Crosslinked rubber composition and transmission belt comprising same

Abstract

The present invention is a crosslinked rubber composition obtained by crosslinking an uncrosslinked rubber composition. The uncrosslinked rubber composition contains a first rubber component of an ethylene-α-olefin elastomer, the α-olefin being propylene, a second rubber component of an ethylene-1-butene-diene terpolymer, and an α,β-unsaturated carboxylate metal salt.

Description

Crosslinked rubber composition and transmission belt using the same

[0001] The present invention relates to a crosslinked rubber composition and a power transmission belt using the same.

[0002] Ethylene-α-olefin elastomers are widely used as rubber components of cross-linked rubber compositions for forming rubber products. For example, Patent Documents 1 and 2 disclose the use of a blend rubber of an ethylene propylene diene terpolymer and an ethylene-1-butene copolymer as a rubber component of a cross-linked rubber composition for forming a belt body of a transmission belt.

[0003] JP 2006-153059 A Japanese Patent No. 4745789 A

[0004] The present invention provides a crosslinked rubber composition obtained by crosslinking an uncrosslinked rubber composition, the uncrosslinked rubber composition comprising a first rubber component which is an ethylene-α-olefin elastomer in which the α-olefin is propylene, a second rubber component which is an ethylene-1-butenediene terpolymer, and an α,β-unsaturated carboxylic acid metal salt.

[0005] The present invention is a power transmission belt at least a portion of which is formed from the crosslinked rubber composition of the present invention.

[0006] 1 is a perspective view of a V-belt segment;

[0007] The embodiments will be described in detail below.

[0008] The crosslinked rubber composition X according to the embodiment is obtained by crosslinking the uncrosslinked rubber composition X'. The uncrosslinked rubber composition X' contains a first rubber component which is an ethylene-α-olefin elastomer in which the α-olefin is propylene, a second rubber component which is an ethylene-1-butenediene terpolymer (EBDM), and an α,β-unsaturated carboxylic acid metal salt as a co-crosslinking agent.

[0009] In the case of a crosslinked rubber composition containing an ethylene propylene diene terpolymer or an ethylene propylene copolymer as a rubber component, the uncrosslinked rubber composition before crosslinking has low adhesiveness. Therefore, when the uncrosslinked rubber composition is used to form an uncrosslinked molded article, for example, when a sheet-shaped uncrosslinked rubber composition is laminated or when the uncrosslinked rubber composition is compounded with a fibrous member or the like, there is a problem that the molding processability is poor due to the poor adhesion of the uncrosslinked rubber composition.

[0010] To address this problem, according to the crosslinked rubber composition X according to the embodiment, the uncrosslinked rubber composition X' before crosslinking contains a first rubber component which is an ethylene-α-olefin elastomer in which the α-olefin is propylene, a second rubber component which is EBDM, and a metal salt of an α,β-unsaturated carboxylic acid as a co-crosslinking agent, thereby making it possible to obtain excellent moldability from the uncrosslinked rubber composition X' before crosslinking while suppressing a decrease in hardness of the crosslinked crosslinked rubber composition X after crosslinking. This is thought to be because the second rubber component increases the tackiness of the uncrosslinked rubber composition X' before crosslinking, while the metal salt of an α,β-unsaturated carboxylic acid increases the crosslink density of the first and second rubber components, thereby suppressing a decrease in hardness of the crosslinked crosslinked rubber composition X after crosslinking.

[0011] Here, the first rubber component contains ethylene propylene diene terpolymer (EPDM) and / or ethylene propylene copolymer (EPR). Therefore, the first rubber component may be composed of only EPDM, only EPR, or a blend rubber of EPDM and EPR. From the viewpoint of obtaining excellent moldability of the uncrosslinked rubber composition X' before crosslinking while suppressing a decrease in hardness of the crosslinked rubber composition X after crosslinking, it is preferable that the first rubber component contains EPDM.

