Fluorine-containing polymer composition, method for producing fluorine-containing polymer composition, and crosslinked rubber article

Abstract

Provided are a fluorine-containing polymer composition capable of forming a crosslinked rubber article having excellent mold releasability, a method for producing the fluorine-containing polymer composition, and a crosslinked rubber article. This fluorine-containing polymer composition contains a fluorine-containing polymer and a crosslinking agent, and is characterized in that the optimal vulcanization time Te determined according to formula A (Te = tC(5) + 10 × (tC(35) - tC(5))) is at least 2.3 minutes. In formula A, in a torque-vulcanization time curve determined at a test temperature of 150°C using a fluorine-containing polymer composition in accordance with JIS K6296-1, if the minimum value of the torque is defined as 0% and the maximum value of the torque is defined as 100%, the vulcanization time when expressing a torque of 5% is defined as tC(5), and the vulcanization time when expressing a torque of 35% is defined as tC(35).

Description

Fluoropolymer composition, method for producing fluoropolymer composition, and crosslinked rubber article

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

[0002] Crosslinked rubber articles obtained by crosslinking fluorine-containing polymers are used in various industrial fields due to their excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. Patent Document 1 describes a fluorine-containing elastic copolymer composition containing an iodine atom and a fluorine-containing elastic copolymer having units a which are units based on tetrafluoroethylene, units b which are units based on a monomer (excluding tetrafluoroethylene) having one polymerizable unsaturated bond, and units c which are units based on a fluorine-containing monomer having two or more polymerizable unsaturated bonds, and which has a metal content within a predetermined range, and a crosslinking agent (see claim 6). Furthermore, Patent Document 1 describes a method for producing a fluorinated elastic copolymer, which comprises emulsion polymerizing tetrafluoroethylene, a monomer having one polymerizable unsaturated bond (excluding tetrafluoroethylene), and a fluorine-containing monomer having two or more polymerizable unsaturated bonds in the presence of a radical polymerization initiator and a predetermined iodine-containing compound to obtain a latex containing a fluorinated elastic copolymer, and then agglomerating the fluorinated copolymer in the latex using an acid containing no metal element (see claim 8), and also discloses a method for producing a fluorinated elastic copolymer composition using the obtained fluorinated elastic copolymer and a crosslinking agent.

[0003] Patent No. 7140118

[0004] In recent years, there has been a demand in various fields for improved performance of crosslinked rubber articles, and specifically, there has been a demand for a fluoropolymer composition that can form crosslinked rubber articles that have excellent releasability from a mold (hereinafter also referred to as "mold releasability"). In response to such demands, the present inventors evaluated crosslinked rubber articles formed using a fluoropolymer composition such as that described in Patent Document 1, and found that there was room for improvement in mold releasability.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a fluoropolymer composition capable of forming a crosslinked rubber article having excellent mold releasability, a method for producing a fluoropolymer composition, and a crosslinked rubber article.

[0006] As a result of intensive investigations into the above-mentioned problems, the present inventors have found that the mold releasability of a crosslinked rubber article can be improved by using a fluoropolymer composition which contains a fluoropolymer and a crosslinking agent and which has an optimum vulcanization time Te calculated from equation A described below of 2.3 minutes or more, and have arrived at the present invention.

[0007] That is, the present inventors have found that the above-mentioned problems can be solved by the following constitution: [1] A fluoropolymer composition comprising a fluoropolymer and a crosslinking agent, characterized in that the optimum vulcanization time Te calculated by the formula A is 2.3 minutes or more. Formula A Te=t Ｃ (5) + 10 × (t Ｃ (35)-t Ｃ (5)) In formula A, in a torque-vulcanization time curve obtained using the above fluoropolymer composition at a test temperature of 150°C in accordance with JIS K6296-1, the minimum torque is set to 0% and the maximum torque is set to 100%, and the vulcanization time at which the torque reaches 5% is defined as t Ｃ (5), and the vulcanization time when the torque reaches 35% is t Ｃ(35). [2] The fluoropolymer composition according to [1], wherein the optimum vulcanization time Te is 60 minutes or less. [3] The fluoropolymer composition according to [1] or [2], wherein the fluoropolymer has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). [4] The fluoropolymer composition according to any of [1] to [3], wherein the crosslinking agent is at least one selected from the group consisting of organic peroxides and compounds having two or more amino groups. [5] The fluoropolymer composition according to any of [1] to [4], further comprising a crosslinking coagent. [6] The fluorine-containing polymer composition according to [5], wherein the crosslinking coagent is at least one selected from the group consisting of a compound represented by the following formula (7), triallyl cyanurate, triallyl isocyanurate, trimethallyl isocyanurate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, triallyl trimellitate, m-phenylenediamine bismaleimide, p-quinonedioxime, p,p'-dibenzoylquinonedioxime, dipropargyl terephthalate, diallyl phthalate, N,N',N'',N'''-tetraallyl terephthalamide, and a vinyl group-containing siloxane oligomer. (CR ４１ R ４２ =CR ４３ ) ２ R ４４ Formula (7) In formula (7), R ４１ , R ４２ and R ４３ each independently represents a hydrogen atom, a fluorine atom, an alkyl group having 1 to 5 carbon atoms, or a fluoroalkyl group having 1 to 5 carbon atoms; R ４４ represents a divalent fluorohydrocarbon group having 1 to 18 carbon atoms or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of the fluorohydrocarbon group. ４１ , multiple R ４２ and multiple R ４３may be the same or different from each other. [7] The fluoropolymer composition according to any of [1] to [6], further comprising a filler. [8] The fluoropolymer composition according to [7], wherein the filler is at least one selected from the group consisting of carbon black, barium sulfate, calcium metasilicate, calcium carbonate, titanium oxide, silicon dioxide, clay, and talc. [9] The fluoropolymer composition according to any of [1] to [8], wherein the fluoropolymer has a storage modulus G' of 200 kPa or more at 100°C and a frequency of 50 cpm.

[10] A method for producing a second fluoropolymer containing units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether) by polymerizing a monomer containing tetrafluoroethylene and perfluoro(alkyl vinyl ether) in an aqueous dispersion containing a first fluoropolymer substantially free of a water-soluble emulsifier and containing units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and an aqueous medium; and a step 2 of adding a crosslinking agent to the second fluoropolymer to obtain a fluoropolymer composition containing the second fluoropolymer and the crosslinking agent, wherein the content of the units based on perfluoro(alkyl vinyl ether) relative to the total content of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether) in the first fluoropolymer is 20 to 95 mol %, and the content of the units based on perfluoro(alkyl vinyl ether) relative to the total content of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether) in the second fluoropolymer is 20 to 95 mol %,

[11] A method for producing a fluoropolymer composition, characterized in that the content of the first fluoropolymer is 0.01 to 4.0 mass% relative to the total mass of the aqueous dispersion before starting polymerization of the monomers.

[12] A crosslinked rubber article obtained by crosslinking a fluoropolymer contained in the fluoropolymer composition according to any one of [1] to [9].

[0008] According to the present invention, there are provided a fluoropolymer composition capable of forming a crosslinked rubber article having excellent mold releasability, a method for producing a fluoropolymer composition, and a crosslinked rubber article.

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

[0010] [Fluoropolymer composition] The fluoropolymer composition of the present invention (hereinafter also referred to as "the composition") is a fluoropolymer composition comprising a fluoropolymer and a crosslinking agent, and has an optimum vulcanization time Te calculated from formula A described below of 2.3 minutes or more. A crosslinked rubber article obtained using the composition (hereinafter "the crosslinked rubber article") has excellent mold releasability. When the composition having an optimum vulcanization time Te of 2.3 minutes or more is used, the time required for crosslinking is somewhat longer, and it is presumed that the distribution of crosslinking points in the crosslinked rubber article tends to become more uniform, resulting in easier release from the mold. On the other hand, when the optimum vulcanization time Te is less than 2.3 minutes, uncrosslinked portions tend to remain in the crosslinked rubber article, making it difficult to release from the mold.

[0011] The optimum vulcanization time Te of the present composition can be calculated by the following formula A: Te=t Ｃ (5) + 10 × (t Ｃ (35)-t Ｃ (5)) In formula A, t Ｃ (5) means the vulcanization time at which the torque reaches 5% in a torque-vulcanization time curve obtained using this composition at a test temperature of 150°C in accordance with JIS K6296-1, where the minimum torque is 0% and the maximum torque is 100%. Ｃ (35) means the vulcanization time at which the torque reaches 35% in a torque-vulcanization time curve obtained using this composition at a test temperature of 150°C, where the minimum torque is 0% and the maximum torque is 100%. Ｃ (5) and t Ｃ A more detailed measurement method for (35) is as described in the Examples section below.

[0012] The optimum vulcanization time Te for the present composition is 2.3 minutes or more, and from the viewpoint of obtaining superior effects of the present invention, it is preferably 3.0 minutes or more, more preferably 3.5 minutes or more, even more preferably 4.0 minutes or more, and particularly preferably 4.5 minutes or more. Since the crosslinked rubber article has low hardness and excellent flexibility, resulting in improved mold releasability, it is preferably 60 minutes or less, more preferably 30 minutes or less, even more preferably 10 minutes or less, and particularly preferably 5.5 minutes or less.

[0013] In this composition, t Ｃ (5) is preferably 0.3 minutes or more, more preferably 0.4 minutes or more, even more preferably 0.5 minutes or more, and particularly preferably 0.8 minutes or more, from the viewpoint of low hardness and excellent flexibility. Also, from the viewpoint of the balance between hardness and breaking elongation, it is preferably 5 minutes or less, more preferably 2 minutes or less, and even more preferably 1 minute or less. Ｃ In view of low hardness and excellent flexibility, (35) is preferably 0.5 minutes or more, more preferably 0.71 minutes or more, and particularly preferably 1 minute or more. In view of the balance between hardness and elongation at break, it is preferably 5 minutes or less, more preferably 2 minutes or less, and even more preferably 1.5 minutes or less.

[0014] [Fluoropolymer] The present composition contains a fluorine-containing polymer. The fluorine-containing polymer can be produced by the fluorine-containing polymer production method described below. The fluorine-containing polymer contained in the present composition may be a polymer that contains fluorine atoms and exhibits rubber properties through crosslinking, preferably having units based on a monomer containing fluorine atoms (hereinafter also referred to as a "fluorine-containing monomer"), and is preferably a perfluorinated polymer. Here, "perfluorinated polymer" refers to a polymer that substantially does not contain 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 perfluorinated polymer may contain a polyvalent atom other than carbon atoms, and the polyvalent atom is preferably an oxygen atom. Here, "substantially does not contain hydrogen atoms" means that the content of hydrogen atoms in the perfluorinated polymer 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.

[0015] The fluorine-containing polymer preferably has units based on tetrafluoroethylene (hereinafter also referred to as "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) from the viewpoints of excellent polymerization reactivity in producing the first fluoropolymer described below and of enabling the fluoropolymer to be produced more efficiently. 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 fluorinated polymer.

[0018] The content of TFE units in the fluoropolymer is preferably 5 to 90 mol%, more preferably 20 to 80 mol%, even more preferably 30 to 80 mol%, and particularly preferably 40 to 75 mol%, based on the total content of TFE units and PAVE units. The content of TFE units is also more preferably 5 to 80 mol%, based on the total content of TFE units and PAVE units. The preferred amount used is also the same when PMVE or PPVE is used as PAVE. The total content of TFE units and PAVE units in the fluoropolymer is preferably 80 to 100 mol%, more preferably 90 to 100 mol%, and even more preferably 95 to 100 mol%, based on the total content of all units in the fluoropolymer.

[0019] The content of TFE units in the fluoropolymer is preferably 5 to 90 mol%, more preferably 20 to 80 mol%, even more preferably 30 to 80 mol%, and particularly preferably 40 to 75 mol%, based on the total content of all units in the fluoropolymer. The content of PAVE units in the fluoropolymer is preferably 10 to 95 mol%, more preferably 20 to 80 mol%, even more preferably 20 to 70 mol%, and particularly preferably 25 to 60 mol%, based on the total content of all units in the fluoropolymer. When PMVE or PPVE is used as PAVE, the suitable amount used is similar.

[0020] The fluorine-containing polymer may contain units (hereinafter also referred to as "other units") based on monomers other than TFE units and PAVE units (hereinafter also referred to as "other monomers"), and preferably contains units based on other monomers. Specific examples of other monomers include a monomer having two or more polymerizable unsaturated bonds (hereinafter also referred to as "BO"), a monomer having one or more atoms of at least one kind selected from the group consisting of a chlorine atom, a bromine atom and an iodine atom (hereinafter also referred to as "R Ｈａｌ "), a monomer having a nitrile group (hereinafter referred to as "R ＣＮ "), and a compound represented by formula (6) described below (hereinafter also referred to as "POAVE").

