Fluororubber article and method for producing same

Abstract

Provided are: a fluororubber article which has a small permanent set when compressed at a high temperature and in which the occurrence of cracks is easily inhibited especially when in contact with stainless steel; and a method for producing the fluororubber article. A fluororubber article according to the present invention is obtained by crosslinking a fluorine-containing copolymer in a crosslinkable fluororubber composition. The fluorine-containing copolymer has a unit based on tetrafluoroethylene and a unit based on a perfluoro(alkyl vinyl ether). The fluoride ion content ratio in an absorbent liquid obtained by heating 1 g of the fluororubber article at 360°C for 60 minutes and causing generated gas to be absorbed in 60 mL of pure water is less than 0.25 mass%.

Description

Fluororubber articles and methods for manufacturing the same

[0001] The present invention relates to fluororubber articles and methods for producing the same.

[0002] Fluororubber articles, which are crosslinked fluorine-containing copolymers, have excellent heat resistance, chemical resistance, oil resistance, and weather resistance, and are therefore widely used in fields such as semiconductor manufacturing, vehicles, aircraft, general machinery, construction, and chemical plants as sealing materials and cushioning materials, for example, in O-rings, packings, oil seals, and gaskets.

[0003] One indicator of the heat resistance required for fluororubber articles used in the applications described above is that they exhibit low permanent deformation and are resistant to cracking when compressed at high temperatures (e.g., 300°C). Various improvement measures have been considered to meet these requirements. For example, Patent Document 1 proposes obtaining crosslinked rubber (fluororubber) articles from a composition containing a predetermined fluorine-containing copolymer.

[0004] International Publication No. 2021 / 210502

[0005] It has been found that even with fluororubber articles obtained using compositions such as those described in Patent Document 1, the results of heat resistance evaluation by high-temperature compression may be affected by the material of the metal component in contact with the fluororubber article. Specifically, it was confirmed that when the material is stainless steel, cracking tends to occur more easily than when it is a Ni-Cr-Mo alloy.

[0006] This invention was made under such circumstances, and aims to provide a fluororubber article and a method for manufacturing the same that exhibits low permanent deformation when compressed at high temperatures, and that particularly suppresses crack formation when in contact with stainless steel.

[0007] This invention is based on the discovery that fluoride ions contained in fluororubber articles are a cause of cracking when the fluororubber articles are compressed at high temperatures, and further, the discovery that the generation of said fluoride ions can be suppressed by a predetermined process in the manufacturing of fluororubber articles.

[0008] The present invention provides the following means: [1] A fluororubber article formed by crosslinking a fluorine-containing copolymer in a crosslinkable fluororubber composition, wherein the fluorine-containing copolymer has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and the fluoride ion content in the absorbent solution obtained by heating 1 g of the fluororubber article at 360°C for 60 minutes and absorbing the generated gas in 60 mL of pure water is less than 0.25% by mass. [2] The fluororubber article according to [1], wherein the fluorine-containing copolymer further has units based on monomers having nitrile groups. [3] The fluororubber article according to [2], composed of a fluororubber having a crosslinked structure including an oxazole ring or a triazine ring. [4] Any fluororubber article according to [1] to [3], wherein the fluorine-containing copolymer is a perfluoropolymer. [5] Any fluororubber article according to [1] to [4], wherein the molar ratio of the tetrafluoroethylene-based units to the perfluoro(alkyl vinyl ether)-based units in the fluorine-containing copolymer is 60 / 40 to 80 / 20. [6] A fluororubber article according to any of [1] to [5], wherein the perfluoro(alkyl vinyl ether) is a monomer represented by the following formula (1). CF ２ =CF-O-R ｆ１ (1) In formula (1), R ｆ１ is a perfluoroalkyl group having 1 to 10 carbon atoms. [7] Any fluororubber article of [1] to [6] having a compression set of 30% or less under holding conditions of 300°C, a compressibility of 25%, and 70 hours. [8] Any fluororubber article of [1] to [7] for use with stainless steel.

[0009] [9] A method for producing a fluororubber article, comprising the step of heating a crosslinkable fluororubber composition containing a fluorine-containing copolymer having units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether) in an atmosphere with a dew point of less than 20°C to crosslink the fluorine-containing copolymer.

[10] The method for producing a fluororubber article according to [9], wherein the step of crosslinking the fluorine-containing copolymer is performed at 200 to 400°C for 1 minute to 48 hours.

[11] The method for producing a fluororubber article according to [9] or

[10] , wherein the step of crosslinking the fluorine-containing copolymer is performed in an air or nitrogen atmosphere.

[0010] According to the present invention, it is possible to provide a fluororubber article that exhibits low permanent deformation when compressed at high temperatures, and in particular, is less prone to cracking when in contact with stainless steel, as well as a method for manufacturing the same.

[0011] The definitions and meanings of terms and notations used in this specification are given below. The notation "X to Y" (where X and Y are numerical values) means a numerical range with X as the lower limit and Y as the upper limit. Within a numerical range (e.g., a range of content), the stepped lower and upper limits may be combined independently. The lower and upper limits of a numerical range may be replaced with the numerical values ​​described in the examples. "Unit" refers to a chemical structure derived from a single monomer molecule constituting the polymer, including those that have undergone partial chemical transformation. The molar ratio of units based on monomers in a fluorine-containing copolymer is: １９ This value was calculated from the F-nuclear magnetic resonance (NMR) spectrum. "Rubber" refers to rubber exhibiting the properties defined by JIS K 6200:2008, and is distinguished from "resin."

[0012] [Fluororubber Article] The fluororubber article of this embodiment (hereinafter referred to as "this embodiment") is a fluororubber article formed by crosslinking a fluorine-containing copolymer in a crosslinkable fluororubber composition, wherein the fluorine-containing copolymer has units based on tetrafluoroethylene (TFE) and units based on perfluoro(alkyl vinyl ether) (PAVE), and fluoride ions (F) in the absorbent solution obtained by heating 1 g of the fluororubber article at 360°C for 60 minutes and absorbing the generated gas in 60 mL of pure water －)(The content is) less than 0.25% by mass. A fluorine rubber article having a crosslinked structure formed by crosslinking a fluorine-containing copolymer has a small permanent strain when compressed at a high temperature (for example, 300 °C), and particularly when in contact with stainless steel, the occurrence of cracks is likely to be suppressed.

[0013] The fluorine rubber article is composed of a fluorine rubber having a crosslinked structure formed by crosslinking a fluorine-containing copolymer in a crosslinkable fluorine rubber composition. The fluorine rubber is a crosslinked product formed by crosslinking a fluorine-containing copolymer having units based on a fluorine-containing monomer, and is a rubber-like elastic body. In the present embodiment, the fluorine-containing copolymer has units based on TFE and units based on PAVE.

