Crosslinked rubber article and fluorine-containing copolymer composition

Abstract

A crosslinked rubber article according to the present disclosure contains a crosslinked product of a fluorine-containing copolymer. When the crosslinked rubber article is subjected to a sputtering treatment by a method of test 1, the arithmetic average height Sa of the surface of the crosslinked rubber article after the sputtering treatment is greater than 1.6 μm, and the aspect ratio Str of the surface of the crosslinked rubber article after the sputtering treatment is 0.90 or less. Test 1: A crosslinked rubber article is placed on a sample table of an ion sputtering apparatus, and a distance between a placement surface of the crosslinked rubber article in the sample table and a target made of platinum is set to 35 mm. Then, the crosslinked rubber article is subjected to a sputtering treatment by setting the degree of vacuum in a sample chamber of the ion sputtering apparatus to 6 kPa and then performing discharge for 30 sec at a target additional current value of 25 mA.

Description

Crosslinked rubber articles, fluorine-containing copolymer compositions

[0001] The present disclosure relates to crosslinked rubber articles and fluorocopolymer compositions.

[0002] Crosslinked rubber articles obtained by crosslinking a fluorocopolymer composition containing a fluorocopolymer (e.g., perfluoroelastomer) are used in various industrial fields because they have excellent heat resistance, chemical resistance, flame retardancy, weather resistance, etc. For example, Patent Document 1 discloses a fluoroelastomer molded article having a surface with a centerline average roughness Ra of 0.65 μm or more.

[0003] WO 01 / 079337

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

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

[0006] As a result of extensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by the following configuration. [1] A crosslinked rubber article comprising a crosslinked product of a fluorine-containing copolymer, wherein, when the crosslinked rubber article is subjected to a sputtering treatment by the method of Test 1, the arithmetic mean height Sa of the surface of the crosslinked rubber article after the sputtering treatment is greater than 1.6 μm and the aspect ratio Str of the surface of the crosslinked rubber article after the sputtering treatment is 0.90 or less. Test 1: The crosslinked rubber article is placed on the sample stage of an ion sputtering apparatus, and the distance between the surface on the sample stage where the crosslinked rubber article is placed and a platinum target is set to 35 mm. Next, the degree of vacuum in the sample chamber of the ion sputtering apparatus is set to 6 kPa, and then the crosslinked rubber article is subjected to a sputtering treatment by discharging at a target additional current value of 25 mA for 30 seconds. [2] The crosslinked rubber article according to [1], wherein the crosslinked product has a heterocyclic structure. [3] The crosslinked rubber article according to [1] or [2], wherein the crosslinked product has at least one of an oxazole structure and a triazine structure. [4] The crosslinked rubber article according to any one of [1] to [3], wherein the fluorine-containing copolymer has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). [5] The crosslinked rubber article according to any one of [1] to [4], wherein the fluorine-containing copolymer has units based on a monomer having a nitrile group. [6] The crosslinked rubber article according to any one of [1] to [5], which is substantially free of a white filler. [7] The crosslinked rubber article according to any one of [1] to [6], which is substantially free of an emulsifier. [8] A fluorocopolymer composition comprising a fluorocopolymer, wherein, when a crosslinked rubber article obtained using the fluorocopolymer composition is subjected to a sputtering treatment by the method of Test 1, the arithmetic mean height Sa of the surface of the crosslinked rubber article after the sputtering treatment is greater than 1.6 μm and the aspect ratio Str of the surface of the crosslinked rubber article after the sputtering treatment is 0.90 or less.Test 1: A crosslinked rubber article obtained using the fluorocopolymer composition was placed on the sample stage of an ion sputtering apparatus, and the distance between the surface of the sample stage on which the crosslinked rubber article was placed and a platinum target was set to 35 mm. Next, the degree of vacuum in the sample chamber of the ion sputtering apparatus was set to 6 kPa, and the crosslinked rubber article was subjected to a sputtering treatment by discharging at a target addition current value of 25 mA for 30 seconds. [9] The fluorocopolymer composition according to [8], wherein the fluorocopolymer has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether).

[10] The fluorocopolymer composition according to [8] or [9], wherein the fluorocopolymer has units based on a monomer having a nitrile group.

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

[10] , further comprising a crosslinking agent.

[12] The fluorocopolymer composition according to any of [8] to

[11] , wherein the fluorocopolymer composition is substantially free of a white filler.

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

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

[0007] According to the present disclosure, it is possible to provide a crosslinked rubber article that is excellent in high-temperature compression set and that is less susceptible to cracking.The present disclosure also provides a fluorine-containing copolymer composition.

[0008] The meanings of terms used in this disclosure are as follows. A numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the upper and lower limits. In numerical ranges described in this specification in stages, the upper or lower limit described in a certain numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in numerical ranges described in this specification, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the Examples. In this specification, each component may be used alone or in combination with two or more substances corresponding to the component. Herein, when two or more substances are used in combination for each component, the content of that component refers to the total content of the substances used in combination, unless otherwise specified. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. A "unit" is a collective term for an atomic group derived from one molecule of the monomer that is formed directly by polymerization of the monomer, and an atomic group obtained by chemically converting a portion of the atomic group. Hereinafter, a "unit based on a monomer" will also be simply referred to as a "unit." The content (mass % or mol %) of each unit relative to all units contained in the 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.

[0009] [Crosslinked Rubber Article] The crosslinked rubber article of the present disclosure (hereinafter also referred to as "the present crosslinked rubber article") is a crosslinked rubber article comprising a crosslinked product of a fluorine-containing copolymer, and when the present crosslinked rubber article is subjected to a sputtering treatment by the method of Test 1 described below, the arithmetic mean height Sa of the surface of the crosslinked rubber article after the sputtering treatment is greater than 1.6 μm, and the aspect ratio Str of the surface of the crosslinked rubber article after the sputtering treatment is 0.90 or less.

[0010] The arithmetic mean height Sa of the surface of this crosslinked rubber article, i.e., the crosslinked rubber article before sputtering, is preferably 0.8 μm or more, more preferably 1.0 μm or more, even more preferably 1.5 μm or more, and particularly preferably 1.9 μm or more, from the viewpoint of the adhesion of the crosslinked rubber article. Specifically, if the arithmetic mean height Sa of the surface of the crosslinked rubber article before sputtering is 0.8 μm or more, adhesion of the crosslinked rubber article to the compressed surface during high-temperature compression can be suppressed, thereby suppressing damage to the crosslinked rubber article when released from compression. The upper limit of the arithmetic mean height Sa of the surface of this crosslinked rubber article, i.e., the crosslinked rubber article before sputtering, is preferably 5.0 μm or less, more preferably 2.0 μm or less, from the viewpoint of the sealing performance of the crosslinked rubber article. Here, the following method can be mentioned, for example, as a method for adjusting the arithmetic mean height Sa of the surface of the crosslinked rubber article before sputtering to the above value. (a) a method of adjusting heating conditions (for example, temperature and time in the primary crosslinking, and temperature and time in the secondary crosslinking) when crosslinking the fluorine-containing copolymer composition by heating; (b) a method of adjusting the dispersibility of components such as the crosslinking agent by adjusting the mixing (kneading) conditions of each component when preparing the fluorine-containing copolymer composition; (c) a method of adjusting the crosslinking density of a crosslinked rubber article by adjusting the content of the crosslinking agent contained in the fluorine-containing copolymer composition or the amount of crosslinkable groups in the fluorine-containing copolymer contained in the fluorine-containing copolymer composition; (d) a method using a fluorine-containing copolymer obtained in the step of producing a fluorine-containing copolymer described below. These methods may be carried out alone, but it is preferable to carry out two or more methods in combination, since it becomes easier to adjust the arithmetic mean height Sa of the surface of the crosslinked rubber article before sputtering treatment to the above value.

[0011] The present inventors have found that if the arithmetic mean height Sa of the surface of a crosslinked rubber article after sputtering is greater than 1.6 μm and the aspect ratio Str of the surface of the crosslinked rubber article after sputtering is 0.90 or less, the crosslinked rubber article has excellent high-temperature compression set and is less likely to crack. The details of this are unclear, but it is presumed to be due to the following reasons. If the arithmetic mean height Sa of the surface of the crosslinked rubber article after sputtering is greater than 1.6 μm, the surface of the crosslinked rubber article can be said to be in a relatively rough state. It is believed that if the surface condition is rough, excessive heat conduction is suppressed when the crosslinked rubber article is compressed at high temperatures, making the crosslinked rubber article less susceptible to thermal decomposition. As a result, it is presumed that a crosslinked rubber article with excellent high-temperature compression set was obtained. Furthermore, if the aspect ratio Str of the surface of the crosslinked rubber article after sputtering is 0.90 or less, it can be said that the surface properties of the crosslinked rubber article exhibit a certain degree of anisotropy. When the surface texture exhibits anisotropy, stress relaxation is likely to occur when the crosslinked rubber article is compressed at high temperatures, which is thought to make it less likely to crack and more likely to recover its shape after compression. This is presumably why a crosslinked rubber article with excellent high-temperature compression set and less likely to crack was obtained. Here, in the present disclosure, the crosslinked rubber article after sputtering is used to measure the arithmetic mean height Sa and aspect ratio Str. The reason for this is that by using the crosslinked rubber article after sputtering, the surface texture of the crosslinked rubber article that cannot be detected before the sputtering can be revealed by the sputtering.

[0012] When this crosslinked rubber article is subjected to sputtering treatment using the method of Test 1 described below, the arithmetic mean height Sa of the surface of the crosslinked rubber article after sputtering is greater than 1.6 μm. From the viewpoint of better effects of the present disclosure, it is preferably 1.9 μm or more, more preferably 2.0 μm or more. The upper limit of the arithmetic mean height Sa of the surface of the crosslinked rubber article after sputtering is preferably 5.0 μm or less, more preferably 4.1 μm or less, from the viewpoint of the sealing performance of the crosslinked rubber article. Here, the arithmetic mean height Sa of the surface of the crosslinked rubber article after sputtering can be adjusted to the above value, for example, by the same method as the arithmetic mean height Sa of the surface of the crosslinked rubber article before sputtering. One preferred embodiment of the present disclosure is a combination in which the arithmetic mean height Sa of the surface of the crosslinked rubber article before sputtering is 1.5 μm or more (preferably 1.9 μm or more) and the arithmetic mean height Sa of the surface of the crosslinked rubber article after sputtering is 1.9 μm or more (preferably 2.0 μm or more). When the arithmetic mean height Sa of the surface of the crosslinked rubber article before and after sputtering is in this combination, the effects of the present disclosure are more pronounced.

[0013] Test 1 was carried out as follows. First, the crosslinked rubber article was placed on the sample stage of an ion sputtering device, and the distance between the surface of the sample stage on which the crosslinked rubber article was placed and the platinum target was set to 35 mm. Next, the degree of vacuum in the sample chamber of the ion sputtering device was set to 6 kPa, and then the crosslinked rubber article was subjected to a sputtering treatment by discharging at a target load current of 25 mA for 30 seconds. In this way, a crosslinked rubber article after sputtering treatment was obtained. Examples of the ion sputtering device include known ion sputtering devices (e.g., E-1030 model, manufactured by Hitachi, Ltd.).

[0014] The value obtained by subtracting the arithmetic mean height Sa of the surface of the crosslinked rubber article (i.e., before sputtering) from the arithmetic mean height Sa of the surface of the crosslinked rubber article after sputtering (hereinafter also referred to as the "Sa difference") is preferably 0 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more, in order to obtain better effects of the present disclosure. The upper limit of the Sa difference is preferably 5 μm or less, more preferably 2.1 μm or less, in order to obtain better sealing properties of the crosslinked rubber article.

[0015] The arithmetic mean height Sa is a parameter defined in ISO 25178, and specifically, can be measured using a known laser microscope equipped with a white light interferometer (for example, a laser microscope equipped with a white light interferometer VK-X3000, manufactured by Keyence Corporation). The form of the crosslinked rubber article (measurement object) when measuring the arithmetic mean height Sa is not particularly limited, but an O-ring is preferred, and a P-26 (standard defined in JIS B2401:2012) O-ring is more preferred.

[0016] When this crosslinked rubber article is subjected to sputtering treatment by the method of Test 1 described above, the aspect ratio Str of the surface of the crosslinked rubber article after sputtering treatment is 0.90 or less, and from the viewpoint of better effects of the present disclosure, it is preferably 0.89 or less, more preferably 0.87 or less. From the viewpoint of adhesion, the lower limit of the aspect ratio Str of the surface of the crosslinked rubber article after sputtering treatment is preferably 0.01 or more, more preferably 0.1 or more. Here, the aspect ratio Str of the surface of the crosslinked rubber article after sputtering treatment can be adjusted to the above value, for example, by the same method as the arithmetic mean height Sa of the surface of the crosslinked rubber article before sputtering treatment.

