Crosslinked rubber article, fluorine-containing copolymer composition, and method for producing crosslinked rubber article

Abstract

A crosslinked rubber article comprising a crosslinked product of a fluorine-containing copolymer having a unit based on a monomer having a nitrile group and a unit based on tetrafluoroethylene, wherein when the 60°-specular gloss of the crosslinked rubber article surface is measured at 10 different sites, the minimum value of the 60°-specular gloss at the 10 different sites is 1.0 to 50.0.

Description

Crosslinked rubber article, fluorine-containing copolymer composition, and method for producing crosslinked rubber article

[0001] The present disclosure relates to crosslinked rubber articles, fluorocopolymer compositions, and methods for making crosslinked rubber articles.

[0002] Crosslinked rubber articles obtained by crosslinking a fluorocopolymer composition containing a fluorocopolymer (e.g., perfluoroelastomer) are used in various industrial fields because they have excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. For example, Patent Document 1 discloses a molded article made of a composition containing a crosslinkable elastomer and a filler.

[0003] JP 2009-030064 A

[0004] The performance required for a crosslinked rubber article includes a small compression set at high temperatures. It is also required that the article is less likely to crack when compressed. Based on these requirements, the present inventors studied the physical properties of crosslinked rubber articles with reference to Patent Document 1 and found that there was room for improvement in at least one of the compression set at high temperatures and the cracking when compressed. Hereinafter, a small compression set at high temperatures will also be referred to as "excellent high-temperature compression set," and a less likely to crack when compressed will also be referred to as "less likely to crack."

[0005] The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a crosslinked rubber article that is excellent in high-temperature compression set and is less likely to crack. Another object of the present disclosure is to provide a fluorine-containing copolymer composition and a method for producing the crosslinked rubber article.

[0006] As a result of intensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by the following configurations. [1] A crosslinked rubber article comprising a crosslinked product of a fluorine-containing copolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, wherein, when the 60° specular gloss is measured at 10 different points on the surface of the crosslinked rubber article, the minimum value of the 60° specular glosses at the 10 different points is 1.0 to 50.0. [2] The crosslinked rubber article according to [1], further comprising a filler. [3] The crosslinked rubber article according to [2], wherein the content of the filler is 30 parts by mass or less per 100 parts by mass of the crosslinked product of the fluorine-containing copolymer. [4] The crosslinked rubber article according to any one of [1] to [3], wherein the absolute difference between the minimum value and the maximum value of the 60° specular glosses at the 10 different points is more than 0.1 and 20.0 or less. [5] The crosslinked rubber article according to any one of [1] to [4], wherein the crosslinked product has at least one of an oxazole structure and a triazine structure. [6] The crosslinked rubber article according to any one of [1] to [5], wherein the fluorocopolymer further has units based on perfluoro(alkyl vinyl ether). [7] The crosslinked rubber article according to any one of [1] to [6], which is substantially free of an emulsifier. [8] A fluorocopolymer composition comprising a fluorocopolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, and a crosslinking agent, wherein a crosslinked rubber article obtained using the fluorocopolymer composition has a 60° specular gloss measured at 10 different points on the surface of the crosslinked rubber article, and the minimum value of the 60° specular gloss measured at the 10 different points is 1.0 to 50.0. [9] The fluorocopolymer composition according to [8], further comprising a filler.

[10] The fluorocopolymer composition according to [9], wherein the content of the filler is 30 parts by mass or less per 100 parts by mass of the fluorocopolymer.

[11] The fluorocopolymer composition according to any one of [8] to

[10] , wherein the crosslinking agent comprises a compound having two amino groups.

[12] The fluorine-containing copolymer composition according to any one of [8] to

[11] , wherein the fluorine-containing copolymer further has units based on perfluoro(alkyl vinyl ether).

[13] The fluorine-containing copolymer composition according to any one of [8] to

[12] , wherein the content of the crosslinking agent is 0.1 to 10 parts by mass per 100 parts by mass of the fluorine-containing copolymer.

[14] The fluorine-containing copolymer composition according to any one of [8] to

[13] , which is substantially free of an emulsifier.

[15] A method for producing a crosslinked rubber article, comprising molding a fluorine-containing copolymer composition using a mold to produce a crosslinked rubber article, wherein the fluorine-containing copolymer composition comprises a fluorine-containing copolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, and a crosslinking agent, and is substantially free of emulsifier, and the mold has a 60° specular gloss of 100.0 or more.

[16] The method for producing a crosslinked rubber article according to

[15] , further comprising a step of producing the fluorine-containing copolymer, which step comprises polymerizing a monomer having a nitrile group and a first monomer containing tetrafluoroethylene in the presence of a compound represented by formula (X) described below and a polymerization initiator, in the presence of an aqueous medium and in the substantial absence of an emulsifier having a fluorine atom, to produce an aqueous dispersion containing particles of the fluorine-containing copolymer having an average particle size of 500 nm or less and no melting point, and recovering the fluorine-containing copolymer from the aqueous dispersion.

[17] The method for producing a crosslinked rubber article according to

[16] , wherein the content of the compound represented by formula (X) described below is 1.0 to 1000 ppm by mass relative to the total mass of the aqueous medium.

[0007] According to the present disclosure, it is possible to provide a crosslinked rubber article that is excellent in high-temperature compression set and is less likely to crack. The present disclosure also provides a fluorocopolymer composition and a method for producing the crosslinked rubber article.

[0008] The meanings of terms used in this disclosure 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 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 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 monomer that is formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a portion of the atomic group. Hereinafter, a "unit based on a monomer" will also be simply referred to as a "unit." The content (mass % or mol %) of each unit relative to all units contained in the fluorine-containing copolymer or fluorine-containing polymer can be determined by analyzing the fluorine-containing copolymer or fluorine-containing polymer by solid-state nuclear magnetic resonance spectroscopy (NMR), and usually, the content of each unit calculated from the charged amount of each monomer substantially coincides with the actual content of each unit.

[0009] [Crosslinked Rubber Article] The crosslinked rubber article of the present disclosure (hereinafter also referred to as "the present crosslinked rubber article") is a crosslinked rubber article comprising a crosslinked product of a fluorine-containing copolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene (hereinafter also referred to as "TFE"). When the 60° specular gloss is measured at 10 different locations on the surface of the crosslinked rubber article, the minimum value of the 60° specular gloss values ​​at the 10 different locations (hereinafter also referred to as "minimum value X") is 1.0 to 50.0. The present crosslinked rubber article has excellent high-temperature compression set and is less susceptible to cracking. The details of the reason for this are unknown, but the inventors speculate as follows. When the minimum value X of the present crosslinked rubber article is 1.0 or more, the surface of the present crosslinked rubber article exhibits appropriate smoothness, and stress concentration can be avoided when the present crosslinked rubber article is compressed, so it is presumed that cracking is less likely to occur. Furthermore, when the minimum value X of the crosslinked rubber article is 50.0 or less, excessive heat conduction during compression at high temperatures can be suppressed, and thermal decomposition of the crosslinked rubber article can be suppressed, so it is presumed that the crosslinked rubber article will have excellent high-temperature compression set. Furthermore, the present inventors have found that the minimum value X has a significant effect on the expression of the above properties.

[0010] [60° Specular Gloss] When the 60° specular gloss of the crosslinked rubber article is measured at 10 different locations on the surface of the crosslinked rubber article, the minimum value of the 60° specular gloss of the 10 different locations is 1.0 to 50.0. From the viewpoint of suppressing cracking after a compression set test, the minimum value X is preferably 5.0 to 40.0, more preferably 10.0 to 30.0.

[0011] The method for measuring the minimum value X will be described in detail. First, the 60° specular gloss is measured at 10 different locations on the surface of a crosslinked rubber article, obtaining a total of 10 measured values ​​of 60° specular gloss. The 60° specular gloss can be measured using a known gloss meter (for example, a Gloss Checker IG-410 manufactured by Horiba, Ltd.). The form of the crosslinked rubber article (measurement object) used to measure the 60° specular gloss is not particularly limited, but an O-ring is preferred, and a P-26 O-ring (standard defined in JIS B2401:2012) is more preferred. Furthermore, the method for manufacturing the measurement object is preferably the method described in the Examples section. Next, the smallest 60° specular gloss measurement value among the 10 measured values ​​of 60° specular gloss is taken as the minimum value X.

[0012] Examples of methods for adjusting the minimum value X include a method of using a mold with a predetermined 60° specular gloss in a method for producing a crosslinked rubber article (for example, using a mold with a high 60° specular gloss tends to reduce the minimum value X), a method of using a compound represented by formula (X) described below in the production of a fluorine-containing copolymer, a method of adjusting the mold temperature, pressure, etc., a method of adjusting the crosslink density of a crosslinked product of the fluorine-containing copolymer (for example, reducing the amount of crosslinking agent used to lower the crosslink density tends to increase the minimum value X), and a method of adjusting the surface roughness of a crosslinked rubber article by sandblasting, corona plasma treatment, etc. (for example, increasing the surface roughness tends to increase the minimum value X).

[0013] The maximum value of the 60° specular gloss at 10 different locations (hereinafter also referred to as "maximum value Y") is preferably 1.0 to 70.0, and from the viewpoint of the balance with the compression set characteristics, it is more preferably 5.0 to 60.0, and even more preferably 10.0 to 50.0. The absolute difference (difference in absolute values) between the minimum value X and the maximum value Y is preferably more than 0.1 and not more than 20.0, and more preferably 1.0 to 20.0, from the viewpoint of heat conduction from the mold.

[0014] The crosslinked product of the fluorine-containing copolymer preferably has a heterocyclic structure, more preferably has at least one of an oxazole structure and a triazine structure, and further preferably has an oxazole structure and a triazine structure. When the fluorine-containing copolymer has units based on a monomer having a nitrile group, methods for introducing a heterocyclic structure into the crosslinked product of the fluorine-containing copolymer include a method of reacting the nitrile group with a crosslinking agent to form a heterocyclic structure (preferably, an oxazole ring), and a method of reacting nitrile groups in the fluorine-containing copolymer with each other to form a heterocyclic structure (preferably, a triazine structure).

[0015] The various components that the crosslinked rubber article may contain are described in detail below.

[0016] [Crosslinked product of fluorine-containing copolymer] This crosslinked rubber article comprises a crosslinked product of the fluorine-containing copolymer that has a unit based on a monomer having a nitrile group and a unit based on TFE.As the crosslinked product of the fluorine-containing copolymer, for example, the crosslinked product obtained by crosslinking the fluorine-containing copolymer that has a unit based on a monomer having a nitrile group and a unit based on TFE with each other can be mentioned, and the fluorine-containing copolymer that is crosslinked from the nitrile group as the starting point, the fluorine-containing copolymer that is crosslinked using the crosslinking agent described later, or both of them are preferred.In addition, as the crosslinked product of the fluorine-containing copolymer, the crosslinked product obtained by crosslinking the fluorine-containing copolymer composition described later is also preferred.In addition, the fluorine-containing copolymer will be described later.

[0017] The content of the crosslinked fluorocopolymer is preferably 80 to 100% by mass, more preferably 85 to 100% by mass, and even more preferably 90 to 100% by mass, based on the total mass of the crosslinked rubber article.

[0018] [Filler] The crosslinked rubber article preferably contains a filler. The filler preferably contains at least one selected from the group consisting of carbon black, barium sulfate, calcium metasilicate, calcium carbonate, titanium oxide, silicon dioxide, aluminum oxide, magnesium oxide, silicon carbide, silicon nitride, aluminum nitride, crystalline zeolite, nanodiamond, clay, and talc, and more preferably contains carbon black.

[0019] The filler may be used alone or in combination of two or more. In the present crosslinked rubber article, the content of the filler is preferably 30 parts by mass or less, more preferably 10 parts by mass or less, per 100 parts by mass of the crosslinked product of the fluorocopolymer. The lower limit is preferably 1 part by mass or more per 100 parts by mass of the crosslinked product of the fluorocopolymer.

