Fluororubber and method for producing same, and fluororubber article

Abstract

Provided are: a fluororubber that 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; a method for producing the same; and a fluororubber article. A fluororubber according to the present invention is a crosslinked product of a fluorine-containing copolymer. The fluorine-containing copolymer has a unit based on tetrafluoroethylene and a unit based on a perfluoro(alkyl vinyl ether), and has an a* of at least 2.05 and a b* of at least 2.05 in the L*a*b* color system.

Description

Fluororubber and its manufacturing method, and fluororubber articles

[0001] This invention relates to fluororubber, a method for producing the same, and a fluororubber article using the fluororubber.

[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] Fluororubber articles are generally manufactured by heating a crosslinkable fluororubber composition containing a fluorine-containing copolymer to crosslink the fluorine-containing copolymer. For example, Patent Document 1 describes a process in which the article is molded into a predetermined shape and subjected to primary crosslinking, followed by secondary crosslinking (post-curing) to complete the crosslinking reaction and release any remaining volatile components. In Patent Document 1, post-curing is performed under a nitrogen atmosphere. Patent Document 2 describes post-curing being performed in an air-circulating oven (air oven).

[0004] Japanese Patent Publication No. 2013-107924 Japanese Patent Publication No. 2023-85272

[0005] Incidentally, 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 (for example, 300°C).

[0006] While good heat resistance is desirable for fluororubber articles under various usage conditions, it has been found that this can be affected by the material of the metal component in contact with the fluororubber article. Specifically, it was confirmed that cracking tends to occur more easily when the material is stainless steel than when it is Ni-Cr-Mo alloy.

[0007] This invention was made under such circumstances, and aims to provide a fluororubber that exhibits low permanent deformation when compressed at high temperatures, and which is particularly effective in suppressing crack formation when in contact with stainless steel, as well as a method for manufacturing the same and a fluororubber article.

[0008] The present invention is based on the finding that the color tone of fluororubber has a correlation with heat resistance, and that the heat treatment conditions of a crosslinkable fluororubber composition for producing fluororubber affect the heat resistance of fluororubber.

[0009] The present invention provides the following means. [1] A fluororubber which is a crosslinked product of a fluorine-containing copolymer, wherein the fluorine-containing copolymer has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), and L ＊ a ＊ b ＊ a in the L*a*b* color system ＊ is 2.05 or more, and b ＊ is 2.05 or more, fluororubber. [2] L ＊ a ＊ b ＊ L in the L*a*b* color system ＊ is 12.0 or more, the fluororubber of [1]. [3] The fluororubber of [1] or [2], wherein the fluorine-containing copolymer further has units based on a monomer having a nitrile group. [4] The fluororubber of [3], which has a crosslinked structure containing an oxazole ring or a triazine ring. [5] The fluororubber according to any one of [1] to [4], wherein the fluorine-containing copolymer is a perfluoropolymer. [6] The fluororubber according to any one of [1] to [5], wherein the molar ratio of the units based on tetrafluoroethylene and the units based on perfluoro(alkyl vinyl ether) in the fluorine-containing copolymer is 60 / 40 to 80 / 20. [7] The fluororubber according to any one of [1] to [6], wherein the perfluoro(alkyl vinyl ether) is a monomer represented by the following formula (1). CF ２ =CF - O - R ｆ１ (1) In the formula (1), R ｆ１ is a perfluoroalkyl group having 1 to 10 carbon atoms.

[0010] [8] A method for producing fluororubber, comprising the step of crosslinking a crosslinkable fluororubber composition containing a fluorine-containing copolymer having units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether) in a gas atmosphere with an oxygen concentration of 2.0 vol% or more and less than 20.9 vol%. [9] The method for producing fluororubber according to [8], wherein the nitrogen concentration in the gas atmosphere is greater than 79.1 vol% and 98.0 vol% or less.

[10] The method for producing fluororubber according to [8] or [9], wherein the step of crosslinking the fluorine-containing copolymer comprises a heat treatment at 200 to 400°C for 1 minute to 48 hours.

[0011]

[11] A fluororubber article made of any of the fluororubbers described in [1] to [7].

[12] A fluororubber article of

[11] having a compression set of 30% or less under holding conditions of 300°C, a compressibility of 25%, and 70 hours.

[13] A fluororubber article of

[11] or

[12] for use with stainless steel.

