Crosslinked rubber composition

Abstract

The crosslinked rubber composition contains a rubber component and cellulose-based fine fibers. The rubber component contains a first ethylene-α-olefin elastomer, a second ethylene-α-olefin elastomer having an ethylene content of 40% by mass or more and 70% by mass or less, an acid, and a second ethylene-α-olefin elastomer kneading reaction product obtained by kneading and reacting the first ethylene-α-olefin elastomer and the second ethylene-α-olefin elastomer kneading reaction product. The rubber component mainly contains the first ethylene-α-olefin elastomer and the second ethylene-α-olefin elastomer kneading reaction product.

Description

[Technical Field]

[0001] The present invention relates to a crosslinked rubber composition. [Background technology]

[0002] It is known that cellulose-based fine fibers are contained in a crosslinked rubber composition. For example, Patent Document 1 discloses a crosslinked rubber composition containing ethylene-propylene-diene monomer (hereinafter referred to as "EPDM"), maleic anhydride-modified polyolefin, and cellulose-based fine fibers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-123639 Summary of the Invention

[0004] The present invention provides a crosslinked rubber composition containing a rubber component and cellulose-based fine fibers, wherein the rubber component comprises a first ethylene-α-olefin elastomer and a second ethylene-α-olefin elastomer having an ethylene content of 40% by mass or more and 70% by mass or less; Maleic Anhydride and Dialkyl peroxides and a second ethylene-α-olefin elastomer kneading reaction product obtained by kneading and reacting the first ethylene-α-olefin elastomer and the second ethylene-α-olefin elastomer, and The first ethylene-α-olefin elastomer and the second ethylene-α-olefin elastomer each contain an ethylene-propylene-diene monomer having a diene component of ethylidene norbornene and a diene content of 4% by mass or more and 12% by mass or less. . DETAILED DESCRIPTION OF THE INVENTION

[0005] The embodiments will be described in detail below.

[0006] The crosslinked rubber composition according to the embodiment contains a rubber component and cellulose-based fine fibers. The rubber component contains a first ethylene-α-olefin elastomer, a second ethylene-α-olefin elastomer having an ethylene content of 40% by mass or more and 70% by mass or less, and a second ethylene-α-olefin elastomer kneading reaction product obtained by kneading and reacting an acid and a reaction initiator, and the first ethylene-α-olefin elastomer and the second ethylene-α-olefin elastomer kneading reaction product are the main components.

[0007] However, a crosslinked rubber composition containing EPDM and cellulose-based fine fibers has a problem in that the hysteresis loss, i.e., energy loss, increases due to the influence of the cellulose-based fine fibers. In contrast, according to the crosslinked rubber composition of the embodiment, the rubber component contains the first ethylene-α-olefin elastomer and the second ethylene-α-olefin elastomer kneading reaction product as the main components, so that the hysteresis loss, i.e., energy loss, can be reduced even though the crosslinked rubber composition contains an ethylene-α-olefin elastomer-based rubber component and cellulose-based fine fibers.

[0008] For this reason, the crosslinked rubber composition according to the embodiment can be suitably used as a material for forming, for example, a transmission belt or a conveyor belt that is repeatedly bent, and can also be used as a material for forming tires, hoses, shoes, etc.

[0009] Here, the crosslinked rubber composition according to the embodiment is prepared by blending and kneading a rubber component composed of a first ethylene-α-olefin elastomer and a previously prepared kneaded reaction product of a second ethylene-α-olefin elastomer with rubber compounding ingredients containing cellulose-based fine fibers and a crosslinking agent to prepare an uncrosslinked rubber composition, and then molding the uncrosslinked rubber composition into a predetermined shape and heating and pressurizing it to crosslink the rubber component. In this case, a masterbatch prepared in advance by dispersing cellulose-based fine fibers in the kneaded reaction product of the first ethylene-α-olefin elastomer and / or the second ethylene-α-olefin elastomer may be used.

[0010] Examples of the first ethylene-α-olefin elastomer include ethylene-propylene copolymer (EPR), EPDM, ethylene-octene copolymer, ethylene-butene copolymer, etc. The first ethylene-α-olefin elastomer preferably contains one or more of these, and more preferably contains EPDM from the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition.

[0011] From the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition, the ethylene content of the first ethylene-α-olefin elastomer is preferably 40% by mass or more and 70% by mass or less, more preferably 50% by mass or more and 60% by mass or less, and even more preferably 51% by mass or more and 53% by mass or less.

