Rubber composition

Abstract

To provide a rubber composition which eliminates surface irregularities on molded products, and suppresses deterioration in mechanical strength and mechanical properties after heating.SOLUTION: A rubber composition comprises the following components a to d. a. Ethylene-propylene-diene rubber. b. Carbon black. c. Cellulose nanofiber. d. At least one selected from talc, mica, and clay.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Patent Document 1 describes an EPDM composition for forming a sealing material for a refrigerant, which contains carbon black to which an organic peroxide is added as a crosslinking agent and a flat filler for enhancing gas barrier properties. Patent Document 2 describes a rubber composition that takes into account cold resistance and oil resistance and contains various rubbers such as EPDM, talc, and carbon black. Patent Documents 3 to 5 describe rubber compositions for tires and the like that contain various rubber components such as EPDM and cellulose nanofibers. According to these patent documents, compositions containing talc or carbon black in rubbers such as EPDM are known, and compositions containing cellulose nanofibers in rubbers such as EPDM are also known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described in the above background art, compositions containing talc or carbon black in rubbers such as EPDM, and compositions containing cellulose nanofibers in rubbers such as EPDM are known. However, these are solely for forming sealing materials for refrigerants and do not consider physical properties at high temperatures. An object of the present invention is to obtain a rubber composition that eliminates the unevenness on the surface of a molded article and suppresses deterioration of mechanical strength and mechanical physical properties after heating.

Means for Solving the Problems

[0005] In order to solve the above problems, the present invention adopts the following configuration. 1. A rubber composition containing the following a to d. a. Ethylene propylene diene rubber b. Carbon black c. Cellulose nanofibers d. One or more selected from talc, mica, and clay 2. The rubber composition according to 1, which contains e. a dispersant.

Effects of the Invention

[0006] According to the present invention, the unevenness on the surface of the rubber sheet obtained from the rubber composition is small, and it can exhibit the effects of having a high 50% modulus, strong tensile strength, high elongation, high heat resistance (as seen in the 50% modulus, tensile strength, and elongation respectively), and high IRM901 resistance.

Modes for Carrying Out the Invention

[0007] The present invention is a rubber composition containing the following a to d. a. Ethylene propylene diene rubber b. Carbon black c. Cellulose nanofibers d. One or more selected from talc, mica, and clay Hereinafter, preferred embodiments of the present invention will be described in detail.

[0008] [a. Ethylene propylene diene rubber] As the a. ethylene propylene diene rubber (hereinafter sometimes referred to as "EPDM") in the rubber composition of the present invention, any known EPDM can be selected. As the non-conjugated diene constituting EPDM, linear non-conjugated dienes such as 1,4-hexadiene, 1,5-hexadiene, 1,6-heptadiene, methyl-tetrahydroindene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, 5-methyl-1,5-heptadiene, 6-methyl-1,5-heptadiene, 6-methyl-1,7-octadiene and 7-methyl-1,6-octadiene; cyclic dienes such as dicyclopentadiene, 1,5-cyclooctadiene, 1,1-cyclooctadiene, 1,6-cyclododecadiene, 1,7-cyclododecadiene, 1,5,9-cyclododecatriene, 1,4-cycloheptadiene, 1,4-cyclohexadiene, 5-ethylidene-2-norbornene, 5-propylidene-5-norbornene, dicyclopentadiene, 5-vinyl-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene and norbornadiene; and trienes such as 2,3-diisopropylidene-5-norbornene and 4-ethylidene-8-methyl-1,7-nonadiene can be mentioned. The non-conjugated diene may be used alone or in combination of two or more. When two or more are used in combination, the combination and ratio may be appropriately selected according to the purpose. The content of EPDM in 100 parts by weight of the rubber composition of the present invention is preferably 20 parts by weight or more, more preferably 30 parts by weight or more. Also, it is preferably 60 parts by weight or less, more preferably 50 parts by weight or less. In the present invention, the diene content in the EPDM used is not particularly limited, but is preferably 4 to 10 parts by weight with respect to 100 parts by weight of the ethylene propylene diene rubber, and the ethylene content is preferably 40 to 70 parts by weight. If the diene content is low, vulcanization may be delayed and the mechanical strength may deteriorate. If the diene content is high, vulcanization may be accelerated and the mechanical strength may deteriorate. If the ethylene content is low, the tensile strength may deteriorate. If the ethylene content is high, the low-temperature properties may deteriorate. Also, the Mooney viscosity (ML(1+4) At 125 °C, it is preferably 20 or more, more preferably 25 or more. Also, it is preferably 70 or less, more preferably 60 or less. If the Mooney viscosity is too low, the rubber becomes too soft and the processability deteriorates. If the Mooney viscosity is too high, the rubber becomes too hard and the processability deteriorates.