[0012] According to the present invention, it is possible to provide fluororubber, a method for manufacturing the same, and fluororubber articles that exhibit low permanent deformation when compressed at high temperatures and that are particularly susceptible to cracking when in contact with stainless steel.

[0013] The definitions and meanings of terms and notations used herein are as follows: 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 composition 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."

[0014] [Fluororubber] The fluororubber of the embodiment of the present invention (hereinafter referred to as "this embodiment") is a fluororubber that is a crosslinked product of a fluorine-containing copolymer, wherein the fluorine-containing copolymer has units based on tetrafluoroethylene (TFE) and units based on perfluoro(alkyl vinyl ether) (PAVE), L ＊ a ＊ b ＊ a in the color system ＊ If b is 2.05 or higher, ＊ The ratio is 2.05 or higher. Fluororubber is a crosslinked material formed by crosslinking a fluorine-containing copolymer having units based on fluorine-containing monomers, and is a rubbery elastic body. In this embodiment, the fluorine-containing copolymer has units based on TFE and units based on PAVE. Fluororubber having the above-described color tone can be used to construct a fluororubber article that exhibits low permanent deformation when compressed at high temperatures (e.g., 300°C), and is particularly resistant to cracking when in contact with stainless steel.

[0015] L ＊ a ＊ b ＊ A color system is a widely used color system for numerically representing color tones (colors). ＊ a ＊ b ＊ a in the color system ＊ This indicates that negative values ​​are colored green, and positive values ​​are colored red. ＊ This indicates that negative values ​​are colored blue, and positive values ​​are colored yellow. ＊ The value represents brightness; 0 is black, 100 is white, and the higher the number, the brighter it is. ＊ a ＊ b ＊ Color tone measurement of color systems can be performed using a colorimeter. Fluororubber L ＊ a ＊ b ＊ Color system L ＊ a ＊ and b ＊ This value is for a crosslinked fluorine-containing copolymer that does not contain colorants.

[0016] Specifically, the color tone is measured using a colorimeter on a rubber sheet obtained by crosslinking a fluorine-containing copolymer in a crosslinkable fluororubber composition that does not contain a coloring agent, using the method described in the examples. The rubber sheet is produced through a primary crosslinking step of 20 minutes at 180°C, followed by a secondary crosslinking step of heating at 90°C for 3 hours under a predetermined gas atmosphere, then raising the temperature to 305°C over 5 hours and holding it for 13 hours.

[0017] The color tone of the fluororubber in this embodiment is a ＊ The value is 2.05 or higher, preferably 2.10 to 20.00, and more preferably 2.50 to 15.00. Also, b ＊ The ratio is 2.05 or higher, preferably 2.10 to 20.00, and more preferably 2.50 to 15.00.

[0018] Fluororubber L ＊ a ＊ b ＊ In a color system, L ＊ From the viewpoint of good heat resistance, the value is preferably 12.0 or higher, more preferably 12.5 to 30.0, and even more preferably 15.0 to 25.0.

[0019] A correlation has been confirmed between the color tone and heat resistance of fluororubber. When fluororubber has a specific red or yellow tint, the permanent deformation when the fluororubber article is compressed at high temperatures is small, and crack formation is suppressed, especially when in contact with stainless steel. Although the detailed reasons are not clear, it is presumed that the heat treatment conditions of the fluorine-containing copolymer during the manufacturing of fluororubber are reflected in the color tone of the fluororubber.

[0020] Fluororubber with a desired color tone is more easily obtained by ensuring that the atmosphere during crosslinking of the fluorine-containing copolymer has a predetermined oxygen concentration. ＊ a ＊ and b ＊ A fluororubber having the desired range can be obtained, for example, by controlling the oxygen concentration as in the manufacturing method of the present invention, heating a crosslinkable fluororubber composition containing a fluorine-containing copolymer, and crosslinking the fluorine-containing copolymer.

[0021] (Fluorine-containing copolymer) The fluorine-containing copolymer used in the fluororubber 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.

[0022] PAVE is preferably a monomer represented by the following formula (1) from the viewpoint of good polymerization reactivity and good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer. 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.

[0023] 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.

[0024] 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 with good heat resistance.

[0025] From the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the nitrile group monomer, it is preferable that the monomer having a fluorine atom is present, and more preferably the monomer represented by the following formula (2). CR ２１ R ２２ =CR ２３ R ２４CN (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.