[0012] When the first ethylene-α-olefin elastomer contains EPDM, the diene component may be, for example, ethylidene. L Examples of the diene component include bornene (ENB), dicyclopentadiene, and 1,4-hexadiene. From the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition, the diene component is preferably ethylidene. L Bornene (ENB) is preferred. In this case, the diene content (ENB content) of the EPDM is preferably 4% by mass or more and 12% by mass or less, more preferably 5% by mass or more and 10% by mass or less, and even more preferably 7% by mass or more and 9% by mass or less, from the same viewpoint as above.

[0013] The second ethylene-α-olefin elastomer kneading reaction product is obtained by kneading and reacting the second ethylene-α-olefin elastomer, an acid, and a reaction initiator. In the second ethylene-α-olefin elastomer kneading reaction product, part or all of the polymer of the second ethylene-α-olefin elastomer is acid-modified by forming radicals at reaction points with the reaction initiator and grafting acids onto the radicals.

[0014] Examples of the second ethylene-α-olefin elastomer include ethylene-propylene copolymer (EPR), EPDM, ethylene-octene copolymer, and ethylene-butene copolymer. The second ethylene-α-olefin elastomer preferably contains one or more of these, and more preferably contains EPDM from the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition. From the same viewpoint as above, the second ethylene-α-olefin elastomer is preferably the same as the first ethylene-α-olefin elastomer.

[0015] The ethylene content of the second ethylene-α-olefin elastomer is 40% by mass or more and 70% by mass or less, but from the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition, it is preferably 45% by mass or more and 65% by mass or less, more preferably 50% by mass or more and 59% by mass or less, and even more preferably 51% by mass or more and 53% by mass or less.

[0016] When the second ethylene-α-olefin elastomer contains EPDM, the diene component may be, for example, ethylidene. L Examples of the diene component include bornene (ENB), dicyclopentadiene, and 1,4-hexadiene. From the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition, the diene component is preferably ethylidene. L Bornene (ENB) is preferred. In this case, the diene content (ENB content) of the EPDM is preferably 4% by mass or more and 12% by mass or less, more preferably 5% by mass or more and 10% by mass or less, and even more preferably 7% by mass or more and 9% by mass or less, from the same viewpoint as above.

[0017] Examples of the acid include carboxylic acids. Examples of the carboxylic acid include maleic anhydride, maleic acid, itaconic anhydride, itaconic acid, fumaric acid, methacrylic acid, acrylic acid, and mercapto acid. The acid preferably contains one or more of these, and more preferably contains maleic anhydride from the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition.

[0018] The amount of acid added to the second ethylene-α-olefin elastomer when preparing the second ethylene-α-olefin elastomer kneading reaction product is preferably 0.1 parts by mass or more and 3 parts by mass or less, more preferably 0.2 parts by mass or more and 2 parts by mass or less, and even more preferably 0.3 parts by mass or more and 1 part by mass or less, per 100 parts by mass of the second ethylene-α-olefin elastomer, from the viewpoint of appropriately acid-modifying the second ethylene-α-olefin elastomer.

[0019] The reaction initiator is a substance that forms radicals at reaction sites where an acid grafts onto the second ethylene-α-olefin elastomer polymer. The reaction initiator is not particularly limited as long as it is such a substance, but preferably contains an organic peroxide. Examples of organic peroxides that can be used as the reaction initiator 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 organic peroxide reaction initiator preferably contains one or more of these, and from the viewpoint of appropriately acid-modifying the second ethylene-α-olefin elastomer, it is more preferable to contain a dialkyl peroxide, and even more preferable to contain dicumyl peroxide.

[0020] The amount of organic peroxide as a reaction initiator added to the second ethylene-α-olefin elastomer when preparing the second ethylene-α-olefin elastomer kneading reaction product is preferably 0.03 parts by mass or more and 0.2 parts by mass or less, more preferably 0.05 parts by mass or more and 0.15 parts by mass or less, and even more preferably 0.08 parts by mass or more and 0.12 parts by mass or less, per 100 parts by mass of the second ethylene-α-olefin elastomer, from the viewpoint of moderately acid-modifying the second ethylene-α-olefin elastomer.

[0021] For the kneading during the preparation of the second ethylene-α-olefin elastomer kneading reaction product, for example, an internal kneader such as a kneader or a Banbury mixer can be used. The kneading temperature of the second ethylene-α-olefin elastomer, acid, and reaction initiator is preferably 140°C or higher and 160°C or lower, more preferably 145°C or higher and 155°C or lower, from the viewpoints of appropriately acid-modifying the second ethylene-α-olefin elastomer and suppressing crosslinking of the second ethylene-α-olefin elastomer by the reaction initiator. The kneading time of the second ethylene-α-olefin elastomer, acid, and reaction initiator is preferably 2 minutes or higher and 10 minutes or lower, more preferably 3 minutes or higher and 7 minutes or lower, from the same viewpoints as above.