[0009] [b. Carbon black] The carbon black used in the present invention is not particularly limited as long as it can be compounded with rubber. Among them, examples of carbon black include carbon black used for improving dispersibility, abrasion resistance, etc., such as hard carbon and soft carbon. By compounding carbon black, the tensile strength of the physical properties in the normal state (physical properties when not aged) can be improved. The content of carbon black with respect to 100 parts by weight of EPDM is preferably 20 parts by weight or more, more preferably 50 parts by weight or more. Also, it is preferably 120 parts by weight or less, more preferably 100 parts by weight or less. If it is less than 20 parts by weight, the tensile strength may be inferior. If it is more than 120 parts by weight, the elongation of the physical properties in the normal state may be inferior.

[0010] The average particle diameter of the primary particles of carbon black is not particularly limited, but is preferably 20 to 100 nm, more preferably 25 to 80 nm. When the average particle diameter of carbon black is less than 20 nm, the area of contact with the base EPDM increases, so the dielectric loss tangent increases, which is not preferable. Also, it is not preferable because it is too fine and difficult to handle. Also, in the case of carbon black with an average particle diameter of more than 100 nm, the tensile strength deteriorates, so it is not preferable.

[0011] [c. Cellulose nanofiber] The cellulose nanofibers used in the present invention are not particularly limited as long as they can be blended into the rubber composition. They may be unmodified cellulose nanofibers, or those modified with one or more selected from carboxylating agents, fluorene compounds, esterifying agents, silylating agents, isocyanate compounds, halogenated alkylating agents, alkylene oxides and / or glycidyl compounds. In order to improve the 50% modulus, heat resistance based on the 50% modulus, and IRM901 resistance of the rubber composition of the present invention, the content of cellulose nanofibers in the rubber composition is preferably 3 parts by weight or more, more preferably 4 parts by weight or more, based on 100 parts by weight of the above EPDM. Further, it is preferably 15 parts by weight or less, more preferably 10 parts by weight or less. The average fiber diameter is not particularly limited, but is preferably 50 to 1000 nm, more preferably 80 to 600 nm. Also, the fiber length is not particularly limited, but is preferably 3 to 80 μm, more preferably 5 to 60 μm. This average fiber diameter is determined as the spherical equivalent diameter (volume average particle diameter) of the particles when the integrated volume reaches 50% using a laser diffraction / scattering method particle size distribution analyzer. By including carbon black and cellulose nanofibers in the rubber composition, the 50% modulus and IRM901 resistance can be improved.

[0012] [d. One or more selected from talc, mica and clay] The rubber composition of the present invention can suppress the formation of irregularities on the surface of the rubber sheet and achieve a particularly high 50% modulus by blending one or more selected from talc, mica and clay. In particular, by blending one or more selected from talc, mica and clay, the content of carbon black can be relatively reduced, the processability can be improved, and in addition, the volume resistivity can be maintained high while maintaining various rubber physical properties. Talc, mica and clay may each be surface-treated or untreated. These particles are scaly. Talc, mica, and clay are not particularly limited respectively, but preferably have an average diameter of 0.1 to 50 μm. This average diameter is the volume average diameter measured by a laser diffraction particle size distribution analyzer. For scaly talc, mica, and clay, the aspect ratio (average diameter / thickness) is not particularly limited, but preferably 5 to 50. Such an aspect ratio can be obtained as an average value based on the measurement results of 100 particles by a scanning electron microscope.

