Perfluoroelastomer, composition, crosslinked rubber article, and method for producing perfluoroelastomer

Abstract

A perfluoroelastomer according to the present disclosure satisfies requirement 1 and has a crosslinkable group. Requirement 1: When the perfluoroelastomer is heated in a nitrogen atmosphere from a starting temperature of 40°C at a heating rate of 10°C / min from 40°C to 90°C, then held at 90°C for 120 minutes, then heated at a heating rate of 1°C / min from 90°C to 200°C, then held at 200°C for 240 minutes, then heated at a heating rate of 1°C / min from 200°C to 305°C, and held at 305°C for 720 minutes, the weight loss is 1.8 mass% or less.

Description

Perfluoroelastomer, composition, crosslinked rubber article, and method for producing perfluoroelastomer

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

[0002] Crosslinked rubber articles obtained by crosslinking a composition containing a 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 fluorine-containing elastomer molded article having a surface with a centerline average roughness Ra of 0.65 μm or more.

[0003] International Publication No. 2001 / 079337

[0004] The performance required for crosslinked rubber articles includes a small compression set. In addition, in terms of the performance and production efficiency of the crosslinked rubber articles, the perfluoroelastomer for producing the crosslinked rubber articles is also required to have a low maximum torque (MH) during primary crosslinking. Based on the above requirement, the present inventors have studied the physical properties of perfluoroelastomers with reference to Patent Document 1, and have found that there is room for improvement in the MH during primary crosslinking of the perfluoroelastomer and the compression set of the resulting crosslinked rubber articles.

[0005] The present disclosure has been made in view of the above problems, and aims to provide a perfluoroelastomer that can be used to produce crosslinked rubber articles with small compression set and that has a low MH during primary crosslinking. The present disclosure also aims to provide a composition related to the perfluoroelastomer, a crosslinked rubber article, and a method for producing the perfluoroelastomer.

[0006] As a result of intensive research into the above-mentioned problems, the present inventors have discovered that if a perfluoroelastomer has a weight loss rate of a predetermined value or less when heated under predetermined conditions, it is possible to produce a crosslinked rubber article with a small compression set and a low MH during primary crosslinking, and have arrived at the present disclosure.

[0007] That is, the inventors have found that the above-mentioned problems can be solved by the following configuration. [1] A perfluoroelastomer that satisfies Requirement 1 and has a crosslinkable group. (Requirement 1) In a nitrogen atmosphere, starting at a temperature of 40°C, the temperature is increased from 40°C to 90°C at a heating rate of 10°C / min, then held at 90°C for 120 minutes, then increased from 90°C to 200°C at a heating rate of 1°C / min, then held at 200°C for 240 minutes, then increased from 200°C to 305°C at a heating rate of 1°C / min, and held at 305°C for 720 minutes, with a weight loss rate of 1.8% by mass or less. [2] The perfluoroelastomer according to [1], which has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). [3] The perfluoroelastomer according to [1] or [2], which has units based on a monomer having a nitrile group. [4] The perfluoroelastomer according to [3], wherein the content of units based on the monomer having a nitrile group is 0.2 to 3.0 mol % based on the total content of all units in the perfluoroelastomer. [5] The perfluoroelastomer according to any one of [1] to [4], which is substantially free of an emulsifier. [6] A composition comprising the perfluoroelastomer according to any one of [1] to [5] and a crosslinking agent. [7] The composition according to [6], wherein the metal content is 50 ppm by mass or less based on the total solid content of the composition. [8] A crosslinked rubber article obtained by crosslinking the composition according to [6] or [7]. [9] A method for producing a perfluoroelastomer, comprising: polymerizing 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 substantially in the absence of an emulsifier having a fluorine atom, to produce an aqueous dispersion containing particles of a first fluorine-containing polymer having an average particle size of 500 nm or less and no melting point; and polymerizing a second monomer containing a monomer having a nitrile group in the aqueous dispersion to produce a perfluoroelastomer.

[0008] According to the present disclosure, it is possible to provide a perfluoroelastomer that can be used to produce a crosslinked rubber article with a small compression set and that has a low MH at the time of primary crosslinking. The present disclosure also provides a composition related to the perfluoroelastomer, a crosslinked rubber article, and a method for producing the perfluoroelastomer.

[0009] 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 polymer is determined by analyzing the polymer by solid-state nuclear magnetic resonance spectroscopy (NMR), and usually, the content of each unit calculated from the amount of each monomer charged substantially coincides with the actual content of each unit.

[0010] [Perfluoroelastomer] The perfluoroelastomer of the present disclosure (hereinafter also referred to as "the present elastomer") satisfies Requirement 1 described below and has crosslinkable groups. The present elastomer can produce crosslinked rubber articles with small compression set and has a low MH during primary crosslinking. Although the details of the reason for this are unknown, it is believed that perfluoroelastomers that satisfy Requirement 1 have a small amount of low-molecular-weight components that can be removed by heating, and that decomposition of high-molecular-weight components due to heating is also suppressed. It is presumed that perfluoroelastomers that satisfy Requirement 1 have a low MH because the reaction rate of the solid-phase reaction during primary crosslinking is reduced due to the small amount of low-molecular-weight components that contribute to the dispersibility of the polymer and crosslinking agent. On the other hand, it is presumed that decomposition of the polymer due to thermal crosslinking during the production of crosslinked rubber articles is also suppressed, so that physical crosslinks in the resulting crosslinked rubber articles are maintained, resulting in a small compression set. To obtain a crosslinked rubber article with a small compression set, a perfluoroelastomer with a high MH at the time of primary crosslinking tends to be required, but the present elastomer has a low MH at the time of primary crosslinking to obtain a crosslinked rubber article with the desired compression set. This means that the compositional range of the amount of crosslinking agent added and the like can be secured when producing a crosslinked rubber article, i.e., the process window is wide, which is advantageous in terms of the performance and production efficiency of the crosslinked rubber article.

[0011] [Requirement 1] The present elastomer satisfies Requirement 1. (Requirement 1) In a nitrogen atmosphere, starting at a temperature of 40°C, the elastomer is heated from 40°C to 90°C at a heating rate of 10°C / min, then held at 90°C for 120 minutes, then heated from 90°C to 200°C at a heating rate of 1°C / min, held at 200°C for 240 minutes, then heated from 200°C to 305°C at a heating rate of 1°C / min, and held at 305°C for 720 minutes. The weight loss rate is 1.8% by mass or less. In other words, the weight loss rate after successively carrying out the heating steps 1 to 6 below is 1.8% by mass or less. Starting temperature: 40°C Atmosphere: Nitrogen atmosphere Step 1: Heat from 40°C to 90°C at a heating rate of 10°C / min Step 2: Hold at 90°C for 120 minutes Step 3: Heat from 90°C to 200°C at a heating rate of 1°C / min Step 4: Hold at 200°C for 240 minutes Step 5: Heat from 200°C to 305°C at a heating rate of 1°C / min Step 6: Hold at 305°C for 720 minutes

[0012] The weight loss rate is measured by thermogravimetric analysis using the above-mentioned condition profile. Specifically, a perfluoroelastomer sample set to 40°C is heated using the above-mentioned profile while thermogravimetric analysis is performed to measure the weight change of the sample. The weight loss rate is calculated from the weight of the sample before heating (immediately before step 1) and after heating (after step 6). An example of an apparatus used for thermogravimetric analysis is a differential thermal thermogravimetric analyzer "NEXTA STA Series STA200" (manufactured by Hitachi High-Tech Corporation). The sample used is a perfluoroelastomer with a water content of 0.5% by mass or less. The water content of the sample is preferably 0.3% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0% by mass. The water content of the perfluoroelastomer can be adjusted by drying. Drying methods include heating, reduced pressure, and a combination of these. When drying the perfluoroelastomer by heating, the heating temperature is preferably 250°C or lower, more preferably 200°C or lower, and even more preferably 150°C or lower. From the viewpoint of drying efficiency, the heating temperature is preferably 60°C or higher. The heating time can be adjusted appropriately depending on the moisture content of the sample, and is preferably 480 to 900 minutes. The moisture content of the sample can be measured using a moisture meter (e.g., a halogen moisture meter). A more specific method for measuring the weight loss rate is as described in the Examples below.