[0022] The content of the first ethylene-α-olefin elastomer and the second ethylene-α-olefin elastomer kneaded reaction product in the rubber component is more than 50% by mass, but from the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition, it is preferably 80% by mass or more, more preferably 90% by mass or more, and most preferably 100% by mass. In addition to the first ethylene-α-olefin elastomer and the second ethylene-α-olefin elastomer kneaded reaction product, the rubber component may contain, for example, chloroprene rubber (CR), chlorosulfonated polyethylene rubber (CSM), hydrogenated acrylonitrile rubber (H-NBR), etc.

[0023] From the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition, the content of the first ethylene-α-olefin elastomer in the rubber component may be greater than, equal to, or less than the content of the second ethylene-α-olefin elastomer kneading reaction product. However, from the viewpoint of balance with other physical properties, etc., it is preferable that the content of the first ethylene-α-olefin elastomer in the rubber component be greater than or equal to the content of the second ethylene-α-olefin elastomer kneading reaction product.

[0024] The mass ratio of the content of the first ethylene-α-olefin elastomer to the content of the second ethylene-α-olefin elastomer kneading reaction product in the rubber component (content of first ethylene-α-olefin elastomer / content of second ethylene-α-olefin elastomer kneading reaction product) is preferably 1 / 99 or more and 99 / 1 or less, more preferably 10 / 90 or more and 90 / 10 or less, even more preferably 50 / 50 or more, and still more preferably 80 / 20 or more.

[0025] From the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition, the acid content of the rubber component is preferably 0.01% by mass or more and 0.5% by mass or less, more preferably 0.1% by mass or more and 0.2% by mass or less. The acid content of the rubber component is a percentage calculated based on the amount of acid blended in the preparation of the second ethylene-α-olefin elastomer kneading reaction product.

[0026] Cellulose-based fine fibers are fiber materials derived from cellulose fine fibers composed of the skeletal components of plant cell walls, which are obtained by finely breaking down plant fibers. Examples of plant sources for cellulose-based fine fibers include wood, bamboo, rice (rice straw), potato, sugarcane (bagasse), aquatic plants, and seaweed. Of these, wood is preferred.

[0027] The cellulose-based fine fibers include cellulose fine fibers themselves and hydrophobized cellulose fine fibers obtained by subjecting cellulose fine fibers to a hydrophobic treatment. The cellulose-based fine fibers preferably contain one or both of these.

[0028] Examples of cellulose-based fine fibers include those with a high aspect ratio produced by mechanical defibration means and those with needle-like crystals produced by chemical defibration means. The cellulose-based fine fibers preferably contain one or both of these, and more preferably contain cellulose-based fine fibers produced by mechanical defibration means from the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition.

[0029] The average fiber diameter of the cellulose-based fine fibers is, for example, 10 nm or more and 1000 nm or less. From the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition, the cellulose-based fine fibers preferably have a wide fiber diameter distribution, and the fiber diameter distribution range is preferably several tens to several hundreds of nm. The average fiber length of the cellulose-based fine fibers is, for example, 0.1 μm or more and 1000 μm or less. From the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition, the amount of the cellulose-based fine fibers in the uncrosslinked rubber composition before crosslinking is preferably 0.1 parts by mass or more and 10 parts by mass or less, more preferably 1 part by mass or more and 5 parts by mass or less, and even more preferably 2 parts by mass or more and 4 parts by mass or less, per 100 parts by mass of the rubber component. The mass ratio of the content of the second ethylene-α-olefin elastomer kneading reaction product to the amount of cellulose-based fine fibers in the uncrosslinked rubber composition before crosslinking (content of second ethylene-α-olefin elastomer kneading reaction product / amount of cellulose-based fine fibers) is preferably 1 or more and 30 or less, more preferably 3 or more and 20 or less, and even more preferably 6 or more and 10 or less, from the same viewpoints as above.

[0030] Examples of the crosslinking agent include organic peroxides and sulfur. As the crosslinking agent, an organic peroxide may be used alone, sulfur may be used alone, or both may be used in combination. From the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition, it is preferable that the crosslinking agent contains an organic peroxide.

[0031] Examples of organic peroxides used as crosslinking agents 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 organic peroxide of the crosslinking agent preferably contains one or more of these, and from the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition, it is more preferable that it contains a dialkyl peroxide, and it is even more preferable that it contains 1,3-di(t-butylperoxy)diisopropylbenzene and / or 1,4-di(t-butylperoxy)diisopropylbenzene.

