JP6045935B2 - Crosslinkable rubber composition for cushioning material and cushioning material using the same - Google Patents

Description

  The present invention relates to a crosslinkable rubber composition for a cushioning material, and more particularly to a crosslinkable nitrile rubber composition excellent in durability (impact resistance) against repeated impacts. The present invention also relates to a cushioning material using the rubber composition.

  A rubber cushioning material (hereinafter also referred to as “rubber cushioning material”) is incorporated in various devices and tools as a member responsible for absorbing an impact by a working member. A typical example of such a device or tool is a nailing machine that drives a piston built in a cylinder by air pressure and drives a nail, a needle, a screw or the like. The nailing machine is provided with a rubber cushioning material (typically a cylindrical rubber cushioning material) for absorbing an impact caused by a piston that repeatedly performs piston motion.

  The rubber cushioning material is required to have excellent durability (impact resistance) against repeated impacts and a long life. This is because the replacement frequency of the rubber cushioning material can be reduced.

  As a means for improving the impact resistance of the rubber cushioning material, it is conceivable to increase the rubber cushioning material, but in this case, the apparatus and tools for mounting the rubber cushioning material are also increased in size and weight, which is not desirable. It is not a means. In particular, in recent years, nailing machines have been reduced in size and pressure, and the increase in the size of rubber cushioning materials goes against this trend.

  Patent Documents 1 and 2 propose a technique for reducing the impact applied to the rubber cushioning material by appropriately controlling the shape of the rubber cushioning material. According to this technique, it is possible to improve the impact resistance of the rubber cushioning material without increasing the size by utilizing the bending of the rubber. However, these documents do not teach any compounding design of the rubber composition that can improve impact resistance.

  Conventionally, hydrogenated nitrile rubber (HNBR), nitrile rubber (NBR), urethane, or the like is generally used as the rubber cushioning material. In general, HNBR and urethane tend to be superior in mechanical properties as compared to NBR. Therefore, rubber cushioning materials using these rubber components tend to be superior in impact resistance. However, the use of HNBR or urethane increases the manufacturing cost of the rubber cushioning material compared with NBR.

JP 2008-094441 A JP 2002-103246 A

  An object of the present invention is to provide a cross-linkable rubber composition for a buffer material that can provide a buffer material having extremely excellent impact resistance despite the use of a general-purpose compounding component, and a buffer material formed by crosslinking the same. There is to do.

The present invention includes the following.
[1] 100 parts by weight of a rubber component containing acrylonitrile butadiene rubber;
Di-2-benzothiazolyl disulfide 1.0-2.5 parts by weight, N-cyclohexyl-2-benzothiazolylsulfenamide 1.0-2.5 parts by weight and tetraalkylthiuram disulfide 1.0-4 A crosslinking accelerator comprising 5 parts by weight;
Cross-linking retarder 0.3 to 1.0 parts by weight;
A crosslinkable rubber composition for a cushioning material, comprising:

  [2] The crosslinkable rubber composition according to [1], wherein the crosslinking retarder is N- (cyclohexylthio) phthalimide.

  [3] The crosslinkable rubber composition according to [1] or [2], wherein the tetraalkylthiuram disulfide is tetramethylthiuram disulfide.

  [4] The crosslinkable rubber composition according to any one of [1] to [3], wherein the content of a structural unit derived from acrylonitrile in the acrylonitrile butadiene rubber is 25 to 43% by weight.

  [5] The crosslinkable rubber composition according to any one of [1] to [4], further containing 0.3 to 1.0 part by weight of sulfur with respect to 100 parts by weight of the rubber component.

  [6] The crosslinkable rubber composition according to any one of [1] to [5], further containing 80 to 120 parts by weight of carbon black with respect to 100 parts by weight of the rubber component.

  [7] A cushioning material comprising a crosslinked product of the crosslinkable rubber composition according to any one of [1] to [6].

  [8] The cushioning material according to [7], wherein the tensile strength measured according to JIS K6251 is 18 MPa or more, the elongation at break is 150% or more, and the 100% tensile stress is 8 to 18 MPa.

  According to the cross-linkable rubber composition of the present invention, general-purpose and inexpensive NBR is used as a rubber component, and the other compounding components are also general-purpose, but the types, combinations and By appropriately controlling the content, it is possible to provide a cushioning material that is extremely excellent in impact resistance while reducing manufacturing costs.

