Seal member

Abstract

This seal member is formed from a rubber composition obtained by crosslinking a non-crosslinked rubber composition. The non-crosslinked rubber composition contains FKM, a peroxide, an acidic or neutral reinforcing filler, and a basic filler.

Description

Sealing material

[0001] The present invention relates to a sealing material.

[0002] A sealing material formed of a rubber composition in which silica is blended with FKM is known (for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2024-089962

[0004] The sealing material of the present invention is formed of a rubber composition obtained by heating and crosslinking an uncrosslinked rubber composition, and the uncrosslinked rubber composition contains FKM, a peroxide, an acidic to neutral reinforcing filler, and a basic filler.

[0005] Hereinafter, embodiments will be described in detail.

[0006] The sealing material according to the embodiment is formed of a rubber composition X obtained by heating and crosslinking an uncrosslinked rubber composition X'. The uncrosslinked rubber composition X' contains FKM, a peroxide, an acidic to neutral reinforcing filler, and a basic filler.

[0007] According to the sealing material according to the embodiment, since the uncrosslinked rubber composition X' before crosslinking of the rubber composition X forming it contains FKM, a peroxide, an acidic to neutral reinforcing filler, and a basic filler, excellent crosslinkability of the uncrosslinked rubber composition X' can be obtained, and the compression set CS of the rubber composition X after crosslinking forming the sealing material can be reduced.

[0008] In this application, "FKM" refers to a copolymer containing one or more monomers from among vinylidene fluoride (VdF), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), and perfluoromethyl vinyl ether (PMVE). Examples of FKM include binary FKMs of vinylidene fluoride (VdF) / hexafluoropropylene (HFP) binary copolymers, ternary FKMs of vinylidene fluoride (VdF) / hexafluoropropylene (HFP) / tetrafluoroethylene (TFE) ternary copolymers, and quaternary FKMs of 4-bromide-3,3,4,4-tetrafluoro-1-butene / ethylene (E) / tetrafluoroethylene (TFE) / perfluoromethyl vinyl ether (PMVE) quaternary copolymers. The FKM preferably contains one or more of the binary FKM, ternary FKM, and quaternary FKM, and more preferably contains binary FKM from the viewpoint of obtaining excellent crosslinking properties of the uncrosslinked rubber composition X' and reducing the compression set CS of the crosslinked rubber composition X that forms the sealing material.

[0009] Examples of peroxides include dialkyl peroxides, peroxyketals, and peroxyesters. Examples of dialkyl peroxides include dicumyl peroxide, 1,3-di(t-butylperoxy)diisopropylbenzene, 1,4-di(t-butylperoxy)diisopropylbenzene, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane-3. Examples of peroxyketals include 1,1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-butylperoxy)cyclohexane, and n-butyl-4,4-di(t-butylperoxy)valerate. Examples of peroxyesters include 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-hexylperoxybenzoate, and t-butylperoxybenzoate. The peroxide preferably contains one or more of these, and more preferably contains dialkyl peroxide and / or peroxyester, and even more preferably contains 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and / or t-butylperoxybenzoate, from the viewpoint of obtaining excellent crosslinking properties of the uncrosslinked rubber composition X' and reducing the compression set CS of the crosslinked rubber composition X that forms the sealing material.

[0010] The peroxide content A in the uncrosslinked rubber composition X' is preferably 0.5 parts by mass or more and 3 parts by mass or less, more preferably 1 part by mass or more and 2 parts by mass or less, per 100 parts by mass of FKM, from the viewpoint of obtaining excellent crosslinkability of the uncrosslinked rubber composition X' and reducing the compression set CS of the crosslinked rubber composition X that forms the sealing material.