[0032] The amount of organic peroxide used as a crosslinking agent in the uncrosslinked rubber composition before crosslinking is preferably 0.5 parts by mass or more and 8 parts by mass or less, more preferably 2 parts by mass or more and 4 parts by mass or less, per 100 parts by mass of the rubber component, from the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition.

[0033] The crosslinked rubber composition according to the embodiment may contain carbon black. Examples of carbon black include channel black, furnace black, thermal black, and acetylene black. Examples of furnace black include SAF, ISAF, N-339, HAF, N-351, MAF, FEF, SRF, GPF, ECF, and N-234. Examples of thermal black include FT and MT. The carbon black preferably contains one or more of these, and from the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition, more preferably contains furnace black, even more preferably contains carbon black having an arithmetic mean particle size of 20 μm to 25 μm, and even more preferably contains ISAF.

[0034] The amount of carbon black in the uncrosslinked rubber composition before crosslinking is preferably 20 parts by mass or more and 60 parts by mass or less, more preferably 30 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of the rubber component, from the viewpoint of reducing the hysteresis loss of the crosslinked rubber composition.

[0035] The crosslinked rubber composition according to the embodiment may contain other rubber compounding agents, such as process oil, processing aid, vulcanization accelerator, vulcanization accelerator aid, antioxidant, co-crosslinking agent, etc. [Example]

[0036] (Masterbatch) A powdered cellulose dispersion was prepared by dispersing powdered cellulose (KC Flock W-GK, manufactured by Nippon Paper Industries Co., Ltd.) in toluene. The powdered cellulose dispersion was then subjected to shearing using a high-pressure homogenizer, causing the powdered cellulose to collide with itself and defibrate into cellulose fine fibers. This resulted in a cellulose fine fiber dispersion in which non-hydrophobized cellulose fine fibers produced by mechanical defibration were dispersed in toluene. This cellulose fine fiber dispersion was then mixed with an EPDM solution prepared by dissolving a first ethylene-α-olefin elastomer, EP33, manufactured by Eneos Materials Corporation, ethylene content: 52% by mass, diene content (ENB content): 8.1% by mass, in toluene, so that the cellulose fine fiber content was 20 parts by mass per 100 parts by mass of EPDM. The toluene was then evaporated to prepare a masterbatch in which cellulose fine fibers (fiber diameter: tens to hundreds of nanometers) were dispersed in EPDM.

[0037] (Second ethylene-α-olefin elastomer kneading reaction product) EPDM (EP33 manufactured by Eneos Materials Co., Ltd.) was placed in an internal mixer and masticated, and then 1 part by mass of maleic anhydride and 0.1 part by mass of an organic peroxide reaction initiator (Percumyl D manufactured by NOF Corporation, dicumyl peroxide) were added per 100 parts by mass of EPDM, and the mixture was kneaded at 150°C for 5 minutes to produce a second ethylene-α-olefin elastomer kneaded reaction product.

[0038] (Crosslinked rubber composition) The crosslinked rubber compositions of the following Examples 1 to 3 and Comparative Example were prepared. The constitutions of each are also shown in Table 1.

[0039] Example 1 The masterbatch, the first ethylene-α-olefin elastomer, and the second ethylene-α-olefin elastomer kneaded reaction product were added to an internal kneader in a mass ratio of masterbatch / first ethylene-α-olefin elastomer / second ethylene-α-olefin elastomer kneaded reaction product = 18 / 75 / 10 and kneaded to produce a kneaded product in which 3 parts by mass of cellulose fine fibers were dispersed in 100 parts by mass of rubber components in a mass ratio of first ethylene-α-olefin elastomer / second ethylene-α-olefin elastomer kneaded reaction product = 90 / 10. Subsequently, 40 parts by mass of ISAF, 10 parts by mass of process oil, 1 part by mass of stearic acid, 5 parts by mass of zinc oxide, and 7 parts by mass (effective amount 2.8 parts by mass) of organic peroxide (Peroximon F-40 manufactured by NOF Corporation, a mixture of 1,3-di(t-butylperoxy)diisopropylbenzene and 1,4-di(t-butylperoxy)diisopropylbenzene, purity 40%) per 100 parts by mass of the rubber component were added and kneaded to prepare an uncrosslinked rubber composition. This uncrosslinked rubber composition was heated and pressurized to prepare a crosslinked rubber composition designated as Example 1.

[0040] <Examples 2 and 3> Example 2 was a crosslinked rubber composition prepared in the same manner as Example 1, except that the rubber components were the first ethylene-α-olefin elastomer / second ethylene-α-olefin elastomer kneaded reaction product in a mass ratio of 80 / 20.

