WO2025004405A1 - Rubber composition for tire and tire - Google Patents

Abstract

The problem addressed by the present invention is to provide a rubber composition for a tire that can achieve both low fuel consumption and wear resistance of the tire. The solution to the problem is a rubber composition for a tire that contains a rubber component and carbon black having a dibutyl phthalate (DBP) absorption level of 130 mL/100 g or more, the rubber composition being characterized in that the rubber component includes a copolymer of cyclopentene and a norbornene compound represented by general formula (1) [in the formula, R¹-R⁴ each independently represent a hydrogen atom, a C1-20 hydrocarbon group, or a substituent containing a halogen atom, a silicon atom, an oxygen atom, or a nitrogen atom, R² and R³ may bond to each other to form a ring, and m is an integer of 0-2].

Description

Rubber composition for tires and tires

The present invention relates to a rubber composition for tires and a tire.

In response to the recent trend toward global carbon dioxide emission regulations in response to growing interest in environmental issues, there is an increasing demand for improved fuel efficiency in automobiles. In order to meet such demands, there is also a demand for improved fuel efficiency in tires (i.e., reduced rolling resistance).
From the viewpoint of tire economics, in the development of rubber compositions for tires, it is also required to improve abrasion resistance in addition to low fuel consumption.

However, fuel economy and abrasion resistance are generally in a trade-off relationship, making it difficult to achieve both. For example, methods of increasing the amount of filler mixed in, using fine particle size fillers, and using highly structured fillers are known for improving abrasion resistance, but adopting these methods has the problem that while abrasion resistance improves, fuel economy deteriorates.

In response to this, the following Patent Documents 1 and 2 disclose rubber compounds for passenger car tires and rubber compounds for heavy-duty truck and bus tires that contain specific long-chain branched cyclopentene ring-opening rubber (LCB-CPR), and these rubber compounds are said to be effective in reducing tire rolling resistance, improving wet skid resistance, and improving abrasion resistance.

International Publication No. 2021/178233 International Publication No. 2021/178235

However, after investigations, the inventors found that even with the technologies described in Patent Documents 1 and 2, it is difficult to achieve both low fuel consumption and high wear resistance in a tire, and that there is still room for improvement.

Therefore, an object of the present invention is to provide a rubber composition for tires that can solve the above-mentioned problems of the conventional techniques and achieve both low fuel consumption and high wear resistance for tires.
Another object of the present invention is to provide a tire which achieves both low fuel consumption and high wear resistance.

The key features of the rubber composition for tires and tire of the present invention that solve the above problems are as follows:

［式中、Ｒ^１～Ｒ^４は、それぞれ独立して水素原子、炭素数１～２０の炭化水素基、又は、ハロゲン原子、ケイ素原子、酸素原子若しくは窒素原子を含む置換基を示し、Ｒ^２とＲ^３とは、互いに結合して環を形成してもよく、ｍは、０～２の整数である。］で表されるノルボルネン系化合物との共重合体を含むことを特徴とする、タイヤ用ゴム組成物。 [1] A rubber composition comprising a rubber component and carbon black having a dibutyl phthalate (DBP) absorption amount of 130 mL/100 g or more,
The rubber component is a compound represented by the following general formula (1):

[wherein R ¹ to R ⁴ each independently represent 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.]

[2] The rubber composition for tires according to [1], wherein the norbornene-based compound represented by the above general formula (1) is 2-norbornene and/or dicyclopentadiene.

[3] The rubber composition for tires according to [1] or [2], 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.

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

[5] The rubber composition for tires according to any one of [1] to [4], wherein the copolymer of cyclopentene and a norbornene-based compound has a content of cyclopentene-derived structural units of 20 to 75 mass %.

[6] The rubber composition for tires according to any one of [2] to [5], wherein the copolymer of cyclopentene and a norbornene-based compound has a content of structural units derived from 2-norbornene of 10 to 60 mass %.

[7] The rubber composition for tires according to any one of [2] to [6], wherein the copolymer of cyclopentene and a norbornene-based compound has a content of structural units derived from dicyclopentadiene of 10 to 60 mass %.

[8] The rubber composition for tires according to any one of [1] to [7], wherein the carbon black content is 5 to 80 parts by mass per 100 parts by mass of the rubber component.

[9] The rubber composition for tires according to any one of [1] to [8], wherein the rubber component further contains butadiene rubber.

[10] The rubber composition for tires according to any one of [1] to [9], wherein the copolymer of cyclopentene and a norbornene-based compound is a terpolymer of cyclopentene, 2-norbornene, and dicyclopentadiene.

[11] A tire comprising the rubber composition for tires described in any one of [1] to [10].

According to the present invention, it is possible to provide a rubber composition for tires that can achieve both low fuel consumption and high wear resistance for tires.
Moreover, according to the present invention, a tire that achieves both low fuel consumption and high wear resistance can be provided.