[0012] The ethylene content of the first rubber component is preferably 40% by mass or more and 70% by mass or less, more preferably 45% by mass or more and 55% by mass or less, and even more preferably 50% by mass or more and 53% by mass or less, from the viewpoint of obtaining excellent moldability of the uncrosslinked rubber composition X' before crosslinking while suppressing a decrease in hardness of the crosslinked rubber composition X after crosslinking.

[0013] When the first rubber component contains EPDM, examples of the diene component include 5-ethylidene-2-nobornene (ENB), 5-vinyl-2-nobornene (VNB), dicyclopentadiene, and 1,4-hexadiene. Among these, ENB is preferred as the diene component from the viewpoint of obtaining excellent moldability of the uncrosslinked rubber composition X' before crosslinking while suppressing a decrease in hardness of the crosslinked rubber composition X after crosslinking. In this case, the ENB content (diene content) of the EPDM contained in the first rubber component is preferably 4% by mass or more and 12% by mass or less, more preferably 6% by mass or more and 10% by mass or less, and even more preferably 7.5% by mass or more and 8.5% by mass or less, from the same viewpoints as above.

[0014] The ethylene content of the EBDM of the second rubber component is preferably 40% by mass or more and 60% by mass or less, more preferably 45% by mass or more and 55% by mass or less, and even more preferably 48% by mass or more and 52% by mass or less, from the viewpoint of obtaining excellent moldability of the uncrosslinked rubber composition X' before crosslinking while suppressing a decrease in hardness of the crosslinked rubber composition X after crosslinking.

[0015] From the viewpoint of homogenizing the crosslinked rubber composition X after crosslinking, it is preferable that the difference between the ethylene content of the second rubber component and the ethylene content of the first rubber component is small. Specifically, from the same viewpoint as above, the difference between the ethylene content of the first rubber component and the ethylene content of the second rubber component is preferably 10% by mass or less, more preferably 7% by mass or less, even more preferably 5% by mass or less, and still more preferably 3% by mass or less. From the same viewpoint as above, it is preferable that the ethylene content of the second rubber component is less than the ethylene content of the first rubber component. From the same viewpoint as above, the content ratio of the ethylene content of the second rubber component to the ethylene content of the first rubber component is preferably 0.9 or more and less than 1, more preferably 0.93 or more and 0.99 or less, and even more preferably 0.95 or more and 0.98 or less.

[0016] Examples of the diene component of the second rubber component include ENB, VNB, dicyclopentadiene, and 1,4-hexadiene. Of these, ENB is preferred as the diene component from the viewpoint of obtaining excellent moldability of the uncrosslinked rubber composition X' before crosslinking while suppressing a decrease in hardness of the crosslinked rubber composition X after crosslinking. In this case, from the same viewpoint, the ENB content (diene content) of the EBDM of the second rubber component is preferably 4% by mass or more and 10% by mass or less, more preferably 6% by mass or more and 8% by mass or less, and even more preferably 6.5% by mass or more and 7.5% by mass or less.

[0017] When the first rubber component contains EPDM containing ENB as a diene component, it is preferable that the difference between the ENB content of the EBDM of the second rubber component and the ENB content of the EPDM contained in the first rubber component is small, from the viewpoint of homogenizing the crosslinked rubber composition X after crosslinking. Specifically, from the same viewpoint as above, the difference between the ENB content of the EPDM contained in the first rubber component and the ENB content of the EBDM of the second rubber component is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1.5% by mass or less. From the same viewpoint as above, it is preferable that the ENB content of the EBDM of the second rubber component is less than the ENB content of the EPDM contained in the first rubber component. From the same viewpoint as above, the content ratio of the ENB content of the EBDM of the second rubber component to the ENB content of the EPDM contained in the first rubber component is preferably 0.8 or more and less than 1, more preferably 0.83 or more and 0.95 or less, and even more preferably 0.85 or more and 0.9 or less.