  The shock-absorbing material according to the present invention can be suitably used as a shock-absorbing material for a nailing machine, or as a shock-absorbing material for installation at a location that receives repeated impacts in other devices and tools. Moreover, since NBR is excellent in oil resistance, it is not limited to a pneumatic cylinder such as a nailing machine, but is also effective as a shock absorber for a device or a tool including a hydraulic cylinder.

<Crosslinkable rubber composition for cushioning material>
The crosslinkable rubber composition for cushioning material of the present invention is
[A] rubber component,
[B] a crosslinking accelerator, and [C] a crosslinking retarder. Hereinafter, each component contained in the crosslinkable rubber composition for a cushioning material of the present invention and optionally contained components will be described in detail.

[A] Rubber component The rubber component includes nitrile rubber (NBR; acrylonitrile butadiene rubber). By using a general-purpose NBR, it is possible to produce a cushioning material at a lower cost than when HNBR or urethane is used. Another advantage of the crosslinkable rubber composition according to the present invention is that although NBR, which can be said to be disadvantageous compared to HNBR and urethane, is used as a rubber component in terms of mechanical properties, and other compounding components Although it is general-purpose, it is possible to provide a cushioning material having extremely excellent impact resistance.

  Although the content rate of the structural unit derived from acrylonitrile in NBR is not specifically limited, Preferably it is 25 to 43 weight%, More preferably, it is 27 to 40 weight%, More preferably, it is 29 to 37 weight%. When the content of the structural unit derived from acrylonitrile is within this range, both the cold resistance and the oil resistance of the obtained buffer material can be achieved.

  NBR may consist only of acrylonitrile and butadiene (1,3-butadiene), but may also contain structural units derived from other monomers. Specific examples of other monomers include, for example, ethylenically unsaturated carboxylic acids such as (meth) acrylic acid; esters of ethylenically unsaturated carboxylic acids (eg alkyl esters); isoprene. By copolymerizing other monomers, it may be possible to further improve the crosslinking characteristics of the rubber composition, the impact resistance, the tensile strength, the hardness, etc. of the resulting buffer material. Only 1 type may be used for another monomer and it may use 2 or more types together.

  The content of the structural unit derived from the other monomer in NBR is, for example, 20% by weight or less, preferably 15% by weight or less, more preferably 10% by weight or less, and further preferably 8% by weight or less. is there. Further, in the case where NBR includes a structural unit derived from another monomer, the content thereof is 0.1% by weight or more in order to express the intended effect of including the structural unit derived from another monomer. Preferably, it is 0.2% by weight or more, more preferably 0.5% by weight or more.

  The rubber component can contain other rubber components other than NBR. Specific examples of other rubber components include, for example, ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber (EPM), hydrogenated nitrile rubber (HNBR; hydrogenated acrylonitrile butadiene rubber), urethane rubber, butyl rubber (IIR), Includes fluoro rubber (FKM) and silicone rubber (Q). Other rubber components may be used alone or in combination of two or more.

  However, the content of other rubber components is preferably within a range that does not impair the gist of the present invention or the effects of the present invention. Specifically, the content of other rubber components in the rubber component is preferably 30% by weight or less, more preferably 15% by weight or less, and even more preferably 5% by weight or less, Particularly preferred is 0% by weight.

[B] Crosslinking accelerator The crosslinkable rubber composition of the present invention contains a combination of three specific compounds as a crosslinking accelerator. The three specific compounds are di-2-benzothiazolyl disulfide, N-cyclohexyl-2-benzothiazolylsulfenamide and tetraalkylthiuram disulfide, and their content is 100 parts by weight of rubber component 1.0 to 2.5 parts by weight, 1.0 to 2.5 parts by weight, and 1.0 to 4.5 parts by weight, respectively.