[0017] The aspect ratio Str of the surface of the present crosslinked rubber article, i.e., the crosslinked rubber article before sputtering, is preferably 0.95 or less, more preferably 0.93 or less, and even more preferably 0.92 or less, in order to obtain better effects of the present disclosure. The lower limit of the aspect ratio Str of the surface of the present crosslinked rubber article (i.e., before sputtering) is preferably 0.01 or more, more preferably 0.1 or more, in terms of adhesion. Here, the aspect ratio Str of the surface of the crosslinked rubber article before sputtering can be adjusted to the above value, for example, by the same method as for the arithmetic mean height Sa of the surface of the crosslinked rubber article before sputtering.

[0018] The value obtained by subtracting the aspect ratio Str of the surface of the crosslinked rubber article after sputtering from the aspect ratio Str of the surface of the crosslinked rubber article (i.e., the crosslinked rubber article before sputtering) (hereinafter also referred to as the "Str difference") is preferably 0 or more, more preferably 0.02 or more, and even more preferably 0.03 or more, in terms of superior effects of the present disclosure. The upper limit of the Str difference is preferably 0.5 or less, more preferably 0.1 or less, in terms of sealing performance.

[0019] The aspect ratio Str is a parameter defined in ISO 25178, and specifically, can be measured using a known laser microscope equipped with a white light interferometer (for example, a laser microscope equipped with a white light interferometer VK-X3000, manufactured by Keyence Corporation). Here, the aspect ratio Str indicates a value of 0 to 1, and the closer to 0 the surface is, the stronger the directionality (anisotropy) in a single direction, and the closer to 1 the surface is, the more isotropic it is. Note that the form of the crosslinked rubber article (measurement object) when measuring the aspect ratio Str is not particularly limited, but an O-ring is preferred, and a P-26 (standard defined in JIS B2401:2012) O-ring is more preferred.

[0020] The crosslinked product of the fluorine-containing copolymer preferably has a heterocyclic structure, more preferably at least one of an oxazole structure and a triazine structure. When the fluorine-containing copolymer has nitrile groups, methods for introducing a heterocyclic structure into the crosslinked product of the fluorine-containing copolymer include a method in which the nitrile groups are reacted with a crosslinking agent to form a heterocyclic structure (preferably an oxazole ring), and a method in which nitrile groups in the fluorine-containing copolymer are reacted with each other to form a heterocyclic structure (preferably a triazine structure).

[0021] The various components that the crosslinked rubber article may contain are described in detail below.

[0022] [Crosslinked product of fluorine-containing copolymer] The present crosslinked rubber article comprises a crosslinked product of a fluorine-containing copolymer. When the fluorine-containing copolymer has units based on a monomer having a nitrile group, for example, the crosslinked product of the fluorine-containing copolymer may be a crosslinked product obtained by crosslinking fluorine-containing copolymers together, and preferred are fluorine-containing copolymers crosslinked from nitrile groups as the starting point, fluorine-containing copolymers crosslinked using a crosslinking agent described below, and both of them. Furthermore, the crosslinked product of the fluorine-containing copolymer is also preferably a crosslinked product obtained by crosslinking a fluorine-containing copolymer composition described below. Furthermore, the fluorine-containing copolymer will be described later.

[0023] The content of the crosslinked fluorocopolymer is preferably 80 to 100% by mass, more preferably 85 to 100% by mass, and even more preferably 90 to 100% by mass, based on the total mass of the crosslinked rubber article.

[0024] [Filler] The crosslinked rubber article may contain a filler. Examples of fillers include carbon black and white fillers, with carbon black being preferred. Specific examples of white fillers include titanium oxide, silicon oxide, aluminum oxide, barium sulfate, talc, clay, magnesium carbonate, aluminum hydroxide, and calcium sulfate.

[0025] The filler may be used alone or in combination of two or more. In the present crosslinked rubber article, the content of the filler is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, per 100 parts by mass of the crosslinked product of the fluorocopolymer. The lower limit is preferably 1 part by mass or more per 100 parts by mass of the crosslinked product of the fluorocopolymer.

[0026] Here, one preferred embodiment of the present crosslinked rubber article is one that is substantially free of white filler. This has the advantage that the present crosslinked rubber article is substantially free of metal components and can be used in parts of semiconductor manufacturing equipment where metal components are avoided. The fact that the present crosslinked rubber article is "substantially free of white filler" means that the content of white filler is 5% by mass or less, preferably 1% by mass or less, and more preferably 0.1% by mass or less, relative to the total mass of the present crosslinked rubber article. The lower limit is 0% by mass. Specific examples of white filler are as described above.

[0027] [Other Components] The present crosslinked rubber article may contain components other than those described above (hereinafter also referred to as "other components"). It is also preferable that the crosslinked rubber article contain a product other than the above-mentioned fluorine-containing copolymer obtained by crosslinking a fluorine-containing copolymer contained in the fluorine-containing copolymer composition using the fluorine-containing copolymer composition described below. Specific examples of other components include acid acceptors (e.g., fatty acid esters, fatty acid metal salts, and divalent metal oxides (magnesium oxide, calcium oxide, zinc oxide, lead oxide, etc.)), reinforcing materials (e.g., fluorine-containing copolymers other than the above-mentioned fluorine-containing copolymers, polytetrafluoroethylene (PTFE), aromatic polyesters, polyamideimides, and thermoplastic polyimides), scorch retarders (e.g., phenolic hydroxyl group-containing compounds such as bisphenol A, quinones such as hydroquinone, and α-methylstyrene dimers such as 2,4-di(3-isopropylphenyl)-4-methyl-1-pentene), crown ethers (e.g., 18-crown-6), and mold release agents (e.g., sodium stearate). The other components may be used alone or in combination of two or more.

[0028] The crosslinked rubber article preferably contains substantially no emulsifier, since the effects of the present disclosure are more excellent. The crosslinked rubber article being "substantially free of emulsifier" means that the emulsifier content is 10 ppm by mass or less, preferably 100 ppb by mass or less, and more preferably 50 ppb by mass or less, relative to the total mass of the crosslinked rubber article. The lower limit is 0 ppb by mass. Specific examples of emulsifiers include emulsifiers having fluorine atoms and emulsifiers not having fluorine atoms, as described below.

[0029] [Uses] The crosslinked rubber article is suitable for use as a material for O-rings, sheets, gaskets, oil seals, diaphragms, V-rings, and the like. The present invention can also be applied to heat-resistant and chemical-resistant sealing materials, heat-resistant and oil-resistant sealing materials, wire coating materials, sealing materials for semiconductor manufacturing equipment, sealing materials for liquid crystal display panel manufacturing equipment, sealing materials for light-emitting diode manufacturing equipment, corrosion-resistant rubber paints, sealing materials for urea-resistant greases, and the like, rubber paints, adhesive rubbers, hoses, tubes, calendered sheets (rolls), sponges, rubber rolls, oil drilling components, heat-dissipating sheets, solution-crosslinked products, rubber sponges, bearing seals (urea-resistant greases, etc.), linings (chemical-resistant), insulating sheets for automobiles, insulating sheets for electronic devices, rubber bands for watches, endoscope packings (amine-resistant), bellows hoses (processed from calendered sheets), water heater packings / valves, fenders (offshore civil engineering, ships), fibers and nonwoven fabrics (protective clothing, etc.), circuit board sealing materials, rubber gloves, stators for uniaxial eccentric screw pumps, parts for urea SCR systems, vibration-proofing agents, vibration-damping agents, sealants, additives for other materials, and toys.

[0030] [Fluorocopolymer Composition] The fluorocopolymer composition of the present disclosure (hereinafter also referred to as "the composition") is a fluorocopolymer composition containing a fluorocopolymer, and when a crosslinked rubber article obtained using the fluorocopolymer composition is subjected to a sputtering treatment by the method of Test 1 described above, the arithmetic mean height Sa of the surface of the crosslinked rubber article after the sputtering treatment is greater than 1.6 μm and the aspect ratio Str of the surface of the crosslinked rubber article after the sputtering treatment is 0.90 or less.

[0031] The preferred embodiments of the crosslinked rubber article obtained using this composition are the same as those of the above-described crosslinked rubber article. The measurement methods and preferred embodiments of the arithmetic mean height Sa of the surface of the crosslinked rubber article after sputtering and the aspect ratio Str of the surface of the crosslinked rubber article after sputtering are the same as those of the above-described crosslinked rubber article.

[0032] [Fluorine-containing copolymer] The fluorine-containing copolymer preferably contains units based on tetrafluoroethylene (hereinafter also referred to as "TFE"), and preferably contains units based on TFE and units based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as "PAVE"). Hereinafter, the units based on TFE will also be referred to as "TFE units", and the units based on PAVE will also be referred to as "PAVE units".

[0033] The PAVE from which the PAVE unit is derived is preferably a monomer represented by formula (1) from the viewpoint of more efficient production of the fluorine-containing copolymer. ２ =CF-O-R ｆ１ (1) In formula (1), R ｆ１ represents a perfluoroalkyl group having 1 to 10 carbon atoms. ｆ１ From the viewpoint of better polymerization reactivity, the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 8, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 3. The perfluoroalkyl group may be linear or branched.

[0034] Specific examples of PAVE include perfluoro(methyl vinyl ether) (hereinafter also referred to as "PMVE"), perfluoro(ethyl vinyl ether) (hereinafter also referred to as "PEVE"), and perfluoro(propyl vinyl ether) (hereinafter also referred to as "PPVE"), and from the viewpoint of more efficient production of the fluorinated copolymer, PMVE or PPVE is preferred, and PMVE is more preferred. The preferred range of the content of units based on specific examples of PAVE is preferably the same as the preferred range of the content of PAVE units described below.

[0035] The content of TFE units is preferably 20.0 to 80.0 mol%, more preferably 50.0 to 80.0 mol%, and even more preferably 60.0 to 80.0 mol%, based on the total content of TFE units and PAVE units. The content of PAVE units is preferably 20.0 to 80.0 mol%, more preferably 20.0 to 50.0 mol%, and even more preferably 20.0 to 40.0 mol%, based on the total content of TFE units and PAVE units. The total content of TFE units and PAVE units is preferably 50.0 to 99.95 mol%, more preferably 70.0 to 99.9 mol%, and even more preferably 75.0 to 99.7 mol%, based on the total content of all units in the fluorine-containing copolymer.

[0036] The content of TFE units is preferably 20.0 to 80.0 mol%, more preferably 50.0 to 80.0 mol%, and even more preferably 60.0 to 80.0 mol%, based on the total content of all units in the fluorine-containing copolymer. The content of PAVE units is preferably 20.0 to 80.0 mol%, more preferably 20.0 to 50.0 mol%, and even more preferably 20.0 to 40.0 mol%, based on the total content of all units in the fluorine-containing copolymer.

[0037] The fluorine-containing copolymer preferably has a crosslinkable group. The crosslinkable group is not particularly limited as long as it is a functional group that can be crosslinked by a crosslinking reaction, and specific examples include a nitrile group, a polymerizable unsaturated bond, a chlorine atom, a bromine atom, and an iodine atom, with a nitrile group being preferred. The fluorine-containing copolymer preferably has the crosslinkable group at least at one of the end and the side chain, more preferably at the side chain. During production of the fluorine-containing copolymer, a crosslinkable group can be introduced into the side chain by polymerizing using a monomer having a crosslinkable group. Furthermore, during polymerization, a crosslinkable group can be introduced into the end by polymerizing a monomer using a chain transfer agent having a crosslinkable group. Among these, the fluorine-containing copolymer preferably has units based on a monomer having a crosslinkable group, and more preferably has units based on a monomer having a nitrile group.

[0038] The monomer having a crosslinkable group may be a monomer having a nitrile group (hereinafter referred to as "R ＣＮ"), a monomer having two or more polymerizable unsaturated bonds (hereinafter also referred to as "BO"), a monomer having one or more atoms of at least one kind selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom (hereinafter also referred to as "R Ｈａｌ "), and a compound represented by formula (6) (hereinafter also referred to as "POAVE"), which will be described later, ＣＮ is preferred.

[0039] 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).

[0040] 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 R ５３ is preferably a fluorine atom or a hydrogen atom, and R ５１ , R ５２ , and R ５３ It is more preferred that all of R are fluorine atoms or all of R are hydrogen atoms, and in view of the superior mold releasability and heat resistance of the crosslinked rubber article, ５１ , R ５２ , and R ５３ It is particularly preferred that all of R are fluorine atoms. ５４R 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.