[0021] 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, from the viewpoint of more excellent polymerization reactivity. BO preferably contains a fluorine atom, from the viewpoint of further reducing the compression set of the crosslinked rubber article at high temperatures.

[0022] BO is preferably a monomer represented by formula (2) in view of better releasability of the crosslinked rubber article. ２１ R ２２ =CR ２３ -) ａ１ R ２４ (2) In formula (2), R ２１ , R ２２ , and R ２３ each independently represents a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group; a1 represents an integer of 2 to 6; R ２４ represents an a1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of an a1-valent perfluorohydrocarbon group having 1 to 10 carbon atoms. ２１ , multiple R ２２ and multiple R ２３ may be the same or different, and are particularly preferably the same. a1 is preferably 2 or 3, and particularly preferably 2. In view of better polymerization reactivity of BO, R ２１ , R ２２ , and R ２３ is preferably a fluorine atom or a hydrogen atom, and R ２１ , R ２２ , and R ２３ are more preferably all fluorine atoms or all hydrogen atoms, and in view of better mold releasability of the crosslinked rubber article, R ２１ , R ２２ , and R ２３ It is particularly preferred that all of R are fluorine atoms. ２４R 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.

[0023] 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).

[0024] (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.

[0025] (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.

[0026] Specific examples of the monomer represented by formula (3) include CF ２ = CFO (CF ２ ) ２ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ３ OCF = CF ２ , C.F. ２= CFO (CF ２ ) ４ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ６ OCF = CF ２、 CF ２ = CFO (CF ２ ) ８ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ２ OCF (CF ３ )CF ２ OCF = CF ２ , C.F. ２ = CFO (CF ２ ) ２ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , C.F. ２ = CFOCF ２ O (CF ２ CF ２ O) ２ CF = CF ２ , C.F. ２ = CFO (CF ２ O) ３ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , C.F. ２ = CFOCF ２ CF (CF ３ ) O(CF ２ ) ２ OCF (CF ３ )CF ２ OCF = CF ２ , and CF ２ = CFOCF ２ CF ２ O (CF ２ O) ２ CF ２ CF ２ OCF = CF ２ Among the monomers represented by formula (3), a more preferred specific example of the monomer is CF ２ = CFO (CF ２ ) ３OCF = CF ２ (hereinafter also referred to as "C3DVE"), and CF ２ = CFO (CF ２ ) ４ OCF = CF ２ (hereinafter also referred to as "C4DVE").

[0027] 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.

[0028] 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 wherein R may be the same or different; 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.

[0029] 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).

[0030] 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 ５３ each independently represents a hydrogen atom, a fluorine atom, or a methyl group; R ５４ represents a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms. ＣＮ From the viewpoint of excellent polymerization reactivity of R ５１ , R ５２ , and R５３ 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 ) ３ CN is exemplified, and 8CNVE or MV5CN is preferred in that the crosslinked rubber article has better mold releasability and heat resistance.

[0031] 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.

[0032] R ｆ２ In the formula, the perfluoroalkyl group may be linear or branched. ｆ２ The number of carbon atoms in is preferably 1 to 3. When n is 0, m is preferably 1 or 2. When n is 1, m is preferably an integer of 2 to 4. When n is 2 or 3, m is preferably 0. n is preferably an integer of 1 to 3. R ｆ２ When the number of carbon atoms, n, and m are within the above ranges, the low-temperature properties of the crosslinked rubber article are excellent, and the productivity of the crosslinked rubber article is improved.

[0033] Specific examples of POAVE include the following. The abbreviation for the compound is given in parentheses after the formula. CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ４ -OCF ３ (C9PEVE), CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ２ -OCF ３ (C7PEVE), CF ２ =CF-(OCF ２ CF ２ ) ２ -OCF ２ CF ３ (EEAVE), CF ２ =CF-(OCF ２ CF ２ ) ３ -OCF ２ CF ３ (EEEAVE), CF ２ =CF-OCF ２ -OCF ３ , C.F. ２ =CF-OCF ２ -OCF ２ -OCF３ 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.

[0034] The content of other units in the fluoropolymer is preferably from 0.01 to 20 mol %, more preferably from 0.01 to 10 mol %, and still more preferably from 0.01 to 5 mol %, based on the total content of all units in the fluoropolymer.

[0035] From the viewpoint of more excellent crosslinkability, the fluorine-containing polymer preferably contains at least one selected from the group consisting of a polymerizable unsaturated bond, a chlorine atom, a bromine atom, an iodine atom, and a nitrile group, and more preferably contains at least one selected from the group consisting of a chlorine atom, a bromine atom, an iodine atom, and a nitrile group. In particular, it is preferable that the fluorine-containing polymer has the above-mentioned atom or group at at least one of the end and the side chain. When producing a fluorine-containing polymer, by using the above-mentioned other monomer in addition to TFE and PAVE, any one of a polymerizable unsaturated bond, a chlorine atom, a bromine atom, an iodine atom, and a nitrile group can be introduced into the side chain or end of the fluorine-containing polymer. Furthermore, by polymerizing a monomer using a chain transfer agent having an iodine atom, an iodine atom can be introduced into the end of the fluorine-containing polymer. When the fluorine-containing polymer contains iodine atoms, the content of iodine atoms is preferably from 0.01 to 5.00 mass%, more preferably from 0.01 to 2.00 mass%, and even more preferably from 0.01 to 1.00 mass%, relative to the total mass of the fluorine-containing polymer.

[0036] The content of the fluorine-containing polymer is preferably from 50 to 99 mass %, more preferably from 70 to 99 mass %, particularly preferably from 80 to 99 mass %, based on the total mass of the composition.

[0037] The storage modulus G' of the fluoropolymer at 100°C and a frequency of 50 cpm is preferably 200 kPa or more, more preferably 240 kPa or more, from the viewpoint of achieving both flexibility and scorch resistance of the crosslinked rubber, and is preferably 650 kPa or less, more preferably 500 kPa or less, and even more preferably 400 kPa or less, from the viewpoint of moldability of the crosslinked rubber article. The storage modulus G' is a value measured in accordance with ASTM D6204, and detailed measurement conditions are as shown in the Examples. One example of a method for adjusting the storage modulus is a method of adjusting the amount and order of use of the above-mentioned respective monomers.

[0038] The fluoropolymer preferably satisfies at least one of the following requirements 1 and 2, and more preferably satisfies both requirements 1 and 2. Requirement 1: The 2% weight loss temperature of the fluoropolymer is 300° C. or higher and lower than 420° C. Requirement 2: The difference ΔTd between the 5% weight loss temperature of the fluoropolymer and the 2% weight loss temperature of the fluoropolymer is 20° C. or higher.

[0039] If requirement 1 is satisfied, it indicates that the fluorine-containing polymer contains a certain amount of low-molecular-weight components, and the crosslinking reactivity of the fluorine-containing polymer is improved, thereby Ｃ It is presumed that the value of (5) becomes small, and a fluoropolymer composition that satisfies the above-mentioned optimum vulcanization time Te can be easily obtained. Furthermore, when requirement 2 is satisfied, it indicates that the fluoropolymer contains a high molecular weight component, and the dispersibility of the crosslinking agent and crosslinking aid during kneading is improved, thereby improving the reactivity, and t Ｃ It is presumed that the value of (35) becomes small, and a fluoropolymer composition satisfying the above-mentioned optimum vulcanization time Te can be easily obtained. A fluoropolymer satisfying requirement 1 or requirement 2 can be easily obtained by the production method of a fluoropolymer described below.

[0040] In this specification, the "2% weight loss temperature" and "5% weight loss temperature" are measured by thermogravimetric analysis of the fluoropolymer to be measured. Specifically, a fluoropolymer sample that has not been heated to a temperature of 100°C or higher is subjected to thermogravimetric analysis in which the change in weight of the sample is measured while the temperature is increased from 30°C to 550°C at a heating rate of 10°C / min in an air atmosphere. As a result of the thermogravimetric analysis, the temperature at which the mass of the sample is 98% by mass of the mass of the sample before heating is the 2% mass loss temperature, and the temperature at which the mass of the sample is 95% by mass of the mass of the sample before heating is the 5% mass loss temperature. ΔTd in requirement 2 is calculated from the 5% weight loss temperature and the 2% weight loss temperature. 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). More specific methods for thermogravimetric analysis to measure each weight loss temperature and to create the thermogravimetric curve described later are as described in the Examples described later.

[0041] The 2% weight loss temperature of the fluoropolymer is preferably 300° C. or higher and lower than 420° C., more preferably 350 to 415° C., and even more preferably 370 to 410° C. The 5% weight loss temperature of the fluoropolymer is preferably 320 to 500° C., more preferably 380 to 480° C., and even more preferably 420 to 460° C.

[0042] The fluoropolymer preferably has a ΔTd of 20°C or higher, preferably from 20 to 100°C, more preferably from 25 to 70°C.

[0043] <Method for producing fluorine-containing polymer> As the method for producing fluorine-containing polymer, for example, in the presence of polymerization initiator, there can be mentioned a method of copolymerizing monomers such as TFE and PAVE, and other monomers that are optionally used.As the polymerization method, there can be mentioned, for example, emulsion polymerization, solution polymerization, suspension polymerization, and emulsion polymerization is preferred from the viewpoint of excellent productivity and adjustment of molecular weight and copolymerization composition.When producing fluorine-containing polymer by emulsion polymerization, for example, it can be carried out by heating the above-mentioned monomers in the presence of aqueous medium, polymerization initiator, and optionally used emulsifier.

[0044] A preferred embodiment of the method for producing a fluoropolymer is a method for producing a fluoropolymer by polymerizing a monomer containing TFE and PAVE (hereinafter also referred to as a "specific monomer") in an aqueous dispersion (hereinafter also referred to as a "first aqueous dispersion") containing a first fluoropolymer that is substantially free of a water-soluble emulsifier and contains TFE units and PAVE units, and an aqueous medium, to produce a polymer (hereinafter also referred to as a "second fluoropolymer"), and then subjecting the resulting aqueous dispersion (hereinafter also referred to as a "second aqueous dispersion") containing the fluoropolymer to agitation to coagulate the fluoropolymer and recovering the coagulated fluoropolymer. In this production method, the step of polymerizing the above-mentioned specific monomer in the first aqueous dispersion to obtain a second aqueous dispersion containing a fluoropolymer is also referred to as a "second aqueous dispersion production step", and the step of subjecting the second aqueous dispersion to agitation to coagulate the fluoropolymer and recovering the coagulated fluoropolymer is also referred to as a "recovery step". When the fluoropolymer used in this production method is used, a fluoropolymer composition that satisfies the above-mentioned optimum vulcanization time Te can be easily obtained. Each step will now be described.

[0045] (Second aqueous dispersion production step) In the second aqueous dispersion production step, specific monomers containing TFE and PAVE are polymerized in a first aqueous dispersion which is substantially free of a water-soluble emulsifier and which contains a first fluorine-containing polymer and an aqueous medium.

[0046] Since the first aqueous dispersion does not use a water-soluble emulsifier, it is substantially free of water-soluble emulsifiers. "Substantially free of water-soluble emulsifiers" means that the content of water-soluble emulsifiers in the first aqueous dispersion is 10 mass ppm or less, preferably 100 mass ppb or less, and more preferably 50 mass ppb or less, relative to the total mass of the first aqueous dispersion. It is also preferable that the content is below the quantitation limit of the measurement method in the examples. An example of a lower limit is 1 mass ppb. The content of water-soluble 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.

[0047] The water-soluble emulsifier means an emulsifier having a solubility of 100 mg or more in 1000 g of water at 25°C. Examples of the water-soluble emulsifier include water-soluble emulsifiers containing fluorine atoms and emulsifiers not containing fluorine atoms. Note that neither the first fluorine-containing polymer nor the second fluorine-containing polymer described below falls under the category of emulsifiers. The water-soluble emulsifier may be either ionic or nonionic.

[0048] Examples of the emulsifier having fluorine atoms include anionic fluorine-containing emulsifiers, such as emulsifiers containing fluorine atoms whose total carbon number excluding the anionic group is 20 or less, and fluorine-containing emulsifiers whose anionic moiety has a molecular weight of 800 or less.

