Rubber composition, fluorine-containing elastomer, and sealing material

Abstract

The present invention addresses the problem of providing: a novel rubber composition for producing a sealing material that has a specific plasma resistance and a specific hardness; a fluorine-containing elastomer that is obtained by crosslinking the rubber composition; and a sealing material that contains the fluorine-containing elastomer.　The problem can be solved by a rubber composition which contains (a) a crosslinking reactive fluorine rubber, (b) a crosslinking reactive perfluoro rubber, (c) a fluorine oligomer that has a perfluoro skeleton, and (d) a fluororesin.

Description

Rubber composition, fluorine-containing elastomer and sealing material

[0001] The disclosure of the present application relates to a sealing material used in a portion where plasma resistance is required, and a rubber composition and a fluorine-containing elastomer for forming the sealing material.

[0002] Fluorine-containing elastomers are mainly used for sealing materials that require plasma resistance. While the sealing material is required to be plasma resistant, it is also required to have a predetermined hardness. Patent Document 1 discloses that by using (a) a cross-linkable reactive fluororubber or (b) a cross-linkable reactive perfluororubber as a rubber component, adding (c) a fluorooligomer with a perfluoro skeleton, and further combining it with a newly developed cross-linking agent, it is possible to provide a sealing material that has a predetermined hardness while maintaining plasma resistance.

[0003] International Publication No. 2021 / 230231

[0004] However, the invention described in Patent Document 1 requires the use of an expensive crosslinking agent to achieve a predetermined hardness of the sealing material. In actual manufacturing sites, products must be manufactured while taking into consideration various factors such as the cost and availability of materials. Therefore, there is a need to develop a new rubber composition for manufacturing a sealing material having a predetermined plasma resistance and a predetermined hardness.

[0005] The present invention has been disclosed in order to solve the above-mentioned problems. As a result of extensive research, the present inventors have newly discovered that the above-mentioned problems can be solved by using a combination of (a) a cross-linkable reactive fluororubber, (b) a cross-linkable reactive perfluororubber, (c) a fluorooligomer having a perfluoro skeleton, and (d) a fluororesin.

[0006] That is, an object of the disclosure of the present application is to provide a new rubber composition for producing a sealing material having predetermined plasma resistance and predetermined hardness, a fluorine-containing elastomer obtained by crosslinking the rubber composition, and a sealing material containing the fluorine-containing elastomer.

[0007] The disclosure of the present application relates to a rubber composition, a fluorine-containing elastomer, and a sealing material, which are shown below.

[0008] (1) A rubber composition comprising (a) a crosslinkable fluororubber, (b) a crosslinkable perfluororubber, (c) a fluorooligomer having a perfluoro skeleton, and (d) a fluororesin. (2) The rubber composition according to (1) above, in which the (c) component is contained in an amount of 0.1 phr or more and 40 phr or less per 100 phr of the rubber components (a) and (b). (3) The rubber composition according to (1) above, in which the weight ratio of the (d) component to the (c) component is 0.1 or more. (4) The rubber composition according to (2) above, in which the weight ratio of the (d) component to the (c) component is 0.1 or more. (5) The rubber composition according to (1) above, in which the weight ratio of the (d) component to the (b) component is 0.1 or more and 2 or less. (6) The rubber composition according to (2) above, in which the weight ratio of the (d) component to the (b) component is 0.1 or more and 2 or less. (7) The rubber composition according to (3) above, wherein the weight ratio of component (d) / component (b) is 0.1 or more and 2 or less. (8) The rubber composition according to (4) above, wherein the weight ratio of component (d) / component (b) is 0.1 or more and 2 or less. (9) A fluorine-containing elastomer obtained by crosslinking the rubber composition according to any one of (1) to (8) above. (10) The fluorine-containing elastomer according to (9) above, wherein component (a) and component (b) are incompatible with each other and have a phase-separated structure, component (d) is dispersed in component (b), and when the component (d) dispersed in component (b) is compared with the component (d) not dispersed in component (b), the component (d) dispersed in component (b) is greater in amount. (11) A sealing material comprising the fluorine-containing elastomer according to (9) above. (12) A surface wave plasma etching apparatus is used to obtain a fluorine-containing elastomer having a gas flow rate of O ２ (2000sccm)+CF ４ (11) The fluorine-containing elastomer according to (10) above, which has a weight loss rate of 2% or less when exposed to plasma under conditions of a pressure of 40 sscm, a treatment pressure of 133 Pa, an output of 3 kW and an exposure time of 2 hours.