[0041] BO is a monomer having two or more polymerizable unsaturated bonds. Examples of the polymerizable unsaturated bond include a carbon atom-carbon atom double bond (C═C) and a carbon atom-carbon atom triple bond (C≡C). The number of polymerizable unsaturated bonds that BO has is preferably 2 to 6, more preferably 2 or 3, and even more preferably 2, in terms of better polymerization reactivity. BO preferably contains a fluorine atom in terms of reducing the compression set of a crosslinked rubber article at high temperatures.

[0042] 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 terms 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. ２４ R may be linear, branched, or cyclic, preferably linear or branched, and particularly preferably linear. ２４ The number of carbon atoms in R is preferably 2 to 8, more preferably 3 to 7, still more preferably 3 to 6, and particularly preferably 3 to 5. ２４ Although R may or may not have an etheric oxygen atom, it is preferable that R has an etheric oxygen atom in view of better crosslinking reactivity and rubber physical properties. ２４ The number of etheric oxygen atoms in R is preferably 1 to 6, more preferably 1 to 3, and even more preferably 1 or 2. ２４ The etheric oxygen atom in R ２４ It is preferred that the nucleotide sequence is located at the end of the nucleotide sequence.

[0043] 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).

[0044] (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.

[0045] (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.

[0046] 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(CF３ )CF ２ O) ２ CF = CF ２ , C.F. ２ = CFOCF ２ O (CF ２ CF ２ O) ２ CF = CF ２ , C.F. ２ = CFO (CF ２ O) ３ O(CF(CF ３ )CF ２ O) ２ CF = CF ２ , C.F. ２ = CFOCF ２ CF (CF ３ ) O(CF ２ ) ２ OCF (CF ３ )CF ２ OCF = CF ２ , and CF ２ = CFOCF ２ CF ２ O (CF ２ O) ２ CF ２ CF ２ OCF = CF ２ Among the monomers represented by formula (3), a more preferred specific example of the monomer is CF ２ = CFO (CF ２ ) ３ OCF = CF ２ (hereinafter also referred to as "C3DVE"), and CF ２ = CFO (CF ２ ) ４ OCF = CF ２ (hereinafter also referred to as "C4DVE").

[0047] 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.

[0048] 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 ２ Br, bromotrifluoroethylene, 4-bromo-3,3,4,4-tetrafluorobutene-1 (BTFB), vinyl bromide, 1-bromo-2,2-difluoroethylene, perfluoroallyl bromide, 4-bromo-1,1,2-trifluorobutene-1, 4-bromo-1,1,3,3,4,4-hexafluorobutene, 4-bromo-3-chloro-1,1,3,4,4-pentafluorobutene, 6-bromo-5,5,6,6-tetrafluorohexene, and 4-bromoperfluorobutene-1,3,3-difluoroallyl bromide. Also included are 2-bromo-perfluoroethyl perfluorovinyl ether and CF ２ Br-R ｆ -O-CF=CF ２ (R ｆ is a perfluoroalkylene group), for example, CF ２ BrCF ２ O-CF=CF ２ , ROCF = CFBr, and ROCBr = CF ２ (wherein R is a lower alkyl group or a fluoroalkyl group), more specifically fluorovinyl ethers such as CH ３ OCF = CFBr and CF ３ CH ２Specific examples of the monomer having an iodine atom include the monomer represented by the formula: CHR=CH-Z-CH ２ CHR-I (wherein R is —H or —CH ３ Z is a linear or branched C alkyl group optionally containing one or more ethereal oxygen atoms; １ ~C １８ iodinated olefins of the formula I(CH) as disclosed in U.S. Pat. No. 5,717,036, which are (per)fluoroalkylene groups or (per)fluoropolyoxyalkylene groups as disclosed in U.S. Pat. No. 5,674,959. ２ CF ２ CF ２ ) ｎ OCF = CF ２ and ICH ２ CF ２ O[CF(CF ３ )CF ２ O] ｎ CF = CF ２ (wherein n = 1 to 3) and the like. Also included are iodoethylene, 4-iodo-3,3,4,4-tetrafluorobutene-1 (ITFB), 3-chloro-4-iodo-3,4,4-trifluorobutene, 2-iodo-1,1,2,2-tetrafluoro-1-(vinyloxy)ethane, 2-iodo-1-(perfluorovinyloxy)-1,1,-2,2-tetrafluoroethylene, 1,1,2,3,3,3-hexafluoro-2-iodo-1-(perfluorovinyloxy)propane, 2-iodoethyl vinyl ether, 3,3,4,5,5,5-hexafluoro-4-iodopentene, and iodotrifluoroethylene, as disclosed in U.S. Pat. No. 4,694,045. Also included are allyl iodide and 2-iodo-perfluoroethyl perfluorovinyl ether.

[0049] 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.

[0050] R ｆ２ In the formula, the perfluoroalkyl group may be linear or branched. ｆ２ The number of carbon atoms in is preferably 1 to 3. When n is 0, m is preferably 3 or 4. When n is 1, m is preferably an integer of 2 to 4. When n is 2 or 3, m is preferably 0. n is preferably an integer of 1 to 3. R ｆ２ When the number of carbon atoms, n, and m are within the above ranges, the low-temperature properties of the crosslinked rubber article are excellent, and the productivity of the crosslinked rubber article is improved.

[0051] Specific examples of POAVE include the following. The abbreviation for the compound is given in parentheses after the formula. CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ４ -OCF ３ (C9PEVE), CF ２ =CF-OCF ２ CF ２ -(OCF ２ ) ２ -OCF ３ (C7PEVE), CF ２ =CF-(OCF ２ CF ２ ) ２ -OCF ２ CF ３ (EEAVE), CF ２ =CF-(OCF ２ CF ２ ) ３ -OCF ２ CF ３ (EEEAVE), CF ２ =CF-OCF ２ -OCF ３ , C.F. ２ =CF-OCF ２ -OCF ２ -OCF ３As 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.

[0052] The content of units based on monomers having a crosslinkable group is preferably from 0.01 to 20 mol %, more preferably from 0.01 to 15 mol %, and even more preferably from 0.03 to 10 mol %, based on the total content of all units in the fluorine-containing copolymer. ＣＮ The content of units based on the formula (I) is preferably from 0.01 to 10 mol %, more preferably from 0.05 to 10 mol %, and even more preferably from 0.1 to 5 mol %, based on the total content of all units in the fluorine-containing copolymer.

[0053] The fluorine-containing copolymer may have units other than TFE units, PAVE units and units derived from a monomer having a crosslinkable group.

[0054] The fluorine-containing copolymer is preferably a perfluoropolymer. "Perfluoropolymer" refers to a polymer that does not substantially contain hydrogen atoms bonded to carbon atoms, has fluorine atoms instead of those hydrogen atoms, and has a main chain consisting of a chain of carbon atoms. The side chain of the perfluoropolymer may have a polyvalent atom other than carbon atoms, and the polyvalent atom is preferably an oxygen atom. "Substantially does not contain hydrogen atoms" means that the content of hydrogen atoms in the perfluoropolymer is 0.5% by mass or less, preferably 0.1% by mass or less, more preferably 0.07% by mass or less, and even more preferably 0.05% by mass or less. The lower limit can be 0% by mass. When the content of hydrogen atoms is within the above range, good heat resistance or chemical resistance is likely to be obtained.

[0055] The fluorine-containing copolymer is also preferably a perfluoroelastomer. A "perfluoroelastomer" is a perfluoropolymer having a glass transition temperature of 20°C or lower and a melting peak (ΔH) of 4.5 J / g or lower, and further, a polymer in which the proportion of fluorine atoms contained in the perfluoropolymer is 65 mass% or higher.

[0056] Fillers The composition may contain fillers, including, for example, the fillers that may be contained in the crosslinked rubber article described above.

[0057] The filler may be used alone or in combination of two or more. The content of the filler is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, per 100 parts by mass of the fluorocopolymer. The lower limit is preferably 1 part by mass or more per 100 parts by mass of the fluorocopolymer.

[0058] One preferred embodiment of the present composition is one that is substantially free of white filler. This results in the present crosslinked rubber article being substantially free of metal components, which has the advantage of being usable in areas of semiconductor manufacturing equipment where metal components are avoided. The phrase "substantially free of white filler" means that the content of white filler is 5% by mass or less, preferably 1% by mass or less, and more preferably 0.1% by mass or less, relative to the total mass of the composition. The lower limit is 0% by mass. Specific examples of white filler are as described above.

[0059] [Crosslinking Agent] Specific examples of the crosslinking agent include a compound having two or more amino groups (hereinafter also referred to as a "polyamine compound") and an organic peroxide. Polyamine compounds are preferred, and compounds having two amino groups are more preferred, since they provide excellent crosslinkability for the fluorocopolymer and enable the production of crosslinked rubber articles with smaller compression set.

[0060] The polyamine compound may be a compound in which a hydrogen atom of an aliphatic hydrocarbon is substituted with an amino group, or a compound in which a hydrogen atom of an aromatic hydrocarbon is substituted with an amino group, but from the viewpoint of achieving better effects of the present disclosure, a compound in which a hydrogen atom of an aromatic hydrocarbon is substituted with an amino group is preferred. The polyamine compound preferably contains a fluorine atom. This improves compatibility with the fluorine-containing copolymer, thereby allowing a crosslinked rubber article to be obtained with a smaller compression set at high temperatures.

[0061] Specific examples of the polyamine compound include hexamethylenediamine, hexamethylenediamine carbamate, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis(3-amino-4-hydroxyphenyl)propane, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (hereinafter also referred to as "BOAP", also known as bisaminophenol AF), 2,2-bis(3,4-diaminophenyl)propane, 2,2-bis(3,4-diaminophenyl)hexafluoropropane, 2,2-bis(3-amino-4-(N-phenylamino)phenyl)hexafluoropropane, 4,4'-methylenedianiline, m-phenylenediamine, adipic acid dihydrazide, and the compound represented by formula (XII) of Japanese Patent No. 5,833,657, with BOAP being preferred.

[0062] The content of the crosslinking agent is preferably from 0.1 to 10 parts by mass, more preferably from 0.3 to 5 parts by mass, and even more preferably from 0.5 to 3 parts by mass, per 100 parts by mass of the fluorine-containing copolymer.

[0063] In order to obtain a more excellent effect of the present disclosure, it is preferable that the present composition is substantially free of an emulsifier. The phrase "substantially free of an emulsifier" means that the content of the emulsifier is 10 mass ppm or less, preferably 100 mass ppb or less, more preferably 50 mass ppb or less, and particularly preferably 25 mass ppb or less, relative to the total mass of the present composition. The lower limit is 0 mass ppb. Specific examples of the emulsifier include emulsifiers having fluorine atoms and emulsifiers not having fluorine atoms, which will be described later.

[0064] [Method for producing crosslinked rubber article] The method for producing the present crosslinked rubber article is not particularly limited as long as it can produce the present crosslinked rubber article. The method for producing the present crosslinked rubber article preferably comprises a step of crosslinking the fluorocopolymer using a fluorocopolymer composition containing the above-mentioned fluorocopolymer. A method of crosslinking the fluorocopolymer is preferably a method of heating the fluorocopolymer composition. The fluorocopolymer composition is as described above. Specific examples of the crosslinking method by heating include hot press crosslinking, steam crosslinking, injection molding crosslinking, hot air crosslinking, molten salt crosslinking, fluidized bed crosslinking, and funnel crosslinking. The heating conditions are preferably 100 to 400°C for 1 second to 24 hours.

[0065] The crosslinked rubber obtained by heating the present fluorocopolymer composition (by primary crosslinking) may be further heated to cause secondary crosslinking. By carrying out secondary crosslinking, the mechanical properties, compression set, and other properties of the crosslinked rubber can be stabilized or improved. The heating conditions for carrying out secondary crosslinking are preferably 80 to 350°C for 30 minutes to 48 hours.

[0066] As a crosslinking method other than heating, the composition may be irradiated with radiation, and specific examples of the radiation to be irradiated include electron beams and ultraviolet rays.

[0067] The method for producing the crosslinked rubber article of the present invention is also preferably a method for producing a crosslinked rubber article by molding a fluorocopolymer composition using a mold. Specifically, it is preferable to fill a mold with the fluorocopolymer composition and mold the fluorocopolymer composition, and it is more preferable to further subject the molded fluorocopolymer composition to the above-mentioned crosslinking step. The shape of the mold is not particularly limited, but an O-ring type is preferred, and a P-26 (JIS B2401:2012) O-ring type is more preferred.

[0068] The method for producing the crosslinked rubber article preferably comprises, for example, the steps of producing a fluorocopolymer, preparing a fluorocopolymer composition containing the fluorocopolymer, and crosslinking the fluorocopolymer using the fluorocopolymer composition. The fluorocopolymer and the fluorocopolymer composition are as described above.