[0014] When the fluorine rubber article is compressed at a high temperature, it has been found that when the metal member in contact is stainless steel, cracks are more likely to occur than in the case of a Ni-Cr-Mo alloy. This is considered to be because, at a high temperature, F of hydrogen fluoride (HF) generated from the fluorine rubber article － has an effect of deteriorating the fluorine rubber article and the metal member in contact. Since stainless steel is inferior in chemical resistance to a Ni-Cr-Mo alloy, it is presumed that cracks are more likely to occur when in contact with stainless steel. Therefore, it is preferable that less F － is generated from the fluorine rubber article. However, the F content in the fluorine rubber article is extremely small, and direct quantification is difficult with the current analytical methods. Therefore, in the present invention, 1 g of the fluorine rubber article is heated at 360 °C for 60 minutes, and the F － content ratio in the absorption liquid obtained by absorbing the generated gas in 60 mL of pure water is used as an alternative and an indirect evaluation index. The quantification of the F － content ratio in the absorption liquid can be performed by ion chromatography, and specifically, it is performed by the method described in the examples. － －

[0015] When the F － content ratio in the absorption liquid is less than 0.25% by mass, the occurrence of cracks when the fluorine rubber article is compressed at a high temperature is likely to be suppressed, and the occurrence of bleed is also likely to be suppressed. The F －The content is preferably 0.20% by mass or less, and more preferably 0.15% by mass or less.

[0016] F in the aforementioned absorbent solution － The content ratio can be easily controlled within the above range by going through a process of crosslinking a fluorine-containing copolymer in an atmosphere containing a predetermined amount of moisture. F in the absorbent liquid － Fluororubber articles having a content of less than 0.25% by mass can be obtained, for example, by controlling the dew point of the heat treatment atmosphere and heating a crosslinkable fluororubber composition containing a fluorine-containing copolymer to crosslink the fluorine-containing copolymer, as in the manufacturing method of the present invention.

[0017] (Fluorine-containing copolymer) The fluorine-containing copolymer of this embodiment is a copolymer having units based on TFE (hereinafter also referred to as TFE units) and units based on PAVE (hereinafter also referred to as PAVE units). The fluorine-containing copolymer itself does not have rubber elasticity, but it acquires rubber elasticity by crosslinking.

[0018] The content of the fluorine-containing copolymer in the crosslinkable fluororubber composition is preferably 60.0 to 99.9% by mass, more preferably 70.0 to 99.9% by mass, and even more preferably 80.0 to 99.9% by mass, from the viewpoint of good heat resistance of the fluororubber article formed by crosslinking the fluorine-containing copolymer.

[0019] PAVE is preferred as a monomer represented by the following formula (1) from the viewpoint of good polymerization reactivity and good heat resistance of fluororubber articles formed by crosslinking fluorine-containing copolymers. CF ２ =CF-O-R ｆ１ (1) In formula (1), R ｆ１ R is a perfluoroalkyl group having 1 to 10 carbon atoms. The perfluoroalkyl group may be linear or branched. ｆ１ From the viewpoint of good polymerization reactivity, the number of carbon atoms is preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and even more preferably 1 to 3.

[0020] Specific examples of PAVE include perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether) (PEVE), and perfluoro(propyl vinyl ether) (PPVE). PAVE may be used alone or in combination of two or more types. Of these, PMVE and PPVE are preferred, with PMVE being more preferred, from the viewpoint of good polymerization reactivity and availability.

[0021] In addition to TFE and PAVE units, fluorine-containing copolymers preferably have units based on monomers containing nitrile groups. The nitrile groups in the units based on monomers containing nitrile groups act as crosslinking structures, making it easier to obtain fluororubber articles with good heat resistance.

[0022] From the viewpoint of good heat resistance of fluororubber articles formed by crosslinking fluorine-containing copolymers, monomers having nitrile groups preferably have fluorine atoms, and monomers represented by the following formula (2) are more preferable. CR ２１ R ２２ =CR ２３ R ２４ CN (2) In formula (2), R ２１ ~R ２３ Each of these is independently a hydrogen atom, a fluorine atom, or a methyl group. ２４ This refers to a divalent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or carbon-carbon of the perfluorohydrocarbon group.

[0023] R ２１ ~R ２３ From the viewpoint of good polymerization reactivity, fluorine atoms or hydrogen atoms are preferred, more preferably both are fluorine atoms or hydrogen atoms, and from the viewpoint of good heat resistance of the fluororubber article formed by crosslinking the fluorine-containing copolymer, it is particularly preferred that both are fluorine atoms. ２４ The structure may be linear, branched, or cyclic, but from the viewpoint of good polymerization reactivity, linear or branched structures are preferred. ２４ The number of carbon atoms is preferably 2 to 8, more preferably 3 to 7, even more preferably 3 to 6, and even more preferably 3 to 5.２４ From the viewpoint of good rubber elasticity of fluororubber articles formed by crosslinking fluorine-containing copolymers, it is preferable that the material has etheric oxygen atoms. ２４ The number of etheric oxygen atoms in is preferably 1 to 3, more preferably 1 or 2.

[0024] A specific example of a monomer having a nitrile group is CF ２ = CFOCF ２ CF (CF ３ ) OCF ２ CF ２ CN (abbreviation 8CNVE), CF ２ = CFO (CF ２ ) ５ CN (abbreviated as MV5CN), CF ２ = CFOCF ２ CF ２ CF ２ OCF (CF ３ ) CN, CF ２ = CFO (CF ２ ) ３ Examples include CN. The monomer having a nitrile group may be used alone or in combination of two or more. Of these, 8CNVE and MV5CN are preferred, and 8CNVE is more preferred, from the viewpoint of good heat resistance and release properties of the fluororubber article formed by crosslinking the fluorine-containing copolymer.

[0025] From the viewpoint of good rubber elasticity and heat resistance of the crosslinked fluororubber article, the fluorine-containing copolymer may have units based on other monomers in addition to TFE units, PAVE units, and monomers having nitrile groups. Examples of other monomers include vinylidene fluoride (VdF), hexafluoropropylene, chlorotrifluoroethylene, monomers having two or more polymerizable unsaturated bonds (DV), monomers represented by the following formula (6), ethylene, propylene, etc. Other monomers that also have halogen atoms other than fluorine (e.g., bromotrifluoroethylene, iodotrifluoroethylene) are also examples.

[0026] Examples of polymerizable unsaturated bonds in DV include carbon-carbon double bonds (C=C) and carbon-carbon triple bonds (C≡C). From the viewpoint of good polymerization reactivity, the number of polymerizable unsaturated bonds in DV is preferably 2 to 6, more preferably 2 or 3, and particularly preferably 2. From the viewpoint of good heat resistance of fluororubber articles formed by crosslinking fluorine-containing copolymers, DV preferably contains fluorine atoms.