[0009] By using the rubber composition disclosed in the present application, a fluorine-containing elastomer having a predetermined plasma resistance and a predetermined hardness, and a sealing material containing the fluorine-containing elastomer can be obtained.

[0010] FIG. 1 is a photograph, substituted for a drawing, of the molded bodies (O-rings) produced in Comparative Examples 1 to 3. Lane A is a photograph before plasma irradiation, Lane B is a photograph after 2 hours of plasma irradiation, and Lane C is a photograph of the molded body transferred after 2 hours of plasma irradiation. FIG. 2 is a photograph, substituted for a drawing, of the molded bodies (O-rings) of Comparative Example 4 and Example 1. Lane A is a photograph before plasma irradiation, and Lane B is a photograph after 5 hours of plasma irradiation. FIG. 3 is a photograph, substituted for a drawing, of the cross section of the molded body of Example 4, where the elastic modulus was mapped using a scanning probe microscope (SPM).

[0011] The rubber composition, the fluorine-containing elastomer, and the sealing material disclosed in the present application will be described in detail below.

[0012] 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.

[0013] (Embodiment of Rubber Composition) A rubber composition according to an embodiment includes (a) a cross-linkable reactive fluororubber, (b) a cross-linkable reactive perfluororubber, (c) a fluorooligomer having a perfluoro skeleton, and (d) a fluororesin.

[0014] <Regarding Component (a) and Component (b)> First, the cross-linkable reactive fluororubber (hereinafter sometimes referred to as "FKM") which is component (a) and the cross-linkable reactive perfluororubber (hereinafter sometimes referred to as "FFKM") which is component (b) will be described. When FKM and FFKM are collectively referred to, they may be simply referred to as "fluorine-containing cross-linkable reactive rubber."

[0015] "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.

[0016] 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)

[0017] 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).

[0018] 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.

[0019] 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.

[0020] CF ２ = CFOCF ２ OR ｆ３ (a-5) (In formula (a-5), R ｆ３is a linear or branched perfluoroalkyl having 2 to 6 carbon atoms, a cyclic perfluoroalkyl having 5 or 6 carbon atoms, or a linear or branched perfluorooxyalkyl having 2 to 6 carbon atoms and containing 1 to 3 oxygen atoms.

[0021] 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."

[0022] CF ２ = CFOCF ２ OCF ２ CF ３ (a-6) CF ２ = CFOCF ２ OCF ２ CF 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).

[0023] The composition (molar ratio) of the fluorine-containing monomers used to produce the fluorine-containing crosslinkable reactive rubber is not particularly limited.

[0024] 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).

[0025] 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.

[0026] 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.

[0027] In one embodiment, the fluorine-containing crosslinkable reactive rubber may or may not contain units derived from vinylidene fluoride.

[0028] 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.

[0029] 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.

[0030] FKM is inexpensive and has a certain degree of plasma resistance and heat resistance, but when higher plasma resistance is required, it is mixed with FFKM. The rubber composition according to the embodiment contains FKM and FFKM as essential components. Note that FKM and FFKM are incompatible. Therefore, FKM and FFKM form a phase-separated structure such as a sea-island structure or a co-continuous structure depending on the compounding ratio.

[0031] As described above, FKM contains hydrogen in its chemical structure. On the other hand, FFKM does not contain hydrogen in its chemical structure and contains more fluorine than FKM. Therefore, FFKM has better plasma resistance than FKM. Furthermore, FKM and FFKM are not compatible due to differences in properties based on differences in chemical structure, resulting in a phase-separated structure as described above. As the proportion of FFKM among the rubber components (FKM and FFKM) contained in the fluorine-containing elastomer increases, plasma resistance and heat resistance improve, but FFKM is more expensive than FKM, resulting in increased costs. The proportion of FKM and FFKM in the fluorine-containing cross-linking reactive rubber may be appropriately set taking into consideration the properties and cost required of the fluorine-containing elastomer. Although not limited thereto, for example, the proportion of FKM per 100 phr of the fluorine-containing cross-linking reactive rubber may be 0.1 to 99.9 phr. From the viewpoint of cost rather than technical viewpoint, the ratio of FKM to 100 phr of the fluorinated cross-linking reactive rubber may be set to 50.1 to 99.9. Note that, although a specific numerical range is not described, any single decimal place number within the range of 0.1 to 99.9 may be selected to specify the range, such as a to b.

[0032] In the fluorine-containing elastomer disclosed in the present application, the FFKM also functions as a phase for dispersing the fluororesin, which is a filler for increasing hardness.

