JP6627295B2 - Pneumatic tire - Google Patents

Description

The present invention relates to a pneumatic tire manufactured using a predetermined rubber composition.

Among the tires, in particular, a rubber composition mainly composed of natural rubber and polybutadiene rubber has been used for the sidewalls of heavy duty tires such as trucks and buses in view of flex crack growth resistance and strength.

In recent years, due to increasing interest in environmental issues, there has been an increasing demand for low fuel consumption for automobiles, and rubber compositions used for automobile tires are also required to have excellent fuel economy. .

As a method of improving the fuel economy, use of a low-reinforcing filler, reduction of the filler, use of silica, and the like are known.In these methods, for example, in the case of a sidewall, the reinforcing property And fracture characteristics such as rubber hardness (steering stability), flex crack growth resistance, and chip cut resistance deteriorate. In particular, since the sidewall of a heavy-duty tire easily generates heat, the above-described method has been employed to suppress the heat generation. However, the above-described destruction characteristics are deteriorated, and the above-described destruction characteristics and low fuel consumption are compatible. That was very difficult. As described above, it is difficult to achieve both fuel efficiency and fracture characteristics such as rubber hardness, flex crack growth resistance, and chip cut resistance.

As a method for improving the fuel economy, for example, Patent Document 1 proposes a method using a diene rubber (modified rubber) modified with an organosilicon compound containing an amino group and an alkoxy group. It has not been studied to achieve both characteristics and fuel economy.

JP-A-2000-344955

An object of the present invention is to solve the above-mentioned problems and to provide a pneumatic tire in which steering stability, flex crack growth resistance, chip cut resistance, and fuel economy are improved satisfactorily.

The present invention is a pneumatic tire manufactured using a rubber composition, wherein the rubber composition is obtained by copolymerizing an aromatic vinyl compound and a conjugated diene compound, and has a hydrogenation rate of a conjugated diene portion. It contains a hydrogenated copolymer of 75 mol% or more and a carbon black having a nitrogen adsorption specific surface area of 5 to 200 m ² / g, and the content of the hydrogenated copolymer in 100% by mass of a rubber component is 75% by mass. % Or more, and the content of the carbon black with respect to 100 parts by mass of the rubber component is 30 to 70 parts by mass.

The hydrogenated copolymer preferably has a weight average molecular weight of 200,000 to 2,000,000.

The hydrogenated copolymer preferably has a hydrogenation rate of 90 mol% or more.

The hydrogenated copolymer is preferably a hydrogenated styrene-butadiene copolymer.

Preferably, the hydrogenated styrene-butadiene copolymer is a hydrogenated modified styrene-butadiene copolymer.

The hydrogenated styrene-butadiene copolymer preferably has a styrene content of 5 to 40% by mass.

It is preferable that the rubber composition further contains a polybutadiene rubber.

The content of the polybutadiene rubber in 100% by mass of the rubber component is preferably 5 to 25% by mass.

It is preferable that the tire is a pneumatic tire having a sidewall manufactured using the rubber composition.

According to the present invention, a pneumatic tire manufactured using a rubber composition containing a specific amount of a specific hydrogenated copolymer having a hydrogenation ratio of 75 mol% or more and carbon black having a specific nitrogen adsorption specific surface area, respectively. Therefore, it has good handling stability, flex crack growth resistance, chip cut resistance, and low fuel consumption.

The pneumatic tire of the present invention provides a conjugated diene of a copolymer obtained by copolymerizing an aromatic vinyl compound and a conjugated diene compound (hereinafter also referred to as a copolymer of an aromatic vinyl compound and a conjugated diene compound). Part of a hydrogenated copolymer having a hydrogenation rate of at least 75 mol% in a rubber component of at least 75 mass% in 100 mass%, and a nitrogen adsorption specific surface area of 5 to 200 m ² / g. Was prepared using a rubber composition containing 30 to 70 parts by mass with respect to 100 parts by mass of the rubber component.

The rubber composition in the present invention not only contains carbon black having a specific nitrogen adsorption specific surface area of 30 to 70 parts by mass with respect to 100 parts by mass of the rubber component, but also has a hydrogenation rate of the conjugated diene portion of 75 mol% or more. When the specific hydrogenated copolymer is contained in an amount of 75% by mass or more in 100% by mass of the rubber component, steering stability, flex crack growth resistance, chip cut resistance, and fuel economy can be remarkably improved.

The rubber composition of the present invention is characterized in that it contains, as a rubber component, a hydrogenated copolymer in which a conjugated diene portion of a copolymer of an aromatic vinyl compound and a conjugated diene compound is hydrogenated. Since ordinary rubber has a large number of double bonds serving as reaction points for cross-linking, the cross-linking density is considered to be high, and the cross-linking density is considered to be a starting point of destruction due to stress concentration. In the present invention, the number of reaction sites for crosslinking is reduced by reducing the number of double bonds by hydrogenation. This is expected to reduce cross-linkage density and alleviate stress concentration, thereby improving chip-cut resistance and the like.

Examples of the aromatic vinyl compound include styrene, α-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene, and 2,4,6-trimethylstyrene. These may be used alone or in combination of two or more. Among them, practical viewpoints such as availability of monomers and the reason that the effects of the present invention can be more preferably obtained. To styrene are particularly preferred.

Examples of the conjugated diene compound include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, and 1,3-hexadiene. These may be used alone or in combination of two or more. Among them, practical viewpoints such as availability of monomers and the reason that the effects of the present invention can be more preferably obtained. To 1,3-butadiene and isoprene are preferred, and 1,3-butadiene is more preferred.

As the copolymer of the aromatic vinyl compound and the conjugated diene compound, a copolymer of styrene and 1,3-butadiene (styrene-butadiene copolymer) is preferable. Therefore, the hydrogenated copolymer is preferably a hydrogenated styrene butadiene copolymer. Further, the hydrogenated styrene-butadiene copolymer is preferably a hydrogenated modified styrene-butadiene copolymer modified by a method described below.

The styrene-butadiene copolymer is not particularly limited in the order of copolymerization as long as it copolymerizes styrene and 1,3-butadiene, and may be a random copolymer or a block copolymer, but a random copolymer is preferred. . The same applies to a copolymer of an aromatic vinyl compound and a conjugated diene compound other than the styrene-butadiene copolymer.