[0027] From the viewpoint of good heat resistance of fluororubber articles formed by crosslinking fluorine-containing copolymers, DV is preferably a monomer represented by the following formula (3). (CR ３１ R ３２ =CR ３３ ) ａ３ R ３４ (3) In formula (3), R ３１ ~R ３３ Each of these is independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. a3 is an integer from 2 to 6. R ３４ This refers to a 3-valent perfluorohydrocarbon group having 1 to 10 carbon atoms, or a group having an etheric oxygen atom at the terminal or carbon-carbon of the perfluorohydrocarbon group.

[0028] Multiple R ３１ ~R ３３ They may be identical or different from each other, but being identical is particularly preferable. ３１ ~R ３３ From the viewpoint of good polymerization reactivity, fluorine atoms or hydrogen atoms are preferred, more preferably both are fluorine atoms or hydrogen atoms, and from the viewpoint of good heat resistance of the fluororubber article formed by crosslinking the fluorine-containing copolymer, it is particularly preferred that both are fluorine atoms. a3 is preferably 2 or 3, particularly preferably 2. R ３４ The structure may be linear, branched, or cyclic, but from the viewpoint of good polymerization reactivity, linear or branched structures are preferred, and linear structures are more preferred. ３４ The number of carbon atoms is preferably 2 to 10, more preferably 3 to 8, even more preferably 3 to 6, and even more preferably 3 to 5. ３４From the perspective of good rubber elasticity of the fluorine rubber article formed by cross-linking the fluorine-containing copolymer, it preferably has an etheric oxygen atom. R ３４ The number of etheric oxygen atoms in R is preferably 1 to 3, more preferably 1 or 2. R ３４ The etheric oxygen atom in R ３４ is preferably bonded to the terminal carbon atom of R.

[0029] DV, among the monomers represented by formula (3), the monomers represented by the following formula (4) or (5) are more preferred. (CF ２ =CF) ２ R ４１ (4) (CH ２ =CH) ２ R ５１ (5) In formula (4) or (5), R ４１ and R ５１ are a divalent perfluorohydrocarbon group having 2 to 10 carbon atoms or a group having an etheric oxygen atom at the terminal or between carbon-carbon atoms of the perfluorohydrocarbon group.

[0030] Specific examples of DV include, among the monomers represented by formula (4), CF ２ =CFO(CF ２ ) ２ OCF=CF ２ , CF ２ =CFO(CF ２ ) ３ OCF=CF ２ , CF ２ =CFO(CF ２ ) ４ OCF=CF ２ , CF ２ =CFO(CF[[ID=5S]] ２ ) ６ OCF=CF ２ , CF ２ =CFO(CF ２ ) ８ OCF=CF ２ , CF ２ =CFO(CF ２ ) ２ OCF(CF ３ )CF ２ OCF=CF ２ , CF ２= CFO (CF ２ ) ２ O[CF(CF ３ ) CF ２ O] ２ CF = CF ２ CF ２ = CFOCF ２ O(CF) ２ CF ２ O) ２ CF = CF ２ CF ２ = CFO (CF ２ O) ３ O[CF(CF ３ ) CF ２ O] ２ CF = CF ２ CF ２ = CFOCF ２ CF (CF ３ ) O (CF ２ ) ２ OCF (CF ３ ) CF ２ OCF = CF ２ CF ２ = CFO (CF ２ ) ２ O(CF) ２ O) ２ (CF ２ ) ２ OCF = CF ２ Furthermore, among the monomers represented by formula (5), CH ２ =CH(CF ２ ) ２ CH=CH ２ ,CH ２ =CH(CF ２ ) ４ CH=CH ２ ,CH ２ =CH(CF ２ ) ６ CH=CH ２ These include: DV may be a single type or two or more types may be used in combination. Of these, CF ２ = CFO (CF ２ ) ３ OCF = CF ２ CF ２ = CFO (CF ２ ) ４ OCF = CF ２ ,CH２ =CH(CF ２ ) ６ CH=CH ２ It is preferable.

[0031] Equation (6) is shown below. CF ２ =CF-O-R ｆ６ (6) In formula (6), R ｆ６ R is a perfluoroalkyl group containing 1 to 5 etheric oxygen atoms with 1 to 8 carbon atoms. ｆ６ The number of carbon atoms is preferably 1 to 6, more preferably 1 to 5.

[0032] Specific examples of monomers represented by formula (6) include perfluoro(3,6-dioxa-1-heptene), perfluoro(3,6-dioxa-1-octene), and perfluoro(5-methyl-3,6-dioxa-1-nonene).

[0033] Of the total units of the fluorine-containing copolymer, the content of TFE units is preferably 60 to 80 mol%, more preferably 63 to 75 mol%, and even more preferably 66 to 72 mol%, from the viewpoint of good heat resistance of the fluororubber article formed by crosslinking the fluorine-containing copolymer. Of the total units of the fluorine-containing copolymer, the content of PAVE units is preferably 19 to 40 mol%, more preferably 24 to 37 mol%, and even more preferably 27 to 34 mol%, from the viewpoint of good rubber elasticity and heat resistance of the fluororubber article formed by crosslinking the fluorine-containing copolymer. The preferred amount of use is the same whether PAVE is PMVE, PEVE, or PPVE, or whether a mixture of two or more of these is used. From a similar viewpoint, the molar ratio of TFE units to PAVE units in the fluorine-containing copolymer is preferably 60 / 40 to 80 / 20, more preferably 62 / 38 to 78 / 22, and even more preferably 65 / 35 to 75 / 25.

[0034] When the fluorine-containing copolymer contains units based on monomers having nitrile groups, the content of units based on monomers having nitrile groups in the total units is preferably 0.05 to 5 mol%, more preferably 0.1 to 3 mol%, and even more preferably 0.2 to 1.5 mol%, from the viewpoint of good heat resistance of the fluororubber article formed by crosslinking the fluorine-containing copolymer.

[0035] When a fluorine-containing copolymer contains units based on other monomers in addition to TFE units, PAVE units, and units based on monomers having nitrile groups, the content of the units based on other monomers is preferably 0.01 to 10 mol%, more preferably 0.05 to 10 mol%, and even more preferably 0.1 to 5 mol%, of the total units, from the viewpoint of good heat resistance of the fluororubber article formed by crosslinking the fluorine-containing copolymer.

[0036] From the viewpoint of good heat resistance of fluororubber articles formed by crosslinking fluorine-containing copolymers, the fluorine-containing copolymer is preferably a perfluoropolymer. Here, a perfluoropolymer refers to a polymer that substantially does not contain hydrogen atoms bonded to carbon atoms, and instead has fluorine atoms, with a main chain consisting of a chain of carbon atoms. The side chains of the perfluoropolymer may contain polyvalent atoms other than carbon atoms, and oxygen atoms are preferred as such polyvalent atoms. "Substantially free of hydrogen atoms" means that the hydrogen atom content in the perfluoropolymer is 0.5% by mass or less, preferably 0.1% by mass or less, more preferably 0.07% by mass or less, and even more preferably 0.05% by mass or less. If the hydrogen atom content is within the above range, fluororubber articles with good heat resistance and chemical resistance are easily obtained. The hydrogen atom content can be identified and quantified by well-known methods such as NMR spectroscopy.