[0033] In one embodiment, the fluorine-containing cross-linking 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 cross-linking reactive rubber contains such units, it preferably contains iodine and / or bromine, more preferably iodine, as a radical attack site during cross-linking (curing). Fluorine-containing cross-linking reactive rubbers that can be cured with peroxides are described, for example, in JP 2006-9010 A. When the fluorine-containing cross-linking reactive rubber contains such units, it generally contains 0.001% by mass to 5% by mass, preferably 0.01% by mass to 2.5% by mass, of iodine relative to the total polymer mass. The iodine atoms may be present along the chain and / or at the terminal positions of the fluorine-containing cross-linking reactive rubber.

[0034] <Regarding Component (c)> Next, the component (c), a fluorine oligomer having a perfluoro skeleton (hereinafter sometimes referred to as "PFPE"), will be described. PFPE has the function of improving the plasma resistance of a fluorine-containing elastomer while also reducing its hardness. PFPE is an oligomer composed of the elements C, F, and O (in which all hydrogen atoms in a hydrocarbon have been replaced with fluorine), and examples include fluorine oligomers (c-1) to (c-8) having the following basic skeleton:

[0035]

[0036]

[0037] The molecular weight of the PFPEs represented by the formulas (c-1) to (c-8) varies depending on the values ​​of n and m. Generally, the higher the molecular weight, the higher the viscosity and boiling point. PFPEs containing the above basic skeleton may be synthesized, or commercially available fluorine-based solvents (oils, greases) may be used. Commercially available PFPEs are available in various grades, with properties such as viscosity varying depending on the values ​​of n and m. Examples include the Krytox (registered trademark) series manufactured by DuPont; the Fomblin (registered trademark) series and Galden (registered trademark) series manufactured by Solvay; and the Demnum (registered trademark) series manufactured by Daikin. Note that the above-mentioned products and skeletons are merely exemplary, and other skeletons and products may be used as long as they do not contain hydrogen. Furthermore, as shown in the formulas (c-1) to (c-8), the PFPEs contain ether bonds in the basic skeleton, and PFPEs do not bond (crosslink) to each other during crosslinking (curing) of the rubber composition. The above-described PFPEs may be used alone or in combination.

[0038] In the rubber composition according to the embodiment, a non-reactive PFPE is used as the component (c). Alternatively, a reactive compound may be formed by bonding a reactive group to a perfluoro skeleton.

[0039] The term "reactive" compounds means that the reactive compounds can react with each other during crosslinking (curing) of the rubber composition. This reaction can bond the reactive compounds to each other. The reactive compounds can also react with components (a) and (b). This reaction can bond the reactive compounds to components (a) and (b). The reactive compounds preferably contain an alkenyl group as a group that imparts such reactivity (reactive group).

[0040] Examples of the alkenyl group include a vinyl group, an allyl group, a butenyl group, a pentenyl group, a hexenyl group, a heptenyl group, etc. Of these, the vinyl group is preferred as the alkenyl group.

[0041] The reactive compound preferably has two or more alkenyl groups in the molecule. The two or more alkenyl groups may be the same or different.

[0042] In one embodiment, the reactive compound is a compound having a perfluoro skeleton with an alkenyl group. The perfluoro skeleton compound having an alkenyl group in the molecule may have, for example, a divalent perfluoropolyether structure or a divalent perfluoroalkylene structure.

[0043] In one embodiment, the reactive compound has a divalent perfluoropolyether structure or a divalent perfluoroalkylene structure and has two or more alkenyl groups at the terminal or side chain. Examples of such reactive compounds that can be used include the fluorine-based elastomers described in JP-A-2003-183402, paragraphs

[0016] to

[0022] , and the perfluoro compounds described in JP-A-11-116684 and JP-A-11-116685, paragraphs

[0006] to

[0014] .

[0044] In one embodiment, the reactive compound is represented by the following formula (c-9): CH ２ =CH-(X) ｐ - (R ｆ -Q) ａ -R ｆ -(X) ｐ -CH=CH ２ (c-9) In formula (c-9), two Xs each independently represent —CH２ -, -CH ２ O-, CH ２ OCH ２ -, -Y-NR １ SO ２ -or-Y-NR １ -CO- (where Y is -CH ２ - or -Si(CH ３ ) ２ -Ph- (Ph: phenylene group). １ is a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group. ｆ is a divalent perfluoroalkylene group or a divalent perfluoropolyether group. Two p's are each independently 0 or 1. a is an integer of 0 or greater. Q is a divalent group represented by any of the following formulas (c-10) to (c-12):