[0069] [Process for producing fluorine-containing copolymer] As the process for producing fluorine-containing copolymer, for example, in the presence of polymerization initiator, the method of copolymerizing a monomer comprising at least one of TFE and PAVE with a monomer having crosslinkable group can be enumerated.Polymerization method can be enumerated for example in aqueous medium (for example, polymerization without using emulsifier, emulsion polymerization using emulsifier), solution polymerization and suspension polymerization.In view of easy adjustment of molecular weight and composition of fluorine-containing copolymer, and excellent productivity, polymerization in aqueous medium is preferred.When producing fluorine-containing polymer in aqueous medium, it can be carried out by heating the above-mentioned monomer in the presence of aqueous medium and polymerization initiator.An emulsifier may or may not be contained in aqueous medium.

[0070] As a first preferred embodiment of the step of producing a fluorine-containing copolymer, under the condition that an aqueous medium is present and an emulsifier having a fluorine atom is substantially absent, a compound represented by formula (X) described below (hereinafter also referred to as "compound X") and a polymerization initiator are used to polymerize a first monomer A comprising TFE and a monomer having a crosslinkable group, to produce an aqueous dispersion (hereinafter also referred to as "first aqueous dispersion A") comprising particles of the first fluorine-containing copolymer A having an average particle size of 500 nm or less, and recover the first fluorine-containing copolymer A from the first aqueous dispersion A (hereinafter also referred to as "production method A"). Hereinafter, in production method A, the step of producing the first aqueous dispersion A is also referred to as "step A1", and the step of recovering the fluorine-containing copolymer from the first aqueous dispersion A is also referred to as "step A2".

[0071] A second preferred embodiment of the step of producing a fluorine-containing copolymer includes polymerizing a first monomer B containing TFE using a compound X and a polymerization initiator described below in the presence of an aqueous medium and substantially no emulsifier having a fluorine atom to produce an aqueous dispersion containing particles of a first fluorine-containing polymer B having an average particle size of 500 nm or less (hereinafter also referred to as "first aqueous dispersion B"). In the first aqueous dispersion B, a second monomer B containing a monomer having a crosslinkable group is polymerized to produce a second aqueous dispersion B containing a second fluorine-containing copolymer B, and a step of recovering the fluorine-containing copolymer from the second aqueous dispersion B (hereinafter also referred to as "production method B"). Hereinafter, in production method B, the step of producing the first aqueous dispersion B will be referred to as "step B1", the step of producing the second aqueous dispersion B will be referred to as "step B2", and the step of recovering the fluorine-containing copolymer from the second aqueous dispersion B will be referred to as "step B3". Each step will be described in detail below.

[0072] <Production method A> (Step A1) In step A1, a first monomer A containing TFE and a monomer having a crosslinkable group is polymerized in the presence of compound X and a polymerization initiator under conditions in which an aqueous medium is present and an emulsifier having a fluorine atom is substantially absent, to synthesize a first fluorinated copolymer A and obtain a first aqueous dispersion A. This suppresses a decrease in the molecular weight of the polymer produced, making it easy to obtain the fluorinated copolymer.

[0073] -Emulsifier- "Under conditions in which an emulsifier having a fluorine atom is substantially absent" means that the content of the emulsifier having a fluorine atom is 10 ppm by mass or less, preferably 150 ppb by mass or less, more preferably 50 ppb by mass or less, and particularly preferably 25 ppb by mass or less, relative to the total mass of the aqueous medium. The lower limit is 0 ppb by mass. Step A1 is preferably performed under conditions in which an emulsifier having a fluorine atom and an emulsifier not having a fluorine atom are substantially absent. "Substantially absent" means that the content of the emulsifier is 10 ppm by mass or less, preferably 150 ppb by mass or less, more preferably 50 ppb by mass or less, relative to the total mass of the aqueous medium. The lower limit is 0 ppb by mass. The contents of various emulsifiers can be measured using a liquid chromatograph mass spectrometer. Specifically, the measurement method described in paragraphs

[0721] to

[0732] of WO 2018 / 181904 can be mentioned.

[0074] The emulsifier includes a water-soluble emulsifier. A water-soluble emulsifier means an emulsifier having a solubility of 100 mg or more in 1000 g of water at 25°C, and a water-insoluble emulsifier means an emulsifier other than the water-soluble emulsifiers. The water-soluble emulsifier may be either ionic or nonionic. Examples of the emulsifier include those having no carbon-carbon double bond. Compound X described below, the first fluorine-containing copolymer described below, and the fluorine-containing copolymer (second fluorine-containing copolymer) described below do not fall under the category of emulsifiers.

[0075] Examples of emulsifiers having fluorine atoms include anionic fluorine-containing emulsifiers. Examples of anionic fluorine-containing emulsifiers include emulsifiers containing fluorine atoms in which the total number of carbon atoms in the moiety excluding the anionic group is 20 or less. Examples of fluorine-containing emulsifiers containing fluorine atoms in which the total number of carbon atoms in the moiety excluding the anionic group is 20 or less include emulsifiers containing fluorine atoms in which the molecular weight of the anionic moiety is 800 or less. The above-mentioned "anionic moiety" means the moiety excluding the cation of the fluorine-containing emulsifier.

[0076] The fluorine-free emulsifier is an emulsifier that does not contain fluorine atoms and has a hydrocarbon group such as an alkyl group as a hydrophobic moiety. It is also possible to substitute a hydrogen atom of the hydrocarbon group of the fluorine-free emulsifier with a halogen atom other than a fluorine atom.

[0077] The emulsifiers having no fluorine atoms include anionic hydrocarbon emulsifiers and nonionic hydrocarbon emulsifiers.

[0078] Anionic hydrocarbon emulsifiers refer to emulsifiers having a negatively charged hydrophilic moiety, such as a carboxylic acid group, a sulfonic acid group, a sulfate group, a phosphonic acid group, or a phosphate group, and a hydrocarbon group, such as an alkyl group, as a hydrophobic moiety. Specific examples of anionic hydrocarbon emulsifiers include sodium dodecyl sulfate, highly branched C10 tertiary carboxylic acid supplied by Resolution Performance Products as Versatic® 10, linear alkyl polyethersulfonate sodium supplied by BASF as the Avanel® S series, and sulfosuccinate emulsifier Lankropol® K8300 available from AkzoNobelSurfaceChemistry LLC.

[0079] Nonionic hydrocarbon emulsifiers are emulsifiers that exhibit surface activity in water without dissociating into ions and have hydrocarbon groups such as alkyl groups as their hydrophobic moieties. The hydrophilic moieties of nonionic hydrocarbon emulsifiers include water-soluble functional groups such as polyethylene oxide chains obtained from the polymerization of ethylene oxide. Nonionic hydrocarbon emulsifiers include polyalkylene oxide block copolymers, such as block copolymers having polyethylene oxide and polypropylene oxide.

[0080] Further, other nonionic hydrocarbon emulsifiers include those described in paragraphs

[0043] to

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

[0081] The emulsifier with fluorine atom and the emulsifier without fluorine atom can contain silicon atom.The emulsifier with silicon atom can include siloxane emulsifier.Siloxane emulsifier is a hydrocarbon-containing emulsifier with siloxane skeleton.The siloxane emulsifier can include the emulsifier described in U.S. Patent No. 6,841,616 (Wille et al.) and U.S. Patent No. 7,977,438 (Brothers et al.).

[0082] The emulsifier having a fluorine atom and the emulsifier not having a fluorine atom may be a polymer emulsifier. Examples of polymer emulsifiers include polymers obtained by polymerizing a monomer having a fluorine atom or a monomer not having a fluorine atom. Furthermore, examples of polymer emulsifiers made of polymers obtained by polymerizing a monomer having a fluorine atom or a monomer not having a fluorine atom include polymers having a hydrophilic group in the side chain. Examples of such polymer emulsifiers include polymers obtained by polymerizing units based on a compound having a polymerization-reactive site and a hydrophilic group. Furthermore, even if a polymer does not originally have a hydrophilic group, examples include polymers obtained by post-treating a polymer obtained by polymerizing a compound having a group that can become a hydrophilic group, such as by hydrolysis. Preferably, the polymer emulsifier is water-soluble.

[0083] -Aqueous Medium- Specific examples of the aqueous medium include water and a mixed solvent of water and a water-soluble organic solvent. Specific examples of the water-soluble organic solvent include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol.

[0084] Before the polymerization of the first monomer A is initiated, the content of the aqueous medium is preferably 20 to 80% by volume, and more preferably 40 to 70% by volume, relative to the volume of the reactor. In this specification, "before the polymerization of the monomer is initiated" means immediately before the start of polymerization. Here, examples of the "start of polymerization" include the time when the monomer and the polymerization initiator are brought into coexistence in the reactor after the temperature inside the reactor is raised to a polymerization temperature or higher, and the time when the temperature inside the reactor is raised to a polymerization temperature or higher after the monomer and the polymerization initiator are brought into coexistence in the reactor.

[0085] Compound X Compound X is a compound represented by formula (X). Compound X can be polymerized with a monomer described below.

[0086] C(X １ ) (X ２ ) = C(X ３ ) CONH-R-Z (X) In formula (X), １ , X ２ and X ３ are each independently a hydrogen atom, a fluorine atom, a perfluoromethyl group or an alkyl group, R is an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms, Z is —SO ３ M, -OSO ３ M, -P (=O) (OM) ２ , -OP(=O)(OM) ２ or -COOM, where M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ When a plurality of M's are present, the plurality of M's may be the same or different from each other, R Ｍ１ and R Ｍ２ are each independently a hydrogen atom or a substituent, and R Ｍ１ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ１ may be the same or different from each other, R Ｍ２ Any two of R may be bonded to each other to form a ring, and multiple R Ｍ２ may be the same or different from each other.

[0087] X １ , X ２ and X ３ are each independently a fluorine atom, a perfluoromethyl group, a hydrogen atom, or an alkyl group. The alkyl group may be linear, branched, or cyclic. The alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1. X １ , X ２ and X ３As the alkyl group, a fluorine atom or a hydrogen atom is preferred, and a hydrogen atom is preferred in terms of excellent polymerization reactivity.

[0088] R is an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms. The alkylene group or the fluoroalkylene group may be linear, branched, or cyclic, and is preferably branched. The alkylene group or the fluoroalkylene group has 1 to 6 carbon atoms, preferably 2 to 4 carbon atoms, and more preferably 4 carbon atoms. R is preferably an alkylene group having 1 to 6 carbon atoms.

[0089] Z is -SO ３ M, -OSO ３ M, -P (=O) (OM) ２ , -OP(=O)(OM) ２ or -COOM. Z is -SO ３ M is preferred, and —SO ３ Na is more preferred.

[0090] M is a hydrogen atom, a metal atom, N(R Ｍ１ ) ４ or P(R Ｍ２ ) ４ and R Ｍ１ and R Ｍ２ are each independently a hydrogen atom or a substituent. The metal atom represented by M is preferably a metal atom of Group 1, more preferably Li, Na or K. Ｍ１ and R Ｍ２ The substituent represented by the formula (I) is preferably a monovalent organic group, more preferably a monovalent hydrocarbon group, and even more preferably an alkyl group or an aromatic hydrocarbon group. The substituent preferably has 1 to 10 carbon atoms. The alkyl group may be linear, branched, or cyclic. The aromatic hydrocarbon group may be monocyclic or polycyclic. The aromatic hydrocarbon group is preferably a phenyl group.

[0091] Specific examples of compound X include 2-acrylamido-2-methyl-1-propanesulfonic acid, N-tigloylglycine, 6-acrylamidohexanoic acid, 1,1-difluoro-2-methyl-2-[(1-oxo-2-propen-1-yl)amino]-1-propanesulfonic acid, 3-methyl-3-[(2-methyl-1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, 2,3-dimethyl-3-[(1-oxo-2-propen-1-yl)amino]-2-butanesulfonic acid, and metal salts thereof. Examples of the metal salts include metal salts of the metal atom represented by M. As the compound X, (meth)acrylamides having a sulfonic acid group and metal salts thereof are preferred, and 2-acrylamido-2-methyl-1-propanesulfonic acid, sodium 2-acrylamido-2-methyl-1-propanesulfonate, 2-methacrylamido-2-methyl-1-propanesulfonic acid, or sodium 2-methacrylamido-2-methyl-1-propanesulfonate is preferred. Note that the term "(meth)acrylamide" as used above is a concept that encompasses both acrylamide and methacrylamide.

[0092] Before starting polymerization of the first monomer A, the content of the compound X is preferably 1.0 to 1000 ppm by mass, more preferably 1.0 to 500 ppm by mass, still more preferably 3.0 to 100 ppm by mass, and particularly preferably 5.0 to 30.0 ppm by mass, relative to the total mass of the aqueous medium.