[0011] The reinforcing filler is acidic to neutral. "Acidic to neutral" means that the pH of the dispersion obtained by dispersing the reinforcing filler in water is 7 or less. Examples of reinforcing fillers include acidic to neutral fumed silica, acidic to neutral carbon black, and acidic to neutral resin powder. Examples of acidic to neutral fumed silica include untreated hydrophilic fumed silica, hydrophobic fumed silica surface-treated with dimethyldichlorosilane, hydrophobic fumed silica surface-modified with trimethylsilyl groups, hydrophobic fumed silica surface-treated with octylsilane, and hydrophobic fumed silica surface-treated with dimethyl silicone oil. The reinforcing filler preferably contains one or more of these, and more preferably contains acidic to neutral fumed silica, and even more preferably contains hydrophobic fumed silica surface-treated with dimethyldichlorosilane, from the viewpoint of obtaining excellent crosslinking properties of the uncrosslinked rubber composition X' and reducing the compression set CS of the crosslinked rubber composition X that forms the sealing material. The average particle size of the reinforcing filler is, for example, 10 μm or more and 20 μm or less. In the case of acidic to neutral fumed silica, its specific surface area by the BET method is, for example, 70 m². ２ / g or more 150m ２ It is / g.

[0012] The amount of reinforcing filler B in the uncrosslinked rubber composition X' is preferably 3 to 25 parts by mass, more preferably 5 to 15 parts by mass, and even more preferably 10 to 12 parts by mass, per 100 parts by mass of FKM, from the viewpoint of obtaining excellent crosslinkability of the uncrosslinked rubber composition X' and reducing the compression set CS of the crosslinked rubber composition X that forms the sealing material.

[0013] Basic fillers are basic. This "basicity" means that the pH of the dispersion obtained by dispersing the basic filler in water is greater than 7. Examples of basic fillers include hydrophobic fumed silica, basic wet silica, basic phenolic resin powder, metal oxide powder, and powdered metal hydroxide, all surface-modified with basic groups such as amino groups. It is preferable that the basic filler contains one or more of these, and it is more preferable to include hydrophobic fumed silica and / or basic wet silica surface-modified with basic groups, from the viewpoint of obtaining excellent crosslinkability of the uncrosslinked rubber composition X' and reducing the compression set CS of the crosslinked rubber composition X that forms the sealing material. The average particle size of the basic filler is, for example, 5 μm to 15 μm. In the case of hydrophobic fumed silica or basic wet silica surface-modified with basic groups, the specific surface area by the BET method is, for example, 100 m². ２ / g or more 200m ２ It is less than / g.

[0014] The basic filler content C in the uncrosslinked rubber composition X' is preferably 0.1 parts by mass or more and 3 parts by mass or less, more preferably 0.3 parts by mass or more and 1.5 parts by mass or less, and even more preferably 0.5 parts by mass or more and 1 part by mass or less, per 100 parts by mass of FKM, from the viewpoint of obtaining excellent crosslinkability of the uncrosslinked rubber composition X' and reducing the compression set CS of the crosslinked rubber composition X that forms the sealing material.

[0015] The amount of reinforcing filler B in the uncrosslinked rubber composition X' is preferably greater than the amount of basic filler C, from the viewpoint of obtaining excellent crosslinkability of the uncrosslinked rubber composition X' and reducing the compression set CS of the crosslinked rubber composition X that forms the sealing material. From the same viewpoint, the mass ratio of the amount of reinforcing filler B in the uncrosslinked rubber composition X' to the amount of basic filler C is preferably 4 to 50, more preferably 5 to 40, and even more preferably 10 to 25.

[0016] The sum of the reinforcing filler content B and the basic filler content C in the uncrosslinked rubber composition X' is preferably 3 to 30 parts by mass, more preferably 5 to 20 parts by mass, and even more preferably 10 to 15 parts by mass, per 100 parts by mass of FKM, from the viewpoint of obtaining excellent crosslinkability of the uncrosslinked rubber composition X' and reducing the compression set CS of the crosslinked rubber composition X that forms the sealing material.