[0045]

[0046] In formulas (c-10) to (c-12), X, p, R １ is as defined in formula (c-9). ３ is a substituted or unsubstituted divalent hydrocarbon group. ４ is a substituted or unsubstituted divalent hydrocarbon group which may have one or more of an oxygen atom, a nitrogen atom, a silicon atom, and a sulfur atom interposed in the bond, or a functional group represented by the following formula (c-13) or (c-14):

[0047]

[0048] In formulas (c-13) and (c-14), R ５ represents a substituted or unsubstituted monovalent hydrocarbon group, R ６ is a group containing one or more atoms selected from carbon atoms, oxygen atoms, nitrogen atoms, silicon atoms and sulfur atoms in the main chain structure.

[0049] In one embodiment, a=0 in formula (c-9). In this case, formula (c-9) is represented by the following formula (c-15): CH ２ =CH-(X) ｐ -R ｆ -(X) ｐ -CH=CH ２(c-15) In formula (c-15), X, p, R ｆ is as defined in formula (c-9).

[0050] R ｆ Specific examples of -C include the following groups: ｍ F ２ｎ -(m, n: integers of 1 or more) -[CF(CF ３ ) OCF ２ ] ｐ -(CF ２ ) ｒ -[CF ２ OCF (CF ３ )] ｑ -CF ２ CF ２ - [OCF ２ CF ２ CF ２ ] ｗ -OCF ２ CF ２ -

[0051] In addition to the above examples, the reactive compound may also be a compound with a siloxane skeleton having an alkenyl group. Examples of the compound with a siloxane skeleton having an alkenyl group in the molecule include a polymer of methylvinylsiloxane, a polymer of dimethylsiloxane, a copolymer of dimethylsiloxane and methylvinylsiloxane, and a copolymer of dimethylsiloxane, methylvinylsiloxane, and methylphenylsiloxane. Other examples include organopolysiloxanes containing an alkenyl group in the molecule, which are addition polymerization liquid silicone rubbers.

[0052] The reactive compound is also available as a commercially available product, for example, "SIFEL" (registered trademark) manufactured by Shin-Etsu Chemical Co., Ltd.

[0053] As described above, the addition of a perfluoro-skeleton fluorine oligomer and a reactive compound that can be used instead (hereinafter, the perfluoro-skeleton fluorine oligomer and the reactive compound may be collectively referred to as "compound C") can significantly improve the plasma resistance of fluorine-containing elastomers crosslinked with FKM and FFKM, while adding a large amount of compound C reduces the hardness of the fluorine-containing elastomer. Furthermore, because compound C is a liquid lubricant with fluidity, it is difficult to knead or mix a large amount of compound C with the rubber components FKM and FFKM. Therefore, the lower limit of the compound C component relative to 100 phr of the FKM component and FFKM component, which are the rubber components, is, for example, 0.1 phr or more, 0.2 phr or more, 0.3 phr or more, 0.4 phr or more, 0.5 phr or more, 0.6 phr or more, 0.7 phr or more, 0.8 phr or more, 0.9 phr or more, 1.0 phr or more, 1.1 phr or more, 1.2 phr or more, 1.3 phr or more, 1.4 phr or more, 1.5 phr or more, 1.6 phr or more, 1.7 phr or more, 1.8 phr or more, 1.9 phr or more, or 2.0 phr or more. On the other hand, the upper limit of the compound C component may be, for example, 40 phr or less, 39 phr or less, 38 phr or less, 37 phr or less, 36 phr or less, 35 phr or less, 34 phr or less, 33 phr or less, 32 phr or less, 31 phr or less, 30 phr or less, 29 phr or less, 28 phr or less, 27 phr or less, 26 phr or less, 25 phr or less, 24 phr or less, 23 phr or less, 22 phr or less, 21 phr or less, or 20 phr or less.

[0054] <Regarding Component (d)> Next, the fluororesin, which is component (d), will be described. The fluororesin is added for the purpose of improving the plasma resistance and hardness of the fluorine-containing elastomer. There are no particular restrictions on the fluororesin, as long as it improves plasma resistance and hardness. Examples of the fluororesin include, but are not limited to, polytetrafluoroethylene (PTFE), perfluoroalkoxy fluororesin (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene (CTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF). The molecular weight of the fluororesin is not particularly limited as long as it is within a range in which the effects disclosed in the present application can be obtained. Although not limited thereto, examples of the lower limit include 10,000 or more, 50,000 or more, 100,000 or more, 200,000 or more, 300,000 or more, 400,000 or more, 500,000 or more, 600,000 or more, 700,000 or more, 800,000 or more, 1 million or more, etc. On the other hand, examples of the upper limit include 12 million or less, 11 million or less, 10 million or less, 9 million or less, 8 million or less, 7 million or less, 6 million or less, 5 million or less, etc.