[0013] The weight loss rate is preferably 1.5% by mass or less, more preferably 1.3% by mass or less, from the viewpoint of achieving superior effects of the present disclosure. The lower limit is 0% by mass, and may be 0.1% by mass or more. To suppress the generation of substances that cause weight loss, it is preferable to produce a perfluoroelastomer by polymerizing monomers in an aqueous medium. The aqueous medium may or may not contain an emulsifier. Methods for suppressing the weight loss rate include, for example, adjusting the amount of polymerization initiator used during polymerization and the polymerization pressure. This suppresses the generation of substances that cause weight loss. Since residual emulsifier in the perfluoroelastomer can cause weight loss, it is also preferable that the perfluoroelastomer obtained by polymerization is substantially free of emulsifier. To reduce the amount of emulsifier, it is also preferable to polymerize the monomers under conditions substantially free of emulsifier. More specifically, a perfluoroelastomer can be synthesized under conditions substantially free of emulsifier by polymerizing monomers in an aqueous medium in the presence of Compound X, which will be described later. Specific details of this method will be described later. The phrase "the elastomer is substantially free of emulsifiers" means that the content of emulsifiers is 10 ppm by mass or less, more 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 elastomer. The lower limit is 0 ppb by mass.

[0014] [Composition] In the present disclosure, a "perfluoroelastomer" refers to a perfluoropolymer having a glass transition temperature of 20°C or less, a melting peak (ΔH) of 4.5 J / g or less, and a fluorine atom content of 65% by mass or more. Here, "perfluoropolymer" refers to a polymer that is substantially free of hydrogen atoms bonded to carbon atoms, has fluorine atoms in place of those hydrogen atoms, and has a main chain consisting of a chain of carbon atoms. The side chain of the perfluoropolymer may contain a polyvalent atom other than carbon atoms, and oxygen atoms are preferred as the polyvalent atom. Here, "substantially free of hydrogen atoms" means that the hydrogen atom content 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 is 0% by mass. When the hydrogen atom content is within the above range, good heat resistance or chemical resistance is likely to be obtained. The composition of this elastomer will be described below.

[0015] The present elastomer preferably contains units based on tetrafluoroethylene (hereinafter also referred to as "TFE"), and more preferably contains units based on TFE and units based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"). Hereinafter, the units based on TFE will also be referred to as "TFE units," and the units based on PAVE will also be referred to as "PAVE units."

[0016] The PAVE from which the PAVE units are derived is preferably a monomer represented by formula (1) in terms of more efficient production of the present elastomer. 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.

[0017] 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 present elastomer.

[0018] 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. 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. The total content of TFE units and PAVE units is preferably 50.0 to 99.95 mol%, more preferably 70.0 to 99.9 mol%, and even more preferably 75.0 to 99.7 mol%, based on the total content of all units in the elastomer.

[0019] 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 all units in the elastomer. 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 all units in the elastomer.

[0020] The present elastomer has a crosslinkable group. The crosslinkable group is not particularly limited as long as it is a functional group capable of crosslinking through a crosslinking reaction. Specific examples include a nitrile group, a polymerizable unsaturated bond, a chlorine atom, a bromine atom, and an iodine atom, with a nitrile group being preferred. The present elastomer preferably has the crosslinkable group at at least one of the terminal and the side chain, more preferably at the side chain. During production of the present elastomer, a crosslinkable group can be introduced into the side chain by polymerizing a monomer having a crosslinkable group. Furthermore, during polymerization, a crosslinkable group can be introduced into the terminal by polymerizing a monomer using a chain transfer agent having a crosslinkable group. The present elastomer preferably has units based on a monomer having a crosslinkable group, more preferably a monomer having a nitrile group.

[0021] The monomer having a crosslinkable group may be a monomer having a nitrile group (hereinafter referred to as "R ＣＮ "), 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) (hereinafter also referred to as "POAVE"), which will be described later, ＣＮ is preferred.

[0022] R ＣＮ From the viewpoint of polymerization reactivity, it is preferable that the copolymer has a polymerizable unsaturated bond, and more preferably has one polymerizable unsaturated bond. Specific examples of the polymerizable unsaturated bond include a carbon-carbon double bond (C═C) and a carbon-carbon triple bond (C≡C).

[0023] R ＣＮ is 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 ５３each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R ５４ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms. 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 particularly preferred that all of R are fluorine atoms. ５４ R may be linear, branched, or cyclic, and is preferably linear or branched. ５４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5. ５４ R may or may not have an etheric oxygen atom, but preferably has an etheric oxygen atom in order to obtain better rubber properties. ５４ The number of etheric oxygen atoms in the formula (5) is preferably 1 to 3, and particularly preferably 1 or 2. Specific examples of the monomer represented by formula (5) include CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CN (hereinafter also referred to as "8CNVE"), CF ２ = CFO (CF ２ ) ５ CN (hereinafter also referred to as "MV5CN"), CF ２ = CFOCF ２ CF ２ CF ２ OCF (CF ３ ) CN and CF ２ = CFO (CF ２ ) ３CN is exemplified, and 8CNVE or MV5CN is preferred in that the crosslinked rubber article has better mold releasability and heat resistance.

[0024] 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.

[0025] BO is preferably a monomer represented by formula (2) in view of better releasability of the crosslinked rubber article. ２１ R ２２ =CR ２３ -) ａ１ R ２４ (2) In formula (2), R ２１ , R ２２ , and R ２３ each independently represents a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group; a1 represents an integer of 2 to 6; R ２４ represents an a1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of an a1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms. ２１ , multiple R ２２ and multiple R ２３ may be the same or different, and are particularly preferably the same. a1 is preferably 2 or 3, and particularly preferably 2. In view of better polymerization reactivity of BO, R ２１ , R ２２ , and R ２３ is preferably a fluorine atom or a hydrogen atom, and R ２１ , R ２２ , and R ２３ are more preferably all fluorine atoms or all hydrogen atoms, and in view of better mold releasability of the crosslinked rubber article, R ２１ , R２２ , and R ２３ It is particularly preferred that all of R are fluorine atoms. ２４ R may be linear, branched, or cyclic, preferably linear or branched, and particularly preferably linear. ２４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5. ２４ Although R may or may not have an etheric oxygen atom, it is preferable that R has an etheric oxygen atom in view of better crosslinking reactivity and rubber physical properties. ２４ The number of etheric oxygen atoms in R is preferably 1 to 6, more preferably 1 to 3, and 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.

[0026] 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).

[0027] (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.

[0028] (CH ２ =CH-) ２ R ４１ (4) In formula (4), R ４１ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms.

