used.

[0056] The specific monomer preferably consists of only TFE and PAVE, or contains TFE and PAVE and at least one monomer selected from the group consisting of a monomer having two or more polymerizable unsaturated bonds, 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, and a monomer having a nitrile group.

[0057] The amount of the specific monomer used is preferably 1 to 80 parts by mass, more preferably 1 to 70 parts by mass, and even more preferably 1 to 65 parts by mass, per 100 parts by mass of the aqueous medium contained in the first aqueous dispersion.

[0058] <Polymerization Initiator> In the present production method, the specific monomer is preferably polymerized in the presence of a polymerization initiator. The polymerization initiator is preferably an oil-soluble radical initiator, a water-soluble radical initiator, or a water-soluble redox catalyst. Specific examples of oil-soluble radical initiators include oil-soluble organic peroxides such as tert-butyl peroxypivalate (hereinafter also referred to as "PBPV") and diisopropyl peroxydicarbonate (hereinafter also referred to as "IPP"). Specific examples of water-soluble radical initiators include persulfates such as ammonium persulfate and potassium persulfate, and water-soluble organic peroxides such as disuccinic acid peroxide, bisglutaric acid peroxide, and tert-butyl hydroperoxide (hereinafter also referred to as "TBHP"). The water-soluble redox catalyst is preferably a combination of an oxidizing agent such as bromic acid or a salt thereof, chloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, or hydrogen peroxide, and a reducing agent such as sulfurous acid or a salt thereof, hydrogen sulfite or a salt thereof, thiosulfuric acid or a salt thereof, organic acid, or inorganic salt. The persulfate is preferably potassium persulfate or ammonium persulfate. The sulfite is preferably sodium sulfite. The inorganic salt may be a combination of a sulfate anion, a sulfite anion, or a chloride anion with a metal ion. The metal ion is preferably a transition metal, such as manganese, iron, cobalt, nickel, copper, zinc, cerium, or silver ion, with iron ion being preferred. The inorganic salt is preferably iron(II) sulfate. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator. From the viewpoint of more efficient production of a fluorine-containing polymer, an oil-soluble radical initiator is more preferred, and an oil-soluble organic peroxide is even more preferred. Two or more polymerization initiators may be used in combination.

[0059] The amount of the polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, per 100 parts by mass of the specific monomer used.

[0060] <Step> In the present production method, the specific monomer is polymerized in the first aqueous dispersion to produce the second fluorine-containing polymer.

[0061] The second fluorine-containing polymer obtained by the present production method contains units based on the above-mentioned specific monomer (hereinafter also referred to as "specific units").

[0062] In the second fluorine-containing polymer, the content of PAVE units relative to the total of TFE units and PAVE units is 20 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 60 mol%, and even more preferably 30 to 55 mol%. The total content of TFE units and PAVE units in the second fluorine-containing polymer is preferably 80 to 100 mol%, more preferably 90 to 100 mol%, and even more preferably 95 to 100 mol%, relative to all units of the second fluorine-containing polymer.

[0063] The specific monomer is added to the reaction system (i.e., polymerization reaction vessel) by a conventional method. For example, the specific monomer may be added to the reaction system continuously or intermittently so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer may be dissolved in an aqueous medium, and the resulting solution may be added to the reaction system continuously or intermittently. When a polymerization initiator is used, the polymerization initiator may be added to the reaction system all at once or in portions.

[0064] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. In the case of batch processing, the polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 700 minutes.

[0065] 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. "In the substantial absence of an emulsifier" refers to an environment in which the content of the emulsifier is 0.03 mass ppm or less, preferably 0.02 mass ppm or less, and more preferably 0 mass ppm, relative to the total mass of the aqueous medium contained in the aqueous dispersion.

[0066] In this production method, particles containing the second fluorine-containing polymer are produced. Specifically, this production method produces a second aqueous dispersion in which particles containing the second fluorine-containing polymer are dispersed in the aqueous medium. The particles containing the second fluorine-containing polymer may or may not contain the first fluorine-containing polymer.

[0067] [Second aqueous dispersion] The second aqueous dispersion is an aqueous dispersion obtained by the present production method. Specifically, the second aqueous dispersion is an aqueous dispersion containing an aqueous medium and particles containing a fluorine-containing polymer (hereinafter also referred to as "specific particles"), in which the average particle size of the particles is 1 μm or less, the particles contain units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), the fluorine-containing polymer has at least one of a chlorine atom, a bromine atom, an iodine atom, and a nitrile group at at least one of its terminals and side chains, and the total content of emulsifiers is 100 ppm by mass or less based on the total mass of the aqueous dispersion.

[0068] <Specific Particles> The second aqueous dispersion can be easily obtained by the above-mentioned production method. Therefore, the specific particles contained in the second aqueous dispersion are preferably particles containing the above-mentioned second fluorine-containing polymer. When the specific particles contain the second fluorine-containing polymer, the specific particles may or may not contain the first fluorine-containing polymer. In addition to the specific particles, the second aqueous dispersion may further contain particles of the above-mentioned first fluorine-containing polymer.

[0069] The specific particles contain TFE units and PAVE units.The details of the TFE units are the same as the TFE units contained in the first fluorine-containing polymer described above, and the preferred embodiments are also the same.The details of the PAVE units are the same as the PAVE units contained in the first fluorine-containing polymer described above, and the preferred embodiments are also the same.In addition, the content of the TFE units and PAVE units relative to the total units of the fluorine-containing polymer is the same as the content of each unit in the second fluorine-containing polymer described above, and the preferred embodiments are also the same.

[0070] In this specification, when the specific particles contain 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 the specific particles contain two or more types of fluorine-containing polymer, "all units of the fluorine-containing polymer" means all units contained in the two or more types of fluorine-containing polymer.

[0071] The specific particles may contain units based on other monomers than the specific units, for example, other monomers in the second fluorine-containing polymer.

[0072] The fluorine-containing polymer contained in the specific particles has at least one of a chlorine atom, a bromine atom, an iodine atom, and a nitrile group at at least one of the terminal and side chain of the fluorine-containing polymer. By using the above-mentioned other monomers during the production of the fluorine-containing polymer contained in the specific particles, the chlorine atom, the bromine atom, the iodine atom, and the nitrile group can be introduced.

[0073] When the fluorine-containing polymer contained in the specific particles has an iodine atom, it is also preferable that the fluorine-containing polymer is polymerized using a compound represented by formula (I). When a compound represented by formula (I) (a chain transfer agent having an iodine atom) is used, an iodine atom can be introduced into the end of the fluorine-containing polymer (polymer chain). (R ｆ ) - (X) ２ (I) In formula (I), R ｆ is a fluoroalkylene group having 1 to 16 carbon atoms or an aromatic ring group, and X is an iodine atom or a bromine atom, and at least one of X is an iodine atom. ｆ The fluoroalkylene group of R may be linear or branched. ｆ Preferably, X is a perfluoroalkylene group. Preferably, all of X are iodine atoms.