[0055] As shown in the examples and comparative examples described below, when a fluororesin is dispersed in an FKM having lower plasma resistance than an FFKM, the fluororesin is likely to fall off as particles from the fluorine-containing elastomer (sealing material) when the FKM is abraded and gasified by plasma irradiation. Of the two incompatible phases of FKM and FFKM, it is preferable that the fluororesin be present (dispersed) in greater amounts in the FFKM, which has higher plasma resistance. Examples of such fluororesins include PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PCTFE (polychlorotrifluoroethylene), ETFE (ethylene-tetrafluoroethylene), and PVDF (polyvinylidene fluoride). Among the fluororesins listed above, PTFE, PFA, and FEP, which have high affinity with FFKM, are preferred.

[0056] It is preferable that products such as sealing materials using fluorine-containing elastomers generate fewer particles when used in a plasma environment, but depending on the required usage environment, the amount of particles generated may be acceptable as long as it is below a specified value. Therefore, it is preferable that a larger amount of fluororesin is dispersed in the FFKM, but it is also acceptable that the fluororesin is dispersed in the FKM. In other words, when comparing the fluororesin dispersed in the FFKM with the fluororesin not dispersed in the FFKM (for example, dispersed in the FKM), it can be said that there is more fluororesin dispersed in the FFKM.

[0057] The shape of the fluororesin is not particularly limited as long as it can be dispersed in a large amount in the FFKM, but it is preferably in the form of particles, and may also be in the form of fibers.

[0058] The average particle size of the primary particles of the particulate fluororesin is not particularly limited as long as it is within a range in which the hardness of the fluorine-containing elastomer can be improved. Although not limited thereto, examples of the lower limit of the average particle size include 0.05 μm or more, 0.06 μm or more, 0.07 μm or more, 0.08 μm or more, 0.09 μm or more, 0.1 μm or more, 0.125 μm or more, 0.15 μm or more, 0.175 μm or more, 0.2 μm or more, 0.25 μm or more, 0.3 μm or more, 0.4 μm or more, and 0.5 μm or more. On the other hand, the upper limit of the average particle size may be, for example, 50 μm or less, 47.5 μm or less, 45 μm or less, 42.5 μm or less, 40 μm or less, 37.5 μm or less, 35 μm or less, 32.5 μm or less, 30 μm or less, 27.5 μm or less, or 25 μm or less.

[0059] The average particle size may be measured by a known method such as a laser diffraction / scattering method. A commercially available fluororesin may be used. In the case of a commercially available product, the particle size listed in the catalog or the like may be used as the average particle size.

[0060] Examples of commercially available hydrogen-free fluororesins include PTFE such as TLP 10F-1, MP-1300-J, and the Teflon (registered trademark) PTFE series manufactured by Mitsui-Chemours Fluoroproducts, and the Polyflon PTFE series manufactured by Daikin Industries, Ltd.; PFA such as the Neoflon PFA powder paint series manufactured by Daikin Industries, Ltd.; and FEP such as the FEP powder paint series manufactured by Daikin Industries, Ltd.

[0061] Examples of commercially available hydrogen-containing fluororesins include ETFE such as Fluon (registered trademark) LM-2150 manufactured by AGC and Neoflon ETFE EC-6520 manufactured by Daikin Industries, Ltd.; and PVDF such as KYNAR (registered trademark) series PVDF manufactured by ARKEMA and KF Polymer series manufactured by Kureha Corporation.

[0062] The fluororesin is added to increase the hardness of the fluorine-containing elastomer, which decreases with the addition of compound C. Therefore, the amount of fluororesin added can be appropriately adjusted depending on the amount of compound C added and the required hardness. The lower limit of the weight ratio of the fluororesin to compound C (fluororesin / compound C) is not limited, and examples thereof include 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, and 1.0 or more. On the other hand, if the weight ratio of fluororesin / compound C becomes too large, the hardness may become too high. The upper limit of the weight ratio can also be appropriately adjusted taking into account the required hardness, etc., and is not limited, and examples thereof include 6 or less, 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, and 3.0 or less.

