JP7803389B2 - Rubber composition for tires and tires - Google Patents

Description

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

Various methods for improving fuel economy have been studied (see, for example, Patent Document 1). However, there has been insufficient research into improving fuel economy at room temperature and low temperatures (reducing rolling resistance).

Japanese Patent Application Laid-Open No. 2000-344955

The present invention aims to solve the above problems and provide a rubber composition for tires and a tire that can improve overall fuel economy at both normal and low temperatures.

The present invention relates to a rubber composition for tires, which contains a rubber component including styrene-butadiene rubber, butadiene rubber, and isoprene-based rubber, silica, a mercapto-based silane coupling agent, and carbon black, and in which the trans content of the butadiene rubber plus the vinyl content is greater than the content of the carbon black.

It is preferable that the cis content of the butadiene rubber is less than the silica content.

It is preferable that the average particle size of the silica is 16 nm or less.

The carbon black preferably has a cetyltrimethylammonium bromide adsorption specific surface area of 110 m ² /g or more.

It is preferable that the rubber composition contains sulfur, and that the sulfur content/isoprene-based rubber content be greater than 0.50.

It is preferable that the total amount of styrene in the rubber component is 18% by mass or less.

The rubber composition preferably contains a dialkyldithiophosphate compound.

The present invention also relates to a tire using the rubber composition.

The present invention relates to a rubber composition for tires that contains a rubber component including styrene-butadiene rubber, butadiene rubber, and isoprene-based rubber, silica, a mercapto-based silane coupling agent, and carbon black, and in which the trans content of the butadiene rubber plus the vinyl content is greater than the carbon black content, thereby improving overall fuel economy at both normal and low temperatures.

The rubber composition for tires of the present invention contains a rubber component including styrene-butadiene rubber, butadiene rubber, and isoprene-based rubber, silica, a mercapto-based silane coupling agent, and carbon black, and the trans content of the butadiene rubber plus the vinyl content is greater than the carbon black content.

The reason why the above-mentioned effects can be obtained with the above rubber composition is presumed to be as follows.
The rubber composition contains styrene-butadiene rubber, butadiene rubber, isoprene rubber, silica, a mercapto-silane coupling agent, and carbon black, and satisfies the relationship of trans content + vinyl content of butadiene rubber > carbon black content, which reduces the amount of trans moieties and vinyl moieties of the highly mobile butadiene rubber that bond with carbon black and makes it easier for them to bond with silica, thereby reducing heat buildup and improving fuel economy.
Furthermore, the highly reactive mercapto silane coupling agent promotes hydrophobicity of the silica surface, resulting in uniform dispersion of the silica and reducing the temperature dependency of heat buildup (tan δ).
It is believed that the combination of these effects significantly improves the overall fuel economy at normal and low temperatures.

The rubber composition contains a rubber component.
Here, the rubber component is a component that contributes to crosslinking, and generally has a weight average molecular weight (Mw) of 10,000 or more.

The weight average molecular weight of the rubber component is preferably 50,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more, and is preferably 2,000,000 or less, more preferably 1,700,000 or less, and even more preferably 1,400,000 or less. Within the above ranges, better effects tend to be obtained.

In this specification, the weight average molecular weight (Mw) can be determined by converting it into standard polystyrene based on measurements obtained using a gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corporation; detector: differential refractometer; column: TSKGEL SUPERMULTIPORE HZ-M, manufactured by Tosoh Corporation).

The total styrene content in the rubber component is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 18% by mass or less, and is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. Within the above ranges, better effects tend to be obtained.

Here, the total styrene amount in the rubber component is the total content of styrene moieties contained in the entire rubber component (unit: mass %) and can be calculated by Σ (content of each rubber component × styrene amount in each rubber component/100). For example, if 100% by mass of the rubber component contains 85% by mass of SBR with a styrene content of 40% by mass, 5% by mass of SBR with a styrene content of 25% by mass, and 10% by mass of BR with a styrene content of 0% by mass, the total styrene amount in the rubber component is 35.25% by mass (= 85 × 40/100 + 5 × 25/100 + 10 × 0/100).

The total vinyl content in the rubber component is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 28% by mass or less, and is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. Within the above ranges, better effects tend to be obtained.

Here, the total vinyl content in the rubber component is the total content (unit: mass%) of vinyl moieties contained in the entire rubber component, and can be calculated by Σ (content of each rubber component × vinyl content in each rubber component/100). For example, if 100 mass% of the rubber component contains 85 mass% SBR with a vinyl content of 30 mass%, 5 mass% SBR with a vinyl content of 20 mass%, and 10 mass% BR with a vinyl content of 10 mass%, the total vinyl content in the rubber component is 27.5 mass% (= 85 × 30/100 + 5 × 20/100 + 10 × 10/100).

From the standpoint of overall performance, such as fuel economy at room temperature and low temperature, it is preferable that the total vinyl content in the rubber component of the above rubber composition be equal to or greater than the total styrene content in the rubber component.

The ratio of the total vinyl content in the rubber component to the total styrene content in the rubber component is preferably 1.2 or more, more preferably 1.4 or more, and even more preferably 1.6 or more, and is preferably 3.5 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. Being within the above ranges tends to produce better effects.