[0013] In the present invention, clay can be used without particular limitation as long as it contains aluminum silicate as a main component. Examples include hard clay, soft clay, fired clay, etc. Generally, hard clay has 80% or more of the portion with a particle size of 2 μm or less, and soft clay has around 50%. In the present invention, it is particularly preferable to use hard clay among clays. The total content of one or more selected from talc, mica, and clay is preferably 5 parts by weight or more, more preferably 6 parts by weight or more, based on 100 parts by weight of EPDM. Also, it is preferably 50 parts by weight or less, more preferably 40 parts by weight or less. The higher the content, the more the unevenness on the surface of the molded body obtained from the rubber composition can be reduced. However, if the content exceeds 70 parts by weight, the heat resistance of the obtained rubber molded body may be low (the 50% modulus change rate is large). If the content of one or more selected from talc, mica, and clay is too small, the surface unevenness of the rubber sheet may be prominent, resulting in a low 50% modulus, low heat resistance (based on the 50% modulus), and low IRM901 resistance. If silica is contained instead of one or more selected from talc, mica, and clay, when a sheet is produced from the rubber composition, excessive unevenness may be formed on the surface, and the processability and IRM901 resistance may be reduced.

[0014] [e. Dispersant] In the present invention, the e. dispersant that may be used is an agent compounded into the rubber composition for the purpose of improving the dispersibility of cellulose nanofibers at the stage of processing the rubber composition. Such a dispersant is at least one selected from silane coupling agents, maleic anhydride modifiers such as maleic anhydride-modified liquid polybutadiene and maleic anhydride-modified polyolefin resin. And the content ratio of these dispersants in the rubber composition of the present invention is not particularly limited as long as it can exhibit the effect as a dispersant.

[0015] [Vulcanizing agent] In the present invention, the vulcanizing agent that may be used may be a known one, and the content of the vulcanizing agent may also be within a known range. As such a vulcanizing agent, a sulfur-based vulcanizing agent, an organic peroxide vulcanizing agent, a sulfur-containing organic compound vulcanizing agent, etc. can be appropriately selected and used.

[0016] Examples of the sulfur-based vulcanizing agent include powdered sulfur, sulfur flowers, highly dispersible sulfur, insoluble sulfur, precipitated sulfur, surface-treated sulfur, colloidal sulfur, sulfur chloride, sulfur monochloride, sulfur dichloride, etc. These sulfur-based vulcanizing agents can be used alone or in combination of two or more. In addition, when a sulfur-based vulcanizing agent is used as the vulcanizing / crosslinking agent, a vulcanization accelerator can also be used in combination.

[0017] Examples of the organic peroxide vulcanizing agent include 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane, di-tert-butyl peroxide, tert-butyl cumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne, 1,3-bis(tert-butylperoxy-isopropyl)benzene (peroxy P), tert-butylperoxy-isopropyl carbonate, acetylcyclohexylsulfonyl peroxide, isobutyl peroxide, diisopropyl peroxydicarbonate, diallyl peroxydicarbonate, dipropyl peroxydicarbonate, di(2-ethoxyethyl) peroxydicarbonate, di(methoxyisopropyl) peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, tert-hexyl peroxyneodecanoate, di(3-methyl-3-methyloxybutyl) peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-hexyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, 2,4-dichlorobenzoyl peroxide, tert-hexyl peroxy pivalate, tert-butyl peroxy pivalate, 3,3,5-trimethylhexanoyl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, cumyl peroxy octoate, acetyl peroxide, tert-butyl peroxy (2-ethylhexanoate), benzoyl peroxide, tert-butyl peroxyisobutyrate, 1,1-bis(tert-butylperoxy)cyclohexane, tert-butyl peroxymaleic acid, tert-butyl peroxy laurate, tert-butyl peroxy-3,3,5-trimethylhexanoate, cyclohexanone peroxide, tert-butyl peroxyallyl carbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,2-bis(tert-butylperoxy)octane, tert-butyl peroxyacetate, 2,2-bis(tert-butylperoxy)butane, tert-butyl peroxybenzoate, butyl-4,4-bis(tert-butylperoxy)valerate, di-tert-butyldiperoxyisophthalate, methyl ethyl ketone peroxide, α,α'-Bis(tert-butylperoxy-m-isopropyl)cyclohexane, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, cumene hydroperoxide, tert-butyl hydroperoxide, etc. can be mentioned. These organic peroxide vulcanizing agents can be used alone or in combination of two or more kinds.,