[0018] The content A1 of the first rubber component in the uncrosslinked rubber composition X' is preferably larger than the content A2 of the second rubber component, from the viewpoint of obtaining excellent moldability of the uncrosslinked rubber composition X' before crosslinking while suppressing a decrease in hardness of the crosslinked rubber composition X after crosslinking. From the same viewpoints as above, the mass ratio (A1 / A2) of the content A1 of the first rubber component to the content A2 of the second rubber component is preferably larger than 50 / 50 and not larger than 95 / 5, more preferably 60 / 40 or larger and 85 / 15 or smaller, and even more preferably 65 / 35 or larger and 75 / 25 or smaller.

[0019] The uncrosslinked rubber composition X′ may contain a rubber component other than the first and second rubber components in an amount less than the total amount of the first and second rubber components. Examples of the rubber component other than the first and second rubber components include ethylene-1-butene copolymer (EBR), chloroprene rubber (CR), and hydrogenated nitrile rubber (H-NBR).

[0020] Examples of the metal salt of α,β-unsaturated carboxylic acid include metal diacrylate and metal dimethacrylate. Examples of the metal salt of diacrylate include zinc diacrylate and magnesium diacrylate. Examples of the metal salt of dimethacrylate include zinc dimethacrylate and magnesium dimethacrylate. The α,β-unsaturated carboxylic acid metal salt preferably contains one or more of these. From the viewpoint of obtaining excellent moldability of the uncrosslinked rubber composition X' before crosslinking while suppressing a decrease in hardness of the crosslinked rubber composition X after crosslinking, it is more preferable to contain metal dimethacrylate, and even more preferable to contain zinc dimethacrylate. An example of a commercially available zinc dimethacrylate of the α,β-unsaturated carboxylic acid metal salt is Acta ZMA manufactured by Kawaguchi Chemical Industry Co., Ltd.

[0021] From the viewpoint of obtaining excellent moldability of the uncrosslinked rubber composition X' before crosslinking while suppressing a decrease in hardness of the crosslinked rubber composition X after crosslinking, the content B of the α,β-unsaturated carboxylic acid metal salt in the uncrosslinked rubber composition X' is preferably 5 parts by mass or more and 100 parts by mass or less, more preferably 10 parts by mass or more and 30 parts by mass or less, and even more preferably 15 parts by mass or more and 25 parts by mass or less, relative to 100 parts by mass of the total content of the first and second rubber components. From the same viewpoint as above, the mass ratio (B / A2) of the content B of the α,β-unsaturated carboxylic acid metal salt in the uncrosslinked rubber composition X' to the content A2 of the second rubber component is preferably 0.4 or more and 2 or less, more preferably 0.5 or more and less than 1, and even more preferably 0.6 or more and 0.7 or less. The content B of the α,β-unsaturated carboxylic acid metal salt in the uncrosslinked rubber composition X' is preferably less than the content A2 of the second rubber component.

[0022] From the viewpoint of obtaining excellent moldability of the uncrosslinked rubber composition X' before crosslinking, it is preferable that the uncrosslinked rubber composition X' further contain a tackifier. Examples of tackifiers include phenolic resin-based tackifiers, petroleum resin-based tackifiers, rosin resin-based tackifiers, terpene resin-based tackifiers, and coumarone-indene resin-based tackifiers. Examples of phenolic resin-based tackifiers include alkylphenol resins, alkylphenol formaldehyde resins, and phenol formaldehyde resins. Examples of petroleum resin-based tackifiers include C5-C9 petroleum resins made from C5 fractions and C9 fractions, C5 petroleum resins made from C5 fractions, C9 petroleum resins made from C9 fractions, and dicyclopentadiene petroleum resins. Examples of rosin resin-based tackifiers include rosin ester resins and hydrogenated rosin ester resins. Examples of terpene resin-based tackifiers include polyterpene resins and styrene-modified terpene resins. Examples of coumarone-indene resin-based tackifiers include coumarone-indene resins and hydrogenated coumarone-indene resins. The tackifier preferably contains one or more of these. From the viewpoint of preventing a decrease in the hardness of the crosslinked rubber composition X after crosslinking, it is preferable to contain a phenolic resin-based tackifier and / or a petroleum resin-based tackifier, and more preferably an alkylphenol resin and / or a C5-C9 petroleum resin. Examples of commercially available alkylphenol resin tackifiers include Tamanol (registered trademark) 100S, 200N, 510, 521, 526, 586, and 7509 manufactured by Arakawa Chemical Industries, Ltd. Examples of commercially available C5-C9 petroleum resin tackifiers include Petrotack (registered trademark) 60, 70, 90, 90V, 90HS, and 100V manufactured by Tosoh Corporation.