[0049] The fluorine-atom-free emulsifier does not have a fluorine atom but has a hydrocarbon group such as an alkyl group. The hydrogen atom of the hydrocarbon group of the fluorine-atom-free emulsifier can be substituted with a halogen atom other than a fluorine atom. Examples of the fluorine-atom-free emulsifier include hydrocarbon emulsifiers, and specific examples thereof include ionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0050] Ionic hydrocarbon emulsifiers include anionic hydrocarbon emulsifiers, which have a negatively charged hydrophilic moiety, such as a carboxylic acid group, a sulfonic acid group, a sulfate group, a phosphonic acid group, or a phosphate group, and a hydrocarbon moiety, such as an alkyl group, as a hydrophobic moiety. Examples of anionic hydrocarbon emulsifiers include the highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10, linear alkyl polyethersulfonate sodium supplied by BASF as the Avanel® S series, sodium dodecyl sulfate, and the sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobelSurfaceChemistry LLC.

[0051] Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity in water without dissociating into ions and have a hydrocarbon group such as an alkyl group as the hydrophobic moiety. Examples of the hydrophilic moiety of nonionic hydrocarbon emulsifiers include water-soluble functional groups such as polyethylene oxide chains obtained by polymerization of ethylene oxide. Examples of nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, for example, block copolymers having polyethylene oxide and polypropylene oxide. Examples of nonionic hydrocarbon emulsifiers include the emulsifiers described in paragraphs

[0043] to

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

[0052] The emulsifier with fluorine atom and the emulsifier without fluorine atom can contain silicon atom.The emulsifier containing silicon atom can include siloxane emulsifier.The siloxane emulsifier can include the emulsifier described in U.S. Patent No. 6,841,616 (Wille et al.) and U.S. Patent No. 7,977,438 (Brothers et al.).

[0053] The emulsifier having a fluorine atom and the emulsifier not having a fluorine atom may be a polymer emulsifier. Examples of the polymer emulsifier include a water-soluble polymer having a hydrophilic group in a side chain. Examples of such a polymer emulsifier include a polymer containing a unit based on a compound having a site capable of reacting by polymerization and a hydrophilic group. Further examples include polymers obtained by subjecting a polymer based on a compound having a group that can become a hydrophilic group, even if it does not have hydrophilicity during polymerization, to post-treatment such as hydrolysis.

[0054] It is preferable that the first aqueous dispersion is substantially free of an emulsifier represented by any of formulae (S1) to (S4). When no emulsifier is used in producing the first fluoropolymer contained in the first aqueous dispersion, the amount of the compound represented by any of formulae (S1) to (S4) generated can be suppressed, making it easier to adjust the content of these compounds.

[0055] H-(CF ２ ) ｎ１ -COOM (S1) F-(CF ２ ) ｎ１ -COOM (S2) H-(CF２ ) ｎ２ -SO ３ M (S3) F-(CF ２ ) ｎ２ -SO ３ M (S4) In formulas (S1) to (S4), n1 is an integer of 3 to 19, n2 is an integer of 4 to 20, and each M is independently a hydrogen atom, Na, K, or NH ４ is.

[0056] The first fluorine-containing polymer is a fluorine-containing polymer that comprises TFE units and PAVE units.It is presumed that the first fluorine-containing polymer adsorbs and incorporates the specific monomer at the hydrophobic part during the polymerization of the specific monomer described below, and solubilizes the specific monomer even when the first aqueous dispersion does not contain an emulsifier, making the polymerization of the specific monomer easier to proceed.It is also presumed that the first fluorine-containing polymer contributes to the dispersion stabilization in the first aqueous dispersion.

[0057] The details of PAVE are the same as those of the PAVE from which the PAVE units in the fluorine-containing polymer are derived, and the preferred embodiments are also the same.

[0058] In the first fluoropolymer, the content of TFE units relative to the total of TFE units and PAVE units is preferably 20 to 95 mol%, more preferably 40 to 85 mol%, and from the viewpoint of more efficient production of the fluoropolymer, it is even more preferably 50 to 75 mol%, and particularly preferably 60 to 70 mol%. In the first fluoropolymer, the content of PAVE units relative to the total of TFE units and PAVE units is preferably 5 to 80 mol%, more preferably 15 to 60 mol%, and from the viewpoint of more efficient production of the fluoropolymer, it is even more preferably 25 to 55 mol%, and particularly preferably 30 to 40 mol%. When PMVE or PPVE is used as PAVE, the suitable amount used is similar. The total content of TFE units and PAVE units in the first fluorinated polymer is preferably from 99.0 to 100.0 mol%, more preferably from 99.5 to 100.0 mol%, and even more preferably from 99.9 to 100.0 mol%, based on the total content of all units in the first fluorinated polymer.

[0059] The first fluorine-containing polymer may contain units based on monomers other than TFE and PAVE, and from the viewpoint of more efficient production of the fluorine-containing polymer, it is also preferable that it is substantially free of units based on other monomers. "Substantially free of units based on other monomers" means that the content of units based on other monomers is 0.01 mol% or less, and preferably 0 mol%, based on the total content of all units in the first fluorine-containing polymer.

[0060] The content of the first fluorine-containing polymer before the start of polymerization of the specific monomer is preferably 0.01 to 4.0% by mass, more preferably 0.01 to 0.6% by mass, and even more preferably 0.01 to 0.5% by mass, relative to the total mass of the first aqueous dispersion, from the viewpoint of more efficient production of the fluorine-containing polymer. In this specification, "before the start of polymerization of the specific monomer" means immediately before the start of polymerization. Examples of "start of polymerization" include the time when the reactor is heated to a polymerization temperature or higher and then the monomer (or, if a polymerization initiator is used, the polymerization initiator and the monomer) is allowed to coexist in the reactor, and the time when the reactor is heated to a polymerization temperature or higher and then the monomer (or, if a polymerization initiator is used, the polymerization initiator and the monomer) is allowed to coexist in the reactor. The first aqueous dispersion before the start of polymerization of the specific monomer does not contain the specific monomer or the polymerization initiator.

[0061] The content (solids concentration) of the first fluoropolymer in the first aqueous dispersion can be measured, for example, by the following method. 2.0 g of the first aqueous dispersion is heated at 170°C for 20 minutes, and then the mass of the residue is weighed and the solids concentration is calculated by the following formula: "Solids concentration (mass%) = 100 × mass (g) of heated residue of first aqueous dispersion / mass (2.0 g) of first aqueous dispersion"

[0062] A preferred embodiment of the second aqueous dispersion production step is one in which the content of PAVE units in the first fluoropolymer is 20 to 95 mol % relative to the total content of TFE units and PAVE units, and the content of the first fluoropolymer before the start of polymerization of the specific monomer is 0.01 to 4.0 mass % relative to the total mass of the first aqueous dispersion.

[0063] As a method for producing the first fluorine-containing polymer, a method of polymerizing monomers containing TFE and PAVE in an aqueous medium in the presence of a polymerization initiator is preferred. This gives the first fluorine-containing polymer dispersed in the aqueous medium in the form of particles. The aqueous medium thus obtained in which the particles of the first fluorine-containing polymer are dispersed may be used as is as the first aqueous dispersion. Alternatively, the solvent may be replaced, and the first fluorine-containing polymer may be dispersed in another aqueous medium, which may be used as the first aqueous dispersion.

[0064] The polymerization initiator used for polymerizing the first fluorine-containing polymer is preferably a water-soluble polymerization initiator, more preferably a persulfate such as ammonium persulfate, sodium persulfate, or potassium persulfate, or an organic polymerization initiator such as disuccinic acid peroxide or azobisisobutylamidine dihydrochloride, still more preferably a persulfate, and particularly preferably ammonium persulfate.

[0065] The aqueous medium used in producing the first fluorinated polymer includes water and a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0066] In producing the first fluorine-containing polymer, the aqueous medium containing the monomers preferably does not contain an emulsifier. The emulsifier (type and the like) is as described above.

[0067] The first aqueous dispersion containing the first fluorine-containing polymer is preferably used for polymerization of a specific monomer after being subjected to a purification treatment to reduce or inactivate the polymerization initiator and its decomposition products. By removing the polymerization initiator and its decomposition products that may be contained in the first aqueous dispersion containing the first fluorine-containing polymer through the purification treatment, a fluorine-containing polymer having desired physical properties is easily obtained. Examples of the purification treatment method include a heat treatment and a method of passing the dispersion through an ion exchange resin (preferably an anion exchange resin). The purification treatment may be performed multiple times.

[0068] Specific examples of the aqueous medium contained in the first aqueous dispersion include the aqueous medium used in the production of the first fluoropolymer described above. As described above, the aqueous medium used as the polymerization solvent in the production of the first fluoropolymer may be used. Before the start of polymerization of the specific monomer, the content of the aqueous medium is preferably 60 to 99.9 mass%, more preferably 96 to 99.9 mass%, and even more preferably 98 to 99.9 mass%, based on the total mass of the first aqueous dispersion.

[0069] The first aqueous dispersion may contain other components in addition to the first fluorinated polymer and the aqueous medium. Specific examples of the other components include a reducing agent, a pH adjuster, and a chain transfer agent, which will be described later. Specific examples of the pH adjuster include inorganic salts and ammonia. Specific examples of the inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium hydrogen carbonate and sodium carbonate. Specific examples of more preferred phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate. When the first aqueous dispersion contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium.

[0070] Specific Monomer The specific monomer is a monomer including TFE and PAVE. Preferred embodiments of TFE and PAVE as the specific monomer are the same as the preferred embodiments of TFE and PAVE in the first fluorine-containing polymer described above. The total amount of TFE and PAVE used is preferably 80 to 100 mol%, more preferably 90 to 100 mol%, and even more preferably 95 to 100 mol%, based on the amount of the specific monomer used.

[0071] The specific monomer may contain a monomer other than TFE and PAVE (hereinafter also referred to as "other monomer"). Specific examples of the other monomer include the above-mentioned BO, R Ｈａｌ , R ＣＮ and POAVE. Preferred embodiments of these other monomers are the same as the preferred embodiments of other monomers in the description of units based on other monomers that may be contained in the fluorine-containing polymer.

[0072] The amount of the other monomer used is preferably 0 to 20 mol %, more preferably 0 to 10 mol %, and even more preferably 0 to 5 mol %, based on the amount of the specific monomer used.

[0073] The specific monomer consists of only TFE and PAVE, or contains TFE and PAVE, and BO, R Ｈａｌ and R ＣＮ It is preferable that the polymer contains at least one monomer selected from the group consisting of:

[0074] In the second aqueous dispersion production process, the specific monomer is preferably polymerized in the presence of a polymerization initiator. The polymerization initiator is preferably an oil-soluble radical initiator, a water-soluble radical initiator, or a water-soluble redox catalyst. Specific examples of oil-soluble radical initiators include oil-soluble organic peroxides such as tert-butyl peroxypivalate (hereinafter also referred to as "PBPV") and diisopropyl peroxydicarbonate (hereinafter also referred to as "IPP"). Specific examples of water-soluble radical initiators include persulfates such as ammonium persulfate and potassium persulfate, 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, organic acid, or inorganic salt. The persulfate is preferably potassium persulfate or ammonium persulfate. The sulfite is preferably sodium sulfite. The inorganic salt may be a combination of a sulfate anion, a sulfite anion, or a chloride anion with a metal ion. The metal ion is preferably a transition metal, such as manganese, iron, cobalt, nickel, copper, zinc, cerium, or silver ion, with iron ion being preferred. The inorganic salt is preferably iron(II) sulfate. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator. From the viewpoint of more efficient production of a fluorine-containing polymer, a water-soluble radical initiator is more preferred, and a water-soluble organic peroxide is even more preferred. Two or more polymerization initiators may be used in combination.

[0075] The amount of the polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, per 100 parts by mass of the specific monomer used.

[0076] Chain Transfer Agent In the second aqueous dispersion production step, the specific monomer is also preferably polymerized in the presence of a chain transfer agent. Specific examples of the chain transfer agent include chain transfer agents having an iodine atom, ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane, and chain transfer agents having an iodine atom are preferred. By polymerizing the specific monomer using a chain transfer agent having an iodine atom, a fluorine-containing polymer having an iodine atom at its terminal can be produced.

[0077] The chain transfer agent having an iodine atom is preferably a compound represented by formula (I): (R ｆ ) - (X) ２ (I) In formula (I), R ｆ is a fluoroalkylene group having 1 to 16 carbon atoms or an aromatic ring group, and X is an iodine atom or a bromine atom, and at least one of X is an iodine atom. ｆ The fluoroalkylene group of R may be linear or branched. ｆ Preferably, X is a perfluoroalkylene group. Preferably, all of X are iodine atoms.

