Rubber composition, fluoroelastomer, sealing material, and method for storing rubber composition

Abstract

The present invention addresses the problem of providing a rubber composition having excellent storage characteristics.　This rubber composition comprises (a) a crosslinking-reactive fluororubber and / or a crosslinking-reactive perfluororubber, (b) a crosslinking agent, and (c) a compound having a phenolic hydroxy group, wherein the crosslinking agent includes at least a compound represented by formula (1) (in formula (1), A is a single bond, -O-, an alkylene group, or a fluoroalkylene group; and R1, R2, and R3 are each independently a hydrogen atom, a fluorine atom, an alkyl group, or a fluoroalkyl group, with the proviso that at least one of R1, R2, and R3 is a fluorine atom or a fluoroalkyl group).

Description

Rubber composition, fluorine-containing elastomer, sealing material, and method for storing rubber composition

[0001] The disclosure in this application relates to a rubber composition having excellent storage properties, a fluorine-containing elastomer obtained by crosslinking the rubber composition, a sealing material, and a method for storing the rubber composition.

[0002] Fluorine-containing elastomers are mainly used for sealing materials that require plasma resistance. For example, Patent Document 1 describes a composition containing a perfluoroelastomer, 55 to 75 parts by weight of carbon black per 100 parts by weight of the perfluoroelastomer, and a crosslinking agent represented by the following formula (1):

[0003] Patent No. 7066010

[0004] A fluorine-containing elastomer such as a sealing member is formed by molding and crosslinking the rubber composition (hereinafter, this may be referred to as a "molded product"). Incidentally, in preparation for the occurrence of unexpected defective products, the rubber composition before crosslinking after the materials have been kneaded may be separated from the production line and stored. The separated and stored rubber composition before crosslinking (hereinafter, this may be referred to as a "stored product") is a precaution in case of unexpected defective products, so it is desirable that the separated rubber composition deteriorates little for about three months, preferably about six months, at room temperature.

[0005] The properties required for molded products vary depending on the user. For example, when carbon black is used to adjust the hardness, the molded product will be black, but in some cases, users may require a non-black molded product. However, the present inventors have newly discovered that when the compound represented by formula (1) is used as a crosslinking agent without using carbon black, a problem occurs in that the storage properties (pot life) of the stored product are deteriorated.

[0006] The present invention has been disclosed in order to solve the above-mentioned problems. As a result of intensive research, the present inventors have newly discovered that when the compound represented by formula (1) is used as a crosslinking agent, deterioration of storage properties of stored products caused by the compound represented by formula (1) can be suppressed by using the compound in combination with a compound containing a phenolic hydroxy group.

[0007] That is, an object of the disclosure of the present application is to provide a rubber composition, a fluorine-containing elastomer, a sealing material, and a method for storing a rubber composition, which have excellent storage properties.

[0008] The disclosure of the present application relates to a rubber composition, a fluorine-containing elastomer, a sealing material, and a method for storing a rubber composition, which are shown below.

[0009] (1) A rubber composition comprising: (a) a crosslinkable reactive fluororubber and / or a crosslinkable reactive perfluororubber; (b) a crosslinking agent; and (c) a compound containing a phenolic hydroxy group, wherein the crosslinking agent contains at least a compound represented by the following formula (1): (In formula (1), A is a single bond, —O—, an alkylene group, or a fluorinated alkylene group. R １ , R ２ , R ３ are each independently a hydrogen atom, a fluorine atom, an alkyl group, or a fluorinated alkyl group, provided that R １ , R ２ , R ３wherein at least one of the groups is a fluorine atom or a fluorinated alkyl group.) A rubber composition. (2) The rubber composition according to (1) above, wherein the compound containing a phenolic hydroxy group is dibutylhydroxytoluene. (3) The rubber composition according to (2) above, comprising: 0.5 to 20% by weight of the compound represented by formula (1); and 0.005 to 1% by weight of the dibutylhydroxytoluene, relative to 100 parts by weight of the component (a). (4) The rubber composition according to any one of (1) to (3) above, further comprising 30% by weight or less of an acid acceptor, relative to 100 parts by weight of the component (a). (5) The rubber composition according to any one of (1) to (4) above, further comprising a filler. (6) The rubber composition according to any one of (1) to (5) above, wherein the torque change rate after storage at 60°C for 22 days is less than -32.6%. (7) A fluorine-containing elastomer obtained by crosslinking the rubber composition according to any one of (1) to (6) above. (8) A sealing material comprising the fluorine-containing elastomer described in (7) above. (9) The fluorine-containing elastomer described in (7) above, which has a compression set of less than 80% when heated at 250°C for 336 hours. (10) A method for storing the rubber composition described in any one of (1) to (6) above, comprising: a kneading step of kneading the rubber composition; a separating step of separating the kneaded rubber composition; and a storage step of storing the rubber composition separated in the separating step.