The rubber composition for tires and tires of the present invention will be described in detail below with reference to examples based on the embodiments.

<Definition>
The compounds described herein may be derived in whole or in part from fossil sources, from biological sources such as plant sources, from recycled sources such as used tires, or from a mixture of two or more of fossil, biological and/or renewable sources.

［式中、Ｒ^１～Ｒ^４は、それぞれ独立して水素原子、炭素数１～２０の炭化水素基、又は、ハロゲン原子、ケイ素原子、酸素原子若しくは窒素原子を含む置換基を示し、Ｒ^２とＲ^３とは、互いに結合して環を形成してもよく、ｍは、０～２の整数である。］で表されるノルボルネン系化合物との共重合体（単に「シクロペンテンとノルボルネン系化合物との共重合体」や「共重合体」とも呼ぶ。）を含むことを特徴とする。 <Rubber composition for tires>
The rubber composition for tires of the present embodiment includes a rubber component and carbon black having a dibutyl phthalate (DBP) absorption amount of 130 mL/100 g or more. In the rubber composition for tires of the present embodiment, the rubber component is a cyclopentene and a carboxylic acid represented by the following general formula (1):

[wherein R ¹ to R ⁴ each independently represent 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.]

In the rubber composition for tires of this embodiment, the copolymer of cyclopentene and norbornene-based compound is characterized in that it has crosslinking points and that polymer chains are entangled with each other. Also, the carbon black contained in the rubber composition for tires of this embodiment, which has a DBP absorption of 130 mL/100 g or more, has a higher structure than general carbon black.
In general, when carbon black is blended with a rubber component, a reinforcing layer made of the carbon black and the rubber component is formed around the carbon black, and this reinforcing layer contributes to improving the reinforcing properties of the rubber composition, thereby improving the abrasion resistance, etc.
In the rubber composition for tires of this embodiment, by combining the copolymer of cyclopentene and norbornene-based compound with the highly structured carbon black, the reinforcing layer formed around the highly structured carbon black is further developed by the entanglement of the polymer chains, so that the wear resistance can be further improved. In addition, in the rubber composition for tires of this embodiment, the reinforcing layer is developed by the entanglement of the polymer chains, so that the hysteresis loss is reduced and fuel economy can be improved.
Therefore, by applying the rubber composition for tires of the present embodiment to tires, it is possible to achieve both low fuel consumption and high wear resistance for the tires.

(Rubber component)
The rubber composition for a tire of the present 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 the present embodiment contains a copolymer of cyclopentene and a norbornene-based compound represented by the above general formula (1), and may further contain other rubbers.

- Copolymer of cyclopentene and norbornene compounds -
The copolymer of cyclopentene and a norbornene-based compound contains a structural unit derived from cyclopentene and a structural unit derived from a norbornene-based compound represented by the above general formula (1). In a preferred embodiment, the copolymer of cyclopentene and a norbornene-based compound is a ring-opened copolymer, and in particular, a cyclopentene ring-opened copolymer.

In the above general formula (1), R ¹ to R ⁴ each independently represent 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 a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a neopentyl group, a hexyl group, and an octyl group; alkenyl groups such as a vinyl group, an allyl group, a 2-pentenyl group, a 3-pentenyl group, and a 4-methyl-3-pentenyl group; aryl groups such as a phenyl group, a tolyl group, a 2,6-dimethylphenyl group, a 2,6-diisopropylphenyl group, and a naphthyl group; and aralkyl groups such as a benzyl group and a phenethyl group.

