Rubber composition for tire, and tire

Abstract

The present invention addresses the problem of providing a rubber composition for a tire, with which it is possible to achieve both wear resistance and low fuel consumption of a tire. The solution for the problem is a rubber composition for a tire, which comprises a rubber component and a filler, and which is characterized in that: the rubber component comprises a copolymer of cyclopentene and a norbornene-based compound represented by general formula (1) (wherein R1 to R4 each independently represent a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, or a substituent that contains a halogen atom, a silicon atom, an oxygen atom, or a nitrogen atom, R2 and R3 may be bonded to each other to form a ring, and m is an integer of 0 to 2), and an isoprene skeleton rubber; and the copolymer of cyclopentene and the norbornene-based compound has a content ratio of a structural unit derived from the norbornene-based compound of 35 mass% or less.

Description

Rubber composition for tires and tires

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

[0002] In connection with the recent trend toward global carbon dioxide emission regulations accompanying growing interest in environmental issues, there is an increasing demand for improved fuel economy in automobiles. To meet such demands, tire performance is also required to improve fuel economy (i.e., reduce rolling resistance). Furthermore, from the viewpoint of tire economics, in the development of rubber compositions for tires, it is also required to improve wear resistance in addition to fuel economy.

[0003] However, since fuel economy and abrasion resistance are generally in a trade-off relationship, it is difficult to achieve both. For example, a method of increasing the amount of filler compounded in a rubber composition to improve abrasion resistance is known. However, increasing the amount of filler compounded improves abrasion resistance, but this increases the unvulcanized viscosity of the rubber composition, which deteriorates processability, or worsens the dispersibility of the filler, which deteriorates fuel economy.

[0004] In response to this, Patent Documents 1 and 2 listed below disclose rubber compounds for passenger car tires and rubber compounds for heavy-duty truck and bus tires, each containing a specific long-chain branched cyclopentene ring-opening rubber (LCB-CPR), and these rubber compounds are said to be effective in reducing the rolling resistance of tires, improving wet skid resistance, and improving abrasion resistance.

[0005] International Publication No. 2021 / 178233 International Publication No. 2021 / 178235

[0006] However, even with the techniques described in Patent Documents 1 and 2, it is difficult to achieve both low fuel consumption and high wear resistance in a tire, and there is still room for improvement.

[0007] Furthermore, rubber compositions for large tires are often formulated with isoprene-skeleton rubbers such as natural rubber. However, the inventors have conducted research and found that when a rubber composition is prepared by blending a cyclopentene-based polymer such as the cyclopentene ring-opening rubber disclosed in Patent Documents 1 and 2 with an isoprene-skeleton rubber, the abrasion resistance of the rubber composition deteriorates.

[0008] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a rubber composition for a tire that can achieve both low fuel consumption and high wear resistance for the tire.A further object of the present invention is to provide a tire that achieves both low fuel consumption and high wear resistance.

[0009] The rubber composition for a tire and the tire of the present invention that solve the above problems are summarized as follows.

[0010] [1] A rubber composition comprising a rubber component and a filler, wherein the rubber component is a rubber composition containing cyclopentene and the following general formula (1): [In the formula, R １ ~R ４ each independently represents a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, or a substituent containing a halogen atom, a silicon atom, an oxygen atom, or a nitrogen atom; R ２ and R ３ may be bonded to each other to form a ring, and m is an integer of 0 to 2.] and an isoprene skeleton rubber, wherein the copolymer of cyclopentene and the norbornene compound contains 35 mass % or less of structural units derived from the norbornene compound.

[0011] [2] The rubber composition for a tire according to [1], wherein the content of the copolymer of cyclopentene and a norbornene-based compound is 20 to 90 parts by mass per 100 parts by mass of the rubber component.

[0012] [3] The rubber composition for a tire according to [1] or [2], wherein the copolymer of cyclopentene and a norbornene-based compound has a weight average molecular weight (Mw) of 200,000 to 1,000,000.

[0013] [4] The rubber composition for a tire according to any one of [1] to [3], wherein the copolymer of cyclopentene and a norbornene-based compound has a content of cyclopentene-derived structural units of 65 to 90 mass %.

[0014] [5] The rubber composition for a tire according to any one of [1] to [4], wherein the copolymer of cyclopentene and a norbornene-based compound has a content of structural units derived from dicyclopentadiene of 35% by mass or less.

[0015] [6] The rubber composition for a tire according to any one of [1] to [5], wherein the copolymer of cyclopentene and a norbornene-based compound has a content of structural units derived from dicyclopentadiene of 30% by mass or less.

[0016] [7] The rubber composition for a tire according to any one of [1] to [6], which contains carbon black as the filler.

[0017] [8] The rubber composition for a tire according to [7], wherein the carbon black content is 5 to 80 parts by mass per 100 parts by mass of the rubber component.

[0018] [9] A tire comprising the rubber composition for a tire according to any one of [1] to [8].

[0019] According to the present invention, it is possible to provide a rubber composition for a tire that can achieve both low fuel consumption and high wear resistance for the tire. Also, according to the present invention, it is possible to provide a tire that achieves both low fuel consumption and high wear resistance.

[0020] The rubber composition for a tire and the tire of the present invention will be described in detail below by way of example based on embodiments thereof.

[0021] <Definitions> The compounds described herein may be derived in part or in whole from fossil resources, from biological resources such as plant resources, from recycled resources such as used tires, or from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0022] <Rubber composition for tire> The rubber composition for tire of this embodiment includes a rubber component and a filler. In the rubber composition for tire of this embodiment, the rubber component is a compound represented by the following general formula (1): [In the formula, R １ ~R ４ each independently represents a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, or a substituent containing a halogen atom, a silicon atom, an oxygen atom, or a nitrogen atom; R ２ and R ３ may be bonded to each other to form a ring, and m is an integer of 0 to 2.] (also simply referred to as "copolymer of cyclopentene and a norbornene compound" or "copolymer"), and an isoprene skeleton rubber, wherein the copolymer of cyclopentene and a norbornene compound contains structural units derived from the norbornene compound in a proportion of 35 mass% or less.

[0023] In the rubber composition for tires of this embodiment, the copolymer of cyclopentene and a norbornene-based compound is characterized by having crosslinking points and by entanglement of polymer chains. Meanwhile, when a filler is compounded with a rubber component, a reinforcing layer composed of the filler and the rubber component is generally formed around the filler, and this reinforcing layer contributes to improving the reinforcement properties of the rubber composition, thereby improving abrasion resistance, etc. In the rubber composition for tires of this embodiment, the reinforcing layer formed around the filler is further developed due to the entanglement of the polymer chains described above, thereby further improving abrasion resistance. Furthermore, in the rubber composition for tires of this embodiment, the reinforcing layer is developed due to the entanglement of the polymer chains, thereby reducing hysteresis loss and improving fuel economy. Meanwhile, the rubber composition for tires of this embodiment contains an isoprene-skeleton rubber as a rubber component, and the isoprene-skeleton rubber contributes to improving fracture resistance. However, as described above, when an isoprene-based rubber is combined with the copolymer of cyclopentene and a norbornene-based compound, which is characterized by entanglement of polymer chains, the abrasion resistance of the rubber composition deteriorates. In contrast, by reducing the content of structural units derived from norbornene-based compounds in the copolymer of cyclopentene and a norbornene-based compound, specifically to 35% by mass or less, the abrasion resistance of the rubber composition can be improved, and the fuel economy of the rubber composition can also be improved. Therefore, by applying the rubber composition for tires of this embodiment to tires, both fuel economy and abrasion resistance of the tire can be achieved.