[0020] [Emulsifier] The crosslinked rubber article may contain an emulsifier, but preferably does not substantially contain an emulsifier. Emulsifier is a general term for emulsifiers containing fluorine atoms, as described below, and emulsifiers not containing fluorine atoms, as described below. Furthermore, "substantially not containing an emulsifier" means that the emulsifier content is 10 ppm by mass or less, preferably 150 ppb by mass or less, more preferably 50 ppb by mass or less, and particularly preferably 25 ppb by mass or less, relative to the total mass of the crosslinked rubber article. It is also preferable that the content is below the quantitation limit of the measurement method using a liquid chromatograph mass spectrometer described below. An example of a lower limit is 1 ppb by mass. The content of various emulsifiers can be measured using a liquid chromatograph mass spectrometer. Specific examples include the measurement methods described in paragraphs

[0721] to

[0732] of WO 2018 / 181904. If the measurement using the liquid chromatograph mass spectrometer reveals a concentration below the limit of quantitation, it can be determined to be 0 mass ppb.

[0021] [Other Components] The present crosslinked rubber article may contain components other than those described above (hereinafter also referred to as "other components"). It is also preferable that the crosslinked rubber article contains a product other than the above-mentioned crosslinked product of the fluorocopolymer, which is obtained by crosslinking the fluorocopolymer contained in the fluorocopolymer composition using the fluorocopolymer composition described below. Specific examples of other components include acid acceptors (for example, fatty acid esters, fatty acid metal salts, and oxides of divalent metals (magnesium oxide, calcium oxide, zinc oxide, lead oxide, etc.)), reinforcing materials (for example, fluorine-containing copolymers other than the above-mentioned fluorine-containing copolymers (for example, tetrafluoroethylene-fluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, and ethylene-tetrafluoroethylene copolymers), polytetrafluoroethylene (PTFE), aromatic polyesters, polyamideimides, and thermoplastic polyimides), scorch retarders (for example, phenolic hydroxyl group-containing compounds such as bisphenol A, quinones such as hydroquinone, and α-methylstyrene dimers such as 2,4-di(3-isopropylphenyl)-4-methyl-1-pentene), crown ethers (for example, 18-crown-6), and mold release agents (for example, sodium stearate). These other components may be used alone or in combination of two or more.

[0022] [Uses] The crosslinked rubber article is suitable for use as a material for O-rings, sheets, gaskets, oil seals, diaphragms, V-rings, and the like. The present invention can also be applied to heat-resistant and chemical-resistant sealing materials, heat-resistant and oil-resistant sealing materials, wire coating materials, sealing materials for semiconductor manufacturing equipment, sealing materials for liquid crystal display panel manufacturing equipment, sealing materials for light-emitting diode manufacturing equipment, corrosion-resistant rubber paints, sealing materials for urea-resistant greases, and the like, rubber paints, adhesive rubbers, hoses, tubes, calendered sheets (rolls), sponges, rubber rolls, oil drilling components, heat-dissipating sheets, solution-crosslinked products, rubber sponges, bearing seals (urea-resistant greases, etc.), linings (chemical-resistant), insulating sheets for automobiles, insulating sheets for electronic devices, rubber bands for watches, endoscope packings (amine-resistant), bellows hoses (processed from calendered sheets), water heater packings / valves, fenders (offshore civil engineering, ships), fibers and nonwoven fabrics (protective clothing, etc.), circuit board sealing materials, rubber gloves, stators for uniaxial eccentric screw pumps, parts for urea SCR systems, vibration-proofing agents, vibration-damping agents, sealants, additives for other materials, and toys.

[0023] [Fluorocopolymer composition] The fluorine-containing copolymer composition of the present disclosure (hereinafter also referred to as "the present fluorine-containing copolymer composition") contains a fluorine-containing copolymer having units based on a monomer having a nitrile group and units based on TFE. In addition, the present fluorine-containing copolymer composition preferably further contains a crosslinking agent.

[0024] In a crosslinked rubber article obtained using the present fluorine-containing copolymer composition, when the 60° specular gloss is measured at 10 different locations on the surface of the crosslinked rubber article, it is preferable that the minimum value among the 60° specular gloss values ​​measured at the 10 different locations is 1.0 to 50.0. The minimum value is synonymous with the above-mentioned minimum value X, and preferred embodiments are also the same. Furthermore, the measurement method and preferred embodiments of the 60° specular gloss (e.g., maximum value Y and the absolute difference between minimum value X and maximum value Y) are the same as the preferred embodiments of the 60° specular gloss of the above-mentioned crosslinked rubber article.

[0025] The present fluorocopolymer composition is preferably used for producing crosslinked rubber articles. The maximum torque (MH) of the present fluorocopolymer composition during the primary vulcanization is preferably 1 to 75 dNm, more preferably 15 to 70 dNm, and even more preferably 40 to 65 dNm. Furthermore, the MH-ML of the present fluorocopolymer composition during the primary vulcanization is preferably 1 to 60 dNm, more preferably 10 to 55 dNm, and even more preferably 25 to 50 dNm. ML is the minimum torque value.

[0026] [Fluorine-containing copolymer] The fluorine-containing copolymer has a unit based on a monomer having a nitrile group and a unit based on TFE.Furthermore, the fluorine-containing copolymer preferably has a unit based on a monomer having a nitrile group, a unit based on TFE, and a unit based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE").Hereinafter, the unit based on TFE is also referred to as "TFE unit", and the unit based on PAVE is also referred to as "PAVE unit".

[0027] The fluorine-containing copolymer preferably has a nitrile group at least at one of the terminal and the side chain, and more preferably has a nitrile group at the side chain. ＣＮ "), a nitrile group can be introduced into the side chain of the fluorine-containing copolymer. Furthermore, when producing the fluorine-containing copolymer, a nitrile group can be introduced into the terminal of the fluorine-containing copolymer by polymerizing a monomer using a chain transfer agent having a nitrile group. The fluorine-containing copolymer can be produced by polymerizing a monomer using a chain transfer agent having a nitrile group. ＣＮ It is preferable that the unit is based on the following formula: ＣＮ The unit based on "R ＣＮ Also called "unit."

[0028] From the viewpoint of polymerization reactivity, RCN preferably has a polymerizable unsaturated bond, more preferably 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).

[0029] R ＣＮis preferably a monomer represented by the following formula (5) in view of better mold releasability and heat resistance of the crosslinked rubber article: ５１ R ５２ =CR ５３ -R ５４ -CN (5) In formula (5), R ５１ , R ５２ , and R ５３ each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R ５４ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms. ＣＮ From the viewpoint of excellent polymerization reactivity of R ５１ , R ５２ , and R ５３ is preferably a fluorine atom or a hydrogen atom, and R ５１ , R ５２ , and R ５３ It is more preferred that all of R are fluorine atoms or all of R are hydrogen atoms, and in view of the superior mold releasability and heat resistance of the crosslinked rubber article, ５１ , R ５２ , and R ５３ It is more preferable that all of R are fluorine atoms. ５４ R may be linear, branched, or cyclic, and is preferably linear or branched. ５４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5. ５４ R may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in order to obtain better rubber properties. ５４ The number of etheric oxygen atoms in the formula (5) is preferably 1 to 3, and more preferably 1 or 2. Specific examples of the monomer represented by the formula (5) include CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CN (hereinafter also referred to as "8CNVE"), CF ２ = CFO (CF ２) ５ CN (hereinafter also referred to as "MV5CN"), CF ２ = CFOCF ２ CF ２ CF ２ OCF (CF ３ ) CN and CF ２ = CFO (CF ２ ) ３ CN is exemplified, and 8CNVE or MV5CN is preferred in that the crosslinked rubber article has better mold releasability and heat resistance.

[0030] The PAVE from which the PAVE unit is derived is preferably a monomer represented by formula (1) from the viewpoint of more efficient production of the fluorine-containing copolymer. 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.

[0031] 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 PMVE or PPVE are preferred, with PMVE being more preferred, from the viewpoint of enabling more efficient production of the fluorinated copolymer.

[0032] The fluorine-containing copolymer may have a crosslinkable group other than a nitrile group. The crosslinkable group is not particularly limited as long as it is a functional group other than a nitrile group that can be crosslinked by a crosslinking reaction, and examples thereof include a polymerizable unsaturated bond, a chlorine atom, a bromine atom, and an iodine atom. The fluorine-containing copolymer preferably has the crosslinkable group other than the nitrile group at at least one of the terminal and the side chain, more preferably at the side chain. The crosslinkability other than the nitrile group can be introduced into the fluorine-containing copolymer by the same method as the above-mentioned method for introducing the nitrile group.

[0033] The monomer having a crosslinkable group other than the nitrile group includes a monomer having two or more polymerizable unsaturated bonds (hereinafter also referred to as "BO"), a monomer having one or more atoms of at least one kind selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom (hereinafter also referred to as "R Ｈａｌ "), and a compound represented by formula (6) described below (hereinafter also referred to as "POAVE").

[0034] BO is a monomer having two or more polymerizable unsaturated bonds. Examples of the polymerizable unsaturated bond include a carbon atom-carbon atom double bond (C═C) and a carbon atom-carbon atom triple bond (C≡C). The number of polymerizable unsaturated bonds that BO has is preferably 2 to 6, more preferably 2 or 3, and even more preferably 2, in terms of better polymerization reactivity. BO preferably contains a fluorine atom in terms of reducing the compression set of a crosslinked rubber article at high temperatures.

[0035] BO is preferably a monomer represented by formula (2) in view of better releasability of the crosslinked rubber article. ２１ R ２２ =CR ２３ -) ａ１ R ２４ (2) In formula (2), R ２１ , R ２２ , and R ２３ each independently represents a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group; a1 represents an integer of 2 to 6; R ２４ represents an a1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of an a1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms. ２１ , multiple R ２２ and multiple R ２３ may be the same or different, and are particularly preferably the same. a1 is preferably 2 or 3, and more preferably 2. In terms of better polymerization reactivity of BO, R ２１ , R ２２ , and R ２３is preferably a fluorine atom or a hydrogen atom, and R ２１ , R ２２ , and R ２３ are more preferably all fluorine atoms or all hydrogen atoms, and in view of better mold releasability of the crosslinked rubber article, R ２１ , R ２２ , and R ２３ It is more preferable that all of R are fluorine atoms. ２４ R may be linear, branched, or cyclic, preferably linear or branched, more preferably linear. ２４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5. ２４ Although R may or may not have an etheric oxygen atom, it is preferable that R has an etheric oxygen atom in view of better crosslinking reactivity and rubber physical properties. ２４ The number of etheric oxygen atoms in R is preferably 1 to 6, more preferably 1 to 3, and even more 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.

[0036] 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).

[0037] (CF ２ =CF-) ２ R ３１ (3) In formula (3), R ３１ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms.

[0038] (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 a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms.

[0039] 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 (CF ３ )CF ２ OCF = CF ２ , and CF 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 also referred to as "C3DVE"), and CF ２ = CFO (CF ２ ) ４ OCF = CF ２ (hereinafter also referred to as "C4DVE").

[0040] Specific examples of the monomer represented by formula (4) include CH ２ =CH(CF ２ ) ２ CH=CH ２ , C.H. ２ =CH(CF ２ ) ４ CH=CH ２ , and C.H. ２ =CH(CF ２ ) ６ CH=CH ２ Among the monomers represented by formula (4), specific examples of more preferred monomers include CH ２ =CH(CF ２ ) ６ CH=CH ２ (hereinafter also referred to as "C6DV"). Among them, C3DVE or C4DVE is preferable for BO.