[0018] When using an organic peroxide vulcanizing agent, a co-vulcanizing agent can also be used in combination. Examples of co-vulcanizing agents include p-quinonedioxime, p-benzoquinonedioxime, p,p'-dibenzoylquinonedioxime, N-methyl-N'-4-dinitrosoaniline, N,N-m-phenylenebismaleimide, dinitrosobenzene, divinylbenzene, triallyl cyanurate, triallyl isocyanurate, triazine thiol, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, erythritol tetra(meth)acrylate, divinyl adipate, vinyl butyrate, vinyl stearate, liquid polybutadiene rubber, liquid polyisoprene rubber, liquid styrene-butadiene rubber, liquid acrylonitrile-butadiene rubber, magnesium (meth)acrylate, calcium (meth)acrylate, aluminum (meth)acrylate, zinc (meth)acrylate, stannous (meth)acrylate, hexamethylenediamine carbamate, amylphenol disulfide polymer, etc. These co-vulcanizing agents can be used alone or in combination of two or more kinds.,

[0019] Examples of the sulfur-containing organic vulcanizing agent include thiuram polysulfides such as morpholine disulfide, alkylphenol disulfide, N,N'-dithio-bis(hexahydro-2H-azepinone-2), and tetramethylthiuram disulfide, and 2-(4'-morpholino·dithio)benzothiazole. These sulfur-containing organic vulcanizing agents can be used alone or in combination of two or more.

[0020] Without losing the properties of the rubber composition of the present invention and the molded article obtained from the rubber composition, and without impairing the effects of the present invention, in addition to the above, known vulcanization accelerators, vulcanization acceleration aids, liquid rubbers, plasticizers, softeners, anti-aging agents, thermoplastic resins, flame retardants, thermoplastic elastomers, thermosetting resins, fillers, crosslinking aids, antioxidants, activators, ultraviolet absorbers, tackifiers, lubricants, water scavengers, waxes, activators, light stabilizers, internal mold release agents, scorch inhibitors, foaming agents, foaming aids, antibacterial agents, rust preventives, fungicides, mastication accelerators, heat storage agents, electronic conductivity imparting agents, ionic conductivity imparting agents, phosphorescent agents, colorants, stress luminescent agents, ferrite-based soft magnetic powder, metal-based soft magnetic powder, hydrotalcite, carbon nanofiber, carbon nanohorn, carbon nanocone, carbon nanotube, carbon nanocoil, carbon microcoil, carbon nanowall, carbon nanochaplet, fullerene, carbon black, graphite, graphene, carbon nanoflake, and derivatives thereof, silica, hollow nanosilica, etc. can be contained. However, it is preferably not to contain silica and / or expandable graphite.

[0021] [Rubber components that may be used in combination] For the EPDM according to the present invention, one or more selected from the following rubbers may be contained within a range not inhibiting the effects of the present invention. Also, it may not be contained. Acrylic rubber (ACM), rubbery copolymer of ethyl acrylate or other acrylic esters and ethylene (AEM), rubbery copolymer of ethyl acrylate or other acrylic esters and acrylonitrile (ANM), chlorosulfonated polyethylene, chlorinated polyethylene (CPE), rubbery copolymer of ethylene and propylene (EPM), rubbery copolymer of ethylene and vinyl acetate (EVM), rubbery copolymer of tetrafluoroethylene and propylene (FEPM), rubbery copolymer in which all side chains are fluoro and perfluoroalkyl or perfluoroalkoxy groups (FFKM), rubbery copolymer having fluoro and perfluoroalkyl or perfluoroalkoxy groups in the side chains (FKM), polyisobutene or polyisobutylene (IM), rubbery copolymer of acrylonitrile and butadiene in which the main chain is fully hydrogenated (HNBM), rubbery copolymer of styrene, ethylene and butene (SEBM), rubbery copolymer of styrene, ethylene and propylene (SEPM), acrylonitrile-butadiene copolymer rubber, etc. can be mentioned.

[0022] As rubbers having carbon and oxygen in the main chain, epichlorohydrin rubber (EO), polychloromethyloxirane (CO), rubbery copolymer of ethylene oxide and epichlorohydrin (ECO), rubbery copolymer of epichlorohydrin and allyl glycidyl ether (GCO), rubbery copolymer of ethylene oxide, epichlorohydrin and allyl glycidyl ether (GECO), rubbery copolymer of propylene oxide and allyl glycidyl ether (GPO), etc. can be mentioned.