Examples of the norbornene-based compounds represented by the above 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 . unsubstituted or hydrocarbon-substituted bicyclo[2.2.1]hept-2 ^- enes such as tetracyclo[10.2.1.0 ^2,11 . 0 ^4,9 ]pentadeca-4,6,8,13-tetraene (also referred to as "1,4-methano-1,4,4a,9,9a,10-hexahydroanthracene"), dicyclopentadiene, methyldicyclopentadiene, and dihydrodicyclopentadiene (also referred to as "tricyclo[5.2.1.0 ^2,6 ]dec-8-ene");
Tetracyclo[6.2.1.1 ^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} ] dodec-4-ene and other unsubstituted or hydrocarbon-substituted tetracyclo[6.2.1.1 ^{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-4-enes having an alkoxycarbonyl group, such as methyl tetracyclo[6.2.1.1 3,6 . 0 ^2,7 ]dodec-9-ene-4-carboxylate and methyl 4-methyltetracyclo[6.2.1.1 ^{3,6 .} 0 ^2,7 ]dodec-9-ene-4-carboxylate;
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 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 acid anhydride, and other tetracyclo[6.2.1.1 ^3,6 . 0 ^2,7 ] dodec-4-enes having a hydroxycarbonyl group or an acid anhydride group;
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- ⁴ -enes having a hydroxyl group, such as tetracyclo[6.2.1.1 ^3,6 . 0 ^2,7 ]dodec-9-ene-4-methanol and tetracyclo[6.2.1.1 ^3,6 . 0 2,7 ]dodec-9-en-4-ol;
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-4-enes having a hydrocarbonyl group, such as tetracyclo[6.2.1.1 ^3,6 . 0 ^2,7 ]dodec-9-ene-4-carbaldehyde;
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;
Tetracyclo[6.2.1.1 ^3,6 . 0 ^2,7 ] dodec-4-enes having a carbonyloxy group, such as 9-tetracyclo[6.2.1.1 ^{3,6 .} 0 ^2,7 ] dodec-4-enyl acetate, 9-tetracyclo[6.2.1.1 ^3,6 . 0 ^2,7 ] dodec-4-enyl acrylate, and 9-tetracyclo[6.2.1.1 ^3,6 . 0 ^2,7 ] dodec-4-enyl methacrylate;
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-4-enes having a functional group containing a nitrogen atom, such as 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, and tetracyclo[6.2.1.1 ^3,6 . ^{0 2,7 ]} dodec-9-ene-4,5-dicarboxylic acid imide;
Bicyclo[2.2.1]hept-2-enes having a halogen atom, such as 5-chloro-2-norbornene;
Tetracyclo[6.2.1.1 ^3,6 . 0 ^2,7 ]dodec-4-enes having halogen atoms, such as 9-chlorotetracyclo[6.2.1.1 ^3,6 . 0 ^2,7 ]dodec-4-ene;
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;
Examples of the norbornene-based compound include tetracyclo[6.2.1.1 ^3,6 . 0 ^2,7 ]dodec-4-enes having a functional group containing a silicon atom, such as 4-trimethoxysilyltetracyclo[6.2.1.1 ^3,6 . 0 ^2,7 ]dodec-9-ene and 4-triethoxysilyltetracyclo[6.2.1.1 ^3,6 . 0 ^2,7 ]dodec-9-ene. The norbornene-based compound may be used alone or in combination of two or more.

The norbornene-based compound represented by the above general formula (1) is preferably one in which m is 0 or 1, and more preferably one in which m is 0. In addition, in the above general formula (1), R ¹ to R ⁴ may be the same or different.

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

In addition, as the norbornene-based compound represented by the above general formula (1), a compound in which R ² and R ³ are bonded to each other to form a ring is also preferred. Here, specific examples of the ring structure formed by R ² and R ³ being bonded to each other 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 in particular, a compound having a cyclopentene ring alone, or a compound having a polycyclic structure of a cyclopentane ring and a benzene ring is preferred. In addition, R ¹ and R ⁴ other than R ² and R ³ forming a ring structure 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, it is preferable that m is 0. As the norbornene-based compound in which ^R2 and ^R3 in the above general formula (1) 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.

The copolymer of cyclopentene and a norbornene-based compound preferably has a content of cyclopentene-derived structural units of 20 to 75 mass%, more preferably 25 to 70 mass%, even more preferably 30 to 65 mass%, and particularly preferably 35 to 60 mass%, based on all repeating structural units of the copolymer. By setting the content of cyclopentene-derived structural units in the copolymer to the range of 20 to 75 mass%, the fuel economy and abrasion resistance of a rubber composition containing the copolymer can be further improved.

The copolymer of cyclopentene and a norbornene-based compound preferably contains structural units derived from a norbornene-based compound represented by the above general formula (1) in a proportion of 10 to 80 mass %, more preferably 20 to 70 mass %, even more preferably 25 to 65 mass %, and particularly preferably 40 to 65 mass %, based on all repeating structural units of the copolymer. By setting the content of structural units derived from a norbornene-based compound represented by general formula (1) in the copolymer to the range of 10 to 80 mass %, the fuel economy and abrasion resistance of a rubber composition containing the copolymer can be further improved.

In the copolymer of cyclopentene and a norbornene-based compound, the norbornene-based compound represented by the above general formula (1) is preferably 2-norbornene and/or dicyclopentadiene. Since 2-norbornene and dicyclopentadiene are easily available, a copolymer of cyclopentene and 2-norbornene and/or dicyclopentadiene is also easily available. Therefore, a rubber composition for tires containing a copolymer of cyclopentene and 2-norbornene and/or dicyclopentadiene is advantageous in terms of cost.

When 2-norbornene is used as the norbornene-based compound represented by the above general formula (1), the copolymer of cyclopentene and a norbornene-based compound preferably contains 10 to 60 mass% of structural units derived from 2-norbornene relative to the total repeating structural units of the copolymer, and more preferably 20 to 60 mass%. By setting the content of structural units derived from 2-norbornene in the copolymer to the range of 10 to 60 mass%, the fuel economy and wear resistance of a rubber composition containing the copolymer can be further improved.