[0017] The uncrosslinked rubber composition X' may further contain a crosslinking aid. Examples of crosslinking aids include triallyl cyanurate, trimethyl isocyanurate, triallyl isocyanurate, triacrylic formal, triallyl trimellitate, N,N'-m-phenylene bismaleimide, dipropagyl terephthalate, diallyl phthalate, tetraallyl terephthalate amide, triallyl phosphate, bismaleimide, and fluorinated triallyl isocyanurate (1,3,5-tris(2,3,3-trifluoro-2-propenyl)-1,3,5-triazine). Examples include -2,4,6-trione), tris(diallylamine)-S-triazine, triallyl phosphite, N,N-diallylcrylamide, 1,6-divindodecafluorohexane, hexaarylphosphoramide, N,N,N',N'-tetraallylphthalamide, N,N,N',N'-tetraallylmalonamide, trivinyl isocyanurate, 2,4,6-trivinylmethyltrisiloxane, tri(5-norbornene-2-methylene)cyanurate, and triallyl phosphite. The crosslinking aid preferably contains one or more of these, and more preferably contains triallyl isocyanurate from the viewpoint of obtaining excellent crosslinkability of the uncrosslinked rubber composition X' and reducing the compression set CS of the crosslinked rubber composition X that forms the sealing material.

[0018] The amount of crosslinking aid D in the uncrosslinked rubber composition is preferably 1 to 10 parts by mass, more preferably 3 to 5 parts by mass, per 100 parts by mass of FKM, from the viewpoint of obtaining excellent crosslinkability of the uncrosslinked rubber composition X' and reducing the compression set CS of the crosslinked rubber composition X that forms the sealing material.

[0019] The uncrosslinked rubber composition X' may also contain rubber components other than FKM, plasticizers, processing aids, vulcanization accelerators, antioxidants, surfactants, and the like.

[0020] Based on JIS K6300-2:2001, the time (t90) from the start of vulcanization to obtaining 90% of the maximum torque, as determined from the vulcanization curve obtained using a torsional vibration type flat die vulcanization tester (e.g., Curlastometer® manufactured by ENEOS Material Trading Co., Ltd.) for the uncrosslinked rubber composition X', is preferably 7 minutes or less, more preferably 5 minutes or less, and even more preferably 3 minutes or less, as determined from the viewpoint of obtaining excellent crosslinkability of the uncrosslinked rubber composition X'.

[0021] The sealing material according to this embodiment can be manufactured by molding an uncrosslinked rubber composition X' into a sealing material shape and then heating it to crosslink it to obtain a rubber composition X.

[0022] Specifically, first, an uncrosslinked rubber composition X' is prepared by kneading using an open-type rubber kneader such as an open roll kneader, or a closed-type rubber kneader such as a kneader. Next, a predetermined amount of the uncrosslinked rubber composition X' is filled into a cavity shaped like a seal material in a preheated mold and the mold is clamped. In this state, primary crosslinking is performed by heating while maintaining a predetermined temperature and pressure for a predetermined time. This primary crosslinking may be performed by press molding or by injection molding. The primary crosslinking temperature is, for example, 150°C to 180°C. The primary crosslinking pressure is, for example, 0.1 MPa to 25 MPa. The primary crosslinking time is, for example, 3 minutes to 20 minutes. Then, the mold is opened and the seal material formed from the crosslinked rubber composition X is demolded and removed from the inside.

[0023] Alternatively, the sealing material of the molded product demolded from the mold may be placed in a preheated oven and heated at a predetermined temperature for a predetermined time to induce secondary crosslinking. The secondary crosslinking temperature is higher than the primary crosslinking temperature, for example, between 190°C and 210°C. The secondary crosslinking time is longer than the primary crosslinking time, for example, between 3 hours and 5 hours.

[0024] Furthermore, post-crosslinking may be performed by irradiating the sealing material with radiation after primary or secondary crosslinking. In this case, examples of radiation include alpha rays, beta rays, gamma rays, electron beams, and ions. Of these, electron beams or gamma rays are preferred. The radiation dose is, for example, 20 kGy or more and 100 kGy or less.