[0078] Specific examples of the compound represented by formula (I) include 1,2-diiodoperfluoroethane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane (hereinafter also referred to as "C4DI"), 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,3-diiodo-2-chloroperfluoropropane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoperfluoropropane, 1,3-diiodoper ...4-diiodoperfluorobutane (hereinafter also referred to as "C4DI"), 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, 1,3-diiodoperfluoropropane, 1,5-diiodo-2,4-dichloroperfluoropentane, 1,12-diiodoperfluorododecane, 1,16-diiodoperfluorohexadecane, diiodomethane, 1,2-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorobutane, 1,5-diiodoperfluoropentane, 1,12-diiodoperfluorododecane, 1,16 Examples of the compound represented by formula (I) include iodoethane, 1,3-diiodo-n-propane, (2-iodoethyl)-substituted benzene, 1-iodo-4-bromoperfluorobutane, 1-iodo-6-bromoperfluorohexane, 1-iodo-8-bromoperfluoroctane, 1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 2-bromo-3-iodoperfluorobutane, 3-bromo-4-iodoperfluorobutene-1, 2-bromo-4-iodoperfluorobutene-1, monoiodomonobromo-substituted benzene, and diiodomonobromo-substituted benzene. C4DI is preferred as the compound represented by formula (I).

[0079] The amount of the chain transfer agent used is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 1 to 3 parts by mass, per 100 parts by mass of the specific monomer used.

[0080] From the viewpoint of better crosslinkability of the produced fluoropolymer, the method for producing a fluoropolymer according to the present invention is preferably carried out in such a manner that the specific monomer is selected from the group consisting of BO, R Ｈａｌ and R ＣＮ or the first aqueous dispersion preferably contains a chain transfer agent containing an iodine atom.

[0081] The second aqueous dispersion production step is a step of polymerizing the specific monomer in the first aqueous dispersion to obtain a second aqueous dispersion containing a fluorine-containing polymer. The specific monomer is added to the reaction system (i.e., polymerization reaction vessel) by a conventional method. For example, the specific monomer may be continuously or intermittently added to the reaction system so that the polymerization pressure reaches a predetermined pressure. Alternatively, the specific monomer may be dissolved in an aqueous medium, and the resulting solution may be continuously or intermittently added to the reaction system. When a polymerization initiator is used, the polymerization initiator may be added to the reaction system all at once or in portions. When other components (e.g., chain transfer agents) other than those mentioned above are used, the other components may be added to the reaction system all at once or in portions.

[0082] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. In the case of batch processing, the polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 700 minutes.

[0083] The polymerization of the specific monomer is preferably carried out in a reaction system substantially free of an emulsifier. Examples of the emulsifier include the emulsifiers described above. The absence of an emulsifier means an environment in which the content of the emulsifier is 0.03 ppm by mass or less, preferably 0.02 ppm by mass or less, and more preferably 0 ppm by mass, relative to the total mass of the aqueous medium contained in the first aqueous dispersion.

[0084] In the second aqueous dispersion production step, a fluoropolymer is produced, and a second aqueous dispersion in which particles containing the fluoropolymer are dispersed in an aqueous medium is obtained.

[0085] Second aqueous dispersion The second aqueous dispersion is an aqueous dispersion containing the second fluorine-containing polymer obtained by the second aqueous dispersion production step. In other words, the second aqueous dispersion is an aqueous dispersion in which particles containing a fluorine-containing polymer (hereinafter also referred to as "specific particles") are dispersed in an aqueous medium. The specific particles may or may not contain the first fluorine-containing polymer. In other words, the specific particles are particles containing the second fluorine-containing polymer, or particles containing the first fluorine-containing polymer and the second fluorine-containing polymer. The second aqueous dispersion may contain the first fluorine-containing polymer dispersed in the form of particles.

[0086] The preferred embodiment of the fluoropolymer contained in the second aqueous dispersion is as described above. The content of the fluoropolymer-containing specific particles is preferably 1 to 50 mass%, more preferably 1 to 40 mass%, and even more preferably 1 to 30 mass%, based on the total mass of the second aqueous dispersion, from the viewpoint of dispersion stability of the specific particles.

[0087] The average particle size of the specific particles is preferably 1 μm or less, and from the viewpoint of dispersion stability of the specific particles, it is more preferably 500 nm or less, and even more preferably 400 nm or less. From the viewpoint of recovery efficiency in the recovery step described below, the average particle size of the specific particles is preferably 50 nm or more, more preferably 70 nm or more, and even more preferably 100 nm or more. The average particle size of the specific particles is a particle size calculated by analyzing an autocorrelation function obtained by dynamic light scattering using a monodisperse cumulant method.

[0088] Specific examples and preferred embodiments of the aqueous medium contained in the second aqueous dispersion are the same as those of the aqueous medium contained in the first aqueous dispersion. The content of the aqueous medium is preferably 50 to 99 mass%, more preferably 60 to 99 mass%, and even more preferably 70 to 99 mass%, based on the total mass of the second aqueous dispersion, from the viewpoint of dispersion stability of the specific particles.

[0089] The content of the emulsifier in the second aqueous dispersion is preferably 100 mass ppm or less, more preferably 75 mass ppm or less, even more preferably 50 mass ppm or less, and particularly preferably 1 mass ppm or less, relative to the total mass of the second aqueous dispersion. It is also preferably below the quantitation limit of the above-mentioned method for measuring the content of the emulsifier. An example of a lower limit is 1 mass ppb. The content of the emulsifier can be measured by the same method as that for the first aqueous dispersion described above. Specific examples of the emulsifier are as described above. The emulsifier in the second aqueous dispersion may or may not be water-soluble.

[0090] (Recovery Step) The recovery step is a step of subjecting the second aqueous dispersion obtained in the second aqueous dispersion production step to a stirring treatment to coagulate the fluoropolymer and obtain the coagulated fluoropolymer.

[0091] Stirring Treatment: Known stirring treatments that impart shear force to the second aqueous dispersion can be used. Known stirring treatments that impart shear force to the second aqueous dispersion can be used. Among these, stirring treatments using a stirring device that rotates a stirring shaft equipped with stirring blades are preferred. Specific examples of the shape of the stirring blades include paddle blades, inclined paddle blades, propeller blades, disk blades, three-bladed swept blades, anchor blades, turbine blades, and disk turbine blades. Paddle blades or disk turbine blades are preferred due to their excellent stirring efficiency. The number of stirring blades is preferably 1 to 10, more preferably 2 to 4. Specific examples of the shape of the vessel used in the stirring treatment include cylindrical, conical, elliptical, rectangular, and pyramidal shapes. Cylindrical shapes are preferred due to their mixability and fluidity. The stirring device may be equipped with a baffle.

[0092] The stirring time is preferably 0.1 to 24 hours, more preferably 0.1 to 12 hours, and even more preferably 0.1 to 6 hours. The peripheral speed of stirring is preferably 2 to 50 m / s, more preferably 3 to 30 m / s, and even more preferably 5 to 30 m / s. The peripheral speed may be constant during stirring or may change during stirring. It is also preferable that the peripheral speed is faster than the peripheral speed in step 1. The peripheral speed of stirring represents the speed of the blade at the tip of the stirring blade. The temperature of the aqueous dispersion during stirring treatment is preferably 10 to 90°C, more preferably 10 to 80°C, and even more preferably 15 to 70°C.

[0093] By the stirring treatment, a solid material containing an aggregated fluorine-containing polymer is obtained. In this specification, the term "solid material" refers to a solid that is not stably dispersed in an aqueous medium, and a dispersoid stably dispersed in an aqueous medium is considered not to be a solid material even if it is a solid that is insoluble in the aqueous medium. For example, among the insoluble components (e.g., specific particles) contained in the second aqueous dispersion after stirring, the dispersoid stably dispersed in the aqueous medium is not included in the solid material, and the sediment and floating matter that are not stably dispersed in the aqueous medium are included in the solid material. Examples of the solid material include agglomerates of the fluorine-containing polymer. Examples of the stably dispersed dispersoid include dispersoids that pass through Type 5A filter paper specified in JIS P 3801 [Filter paper (for chemical analysis)]. The particle size of the solid material is, for example, 500 μm or more, and preferably 1000 μm or more.

[0094] The fluoropolymer agglomerates separated by the stirring treatment are recovered to give a fluoropolymer containing TFE units and PAVE units. Specific examples of the method for recovering the fluoropolymer agglomerates include filtration and centrifugation, with filtration being preferred.

[0095] Washing Step Preferably, the method for producing a fluoropolymer further comprises a step of washing the recovered fluoropolymer (hereinafter also referred to as "Step 3"). Step 3 makes it possible to remove other components (e.g., emulsifier, monomer, polymerization initiator, and reaction products thereof) adhered to the fluoropolymer, making it easier to obtain a crosslinked rubber article with desired physical properties. Examples of the washing liquid in the washing step include the aqueous media described above, with water being preferred and ultrapure water being more preferred. Specific examples of washing methods include a method of immersing the recovered fluoropolymer in a washing liquid and a method of showering the recovered fluoropolymer with a washing liquid. The amount of washing liquid in the washing step is preferably 1 to 50 times, more preferably 3 to 30 times, and even more preferably 5 to 15 times the total mass of the fluoropolymer. The temperature of the washing liquid in the washing step is preferably 5 to 50°C, more preferably 10 to 40°C, and more preferably 15 to 30°C.

[0096] A fluoropolymer can be obtained by the above production method. In particular, it is preferable to produce a fluoropolymer having a PAVE unit content of 20 to 95 mol% based on the total content of TFE units and PAVE units in the fluoropolymer by the above production method.

[0097] <Solid composition> The fluoropolymer obtained by the above-mentioned production method may be in the form of a solid composition. In this specification, a solid composition means a composition having a solid content mass of 99 mass% or more. The solid content mass is calculated by the following method based on the masses before and after heating. 2.0 g of the solid composition is heated at 170°C for 20 minutes, and then the mass of the residue is weighed and the solid content mass is calculated by the following formula: Solid content mass (mass%) = 100 × (mass of residue) / (mass of solid composition) The content of the fluoropolymer in the solid composition is preferably 99.0 to 100 mass%, more preferably 99.5 to 100 mass%, and even more preferably 99.8 to 100 mass%, based on the total mass of the solid composition.

[0098] It is preferable that the solid composition containing a fluorine-containing polymer is substantially free of an emulsifier. "The solid composition is substantially free of an emulsifier" 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, based on the total mass of the solid composition. The lower limit of the emulsifier content is 0 ppb by mass. The method for measuring the emulsifier content and the emulsifier that may be contained in the solid composition are as described above.

[0099] The solid composition preferably contains the compound represented by formula (S1) in an amount of 10 ppm by mass or less, more preferably 150 ppb by mass or less, and even more preferably 50 ppm by mass or less. The lower limit of the content of formula (S1) is 0 ppb by mass.

[0100] The metal content of the solid composition is preferably 50 ppm by mass or less, more preferably 20 ppm by mass or less, and even more preferably 10 ppm by mass or less, relative to the total mass of the solid composition. It is also preferably below the measurement limit of the following measurement method. The lower limit can be 1 ppb by mass. The metal content is the total content of 29 metal elements (Fe, Na, K, Li, Be, Mg, Al, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Mo, Ag, Cd, In, Sn, Cs, Ba, Pb, and Bi) measured by the absolute calibration curve method using an inductively coupled plasma mass spectrometer. The metal content of the solid composition can be measured by ashing the solid composition, dissolving the resulting ash in acid, and measuring the resulting solution using an inductively coupled plasma mass spectrometer. In the process for producing a fluoropolymer, by using a stirring device equipped with the above-mentioned stirring blades, it is not necessary to use a metal-containing flocculant when recovering the fluoropolymer, and therefore the metal content of the solid composition can be easily adjusted to be within the above-mentioned range.

[0101] The solid composition is also preferably a fluorine-containing elastomer. A "fluorine-containing elastomer" is an elastic fluorine-containing polymer having no melting point and exhibiting a storage modulus G' of 80 kPa or more at 100°C and a frequency of 50 cpm, as measured in accordance with ASTM D6204, and is distinguished from a fluororesin.

[0102] (Shape) The solid composition containing the fluoropolymer can be transformed into an appropriate shape depending on the manufacturing method and application of the crosslinked rubber article. The solid composition may be, for example, a sheet, granules, a tube, or a fiber, or may be in an irregular shape.

[0103] <Crosslinking Agent> The present composition contains a crosslinking agent. The crosslinking agent is preferably at least one selected from the group consisting of organic peroxides and compounds having two or more amino groups (hereinafter also referred to as "polyamine compounds"). In view of better crosslinking reactivity of the fluoropolymer, it is preferable to contain an organic peroxide. Only one type of crosslinking agent may be contained, or two or more types may be contained.