When dicyclopentadiene is used as the norbornene-based compound represented by the above general formula (1), the copolymer of cyclopentene and a norbornene-based compound preferably has a content of dicyclopentadiene-derived structural units of 10 to 60 mass%, and more preferably 20 to 50 mass%, relative to the total repeating structural units of the copolymer. By setting the content of dicyclopentadiene-derived structural units in the copolymer to the range of 10 to 60 mass%, the fuel economy and wear resistance of a rubber composition containing the copolymer can be further improved.

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

The copolymer of cyclopentene and a norbornene compound may be a copolymer of cyclopentene and a norbornene compound represented by the general formula (1) with 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 aromatic rings 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 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 preferable that the copolymer does not substantially contain structural units derived from other monomers.

The copolymer of cyclopentene and 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. A copolymer having a weight average molecular weight (Mw) in the range of 200,000 to 1,000,000 is easy to manufacture and has good processability (workability). In addition, 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.
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 calculated as polystyrene, measured by gel permeation chromatography (GPC).

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 is the ratio of the cis structure and the trans structure of the double bond 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 in the above range, the fuel economy and wear resistance of the rubber composition containing the copolymer can be further improved.

The copolymer of cyclopentene and a norbornene-based compound preferably has a glass transition temperature (Tg) of -80°C to 10°C, more preferably -75°C to 0°C, and even more preferably -70°C to -10°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-based compound used.

The copolymer of cyclopentene and a norbornene compound may have a modified group at the polymer chain end. By having such a modified end group, the affinity for silica and the like can be further increased, and the dispersibility of silica and the like in the rubber composition can be increased, and as a result, the processability (workability), fuel efficiency, and wear resistance of the rubber composition can be further improved. The modified group to be introduced into 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 an atom of Group 15 of the periodic table, an atom of Group 16 of the periodic table, and a silicon atom. As the modified group for forming the modified end group, from the viewpoint of increasing the affinity for silica and the like, a modified group containing an atom selected from the group consisting of a nitrogen atom, an oxygen atom, a phosphorus atom, a sulfur atom, and a silicon atom is more preferable, and among these, a modified group containing an atom selected from the group consisting of a nitrogen atom, an oxygen atom, and a silicon atom is even more preferable.

Examples of the modified group containing a nitrogen atom include an amino group, a pyridyl group, an imino group, an amide group, a nitro group, a urethane bond group, or a hydrocarbon group containing any of these groups. Examples of the modified group containing an oxygen atom include a hydroxyl group, a carboxylic acid group, an ether group, an ester group, a carbonyl group, an aldehyde group, an epoxy group, or a hydrocarbon group containing any of these groups. Examples of the modified group containing a silicon atom include an alkylsilyl group, an oxysilyl group, or a hydrocarbon group containing any of these groups. Examples of the modified group containing a phosphorus atom include a phosphate group, a phosphino group, or a hydrocarbon group containing any of these groups. Examples of the modified group containing a sulfur atom include a sulfonyl group, a thiol group, a thioether group, or a hydrocarbon group containing any of these groups. The modified group may also be a modified group containing a plurality 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 silica, etc., oxysilyl groups are particularly preferred. Here, the oxysilyl group refers to a group having a silicon-oxygen bond.

The oxysilyl group includes an alkoxysilyl group, an aryloxysilyl group, an acyloxy group, an alkylsiloxysilyl group, and an arylsiloxysilyl group. In addition, an alkoxysilyl group, an aryloxysilyl group, or a hydroxysilyl group obtained by hydrolysis of an acyloxy group can be mentioned. 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.

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

The copolymer of cyclopentene and a norbornene compound preferably has a Mooney viscosity (ML ₁₊₄ , 100° C.) of 20-150, more preferably 22-120, and particularly preferably 25-90.

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

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 above general formula (1), but ruthenium carbene complexes and halogen-containing Group 6 transition metal compounds of the periodic table (hereinafter also referred to as "Group 6 transition metal compounds of the periodic table"). These ring-opening polymerization catalysts may be used alone or in combination of two or more.

The ruthenium carbene complexes include bis(tricyclohexylphosphine)benzylidene ruthenium dichloride, bis(triphenylphosphine)-3,3-diphenylpropenylidene ruthenium dichloride, bis(tricyclohexylphosphine)t-butylvinylidene ruthenium dichloride, dichloro-(3-phenyl-1H-inden-1-ylidene)bis(tricyclohexylphosphine)ruthenium, bis(1,3-diisopropylimidazolin-2-ylidene)benzylidene ruthenium dichloride, bis(1,3-dicyclohexylimidazolin-2-ylidene)benzylidene ruthenium dichloride, and bis(1,3-dicyclohexylimidazolin-2-ylidene)benzylidene ruthenium dichloride. Examples include (1,3-dimesitylimidazolin-2-ylidene)benzylidene ruthenium dichloride, (1,3-dimesitylimidazolin-2-ylidene)(tricyclohexylphosphine)benzylidene ruthenium dichloride, (1,3-dimesitylimidazolin-2-ylidene)(tricyclohexylphosphine)benzylidene ruthenium dichloride, bis(tricyclohexylphosphine)ethoxymethylidene ruthenium dichloride, (1,3-dimesitylimidazolin-2-ylidene)(tricyclohexylphosphine)ethoxymethylidene ruthenium dichloride, etc.