[0023] Examples of rubbers having unsaturated carbon-carbon bonds in the main chain include acrylate butadiene rubber (ABR), butadiene rubber (BR), chloroprene rubber (CR), epoxidized natural rubber (ENR), hydrogenated rubbery copolymer of acrylonitrile and butadiene (HNBR), rubbery copolymer of isobutene and isoprene (IIR), isoprene rubber (IR), rubbery copolymer of α-methylstyrene and butadiene (MSBR), rubbery copolymer of acrylonitrile, butadiene and isoprene (NBIR), rubbery copolymer of acrylonitrile and butadiene (NBR), rubbery copolymer of acrylonitrile and isoprene (NIR), natural rubber (NR), norbornene rubber (NOR), rubbery copolymer of vinylpyridine and butadiene (PBR), rubbery copolymer of vinylpyridine, styrene and butadiene (PSBR), rubbery copolymer of styrene and butadiene (SBR), rubbery copolymer of styrene and butadiene synthesized by emulsion polymerization (E-SBR), rubbery copolymer of styrene and butadiene synthesized by solution polymerization (S-SBR), rubbery copolymer of styrene, isoprene and butadiene (SIBR), brominated rubbery copolymer of isobutene and isoprene (BIIR), chlorinated rubbery copolymer of isobutene and isoprene (CIIR), etc.

[0024] Examples of rubbers having silicon and oxygen in the main chain include silicone rubber (FMQ) having methyl and fluoro substituents in the polymer chain, silicone rubber (FVMQ) having methyl, vinyl and fluoro substituents in the polymer chain, silicone rubber (MQ) having a methyl substituent in the polymer chain, silicone rubber (PMQ) having methyl and phenyl substituents in the polymer chain, silicone rubber (PVMQ) having methyl, vinyl and phenyl substituents in the polymer chain, silicone rubber (VMQ) having methyl and vinyl substituents in the polymer chain, etc.

[0025] Examples of rubbers having carbon, oxygen, and nitrogen in the main chain include rubbery copolymers of tetrafluoroethylene, nitroso methane trifluoride, and nitroso perfluorobutyric acid (AFMU), polyester urethane (AU), polyether urethane (EU), etc. Examples of rubbers having sulfur, oxygen, and carbon in the main chain include rubbers (OT) having either a -CH2-CH2-O-CH2-O-CH2-CH2- group or an R group (R is an aliphatic hydrocarbon) between the polysulfide bonds in the polymer chain, and rubbers (EOT) having a -CH2-CH2-O-CH2-O-CH2-CH2- group and usually a -CH2-CH2- group (and in some cases other aliphatic groups) between the polysulfide bonds in the polymer chain, etc.

[0026] Examples of rubbers having phosphorus and nitrogen in the main chain include rubbers (FZ) having a -P=N- chain and a fluoroalkoxy group bonded to the phosphorus atom in the chain, rubbers (PZ) having a -P=N- chain and an alkoxy (phenoxy and substituted phenoxy) group bonded to the phosphorus atom in the chain, etc. These rubbers described above may also be epoxy, carboxy, amino, or acid-modified rubbers.

[0027] Among these, ACM, AEM, ANM, EPDM, EPM, EVM, FEPM, FFKM, FKM, IM, NBM, SEBM, SEPM, GPO, ABR, BR, FZ, NR, HNBR, IIR, IR, MSBR, NBIR, NBR, NIR, NOR, PBR, PSBR, SBR, E - SBR, S - SBR, SIBR, FMQ, FVMQ, MQ, PMQ, PVMQ, VMQ, AFMU, AU, EU, OT, EOT, PZ, HSBR, SEBC, CEBC, SEBS that do not contain chlorine or bromine which cause corrosion and contamination to metals are preferred. For FMQ, FVMQ, MQ, PMQ, PVMQ, VMQ, those that have been subjected to high - temperature heat treatment (for example, at 200°C for 24 hours) to completely remove low - molecular - weight cyclic siloxanes (D4 - D20) which are the cause of poor contact are preferred. More preferably, ACM, AEM, ANM, EPDM, EPM, EVM, FEPM, FFKM, FKM, NBM, HNBR, NBR, IIR, NOR, AFMU, AU, EU, FZ, PZ, CEBC, and even more preferably, ACM, AEM, ANM, EPM, EPDM, FFKM, FKM, NBM, HNBR, NBR, IIR, NOR. These may be used alone or in combination of two or more.