The hydrogenation rate of the hydrogenated copolymer (the ratio of the hydrogenated copolymer to the conjugated diene portion of the copolymer of the aromatic vinyl compound and the conjugated diene compound) is at least 75 mol%, preferably at least 80 mol%, It is more preferably at least 90 mol%, further preferably at least 93 mol%. If the hydrogenation rate is less than 75 mol%, it is difficult to improve the fuel economy, chip cut resistance and flex crack growth resistance. Further, the hydrogenation rate of the hydrogenated copolymer is preferably at most 99 mol%, more preferably at most 98 mol%. If the hydrogenation rate exceeds 99 mol%, the rubber composition may be hardened.
In addition, the hydrogenation rate can be calculated from the spectrum reduction rate of the unsaturated bond part of the spectrum obtained by measuring H ¹ -NMR.

The weight average molecular weight (Mw) of the hydrogenated copolymer is preferably 200,000 or more, more preferably 400,000 or more. If Mw is less than 200,000, there is a possibility that good steering stability, flex crack growth resistance, chip cut resistance, and low fuel consumption cannot be obtained. Further, the Mw of the hydrogenated copolymer is preferably 2,000,000 or less, more preferably 1,000,000 or less, and further preferably 700,000 or less. When Mw exceeds 2,000,000, workability tends to decrease.

In addition, in this specification, weight average molecular weight (Mw) and number average molecular weight (Mn) are gel permeation chromatograph (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: It can be determined in terms of standard polystyrene based on the measured value by TSKEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation.

The Mooney viscosity (ML _{1 + 4} , 100 ° C.) of the hydrogenated copolymer is preferably 50 or more, more preferably 60 or more, and further preferably 80 or more. If it is less than 50, good fuel economy, steering stability, flex crack growth resistance and chip cut resistance may not be obtained. Further, the Mooney viscosity is preferably 120 or less, more preferably 110 or less, and further preferably 100 or less. If it exceeds 120, workability tends to deteriorate.
In this specification, the Mooney viscosity (ML _{1 + 4} , 100 ° C.) is a value obtained by measuring the Mooney viscosity at 100 ° C. according to JIS K 6300.

When the hydrogenated copolymer is a hydrogenated styrene-butadiene copolymer, the styrene content of the hydrogenated styrene-butadiene copolymer is preferably 5% by mass or more, more preferably 10% by mass or more, and still more preferably 15% by mass. %, Particularly preferably at least 20% by mass, most preferably at least 25% by mass. If the styrene content is less than 5% by mass, sufficient fuel economy may not be obtained. The styrene content of the hydrogenated styrene-butadiene copolymer is preferably 40% by mass or less, more preferably 35% by mass or less. If the styrene content exceeds 40% by mass, sufficient steering stability, flex crack growth resistance and chip cut resistance cannot be obtained, and fuel economy may be deteriorated. When the styrene content is within the above range, the effects of the present invention can be more suitably obtained.
The styrene content is measured by a method described in Examples described later.

The hydrogenated copolymer can be synthesized, for example, by subjecting a polymer obtained by polymerizing an aromatic vinyl compound and a conjugated diene compound to a hydrogenation treatment, and specifically, by the following method.

<Method for producing copolymer>
(Polymerization method)
The polymerization method of the copolymer of the aromatic vinyl compound and the conjugated diene compound is not particularly limited, and any of a solution polymerization method, a gas phase polymerization method, and a bulk polymerization method can be used, but the solution polymerization method is particularly preferable. Further, the polymerization system may be any of a batch system and a continuous system.

When the solution polymerization method is used, the monomer concentration in the solvent (the total of styrene and 1,3-butadiene in the case of a styrene-butadiene copolymer) is preferably 5% by mass or more, more preferably 10% by mass or more. . When the monomer concentration in the solution is less than 5% by mass, the amount of the obtained copolymer is small, and the cost tends to be high. Further, the monomer concentration in the solvent is preferably 50% by mass or less, more preferably 30% by mass or less. When the monomer concentration in the solvent exceeds 50% by mass, the solution viscosity becomes too high, stirring becomes difficult, and the polymerization tends to be difficult.

(Polymerization initiator in anionic polymerization)
When performing anionic polymerization, the polymerization initiator is not particularly limited, but an organic lithium compound is preferably used. As the organic lithium compound, those having an alkyl group having 2 to 20 carbon atoms are preferable. For example, ethyl lithium, n-propyl lithium, isopropyl lithium, n-butyl lithium, sec-butyl lithium, tert-butyl lithium, tert-butyl lithium Reaction products of octyl lithium, n-decyl lithium, phenyl lithium, 2-naphthyl lithium, 2-butyl-phenyl lithium, 4-phenyl-butyl lithium, cyclohexyl lithium, cyclopentyl lithium, diisopropenyl benzene and butyl lithium, etc. Among these, n-butyllithium or sec-butyllithium is preferred from the viewpoint of availability, safety and the like.

The polymerization reaction may be carried out in the presence of a compound (R) obtained by mixing at least one of the above-mentioned organolithium compounds and a compound (B1) having a functional group that interacts with silica. By performing the polymerization in the presence of the compound (R), a functional group having an interaction with silica can be introduced to the polymerization initiation terminal of the copolymer. As a result, a copolymer having a modified starting end is obtained. Note that in this specification, “interaction” means that a covalent bond is formed between molecules or an intermolecular force weaker than a covalent bond (for example, an ion-dipole interaction, a dipole-dipole interaction, It means forming an electromagnetic force acting between molecules such as hydrogen bonding and van der Waals force. The “functional group that interacts with silica” refers to a group having at least one atom that interacts with silica, such as a nitrogen atom, a sulfur atom, a phosphorus atom, and an oxygen atom.

The compound (R) is preferably a reaction product of an organolithium compound and a nitrogen-containing compound such as a secondary amine compound. Specific examples of the nitrogen-containing compound include, for example, dimethylamine, diethylamine, dipropylamine, dibutylamine, dodecamethyleneimine, N, N′-dimethyl-N′-trimethylsilyl-1,6-diaminohexane, piperidine, pyrrolidine, Hexamethyleneimine, heptamethyleneimine, dicyclohexylamine, N-methylbenzylamine, di- (2-ethylhexyl) amine, diallylamine, morpholine, N- (trimethylsilyl) piperazine, N- (tert-butyldimethylsilyl) piperazine, 1, 3-ditrimethylsilyl-1,3,5-triazinan and the like. When the polymerization is performed in the presence of the compound (R), the compound (R) is prepared by previously mixing the organolithium compound and the compound (B1), and the prepared compound (R) is added to the polymerization system. To perform polymerization. Alternatively, the polymerization may be carried out by adding the organolithium compound and the compound (B1) to the polymerization system and mixing the two in the polymerization system to prepare the compound (R).

(Method of anionic polymerization)
The method for producing a copolymer by anionic polymerization using the polymerization initiator is not particularly limited, and a conventionally known method can be used.
Specifically, an organic solvent inert to the reaction, for example, aliphatic, alicyclic, in a hydrocarbon solvent such as an aromatic hydrocarbon compound, for example, butyllithium as a polymerization initiator, if necessary, randomizer By subjecting styrene, 1,3-butadiene, and the like to anionic polymerization in the presence of styrene, an intended copolymer such as a styrene-butadiene copolymer can be obtained.