[0024] (Rubber Component) The rubber composition for a tire of this embodiment contains a rubber component, and the rubber component provides rubber elasticity to the composition. The rubber component of the rubber composition for a tire of this embodiment contains a copolymer of cyclopentene and a norbornene-based compound represented by the above general formula (1), an isoprene skeleton rubber, and may further contain other rubbers.

[0025] - Copolymer of cyclopentene and norbornene-based compound - The copolymer of cyclopentene and norbornene-based compound contains structural units derived from cyclopentene and structural units derived from the norbornene-based compound represented by the above general formula (1). In a preferred embodiment, the copolymer of cyclopentene and norbornene-based compound is a ring-opening copolymer, particularly a cyclopentene ring-opening copolymer. In a preferred embodiment, the copolymer is a linear or branched polymer, particularly a linear polymer.

[0026] In the above general formula (1), R １ ~R ４ each independently represents a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, or a substituent containing a halogen atom, a silicon atom, an oxygen atom, or a nitrogen atom; R ２ and R ３ may be bonded to each other to form a ring, and m is an integer of 0 to 2. Here, examples of the hydrocarbon group having 1 to 20 carbon atoms include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, neopentyl, hexyl, and octyl groups; alkenyl groups such as vinyl, allyl, 2-pentenyl, 3-pentenyl, and 4-methyl-3-pentenyl groups; aryl groups such as phenyl, tolyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, and naphthyl groups; and aralkyl groups such as benzyl and phenethyl groups.

[0027] Examples of the norbornene compounds represented by the general formula (1) include 2-norbornene, 5-methyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-hexyl-2-norbornene, 5-decyl-2-norbornene, 5-cyclohexyl-2-norbornene, 5-cyclopentyl-2-norbornene, 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene, 5-propenyl-2-norbornene, 5-cyclohexenyl-2-norbornene, 5-cyclopentenyl-2-norbornene, 5-phenyl-2-norbornene, tetracyclo[9.2.1.0] ２，１０ .0 ３，８]tetradeca-3,5,7,12-tetraene (also called "1,4-methano-1,4,4a,9a-tetrahydro-9H-fluorene"), tetracyclo[10.2.1.0 ２，１１ .0 ４，９ ]pentadeca-4,6,8,13-tetraene (also called "1,4-methano-1,4,4a,9,9a,10-hexahydroanthracene"), dicyclopentadiene, methyldicyclopentadiene, dihydrodicyclopentadiene ("tricyclo[5.2.1.0 ２，６ Bicyclo[2.2.1]hept-2-enes, such as unsubstituted or hydrocarbon-substituted bicyclo[2.2.1]hept-2-enes, such as tetracyclo[6.2.1.1]dec-8-enes; ３，６ .0 ２，７ ] dodec-4-ene, 9-methyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-ethyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-cyclohexyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-cyclopentyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-methylenetetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-ethylidenetetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-vinyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-propenyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-cyclohexenyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-cyclopentenyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-phenyltetracyclo[6.2.1.1 ３，６ .0 ２，７] tetracyclo[6.2.1.1] dodec-4-ene and the like, which are unsubstituted or have hydrocarbon substituents; ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having an alkoxycarbonyl group such as methyl 5-norbornene-2-carboxylate, ethyl 5-norbornene-2-carboxylate, methyl 2-methyl-5-norbornene-2-carboxylate, and ethyl 2-methyl-5-norbornene-2-carboxylate; tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4-carboxylate methyl, 4-methyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] tetracyclo[6.2.1.1] having an alkoxycarbonyl group, such as methyl dodec-9-ene-4-carboxylate ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having a hydroxycarbonyl group or an acid anhydride group, such as 5-norbornene-2-carboxylic acid, 5-norbornene-2,3-dicarboxylic acid, and 5-norbornene-2,3-dicarboxylic acid anhydride; tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4-carboxylic acid, tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4,5-dicarboxylic acid, tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4,5-dicarboxylic anhydride, or other tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having a hydroxyl group such as 5-hydroxy-2-norbornene, 5-hydroxymethyl-2-norbornene, 5,6-di(hydroxymethyl)-2-norbornene, 5,5-di(hydroxymethyl)-2-norbornene, 5-(2-hydroxyethoxycarbonyl)-2-norbornene, and 5-methyl-5-(2-hydroxyethoxycarbonyl)-2-norbornene; tetracyclo[6.2.1.1 ３，６.0 ２，７ ] dodec-9-ene-4-methanol, tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-en-4-ol and other hydroxyl group-containing tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having a hydrocarbonyl group such as 5-norbornene-2-carbaldehyde; tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4-carbaldehyde, and the like. ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having an alkoxycarbonyl group and a hydroxycarbonyl group, such as 3-methoxycarbonyl-5-norbornene-2-carboxylic acid; bicyclo[2.2.1]hept-2-enes having a carbonyloxy group, such as 5-norbornen-2-yl acetate, 2-methyl-5-norbornen-2-yl acetate, 5-norbornen-2-yl acrylate, and 5-norbornen-2-yl methacrylate; 9-tetracyclo[6.2.1.1] acetate ３，６ .0 ２，７ ] dodec-4-enyl acrylate, 9-tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-enyl, methacrylic acid 9-tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] tetracyclo[6.2.1.1] having a carbonyloxy group such as dodec-4-enyl ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having a functional group containing a nitrogen atom, such as 5-norbornene-2-carbonitrile, 5-norbornene-2-carboxamide, and 5-norbornene-2,3-dicarboxylic acid imide; tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4-carbonitrile, tetracyclo[6.2.1.1 ３，６ .0 ２，７] dodec-9-ene-4-carboxamide, tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4,5-dicarboxylic acid imide, or the like. ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having a halogen atom such as 5-chloro-2-norbornene; 9-chlorotetracyclo[6.2.1.1 ３，６ .0 ２，７ ] tetracyclo[6.2.1.1] dodec-4-ene having a halogen atom, ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having a functional group containing a silicon atom, such as 5-trimethoxysilyl-2-norbornene and 5-triethoxysilyl-2-norbornene; 4-trimethoxysilyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene, 4-triethoxysilyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] tetracyclo[6.2.1.1] having a functional group containing a silicon atom, such as dodec-9-ene ３，６ .0 ２，７ ] dodec-4-enes; etc. The norbornene-based compounds may be used singly or in combination of two or more.

[0028] The norbornene-based compound represented by the general formula (1) is preferably one in which m is 0 or 1, more preferably one in which m is 0. １ ~R ４ may be the same or different.