The styrene content and vinyl content in each rubber component can be measured by nuclear magnetic resonance (NMR) method.
In the examples of this specification, the total styrene amount and the total vinyl amount in the rubber component are calculated according to the above-mentioned formulas, but they may also be analyzed from the tire using, for example, a pyrolysis gas chromatograph mass spectrometer (Py-GC/MS) or the like.

The rubber composition contains styrene-butadiene rubber (SBR), butadiene rubber (BR), and isoprene-based rubber as rubber components.

SBR is not particularly limited, and examples include emulsion-polymerized styrene-butadiene rubber (E-SBR) and solution-polymerized styrene-butadiene rubber (S-SBR). Commercially available products include those from Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, and Zeon Corporation.

The styrene content of the SBR is preferably 10% by mass or more, more preferably 25% by mass or more, even more preferably 35% by mass or more, and is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 45% by mass or less. Within the above ranges, better effects tend to be achieved.

The vinyl content of the SBR is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, and is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. Within the above ranges, better effects tend to be achieved.

The styrene content and vinyl content of the SBR mentioned above refer to the styrene content and vinyl content of the SBR when there is one type of SBR, and refer to the average styrene content and average vinyl content when there are multiple types of SBR.
The average styrene content of the SBR can be calculated by {Σ(content of each SBR × styrene content of each SBR)}/total content of all SBRs. For example, when 100% by mass of the rubber component contains 85% by mass of SBR with a styrene content of 40% by mass and 5% by mass of SBR with a styrene content of 25% by mass, the average styrene content of the SBR is 39.2% by mass (=(85×40+5×25)/(85+5)).
Similarly, the average vinyl content of SBR can be calculated by {Σ(content of each SBR × vinyl content of each SBR)}/total content of all SBRs. For example, when 100% by mass of the rubber component contains 85% by mass of SBR with a vinyl content of 30% by mass and 5% by mass of SBR with a vinyl content of 20% by mass, the average vinyl content of SBR is 29.4% by mass (=(85×30+5×20)/(85+5)).

Within 100% by mass of the rubber component, the SBR content is preferably 15% by mass or more, more preferably 45% by mass or more, and even more preferably 55% by mass or more, and is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 65% by mass or less. Within the above ranges, better effects tend to be obtained.

The BR is not particularly limited, and examples include high-cis BR, low-cis BR, and BR containing syndiotactic polybutadiene crystals. Commercially available products include those from Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, and Zeon Corporation.

The cis amount (cis content) of the BR is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, and is preferably 80% by mass or less, more preferably 75% by mass or less, and preferably 70% by mass or less. Within the above ranges, the effect tends to be more favorably obtained.
The cis amount of BR can be measured by infrared absorption spectroscopy.

The vinyl content of the BR is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, and is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. Within the above ranges, the effect tends to be more favorably obtained.
The vinyl content of BR can be measured by infrared absorption spectroscopy.

The trans content of the BR is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. When it is within the above range, the effect tends to be more favorably obtained.
The trans amount of BR can be measured by infrared absorption spectroscopy.

When there is one type of BR, the cis content, vinyl content, and trans content of the BR mentioned above mean the cis content, vinyl content, and trans content of the BR, and when there are multiple types of BR, they mean the average cis content, average vinyl content, and average trans content.
The average cis amount of BR can be calculated by {Σ(content of each BR × cis amount of each BR)}/total amount of all BRs. For example, when 100% by mass of the rubber component contains 20% by mass of BR with a cis amount of 90% by mass and 10% by mass of BR with a cis amount of 40% by mass, the average cis amount of BR is 73.3% by mass (=(20×90+10×40)/(20+10)).
Similarly, the average vinyl content of BR can be calculated by {Σ(content of each BR × vinyl content of each BR)}/total content of all BRs, and the average trans content of BR can be calculated by {Σ(content of each BR × trans content of each BR)}/total content of all BRs.

Within 100% by mass of the rubber component, the BR content is preferably 15% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, and is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. Within the above ranges, better effects tend to be obtained.

Examples of isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. NR, such as SIR20, RSS#3, and TSR20, are commonly used in the tire industry. IR is not particularly limited and can be, for example, IR2200, or other commonly used rubber. Modified NR includes deproteinized natural rubber (DPNR) and high-purity natural rubber (UPNR). Modified NR includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Modified IR includes epoxidized isoprene rubber, hydrogenated isoprene rubber, and grafted isoprene rubber. These may be used alone or in combination. NR and IR are preferred.

Within 100% by mass of the rubber component, the content of isoprene-based rubber is preferably 1% by mass or more, more preferably 2% by mass or more, and is preferably 10% by mass or less, more preferably 6% by mass or less, and even more preferably 4% by mass or less. Within the above ranges, better effects tend to be achieved.

Other rubber components that can be used besides SBR, BR, and isoprene-based rubber include diene-based rubbers such as acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), and styrene-isoprene-butadiene copolymer rubber (SIBR). These may be used alone or in combination of two or more. Of these, BR is preferred.