(Hydrocarbon solvents in anionic polymerization)
The hydrocarbon solvent preferably has 3 to 8 carbon atoms, for example, propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, cyclohexane, propene, 1-butene, isobutene, trans-2. -Butene, cis-2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene, ethylbenzene and the like. These may be used alone or as a mixture of two or more.

(Randomizer in anionic polymerization)
The randomizer is used to control the microstructure of the conjugated diene moiety in the copolymer, for example, increase the 1,2-bond in butadiene, increase the 3,4-bond in isoprene, or the composition of the monomer unit in the copolymer. A compound having an effect of controlling distribution, for example, randomizing styrene units and butadiene units in a styrene-butadiene copolymer. The randomizer is not particularly limited, and any one of known compounds generally used as conventional randomizers can be used. For example, dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, bistetrahydrofurylpropane, triethylamine, pyridine, N-methylmorpholine, N, N, N ', N'-tetramethylethylenediamine, 1,2-di Examples thereof include ethers such as piperidinoethane and tertiary amines. Further, potassium salts such as potassium-t-amylate and potassium-t-butoxide, and sodium salts such as sodium-t-amylate can also be used. One of these randomizers may be used alone, or two or more thereof may be used in combination. The amount of the randomizer to be used is preferably at least 0.01 molar equivalent, more preferably at least 0.05 molar equivalent, per 1 mol of the organic lithium compound. If the used amount of the randomizer is less than 0.01 molar equivalent, the effect of addition is small and randomization tends to be difficult. Further, the use amount of the randomizer is preferably at most 1,000 molar equivalents, more preferably at most 500 molar equivalents, per mol of the organic lithium compound. When the use amount of the randomizer exceeds 1000 molar equivalents, the reaction rate of the monomer greatly changes, and on the contrary, randomization tends to be difficult.

(Reaction temperature)
The reaction temperature at the time of anionic polymerization is not particularly limited as long as the reaction proceeds suitably, but is usually preferably from -10 ° C to 100 ° C, more preferably from 25 ° C to 70 ° C.

(Denaturation step)
By reacting the active terminal of the copolymer obtained in the above polymerization step with the compound (B2) having a functional group that interacts with silica, the active terminal of the copolymer interacts with silica at the polymerization end terminal of the copolymer. Functional groups can be introduced. As a result, a copolymer having a modified polymerization end is obtained. In the present invention, the term "terminal" means a portion other than the structure derived from the monomer having a carbon-carbon double bond, which is present at the end of the molecular chain.

（式（１）中、Ａ^１は、窒素原子、リン原子及び硫黄原子からなる群より選択される少なくとも一種の原子を有し、活性水素を有さず、かつＲ^５に対して窒素原子、リン原子又は硫黄原子で結合する１価の官能基である。Ｒ^３及びＲ^４はヒドロカルビル基であり、Ｒ^５はヒドロカルビレン基であり、ｎは０〜２の整数である。但し、Ｒ^３及びＲ^４が複数存在する場合、複数のＲ^３及びＲ^４は、それぞれ同じでも異なっていてもよい。）
（ＩＩ）分子中に、環状エーテル基、（チオ）カルボニル基及びイソ（チオ）シアナート基からなる群より選択される少なくとも１種の官能基（ｘ１）と、窒素原子、リン原子、酸素原子及び硫黄原子からなる群より選択される少なくとも一種の原子（但し、窒素原子、リン原子及び硫黄原子は、少なくともいずれかが３置換のヒドロカルビルシリル基で保護されていてもよい。）を有し、かつ活性水素を有していない、前記官能基（ｘ１）とは異なる基（ｘ２）と、を各々１つ以上有する化合物（Ｂ２−２）；
（ＩＩＩ）分子中に、イソ（チオ）シアナート基を２つ以上有する化合物（Ｂ２−３）；
等が挙げられる。化合物（Ｂ２）としては、これらを一種単独で又は二種以上を組み合わせて使用することができる。なお、本明細書において、（チオ）カルボニル基は、カルボニル基及びチオカルボニル基を示し、イソ（チオ）シアナート基は、イソシアナート基及びイソチオシアナート基を示す。 The copolymer used in the above modification reaction (hereinafter also referred to as a terminal modification reaction) may have an unmodified or a modified polymerization initiation terminal as long as it has an active terminal. The compound (B2) is not particularly limited as long as it has a functional group that interacts with silica and can react with a polymerization active terminal. Preferred specific examples of the compound (B2) include, for example, (I) a compound (B2-1) represented by the following formula (1);

(In the formula (1), A ¹ has at least one atom selected from the group consisting of a nitrogen atom, a phosphorus atom and a sulfur atom, has no active hydrogen, and has a nitrogen atom for R ⁵ ; R ³ and R ⁴ are hydrocarbyl groups, R ⁵ is a hydrocarbylene group, and n is an integer of 0 to 2, provided that R is a monovalent functional group linked by a phosphorus atom or a sulfur atom. ^{If 3} and R ⁴ there are a plurality, the plurality of R ³ and R ⁴ may be the same or different.)
(II) In a molecule, at least one functional group (x1) selected from the group consisting of a cyclic ether group, a (thio) carbonyl group and an iso (thio) cyanate group, a nitrogen atom, a phosphorus atom, an oxygen atom, Has at least one atom selected from the group consisting of sulfur atoms (provided that at least one of a nitrogen atom, a phosphorus atom and a sulfur atom may be protected by a trisubstituted hydrocarbylsilyl group), and A compound (B2-2) having at least one group (x2) having no active hydrogen and different from the functional group (x1);
(III) a compound (B2-3) having two or more iso (thio) cyanate groups in the molecule;
And the like. As the compound (B2), these can be used alone or in combination of two or more. In this specification, a (thio) carbonyl group indicates a carbonyl group and a thiocarbonyl group, and an iso (thio) cyanate group indicates an isocyanate group and an isothiocyanate group.

In the above formula (1), the hydrocarbyl group of R ³ and R ⁴ includes a linear or branched alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, or a cycloalkyl group having 6 to 20 carbon atoms. It is preferably an aryl group.
R ⁵ is preferably a linear or branched alkanediyl group having 1 to 20 carbon atoms, a cycloalkylene group having 3 to 20 carbon atoms, or an arylene group having 6 to 20 carbon atoms.
n is preferably 0 or 1 from the viewpoint of increasing the reactivity with the copolymer.
A ¹ has at least one atom selected from the group consisting of a nitrogen atom, a phosphorus atom and a sulfur atom (hereinafter, also referred to as a specific atom), and bonds to R ⁵ at these specific atoms. The specific atom is not bonded to active hydrogen and may be protected by, for example, a trisubstituted hydrocarbylsilyl group. Here, the term "active hydrogen" refers to a hydrogen atom bonded to an atom other than a carbon atom, and preferably refers to a hydrogen atom having a lower binding energy than a carbon-hydrogen bond of polymethylene.