[0025] The hardness HA of the rubber composition X forming the sealing material according to the embodiment is preferably A65 or more and A75 or less, more preferably A68 or more and A72 or less. This hardness HA is measured using a Type A durometer in accordance with JIS K6253-3:2012.

[0026] The tensile strength Tb at break of rubber composition X is preferably 15 MPa or more, more preferably 25 MPa or more. The elongation Eb at break is preferably 400% or more, more preferably 500% or more. The 100% modulus S100 (tensile stress at 100% elongation) is preferably 1.5 MPa or more and 3 MPa or less, more preferably 2 MPa or more and 2.5 MPa or less. These tensile strength Tb at break, elongation Eb at break, and 100% modulus S100 are measured by a tensile test based on JIS K6251:2023.

[0027] The compression set CS of rubber composition X is preferably 30% or less, more preferably 20% or less, and even more preferably 15% or less. This compression set CS is measured according to JIS K6262:2013 with a test time of 72 hours and a test temperature of 200°C.

[0028] The sealing material according to the embodiment preferably has a surface color that is not black, such as beige, brown, or dark brown.

[0029] (Uncrosslinked Rubber Compositions) Crosslinked rubber compositions were prepared for the following examples and comparative examples. Their respective compositions are also shown in Tables 1 to 5.

[0030] <Example 1-1> 100 parts by mass of binary FKM (Daiel® G801, manufactured by Daikin Corporation), 1.5 parts by mass of peroxide 1 (2,5-dimethyl-2,5-di(t-butylperoxy)hexane) (Perhexa® 25B, manufactured by NOF Corporation), and hydrophobic fumed silica surface-treated with dimethyldichlorosilane as a reinforcing filler (Aerosil® R972, manufactured by Nippon Aerosil Co., Ltd., specific surface area by BET method: 90-130 m²). ２ / g, average particle size (primary): 16 μm) 11.7 parts by mass, wet silica (Carplex® #1120, manufactured by DSL Japan, with basic filler 1, specific surface area by BET method: 120 m²) ２ An uncrosslinked rubber composition was prepared by mixing 0.3 parts by mass of (average particle size (primary): 12 μm) and 4 parts by mass of triallyl isocyanurate (TAIC®, manufactured by Mitsubishi Chemical Corporation) as a crosslinking aid, and kneading the mixture. This was designated as Example 1-1.

[0031] <Examples 1-2 to 1-4 and Comparative Example 1> An uncrosslinked rubber composition was prepared in the same manner as in Example 1-1, except that the amounts of reinforcing filler and basic filler 1 were 11.5 parts by mass and 0.5 parts by mass, respectively, per 100 parts by mass of binary FKM, and this was designated as Example 1-2.

[0032] An uncrosslinked rubber composition was prepared in the same manner as in Example 1-1, except that the amounts of reinforcing filler and basic filler 1 were 11.3 parts by mass and 0.7 parts by mass, respectively, per 100 parts by mass of binary FKM, and this was designated as Example 1-3.

[0033] An uncrosslinked rubber composition was prepared in the same manner as in Example 1-1, except that the amounts of reinforcing filler and basic filler 1 were 11.0 parts by mass and 1.0 part by mass, respectively, per 100 parts by mass of binary FKM, and this was designated as Example 1-4.

[0034] A non-crosslinked rubber composition was prepared in the same manner as in Example 1-1, except that the basic filler 1 was not blended and the blending amount of the reinforcing filler was 12.0 parts by mass with respect to 100 parts by mass of the binary FKM, and this was designated as Comparative Example 1.