[0029] 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 、CF ２ =CFO (CF ２ ) ４ OCF = CF ２ 、CF ２ =CFO (CF ２ ) ６ OCF = CF ２、 CF ２ =CFO (CF ２ ) ８ OCF = CF ２ 、CF ２ =CFO (CF ２ ) ２ OCF (CF ３ ) CF ２ OCF = CF ２ 、CF ２ =CFO (CF ２ ) ２ O (CF (CF ３ ) CF ２ O) ２ CF = CF ２ 、CF ２ =CFO CF ２ O (CF ２ CF ２ O) ２ CF = CF ２ 、CF ２ =CFO (CF ２ O) ３ O (CF (CF ３ ) CF ２ O) ２ CF = CF ２ 、CF ２ =CFO CF ２ CF (CF ３ ) O (CF ２ ) ２ OCF (CF ３ ) CF ２ OCF = CF ２ 、及び、CF ２ =CFO CF ２ CF ２ O (CF ２ O) ２ CF ２ CF ２ OCF = CF ２Among the monomers represented by formula (3), a more preferred specific example of the monomer is CF ２ = CFO (CF ２ ) ３ OCF = CF ２ (hereinafter also referred to as "C3DVE"), and CF ２ = CFO (CF ２ ) ４ OCF = CF ２ (hereinafter also referred to as "C4DVE").

[0030] 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.

[0031] 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 OCF ２ CF ２Br, bromotrifluoroethylene, 4-bromo-3,3,4,4-tetrafluorobutene-1 (BTFB), vinyl bromide, 1-bromo-2,2-difluoroethylene, perfluoroallyl bromide, 4-bromo-1,1,2-trifluorobutene-1, 4-bromo-1,1,3,3,4,4-hexafluorobutene, 4-bromo-3-chloro-1,1,3,4,4-pentafluorobutene, 6-bromo-5,5,6,6-tetrafluorohexene, and 4-bromoperfluorobutene-1,3,3-difluoroallyl bromide. Also included are 2-bromo-perfluoroethyl perfluorovinyl ether and CF ２ Br-R ｆ -O-CF=CF ２ (R ｆ is a perfluoroalkylene group), for example, CF ２ BrCF ２ O-CF=CF ２ , ROCF = CFBr, and ROCBr = CF ２ (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(CF ３ )CF ２ O]ｎ CF = CF ２ (wherein n = 1 to 3) and the like. Also included are iodoethylene, 4-iodo-3,3,4,4-tetrafluorobutene-1 (ITFB), 3-chloro-4-iodo-3,4,4-trifluorobutene, 2-iodo-1,1,2,2-tetrafluoro-1-(vinyloxy)ethane, 2-iodo-1-(perfluorovinyloxy)-1,1,-2,2-tetrafluoroethylene, 1,1,2,3,3,3-hexafluoro-2-iodo-1-(perfluorovinyloxy)propane, 2-iodoethyl vinyl ether, 3,3,4,5,5,5-hexafluoro-4-iodopentene, and iodotrifluoroethylene, as disclosed in U.S. Pat. No. 4,694,045. Also included are allyl iodide and 2-iodo-perfluoroethyl perfluorovinyl ether.

[0032] 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.

[0033] 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.

[0034] Specific examples of POAVE include the following. The abbreviation for the compound is given in parentheses after the formula. CF２ =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.

[0035] The content of units based on a monomer having a crosslinkable group is preferably 0.01 to 20.0 mol %, more preferably 0.01 to 15.0 mol %, still more preferably 0.03 to 10.0 mol %, and particularly preferably 0.2 to 3.0 mol %, based on the total content of all units in the present elastomer. ＣＮ The content of units based on the formula (I) is preferably 0.01 to 10.0 mol %, more preferably 0.05 to 10.0 mol %, still more preferably 0.1 to 5.0 mol %, and particularly preferably 0.2 to 3.0 mol %, based on the total content of all units in the elastomer.

[0036] The perfluoroelastomer may have units other than TFE units, PAVE units, and units based on a monomer having a crosslinkable group. "Substantially free of other units" means that the content of other units is 0.01 mol% or less, preferably 0 mol%, based on the total content of all units in the elastomer.

[0037] [Method for producing perfluoroelastomer] As a method for producing the present elastomer, for example, a method of copolymerizing a monomer containing at least one of TFE and PAVE with a monomer having a crosslinkable group in the presence of a polymerization initiator can be mentioned. The polymerization method can be, for example, emulsion polymerization, solution polymerization, and suspension polymerization, and polymerization in an aqueous medium is preferred from the viewpoint of easy adjustment of molecular weight and copolymerization composition and excellent productivity. When producing a fluorine-containing polymer in an aqueous medium, it can be carried out by heating the above-mentioned monomer in the presence of an aqueous medium and a polymerization initiator. The aqueous medium may or may not contain an emulsifier.

[0038] A first preferred embodiment of the method for producing the present elastomer includes a method (hereinafter also referred to as "production method A") in which a first monomer A containing TFE and a monomer having a crosslinkable group is polymerized using a compound represented by formula (X) described below (hereinafter also referred to as "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 to produce an aqueous dispersion containing first fluorine-containing polymer particles having an average particle size of 500 nm or less (hereinafter also referred to as "first aqueous dispersion A"), and the present elastomer is recovered from the first aqueous dispersion A. Hereinafter, in production method A, the step of producing first aqueous dispersion A will be also referred to as "step A1", and the step of recovering the present elastomer from first aqueous dispersion A will be also referred to as "step A2".

[0039]

[0033] A second preferred embodiment of the method for producing the present elastomer includes a method (hereinafter also referred to as "production method B") in which a first monomer B containing TFE is polymerized using a compound 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 a first fluoropolymer B having an average particle size of 500 nm or less (hereinafter also referred to as "first aqueous dispersion B"); a second monomer B containing a monomer having a crosslinkable group is polymerized in the first aqueous dispersion B to produce a second aqueous dispersion B containing a second fluoropolymer B; and the present elastomer is recovered from the second aqueous dispersion B. Hereinafter, in production method B, the step of producing the first aqueous dispersion B will be referred to as "step B1," the step of producing the second aqueous dispersion B will be referred to as "step B2," and the step of recovering the present elastomer from the second aqueous dispersion B will be referred to as "step B3." Each step will be described in detail below.

[0040] <Production method A> (Step A1) In step A1, a first monomer A containing TFE and a monomer having a crosslinkable group is polymerized in the presence of a compound represented by formula (X) described below (hereinafter also referred to as "compound X") and a polymerization initiator in the presence of an aqueous medium and substantially in the absence of an emulsifier having a fluorine atom, to synthesize a first fluorine-containing polymer A and obtain a first aqueous dispersion A. This suppresses a decrease in the molecular weight of the polymer produced, making it easy to obtain the present elastomer.

[0041] -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 0 ppb by mass. The contents 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 mentioned.

[0042] 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 mentioned above. The water-soluble emulsifier may be either ionic or nonionic. Examples of the emulsifier include those having no carbon-carbon double bond. Compound X, the first fluorine-containing polymer, and the present elastomer (second fluorine-containing polymer) described below do not fall under the category of emulsifiers.

[0043] 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.

[0044] 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.

[0045] The emulsifiers having no fluorine atoms include anionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0046] 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.

[0047] 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.

[0048] Further, other nonionic hydrocarbon emulsifiers include those described in paragraphs

[0043] to

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

[0049] 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.).

[0050] 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 units based on a compound having a polymerization-reactive site 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.

[0051] -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.

[0052] 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.

[0053] Compound X Compound X is a compound represented by formula (X). Compound X can be polymerized with a monomer described below.

[0054] 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.