A ¹ is particularly preferably a group that can be turned into an onium ion by an onium salt generator. When the compound (B2) has such a group (A ¹ ), excellent shape retention can be imparted to the modified copolymer.
Specific examples of A ¹ include, for example, a nitrogen-containing group in which two hydrogen atoms of a primary amino group are substituted with two protecting groups, and a hydrogen atom of a secondary amino group is substituted with one protecting group. A nitrogen-containing group, a phosphorus-containing group in which two hydrogen atoms of a tertiary amino group, an imino group, a pyridyl group, and a primary phosphino group are substituted with two protecting groups, and one hydrogen atom of a secondary phosphino group is 1 Examples include a phosphorus-containing group substituted by one protective group, a tertiary phosphino group, and a sulfur-containing group in which one hydrogen atom of a thiol group is substituted by one protective group. Among these, a group having a nitrogen atom is preferable from the viewpoint of good affinity with silica. The "protecting group" is a functional group to be converted to A ¹ in inert functional group to the polymerization active terminal, e.g., 3 hydrocarbylsilyl groups and substituted and the like.

Specific examples of the compound (B2-1) include a nitrogen-containing group in which two hydrogen atoms of a primary amine are substituted with two protecting groups, and one hydrogen atom of a secondary amine is substituted with one protecting group. Examples of the compound having a nitrogen-containing group or a tertiary amino group and an alkoxysilyl group include N, N-bis (trimethylsilyl) aminopropyltrimethoxysilane and N, N-bis (trimethylsilyl) aminopropylmethyl Diethoxysilane, N, N ′, N′-tris (trimethylsilyl) -N- (2-aminoethyl) -3-aminopropyltriethoxysilane, 3- (4-trimethylsilyl-1-piperazino) propylmethyldimethoxysilane, And the like.

Compounds having an imino group or a pyridyl group and an alkoxysilyl group include N- (1,3-dimethylbutylidene) -3- (triethoxysilyl) -1-propanamine, N- (1-methylpropylidene) ) -3- (Triethoxysilyl) -1-propanamine, N- (4-N, N-dimethylaminobenzylidene) -3- (triethoxysilyl) -1-propanamine, N- (cyclohexylidene)- 3- (triethoxysilyl) -1-propanamine and trimethoxysilyl compounds, methyldiethoxysilyl compounds, ethyldimethoxysilyl compounds, N- (3-trimethoxysilylpropyl) -4 corresponding to these triethoxysilyl compounds , 5-Dihydroimidazole, N- (3-triethoxysilylpropyl) -4,5-dihydroimid Sol, N- (3-trimethoxysilylpropyl) -4,5-imidazole, N- (3-triethoxysilylpropyl) -4,5-imidazole, 3-hexamethyleneiminopropyltrimethoxysilane, 3-hexamethylene Examples include iminopropylmethyldimethoxysilane, and compounds in which the alkyl group and alkanediyl group in the above compounds are replaced with an alkyl group having 1 to 6 carbon atoms and an alkanediyl group having 1 to 6 carbon atoms, respectively.

A phosphorus-containing group in which two hydrogen atoms of a primary phosphino group are substituted by two protective groups, a phosphorus-containing group in which one hydrogen atom of a secondary phosphino group is substituted by one protective group, a tertiary phosphino group Or a compound having a sulfur-containing group in which one hydrogen atom of a thiol group is substituted with one protective group and an alkoxysilyl group include P, P-bis (trimethylsilyl) phosphinopropylmethyldimethoxysilane, P , P-bis (trimethylsilyl) phosphinopropyltrimethoxysilane, 3-dimethylphosphinopropyltrimethoxysilane, 3-dimethylphosphinopropylmethyldimethoxysilane, 3-diphenylphosphinopropyltrimethoxysilane, 3-diphenylphosphinopropyl Triethoxysilane, 3- Phenylphosphinopropylmeryldimethoxysilane, S-trimethylsilylmercaptopropylmethyldimethoxysilane, S-trimethylsilylmercaptopropyltrimethoxysilane, S-trimethylsilylmercaptopropyltriethoxysilane, S-trimethylsilylmercaptopropylmethyldiethoxysilane, and in the above compounds Examples thereof include compounds in which an alkyl group and an alkanediyl group are replaced with an alkyl group having 1 to 6 carbon atoms and an alkanediyl group having 1 to 6 carbon atoms, respectively. Other examples of the compound having an iso (thio) cyanate group include 3-isocyanatopropyltrimethoxysilane and 3-isocyanatopropyltriethoxysilane.

In the compound (B2-2), the group (x2) is preferably a group containing a nitrogen atom that is not bonded to active hydrogen, and specific examples thereof include compounds having a cyclic ether group such as Epoxyamine compounds such as glycidyl-1,3-bisaminomethylcyclohexane;
Examples of the compound having a (thio) carbonyl group include 4-aminoacetophenone such as 4-N, N-dimethylaminobenzophenone; and bis (dihydrocarbylaminoalkyl) such as 1,7-bis (methylethylamino) -4-heptanone. Ketones; dihydrocarbylaminoalkyl (meth) acrylates such as 2-dimethylaminoethyl acrylate; hydrocarbyl imidazolidinones such as 1,3-dimethyl-2-imidazolidinone; N-hydrocarbyl pyrrolidones such as 1-phenyl-2-pyrrolidone N-hydrocarbylcaptolactam such as N-methyl-ε-caprolactam; N-dihydrocarbylformamide such as N, N-diethylformamide; N, N-dihydrocarbylacetamide such as N, N-dimethylacetamide; N-dimethyl Acrylamide such as (meth) acrylamide; and the like;
Examples of the compound having an iso (thio) cyanate group include 3-isocyanatopropyltrimethoxysilane.

Examples of the compound (B2-3) include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and p-phenylene diisocyanate. Isocyanate, tris (isocyanatophenyl) thiophosphate, xylene diisocyanate, benzene-1,2,4-triisocyanate, naphthalene-1,2,5,7-tetraisocyanate, 1,4-phenylenediisothiate Ossinate may be mentioned.