[0026] 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 obtained 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 the fluororubber obtained by crosslinking the fluorine-containing copolymer, it is preferable that it has etheric oxygen atoms. ２４ The number of etheric oxygen atoms in is preferably 1 to 3, more preferably 1 or 2.

[0027] 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 ) ３Examples 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, with 8CNVE being more preferred, from the viewpoint of good heat resistance and release properties of the fluororubber obtained by crosslinking the fluorine-containing copolymer.

[0028] From the viewpoint of good rubber elasticity and heat resistance of the fluororubber obtained by crosslinking, 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.

[0029] 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 the fluororubber obtained by crosslinking the fluorine-containing copolymer, DV preferably contains fluorine atoms.

[0030] From the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer, 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 ３４is a trivalent perfluorohydrocarbon group having 1 to 10 carbon atoms or a group having an etheric oxygen atom at the terminal or between carbon-carbon atoms of the perfluorohydrocarbon group.

[0031] A plurality of R ３１ ~R ３３ may be the same as or different from each other, and it is particularly preferable that they are the same. R ３１ ~R ３３ From the viewpoint of good polymerization reactivity, a fluorine atom or a hydrogen atom is preferable, and it is more preferable that both are a fluorine atom or a hydrogen atom. From the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer, it is particularly preferable that both are fluorine atoms. a3 is preferably 2 or 3, and particularly preferably 2. R ３４ may be linear, branched or cyclic, and from the viewpoint of good polymerization reactivity, linear or branched is preferable, and linear is more preferable. The number of carbon atoms of R ３４ is preferably 2 to 10, more preferably 3 to 8, still more preferably 3 to 6, and even more preferably 3 to 5. R ３４ preferably has an etheric oxygen atom from the viewpoint of good rubber elasticity of the fluororubber obtained by crosslinking the fluorine-containing copolymer. The number of etheric oxygen atoms in R ３４ is preferably 1 to 3, more preferably 1 or 2. The etheric oxygen atom in R ３４ is preferably bonded to the terminal carbon atom of R ３４ .

[0032] DV is more preferably a monomer represented by the following formula (4) or (5) among the monomers represented by the formula (3). (CF ２ =CF) ２ R ４１ (4) (CH ２ =CH) ２ R ５１ (5) In the 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.

[0033] 30 of the roots and the roots(4) of the roots ２ SHY(S ２ ) ２ THIS IS THE ２ 、S9 ２ SHY(S ２ ) ３ THIS IS THE ２ 、S9 ２ SHY(S ２ ) ４ THIS IS THE ２ 、S9 ２ SHY(S ２ ) ６ THIS IS THE ２ 、S9 ２ SHY(S ２ ) ８ THIS IS THE ２ 、S9 ２ SHY(S ２ ) ２ 10(5) ３ 49 ２ THIS IS THE ２ 、S9 ２ SHY(S ２ ) ２ THIS IS THE FULL VERSION ３ 49 ２ 90 ２ EXPERIENCE ２ 、S9 ２ THIS IS THE THING ２ 10(10) ２ 9. The ２ 9) ２ EXPERIENCE ２ 、S9 ２ SHY(S ２ 9) ３ THIS IS THE FULL VERSION ３ 49 ２ 90 ２ EXPERIENCE ２ 、S9 ２ THIS IS THE THING ２ 10(40) ３ 10(40) ２ ) ２ 10(5) ３ 49 ２ THIS IS THE ２ 、S9 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 ,CH ２ =CH(CF ２ ) ６ CH=CH ２ It is preferable.

[0034] 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.

[0035] 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).

[0036] 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 obtained 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 obtained 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.

[0037] When a 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 obtained by crosslinking the fluorine-containing copolymer.

[0038] 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 obtained by crosslinking the fluorine-containing copolymer.

[0039] The fluorine-containing copolymer is preferably a perfluoropolymer from the viewpoint of good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer. 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 containing no 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, a fluororubber with good heat resistance and chemical resistance is easily obtained. The hydrogen atom content can be identified and quantified by well-known methods such as NMR spectroscopy.

[0040] (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.