[0104] Specific examples of organic peroxides include dialkyl peroxides, α,α'-bis(tert-butylperoxy)-p-diisopropylbenzene, α,α'-bis(tert-butylperoxy)-m-diisopropylbenzene, benzoyl peroxide, tert-butylperoxybenzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, tert-butylcumyl peroxide, and dicumyl peroxide. Of these, dialkyl peroxides, α,α'-bis(tert-butylperoxy)-p-diisopropylbenzene, and α,α'-bis(tert-butylperoxy)-m-diisopropylbenzene are preferred. Specific examples of dialkyl peroxides include 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroxyperoxide, tert-butylperoxymaleic acid, tert-butylperoxyisopropyl carbonate, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne. Of these, dicumyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane are preferred.

[0105] The polyamine compound may be a compound in which a hydrogen atom of an aliphatic hydrocarbon is substituted with an amino group, or a compound in which a hydrogen atom of an aromatic hydrocarbon is substituted with an amino group, but from the viewpoint of achieving a more excellent effect of the present invention, a compound in which a hydrogen atom of an aromatic hydrocarbon is substituted with an amino group is preferred. The polyamine compound preferably contains a fluorine atom. This improves compatibility with the fluorine-containing polymer, thereby enabling a crosslinked rubber article to be obtained that has a smaller compression set under high temperature and high compression.

[0106] Specific examples of the polyamine compound include hexamethylenediamine, hexamethylenediamine carbamate, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(3-amino-4-hydroxyphenyl)propane, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (hereinafter also referred to as "BOAP"; also known as bisaminophenol AF), 2,2-bis(3,4-diaminophenyl)propane, 2,2-bis(3,4-diaminophenyl)hexafluoropropane, 2,2-bis(3-amino-4-(N-phenylamino)phenyl)hexafluoropropane, 4,4'-methylenedianiline, m-phenylenediamine, adipic acid dihydrazide, and the compound represented by formula (XII) of Japanese Patent No. 5,833,657. BOAP is preferred because it provides better effects for the present invention.

[0107] The content of the crosslinking agent is preferably from 0.3 to 10 parts by mass, more preferably from 0.3 to 5 parts by mass, and even more preferably from 0.5 to 3 parts by mass, per 100 parts by mass of the fluorine-containing polymer.

[0108] <Crosslinking Auxiliary Agent> The present composition may contain a crosslinking auxiliary agent. The crosslinking auxiliary agent is used to improve the crosslinking reactivity of the fluorine-containing polymer. The crosslinking auxiliary agent is preferably a compound having two or more reactive functional groups in the same molecule. Specific examples of the reactive functional group include a carbon-carbon double bond-containing group, a halogen atom, an acid anhydride residue, a carboxy group, an amino group, a cyano group, and a hydroxyl group. The multiple reactive functional groups present in the same molecule of the crosslinking auxiliary may be the same or different. Specific examples of the carbon-carbon double bond-containing group include alkenyl groups such as a vinyl group, an allyl group, and a methallyl group, unsaturated acyl groups such as an acryloyl group and a methacryloyl group, and a maleimide group. The carbon-carbon double bond-containing group is preferably an alkenyl group having 2 to 4 carbon atoms, with an allyl group being particularly preferred.

[0109] Specific examples of the crosslinking aid include a compound represented by the following formula (7), triallyl cyanurate, triallyl isocyanurate, trimethallyl isocyanurate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, triallyl trimellitate, m-phenylenediamine bismaleimide, p-quinonedioxime, p,p'-dibenzoylquinonedioxime, dipropargyl terephthalate, diallyl phthalate, N,N',N",N'"-tetraallyl terephthalamide, and vinyl group-containing siloxane oligomers (polymethylvinylsiloxane, polymethylphenylvinylsiloxane, etc.). Among these, the compound represented by the following formula (7), triallyl cyanurate, triallyl isocyanurate, and trimethallyl isocyanurate are preferred, with the compound represented by the following formula (7) and triallyl isocyanurate being more preferred, and the compound represented by the following formula (7) being particularly preferred from the viewpoint of superior transparency of the crosslinked rubber. The crosslinking aid may be contained in one kind only, or in two or more kinds.

[0110] Equation (7) is as follows: (CR ４１ R ４２ =CR ４３ ) ２ R ４４ Formula (7) In formula (7), R ４１ , R ４２ and R４３ each independently represents a hydrogen atom, a fluorine atom, an alkyl group having 1 to 5 carbon atoms, or a fluoroalkyl group having 1 to 5 carbon atoms; R ４４ represents a divalent fluorohydrocarbon group having 1 to 18 carbon atoms or a group having an etheric oxygen atom at the end or between the carbon-carbon bonds of the fluorohydrocarbon group. ４１ , multiple R ４２ and multiple R ４３ may be the same or different from each other.

[0111] R ４１ , R ４２ and R ４３ When R is an alkyl group or a fluoroalkyl group, it may be linear or branched, but is preferably linear. ４１ , R ４２ and R ４３ When R is an alkyl group or a fluoroalkyl group, the number of carbon atoms therein is preferably 1 to 5, more preferably 1 to 3, and particularly preferably 1 or 2. From the viewpoint of superior polymerization reactivity of BO, R ４１ , R ４２ and R ４３ It is preferred that all of are hydrogen atoms.

[0112] R ４４ The fluorohydrocarbon group in R is preferably a perfluorohydrocarbon group, since the crosslinked rubber article will have better heat resistance. ４４ R may be linear, branched, or cyclic, preferably linear or branched, and particularly preferably linear. ４４ has 1 to 18 carbon atoms, preferably 2 to 8, and particularly preferably 3 to 7. ４４ When R has an etheric oxygen atom, ４４ The number of etheric oxygen atoms in R is preferably 1 to 6, more preferably 1 to 3, and particularly preferably 1 or 2. ４４ has an etheric oxygen atom, the etheric oxygen atom is ４４ The compound represented by formula (7) is preferably present at the terminal of C3DVE, C4DVE, CH ２ =CH(CF ２ )２ CH=CH ２ , C.H. ２ =CH(CF ２ ) ４ CH=CH ２ , C6DV are preferred, and C6DV is particularly preferred.

[0113] In the present composition, the content of the crosslinking aid is preferably 0.1 to 2.5 parts by mass, more preferably 0.1 to 2.0 parts by mass, and even more preferably 0.1 to 1.0 part by mass, per 100 parts by mass of the fluoropolymer. When the content is at least the lower limit of the above range, the hardness of the crosslinked rubber article is superior, and when it is at most the upper limit of the above range, the transparency of the crosslinked rubber article is superior.

[0114] <Filler> The composition may contain a filler. The filler preferably contains at least one selected from the group consisting of carbon black, barium sulfate, calcium metasilicate, calcium carbonate, titanium oxide, silicon dioxide, clay, and talc. Only one type of filler may be contained, or two or more types may be contained.

[0115] The content of the filler in the composition is preferably from 0.1 to 100 parts by mass, more preferably from 1 to 50 parts by mass, and even more preferably from 5 to 30 parts by mass, per 100 parts by mass of the fluoropolymer.

[0116] <Other Components> The present composition may contain components other than those described above (hereinafter also referred to as "other components"). Specific examples of other components include a catalyst, an acid acceptor, a scorch retarder, a crown ether, and a mold release agent. Only one type of other component may be contained, or two or more types may be contained. In the present composition, the total content of the other components is preferably 0.1 to 15 parts by mass, more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the fluoropolymer.

[0117] [Method for producing a fluoropolymer composition] The method for producing a fluoropolymer composition of the present invention (hereinafter also referred to as "method for producing the present composition") comprises: Step 1 of polymerizing a monomer containing TFE and PAVE in an aqueous dispersion (first aqueous dispersion) containing a first fluoropolymer substantially free of a water-soluble emulsifier and containing TFE units and PAVE units, and an aqueous medium, to produce a second fluoropolymer; and Step 2 of adding a crosslinking agent to the second fluoropolymer to obtain a fluoropolymer composition containing the second fluoropolymer and the crosslinking agent. In addition, in the method for producing the present composition, the content of PAVE units in the first fluoropolymer relative to the total content of TFE units and PAVE units is 20 to 95 mol %. In addition, in the method for producing the present composition, the content of PAVE units in the second fluoropolymer relative to the total content of TFE units and PAVE units is 20 to 95 mol %. Furthermore, in the method for producing the composition, the content of the first fluoropolymer is 0.01 to 4.0% by mass relative to the total mass of the first aqueous dispersion before the start of polymerization of the monomers. According to the method for producing the composition, the above-mentioned composition can be easily obtained. In this case, the second fluoropolymer in the fluoropolymer composition obtained by the method for producing the composition corresponds to the above-mentioned fluoropolymer in the composition. The fluoropolymer composition obtained by the method for producing the composition is preferably used for producing a crosslinked rubber article as described below. Each step will be described below.

[0118] [Step 1] In step 1, the above-mentioned specific monomer is polymerized in a first aqueous dispersion. The first aqueous dispersion used in step 1 of the method for producing the present composition is the same as the first aqueous dispersion used in the second aqueous dispersion production step in the above-mentioned method for producing a fluoropolymer. Furthermore, the specific method and preferred embodiments of step 1 in the method for producing the present composition are the same as the specific method and preferred embodiments of the second aqueous dispersion production step in the above-mentioned method for producing a fluoropolymer.

[0119] A second aqueous dispersion containing a second fluorine-containing polymer is obtained in step 1. The second fluorine-containing polymer and second aqueous dispersion obtained in step 1, including preferred embodiments thereof, are the same as the fluorine-containing polymer and second aqueous dispersion in the above-mentioned method for producing a fluorine-containing polymer.

[0120] [Step 2] Step 2 is a step of adding a crosslinking agent to the second fluorine-containing polymer obtained in step 1 to obtain a fluorine-containing polymer composition containing the second fluorine-containing polymer and the crosslinking agent. The crosslinking agent, including preferred embodiments thereof, is the same as the crosslinking agent contained in the present composition described above. The amount of crosslinking agent added is preferably the same as the content of the crosslinking agent in the present composition described above. In step 2, in addition to the crosslinking agent, the components contained in the present composition described above (crosslinking aid, filler, other components) may be added. The crosslinking aid, filler, and other components, including preferred embodiments thereof, are the same as the crosslinking aid, filler, and other components that can be contained in the present composition described above. The amount of each component added is preferably the same as the content of each component in the present composition described above.

[0121] In step 2, it is preferable to mix the above components. The mixing can be performed using a rubber mixing device such as a roll, a kneader, a Banbury mixer, or an extruder. After the above components are mixed to obtain a mixture, the mixture may be molded. Specific examples of methods for molding the mixture include compression molding, injection molding, extrusion molding, calendar molding, or a method in which the mixture is dissolved in a solvent and then dipped or coated onto a substrate or the like to form the mixture.

[0122] <Other Steps> The method for producing the present composition may include steps other than step 1 and step 2 (hereinafter also referred to as "other steps"). Examples of other steps include the recovery step in the above-mentioned method for producing a fluoropolymer. Specific methods and preferred embodiments of the recovery step are the same as those of the above-mentioned method for producing a fluoropolymer. The recovery step is carried out after step 1 and before step 2.

[0123] Use of the fluoropolymer composition obtained by the method for producing the present composition makes it easy to adjust the optimum vulcanization time Te calculated from the above formula A to 2.3 minutes or more, which is preferred. More specifically, in the method for producing the present composition, adjustment of the contents of TFE units and PAVE units in the first fluoropolymer, adjustment of the contents of TFE units and PAVE units in the second fluoropolymer, and adjustment of the content of the first fluoropolymer in the first aqueous dispersion can be carried out in an appropriate combination to bring the optimum vulcanization time Te calculated from the above formula A into the above preferred range. Use of the fluoropolymer obtained by the method for producing the present composition makes it easy to adjust the composition so as to satisfy the above-mentioned requirement 1 relating to the 2% weight loss temperature of the fluoropolymer and requirement 2 relating to the difference ΔTd between the 5% weight loss temperature and the 2% weight loss temperature of the fluoropolymer, which is preferred. More specifically, in the method for producing the composition of the present invention, for example, by adjusting the content of the first fluoropolymer in the first aqueous dispersion, it is possible to adjust the content of low molecular weight components in the entire fluoropolymer and the content of high molecular weight components in the entire fluoropolymer, and the above-mentioned requirements 1 and 2 can be set within preferred ranges.