The rubber component may be modified to introduce a functional group that interacts with a filler such as silica.
Examples of the functional group include an amino group, an amide group, a silyl group, an alkoxysilyl group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imide group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, and an epoxy group. These functional groups may have a substituent. Among these, an amino group (preferably an amino group in which a hydrogen atom of the amino group is substituted with an alkyl group having 1 to 6 carbon atoms), an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms), and an alkoxysilyl group (preferably an alkoxysilyl group having 1 to 6 carbon atoms) are preferred.

Specific examples of compounds (modifiers) having the above functional groups include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, and 3-diethylaminopropyltriethoxysilane.

The rubber composition contains silica.
Examples of silica include dry-process silica (silicic anhydride) and wet-process silica (hydrated silicic acid), but wet-process silica is preferred because it has a large number of silanol groups. Commercially available products include those from EVONIK, Tosoh Silica, Solvay Japan, and Tokuyama. These may be used alone or in combination of two or more.

The average particle size of the silica is preferably 20 nm or less, more preferably 17 nm or less, even more preferably 16 nm or less, and particularly preferably 15 nm or less, and is preferably 6 nm or more, more preferably 9 nm or more, and even more preferably 12 nm or more. Within the above ranges, better effects tend to be obtained.

In this specification, the average particle size of silica is measured by observation with a transmission electron microscope (TEM). Specifically, silica particles are photographed with a transmission electron microscope, and if the particles are spherical, the diameter of the sphere is taken as the particle size. If the particles are needle-shaped or rod-shaped, the minor axis is taken as the particle size. If the particles are irregular, the average particle diameter from the center is taken as the particle diameter. The average particle diameter is the average value of the diameters of 100 microparticles.

The silica content, per 100 parts by mass of the rubber component, is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 60 parts by mass or more, and is preferably 100 parts by mass or less, more preferably 85 parts by mass or less, even more preferably 70 parts by mass or less, and particularly preferably 65 parts by mass or less. Within the above ranges, better effects tend to be obtained.

From the viewpoint of overall performance, such as fuel economy at room temperature and low temperature, it is preferable that the cis content of the BR in the above rubber composition be less than the silica content.

The cis ratio of silica content to BR is preferably 1.03 or more, and preferably 1.50 or less, more preferably 1.30 or less, and even more preferably 1.10 or less. Within the above range, better effects tend to be obtained.

In these relationships, the silica content is the content (unit: parts by mass) relative to 100 parts by mass of the rubber component. The cis content of BR is the cis content (unit: mass%) per 100% by mass of BR, but if there are multiple types of BR, it is the average cis content.

In the rubber composition, the ratio of the silica content to the isoprene-based rubber content is preferably at least 10, more preferably at least 15, and even more preferably at least 20, and is preferably at most 35, more preferably at most 28, and even more preferably at most 24. Within the above ranges, the effect tends to be better obtained.
In this relationship, the silica content is the content (unit: parts by mass) relative to 100 parts by mass of the rubber component, and the isoprene-based rubber content is the content (unit: % by mass) in 100% by mass of the rubber component.

The rubber composition contains a mercapto-based silane coupling agent.
The mercapto-based silane coupling agent is not particularly limited, and examples thereof include 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and the like.
As the mercapto-based silane coupling agent, in addition to the above-mentioned compounds having a mercapto group, compounds having a structure in which the mercapto group is protected by a protecting group (for example, a compound represented by the following formula (S1)) can also be used.

Particularly suitable mercapto-based silane coupling agents include silane coupling agents represented by the following formula (S1) and silane coupling agents containing a bonding unit A represented by the following formula (I) and a bonding unit B represented by the following formula (II).
(wherein R ¹⁰⁰¹ is a monovalent group selected from -Cl, -Br, -OR ¹⁰⁰⁶ , -O(O═)CR ¹⁰⁰⁶ , -ON═CR ¹⁰⁰⁶ R ¹⁰⁰⁷ , -NR ¹⁰⁰⁶ R ¹⁰⁰⁷ and -(OSiR ¹⁰⁰⁶ R ¹⁰⁰⁷ ) _h (OSiR ¹⁰⁰⁶ R ¹⁰⁰⁷ R ¹⁰⁰⁸ ) (R ¹⁰⁰⁶ , R ¹⁰⁰⁷ and R ¹⁰⁰⁸ may be the same or different and each is a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, and h has an average value of 1 to 4), R ¹⁰⁰² is R ¹⁰⁰¹ , a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, R ¹⁰⁰³ is -[O(R ¹⁰⁰⁹ O) _j ]- group (R ¹⁰⁰⁹ is an alkylene group having 1 to 18 carbon atoms, and j is an integer of 1 to 4), R ¹⁰⁰⁴ is a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ¹⁰⁰⁵ is a monovalent hydrocarbon group having 1 to 18 carbon atoms, and x, y, and z are numbers that satisfy the relationships x + y + 2z = 3, 0≦x≦3, 0≦y≦2, and 0≦z≦1).
(In the formula, v is an integer of 0 or more, and w is an integer of 1 or more. R ¹¹ represents hydrogen, halogen, a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, a branched or unbranched alkynyl group having 2 to 30 carbon atoms, or an alkyl group in which the terminal hydrogen atom has been substituted with a hydroxyl group or a carboxyl group. R ¹² represents a branched or unbranched alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group having 2 to 30 carbon atoms, or a branched or unbranched alkynylene group having 2 to 30 carbon atoms. R ¹¹ and R ¹² may together form a ring structure.)