[0093] -Polymerization initiator- The polymerization initiator used in step A1 is preferably a water-soluble polymerization initiator, more preferably a persulfate such as ammonium persulfate, sodium persulfate, or potassium persulfate, or an organic polymerization initiator such as disuccinic acid peroxide or azobisisobutylamidine dihydrochloride, still more preferably a persulfate, and particularly preferably ammonium persulfate.

[0094] The amount of the polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, relative to 100 parts by mass of the total amount of the first monomer used.

[0095] -First Monomer A- The first monomer A contains TFE and a monomer having a crosslinkable group. The amount of TFE used is preferably 5.0 to 80.0 mol %, more preferably 20.0 to 75.0 mol %, and even more preferably 25.0 to 50.0 mol %, based on the amount of the first monomer A used. Examples of the monomer having a crosslinkable group include the monomers having a crosslinkable group described above in the composition of the fluorine-containing copolymer, and R ＣＮ The amount of the monomer having a crosslinkable group used is preferably 0.05 to 10 mol %, more preferably 0.10 to 5.0 mol %, and still more preferably 0.20 to 3.0 mol %, relative to the amount of the first monomer A used.

[0096] The first monomer preferably contains PAVE. Details of PAVE are as described above. The amount of PAVE used is preferably 20.0 to 95.0 mol%, more preferably 25.0 to 80.0 mol%, and even more preferably 50.0 to 75.0 mol%, based on the amount of first monomer A used. The total amount of TFE units and PAVE units used is preferably 50 to 99 mol%, more preferably 70 to 99 mol%, and even more preferably 75 to 99 mol%, based on the amount of first monomer A used.

[0097] The first monomer A may contain a monomer other than TFE, PAVE, and a monomer having a crosslinkable group.

[0098] -Method- The method of step A1 is not particularly limited as long as it is a method of polymerizing the first monomer A using compound X and a polymerization initiator under conditions in which an aqueous medium is present and an emulsifier having a fluorine atom is substantially absent. Examples of the method include a method in which a solution containing an aqueous medium and compound X is prepared, and the first monomer A is polymerized using this solution and a polymerization initiator. More specifically, examples include a method in which the solution and the first monomer A are added to a reactor, the reactor is heated, and a polymerization initiator is added to the reactor to polymerize the first monomer A. Step A1 preferably does not include a step of terminating the polymerization midway and deactivating or purifying the polymerization initiator. Furthermore, step A1 is preferably performed in the same reactor.

[0099] Polymerization of the first monomer A gives a first fluorine-containing copolymer A (corresponding to the fluorine-containing copolymer) dispersed in the form of particles in an aqueous medium. The aqueous dispersion thus obtained in which particles of the first fluorine-containing copolymer A are dispersed may be used as the first aqueous dispersion A as is, or another aqueous medium may be added to give the first aqueous dispersion A. Alternatively, the first aqueous dispersion A may be obtained by solvent substitution, dispersing the particles of the first fluorine-containing copolymer A in another aqueous medium.

[0100] The first monomer A is added to the reactor by a conventional method. For example, the first monomer A may be added continuously or intermittently to the reactor so that the polymerization pressure reaches a predetermined pressure. Alternatively, the first monomer A may be dissolved in an aqueous medium, and the resulting solution may be added continuously or intermittently to the reactor. Different monomers of the first monomer A may be added to the reactor at the same time, or may be added at different times. For example, TFE and PAVE may be added to the reactor in advance, and polymerization may be initiated, followed by addition of TFE, PAVE, and a monomer having a crosslinkable group. When a polymerization initiator is used, the polymerization initiator may be added to the reactor all at once or in portions, and is preferably added intermittently.

[0101] The polymerization temperature is preferably 10 to 95° C., more preferably 15 to 90° C. The polymerization pressure is preferably 0.5 to 4.0 MPaG, more preferably 0.6 to 3.5 MPaG. The polymerization time is preferably 90 to 1,000 minutes, more preferably 90 to 700 minutes.

[0102] -First Aqueous Dispersion A- In step A1, a first aqueous dispersion A is obtained, which is an aqueous dispersion containing particles of the first fluorinated copolymer A having an average particle size of 500 nm or less.

[0103] It is preferable that the first aqueous dispersion A is substantially free of a water-soluble emulsifier. "The first aqueous dispersion A is substantially free of a water-soluble emulsifier" means that the content of the water-soluble emulsifier is 10 mass ppm or less, preferably 150 mass ppb or less, more preferably 50 mass ppb or less, and even more preferably 25 mass ppb or less, relative to the total mass of the first aqueous dispersion A. The lower limit is 0 mass ppb.

[0104] Furthermore, it is preferable that the first aqueous dispersion A is substantially free of a compound represented by any one of formulas (S1) to (S4). "Substantially free of a compound represented by any one of formulas (S1) to (S4)" means that the content of each of the compounds represented by formulas (S1) to (S4) is 10 mass ppm or less, preferably 5 mass ppm or less, more preferably 150 mass ppb or less, even more preferably 50 mass ppb or less, and particularly preferably 25 mass ppb or less, relative to the total mass of the first aqueous dispersion A. The lower limit is 0 mass ppb.

[0105] H-(CF ２ ) ｎ１ -COOM Ｓ (S1) F-(CF ２ ) ｎ１ -COOM Ｓ (S2) H-(CF ２ ) ｎ２ -SO ３ M Ｓ (S3) F-(CF ２ ) ｎ２ -SO ３ M Ｓ(S4) In the formulas (S1) to (S4), n1 is an integer of 3 to 13, n2 is an integer of 4 to 10, and M Ｓ is a hydrogen atom, Na, K, NR ４ (R may be the same or different and is a hydrogen atom or an organic group having 1 to 10 carbon atoms), an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent.

[0106] The content of the particles of the first fluorinated copolymer A is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 10 to 30% by mass, relative to the total mass of the first aqueous dispersion A. The solid content concentration of the first aqueous dispersion A is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, and even more preferably 10 to 30% by mass. The solid content concentration of the first aqueous dispersion A can be measured, for example, by the following method. The solid content concentration of the first aqueous dispersion A is calculated by heating 2.0 g of the first aqueous dispersion at 170°C for 20 minutes, weighing the mass of the residue, and determining the solid content concentration using the following formula: "Solid content concentration (mass %) = 100 × heating residue of first aqueous dispersion A (g) / mass of first aqueous dispersion A (2.0 g)"

[0107] -First Fluorine-Containing Copolymer A- Particles of the first fluorine-containing copolymer A are particles produced in step A1. The average particle size of the particles of the first fluorine-containing copolymer A is 500 nm or less, preferably 300 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less, and particularly preferably 100 nm or less. The lower limit is preferably 2 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more. The average particle size of the particles of the first fluorine-containing copolymer A is a particle size calculated by analyzing an autocorrelation function obtained by dynamic light scattering using the monodisperse cumulant method.

[0108] The number of particles of the first fluorine-containing copolymer A is 1.0 × 10 １４ Preferably, the number of particles / mL or more is 2.0 × 10 １４ More preferably, 3.0 x 10 １４ The upper limit is 2.0 × 10 １５The particle number of the first fluorinated copolymer A is the number of particles per mL of the first aqueous dispersion A. Examples of a method for measuring the particle number include the measurement methods shown in the Examples section.

[0109] The first fluorine-containing copolymer A preferably does not have a melting point. In this specification, "the polymer does not have a melting point" means that when the melting point of the polymer is measured using a differential scanning calorimeter, no melting peak is observed, specifically, no melting peak is observed in a temperature range of 150°C or higher (preferably a temperature range of 150 to 330°C). Note that a glass transition peak does not fall under the above-mentioned melting peak. Specific methods for measuring the melting point include the measurement methods shown in the Examples section.

[0110] The first fluorine-containing copolymer A has units based on the first monomer A. The contents of the various units based on the first monomer A in the first fluorine-containing copolymer A have the same meanings as the contents of the various units in the above-mentioned fluorine-containing copolymer, and preferred embodiments are also the same.

[0111] (Step A2) Step A2 is a step of recovering the first fluorocopolymer A from the first aqueous dispersion A obtained in step A1. By agglomerating the particles of the first fluorocopolymer A from the first aqueous dispersion A, a solid fluorocopolymer A can be obtained.

[0112] Aggregation methods include, but are not limited to, freeze aggregation, acid aggregation, base aggregation, mechanical aggregation, and aggregation using a coagulant. In the case of freeze aggregation, the aggregation temperature is preferably -20 to 0°C. The aggregation time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid aggregation, a method in which a solution containing an acid is added to the second aqueous dispersion is preferred. Examples of acids to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, hydrofluoric acid, etc., with hydrochloric acid being preferred. The concentration of the acid in the acid-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. In the case of base aggregation, a method in which a solution containing a base is added to the second aqueous dispersion is preferred. Examples of bases to be added include sodium hydroxide, potassium hydroxide, ammonium carbonate, etc., with sodium hydroxide being preferred. The concentration of the base in the base-containing solution is preferably 0.1 to 50% by mass, more preferably 1 to 30% by mass, and even more preferably 1 to 10% by mass. For aggregation using a coagulant, known coagulants can be used. Known coagulants include aluminum salts, calcium salts, and magnesium salts. Specific examples include aluminum sulfate, a compound of the general formula M'Al(SO ４ ) ２ ・12H ２ O (wherein M' is a monovalent cation other than lithium), calcium nitrate, and magnesium sulfate are examples of the coagulation agent. Alum is preferred, and potassium alum, where M is potassium, is more preferred. Acid coagulation or freeze coagulation is preferred as the coagulation method.

[0113] <Production Method B> (Step B1) The specific method and preferred embodiment of Step B1 are the same as those of Step A1 described above, except that the first monomer A is the first monomer B, and the obtained aqueous dispersion is the first aqueous dispersion B containing the first fluorinated copolymer B.

[0114] -First Monomer B- The first monomer B includes TFE. The amount of TFE used is preferably 20.0 to 95.0 mol %, more preferably 25.0 to 80.0 mol %, and still more preferably 50.0 to 75.0 mol %, relative to the amount of the first monomer B used.

[0115] The first monomer B may contain a monomer other than TFE. The first monomer B preferably contains PAVE. Details of PAVE are as described above. The amount of PAVE used is preferably 5.0 to 80.0 mol%, more preferably 20.0 to 75.0 mol%, and even more preferably 25.0 to 50.0 mol%, based on the total amount of the first monomer B used. The total amount of TFE and PAVE used is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, based on the total amount of the first monomer B used.

[0116] The first monomer B may contain other monomers than TFE and PAVE, or may be substantially free of other units. "Substantially free of other monomers" means that the amount of other monomers used is 0.01 mol% or less, preferably 0 mol%, relative to the amount of the first monomer B used.

[0117] -First aqueous dispersion B- Step B1 provides a first aqueous dispersion B, which is an aqueous dispersion containing particles of a first fluoropolymer B having an average particle size of 500 nm or less. The first aqueous dispersion B preferably contains substantially no water-soluble emulsifier. Furthermore, the first aqueous dispersion B preferably contains substantially no compound represented by any of formulas (S1) to (S4). The definitions and preferred embodiments of "substantially not containing a water-soluble emulsifier" and "substantially not containing a compound represented by any of formulas (S1) to (S4)" in the first aqueous dispersion B are the same as those for the first aqueous dispersion A described above.

[0118] The solids concentration of the first aqueous dispersion B obtained in step B1 is preferably 1 to 50% by mass, and more preferably 5 to 45% by mass. The solids concentration of the first aqueous dispersion B can be measured, for example, by the following method. The solids concentration of the first aqueous dispersion B is calculated by heating 2.0 g of the first aqueous dispersion B at 170°C for 20 minutes, weighing the mass of the residue, and determining the solids concentration using the following formula: "Solids concentration (mass%) = 100 × heating residue of first aqueous dispersion B (g) / mass of first aqueous dispersion B (2.0 g)"

[0119] The aqueous dispersion in which particles of the first fluoropolymer B obtained by polymerization of the first monomer B are dispersed may be used as the first aqueous dispersion B as it is, or another aqueous medium may be added to form the first aqueous dispersion B. Alternatively, the first aqueous dispersion B may be formed by dispersing particles of the first fluoropolymer B in another aqueous medium by solvent substitution.

[0120] -First Fluorine-Containing Polymer B- Particles of the first fluorine-containing polymer B are particles produced in step B1. The first fluorine-containing polymer B may be the same as or different from the second fluorine-containing copolymer B described below. The average particle size of the particles of the first fluorine-containing polymer B is 500 nm or less, and from the viewpoint of particle dispersion stability, it is preferably 300 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less, and particularly preferably 100 nm or less. The lower limit is preferably 2 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more. The average particle size of the particles of the first fluorine-containing polymer B can be calculated in the same manner as for the particles of the first fluorine-containing polymer A described above.