[0074] 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-diiodoperfluoroethane, 1,3-diiodoperfluoroethane, 1,4-diiodoperfluoroethane (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-diiodoperfluoroethane, 1,5-diiodoperfluoroethane, 1,6-diiodoperfluoroethane, 1,8 ...8-diiodoperfluoroethane, 1,8-diiodoperfluoroethane, Examples of the compound represented by formula (I) include 1-iodoethane, 1,3-diiodo-n-propane, (2-iodoethyl)-substituted benzene, 1-iodo-4-bromoperfluorobutane, 1-iodo-6-bromoperfluorohexane, 1-iodo-8-bromoperfluorooctane, 1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 2-bromo-3-iodoperfluorobutane, 3-bromo-4-iodoperfluorobutene-1, 2-bromo-4-iodoperfluorobutene-1, monoiodomonobromo-substituted benzene, and diiodomonobromo-substituted benzene. C4DI is preferred as the compound represented by formula (I).

[0075] When the fluorine-containing polymer contained in the specific particles has iodine atoms, the proportion of iodine atoms is preferably from 0.01 to 5.00 mass%, more preferably from 0.01 to 2.00 mass%, and still more preferably from 0.01 to 1.00 mass%, relative to the total mass of the fluorine-containing polymer.

[0076] The content of the specific particles is preferably 1 to 50% by mass, more preferably 1 to 40% by mass, and even more preferably 1 to 30% by mass, based on the total mass of the aqueous dispersion, from the viewpoint of dispersion stability of the specific particles.

[0077] The average particle diameter of the specific particles is 1 μm or less, and from the viewpoint of dispersion stability of the specific particles, it is preferably 500 nm or less, more preferably 400 nm or less. From the viewpoint of aggregation, the average particle diameter of the specific particles is preferably 50 nm or more, more preferably 70 nm or more, and even more preferably 100 nm or more. The average particle diameter of the specific particles is determined by measuring the particle size distribution by a laser diffraction / scattering method, determining a cumulative curve with the total volume of the particle group as 100%, and determining the particle diameter at the point on the cumulative curve where the cumulative volume is 50%.

[0078] <Aqueous medium> Specific examples of the aqueous medium contained in the present aqueous dispersion are the same as the specific examples of the aqueous medium used in producing the first fluoropolymer described above. The content of the aqueous medium is preferably from 50 to 99 mass%, more preferably from 60 to 99 mass%, and even more preferably from 70 to 99 mass%, based on the total mass of the present aqueous dispersion, from the viewpoint of dispersion stability of the specific particles.

[0079] <Emulsifier> The content of the emulsifier in the second aqueous dispersion is 100 ppm by mass or less, preferably 75 ppm by mass or less, more preferably 50 ppm by mass or less, and even more preferably 1 ppm by mass or less, relative to the total mass of the second aqueous dispersion. It is also preferably below the quantitation limit of the measurement method in the examples. An example of a lower limit is 1 ppb by mass. The content of the emulsifier can be measured by the method for measuring the content of the emulsifier in the above-mentioned method for producing a fluorine-containing elastomer. Specific examples of the emulsifier are as described above. The emulsifier in the second aqueous dispersion may or may not be water-soluble.

[0080] <Uses> As described above, the second aqueous dispersion does not necessarily require an emulsifier, and therefore can easily be converted into a dispersion in an organic solvent such as N-methylpyrrolidone, acetone, etc. by solvent substitution. For example, the second aqueous dispersion can be converted into a dispersion in an organic solvent by mixing it with an organic solvent and dehydrating it using evaporation or anhydrous sodium sulfate, etc.

[0081] The second aqueous dispersion stably disperses the fluoropolymer even without containing an emulsifier, and is therefore suitable for use in coating applications, binders, etc.

[0082] Furthermore, a solid of the specific particles can be obtained by aggregating the specific particles from the second aqueous dispersion. The solid of the specific particles obtained by aggregating can then be appropriately molded by a known method. Examples of the molding method include injection molding, extrusion molding, coextrusion molding, blow molding, compression molding, inflation molding, transfer molding, and calendar molding.

[0083] Aggregation methods include, but are not limited to, freeze aggregation, acid aggregation, base aggregation, mechanical aggregation, and aggregation using a coagulant. In the case of freeze aggregation, the aggregation temperature is preferably -20 to 0°C. The aggregation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid aggregation, a method in which a solution containing an acid is added to the second aqueous dispersion is preferred. Examples of acids to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, hydrofluoric acid, etc., with nitric acid being preferred. The concentration of the acid in the acid-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. In the case of base aggregation, a method in which a solution containing a base is added to the second aqueous dispersion is preferred. Examples of bases to be added include sodium hydroxide, potassium hydroxide, ammonium carbonate, etc., with sodium hydroxide being preferred. The concentration of the base in the base-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. For aggregation using a coagulant, known coagulants can be used. Known coagulants include aluminum salts, calcium salts, and magnesium salts. Specific examples include aluminum sulfate, a compound of the general formula M'Al(SO ４ ) ２ ・12H ２O (wherein M' is a monovalent cation other than lithium). Examples of suitable coagulation methods include alum, calcium nitrate, and magnesium sulfate represented by the formula: O (wherein M' is a monovalent cation other than lithium). Alum is preferred, and potassium alum, where M is potassium, is more preferred. As the coagulation method, base coagulation is preferred because coagulation proceeds particularly easily. The second aqueous dispersion containing the second fluorine-containing polymer can be used for coagulation with an aqueous dispersion containing a different fluorine-containing polymer, either as is or after appropriate concentration adjustment. Coagulation can be carried out by known methods, such as a method in which a mixed aqueous dispersion is added dropwise to a coagulation liquid, or a method in which a coagulation liquid is added dropwise to a mixed aqueous dispersion. Specific coagulation methods include, but are not limited to, freeze coagulation, acid coagulation, base coagulation, mechanical coagulation, and coagulation using a coagulant. Examples of the different fluorine-containing polymer include a fluorine-containing elastomer and a fluorine-containing resin. Examples of fluorine-containing elastomers include, but are not limited to, HFP / VdF elastomers, which are polymers using hexafluoropropene (hereinafter also referred to as "HFP") and vinylidene fluoride (hereinafter also referred to as "VdF"); TFE / HFP / VdF elastomers, which are polymers using TFE, HFP, and VdF; TFE / propylene elastomers, which are polymers using TFE and propylene; and TFE / HFP / PAVE elastomers, which are polymers using TFE, HFP, and PAVE. Examples of fluorine-containing resins include polymers containing VdF and TFE. Examples of polymers containing TFE include TFE homopolymers and fluorine-containing copolymers of TFE and an olefin other than TFE. Specific examples include, but are not limited to, TFE / ethylene copolymers, TFE / HFP copolymers, and TFE / PAVE copolymers. The aqueous dispersions of different fluorine-containing polymers may or may not contain an emulsifier. The composition obtained by co-agglomeration can be used as a base material for molding by washing and drying as necessary, and can impart excellent heat resistance, mechanical strength, abrasion resistance, transparency, moldability, etc. to molded products.