（一般式（１−１）中、Ｒ^６は水素原子またはヒドロカルビル基であり、複数存在するＲ^６は同じであっても異なっていてもよい。Ａ^４、Ｒ^３、Ｒ^５及びｎは上記式（１）のＡ^１、Ｒ^３、Ｒ^５及びｎと同義である。） As the compound (B2), it is particularly preferable to use the compound (B2-1) in that it has a strong affinity for silica. When the silane compound (B2-1) is used, for the purpose of adjusting the Mooney viscosity of the modified copolymer, together with the silane compound (B2-1), silicon tetrachloride and an epoxy-containing compound (for example, tetraglycidyl-1, 3-bisaminomethylcyclohexane) and the like. The compounds (B2) exemplified above all have the same action in that a modified copolymer having a modified polymerization end can be obtained. Therefore, even those not described in the examples described below can be used in the present invention. In addition, the structure represented by the following formula (1-1) is introduced into the polymer terminal by the reaction between the compound represented by the formula (1) and the modified copolymer.

(In the general formula (1-1), R ⁶ is a hydrogen atom or a hydrocarbyl group, and a plurality of R ⁶ may be the same or different. A ⁴ , R ³ , R ⁵ and n are the same as above. (It is synonymous with A ¹ , R ³ , R ⁵ and n in the formula (1).)

The above terminal modification reaction can be performed, for example, as a solution reaction. This solution reaction may be performed using a solution containing an unreacted monomer after the completion of the polymerization reaction in the polymerization step, and the copolymer contained in the solution is isolated and dissolved in a suitable solvent such as cyclohexane. You may go on. Further, the terminal modification reaction may be performed using either a batch system or a continuous system. At this time, the method of adding the compound (B2) is not particularly limited, and examples thereof include a method of adding the compound (B2) at a time, a method of adding the compound at a time, and a method of adding the compound continuously.

The amount of the compound (B2) used for the terminal modification reaction may be appropriately set according to the type of the compound used for the reaction, but is preferably 0.1 to 0.1% of the metal atom involved in the polymerization reaction of the polymerization initiator. It is at least 1 molar equivalent, more preferably at least 0.3 molar equivalent. When the amount is 0.1 molar equivalent or more, the modification reaction can sufficiently proceed, and the dispersibility of silica can be suitably improved.
The temperature of the terminal modification reaction is usually the same as the temperature of the above-mentioned polymerization reaction, preferably -20 to 150 ° C, more preferably 0 to 120 ° C, and particularly preferably 20 to 100 ° C. preferable. If the temperature of the modification reaction is low, the viscosity of the modified copolymer tends to increase. On the other hand, when the temperature of the denaturation reaction is high, the polymerization active terminal is easily deactivated. The reaction time of the denaturation reaction is preferably from 1 minute to 5 hours, more preferably from 2 minutes to 1 hour.

(Reaction stopped)
The anionic polymerization can be terminated by adding a reaction terminator commonly used in this field. As such a reaction terminator, for example, a polar solvent having an active proton such as alcohol or acetic acid such as methanol, ethanol and isopropanol and a mixture thereof, or a mixture of such a polar solvent and a non-polar solvent such as hexane and cyclohexane. Mixtures are mentioned. The addition amount of the reaction terminator is usually about the same molar amount or about twice the molar amount with respect to the anionic polymerization initiator.

<Coupling>
In the method for producing a copolymer, a coupling agent may be added to a hydrocarbon solution of the copolymer from the start of polymerization of the monomer to the recovery of the polymer described below. Examples of the coupling agent include a compound represented by the following formula (2-1).
^{_{R 1 a ML 4-a (}} 2-1)
(In the formula (2-1), R ¹ represents an alkyl group, an alkenyl group, a cycloalkenyl group or an aryl group, M represents a silicon atom or a tin atom, L represents a halogen atom or a hydrocarbyloxy group, and a represents Represents an integer of 0 to 2)

As the coupling agent represented by the above formula (2-1), silicon tetrachloride, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, tin tetrachloride, methyltrichlorotin, dimethyldichlorotin, trimethylchlorotin, tetramethoxy Examples include silane, methyltrimethoxysilane, dimethoxydimethylsilane, methyltriethoxysilane, ethyltrimethoxysilane, dimethoxydiethylsilane, diethoxydimethylsilane, tetraethoxysilane, ethyltriethoxysilane, and diethoxydiethylsilane.

The amount of the coupling agent to be added is preferably 0.03 mol or more, more preferably 0.05 mol or more, per 1 mol of the alkali metal derived from the alkali metal catalyst in order to enhance the processability of the polymer. In order to enhance fuel economy, the amount is preferably 0.4 mol or less, more preferably 0.3 mol or less.

<Hydrogenation method>
In the method for producing a hydrogenated copolymer, the copolymer described above is hydrogenated to obtain a hydrogenated copolymer having a hydrogenation rate of 75 mol% or more. By hydrogenating the copolymer, there is an advantage that heat resistance is improved. On the other hand, if the hydrogenation rate is low, the effects of improving fuel economy, flex crack growth resistance and chip cut resistance cannot be sufficiently obtained.

The method of hydrogenation and the reaction conditions are not particularly limited, and hydrogenation may be performed by a known method and known conditions. Usually, the reaction is carried out at 20 to 150 ° C. and under a hydrogen pressure of 0.1 to 10 MPa in the presence of a hydrogenation catalyst. The hydrogenation rate can be arbitrarily selected by changing the amount of the hydrogenation catalyst, the hydrogen pressure during the hydrogenation reaction, the reaction time, and the like. As the hydrogenation catalyst, usually, a compound containing any one of metals of Groups 4 to 11 of the periodic table can be used. For example, compounds containing Ti, V, Co, Ni, Zr, Ru, Rh, Pd, Hf, Re, and Pt atoms can be used as the hydrogenation catalyst. More specific hydrogenation catalysts include metallocene compounds such as Ti, Zr, Hf, Co, Ni, Pd, Pt, Ru, Rh, and Re; metals such as Pd, Ni, Pt, Rh, and Ru as carbon; A supported heterogeneous catalyst supported on a carrier such as silica, alumina, or diatomaceous earth; a homogeneous Ziegler-type catalyst obtained by combining an organic salt or acetylacetone salt of a metal element such as Ni or Co with a reducing agent such as organic aluminum; Organometallic compounds or complexes such as Ru and Rh; fullerenes and carbon nanotubes in which hydrogen is stored.

Among these, a metallocene-based compound containing any of Ti, Zr, Hf, Co, and Ni is preferable in that it can be uniformly hydrogenated in an inert organic solvent. Further, a metallocene compound containing any of Ti, Zr and Hf is preferable. In particular, a hydrogenation catalyst obtained by reacting a titanocene compound with an alkyl lithium is preferable because it is an inexpensive and industrially particularly useful catalyst. As specific examples, for example, JP-A-1-275605, JP-A-5-271326, JP-A-5-271325, JP-A-5-222115, JP-A-11-292924, 2000-37632, JP-A-59-133203, JP-A-63-5401, JP-A-62-218403, JP-A-7-90017, JP-B-43-19960, The hydrogenation catalyst described in JP-B-47-40473 can be exemplified. In addition, these hydrogenation catalysts can be used individually by 1 type or in combination of 2 or more types.