[0035]

[0036] <Examples 2-1 to 2-5 and Comparative Example 2> Instead of the basic filler 1, hydrophobic fumed silica surface-modified with an amino group and a trimethylsilyl group of the basic filler 2 (Aerosil (registered trademark) R504, manufactured by Nippon Aerosil Co., Ltd., specific surface area by BET method: 125 to 175 m ２ / g, average particle diameter (primary): 12 μm) was used, and a non-crosslinked rubber composition was prepared in the same manner as in Example 1-1, except that the blending amounts of the reinforcing filler and the basic filler 2 were 11.5 parts by mass and 0.5 parts by mass, respectively, with respect to 100 parts by mass of the binary FKM, and this was designated as Example 2-1.

[0037] A non-crosslinked rubber composition was prepared in the same manner as in Example 2-1, except that the blending amounts of the reinforcing filler and the basic filler 2 were 11.0 parts by mass and 1.0 parts by mass, respectively, with respect to 100 parts by mass of the binary FKM, and this was designated as Example 2-2.

[0038] A non-crosslinked rubber composition was prepared in the same manner as in Example 2-1, except that the blending amounts of the reinforcing filler and the basic filler 2 were 10.5 parts by mass and 1.5 parts by mass, respectively, with respect to 100 parts by mass of the binary FKM, and this was designated as Example 2-3.

[0039] Instead of peroxide 1, t-butyl peroxybenzoate (Perbutyl (registered trademark) Z, manufactured by NOF Corporation) of peroxide 2 was used, and a non-crosslinked rubber composition was prepared in the same manner as in Example 2-2, except that the blending amount was 1 part by mass with respect to 100 parts by mass of the binary FKM, and this was designated as Example 2-4.

[0040] Instead of peroxide 1, peroxide 2 was used, and a non-crosslinked rubber composition was prepared in the same manner as in Example 2-3, except that the blending amount was 1 part by mass with respect to 100 parts by mass of the binary FKM, and this was designated as Example 2-5.

[0041] An uncrosslinked rubber composition was prepared in the same manner as in Example 2-1, except that no reinforcing filler was added and the amount of the basic filler 2 was 10.0 parts by mass with respect to 100 parts by mass of the binary FKM, and this was designated as Comparative Example 2.

[0042]

[0043] <Examples 3-1 to 3-3> An uncrosslinked rubber composition was prepared in the same manner as in Example 1-1, except that the basic phenolic resin powder of the basic filler 3 (Verpal (registered trademark) R200, manufactured by Air Water Performance Chemicals Co., average particle size: 6 μm) was used instead of the basic filler 1, and the amounts of the reinforcing filler and the basic filler 3 were 11.5 parts by mass and 0.5 parts by mass, respectively, with respect to 100 parts by mass of the binary FKM, and this was designated as Example 3-1.

[0044] An uncrosslinked rubber composition was prepared in the same manner as in Example 3-1, except that the amounts of the reinforcing filler and the basic filler 3 were 11.0 parts by mass and 1.0 parts by mass, respectively, with respect to 100 parts by mass of the binary FKM, and this was designated as Example 3-2.

[0045] An uncrosslinked rubber composition was prepared in the same manner as in Example 3-1, except that the amounts of the reinforcing filler and the basic filler 3 were 10.5 parts by mass and 1.5 parts by mass, respectively, with respect to 100 parts by mass of the binary FKM, and this was designated as Example 3-3.

[0046]

[0047] <Examples 4-1 to 4-4 and Comparative Examples 4-1 to 4-2> An uncrosslinked rubber composition was prepared in the same manner as in Example 2-1, except that a ternary FKM (Solvay (registered trademark) PX989S, manufactured by Solvay Japan Co.) was used instead of the binary FKM, and the amounts of the reinforcing filler and the basic filler 2 were 9.0 parts by mass and 1.0 parts by mass, respectively, with respect to 100 parts by mass of the ternary FKM, and this was designated as Example 4-1.

[0048] An uncrosslinked rubber composition was prepared in the same manner as in Example 4-1, except that the amounts of reinforcing filler and basic filler 2 were 8.5 parts by mass and 1.5 parts by mass, respectively, per 100 parts by mass of ternary FKM, and this was designated as Example 4-2.