[0010] By using the rubber composition disclosed in the present application, it is possible to suppress deterioration of storage properties of stored items caused by the compound represented by the above formula (1).

[0011] FIG. 1 is a graph showing the correlation between the torque reduction rate when a rubber composition is stored at room temperature and when it is stored at 60°C.

[0012] The rubber composition, the fluorine-containing elastomer, the sealing material, and the method for storing the rubber composition disclosed in the present application will be described in detail below.

[0013] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. Furthermore, in this specification, numerical values, numerical ranges, and qualitative expressions (e.g., expressions such as "same" and "the same") are to be interpreted as indicating numerical values, numerical ranges, and properties that include errors generally accepted in the technical field.

[0014] (Embodiment of Rubber Composition) A rubber composition according to an embodiment includes (a) a cross-linkable reactive fluororubber and / or a cross-linkable reactive perfluororubber, (b) a cross-linking agent, and (c) a compound containing a phenolic hydroxy group. The cross-linking agent includes at least a compound represented by the following formula (1). Each component will be described in detail below.

[0015] <Regarding Component (a)> First, the cross-linkable reactive fluororubber (hereinafter sometimes referred to as "FKM") and / or cross-linkable reactive perfluororubber (hereinafter sometimes referred to as "FFKM") that are component (a) will be described. When FKM and FFKM are collectively referred to as "fluorine-containing cross-linkable reactive rubber," they may be simply referred to as "fluorine-containing cross-linkable rubber."

[0016] "Crosslinking reactive" means a fluorine-containing rubber that can be crosslinked by a crosslinking reaction. The fluorine-containing crosslinking reactive rubber can contain, for example, a repeating unit derived from a fluorine-containing monomer. The fluorine-containing crosslinking reactive rubber can contain repeating units derived from one or more fluorine-containing monomers.

[0017] Examples of the fluorine-containing monomer include tetrafluoroethylene (TFE) represented by the following formula (a-1) and hexafluoropropylene (HFP) represented by the following formula (a-2): CF ２ =CF ２ (a-1) CF ２ =CFCF ３ (a-2)

[0018] Further, examples of the fluorine-containing monomer include perfluoroolefins having one ethylene-type unsaturated bond, preferably at a terminal position. Specific examples include perfluoroalkyl vinyl ethers (PAVEs) represented by the following formula (a-3), perfluorooxyalkyl vinyl ethers represented by the following formula (a-4), and perfluorovinyl ethers represented by the following formula (a-5).

[0019] CF ２ =CFOR ｆ１ (a-3) (In formula (a-3), R ｆ１ is a perfluoroalkyl having 1 to 6 carbon atoms, such as trifluoromethyl or pentafluoropropyl.

[0020] CF ２ =CFOR ｆ２ (a-4) (In formula (a-4), R ｆ２ is a perfluorooxyalkyl having 1 to 12 carbon atoms and containing one or more ether groups, such as perfluoro-2-propoxypropyl.

[0021] CF ２ = CFOCF ２ OR ｆ３ (a-5) (In formula (a-5), R ｆ３ is a straight-chain or branched perfluoroalkyl having 2 to 6 carbon atoms, a cyclic perfluoroalkyl having 5 or 6 carbon atoms, or a straight-chain or branched perfluorooxyalkyl having 2 to 6 carbon atoms and containing 1 to 3 oxygen atoms.

[0022] In one embodiment, the perfluorovinyl ether represented by formula (a-5) is represented by the following formula (a-6) or formula (a-7): The perfluorovinyl ether represented by formula (a-6) may be referred to as "MOVE1," and the perfluorovinyl ether represented by formula (a-7) may be referred to as "MOVE2."

[0023] CF ２ = CFOCF ２ OCF ２ CF ３ (a-6) CF ２ = CFOCF ２ OCF ２CF ２ OCF ３ (a-7) In one embodiment, the fluorine-containing crosslinkable reactive rubber may be a copolymer containing a repeating unit derived from one or more fluorine-containing monomers selected from the group consisting of formula (a-1) and formula (a-2) and a repeating unit derived from one or more fluorine-containing monomers (comonomers) selected from the group consisting of formula (a-3) to formula (a-5).

[0024] The composition (molar ratio) of the fluorine-containing monomers used to produce the fluorine-containing crosslinkable reactive rubber is not particularly limited.

[0025] In one embodiment, the fluorine-containing crosslinkable reactive rubber is produced using 50 to 85 mol % of one or more fluorine-containing monomers selected from the group consisting of formula (a-1) and formula (a-2), and 15 to 50 mol % of one or more fluorine-containing monomers selected from the group consisting of formula (a-3) to formula (a-5).