[0041] Example 3 was a crosslinked rubber composition prepared in the same manner as Example 1, except that the rubber components were the first ethylene-α-olefin elastomer / second ethylene-α-olefin elastomer kneaded reaction product in a mass ratio of 50 / 50.

[0042] <Comparative Example> A crosslinked rubber composition was prepared as a comparative example in the same manner as in Example 1, except that only the first ethylene-α-olefin elastomer was used as the rubber component.

[0043] [Table 1]

[0044] (Hysteresis loss test method and results) For each of Examples 1 to 3 and the Comparative Example, JIS No. 3 dumbbell-shaped test specimens were prepared by punching out so that the grain direction (the orientation direction of the cellulose-based fine fibers) was the length direction. The test specimens were placed in a tensile tester and subjected to a test in which they were pulled to a strain of 30% at a speed of 500 mm / min, loaded, and then unloaded and returned to their original state. The stress-strain curve obtained at this time was then used to calculate the hysteresis loss, which was the area obtained by integrating the load curve from 0% to 30% strain, i.e., the area obtained by subtracting the load curve from the unload curve relative to the total energy applied by loading. This is the energy loss ratio. The results are shown in Table 1.

[0045] Table 1 shows that the hysteresis loss is reduced by including the second ethylene-α-olefin elastomer kneading reaction product in the rubber component. It also shows that the hysteresis loss is reduced as the content of the second ethylene-α-olefin elastomer kneading reaction product in the rubber component increases. [Industrial Applicability]

[0046] The present invention is useful in the technical field of crosslinked rubber compositions.

Claims

1. A crosslinked rubber composition containing a rubber component and cellulose-based fine fibers, the rubber component comprises a first ethylene-α-olefin elastomer, a second ethylene-α-olefin elastomer having an ethylene content of 40% by mass or more and 70% by mass or less, and a second ethylene-α-olefin elastomer kneading reaction product obtained by kneading and reacting maleic anhydride and an organic peroxide of a dialkyl peroxide, and the rubber component comprises the first ethylene-α-olefin elastomer and the second ethylene-α-olefin elastomer kneading reaction product as main components; A crosslinked rubber composition in which the first ethylene-α-olefin elastomer and the second ethylene-α-olefin elastomer each contain an ethylene-propylene-diene monomer whose diene component is ethylidene norbornene and whose diene content is 4% by mass or more and 12% by mass or less.

2. The crosslinked rubber composition according to claim 1, The crosslinked rubber composition, wherein the ethylene content of the first ethylene-α-olefin elastomer is 40% by mass or more and 70% by mass or less.

3. The crosslinked rubber composition according to claim 1, A crosslinked rubber composition, wherein the content of the first ethylene-α-olefin elastomer in the rubber component is greater than or equal to the content of the second ethylene-α-olefin elastomer kneading reaction product.

4. The crosslinked rubber composition according to claim 3, A crosslinked rubber composition, wherein the mass ratio of the content of the first ethylene-α-olefin elastomer to the content of the second ethylene-α-olefin elastomer kneading reaction product in the rubber component is 50 / 50 or more and 90 / 10 or less.

5. The crosslinked rubber composition according to claim 1, A crosslinked rubber composition, wherein the acid content of the rubber component is 0.01% by mass or more and 0.5% by mass or less.

6. The crosslinked rubber composition according to claim 1, The crosslinked rubber composition, wherein the cellulose-based fine fibers have an average fiber diameter of 10 nm or more and 1,000 nm or less and an average fiber length of 0.1 μm or more and 1,000 μm or less.

7. The crosslinked rubber composition according to claim 1, A crosslinked rubber composition, wherein the blending amount of the cellulose-based fine fibers in the uncrosslinked rubber composition before crosslinking is 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the rubber component.

8. The crosslinked rubber composition according to claim 1, A crosslinked rubber composition in which the mass ratio of the content of the second ethylene-α-olefin elastomer kneading reaction product to the blending amount of the cellulose-based fine fibers in an uncrosslinked rubber composition before crosslinking is 1 or more and 30 or less.

9. The crosslinked rubber composition according to claim 1, A crosslinked rubber composition in which a crosslinking agent blended with an uncrosslinked rubber composition before crosslinking contains a dialkyl peroxide, which is an organic peroxide.

10. The crosslinked rubber composition according to claim 1, A crosslinked rubber composition further containing ISAF carbon black.

11. The crosslinked rubber composition according to claim 10, A crosslinked rubber composition, wherein the amount of carbon black blended in an uncrosslinked rubber composition before crosslinking is 20 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the rubber component.

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