[0023] The content C of the tackifier in the uncrosslinked rubber composition X' is preferably 1 part by mass or more and 10 parts by mass or less, more preferably 2 parts by mass or more and 7 parts by mass or less, and even more preferably 3 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the total content of the first and second rubber components, from the viewpoint of obtaining excellent moldability of the uncrosslinked rubber composition X' before crosslinking while suppressing a decrease in the hardness of the crosslinked rubber composition X after crosslinking. From the same viewpoints as above, the mass ratio (C / A2) of the content C of the tackifier in the uncrosslinked rubber composition X' to the content A2 of the second rubber component is preferably 0.08 or more and 0.25 or less, 0.09 or more and 0.2 or less, or 0.1 or more and 0.15 or less.

[0024] The softening point of the tackifier is preferably 70° C. or higher and 100° C. or lower, from the viewpoint of obtaining excellent moldability of the uncrosslinked rubber composition X′ before crosslinking while suppressing a decrease in hardness of the crosslinked rubber composition X after crosslinking. This softening point is measured by the ring and ball method.

[0025] The uncrosslinked rubber composition X' preferably contains a crosslinking agent for thermally crosslinking the first and second rubber components. Examples of the crosslinking agent include sulfur and organic peroxides. Examples of organic peroxides include α,α'-di(t-butylperoxy)diisopropylbenzene, dicumyl peroxide, 1,3-bis(t-butylperoxyisopropyl)benzene, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane. The organic peroxide preferably contains one or more of these, and more preferably contains α,α'-di(t-butylperoxy)diisopropylbenzene. The crosslinking agent may contain either sulfur or an organic peroxide, or both sulfur and an organic peroxide. The amount D1 of sulfur in the uncrosslinked rubber composition X' is, for example, 0.3 parts by mass or more and 0.7 parts by mass or less, per 100 parts by mass of the total content of the first and second rubber components. The amount D2 of the organic peroxide in the uncrosslinked rubber composition X' is, for example, 2.5 parts by mass or more and 3.5 parts by mass or less per 100 parts by mass of the total amount of the first and second rubber components.

[0026] It is preferable that the uncrosslinked rubber composition X' further contains carbon black from the viewpoint of suppressing a decrease in hardness of the crosslinked rubber composition X after crosslinking. 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. It is preferable that the carbon black contains one or more of these, and from the same viewpoint as above, it is more preferable that it contains furnace black, and even more preferable that it contains ISAF.

[0027] The carbon black content E in the uncrosslinked rubber composition X' is preferably 30 parts by mass or more and 80 parts by mass or less, more preferably 40 parts by mass or more and 60 parts by mass or less, and even more preferably 45 parts by mass or more and 55 parts by mass or less, relative to 100 parts by mass of the total content of the first and second rubber components, from the viewpoint of suppressing a decrease in the hardness of the crosslinked rubber composition X after crosslinking and suppressing an excessive increase in hardness.

[0028] The uncrosslinked rubber composition X' preferably further contains short fibers from the viewpoint of preventing a decrease in the hardness of the crosslinked rubber composition X after crosslinking. Examples of short fibers include para-aramid short fibers, meta-aramid short fibers, polyparaphenylene benzobisoxazole short fibers, nylon 6 short fibers, nylon 6,6 short fibers, nylon 4,6 short fibers, polyethylene terephthalate short fibers, and polyethylene naphthalate short fibers. Examples of para-aramid short fibers include polyparaphenylene terephthalamide (PPTA) short fibers and copolyparaphenylene-3,4'-oxydiphenylene terephthalamide short fibers. The short fibers preferably contain one or more of these, and from the same viewpoint as above, it is more preferable to contain para-aramid short fibers, and even more preferable to contain polyparaphenylene terephthalamide short fibers.