[0041] Radical polymerization initiators known in the production of fluorine-containing copolymers can be used and are appropriately selected depending on the polymerization method.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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 ４ CF ３ (CF ２ ) ２ O(CF) ２ ) ２ OCF ２ COONA, CF ３ (CF ２ ) ２ O(CF)２ CF ２ O) ２ CF ２ COONa, CF ３ (CF ２ ) ３ OCF ２ CF 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 CF​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​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 CF ３ (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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] (Crosslinking Structure) The crosslinking structure in the crosslinked product of the fluorine-containing copolymer is not particularly limited, and examples include crosslinking structures derived from peroxide, polyol, and nitrile. From the viewpoint of good heat resistance of fluororubber, a crosslinking structure derived from nitrile is preferred. As for the nitrile-derived crosslinking structure, a crosslinking structure containing an oxazole ring or a triazine ring is preferred. From the viewpoint of obtaining a high crosslinking density with a small number of nitrile groups, it is more preferable that the fluororubber has a crosslinking structure containing an oxazole ring.

[0054] [Method for Manufacturing Fluororubber] The method for manufacturing fluororubber 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 a gas atmosphere with an oxygen concentration of 2.0 vol% or more and less than 20.9 vol% by crosslinking the fluorine-containing copolymer. By going through such a step, a fluororubber with low permanent deformation when compressed at high temperatures and less prone to cracking can be suitably obtained. Furthermore, the fluororubber according to this embodiment having the predetermined color tone described above can be suitably obtained.

[0055] (Crosslinkable Fluororubber Composition) The crosslinkable fluororubber composition contains a fluorine-containing copolymer having TFE units and PAVE units. The units constituting the fluorine-containing copolymer are the same as those described above, and their explanation is omitted here.

[0056] 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 obtained by crosslinking the fluorine-containing copolymer.

[0057] A crosslinkable fluororubber composition preferably contains a compound for the fluorine-containing copolymer to form a crosslinked structure. As mentioned above, the crosslinked structure in the crosslinked product of the fluorine-containing copolymer preferably contains an oxazole ring or a triazine ring from the viewpoint of good heat resistance of the fluororubber. For this reason, the compound for the fluorine-containing copolymer to form a crosslinked structure is preferably a compound that forms a crosslinked structure containing an oxazole ring or a triazine ring through reaction with the nitrile group of a unit based on a monomer having a nitrile group in the fluorine-containing copolymer.

[0058] 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.

[0059] The amount of 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 ensuring sufficient crosslink density and good heat resistance of the fluororubber obtained by crosslinking the fluorine-containing copolymer, and from the viewpoint of suppressing the influence on the color tone of the obtained fluororubber.

[0060] The crosslinkable fluororubber composition may contain other components in addition to the fluorine-containing copolymer and the compound that forms the crosslinked structure, as long as these components 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. These other components may be used individually or in combination of two or more.

[0061] 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.

[0062] A crosslinkable fluororubber composition can be produced by mixing the above components. The mixing of the components can be carried out using rubber mixing equipment such as rolls, kneaders, Banbury mixers, and extruders. The resulting mixture may be molded according to the application of the fluororubber. Examples of molding methods include compression molding, injection molding, extrusion molding, calendering, and dipping or coating substrates with the mixture after dissolving it in a solvent.

[0063] (Crosslinking process) Various methods exist for crosslinking the fluorine-containing copolymer in the crosslinkable fluororubber composition, such as heating, pressurizing, and radiation irradiation. However, from the viewpoint of ensuring uniform crosslinking of the fluorine-containing copolymer, heating is preferred. Crosslinking of the fluorine-containing copolymer and molding of the crosslinkable fluororubber composition described above may be performed simultaneously.

[0064] 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 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 of the fluororubber, and its application.

[0065] 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.

[0066] In the method for producing fluororubber according to this embodiment, the step of crosslinking the fluorine-containing copolymer preferably includes a heat treatment at 200 to 400°C for 1 minute to 48 hours, and it is more preferable to perform secondary crosslinking by heating in a gas atmosphere with an oxygen concentration of 2.0 to 20.5 vol%. It is even more preferable to perform secondary crosslinking of the fluorine-containing polymer by heating the crosslinkable fluororubber composition to perform primary crosslinking of the fluorine-containing copolymer, and then heat-treating the above gas atmosphere at 200 to 400°C for 1 minute to 48 hours. The preferred temperature and time for secondary crosslinking here are the same as described above.