[0026] In one embodiment, the fluorine-containing crosslinkable reactive rubber is prepared using 50 to 85 mol % of TFE and 15 to 50 mol % of PAVE.

[0027] In one embodiment, the fluorine-containing cross-linkable reactive rubber is produced using 50 to 85 mol % of TFE and 15 to 50 mol % of MOVE, where "MOVE" is one or more selected from the group consisting of MOVE1 and MOVE2.

[0028] In one embodiment, the fluorine-containing crosslinkable reactive rubber may or may not contain units derived from vinylidene fluoride.

[0029] In this specification, FKM refers to a rubber containing hydrogen in its chemical structure among the above-mentioned fluorine-containing cross-linking reactive rubbers. Examples of FKM include fluororubbers (FKM) such as vinylidene fluoride / hexafluoropropylene copolymer (binary FKM), vinylidene fluoride / hexafluoropropylene / tetrafluoroethylene copolymer (ternary FKM), vinylidene fluoride / hexafluoropropylene / perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene / propylene copolymer, hexafluoropropylene / ethylene copolymer, tetrafluoroethylene / ethylene / perfluoroalkyl vinyl ether copolymer, and vinylidene fluoride / 2,3,3,3-tetrafluoropropylene, but are not limited thereto.

[0030] In this specification, FFKM refers to the above-mentioned fluorine-containing cross-linking reactive rubber that does not contain hydrogen in its chemical structure. Examples of FFKM include perfluororubbers such as tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (FFKM), but are not limited thereto.

[0031] FKM is inexpensive and has a certain degree of plasma resistance and heat resistance. On the other hand, FFKM is more expensive than FKM but has higher plasma resistance than FKM. Therefore, depending on the properties required for the molded product, only FKM may be used, only FFKM may be used, or a mixture of FKM and FFKM may be used. When a mixture of FKM and FFKM is used, there are no particular restrictions on the blending ratio, which may be adjusted appropriately depending on the required plasma resistance properties, etc.

[0032] In one embodiment, the fluorine-containing crosslinkable reactive rubber may or may not contain units derived from a fluoroolefin having 3 to 8 carbon atoms containing iodine and / or bromine. When the fluorine-containing crosslinkable reactive rubber contains such units, it preferably contains iodine and / or bromine, more preferably iodine, as a radical attack site during crosslinking (curing). Fluorine-containing crosslinkable reactive rubbers that can be cured with peroxides are described, for example, in JP 2006-9010 A. When the fluorine-containing crosslinkable reactive rubber contains such units, it generally contains 0.001 wt % to 5 wt %, preferably 0.01 wt % to 2.5 wt %, of iodine relative to the total polymer weight. The iodine atoms may be present along the chain and / or at the terminal positions of the fluorine-containing crosslinkable reactive rubber.

[0033] <Regarding Component (b)> The crosslinking agent that is component (b) contains at least a compound represented by the following formula (1).

[0034] In the above formula (1), A is a single bond, —O—, an alkylene group, or a fluorinated alkylene group, preferably a single bond, an alkylene group, or a fluorinated alkylene group, and more preferably a fluorinated alkylene group.

[0035] The alkylene group of the alkylene group or fluorinated alkylene group may be linear or branched, and preferably has 1 to 15 carbon atoms (more preferably 2 to 8 carbon atoms, and even more preferably 3 to 6 carbon atoms). The alkylene group of the fluorinated alkylene group may be partially or completely fluorinated. A perfluoroalkylene group is preferred.

[0036] Examples of the alkylene group include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, and a peptylene group.

[0037] In the above formula (1), R １ , R ２ , R ３ are each independently a hydrogen atom, a fluorine atom, an alkyl group, or a fluorinated alkyl group, provided that R １ , R ２ , R ３At least one of is a fluorine atom or a fluorinated alkyl group.

[0038] The alkyl group of the alkyl group or fluorinated alkyl group may be linear or branched, and preferably has 1 to 15 carbon atoms (more preferably 1 to 6 carbon atoms, and even more preferably 1 to 4 carbon atoms). The fluorinated alkyl group may be partially or completely fluorinated. A perfluoroalkyl group is preferred.

[0039] Examples of the alkyl group include a methyl group, an ethyl group, and a propyl group.

[0040] R １ , R ２ , R ３ are preferably each independently a hydrogen atom or a fluorine atom.

[0041] -CR １ =CR ２ R ３ Examples of the groups include the following:

[0042] In the above formula (1), A and -CR １ =CR ２ R ３ may be at any of the ortho, meta or para positions, but is preferably at the para position, and A and two -CR １ =CR ２ R ３ However, it is more preferable that both are in the para position.

[0043] Specific examples of the compound represented by the formula (1) include compounds represented by the following formulas (2) to (4). In the above formula, R １ , R ２ , R ３ is the same as above. t is preferably 1 to 15 (more preferably 2 to 8, and even more preferably 3 to 6).