[0029] Among the norbornene compounds represented by the general formula (1), from the viewpoint of fuel economy and wear resistance of the rubber composition, R １ ~R ４is preferably a hydrogen atom, a chain hydrocarbon group having 1 to 20 carbon atoms, or a substituent containing a halogen atom, a silicon atom, an oxygen atom, or a nitrogen atom. １ ~R ４ are not particularly limited as long as they are groups that do not bond to each other and do not form a ring, and may be the same or different. R １ ~R ４ is preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. In this case, m is preferably 0 or 1, and more preferably 0. R in the above general formula (1) １ ~R ４ However, as the norbornene-based compound having a substituent containing a hydrogen atom, a chain hydrocarbon group having 1 to 20 carbon atoms, or a halogen atom, a silicon atom, an oxygen atom, or a nitrogen atom, unsubstituted or hydrocarbon-substituted bicyclo[2.2.1]hept-2-enes are preferred, and among these, 2-norbornene is particularly preferred.

[0030] Furthermore, as the norbornene-based compound represented by the general formula (1), R ２ and R ３ Also preferred are compounds in which R and R are bonded to each other to form a ring. ２ and R ３ Specific examples of the ring structure formed by bonding together include a cyclopentane ring, a cyclopentene ring, a cyclohexane ring, a cyclohexene ring, a benzene ring, etc., which may form a polycyclic structure and may further have a substituent. Among these, a cyclopentane ring, a cyclopentene ring, and a benzene ring are preferred, and a compound having a single cyclopentene ring or a polycyclic structure of a cyclopentane ring and a benzene ring is particularly preferred. ２ , R ３ Other than R １ , R ４ may be the same or different, and are preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. In this case, m is preferably 0. ２ and R ３As the norbornene-based compound in which the above are bonded to each other to form a ring, unsubstituted or hydrocarbon-substituted bicyclo[2.2.1]hept-2-enes are preferred, and among these, dicyclopentadiene is particularly preferred.

[0031] The copolymer of cyclopentene and a norbornene compound preferably contains cyclopentene-derived structural units in an amount of 65 to 90 mass%, more preferably 70 to 80 mass%, based on the total repeating structural units of the copolymer. By controlling the content of cyclopentene-derived structural units in the copolymer to fall within the range of 65 to 90 mass%, the fuel economy and wear resistance of a rubber composition containing the copolymer can be further improved.

[0032] The copolymer of cyclopentene and a norbornene compound has a content of structural units derived from the norbornene compound represented by the general formula (1) of 35% by mass or less relative to the total repeating structural units of the copolymer. If the content of structural units derived from the norbornene compound represented by the general formula (1) in the copolymer exceeds 35% by mass, the glass transition temperature (Tg) of the copolymer increases, the hysteresis loss of the rubber composition increases, and the fuel economy of the rubber composition deteriorates. Furthermore, if the content of structural units derived from the norbornene compound represented by the general formula (1) in the copolymer exceeds 35% by mass, the compatibility of the copolymer with an isoprene skeleton rubber deteriorates, and the wear resistance of the rubber composition deteriorates due to blending the copolymer with an isoprene skeleton rubber. On the other hand, when the content of the structural units derived from the norbornene-based compound represented by general formula (1) in the copolymer is 35% by mass or less, the glass transition temperature (Tg) of the copolymer is lowered, the hysteresis loss of the rubber composition is reduced, and the fuel economy of the rubber composition is improved. Furthermore, when the content of the structural units derived from the norbornene-based compound represented by general formula (1) in the copolymer is 35% by mass or less, the compatibility of the copolymer with the isoprene-based rubber is improved, and the wear resistance of the rubber composition is improved. The content of the structural units derived from the norbornene-based compound represented by general formula (1) in the copolymer is preferably 30% by mass or less, from the viewpoint of further lowering the Tg of the copolymer and further improving the compatibility of the copolymer with the isoprene-based rubber, thereby further improving the fuel economy and wear resistance of the rubber composition. Furthermore, the content of the structural unit derived from the norbornene-based compound represented by general formula (1) in the copolymer is preferably 10% by mass or more, and more preferably 20% by mass or more, from the viewpoint of increasing the entanglement of polymer chains, further developing the reinforcing layer formed around the filler, and further improving the fuel economy and abrasion resistance of the rubber composition.

[0033] In the copolymer of cyclopentene and a norbornene-based compound, the norbornene-based compound represented by the general formula (1) is preferably dicyclopentadiene and / or 2-norbornene, and particularly preferably dicyclopentadiene. Because dicyclopentadiene and 2-norbornene are readily available, copolymers of cyclopentene and dicyclopentadiene and / or 2-norbornene are also readily available. Therefore, rubber compositions for tires containing copolymers of cyclopentene and dicyclopentadiene and / or 2-norbornene are advantageous in terms of cost.

[0034] When dicyclopentadiene is used as the norbornene-based compound represented by the general formula (1), the copolymer of cyclopentene and a norbornene-based compound preferably has a dicyclopentadiene-derived structural unit content of 35% by mass or less, more preferably 30% by mass or less, relative to the total repeating structural units of the copolymer. By setting the dicyclopentadiene-derived structural unit content in the copolymer to 35% by mass or less, the fuel economy and wear resistance of a rubber composition containing the copolymer can be further improved. By setting the dicyclopentadiene-derived structural unit content in the copolymer to 30% by mass or less, the fuel economy and wear resistance of a rubber composition containing the copolymer can be further improved. Furthermore, the content of the dicyclopentadiene-derived structural unit in the copolymer is preferably 10% by mass or more, more preferably 20% by mass or more, from the viewpoint of increasing entanglement of polymer chains and further developing a reinforcing layer formed around the filler, thereby further improving the fuel economy and wear resistance of the rubber composition.

[0035] When 2-norbornene is used as the norbornene compound represented by general formula (1), the copolymer of cyclopentene and a norbornene compound preferably contains 10 to 35 mass% of structural units derived from 2-norbornene, and more preferably 20 to 30 mass%, of the total repeating structural units of the copolymer. By setting the content of structural units derived from 2-norbornene in the copolymer to fall within the range of 10 to 35 mass%, the fuel economy and wear resistance of a rubber composition containing the copolymer can be further improved.

[0036] In one embodiment, the copolymer of cyclopentene and a norbornene-based compound may be a terpolymer of cyclopentene (CP), dicyclopentadiene (DCPD), and 2-norbornene (NB). The terpolymer of cyclopentene, dicyclopentadiene, and 2-norbornene is highly effective in improving the fuel economy of the rubber composition.

[0037] The copolymer of cyclopentene and a norbornene-based compound may be obtained by copolymerizing, in addition to cyclopentene and the norbornene-based compound represented by the general formula (1), other monomers copolymerizable therewith. Examples of such other monomers include cyclic monoolefins such as cyclopropene, cyclobutene, methylcyclopentene, cyclohexene, methylcyclohexene, cycloheptene, and cyclooctene; cyclic diolefins such as cyclohexadiene, methylcyclohexadiene, cyclooctadiene, and methylcyclooctadiene; and polycyclic cycloolefins having an aromatic ring such as phenylcyclooctene, 5-phenyl-1,5-cyclooctadiene, and phenylcyclopentene. The content of structural units derived from other monomers in the copolymer of cyclopentene and a norbornene-based compound is preferably 40% by mass or less, more preferably 30% by mass or less, based on the total repeating structural units of the copolymer. It is particularly preferred that the copolymer is substantially free of structural units derived from other monomers.