The periodic table Group 6 transition metal compound is a compound having a periodic table Group 6 transition metal atom (long period periodic table, the same applies below), 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 from the viewpoint of high solubility in cyclopentene. Specific examples of the periodic table Group 6 transition metal compound include molybdenum compounds such as molybdenum pentachloride, molybdenum oxotetrachloride, and molybdenum (phenylimido) tetrachloride; tungsten compounds such as tungsten hexachloride, tungsten oxotetrachloride, tungsten (phenylimido) tetrachloride, monocatecholate tungsten tetrachloride, bis(3,5-ditertiarybutyl)catecholate tungsten dichloride, and bis(2-chloroetherate) tetrachloride; and the like.

The amount of the ring-opening polymerization catalyst used is, in terms of the molar ratio of (ring-opening polymerization catalyst:monomer used in copolymerization), 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 periodic table Group 6 transition metal compound is used, the amount of the periodic table Group 6 transition metal compound used is, in terms of the molar ratio of "Group 6 transition metal atom in the ring-opening polymerization catalyst:monomer used in ring-opening polymerization", 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.

When the above-mentioned Group 6 transition metal compound 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 Group 6 transition metal compound.
(R ⁵ ) _3-x Al(OR ⁶ ) _x ... (2)
In the above general formula (2), ^R5 and ^R6 are each independently a hydrocarbon group having 1 to 20 carbon atoms, and preferably a hydrocarbon group having 1 to 10 carbon atoms. Also, x satisfies 0<x<3.

In the above general formula (2), examples of ^R5 and ^R6 include alkyl groups such as a methyl group, an ethyl group, an isopropyl group, an n-propyl group, an isobutyl group, an n-butyl group, a t-butyl group, an n-hexyl group, a cyclohexyl group, an n-octyl group, and an n-decyl group; and aryl groups such as a phenyl group, a 4-methylphenyl group, a 2,6-dimethylphenyl group, a 2,6-diisopropylphenyl group, and a naphthyl group.

In addition, in the above general formula (2), x is 0<x<3. That is, in general formula (2), the composition ratio of ^R5 to ^OR6 can be any value within the ranges of 0<3-x<3 and 0<x<3, respectively, but from the viewpoint of increasing the polymerization activity, it is preferable that x is 0.5<x<1.5.

The organoaluminum compound represented by the above 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)

In addition, x in the above general formula (2) can be arbitrarily controlled by specifying the reaction ratio of the corresponding trialkylaluminum and alcohol, as shown in the above general formula (3).

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, based on 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, and if it is too large, side reactions tend to occur more easily during ring-opening polymerization.

The polymerization reaction may be carried out without a solvent or in a solution. When copolymerizing in a solution, the solvent used is not particularly limited as long as it is inert in the polymerization reaction and can dissolve the cyclopentene used in the copolymerization, the norbornene compound represented by the above general formula (1), the polymerization catalyst, etc., but 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; alicyclic hydrocarbons such as cyclohexane, cyclopentane, and methylcyclohexane; and the like. Examples of the halogen-based solvent include haloalkanes such as dichloromethane and chloroform; aromatic halogens such as chlorobenzene and dichlorobenzene; and the like. These solvents may be used alone or in combination of two or more.

When cyclopentene is copolymerized with the norbornene-based compound represented by the above general formula (1), an olefin compound or a diolefin compound may be added to the polymerization reaction system as a molecular weight regulator, if necessary, in order 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, 1-octene, etc.; styrenes such as styrene and vinyl toluene; 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; disubstituted olefins such as 2-butene and 3-hexene; etc. 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, and 2,5-dimethyl-1,5-hexadiene.
The amount of the olefin compound and diolefin compound used as the molecular weight regulator 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, more preferably 1/500 to 1/10,000 in terms of molar ratio to the monomer used in the copolymerization.

In addition, when the copolymer of cyclopentene and norbornene-based compounds is to have a modifying group at the polymer chain end, it is preferable to use a modifying group-containing olefinically unsaturated hydrocarbon compound as a molecular weight regulator 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 olefinic carbon-carbon double bond that has metathesis reactivity. 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 may be present in the polymerization reaction system.