[0067] The process of crosslinking fluorine-containing copolymers has conventionally been carried out in a nitrogen or air atmosphere, but it has been found that the oxygen concentration in the atmosphere affects the heat resistance of the fluororubber. Compared to a nitrogen atmosphere (oxygen concentration 0 vol%) or an air atmosphere (oxygen concentration 20.9 vol%), a gas atmosphere with an oxygen concentration of 2.0 vol% or more and less than 20.9 vol%, preferably 10.0 to 20.5 vol%, and more preferably 15.0 to 20.0 vol%, allows for the preferable acquisition of fluororubber with low permanent deformation when compressed at high temperatures and resistance to cracking. The reason for this is not clear, but it is thought that crosslinking under a gas atmosphere with an oxygen concentration within the above range allows the crosslinking reaction of the fluorine-containing copolymer to proceed appropriately, forming a crosslinked structure that enhances heat resistance.

[0068] The nitrogen concentration in the gas atmosphere is preferably greater than 79.1 vol% and 98.0 vol% or less, more preferably 79.5 to 90.0 vol%, and more preferably 80.0 to 85.0 vol%. From the viewpoint of ease of handling, the oxygen and nitrogen concentrations in the atmospheric gas are preferably adjusted by mixing oxygen or air with nitrogen, and from the viewpoint of the stability of the crosslinking reaction, it is even more preferable that the gas atmosphere does not contain any gases other than oxygen and nitrogen.

[0069] [Fluororubber Articles] The fluororubber articles of this embodiment are made of the fluororubber of this embodiment as described above. The fluororubber articles of this embodiment have a small high-temperature compression set and good heat resistance. The compression set under holding conditions of 300°C, a compressibility of 25%, and 70 hours is preferably 30% or less, more preferably 20% or less, and even more preferably 15% or less. The high-temperature compression set is specifically measured by the method described in the examples.

[0070] Furthermore, in the measurement of high-temperature compression set, as described in JIS K 6262:2013, stainless steel is usually used as the material for the compression plate. In contrast, using a Hastelloy (nickel (Ni)-chromium (Cr)-molybdenum (Mo) alloy) compression plate may make the rubber more prone to cracking, and can be said to be a test under more stringent conditions. In this embodiment, even when a Ni-Cr-Mo alloy compression plate is used, the compression set of the fluororubber article under holding conditions of 300°C, 25% compression ratio, and 70 hours can preferably be 30% or less, preferably 20% or less, and more preferably 15% or less.

[0071] The fluororubber article of this embodiment exhibits low permanent deformation when compressed at high temperatures, and is particularly well-suited for use as a component in contact with stainless steel, i.e., for use with stainless steel, because it is less prone to cracking when in contact with stainless steel.

[0072] 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.

[0073] 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.

[0074] Specific 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 semiconductor equipment sealing materials, oil drilling components, wire insulation materials, heat-resistant and chemical-resistant sealing materials, heat-resistant and oil-resistant sealing materials, corrosion-resistant rubber paints, urea-resistant grease sealing materials, rubber paints, adhesive rubber, hoses, tubes, calender sheets (rolls), sponges, rubber rolls, heat dissipation sheets, solution crosslinked materials, rubber sponges, bearing seals, linings, automotive insulating sheets, electronic equipment insulating sheets, rubber bands, packings / valves, fenders, fibers / nonwoven fabrics, substrate sealing materials, rubber gloves, stators for single-screw eccentric pumps, urea SCR system components, vibration dampers, vibration suppressors, and sealing agents.

[0075] The cross-sectional shape of the ring, packing, and seal described above is not particularly limited and may include, for example, an O-shape, square, or ferrule, or it may also be an irregular shape such as a D-shape, X-shape, Y-shape, L-shape, T-shape, or V-shape.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] [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 ) OCF ２ 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

[0081] [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).

[0082] 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).

[0083] 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).

[0084] [Production of Crosslinkable Fluororubber Composition] The fluorine-containing copolymer and BOAP were mixed in the proportions shown in each example in Table 1, and kneaded at room temperature (25°C) for 10 minutes using two rolls to obtain the mixed crosslinkable fluororubber composition.