[0055] 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 ３As the alkyl group, a fluorine atom or a hydrogen atom is preferred, and a hydrogen atom is preferred in terms of excellent polymerization reactivity.

[0056] 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.

[0057] 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.

[0058] M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ and R Ｍ１ and R Ｍ２ are 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.

[0059] 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. Examples of the metal salts include metal salts of the metal atom represented by M. As the compound X, a (meth)acrylamide having a sulfonic acid group or a metal salt thereof is preferred, and 2-acrylamido-2-methyl-1-propanesulfonic acid, 6-acrylamidohexanoic acid, 2-methacrylamido-2-methylpropylsulfonic acid, or a sodium salt or ammonium salt thereof is preferred. Note that the above-mentioned "(meth)acrylamide" is a concept that encompasses both acrylamide and methacrylamide.

[0060] Before the start of polymerization of the first monomer A, the content of the compound X is preferably 1.0 to 1000 ppm by mass, and in terms of achieving better effects of the present disclosure, is more preferably 1.0 to 500 ppm by mass, still more preferably 1.0 to 100 ppm by mass, and particularly preferably 1.0 to 30.0 ppm by mass, relative to the total mass of the aqueous medium.

[0061] -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.

[0062] The amount of the polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, per 100 parts by mass of the first monomer used.

[0063] -First Monomer A- The first monomer A contains TFE and a monomer having a crosslinkable group. 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 25.0 to 50.0 mol %, based on the amount of the first monomer A used. Examples of the monomer having a crosslinkable group include the monomer having a crosslinkable group described above in the composition of the perfluoroelastomer, and R ＣＮ A monomer having a crosslinkable group (preferably R ＣＮ The amount of the first monomer A used is preferably 0.01 to 20.0 mol %, more preferably 0.01 to 15.0 mol %, still more preferably 0.03 to 10.0 mol %, and particularly preferably 0.2 to 3.0 mol %, based on the amount of the first monomer A used.

[0064] The first monomer preferably contains PAVE. Details of PAVE are as described above. The amount of PAVE (preferably PMVE) used 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%, relative to the amount of first monomer A used. The total amount of TFE and PAVE used is preferably 60.0 mol% or more and less than 100.0 mol%, more preferably 70.0 to 99.9 mol%, and even more preferably 75.0 to 99.8 mol%, relative to the amount of first monomer A used.

[0065] The first monomer A may contain a monomer other than TFE, PAVE, and a monomer having a crosslinkable group.

[0066] -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.

[0067] Polymerization of the first monomer A gives a first fluoropolymer A (corresponding to the present elastomer) dispersed in the form of particles in an aqueous medium. The aqueous dispersion thus obtained in which particles of the first fluoropolymer 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 dispersing particles of the first fluoropolymer A in another aqueous medium by solvent substitution.

[0068] The first monomer A is added to the reactor by a conventional method. For example, the first monomer A may be added continuously or intermittently to 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 added continuously or intermittently to the reactor. Different monomers of the first monomer A may be added to the reactor at the same time, or may be added at different times. For example, TFE and PAVE may be added to the reactor in advance, and polymerization may be initiated, followed by addition of TFE, PAVE, and a monomer having a crosslinkable group. 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.

[0069] 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 700 minutes.

[0070] - First Aqueous Dispersion A - In step A1, a first aqueous dispersion A is obtained, which is an aqueous dispersion containing particles of a first fluoropolymer A having an average particle size of 500 nm or less.

[0071] Preferably, the first aqueous dispersion A is substantially free of a water-soluble emulsifier. The phrase "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. The lower limit is 0 mass ppb.

[0072] Furthermore, it is preferable that the first aqueous dispersion A is substantially free of a compound represented by any one of formulas (S1) to (S4). "Substantially free of a compound represented by any one of formulas (S1) to (S4)" means that the content of each of the compounds represented by 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. The lower limit is 0 mass ppb.

[0073] 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.

[0074] The content of the particles of the first fluorine-containing polymer A is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 10 to 30% by 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% by mass, more preferably 10 to 45% by mass, and even more preferably 10 to 30% by 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)"

[0075] -First Fluorine-Containing Polymer A- Particles of the first fluorine-containing polymer A are particles produced in step A1. The average particle size of the particles of the first fluorine-containing polymer A is 500 nm or less, and from the viewpoint of further reducing the weight loss rate in requirement 1 and achieving better effects of the present disclosure, 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 A is a particle size calculated by analyzing an autocorrelation function obtained by dynamic light scattering using the monodisperse cumulant method.

[0076] The number of particles of the first fluoropolymer A is 1.0 × 10 １３ Preferably, the number of particles / mL or more is 1.0 x 10 １４ More preferably, 2.0 × 10 １４The upper limit is 2.0 × 10 １５ The particle number of the first fluoropolymer 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.

[0077] The first fluorine-containing polymer 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 category of the above-mentioned melting peak. Specific methods for measuring the melting point include the measurement methods shown in the Examples section.

[0078] The first fluoropolymer A has units based on the first monomer A. The TFE units preferably account for 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 units of the first fluoropolymer A. The first fluoropolymer A has units derived from a monomer having a crosslinkable group (preferably R ＣＮ units) is preferably 0.01 to 20.0 mol%, more preferably 0.01 to 15.0 mol%, still more preferably 0.03 to 10.0 mol%, and particularly preferably 0.2 to 3.0 mol%, based on all units of the first fluoropolymer A. PAVE units (preferably PMVE units) are preferably 20.0 to 95.0 mol%, more preferably 25.0 to 80.0 mol%, and still more preferably 25.0 to 50.0 mol%, based on all units of the first fluoropolymer A. The total amount of TFE units and PAVE units (preferably PMVE units) is preferably 50.0 to 99.99 mol%, more preferably 70.0 to 99.9 mol%, and still more preferably 75 to 99.8 mol%, based on all units of the first fluoropolymer A.

[0079] (Step A2) Step A2 is a step of recovering the present elastomer from the first aqueous dispersion A obtained in step A1. By agglomerating the particles of the first fluoropolymer A from the first aqueous dispersion A, the present elastomer can be obtained in solid form.

[0080] Aggregation methods include, but are not limited to, freeze aggregation, acid aggregation, base aggregation, mechanical aggregation, and aggregation using a coagulant. In the case of freeze aggregation, the aggregation temperature is preferably -20 to 0°C. The aggregation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid aggregation, a method in which a solution containing an acid is added to the second aqueous dispersion is preferred. Examples of acids to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, hydrofluoric acid, etc., with nitric acid being preferred. The concentration of the acid in the acid-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. In the case of base aggregation, a method in which a solution containing a base is added to the second aqueous dispersion is preferred. Examples of bases to be added include sodium hydroxide, potassium hydroxide, ammonium carbonate, etc., with sodium hydroxide being preferred. The concentration of the base in the base-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. For aggregation using a coagulant, known coagulants can be used. Known coagulants include aluminum salts, calcium salts, and magnesium salts. Specific examples include aluminum sulfate, a compound of the general formula M'Al(SO ４ ) ２ ・12H 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.

[0081] <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.

[0082] -First Monomer B- The first monomer B includes TFE. The first monomer B may include a monomer other than 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 %, based on the amount of the first monomer B used.

[0083] 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 amount of the first monomer B used. The total amount of TFE units and PAVE units (preferably PMVE units) 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 amount of the first monomer B used.

[0084] The first monomer B may contain other monomers in addition to TFE and PAVE.