[0044] Specific examples of the compound represented by the above formula (1) include the following compounds: These compounds can be synthesized, for example, by referring to WO2016 / 017187.

[0045] The crosslinking agent may be one of the compounds exemplified above, or two or more may be used in combination. The lower limit of the amount of crosslinking agent is not particularly limited as long as it is an amount that can crosslink the component (a). Examples of lower limits based on 100 parts by weight of component (a) include, but are not limited to, 0.5% by weight or more, 1.0% by weight or more, 1.5% by weight or more, 2.0% by weight or more, 2.5% by weight or more, 3.0% by weight or more, 3.5% by weight or more, 4.0% by weight or more, 4.5% by weight or more, and 5.0% by weight or more. On the other hand, the greater the amount of crosslinking agent, the more improved the steam resistance and heat resistance tend to be. However, if the amount is too much, the composition may become hard. Therefore, although not limited thereto, examples of the upper limit relative to 100 parts by weight of component (a) include 20% by weight or less, 19% by weight or less, 18% by weight or less, 17% by weight or less, 16% by weight or less, 15% by weight or less, 14% by weight or less, 13% by weight or less, 12% by weight or less, 11% by weight or less, and 10% by weight or less.

[0046] The rubber composition according to the embodiment may contain other crosslinking agents as long as it contains at least the compound represented by formula (1) as a crosslinking agent. Examples of crosslinking agents other than the compound represented by formula (1) include, but are not limited to, triallyl isocyanurate. When the compound represented by formula (1) is used in combination with other crosslinking agents, the amount of the crosslinking agent used in combination should be the amount of the crosslinking agent described above.

[0047] <Regarding Component (c)> The compound containing a phenolic hydroxy group (hereinafter, may be referred to as "compound C") which is component (c) is not particularly limited as long as its use in combination with the compound represented by formula (1) suppresses deterioration of the storage properties of the stored product caused by the compound represented by formula (1). Examples of the compound include, but are not limited to, a compound containing two phenolic hydroxy groups and a compound containing one phenolic hydroxy group.

[0048] The compound containing two phenolic hydroxy groups includes a compound represented by the following formula (2).

[0049] R in the above formula (2) １, R ２ are each independently a hydrogen atom, an organic group having 1 to 12 carbon atoms, or a fluorine-containing organic group having 1 to 12 carbon atoms. The organic group having 1 to 12 carbon atoms and the fluorine-containing organic group having 1 to 12 carbon atoms may be linear, branched, or cyclic, and may or may not contain an unsaturated bond. １ , R ２ When one of R is bonded to the basic skeleton of formula (2) via an unsaturated bond, R １ , R ２ The other is not included.

[0050] Examples of the compound represented by formula (2) include, but are not limited to, bisphenol A, bisphenol AF, bisphenol AP, bisphenol C, bisphenol F, and the like.

[0051] The compound containing one phenolic hydroxy group includes a compound represented by the following formula (3).

[0052] R in the above formula (3) １ , R ２ , R ３ are each independently a hydrogen atom, an organic group having 1 to 12 carbon atoms, or a fluorine-containing organic group having 1 to 12 carbon atoms. The organic group having 1 to 12 carbon atoms and the fluorine-containing organic group having 1 to 12 carbon atoms may be linear, branched, or cyclic, and may or may not contain an unsaturated bond. Furthermore, the organic group having 1 to 12 carbon atoms and the fluorine-containing organic group having 1 to 12 carbon atoms may contain a carboxylic acid derivative.

[0053] Examples of the compound represented by formula (3) include, but are not limited to, dibutylhydroxytoluene (BHT), phenol, p-cresol, m-cresol, o-cresol, p-phenylphenol, m-phenylphenol, o-phenylphenol, allylphenol, p-hydroxybenzoic acid, and methyl p-hydroxybenzoate. There are no particular restrictions on the amount of compound C, as long as it is within a range that can suppress deterioration of the storage characteristics of the stored product. Examples of the amount of compound C, per 100 parts by weight of component (a), include, but are not limited to, lower limits of 0.005 wt % or more, 0.0075 wt % or more, 0.01 wt % or more, 0.015 wt % or more, 0.02 wt % or more, 0.025 wt % or more, 0.03 wt % or more, 0.035 wt % or more, 0.04 wt % or more, and 0.045 wt % or more. On the other hand, as shown in the examples below, increasing the compounding amount of compound C increases T90 (the time required to reach 90% of MH (maximum torque)), which is an indicator of rubber molding time. In other words, the production cycle becomes longer, which reduces production efficiency and increases costs. Therefore, the upper limit of compound C may be set from a cost perspective rather than a technical perspective. Examples of upper limits, relative to 100 parts by weight of component (a), include, but are not limited to, 1% by weight or less, 0.9% by weight or less, 0.8% by weight or less, 0.7% by weight or less, 0.6% by weight or less, 0.5% by weight or less, 0.4% by weight or less, 0.3% by weight or less, 0.2% by weight or less, and 0.1% by weight or less. It is presumed that the combined use of compound C and the compound represented by formula (1) suppresses deterioration of storage properties of stored products caused by the compound represented by formula (1) because compound C functions as an antioxidant and scorch retarder by capturing radicals.