[0084] [Solid Composition] The solid composition of the present invention is a solid composition containing a fluorine-containing polymer, wherein the solid composition contains units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and the solid composition is substantially free of an emulsifier. The phrase "the solid composition is substantially free of an emulsifier" means that the content of the water-soluble emulsifier in the solid composition of the present invention is 500 ppb by mass or less, preferably 300 ppb by mass or less, and more preferably 250 ppb by mass or less, relative to the total mass of the solid composition. It is also preferably below the quantitation limit of the measurement method in the examples. An example of a lower limit is 1 ppb by mass. Specific examples of emulsifiers are as described above.

[0085] In this specification, a solid composition means a composition having a solid content of 99% by mass or more. Here, the solid content is calculated by the following method based on the mass before and after heating. After heating 2.0 g of the solid composition at 170°C for 20 minutes, the mass of the residue is weighed and the solid content is calculated by the following formula: Solid content (mass%) = 100 x (mass of residue) / (mass of solid composition)

[0086] The present solid composition is preferably obtained by an aggregation method using the above-mentioned second aqueous dispersion. Preferred embodiments of the fluoropolymer contained in the present solid composition are the same as the preferred embodiments of the fluoropolymer in the specific particles contained in the above-mentioned second aqueous dispersion. That is, the fluoropolymer contained in the present solid composition is preferably the above-mentioned second fluoropolymer. The second fluoropolymer may contain the first fluoropolymer. The content of the fluoropolymer is preferably 99.0 to 100 mass%, more preferably 99.5 to 100 mass%, and even more preferably 99.8 to 100 mass%, based on the total mass of the present solid composition.

[0087] The total content of emulsifiers in the solid composition is 500 ppb by mass or less, preferably 300 ppb by mass or less, more preferably 250 ppb by mass or less, relative to the total mass of the fluoropolymer. It is also preferably below the quantitation limit of the measurement method in the Examples. The lower limit may be more than 0 ppb by mass. The number of types of emulsifiers contained in the solid composition is the number of types of emulsifiers whose contents exceed the quantitation limit, and emulsifiers 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. In order to obtain a solid composition substantially free of emulsifier, a method may be used in which no hydrocarbon-containing surfactant, fluorine-containing emulsifier, or polymer emulsifier is used during polymerization of the fluoropolymer, i.e., during polymerization of the first fluoropolymer and the second fluoropolymer. The content of the emulsifier can be measured by the above-mentioned method for measuring the content of the emulsifier in the production method of a fluoroelastomer.

[0088] <Physical Properties> Excellent processability can be obtained when the solid composition is substantially free of emulsifiers and has a storage modulus G' within a specific range. Processability is evaluated by roll wrap and roll surface temperature. The better the roll wrap, the stronger the adhesion between the metal roll surface and the solid composition, making molding easier. The higher the roll surface temperature, the less the heating step required for molding becomes necessary. Since emulsifiers inhibit adhesion between the metal surface of the roll and the solid composition, the lower the amount of emulsifier contained, the better the roll wrap. The storage modulus G' affects the roll wrap and roll surface temperature. The storage modulus G' of the solid composition is preferably 200 to 1200 kPa. If it is lower than this range, the roll surface temperature will decrease, and if it is higher than this range, the roll wrap will decrease and processability will deteriorate. From the viewpoint of excellent processability, the storage modulus G' of the solid composition is preferably 400 kPa or more, preferably 1100 KPa or less, more preferably 500 to 1100 KPa, and particularly preferably 500 to 1100 KPa. An example of a method for producing a solid composition containing a fluoropolymer having a storage modulus G' of 200 to 1200 kPa and obtained without using an emulsifier is a method in which the order of addition and number of additions of each monomer are adjusted during the production of the fluorocopolymer. The storage modulus G' of the solid composition of the present invention is a value measured in accordance with ASTM D6204, and detailed measurement conditions are as shown in the Examples. Detailed measurement conditions for the roll wrap property and roll surface temperature of the solid composition of the present invention, and a method for evaluating processability are as shown in the Examples.

[0089] The present invention will be described in detail below with reference to examples. Examples 1 to 5 are working examples, and Examples 6 and 7 are comparative examples. However, the present invention is not limited to these examples.

[0090] [Measurement and Evaluation Methods] Various measurement and evaluation methods are as follows.

[0091] <Average particle size of particles in second aqueous dispersion> The second aqueous dispersion of each example described below was used as a sample and measured using a laser diffraction / scattering particle size distribution analyzer (ELSZ, Otsuka Electronics Co., Ltd.). When the average particle size of particles in the first aqueous dispersion was measured in the same manner as for the second aqueous dispersion, the average particle size of particles in the first aqueous dispersion was found to be identical to the average particle size of particles in the second aqueous dispersion.

[0092] <Proportion of each unit in the polymer> The proportion of each unit in the polymer is １９ It was determined by F-NMR analysis and infrared absorption spectrum analysis.

[0093] <Emulsifier Content> (Preparation of Measurement Sample) The solids 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) based on the total mass of the solids was added to obtain a pulverized powder. The freeze-pulverization conditions were: solid: 3 g, BHT: 0.3 g, run time: 5 min, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 2.5 g of the obtained pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate each fluoropolymer. The supernatant was used as an extract. The content of the compound represented by formula (S1) contained in each extract was determined by converting each compound in formula (S1) where n = 3 to 13, 15, and 17 into a perfluorocarboxylic acid having the same carbon number. Furthermore, the content of the compound represented by formula (S3) contained in the obtained aqueous phase was determined by converting each compound in formula (S3) where n = 4 to 10 and 12 into perfluorosulfonic acid with the same carbon number. Specifically, first, five levels of methanol standard solutions of perfluorocarboxylic acid and perfluorosulfonic acid, and surfactant A, each with known concentrations of 1 to 180 ng / g, were prepared, and a and a' were determined from the respective sample concentrations and peak integral values ​​using first-order approximation according to formulas (A1), (A1'), and (A''). A = a × X (A1) A: peak area of ​​perfluorocarboxylic acid, X: concentration of perfluorocarboxylic acid (ng / g) A' = a' × X' (A1') A': peak area of ​​perfluorosulfonic acid, X': concentration of perfluorosulfonic acid (ng / g) A'' = a'' × X'' (A1'') A'': peak area of ​​surfactant A, X'': concentration of surfactant A (ng / g) The measuring equipment and measuring conditions are shown in Table 1 below.