[0038] The copolymer of cyclopentene and a norbornene-based compound preferably has a weight-average molecular weight (Mw) of 200,000 to 1,000,000, more preferably 200,000 to 800,000, even more preferably 200,000 to 700,000, and particularly preferably 200,000 to 600,000. Copolymers having a weight-average molecular weight (Mw) in the range of 200,000 to 1,000,000 are easy to produce and have good processability (workability). Furthermore, by setting the weight-average molecular weight (Mw) of the copolymer in the range of 200,000 to 1,000,000, the fuel economy and wear resistance of a rubber composition containing the copolymer can be further improved. Furthermore, the copolymer of cyclopentene and a norbornene-based compound preferably has a ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw / Mn, also referred to as "molecular weight distribution") of 1.0 to 5.0, more preferably 1.5 to 2.9, even more preferably 1.5 to 2.5, and particularly preferably 1.5 to 2.3. Here, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the copolymer are values ​​measured by gel permeation chromatography (GPC) and converted into polystyrene.

[0039] The copolymer of cyclopentene and a norbornene-based compound preferably has a cis / trans ratio of 0 / 100 to 60 / 40, more preferably 5 / 95 to 55 / 45, even more preferably 10 / 90 to 50 / 50, and particularly preferably 15 / 85 to 39 / 61. The cis / trans ratio refers to the ratio of cis-structures to trans-structures of double bonds present in the repeating units constituting the copolymer of cyclopentene and a norbornene-based compound (cis / trans ratio). By setting the cis / trans ratio of the copolymer within the above range, the fuel economy and wear resistance of a rubber composition containing the copolymer can be further improved.

[0040] The copolymer of cyclopentene and a norbornene compound preferably has a glass transition temperature (Tg) of -80°C to 10°C, more preferably -75°C to 0°C, more preferably -70°C to -10°C, and even more preferably -70°C to -50°C. By setting the glass transition temperature (Tg) of the copolymer within the above range, the fuel economy and abrasion resistance of a rubber composition containing the copolymer can be further improved. The glass transition temperature of the copolymer can be controlled, for example, by adjusting the type and amount of the norbornene compound used. Here, the glass transition temperature (Tg) of the copolymer is a value measured using a differential scanning calorimeter (DSC) at a temperature increase rate of 10°C / min.

[0041] The copolymer of cyclopentene and a norbornene-based compound may have a modified group at the polymer chain end. The presence of such a terminal modified group can further enhance the affinity for fillers and the dispersibility of the filler in the rubber composition, thereby further improving the processability (workability), fuel economy, and abrasion resistance of the rubber composition. The modifying group introduced at the polymer chain end of the copolymer is not particularly limited, but is preferably a modified group containing an atom selected from the group consisting of Group 15 atoms of the periodic table, Group 16 atoms of the periodic table, and a silicon atom. From the viewpoint of enhancing affinity for fillers, the modifying group for forming the terminal modified group is more preferably a modified group containing an atom selected from the group consisting of nitrogen atoms, oxygen atoms, phosphorus atoms, sulfur atoms, and silicon atoms. Among these, a modified group containing an atom selected from the group consisting of nitrogen atoms, oxygen atoms, and silicon atoms is even more preferred.

[0042] Examples of modifying groups containing nitrogen atoms include amino groups, pyridyl groups, imino groups, amide groups, nitro groups, urethane bond groups, and hydrocarbon groups containing any of these groups. Examples of modifying groups containing oxygen atoms include hydroxyl groups, carboxylic acid groups, ether groups, ester groups, carbonyl groups, aldehyde groups, epoxy groups, and hydrocarbon groups containing any of these groups. Examples of modifying groups containing silicon atoms include alkylsilyl groups, oxysilyl groups, and hydrocarbon groups containing any of these groups. Examples of modifying groups containing phosphorus atoms include phosphate groups, phosphino groups, and hydrocarbon groups containing any of these groups. Examples of modifying groups containing sulfur atoms include sulfonyl groups, thiol groups, thioether groups, and hydrocarbon groups containing any of these groups. The modifying group may also be a modifying group containing multiple of the above groups. Among these, from the viewpoint of further improving the processability (workability), fuel economy, and abrasion resistance of the rubber composition, amino groups, pyridyl groups, imino groups, amide groups, hydroxyl groups, carboxylic acid groups, aldehyde groups, epoxy groups, oxysilyl groups, and hydrocarbon groups containing any of these groups are preferred, and from the viewpoint of affinity for fillers (particularly silica, etc.), oxysilyl groups are particularly preferred. Here, the oxysilyl group refers to a group having a silicon-oxygen bond.

[0043] Examples of the oxysilyl group include an alkoxysilyl group, an aryloxysilyl group, an acyloxy group, an alkylsiloxysilyl group, and an arylsiloxysilyl group.Other examples include a hydroxysilyl group obtained by hydrolyzing an alkoxysilyl group, an aryloxysilyl group, or an acyloxy group.Among these, an alkoxysilyl group is preferred from the viewpoint of affinity with silica.The alkoxysilyl group is a group in which one or more alkoxy groups are bonded to a silicon atom, and specific examples thereof include a trimethoxysilyl group, a dimethoxymethylsilyl group, a methoxydimethylsilyl group, a methoxydichlorosilyl group, a triethoxysilyl group, a diethoxymethylsilyl group, an ethoxydimethylsilyl group, a dimethoxyethoxysilyl group, a methoxydiethoxysilyl group, and a tripropoxysilyl group.

[0044] The introduction rate of the modified group at the polymer chain end of the copolymer of cyclopentene and norbornene compound is not particularly limited, but the percentage value of the number of copolymer chain ends into which the modified group has been introduced / the total number of copolymer chain ends is preferably 10% or more, more preferably 20% or more, even more preferably 30% or more, and particularly preferably 40% or more. The higher the introduction rate of the terminal modified group, the higher the affinity for the filler, which is preferable. The method for measuring the introduction rate of the modified group at the polymer chain end is not particularly limited, but an example of introducing an oxysilyl group as the terminal modified group is as follows: １ It can be determined from the peak area ratio corresponding to the oxysilyl group determined by H-NMR spectrum measurement and the number average molecular weight (Mn) determined by gel permeation chromatography (GPC).

[0045] The copolymer of cyclopentene and a norbornene-based compound has a Mooney viscosity (ML １＋４ , 100°C) is preferably 20 to 150, more preferably 40 to 145, further preferably 60 to 140, and particularly preferably 80 to 135. Here, the Mooney viscosity (ML １＋４ , 100°C) is a value measured in accordance with JIS K6300.

[0046] The method for producing the copolymer of cyclopentene and a norbornene-based compound is not particularly limited, but examples thereof include a method in which cyclopentene and a norbornene-based compound represented by the general formula (1) are copolymerized in the presence of a ring-opening polymerization catalyst.

[0047] The ring-opening polymerization catalyst is not particularly limited as long as it can ring-open copolymerize cyclopentene with the norbornene-based compound represented by the general formula (1), but a ruthenium carbene complex or a halogen atom-containing Group 6 transition metal compound of the periodic table (hereinafter also referred to as "Group 6 transition metal compound of the periodic table") is preferred. These ring-opening polymerization catalysts may be used alone or in combination of two or more.