Examples of the oxysilyl group-containing olefinic unsaturated hydrocarbons include alkoxysilane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, allylmethoxydimethylsilane, allyltriethoxysilane, allylethoxydimethylsilane, styryltrimethoxysilane, styryltriethoxysilane, styrylethyltriethoxysilane, allyltriethoxysilylmethylether, and allyltriethoxysilylmethylethylamine, which introduce a modifying group only at one end (single end) of the polymer chain of the copolymer; vinyltriphenoxysilane, allyltriphenoxysilane, and a aryloxysilane compounds such as allylphenoxydimethylsilane; acyloxysilane compounds such as vinyltriacetoxysilane, allyltriacetoxysilane, allyldiacetoxymethylsilane, and allylacetoxydimethylsilane; alkylsiloxysilane compounds such as allyltris(trimethylsiloxy)silane; arylsiloxysilane compounds such as allyltris(triphenylsiloxy)silane; polysiloxane compounds such as 1-allylheptamethyltrisiloxane, 1-allylnonamethyltetrasiloxane, 1-allylnonamethylcyclopentasiloxane, and 1-allylundecamethylcyclohexasiloxane; and the like. In addition, 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); Examples include acyloxysilane compounds such as 1,4-di(triacetoxysilane); alkylsiloxysilane compounds such as 2-butene-1,4-di[tris(trimethylsiloxy)silane]; arylsiloxysilane compounds such as 2-butene-1,4-di[tris(triphenylsiloxy)silane]; polysiloxane compounds such as 2-butene-1,4-di(heptamethyltrisiloxane) and 2-butene-1,4-di(undecamethylcyclohexasiloxane); etc.

The modifying group-containing olefinically unsaturated hydrocarbon compound acts as a molecular weight regulator in addition to introducing a modifying group to the polymer chain end of the copolymer, so 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 molar ratio to the monomers used in the copolymerization.

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.

If desired, an anti-aging agent 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 anti-aging agent to be added may be determined appropriately depending on the type of the anti-aging agent. 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, the solid is filtered off, and then the solid is dried to obtain a solid copolymer.

The content of the copolymer of cyclopentene and norbornene-based compounds 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 compounds 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 abrasion resistance of the rubber composition is further improved.

-Butadiene rubber-
The rubber component preferably further contains butadiene rubber (BR), which has a low glass transition temperature (Tg), and by containing the butadiene rubber in addition to the copolymer of cyclopentene and a norbornene compound, the rubber composition can further improve fuel economy and abrasion resistance.

When the rubber component contains butadiene rubber, the content of the butadiene rubber is preferably in the range of 10 to 80 parts by mass, and more preferably in the range of 15 to 70 parts by mass, per 100 parts by mass of the rubber component. When the content of the butadiene 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 efficiency and abrasion resistance of the rubber composition is further improved.

-Other rubber-
The rubber component may further contain other rubbers. Examples of such other rubbers include natural rubber (NR), synthetic isoprene rubber (IR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), butyl rubber (IIR), halogenated butyl rubber, ethylene-propylene rubber (EPR, EPDM), fluororubber, silicone rubber, urethane rubber, etc. 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.

(Carbon Black)
The rubber composition for tires of this embodiment contains carbon black having a dibutyl phthalate (DBP) absorption of 130 mL/100 g or more. When the DBP absorption of the carbon black is 130 mL/100 g or more, the above-mentioned reinforcing layer is sufficiently formed, and the tire to which the rubber composition is applied can achieve both low fuel consumption and wear resistance. Here, the DBP absorption of the carbon black is preferably 135 mL/100 g or more from the viewpoint of wear resistance, and is preferably 150 mL/100 g or less from the viewpoint of low fuel consumption.
In this specification, the dibutyl phthalate (DBP) absorption amount of carbon black is a value measured in accordance with JIS K6217-4 and is an index representing the ability of carbon black to absorb dibutyl phthalate (DBP) into voids. A larger DBP absorption amount indicates that the carbon black structure is more developed.

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.

(others)
In addition to the above-mentioned rubber component and carbon black having a DBP absorption of 130 mL/100 g or more, the rubber composition for tires of this embodiment may contain various components commonly used in the rubber industry as necessary, such as fillers other than carbon black having a DBP absorption of 130 mL/100 g or more (carbon black having a DBP absorption of less than 130 mL/100 g, silica, etc.), silane coupling agents, antioxidants, hardened fatty acids, zinc oxide (zinc white), tackifiers, vulcanization accelerators, vulcanizing agents, etc., appropriately selected within ranges that do not impair the objects of the present invention. Commercially available products can be suitably used as these compounding agents.

The antioxidants include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6C), 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ), etc. These antioxidants may be used alone or in combination of two or more. There are no particular restrictions on the content of the antioxidant, and it is preferably in the range of 0.1 to 5 parts by mass, more preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component.

The hardened fatty acid may be stearic acid or the like. There are no particular restrictions on the amount of hardened fatty acid, but it 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.