[0063] As described above, it is preferable that most of the added fluororesin is dispersed in the FFKM. If the amount of fluororesin added relative to the FFKM is too large, the FFKM may not be able to completely disperse (embrace) the added fluororesin, which may result in the fluororesin dispersing (migrating) into the FKM. Therefore, the proportion of fluororesin in the rubber composition may be appropriately adjusted depending on the proportion of FFKM, which is the rubber component. The upper limit of the weight ratio of fluororesin to FFKM (fluororesin / FFKM) is not limited, but examples include 2 or less, 1.9 or less, 1.8 or less, 1.7 or less, 1.6 or less, 1.5 or less, 1.4 or less, 1.3 or less, 1.2 or less, 1.1 or less, and 1.0 or less. On the other hand, the lower limit of the weight ratio of fluororesin / FFKM is not limited, because a small amount of fluororesin does not increase hardness, but examples include 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, and 0.6 or more.

[0064] Carbon black, silica, and the like are known as reinforcing fillers for increasing the hardness of fluorine-containing elastomers. However, the rubber composition according to the embodiment uses a combination of FFKM and a fluororesin that has a high affinity for FFKM as a filler, thereby suppressing particle generation during plasma irradiation. In other words, the rubber composition according to the embodiment uses a fluororesin that has a high affinity for FFKM as a filler, thereby suppressing particle generation while improving plasma resistance and hardness, thereby achieving a remarkable synergistic effect not found in conventional fillers.

[0065] The hardness of the fluorine-containing elastomer obtained by crosslinking the rubber composition according to the embodiment may be adjusted appropriately depending on the intended use of the fluorine-containing elastomer. For example, when a sealing material made from the fluorine-containing elastomer is used as a sealing material for semiconductor devices, the required hardness is approximately 50 to 80. When the sealing material is used as a sealing material for oil drilling rigs, the required hardness is approximately 70 to 90. The lower limit of the hardness of the fluorine-containing elastomer is not limited, but examples thereof include 50 or more, 51 or more, 52 or more, 53 or more, 54 or more, 55 or more, 56 or more, 57 or more, 58 or more, 59 or more, and 60 or more. On the other hand, the upper limit of the hardness of the fluorine-containing elastomer is not limited, but examples thereof include 90 or less, 89 or less, 88 or less, 87 or less, 86 or less, 85 or less, 84 or less, 83 or less, 82 or less, 81 or less, and 80 or less. The proportions of FKM, FFKM, compound C and fluororesin contained in the rubber composition may be adjusted appropriately so as to achieve the above-mentioned hardness.

[0066] <Regarding optional additional components that may be included in the rubber composition> Next, optional additional components that may be included in the rubber composition will be described. (e) Crosslinking agent, co-crosslinking agent The rubber composition may be crosslinked with an organic peroxide. As the organic peroxide crosslinking agent, a known agent for crosslinking fluorine-based elastomers can be used, such as dicumyl peroxide, di-t-butylperoxydiisopropylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, etc.

[0067] As the co-crosslinking agent, known agents for crosslinking fluorine-based elastomers can be used, such as triallyl isocyanurate, triallyl cyanurate, triallyl trimellitate, N,N'-m-phenylenedimaleimide, and trimethylolpropane trimethacrylate. Other examples include acrylate and methacrylate monomers.

[0068] 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), which are compounds described in Patent Document 1, 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.

[0069] (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.)

[0070] Detailed descriptions of the compounds described in the above formulas (e-1) and (e-2) are described in Patent Document 1. Therefore, in this specification, descriptions of the above formulas (e-1) and (e-2) are omitted. The disclosures of Patent Document 1 (WO 2021 / 230231) are incorporated herein by reference.

[0071] The crosslinking agent and the co-crosslinking agent may be contained when the rubber composition is crosslinked. Therefore, the crosslinking agent and the co-crosslinking agent do not need to be contained as essential components when the rubber composition is provided, and the crosslinking agent and the co-crosslinking agent may be added separately when the rubber composition is crosslinked. Of course, the rubber composition according to the embodiment itself may contain the crosslinking agent and the co-crosslinking agent. Furthermore, the above-mentioned crosslinking agents may be used alone or in combination of two or more. Similarly, the above-mentioned co-crosslinking agents may be used alone or in combination of two or more.

[0072] (f) Other Components Optional additional components other than those described in (e) above include, for example, fillers, thickeners, pigments, coupling agents, antioxidants, stabilizers, etc. Examples of fillers include carbon black, silica, etc.

[0073] (Embodiments of Fluorine-Containing Elastomer) A fluorine-containing elastomer according to an 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 by heating, for example, 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 by heating, for example, 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.