[0041] R Ｈａｌ Examples of the monomer having a bromine atom include a monomer having a bromine atom and a monomer having an iodine atom. Specific examples of the monomer having a bromine atom include CF ２ = CFOCF ２ CF ２ CF ２ 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, and 4-bromoperfluorobutene-1,3,3-difluoroallyl bromide. Also included are 2-bromo-perfluoroethyl perfluorovinyl ether and CF ２ Br-R ｆ -O-CF=CF ２ (R ｆ is a perfluoroalkylene group), for example, CF ２ BrCF ２ O-CF=CF ２ , ROCF = CFBr, and ROCBr = CF ２ (wherein R is a lower alkyl group or a fluoroalkyl group), more specifically fluorovinyl ethers such as CH ３ OCF = CFBr and CF ３ CH ２ Specific examples of the monomer having an iodine atom include the monomer represented by the formula: CHR=CH-Z-CH ２ CHR-I (wherein R is —H or —CH ３ Z is a linear or branched C alkyl group optionally containing one or more ethereal oxygen atoms; １ ~C １８ iodinated olefins of the formula I(CH) as disclosed in U.S. Pat. No. 5,717,036, which are (per)fluoroalkylene groups or (per)fluoropolyoxyalkylene groups as disclosed in U.S. Pat. No. 5,674,959. ２ CF ２ CF ２ ) ｎ OCF = CF ２ and ICH ２ CF ２ O[CF(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. Pat. No. 4,694,045. Also included are allyl iodide and 2-iodo-perfluoroethyl perfluorovinyl ether.

[0042] POAVE is a compound represented by formula (6): CF ２ =CF(OCF ２ CF ２ ) ｎ -(OCF ２ ) ｍ -OR ｆ２ (6) In formula (6), R ｆ２ represents a perfluoroalkyl group having 1 to 4 carbon atoms, n represents an integer of 0 to 3, m represents an integer of 0 to 4, and n+m represents an integer of 1 to 7.

[0043] R ｆ２ In the formula, the perfluoroalkyl group may be linear or branched. ｆ２ The number of carbon atoms in is preferably 1 to 3. When n is 0, m is preferably 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 crosslinked rubber article are excellent, and the productivity of the crosslinked rubber article is improved.

[0044] Specific examples of POAVE include the following. The abbreviation for the compound is given in parentheses after the formula. CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ４ -OCF ３ (C9PEVE), CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ２ -OCF ３ (C7PEVE), CF ２ =CF-(OCF ２ CF ２ ) ２ -OCF ２ CF ３ (EEAVE), CF ２ =CF-(OCF ２ CF ２ ) ３ -OCF ２ CF ３ (EEEAVE), CF ２ =CF-OCF ２ -OCF ３ , C.F. ２ =CF-OCF ２ -OCF ２ -OCF ３ As the POAVE, C9PEVE, C7PEVE, EEAVE, or EEEAVE is preferred in terms of superior low-temperature properties and productivity of crosslinked rubber articles. These compounds can be produced from the corresponding alcohols by the method described in WO 00 / 056694.

[0045] Units based on a monomer having a nitrile group (preferably R ＣＮThe content of PAVE units (preferably PMVE units) is preferably 0.05 to 5.0 mol%, more preferably 0.1 to 3.0 mol%, and even more preferably 0.2 to 2.0 mol%, relative to the total content of all units in the fluorine-containing copolymer. The content of TFE units is preferably 20.0 to 80.0 mol%, more preferably 50.0 to 80.0 mol%, even more preferably 60.0 to 80.0 mol%, particularly preferably 63.0 to 75.0, and most preferably 66.0 to 72.0 mol%, relative to the total content of all units in the fluorine-containing copolymer. The content of PAVE units (preferably PMVE units) is preferably 20.0 to 80.0 mol%, more preferably 20.0 to 50.0 mol%, more preferably 20.0 to 40.0 mol%, particularly preferably 24.0 to 36.0 mol%, and most preferably 27.0 to 33.0 mol%, relative to the total content of all units in the fluorine-containing copolymer. The content of units based on monomers having a crosslinkable group other than a nitrile group is preferably from 0.01 to 1.0 mol %, more preferably from 0.05 to 10.0 mol %, and still more preferably from 0.1 to 5.0 mol %, based on the total content of all units in the fluorine-containing copolymer.

[0046] The content of TFE units is preferably 20.0 to 80.0 mol%, more preferably 50.0 to 80.0 mol%, and even more preferably 60.0 to 80.0 mol%, based on the total content of TFE units and PAVE units (preferably PMVE units). The content of PAVE units (preferably PMVE units) is preferably 20.0 to 80.0 mol%, more preferably 20.0 to 50.0 mol%, and even more preferably 20.0 to 40.0 mol%, based on the total content of TFE units and PAVE units (preferably PMVE units). The total content of TFE units and PAVE units (preferably PMVE units) is preferably 50.0 to 99.9 mol%, more preferably 70.0 to 99.9 mol%, and even more preferably 75.0 to 99.9 mol%, based on the total content of all units in the fluorine-containing copolymer. Units based on a monomer having a nitrile group (preferably R ＣＮThe total content of the PAVE units (preferably PMVE units) is preferably from 99.0 to 100.0 mol%, more preferably from 99.5 to 100.0 mol%, and still more preferably 100.0 mol%, based on the total content of all units in the fluorine-containing copolymer.

[0047] The fluorine-containing copolymer is preferably a perfluoropolymer. "Perfluoropolymer" refers to a polymer that does not substantially contain hydrogen atoms bonded to carbon atoms, has fluorine atoms instead of those hydrogen atoms, and has a main chain consisting of a chain of carbon atoms. The side chain of the perfluoropolymer may have a polyvalent atom other than carbon atoms, and the polyvalent atom is preferably an oxygen atom. "Substantially does not contain hydrogen atoms" means that the content of hydrogen atoms in the perfluoropolymer is 0.5% by mass or less, preferably 0.1% by mass or less, more preferably 0.07% by mass or less, and even more preferably 0.05% by mass or less. The lower limit can be 0% by mass. When the content of hydrogen atoms is within the above range, good heat resistance or chemical resistance is likely to be obtained.

[0048] The fluorine-containing copolymer is also preferably a perfluoroelastomer. A "perfluoroelastomer" is a perfluoropolymer having a glass transition temperature of 20°C or lower and a melting peak (ΔH) of 4.5 J / g or lower, and further, a polymer in which the proportion of fluorine atoms contained in the perfluoropolymer is 65 mass% or higher.

[0049] [Filler] The fluorocopolymer composition preferably contains a filler. Examples of the filler include the fillers that can be contained in the present crosslinked rubber article described above.

[0050] The filler may be used alone or in combination of two or more. The content of the filler is preferably 30 parts by mass or less, more preferably 10 parts by mass or less, per 100 parts by mass of the fluorocopolymer. The lower limit is preferably 1 part by mass or more per 100 parts by mass of the fluorocopolymer.

[0051] [Crosslinking Agent] Specific examples of the crosslinking agent include a compound having two or more amino groups (hereinafter also referred to as a "polyamine compound") and an organic peroxide. Polyamine compounds are preferred, and compounds having two amino groups are more preferred, since they provide excellent crosslinkability for the fluorocopolymer and enable the production of crosslinked rubber articles with smaller compression set.

[0052] The polyamine compound may be a compound in which a hydrogen atom of an aliphatic hydrocarbon is substituted with an amino group, or a compound in which a hydrogen atom of an aromatic hydrocarbon is substituted with an amino group, but from the viewpoint of achieving better effects of the present disclosure, a compound in which a hydrogen atom of an aromatic hydrocarbon is substituted with an amino group is preferred. The polyamine compound preferably contains a fluorine atom. This improves compatibility with the fluorine-containing copolymer, thereby allowing a crosslinked rubber article to be obtained with a smaller compression set at high temperatures.

[0053] Specific examples of the polyamine compound include hexamethylenediamine, hexamethylenediamine carbamate, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(3-amino-4-hydroxyphenyl)propane, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (hereinafter also referred to as "BOAP", also known as bisaminophenol AF), 2,2-bis(3,4-diaminophenyl)propane, 2,2-bis(3,4-diaminophenyl)hexafluoropropane, 2,2-bis(3-amino-4-(N-phenylamino)phenyl)hexafluoropropane, 4,4'-methylenedianiline, m-phenylenediamine, adipic acid dihydrazide, and the compound represented by formula (XII) of Japanese Patent No. 5,833,657, with BOAP being preferred.

[0054] The content of the crosslinking agent is preferably from 0.1 to 10 parts by mass, more preferably from 0.3 to 5 parts by mass, and even more preferably from 0.5 to 3 parts by mass, per 100 parts by mass of the fluorine-containing copolymer.

[0055] [Emulsifier] The fluorocopolymer composition may contain an emulsifier, but preferably does not substantially contain an emulsifier. "Emulsifier" is a general term for emulsifiers having fluorine atoms, as described below, and emulsifiers not having fluorine atoms, as described below. Furthermore, "substantially not containing an emulsifier" means that the content of emulsifier is 10 ppm by mass or less, preferably 150 ppb by mass or less, more preferably 50 ppb by mass or less, and particularly preferably 25 ppb by mass or less, relative to the total mass of the fluorocopolymer composition. It is also preferably below the quantitation limit of the measurement method using a liquid chromatograph mass spectrometer described below. An example of a lower limit is 1 ppb by mass. The content of various emulsifiers can be measured using a liquid chromatograph mass spectrometer. Specific examples include the measurement methods described in paragraphs

[0721] to

[0732] of WO 2018 / 181904. If the concentration is below the limit of quantitation in the measurement using the liquid chromatograph mass spectrometer, it can be determined to be 0 mass ppb.

[0056] [Method for producing crosslinked rubber article] The method for producing the present crosslinked rubber article is not particularly limited as long as it can produce the present crosslinked rubber article. The method for producing the present crosslinked rubber article preferably comprises a step of crosslinking the fluorocopolymer using a fluorocopolymer composition containing the above-mentioned fluorocopolymer. A method of crosslinking the fluorocopolymer is preferably a method of heating the fluorocopolymer composition. The fluorocopolymer composition is as described above. Specific examples of the crosslinking method by heating include hot press crosslinking, steam crosslinking, injection molding crosslinking, hot air crosslinking, molten salt crosslinking, fluidized bed crosslinking, and funnel crosslinking. The heating conditions are preferably 100 to 400°C for 1 second to 24 hours.

[0057] The crosslinked rubber obtained by heating the present fluorocopolymer composition (by primary crosslinking) may be further heated to cause secondary crosslinking. By carrying out secondary crosslinking, the mechanical properties, compression set, and other properties of the crosslinked rubber can be stabilized or improved. The heating conditions for carrying out secondary crosslinking are preferably 80 to 350°C for 30 minutes to 48 hours.

[0058] As a crosslinking method other than heating, the composition may be irradiated with radiation, and specific examples of the radiation to be irradiated include electron beams and ultraviolet rays.

[0059] The method for producing the crosslinked rubber article also preferably involves molding a fluorine-containing copolymer composition using a mold to produce a crosslinked rubber article. Specifically, it is preferable to fill a mold with the fluorine-containing copolymer composition and mold the fluorine-containing copolymer composition, and more preferably to subject the molded fluorine-containing copolymer composition to the above-mentioned crosslinking step. The shape of the mold is not particularly limited, but an O-ring type is preferred, and an O-ring type P-26 (standard defined in JIS B2401:2012) is more preferred. The 60° specular gloss of the mold is preferably 100.0 or more, more preferably 120.0 or more, from the viewpoint of ease of adjusting the 60° specular gloss of the crosslinked rubber article (particularly the minimum value X). The upper limit is preferably 300.0 or less. The 60° specular gloss of the mold can be measured using a known gloss meter (for example, Gloss Checker IG-410, manufactured by Horiba, Ltd.).

[0060] The method for producing the crosslinked rubber article preferably comprises, for example, the steps of producing a fluorocopolymer, preparing a fluorocopolymer composition containing the fluorocopolymer, and crosslinking the fluorocopolymer using the fluorocopolymer composition. The fluorocopolymer and the fluorocopolymer composition are as described above.