The amount of 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.

Examples of the tackifier include rosin-based resins, terpene-based resins, petroleum-based resins, phenol-based resins, coal-based resins, xylene-based resins, etc., and among these, petroleum-based resins are preferred. Examples of the petroleum-based resins include _C5 -based resins, _C5 - _C9- based resins, _C9 -based resins, dicyclopentadiene resins, etc. The content of the tackifier is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the rubber component.

The vulcanization accelerator may be a sulfenamide-based vulcanization accelerator, a guanidine-based vulcanization accelerator, a thiazole-based vulcanization accelerator, a thiuram-based vulcanization accelerator, a dithiocarbamate-based vulcanization accelerator, or the like. These vulcanization accelerators may be used alone or in combination of two or more. There are no particular limitations on the content of the vulcanization accelerator, and the content is preferably in the range of 0.1 to 5 parts by mass, and more preferably in the range of 0.2 to 4 parts by mass, per 100 parts by mass of the rubber component.

The vulcanizing agent may be sulfur. 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.

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

There are no particular limitations on the conditions for the kneading, and the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, etc., as well as the conditions for the kneading temperature, kneading time, type of kneading device, etc., can be appropriately selected according to the purpose. Examples of kneading devices include Banbury mixers, intermixes, kneaders, rolls, etc., which are typically used for kneading rubber compositions.

There are no particular limitations on the conditions for the heat-in process, and the heat-in process temperature, heat-in process time, heat-in process equipment, and other conditions can be appropriately selected depending on the purpose. Examples of the heat-in process equipment include a heat-in process roll machine that is typically used for heat-in process of rubber compositions.

There are no particular limitations on the extrusion conditions, and various conditions such as extrusion time, extrusion speed, extrusion equipment, and extrusion temperature can be appropriately selected depending on the purpose. Examples of extrusion equipment include extruders that are typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

There are no particular limitations on the vulcanization equipment, method, conditions, etc., and they can be selected appropriately depending on the purpose. Typical vulcanization equipment includes a mold vulcanizer that uses a mold used to vulcanize rubber compositions. The vulcanization temperature is, for example, about 100 to 190°C.

<Tires>
The tire of the present embodiment is characterized by including the above-mentioned rubber composition for tires. Since the tire of the present embodiment includes the above-mentioned rubber composition for tires, it can achieve both low fuel consumption and wear resistance. The rubber composition is applied to the tread rubber of the tire.

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 which it is applied, or by molding a semi-vulcanized rubber that has been subjected to a pre-vulcanization process or the like, and then further vulcanizing it. The tire of this embodiment is preferably a pneumatic tire, and the gas to be filled in 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.

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

<Method for synthesizing copolymer 1>
In a nitrogen atmosphere, 65 parts by mass of cyclopentene, 35 parts by mass of 2-norbornene, 300 parts by mass of cyclohexane, and 0.066 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 20°C for 2 hours. After the polymerization reaction, the polymerization was stopped by adding an excess of 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 collected and washed with methanol, and then vacuum dried at 50°C for 24 hours to obtain 67 parts by mass of copolymer 1.

<Method for synthesizing copolymer 2>
In 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 stopped by adding an excess of 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 collected and washed with methanol, and then vacuum dried at 50°C for 24 hours to obtain 60 parts by mass of copolymer 2.

<Method for synthesizing copolymer 3>
In a nitrogen atmosphere, 85 parts by mass of cyclopentene, 15 parts by mass of dicyclopentadiene, 570 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 stopped by adding an excess of 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 collected and washed with methanol, and then vacuum dried at 50°C for 24 hours to obtain 40 parts by mass of Copolymer 3.

<Method for synthesizing copolymer 4>
In a nitrogen atmosphere, 76 parts by mass of cyclopentene, 12 parts by mass of 2-norbornene, 12 parts by mass of dicyclopentadiene, 300 parts by mass of cyclohexane, and 0.043 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 stopped by adding an excess of 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 collected and washed with methanol, and then vacuum dried at 50°C for 24 hours to obtain 52 parts by mass of Copolymer 4.

<Method for synthesizing copolymer 5>
In a nitrogen atmosphere, 78 parts by mass of cyclopentene, 22 parts by mass of dicyclopentadiene, 360 parts by mass of cyclohexane, and 0.041 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 stopped by adding an excess of 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 collected and washed with methanol, and then vacuum dried at 50°C for 24 hours to obtain 56 parts by mass of Copolymer 5.

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

(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 and a column temperature of 40°C. As a detector, a differential refractometer "RI-8320" (manufactured by Tosoh Corporation) was used. The weight average molecular weight (Mw) of the copolymer was measured as a polystyrene equivalent value.

(2) Proportion of Structural Units Derived from Each Monomer The proportion of structural units derived from each monomer constituting the copolymer was determined by ¹ H-NMR spectrum measurement.