[0054] The rubber composition disclosed in the present application can suppress deterioration of storage characteristics of stored products caused by the compound represented by formula (1). In other words, it exhibits the effect of excellent storage characteristics. In this specification, "storage characteristics" refers to the torque change rate of a rubber composition when stored at 60°C for 22 days, based on the torque of the rubber composition immediately after dispensing (storage day 0). In this specification, "capable of suppressing deterioration of storage characteristics" means that the torque change rate is less than -32.6%. If the torque drops significantly, the crosslink density decreases, which may result in molding defects (poor shape, sticking to the mold, etc.) and insufficient heat resistance. However, if the torque change rate is less than -32.6%, the likelihood of molding defects or poor heat resistance is reduced. There are no particular restrictions on the storage characteristics as long as the torque change rate is less than -32.6%, but a smaller torque change rate is preferable. Without being limited thereto, the torque change rate of the rubber composition when stored at 60°C for 22 days may be less than -30%, less than -28%, less than -26%, less than -24%, less than -22%, less than -20%, less than -18%, less than -16%, less than -14%, less than -12%, less than -10%, less than -8%, less than -6%, less than -4%, less than -2%, and the like.

[0055] <Regarding optional additional components that may be contained in the rubber composition> Next, optional additional components that may be contained in the rubber composition will be described. (d) Acid Acceptor The rubber composition may contain an acid acceptor. There are no particular restrictions on the acid acceptor as long as it is one that is commonly used in the technical field, and examples thereof include primary amines, secondary amines, tertiary amines, inorganic acid acceptors, etc. Specific examples of any of the primary amine, secondary amine, and tertiary amine include melamine cyanurate (MC), melamine, 1,4-diazabicyclo[2.2.2]octane (DABCO), 1,8-diazabicyclo[5.4.0]undec-7-ene, and 2,2,6,6-tetramethyl-4-piperidone. Specific examples of the inorganic acid acceptor include zinc(II) oxide, calcium(II) oxide, and magnesium(II) oxide.

[0056] As shown in the examples below, when the amount of compound C is small, adding an acid acceptor improves the storage properties of the stored product. The amount of acid acceptor added is not particularly limited as long as it is within a range that improves the storage properties of the stored product. Examples of the amount of acid acceptor added, based on 100 parts by weight of component (a), include, but are not limited to, 30% by weight or less, 28% by weight or less, 26% by weight or less, 24% by weight or less, 22% by weight or less, 20% by weight or less, 18% by weight or less, 16% by weight or less, 14% by weight or less, 12% by weight or less, 10% by weight or less, 8% by weight or less, 6% by weight or less, 4% by weight or less, 2% by weight or less, 1% by weight or less, 0.8% by weight or less, and 0.6% by weight or less. While compound C improves the storage properties of the rubber composition, it also scavenges radicals generated from peroxides during molding, inhibiting the crosslinking reaction. Therefore, using a large amount of compound C may result in molding defects. When compound C and an acid acceptor are used in combination, synergistic effects are achieved in that the storage properties of the rubber composition are improved with a small amount of compound C, and the possibility of molding defects occurring is reduced by being able to reduce the amount of compound C.

[0057] (e) Co-Crosslinking Agent The rubber composition may contain a co-crosslinking agent. Examples of co-crosslinking agents that can be used include known agents used for crosslinking fluorine-based elastomers. Examples include triallyl isocyanurate (TAIC), triallyl cyanurate, triallyl trimellitate, N,N'-m-phenylenedimaleimide, and trimethylolpropane trimethacrylate. Other examples include acrylate and methacrylate monomers. TAIC is a liquid. TAIC may be used as is, or in a mixed form (e.g., TAICWH-60) with a powder such as silica to facilitate mixing with other components. In this case, the TAIC component in the mixed form functions as a co-crosslinking agent, and the powder component such as silica functions as a filler, as described below. Liquid co-crosslinking agents other than TAIC may also be used in a mixed form.