In formula (S1), R ¹⁰⁰⁵ , R ¹⁰⁰⁶ , R ¹⁰⁰⁷ and R ¹⁰⁰⁸ are preferably each independently a group selected from the group consisting of a linear, cyclic or branched alkyl group, alkenyl group, aryl group and aralkyl group having 1 to 18 carbon atoms. Furthermore, when R ¹⁰⁰² is a monovalent hydrocarbon group having 1 to 18 carbon atoms, it is preferably a group selected from the group consisting of a linear, cyclic or branched alkyl group, alkenyl group, aryl group and aralkyl group. R ¹⁰⁰⁹ is preferably a linear, cyclic or branched alkylene group, with a linear one being particularly preferred. Examples of R ¹⁰⁰⁴ include alkylene groups having 1 to 18 carbon atoms, alkenylene groups having 2 to 18 carbon atoms, cycloalkylene groups having 5 to 18 carbon atoms, cycloalkylalkylene groups having 6 to 18 carbon atoms, arylene groups having 6 to 18 carbon atoms, and aralkylene groups having 7 to 18 carbon atoms. The alkylene groups and alkenylene groups may be linear or branched, and the cycloalkylene groups, cycloalkylalkylene groups, arylene groups, and aralkylene groups may have a functional group such as a lower alkyl group on the ring. R ¹⁰⁰⁴ is preferably an alkylene group having 1 to 6 carbon atoms, and particularly preferably a linear alkylene group, such as a methylene group, ethylene group, trimethylene group, tetramethylene group, pentamethylene group, or hexamethylene group.

Specific examples of R ¹⁰⁰² , R ¹⁰⁰⁵ , R ¹⁰⁰⁶ , R ¹⁰⁰⁷ and R ¹⁰⁰⁸ in formula (S1) include 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 pentyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, a cyclopentyl group, a cyclohexyl group, a vinyl group, a propenyl group, an allyl group, a hexenyl group, an octenyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a tolyl group, a xylyl group, a naphthyl group, a benzyl group, a phenethyl group and a naphthylmethyl group.
Examples of R ¹⁰⁰⁹ in formula (S1) include linear alkylene groups such as methylene, ethylene, n-propylene, n-butylene, and hexylene, and branched alkylene groups such as isopropylene, isobutylene, and 2-methylpropylene.

Specific examples of silane coupling agents represented by formula (S1) include 3-hexanoylthiopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, 3-decanoylthiopropyltriethoxysilane, 3-lauroylthiopropyltriethoxysilane, 2-hexanoylthioethyltriethoxysilane, 2-octanoylthioethyltriethoxysilane, 2-decanoylthioethyltriethoxysilane, 2-lauroylthioethyltriethoxysilane, 3-hexanoylthiopropyltrimethoxysilane, 3-octanoylthiopropyltrimethoxysilane, 3-decanoylthiopropyltrimethoxysilane, 3-lauroylthiopropyltrimethoxysilane, 2-hexanoylthioethyltrimethoxysilane, 2-octanoylthioethyltrimethoxysilane, 2-decanoylthioethyltrimethoxysilane, 2-lauroylthioethyltrimethoxysilane, etc. These may be used alone or in combination of two or more. Of these, 3-octanoylthiopropyltriethoxysilane is particularly preferred.

In the silane coupling agent comprising the bond unit A represented by formula (I) and the bond unit B represented by formula (II), the content of bond unit A is preferably 30 mol% or more, more preferably 50 mol% or more, preferably 99 mol% or less, more preferably 90 mol% or less.In addition, the content of bond unit B is preferably 1 mol% or more, more preferably 5 mol% or more, even more preferably 10 mol% or more, preferably 70 mol% or less, more preferably 65 mol% or less, even more preferably 55 mol% or less.In addition, the total content of bond unit A and B is preferably 95 mol% or more, more preferably 98 mol% or more, particularly preferably 100 mol%.
The content of the bonding units A and B includes the case where the bonding units A and B are located at the terminals of the silane coupling agent. When the bonding units A and B are located at the terminals of the silane coupling agent, the form of the bonding units A and B is not particularly limited, as long as they form units corresponding to the formulas (I) and (II) representing the bonding units A and B.

With respect to ^R11 in formulas (I) and (II), examples of halogen include chlorine, bromine, and fluorine. Examples of branched or unbranched alkyl groups having 1 to 30 carbon atoms include methyl and ethyl groups. Examples of branched or unbranched alkenyl groups having 2 to 30 carbon atoms include vinyl and 1-propenyl groups. Examples of branched or unbranched alkynyl groups having 2 to 30 carbon atoms include ethynyl and propynyl groups.

With respect to ^R12 in formulas (I) and (II), examples of branched or unbranched alkylene groups having 1 to 30 carbon atoms include an ethylene group, a propylene group, etc. Examples of branched or unbranched alkenylene groups having 2 to 30 carbon atoms include a vinylene group, a 1-propenylene group, etc. Examples of branched or unbranched alkynylene groups having 2 to 30 carbon atoms include an ethynylene group, a propynylene group, etc.