The content of the hydrogenated copolymer in 100% by mass of the rubber component is 75% by mass or more, and preferably 80% by mass or more. When the content of the hydrogenated copolymer is less than 75% by mass, the effect of the present invention tends to be hardly obtained. Further, the content is preferably 95% by mass or less, more preferably 90% by mass or less, and further preferably 85% by mass or less. If the content exceeds 95% by mass, the resistance to flex crack growth and the resistance to chip cutting may be reduced.

Other rubber components that can be used in addition to the hydrogenated copolymer include conventional styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), butadiene isoprene copolymer rubber, butyl rubber, and the like. Further, natural rubber (NR), ethylene propylene copolymer, ethylene octene copolymer and the like can also be mentioned. Among them, BR, NR, and SBR are preferable, and BR is particularly preferable, in that the effects of the present invention can be sufficiently exerted. These rubber components may be used in combination of two or more. When the hydrogenated copolymer and BR are used in combination, the effects of the present invention are more remarkably exhibited.

The BR is not particularly limited. For example, BR having a high cis content such as BR1220 manufactured by Zeon Corporation, BR150B manufactured by Ube Industries, Ltd., and VCR412, VCR617 manufactured by Ube Industries, Ltd. And BR containing a 2,2-syndiotactic polybutadiene crystal (SPB) and a BR synthesized using a rare earth element catalyst (rare earth BR) can be used.

The content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more. Further, the content is preferably 25% by mass or less, more preferably 20% by mass or less. Within the above range, the effects of the present invention are remarkably exhibited.

The total content of the hydrogenated copolymer and BR in 100% by mass of the rubber component is preferably 80% by mass or more, more preferably 90% by mass or more, and may be 100% by mass. If it is less than 80% by mass, the effect of the present invention may not be sufficiently obtained.

The rubber composition in the present invention contains carbon black having a specific nitrogen adsorption specific surface area.

The carbon black has a nitrogen adsorption specific surface area (N ₂ SA) of 5 to 200 m ² / g. The lower limit is preferably at least 15 m ² / g, more preferably at least 50 m ² / g. Further, the upper limit is preferably 180 m ² / g or less, more preferably 150 m ² / g or less, further preferably 130 m ² / g or less, and particularly preferably 100 m ² / g or less. If it is less than 5 m ² / g, a sufficient reinforcing effect may not be obtained, and if it exceeds 200 m ² / g, the fuel economy may be reduced.
The N ₂ SA of the carbon black in the present invention is measured according to JIS K 6217-2: 2001.

The dibutyl phthalate (DBP) oil absorption of the carbon black is preferably 50 ml / 100 g or more, more preferably 70 ml / 100 g or more, and still more preferably 90 ml / 100 g or more. Further, the DBP oil absorption is preferably 200 ml / 100 g or less, more preferably 150 ml / 100 g or less. If it is less than 50 ml / 100 g, a sufficient reinforcing effect may not be obtained, and if it exceeds 200 ml / 100 g, the fuel economy may be reduced.
The DBP oil absorption of carbon black in the present invention is measured according to JIS K 6217-4: 2001.

The content of the carbon black is 30 parts by mass or more, preferably 35 parts by mass or more, based on 100 parts by mass of the rubber component. The content is at most 70 parts by mass, preferably at most 60 parts by mass, more preferably at most 55 parts by mass. Within the above range, good fuel economy, chip-cut resistance and flex crack growth resistance can be obtained.

The rubber composition in the present invention may further contain a filler other than carbon black. Examples of other fillers include white fillers such as mica such as silica, calcium carbonate, and sericite, aluminum hydroxide, magnesium oxide, magnesium hydroxide, clay, talc, alumina, titanium oxide, and mica.

In addition to the above components, the rubber composition of the present invention may further contain a vulcanizing agent such as sulfur; a thiazole vulcanization accelerator, a thiuram vulcanization accelerator, a sulfenamide vulcanization accelerator, and a guanidine vulcanization accelerator. Vulcanization accelerators such as agents; vulcanization activators such as stearic acid and zinc oxide; organic peroxides; processing aids such as extender oils (oils) and lubricants; Can be used.

As extender oils (oils), aromatic mineral oils (viscosity constants (VGC values) 0.900 to 1.049) and naphthenic mineral oils (VGC values of 0. 850 to 0.899) and paraffinic mineral oil (VGC value 0.790 to 0.849). The polycyclic aromatic content of the extender oil is preferably less than 3% by weight, more preferably less than 1% by weight. The polycyclic aromatic content is measured according to the British Petroleum Institute 346/92 method. Further, the aromatic compound content (CA) of the extension oil is preferably 20% by mass or more. These extender oils may be used in combination of two or more.

Examples of the vulcanization accelerator include thiazole vulcanization accelerators such as 2-mercaptobenzothiazole, dibenzothiazyldisulfide, and N-cyclohexyl-2-benzothiazylsulfenamide; tetramethylthiuram monosulfide, tetramethylthiuram disulfide Thiuram-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazolesulfenamide, Nt-butyl-2-benzothiazolesulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, N- Sulfenamide-based vulcanization accelerators such as oxyethylene-2-benzothiazolesulfenamide and N, N'-diisopropyl-2-benzothiazolesulfenamide; diphenylguanidine, dioltotolylguanidine, orthotolylbiguanidine and the like Guani It can be mentioned emission-based vulcanization accelerator. Among them, a sulfenamide-based vulcanization accelerator is preferable, and N-cyclohexyl-2-benzothiazolesulfenamide is more preferable because the effects of the present invention can be more suitably obtained. It is also preferable to use a guanidine vulcanization accelerator in combination. The amount of the vulcanization accelerator used is preferably 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.

The vulcanizing agent is not particularly limited, but sulfur can be suitably used. The sulfur content is preferably 0.5 to 5 parts by mass, more preferably 1 to 3 parts by mass, based on 100 parts by mass of the rubber component. Thereby, the effect of the present invention can be more suitably obtained.

The rubber composition in the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll, or the like, followed by vulcanization.

The rubber composition of the present invention can be used for each member (tread, sidewall, carcass, belt, bead, etc.) of a tire, and is particularly preferably used as a sidewall of a tire.