[0094] The MRM measurement parameters are shown in Tables 2, 3 and 4.

[0095]

[0096]

[0097]

[0098] Specifically, first, the liquid chromatograph mass spectrometer was used to measure the compounds represented by formula (S1) or (S3) and surfactant A contained in each of the extracts. The peak areas of the compounds represented by formula (S1) and formula (S3) with each carbon number and surfactant A were determined using the MRM method.

[0099] Next, the contents of the compound represented by formula (S1), the compound represented by formula (S3), and surfactant A were calculated using formula (A2), formula (A2'), and formula (A2''), respectively. Note that a in formula (A2) means a determined by the above formula (A1), a' in formula (A2') means a' determined by the above formula (A1'), and a'' in formula (A'') means a'' determined by the above formula (A''). XCm ​​= ACm / a (A2) XCm: content (ng / g) of the compound represented by formula (S1) having carbon number (n+1) in each extract ACm: peak area of ​​the compound represented by formula (S1) having carbon number (n+1) in each extract XCm' = ACm' / a' (A2') XCm': content (ng / g) of the compound represented by formula (S3) having carbon number n in each extract ACm': peak area of ​​the compound represented by formula (S3) having carbon number n in each extract The quantitation limit in this measurement is 1 ng / g. XCm'' = ACm'' / a'' (A2'') XCm'': content (ng / g) of surfactant A in each extract ACm'': peak area of ​​surfactant A in each extract The quantitation limit in this measurement is 1 ng / g.

[0100] The content (ZCm) of the compound represented by formula (S1) in the solid relative to the total mass of the solid was calculated using the following formula (A3): ZCm = XCm × ρ1 × La / W1 (A3) ZCm: content of the compound represented by formula (S1) with carbon number (n + 1) contained in the solid ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid in each example)

[0101] The content (ZCm') of the compound represented by formula (S3) in the solid relative to the total mass of the solid was calculated using the following formula (A4): ZCm' = XCm' × ρ1 × La / W1 (A4) 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 the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid in each example) The content (ZCm'') of surfactant A in the solid relative to the total mass of the solid was calculated using the following formula (A5): ZCm'' = XCm'' × ρ1 × La / W1 (A5) ZCm'': content of surfactant A contained in the solid ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid in each example)

[0102] <Method for measuring iodine content> The solid composition was hot-pressed to form a 100 μm sheet. The obtained sheet-like composition was subjected to X-ray fluorescence analysis using a ZSX Primus II (manufactured by RIGAKU Corporation), and the iodine content in the solid composition (total mass of the first fluoropolymer and the second fluoropolymer) was calculated by the fundamental parameter method.

[0103] <Method for Measuring Storage Modulus G'> A rubber processability analyzer "PREMIER RPA (manufactured by Alpha Technologies, Inc., die shape: D0380)" was used as the measuring device.

[0104] <Sheet Preparation> The solid composition obtained in each example was kneaded for 10 minutes at room temperature using two rolls to prepare 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, a frequency of 30 cpm, and an amplitude angle of 0.2°C for 2 minutes, and then the amplitude angle was changed to 0.5°C and the frequency was increased to 10 cpm, 20 cpm, 50 cpm, 100 cpm, 200 cpm, 500 cpm, 1000 cpm, and 2000 cpm to measure the storage modulus. The storage modulus at 2000 cpm and 100°C was taken as the storage modulus G' (unit: kPa) of the sample. Next, the sample was held at 100°C, a frequency of 30 cpm, and an amplitude angle of 0.2°C for 2 minutes, and then the amplitude angle was changed to 0.5°C and the frequency was increased to 10 cpm, 20 cpm, 50 cpm, 100 cpm, 200 cpm, 500 cpm, 1000 cpm, and 2000 cpm to measure the storage modulus. The storage modulus at 2000 cpm and 100°C was taken as the storage modulus G' (unit: kPa) of the sample.

[0105] <Method for evaluating roll wrapping property> The solid composition obtained in each example was kneaded using a roll kneader (a test roll machine manufactured by Yamatetsu Corporation) to produce a sheet, and the roll wrapping property was confirmed. The roll kneader was equipped with two rolls (roll diameter 8 inches, roll length 18 inches) and two guide members arranged on the gap between the rolls and near both ends of the rolls. The guide members maintain the width of the workpiece, which spreads in the axial direction of the rolls after passing through the rolls, at a predetermined width. 200 g of the solid composition at room temperature (23°C) was weighed out, and the fluoropolymer was charged between the guide members of the roll kneader set under the following conditions. The time (also referred to as the "winding time") from the time the solid composition was charged until the fluoropolymer (bank) accumulated on the roll gap between the guide members disappeared and the fluoropolymer was completely wrapped around the roll was measured. - Roll temperature: 25°C - Roll gap: 2.5 mm - Front roll rotation speed: 12 rpm - Rear roll rotation speed: 10 rpm - Width between guide members: 150 mm The roll temperature was adjusted using a water heater (WTC40, manufactured by Nakamura Scientific Instruments Co., Ltd.). From the measurement time, the roll wrapping property of the solid composition was evaluated based on the following evaluation criteria. (Evaluation criteria for roll wrapping property) ◯: The wrapping time was 2 minutes or less. Δ: The wrapping time was more than 2 minutes but less than 3 minutes. ×: None of the fluoropolymer was wrapped around the roll, or the wrapping time was more than 3 minutes.

[0106] <Roll surface temperature> The sheet obtained under the above conditions was checked for a sheet surface temperature of 25°C using a contact thermometer (manufactured by Hozan Corporation; product name "DT-510"), and then re-inserted into the rolls with a roll temperature of 25°C. During the test, the temperature control of the water heater was turned off. The other conditions were the same as those for the roll wrapping test. Five minutes after insertion, the wrapped sheet was immediately removed, and the roll surface temperature was measured using the same contact thermometer. The temperature at this time was taken as the roll surface temperature. (Roll surface temperature evaluation criteria) A: Over 45°C B: 35-45°C C: Less than 35°C (Processability) Evaluation of roll wrapping and roll surface temperature A: 3 points for each Evaluation of roll wrapping and roll surface temperature B: 2 points for each Evaluation of roll wrapping and roll surface temperature C: 1 point for each ◎: Total evaluation score of roll wrapping and roll surface temperature: 6 points ○: Total evaluation score of roll wrapping and roll surface temperature: 5 points △: Total evaluation score of roll wrapping and roll surface temperature: 4 points ×: Total evaluation score of roll wrapping and roll surface temperature: 2 points, 3 points

[0107] [Production of Raw Material Liquid A] Ultrapure water (1130 g), 30 mass% aqueous ammonia solution (30 mg), PMVE (72 g), and TFE (14 g) were charged into a 2.2 L stainless steel pressure reactor equipped with an anchor impeller, and the temperature was raised to 90°C while stirring at 600 rpm. Next, an aqueous ammonium persulfate solution (5.0 mass%, 30 cc) was added to initiate polymerization. As the pressure in the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. When 4 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The gas remaining in the reactor was recovered, and the liquid was then withdrawn. This liquid was used as raw material liquid A. Raw material liquid A was freeze-aggregated and then filtered. The resulting fluoropolymer 1A was analyzed by NMR, and the ratio of PMVE units to TFE units was 34 / 66 (molar ratio).