[0037] (Method for producing fluorine-containing copolymers) The method for producing fluorine-containing copolymers is not particularly limited, and known methods can be applied. For example, a fluorine-containing copolymer can be obtained by copolymerizing the monomers constituting the units of the fluorine-containing copolymer by emulsion polymerization, solution polymerization, suspension polymerization, etc., in the presence of a radical polymerization initiator.

[0038] Radical polymerization initiators known in the production of fluorine-containing copolymers can be used and are appropriately selected depending on the polymerization method.

[0039] In emulsion polymerization in an aqueous medium, water-soluble radical polymerization initiators are preferred, such as persulfates including ammonium persulfate, sodium persulfate, and potassium persulfate; disuccinic acid peroxide; azobisisobutylamidine dihydrochloride; tert-butyl hydroperoxide; and peroxydicarbonates. Of these, persulfates are preferred, and ammonium persulfate is more preferred.

[0040] Furthermore, as radical polymerization initiators, redox polymerization initiators can also be used, which consist of persulfates or hydrogen peroxide in combination with reducing agents such as sodium bisulfite, sodium thiosulfate, sodium bisulfite, sodium pyrosulfite, or sodium hydroxymethanesulfinate. In addition, small amounts of metals or metal compounds such as iron, ferrous salts, or silver sulfate may be used in combination with the redox polymerization initiator.

[0041] In solution polymerization using solvents such as 1H-perfluorohexane, organic peroxides such as bis(pentafluoropropionyl) peroxide, pivaloyl-tert-butyl peroxide, and diisopropyl peroxydicarbonate can be used as radical polymerization initiators.

[0042] The radical polymerization initiator may be added all at once or sequentially. The amount of radical polymerization initiator used is preferably 0.0001 to 3 parts by mass, more preferably 0.001 to 2 parts by mass, and even more preferably 0.01 to 1 part by mass, per 100 parts by mass of the total monomers to be polymerized.

[0043] A pH buffer may be added to the reaction system. Examples of pH buffers include disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium bicarbonate, sodium carbonate, and their hydrates.

[0044] Examples of aqueous media used in emulsion polymerization include water, a mixture of water and a water-soluble organic solvent, etc. Examples of water-soluble organic solvents include tert-butanol, propylene glycol, dipropylene glycol, dipropylene glycol monomethyl ether, and tripropylene glycol, and tert-butanol and dipropylene glycol monomethyl ether are preferred from the viewpoint of suppressing a decrease in the polymerization rate of monomers. The inclusion of a water-soluble organic solvent in the aqueous medium improves the dispersibility of monomers and fluorine-containing copolymers, and tends to improve the production efficiency of fluorine-containing copolymers. The content of the water-soluble organic solvent in the aqueous medium is preferably 1 to 40 parts by mass, more preferably 3 to 30 parts by mass, per 100 parts by mass of water.

[0045] Examples of emulsifiers used in emulsion polymerization include hydrocarbon emulsifiers such as sodium lauryl sulfate and sodium dodecylbenzenesulfonate; ammonium perfluorooctanoate, sodium perfluorooctanoate, ammonium perfluorohexanoate, CF ３ (CF ２ ) ２ O(CF(CF ３ ) CF ２ O) ２ CF (CF ３ ) COONH ４ CF ３ (CF ２ ) ２ OCF (CF ３ ) CF ２ OCF (CF ３ ) COONH ４ CF ３ (CF ２ ) ２ O(CF) ２ ) ２ OCF ２ COONH ４ CF ３ (CF ２ ) ２ O(CF) ２ CF ２ O) ２ CF ２ COONH ４ CF ３ (CF ２ )３ OCF ２ CF ２ OCF ２ COONH ４ 、CF ３ (CF ２ ) ３ O(CF ２ CF ２ O) ２ CF ２ COONH<()000208>、CF ３ (CF ２ ) ２ O(CF ２ ) ２ OCF ２ COONa、CF ３ (CF ２ ) ２ O(CF ２ CF ２ O)<00()0220>CF ２ COONa、CF ３ (CF ２ ) ３ OCF ２ CF[[ID=()0]] ２ OCF ２ COONa、CF ３ (CF ２ ) ３ O(CF ２ CF ２ O) ２ CF ２ COONa、C ２ F ５ O(CF ２ ) ２ OCF ２ COONH ４ (abbreviation EEA-NH4)、C ２ F ５ O(CF ２ CF ２ O) ２ CF ２ COONH ４ 、C ２ F ５ O(CF ２ ) ２ OCF ２ COONa、C ２ F ５ O(CF ２ CF ２ O) ２ CF２ COONA, CF ３ O(CF) ２ ) ３ OCF ２ COONH ４ CF ３ O(CF) ２ ) ３ OCF (CF ３ ) COONH ４ CF ３ O(CF) ２ ) ３ OCF ２ COONA, CF ３ O(CF) ２ ) ３ OCF (CF ３ ) COONa, CF ３ O(CF) ２ O) ３ CF ２ COONH ４ CF ３ O(CF) ２ O) ３ CF ２ COONA, CF ３ OCF (CF ３ ) CF ２ OCF (CF ３ ) COONH ４ CF ３ OCF (CF ３ ) CF ２ OCF (CF ３ ) COONa, CF ３ O(CF) ２ CF ２ O) ２ CF ２ COONH ４ CF ３ O(CF) ２ CF ２ O) ２ CF ２ Examples include fluorine-containing emulsifiers such as COONa. The emulsifier may be used alone or in combination of two or more. Among these, ammonium perfluorooctanoate, CF ３ (CF ２ ) ３ O(CF) ２ ) ２ OCF ２ COONH ４ CF３ (CF ２ ) ２ O(CF) ２ ) ２ OCF ２ COONH ４ , EEA-NH4, CF ３ O(CF) ２ ) ３ OCF ２ COONH ４ This is preferable. The emulsifier may be added all at once or sequentially. The amount of emulsifier used is preferably 0.01 to 20 parts by mass, more preferably 0.05 to 15 parts by mass, and even more preferably 0.1 to 10 parts by mass, per 100 parts by mass of aqueous medium.

[0046] Furthermore, the polymerization reaction system does not need to contain substantially no emulsifier. "Substantially no" means that the emulsifier content in the polymerization reaction system is 0.03 ppm by mass or less relative to the total mass of the aqueous medium, preferably 0.02 ppm by mass or less, and more preferably 0 ppm by mass.