[0058] Furthermore, as the co-crosslinking agent, a compound represented by the following formula (e-1) and / or a compound represented by the following formula (e-2) may be used. (In formula (e-1), A is a single bond, —O—, —S—, a heteroatom-containing group, a linear or branched alkylene group, a cycloalkylene group, or an arylene group, and in these groups, no hydrogen atoms are substituted with fluorine atoms, or some or all of the hydrogen atoms are substituted with fluorine atoms. R １ , R ２ , R ３ and R ４ are each independently a hydrogen atom, a fluorine atom, an alkyl group, a fluorinated alkyl group, or a substituted or unsubstituted aryl group. １ are the same or different. ２ are the same or different. ３ are the same or different. ４ are the same or different. １ , R ２ and R ３ At least one of is a fluorine atom or a group containing a fluorine atom. m is an integer of 1 to 5. n is an integer of 1 to 5.

[0059] (In formula (e-2), n and m are each 0 or 1. t is an integer of 2 or more. Z is a t-valent linking group.)

[0060] Detailed descriptions of the compounds described in the above formulas (e-1) and (e-2) are described in WO 2021 / 230231. Therefore, in this specification, descriptions of the above formulas (e-1) and (e-2) are omitted. The disclosures of WO 2021 / 230231 are incorporated herein by reference. The above co-crosslinking agents may be used alone or in combination of two or more.

[0061] (f) Filler The rubber composition according to the embodiment may contain a filler. Fillers known in the field of fluorine-based elastomers can be used as the filler. Examples of fillers include, but are not limited to, carbon black, silica, calcium carbonate, clay, wollastonite, mica, talc, and barium sulfate. The problem of the present application is solved by using the compound represented by formula (1) in combination with compound C in the rubber composition according to the embodiment. As long as the problem of the present application is solved, carbon black may be added to the rubber composition according to the embodiment, for example, to color or adjust the hardness of a molded product. In other words, the rubber composition according to the embodiment may or may not contain carbon black, as long as the compound represented by formula (1) and compound C are included as essential features of the invention.

[0062] (g) Other Components Examples of optional additional components other than those described in (d) to (f) above include initiators such as dicumyl peroxide, di-t-butylperoxydiisopropylbenzene, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, thickeners, pigments, coupling agents, stabilizers, etc. As the optional additional components exemplified above, materials known in the field of fluorine-based elastomers can be used.

[0063] (Embodiments of Fluorine-Containing Elastomer) The fluorine-containing elastomer according to the embodiment can be produced by crosslinking the rubber composition according to any embodiment disclosed in the present application. The conditions for crosslinking the rubber composition (crosslinking conditions) are not particularly limited, and for example, the rubber composition may be heated at 100 to 250°C for 10 minutes to 5 hours. Typically, the raw material (rubber composition) is placed in a mold and crosslinked while being pressed, as the primary crosslinking. The primary crosslinking is performed, for example, by heating at 150 to 200°C for 5 to 60 minutes. The composition is then removed from the mold and subjected to secondary crosslinking in air or an inert gas atmosphere. The secondary crosslinking is performed, for example, by heating at 150 to 300°C for 1 to 100 hours. Crosslinking can be performed using an electric furnace or the like. By providing a thermal history during secondary crosslinking, deformation during use can be prevented. Radiation treatment is not necessarily required for crosslinking, and it is preferable to omit radiation treatment. The rubber composition used to produce the fluorine-containing elastomer according to the embodiment may or may not have been stored. In this specification, the term "rubber composition" refers to a composition that has been stored or not, provided that it is not crosslinked.

[0064] (Embodiments of Sealing Material) A sealing material according to an embodiment comprises a fluorine-containing elastomer according to any of the embodiments disclosed in the present application. The form of the sealing material is not particularly limited, and examples thereof include molded articles such as gaskets and seal rings. The uses of the sealing material are not particularly limited, and it can be widely applied to various devices. However, the sealing material disclosed in the present application has excellent plasma resistance and can be made relatively hard, and is therefore suitable as a sealing material for, for example, semiconductor manufacturing equipment. Examples of semiconductor manufacturing equipment include plasma equipment, etching equipment, and plasma CVD equipment.

[0065] (Embodiment of Storage Method) A storage method according to an embodiment is a method for storing a rubber composition according to any of the embodiments disclosed in the present application. The storage method includes a kneading step of kneading the rubber composition, a separating step of separating the kneaded rubber composition, and a storage step of storing the rubber composition separated in the separating step. The storage step may be performed at room temperature (23±2°C).

[0066] The following examples are provided to specifically explain the embodiments disclosed in the present application, but these examples are merely for the purpose of explaining the embodiments and are not intended to limit or restrict the scope of the invention disclosed in the present application.