[0048] Examples of the ruthenium carbene complex include bis(tricyclohexylphosphine)benzylideneruthenium dichloride, bis(triphenylphosphine)-3,3-diphenylpropenylideneruthenium dichloride, bis(tricyclohexylphosphine)t-butylvinylideneruthenium dichloride, dichloro-(3-phenyl-1H-inden-1-ylidene)bis(tricyclohexylphosphine)ruthenium, bis(1,3-diisopropylimidazolin-2-ylidene)benzylideneruthenium dichloride, and bis(1,3-dicyclohexylimidazolin-2-ylidene)benzylideneruthenium dichloride. (1,3-dimesitylimidazolin-2-ylidene)benzylideneruthenium dichloride, (1,3-dimesitylimidazolin-2-ylidene)(tricyclohexylphosphine)benzylideneruthenium dichloride, (1,3-dimesitylimidazolin-2-ylidene)(tricyclohexylphosphine)benzylideneruthenium dichloride, (1,3-dimesitylimidazolidin-2-ylidene)(tricyclohexylphosphine)benzylideneruthenium dichloride, bis(tricyclohexylphosphine)ethoxymethylideneruthenium dichloride, (1,3-dimesitylimidazolidin-2-ylidene)(tricyclohexylphosphine)ethoxymethylideneruthenium dichloride, and the like.

[0049] The Group 6 transition metal compound of the periodic table is a compound having a Group 6 transition metal atom of the periodic table (long period periodic table, the same applies hereinafter), specifically a compound having a chromium atom, a molybdenum atom, or a tungsten atom, with a compound having a molybdenum atom or a compound having a tungsten atom being preferred, and a compound having a tungsten atom being more preferred in terms of high solubility in cyclopentene. Specific examples of the Group 6 transition metal compound of the periodic table include molybdenum compounds such as molybdenum pentachloride, molybdenum oxotetrachloride, and molybdenum(phenylimido)tetrachloride; and tungsten compounds such as tungsten hexachloride, tungsten oxotetrachloride, tungsten(phenylimido)tetrachloride, monocatecholatetungsten tetrachloride, bis(3,5-ditertiarybutyl)catecholatetungsten dichloride, and bis(2-chloroetherate)tetrachloride.

[0050] The amount of the ring-opening polymerization catalyst used, in terms of the molar ratio of (ring-opening polymerization catalyst:monomer used in copolymerization), is usually in the range of 1:500 to 1:2,000,000, preferably 1:700 to 1:1,500,000, and more preferably 1:1,000 to 1:1,000,000. When the Group 6 transition metal compound of the periodic table is used, the amount of the Group 6 transition metal compound used, in terms of the molar ratio of "Group 6 transition metal atom in the ring-opening polymerization catalyst:monomer used in ring-opening polymerization," is preferably in the range of 1:100 to 1:200,000, more preferably 1:200 to 1:150,000, and even more preferably 1:500 to 1:100,000.

[0051] When the above-mentioned transition metal compound of Group 6 of the periodic table is used as the ring-opening polymerization catalyst, it is preferable to use it in combination with an organoaluminum compound represented by the following general formula (2). The organoaluminum compound acts as a ring-opening polymerization catalyst together with the above-mentioned transition metal compound of Group 6 of the periodic table. (R ５ ) ３－ｘ Al (OR ６ ) ｘ ... (2) In the above general formula (2), R ５ and R ６ are each independently a hydrocarbon group having 1 to 20 carbon atoms, preferably a hydrocarbon group having 1 to 10 carbon atoms, and x is 0<x<3.

[0052] In the above general formula (2), R ５ and R ６ Examples of the alkyl group include alkyl groups such as methyl group, ethyl group, isopropyl group, n-propyl group, isobutyl group, n-butyl group, t-butyl group, n-hexyl group, cyclohexyl group, n-octyl group, and n-decyl group; and aryl groups such as phenyl group, 4-methylphenyl group, 2,6-dimethylphenyl group, 2,6-diisopropylphenyl group, and naphthyl group.

[0053] In addition, in the general formula (2), x is 0<x<3. That is, in the general formula (2), R ５ and OR ６The composition ratio of x to x can take any value within the ranges of 0<3-x<3 and 0<x<3, respectively. However, from the viewpoint of increasing the polymerization activity, x is preferably 0.5<x<1.5.

[0054] The organoaluminum compound represented by the general formula (2) can be synthesized, for example, by reacting trialkylaluminum with an alcohol, as shown in the following general formula (3): (R ５ ) ３ Al + xR ６ OH → (R ５ ) ３－ｘ Al (OR ６ ) ｘ + (R ６ ) ｘ H... (3)

[0055] As shown in the general formula (3), x in the general formula (2) can be arbitrarily controlled by specifying the reaction ratio of the corresponding trialkylaluminum and alcohol.

[0056] The amount of the organoaluminum compound used varies depending on the type of organoaluminum compound used, but is preferably 0.1 to 100 times by mole, more preferably 0.2 to 50 times by mole, and even more preferably 0.5 to 20 times by mole, relative to the Group 6 transition metal atoms constituting the Group 6 transition metal compound. If the amount of the organoaluminum compound used is too small, the polymerization activity may be insufficient, whereas if it is too large, side reactions tend to occur more easily during ring-opening polymerization.

[0057] The polymerization reaction may be carried out in a solventless state or in a solution. When copolymerization is carried out in a solution, the solvent used is not particularly limited as long as it is inert to the polymerization reaction and can dissolve the cyclopentene used in the copolymerization, the norbornene-based compound represented by the general formula (1), the polymerization catalyst, and the like. However, it is preferable to use a hydrocarbon solvent or a halogen-based solvent. Examples of the hydrocarbon solvent include aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; aliphatic hydrocarbons such as hexane, n-heptane, and n-octane; and alicyclic hydrocarbons such as cyclohexane, cyclopentane, and methylcyclohexane. Examples of the halogen-based solvent include haloalkanes such as dichloromethane and chloroform; and aromatic halogens such as chlorobenzene and dichlorobenzene. These solvents may be used alone or in combination of two or more.

[0058] When copolymerizing cyclopentene with the norbornene-based compound represented by the general formula (1), an olefin compound or a diolefin compound may be added to the polymerization reaction system as a molecular weight modifier, if necessary, to adjust the molecular weight of the resulting copolymer. The olefin compound is not particularly limited as long as it is an organic compound having an ethylenically unsaturated bond, and examples thereof include α-olefins such as 1-butene, 1-pentene, 1-hexene, and 1-octene; styrenes such as styrene and vinyltoluene; halogen-containing vinyl compounds such as allyl chloride; alkenyl alcohols such as allyl alcohol and 5-hexenol; silicon-containing vinyl compounds such as allyltrimethoxysilane, allyltriethoxysilane, allyltrichlorosilane, and styryltrimethoxysilane; and disubstituted olefins such as 2-butene and 3-hexene. Examples of the diolefin compound include non-conjugated diolefins such as 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 1,6-heptadiene, 2-methyl-1,4-pentadiene, 2,5-dimethyl-1,5-hexadiene, etc. The amount of the olefin compound or diolefin compound used as a molecular weight modifier may be appropriately selected depending on the molecular weight of the copolymer to be produced, but the molar ratio relative to the monomer used in the copolymerization is usually in the range of 1 / 100 to 1 / 100,000, preferably 1 / 200 to 1 / 50,000, and more preferably 1 / 500 to 1 / 10,000.