[0049] An uncrosslinked rubber composition was prepared in the same manner as in Example 4-1, except that peroxide 2 was used instead of peroxide 1, and the amount of peroxide 2 was 1 part by mass per 100 parts by mass of ternary FKM. This was designated as Example 4-3.

[0050] An uncrosslinked rubber composition was prepared in the same manner as in Example 4-2, except that peroxide 2 was used instead of peroxide 1, and the amount of peroxide 2 was 1 part by mass per 100 parts by mass of ternary FKM. This was designated as Example 4-4.

[0051] An uncrosslinked rubber composition was prepared in the same manner as in Example 4-1, except that basic filler 2 was not included and the amount of reinforcing filler was 10.0 parts by mass per 100 parts by mass of ternary FKM. This was designated as Comparative Example 4-1.

[0052] An uncrosslinked rubber composition was prepared in the same manner as in Example 4-3, except that basic filler 2 was not included and the amount of reinforcing filler was 10.0 parts by mass per 100 parts by mass of ternary FKM. This was designated as Comparative Example 4-2.

[0053]

[0054] <Examples 5-1 to 5-2 and Comparative Example 5> An uncrosslinked rubber composition was prepared in the same manner as in Example 2-4, except that a quaternary FKM (Viton® VTR9213, manufactured by Chemours) was used instead of a binary FKM, and the amounts of reinforcing filler and basic filler 2 were set to 8.5 parts by mass and 1.5 parts by mass, respectively, per 100 parts by mass of quaternary FKM. This was designated as Example 5-1.

[0055] An uncrosslinked rubber composition was prepared in the same manner as in Example 5-1, except that the amounts of reinforcing filler and basic filler 2 were 8.0 parts by mass and 2.0 parts by mass, respectively, per 100 parts by mass of quaternary FKM, and this was designated as Example 5-2.

[0056] An uncrosslinked rubber composition was prepared in the same manner as in Example 5-1, except that basic filler 2 was not included and the amount of reinforcing filler was 10.0 parts by mass per 100 parts by mass of quaternary FKM. This was designated as Comparative Example 5.

[0057]

[0058] (Rubber sheets for test specimens and test specimens for compression set testing) For each of the uncrosslinked rubber compositions of the above examples and comparative examples, a mold for molding rubber sheets was placed in it, and primary crosslinking was performed by setting it in a press molding machine and heating and pressurizing it. The primary crosslinking temperature was 165°C for those using peroxide 1 and 155°C for those using peroxide 2. The primary crosslinking time was 10 minutes. The primary crosslinked material was demolded from the mold, and a rubber sheet for test specimens was prepared by heating it in an oven at a temperature of 200°C for 4 hours to induce secondary crosslinking. Similarly, test specimens for compression set testing were prepared.

[0059] (Test Method and Results) The following tests were performed on the uncrosslinked rubber compositions of the above examples and comparative examples, as well as on the rubber sheets for test specimens and test specimens for compression set testing prepared by crosslinking them. The test results are shown in Tables 1 to 5. In Comparative Example 4-1, the crosslinking of the uncrosslinked rubber composition did not proceed, and a crosslinked rubber composition could not be obtained.

[0060] <t90> For each of the uncrosslinked rubber compositions of the above examples and comparative examples, the time (t90) from the start of vulcanization to obtaining 90% of the maximum torque was determined from the vulcanization curve obtained by die vulcanization test method A using a torsional vibration type flat plate die vulcanization test machine (Curlastometer®, manufactured by ENEOS Material Trading Co., Ltd.) in accordance with JIS K6300-2:2001. The test temperature was 165°C for those using peroxide 1 and 155°C for those using peroxide 2.

[0061] <Hardness> Test specimens were prepared by crosslinking each of the uncrosslinked rubber compositions of the above examples and comparative examples, and the rubber sheets were stacked to form test specimens. The hardness was measured using a Type A durometer in accordance with JIS K6253-3:2012.