[0067] <Materials> The materials used in the examples and comparative examples are as follows. (a) Component (FKM, FFKM) FKM: Daiel G912, manufactured by Daikin Industries, Ltd. FFKM: AFLAS (registered trademark) Premium PM3000, manufactured by AGC Inc. FFKM: LJ213091, manufactured by 3M Japan Ltd. (b) Component (Crosslinking Agent) Compound represented by formula (1): The following compound was synthesized in-house. In the tables below, this compound is referred to as FN-10. Component (c) (compound containing a phenolic hydroxy group) BHT: 2,6-di-t-butyl-p-cresol manufactured by Nacalai Tesque, Inc. Component (d) (acid acceptor) Melamine cyanurate: MC6000 manufactured by Nissan Chemical Industries, Ltd. Melamine: melamine manufactured by Nacalai Tesque, Inc. DABCO: triethylenediamine manufactured by Nacalai Tesque, Inc. Component (e) (co-crosslinking agent) TAICWH-60: Taik WH-60 manufactured by Mitsubishi Chemical Corporation Component (f) (filler) Aerosil R972: Nippon Aerosil Co., Ltd. Component (g) (initiator) Perhexa 25B: manufactured by NOF Corporation

[0068] <Preparation of Rubber Compositions> Rubber compositions were prepared by kneading materials in the blending ratios (weight ratios) shown in Tables 1 to 7 below using an open roll.

[0069] The obtained rubber compositions were evaluated as follows. (1) Torque Measurement Measurement was performed using a rubber vulcanization tester (Premier MDR) manufactured by Alpha Technologies under the following conditions: Measurement conditions: 155°C x 30 min Angle: 0.5° a: Maximum torque (MAX [dNm]) b: Optimum vulcanization point (T90 [min], time to reach 90% of the maximum torque)

[0070] (2) Torque Change Rate The torque change rate was calculated by the following formula, where the measured value of the maximum torque of the rubber composition immediately after dispensing (storage day 0) measured by the method in (1) above is defined as A, and the measured value after storage for a predetermined number of days is defined as B. The storage was carried out at 60°C for 7 days, 14 days, and 22 days, and at room temperature for 14 days, 59 days, and 92 days.

[0071] (3) Heat Resistance CS% (3-1) Sample Preparation Method The above-mentioned materials were molded at 155°C for 15 minutes and subjected to secondary crosslinking at 160°C for 15 hours to prepare samples (O-rings). (3-2) Experimental Method The obtained O-rings were cut into 30 mm lengths to prepare test specimens. These specimens were then bolted together using two flat plates and a spacer to compress the specimen by 25%. The test specimens were then subjected to heat exposure in a gear oven under specified conditions (atmospheric environment, 200 and 250°C for 70 minutes, 336 hours). The specimens were then removed from the gear oven, opened while still hot, and allowed to cool to room temperature. The wire diameter was measured, and the permanent compression set was calculated using the following formula (unit: %). This permanent compression set was taken as heat resistance. Compression set = (initial wire diameter - wire diameter after heat exposure) / (initial wire diameter - spacer thickness) x 100

[0072] [Correlation between storage at room temperature and storage at 60°C] Example 1, Comparative Example 1 The correlation between the torque reduction rate when the extracted rubber composition was stored at room temperature and when it was stored at 60°C was investigated. Table 1 shows the formulation of the rubber composition used in the experiment. Tables 2 and 3 show the maximum torque and the rate of change in maximum torque when stored for a specified number of days at room temperature and 60°C. A graph prepared based on the results in Table 2 is shown in Figure 1.

[0073] As is clear from Tables 2 and 3 and Figure 1, the maximum torque of the extracted rubber composition decreased almost linearly with increasing storage time, whether it was stored at room temperature or at 60°C. The torque decrease rate after 22 days of storage at 60°C was approximately -55%, and as is clear from Figure 1, it took at least 92 days or more for the torque decrease rate after storage at room temperature to exceed -55%. Therefore, it was confirmed that storage of the rubber composition at 60°C for 22 days was equivalent to storage at room temperature for at least three months or more. As described above, it is generally required that the extracted rubber composition can be stored at room temperature for approximately three months. Therefore, in the following experiment, from the perspective of experimental efficiency, the characteristics of the rubber composition after storage at 60°C for 22 days were examined.

[0074] [Types of cross-linkable reactive rubbers and blending ratios of BHT and acid acceptor] <Examples 2 to 7, Comparative Examples 2 and 3> Rubber compositions were prepared in the same manner as in Example 1 above, except that the blends shown in the following Table 4 were used, and the torque change rate was examined. The results of the torque change rate are also shown in Table 4.

[0075] As shown in Table 4, in both cases where the fluorine-containing cross-linked reactive rubber was FFKM (Examples 2 to 5) and FKM (Examples 6 to 7), the combined use of the compound represented by formula (1) and BHT improved storage properties compared to Comparative Examples 2 and 3, in which BHT was not used. Compared to FFKM, the storage properties of FKM were improved even with a smaller blend amount of BHT. Furthermore, the results of Examples 2 to 5 confirmed that the greater the blend amount of BHT, the better the storage properties. Furthermore, the results of Examples 4-5 and 6-7 confirmed that the combined use of BHT and an acid acceptor further improved storage properties.