[0061] [Step of Producing a Fluorine-Containing Copolymer] The step of producing a fluorine-containing copolymer may, for example, be carried out by reacting R ＣＮ and a method of polymerizing a monomer containing TFE. Examples of the polymerization method include emulsion polymerization, solution polymerization, and suspension polymerization, and polymerization in an aqueous medium is preferred because it is easy to adjust the molecular weight and the composition of the fluorine-containing copolymer and is excellent in productivity. When producing a fluorine-containing polymer in an aqueous medium, it can be carried out by heating the monomer in the presence of an aqueous medium and a polymerization initiator. The aqueous medium may or may not contain an emulsifier.

[0062] In a first preferred embodiment of the step of producing a fluorine-containing copolymer, a compound represented by formula (X) described below (hereinafter also referred to as "compound X") and a polymerization initiator are used to react with R ＣＮ and TFE to produce an aqueous dispersion containing particles of a first fluoropolymer A having an average particle size of 500 nm or less (hereinafter also referred to as "first aqueous dispersion A"), and recovering the first fluorocopolymer A from the first aqueous dispersion A (hereinafter also referred to as "production method A"). Hereinafter, in production method A, the step of producing the first aqueous dispersion A will also be referred to as "step A1", and the step of recovering the fluorocopolymer from the first aqueous dispersion A will also be referred to as "step A2".

[0063] In a second preferred embodiment of the step of producing a fluorine-containing copolymer, a first monomer B containing TFE is polymerized using a compound X and a polymerization initiator described below in the presence of an aqueous medium and in the substantial absence of an emulsifier having a fluorine atom to produce an aqueous dispersion containing particles of a first fluorine-containing polymer B having an average particle size of 500 nm or less (hereinafter also referred to as "first aqueous dispersion B"); and ＣＮ and a step (hereinafter also referred to as "production method B") of polymerizing a second monomer B containing

[0064] <Production Method A> (Step A1) In Step A1, TFE and R are reacted in the presence of Compound X and a polymerization initiator in the presence of an aqueous medium and in the substantial absence of an emulsifier having a fluorine atom. ＣＮ A first fluorocopolymer A is synthesized by polymerizing a first monomer A containing the following compound to obtain a first aqueous dispersion A. This prevents a decrease in the molecular weight of the polymer produced, and makes it easy to obtain the fluorocopolymer.

[0065] -Emulsifier- "Under conditions in which an emulsifier having a fluorine atom is substantially absent" means that the content of the emulsifier having a fluorine atom is 10 ppm by mass or less, preferably 150 ppb by mass or less, more preferably 50 ppb by mass or less, and particularly preferably 25 ppb by mass or less, relative to the total mass of the aqueous medium. The lower limit is 0 ppb by mass. Step A1 is preferably performed under conditions in which an emulsifier having a fluorine atom and an emulsifier not having a fluorine atom are substantially absent. "Substantially absent" means that the content of the emulsifier is 10 ppm by mass or less, preferably 150 ppb by mass or less, more preferably 50 ppb by mass or less, and particularly preferably 25 ppb by mass or less, relative to the total mass of the aqueous medium. The lower limit is also preferably 1 ppb by mass. The content of various emulsifiers can be measured using a liquid chromatograph mass spectrometer. Specifically, the measurement method described in paragraphs

[0721] to

[0732] of WO 2018 / 181904 can be used. If the content is below the quantitation limit in the measurement using the liquid chromatograph mass spectrometer, it can be determined to be 0 ppb by mass.

[0066] The emulsifier includes a water-soluble emulsifier. A water-soluble emulsifier means an emulsifier having a solubility of 100 mg or more in 1000 g of water at 25°C, and a water-insoluble emulsifier means an emulsifier other than the water-soluble emulsifiers. The water-soluble emulsifier may be either ionic or nonionic. Examples of the emulsifier include those having no carbon-carbon double bond. Compound X described below, the first fluorine-containing copolymer described below, and the fluorine-containing copolymer (second fluorine-containing copolymer) described below do not fall under the category of emulsifiers.

[0067] Examples of emulsifiers having fluorine atoms include anionic fluorine-containing emulsifiers. Examples of anionic fluorine-containing emulsifiers include emulsifiers containing fluorine atoms in which the total number of carbon atoms in the moiety excluding the anionic group is 20 or less. Examples of fluorine-containing emulsifiers containing fluorine atoms in which the total number of carbon atoms in the moiety excluding the anionic group is 20 or less include emulsifiers containing fluorine atoms in which the molecular weight of the anionic moiety is 800 or less. The above-mentioned "anionic moiety" means the moiety excluding the cation of the fluorine-containing emulsifier.

[0068] The fluorine-free emulsifier is an emulsifier that does not contain fluorine atoms and has a hydrocarbon group such as an alkyl group as a hydrophobic moiety. It is also possible to substitute a hydrogen atom of the hydrocarbon group of the fluorine-free emulsifier with a halogen atom other than a fluorine atom.

[0069] The emulsifiers having no fluorine atoms include anionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0070] Anionic hydrocarbon emulsifiers refer to emulsifiers having a negatively charged hydrophilic moiety, such as a carboxylic acid group, a sulfonic acid group, a sulfate group, a phosphonic acid group, or a phosphate group, and a hydrocarbon group, such as an alkyl group, as a hydrophobic moiety. Specific examples of anionic hydrocarbon emulsifiers include sodium dodecyl sulfate, highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10, linear alkyl polyethersulfonate sodium supplied by BASF as the Avanel® S series, and sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobelSurfaceChemistry LLC.

[0071] Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity in water without dissociating into ions and have hydrocarbon groups such as alkyl groups as their hydrophobic moieties. The hydrophilic moieties of nonionic hydrocarbon emulsifiers include water-soluble functional groups such as polyethylene oxide chains obtained from the polymerization of ethylene oxide. Nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, such as block copolymers having polyethylene oxide and polypropylene oxide.

[0072] Further, other nonionic hydrocarbon emulsifiers include those described in paragraphs

[0043] to

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

[0073] The emulsifier with fluorine atom and the emulsifier without fluorine atom can contain silicon atom.The emulsifier with silicon atom can include siloxane emulsifier.Siloxane emulsifier is a hydrocarbon-containing emulsifier with siloxane skeleton.The siloxane emulsifier can include the emulsifier described in U.S. Patent No. 6,841,616 (Wille et al.) and U.S. Patent No. 7,977,438 (Brothers et al.).

[0074] The emulsifier having a fluorine atom and the emulsifier not having a fluorine atom may be a polymer emulsifier. Examples of polymer emulsifiers include polymers obtained by polymerizing a monomer having a fluorine atom or a monomer not having a fluorine atom. Furthermore, examples of polymer emulsifiers made of polymers obtained by polymerizing a monomer having a fluorine atom or a monomer not having a fluorine atom include polymers having a hydrophilic group in the side chain. Examples of such polymer emulsifiers include polymers obtained by polymerizing a compound having a site capable of polymerization reaction and a hydrophilic group. Furthermore, even if a polymer does not originally have a hydrophilic group, examples include polymers obtained by post-treating a polymer obtained by polymerizing a compound having a group that can become a hydrophilic group, such as by hydrolysis. Preferably, the polymer emulsifier is water-soluble.

[0075] -Aqueous Medium- Specific examples of the aqueous medium 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.

[0076] Before the polymerization of the first monomer A is initiated, the content of the aqueous medium is preferably 20 to 80% by volume, and more preferably 40 to 70% by volume, relative to the volume of the reactor. In this specification, "before the polymerization of the monomer is initiated" means immediately before the start of polymerization. Here, examples of the "start of polymerization" include the time when the monomer and the polymerization initiator are brought into coexistence in the reactor after the temperature inside the reactor is raised to a polymerization temperature or higher, and the time when the temperature inside the reactor is raised to a polymerization temperature or higher after the monomer and the polymerization initiator are brought into coexistence in the reactor.

[0077] Compound X Compound X is a compound represented by formula (X). Compound X can be polymerized with a monomer described below.

[0078] C(X １ ) (X ２ ) = C(X ３ ) CONH-R-Z (X) In formula (X), １ , X ２ and X ３ are each independently a hydrogen atom, a fluorine atom, a perfluoromethyl group or an alkyl group, R is an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms, Z is -SO ３ M, -OSO ３ M, -P (=O) (OM) ２ , -OP(=O)(OM) ２ or -COOM, where M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ When a plurality of M's are present, the plurality of M's may be the same or different from each other, R Ｍ１ and R Ｍ２ are each independently a hydrogen atom or a substituent, and R Ｍ１Any two of R may be bonded to each other to form a ring, and multiple R Ｍ１ may be the same or different from each other, R Ｍ２ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ２ may be the same or different from each other.

[0079] X １ , X ２ and X ３ are each independently a fluorine atom, a perfluoromethyl group, a hydrogen atom, or an alkyl group. The alkyl group may be linear, branched, or cyclic. The alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1. X １ , X ２ and X ３ As the alkyl group, a fluorine atom or a hydrogen atom is preferred, and a hydrogen atom is preferred in terms of excellent polymerization reactivity.

[0080] R is an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms. The alkylene group or the fluoroalkylene group may be linear, branched, or cyclic, and is preferably branched. The alkylene group or the fluoroalkylene group has 1 to 6 carbon atoms, preferably 2 to 4 carbon atoms, and more preferably 4 carbon atoms. R is preferably an alkylene group having 1 to 6 carbon atoms.

[0081] Z is -SO ３ M, -OSO ３ M, -P (=O) (OM) ２ , -OP(=O)(OM) ２ or -COOM. Z is -SO ３ M is preferred, and —SO ３ Na is more preferred.

[0082] M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ and R Ｍ１ and R Ｍ２are each independently a hydrogen atom or a substituent. The metal atom represented by M is preferably a metal atom of Group 1, more preferably Li, Na or K. Ｍ１ and R Ｍ２ The substituent represented by the formula (I) is preferably a monovalent organic group, more preferably a monovalent hydrocarbon group, and even more preferably an alkyl group or an aromatic hydrocarbon group. The substituent preferably has 1 to 10 carbon atoms. The alkyl group may be linear, branched, or cyclic. The aromatic hydrocarbon group may be monocyclic or polycyclic. The aromatic hydrocarbon group is preferably a phenyl group.

[0083] Specific examples of compound X include 2-acrylamido-2-methyl-1-propanesulfonic acid, N-tigloylglycine, 6-acrylamidohexanoic acid, 1,1-Difluoro-2-methyl-2-[(1-oxo-2-propen-1-yl)amino]-1-propanesulfonic acid, 3-Methyl-3-[(2-methyl-1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, 2-Methacrylamido-2-methylpropanesulfonic acid, 2,3-Dimethyl-3-[(1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, and metal salts thereof. Compound X is preferably a (meth)acrylamide having a sulfonic acid group, and 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-methacrylamido-2-methylpropylsulfonic acid, or 2,3-dimethyl-3-[(1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid is preferred. Examples of the metal salt include metal salts of the metal atom represented by M. Compound X is preferably a (meth)acrylamide having a sulfonic acid group or a metal salt thereof, and 2-acrylamido-2-methyl-1-propanesulfonic acid, sodium 2-acrylamido-2-methyl-1-propanesulfonate, 2-methacrylamido-2-methyl-1-propanesulfonic acid, or sodium 2-methacrylamido-2-methyl-1-propanesulfonate is preferred. The term "(meth)acrylamide" as used herein encompasses both acrylamide and methacrylamide.

[0084] Before starting polymerization of the first monomer A, the content of the compound X is preferably 0.1 to 1000.0 ppm by mass, more preferably 0.1 to 500.0 ppm by mass, still more preferably 0.5 to 100.0 ppm by mass, and particularly preferably 1 to 30.0 ppm by mass, relative to the total mass of the aqueous medium.

[0085] -Polymerization initiator- The polymerization initiator used in step A1 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.

[0086] The amount of the polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, relative to 100 parts by mass of the total amount of the first monomer used.