[0074] (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.

[0075] 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.

[0076] <Materials> The components used in the examples and comparative examples are as follows. (a) FKM: Daiel G912, manufactured by Daikin Industries, Ltd. (b) FFKM: AFLAS (registered trademark) FFKM PM3000, manufactured by AGC Inc. (c) Compound C (PFPE): Krytox VPF16256, manufactured by DuPont (d) Fluorine resin: PFA: Neoflon ACX-34, manufactured by Daikin Industries, Ltd. PTFE: TLP-10-1 (average particle size 0.2 μm), manufactured by Mitsui-Chemours Fluoroproducts Co., Ltd. MP-1300-J (average particle size 11 μm), manufactured by Mitsui-Chemours Fluoroproducts Co., Ltd. Crosslinking agent: 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, Perhexa 25B, manufactured by NOF Corporation Co-crosslinking agent: TAIC (triallyl isocyanurate), manufactured by Mitsubishi Chemical Corporation

[0077] [Examples 1 to 6, Comparative Examples 1 to 4] Rubber compositions having the compositions (weight ratios) shown in Table 1 were kneaded using an open roll, then placed in a mold and heat-treated in the atmosphere at 160°C for 10 minutes (15 minutes for Comparative Examples 1 and 3) to perform primary crosslinking while press-molding. The mixture was then removed from the mold and subjected to secondary crosslinking in air at 200°C for 4 hours. In this way, molded articles of fluorine-containing elastomer were obtained. The molded articles were shaped like O-rings (AS568-214; inner diameter 24.99 mm, thickness 3.53 mm).

[0078] The resulting fluorine-containing elastomer was evaluated as follows: (1) Hardness The molded article (O-ring) was placed in a micro rubber hardness tester manufactured by BAREISS (model: HPEII shore AM / M) to measure the hardness.

[0079] (2) Heat Resistance The obtained O-ring was bolted to two flat plates using a spacer so as to compress it by 25% to prepare a fastened body, and this fastened body was exposed to heat in a gear oven under specified conditions (150°C x 72 hours in an atmospheric environment). After that, it was removed from the gear oven, and the O-ring was opened while the fastened body was still hot, and it was allowed to cool to room temperature for 30 minutes. The thickness was measured before and after the test in accordance with JIS K 6262, and the compression set was calculated using the following formula (unit: %). This compression set (CS) was taken as heat resistance. Compression set = (thickness before test - thickness after test) / (thickness before test - spacer thickness) x 100

[0080] (3) Tensile Properties Using a bench-top precision universal testing machine (Shimadzu Corporation, Model: Autograph AGS-500NX), the breaking strength [MPa], elongation at break [%], and M100 [MPa] of the molded body (O-ring) were measured at room temperature of 25±2°C and a tensile speed of 300 mm / min.

[0081] (4) Plasma Resistance (4-1) Weight Reduction Rate [%] A molded body (O-ring) was exposed to plasma under the following conditions, and the weight reduction rate of the molded body before and after exposure was calculated. Apparatus: Surface wave plasma etching apparatus manufactured by Shinko Seiki Co., Ltd. Gas: O ２ (2000sccm)+CF ４ (40 sccm) Treatment pressure: 133 Pa Output: 3 kW Exposure time: 2 hours (Examples 1 to 6, Comparative Examples 1 to 4), 5 hours (Comparative Example 4 and Example 1) Weight loss rate [%] = [(Weight before plasma exposure - Weight immediately after plasma exposure) / (Weight before plasma exposure)] × 100 (4-2) Particles The presence or absence of particles due to the above plasma exposure was visually observed. Furthermore, for some Examples and Comparative Examples, photographs of the molded body before and after plasma exposure were taken, and also photographs were taken of the samples after plasma exposure after being pressed against black tape.

[0082] The results are shown in Table 1. Figure 1 shows the molded bodies (O-rings) of Comparative Examples 1 to 3, where lane A is a photograph before plasma irradiation, lane B is a photograph after 2 hours of plasma irradiation, and lane C is a photograph of the molded body after 2 hours of plasma irradiation transferred onto black tape. Figure 2 shows the molded bodies (O-rings) of Comparative Example 4 and Example 1, where lane A is a photograph before plasma irradiation and lane B is a photograph after 5 hours of plasma irradiation.

[0083] FIG. 3 shows an image of the cross section of the molded article of Example 4, where the elastic modulus was mapped using a scanning probe microscope SPM (Dimension Icon, manufactured by Bruker).