[0121] The number of particles of the first fluorinated polymer B is 1.0 × 10 １４ Preferably, the number of particles / mL or more is 2.0 × 10 １４ More preferably, 3.0 x 10 １４ The upper limit is 2.0 × 10 １５ The particle number of the first fluoropolymer B is the number of particles per mL of the first aqueous dispersion B. Examples of a method for measuring the particle number include the measurement methods shown in the Examples section.

[0122] The first fluorine-containing polymer B preferably does not have a melting point.

[0123] The 1% by mass weight loss temperature on heat of the first fluoropolymer B is preferably 150°C or higher, more preferably 200°C or higher, and even more preferably 250°C or higher. The upper limit is preferably 600°C or lower. The 1% by mass weight loss temperature on heat can be measured, for example, using a thermogravimetric analyzer. Specific methods for measuring the 1% by mass weight loss temperature on heat include the measurement methods shown in the Examples section.

[0124] The first fluoropolymer B contains units based on the first monomer B. The first fluoropolymer B contains TFE units. The content of TFE units is preferably 20.0 to 95.0 mol%, more preferably 25.0 to 80.0 mol%, and even more preferably 50.0 to 75.0 mol%, based on all units of the first fluoropolymer B. The first fluoropolymer B preferably contains PAVE units. The content of PAVE units is preferably 5.0 to 80.0 mol%, more preferably 20.0 to 75.0 mol%, and even more preferably 25.0 to 50.0 mol%, based on all units of the first fluoropolymer B. The total content of TFE units and PAVE units is preferably 99.0 to 100.0 mol%, more preferably 99.5 to 100.0 mol%, and even more preferably 99.9 to 100.0 mol%, based on all units of the first fluoropolymer B. The first fluorine-containing polymer B may contain units other than TFE units and PAVE units, or may be substantially free of other units. "Substantially free of other units" means that the content of other monomers is 0.01 mol% or less, preferably 0 mol%, based on the total units of the first fluorine-containing polymer B.

[0125] (Step B2) Step B2 is a step of polymerizing a second monomer B containing a monomer having a crosslinkable group in the first aqueous dispersion B obtained in step B1 to obtain a second aqueous dispersion B containing a second fluorinated copolymer B.

[0126] Preferred embodiments of the first aqueous dispersion B are as described above. It is preferable to carry out a purification treatment to reduce or inactivate the polymerization initiator and its decomposition products from the first aqueous dispersion B before using it for polymerization of the second monomer B. In the purification treatment, the polymerization initiator and its decomposition products that may be contained in the first aqueous dispersion B are removed, making it easy to obtain a second fluorinated copolymer B with desired physical property values. Examples of purification methods include heat treatment and a method of removal using an ion exchange resin. As the ion exchange resin, an anion exchange resin is preferred. Purification may be carried out multiple times.

[0127] The first aqueous dispersion B may contain components other than the aqueous medium and the first fluoropolymer B. Specific examples of other components that the first aqueous dispersion B may contain include a chain transfer agent, a reducing agent, and a pH adjuster. Specific examples of chain transfer agents include ethyl acetate, methanol, ethanol, t-butyl methyl ether, diethyl ether, n-pentane, cyclohexane, methane, and propane. Furthermore, examples of chain transfer agents include compounds represented by formula (I) described below. Specific examples of pH adjusters include inorganic salts and ammonia. Specific examples of inorganic salts include phosphates such as disodium hydrogen phosphate and sodium dihydrogen phosphate, and carbonates such as sodium bicarbonate and sodium carbonate. More preferred examples of phosphates include disodium hydrogen phosphate dihydrate and disodium hydrogen phosphate dodecahydrate. When the first aqueous dispersion B contains a chain transfer agent, the content of the chain transfer agent is preferably 0.1 to 5 parts by mass per 100 parts by mass of the aqueous medium. When the first aqueous dispersion B contains a pH adjuster, the content of the pH adjuster is preferably 0.01 to 3.0 parts by mass per 100 parts by mass of the aqueous medium.

[0128] In step B2, the content of the particles of the first fluoropolymer B before the start of polymerization of the second monomer B is preferably from 0.01 to 5 mass%, more preferably from 0.1 to 3 mass%, relative to the total mass of the first aqueous dispersion B. Note that the first aqueous dispersion B before the start of polymerization of the second monomer B does not contain the second monomer B or the polymerization initiator.

[0129] - Second Monomer B - The second monomer B includes a monomer having a crosslinkable group. Examples of the monomer having a crosslinkable group include the above-mentioned monomers having a crosslinkable group, and the above-mentioned R ＣＮ The amount of the monomer having a crosslinkable group used is preferably 0.05 to 10 mol %, more preferably 0.10 to 5 mol %, and even more preferably 0.20 to 3 mol %, relative to the amount of the second monomer B used.

[0130] The second monomer B may contain a monomer other than the monomer having a crosslinkable group. The second monomer B preferably contains at least one selected from the group consisting of TFE and PAVE, and more preferably contains TFE and PAVE. The amount of TFE used is preferably 5.0 to 80.0 mol%, more preferably 20.0 to 75.0 mol%, and even more preferably 50.0 to 75.0 mol%, based on the total amount of the second monomer B used. The amount of PAVE used is preferably 20.0 to 95.0 mol%, more preferably 25.0 to 80.0 mol%, and even more preferably 25.0 to 50.0 mol%, based on the total amount of the second monomer B used. The amount of TFE units and PAVE units used is preferably 70 to 99 mol%, more preferably 75 to 99 mol%, and even more preferably 80 to 99 mol%, based on the total amount of the second monomer B used.

[0131] The second monomer B may contain other monomers in addition to TFE, PAVE, and the monomer having a crosslinkable group. It is also preferable that the second monomer B is substantially free of other monomers. "Substantially free of other monomers" means that the amount of other monomers used is 0.01 mol% or less, preferably 0 mol%, relative to the amount of the second monomer B used.

[0132] In step B2, it is preferable to polymerize the second monomer B using a polymerization initiator. The polymerization initiator is preferably an oil-soluble radical initiator, a water-soluble radical initiator, or a water-soluble redox catalyst. Specific examples of oil-soluble radical initiators include oil-soluble organic peroxides such as tert-butyl peroxypivalate (hereinafter also referred to as "PBPV") and diisopropyl peroxydicarbonate (hereinafter also referred to as "IPP"). Specific examples of water-soluble radical initiators include persulfates such as ammonium persulfate and potassium persulfate, disuccinic acid peroxide, bisglutaric acid peroxide, and water-soluble organic peroxides such as tert-butyl hydroperoxide (hereinafter also referred to as "TBHP"). The water-soluble redox catalyst is preferably a combination of an oxidizing agent such as bromic acid or a salt thereof, chloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, or hydrogen peroxide, and a reducing agent such as sulfurous acid or a salt thereof, hydrogen sulfite or a salt thereof, thiosulfuric acid or a salt thereof, an organic acid, or an inorganic salt. The persulfate is preferably potassium persulfate or ammonium persulfate. The sulfite is preferably sodium sulfite. The inorganic salt may be a combination of a sulfate anion, a sulfite anion, or a chloride anion with a metal ion. The metal ion is preferably a transition metal, such as manganese, iron, cobalt, nickel, copper, zinc, cerium, or silver ion, with iron ion being preferred. The inorganic salt is preferably iron(II) sulfate. The polymerization initiator is preferably an oil-soluble radical initiator or a water-soluble radical initiator. From the viewpoint of more efficient production of the fluorine-containing copolymer, a water-soluble radical initiator is more preferred, and a persulfate is even more preferred. Two or more polymerization initiators may be used in combination.

[0133] The amount of the polymerization initiator used is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 3 parts by mass, and even more preferably 0.01 to 2 parts by mass, relative to 100 parts by mass of the second monomer B used.

[0134] -Method- In step B2, a second fluorine-containing copolymer B (corresponding to the fluorine-containing copolymer) is produced by polymerizing the second monomer B in the first aqueous dispersion B. Examples of the method for polymerizing the second monomer B include the above-mentioned method for polymerizing the first monomer B.

[0135] The polymerization of the second monomer B is preferably carried out under conditions in which an emulsifier having a fluorine atom is substantially absent, more preferably under conditions in which an emulsifier is substantially absent. "Substantially absent" means that in the method for producing the second fluorine-containing copolymer B, the content of the emulsifier is 10 mass ppm or less, preferably 150 mass ppb or less, more preferably 50 mass ppb or less, relative to the total mass of the first aqueous dispersion B. The lower limit is 0 mass ppb.

[0136] - Second Fluorine-Containing Copolymer B - In step B2, the second fluorine-containing copolymer B is produced, and a second aqueous dispersion in which particles of the second fluorine-containing copolymer B are dispersed in an aqueous medium is obtained.

[0137] The second fluorine-containing copolymer B may be in the form of particles. The particles of the second fluorine-containing copolymer B may contain the first fluorine-containing polymer B, or may not contain the first fluorine-containing polymer B. The average particle size of the particles of the second fluorine-containing copolymer B is preferably 500 nm or less, preferably 500 nm or less, and from the viewpoint of particle dispersion stability, more preferably 400 nm or less, even more preferably 350 nm or less, particularly preferably 300 nm or less. The lower limit is preferably 10 nm or more, more preferably 30 nm or more, even more preferably 50 nm or more. The average particle size of the particles of the second fluorine-containing copolymer B can be measured in the same manner as the average particle size of the particles of the first fluorine-containing polymer B.

[0138] The number of particles of the second fluorine-containing copolymer B is 1.0 × 10 １４ Preferably, the number of particles / mL or more is 2.0 × 10 １４ More preferably, 3.0 x 10 １４ More preferably, 5.0 x 10 １４ The upper limit is 10.0 × 10 １５The number of particles of the second fluorinated copolymer B is the number of particles per mL of the second aqueous dispersion B. Examples of a method for measuring the number of particles include the measurement methods shown in the Examples section.

[0139] The second fluorine-containing copolymer B preferably does not have a melting point.

[0140] The second fluorine-containing copolymer B contains units based on the second monomer B. Preferably, the second fluorine-containing copolymer B also contains units based on the first monomer B and the second monomer B. The contents of the various units based on the first monomer B and the second monomer B in the second fluorine-containing copolymer B have the same meanings as the contents of the various units in the above-mentioned fluorine-containing copolymer, and preferred embodiments are also the same.

[0141] - Second aqueous dispersion B - Step B2 provides second aqueous dispersion B, which is an aqueous dispersion containing particles of second fluorocopolymer B. The second aqueous dispersion B is preferably an aqueous dispersion containing fluorocopolymer particles (hereinafter also referred to as "specific particles") and an aqueous medium.

[0142] The second aqueous dispersion B preferably does not substantially contain an emulsifier having a fluorine atom, and more preferably does not substantially contain an emulsifier. The term "the second aqueous dispersion B does not substantially contain an emulsifier" means that the content of the emulsifier is 10 mass ppm or less, preferably 150 mass ppb or less, and more preferably 50 mass ppb or less, relative to the total mass of the second aqueous dispersion B. The lower limit is 0 mass ppb.

[0143] The specific particles are preferably particles of the above-mentioned second fluorine-containing copolymer B. When the specific particles contain the second fluorine-containing copolymer B, the specific particles may or may not contain the first fluorine-containing polymer B. The second aqueous dispersion B may further contain particles of the first fluorine-containing polymer B in addition to the specific particles.

[0144] The preferred embodiments of the specific particle number and average particle diameter are the same as the preferred embodiments of the particle number and average particle diameter of the second fluorine-containing copolymer B. The specific particle number is 1 × 10 １４It is preferable that the concentration of the particles is 500 nm or less and the average particle size of the particles is 500 nm or less.

[0145] The content of the specific particles is preferably 1 to 50 mass %, more preferably 1 to 45 mass %, and even more preferably 1 to 40 mass %, relative to the total mass of the second aqueous dispersion B, from the viewpoint of dispersion stability of the specific particles.

[0146] Specific examples and preferred embodiments of the aqueous medium contained in the second aqueous dispersion B are the same as the specific examples and preferred embodiments of the aqueous medium contained in the first aqueous dispersion B. The content of the aqueous medium is preferably 50 to 99 mass%, more preferably 60 to 99 mass%, and even more preferably 70 to 99 mass%, relative to the total mass of the second aqueous dispersion B, from the viewpoint of dispersion stability of the specific particles.

[0147] <Step B3> Step B3 is a step of recovering a fluorocopolymer from the second aqueous dispersion B obtained in step B2. A solid fluorocopolymer can be obtained by aggregating particles of the second fluorocopolymer B from the second aqueous dispersion B. As the aggregation method, the methods listed in step A2 above can be used.