[0059] Furthermore, when the copolymer of cyclopentene and a norbornene-based compound is intended to have a modifying group at the polymer chain end, it is preferable to use a modifying group-containing olefinically unsaturated hydrocarbon compound as the molecular weight modifier instead of the above-mentioned olefin compound or diolefin compound. By using a modifying group-containing olefinically unsaturated hydrocarbon compound, the modifying group can be suitably introduced at the polymer chain end of the copolymer obtained by copolymerization. The modifying group-containing olefinically unsaturated hydrocarbon compound is not particularly limited as long as it has a modifying group and one metathesis-reactive olefinic carbon-carbon double bond. For example, when it is desired to introduce an oxysilyl group at the polymer chain end of the copolymer, an oxysilyl group-containing olefinically unsaturated hydrocarbon can be present in the polymerization reaction system.

[0060] Examples of the oxysilyl group-containing olefinically unsaturated hydrocarbon include those which introduce a modifying group only at one end (one end) of the polymer chain of the copolymer, such as alkoxysilane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, allylmethoxydimethylsilane, allyltriethoxysilane, allylethoxydimethylsilane, styryltrimethoxysilane, styryltriethoxysilane, styrylethyltriethoxysilane, allyltriethoxysilylmethyl ether, and allyltriethoxysilylmethylethylamine; vinyltriphenoxysilane, allyltriphenoxysilane, and aryltriethoxysilane; aryloxysilane compounds such as vinyltriacetoxysilane, allyltriacetoxysilane, allyldiacetoxymethylsilane, and allylacetoxydimethylsilane; acyloxysilane compounds such as vinyltriacetoxysilane, allyltriacetoxysilane, allyldiacetoxymethylsilane, and allylacetoxydimethylsilane; alkylsiloxysilane compounds such as allyltris(trimethylsiloxy)silane; arylsiloxysilane compounds such as allyltris(triphenylsiloxy)silane; and polysiloxane compounds such as 1-allylheptamethyltrisiloxane, 1-allylnonamethyltetrasiloxane, 1-allylnonamethylcyclopentasiloxane, and 1-allylundecamethylcyclohexasiloxane. Furthermore, examples of compounds for introducing modifying groups into both ends (both ends) of the polymer chain of the copolymer include alkoxysilane compounds such as bis(trimethoxysilyl)ethylene, bis(triethoxysilyl)ethylene, 2-butene-1,4-di(trimethoxysilane), 2-butene-1,4-di(triethoxysilane), and 1,4-di(trimethoxysilylmethoxy)-2-butene; aryloxysilane compounds such as 2-butene-1,4-di(triphenoxysilane); and 2-butene. acyloxysilane compounds such as 2-butene-1,4-di[tris(trimethylsiloxy)silane]; alkylsiloxysilane compounds such as 2-butene-1,4-di[tris(triphenylsiloxy)silane]; arylsiloxysilane compounds such as 2-butene-1,4-di[heptamethyltrisiloxane] and 2-butene-1,4-di(undecamethylcyclohexasiloxane); and the like.

[0061] The modifying group-containing olefinically unsaturated hydrocarbon compound acts as a molecular weight modifier in addition to the function of introducing a modifying group into the polymer chain terminal of the copolymer. Therefore, the amount of the modifying group-containing olefinically unsaturated hydrocarbon compound used may be appropriately selected depending on the molecular weight of the copolymer to be produced, but is usually in the range of 1 / 100 to 1 / 100,000, preferably 1 / 200 to 1 / 50,000, and more preferably 1 / 500 to 1 / 10,000 in terms of molar ratio relative to the monomers used in copolymerization.

[0062] The polymerization reaction temperature is not particularly limited, but is preferably −100° C. or higher, more preferably −50° C. or higher, even more preferably 0° C. or higher, and particularly preferably 20° C. or higher. The upper limit of the polymerization reaction temperature is not particularly limited, but is preferably less than 120° C., more preferably less than 100° C., even more preferably less than 90° C., and particularly preferably less than 80° C. The polymerization reaction time is not particularly limited, but is preferably 1 minute to 72 hours, and more preferably 10 minutes to 20 hours.

[0063] If desired, an antioxidant such as a phenol-based stabilizer, a phosphorus-based stabilizer, or a sulfur-based stabilizer may be added to the copolymer obtained by the polymerization reaction. The amount of the antioxidant to be added may be determined appropriately depending on the type of the antioxidant. Furthermore, if desired, an extender oil may be blended into the copolymer. When the copolymer is obtained as a polymerization solution, a known recovery method may be used to recover the copolymer from the polymerization solution. For example, a method may be used in which the solvent is separated by steam stripping or the like, the solid is filtered off, and then the solid is dried to obtain a solid copolymer.

[0064] The content of the copolymer of cyclopentene and norbornene-based compound is preferably 20 to 90 parts by mass, and more preferably 30 to 85 parts by mass, per 100 parts by mass of the rubber component. When the content of the copolymer of cyclopentene and norbornene-based compound is in the range of 20 to 90 parts by mass per 100 parts by mass of the rubber component, the balance between fuel economy and wear resistance of the rubber composition is further improved.

[0065] -Isoprene Skeleton Rubber- The rubber component includes an isoprene skeleton rubber. The isoprene skeleton rubber is a rubber whose main skeleton is isoprene units, and specific examples include natural rubber (NR) and synthetic isoprene rubber (IR). When the rubber component contains an isoprene skeleton rubber, the fracture resistance of the rubber composition can be improved, and the fracture resistance of a tire to which the rubber composition is applied can also be improved. Furthermore, when the isoprene skeleton rubber is blended with the copolymer of cyclopentene and a norbornene compound and used in the rubber composition, the wear resistance of the rubber composition can be improved.

[0066] The content of the isoprene skeleton rubber is preferably 10 to 80 parts by mass, and more preferably 15 to 70 parts by mass, per 100 parts by mass of the rubber component. When the content of the isoprene skeleton rubber is in the range of 10 to 80 parts by mass per 100 parts by mass of the rubber component, the balance between fuel economy and wear resistance of the rubber composition is further improved.

[0067] -Other Rubber- The rubber component may further contain other rubber. Examples of such other rubber include styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), butyl rubber (IIR), halogenated butyl rubber, ethylene-propylene rubber (EPR, EPDM), fluororubber, silicone rubber, and urethane rubber. The content of these other rubbers is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the rubber component.

[0068] (Filler) The rubber composition for a tire of this embodiment contains a filler. By containing a filler, the reinforcing property of the rubber composition is improved. Examples of the filler include carbon black, silica, clay, talc, calcium carbonate, aluminum hydroxide, etc., and among these, carbon black is preferred.

[0069] The content of the filler is preferably in the range of 5 to 80 parts by mass per 100 parts by mass of the rubber component. When the content of the filler is 5 parts by mass or more per 100 parts by mass of the rubber component, the abrasion resistance of the rubber composition is further improved, and when the content is 80 parts by mass or less, the fuel economy of the rubber composition is further improved. From the viewpoint of abrasion resistance, the content of the filler is more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of the rubber component, and from the viewpoint of fuel economy, it is more preferably 70 parts by mass or less, and even more preferably 60 parts by mass or less.