[0047] The conditions for the polymerization reaction, such as pressure and temperature, are set appropriately according to the monomer composition and the decomposition temperature of the radical polymerization initiator. Typically, the pressure is preferably 0.1 to 20 MPaG, more preferably 0.3 to 10 MPaG, and even more preferably 0.3 to 5 MPaG. The temperature is preferably 0 to 100°C, more preferably 10 to 90°C, and even more preferably 20 to 85°C.

[0048] In emulsion polymerization, the fluorine-containing copolymer is obtained as latex and can be purified by appropriate aggregation. In solution polymerization, it can be purified by washing with an aqueous medium such as methanol.

[0049] The method for agglomerating fluorine-containing copolymers is not particularly limited, but examples include freeze agglomeration, acid agglomeration, base agglomeration, mechanical agglomeration using a stirring device that rotates a stirring shaft equipped with a stirring blade, and agglomeration using a coagulant. In the case of freeze agglomeration, the agglomeration temperature is preferably -20 to 0°C. The agglomeration time is preferably 1 hour or more, more preferably 2 hours or more. In the case of acid agglomeration, examples of acids to be added include hydrochloric acid, nitric acid, sulfuric acid, oxalic acid, etc., with nitric acid being preferred. The concentration of added acid 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 agglomeration, examples of bases to be added include sodium hydroxide, potassium hydroxide, ammonium carbonate, etc., with sodium hydroxide being preferred. The concentration of added base 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 agglomeration using a coagulant, known coagulants can be used, such as aluminum salts, calcium salts, and magnesium salts. Specifically, examples include aluminum sulfate, alum (potassium aluminum sulfate dodecahydrate), calcium nitrate, and magnesium sulfate, with alum being preferred.

[0050] (Crosslinked Structure) The crosslinked structure obtained by crosslinking a fluorine-containing copolymer is not particularly limited, and examples include crosslinked structures derived from peroxide, polyol, and nitrile. From the viewpoint of good heat resistance of the fluororubber article, a crosslinked structure derived from nitrile is preferred. As a nitrile-derived crosslinked structure, a crosslinked structure containing an oxazole ring or a triazine ring is preferred. That is, the fluororubber article of this embodiment is preferably composed of fluororubber having a crosslinked structure containing an oxazole ring or a triazine ring. From the viewpoint of obtaining a high crosslink density with a small number of nitrile groups, it is more preferable that the fluororubber has a crosslinked structure containing an oxazole ring.

[0051] Examples of crosslinking agents that form a crosslinking structure containing an oxazole ring include bisaminophenol compounds such as 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (abbreviated as BOAP, also known as bisaminophenol AF). Examples of crosslinking catalysts that form a crosslinking structure containing a triazine ring include urea, silicon nitride, 1,8-diazabicyclo[5.4.0]-7-undecene (DBU), 1,5-diazabicyclo[4.3.0]-5-nonene (DBN), phosphonium salts such as quaternary phosphonium salts, and sulfonium salts.

[0052] The content of the crosslinking agent or crosslinking catalyst in the crosslinkable fluororubber composition is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the fluorine-containing copolymer, from the viewpoint of sufficient crosslinking density and good heat resistance of the fluororubber article formed by crosslinking the fluorine-containing copolymer.

[0053] (Crosslinkable Fluororubber Composition) The crosslinkable fluororubber composition preferably contains a fluorine-containing copolymer and further contains a compound that forms a crosslinked structure. In addition to the fluorine-containing copolymer and the compound that forms the crosslinked structure, the crosslinkable fluororubber composition may contain other components as long as they do not impair the effects of the present invention. Examples of other components include fillers and reinforcing materials (e.g., carbon black, barium sulfate, calcium metasilicate, calcium carbonate, titanium dioxide, silicon dioxide, clay, talc, etc.), scorch retarders (e.g., phenolic hydroxyl group-containing compounds such as bisphenol A, quinones such as hydroquinone, α-methylstyrene dimers such as 2,4-di(3-isopropylphenyl)-4-methyl-1-pentene, etc.), crown ethers (e.g., 18-crown-6, etc.), mold release agents (e.g., sodium stearate, etc.), pigments, etc. The other components may be used individually or in combination of two or more.

[0054] If the crosslinkable fluororubber composition contains other components, the total content of the other components is preferably more than 0 parts by mass and 30 parts by mass or less, more preferably more than 0 parts by mass and 25 parts by mass or less, and even more preferably more than 0 parts by mass and 20 parts by mass or less, based on 100 parts by mass of the fluorine-containing copolymer.

[0055] A crosslinkable fluororubber composition can be produced by mixing the above components. The mixing of the components can be carried out using a rubber mixing device such as a roll, kneader, Banbury mixer, or extruder. The resulting mixture may be molded according to the intended use of the fluororubber article. Examples of molding methods include compression molding, injection molding, extrusion molding, calendering, and dipping or coating a substrate or the like by dissolving it in a solvent.

[0056] (Physical Properties and Applications) The fluororubber articles of this embodiment have low high-temperature compression set and good heat resistance. The compression set under holding conditions of 300°C, 25% compressibility, and 70 hours is preferably 30% or less, more preferably 25% or less, and even more preferably 20% or less. The high-temperature compression set is specifically measured by the method described in the examples.

[0057] Furthermore, as described in JIS K 6262:2013, stainless steel is typically used as the material for the compression plate when measuring high-temperature compression set. In this embodiment, whether a Ni-Cr-Mo alloy compression plate is used or stainless steel is used, the compression set under holding conditions of 300°C, 25% compressibility, and 70 hours is preferably 30% or less, preferably 25% or less, and more preferably 20% or less.

[0058] The fluororubber article of this embodiment exhibits low permanent deformation when compressed at high temperatures, and is particularly susceptible to cracking and bleeding when in contact with stainless steel. Therefore, it is suitable for use as a component in contact with stainless steel, i.e., for use with stainless steel.

[0059] Stainless steel is an alloy containing iron and chromium. In addition to iron and chromium, stainless steel may also contain other elements such as carbon, silicon, manganese, phosphorus, sulfur, nickel, cobalt, molybdenum, copper, nitrogen, lead, aluminum, selenium, niobium, and titanium. Examples of stainless steel include SUS403, SUS410, SUS410J1, SUS410F2, SUS416, SUS420J1, SUS420J2, SUS420F, SUS420F2, SUS431, SUS440A, SUS440B, SUS440C, SUS440F, SUS405, SUS410L, SUS430, SUS430F, SUS434, SUS447J1, SUSXM27, SUS329J1, SUS329J3L, SUS329J4L, SUS201, SUS202, SUS301, SUS302, SUS303, and SUS303S. e, SUS303Cu, SUS304, SUS304L, SUS304N1, SUS304N2, SUS304LN, SUS304J3, S US305, SUS309S, SUS310S, SUS316, SUS316L, SUS316N, SUS316LN, SUS316Ti, S Examples include US316J1, SUS316J1L, SUS316F, SUS317, SUS317L, SUS317LN, SUS317J1, SUS836L, SUS890L, SUS321, SUS347, SUSXM7, SUSXM15J1, SUS630, SUS631, etc. SUS405 is preferred from the viewpoint of availability and good bonding with fluororubber.