  By using a predetermined amount of each of the crosslinking accelerators containing a combination of such specific compounds, a buffer obtained in combination with using a predetermined amount of other predetermined blending components [A] and [C]. The impact resistance of the material can be significantly improved. When any one or more of the crosslinking accelerator components constituting the above combination are not included (or when other crosslinking accelerator components are included thereon), or any one of the crosslinking accelerator components constituting the above combination When the above content is less than the predetermined content, extremely high impact resistance cannot be obtained. In addition, when the content of any one or more of the crosslinking accelerator components constituting the combination is larger than the predetermined content, the crosslinking rate is too high (the time until the completion of crosslinking is too short) and the buffering is performed. Molding into the material itself can be difficult. From the viewpoint of improving impact resistance of the buffer material and moldability to the buffer material, the content of di-2-benzothiazolyl disulfide and N-cyclohexyl-2-benzothiazolylsulfenamide is 100 parts by weight of a rubber component. Each is preferably 1.2 to 2.2 parts by weight.

  Examples of the tetraalkyl thiuram disulfide include tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, and tetrabutyl thiuram disulfide. When tetramethylthiuram disulfide is used, its content is preferably 1.0 to 2.5 parts by weight with respect to 100 parts by weight of the rubber component. In the case of using tetraethylthiuram disulfide, the content thereof is preferably 1.2 to 3.1 parts by weight with respect to 100 parts by weight of the rubber component. When tetrabutyl thiuram disulfide is used, its content is preferably 1.7 to 4.3 parts by weight with respect to 100 parts by weight of the rubber component.

  Tetraalkylthiuram disulfide may be used alone or in combination of two or more. Among them, tetramethylthiuram disulfide and / or tetraethylthiuram disulfide is preferably used, and tetramethylthiuram disulfide alone or tetraethyl. Thiuram disulfide alone is more preferably used.

  The crosslinkable rubber composition of the present invention may contain a crosslinking accelerator other than the above three specific compounds. However, from the viewpoint of effectively improving the impact resistance of the buffer material and the moldability to the buffer material, the content of the other crosslinking accelerator is 10% by weight or less of the total amount of the above three compounds. Preferably, it is preferably 5% by weight or less, and more preferably 0% by weight.

[C] Crosslinking retarder The crosslinking retarder has a function of delaying the initiation time of crosslinking at the crosslinking / molding temperature (securing the initial flow time in the mold of the crosslinkable rubber composition) and partial crosslinking. It is an additive having an inhibitory function, and is an additive that is optionally blended depending on whether or not such a function is desired. However, in the present invention, it is blended as an essential component in the crosslinkable rubber composition. The In this invention, the compounding quantity of a crosslinking retarder shall be 0.3-1.0 weight part with respect to 100 weight part of rubber components.

  By including the predetermined amount of the crosslinking retarder in the crosslinkable rubber composition, the above-mentioned crosslinking initiation time delay effect and partial crosslinking inhibition effect can be obtained to an appropriate degree, and other predetermined blending components Combined with the use of a predetermined amount of [A] and [B], the shock resistance of the obtained cushioning material can be significantly improved. In order to obtain these effects more effectively, the content of the crosslinking retarder is preferably 0.4 to 0.8 parts by weight with respect to 100 parts by weight of the rubber component.

  When the crosslinking retarder is not included or when the content is less than 0.3 parts by weight with respect to 100 parts by weight of the rubber component, the above effect cannot be obtained or the effect is insufficient. Alternatively, the crosslinking rate may be too high, making it difficult to form the buffer material. On the other hand, when the content of the crosslinking retarder exceeds 1.0 part by weight with respect to 100 parts by weight of the rubber component, the crosslinking is excessively inhibited, so that a remarkable impact resistance cannot be imparted to the buffer material. In addition, other physical properties (hardness, 100% tensile stress, etc.) may be lowered.

  Although it does not restrict | limit especially as a crosslinking retarder, For example, N- (cyclohexylthio) phthalimide, N- (2-ethylhexyl thio) phthalimide, N- (cyclohexyl thio) maleimide, N- (4-t-butylphenylthio) succinimide Thioimide derivatives such as benzoic acid, salicylic acid and the like; N-isopropylthio-N-cyclohexyl-benzothiazyl-2-sulfonamide, N-cyclohexyl-N-trichloromethylthio-benzyl-2-sulfonamide, N -Amide derivatives such as phenyl-N-trichloromethylthiobenzenesulfonamide; aromatic dicarboxylic acids such as orthophthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, and acid anhydrides thereof. Only one type of crosslinking retarder may be used, or two or more types may be used in combination.