[0085] -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 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 "substantially no emulsifier" and "substantially no compound represented by any of formulas (S1) to (S4)" in the first aqueous dispersion B are the same as those for the first aqueous dispersion A described above.

[0086] The solid content 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 solid content concentration of the first aqueous dispersion B can be measured, for example, by the following method. The solid content 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 solid content concentration using the following formula: "Solid content concentration (mass %) = 100 × heating residue of first aqueous dispersion B (g) / mass of first aqueous dispersion B (2.0 g)"

[0087] 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.

[0088] -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 polymer 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.

[0089] The number of particles of the first fluorinated polymer B is 1.0 × 10 １３ Preferably, the number of particles / mL or more is 1.0 x 10 １４ More preferably, 2.0 × 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.

[0090] The first fluorine-containing polymer B preferably does not have a melting point.

[0091] 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.

[0092] 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. "Substantially free of other units" means that the content of other monomers is 0.01 mol% or less, based on all units of the first fluoropolymer B, and is preferably 0 mol%.

[0093] (Step B2) Step B2 is a step of polymerizing a second monomer B containing a monomer having a crosslinkable group in the first aqueous dispersion B obtained in step B1 to obtain a second aqueous dispersion B containing a second fluorine-containing polymer B.

[0094] Suitable embodiments of the first aqueous dispersion B are as described above. It is preferable to use the first aqueous dispersion B for polymerization of the second monomer B after carrying out a purification treatment to reduce or inactivate the polymerization initiator and its decomposition products from the first aqueous dispersion 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 fluorine-containing polymer B having desired physical property values. Examples of the purification method include a 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.

[0095] 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, and carbonates such as sodium bicarbonate and sodium carbonate. More preferred examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate. When the first aqueous dispersion 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.

[0096] 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.

[0097] - Second Monomer B - The second monomer B includes a monomer having a crosslinkable group. Examples of the monomer having a crosslinkable group include the above-mentioned monomers having a crosslinkable group, and the above-mentioned R ＣＮ A monomer having a crosslinkable group (preferably R ＣＮ The amount of the second monomer B used is preferably 0.05 to 10.0 mol %, more preferably 0.1 to 5.0 mol %, and even more preferably 0.2 to 3.0 mol %.

[0098] The second monomer B may contain a monomer other than the monomer having a crosslinkable group. The second monomer B preferably contains at least one selected from the group consisting of TFE and PAVE (preferably PMVE), 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%, relative to the amount of the second monomer B used. The amount of PAVE (preferably PMVE) 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%, relative to the amount of the second monomer B used. The amount of TFE units and PAVE units (preferably PMVE units) used is preferably 50.0 to 99.95 mol %, more preferably 75.0 to 99.9 mol %, and even more preferably 80.0 to 99.8 mol %, based on the amount of second monomer B used.

[0099] The second monomer B may contain a monomer other than TFE, PAVE, and a monomer having a crosslinkable group.

[0100] 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.

[0101] 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.

[0102] -Method- In step B2, a second fluorine-containing polymer B (corresponding to the present elastomer) 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.

[0103] The polymerization of the second monomer B is preferably carried out under conditions in which an emulsifier having a fluorine atom is substantially absent, more preferably under conditions in which an emulsifier is substantially absent. "Substantially absent" means that, in the method for producing the second fluorine-containing polymer B, 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 first aqueous dispersion B. The lower limit is 0 ppb by mass.

[0104] - Second Fluorine-Containing Polymer B - In step B2, the second fluorine-containing polymer B is produced, and a second aqueous dispersion in which particles of the second fluorine-containing polymer B are dispersed in an aqueous medium is obtained.

[0105] The second fluorine-containing polymer B may be in the form of particles. The particles of the second fluorine-containing polymer B may or may not contain the first fluorine-containing polymer B. The average particle size of the particles of the second fluorine-containing polymer 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 polymer B can be measured in the same manner as the average particle size of the particles of the first fluorine-containing polymer B.

[0106] The number of particles of the second fluorine-containing 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 More preferably, 5.0 x 10 １４ The upper limit is 10.0 × 10 １５The number of particles of the second fluoropolymer 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.

[0107] The second fluorine-containing polymer B preferably does not have a melting point.

[0108] The second fluorine-containing polymer B contains units derived from the second monomer B. ＣＮ The amount of PAVE units (preferably PMVE units) is preferably 0.05 to 10.0 mol%, more preferably 0.1 to 5.0 mol%, and even more preferably 0.2 to 3.0 mol%, based on all units of the second fluorine-containing polymer B. The amount of TFE units 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 all units of the second fluorine-containing polymer B. The amount of PAVE units (preferably PMVE units) 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 all units of the second fluorine-containing polymer B. The total amount of TFE units and PAVE units is preferably 50.0 to 99.95 mol%, more preferably 75.0 to 99.9 mol%, and even more preferably 80.0 to 99.8 mol%, based on all units of the second fluorine-containing polymer B. The amount of units other than those mentioned above is preferably 0 to 90.0 mol%, more preferably 0 to 80.0 mol%, and even more preferably 0 to 70.0 mol%, based on all units of the second fluorine-containing polymer B. The second fluorine-containing polymer B may or may not be copolymerized with the first fluorine-containing polymer B.

[0109] - Second aqueous dispersion B - Step B2 provides a second aqueous dispersion B, which is an aqueous dispersion containing particles of the second fluoropolymer B. The second aqueous dispersion B is preferably an aqueous dispersion containing particles of the present elastomer (hereinafter also referred to as "specific particles") and an aqueous medium.

[0110] 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 term "the second aqueous dispersion B does not substantially contain an emulsifier" means that the content of the emulsifier is 10 mass ppm or less, preferably 150 mass ppb or less, more preferably 50 mass ppb or less, and particularly preferably 25 mass ppb or less, relative to the total mass of the second aqueous dispersion B. The lower limit is 0 mass ppb.

[0111] The specific particles are preferably particles of the above-mentioned second fluoropolymer B. When the specific particles contain the second fluoropolymer B, the specific particles may or may not contain the first fluoropolymer B. The second aqueous dispersion B may further contain particles of the first fluoropolymer B in addition to the specific particles.

[0112] 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 polymer B. The specific particle number is 1×10 １３ 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.

[0113] 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.

[0114] 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.

[0115] <Step B3> Step B3 is a step of recovering the present elastomer from the second aqueous dispersion B obtained in step B2. A solid present elastomer can be obtained by agglomerating the particles of the second fluoropolymer B from the second aqueous dispersion B. As the agglomeration method, the methods exemplified in step A2 above can be used.

[0116] [Composition] The composition of the present disclosure (hereinafter also referred to as "the composition") contains the elastomer and a crosslinking agent. Specific examples of the crosslinking agent include a compound having two or more amino groups (hereinafter also referred to as "polyamine compound") and an organic peroxide. Polyamine compounds are preferred because they provide excellent crosslinkability of the elastomer and allow crosslinked rubber articles with smaller compression set to be obtained.

[0117] 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. However, from the viewpoint of achieving superior 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 present elastomer, resulting in a crosslinked rubber article with smaller compression set under high temperature and high compression.

[0118] Specific examples of polyamine compounds 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. BOAP is preferred because it provides better effects according to the present disclosure.

[0119] The content of the crosslinking agent is preferably 0.3 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the present elastomer.