[0060] The surface of the stainless steel in contact with the fluororubber article is preferably smooth. Here, "smooth" means that the arithmetic mean roughness Ra of the surface roughness according to JIS B 0601:2001 (ISO 4287-1997) is 0.1 μm or less.

[0061] Examples of fluororubber articles in this embodiment include sealing materials and cushioning materials such as rings, packings, oil seals, gaskets, diaphragms, and sheets. Other examples include articles used in applications such as sealing materials for semiconductor devices, components for oil drilling, wire coverings, heat-resistant and chemical-resistant sealing materials, heat-resistant and oil-resistant sealing materials, corrosion-resistant rubber paints, sealing materials for urea-based greases, rubber paints, adhesive rubber, hoses, tubes, calender sheets (rolls), sponges, rubber rolls, heat dissipation sheets, solution crosslinked materials, rubber sponges, bearing seals, linings, insulating sheets for automobiles, insulating sheets for electronic equipment, rubber bands, packings / valves, fenders, fibers / nonwoven fabrics, substrate sealing materials, rubber gloves, stators for single-screw eccentric pumps, components for urea SCR systems, vibration dampers, vibration suppressors, and sealing agents.

[0062] The cross-sectional shape of the rings, packings, and seals described above is not particularly limited and may include, for example, O-shaped, square, or ferrule shapes, or other shapes such as D-shaped, X-shaped, Y-shaped, L-shaped, T-shaped, or V-shaped.

[0063] Fields in which fluororubber products are used include, for example, semiconductor-related industries, beverage and food manufacturing equipment, pharmaceutical manufacturing equipment, medical components, chemical transport equipment, nuclear power plant equipment, sheet metal processing equipment, general industry, electrical work, fuel cells, electronic components, optical instrument components, aerospace equipment components, petrochemical plant equipment, oil and gas and other energy resource exploration and extraction equipment components, petroleum refining, petroleum transport equipment components, automobiles, aircraft, space and rockets, ships, chemical industry such as chemical plants, pharmaceuticals and other chemicals, photographic equipment such as developing machines, printing machines, painting equipment, analytical instruments and measuring instruments, and food processing equipment for food plants and household goods.

[0064] In the semiconductor-related fields mentioned above, for example, it can be used in semiconductor manufacturing equipment, organic electroluminescent (EL) panel manufacturing equipment, field emission display panel manufacturing equipment, plasma address liquid crystal panel manufacturing equipment, plasma display panel manufacturing equipment, liquid crystal panel manufacturing equipment, solar cell substrate manufacturing equipment, plasma panel manufacturing equipment, semiconductor transport equipment, etc. More specifically, reactive ion beam etching equipment, ion beam etching equipment, sputter etching equipment, plasma etching equipment, reactive ion etching equipment, dry etching equipment, wet etching equipment, chemical vapor deposition (CVD) equipment, gas control equipment such as semiconductor gas control equipment, oxidation diffusion equipment, sputtering equipment, plasma ashing equipment, ashing equipment, cleaning equipment, ion implantation equipment, plasma CVD equipment, exhaust equipment, exposure equipment, polishing equipment, film deposition equipment, dry etching cleaning equipment, ultraviolet (UV) / ozone cleaning equipment, ion beam cleaning equipment, laser beam cleaning equipment, plasma cleaning equipment, gas etching cleaning equipment, extraction cleaning equipment, Soxhlet extraction cleaning equipment, high temperature high pressure extraction cleaning equipment, microwave extraction cleaning equipment, supercritical extraction cleaning equipment, cleaning equipment using hydrofluoric acid, hydrochloric acid, sulfuric acid, ozonated water, etc., stepper, coater / developer, chemical mechanical polishing (CMP) equipment, excimer laser exposure machine, chemical solution piping, gas piping, plasma processing equipment (for example, nitrogen trifluoride (NF) ３ Examples include plasma treatment, oxygen plasma treatment, fluorine plasma treatment, etc.), heat treatment film deposition equipment, wafer transport equipment, wafer cleaning equipment, silicon wafer cleaning equipment, silicon wafer processing equipment, reduced pressure CVD (LPCVD) equipment, lamp annealing equipment, and reflow equipment.

[0065] Examples of applications in the semiconductor-related field include hoses and tubes for wafer cleaning solutions, resist developer tanks, stripping solution tanks, linings and coatings for wafer cleaning solution tanks and wet etching tanks, pump diaphragms, rolls for wafer transport, gate valves, quartz windows, chambers, chamber lids, gates, bell jars, couplings, various sealing materials such as O-rings and gaskets for pumps, various sealing materials such as O-rings for resist developers and stripping solutions, hoses and tubes, sealants for clean facilities such as cleanrooms, sealing materials for semiconductor manufacturing equipment and device storage facilities such as wafers, and diaphragms for chemical transfer in semiconductor manufacturing processes.

[0066] [Method for Manufacturing Fluororubber Articles] The method for manufacturing fluororubber articles according to this embodiment includes a step of crosslinking a crosslinkable fluororubber composition containing a fluorine-containing copolymer having TFE units and PAVE units in an atmosphere with a dew point of less than 20°C. By going through this crosslinking step in an atmosphere containing a predetermined amount of moisture, a fluororubber article can be suitably obtained that exhibits low permanent deformation when compressed at high temperatures and is less prone to cracking.

[0067] The crosslinkable fluororubber composition in the manufacturing method of this embodiment may include a fluorine-containing copolymer having TFE units and PAVE units, and may be the crosslinkable fluororubber composition described above. Each unit constituting the fluorine-containing copolymer is the same as that described above. For this reason, a detailed explanation of the crosslinkable fluororubber composition is omitted.

[0068] Various methods exist for crosslinking the fluorine-containing copolymer in a crosslinkable fluororubber composition, including heating, pressurization, and radiation irradiation. However, from the viewpoint of ensuring uniform crosslinking of the fluorine-containing copolymer, heating is preferred. The crosslinking of the fluorine-containing copolymer and the molding of the crosslinkable fluororubber composition described above may be performed simultaneously.