[0028] [Manufacture and Molding of Rubber Composition] As a process for obtaining the rubber composition of the present invention, a process of kneading the compounded materials using a processing machine such as a normal two - roll mill, a pressure kneader, a Banbury mixer, an internal mixer, etc. can be adopted. Also, after the above - mentioned kneading process, it is molded into a desired shape and structure. This molded product can be vulcanized to obtain a molded body made of the rubber composition of the present invention. Note that vulcanization conditions such as steam vulcanization can be arbitrarily selected from known conditions. The molded body made of the rubber composition of the present invention may have a shape and structure in which a sheet - like material, a hose, or other rubber molded bodies can be formed. Also, considering the property of having excellent heat resistance and oil resistance, it can be used for applications that require heat resistance and oil resistance from the external environment, such as at least a part of the rubber layer like a hose for brake fluid, especially the outer rubber layer.

[0029] The rubber composition of the present invention is excellent in processability, and the molded body obtained therefrom has few irregularities on the surface, high initial modulus, excellent heat resistance, low volume change rate during heating, and excellent volume resistivity. As the obtained molded body, it may be integrated with molded bodies such as other rubber compositions and resin compositions, and further molded bodies such as other fiber reinforcing layers, or it may be a molded body composed only of the rubber composition layer of the present invention. The main uses of the rubber composition of the present invention are for seal members, hoses for hot water supply, hoses for water supply, hoses for refrigerants, hoses for fuels, hoses for brake fluids, and hoses for working fluids other than brake fluids. It may also be used for tires, or it may not be used for tires.

[0030] The preferable properties after crosslinking of the rubber composition of the present invention are shown as the properties of the test pieces described in the following examples and the results measured under the respective measurement conditions described in the examples, and the results obtained by the method described in the examples. The 50% modulus is preferably 4.0 MPa or more, more preferably 4.3 MPa or more. The tensile strength is preferably 9.0 MPa or more, more preferably 10.0 MPa or more. The elongation is preferably 200% or more, more preferably 250% or more. The heat resistance (50% modulus change rate) is preferably 50% or less, more preferably 45% or less. The resistance to IRM901 (volume change rate) is preferably 75% or less, more preferably 70% or less.

[0031] (Examples) Next, the present invention will be described more specifically based on examples, but the present invention is not limited thereto. The following materials were mixed so as to have the composition (values are in parts by weight) shown in Table 1 below, molded into a sheet shape, and press-vulcanized at 180°C for 8 minutes to obtain test pieces having a length, width, and thickness of 100 mm × 100 mm × 2 mm.

[0032] EPDM: ENP content 8.1%, ethylene content 52%, Mooney viscosity (ML (1+4) 125°C) 28 FEF: Carbon Black SPHERON SO-1 (Cabot Japan Ltd.) CNF-filled EPDM Masterbatch: (100 parts by weight of EPDM + 20 parts by weight of CNF) PIGMOTEX CLEAR BC5010 (Sunshine Pigment Co., Ltd.) Talc: ImerFlex T20 (Imerys Specialties Japan Ltd.) Silica: Precipitated Silica Nipsil VN3 (Tokyo Titanium Co., Ltd.) (BET specific surface area 180 - 230 m 2 / g), pH = 6.0 Mica: MS325A (Shiraishi Calcium Co., Ltd.) Amino-silane treated aluminum silicate Clay: Crown Clay (Active Minerals international, LLC) Silane coupling agent: Bis[3-(triethoxysilyl)propyl]tetrasulfide Maleic anhydride modified liquid polybutadiene: Ricobond 1756HS (Cray Valley) Maleic anhydride modified polyolefin resin: Yumex 5200 (Sanyo Chemical Industries, Ltd.) Softening agent: SUNPAR 150S (Process oil containing 55% or more paraffinic hydrocarbons) (Nippon Sun Oil Co., Ltd.) 35 parts by weight Three types of zinc oxide: Vulcanization accelerator promoter (Shodo Chemical Industry Co., Ltd.) 5 parts by weight Stearic acid 1 part by weight Breakdown of sulfur + vulcanization accelerator in the table Vulcanizing agent: Sulfur 200 mesh (Hosoi Chemical Industry Co., Ltd.) 0.5 part by weight Vulcanizing agent: Morpholine disulfide 2 parts by weight Vulcanization accelerator: Dibenzothiazolyl disulfide 1 part by weight Vulcanization accelerator: Zinc dibutyldithiocarbamate 1 part by weight Vulcanization accelerator: Tetramethylthiuram disulfide 0.5 part by weight