In a silane coupling agent containing a bonding unit A represented by formula (I) and a bonding unit B represented by formula (II), the total number of repetitions (v+w) of bonding unit A (v) and bonding unit B (w) is preferably in the range of 3 to 300.

The rubber composition may contain other silane coupling agents in addition to the mercapto-based silane coupling agent. Usable silane coupling agents are not particularly limited, and examples include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, and bis(4-trimethoxysilylbutyl). Examples include sulfide-based compounds such as triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilylpropyl methacrylate monosulfide; vinyl-based compounds such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based compounds such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based compounds such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based compounds such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. These compounds may be used alone or in combination of two or more.

Commercially available silane coupling agents include those from Degussa, Momentive, Shin-Etsu Silicones, Tokyo Chemical Industry, Azumax, and Dow Corning Toray.

The content of the silane coupling agent is preferably 3 parts by mass or more, more preferably 6 parts by mass or more, and even more preferably 8 parts by mass or more, per 100 parts by mass of silica, and is preferably 15 parts by mass or less, more preferably 12 parts by mass or less, and even more preferably 10 parts by mass or less. Within the above range, better effects tend to be obtained.

The rubber composition contains carbon black.
The carbon black is not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available products include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nichika Carbon Co., Ltd., Columbia Carbon Co., Ltd., and the like. These may be used alone or in combination of two or more.

The cetyltrimethylammonium bromide (CTAB) specific surface area of the carbon black is preferably 110 m ² /g or more, more preferably 120 m ² /g or more, even more preferably 130 m ² /g or more, and is preferably 200 m ² /g or less, more preferably 160 m ² /g or less, even more preferably 140 m ² /g or less. Within the above ranges, better effects tend to be obtained.
The CTAB specific surface area of carbon black is a value measured in accordance with JIS K6217-3:2001.

The carbon black content, per 100 parts by mass of the rubber component, is preferably at least 1 part by mass, more preferably at least 3 parts by mass, and is preferably at most 30 parts by mass, more preferably at most 20 parts by mass, and even more preferably at most 10 parts by mass. Within the above ranges, better effects tend to be obtained.

In the above rubber composition, the trans content of BR + vinyl content > carbon black content.

The ratio (trans amount of BR + vinyl amount) / carbon black content is preferably 3 or more, more preferably 9 or more, and particularly preferably 12 or more, and is preferably 25 or less, more preferably 20 or less, and even more preferably 15 or less. Being within the above range tends to produce better effects.

In these relationships, the carbon black content is the content (unit: parts by mass) per 100 parts by mass of the rubber component. The trans content and vinyl content of BR are the trans content and vinyl content (unit: mass%) per 100% by mass of BR, but if there are multiple types of BR, they are the average trans content and average vinyl content.

The rubber composition preferably contains a dialkyldithiophosphate compound.
As the dialkyldithiophosphate compound, for example, a salt of a dialkyldithiophosphate with a metal such as zinc or molybdenum can be used. Commercially available products include those manufactured by Rhein Chemie, etc. These may be used alone or in combination of two or more. Among these, the compound represented by the following formula (1) (zinc dialkyldithiophosphate) is preferred.
(In the formula, R ¹ to R ⁴ each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 5 to 12 carbon atoms.)

In formula (1), examples of the linear or branched alkyl group represented by R ¹ to R ⁴ include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a 4-methylpentyl group, a 2-ethylhexyl group, an octyl group, an octadecyl group, etc., while examples of the cycloalkyl group include a cyclopentyl group, a cyclohexyl group, a cyclooctyl group, etc. Among these, from the viewpoints of ease of dispersion in the rubber composition and ease of production, R ¹ to R ⁴ are preferably linear or branched alkyl groups having 2 to 8 carbon atoms, more preferably an n-butyl group, an n-propyl group, an isopropyl group, or an n-octyl group, and even more preferably an n-butyl group.

The amount of the dialkyldithiophosphate compound per 100 parts by mass of the rubber component is preferably at least 0.5 parts by mass, more preferably at least 0.8 parts by mass, and even more preferably at least 1 part by mass, and is preferably at most 3 parts by mass, more preferably at most 2.5 parts by mass, and even more preferably at most 2 parts by mass. Within the above ranges, better effects tend to be obtained.

The rubber composition preferably contains sulfur.
Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, etc., which are commonly used in the rubber industry. Commercially available products include those from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. These may be used alone or in combination of two or more.

The sulfur content, per 100 parts by mass of the rubber component, is preferably at least 0.8 parts by mass, more preferably at least 1.4 parts by mass, and even more preferably at least 1.6 parts by mass, and is preferably at most 6 parts by mass, more preferably at most 3 parts by mass, and even more preferably at most 2 parts by mass. Within the above ranges, better effects tend to be achieved.

From the viewpoint of overall performance such as fuel economy at normal and low temperatures, the ratio of sulfur content to isoprene-based rubber content in the rubber composition is preferably more than 0.5, more preferably 0.6 or more, and is preferably 1.5 or less, more preferably 1.2 or less, and even more preferably 0.9 or less. When the ratio is within the above range, better effects tend to be obtained.
In this relationship, the sulfur content is the content (unit: parts by mass) relative to 100 parts by mass of the rubber component, and the isoprene-based rubber content is the content (unit: % by mass) in 100% by mass of the rubber component.