[0029] The content F of short fibers in the uncrosslinked rubber composition X' is preferably 10 parts by mass or more and 40 parts by mass or less, more preferably 15 parts by mass or more and 30 parts by mass or less, and even more preferably 20 parts by mass or more and 25 parts by mass or less, relative to 100 parts by mass of the total content of the first and second rubber components, from the viewpoint of preventing a decrease in the hardness of the crosslinked rubber composition X after crosslinking and preventing the hardness from becoming excessively high.

[0030] The uncrosslinked rubber composition X' may further contain process oil, a vulcanization accelerator, a vulcanization accelerator aid, a processing aid, an antioxidant, and the like, as required.

[0031] The uncrosslinked rubber composition X' can be prepared by charging the first and second rubber components into a rubber kneading machine such as a kneader, a Banbury mixer, or an open roll mixer, masticating the mixture, and then adding rubber compounding ingredients containing an α,β-unsaturated carboxylic acid metal salt and a crosslinking agent to the mixture and kneading them together. The uncrosslinked rubber composition X' is then used to mold an uncrosslinked molded article, and the uncrosslinked molded article is heated and pressurized to crosslink the uncrosslinked rubber composition X', thereby obtaining the crosslinked rubber composition X according to the embodiment.

[0032] The hardness of the crosslinked rubber composition X according to the embodiment, as measured by a Type A durometer, is preferably A86 or more, more preferably A88 or more, and even more preferably A90 or more. This hardness is measured using a Type A durometer in accordance with JIS K6253-3:2012.

[0033] The crosslinked rubber composition X according to the embodiment can be suitably used to form at least a part of a transmission belt, for example.

[0034] Specifically, for example, in the V-belt B of the friction power transmission belt shown in Fig. 1, the rubber belt body 10 is composed of an adhesive rubber layer 101 in which core wires 11 are embedded, an inner compressed rubber layer 102 whose inner circumferential surface is covered with a reinforcing cloth 12, and an outer tensile rubber layer 103 whose outer circumferential surface is covered with a reinforcing cloth 13, and any one, two, or all three layers of the adhesive rubber layer 101, the compressed rubber layer 102, and the tensile rubber layer 103 can be formed from the crosslinked rubber composition X according to the embodiment. In the toothed belt C of the intermeshing power transmission belt shown in Fig. 2, the rubber belt body 20 is composed of a back rubber portion 201 in which core wires 21 are embedded and a tooth rubber portion 202 covered with a reinforcing cloth 22, and one or both of the back rubber portion 201 and the tooth rubber portion 202 can be formed from the crosslinked rubber composition X. The cords 11, 21 are provided with adhesive layers for bonding to the belt bodies 10, 20, and these adhesive layers can be formed from the crosslinked rubber composition X. The reinforcing fabrics 12, 13, 22 are provided with internally impregnated adhesive portions and / or internal adhesive layers for bonding to the belt bodies 10, 20, and these internally impregnated adhesive portions and / or internal adhesive layers can be formed from the crosslinked rubber composition X.

[0035] The manufacturing method of these V-belts B and toothed belts C may include a step of laminating a sheet-like uncrosslinked rubber composition X' and / or a step of compounding the uncrosslinked rubber composition X' with the core wires 11, 21 of the fiber member and the reinforcing fabrics 12, 13, 22 to form a cylindrical uncrosslinked slab (uncrosslinked molded body), and a step of heating and pressurizing the uncrosslinked slab to crosslink the uncrosslinked rubber composition X' and form a crosslinked rubber composition X, thereby producing a cylindrical belt slab. In this case, the process of molding a cylindrical uncrosslinked slab includes a step of laminating sheet-like uncrosslinked rubber composition X' and / or a step of compounding uncrosslinked rubber composition X' with the core wires 11, 21 of the fiber member and the reinforcing cloths 12, 13, 22. Since the adhesiveness of uncrosslinked rubber composition X' is increased, high adhesion between sheets of sheet-like uncrosslinked rubber composition X' and / or high adhesion of uncrosslinked rubber composition X' to the core wires 11, 21 and the reinforcing cloths 12, 13, 22 can be obtained, and excellent molding processability can be obtained by using uncrosslinked rubber composition X' when molding the uncrosslinked slab.