[0124] [Crosslinked Rubber Article] The crosslinked rubber article of the present invention is a rubber article obtained by crosslinking the fluoropolymer in the present composition described above. A preferred method for crosslinking the fluoropolymer in the present composition is a method in which the present composition is heated. Specific examples of crosslinking methods by heating include hot press crosslinking, steam crosslinking, and hot air crosslinking. The heating conditions are preferably 100 to 400°C for 1 second to 24 hours.

[0125] 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.

[0126] As a crosslinking method other than crosslinking the fluoropolymer by heating, there is mentioned a method of crosslinking the fluoropolymer by irradiating the present composition with radiation. Specific examples of the radiation to be irradiated include electron beams and ultraviolet rays.

[0127] The hardness (Shore-A) of the crosslinked rubber article is preferably 72 to 100, more preferably 73 to 80, and even more preferably 73 to 75. The hardness of the crosslinked rubber article is measured by the method described in the Examples section below.

[0128] [Uses] 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.

[0129] The present invention will be described in detail below with reference to examples. Examples 1 to 3 are working examples, and Examples 4 to 6 are comparative examples. However, the present invention is not limited to these examples.

[0130] <Method for Quantifying Emulsifier Contained in Solid Composition> (Preparation of Measurement Sample) The solid compositions obtained in each example described below were freeze-pulverized using a freeze-pulverizer Freezer Mill 6775 (manufactured by SPEX) under the following conditions. Before freeze-pulverization, 10% by mass of dibutylhydroxytoluene (BHT) was added to the solid composition in advance, based on the total mass of the solid composition, to obtain a pulverized powder. The freeze-pulverization conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 minutes, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 0.25 g of the obtained pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate each fluoropolymer. The supernatant was used as an extract. The obtained extract was subjected to LC / MS / MS analysis. The fluorine-containing emulsifier and hydrocarbon emulsifier in the extract were measured using a liquid chromatograph mass spectrometer. The measurement equipment configuration and LC-MS measurement conditions are shown in Table 1. Using aqueous solutions of fluorine-containing emulsifier and hydrocarbon emulsifier with known concentrations, aqueous solutions with five or more levels of content were prepared, and LC / MS analysis was performed on the aqueous solutions with each content. The relationship between the content and the area relative to the content was plotted to draw a calibration curve. Using the calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing emulsifier and hydrocarbon emulsifier in the extract was converted into the content of the fluorine-containing emulsifier and hydrocarbon emulsifier.

[0131]

[0132] The MRM measurement parameters are appropriately selected depending on the structures of the emulsifier having a fluorine atom and the 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 emulsifier having a fluorine atom and the 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 an example, the MRM measurement parameters for compounds (S2) and (S4), which are emulsifiers having a fluorine atom, are shown in the table below. In formulas (S2) and (S4), M Ｓ represents a hydrogen atom, a metal atom, 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.

[0133]

[0134]

[0135] (Quantitative Analysis of Fluorine-Containing Emulsifier and Hydrocarbon Emulsifier Contained in Solid Composition) Specifically, five levels of methanol standard solutions of fluorine-containing emulsifier and hydrocarbon emulsifier with known concentrations of 1 to 180 ng / g were prepared, and a was calculated from the sample concentration and peak integral value of each emulsifier using a first-order approximation according to formula (A1-1): A = a × X (A1-1), where A is the peak area of ​​each emulsifier and X is the concentration (ng / g) of each emulsifier.

[0136] Next, the amount of emulsifier contained in the extract was calculated using formula (A1-2). Note that a in formula (A1-2) means a obtained by the above formula (A1-1). XCm = ACm / a (A1-2) XCm: content (ng / g) of emulsifier in each extract ACm: peak area of ​​emulsifier in each extract The quantitation limit in this measurement is 1 ng / g.

[0137] The content of the emulsifier in the solid composition relative to the total mass of the solid composition (ZCm) was calculated using the following formula (A1-3): ZCm = XCm × ρ1 × La / W1 (A1-3) ZCm: content of the emulsifier contained in the solid composition ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid composition in each example)

[0138] <Method for Quantifying Formula (S1) and Formula (S3) Contained in Solid Composition> The solid compositions obtained in each example described below were freeze-pulverized using a freeze-pulverizer Freezer Mill 6775 (manufactured by SPEX) under the following conditions. Before freeze-pulverization, 10% by mass of dibutylhydroxytoluene (BHT) was added to the solid composition in advance, based on the total mass of the solid composition, to obtain a pulverized powder. The freeze-pulverization conditions were: solid composition: 3 g, BHT: 0.3 g, run time: 5 minutes, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 2.5 g of the obtained pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate each fluoropolymer. The supernatant was used as the extract. The obtained extract was subjected to LC / MS / MS analysis. The fluorine-containing emulsifier in the extract was measured using a liquid chromatograph mass spectrometer. The measurement equipment configuration and LC-MS measurement conditions were as described above. Using aqueous solutions of emulsifiers containing fluorine atoms with known concentrations, methanol solutions with five or more different concentrations were prepared. LC / MS analysis of the methanol solutions with each concentration was performed. The relationship between the content and the area relative to the content was plotted to create a calibration curve. Using the calibration curve, the area of ​​the LC / MS chromatogram of the emulsifier containing fluorine atoms in the extract was converted to the content of the emulsifier containing fluorine atoms. The content of the compound represented by formula (S1) contained in each extract was determined by converting each compound in formula (S1) where n1 = 3 to 13 into a perfluorocarboxylic acid (formula (S2)) with the same carbon number. Furthermore, the content of the compound represented by formula (S3) contained in each extract was determined by converting each compound in formula (S3) where n2 = 4 to 10 into a perfluorosulfonic acid (formula (S4)) with the same carbon number. The MRM parameters for formulas (S1) and (S3) are shown in Tables 4 and 5. Specifically, five levels of methanol standard solutions of perfluorocarboxylic acid and perfluorosulfonic acid with known concentrations ranging from 1 to 180 ng / g were first prepared, and a and a' were calculated from the respective sample concentrations and peak integral values ​​using linear approximation according to formulas (A2-1) and (A2-1').A = a × X (A2-1) A: peak area of ​​perfluorocarboxylic acid, X: concentration of perfluorocarboxylic acid (ng / g) A' = a' × X' (A2-1') A': peak area of ​​perfluorosulfonic acid, X': concentration of perfluorosulfonic acid (ng / g).

[0139]

[0140]

[0141] Specifically, first, the peak areas of the compounds represented by formula (S1) and formula (S3) contained in each of the extracts were determined using the liquid chromatograph mass spectrometer.

[0142] Next, the contents of the compound represented by formula (S1) and the compound represented by formula (S3) were calculated using formulas (A2-2) and (A2-2'), respectively. Note that a in formula (A2-2) means a calculated using formula (A2-1) above, and a' in formula (A2-2') means a' calculated using formula (A2-1') above. XCm ​​= ACm / a (A2-2) XCm: content (ng / g) of the compound represented by formula (S1) and having carbon number (n+1) in each extract ACm: peak area of ​​the compound represented by formula (S1) and having carbon number (n+1) in each extract XCm' = ACm' / a' (A2-2') XCm': content (ng / g) of the compound represented by formula (S3) and having carbon number n in each extract ACm': peak area of ​​the compound represented by formula (S3) and having carbon number n in each extract The quantitation limit in this measurement is 1 ng / g.

[0143] The content (ZCm) of the compound represented by formula (S1) in the solid relative to the total mass of the solid was calculated using the following formula (A2-3): ZCm = XCm × ρ1 × La / W1 (A2-3) ZCm: content of the compound represented by formula (S1) with carbon number (n+1) contained in the solid ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid in each example)

[0144] The content (ZCm') of the compound represented by formula (S3) in the solid relative to the total mass of the solid was calculated using the following formula (A2-4): ZCm' = XCm' × ρ1 × La / W1 (A2-4) ZCm': content of the compound represented by formula (S3) with carbon number n contained in the solid ρ1: density of the extraction solvent (methanol in each example) La: volume of the extraction solvent (5 mL in each example) W1: mass of the sample used for extraction (2.5 g of solid in each example)

[0145] [Production of Raw Material Liquid A] Ultrapure water (1130 g), 30 mass% aqueous ammonia solution (30 mg), PMVE (72 g), and TFE (14 g) were charged into a 2.2 L stainless steel pressure reactor equipped with an anchor impeller, and the temperature was raised to 90°C while stirring at 600 rpm. Next, an aqueous ammonium persulfate solution (5.0 mass%, 30 cc) was added to initiate polymerization. As the pressure in the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. When 4 g of TFE had been injected, the reactor was cooled to terminate the polymerization reaction. The gas remaining in the reactor was recovered, and the liquid was then withdrawn. This liquid was used as raw material liquid A. Raw material liquid A was freeze-aggregated and then filtered. The resulting fluoropolymer 1A was analyzed by NMR, and the ratio of PMVE units to TFE units was 34 / 66 (molar ratio).

[0146] [Production of Raw Material Solution B] To the raw material solution A, HPR4002Cl (anion exchange resin, manufactured by DuPont, 200 g) was added. 150 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration. Next, AmberLite (registered trademark) HPR650H (cation exchange resin, manufactured by DuPont, 50 g) was added to the filtrate. 60 minutes after the start of stirring, the raw material solution was separated from the ion exchange resin by filtration to obtain raw material solution B. In raw material solution B, particles of fluoropolymer 1A were dispersed in an aqueous medium, and the content of fluoropolymer 1A was 0.6 mass% based on the total mass of raw material solution B.

[0147] [Example 1] (Production of fluoropolymer) A stainless steel pressure reactor having an internal volume of 2.2 L and equipped with an anchor impeller was charged with raw material liquid B (1000 g) and ultrapure water (175 g) to obtain aqueous dispersion B (first aqueous dispersion). The content of fluoropolymer 1A was 0.4 mass% based on the total mass of aqueous dispersion B.

[0148] Aqueous dispersion B contained substantially no water-soluble emulsifier. Specifically, the contents of emulsifier A and the compounds represented by formulae (S1) to (S4), which will be described later, were measured by the following method. Note that, in the production of aqueous dispersion B, emulsifiers other than emulsifier A and the compounds represented by formulae (S1) to (S4) were not produced from the components used in the production of aqueous dispersion B, nor were any emulsifiers used, and therefore are not contained in aqueous dispersion B. The solids content of aqueous dispersion B was measured, and an amount of aqueous dispersion B corresponding to 0.05 g of solids was weighed into a 100 mL screw tube. Subsequently, 40 g of water and methanol were added to the weighed aqueous dispersion B so that the water / methanol ratio was 50 / 50 by volume. The mixture was then shaken vigorously until coagulation occurred. The solids were removed, and the liquid phase was centrifuged at 4,000 rpm for 1 hour, and the supernatant was extracted. The measurement was carried out in the same manner as the above-mentioned method for measuring the content of the emulsifier, except for the method for preparing the sample. As a result, the content of the compound represented by any one of Formulas (S1) to (S4) was also below the quantitation limit for aqueous dispersion B.

[0149] Perfluoro-1,4-diiodobutane (2.0 g), PMVE (72 g), and TFE (14 g) were charged into aqueous dispersion B, and the temperature was raised to 80°C while stirring at 600 rpm. TFE and PMVE were injected into the reactor until the pressure reached 1.2 MPa [gauge], and an aqueous ammonium persulfate solution (APS aqueous solution, 1.0 mass%, 20 ml) was added to initiate polymerization. As the polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain the pressure constant. When 160 g of TFE and 133 g of PMVE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 300 minutes.

[0150] After the polymerization reaction was completed, the gas remaining in the reactor was recovered, and then the liquid was extracted from the reactor. This liquid was designated as aqueous dispersion 1. Aqueous dispersion 1 was a dispersion in which particles (average particle diameter 92.7 nm) containing fluoropolymer 1B were dispersed in an aqueous medium, and the solids concentration was 20.5 mass%. The aqueous dispersion was stirred with a disc turbine blade for 150 minutes at 1000 rpm, and then the aggregates were collected by filtration. The collected aggregates were washed with 2000 g of ultrapure water at 25 ° C. and dried to obtain a rubbery fluoropolymer 1B.

[0151] The obtained fluoropolymer 1B was analyzed by NMR, and as a result, the content of TFE units was 66 mol % based on the total content of all units in fluoropolymer 1B, and the content of PAVE units (PMVE units) was 34 mol % based on the total content of all units in fluoropolymer 1B. Furthermore, as a result of the NMR analysis, the content of iodine atoms in fluoropolymer 1B was 0.05 mass % based on the total mass of fluoropolymer 1B.