[0148] [Step of Preparing Fluorine-Containing Copolymer Composition] The step of preparing a fluorine-containing copolymer composition is a step of preparing a fluorine-containing copolymer composition containing the above-mentioned fluorine-containing copolymer. The fluorine-containing copolymer composition has the same meaning as the above-mentioned fluorine-containing copolymer composition, and the preferred embodiments are also the same. Examples of methods for preparing the fluorine-containing copolymer composition include a method of mixing the above-mentioned components contained in the fluorine-containing copolymer composition. The components can be mixed using a rubber mixing device such as a roll, kneader, Banbury mixer, or extruder. After obtaining a mixture of the above-mentioned components, the mixture may be molded. Specific examples of methods for molding the mixture include compression molding, injection molding, extrusion molding, calendar molding, or a method of dissolving the mixture in a solvent and dipping or coating it onto a substrate or the like to mold it.

[0149] [Step of crosslinking the fluorocopolymer] The step of crosslinking the fluorocopolymer is a step of crosslinking the fluorocopolymer using a fluorocopolymer composition. The method for crosslinking the fluorocopolymer is the same as the crosslinking method in the above-mentioned method for producing a crosslinked rubber article, and preferred embodiments are also the same.

[0150] The present disclosure will be described in detail below using examples. Examples 1 and 2 are working examples, and Examples 3 to 5 are comparative examples. However, the present disclosure is not limited to these examples. The blending amounts of each component in the tables below are based on mass.

[0151] [Measurement and Evaluation Methods] [Water Content] Using the fluorocopolymer of each example described below, the water content was measured with a halogen moisture meter.

[0152] [Melting point] The aqueous dispersion of each example described below was freeze-aggregated and then filtered to obtain a fluorocopolymer. A 5 mg sample of the obtained fluorocopolymer was weighed out and placed in an aluminum pan, and heated from 20°C to 360°C at a heating rate of 10°C / min in an air atmosphere using a Hitachi DSC600, and the presence or absence of a melting peak was confirmed.

[0153] [Solid content concentration of aqueous dispersion] 2.0 g of the aqueous dispersion of each example described below was heated at 170°C for 20 minutes, and then the mass (g) of the residue was weighed and the solid content concentration was calculated using the following formula: Solid content concentration of aqueous dispersion (mass%) = 100 × (mass of residue) / (mass of aqueous dispersion (2.0 g))

[0154] [Average particle size of fluorocopolymer particles] The aqueous dispersion of each example described below was degassed at 25°C for 5 minutes, pressurized with nitrogen gas to 0.2 MPaG, purged, and returned to atmospheric pressure to obtain a measurement sample. The average particle size of the obtained measurement sample was measured using a dynamic light scattering particle size distribution measurement device (Otsuka Electronics Co., Ltd., ELSZ) with an accumulation number set to 100, and this was taken as the average particle size of the particles in each aqueous dispersion.

[0155] [Proportion of each unit in fluorine-containing copolymer] The proportion of each unit in each example of fluorine-containing copolymer described later is １９ It was determined by F-NMR analysis and infrared absorption spectrum analysis.

[0156] [Arithmetic mean height Sa and aspect ratio Str of crosslinked rubber article before sputtering treatment] The crosslinked rubber article (O-ring) obtained in each example was cut along the thickness direction to a length of 5 to 10 mm, and then further cut along the length direction (i.e., the direction perpendicular to the thickness direction) to obtain test pieces of the crosslinked rubber article (length 5 to 10 mm, thickness 1.0 to 3.5 mm). The test pieces were placed on the sample stage of the laser microscope equipped with a white light interferometer described below, and the surface of the test pieces other than the cut surface was observed. The field of view was autofocused at 10x magnification (objective lens), and image data of the entire observation range (1062 μm × 1416 μm) was obtained. The obtained image data was subjected to surface shape correction (waviness correction: correction strength 5) using an analysis tool attached to the laser microscope equipped with a white light interferometer, and the arithmetic mean height Sa and aspect ratio Str of the entire observation range were determined. The values ​​obtained in this manner were used as the arithmetic mean height Sa and aspect ratio Str of the crosslinked rubber article before sputtering treatment. Laser microscope equipped with white light interferometer: Controller model VK-X3000, measurement model VK-X3100, manufactured by Keyence Corporation

[0157] [Arithmetic mean height Sa and aspect ratio Str of crosslinked rubber article after sputtering] The crosslinked rubber article (O-ring) obtained in each example was cut in the same manner as the crosslinked rubber article before sputtering to obtain a test piece of the crosslinked rubber article (length 5-10 mm, thickness 1.0-3.5 mm). Next, carbon tape was attached to the surface of a circular sample stage (diameter 12 mm, height 5 mm) of an ion sputtering apparatus (E-1030 model, manufactured by Hitachi, Ltd.), and then the flat portion of the test piece of the crosslinked rubber article (i.e., the cut surface along the length direction) was placed on the sample stage, and the distance between the sample surface on the sample stage where the test piece was placed and the platinum target was set to 35 mm. Next, the atmospheric gas in the sample chamber of the ion sputtering apparatus was replaced with argon, and the vacuum level in the sample chamber was reduced to 6 kPa. The test piece was then subjected to sputtering by discharging at a target load current of 25 mA for 30 seconds. After the sputtering process, the inside of the ion sputtering apparatus was purged with air to atmospheric pressure, and the test piece was then removed from the sample stage. In this way, the test piece after the sputtering process was obtained. The arithmetic mean height Sa and aspect ratio Str of the crosslinked rubber article after the sputtering process were determined in the same manner as the arithmetic mean height Sa and aspect ratio Str of the crosslinked rubber article before the sputtering process described above, except that the test piece after the sputtering process (the crosslinked rubber article after the sputtering process) was used instead of the test piece before the sputtering process (the crosslinked rubber article before the sputtering process).

[0158] [High-Temperature Compression Set (CS), Cracking] Compression set was measured according to the method described in ASTM D395 or JIS K6262. The O-rings (original thickness (wire diameter) = 3.5 mm) prepared in each example were compressed to a compression ratio of 18% using a compression device. Next, the compression device with the compressed O-rings fixed thereto was placed in an electric furnace and left at 300 ° C for 70 hours, after which the compression device was removed from the electric furnace, the O-rings were immediately removed from the compression device, and the removed O-rings were left in a thermostatic chamber at 23 ° C for 30 minutes, and the thickness of the O-rings (thickness after compression treatment) was measured. The test was performed using two O-rings, and the arithmetic average of the measured values ​​of the two O-rings was used. The compression set rate was calculated using the following formula. The closer the compression set rate is to 0%, the smaller the compression set is, and the more preferable it is. Compression set rate (%) = {original thickness of O-ring (wire diameter) - thickness of O-ring 30 minutes after removal from the compression device (thickness after compression treatment)} ÷ {original thickness of O-ring (wire diameter) - thickness of spacer} x 100 Furthermore, the two O-rings after the above-mentioned compression set test were visually inspected for cracks, and if cracks were found in at least one O-ring, it was judged that cracks were present. Evaluation was performed according to the compression set rate value and the presence or absence of cracks using the following evaluation criteria. "A" indicates that cracks are suppressed and that high-temperature compression set is excellent. "A": No cracks are present and the compression set rate is 16% or less "B": No cracks are present, but the compression set rate is more than 16% and less than 20% "C": Cracks are present and / or the compression set rate is more than 20%

[0159] [Method for measuring emulsifier contained in 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 min, rate: 15 cps, cycle: 3. 5 mL of methanol was added to 2.5 g of the obtained pulverized powder, and the mixture was subjected to ultrasonic treatment at 50°C for 2 hours and centrifuged (5000 rpm, 5 minutes) to precipitate each fluoropolymer. The supernatant was used as an extract. The 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 configuration of the measuring equipment and the LC-MS measurement conditions are shown in Table 1. Using aqueous solutions of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured with known concentrations, aqueous solutions with five or more levels of content were prepared, and LC / MS analysis was performed on the aqueous solutions with each content. The relationship between the content and the area relative to the content was plotted to draw a calibration curve. Using the calibration curve, the area of ​​the LC / MS chromatogram of the fluorine-containing emulsifier and hydrocarbon emulsifier in the extract was converted into the content of the fluorine-containing emulsifier and hydrocarbon emulsifier.

[0160]

[0161] The MRM measurement parameters are appropriately selected depending on the structures of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured. Literature values ​​can be used for the MRM parameters, or they can be calculated using an LC-MS device. The specific procedure for determining the MRM parameters using an LC-MS device is as follows. Using an LC / MS device (Shimadzu Corporation, LCMS-8060NX), a search for product ions is selected, the molecular weights of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured are input, and precursor ions, precursor adjustment, voltage optimization, and product m / z optimization are performed. The calculated MRM measurement parameters are used. As examples of the measurement targets, the MRM measurement parameters for compounds (S2) and (S4), which are emulsifiers having fluorine atoms, are shown in the table. Note that in formulas (S2) and (S4), M Ｓ represents a hydrogen atom, a metal atom (Na, K), NR ４ (R may be the same or different and represents a hydrogen atom or an organic group having 1 to 10 carbon atoms), an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. F-(CF ２ ) ｎ１ -COOM Ｓ (S2) F-(CF ２ ) ｎ２ -SO ３ M Ｓ (S4) where n1 is an integer from 3 to 17, and n2 is an integer from 4 to 12.

[0162]

[0163]

[0164] (Quantitative Determination of Fluorine-Containing Emulsifier and Hydrocarbon Emulsifier Contained in Solid Composition) Specifically, first, five levels of methanol standard solutions of the fluorine-containing emulsifier and hydrocarbon emulsifier to be measured, each having a known concentration of 1 to 180 ng / g, were prepared, and a was calculated from the sample concentration and peak integral value of each sample by linear approximation using formula (A1): A = a × X (A1), where A is the peak area of ​​each emulsifier, and X is the concentration (ng / g) of each emulsifier.

[0165] Subsequently, the amounts of the fluorine-containing emulsifier and hydrocarbon emulsifier contained in the above extracts (hereinafter also referred to as emulsifier amounts) were calculated using formula (A2). Note that a in formula (A2) means a determined by the above formula (A1). XCm = ACm / a (A2) XCm: content (ng / g) of emulsifier in each extract ACm: peak area of ​​emulsifier in each extract The quantitation limit in this measurement is 1 ng / g.

[0166] The content of the emulsifier in the composition relative to the total mass of the composition (ZCm) was calculated using the following formula (A3): ZCm = XCm × ρ1 × La / W1 (A3), where ZCm is the content of the emulsifier contained in the solid composition, ρ1 is the density of the extraction solvent (methanol in each example), La is the volume of the extraction solvent (5 mL in each example), and W1 is the mass of the sample used for extraction (2.5 g of solid composition in each example).

[0167] [Example 1] Ultrapure water (1206 g), a 50% by mass aqueous solution of sodium 2-acrylamido-2-methyl-1-propanesulfonate (NaAAMPS, corresponding to Compound X) (30 μL), PMVE (82 g), and TFE (17 g) were added to a 2.2 L stainless steel pressure reactor, and the temperature was raised to 80°C while stirring at 600 rpm. The internal pressure of the reactor at 80°C was 1.4 MPaG. Next, an aqueous solution of ammonium persulfate (2.5% by mass, 7 g) was added to initiate polymerization. As the pressure in the reactor decreased with the initiation of polymerization, TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the initiation of polymerization reached 8 g, 6 g of PMVE was injected. When the polymerization pressure decreased to 1.4 MPa, the stirring speed was reduced to 380 rpm, and CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２3.4 g of CN (8CNVE) was added. Thereafter, while intermittently adding an aqueous ammonium persulfate solution, 12 g of PMVE was injected every time 16 g of TFE was injected. When the amount of TFE added after the initiation of polymerization reached 168 g, the addition of TFE and PMVE injected after the initiation of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was extracted to obtain a first aqueous dispersion A1. The total amount of ammonium persulfate added was 0.7 g. The total amount of monomers added before the initiation of polymerization was 17 g of TFE and 82 g of PMVE. The total amount of monomers added after the initiation of polymerization was 168 g of TFE and 108 g of PMVE. The total amount of TFE added was 185 g, and the total amount of PMVE added was 190 g. The first aqueous dispersion A1 was coagulated with a 5% by mass aqueous solution of nitric acid, and then filtered, and the obtained solid was washed with ultrapure water. Thereafter, it was vacuum dried at 100 ° C. for 12 hours to obtain a fluorine-containing copolymer A1 (solid composition). The obtained fluorine-containing copolymer A1 was analyzed by NMR, and the composition was PMVE / TFE / 8CNVE = 31.8 / 67.7 / 0.5 (molar ratio). In addition, the fluorine-containing copolymer A1 had an average particle size of 123.8 nm and no melting point. The water content of the fluorine-containing copolymer A1 was 0.0% by mass. The fluorine-containing copolymer A1 was a perfluoroelastomer.