[0069] For crosslinking by heating, for example, heating is performed at 80 to 400°C for 1 minute to 48 hours. After primary crosslinking by heating once, secondary crosslinking may be performed by changing the temperature and heating further. From the viewpoint of appropriate progress of the crosslinking reaction of the fluorine-containing copolymer, for example, primary crosslinking is performed at 80 to 200°C for 1 minute to 6 hours, followed by secondary crosslinking at 200 to 400°C for 1 minute to 48 hours. In the secondary crosslinking process, the high-temperature compression set and other rubber properties of the fluororubber article can be stabilized or improved. Temperature control may involve gradually increasing or decreasing the temperature. The heating temperature and time are set appropriately according to the composition of the crosslinkable fluororubber composition, the shape and application of the fluororubber article, etc.

[0070] The heating temperature for primary crosslinking is more preferably 100 to 200°C, and even more preferably 150 to 200°C. The heating time is more preferably 1 minute to 2 hours, even more preferably 1 minute to 1 hour, and even more preferably 1 minute to 30 minutes. The heating temperature for secondary crosslinking is more preferably 200 to 350°C, even more preferably 250 to 320°C, and even more preferably 280 to 310°C. The heating time is more preferably 1 to 24 hours, and even more preferably 5 to 20 hours.

[0071] In the method for manufacturing fluororubber articles of this embodiment, secondary crosslinking is preferably performed in an atmosphere with a dew point of less than 20°C, and it is more preferable that the crosslinkable fluororubber composition, which has been primary crosslinked, is heated in the above atmosphere at 200 to 400°C for 1 minute to 48 hours during the secondary crosslinking process. The atmospheric gas at this time is preferably air or nitrogen from the viewpoint of ease of handling, etc. The preferred temperature and time for secondary crosslinking here are the same as above.

[0072] During the crosslinking process at high temperatures, it is presumed that a side reaction occurs during the crosslinking reaction of the fluorine-containing copolymer, involving the generation of hydrogen fluoride due to moisture. This hydrogen fluoride (or F) is present in the resulting fluororubber. －The remaining residue is presumed to reduce the high-temperature heat resistance of fluororubber articles, causing cracking and bleeding during high-temperature compression. Therefore, by controlling the moisture (humidity) in the atmosphere during the crosslinking process to a low level, specifically by creating an atmosphere with a dew point of less than 20°C, it is possible to suitably obtain fluororubber articles that exhibit small permanent deformation when compressed at high temperatures and are less prone to cracking.

[0073] Since the crosslinking process is not necessarily carried out in a closed system, it is convenient in the manufacturing process to use the dew point of the gas supplied to the furnace where secondary crosslinking is performed, measured at 25°C immediately before the start of the crosslinking process, as an indicator of moisture in the atmosphere. The dew point is preferably as low as possible, more preferably 15°C or lower, even more preferably 10°C or lower, and even more preferably 0°C or lower, with the lower limit practically being -70°C or higher.

[0074] The dew point of the atmosphere during the crosslinking process can be adjusted to a lower level by, if necessary, applying moisture removal treatments to the atmospheric gas during the crosslinking process, such as using a desiccant or heat drying. Examples of desiccants include inorganic materials (calcium oxide, calcium hydroxide, silica gel, calcium chloride, zeolite, lithium chloride, etc.), superabsorbent polymers, and combinations thereof.

[0075] The present invention will be described in detail below based on examples, but the present invention is not limited to the following examples, and various modifications are possible without departing from the spirit of the invention.

[0076] [Compounds Used] The following is an explanation of the abbreviations for the various compounds used. • EEA-NH4: Ammonium perfluoro(2-ethoxy-ethoxy)acetate (C ２ F ５ O(CF) ２ ) ２ OCF ２ COONH ４ ); Emulsifier: 8CNVE: Perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene) (CF ２ = CFCF ２ CF (CF ３ ) OCF２ CF ２ CN) ・TFE: Tetrafluoroethylene ・PMVE: Perfluoro(methyl vinyl ether) ・APS: Ammonium persulfate; radical polymerization initiator ・BOAP: 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, manufactured by Tokyo Chemical Industry Co., Ltd.; crosslinking agent ・Nitrogen: High-purity nitrogen (Grade 1), manufactured by Taiyo Nippon Sanso Corporation ・Air: High-purity compressed air (Grade 1), manufactured by Taiyo Nippon Sanso Corporation

[0077] [Synthesis of Fluorine-Containing Copolymer] After degassing the inside of a 20 L stainless steel pressure reactor equipped with anchor blades, 7.2 L of ultrapure water, 880 g of a 30% by mass aqueous solution of EEA-NH4, 7.3 g of 8CNVE, and 15.9 g of a 5% by mass aqueous solution of disodium hydrogen phosphate dodecahydrate were charged. After purging the reactor with nitrogen, the anchor blades (375 min) －１ While stirring, 137 g of TFE and 635 g of PMVE were injected under pressure, and the reactor temperature was raised to 80°C. The reactor pressure was 0.90 MPaG. Polymerization was started by adding 28 mL of a 3% by mass aqueous solution of APS to the reactor (molar ratio of each monomer before polymerization: TFE / PMVE / 8CNVE = 26.3 / 73.3 / 0.4).

[0078] As polymerization progressed, when the reactor pressure reached 0.89 MPaG, TFE was injected to increase the pressure to 0.90 MPaG. This operation was repeated, and each time the total amount of TFE injected reached 119.3 g, 3.7 g of 8CNVE, 74 g of PMVE, and then another 3.7 g of 8CNVE were injected in that order. In addition, when the polymerization rate began to decrease, a 3% by mass aqueous solution of APS was added as needed (total added amount: 35 mL). After the injection of each monomer was completed when the total amount of TFE injected reached 1073.7 g, 119.3 g of TFE was injected to complete the injection of each monomer (total added amounts of each monomer: TFE 1193 g, PMVE 666 g, 8CNVE 66.6 g). The reactor temperature was lowered to 10°C to stop the polymerization reaction, yielding a latex containing a fluorine-containing copolymer (polymerization time: 6.25 hours; additional monomer molar ratio: TFE / PMVE / 8CNVE = 74.0 / 25.0 / 1.0).

[0079] The obtained latex was added to a 5% by mass aqueous solution of potassium aluminum sulfate to agglomerate the fluorine-containing copolymer. The fluorine-containing copolymer was separated by filtration, washed with ultrapure water, and then vacuum-dried at 50°C to obtain a white fluorine-containing copolymer (molar composition ratio of units based on each monomer: TFE units / PMVE units / 8CNVE units = 70.9 / 28.6 / 0.5).