[0084] From the results shown in Table 1 and FIGS. 1 and 2, it was confirmed that the rubber composition, fluorine-containing elastomer, and sealing material disclosed in the present application have the following effects (or technical features).

[0085] (1) The plasma resistance of the molded body of Comparative Example 4, which contained the three components FKM, FFKM, and compound C, was significantly inferior to that of the molded body of Comparative Examples 1 to 3, which did not contain any of these three components. Therefore, it was confirmed that including the three components FKM, FFKM, and compound C is important for improving plasma resistance. On the other hand, as shown in Comparative Examples 3 and 4, it was confirmed that the addition of compound C reduces the hardness of the molded body. However, a comparison of Comparative Example 4 and Examples 1 to 6 confirmed that the addition of a fluororesin to FKM, FFKM, and compound C increased the hardness of the molded body and improved its plasma resistance. From these results, it was confirmed that mixing the four components of FKM, FFKM, compound C, and fluororesin is important for forming a molded body that has excellent plasma resistance and high hardness.

[0086] (2) Because the sealing material of Comparative Example 1 does not contain FFKM or Compound C, the fluororesin is dispersed in the FKM. Since the FKM has inferior plasma resistance compared to the FFKM and Compound C, as shown in Table 1 and Figure 1, when the FKM was scraped off by plasma irradiation, fluororesin particles were exposed on the surface of the molded body in a sufficient amount to be easily seen with the naked eye. In contrast, no fluororesin particles were generated in the Examples. Therefore, an SPM image of Example 4 was taken. Since the higher the elastic modulus in an SPM image, the brighter the image becomes, the fluororesin appears white, the FKM appears gray, and the FFKM appears black. As shown in Figure 3, it was confirmed that most of the fluororesin (white clumps) was dispersed in the black FFKM. Therefore, it was confirmed that when the fluororesin is dispersed in the FFKM, even if the FKM is scraped off by plasma irradiation, the fluororesin is less likely to be generated as particles.

[0087] (3) From the results of Comparative Example 4 and Examples 1 to 3, it was confirmed that the greater the proportion of fluororesin added to the rubber composition, the higher the hardness of the molded body and the better the plasma resistance.

[0088] (4) From the results of Examples 3 to 5, it was confirmed that the particle size of the fluororesin does not have a significant effect on the hardness and plasma resistance of the sealing material.

[0089] (5) From the results of Comparative Example 4 and Examples 1 to 7, it was confirmed that by mixing the four components of FKM, FFKM, compound C, and fluororesin, it is easy to adjust the balance of hardness, heat resistance, tensile properties, and plasma resistance.

[0090] The rubber composition, fluorine-containing elastomer, and sealing material disclosed in the present application can increase hardness while improving plasma resistance, and are therefore 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 cross-linkable reactive fluororubber; (b) a cross-linkable reactive perfluororubber; (c) a fluorooligomer having a perfluoro skeleton; and (d) a fluororesin.

2. The rubber composition according to claim 1, wherein the content of component (c) is 0.1 phr or more and 40 phr or less per 100 phr of the rubber components (a) and (b).

3. The rubber composition according to claim 1, wherein the weight ratio of component (d) / component (c) is 0.1 or more.

4. The rubber composition according to claim 2, wherein the weight ratio of component (d) / component (c) is 0.1 or more.

5. The rubber composition according to claim 1, wherein the weight ratio of component (d) / component (b) is 0.1 or more and 2 or less.

6. The rubber composition according to claim 2, wherein the weight ratio of component (d) / component (b) is 0.1 or more and 2 or less.

7. The rubber composition according to claim 3, wherein the weight ratio of component (d) / component (b) is 0.1 or more and 2 or less.

8. The rubber composition according to claim 4, wherein the weight ratio of component (d) / component (b) is 0.1 or more and 2 or less.

9. A fluorine-containing elastomer obtained by crosslinking the rubber composition according to any one of claims 1 to 8.

10. The fluorine-containing elastomer according to claim 9, wherein the components (a) and (b) are incompatible with each other and have a phase-separated structure, the component (d) is dispersed in the component (b), and the amount of the component (d) dispersed in the component (b) is greater than the amount of the component (d) not dispersed in the component (b).

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

12. Using a surface wave plasma etching device, gas flow rate O ２ (2000sccm)+CF ４ 11. The fluorine-containing elastomer according to claim 10, which has a weight loss rate of 2% or less when exposed to plasma under conditions of a pressure of 40 sscm, a treatment pressure of 133 Pa, an output of 3 kW, and an exposure time of 2 hours.

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