  Among the above, from the viewpoint of improving the impact resistance of the buffer material, as the crosslinking retarder, N- (cyclohexylthio) phthalimide, N- (2-ethylhexylthio) phthalimide, N- (cyclohexylthio) maleimide, N- ( Thioimide derivatives such as 4-t-butylphenylthio) succinimide are preferably used, and N- (cyclohexylthio) phthalimide is more preferably used.

[D] Crosslinking agent The crosslinkable rubber composition of the present invention usually contains a crosslinking agent. As the crosslinking agent, a sulfur-based crosslinking agent, an organic peroxide crosslinking agent, or the like can be used. Only 1 type may be used for a crosslinking agent and it may use 2 or more types together.

  Examples of sulfur-based crosslinking agents include powdered sulfur, sulfur white, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, and the like; sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, and polymer polysulfide. And the like. Only 1 type may be used for a sulfur type crosslinking agent, and 2 or more types may be used together.

  Examples of the organic peroxide crosslinking agent include dicumyl peroxide, t-butyl dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, di-t-butyl peroxide, t-butyl dicumyl peroxide, and benzoyl. Peroxide, acetyl peroxide, isobutyryl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, 2,5-dimethyl-2,5-di (benzoylperoxy) Hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, α, α′-bis (t-butylperoxyisopropyl) benzene, t-butylperoxyisopropyl carbonate, parachlorobenzoylper Oxide, t-butyl perbenzoate, 3,3,5-trimethylhexano Peroxide, n-butyl-4,4-bis (t-butylperoxy) valerate, di-sec-butylperoxydicarbonate, 1,1-di (t-butylperoxy) -3,3,5- Examples thereof include trimethylcyclohexane and 1,1-di (t-butylperoxy) cyclododecane. Only one organic peroxide crosslinking agent may be used, or two or more organic peroxide crosslinking agents may be used in combination.

  Among the above, from the viewpoint of improving the impact resistance of the buffer material, powdery sulfur, sulfur white, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur and the like are preferably used as the crosslinking agent.

  The content of the crosslinking agent in the crosslinkable rubber composition is usually 0.1 to 10 parts by weight, preferably 0.2 to 5.0 parts by weight, more preferably 100 parts by weight of the rubber component. 0.3 to 1.0 part by weight. Within this range, the crosslinking reaction can proceed sufficiently, so that it is possible to obtain a cushioning material that is excellent in hardness, mechanical strength, compression set resistance, and the like, and excellent in impact resistance. .

[E] Other components The crosslinkable rubber composition of the present invention can contain components other than the above-described components as necessary. Examples of other components include fillers (meaning including extender pigments and colored pigments), co-crosslinking agents, anti-aging agents, antioxidants, processing aids (stearic acid, zinc oxide, etc.), stabilizers, Examples include tackifiers, silane coupling agents, plasticizers, flame retardants, mold release agents, waxes, and lubricants. Only 1 type may be used for an additive and it may use 2 or more types together.

  When the crosslinkable rubber composition contains the above-mentioned additive, the content thereof may be an amount usually used in the art.

  Specific examples of fillers include carbon black, silica, alumina, zinc oxide, titanium dioxide, clay, talc, diatomaceous earth, barium sulfate, calcium carbonate, magnesium carbonate, calcium oxide, mica, graphite, aluminum hydroxide, aluminum silicate, hydro Includes talcite, granular or powdered resin, metal powder, glass powder, ceramic powder and the like.

  Among these, the crosslinkable rubber composition of the present invention preferably contains carbon black and / or silica as a reinforcing agent, and more preferably contains carbon black. In order to obtain a sufficient reinforcing effect, the content of the reinforcing agent is preferably 80 to 120 parts by weight, more preferably 85 to 115 parts by weight with respect to 100 parts by weight of the rubber component.

  Specific examples of the co-crosslinking agent include quinone dioxime, ethylene glycol dimethacrylate, divinylbenzene, diallyl phthalate, triallyl isocyanurate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, 1,2-polybutadiene, metal methacrylate salt , Metal acrylates and the like. The content of the liquid co-crosslinking agent in the crosslinkable rubber composition is preferably 20 parts by weight or less, more preferably 10 parts by weight or less with respect to 100 parts by weight of the rubber component.

  Specific examples of the antioxidant include phenol derivatives, aromatic amine derivatives, amine-ketone condensates, benzimidazole derivatives, dithiocarbamic acid derivatives, thiourea derivatives and the like.