[0085] [Manufacturing of Rubber Sheets] The crosslinkable fluororubber composition was filled into a mold and heated and compressed at 180°C for 20 minutes using a hydraulic press ("SA-301 50T type", manufactured by Tester Sangyo Co., Ltd., ram diameter 180 mm) (primary crosslinking). Then, in an inert oven ("DN411I", manufactured by Yamato Scientific Co., Ltd.), under a gas atmosphere in which the nitrogen / oxygen concentration was adjusted as shown in each example in Table 1, it was heated at 90°C for 3 hours, and then the temperature was raised to 305°C over 5 hours and held for 13 hours (secondary crosslinking). The nitrogen / oxygen concentration was measured at 25°C using a nitrogen / oxygen concentration meter ("NCM-02", manufactured by Apollo Seikou Co., Ltd.). After that, it was cooled to 25°C to produce a rubber sheet of 100 mm × 60 mm × 1 mm thickness.

[0086] [Manufacturing of O-rings] A crosslinkable fluororubber composition was filled into a mold, and O-rings (P-26) were manufactured under the same manufacturing conditions as for the rubber sheets described above.

[0087] [Measurement and Evaluation of Fluororubber] (Color Tone) The color tone of the rubber sheet obtained above was measured using a colorimeter ("SM-T", manufactured by Suga Test Instruments Co., Ltd.; aperture size diameter 15 mm, light source D65, 10° field of view) under the following conditions, referring to JIS Z 8781-4:2003. On the main surface of the rubber sheet that faced the cavity of the mold, L ＊ a ＊ b ＊ L in color systems ＊ a ＊ and b ＊ The values ​​were measured, and the arithmetic mean of the measurements from five rubber sheets was calculated and is shown in Table 1.

[0088] (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.

[0089] 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 = (t ０ -t １ ) / (t ０ -t ２ )×100=(3.5-t １ ) / 111 The smaller the high-temperature compression set, the better the heat resistance.

[0090] Table 1 shows the blending ratios, nitrogen and oxygen concentrations in the gas atmosphere during secondary crosslinking, color tone measurement, and high-temperature compression set measurement results for each example of the crosslinkable fluororubber composition. Examples 1, 2, 4, 5, 7, and 8 are examples, while Examples 3, 6, and 9 are comparative examples.

[0091]

[0092] As can be seen from the results shown in Table 1, the fluororubber obtained by secondary crosslinking under a gas atmosphere with a predetermined oxygen concentration is L ＊ a ＊ b ＊ a in the color system ＊ and b ＊It was observed that the material was prone to becoming larger, taking on a reddish and yellowish tint, and was resistant to cracking even under high-temperature compression (Examples 1, 2, 4, 5, 7, and 8). Furthermore, it was confirmed that a higher oxygen concentration in the gas atmosphere during secondary crosslinking made the fluororubber less prone to cracking, and in particular, the occurrence of cracks when it came into contact with stainless steel and was subjected to high-temperature compression was suppressed (Examples 1, 4, and 7).

Claims

1. A fluororubber that is a crosslinked product of a fluorine-containing copolymer, wherein the fluorine-containing copolymer has units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether), L ＊ a ＊ b ＊ a in the color system ＊ is 2.05 or higher, and b ＊ Fluororubber with a value of 2.05 or higher.

2. L ＊ a ＊ b ＊ L in the color system ＊ The fluororubber according to claim 1, wherein L is 12.0 or more.

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

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

5. The fluororubber according to claim 1, wherein the fluorine-containing copolymer is a perfluoropolymer.

6. The fluororubber according to claim 1, wherein the molar ratio of units based on tetrafluoroethylene to units based on perfluoro(alkyl vinyl ether) in the fluorine-containing copolymer is 60 / 40 to 80 / 20.

7. The fluororubber according to claim 1, 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.

8. A method for producing fluororubber, 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 a gas atmosphere with an oxygen concentration of 2.0 vol% or more and less than 20.9 vol% to crosslink the fluorine-containing copolymer.

9. The method for producing fluororubber according to claim 8, wherein the nitrogen concentration in the gas atmosphere is greater than 79.1 vol% and less than or equal to 98.0 vol%.

10. The method for producing fluororubber according to claim 8 or 9, wherein the step of crosslinking the fluorine-containing copolymer includes a heat treatment at 200 to 400°C for 1 minute to 48 hours.

11. A fluororubber article made of fluororubber as described in any one of claims 1 to 7.

12. The fluororubber article according to claim 11, wherein the compression set under holding conditions of 300°C, a compressibility of 25%, and 70 hours is 30% or less.

13. The fluororubber article according to claim 11, which is for use with stainless steel.

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