[0087] -First Monomer A- The first monomer A is R ＣＮ and TFE. ＣＮ and TFE are the R ＣＮ and TFE, and the preferred embodiments are also the same.

[0088] The first monomer A preferably contains PAVE. Details of PAVE are as described above.

[0089] The first monomer A may contain a monomer having a crosslinkable group other than a nitrile group in the above-mentioned fluorine-containing copolymer. Further, the first monomer A may contain a monomer other than the monomer having a nitrile group, TFE, PAVE, and the monomer having a crosslinkable group other than a nitrile group.

[0090] Monomers having a nitrile group (R ＣＮThe amount of the monomer having a crosslinkable group other than a nitrile group is preferably 0.01 to 15 mol%, more preferably 0.05 to 10 mol%, and even more preferably 0.1 to 5 mol%, based on the total amount of the first monomer A. The amount of TFE is preferably 20.0 to 80.0 mol%, more preferably 50.0 to 80.0 mol%, and even more preferably 60.0 to 80.0 mol%, based on the total amount of the first monomer A. The amount of PAVE (preferably PMVE) is preferably 20.0 to 80.0 mol%, more preferably 20.0 to 50.0 mol%, and even more preferably 20.0 to 40.0 mol%, based on the total amount of the first monomer A. The amount of the monomer having a crosslinkable group other than a nitrile group is preferably 0.01 to 15 mol%, more preferably 0.05 to 10 mol%, and even more preferably 0.1 to 5 mol%, based on the total amount of the first monomer A.

[0091] The amount of TFE used is preferably 20.0 to 80.0 mol%, more preferably 50.0 to 80.0 mol%, and even more preferably 60.0 to 80.0 mol%, based on the total amount of TFE and PAVE used. The amount of PAVE (preferably PMVE) used is preferably 20.0 to 80.0 mol%, more preferably 20.0 to 50.0 mol%, and even more preferably 20.0 to 40.0 mol%, based on the total amount of TFE and PAVE used. The total amount of TFE and PAVE (preferably PMVE units) used is preferably 50.0 to 99.9 mol%, more preferably 70.0 to 99.9 mol%, and even more preferably 75.0 to 99.9 mol%, based on the total amount of the first monomer A used. ＣＮ The total amount of the first monomer A used is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 100.0 mol%, based on the total amount of the first monomer A used.

[0092] -Method- The method of step A1 is not particularly limited as long as it is a method of polymerizing the first monomer A using compound X and a polymerization initiator under conditions in which an aqueous medium is present and an emulsifier having a fluorine atom is substantially absent. Examples of the method include a method in which a solution containing an aqueous medium and compound X is prepared, and the first monomer A is polymerized using this solution and a polymerization initiator. More specifically, examples include a method in which the solution and the first monomer A are added to a reactor, the reactor is heated, and a polymerization initiator is added to the reactor to polymerize the first monomer A. Step A1 preferably does not include a step of terminating the polymerization midway and deactivating or purifying the polymerization initiator. Furthermore, step A1 is preferably performed in the same reactor.

[0093] Polymerization of the first monomer A gives a first fluorine-containing copolymer A (corresponding to the fluorine-containing copolymer) dispersed in the form of particles in an aqueous medium. The aqueous dispersion thus obtained in which particles of the first fluorine-containing copolymer A are dispersed may be used as the first aqueous dispersion A as is, or another aqueous medium may be added to give the first aqueous dispersion A. Alternatively, the first aqueous dispersion A may be obtained by solvent substitution, dispersing the particles of the first fluorine-containing copolymer A in another aqueous medium.

[0094] The first monomer A is charged into the reactor by a conventional method. For example, the first monomer A may be continuously or intermittently charged into the reactor so that the polymerization pressure reaches a predetermined pressure. Alternatively, the first monomer A may be dissolved in an aqueous medium, and the resulting solution may be continuously or intermittently charged into the reactor. Different monomers of the first monomer A may be charged into the reactor at the same time, or may be charged at different times. For example, TFE and PAVE may be charged into the reactor in advance, and after the polymerization has started, TFE, PAVE, and R ＣＮ When a polymerization initiator is used, the polymerization initiator may be added to the reactor all at once or in portions, and is preferably added intermittently.

[0095] 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. The polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 800 minutes.

[0096] -First Aqueous Dispersion A- In step A1, a first aqueous dispersion A is obtained, which is an aqueous dispersion containing particles of the first fluorinated copolymer A having an average particle size of 500 nm or less.

[0097] It is preferable that the first aqueous dispersion A does not substantially contain a water-soluble emulsifier. The first aqueous dispersion A is substantially free of a water-soluble emulsifier means that the content of the water-soluble emulsifier is 10 mass ppm or less, more preferably 150 mass ppb or less, even more preferably 50 mass ppb or less, and particularly preferably 25 mass ppb or less, relative to the total mass of the first aqueous dispersion A. It is also preferable that the content is below the quantitation limit of the measurement method using the above-mentioned liquid chromatograph mass spectrometer (the measurement method described in WO 2018 / 181904). The lower limit is 1 mass ppb.

[0098] Furthermore, it is preferable that the first aqueous dispersion A is substantially free of a compound represented by any of formulas (S1) to (S4). Substantially free of a compound represented by any of formulas (S1) to (S4) means that the content of the compound represented by any of formulas (S1) to (S4) is 10 mass ppm or less, preferably 5 mass ppm or less, more preferably 150 mass ppb or less, even more preferably 50 mass ppb or less, and particularly preferably 25 mass ppb or less, relative to the total mass of the first aqueous dispersion A. It is also preferable that the content is below the quantitation limit of the measurement method using the liquid chromatograph mass spectrometer described above (the measurement method described in WO 2018 / 181904). The lower limit is 1 mass ppb.

[0099] H-(CF ２ ) ｎ１ -COOM Ｓ (S1) F-(CF ２ ) ｎ１ -COOM Ｓ (S2) H-(CF ２ )ｎ２ -SO ３ M Ｓ (S3) F-(CF ２ ) ｎ２ -SO ３ M Ｓ (S4) In the formulas (S1) to (S4), n1 is an integer of 3 to 13, n2 is an integer of 4 to 10, and M Ｓ is a hydrogen atom, Na, K, NR ４ (R may be the same or different and is a hydrogen atom or an organic group having 1 to 10 carbon atoms), an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent.

[0100] The content of the particles of the first fluorine-containing copolymer A is preferably 5 to 50 mass%, more preferably 10 to 45 mass%, and even more preferably 10 to 30 mass%, relative to the total mass of the first aqueous dispersion A. The solid content concentration of the first aqueous dispersion A is preferably 5 to 50 mass%, more preferably 10 to 45 mass%, and even more preferably 10 to 30 mass%. The solid content concentration of the first aqueous dispersion A can be measured, for example, by the following method. The solid content concentration of the first aqueous dispersion A is calculated 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 solid content concentration using the following formula: "Solid content concentration (mass%) = 100 × heating residue of first aqueous dispersion A (g) / mass of first aqueous dispersion A (2.0 g)"

[0101] -First Fluorine-Containing Copolymer A- Particles of the first fluorine-containing copolymer A are particles produced in step A1. The average particle size of the particles of the first fluorine-containing copolymer A is 500 nm or less, preferably 300 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less, and particularly preferably 100 nm or less. The lower limit is preferably 2 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more. The average particle size of the particles of the first fluorine-containing copolymer A is a particle size calculated by analyzing an autocorrelation function obtained by dynamic light scattering using the monodisperse cumulant method.

[0102] The number of particles of the first fluorine-containing copolymer A is 1.0 × 10 １４Preferably, the number of particles / mL or more is 2.0 × 10 １４ More preferably, 3.0 x 10 １４ The upper limit is 2.0 × 10 １５ The particle number of the first fluorinated copolymer A is the number of particles per mL of the first aqueous dispersion A. Examples of a method for measuring the particle number include the measurement methods shown in the Examples section.

[0103] The first fluorine-containing copolymer A preferably does not have a melting point. In this specification, "the polymer does not have a melting point" means that when the melting point of the polymer is measured using a differential scanning calorimeter, no melting peak is observed, specifically, no melting peak is observed in a temperature range of 150°C or higher (preferably a temperature range of 150 to 330°C). Note that a glass transition peak does not fall under the above-mentioned melting peak. Specific methods for measuring the melting point include the measurement methods shown in the Examples section.

[0104] The first fluorine-containing copolymer A has units based on the first monomer A. The contents of the various units based on the first monomer A in the first fluorine-containing copolymer A have the same meanings as the contents of the various units in the above-mentioned fluorine-containing copolymer, and preferred embodiments are also the same.

[0105] (Step A2) Step A2 is a step of recovering the first fluorocopolymer A from the first aqueous dispersion A obtained in step A1. By agglomerating the particles of the first fluorocopolymer A from the first aqueous dispersion A, a solid fluorocopolymer A can be obtained.

[0106] 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, and hydrofluoric acid, with hydrochloric 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, and ammonium carbonate, 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 ２ O (wherein M' is a monovalent cation other than lithium), calcium nitrate, and magnesium sulfate are examples of the coagulation agent. Alum is preferred, and potassium alum, where M is potassium, is more preferred. Acid coagulation or freeze coagulation is preferred as the coagulation method.

[0107] <Production Method B> (Step B1) The specific method and preferred embodiments of Step B1 are the same as those of Step A1 described above, except that the first monomer A is the first monomer B and the resulting aqueous dispersion is the first aqueous dispersion B containing the first fluoropolymer B.

[0108] -First Monomer B- The first monomer B includes TFE. The amount of TFE used is preferably 20.0 to 95.0 mol %, more preferably 25.0 to 80.0 mol %, and still more preferably 50.0 to 75.0 mol %, relative to the amount of the first monomer B used.

[0109] The first monomer B may contain a monomer other than TFE. The first monomer B preferably contains PAVE. Details of PAVE are as described above. The amount of PAVE (preferably PMVE) used is preferably 5.0 to 80.0 mol%, more preferably 20.0 to 75.0 mol%, and even more preferably 25.0 to 50.0 mol%, based on the total amount of the first monomer B used. The total amount of TFE and PAVE used is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, based on the total amount of the first monomer B used.

[0110] The first monomer B may contain a monomer other than TFE and PAVE. Examples of the other monomer include the above-mentioned monomers having a crosslinkable group other than the nitrile group. In addition, the first monomer B may contain a monomer having a crosslinkable group other than the nitrile group. ＣＮ It is also preferred that it does not contain

[0111] -First aqueous dispersion B- Step B1 provides a first aqueous dispersion B, which is an aqueous dispersion containing particles of a first fluoropolymer B having an average particle size of 500 nm or less. The first aqueous dispersion B preferably contains substantially no water-soluble emulsifier. The first aqueous dispersion B preferably contains substantially no compound represented by any of formulas (S1) to (S4). The definitions and preferred embodiments of the first aqueous dispersion B containing substantially no water-soluble emulsifier and substantially no compound represented by any of formulas (S1) to (S4) are the same as those for the first aqueous dispersion A described above.

[0112] The solids concentration of the first aqueous dispersion B obtained in step B1 is preferably 1 to 50% by mass, and more preferably 5 to 45% by mass. The solids concentration of the first aqueous dispersion B can be measured, for example, by the following method. The solids concentration of the first aqueous dispersion B is calculated by heating 2.0 g of the first aqueous dispersion B at 170°C for 20 minutes, weighing the mass of the residue, and determining the solids concentration using the following formula: "Solids concentration (mass%) = 100 × heating residue of first aqueous dispersion B (g) / mass of first aqueous dispersion B (2.0 g)"

[0113] The aqueous dispersion in which particles of the first fluoropolymer B obtained by polymerization of the first monomer B are dispersed may be used as the first aqueous dispersion B as it is, or another aqueous medium may be added to form the first aqueous dispersion B. Alternatively, the first aqueous dispersion B may be formed by dispersing particles of the first fluoropolymer B in another aqueous medium by solvent substitution.