[0108] [Production of Raw Material Solution B] To the raw material solution A, HPR4002Cl (anion exchange resin, manufactured by DuPont, 200 g) was added. 150 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration. Next, AmberLite (registered trademark) HPR650H (cation exchange resin, manufactured by DuPont, 50 g) was added to the filtrate. 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration to obtain raw material solution B. In raw material solution B, particles of fluoropolymer 1A were dispersed in an aqueous medium, and the content of fluoropolymer 1A was 0.6 mass% based on the total mass of raw material solution B.

[0109] [Example 1] A 2.2 L stainless steel pressure reactor equipped with an anchor impeller was charged with raw material solution B (1000 g) and ultrapure water (175 g) to obtain aqueous dispersion B (first aqueous dispersion). PMVE (72 g) and TFE (14 g) were then charged, and the temperature was raised to 80 °C while stirring at 600 rpm. TFE and PMVE were injected until the reactor pressure reached 1.2 MPa [gauge], and an aqueous ammonium persulfate solution (2.5% by mass, 7 ml) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE and PMVE were added alternately to maintain a constant pressure. After 80 g of TFE and 63 g of PMVE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 138 minutes.

[0110] The content of fluoropolymer 1A in aqueous dispersion B was 0.5% by mass based on the total mass of aqueous dispersion B. When the amount of the aqueous medium used in the aqueous dispersion B used for polymerization was taken as 100 parts by mass, the amount of the monomer used for polymerization was 12.2 parts by mass. Aqueous dispersion B did not substantially contain a water-soluble emulsifier. Specifically, surfactant A (C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４The contents of the surfactant A and the compounds represented by formulas (S1) to (S4) were measured by the following method. In the production of aqueous dispersion B, emulsifiers other than surfactant A and the compounds represented by formulas (S1) to (S4) were not produced from the components used in the production of aqueous dispersion B and were not used, and therefore are not included in aqueous dispersion B. The solids content of aqueous dispersion B was measured, and an amount of aqueous dispersion B corresponding to 0.05 g of solids was weighed into a 100 mL screw tube. Then, 40 g of water and methanol were added to the weighed aqueous dispersion B to achieve a water / methanol ratio of 50 / 50 by volume. The mixture was then shaken vigorously until coagulation occurred. The solids were removed, and the liquid phase was centrifuged at 4,000 rpm for 1 hour, and the supernatant was extracted. Except for the sample preparation method, the measurement was performed using the same method as the above-mentioned method for measuring the emulsifier content. As a result, the content of the compound represented by any of formulas (S1) to (S4) relative to aqueous dispersion B was also below the limit of quantitation.

[0111] After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated as aqueous dispersion 1 (second aqueous dispersion). Aqueous dispersion 1 was a dispersion in which particles (average particle size 144.1 nm) containing fluoropolymer 2A were dispersed in an aqueous medium, and had a solids concentration of 11.5% by mass. The content of the emulsifier in aqueous dispersion 1 was 100 ppm by mass or less. Specifically, the contents of surfactant A and the compounds represented by formulae (S1) to (S4) were measured in the same manner as for aqueous dispersion B. Note that in producing aqueous dispersion 1, emulsifiers other than surfactant A and the compounds represented by formulae (S1) to (S4) were not produced from the components used in producing aqueous dispersion 1, and were not used either, and therefore are not contained in aqueous dispersion 1.

[0112] Coagulation was carried out by adding an aqueous aluminum sulfate solution to the aqueous dispersion 1. The obtained coagulation product was washed with water and dried to obtain a rubbery fluorine-containing copolymer-containing solid composition 1. The obtained solid composition 1 was analyzed by NMR, and as a result, it was found that the ratio of PMVE units to TFE units was 66 / 34 (molar ratio).

[0113] [Raw material liquid C] Ultrapure water (180 g), PMVE (72 g), and TFE (14 g) were charged into a 2.2 L stainless steel pressure reactor equipped with an anchor impeller, and the temperature was raised to 90°C while stirring at 600 rpm. Next, an aqueous ammonium persulfate solution (5.0 mass%, 30 cc) was added to initiate polymerization. As the polymerization started, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 4 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The gas remaining in the reactor was recovered, and the liquid was then withdrawn. This liquid was used as raw material liquid C. Raw material liquid C was freeze-coagulated and then filtered to obtain fluoropolymer 1C, which was analyzed by NMR and found to have a PMVE unit / TFE unit ratio of 30 / 70.

[0114] [Starting Solution D] Starting solution D was produced in the same manner as starting solution B, except that starting solution C was used instead of starting solution A.

[0115] [Example 2] A 2.2 L stainless steel pressure reactor equipped with an anchor impeller was charged with raw material solution D (1000 g) and ultrapure water (175 g) to obtain aqueous dispersion D (first aqueous dispersion). PMVE (43 g) and TFE (32 g) were then charged, and the temperature was raised to 80 ° C. while stirring at 600 rpm. TFE and PMVE were injected into the reactor until the pressure reached 1.2 MPa [gauge], and an aqueous ammonium persulfate solution (2.5% by mass, 7 ml) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE and PMVE were added alternately to maintain a constant pressure. After 80 g of TFE and 63 g of PMVE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 173 minutes.

[0116] The content of fluoropolymer 1C in aqueous dispersion D was 0.4% by mass relative to the total mass of aqueous dispersion D. When the amount of the aqueous medium used in aqueous dispersion D used for polymerization was taken as 100 parts by mass, the amount of the monomer used in polymerization was 25.1 parts by mass. Aqueous dispersion D did not substantially contain an emulsifier. Specifically, the contents of surfactant A and the compounds represented by formulae (S1) to (S4) were measured in the same manner as for aqueous dispersion B. In producing aqueous dispersion D, emulsifiers other than surfactant A and the compounds represented by formulae (S1) to (S4) were not generated from the components used in producing aqueous dispersion D, and were not used either, and therefore are not contained in aqueous dispersion D.