[0062] <Density> Test specimens were cut from rubber sheets prepared by crosslinking each of the uncrosslinked rubber compositions of the above examples and comparative examples, and their density was measured according to JIS K6268:1998.

[0063] <Tensile Properties> Test specimens were cut from rubber sheets prepared by crosslinking each of the uncrosslinked rubber compositions of the above examples and comparative examples, and the tensile strength Tb at break, elongation Eb at break, and 100% modulus S100 (tensile stress at 100% elongation) were measured according to JIS K6251:2023.

[0064] <Compression Set> For the compression set test specimens prepared by crosslinking each of the uncrosslinked rubber compositions of the above examples and comparative examples, the compression set CS was measured according to JIS K6262:2013, with a test time of 72 hours and a test temperature of 200°C.

[0065] <Surface Color Tone> The surface color tone of the test rubber sheets prepared by crosslinking each of the uncrosslinked rubber compositions of Examples 1-1 to 1-4 and Comparative Example 1, Examples 2-1 to 2-3 and Comparative Example 2, and Examples 3-1 to 3-3 was evaluated visually.

[0066] This invention is useful in the field of sealing materials.

Claims

1. A sealing material formed from a rubber composition obtained by heating and crosslinking an uncrosslinked rubber composition, wherein the uncrosslinked rubber composition contains FKM, a peroxide, an acidic to neutral reinforcing filler, and a basic filler.

2. The sealing material according to claim 1, wherein the FKM includes a binary FKM.

3. A sealing material according to claim 1 or 2, wherein the peroxide comprises 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and / or t-butylperoxybenzoate.

4. A sealing material according to any one of claims 1 to 3, wherein the reinforcing filler contains acidic to neutral fumed silica.

5. The sealing material according to claim 4, wherein the reinforcing filler comprises hydrophobic fumed silica surface-treated with dimethyldichlorosilane.

6. A sealing material according to any one of claims 1 to 5, wherein the content of the reinforcing filler in the uncrosslinked rubber composition is 3 parts by mass or more and 25 parts by mass or less per 100 parts by mass of the FKM.

7. A sealing material according to any one of claims 1 to 6, wherein the basic filler comprises one or more of fumed silica, basic wet silica, and basic phenolic resin powder surface-modified with basic groups.

8. A sealing material according to any one of claims 1 to 7, wherein the content of the basic filler in the uncrosslinked rubber composition is 3 parts by mass or less per 100 parts by mass of the FKM.

9. A sealing material according to any one of claims 1 to 8, wherein the content of the reinforcing filler in the uncrosslinked rubber composition is greater than the content of the basic filler.

10. A sealing material according to claim 9, wherein the mass ratio of the content of the reinforcing filler in the uncrosslinked rubber composition to the content of the basic filler is 4 or more and 50 or less.

11. A sealing material according to any one of claims 1 to 10, wherein the sum of the content of the reinforcing filler and the content of the basic filler in the uncrosslinked rubber composition is 3 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the FKM.

12. A sealing material according to any one of claims 1 to 11, wherein the time from the start of vulcanization to obtaining 90% of the maximum torque, as determined from a vulcanization curve obtained by die vulcanization test method A based on JIS K6300-2:2001 for the uncrosslinked rubber composition, with the heating temperature of the uncrosslinked rubber composition as the test temperature, is 7 minutes or less.

13. A sealing material according to any one of claims 1 to 12, wherein the hardness of the rubber composition, as measured by a Type A durometer based on JIS K6253-3:2012, is A65 or more and A75 or less.

14. A sealing material according to any one of claims 1 to 13, wherein the compression set of the rubber composition, measured at a test time of 72 hours and a test temperature of 200°C according to JIS K6262:2013, is 30% or less.

15. A sealing material according to any one of claims 1 to 14, wherein the surface color of the sealing material is not black.

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