The rubber composition may contain a processing aid.
Examples of processing aids include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, and mixtures of fatty acid metal salts and fatty acid amides. Commercially available products include those from Rhein Chemie and Struktol. These may be used alone or in combination of two or more. Of these, fatty acid metal salts are preferred.

Fatty acids that make up the fatty acid metal salt include saturated or unsaturated fatty acids (preferably saturated or unsaturated fatty acids having 6 to 28 carbon atoms (more preferably 10 to 25 carbon atoms, and even more preferably 14 to 20 carbon atoms)), such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, arachidic acid, behenic acid, and nervonic acid. These can be used alone or in combination of two or more. Of these, saturated fatty acids are preferred, and saturated fatty acids having 14 to 20 carbon atoms are more preferred.

Metals that constitute fatty acid metal salts include, for example, alkali metals such as potassium and sodium, alkaline earth metals such as magnesium, calcium and barium, zinc, nickel, molybdenum, etc. These may be used alone or in combination of two or more. Of these, zinc is preferred.

The content of the processing aid per 100 parts by mass of the rubber component is preferably at least 1 part by mass, more preferably at least 1.5 parts by mass, and even more preferably at least 2 parts by mass, and is preferably at most 8 parts by mass, more preferably at most 6 parts by mass, and even more preferably at most 4 parts by mass. Within the above ranges, better effects tend to be obtained.

The rubber composition may contain a resin.
The resins that can be used are not particularly limited as long as they are those commonly used in the tire industry, and examples thereof include aromatic resins, terpene resins, etc. These may be used alone or in combination of two or more.

Commercially available resins include those from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JXTG Nippon Oil & Energy Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Co., Ltd.

The resin content, per 100 parts by mass of the rubber component, is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 25 parts by mass or less. Within the above ranges, better effects tend to be obtained.

The rubber composition may contain an antioxidant.
Examples of the antioxidant include naphthylamine-based antioxidants such as phenyl-α-naphthylamine; diphenylamine-based antioxidants such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine;N-isopropyl-N'-phenyl-p-phenylenediamine,N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and N,N'-di-2-naphthyl-p-phenylenediamine. Examples of such antioxidants include p-phenylenediamine-based antioxidants such as quinolone; quinoline-based antioxidants such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Commercially available products include those available from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., Flexis, and the like. These antioxidants may be used alone or in combination of two or more.

The content of the antioxidant is preferably at least 1 part by mass, more preferably at least 3 parts by mass, and even more preferably at least 4 parts by mass, per 100 parts by mass of the rubber component, and is preferably at most 12 parts by mass, more preferably at most 10 parts by mass, and even more preferably at most 8 parts by mass. Within the above ranges, better effects tend to be obtained.

The rubber composition may contain oil.
Examples of oils include process oils, vegetable oils, and mixtures thereof. Examples of process oils that can be used include paraffin-based process oils, aromatic process oils, and naphthenic process oils. Examples of vegetable oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice bran oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. Commercially available products include those from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., JXTG Nippon Oil & Energy Corporation, Oriso Co., Ltd., H&R Corporation, Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., and the like. These may be used alone or in combination of two or more.

The oil content, per 100 parts by mass of the rubber component, is preferably 5 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 25 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less. Within the above ranges, better effects tend to be obtained.

From the standpoint of overall performance, such as fuel economy at room temperature and low temperature, it is preferable that the oil content of the above rubber composition be greater than or equal to the total styrene content in the rubber component.

The ratio of oil content to total styrene content in the rubber component is preferably 1.2 or more, more preferably 1.4 or more, and even more preferably 1.5 or more, and is preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. Being within the above ranges tends to produce better effects.

In these relationships, the total styrene amount in the rubber component is the total content (unit: mass%) of styrene moieties contained in the entire rubber component, and the oil content is the content (unit: mass parts) per 100 parts by mass of the rubber component.

The rubber composition may contain a wax.
The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax; natural waxes such as vegetable wax and animal wax; and synthetic waxes such as polymers of ethylene, propylene, etc. Commercially available products include those from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. These may be used alone or in combination of two or more.

The wax content is preferably at least 1 part by mass, more preferably at least 2 parts by mass, per 100 parts by mass of the rubber component, and is preferably at most 10 parts by mass, more preferably at most 6 parts by mass. Within the above ranges, better effects tend to be achieved.

The rubber composition may contain stearic acid.
As the stearic acid, conventionally known ones can be used, and commercially available products that can be used include those available from NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc. These may be used alone or in combination of two or more.

The amount of stearic acid per 100 parts by mass of the rubber component is preferably at least 1 part by mass, more preferably at least 2.5 parts by mass, and is preferably at most 10 parts by mass, more preferably at most 6 parts by mass. Within the above ranges, better effects tend to be achieved.

The rubber composition may contain zinc oxide.
As the zinc oxide, conventionally known ones can be used, and commercially available products include those available from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. These may be used alone or in combination of two or more kinds.