  The crosslinkable rubber composition of the present invention can be prepared by uniformly kneading the above-described components. As the kneader, conventionally known ones such as a mixing roll, a pressure kneader, an internal mixer (Banbury mixer) can be used. At this time, among the blended components, the components other than the components that contribute to the crosslinking reaction (crosslinking accelerator, crosslinking retarder, crosslinking agent, etc.) are first kneaded uniformly, and then the components that contribute to the crosslinking reaction. You may make it knead | mix. The kneading temperature is, for example, around room temperature.

<Buffer material>
The buffer material (impact absorber) of the present invention is composed of a cross-linked product of the cross-linkable rubber composition according to the present invention. The buffer material can be produced by crosslinking (vulcanizing) and molding the crosslinkable rubber composition. As the crosslinking / molding method, conventionally known methods such as injection molding, compression molding, and transfer molding can be employed.

  The heating temperature (crosslinking temperature) at the time of molding is, for example, about 100 to 200 ° C., and the heating time (crosslinking time) is, for example, about 0.5 to 120 minutes.

  Although the cushioning material of the present invention uses general-purpose and inexpensive NBR as a rubber component and is also general-purpose for other compounding components, the types, combinations, and contents of the compounding components are as described above. Thus, by using the appropriately controlled crosslinkable rubber composition, it exhibits excellent physical properties as a rubber cushioning material, and is particularly excellent in impact resistance (durability against repeated impacts). The buffer material of the present invention typically has a tensile strength measured according to JIS K6251 of 18 MPa or more (preferably 20 MPa or more), an elongation at break of 150% or more (preferably 170% or more), The 100% tensile stress is 8 to 18 MPa (preferably 9 to 16 MPa).

  The shock-absorbing material of the present invention can be suitably used as a shock-absorbing material for a nailing machine or as a shock-absorbing material for installation at a location that receives repeated impacts in other devices and tools. Moreover, since NBR is excellent in oil resistance, it is not limited to a pneumatic cylinder such as a nailing machine, but is also effective as a shock absorber for a device or a tool including a hydraulic cylinder.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to these.

<Examples 1-5, Comparative Examples 1-10>
(1) Preparation of crosslinkable rubber composition and production of buffer material According to the following procedure, a crosslinkable rubber composition was prepared, and then a buffer material was produced. First, according to the compounding composition shown in Table 1 (the unit of the compounding amount in Table 1 is parts by weight), predetermined amounts of rubber component, anti-aging agent, processing aid and filler were kneaded by a pressure kneader. At this time, the rotation speed of the pressure kneader was 30 rpm, and the kneading time was the time required for the maximum temperature of the kneaded product to reach 120 ° C. After cooling, the obtained kneaded product was charged with a crosslinking agent, a crosslinking accelerator and a crosslinking retarder, and kneaded with a mixing roll to prepare a crosslinkable rubber composition.

  Next, the obtained crosslinkable rubber composition was molded and crosslinked at a temperature of 160 to 180 ° C. using a compression (direct pressure) molding machine to obtain a molded product (buffer material).

The detail of each component used in the Example and the comparative example is as follows.
[1] NBR: acrylonitrile butadiene rubber [“Nipol 1042” manufactured by Nippon Zeon Co., Ltd. (content of acrylonitrile-derived structural unit: 33.5 wt%)],
[2] Urethane rubber: General millable urethane rubber,
[3] HNBR: General hydrogenated nitrile rubber (content of structural unit derived from acrylonitrile 36.2% by weight, iodine value 28 mg / 100 mg),
[4] Anti-aging agent: octylated diphenylamine,
[5] Processing aid: stearic acid and zinc oxide (the blending amounts in Table 1 are the total amount thereof),
[6] Filler: Furnace black,
[7] Cross-linking agent: sulfur [“Jinhua stamp fine powder sulfur” manufactured by Tsurumi Chemical Co., Ltd.]
[8] Cross-linking accelerator 1: di-2-benzothiazolyl disulfide [“Noxeller DM-P” manufactured by Ouchi Shinsei Chemical Co., Ltd.]
[9] Cross-linking accelerator 2: N-cyclohexyl-2-benzothiazolylsulfenamide [“Noxeller CZ-G” manufactured by Ouchi Shinsei Chemical Co., Ltd.]
[10] Crosslinking accelerator 3: Tetramethylthiuram disulfide [“Noxeller TT-P” manufactured by Ouchi Shinsei Chemical Co., Ltd.]
[11] Cross-linking accelerator 4: 2-mercaptobenzothiazole ["Noxeller MP" manufactured by Ouchi Shinsei Chemical Co., Ltd.]
[12] Cross-linking accelerator 5: zinc dibutyldithiocarbamate [“Noxeller BZ-P” manufactured by Ouchi Shinsei Chemical Co., Ltd.]
[13] Crosslinking retarder: N- (cyclohexylthio) phthalimide [“Anscorch CTP” manufactured by Kawaguchi Chemical Co., Ltd.].