[0117] After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated as aqueous dispersion 3 (second aqueous dispersion). Aqueous dispersion 2 was a dispersion in which particles (average particle diameter 174.1 nm) containing fluoropolymer 2C were dispersed in an aqueous medium, and had a solids concentration of 11.5% by mass. The content of the emulsifier in aqueous dispersion 2 was 100 ppm by mass or less. Specifically, the contents of surfactant A and the compounds represented by formulae (S1) to (S4) were measured in the same manner as for aqueous dispersion B. Note that in producing aqueous dispersion 2, emulsifiers other than surfactant A and the compounds represented by formulae (S1) to (S4) were not produced from the components used in producing aqueous dispersion 2, and were not used, and therefore are not contained in aqueous dispersion 2.

[0118] Coagulation was carried out by adding an aqueous aluminum sulfate solution to the aqueous dispersion 2. The obtained coagulated product was washed with water and dried to obtain a rubbery fluorine-containing copolymer-containing solid composition 2. The obtained solid composition 2 was analyzed by NMR, and as a result, it was found that the ratio of PMVE units to TFE units was 34 / 66 (molar ratio).

[0119] [Raw material liquid E] A fluoropolymer 1E was polymerized in the same procedure as in the production of raw material liquid A, except that the amounts of each component were appropriately changed, and this liquid was designated as raw material liquid E. Raw material liquid E was freeze-coagulated and then filtered, and the resulting fluoropolymer 1E was analyzed by NMR, revealing that the ratio of PMVE units to TFE units was 32 / 68 (molar ratio).

[0120] [Starting Solution F] Starting solution F was produced in the same manner as starting solution B, except that starting solution E was used instead of starting solution A.

[0121] [Example 3] A 2.2 L stainless steel pressure reactor equipped with an anchor blade was charged with raw material solution F (1000 g) and ultrapure water (182 g), and aqueous dispersion F (first aqueous dispersion) was obtained. PMVE (90 g) and TFE (18 g) were charged thereto, and the temperature was raised to 80 ° C. while stirring at 600 rpm. TFE and PMVE were injected until the pressure in the reactor reached 1.5 MPa [gauge], and an aqueous ammonium persulfate solution (0.5 mass%, 16 ml) was added to initiate polymerization. As the pressure in the reactor decreased with the start of polymerization, TFE and PMVE were added alternately to maintain a constant pressure. At the point where 6.0 g of TFE had been added, C4DI (2.0 g) and ultrapure water (10 cc) were injected. After 154 g of TFE and 133 g of PMVE were injected, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 300 minutes.

[0122] The content of fluoropolymer 1E in aqueous dispersion F was 0.4% by mass relative to the total mass of aqueous dispersion F. When the amount of the aqueous medium used in aqueous dispersion F used for polymerization was taken as 100 parts by mass, the amount of the monomer used in polymerization was 40.6 parts by mass. Aqueous dispersion F did not substantially contain an emulsifier. Specifically, the contents of surfactant A and the compounds represented by formulae (S1) to (S4) were measured in the same manner as for aqueous dispersion B. In producing aqueous dispersion F, emulsifiers other than surfactant A and the compounds represented by formulae (S1) to (S4) were not generated from the components used in producing aqueous dispersion F, and were not used either, and therefore are not contained in aqueous dispersion F.

[0123] The gas remaining in the reactor was recovered, and then the liquid was withdrawn. This liquid was designated as Aqueous Dispersion 3. Aqueous Dispersion 3 was a dispersion in which particles (average particle size: 89.9 nm) containing fluoropolymer 2E were dispersed in an aqueous medium, and had a solids concentration of 19.3% by mass. The content of the emulsifier in Aqueous Dispersion 3 was 100 ppm by mass or less. Specifically, the contents of surfactant A and the compounds represented by formulae (S1) to (S4) were measured in the same manner as for Aqueous Dispersion B. Note that in producing Aqueous Dispersion 3, emulsifiers other than surfactant A and the compounds represented by formulae (S1) to (S4) were not produced from the components used in producing Aqueous Dispersion 3, and were not used either, and therefore are not contained in Aqueous Dispersion 3.

[0124] An aqueous aluminum sulfate solution was added to the aqueous dispersion to carry out coagulation. The obtained coagulum was washed with water and dried to obtain a solid composition 3 containing a rubber-like fluorine-containing copolymer. The obtained solid composition 3 was analyzed by NMR, and the result was that the PMVE unit / TFE unit was 35 / 65 (molar ratio). The iodine content relative to the total mass of the fluorine-containing polymer 1E and the fluorine-containing polymer 2E was 0.04 mass%.

[0125] [Starting material liquid G] A fluoropolymer 1G was polymerized in the same procedure as in the production of starting material liquid A, except that the amounts of each component were appropriately changed, and this liquid was designated starting material liquid G. Starting material liquid G was freeze-coagulated and then filtered, and the resulting fluoropolymer 1G was analyzed by NMR, revealing that the ratio of PMVE units to TFE units was 32 / 68 (molar ratio).

[0126] [Starting Solution H] Starting solution H was produced in the same manner as starting solution B, except that starting solution G was used instead of starting solution A.

[0127] [Example 4] A 2.2 L stainless steel pressure reactor equipped with an anchor blade was charged with raw material solution H (1000 g) and ultrapure water (182 g), and aqueous dispersion H (first aqueous dispersion) was obtained. PMVE (90 g) and TFE (18 g) were charged thereto, and the temperature was raised to 75 ° C. while stirring at 600 rpm. TFE and PMVE were injected until the pressure in the reactor reached 1.5 MPa [gauge], and an aqueous ammonium persulfate solution (0.5 mass%, 16 ml) was added to initiate polymerization. As the pressure in the reactor decreased with the start of polymerization, TFE and PMVE were added alternately to maintain a constant pressure. At the point where 6.0 g of TFE had been added, C4DI (2.0 g) and ultrapure water (10 cc) were injected. After 160 g of TFE and 133 g of PMVE were injected, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 440 minutes.

[0128] The content of fluoropolymer 1G was 0.4% by mass relative to the total mass of aqueous dispersion H. When the amount of the aqueous medium used in aqueous dispersion H used for polymerization was taken as 100 parts by mass, the amount of the monomer used in polymerization was 40.6 parts by mass. Aqueous dispersion H did not substantially contain an emulsifier. Specifically, the contents of surfactant A and the compounds represented by formulae (S1) to (S4) were measured in the same manner as for aqueous dispersion B. In producing aqueous dispersion H, emulsifiers other than surfactant A and the compounds represented by formulae (S1) to (S4) were not generated from the components used in producing aqueous dispersion H, and were not used either, and therefore are not contained in aqueous dispersion H.