[0076] [Regarding the type of acid acceptor] <Examples 8 to 10> Rubber compositions were prepared in the same manner as in Example 1 above, except that the formulations shown in Table 5 below were used, and the torque change rate was examined. The results of the torque change rate and color tone are also shown in Table 5. For comparison, the results of Example 3 are also shown.

[0077] As shown in Table 5, it was confirmed that the storage properties of the rubber composition were improved by using BHT in combination with any acid acceptor, regardless of the type of acid acceptor. In addition, in Examples 3 and 8 to 10, the color tone was not black because carbon black was not used, and it was confirmed that the color tone of the rubber composition could be adjusted by the type of acid acceptor used.

[0078] [Effect of Including Acid Acceptor] <Examples 11 and 12> Rubber compositions were prepared in the same manner as in Example 1, except that the formulations shown in Table 6 below were used, and heat resistance was examined in the same manner as in "(3) Heat Resistance CS%" above. The heat resistance results are also shown in Table 6.

[0079]

[0080] The higher the heat resistance CS [%] value shown in Table 6, the lower the heat resistance, and generally, if it exceeds 80%, the sealability is rated as x. As is clear from Table 6, the heat resistance CS [%] value of Example 12, in which MC6000 as an acid acceptor was added, was lower than the value of Example 11, in which MC6000 was not added. From the above results, it was confirmed that the acid acceptor exerts two different effects at the same time, namely, improving the storage properties of the rubber composition and improving the heat resistance of the molded article obtained by crosslinking the rubber composition.

[0081] [Relationship between BHT Amount and T90] Example 13 Rubber compositions were prepared in the same manner as in Example 1, except that the amount of BHT in Example 1 was changed to the weight shown in Table 7, and T90 [min] was measured. The results of T90 [min] are also shown in Table 7.

[0082] As is clear from Table 7, the T90 time increased as the compounded amount of BHT increased. Therefore, it was confirmed that the upper limit of the compounded amount of BHT in the rubber composition disclosed in the present application may be appropriately set from the viewpoint of production efficiency, not from the viewpoint of technical aspects.

[0083] The rubber composition disclosed in the present application has improved storage properties, and therefore, even if a defective product is suddenly produced, molded products can be provided using the same rubber composition lot. Therefore, the rubber composition disclosed in the present application is useful in the sealing material industry, which requires plasma resistance and a predetermined hardness, and in the semiconductor industry, such as in plasma processing equipment and semiconductor manufacturing equipment, which use the sealing material.

Claims

1. A rubber composition comprising: (a) a crosslinkable reactive fluororubber and / or a crosslinkable reactive perfluororubber; (b) a crosslinking agent; and (c) a compound containing a phenolic hydroxy group, wherein the crosslinking agent contains at least a compound represented by the following formula (1): (In formula (1), A is a single bond, —O—, an alkylene group, or a fluorinated alkylene group. R １ , R ２ , R ３ are each independently a hydrogen atom, a fluorine atom, an alkyl group, or a fluorinated alkyl group, provided that R １ , R ２ , R ３ At least one of the groups is a fluorine atom or a fluorinated alkyl group.

2. The rubber composition according to claim 1, wherein the compound containing a phenolic hydroxy group is dibutylhydroxytoluene.

3. The rubber composition according to claim 2, comprising, relative to 100 parts by weight of component (a), 0.5 to 20% by weight of the compound represented by formula (1), and 0.005 to 1% by weight of dibutylhydroxytoluene.

4. The rubber composition according to claim 1, further comprising 30% by weight or less of an acid acceptor per 100 parts by weight of said component (a).

5. The rubber composition according to claim 2, further comprising 30% by weight or less of an acid acceptor per 100 parts by weight of said component (a).

6. The rubber composition according to claim 3, further comprising 30% by weight or less of an acid acceptor per 100 parts by weight of said component (a).

7. The rubber composition according to any one of claims 1 to 6, further comprising a filler.

8. The rubber composition according to any one of claims 1 to 6, wherein the rate of change in torque after storage at 60°C for 22 days is less than -32.6%.

9. A fluorine-containing elastomer obtained by crosslinking the rubber composition according to any one of claims 1 to 6.

10. A fluorine-containing elastomer obtained by crosslinking the rubber composition according to claim 7.

11. A sealing material comprising the fluorine-containing elastomer according to claim 9.

12. A sealing material comprising the fluorine-containing elastomer according to claim 10.

13. The fluorine-containing elastomer according to claim 9, which has a compression set of less than 80% when heated at 250°C for 336 hours.

14. A method for storing a rubber composition according to any one of claims 1 to 6, comprising: a kneading step of kneading the rubber composition; a separating step of separating the kneaded rubber composition; and a storage step of storing the rubber composition separated in the separating step.

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