(2) Evaluation of buffer material The following items were measured and evaluated for the obtained molded product (buffer material). The results are also shown in Table 1.

[A] Normal property of buffer material According to JIS K6251, a dumbbell-shaped No. 3 type test piece was punched out from a sheet-like molded product produced in a thickness of 2 mm according to JIS K6250. This test piece was pulled at 500 mm / min, and the tensile strength, elongation at break, and 100% tensile stress were measured. Further, according to JIS K6253, the hardness of the sheet-like molded product was measured with a type A durometer hardness tester. All these tests were conducted at a temperature of 25 ° C.

[A] Durability of cushioning material The shock-absorbing material molded into a predetermined cylindrical shape is mounted on a commercially available nailing machine (a general nailing machine with a specified supply pressure of 0.3 to 0.8 MPa), and the supply air pressure is 0. An operation test was performed under the conditions of 0.7 MPa and a piston speed of about 1.2 seconds / cycle, and the number of piston operation cycles until the piston did not operate normally was measured.

  As the number of piston operations increases, the rubber cushioning material deteriorates or is damaged due to repeated impacts.If the degree exceeds a certain limit, the cushioning material breaks into the piston seal part or wears the cushioning material. The normal operation of the piston is hindered by a reduction in the lubricating effect of the lubricant due to the generation of powder.

  As shown in Table 1, the cushioning materials of Examples 1 to 5 are extremely high despite using general-purpose and inexpensive NBR as a rubber component and general-purpose components for other compounding components. The service life (impact resistance) is shown. It also had excellent tensile strength, elongation at break and 100% tensile stress. On the other hand, the shock-absorbing materials of Comparative Examples 1, 3, 5 to 8 and 10 have a low service life. Further, any of tensile strength, elongation at break or 100% tensile stress tended to be inferior. In Comparative Examples 2 and 4, the crosslinking rate was too fast, and it was difficult to form the buffer material itself.

Claims (8)

100 parts by weight of a rubber component containing acrylonitrile butadiene rubber;
Di-2-benzothiazolyl disulfide 1.0-2.5 parts by weight, N-cyclohexyl-2-benzothiazolylsulfenamide 1.0-2.5 parts by weight and tetraalkylthiuram disulfide 1.0-4 A crosslinking accelerator comprising 5 parts by weight;
Cross-linking retarder 0.3 to 1.0 parts by weight;
A crosslinkable rubber composition for a buffer material, comprising:   The crosslinkable rubber composition according to claim 1, wherein the crosslinking retarder is N- (cyclohexylthio) phthalimide.   The crosslinkable rubber composition according to claim 1 or 2, wherein the tetraalkylthiuram disulfide is tetramethylthiuram disulfide.   The crosslinkable rubber composition according to any one of claims 1 to 3, wherein a content of a structural unit derived from acrylonitrile in the acrylonitrile butadiene rubber is 25 to 43% by weight.   The crosslinkable rubber composition according to any one of claims 1 to 4, further comprising 0.3 to 1.0 part by weight of sulfur with respect to 100 parts by weight of the rubber component.   The crosslinkable rubber composition according to any one of claims 1 to 5, further comprising 80 to 120 parts by weight of carbon black with respect to 100 parts by weight of the rubber component.   The buffer material which consists of a crosslinked material of the crosslinkable rubber composition of any one of Claims 1-6.   The buffer material according to claim 7, wherein the tensile strength measured according to JIS K6251 is 18 MPa or more, the elongation at break is 150% or more, and the 100% tensile stress is 8 to 18 MPa.