[0120] The composition may contain components other than the elastomer and crosslinking agent. Specific examples of other components include acid acceptors (e.g., fatty acid esters, fatty acid metal salts, and divalent metal oxides (magnesium oxide, calcium oxide, zinc oxide, lead oxide, etc.)), fillers and reinforcing materials (e.g., carbon black, barium sulfate, calcium metasilicate, calcium carbonate, titanium oxide, silicon dioxide, fluorine-containing copolymers other than the elastomer (e.g., tetrafluoroethylene-fluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, and ethylene-tetrafluoroethylene copolymers), polytetrafluoroethylene (PTFE), aromatic polyesters, polyamideimides, thermoplastic polyimides, clay, and talc), scorch retarders (e.g., 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 (e.g., 18-crown-6), and mold release agents (e.g., sodium stearate).

[0121] When the present composition contains other components, the total content of the other components is preferably 0.1 to 30 parts by mass, more preferably 1 to 15 parts by mass, and even more preferably 3 to 8 parts by mass, per 100 parts by mass of the present elastomer.

[0122] The present composition can be produced by mixing the above components. The components can be mixed using a rubber mixing device such as a roll, kneader, Banbury mixer, or extruder. Alternatively, the mixture obtained by mixing the above components may be molded. Specific examples of methods for molding the mixture include compression molding, injection molding, extrusion molding, calendar molding, or a method in which the mixture is dissolved in a solvent and then dipped or coated onto a substrate or the like.

[0123] The present composition is preferably used for producing crosslinked rubber articles. The maximum torque (MH) of the present composition during primary crosslinking is preferably 30 to 100 dNM, more preferably 40 to 90 dNM, even more preferably 50 to 80 dNM, and particularly preferably 50 to 65 dNM. Furthermore, the difference (MH-ML) between the maximum torque (MH) and the minimum torque (ML) during primary crosslinking of the present composition is preferably 30 to 90 dNM, more preferably 40 to 80 dNM, even more preferably 50 to 70 dNM, and particularly preferably 50 to 60 dNM.

[0124] The metal content of the composition is preferably 50 ppm by mass or less, more preferably 30 ppm by mass or less, based on the total solid content of the composition. The lower limit is 0 ppm by mass. By having a metal content of 50 ppm by mass or less, it is possible to suppress environmental pollution, particularly when the composition is used as a semiconductor manufacturing equipment component.

[0125] The metal content is the total content of 29 metal elements (Fe, Na, K, Li, Be, Mg, Al, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Mo, Ag, Cd, In, Sn, Cs, Ba, Pb, and Bi) measured by the absolute calibration curve method using an inductively coupled plasma mass spectrometer.

[0126] [Crosslinked Rubber Article] The crosslinked rubber article of the present disclosure is a rubber article obtained by crosslinking the elastomer in the composition described above. A preferred method for crosslinking the elastomer in the composition is to heat the composition. Specific examples of crosslinking methods using heat include hot press crosslinking, steam crosslinking, injection molding crosslinking, hot air crosslinking, molten salt crosslinking, fluidized bed crosslinking, and funnel crosslinking. Heating conditions are preferably 100 to 400°C for 1 second to 24 hours.

[0127] The crosslinked rubber obtained by heating the composition (first crosslinking) may be further heated to cause second crosslinking. By performing second crosslinking, the mechanical properties, compression set, and other properties of the crosslinked rubber can be stabilized or improved. The heating conditions for performing second crosslinking are preferably 80 to 350°C for 30 minutes to 48 hours.

[0128] 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.

[0129] <Applications> The crosslinked rubber articles are suitable for materials such as O-rings, sheets, gaskets, oil seals, diaphragms, and V-rings. 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.

[0130] [Method for producing perfluoroelastomer] The method for producing a perfluoroelastomer of the present disclosure (hereinafter also referred to as "the present production method") is a method for producing a second fluoropolymer by polymerizing a first monomer containing tetrafluoroethylene in the presence of compound X and a polymerization initiator in the presence of an aqueous medium and substantially no emulsifier containing fluorine atoms to produce an aqueous dispersion containing particles of a first fluoropolymer having an average particle size of 500 nm or less and no melting point, and then polymerizing a second monomer containing a monomer having a nitrile group in the aqueous dispersion. According to this production method, a perfluoroelastomer can be obtained that has a low MH during primary crosslinking and can be used to produce crosslinked rubber articles with a small compression set. Although the details of the reason for this are unknown, it is thought that by synthesizing the first fluoropolymer using compound X under conditions substantially free of an emulsifier containing fluorine atoms, first fluoropolymer particles with excellent dispersibility can be obtained without using an emulsifier containing fluorine atoms that is likely to remain as a low-molecular-weight component. Furthermore, it is presumed that by polymerizing the second monomer in the presence of the first fluoropolymer particles, a second fluoropolymer can be polymerized in which polymer decomposition is suppressed without using a low molecular weight component, and as a result, the present elastomer which satisfies requirement 1 can be obtained.

[0131] In this production method, the specific method and preferred embodiments of the step of polymerizing a first monomer containing tetrafluoroethylene in the presence of 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, to produce an aqueous dispersion containing particles of a first fluorine-containing polymer having an average particle size of 500 nm or less and no melting point, are the same as those of the above-mentioned step B1. Furthermore, the specific method and preferred embodiments of the step of polymerizing a second monomer containing a monomer having a nitrile group in the above-mentioned aqueous dispersion, to produce a second fluorine-containing polymer, are the same as those of the above-mentioned step B2, except that the above-mentioned monomer having a crosslinkable group is a monomer having a nitrile group.

[0132] The monomer having a nitrile group in this production method is the above-mentioned R ＣＮThe amount of the monomer having a nitrile group used in the present production method is preferably 0.05 to 10.0 mol %, more preferably 0.1 to 5.0 mol %, and even more preferably 0.2 to 3.0 mol %, based on the amount of the second monomer used.

[0133] The present disclosure will be described in detail below with reference to examples. Examples 1 to 4 are working examples, and Example 5 is a comparative example. However, the present disclosure is not limited to these examples.

[0134] [Measurement and Evaluation Methods] [Requirement 1] A 10 mg sample of the perfluoroelastomer obtained in each example was weighed into an aluminum pan and placed in a Hitachi STA200. The starting temperature was set to 40°C, and once the sample temperature stabilized, the sample was continuously heated in a nitrogen atmosphere (nitrogen gas flow rate 100 mL / min) according to the following profile of steps 1 to 6, while measuring the change in mass. The weight loss rate at the end of all the above steps was calculated, with the mass of the sample before heating from 40°C being taken as 100% by mass. The above thermogravimetric analysis was performed using a differential thermal thermogravimetric analyzer "NEXTA STA Series STA200" (Hitachi High-Tech Corporation). Step 1: Heat from 40°C to 90°C at a rate of 10°C / min. Step 2: Hold at 90°C for 120 minutes. Step 3: Heat from 90°C to 200°C at a rate of 1°C / min. Step 4: Hold at 200°C for 240 minutes. Step 5: Heat from 200°C to 305°C at a rate of 1°C / min. Step 6: Hold at 305°C for 720 minutes.

[0135] [Water Content] The water content of the perfluoroelastomer obtained in each example was measured using a halogen moisture meter.

[0136] [Melting point] The first aqueous dispersion or second aqueous dispersion of each example described below (hereinafter also collectively referred to as "the aqueous dispersion of each example") was freeze-aggregated and then filtered to obtain a first fluorine-containing polymer or a second fluorine-containing polymer. A 5 mg sample of the obtained first fluorine-containing polymer or second fluorine-containing polymer 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.