[0114] -First Fluorine-Containing Polymer B- Particles of the first fluorine-containing polymer B are particles produced in step B1. The first fluorine-containing polymer B may be the same as or different from the second fluorine-containing copolymer B described below. The average particle size of the particles of the first fluorine-containing polymer B is 500 nm or less, and from the viewpoint of particle dispersion stability, it is preferably 300 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less, and particularly preferably 100 nm or less. The lower limit is preferably 2 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more. The average particle size of the particles of the first fluorine-containing polymer B can be calculated in the same manner as for the particles of the first fluorine-containing polymer A described above.

[0115] The number of particles of the first fluorinated polymer B is 1.0 × 10 １４ Preferably, the number of particles / mL or more is 2.0 × 10 １４ More preferably, 3.0 x 10 １４ The upper limit is 2.0 × 10 １５ The particle number of the first fluoropolymer B is the number of particles per mL of the first aqueous dispersion B. Examples of a method for measuring the particle number include the measurement methods shown in the Examples section.

[0116] The first fluorine-containing polymer B preferably does not have a melting point.

[0117] The 1% by mass weight loss temperature on heat of the first fluoropolymer B is preferably 150°C or higher, more preferably 200°C or higher, and even more preferably 250°C or higher. The upper limit is preferably 600°C or lower. The 1% by mass weight loss temperature on heat can be measured, for example, using a thermogravimetric analyzer. Specific methods for measuring the 1% by mass weight loss temperature on heat include the measurement methods shown in the Examples section.

[0118] The first fluoropolymer B contains units based on the first monomer B. The first fluoropolymer B contains TFE units. The content of TFE units is preferably 20.0 to 95.0 mol%, more preferably 25.0 to 80.0 mol%, and even more preferably 50.0 to 75.0 mol%, based on all units of the first fluoropolymer B. The first fluoropolymer B preferably contains PAVE units (preferably PMVE units). The content of PAVE units (preferably PMVE units) is preferably 5.0 to 80.0 mol%, more preferably 20.0 to 75.0 mol%, and even more preferably 25.0 to 50.0 mol%, based on all units of the first fluoropolymer B. The total content of TFE units and PAVE units (preferably PMVE units) is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, based on all units of the first fluoropolymer B. The first fluoropolymer B may contain units other than TFE units and PAVE units, or may be substantially free of other units. Examples of other units include the above-mentioned units based on a monomer having a crosslinkable group other than a nitrile group. "Substantially free of other units" means that the content of other monomers is 0.01 mol% or less, preferably 0 mol%, based on all units of the first fluoropolymer B. In addition, the first fluoropolymer B may contain a copolymer of R ＣＮ It is also preferred that it does not contain units.

[0119] (Step B2) In step B2, R ＣＮ to obtain a second aqueous dispersion B containing a second fluorine-containing copolymer B.

[0120] Preferred embodiments of the first aqueous dispersion B are as described above. It is preferable to carry out a purification treatment to reduce or inactivate the polymerization initiator and its decomposition products from the first aqueous dispersion B before using it for polymerization of the second monomer B. In the purification treatment, the polymerization initiator and its decomposition products that may be contained in the first aqueous dispersion B are removed, making it easy to obtain a second fluorinated copolymer B with desired physical property values. Examples of purification methods include heat treatment and a method of removal using an ion exchange resin. As the ion exchange resin, an anion exchange resin is preferred. Purification may be carried out multiple times.

[0121] The first aqueous dispersion B may contain components other than the aqueous medium and the first fluoropolymer B. Specific examples of other components that the first aqueous dispersion B 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 pH adjusters include inorganic salts and ammonia. Specific examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, sodium bicarbonate, and carbonates such as sodium carbonate. More preferred examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate. When the first aqueous dispersion B 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. When the first aqueous dispersion B 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.

[0122] In step B2, the content of the particles of the first fluoropolymer B before the start of polymerization of the second monomer B is preferably from 0.01 to 5 mass%, more preferably from 0.1 to 3 mass%, relative to the total mass of the first aqueous dispersion B. Note that the first aqueous dispersion B before the start of polymerization of the second monomer B does not contain the second monomer B or the polymerization initiator.

[0123] - Second Monomer B - The second monomer B is R ＣＮ Includes. ＣＮ is R in the above-mentioned fluorine-containing copolymer. ＣＮ The same definition and preferred embodiments are also the same. ＣＮ The amount of the second monomer B used is preferably 1 to 50 mol %, more preferably 2 to 20 mol %, and even more preferably 3 to 10 mol %, based on the total amount of the second monomer B used.

[0124] The second monomer B is R ＣＮ The second monomer B may contain a monomer other than the above. The second monomer B preferably contains at least one selected from the group consisting of TFE and PAVE, and more preferably contains TFE and PAVE. The amount of TFE used is preferably 5.0 to 80.0 mol%, more preferably 20.0 to 75.0 mol%, and even more preferably 50.0 to 75.0 mol%, based on the total amount of the second monomer B used. The amount of PAVE used is preferably 20.0 to 95.0 mol%, more preferably 25.0 to 80.0 mol%, and even more preferably 25.0 to 50.0 mol%, based on the total amount of the second monomer B used. The amount of TFE units and PAVE units used is preferably 60 to 9 mol%, more preferably 65 to 98 mol%, and even more preferably 70 to 97 mol%, based on the total amount of the second monomer B used.

[0125] The second monomer B may contain a monomer having a crosslinkable group other than a nitrile group in the above-mentioned fluorine-containing copolymer. Further, the second monomer B may contain a monomer other than the monomer having a nitrile group, TFE, PAVE, and the monomer having a crosslinkable group other than a nitrile group.

[0126] In step B2, it is preferable to polymerize the second monomer B using 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, disuccinic acid peroxide, bisglutaric acid peroxide, and water-soluble organic peroxides such as 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, an organic acid, or an 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, a water-soluble radical initiator is more preferred, and a persulfate is even more preferred. Two or more polymerization initiators may be used in combination.

[0127] The amount of the polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, relative to 100 parts by mass of the second monomer B used.

[0128] -Method- In step B2, a second fluorine-containing copolymer B (corresponding to the fluorine-containing copolymer) is produced by polymerizing the second monomer B in the first aqueous dispersion B. Examples of the method for polymerizing the second monomer B include the above-mentioned method for polymerizing the first monomer B.

[0129] The polymerization of the second monomer B is preferably carried out under conditions in which an emulsifier having a fluorine atom is substantially absent, and more preferably under conditions in which an emulsifier is substantially absent. Substantially absent emulsifier means that in the method for producing the second fluorine-containing copolymer B, the content of the emulsifier is 10 mass ppm or less relative to the total mass of the first aqueous dispersion B, preferably 150 mass ppb or less, more preferably 50 mass ppb or less, and particularly preferably 25 mass ppb or less. It is also preferable that the content is below the quantitation limit of the measurement method using the above-mentioned liquid chromatograph mass spectrometer (the measurement method described in WO 2018 / 181904). The lower limit is 1 mass ppb.

[0130] - Second Fluorine-Containing Copolymer B - In step B2, the second fluorine-containing copolymer B is produced, and a second aqueous dispersion in which particles of the second fluorine-containing copolymer B are dispersed in an aqueous medium is obtained.

[0131] The second fluorine-containing copolymer B may be in the form of particles. The particles of the second fluorine-containing copolymer B may contain the first fluorine-containing polymer B, or may not contain the first fluorine-containing polymer B. The average particle size of the particles of the second fluorine-containing copolymer B is preferably 500 nm or less, preferably 500 nm or less, and from the viewpoint of particle dispersion stability, more preferably 400 nm or less, even more preferably 350 nm or less, particularly preferably 300 nm or less. The lower limit is preferably 10 nm or more, more preferably 30 nm or more, even more preferably 50 nm or more. The average particle size of the particles of the second fluorine-containing copolymer B can be measured in the same manner as the average particle size of the particles of the first fluorine-containing polymer B.

[0132] The number of particles of the second fluorine-containing copolymer B is 1.0 × 10 １４ Preferably, the number of particles / mL or more is 2.0 × 10 １４ More preferably, 3.0 x 10 １４More preferably, 5.0 x 10 １４ The upper limit is 10.0 × 10 １５ The number of particles of the second fluorinated copolymer B is the number of particles per mL of the second aqueous dispersion B. Examples of a method for measuring the number of particles include the measurement methods shown in the Examples section.

[0133] The second fluorine-containing copolymer B preferably does not have a melting point.

[0134] The second fluorine-containing copolymer B contains units based on the second monomer B. Preferably, the second fluorine-containing copolymer B also contains units based on the first monomer B and the second monomer B. The contents of the various units based on the first monomer B and the second monomer B in the second fluorine-containing copolymer B have the same meanings as the contents of the various units in the above-mentioned fluorine-containing copolymer, and preferred embodiments are also the same.

[0135] - Second aqueous dispersion B - Step B2 provides second aqueous dispersion B, which is an aqueous dispersion containing particles of second fluorocopolymer B. The second aqueous dispersion B is preferably an aqueous dispersion containing fluorocopolymer particles (hereinafter also referred to as "specific particles") and an aqueous medium.

[0136] The second aqueous dispersion B preferably does not substantially contain an emulsifier having a fluorine atom, and more preferably does not substantially contain an emulsifier. The second aqueous dispersion B substantially does not contain an emulsifier means that the content of the emulsifier is 10 mass ppm or less relative to the total mass of the second aqueous dispersion B, preferably 150 mass ppb or less, more preferably 50 mass ppb or less, and particularly preferably 25 mass ppb or less. It is also preferable that the content is below the quantitation limit of the measurement method using the above-mentioned liquid chromatograph mass spectrometer (the measurement method described in WO 2018 / 181904). The lower limit is 1 mass ppb.

[0137] The specific particles are preferably particles of the above-mentioned second fluorine-containing copolymer B. When the specific particles contain the second fluorine-containing copolymer B, the specific particles may or may not contain the first fluorine-containing polymer B. The second aqueous dispersion B may further contain particles of the first fluorine-containing polymer B in addition to the specific particles.

[0138] The preferred embodiments of the specific particle number and average particle diameter are the same as the preferred embodiments of the particle number and average particle diameter of the second fluorine-containing copolymer B. The specific particle number is 1 × 10 １４ It is preferable that the concentration of the particles is 500 nm or less and the average particle size of the particles is 500 nm or less.

[0139] The content of the specific particles is preferably 1 to 50 mass %, more preferably 1 to 45 mass %, and even more preferably 1 to 40 mass %, relative to the total mass of the second aqueous dispersion B, from the viewpoint of dispersion stability of the specific particles.

[0140] Specific examples and preferred embodiments of the aqueous medium contained in the second aqueous dispersion B are the same as the specific examples and preferred embodiments of the aqueous medium contained in the first aqueous dispersion B. The content of the aqueous medium is preferably 50 to 99 mass%, more preferably 60 to 99 mass%, and even more preferably 70 to 99 mass%, relative to the total mass of the second aqueous dispersion B, from the viewpoint of dispersion stability of the specific particles.

[0141] (Step B3) Step B3 is a step of recovering a fluorocopolymer from the second aqueous dispersion B obtained in step B2. A solid fluorocopolymer can be obtained by aggregating particles of the second fluorocopolymer B from the second aqueous dispersion B. As the aggregation method, the methods listed in step A2 above can be used.

[0142] [Step of Preparing Fluorine-Containing Copolymer Composition] The step of preparing a fluorine-containing copolymer composition is a step of preparing a fluorine-containing copolymer composition containing the above-mentioned fluorine-containing copolymer. The fluorine-containing copolymer composition has the same meaning as the above-mentioned fluorine-containing copolymer composition, and the preferred embodiments are also the same. Examples of methods for preparing the fluorine-containing copolymer composition include a method of mixing the above-mentioned components contained in the fluorine-containing copolymer composition. The components can be mixed using a rubber mixing device such as a roll, kneader, Banbury mixer, or extruder. After obtaining a mixture of the above-mentioned components, the mixture may be molded. Specific examples of methods for molding the mixture include compression molding, injection molding, extrusion molding, calendar molding, or a method of dissolving the mixture in a solvent and dipping or coating it onto a substrate or the like to mold it.