[0070] -Carbon Black- The rubber composition for a tire of this embodiment preferably contains carbon black as the filler. The carbon black has a significant effect of reinforcing the rubber composition and improving the abrasion resistance of the rubber composition, and therefore a rubber composition for a tire containing carbon black as a filler has further improved abrasion resistance. The carbon black is not particularly limited, and examples include GPF, FEF, HAF, ISAF, and SAF grade carbon black. These carbon blacks may be used alone or in combination of two or more types. Furthermore, the carbon black may be recycled carbon black.

[0071] The carbon black content is preferably in the range of 5 to 80 parts by mass per 100 parts by mass of the rubber component. When the carbon black content is 5 parts by mass or more per 100 parts by mass of the rubber component, the abrasion resistance of the rubber composition is further improved, and when the carbon black content is 80 parts by mass or less, the fuel economy of the rubber composition is further improved. From the viewpoint of abrasion resistance, the carbon black content is more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of the rubber component, and from the viewpoint of fuel economy, it is more preferably 70 parts by mass or less, and even more preferably 60 parts by mass or less.

[0072] From the viewpoint of the abrasion resistance of the rubber composition, the proportion of carbon black in the filler is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass.

[0073] (Others) In addition to the rubber component and filler described above, the rubber composition for a tire of this embodiment may contain, as necessary, various components commonly used in the rubber industry, such as a silane coupling agent, an antioxidant, a hardened fatty acid, zinc oxide (zinc white), a tackifier, a vulcanization accelerator, a vulcanizing agent, etc., appropriately selected within a range that does not impair the object of the present invention. Commercially available products can be suitably used as these compounding ingredients.

[0074] Examples of the antioxidant include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6C) and 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ). These antioxidants may be used alone or in combination of two or more. The content of the antioxidant is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component.

[0075] Examples of the hardened fatty acid include stearic acid, etc. The content of the hardened fatty acid is not particularly limited, but is preferably in the range of 0.1 to 5 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component.

[0076] The content of the zinc oxide (zinc white) is not particularly limited, but is preferably in the range of 0.1 to 10 parts by mass, and more preferably 1 to 8 parts by mass, per 100 parts by mass of the rubber component.

[0077] Examples of the tackifier include rosin-based resins, terpene-based resins, petroleum-based resins, phenol-based resins, coal-based resins, and xylene-based resins, and among these, petroleum-based resins are preferred. ５ based resin, C ５ -C ９ based resin, C ９ The content of the tackifier is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, and more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the rubber component.

[0078] Examples of the vulcanization accelerator include sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, thiazole vulcanization accelerators, thiuram vulcanization accelerators, and dithiocarbamate vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. The content of the vulcanization accelerator is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, more preferably 0.2 to 4 parts by mass, per 100 parts by mass of the rubber component.

[0079] The vulcanizing agent may be sulfur, etc. The content of the vulcanizing agent is preferably in the range of 0.1 to 6 parts by mass, more preferably 0.5 to 3 parts by mass, in terms of sulfur content, per 100 parts by mass of the rubber component.

[0080] (Method for producing rubber composition for tire) The method for producing the rubber composition for tire is not particularly limited, but the rubber composition for tire can be produced, for example, by blending various components appropriately selected as necessary with the above-mentioned rubber component and filler, and kneading, heating, extruding, etc. Furthermore, the obtained rubber composition can be vulcanized to produce a vulcanized rubber.

[0081] The conditions for the kneading are not particularly limited, and various conditions such as the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, the kneading temperature, the kneading time, the type of kneading device, etc. can be appropriately selected depending on the purpose. Examples of the kneading device include a Banbury mixer, an intermix, a kneader, a roll, etc. that are usually used for kneading rubber compositions.

[0082] The conditions for the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, and heat-in device can be appropriately selected depending on the purpose. Examples of the heat-in device include a heat-in roll mill typically used for heat-in of rubber compositions.

[0083] The extrusion conditions are not particularly limited, and various conditions such as extrusion time, extrusion speed, extrusion device, and extrusion temperature can be appropriately selected depending on the purpose. Examples of the extrusion device include an extruder typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

[0084] The vulcanization apparatus, method, conditions, etc. are not particularly limited and can be appropriately selected depending on the purpose. Examples of vulcanization apparatus include a molding vulcanizer using a mold used for vulcanizing rubber compositions. The vulcanization temperature is, for example, about 100 to 190°C.

[0085] <Tire> The tire of this embodiment is characterized by including the above-described rubber composition for a tire. Since the tire of this embodiment includes the above-described rubber composition for a tire, it can achieve both low fuel consumption and wear resistance. Note that an example of a portion of the tire to which the rubber composition is applied is the tread rubber.

[0086] The tire of this embodiment may be obtained by molding an unvulcanized rubber composition and then vulcanizing it, depending on the type of tire to be applied, or by molding a semi-vulcanized rubber that has been subjected to a pre-vulcanization step or the like and then further vulcanizing it. The tire of this embodiment is preferably a pneumatic tire, and the gas to be filled into the pneumatic tire may be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

[0087] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0088] <Synthesis Method of Copolymer 1> Under a nitrogen atmosphere, 77 parts by mass of cyclopentene, 23 parts by mass of dicyclopentadiene, 300 parts by mass of cyclohexane, and 0.069 parts by mass of 1-hexene were added to a glass reaction vessel equipped with a stirrer. Next, 0.024 parts by mass of the ring-opening polymerization catalyst dichloro-(3-phenyl-1H-inden-1-ylidene)bis(tricyclohexylphosphine)ruthenium(II) dissolved in 1 part by mass of toluene was added, and the polymerization reaction was carried out at 40°C for 2 hours. After the polymerization reaction, the polymerization was terminated by adding excess vinyl ethyl ether. The polymerization solution was poured into a large excess of methanol containing 2,6-di-t-butyl-p-cresol (BHT), and the precipitated polymer was recovered, washed with methanol, and then vacuum-dried at 50°C for 24 hours to obtain 60 parts by mass of Copolymer 1.

[0089] <Synthesis Method of Copolymer 2> Under a nitrogen atmosphere, 88 parts by mass of cyclopentene, 12 parts by mass of dicyclopentadiene, 300 parts by mass of cyclohexane, and 0.032 parts by mass of 1-hexene were added to a glass reaction vessel equipped with a stirrer. Next, 0.025 parts by mass of the ring-opening polymerization catalyst dichloro-(3-phenyl-1H-inden-1-ylidene)bis(tricyclohexylphosphine)ruthenium(II) dissolved in 1 part by mass of toluene was added, and the polymerization reaction was carried out at 40°C for 2 hours. After the polymerization reaction, the polymerization was terminated by adding excess vinyl ethyl ether. The polymerization solution was poured into a large excess of methanol containing 2,6-di-t-butyl-p-cresol (BHT), and the precipitated polymer was recovered, washed with methanol, and then vacuum-dried at 50°C for 24 hours to obtain 54 parts by mass of Copolymer 2.