[0036] The manufacturing method of the V-belt B or the toothed belt C may include a step of immersing the core wires 11, 21 in a rubber cement prepared by dissolving the uncrosslinked rubber composition X' in an organic solvent, followed by heating to perform an adhesion treatment, thereby coating the outer periphery of the core wires 11, 21 with an overcoat layer of the uncrosslinked rubber composition X'. The overcoat layer is formed in the adhesive layer at the interface between the core wires 11, 21 and the belt body 10, 20 when the uncrosslinked slab is heated and pressurized. At this time, the overcoat layer of the uncrosslinked rubber composition X' provides high adhesiveness to the core wires 11, 21, and therefore excellent moldability can be achieved in molding the uncrosslinked slab due to the overcoat layer of the uncrosslinked rubber composition X'.

[0037] The manufacturing method of the V-belt B or the toothed belt C may include a step of subjecting the reinforcing fabrics 12, 13, and 22 to a soaking adhesion treatment in which the reinforcing fabrics 12, 13, and 22 are immersed in a low-viscosity rubber cement prepared by dissolving the uncrosslinked rubber composition X' in an organic solvent and then heated, thereby coating the surfaces of the yarns constituting the reinforcing fabrics 12, 13, and 22 with a soaking layer of the uncrosslinked rubber composition X', and / or a step of subjecting the surfaces of the reinforcing fabrics 12, 13, and 22 facing the belt main bodies 10 and 20 to a coating adhesion treatment in which a high-viscosity rubber cement prepared by dissolving the uncrosslinked rubber composition X' in an organic solvent is coated on the surfaces of the reinforcing fabrics 12, 13, and 22 facing the belt main bodies 10 and 20, and then heated, thereby coating the surfaces of the reinforcing fabrics 12, 13, and 22 facing the belt main bodies 10 and 20 with a coating layer of the uncrosslinked rubber composition X'. The soaking layer is formed in an internal impregnation adhesion portion that covers the surfaces of the yarns inside the reinforcing fabrics 12, 13, and 22 when the uncrosslinked slab is heated and pressurized. The coating layer is formed on the inner adhesive layer of the reinforcing fabrics 12, 13, 22 at the interface with the belt main body 10, 20 when the uncrosslinked slab is heated and pressed. At this time, the soaking layer and / or coating layer of the uncrosslinked rubber composition X' provides high adhesiveness to the reinforcing fabrics 12, 13, 22, so that the soaking layer and / or coating layer of the uncrosslinked rubber composition X' provides excellent molding processability when molding the uncrosslinked slab.

[0038] (Uncrosslinked Rubber Composition) The following uncrosslinked rubber compositions were prepared in Examples 1 to 5 and Comparative Examples 1 and 2. The compositions of each are also shown in Table 1.