[0129] After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated as aqueous dispersion 4 (second aqueous dispersion). Aqueous dispersion 4 was a dispersion in which particles (average particle size 90.5 nm) containing fluoropolymer 2G were dispersed in an aqueous medium, and had a solids concentration of 20.1% by mass. The content of the emulsifier in aqueous dispersion 4 was 100 ppm by mass or less. Specifically, the contents of surfactant A and the compounds represented by formulae (S1) to (S4) were measured in the same manner as for aqueous dispersion B. Note that in producing aqueous dispersion 4, emulsifiers other than surfactant A and the compounds represented by formulae (S1) to (S4) were not produced from the components used in producing aqueous dispersion 4, and were not used, and therefore are not contained in aqueous dispersion 4.

[0130] An aqueous aluminum sulfate solution was added to the aqueous dispersion to carry out coagulation. The obtained coagulum was washed with water and dried to obtain a solid composition 4 containing a rubber-like fluorine-containing copolymer. The obtained solid composition 4 was analyzed by NMR, and the result was that the PMVE unit / TFE unit was 34 / 66 (molar ratio). The iodine content relative to the total mass of the fluorine-containing polymer 1H and the fluorine-containing polymer 2H was 0.04% by mass.

[0131] [Starting material liquid P] A fluoropolymer 1P was polymerized in the same procedure as in the production of starting material liquid A, except that the amounts of each component were appropriately changed, and this liquid was used as starting material liquid P. Starting material liquid P was freeze-coagulated and then filtered to obtain fluoropolymer 1N, which was analyzed by NMR and found to have a PMVE unit / TFE unit ratio of 34 / 66.

[0132] [Starting Solution Q] Starting solution Q was produced in the same manner as starting solution B, except that starting solution P was used instead of starting solution A.

[0133] [Example 5] A 2.2 L stainless steel pressure reactor equipped with an anchor impeller was charged with raw material solution Q (850 g), ultrapure water (332 g), and disodium hydrogen phosphate dodecahydrate (0.11 g), to obtain aqueous dispersion Q (first aqueous dispersion). PMVE (90 g), TFE (18 g), and 8CNVE (1.1 g) were then charged, and the temperature was raised to 80 ° C. while stirring at 600 rpm. TFE and PMVE were injected until the pressure in the reactor reached 1.5 MPa [gauge], and an aqueous ammonium persulfate solution (3% by mass, 18 ml) was added to initiate polymerization. As the pressure in the reactor decreased with the start of polymerization, TFE and PMVE were added alternately to maintain a constant pressure. For every 16 g of TFE added, 12 g of PMVE and 1.26 g of 8CNVE were added. To maintain a constant polymerization rate, an aqueous ammonium persulfate solution was added appropriately. When 160 g of TFE, 108 g of PMVE, and 12.6 g of 8CNVE were injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 130 minutes. The total amount of 3 mass% ammonium persulfate aqueous solution added was 24 ml. The content of fluoropolymer 1P was 0.6 mass% relative to the total mass of aqueous dispersion Q. Furthermore, when the amount of aqueous medium used in aqueous dispersion Q used in the polymerization was taken as 100 mass parts, the amount of monomer used in the polymerization was 23 mass parts. Aqueous dispersion Q did not substantially contain an emulsifier. Specifically, the contents of surfactant A and the compounds represented by formulae (S1) to (S4) were measured in the same manner as for aqueous dispersion B. In addition, in producing aqueous dispersion Q, emulsifiers other than surfactant A and the compounds represented by formulae (S1) to (S4) are not produced from the components used in producing aqueous dispersion Q, and are not used either, and therefore are not included in aqueous dispersion Q.

[0134] After recovering the gas remaining in the reactor, the liquid was withdrawn. This liquid was designated Aqueous Dispersion 5 (Second Aqueous Dispersion). Aqueous Dispersion 5 was a dispersion in which particles (average particle diameter 45.5 nm) containing fluoropolymer 2P were dispersed in an aqueous medium, and had a solids concentration of 19.1% by mass. The emulsifier content in Aqueous Dispersion 5 was 100 ppm by mass or less. Specifically, the contents of surfactant A and the compounds represented by formulae (S1) to (S4) were measured in the same manner as for Aqueous Dispersion B. Note that in producing Aqueous Dispersion 5, emulsifiers other than surfactant A and the compounds represented by formulae (S1) to (S4) were not produced from the components used in producing Aqueous Dispersion 5, nor were they used, and therefore are not contained in Aqueous Dispersion 5. A 3% by mass aqueous solution of nitric acid was added to the aqueous dispersion to perform coagulation. The obtained coagulum was washed with water and dried to obtain a solid composition 5 containing a rubbery fluorocopolymer. The obtained solid composition 5 was analyzed by NMR, and as a result, it was found that the ratio of PMVE units / TFE units / 8CNVE units was 68.3 / 31.2 / 0.5 (molar ratio).

[0135] [Raw material solution K] Ultrapure water (593 g) and MMA (methyl methacrylate, 2.8 g) were charged into a 1.0 L glass reactor and heated to 60°C while stirring at 500 rpm. Next, an aqueous ammonium persulfate solution (10% by mass, 6.0 cc) was added, and polymerization was carried out for 60 minutes. After completion of the polymerization reaction, the liquid was withdrawn, and this liquid was used as raw material solution K. Raw material solution K was heated to remove water, and the residue was then dried by heating to obtain a hydrocarbon polymer (poly-MMA).

[0136] [Raw material solution L] To the raw material solution K (490 g) was added 20 g of Purolite A300 (anion exchange resin, manufactured by Purolite Corporation). 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration to obtain raw material solution L. Raw material solution L contained particles (average particle size 116 nm) of a hydrocarbon polymer (polyMMA) dispersed in an aqueous medium. Based on the amount of MMA charged, the content of the hydrocarbon polymer was 0.47% by mass relative to the total mass of raw material solution L.

[0137] [Example 6] A 2.2 L stainless steel pressure reactor equipped with an anchor impeller was charged with raw material liquid L (3.91 g) and ultrapure water (1162 g) to obtain aqueous dispersion L. Aqueous dispersion L was heated to 80°C while stirring at 600 rpm, and PMVE (72 g) and TFE (14 g) were added. An aqueous ammonium persulfate solution (20% by mass, 5 mL) was then added to initiate polymerization. Since the pressure in the reactor decreased with the initiation of polymerization, TFE and PMVE were further added to maintain the pressure at a constant 1.2 MPa [gauge]. After injecting 160 g of TFE and 133 g of PMVE, the reactor was cooled to terminate the polymerization reaction. The polymerization time was 411 minutes. The gas remaining in the reactor was recovered, and the liquid was extracted. This liquid was designated aqueous dispersion 6. Aqueous dispersion 6 was a dispersion in which particles containing fluoropolymer 2L (average particle diameter 195.2 nm) were dispersed in an aqueous medium, and had a solids concentration of 20.7 mass%. An aqueous aluminum sulfate solution was added to the aqueous dispersion to carry out coagulation. The obtained coagulum was washed with water and dried to obtain solid composition 6 containing rubber-like fluoropolymer 2L.