The pneumatic tire of the present invention is manufactured by a usual method using the above rubber composition. That is, the rubber component containing the hydrogenated copolymer and the rubber composition containing the various compounding agents as needed are extruded according to the shape of each tire member such as a sidewall at an unvulcanized stage, An unvulcanized tire is formed by molding together with other tire members by a usual method on a tire molding machine. By heating and pressurizing the unvulcanized tire in a vulcanizer, the pneumatic tire of the present invention is obtained.

The pneumatic tire of the present invention is suitably used as a tire for passenger cars, a tire for heavy loads such as trucks and buses, a tire for motorcycles, a tire for competition, and the like, and is particularly preferably used as a tire for heavy loads.

The present invention will be specifically described based on examples, but the present invention is not limited to these.

Hereinafter, various chemicals used in the synthesis and polymerization will be described together. The chemicals were purified as necessary according to a standard method.
n-hexane: Styrene manufactured by Kanto Chemical Co., Ltd .: Butadiene manufactured by Kanto Chemical Co., Ltd .: 1,3-butadiene TMEDA manufactured by Tokyo Chemical Industry Co., Ltd .: N, N, N ′, N manufactured by Kanto Chemical Co., Ltd. '-Tetramethylethylenediamine n-butyllithium solution: 1.6M n-butyllithium hexane solution manufactured by Kanto Chemical Co., Ltd. 2,6-di-tert-butyl-p-cresol: manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Nocrack 200
Alcohol: Methanol amine modifier manufactured by Tokyo Chemical Industry Co., Ltd .: N, N-bis (trimethylsilyl) aminopropylmethyldiethoxysilane

The method for evaluating the obtained copolymer will be described below.

(Measurement of hydrogenation rate of conjugated diene part of copolymer)
A solution having a concentration of 15% by mass was prepared using carbon tetrachloride as a solvent, and the solution was calculated from the spectrum reduction rate of the unsaturated bond portion in H ¹ -NMR at 100 MHz.

(Measurement of styrene content)
H ¹ -NMR was measured at 25 ° C. using a JEOL JNM-A400 NMR apparatus, and a phenyl proton based on styrene units of 6.5 to 7.2 ppm and 4.9 to 5.4 ppm of butadiene obtained from the spectrum were measured. The styrene content was determined from the ratio of vinyl protons based on units.

(Measurement of weight average molecular weight (Mw) and number average molecular weight (Mn))
The weight average molecular weight (Mw) and number average molecular weight (Mn) of the copolymer were determined by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: Tosoh Corporation) ) Was measured in terms of standard polystyrene based on the value measured by TSKGEL SUPERMULTIPORE HZ-M). When the copolymer has a modifying group, Mw and Mn were measured before performing the modifying treatment. This is because when a copolymer having a modifying group is measured, the modifying group interacts with the silica gel of the column, and accurate Mw and Mn cannot be obtained.

(Mooney viscosity (ML _{1 + 4} ))
The Mooney viscosity of the polymer was measured at 100 ° C. according to JIS K 6300 (1994).

<Production example of copolymer>
Synthesis Example 1 (Synthesis of copolymer (1): hydrogenation rate: 0 mol%, SBR)
2000 ml of n-hexane, 60 g of styrene, 140 g of 1,3-butadiene, 0.93 g of TMEDA and 0.45 mmol of n-butyllithium were added to a heat-resistant reaction vessel sufficiently purged with nitrogen, and the mixture was stirred at 50 ° C. for 5 hours to carry out a polymerization reaction. went. Thereafter, the reaction was stopped by adding alcohol, and 1 g of 2,6-tert-butyl-p-cresol was added to the reaction solution, followed by reprecipitation purification to obtain a copolymer (1). The obtained copolymer (1) had a weight average molecular weight (Mw) of 490,000 and a styrene content of 30% by mass.

Synthesis Example 2 (Synthesis of copolymer (2): hydrogenation ratio 60 mol%, hydrogenated SBR)
Copolymer (2) was obtained according to the same recipe as copolymer (1) except that the obtained polymer was hydrogenated. That is, after the polymerization conversion reaction in the copolymer (1), alcohol was not added to stop the polymerization reaction, and then the mixture was stirred for 20 minutes while supplying hydrogen gas at a pressure of 0.4 MPa-Gauge to obtain unreacted polymer. It was reacted with terminal lithium to obtain lithium hydride. The hydrogen gas supply pressure was set to 0.7 MPa-Gauge, the reaction temperature was set to 90 ° C., and hydrogenation was performed using a catalyst mainly composed of titanocene dichloride. When the amount of hydrogen absorbed reaches the target amount of hydrogenation, the reaction temperature is set to normal temperature, the hydrogen pressure is returned to normal pressure, the reaction solution is taken out of the reaction vessel, the reaction solution is stirred into water, and the solvent is steamed. The copolymer (2) was obtained by removing by stripping. The hydrogenation ratio of the obtained copolymer (2) was 60 mol%, and the weight average molecular weight (Mw) was 450,000.

Synthesis Example 3 (Synthesis of copolymer (3): hydrogenation ratio 80 mol%, hydrogenated SBR)
Copolymer (3) was obtained according to the same recipe as copolymer (2) except that the integrated amount of hydrogen suction was adjusted so as to obtain the target hydrogenation rate. The hydrogenation ratio of the obtained copolymer (3) was 80 mol%, and the weight average molecular weight (Mw) was 480,000.

Synthesis Example 4 (Synthesis of copolymer (4): hydrogenation rate 95 mol%, hydrogenated SBR)
Copolymer (4) was obtained according to the same recipe as copolymer (2) except that the integrated amount of hydrogen suction was adjusted so as to obtain the target hydrogenation rate. The hydrogenation ratio of the obtained copolymer (4) was 95 mol%, and the weight average molecular weight (Mw) was 450,000.

Synthesis Example 5 (Synthesis of copolymer (5): hydrogenation rate: 95 mol%)
Copolymer (5) was obtained according to the same recipe as copolymer (2) except that the integrated amount of hydrogen suction was adjusted so as to obtain the desired hydrogenation rate. The obtained copolymer (5) had a weight average molecular weight (Mw) of 2,000,000 and a hydrogenation ratio of 95 mol%.

Synthesis Example 6 (Synthesis of copolymer (6): hydrogenation rate: 95 mol%)
Copolymer (6) was obtained according to the same recipe as copolymer (2) except that the integrated amount of hydrogen suction was adjusted so that the target hydrogenation rate was attained. The obtained copolymer (6) had a weight average molecular weight (Mw) of 200,000 and a hydrogenation ratio of 95 mol%.