[0039] Example 1 A first rubber component, EPDM (EP33 manufactured by ENEOS Materials Corporation, ethylene content: 52 mass%, ENB content: 8.1 mass%), and a second rubber component, EBDM (K-9330M manufactured by Mitsui Chemicals, Inc., ethylene content: 50 mass%, ENB content: 7.1 mass%), were charged into a kneader and masticated such that the mass ratio of the first rubber component / the second rubber component was 83.7 / 16.3. Then, zinc dimethacrylate (Acter ZMA) was added as a co-crosslinking agent, with respect to 100 parts by mass of the total content of the first and second rubber components. 20 parts by mass of ethylenediamine diisopropyl ether (manufactured by Kawaguchi Chemical Industry Co., Ltd.), 50 parts by mass of carbon black ISAF, 10 parts by mass of process oil, 5 parts by mass of zinc oxide as a vulcanization accelerator aid, and 0.5 parts by mass of stearic acid as a processing aid were added and kneaded, and finally, 0.5 part by mass of sulfur (Seimi OT, manufactured by Tsurumi Chemical Industry Co., Ltd.) as a crosslinking agent and 7 parts by mass (2.8 parts by mass of active ingredient) of α,α'-di(t-butylperoxy)diisopropylbenzene as an organic peroxide (Peroximon F-40, manufactured by NOF Corporation, purity: 40%) per 100 parts by mass of the total amount of the first and second rubber components were added and further kneaded. The kneaded mixture was discharged from the kneader and cooled, and then recharged into the kneader and kneaded, to which 22 parts by mass of PPTA short fibers (Kevlar 119 manufactured by DuPont, fiber length: 3 mm) were added relative to 100 parts by mass of the total content of the first and second rubber components, and kneaded to prepare an uncrosslinked rubber composition, which was designated Example 1. The kneading temperature was set to a temperature higher than the softening point of the tackifier used in Example 4 described below.

[0040] Here, the difference between the ethylene content of the first rubber component and the ethylene content of the second rubber component is 2% by mass. The content ratio of the ethylene content of the second rubber component to the ethylene content of the first rubber component is 0.96. The difference between the ENB content of the EPDM of the first rubber component and the ENB content of the EBDM of the second rubber component is 1% by mass. The content ratio of the ENB content of the EBDM of the second rubber component to the ENB content of the EPDM of the first rubber component is 0.88.

[0041] Example 2 An uncrosslinked rubber composition was prepared in the same manner as in Example 1, except that the mass ratio of the first rubber component to the second rubber component was set to first rubber component / second rubber component = 67.5 / 32.5.

[0042] Example 3 An uncrosslinked rubber composition was prepared in the same manner as in Example 1, except that the mass ratio of the first rubber component to the second rubber component was set to first rubber component / second rubber component = 51.2 / 48.8, and this was designated as Example 3.

[0043] Example 4 An uncrosslinked rubber composition was prepared in the same manner as in Example 2, except that an alkylphenol resin (Tamanol 510 manufactured by Arakawa Chemical Industries, Ltd., softening point: 75°C to 95°C) serving as a tackifier was blended in an amount of 4 parts by mass relative to 100 parts by mass of the total amount of the first and second rubber components, and this was designated Example 4.

[0044] Example 5 An uncrosslinked rubber composition was prepared in the same manner as in Example 4, except that the amount of zinc dimethacrylate was 40 parts by mass relative to 100 parts by mass of the total content of the first and second rubber components.

[0045] Comparative Example 1 An uncrosslinked rubber composition was prepared in the same manner as in Example 1, except that only EPDM, the first rubber component, was used as the rubber component.

[0046] Comparative Example 2 An uncrosslinked rubber composition was prepared in the same manner as in Example 2, except that zinc dimethacrylate was not blended, and this was designated as Comparative Example 2.

[0047]

[0048] (Test Methods and Results) The following tests were carried out on the uncrosslinked rubber compositions and crosslinked rubber compositions obtained by crosslinking the uncrosslinked rubber compositions of Examples 1 to 5 and Comparative Examples 1 and 2. The test results are shown in Table 1.

[0049] <Adhesion> A tack test was carried out on each of the uncrosslinked rubber compositions of Examples 1 to 5 and Comparative Examples 1 and 2 using a pickup-type tack meter (Tack Tester IMC-1567, manufactured by Imoto Machinery Co., Ltd.). The tack meter has a cylindrical aluminum adhesive disc with a diameter of 50 mm and a thickness of 14 mm, with its axis extending horizontally back and forth, and a fixing plate below it for setting the test specimen. The adhesive disc has its upper end connected to a load cell and is movable up and down together with the load cell. The specific test method is as follows.