The zinc oxide content is preferably at least 1 part by mass, more preferably at least 3 parts by mass, per 100 parts by mass of the rubber component, and is preferably at most 10 parts by mass, more preferably at most 6 parts by mass. Within the above ranges, better effects tend to be achieved.

The rubber composition may contain a vulcanization accelerator.
Examples of vulcanization accelerators include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole and di-2-benzothiazolyl disulfide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD) and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazylsulfenamide (CBS), N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-oxyethylene-2-benzothiazolesulfenamide and N,N'-diisopropyl-2-benzothiazolesulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, di-orthotolylguanidine, and orthotolylbiguanidine. Commercially available products include those from Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., and the like. These may be used alone or in combination of two or more.

The content of the vulcanization accelerator is preferably at least 1 part by mass, more preferably at least 3 parts by mass, and even more preferably at least 4.5 parts by mass, per 100 parts by mass of the rubber component, and is preferably at most 10 parts by mass, more preferably at most 8 parts by mass, and even more preferably at most 6 parts by mass. Within the above ranges, better effects tend to be obtained.

In addition to the above components, the rubber composition may further contain additives commonly used in the tire industry, such as organic peroxides; fillers such as talc, alumina, clay, aluminum hydroxide, and mica; etc. The content of these additives is preferably 0.1 to 200 parts by mass per 100 parts by mass of the rubber component.

The rubber composition can be produced, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or Banbury mixer, followed by vulcanization.

As for kneading conditions, in the base kneading step in which additives other than the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 100 to 180°C, preferably 120 to 170°C. In the finish kneading step in which the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 120°C or lower, preferably 85 to 110°C. Furthermore, the composition kneaded with the vulcanizing agent and vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. The vulcanization temperature is usually 140 to 190°C, preferably 150 to 185°C. The vulcanization time is usually 5 to 15 minutes.
From the viewpoint of overall performance such as fuel economy at room temperature and low temperature, it is preferable that the isoprene-based rubber is kneaded with a vulcanizing agent such as sulfur to form a masterbatch, and then kneaded in the final kneading step.

The above rubber composition can be used (as a rubber composition for tires) in tire components such as treads (cap treads), sidewalls, base treads, undertreads, shoulders, clinches, bead apexes, breaker cushion rubber, carcass cord covering rubber, insulation, chafers, inner liners, and side reinforcing layers of run-flat tires. It is particularly suitable for treads.

The tire of the present invention is produced by a conventional method using the above rubber composition.
That is, the rubber composition is extruded in an unvulcanized state to match the shape of the tread, etc., and molded together with other tire components in a tire building machine by a conventional method to form an unvulcanized tire. This unvulcanized tire is then heated and pressurized in a vulcanizer to obtain a tire.

The above-mentioned tires (pneumatic tires, etc.) can be used for passenger car tires; truck and bus tires; motorcycle tires; high-performance tires; winter tires such as studless tires; run-flat tires with side reinforcing layers; tires with sound-absorbing material that has sound-absorbing material such as sponge in the tire cavity; tires with sealing material that has a sealant inside or in the tire cavity that can seal in the event of a puncture; and tires with electronic components that have electronic components such as sensors and wireless tags inside or in the tire cavity, and are suitable for passenger car tires.

The size of the above tire is not particularly limited, and can be selected appropriately, for example, with a tire width in the range of 100 to 400 mm, an aspect ratio in the range of 25 to 85%, and a rim diameter in the range of 10 to 25 inches. Specific examples include 105/50R16, 115/50R17, 125/55R20, 135/45R21, 145/45R21, 155/45R18, 165/45R22, 175/45R23, 185/60R20, 195/55R14, 205/40R16, 215/40R16, 225/40R17, 235/40R17, 245/40R16, 255/40R17, 265/40R17, 275/35R18, 285/30R19, and 295/45R20.

It is preferable that the tire outer diameter Dt and the tire section width Wt of the tire satisfy the following relational expression.
The tire outer diameter (Dt) is the outer diameter of the tire when mounted on an applicable rim and under an internal pressure of 250 kPa with no load. The tire cross-sectional width (Wt) is the linear distance between the sidewalls, including any markings or letters on the tire sidewalls, when mounted on an applicable rim and under an internal pressure of 250 kPa with no load, i.e., the width excluding the markings and letters on the tire sidewalls from the total width.

Specific examples of tires that can satisfy the above formula include 145/60R18, 145/60R19, 155/55R18, 155/55R19, 155/70R17, 155/70R19, 165/55R20, 165/55R21, 165/60R19, 165/65R19, 165/70R18, 175/55R19, 175/55R20, 175/55R22, 175/60R18, 185/55R19, 185/60R20, 195/50R20, and 195/55R20.

Tires that satisfy the above formula are preferably used as pneumatic tires for passenger cars. This is because pneumatic tires for passenger cars that satisfy the above formula tend to be more suitable for solving the problem in question.

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

The various chemicals used in the examples and comparative examples are described below.