Synthesis Example 7 (Synthesis of copolymer (7): hydrogenation rate: 95 mol%, hydrogenated SBR)
2000 ml of n-hexane, 60 g of styrene, 140 g of 1,3-butadiene, 0.93 g of TMEDA and 0.45 mmol of n-butyllithium were added to a heat-resistant reaction vessel sufficiently purged with nitrogen, and the mixture was stirred at 50 ° C. for 5 hours to carry out a polymerization reaction. went. Thereafter, 0.15 mol of an amine-based modifier was added, and the mixture was stirred at 0 ° C for 1 hour. In the subsequent steps, a copolymer (7) was obtained by the same formulation as the copolymer (2) except that the integrated amount of hydrogen suction was adjusted. The hydrogenation ratio of the obtained copolymer (7) was 95 mol%, and the weight average molecular weight (Mw) before modification was 440,000.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described.
Copolymers (1) to (7): Polybutadiene rubber synthesized by the above method: Ubepol BR150B manufactured by Ube Industries, Ltd.
Carbon black 1: Show black N330 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 75 m ² / g, DBP oil absorption: 102 ml / 100 g)
Carbon black 2: Show Black N220 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 125 m ² / g, DBP oil absorption: 115 ml / 100 g)
Oil: X-140 manufactured by Japan Energy Co., Ltd.
Anti-aging agent: Antigen 3C manufactured by Sumitomo Chemical Co., Ltd.
Stearic acid: beaded stearic acid zinc oxide manufactured by NOF CORPORATION: Zinc flower No. 1 wax manufactured by Mitsui Mining & Smelting Co., Ltd .: Sannoc N manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Sulfur: powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd. 1: Succinol CZ (N-cyclohexyl-2-benzothiazole sulfenamide) manufactured by Sumitomo Chemical Co., Ltd.
Vulcanization accelerator 2: Succinol D (1,3-diphenylguanidine) manufactured by Sumitomo Chemical Co., Ltd.

(Examples and Comparative Examples)
According to the compounding content shown in Table 2, materials other than sulfur and the vulcanization accelerator were kneaded for 5 minutes at 150 ° C. using a 1.7 L Banbury mixer manufactured by Kobe Steel, Ltd. Obtained. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and the mixture was kneaded with an open roll at 80 ° C. for 5 minutes to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press-vulcanized at 170 ° C. for 20 minutes using a 0.5 mm thick mold to obtain a vulcanized rubber composition.
Further, the obtained unvulcanized rubber composition is molded into a sidewall shape, and is bonded together with other tire members on a tire molding machine to form an unvulcanized tire, and vulcanized at 170 ° C. for 12 minutes, Test tires (size: 195 / 65R15) were manufactured.

<Evaluation items and test methods>
The following evaluation was performed about the obtained vulcanized rubber composition and the test tire. Table 2 shows the results.

(Fuel efficiency index)
Using a spectrometer manufactured by Kamishima Seisakusho, tan δ of the vulcanized rubber composition was measured at a dynamic strain amplitude of 1%, a frequency of 10 Hz and a temperature of 50 ° C. The value of the reciprocal of tan δ was indicated as an index by setting Comparative Example 1 to 100. The larger the value, the smaller the rolling resistance and the better the fuel economy.

(Rubber hardness index)
The rubber hardness was measured with a type A durometer according to JIS K 6253 “Testing method for hardness of vulcanized rubber and thermoplastic rubber”. The rubber hardness index was calculated by the following calculation formula, with the rubber hardness of Comparative Example 1 being 100. The higher the rubber hardness index, the better the steering stability.
(Rubber hardness index) = (Rubber hardness of each compound) / (Rubber hardness of Comparative Example 1) × 100

(Flex crack growth resistance index)
According to JIS K 6260, "Method of Dematch Bending Crack Growth Test for Vulcanized Rubber and Thermoplastic Rubber", a 1 mm crack is generated in the vulcanized rubber composition at room temperature and 25 ° C., and the crack grows 1 mm. The number of flexures up to was measured. In addition, this measurement was performed twice in total, one measurement at 70% elongation and one measurement at 110% elongation, and the average value was calculated. The flex crack growth resistance index was calculated by a calculation formula. Also, the larger the numerical value, the better the flex crack growth resistance. 70% and 110% indicate the elongation relative to the length of the original vulcanized rubber composition.
(Mean value of number of bending times of each compounding) (flex crack growth resistance index) = / (average value of the number of bending times of Comparative Example 1) × 100

(Chip cut resistance index)
Each of the test pieces cut out from the test tires was aged with air in a gear oven tester at 80 ° C. for 10 days, and then subjected to a tensile test in accordance with JIS K6251. The time elongation (EB) was measured. Then, a numerical value of the product of the obtained breaking strength and elongation at break (TB × EB) was calculated, and the product was indicated by an index according to the following formula to evaluate chip-cut resistance. The higher the index, the better.
(Chip cut resistance index) = (TB × EB of each composition) / (TB × EB of Comparative Example 1) × 100

As shown in Table 2, a hydrogenated styrene-butadiene copolymer having a hydrogenation rate of 75 mol% or more was used as a rubber composition containing at least 75 mass% in 100 mass% of a rubber component and a specific amount of carbon black. In Nos. 1 to 8, it was clarified that fuel economy, steering stability, chip-cut resistance, and flex crack growth resistance could be improved satisfactorily.

Claims (8)

A pneumatic tire having a sidewall produced using a rubber composition,
The rubber composition comprises a hydrogenated copolymer obtained by copolymerizing an aromatic vinyl compound and a conjugated diene compound, wherein the hydrogenation rate of the conjugated diene portion is 75 mol% or more, and a nitrogen adsorption specific surface area of 5%. ２００200 m ² / g of carbon black,
The content of the hydrogenated copolymer in 100% by mass of the rubber component is 75% by mass or more,
A pneumatic tire having a carbon black content of 30 to 70 parts by mass based on 100 parts by mass of a rubber component. The pneumatic tire according to claim 1, wherein the hydrogenated copolymer has a weight average molecular weight of 200,000 to 2,000,000. The pneumatic tire according to claim 1 or 2, wherein the hydrogenated copolymer has a hydrogenation rate of 90 mol% or more. The pneumatic tire according to any one of claims 1 to 3, wherein the hydrogenated copolymer is a hydrogenated styrene butadiene copolymer. The pneumatic tire according to claim 4, wherein the hydrogenated styrene butadiene copolymer is a hydrogenated modified styrene butadiene copolymer. The pneumatic tire according to claim 4 or 5, wherein the hydrogenated styrene-butadiene copolymer has a styrene content of 5 to 40% by mass. The pneumatic tire according to any one of claims 1 to 6, wherein the rubber composition further includes a polybutadiene rubber. The pneumatic tire according to claim 7, wherein the content of the polybutadiene rubber in 100% by mass of the rubber component is 5 to 25% by mass.