[0050] Each uncrosslinked rubber composition was molded into a sheet, from which a strip-shaped test piece for the tackiness test was cut. The test piece was horizontally attached to the fixed plate of the tack meter with double-sided tape. The adhesive disc was lowered at a rate of 30 mm / min so as to approach the fixed plate, and the outer surface of the adhesive disc was pressed against the test piece with a load of 4.9 N. After 10 seconds, the adhesive disc was raised at a rate of 30 mm / min so as to separate from the fixed plate. The peel force (tack force) when the adhesive disc was peeled from the test piece was measured with a load cell. The adhesive strength was evaluated as a relative value when the peel force of Comparative Example 1 was set to 1.

[0051] <Hardness> Each of the uncrosslinked rubber compositions of Examples 1 to 5 and Comparative Examples 1 and 2 was heated and pressed to prepare a sheet-shaped crosslinked rubber composition, and the hardness of each of these test pieces was measured using a Type A durometer in accordance with JIS K6253-3:2012.

[0052] The present invention is useful in the technical fields of crosslinked rubber compositions and power transmission belts using the same.

[0053] B V-belt C Toothed belt 10, 20 Belt body 101 Adhesive rubber layer 102 Compression rubber layer 103 Tension rubber layer 11, 21 Cord 12, 13, 22 Reinforcing fabric 201 Back rubber portion 202 Tooth rubber portion

Claims

1. A crosslinked rubber composition obtained by crosslinking an uncrosslinked rubber composition, wherein the uncrosslinked rubber composition contains a first rubber component which is an ethylene-α-olefin elastomer in which the α-olefin is propylene, a second rubber component which is an ethylene-1-butenediene terpolymer, and a metal salt of an α,β-unsaturated carboxylic acid.

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

3. A crosslinked rubber composition according to claim 1 or 2, wherein the first rubber component comprises an ethylene propylene diene terpolymer.

4. A crosslinked rubber composition according to claim 3, wherein the diene component of the ethylene propylene diene terpolymer contained in the first rubber component is 5-ethylidene-2-nobornene, and the ENB content of the ethylene propylene diene terpolymer contained in the first rubber component is 4% by mass or more and 12% by mass or less.

5. A crosslinked rubber composition according to any one of claims 1 to 4, wherein the ethylene content of the second rubber component is 40% by mass or more and 60% by mass or less.

6. A crosslinked rubber composition according to any one of claims 1 to 5, wherein the difference between the ethylene content of the first rubber component and the ethylene content of the second rubber component is 10% by mass or less.

7. A crosslinked rubber composition according to any one of claims 1 to 6, wherein the ethylene content of the second rubber component is lower than the ethylene content of the first rubber component.

8. A cross-linked rubber composition according to any one of claims 1 to 7, wherein the diene component of the ethylene-1-butenediene terpolymer of the second rubber component is 5-ethylidene-2-nobornene, and the ENB content of the ethylene-1-butenediene terpolymer of the second rubber component is 4% by mass or more and 10% by mass or less.

9. A crosslinked rubber composition according to any one of claims 1 to 8, wherein the content of the first rubber component in the uncrosslinked rubber composition is greater than the content of the second rubber component.

10. A crosslinked rubber composition according to any one of claims 1 to 9, wherein the metal salt of an α,β-unsaturated carboxylic acid comprises a metal salt of dimethacrylate.

11. A crosslinked rubber composition according to any one of claims 1 to 10, wherein the content of the α,β-unsaturated carboxylic acid metal salt in the uncrosslinked rubber composition is less than the content of the second rubber component.

12. The crosslinked rubber composition according to any one of claims 1 to 11, wherein the uncrosslinked rubber composition further contains a tackifier.

13. The crosslinked rubber composition according to claim 12, wherein the tackifier comprises a phenolic resin-based tackifier.

14. A crosslinked rubber composition according to any one of claims 1 to 13, wherein the mass ratio of the content of the tackifier to the content of the second rubber component in the uncrosslinked rubber composition is 0.08 or more and 0.25 or less.

15. A power transmission belt at least a portion of which is formed from the crosslinked rubber composition according to any one of claims 1 to 14.

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