[0090] <Synthesis Method of Copolymer 3> Under a nitrogen atmosphere, 88 parts by mass of cyclopentene, 12 parts by mass of dicyclopentadiene, 300 parts by mass of cyclohexane, and 0.027 parts by mass of 1-hexene were added to a glass reaction vessel equipped with a stirrer. Next, 0.025 parts by mass of the ring-opening polymerization catalyst dichloro-(3-phenyl-1H-inden-1-ylidene)bis(tricyclohexylphosphine)ruthenium(II) dissolved in 1 part by mass of toluene was added, and the polymerization reaction was carried out at 40°C for 2 hours. After the polymerization reaction, the polymerization was terminated by adding excess vinyl ethyl ether. The polymerization solution was poured into a large excess of methanol containing 2,6-di-t-butyl-p-cresol (BHT), and the precipitated polymer was recovered, washed with methanol, and then vacuum-dried at 50°C for 24 hours to obtain 52 parts by mass of Copolymer 3.

[0091] <Analysis of Copolymers> The molecular weight of each synthesized copolymer and the proportion of structural units derived from each monomer were measured by the following method. The results are shown in Table 1.

[0092] (1) Molecular Weight Measurement was performed using a gel permeation chromatography (GPC) system "HLC-8220" (manufactured by Tosoh Corporation) with two H-type columns "HZ-M" (manufactured by Tosoh Corporation) connected in series, with tetrahydrofuran as the solvent, at a column temperature of 40°C. A differential refractometer "RI-8320" (manufactured by Tosoh Corporation) was used as the detector. The weight average molecular weight (Mw) of the copolymer was measured as a polystyrene equivalent value.

[0093] (2) Proportion of structural units derived from each monomer The proportion of structural units derived from each monomer constituting the copolymer is １ It was determined by H-NMR spectrum measurement.

[0094]

[0095] <Preparation of Rubber Composition> Each component was blended and kneaded according to the formulation shown in Table 2 to prepare each rubber composition of the examples and comparative examples.

[0096] Each rubber composition further contained, as compounding ingredients other than the components shown in Table 2, 2 parts by mass of hardened fatty acid, 3.5 parts by mass of zinc oxide, 2.5 parts by mass of antioxidant (total amount of two types), 1 part by mass of resin, 1.4 parts by mass of sulfenamide vulcanization accelerator, and 1.05 parts by mass of sulfur per 100 parts by mass of the rubber component.

[0097] <Evaluation of Rubber Composition> The resulting rubber compositions were evaluated for fuel economy and abrasion resistance by the following methods. The results are shown in Table 2.

[0098] (3) Fuel Economy The loss tangent (tanδ) of a test piece made from the obtained rubber composition was measured using a viscoelasticity measuring device (TA Instruments) under conditions of a temperature of 50°C, a strain of 10%, and a frequency of 15 Hz. In addition, the modulus (M50) [MPa] at 50% strain of a test piece made from the obtained rubber composition was measured at room temperature. The evaluation results were indexed, with tanδ / M50 of Comparative Example 1 set to 100. The smaller the index value, the better the fuel economy.

[0099] (4) Abrasion Resistance In accordance with JIS K 6264-2:2005, sandpaper was attached to the grinding wheel using a Lambourn abrasion tester manufactured by Ueshima Seisakusho, and the amount of abrasion was measured at room temperature at a slip rate of 4.6%. The evaluation results were indexed, with the reciprocal of the amount of abrasion of Comparative Example 1 set as 100. A larger index value indicates a smaller amount of abrasion and better abrasion resistance.

[0100]

[0101] *1 NR: Natural rubber *2 BR: Butadiene rubber, manufactured by UBE Elastomers, product name "BR150L" *3 Copolymer 1: A copolymer of cyclopentene and norbornene compounds synthesized by the above method, with a glass transition temperature (Tg) of -42 ° C. and a Mooney viscosity (ML １＋４ *4 Copolymer 2: A copolymer of cyclopentene and norbornene compound synthesized by the above method, with a glass transition temperature (Tg) of -68°C and a Mooney viscosity (ML １＋４ *5 Copolymer 3: A copolymer of cyclopentene and norbornene compound synthesized by the above method, having a glass transition temperature (Tg) of -68°C and a Mooney viscosity (ML １＋４ , 100 °C) is 128 *6 Carbon black 1: CTAB adsorption specific surface area = 130 m ２ / g *7 Carbon black 2: N234, manufactured by Tokai Carbon Co., Ltd., trade name "SEAT 7HM", CTAB adsorption specific surface area = 119 m ２ / g

[0102] The results shown in Table 2 show that the rubber compositions of the examples, which contain an isoprene-skeleton rubber (natural rubber) and a copolymer of cyclopentene and a norbornene-based compound in which the content of structural units derived from a norbornene-based compound (dicyclopentadiene) is 35 mass% or less, are able to achieve both low fuel consumption and wear resistance.

[0103] On the other hand, the rubber composition of Comparative Example 3, which contains an isoprene-skeleton rubber (natural rubber) and a copolymer of cyclopentene and a norbornene-based compound but in which the copolymer contains more than 35% by mass of structural units derived from a norbornene-based compound (dicyclopentadiene), shows poor fuel economy and wear resistance.Furthermore, the rubber composition of Comparative Example 4, which does not contain an isoprene-skeleton rubber and contains a copolymer of cyclopentene and a norbornene-based compound in which the copolymer contains more than 35% by mass of structural units derived from a norbornene-based compound (dicyclopentadiene), shows significantly poor wear resistance.

Claims

1. A rubber composition comprising a rubber component and a filler, wherein the rubber component is a rubber composition containing cyclopentene and a compound represented by the following general formula (1): [In the formula, R １ ~R ４ each independently represents a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, or a substituent containing a halogen atom, a silicon atom, an oxygen atom, or a nitrogen atom; R ２ and R ３ may be bonded to each other to form a ring, and m is an integer of 0 to 2.] and an isoprene skeleton rubber, wherein the copolymer of cyclopentene and the norbornene compound contains 35 mass % or less of structural units derived from the norbornene compound.

2. The rubber composition for tires according to claim 1, wherein the content of the copolymer of cyclopentene and a norbornene compound is 20 to 90 parts by mass per 100 parts by mass of the rubber component.

3. The rubber composition for tires according to claim 1, wherein the copolymer of cyclopentene and a norbornene compound has a weight average molecular weight (Mw) of 200,000 to 1,000,000.

4. The rubber composition for tires according to claim 1, wherein the copolymer of cyclopentene and a norbornene-based compound contains 65 to 90 mass % of structural units derived from cyclopentene.

5. The rubber composition for tires according to claim 1, wherein the copolymer of cyclopentene and a norbornene-based compound contains 35 mass % or less of structural units derived from dicyclopentadiene.

6. The rubber composition for tires according to claim 1, wherein the copolymer of cyclopentene and a norbornene-based compound contains 30 mass % or less of structural units derived from dicyclopentadiene.

7. The rubber composition for tires according to claim 1, which contains carbon black as the filler.

8. The rubber composition for tires according to claim 7, wherein the content of the carbon black is 5 to 80 parts by mass per 100 parts by mass of the rubber component.

9. A tire comprising the rubber composition for tires according to any one of claims 1 to 8.

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