[0152] [Production of Fluoropolymer Composition] The components and amounts shown in Table 6 were mixed and kneaded using a twin roll mill at room temperature for 10 minutes to obtain a mixture. The gap between the twin roll mills was adjusted, and the resulting mixture was processed into a 3 mm thick sheet to obtain Fluoropolymer Composition 1. Of the components in Table 6, details of the components other than Fluoropolymer 1B are as follows: CB: MT Carbon N990, manufactured by Vanderbilt, carbon black Crosslinking aid: TAIC-WH60, manufactured by Mitsubishi Chemical, triallyl isocyanurate 60% by mass diluted with silica Crosslinking agent: Perhexa 25B, manufactured by NOF Corp., 2,5-dimethyl-2.5-di(t-butylperoxy)hexane Mold release agent: Nonsal SN-1, manufactured by NOF Corp., sodium stearate

[0153]

[0154] [Production of crosslinked rubber article] A 50T hydraulic press (model: SA-301 50T type, manufactured by Tester Sangyo Co., Ltd., ram diameter: 180 mm) was prepared as a press device. The cavity of the mold provided in the press device was rectangular, measuring 150 mm in length and 80 mm in width. The sheet-like fluoropolymer composition 1 obtained as above was filled into the mold cavity, and pressure treatment was carried out at 150°C for 20 minutes to obtain a crosslinked rubber article 1 in the form of a flat plate, measuring 150 mm in length, 80 mm in width and 2 mm in thickness, containing a crosslinked product of fluoropolymer 1B.

[0155] [Production of Raw Material Liquid C] A fluoropolymer 1C was polymerized in the same procedure as in the production of Raw Material Liquid A, except that the amounts of each monomer component were appropriately changed, and this liquid was used as Raw Material Liquid C. Raw Material Liquid C was freeze-coagulated and then filtered off, and the resulting fluoropolymer 1C was analyzed by NMR, revealing that the ratio of PMVE units to TFE units was 32 / 68 (molar ratio).

[0156] [Production of Raw Material Liquid D] Raw material liquid D was produced in the same procedure as for raw material liquid B, except that raw material liquid C was used instead of raw material liquid A. Raw material liquid D contained particles of fluoropolymer 1C dispersed in an aqueous medium, and the content of fluoropolymer 1C was 0.6% by mass relative to the total mass of raw material liquid D.

[0157] [Example 2] A stainless steel pressure reactor having an internal volume of 2.2 L and equipped with an anchor impeller was charged with raw material liquid D (1000 g) and ultrapure water (175 g), to obtain aqueous dispersion D (first aqueous dispersion). The content of fluoropolymer 1C was 0.4 mass% based on the total mass of aqueous dispersion D. Furthermore, aqueous dispersion D did not substantially contain a water-soluble emulsifier. The content of the emulsifier was confirmed by the same method as for aqueous dispersion B described above.

[0158] PMVE (72 g), perfluoro-1,4-diiodobutane (1.7 g), and TFE (14 g) were charged to aqueous dispersion D, and the temperature was raised to 80°C while stirring at 600 rpm. TFE and PMVE were injected into the reactor until the pressure reached 1.5 MPa [gauge], and an aqueous APS solution (0.5% by mass, 16 mL) was added to initiate polymerization. As the polymerization began, the pressure in the reactor decreased, so TFE was added to maintain the pressure constant. When 256 g of TFE and 217 g of PMVE had been added, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 290 minutes.

[0159] After the polymerization reaction was completed, the gas remaining in the reactor was recovered, and then the liquid was extracted from the reactor. This liquid was designated as aqueous dispersion 2. Aqueous dispersion 2 was a dispersion in which particles (average particle diameter 140.3 nm) containing fluoropolymer 1D were dispersed in an aqueous medium, and had a solids concentration of 28.6% by mass. The aqueous dispersion 2 was stirred with a paddle blade for 150 minutes at 1000 rpm, and then the aggregates were collected by filtration. The collected aggregates were washed with 2000 g of ultrapure water at 25 ° C. and dried to obtain a rubbery fluoropolymer 1D.

[0160] The obtained fluoropolymer 1D was analyzed by NMR, and as a result, the content of TFE units was 68 mol % based on the total content of all units in the fluoropolymer 1D, and the content of PAVE units (PMVE units) was 32 mol % based on the total content of all units in the fluoropolymer 1D. Furthermore, as a result of the NMR analysis, the content of iodine atoms in the fluoropolymer 1D was 0.04 mass % based on the total mass of the fluoropolymer 1D.

[0161] A fluoropolymer composition 2 processed into a sheet having a thickness of 3 mm was obtained in the same manner as in Example 1, except that fluoropolymer 1D was used instead of fluoropolymer 1B.

[0162] A crosslinked rubber article 2 in the shape of a flat plate measuring 150 mm in length, 80 mm in width and 2 mm in thickness, containing a crosslinked product of fluoropolymer 1D was obtained in the same manner as in Example 1, except that sheet-shaped fluoropolymer composition 2 was used instead of sheet-shaped fluoropolymer composition 1.

[0163] [Production of Raw Material Liquid E] A fluoropolymer 1E was polymerized in the same procedure as in the production of Raw Material Liquid A, except that the amounts of each monomer component were appropriately changed, and this liquid was used as Raw Material Liquid E. Raw Material Liquid E was freeze-coagulated and then filtered, and the resulting fluoropolymer 1E was analyzed by NMR, revealing that the ratio of PMVE units to TFE units was 30 / 70 (molar ratio).

[0164] [Production of Raw Material Liquid F] Raw material liquid F was produced in the same procedure as for raw material liquid B, except that raw material liquid E was used instead of raw material liquid A. Raw material liquid F contained particles of fluoropolymer 1E dispersed in an aqueous medium, and the content of fluoropolymer 1E was 0.5% by mass relative to the total mass of raw material liquid F.

[0165] [Example 3] A stainless steel pressure reactor having an internal volume of 2.2 L and equipped with an anchor impeller was charged with raw material liquid F (1000 g) to obtain aqueous dispersion F (first aqueous dispersion). The content of fluoropolymer 1E was 0.4 mass% relative to the total mass of aqueous dispersion F.

[0166] Ultrapure water (175 g), PMVE (72 g), and TFE (14 g) were charged to aqueous dispersion F, and the temperature was raised to 80 ° C. while stirring at 600 rpm. TFE and PMVE were injected until the pressure in the reactor reached 1.5 MPa [gauge], and an aqueous APS solution (0.5 mass%, 16 mL) was added to initiate polymerization. As the pressure in the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. When 6 g of TFE had been added, perfluoro-1,4-diiodobutane (2.3 g) was injected. When 256 g of TFE and 217 g of PMVE had been added, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 320 minutes.

[0167] After the polymerization reaction was completed, the gas remaining in the reactor was recovered, and then the liquid was extracted from the reactor. This liquid was designated as aqueous dispersion 3. Aqueous dispersion 3 was a dispersion in which particles (average particle diameter 96 nm) containing fluoropolymer 1F were dispersed in an aqueous medium, and the solids concentration was 27.6 mass%. The aqueous dispersion was stirred with six turbine blades for 150 minutes at 1000 rpm, and then the aggregates were collected by filtration. The collected aggregates were washed with 2000 g of ultrapure water at 25 ° C. and dried to obtain a rubbery fluoropolymer 1F.

[0168] The obtained fluoropolymer 1F was analyzed by NMR, and as a result, the content of TFE units was 65 mol % based on the total content of all units in fluoropolymer 1F, and the content of PAVE units (PMVE units) was 35 mol % based on the total content of all units in fluoropolymer 1F. Furthermore, as a result of the NMR analysis, the content of iodine atoms in fluoropolymer 1F was 0.05 mass % based on the total mass of fluoropolymer 1F.

[0169] Fluorine-containing polymer composition 3 processed into a sheet having a thickness of 3 mm was obtained in the same manner as in Example 1, except that Fluorine-containing polymer 1F was used instead of Fluorine-containing polymer 1B.

[0170] A crosslinked rubber article 3 in the shape of a flat plate measuring 150 mm in length, 80 mm in width and 2 mm in thickness, containing a crosslinked product of fluoropolymer 1F was obtained in the same manner as in Example 1, except that sheet-like fluoropolymer composition 3 was used instead of sheet-like fluoropolymer composition 1.

[0171] [Example 4] A stainless steel pressure reactor having an internal volume of 2.1 L and equipped with an anchor blade was degassed, and then ultrapure water (980 g), an emulsifier C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４A 30% by mass solution (201.7 g) of (emulsifier A) and a 5% by mass aqueous solution (2.3 g) of disodium hydrogen phosphate dodecahydrate were charged, and the gas phase was replaced with nitrogen. While stirring at a speed of 600 rpm using an anchor blade, PMVE (72 g) and TFE (14 g) were injected into the vessel, and the internal temperature was then raised to 80 ° C. Next, an aqueous solution of APS (0.5% by mass, 16 mL) was added to initiate polymerization. As the pressure in the reactor decreased with the start of polymerization, TFE and PMVE were added, and the pressure was maintained constant at 1.2 MPa [gauge]. When 6 g of TFE had been injected, perfluoro-1,4-diiodobutane (2.0 g) was injected. When 256 g of TFE and 217 g of PMVE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 185 minutes. After the polymerization reaction was completed, the gas remaining in the reactor was recovered, and then the liquid was extracted from the reactor. This liquid was designated as aqueous dispersion 4. Aqueous dispersion 4 was a dispersion in which particles containing fluoropolymer 4 (average particle diameter 90 nm) were dispersed in an aqueous medium, and the solids concentration was 30.0 mass%. An aqueous aluminum sulfate solution was added to carry out coagulation. After drying, a rubber-like fluoropolymer 4 was obtained.

[0172] The obtained fluoropolymer 4 was analyzed by NMR, and as a result, the content of TFE units was 65 mol % based on the total content of all units in fluoropolymer 4, and the content of PAVE units (PMVE units) was 35 mol % based on the total content of all units in fluoropolymer 4. Furthermore, as a result of the NMR analysis, the content of iodine atoms in fluoropolymer 4 was 0.05 mass % based on the total mass of fluoropolymer 4.

[0173] Fluorine-containing polymer composition 4 formed into a sheet having a thickness of 3 mm was obtained in the same manner as in Example 1, except that Fluorine-containing polymer 4 was used instead of Fluorine-containing polymer 1B.

[0174] A crosslinked rubber article 4 in the shape of a flat plate having a length of 150 mm, a width of 80 mm and a thickness of 2 mm, containing a crosslinked product of fluoropolymer 4 was obtained in the same manner as in Example 1, except that sheet-like fluoropolymer composition 4 was used instead of sheet-like fluoropolymer composition 1.

[0175] [Example 5] A stainless steel pressure reactor having an internal volume of 2.1 L and equipped with an anchor blade was degassed, and then ultrapure water (980 g), an emulsifier C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４ A 30% by mass solution (201.7 g) of (emulsifier A) and a 5% by mass aqueous solution (2.3 g) of disodium hydrogen phosphate dodecahydrate were charged, and the gas phase was replaced with nitrogen. While stirring at a speed of 600 rpm using an anchor blade, PMVE (72 g) and TFE (14 g) were injected into the vessel, and the internal temperature was then raised to 80 ° C. Next, an aqueous APS solution (0.5% by mass, 16 mL) was added to initiate polymerization. As the pressure in the reactor decreased with the start of polymerization, TFE and PMVE were added, and the pressure was maintained constant at 0.88 MPa [gauge]. When 6 g of TFE had been injected, perfluoro-1,4-diiodobutane (1.6 g) was injected. When 256 g of TFE and 217 g of PMVE had been injected, the reactor was cooled and the polymerization reaction was terminated. The polymerization time was 250 minutes. After the polymerization reaction was completed, the gas remaining in the reactor was recovered, and then the liquid was extracted from the reactor. This liquid was designated as aqueous dispersion 5. Aqueous dispersion 5 was a dispersion in which particles containing fluoropolymer 5 (average particle diameter 105 nm) were dispersed in an aqueous medium, and the solids concentration was 28.5 mass%. An aqueous aluminum sulfate solution was added to carry out coagulation. After drying, a rubbery fluoropolymer 5 was obtained.

[0176] The obtained fluoropolymer 5 was analyzed by NMR, and as a result, the content of TFE units was 65 mol % based on the total content of all units in fluoropolymer 5, and the content of PAVE units (PMVE units) was 35 mol % based on the total content of all units in fluoropolymer 5. Furthermore, as a result of the NMR analysis, the content of iodine atoms in fluoropolymer 5 was 0.03 mass % based on the total mass of fluoropolymer 5.