[0080] [Manufacturing of O-rings] 100 parts by mass of fluorine-containing copolymer and 1.0 part by mass of BOAP were mixed and kneaded in a two-roll machine at room temperature (25°C) for 10 minutes to obtain a crosslinkable fluororubber composition. The obtained crosslinkable fluororubber composition was filled into a mold and, while degassing the mold with a diaphragm pump, was heated and compressed at 180°C for 20 minutes in a hydraulic press ("SA-301 50T type", manufactured by Tester Sangyo Co., Ltd., ram diameter 180 mm) (primary crosslinking). Subsequently, in an inert oven ("DN411I", manufactured by Yamato Scientific Co., Ltd.), under the atmosphere of the gas (nitrogen or air) shown in Table 1, a heat treatment was performed by heating at 90°C for 3 hours, then raising the temperature to 305°C over 5 hours and holding for 13 hours (secondary crosslinking). The dew point in the gas atmosphere was adjusted to the test conditions by spraying water ("Dia Spray Long Pistol," manufactured by Fullpla Co., Ltd.) before introducing gas (nitrogen or air) into the inert oven, as needed. The dew point was measured at 25°C immediately before the start of the secondary crosslinking heat treatment using a handheld thermometer / hygrometer ("HN-EHSP," probe type, manufactured by Chino Corporation). After the secondary crosslinking heat treatment, the material was cooled to 25°C to produce the O-ring (P-26).

[0081] [Measurement and Evaluation of Fluororubber Articles] (Fluoride Ion Content) The O-ring (P-26) obtained above was cut in the thickness direction in 3 mm increments along its outer circumference to prepare pellet-shaped samples. After accurately weighing 1 g of the sample, it was heated at 360°C for 60 minutes, and the resulting gas was absorbed into an absorption solution (30 mL x 2 sets of pure water) using air as a carrier gas (flow rate 500 mL / min). 0.1 mL of the measurement sample solution taken from this absorption solution was subjected to ion chromatography ("Dionex ICS-5000"). ＋ Fluoride ions (F) (manufactured by Thermo Fisher Scientific Co., Ltd.)－ A quantitative analysis of ) was performed, and the value multiplied by 600 was used to determine the F in the absorption solution (60 mL). － The mass was given as [g]. Similarly, the F of the absorbent solution (blank) before gas absorption was also expressed. － The mass [g] is also measured, and F is calculated using the following formula. － The percentage of content was calculated. F － Content percentage [%] = {(F in the absorbent solution) － Mass [g]) - (F of the blank) － Mass [g])} / (sample mass [g])

[0082] Table 1 shows the arithmetic mean F of the five samples. － The percentage of content is shown. F in the absorbent solution － The content ratio is F in fluororubber articles. － This is an indirect evaluation index of the content. F in the absorption solution － The higher the content, the greater the F content in the fluororubber article. － It can be said that the content is high.

[0083] (High-temperature compression set) The P-26 O-ring (P-26) obtained above was cut in half in the thickness direction to make a test specimen, and the high-temperature compression set was measured using a method based on JIS K 6262:2013. Test specimen (thickness t ０ (3.5 mm) is compressed to a compression ratio of 25% (thickness t of the compressed test piece) using a compression device. ２ The specimen was compressed to 2.6 mm. A high-temperature compression test was performed by placing the compression device in an electric furnace at 300°C for 70 hours with the specimen compressed and fixed. The compression plate of the compression device was made of Ni-Cr-Mo alloy ("Hastelloy® C-22", manufactured by Haynes International) or stainless steel (SUS405). After removing the compression device from the electric furnace and placing the specimen in a constant temperature room at 23°C for 30 minutes, the thickness of the specimen was reduced to t １ [mm] was measured.

[0084] The above high-temperature compression test was performed on five test specimens, and the presence or absence of cracks was visually confirmed. The t values ​​were measured on the test specimens that did not crack. １ Using the arithmetic mean of , the compression set CS [%] was calculated using the following formula. Note that if all five test specimens fractured, it is indicated as "-" in Table 1. CS = (t０ -t １ ) / (t ０ -t ２ )×100=(3.5-t １ ) / 111 The smaller the high-temperature compression set, the better the heat resistance. In addition, the presence or absence of bleeding was visually confirmed in the test specimens after the high-temperature compression test using stainless steel compression plates.

[0085] Table 1 shows the gas atmosphere, dew point, and high-temperature compression set measurement results during the heat treatment of the secondary crosslinking in each example. Examples 1, 2, 4, and 5 are examples, while Examples 3 and 6 are comparative examples.

[0086]

[0087] As can be seen from the results shown in Table 1, F in the absorbent solution － The content is less than 0.25% by mass, and F in fluororubber articles － When the content was low (Examples 1, 2, 4, and 5), it was observed that cracking of the fluororubber articles was suppressed even when they were compressed at high temperatures in contact with either Ni-Cr-Mo alloy or stainless steel. It was also observed that bleeding occurred when compressed at high temperatures in contact with stainless steel. The dew point of the gas atmosphere in the secondary crosslinking was less than 20°C, which suppressed the occurrence of F in the fluororubber articles. － It is presumed that the content has been reduced.

Claims

1. A fluororubber article formed by crosslinking a fluorine-containing copolymer in a crosslinkable fluororubber composition, wherein the fluorine-containing copolymer has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and the fluoride ion content in the absorbent solution obtained by heating 1 g of the fluororubber article at 360°C for 60 minutes and absorbing the generated gas in 60 mL of pure water is less than 0.25% by mass.

2. The fluororubber article according to claim 1, wherein the fluorine-containing copolymer further comprises units based on monomers having nitrile groups.

3. The fluororubber article according to claim 2, comprising a fluororubber having a crosslinked structure containing an oxazole ring or a triazine ring.

4. The fluororubber article according to any one of claims 1 to 3, wherein the fluorine-containing copolymer is a perfluoropolymer.

5. The fluororubber article according to any one of claims 1 to 3, wherein the molar ratio of the tetrafluoroethylene-based units to the perfluoro(alkyl vinyl ether)-based units in the fluorine-containing copolymer is 60 / 40 to 80 / 20.

6. The fluororubber article according to any one of claims 1 to 3, wherein the perfluoro(alkyl vinyl ether) is a monomer represented by the following formula (1). CF ２ =CF-O-R ｆ１ (1) In formula (1), R ｆ１ These are perfluoroalkyl groups having 1 to 10 carbon atoms.

7. A fluororubber article according to any one of claims 1 to 3, wherein the compression set under holding conditions of 300°C, a compressibility of 25%, and 70 hours is 30% or less.

8. A fluororubber article according to any one of claims 1 to 3, for use with stainless steel.

9. A method for producing a fluororubber article, comprising the step of heating a crosslinkable fluororubber composition containing a fluorine-containing copolymer having units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether) in an atmosphere with a dew point of less than 20°C to crosslink the fluorine-containing copolymer.

10. The method for producing a fluororubber article according to claim 9, wherein the step of crosslinking the fluorine-containing copolymer is performed at 200 to 400°C for 1 minute to 48 hours.

11. The method for producing a fluororubber article according to claim 9 or 10, wherein the step of crosslinking the fluorine-containing copolymer is carried out in an air or nitrogen atmosphere.

Images