(Rubber component)
SBR: Synthesized in Production Example 1 below (styrene content: 35% by mass, vinyl content: 50% by mass, Mw: 600,000)
BR1: N103 manufactured by Asahi Kasei Chemicals Corporation (cis content: 38% by mass, vinyl content: 12% by mass, trans content: 50% by mass)
BR2: BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass, vinyl content: 1% by mass, trans content: 2% by mass)
Liquid IR: LIR-50 manufactured by Kuraray Co., Ltd.
NR: TSR20

(Chemicals other than rubber components)
Carbon black 1: N220 (CTAB: 111 m ² /g)
Carbon black 2: N134 (CTAB: 135 m ² /g)
Silica 1: Ultrasil VN3 (average particle size: 17 nm) manufactured by Evonik Degussa
Silica 2: Ultrasil 9100GR (average particle size: 15 nm) manufactured by Evonik Degussa
Silane coupling agent 1: Si266 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa
Silane coupling agent 2: NXT (3-octanoylthiopropyltriethoxysilane) manufactured by Momentive
Silane coupling agent 3: NXT-Z45 manufactured by Momentive (a copolymer of bonding unit A and bonding unit B (bonding unit A: 55 mol %, bonding unit B: 45 mol %))
Dialkyldithiophosphate compound: TP-50 manufactured by Rhein Chemie (a mixture of zinc dithiophosphate and polymer, R ¹ to R ⁴ in formula (1) are n-butyl groups, active ingredient: 50% by mass)
Oil: A/O Mix manufactured by Sankyo Yuka Kogyo Co., Ltd.
Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd.
Antioxidant 1: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Antioxidant 2: Antigen FR manufactured by Sumitomo Chemical Co., Ltd. (a quinoline-based antioxidant, purified from the reaction product of amine and ketone, with no residual amine)
Processing aid: EF44 (zinc salt of saturated fatty acid) manufactured by Struktol
Stearic acid: NOF Corporation's "Tsubaki" stearic acid
Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: HK-200-5 (powdered sulfur containing 5% by mass of oil) manufactured by Hosoi Chemical Industry Co., Ltd.
Vulcanization accelerator 1: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator 2: Noccela D (diphenyl guanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

(Production Example 1)
Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene were charged into a nitrogen-purged autoclave reactor. After adjusting the temperature of the reactor contents to 20°C, n-butyllithium was added to initiate polymerization. Polymerization was carried out under adiabatic conditions, with the maximum temperature reaching 85°C. When the polymerization conversion reached 99%, 1,3-butadiene was added, and polymerization was continued for an additional 5 minutes. 3-diethylaminopropyltriethoxysilane was then added as a modifier, and the reaction was continued. After completion of the polymerization reaction, 2,6-di-tert-butyl-p-cresol was added. Next, the solvent was removed by steam stripping, and the mixture was dried using a heated roll adjusted to 110°C to obtain SBR (modified SBR).

Examples and Comparative Examples
According to the formulation shown in Table 1, materials other than the isoprene-based rubber, sulfur, and vulcanization accelerator were kneaded for 5 minutes at 150°C using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded product (base kneading step). Next, the isoprene-based rubber, sulfur, and vulcanization accelerator were added to the obtained kneaded product, and the mixture was kneaded for 5 minutes at 80°C using an open roll to obtain an unvulcanized rubber composition (finish kneading step). The obtained unvulcanized rubber composition was molded into a tread shape and laminated with other tire components to form an unvulcanized tire. The tire was press-vulcanized for 12 minutes at 150°C to produce a test tire (size: 175/60R18). The obtained test tire was subjected to the following evaluations, and the results are shown in Table 1.
The isoprene-based rubber (liquid IR, NR) was previously mixed with sulfur to form a masterbatch, which was then mixed in the final mixing step.
In Table 1, the rubber content in the oil-extended rubber is listed in the rubber column, and the oil content in the oil-extended rubber is added to the oil column.

(low fuel consumption)
Using a rolling resistance tester, the rolling resistance of each test tire was measured when it was run at a speed (80 km/h), and the rolling resistance was expressed as an index, with Comparative Example 2 being set at 100. The measurements were carried out at 30°C and 0°C. A larger index indicates lower rolling resistance and better fuel economy.

As can be seen from Table 1, the Examples were superior to the Comparative Examples in overall fuel economy performance (total of all indexes) at the targeted normal temperature (30° C.) and low temperature (0° C.).

Claims (6)

The rubber composition contains a rubber component including styrene-butadiene rubber, butadiene rubber, and isoprene-based rubber, silica, a mercapto-based silane coupling agent, and carbon black,
the trans amount of the butadiene rubber plus the vinyl amount is greater than the carbon black content,
The rubber composition for tires has a ratio of the content of silica to the content of isoprene-based rubber of 10 or more and 35 or less. The rubber composition for tires according to claim 1, wherein the cis content of the butadiene rubber is less than the silica content. The rubber composition for tires according to claim 1 or 2, wherein the average particle size of the silica is 16 nm or less. 4. The rubber composition for a tire according to claim 1, wherein the carbon black has a cetyltrimethylammonium bromide adsorption specific surface area of 110 m ² /g or more. The rubber composition for tires according to any one of claims 1 to 4, wherein the total amount of styrene in the rubber component is 18% by mass or less. A tire using the rubber composition described in any one of claims 1 to 5.