[0138] [Example 7] A stainless steel pressure reactor with an internal volume of 2.1 L and equipped with an anchor impeller was degassed, and the gas phase was replaced with nitrogen. Ultrapure water (1004 g), emulsifier C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４A 30% by mass solution (80.1 g) of (Surfactant A) and a 5% by mass aqueous solution (10.49 g) of disodium hydrogen phosphate dodecahydrate were charged to obtain aqueous dispersion M. PMVE (72 g) and TFE (14 g) were then pressure-charged into the vessel, and the internal temperature was raised to 80 ° C. Next, an aqueous ammonium persulfate solution (1.0% by mass, 20 mL) was added to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, TFE and PMVE were further added to maintain the pressure at a constant 1.2 MPa [gauge]. When 160 g of TFE and 133 g of PMVE were pressure-charged, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 262 minutes. After recovering the gas remaining in the reactor, the liquid was extracted. This liquid was designated aqueous dispersion 7. Aqueous dispersion 7 was a dispersion in which particles containing fluoropolymer 2M (average particle diameter 80.0 nm) were dispersed in an aqueous medium, and had a solids concentration of 20.0 mass%. An aqueous aluminum sulfate solution was added to the aqueous dispersion to carry out coagulation. The obtained coagulum was washed with water and dried to obtain solid composition 7 containing rubber-like fluoropolymer 2M.

[0139] [Evaluation] <2% mass loss temperature> 10 mg of the solid composition (sample) was weighed into an aluminum pan and heated from 30°C to 550°C at a rate of 10°C / min in an air atmosphere. The temperature at which the mass of the sample before heating became 98% was defined as the 2% mass loss temperature. The higher the 2% mass loss temperature, the more excellent the heat resistance. The apparatus used was a NEXTA STA series STA200 manufactured by Hitachi High-Tech Corporation.

[0140] <Aqueous Dispersion Stability> Using a 60 mm diameter disc turbine, 30 g of each of the aqueous dispersions 1 to 7 was stirred at high speed at 2000 rpm for 180 min, and the precipitation rate shown below that occurred was measured to evaluate the aqueous dispersion stability. The lower the precipitation rate value, the better the aqueous dispersion stability. Precipitation rate (%) = 100 × precipitated aggregates (g) / (30 (g) × concentration of fluoropolymer (% by mass) / 100)

[0141]

[0142] In Table 5, the content of formula (S2) means the total content of each compound in formula (S2) where n1 is an integer from 3 to 19, relative to the total mass of the solid composition; the content of formula (S3) means the total content of each compound in formula (S3) where n2 is an integer from 4 to 20, relative to the total mass of the solid composition; and the content of formula (S4) means the total content of each compound in formula (S4) where n2 is an integer from 4 to 20, relative to the total mass of the solid composition. Note that in producing Solid Compositions 1 to 5, emulsifiers other than the compounds represented by formulas (S1) to (S4) and surfactant A were not produced from the components used in producing Solid Compositions 1 to 5, and were not used either, and are therefore not included in Solid Compositions 1 to 5.

[0143] <Processability evaluation results>

[0144]

[0145] It was shown that the method for producing a fluorine-containing elastomer of the present invention can efficiently produce a fluorine-containing elastomer having excellent aqueous dispersion stability without necessarily using an emulsifier, even when using an aqueous medium with a small environmental load (Examples 1 to 5). In contrast, the aqueous dispersion stability of the fluorine-containing elastomer obtained in Example 6 was poor. Moreover, Example 7 is a method for producing a fluorine-containing elastomer using an emulsifier, and it was confirmed that in all of Examples 1 to 5, even when an emulsifier was not substantially used, the efficiency and aqueous dispersion stability were similar to those when an emulsifier was used.

[0146] The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2023-117444, filed on July 19, 2023, are hereby incorporated by reference as the disclosure of the present invention.

Claims

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 fluorine-containing elastomer, comprising polymerizing a monomer containing tetrafluoroethylene and a perfluoro(alkyl vinyl ether) to produce a second fluorine-containing polymer, a step of producing the first fluoropolymer under conditions substantially free of an emulsifier, before producing the second fluoropolymer; the content of units based on perfluoro(alkyl vinyl ether) in the first fluorinated polymer is 20 to 95 mol % relative to the total of units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether); the content of units based on perfluoro(alkyl vinyl ether) in the second fluorinated polymer is 20 to 95 mol % relative to the total of units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), The method for producing a fluorine-containing elastomer, 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 initiation of polymerization of the monomers.

2. the monomers consist solely of tetrafluoroethylene and perfluoro(alkyl vinyl ether), or 2. The method for producing a fluorine-containing elastomer according to claim 1, comprising at least one monomer selected from the group consisting of a monomer having tetrafluoroethylene and perfluoro(alkyl vinyl ether) and having two or more polymerizable unsaturated bonds, 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, and a monomer having a nitrile group.

3. The process for producing a fluorine-containing elastomer according to claim 1 or 2, wherein the amount of the monomer used is 1 to 80 parts by mass per 100 parts by mass of the aqueous medium used.

4. The process for producing a fluorine-containing elastomer according to claim 1 or 2, wherein the monomers are polymerized in the presence of a polymerization initiator.

5. An aqueous dispersion substantially free of a water-soluble emulsifier, comprising an aqueous medium and particles containing a fluorine-containing polymer, The average particle size of the particles is 1 μm or less, the particles comprise tetrafluoroethylene-based units and perfluoro(alkyl vinyl ether)-based units; the fluorine-containing polymer has at least one of a chlorine atom, a bromine atom, an iodine atom, and a nitrile group at at least one of an end and a side chain, The aqueous dispersion has an emulsifier content of 100 ppm by mass or less based on the total mass of the aqueous dispersion.

6. The particles are composed of only tetrafluoroethylene-based units and perfluoro(alkyl vinyl ether)-based units, or The aqueous dispersion according to claim 5, comprising a unit based on tetrafluoroethylene and a unit based on perfluoro(alkyl vinyl ether), and at least one unit selected from the group consisting of a unit based on a monomer having two or more polymerizable unsaturated bonds, a unit based on 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, and a unit based on a monomer having a nitrile group.

7. A solid composition comprising a fluorine-containing polymer, the solid composition comprises tetrafluoroethylene-based units and perfluoro(alkyl vinyl ether)-based units; The solid composition is substantially free of an emulsifier and has a storage modulus G' of 200 to 1200 kPa.

8. 8. The solid composition according to claim 7, wherein the fluorine-containing polymer has at least one of a chlorine atom, a bromine atom, an iodine atom and a nitrile group at at least one of an end and a side chain.

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