[0143] [Step of crosslinking the fluorocopolymer] The step of crosslinking the fluorocopolymer is a step of crosslinking the fluorocopolymer using a fluorocopolymer composition. The method for crosslinking the fluorocopolymer is the same as the crosslinking method in the above-mentioned method for producing a crosslinked rubber article, and preferred embodiments are also the same.

[0144] [Fluorocopolymer composition] An example of a preferred embodiment of the present fluorine-containing copolymer composition is a fluorine-containing copolymer composition comprising a fluorine-containing copolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, and a crosslinking agent, wherein, when a crosslinked rubber article obtained using the fluorine-containing copolymer composition is subjected to measurement of 60° specular gloss at 10 different points on the surface of the crosslinked rubber article, the minimum value of the 60° specular gloss at 10 different points is from 1.0 to 50.0. The definition of each requirement in the preferred embodiment and preferred embodiments of those requirements are the same as those for the above-mentioned fluorine-containing copolymer composition.

[0145] [Method for producing crosslinked rubber article] One example of a preferred embodiment of the method for producing a crosslinked rubber article is a method for producing a crosslinked rubber article by molding a fluorocopolymer composition using a mold to produce a crosslinked rubber article, wherein the fluorocopolymer composition comprises a fluorocopolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, and a crosslinking agent, and is substantially free of an emulsifier, and the 60° specular gloss of the mold is 100.0 or more. The definitions of each requirement in the preferred embodiment and preferred embodiments of those requirements are the same as those in the method for producing a crosslinked rubber article described above.

[0146] The present disclosure will be described in detail below with reference to examples. Examples 1 to 3 are working examples, and Examples 4 and 5 are comparative examples. However, the present disclosure is not limited to these examples.

[0147] [Measurement and Evaluation Methods] [Water Content] Using the fluorocopolymer of each example described below, the water content was measured with a halogen moisture meter.

[0148] [Melting Point] A 5 mg sample of the fluorocopolymer of each example described below was weighed out and placed in an aluminum pan, and heated from 20°C to 360°C at a heating rate of 10°C / min in an air atmosphere using a Hitachi DSC600, to confirm the presence or absence of a melting peak.

[0149] [Average particle size of fluorocopolymer particles] The aqueous dispersion of each example described below was degassed at 25°C for 5 minutes, pressurized with nitrogen gas to 0.2 MPaG, purged, and returned to atmospheric pressure to obtain a measurement sample. The average particle size of the obtained measurement sample was measured using a dynamic light scattering particle size distribution measurement device (Otsuka Electronics Co., Ltd., ELSZ) with an accumulation number set to 100, and this was taken as the average particle size of the particles in each aqueous dispersion.

[0150] <Method for Measuring Emulsifiers Contained in Crosslinked Rubber Articles and Fluorocopolymer Compositions> (Preparation of Measurement Samples) The solid compositions obtained in each of the examples described below were freeze-pulverized using a freeze-pulverizer Freezer Mill 6775 (manufactured by SPEX) under the following conditions. Before freeze-pulverization, 10% by mass of dibutylhydroxytoluene (BHT) was added to the solid composition to obtain a pulverized powder. The freeze-pulverization conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 min, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 2.50 g of the resulting pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate the pulverized powder (fluoropolymer). The supernatant was used as the extract. The resulting extract was analyzed by LC / MS / MS. The fluorine-containing emulsifier and hydrocarbon emulsifier in the extract were measured using a liquid chromatograph mass spectrometer. The configuration of the measuring equipment and the LC-MS measurement conditions are shown in Table 1. Using aqueous solutions of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured with known concentrations, aqueous solutions with five or more levels of content were prepared, and LC / MS analysis was performed on the aqueous solutions with each content. The relationship between the content and the area relative to the content was plotted to draw a calibration curve. Using the calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing emulsifier and hydrocarbon emulsifier in the extract was converted into the content of the fluorine-containing emulsifier and hydrocarbon emulsifier.

[0151]

[0152] The MRM measurement parameters are appropriately selected depending on the structures of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured. Literature values ​​can be used for the MRM parameters, or they can be calculated using an LC-MS device. The specific procedure for determining the MRM parameters using an LC-MS device is as follows. Using an LC / MS device (Shimadzu Corporation, LCMS-8060NX), a search for product ions is selected, the molecular weights of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured are input, and precursor ions, precursor adjustment, voltage optimization, and product m / z optimization are performed. The calculated MRM measurement parameters are used. As examples of the measurement targets, the MRM measurement parameters for compounds (S2) and (S4), which are emulsifiers having fluorine atoms, are shown in the table. Note that in formulas (S2) and (S4), M Ｓ represents a hydrogen atom, a metal atom (Na, K), NR ４ (R may be the same or different and represents a hydrogen atom or an organic group having 1 to 10 carbon atoms), an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. F-(CF ２ ) ｎ１ -COOM Ｓ (S2) F-(CF ２ ) ｎ２ -SO ３ M Ｓ (S4) where n1 is an integer from 3 to 17, and n2 is an integer from 4 to 12.

[0153]

[0154]

[0155] (Quantitative Analysis of Fluorine Emulsifier and Hydrocarbon Emulsifier Contained in Solid Composition) Specifically, five levels of methanol standard solutions of the fluorine emulsifier and hydrocarbon emulsifier to be measured, each with known concentrations ranging from 1 to 180 ng / g, were prepared, and a was calculated from the sample concentration and peak integral value of each sample using a linear approximation according to formula (A1): A = a × X (A1), where A is the peak area of ​​each emulsifier, and X is the concentration (ng / g) of each emulsifier.

[0156] Subsequently, the amounts of the fluorine-containing emulsifier and hydrocarbon emulsifier contained in the above extracts (hereinafter also referred to as emulsifier amounts) were calculated using formula (A2). Note that a in formula (A2) means a determined by the above formula (A1). XCm = ACm / a (A2) XCm: content (ng / g) of emulsifier in each extract ACm: peak area of ​​emulsifier in each extract The quantitation limit in this measurement is 1 ng / g.

[0157] The content of the emulsifier in the composition relative to the total mass of the composition (ZCm) was calculated using the following formula (A3): ZCm = XCm × ρ1 × La / W1 (A3), where ZCm is the content of the emulsifier contained in the solid composition, ρ1 is the density of the extraction solvent (methanol in each example), La is the volume of the extraction solvent (5 mL in each example), and W1 is the mass of the sample used for extraction (2.5 g of solid composition in each example).

[0158] [Proportion of each unit in fluorine-containing copolymer] The proportion of each unit in each example of fluorine-containing copolymer described later is １９ It was determined by F-NMR analysis and infrared absorption spectrum analysis.

[0159] [Heterocyclic structure in crosslinked product of fluorine-containing copolymer] The heterocyclic structure in the crosslinked product of the fluorine-containing copolymer in each example described below is １ The crosslinked fluorine-containing copolymers in Examples 1 to 3 had an oxazole ring and a triazine ring structure.

[0160] [60° Specular Gloss (Minimum X and Maximum Y)] The fluorine-containing copolymer composition of each example described below was filled into a mold (material: S55C, Cr-plated, 60° specular gloss: 155.0), and subjected to primary crosslinking and secondary crosslinking under the same conditions as those for the O-rings of each example described below. The resulting product was then cooled to 23°C to obtain a sheet (crosslinked rubber article) measuring 100 mm in length, 60 mm in width, and 1 mm in thickness. The 60° specular gloss of the resulting sheet was then measured using a Gloss Checker IG-410 (manufactured by HORIBA, Ltd.) with the range set to 1 to 100. The 60° specular gloss was measured at 10 different points on the sheet, and the maximum value Y, minimum value X, and the absolute values ​​of the maximum value Y and minimum value X were calculated from the measured values. The gloss of the mold was measured using a gloss checker IG-410 (manufactured by Horiba Ltd.) with the range set to 1 to 100, and the 60° specular gloss of the mold was measured.

[0161] [MH and ML] The fluorine-containing copolymer composition of each example described below was cut into 10 g pieces to obtain cut pieces. The obtained cut pieces were sandwiched between two polyester films (manufactured by ALFA Technologies, PART #F0311-S, 130 mm x 130 mm x 24 μm) on both sides of the main surface to obtain a measurement sample. The measurement sample was placed on a die, and the torque (dNm) was measured using a method in accordance with JIS K6296-1 under the following conditions: measurement device: PREMER RPA (manufactured by Alpha Technologies), die shape: D0380, 180°C (test temperature), 20 minutes (vulcanization time), 100 cpm, angle: 3.00 deg., and the torque-vulcanization time curve for the primary crosslink was obtained. From the obtained torque-vulcanization time curve, the minimum torque value (ML) and the maximum torque value (MH) were identified.

[0162] [High-Temperature Compression Set (CS)] The compression set was measured with reference to the method described in ASTM D395 or JIS K6262. An O-ring (original thickness (wire diameter) = 3.5 mm) prepared using the fluorine-containing copolymer composition of each example was compressed to a compression ratio of 18% using a compression device. Next, the compression device with the compressed O-ring fixed thereto was placed in an electric furnace and left at 300°C for 70 hours, after which the compression device was removed from the electric furnace, the O-ring was immediately removed from the compression device, and the removed O-ring was left in a thermostatic chamber at 23°C for 30 minutes, and the thickness of the O-ring (thickness after compression treatment) was measured. The test was performed using two O-rings, and the arithmetic average of the measured values ​​of the two O-rings was used. The compression set rate was calculated using the following formula, and the high-temperature compression set was evaluated according to the following evaluation criteria. The closer the compression set rate is to 0%, the smaller the compression set is, and therefore preferable. Compression set rate (%) = (original thickness (wire diameter) - thickness 30 minutes after removing the O-ring from the compression device (thickness after compression treatment) ÷ (original thickness of O-ring - thickness of spacer)) x 100 "A": Compression set rate is 15% or less "B": Compression set rate is more than 15%

[0163] [Cracks] After the measurement of the above-mentioned <Measurement of High-Temperature Compression Set>, the presence or absence of cracks was visually evaluated for each of the two O-rings.

[0164] [Example 1] Ultrapure water (1206 g), a 50 mass% aqueous solution of sodium 2-acrylamido-2-methyl-1-propanesulfonate (NaAAMPS, corresponding to Compound X) (10 μL), PMVE (82 g), and TFE (17 g) were added to a 2.2 L stainless steel pressure reactor, and the temperature was raised to 80°C while stirring at 600 rpm. The internal pressure of the reactor at 80°C was 1.4 MPaG. Next, an aqueous solution of ammonium persulfate (2.5 mass%, 7 g) was added to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the initiation of polymerization reached 8 g, 6 g of PMVE was injected. When the polymerization pressure decreased to 1.4 MPa, the stirring speed was reduced to 380 rpm, and CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF２ 3.4 g of CN (8CNVE) was added. Thereafter, while intermittently adding an aqueous ammonium persulfate solution, 12 g of PMVE was injected every time 16 g of TFE was injected. When the amount of TFE added after the initiation of polymerization reached 168 g, the addition of TFE and PMVE injected after the initiation of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was extracted to obtain a first aqueous dispersion A1. The total amount of ammonium persulfate added was 0.7 g. The total amount of monomers added before the initiation of polymerization was 17 g of TFE and 82 g of PMVE. The total amount of monomers added after the initiation of polymerization was 168 g of TFE and 108 g of PMVE. The total amount of TFE added was 185 g, and the total amount of PMVE added was 190 g. The first aqueous dispersion A1 was coagulated with a 5% by mass aqueous solution of nitric acid, and then filtered, and the obtained solid was washed with ultrapure water. Thereafter, it was vacuum dried at 100 ° C. for 12 hours to obtain a fluorine-containing copolymer A1 (solid composition). The obtained fluorine-containing copolymer A1 was analyzed by NMR, and the composition was PMVE / TFE / 8CNVE=31.8 / 67.7 / 0.5 (molar ratio). In addition, the fluorine-containing copolymer A1 had an average particle size of 124 nm and no melting point. The water content of the fluorine-containing copolymer A1 was 0.0% by mass.