[0033] (Unevenness on the surface of the rubber sheet) The surface of the rubber sheet was observed with a digital microscope, and the degree of unevenness was evaluated by the following surface roughness Sa. The surface roughness Sa refers to the arithmetic mean height and represents the average of the absolute values of the height differences of each point with respect to the average plane of the surface. ○: No unevenness (smooth), surface roughness Sa: less than 50 μm △: Slight unevenness, surface roughness Sa: 50 - 100 μm ×: Obvious unevenness, surface roughness Sa: more than 100 μm

[0034] (50% modulus) An unvulcanized rubber composition with a thickness of 2 mm was vulcanized by press heating at 180 °C for 8 minutes, and then a dumbbell-shaped No. 3 test piece defined in JIS K6251 was prepared. In accordance with JIS K6251 "Vulcanized Rubber and Thermoplastic Rubber - Method for Determining Tensile Properties", the 50% elongation tensile stress (M50) was measured.

[0035] (Tensile strength) For the dumbbell-shaped No. 3 test piece obtained by the same method as that adopted during the measurement of the above 50% modulus, the tensile strength at break was measured in accordance with JIS K6251.

[0036] (Elongation) For the dumbbell-shaped No. 3 test piece obtained by the same method as that adopted during the measurement of the above 50% modulus, the elongation at break was measured in accordance with JIS K6251.

[0037] (Heat resistance (50% modulus change rate)) For the dumbbell-shaped No. 3 test piece obtained by the same method as that adopted during the measurement of the above 50% modulus, the 50% elongation tensile stress (M50) was measured in accordance with JIS K6251 before and after heat treatment at 150 °C for 70 hours. The increase rate of the value of the 50% elongation tensile stress after heat treatment with respect to the value before heat treatment was defined as the heat resistance (50% modulus change rate).

[0038] (Resistance to IRM901 (volume change rate)) An uncrosslinked rubber composition with a thickness of 2 mm was crosslinked by press heating and then punched into a size of 20 mm × 30 mm to obtain a test piece. This test piece was immersed in a test lubricating oil IRM901 at 100 °C for 70 hours. The increase rate of the volume after immersion with respect to the volume of the test piece before immersion was defined as the IRM901 resistance (volume change rate).

[0039]

Table 1

[0040]

Table 2

[0041]

Table 3

[0042] According to each example in accordance with the present invention, the surface of the rubber sheet had only slight unevenness, and had a high 50% modulus, strong tensile strength, high elongation, and high heat resistance (as seen in terms of 50% modulus, tensile strength, and elongation respectively), and it was possible to suppress a decrease in these physical properties due to high-temperature treatment, and all had high IRM901 resistance. On the other hand, according to Comparative Example 1 that does not contain cellulose nanofibers, talc, mica, or clay, and Comparative Example 2 that does not contain cellulose nanofibers, the results showed a low 50% modulus, heat resistance based on the low 50% modulus, and low IRM901 resistance. According to Comparative Example 3 that contains cellulose nanofibers but does not contain talc, mica, or clay, obvious unevenness occurred on the surface of the rubber sheet. According to Comparative Example 4 that contains an excessive amount of talc, the tensile strength decreased, and the change rate of the 50% modulus after the heat resistance test increased. According to Comparative Examples 5, 7, and 8 with low cellulose nanofiber contents, the 50% modulus was low and the change rate of the 50% modulus after the heat resistance test was high. Furthermore, according to Comparative Example 7, the result showed low IRM901 resistance. According to Comparative Example 6 with an excessively high cellulose nanofiber content, obvious unevenness occurred on the rubber sheet and the elongation rate was low. In Comparative Examples 9 and 10 with a relatively high cellulose nanofiber content, according to Comparative Example 10 with a relatively high talc content as well, the results remained at low tensile strength and elongation rate. According to Comparative Example 11 containing no talc, mica, or clay but containing silica, obvious unevenness occurred on the surface of the rubber sheet and the result showed low IRM901 resistance.

Claims

Claim 1 A rubber composition containing the following a to d. a. Ethylene propylene diene rubber b. Carbon black c. Cellulose nanofiber d. One or more selected from talc, mica, and clay Claim 2 The rubber composition according to claim 1, containing a dispersant.

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