[0177] Fluoropolymer composition 5 processed into a sheet having a thickness of 3 mm was obtained in the same manner as in Example 1, except that Fluoropolymer 5 was used instead of Fluoropolymer 1B.

[0178] A crosslinked rubber article 5 in the shape of a flat plate having a length of 150 mm, a width of 80 mm and a thickness of 2 mm, containing a crosslinked product of fluoropolymer 5 was obtained in the same manner as in Example 1, except that sheet-like fluoropolymer composition 5 was used instead of sheet-like fluoropolymer composition 1.

[0179] [Example 6] A stainless steel pressure reactor having an internal volume of 2.1 L and equipped with an anchor blade was degassed, and then ultrapure water (980 g), an emulsifier C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４ A 30% by mass solution (201.7 g) of (emulsifier A) and a 5% by mass aqueous solution (2.3 g) of disodium hydrogen phosphate dodecahydrate were charged, and the gas phase was replaced with nitrogen. While stirring at a speed of 600 rpm using an anchor blade, PMVE (72 g) and TFE (14 g) were injected into the vessel, and the internal temperature was then raised to 80 ° C. Next, an aqueous solution of APS (0.5% by mass, 16 mL) was added, and polymerization was initiated. As the pressure in the reactor decreased with the start of polymerization, TFE and PMVE were added, and the pressure was maintained constant at 0.88 MPa [gauge]. When 6 g of TFE had been injected, perfluoro-1,4-diiodobutane (3.0 g) was injected. When 256 g of TFE and 217 g of PMVE had been injected, the reactor was cooled, and the polymerization reaction was terminated. The polymerization time was 500 minutes. After the polymerization reaction was completed, the gas remaining in the reactor was collected, and the liquid was then extracted from the reactor. This liquid was designated as aqueous dispersion 6. Aqueous dispersion 6 was a dispersion in which particles containing fluoropolymer 6 (average particle diameter 105 nm) were dispersed in an aqueous medium, and had a solids concentration of 28.5 mass%. An aqueous aluminum sulfate solution was added to carry out coagulation. After drying, a rubber-like fluoropolymer 6 was obtained.

[0180] The obtained fluoropolymer 6 was analyzed by NMR, and as a result, the content of TFE units was 65 mol % based on the total content of all units in fluoropolymer 6, and the content of PAVE units (PMVE units) was 35 mol % based on the total content of all units in fluoropolymer 6. Furthermore, as a result of the NMR analysis, the content of iodine atoms in fluoropolymer 6 was 0.07 mass % based on the total mass of fluoropolymer 6.

[0181] Fluorine-containing polymer composition 6 formed into a sheet having a thickness of 3 mm was obtained in the same manner as in Example 1, except that Fluorine-containing polymer 6 was used instead of Fluorine-containing polymer 1B.

[0182] A crosslinked rubber article 6 in the shape of a flat plate measuring 150 mm in length, 80 mm in width and 2 mm in thickness, containing a crosslinked product of fluoropolymer 6 was obtained in the same manner as in Example 1, except that sheet-like fluoropolymer composition 6 was used instead of sheet-like fluoropolymer composition 1.

[0183] [Measurement and Evaluation Methods] Various measurement and evaluation methods are as follows.

[0184] [Average Particle Diameter] The average particle diameter of particles in the aqueous dispersion was measured using the aqueous dispersion of each example as a sample with a dynamic light scattering particle size measuring device (ELSZ, manufactured by Otsuka Electronics Co., Ltd.).

[0185] [Method for measuring iodine content] A solid composition comprising a fluoropolymer was hot-pressed to form a 300 μm sheet. The obtained sheet-like composition was subjected to X-ray fluorescence analysis using a ZSX Primus II (manufactured by RIGAKU Corporation), and the iodine content in the solid composition (fluoropolymer) was calculated by the fundamental parameter method.

[0186] [2% Weight Loss Temperature and 5% Weight Loss Temperature] A 10 mg sample was weighed out from the fluoropolymer obtained in each example and transferred to an aluminum pan. The sample was heated from 30°C to 550°C at a heating rate of 10°C / min in an air atmosphere, while measuring the change in mass of the sample. The temperature at which the sample mass became 98% by mass, assuming that the sample mass before heating was 100% by mass, was defined as the 2% mass loss temperature. Similarly, the temperature at which the sample mass became 95% by mass was defined as the 5% mass loss temperature. The above thermogravimetric analysis was carried out using a differential thermal thermogravimetric analyzer "NEXTA STA series STA200" (manufactured by Hitachi High-Technologies Corporation).

[0187] [Optimum vulcanization time Te] The 3 mm thick sheet-like fluorine-containing copolymer composition obtained in each example was cut into 10 g pieces to obtain cut pieces. The obtained cut pieces were sandwiched between two polyester films (ALFA Technologies, PART #F0311-S, 130 mm x 130 mm x 24 μm) on both sides of the main surface to obtain a measurement sample. The measurement sample was placed on a die. Next, torque (dNm) was measured using a measurement device (manufactured by Alpha Technologies) with a die shape of D0380, at 150°C (test temperature), 20 minutes (vulcanization time), 100 cpm, and an angle of 3.00°, in accordance with JIS K6296-1, to obtain a torque-vulcanization time curve. From the obtained torque-vulcanization time curve, tc(5), the vulcanization time (unit: minutes) at which the torque reached 5%, and tc(35), the vulcanization time (unit: minutes) at which the torque reached 35%, were calculated, with the minimum torque being 0% and the maximum torque being 100%, respectively. Furthermore, the optimum vulcanization time Te (unit: minutes) was calculated using the above-mentioned formula A. The results are shown in Table 2.

[0188] [Storage Modulus] A PREMER RPA (manufactured by Alpha Technologies, die shape: D0380) was used as the measuring device. The fluoropolymer obtained in each example was kneaded for 10 minutes at room temperature using two rolls to prepare a sheet having a thickness of 3 mm. The thickness of the sheet was adjusted by adjusting the gap between the two rolls. The obtained sheet was cut to a weight of approximately 10 g to obtain a cut sheet. The cut sheet was sandwiched between two polyester films (ALFA Technologies PART#F0311-S, 130 mm x 130 mm x 24 μm) to obtain a sample for measurement. The sample was placed on the die of the measuring device. The die temperature was previously set to 100°C. Next, the sample was held at 100°C for 2 minutes under conditions of 30 cpm frequency and 0.2°C amplitude angle, and then the amplitude angle was set to 0.5° and the frequency was increased to 10 cpm, 20 cpm, and 50 cpm to measure the storage modulus. The storage modulus at 50 cpm and 100°C was taken as the storage modulus G' (unit: kPa) of the sample.

[0189] [Mold Releasability] The fluoropolymer composition obtained in each example was introduced into a sheet-like mold, and the fluoropolymer composition was subjected to a pressure treatment at 150°C for 20 minutes to obtain a crosslinked rubber article (100 mm long x 60 mm wide x 1 mm thick) adhering to the mold. Immediately after the pressure treatment, air was sprayed onto the interface between the crosslinked rubber article and the mold using an air gun (product name: Cyclone Duster, manufactured by Chuo Kuuki Co., Ltd.), and the mold releasability was evaluated according to the following criteria. <Air spray conditions using air gun> Pressure: 0.5 MPa Air spray duration: 3 seconds was defined as one spray. <Evaluation criteria> ⊚: The crosslinked rubber article was released from the mold after one spray. ◯: The crosslinked rubber article was released from the mold after two sprays. Δ: The crosslinked rubber article was released from the mold after 3 to 5 sprays. ×: The crosslinked rubber article did not release from the mold after five sprays.

[0190] [Hardness] Using the flat test pieces of the crosslinked rubber articles obtained in each example, the hardness (Shore-A) was measured using a Type A durometer in accordance with JIS K6253-3:2012. The measurement device used was an automatic rubber hardness tester (Digitest Shore A, manufactured by H. Burleith Testing Instruments Co., Ltd.). The test was carried out using three test pieces, and the arithmetic average of the measured values ​​for the three test pieces was recorded.

[0191] The measurement results and evaluation results are shown in Table 7 below.

[0192]

[0193] As shown in Table 7, it was confirmed that crosslinked rubber articles obtained using fluoropolymer compositions having an optimum vulcanization time Te of 2.3 minutes or more had excellent mold releasability (Examples 1 to 3). In contrast, it was confirmed that crosslinked rubber articles obtained using fluoropolymer compositions having an optimum vulcanization time of less than 2.3 minutes had poor mold releasability (Examples 4 to 6). The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2023-222377, filed on December 28, 2023, are incorporated herein by reference.

Claims

1. A fluorine-containing polymer composition comprising a fluorine-containing polymer and a crosslinking agent, wherein the optimum vulcanization time Te determined by Formula A is 2.3 minutes or more. The fluorine-containing polymer composition is characterized in that: Formula A Te = t Ｃ (5) + 10 × (t Ｃ (35) - t Ｃ (5)) In Formula A, based on JIS K6296-1, in the torque-vulcanization time curve obtained under the condition of a test temperature of 150 °C using the fluorine-containing polymer composition, when the minimum value of torque is 0% and the maximum value of torque is 100%, the vulcanization time when showing 5% of torque is t Ｃ (5), and the vulcanization time when showing 35% of torque is t Ｃ (35).

2. The fluoropolymer composition according to claim 1, wherein the optimum vulcanization time Te is 60 minutes or less.

3. The fluoropolymer composition according to claim 1, wherein the fluoropolymer has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether).

4. The fluoropolymer composition according to claim 1, wherein the crosslinking agent is at least one selected from the group consisting of organic peroxides and compounds having two or more amino groups.

5. The fluoropolymer composition according to claim 1, further comprising a crosslinking aid.

6. The crosslinking aid is at least one selected from the group consisting of a compound represented by the following formula (7), triallyl cyanurate, triallyl isocyanurate, trimethallyl isocyanurate, 1,3,5-triacryloylhexahydro-1,3,5-triazine, triallyl trimellitate, m-phenylenediamine bismaleimide, p-quinone dioxime, p,p'-dibenzoylquinone dioxime, dipropargyl terephthalate, diallyl phthalate, N,N',N'',N''' -tetraallyl terephthalamide, and a vinyl group-containing siloxane oligomer. The fluorine-containing polymer composition according to claim 5. (CR ４１ R ４２ =CR ４３ ) ２ R ４４ Formula (7) In formula (7), R ４１ , R ４２ and R ４３ each independently represents a hydrogen atom, a fluorine atom, an alkyl group having 1 to 5 carbon atoms, or a fluoroalkyl group having 1 to 5 carbon atoms, and R ４４ represents a divalent fluorohydrocarbon group having 1 to 18 carbon atoms or a group having an etheric oxygen atom at the terminal or between carbon-carbon bonds of the fluorohydrocarbon group. A plurality of R ４１ , a plurality of R ４２ and a plurality of R ４３ may be the same as or different from each other.

7. The fluoropolymer composition according to claim 1, further comprising a filler.

8. The fluoropolymer composition according to claim 7, wherein the filler is at least one selected from the group consisting of carbon black, barium sulfate, calcium metasilicate, calcium carbonate, titanium oxide, silicon dioxide, clay, and talc.

9. The fluoropolymer composition according to claim 1, wherein the storage elastic modulus G' of the fluoropolymer at 100 °C and a frequency of 50 cpm is 200 kPa or more.

10. A method for producing a fluorine-containing polymer composition, comprising: Step 1 of polymerizing a monomer containing tetrafluoroethylene and perfluoro(alkyl vinyl ether) in an aqueous dispersion containing a first fluorine-containing polymer that substantially does not contain a water-soluble emulsifier and contains units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and an aqueous medium, to produce a second fluorine-containing polymer containing units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether); and Step 2 of adding a crosslinking agent to the second fluorine-containing polymer to obtain a fluorine-containing polymer composition containing the second fluorine-containing polymer and the crosslinking agent, wherein the content of the units based on perfluoro(alkyl vinyl ether) in the first fluorine-containing polymer is 20 to 95 mol% with respect to the total content of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether) in the first fluorine-containing polymer, the content of the units based on perfluoro(alkyl vinyl ether) in the second fluorine-containing polymer is 20 to 95 mol% with respect to the total content of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether) in the second fluorine-containing polymer, and the content of the first fluorine-containing polymer is 0.01 to 4.0% by mass with respect to the total mass of the aqueous dispersion before the polymerization of the monomer is initiated.

11. A crosslinked rubber article obtained by crosslinking the fluorine-containing polymer contained in the fluorine-containing polymer composition according to any one of claims 1 to 9.

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