[0165] Next, the components were mixed in the amounts shown in Table 4 and kneaded for 10 minutes at room temperature using a two-roll mill. The gap between the two roll mills was adjusted, and the resulting mixture was processed into a sheet having a thickness of 3 mm to obtain a fluorocopolymer composition 1 of Example 1.

[0166] Furthermore, fluorine-containing copolymer composition 1 was hot-pressed at 180°C for 20 minutes using a hydraulic press (model: SA-301 50T type, manufactured by Tester Sangyo Co., Ltd., ram diameter: 180 mm) to carry out primary crosslinking, thereby obtaining O-ring 1 (P-26 (standard defined in JIS B2401:2012)). Next, the obtained O-ring 1 was heated in an oven (DN411I, manufactured by Yamato Scientific Co., Ltd.) at 90°C for 2 hours under a nitrogen atmosphere, then heated to 200°C over 2 hours, heated at 200°C for 4 hours, further heated to 305°C over 2 hours, and heated at 305°C for 12 hours, thereby carrying out secondary crosslinking. Thereafter, the O-ring was cooled to 23°C to obtain the O-ring of Example 1, which was a crosslinked rubber article.

[0167] [Example 2] Ultrapure water (1206 g), a 50% by mass aqueous solution of NaAAMPS (30 μL), PMVE (81 g), and TFE (17 g) were added to a 2.2 L stainless steel pressure reactor, and the temperature was raised to 80 ° C. while stirring at 600 rpm. The pressure inside the reactor at 80 ° C. was 1.4 MPaG. Next, an aqueous solution of ammonium persulfate (2.5% by mass, 7 g) was added to initiate polymerization. As the pressure inside the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. This process was repeated, and 25 g of TFE was added. When the polymerization pressure decreased to 1.4 MPa, the stirring speed was reduced to 380 rpm, and 3.4 g of 8CNVE was added. Thereafter, while intermittently adding the aqueous solution of ammonium persulfate, 12 g of PMVE and 1.3 g of 8CNVE were injected every time 16 g of TFE was injected. When the amount of TFE added after the start of polymerization reached 185 g, the addition of TFE and PMVE injected after the start of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was extracted to obtain a first aqueous dispersion A2. The total amount of ammonium persulfate added was 0.7 g, and the total amount of 8CNVE added was 16.0 g. The total amounts of monomers added before the start of polymerization were 17 g of TFE and 81 g of PMVE. The total amounts of monomers added after the start of polymerization were 185 g of TFE and 108 g of PMVE. The total amount of TFE added was 202 g, and the total amount of PMVE added was 189 g. The first aqueous dispersion A2 was coagulated with a 5% by mass aqueous nitric acid solution, then filtered, and the resulting solid was washed with ultrapure water. Thereafter, the mixture was vacuum dried at 100°C for 12 hours to obtain a fluorine-containing copolymer A2 (solid composition). The obtained fluorine-containing copolymer A2 was analyzed by NMR, and as a result, the composition was PMVE / TFE / 8CNVE = 30.5 / 69.1 / 0.47 (molar ratio). Furthermore, the fluorine-containing copolymer A2 had an average particle size of 75nm and no melting point. The water content of the fluorine-containing copolymer A2 was 0.0% by mass.

[0168] Next, a fluorocopolymer composition 2 of Example 2 processed into a sheet having a thickness of 3 mm was obtained in the same procedure as in Example 1, except that the components were formulated in the amounts shown in Table 4, and an O-ring of Example 2 which was a crosslinked rubber article was obtained.

[0169] [Example 3] A fluorocopolymer composition 3 of Example 3 processed into a sheet shape having a thickness of 3 mm was obtained in the same procedure as in Example 1, except that the components were formulated in the amounts shown in Table 4, and an O-ring of Example 3 which was a crosslinked rubber article was obtained.

[0170] [Example 4] A 2.1 L stainless steel pressure reactor was charged with ultrapure water (1004 g), C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４A 30% by mass aqueous solution (80.1 g) of the compound, a 5% by mass aqueous solution (10.49 g) of disodium hydrogen phosphate dodecahydrate, 8CNVE (1.10 g), PMVE (55 g), and TFE (11 g) were added, and the temperature was raised to 80°C while stirring at 600 rpm. The internal pressure of the reactor at 80°C was 0.974 MPaG. Next, an aqueous ammonium persulfate solution (3.0% by mass, 18 g) was added to initiate polymerization. As the polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain the pressure constant. Thereafter, while intermittently adding the aqueous ammonium persulfate solution, 12 g of PMVE and 1.3 g of 8CNVE were injected every time 16 g of TFE was injected. When the amount of TFE added after the start of polymerization reached 408 g, the addition of TFE and PMVE injected after the start of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was extracted to obtain a first aqueous dispersion C1. The total amount of ammonium persulfate added was 0.72 g, and the total amount of 8CNVE added was 16.0 g. The total amount of monomers added before the start of polymerization was 17 g of TFE and 81 g of PMVE. The total amount of monomers added after the start of polymerization was 408 g of TFE and 294 g of PMVE. The total amount of TFE added was 425 g, and the total amount of PMVE added was 375 g. The first aqueous dispersion C1 was coagulated with a 5% by mass aqueous nitric acid solution and then filtered, and the obtained first fluorine-containing polymer C1 was washed with ultrapure water. Thereafter, it was vacuum dried at 100 ° C. for 12 hours. The obtained first fluorine-containing polymer C1 (solid composition) was analyzed by NMR, and as a result, it was found that the composition was PMVE / TFE / 8CNVE=30.5 / 69.0 / 0.5 (molar ratio). The first fluorine-containing polymer C1 did not have a melting point.

[0171] A fluorocopolymer composition 4 of Example 4 processed into a sheet shape having a thickness of 3 mm was obtained in the same procedure as in Example 1, except that the components were formulated in the amounts shown in Table 4, and an O-ring of Example 4 which was a crosslinked rubber article was obtained.

[0172] [Example 5] A fluorocopolymer composition 5 of Example 5 processed into a sheet shape having a thickness of 3 mm was obtained in the same procedure as in Example 4, except that the components were formulated in the amounts shown in Table 4, and an O-ring of Example 5 which was a crosslinked rubber article was obtained.

[0173] In the production of Examples 1 to 3, polymerization of the fluorine-containing copolymer was carried out under conditions in which neither an emulsifier having a fluorine atom nor an emulsifier having a fluorine atom was substantially present. Moreover, the aqueous dispersions obtained in Examples 1 to 3 did not substantially contain either an emulsifier having a fluorine atom or an emulsifier having a fluorine atom.

[0174] In the table, "MH - ML" indicates the value (dNm) obtained by subtracting ML from MH measured by the above-mentioned method. "Crack" indicates the evaluation result of cracks as described above, and indicates the number of cracks that occurred among the two measurement samples prepared. For example, "0 / 2" indicates that cracks occurred in 0 of the two measurement samples. "|Y - X|" indicates the absolute value of the value obtained by subtracting the minimum value X from the maximum value Y measured by the above-mentioned method.

[0175]

[0176] Carbon Black: MT Carbon N990, manufactured by Cancarb, carbon black. BOAP: crosslinking agent, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane.

[0177] It was confirmed that the crosslinked rubber article had excellent high-temperature compression set and was less susceptible to cracking. It was confirmed that no hydrocarbon emulsifier was detected in Examples 1 to 5, and that the amount of fluorine-containing emulsifier was very small in Examples 1 to 3.

[0178] The disclosure of Japanese Patent Application No. 2024-098631, filed on June 19, 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. A crosslinked rubber article comprising a crosslinked product of a fluorine-containing copolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, wherein, when the 60° specular gloss of the surface of the crosslinked rubber article is measured at 10 different points, the minimum value of the 60° specular gloss of the 10 different points is 1.0 to 50.

0.

2. The crosslinked rubber article of claim 1, further comprising a filler.

3. The crosslinked rubber article according to claim 2, wherein the content of said filler is 30 parts by mass or less per 100 parts by mass of said crosslinked fluorine-containing copolymer.

4. The crosslinked rubber article according to claim 1, wherein the absolute difference between the minimum value and the maximum value among the 10 different 60° specular gloss values ​​is more than 0.1 and not more than 20.

0.

5. The crosslinked rubber article according to claim 1, wherein the crosslinked product has at least one of an oxazole structure and a triazine structure.

6. The crosslinked rubber article according to claim 1, wherein said fluorine-containing copolymer further has units based on perfluoro(alkyl vinyl ether).

7. The crosslinked rubber article of claim 1, which is substantially free of emulsifiers.

8. A fluorine-containing copolymer composition comprising a fluorine-containing copolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, and a crosslinking agent, wherein a crosslinked rubber article obtained using the fluorine-containing copolymer composition has a 60° specular gloss measured at 10 different points on the surface of the crosslinked rubber article, and the minimum value of the 60° specular gloss measured at the 10 different points is 1.0 to 50.

0.

9. The fluorine-containing copolymer composition according to claim 8, further comprising a filler.

10. The fluorine-containing copolymer composition according to claim 9, wherein the content of said filler is 30 parts by mass or less per 100 parts by mass of said fluorine-containing copolymer.

11. The fluorine-containing copolymer composition according to claim 8, wherein said crosslinking agent comprises a compound having two amino groups.

12. The fluorine-containing copolymer composition according to claim 8, wherein said fluorine-containing copolymer further has units based on perfluoro(alkyl vinyl ether).

13. The fluorine-containing copolymer composition according to claim 8, wherein the content of said crosslinking agent is 0.1 to 10 parts by mass per 100 parts by mass of said fluorine-containing copolymer.

14. The fluorine-containing copolymer composition according to claim 8, which is substantially free of emulsifiers.

15. A method for producing a crosslinked rubber article, comprising molding a fluorocopolymer composition using a mold to produce a crosslinked rubber article, wherein the fluorocopolymer composition comprises a fluorocopolymer having units based on a monomer having a nitrile group and units based on tetrafluoroethylene, and a crosslinking agent, and is substantially free of an emulsifier, and the 60° specular gloss of the mold is 100.0 or more.

16. A method for producing a crosslinked rubber article according to claim 15, further comprising a step of producing the fluorine-containing copolymer, wherein the step of producing the fluorine-containing copolymer comprises polymerizing a monomer having a nitrile group and a first monomer containing tetrafluoroethylene in the presence of a compound represented by formula (X) and a polymerization initiator in the presence of an aqueous medium and in the substantial absence of an emulsifier having a fluorine atom, to produce an aqueous dispersion containing particles of the fluorine-containing copolymer having an average particle size of 500 nm or less and no melting point, and recovering the fluorine-containing copolymer from the aqueous dispersion. C(X １ ) (X ２ ) = C(X ３ ) CONH-R-Z (X) In formula (X), １ , X ２ and X ３ are each independently a hydrogen atom, a fluorine atom, a perfluoromethyl group or an alkyl group, R is an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms, Z is -SO ３ M, -OSO ３ M, -P (=O) (OM) ２ , -OP(=O)(OM) ２ or -COOM, where M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ When a plurality of M's are present, the plurality of M's may be the same or different from each other, R Ｍ１ and R Ｍ２ are each independently a hydrogen atom or a substituent, and R Ｍ１ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ１ may be the same or different from each other, R Ｍ２ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ２ may be the same or different from each other.

17. The method for producing a crosslinked rubber article according to claim 16, wherein the content of the compound represented by formula (X) is 1.0 to 1,000 ppm by mass relative to the total mass of the aqueous medium.

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