[0137] [Solid content concentration of aqueous dispersion] 2.0 g of the aqueous dispersion of each example described below was heated at 170°C for 20 minutes, and then the mass (g) of the residue was weighed and the solid content concentration was calculated using the following formula: Solid content concentration of aqueous dispersion (mass%) = 100 × (mass of residue) / (mass of aqueous dispersion (2.0 g))

[0138] [Average particle size of the first fluorine-containing polymer particles and the second fluorine-containing polymer particles] The aqueous dispersion of each example described below was degassed at 25 ° C. for 5 minutes, and nitrogen gas was pressurized to 0.2 MPaG, then purged, and the pressure was 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 measuring device (Otsuka Electronics Co., Ltd., ELSZ) with an integrated number set to 100, and was taken as the average particle size of the particles in each aqueous dispersion. Note that, when the average particle size of the particles of the first fluorine-containing polymer in the raw material liquid B described below was measured in the same manner as in the first aqueous dispersion, the average particle size of the particles of the first fluorine-containing polymer in the raw material liquid B was the same as the average particle size of the particles of the first fluorine-containing polymer in the first aqueous dispersion.

[0139] [Proportion of each unit in the polymer] The proportion of each unit in the polymer is １９ It was determined by F-NMR analysis and infrared absorption spectrum analysis.

[0140] [MH and ML] <Production of Composition> The components and amounts shown in Table 1 were mixed and kneaded for 10 minutes at room temperature using a twin roll mill to obtain a mixture. The gap between the twin rolls was adjusted, and the obtained mixture was processed into a sheet of Composition 1 with a thickness of 3 mm. Of the components in Table 1, details of the components other than the perfluoroelastomer are as follows: CB: MT Carbon N990, manufactured by Cancarb Ltd., carbon black Crosslinker: BOAP (2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane)

[0141]

[0142] <Measurement of MH and ML> The obtained composition 1 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.

[0143] [Compression set] <Production of crosslinked rubber article> Composition 1 obtained in the above [MH and ML] tests 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 an 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 to carry out secondary crosslinking. Thereafter, the O-ring was cooled to 23°C to obtain an O-ring, which is a crosslinked rubber article.

[0144] <Measurement of Compression Set> The compression set was measured according to the method described in ASTM D395 or JIS K6262. The O-rings (original thickness (wire diameter) = 3.5 mm) prepared in each example were compressed to a compression rate of 18% using a compression device. Next, the compression device with the compressed O-rings 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-rings were immediately removed from the compression device, and the removed O-rings were left in a constant temperature room at 23°C for 30 minutes, and the thickness of the O-rings (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. The closer the compression set rate is to 0%, the smaller the compression set is, and the more preferable it is. Compression set rate (%) = {original thickness of O-ring (wire diameter) - thickness of O-ring 30 minutes after removal from compression device (thickness after compression treatment)} ÷ {original thickness of O-ring (wire diameter) - thickness of spacer} × 100

[0145] <Method for Measuring Emulsifier Contained in Perfluoroelastomer> (Preparation of Measurement Sample) The solid compositions obtained in each example described below were freeze-pulverized using a freeze-pulverizer Freezer Mill 6775 (manufactured by SPEX) under the following conditions. Before freeze-pulverization, 10% by mass of dibutylhydroxytoluene (BHT) was added to the solid composition to obtain a pulverized powder. The freeze-pulverization conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 minutes, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 2.50 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 each fluoropolymer. The supernatant was used as the extract. The resulting extract was analyzed by LC / MS / MS. The fluorine-containing emulsifier and hydrocarbon emulsifier in the extract were measured using a liquid chromatograph mass spectrometer. The configuration of the measuring equipment and the LC-MS measurement conditions are shown in Table 2. 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.

[0146]

[0147] 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.

[0148]

[0149]

[0150] (Quantitative determination of fluorine-containing emulsifier and hydrocarbon emulsifier contained in perfluoroelastomer) Specifically, five levels of methanol standard solutions of the fluorine-containing emulsifier to be measured and the hydrocarbon emulsifier, each with known concentrations of 1 to 180 ng / g, were prepared, and a was calculated from the sample concentration and peak integral value of each sample using a first-order 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.

[0151] 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.

[0152] The content of the emulsifier in the perfluoroelastomer relative to the total mass of the perfluoroelastomer (ZCm) was calculated by the following formula (A3): ZCm = XCm × ρ1 × La / W1 (A3) ZCm: content of the emulsifier contained in the solid composition ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid composition in each example)

[0153] <Metal Content> The perfluoroelastomer was placed in a platinum crucible and incinerated in a high-temperature electric heating furnace, followed by a sulfuric acid white smoke treatment. The resulting solution was then dissolved in dilute nitric acid. The total content of 29 metal elements (Fe, Na, K, Li, Be, Mg, Al, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Mo, Ag, Cd, In, Sn, Cs, Ba, Pb, and Bi) was determined using an inductively coupled plasma mass spectrometer (ICP-MS 7500cs, manufactured by Agilent Technologies) and the absolute calibration curve method.

[0154] [Example 1] Ultrapure water (1206 g), a 50% by mass aqueous solution of sodium 2-acrylamido-2-methyl-1-propanesulfonate (NaAAMPS, corresponding to Compound X) (30 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% by 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 CF ２ 3.4 g of CN (8CNVE) was added. Thereafter, while intermittently adding an 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 168 g, the addition of TFE, PMVE, and 8CNVE 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 A1. The total amount of ammonium persulfate added was 0.7 g. The total amount of monomers added before the start of polymerization was 17 g of TFE and 82 g of PMVE. The total amount of monomers added after the start of polymerization was 168 g of TFE, 114 g of PMVE, and 16.0 g of 8CNVE. The total amount of TFE added was 185 g, the total amount of PMVE added was 196 g, and the total amount of 8CNVE added was 16.0 g. The first aqueous dispersion A1 was subjected to nitric acid coagulation, filtered, and the obtained solid was washed with ultrapure water. Thereafter, it was vacuum dried at 100 ° C. for 12 hours to obtain perfluoroelastomer A1. The obtained perfluoroelastomer A1 was analyzed by NMR, and the composition was as shown in Table 5. Furthermore, perfluoroelastomer A1 did not have a melting point. The water content of perfluoroelastomer A1 was 0.0 mass%.

[0155] [Example 2] Ultrapure water (1206 g), a 50% by mass aqueous solution of NaAAMPS (10 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 was repeated, and when the amount of TFE added after the start 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 3.4 g of 8CNVE was added. Thereafter, while intermittently adding an 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 168 g, the addition of TFE, PMVE, and 8CNVE 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. 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 168 g of TFE, 114 g of PMVE, and 16.0 g of 8CNVE. The total amount of TFE added was 185 g, the total amount of PMVE added was 195 g, and the total amount of 8CNVE added was 16.0 g. The first aqueous dispersion A2 was subjected to nitric acid coagulation, filtered, and the obtained solid was washed with ultrapure water. Then, it was vacuum dried at 100 ° C for 12 hours to obtain perfluoroelastomer A2. The obtained perfluoroelastomer A2 was analyzed by NMR, and the composition was as shown in Table 5. Furthermore, perfluoroelastomer A2 did not have a melting point. The water content of perfluoroelastomer A2 was 0.1 mass%.