[0168] Next, the components and amounts shown in Table 4 were mixed and kneaded using a twin roll at room temperature for 10 minutes to obtain a mixture. The gap between the twin rolls was adjusted, and the obtained mixture was processed into a 3 mm thick sheet to obtain Fluorine-containing copolymer composition 1 of Example 1. Of the components in Table 1, details of the components other than the fluorine-containing copolymer are as follows: MT-C: MT Carbon N990, manufactured by Cancarb Ltd., carbon black BOAP: 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, crosslinking agent.

[0169] Furthermore, fluorine-containing copolymer composition 1 was hot-pressed at 180°C for 20 minutes using a hydraulic press (model: SA-301 50T type, manufactured by Tester Sangyo Co., Ltd., ram diameter: 180 mm) to carry out primary crosslinking, thereby obtaining O-ring 1 (P-26 (standard defined in JIS B2401:2012)). Next, the obtained O-ring 1 was heated in an oven (DN411I, manufactured by Yamato Scientific Co., Ltd.) at 90°C for 2 hours under a nitrogen atmosphere, then heated to 200°C over 2 hours, heated at 200°C for 4 hours, further heated to 305°C over 2 hours, and heated at 305°C for 12 hours, thereby carrying out secondary crosslinking. Thereafter, the O-ring was cooled to 23°C to obtain the O-ring of Example 1, which was a crosslinked rubber article.

[0170] [Example 2] Ultrapure water (1206 g), a 50% by mass aqueous solution of NaAAMPS (10 μL), PMVE (81 g), and TFE (17 g) were added to a 2.2 L stainless steel pressure reactor, and the temperature was raised to 80 ° C. while stirring at 600 rpm. The pressure inside the reactor at 80 ° C. was 1.4 MPaG. Next, an aqueous solution of ammonium persulfate (2.5% by mass, 7 g) was added to initiate polymerization. As the pressure inside the reactor decreased with the start of polymerization, TFE was added to maintain the pressure constant. This was repeated, and when the amount of TFE added after the start of polymerization reached 25 g, the stirring speed was reduced to 380 rpm, and 3.4 g of 8CNVE was added. Thereafter, while intermittently adding the aqueous solution of ammonium persulfate, 12 g of PMVE and 1.3 g of 8CNVE were injected every time 16 g of TFE was injected. When the amount of TFE added after the start of polymerization reached 400 g, the addition of TFE and PMVE injected after the start of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was extracted to obtain a first aqueous dispersion A2. The total amount of ammonium persulfate added was 1.5 g, and the total amount of 8CNVE added was 33.6 g. The total amounts of monomers added before the start of polymerization were 17 g of TFE and 81 g of PMVE. The total amounts of monomers added after the start of polymerization were 400 g of TFE and 288 g of PMVE. The total amount of TFE added was 417 g, and the total amount of PMVE added was 369 g. The first aqueous dispersion A2 was coagulated with a 5% by mass aqueous nitric acid solution, then filtered, and the resulting solid was washed with ultrapure water. Thereafter, the mixture was vacuum dried at 100°C for 12 hours to obtain a fluorine-containing copolymer A2 (solid composition). The obtained fluorine-containing copolymer A2 was analyzed by NMR, and as a result, the composition was PMVE / TFE / 8CNVE = 29.7 / 69.6 / 0.7 (molar ratio). Furthermore, the fluorine-containing copolymer A2 had an average particle size of 150nm and no melting point. The water content of the fluorine-containing copolymer A2 was 0.0% by mass. The fluorine-containing copolymer A2 corresponded to both a perfluoropolymer and a perfluoroelastomer.

[0171] Next, a fluorocopolymer composition 2 of Example 2 processed into a sheet having a thickness of 3 mm was obtained in the same procedure as in Example 1, except that the components were formulated in the amounts shown in Table 4, and an O-ring of Example 2 which was a crosslinked rubber article was obtained.

[0172] [Example 3] A stainless steel pressure reactor having an internal volume of 20 L and equipped with an anchor blade was degassed, and then 7.2 L of ultrapure water and C, a water-soluble emulsifier having fluorine atoms, were added. ２ F ５ OCF ２ CF ２ OCF ２ COONH ４880 g of a 30% by mass aqueous solution of 8CNVE, 7.3 g of C3DVE, 6.8 g of C3DVE, and 15.9 g of a 5% by mass aqueous solution of disodium hydrogen phosphate dodecahydrate were charged. While stirring using an anchor blade, 137 g of TFE and 635 g of PMVE were charged into the vessel, and the internal temperature was then raised to 80°C. The pressure inside the reactor was 0.90 MPa [gauge]. 40 mL of a 3% by mass aqueous solution of ammonium persulfate (APS) was added to initiate polymerization. Hereinafter, the monomer injected before the start of polymerization will also be referred to as the "initial added monomer." After the start of polymerization, as the polymerization progressed, monomers were injected as follows. Hereinafter, injection of a monomer after the start of polymerization will also be referred to as "post-addition," and a monomer injected after the start of polymerization will also be referred to as the "post-added monomer." When the reactor pressure dropped to 0.89 MPa [gauge], TFE, 8CNVE, and PMVE were added under pressure, and the reactor pressure was increased to 0.90 MPa [gauge]. This was repeated every time the reactor pressure dropped to 0.89 MPa [gauge]. When the polymerization rate began to slow, a 3% by mass aqueous solution of APS was appropriately added. The total amount of the 3% by mass aqueous solution of APS added after the start of polymerization was 40 mL. When the total added mass of TFE reached 1193 g, the addition of the post-added monomer was stopped, the reactor was cooled, and the polymerization reaction was terminated to obtain a latex containing a fluorine-containing copolymer. The polymerization time was 429 minutes. The total added masses of the post-added monomers were 1193 g of TFE, 668 g of PMVE, and 66.7 g of 8CNVE. The obtained latex was added to a 3% by mass aqueous solution of nitric acid (manufactured by Kanto Chemical Co., Ltd., special grade), to coagulate the fluorine-containing copolymer. The fluorine-containing copolymer was filtered, washed with water, and vacuum dried to obtain a white fluorine-containing copolymer C1 (solid composition). The content (molar ratio) of each unit in the obtained fluorine-containing copolymer C1 was TFE unit / PMVE unit / 8CNVE unit / C3DVE unit=69.8 / 29.5 / 0.6 / 0.1. Note that the filtrate after coagulating the latex after polymerization to take out the fluorine-containing copolymer C1 and the filtrate remaining after washing the latex were filtered with a disk filter, and the obtained liquid was analyzed with an ion chromatograph measuring device, and no fluoride ions of 3% by mass or more were detected relative to the amount of C3DVE charged.Therefore, it was assumed that all of the C3DVE used in the charging had been polymerized, and the content of C3DVE units relative to all units in the fluorocopolymer C1 was calculated based on the amount of C3DVE charged.

[0173] Next, the components were mixed in the amounts shown in Table 4, and the procedure of Example 1 was repeated except that the conditions for primary crosslinking were changed to 160°C and 50 minutes, to give a fluorocopolymer composition 3 of Example 3 which was processed into a sheet having a thickness of 3 mm, and an O-ring of Example 3 which was a crosslinked rubber article was obtained.

[0174] [Example 4] A 2.1 L stainless steel pressure reactor was charged with ultrapure water (1004 g), C ２ F ５ OCF ２ CF ２ OCF ２ COONH ４A 30% by mass aqueous solution (80.1 g) of the compound, a 5% by mass aqueous solution (10.49 g) of disodium hydrogen phosphate dodecahydrate, 8CNVE (1.10 g), PMVE (55 g), and TFE (11 g) were added, and the temperature was raised to 80°C while stirring at 600 rpm. The internal pressure of the reactor at 80°C was 0.974 MPaG. Next, an aqueous ammonium persulfate solution (3.0% by mass, 18 g) was added to initiate polymerization. As the polymerization began, the pressure inside the reactor decreased, so TFE was added to maintain the pressure constant. Thereafter, while intermittently adding the aqueous ammonium persulfate solution, 12 g of PMVE and 1.3 g of 8CNVE were injected every time 16 g of TFE was injected. When the amount of TFE added after the start of polymerization reached 408 g, the addition of TFE and PMVE injected after the start of polymerization was stopped, the temperature inside the reactor was cooled to 10 ° C., the polymerization reaction was stopped, the gas remaining in the reactor was recovered, and the liquid was extracted to obtain a first aqueous dispersion C2. The total amount of ammonium persulfate added was 0.72 g, and the total amount of 8CNVE added was 16.0 g. The total amounts of monomers added before the start of polymerization were 17 g of TFE and 81 g of PMVE. The total amounts of monomers added after the start of polymerization were 408 g of TFE and 294 g of PMVE. The total amount of TFE added was 425 g, and the total amount of PMVE added was 375 g. The first aqueous dispersion C2 was coagulated with a 5.0% aqueous nitric acid solution, filtered, and the resulting solid was washed with ultrapure water. Thereafter, the mixture was vacuum dried at 100°C for 12 hours to obtain a fluorine-containing copolymer C2 (solid composition). The obtained fluorine-containing copolymer C2 was analyzed by NMR, and as a result, it was found that the molar ratio of PMVE / TFE / 8CNVE was 30.5 / 69.0 / 0.5. In addition, the fluorine-containing copolymer C2 did not have a melting point.

[0175] Next, the same procedure as in Example 1 was followed, except that the components were formulated in the amounts shown in Table 4, to give a fluorocopolymer composition 4 of Example 4 processed into a sheet having a thickness of 3 mm, and an O-ring of Example 4 which was a crosslinked rubber article was obtained.

[0176] [Example 5] Next, in the same procedure as in Example 1, except that the components were formulated in the amounts shown in Table 4, a fluorocopolymer composition 5 of Example 5 processed into a sheet having a thickness of 3 mm was obtained, and an O-ring of Example 5 which was a crosslinked rubber article was obtained.

[0177]

[0178] It was confirmed that the crosslinked rubber article had excellent high-temperature compression set and was less susceptible to cracking. It was confirmed that no hydrocarbon emulsifier was detected in Examples 1 to 5, and that the amount of fluorine-containing emulsifier was very small in Examples 1 and 2.

[0179] The disclosure of Japanese Patent Application No. 2024-098681, filed on June 19, 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. A crosslinked rubber article comprising a crosslinked product of a fluorine-containing copolymer, wherein, when the crosslinked rubber article is subjected to a sputtering treatment by the method of Test 1, the arithmetic mean height Sa of the surface of the crosslinked rubber article after the sputtering treatment is greater than 1.6 μm and the aspect ratio Str of the surface of the crosslinked rubber article after the sputtering treatment is 0.90 or less. Test 1: The crosslinked rubber article is placed on the sample stage of an ion sputtering apparatus, and the distance between the surface on the sample stage where the crosslinked rubber article is placed and the platinum target is set to 35 mm. Next, the degree of vacuum in the sample chamber of the ion sputtering apparatus is set to 6 kPa, and then the crosslinked rubber article is subjected to a sputtering treatment by discharging at a target additional current value of 25 mA for 30 seconds.

2. The crosslinked rubber article according to claim 1, wherein the crosslinked product has a heterocyclic structure.

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

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

5. The crosslinked rubber article according to claim 1, wherein the fluorine-containing copolymer has units derived from a monomer having a nitrile group.

6. The crosslinked rubber article of claim 1, which is substantially free of white fillers.

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

8. A fluorocopolymer composition comprising a fluorocopolymer, wherein, when a crosslinked rubber article obtained using the fluorocopolymer composition is subjected to sputtering treatment by the method of Test 1, the arithmetic mean height Sa of the surface of the crosslinked rubber article after the sputtering treatment is greater than 1.6 μm and the aspect ratio Str of the surface of the crosslinked rubber article after the sputtering treatment is 0.90 or less. Test 1: A crosslinked rubber article obtained using the fluorocopolymer composition is placed on the sample stage of an ion sputtering apparatus, and the distance between the surface on the sample stage where the crosslinked rubber article is placed and a platinum target is set to 35 mm. Next, the degree of vacuum in the sample chamber of the ion sputtering apparatus is set to 6 kPa, and then the crosslinked rubber article is subjected to sputtering treatment by discharging at a target added current value of 25 mA for 30 seconds.

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

10. The fluorine-containing copolymer composition according to claim 8, wherein said fluorine-containing copolymer has units based on a monomer having a nitrile group.

11. The fluorine-containing copolymer composition according to claim 8, further comprising a crosslinking agent.

12. The fluorine-containing copolymer composition according to claim 8, which is substantially free of white filler.

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

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