<Preparation of Rubber Composition>
According to the compounding recipe shown in Table 2, the components were compounded and kneaded to prepare the rubber compositions of the examples and comparative examples.

In addition to the components shown in Table 2, each rubber composition further contains the following compounding ingredients per 100 parts by mass of rubber component: 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.

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

(3) Fuel economy The loss tangent (tan δ) of a test piece made from the obtained rubber composition was measured using a viscoelasticity measuring device (TA Instruments) under the 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 the test piece made from the obtained rubber composition was measured at room temperature. The evaluation results were indexed with tan δ/M50 of Comparative Example 1 set to 100. The smaller the index value, the smaller the tan δ and the better the fuel economy.

(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 with a slip rate of 12%. The evaluation results were indexed, with the reciprocal of the amount of abrasion in Comparative Example 1 set as 100. A larger index value indicates a smaller amount of abrasion and better abrasion resistance.

*1 NR: Natural rubber *2 BR: Butadiene rubber, manufactured by UBE Elastomers, product name "BR150L"
*3 Copolymer 1: A copolymer of cyclopentene and a norbornene-based compound synthesized by the above method *4 Copolymer 2: A copolymer of cyclopentene and a norbornene-based compound synthesized by the above method *5 Copolymer 3: A copolymer of cyclopentene and a norbornene-based compound synthesized by the above method *6 Copolymer 4: A copolymer of cyclopentene and a norbornene-based compound synthesized by the above method *7 Copolymer 5: A copolymer of cyclopentene and a norbornene-based compound synthesized by the above method *8 Carbon black 1: Carbon black produced under specified raw material introduction conditions (introduction amount: 435 kg / h, spray pressure: 2.0 MPa, preheating temperature: 170 ° C.), air introduction conditions (introduction amount: 3300 L / h, preheating temperature: 600 ° C.), fuel introduction amount: 135 kg / h, cooling water introduction conditions (reaction time: 30 msec), DBP absorption amount = 136 mL / 100 g
*9 Carbon black 2: DBP absorption = 140 mL / 100 g
*10 Carbon black 3: DBP absorption = 92 mL / 100 g
*11 Carbon black 4: N550, manufactured by Asahi Carbon Co., Ltd., product name "#65", DBP absorption capacity = 121 mL / 100 g
*12 Carbon black 5: N234, manufactured by Tokai Carbon Co., Ltd., trade name "Seat 7HM", DBP absorption capacity = 125 mL / 100 g

The results shown in Table 2 show that the rubber composition of the embodiment, which contains a copolymer of cyclopentene and a norbornene compound and carbon black with a DBP absorption of 130 mL/100 g or more, achieves both low fuel consumption and abrasion resistance.

On the other hand, it can be seen that the rubber composition of Comparative Example 2, which contains carbon black having a DBP absorption amount of 130 mL/100 g or more but does not contain a copolymer of cyclopentene and a norbornene compound, has deteriorated fuel economy and abrasion resistance.
In addition, it is found that the rubber compositions of Comparative Examples 3, 4, and 5, which contain a copolymer of cyclopentene and a norbornene-based compound but have a DBP absorption of less than 130 mL/100 g of carbon black, have deteriorated wear resistance.

Claims (11)

The rubber composition includes a rubber component and carbon black having a dibutyl phthalate (DBP) absorption amount of 130 mL/100 g or more,
The rubber component is a compound represented by the following general formula (1):

[wherein R ¹ to R ⁴ each independently represent 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.] The rubber composition for tires according to claim 1, wherein the norbornene-based compound represented by the above general formula (1) is 2-norbornene and/or dicyclopentadiene. The rubber composition for tires according to claim 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. The rubber composition for tires according to claim 1, wherein the copolymer of cyclopentene and a norbornene-based compound has a weight average molecular weight (Mw) of 200,000 to 1,000,000. The rubber composition for tires according to claim 1, wherein the copolymer of cyclopentene and a norbornene-based compound has a content of cyclopentene-derived structural units of 20 to 75 mass %. The rubber composition for tires according to claim 2, wherein the copolymer of cyclopentene and a norbornene-based compound has a content of structural units derived from 2-norbornene of 10 to 60 mass %. The rubber composition for tires according to claim 2, wherein the copolymer of cyclopentene and a norbornene-based compound has a content of structural units derived from dicyclopentadiene of 10 to 60 mass %. The rubber composition for tires according to claim 1, wherein the carbon black content is 5 to 80 parts by mass per 100 parts by mass of the rubber component. The rubber composition for tires according to claim 1, wherein the rubber component further contains butadiene rubber. The rubber composition for tires according to claim 1, wherein the copolymer of cyclopentene and a norbornene-based compound is a ternary copolymer of cyclopentene, 2-norbornene, and dicyclopentadiene. A tire comprising the rubber composition for tires according to claim 1.