[0156] [Example 3] Ultrapure water (1206 g), 50% by mass NaAAMPS aqueous solution (10 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 ammonium persulfate solution (2.5% by mass, 7 g) was added to initiate polymerization. As the polymerization started, the pressure inside the reactor decreased, so TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the start of polymerization reached 8 g, 6 g of PMVE was injected. When the polymerization pressure dropped to 1.4 MPa, the stirring speed was reduced to 380 rpm, and 3.4 g of 8CNVE was added. After that, while intermittently adding an 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 A3. The total amount of ammonium persulfate added was 1.75 g, and the total amount of 8CNVE added was 33.6 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 A3 was coagulated with nitric acid, filtered, and the obtained solid was washed with ultrapure water. It was then vacuum dried at 100 ° C. for 12 hours to obtain perfluoroelastomer A3. The obtained perfluoroelastomer A3 was analyzed by NMR, and the composition was as shown in Table 5. Furthermore, perfluoroelastomer A3 did not have a melting point. The water content of perfluoroelastomer A3 was 0.2 mass%.

[0157] [Example 4] <Production of Raw Material Solution A> Ultrapure water (1206 g), a 50% by mass aqueous solution of NaAAMPS (20 μL, 10 mg of NaAAMPS), PMVE (72 g), and TFE (15 g) were added to a 2.2 L stainless steel pressure reactor, and the temperature was raised to 90 ° C. while stirring at 600 rpm. The internal pressure of the reactor at 90 ° C. was 1.4 MPaG. Next, an aqueous solution of ammonium persulfate (2.5% by mass, 4 g) was added to initiate polymerization. Since the pressure in the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the start of polymerization reached 25 g, the addition of TFE injected after the start of polymerization was stopped, the internal temperature of the reactor was cooled to 10 ° C., the polymerization reaction was stopped, and the gas remaining in the reactor was recovered. The liquid was then extracted to obtain raw material solution A (first aqueous dispersion A4). The total amounts of monomers added before the start of polymerization were 15 g of TFE and 72 g of PMVE. The total amounts of monomers added after the start of polymerization were 25 g of TFE and 0 g of PMVE. The total amount of TFE added was 40 g, and the total amount of PMVE added was 72 g. The average particle size of the particles of the first fluoropolymer A4 in the raw material solution A was 43.5 nm, and the number of particles of the first fluoropolymer A4 was 3.9 × 10 １４ The concentration of the solids in raw material solution A was 3.3% by mass. Raw material solution A was freeze-coagulated and then filtered, and the obtained first fluoropolymer A4 was washed with ultrapure water. It was then vacuum-dried at 100°C. The obtained first fluoropolymer A4 was analyzed by NMR, and the result was that the mole ratio of PMVE / TFE was 33 / 67. The 1% by mass thermal weight loss temperature of first fluoropolymer A4 was 350°C. Furthermore, first fluoropolymer A4 did not have a melting point.

[0158] <Production of Raw Material Solution B> HPR4002Cl (anion exchange resin, manufactured by DuPont, 40 g) was added to raw material solution A (1000 g). 60 minutes after the start of stirring, the raw material solution A and the ion exchange resin were separated by filtration. Dowex Monosphere 650C (cation exchange resin, manufactured by DuPont, 40 g) was added to the filtered raw material solution A. 60 minutes after the start of stirring, the ion exchange resin was separated by filtration to obtain raw material solution B. The average particle size and particle number of the first fluorine-containing polymer A4 in raw material solution B were equivalent to those in raw material solution A, and the first fluorine-containing polymer A4 in raw material solution B had no melting point.

[0159] <Production of second fluorine-containing polymer> Raw material liquid B (850 g), ultrapure water (332 g), 8CNVE (3.4 g), 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 380 rpm. The pressure inside the reactor at 80 ° C. was 1.4 MPaG. Next, an aqueous ammonium persulfate solution (2.5 mass%, 7 g) was added to initiate polymerization. As the polymerization started, 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 second aqueous dispersion A5. The total amount of ammonium persulfate added was 0.7 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 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 189 g. The second aqueous dispersion A5 was subjected to nitric acid coagulation, filtered, and the resulting solid was washed with ultrapure water. It was then vacuum dried at 100 ° C. for 12 hours to obtain perfluoroelastomer A5. The resulting perfluoroelastomer A5 was analyzed by NMR, and the composition was shown in Table 5. The second fluorine-containing polymer A5 had no melting point. The water content of perfluoroelastomer A5 was 0.2% by mass.

[0160] [Example 5] 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 A6. 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 A6 was subjected to nitric acid coagulation, filtered, and the resulting solid was washed with ultrapure water. It was then vacuum dried at 100 ° C. for 12 hours to obtain a perfluoroelastomer A6. The resulting perfluoroelastomer A6 was analyzed by NMR, and the composition was shown in Table 5. The perfluoroelastomer A6 had no melting point and a water content of 0.2% by mass.

[0161] In the production of Examples 1 to 4, the polymerization of the first fluorine-containing polymer 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 4 did not substantially contain any emulsifier having a fluorine atom nor any emulsifier having a fluorine atom.

[0162] The solids concentration and particle size of the fluoropolymer particles of the aqueous dispersion obtained in each example, the composition, water content, weight loss rate, MH, ML, MH-ML, and compression set (CS) of the obtained perfluoroelastomer are shown in Table 5. The aqueous dispersions of Examples 1 to 3 and 5 are values ​​for the first aqueous dispersion, and the aqueous dispersion of Example 4 is a value for the second aqueous dispersion.

[0163]

[0164] As shown in Examples 1 to 5, the crosslinked rubber articles of Examples 1 to 5 exhibited comparable compression set rates, while the perfluoroelastomers of Examples 1 to 4 had smaller MH at the time of primary crosslinking than the perfluoroelastomer of Example 5. In other words, it was demonstrated that this elastomer can produce crosslinked rubber articles with small compression set and has a low MH at the time of primary crosslinking. No hydrocarbon emulsifier was detected in Examples 1 to 5, and it was confirmed that the amount of fluorine-containing emulsifier was very small in Examples 1 to 4.

[0165] The disclosure of Japanese Patent Application No. 2024-098661, 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 perfluoroelastomer having a crosslinkable group that satisfies Requirement 1. (Requirement 1) In a nitrogen atmosphere, starting at a temperature of 40°C, the sample is heated from 40°C to 90°C at a heating rate of 10°C / min, then held at 90°C for 120 minutes, then heated from 90°C to 200°C at a heating rate of 1°C / min, then held at 200°C for 240 minutes, then heated from 200°C to 305°C at a heating rate of 1°C / min, and held at 305°C for 720 minutes, with a weight loss of 1.8% by mass or less.

2. The perfluoroelastomer according to claim 1, which has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether).

3. The perfluoroelastomer according to claim 1 or 2, which has units based on a monomer having a nitrile group.

4. The perfluoroelastomer according to claim 3, wherein the content of units based on the monomer having a nitrile group is 0.2 to 3.0 mol % based on the total content of all units in the perfluoroelastomer.

5. The perfluoroelastomer according to claim 1 or 2, which is substantially free of emulsifiers.

6. A composition comprising the perfluoroelastomer according to claim 1 or 2 and a crosslinking agent.

7. The composition according to claim 6, wherein the metal content is 50 ppm by mass or less based on the total solid content of the composition.

8. A crosslinked rubber article obtained by crosslinking the composition according to claim 6.

9. A method for producing a perfluoroelastomer, comprising polymerizing 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 substantially in the absence of an emulsifier having a fluorine atom to produce an aqueous dispersion containing particles of a first fluorine-containing polymer having an average particle size of 500 nm or less and no melting point, and polymerizing a second monomer containing a monomer having a nitrile group in the aqueous dispersion to produce a perfluoroelastomer. 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.

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