JP7637670B2 - tire - Google Patents

Description

The present invention relates to tires.

In the case of motorcycle tire treads, a tire has been developed that divides the tread into three parts in the tire width direction and uses two types of tread rubber to achieve a certain degree of compatibility between the performance required for straight-line driving and the performance required for cornering.
For example, Patent Document 1 discloses a motorcycle tire including a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, the tread portion being divided into three in the tire width direction by a center portion including the tire equatorial plane and a pair of shoulder portions including the tread ends. In the motorcycle tire of Patent Document 1, the tread rubber of the center portion and the tread rubber of the shoulder portions both contain a rubber component including a styrene-butadiene rubber and a modified conjugated diene polymer, and silica, and contains 40 to 120 parts by mass of a filler per 100 parts by mass of the rubber component, and the silica content in the filler is 80% by mass or more.

International Publication No. 2017/204236

In a two-wheel tire tread as shown in Patent Document 1, in addition to wear resistance, it is desired to achieve both dry grip performance (grip performance on a dry road surface) and wet grip performance (grip performance on a wet road surface). One of the means for achieving this high level of compatibility is tread division. The center rubber is required to achieve high levels of wear resistance and wet grip performance, and improvements in the dispersion of fillers in the rubber have been studied.
When the amount of filler in the rubber is small, the filler disperses better and the abrasion resistance improves, but it is difficult to improve wet grip performance. Therefore, there is room for further improvement in the technology for achieving a high level of wet grip without compromising abrasion resistance in the center rubber.

The present invention aims to provide a tire that has excellent wear resistance and wet grip performance, and has as its objective the achievement of this objective.

<1> A tire comprising a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, the tread portion being divided into at least three portions in the tire width direction by a center portion including a tire equatorial plane and a pair of shoulder portions including tread ends,
The tire has a tread rubber in the center portion which is a vulcanized rubber of a rubber composition containing a rubber component including at least one type of modified styrene-butadiene copolymer rubber and 75 parts by mass or more of silica per 100 parts by mass of the rubber component, and wherein ΔE' is the difference between the storage modulus _E'0.1 of the tread rubber in the center portion at 25°C and 0.1% strain and the storage modulus _E'4 at 25°C and 4% strain, and ΔE'/ _E'4 is 0.900 or less.
The tire includes a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, the tread portion being divided into three portions in the tire width direction by a center portion including the tire equatorial plane and a pair of shoulder portions including tread ends,
The tread rubber of the center portion is preferably a vulcanized rubber of a rubber composition containing a rubber component including at least one type of modified styrene-butadiene copolymer rubber and 75 parts by mass or more of silica per 100 parts by mass of the rubber component, and the tire has a ΔE'_/E'4 ratio of 0.900 or less, where ΔE' is the difference between the storage modulus _E'0.1 at 25°C and 0.1% strain of the tread rubber of the center portion and the storage modulus _E'4 at 25°C and 4% strain.

<2> The tire according to <1>, wherein the content of the silica in the rubber composition is 120 parts by mass or less per 100 parts by mass of the rubber component.
<3> The tire according to <1> or <2>, wherein the rubber composition further contains carbon black, and a ratio of the silica to a total amount of the silica and the carbon black is 70 mass% or more.

<4> The tire according to any one of <1> to <3>, wherein the rubber composition further contains 2 to 85 parts by mass of a softener per 100 parts by mass of the rubber component.
<5> The tire according to <4>, wherein the softener contains a resin, and the resin is at least one selected from the group consisting of a _C5 resin, a _C9 resin, a _C5 - _C9 resin, a terpene resin, a terpene-aromatic compound resin, a rosin resin, a dicyclopentadiene resin, and an alkylphenol resin.
<6> The tire according to <5>, wherein the ratio of the resin to the total amount of the softener is 20 to 90 mass %.

<7> The tire according to any one of <1> to <6>, wherein the rubber component further contains a modified butadiene rubber.
<8> The tire according to any one of <1> to <7>, wherein the modified styrene-butadiene copolymer rubber has a weight average molecular weight of 20×10 ⁴ or more and 300×10 ⁴ or less, contains 0.25 mass % or more and 30 mass % or less of a modified styrene-butadiene copolymer rubber having a molecular weight of 200×10 ⁴ or more and 500×10 ⁴ or less, based on a total amount of the modified styrene-butadiene copolymer rubber, and has a shrinkage factor (g') of less than 0.64.

<9> The tire according to any one of <1> to <8>, wherein the modified styrene-butadiene copolymer rubber has branches and a degree of branching of 5 or more.
<10> The modified styrene-butadiene copolymer rubber has one or more coupling residues and a styrene-butadiene copolymer rubber chain bonded to the coupling residues,
The tire according to <10>, wherein the branch includes a branch in which five or more of the styrene-butadiene copolymer rubber chains are bonded to one of the coupling residues.
<11> The tire according to any one of <1> to <10>, wherein the modified styrene-butadiene copolymer rubber is represented by the following formula (I):

In formula (I), D represents a styrene-butadiene copolymer rubber chain. ^{R 1} , R ² and R ³ each independently represent a single bond or an alkylene group having 1 to 20 carbon atoms. ^{R 4} and R ⁷ each independently represent an alkyl group having 1 to 20 carbon atoms. ^{R 5} , R ⁸ and R ⁹ each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. R ⁶ and R ¹⁰ each independently represent an alkylene group having 1 to 20 carbon atoms. R ¹¹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. m and x each independently represent an integer of 1 to 3, and x≦m. p represents 1 or 2. y represents an integer of 1 to 3, and y≦(p+1). z represents an integer of 1 or 2. i represents an integer of 0 to 6, j represents an integer of 0 to 6, k represents an integer of 0 to 6, and (i+j+k) is an integer of 3 to 10. ((x×i)+(y×j)+(z×k)) is an integer of 5 to 30. A represents a hydrocarbon group having 1 to 20 carbon atoms, or an organic group having at least one atom selected from the group consisting of oxygen atoms, nitrogen atoms, silicon atoms, sulfur atoms and phosphorus atoms and having no active hydrogen.
<12> The tire according to <11>, wherein in formula (I), A is represented by the following formula (II), the following formula (III), the following formula (IV), or the following formula (V):

In formula (II), ^B1 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10.
In formula (III), ^B2 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, ^B3 represents an alkyl group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10.
In formula (IV), ^B4 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10.
In formula (V), ^B5 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10.
<13> The tire according to any one of <1> to <12>, wherein the modified styrene-butadiene copolymer rubber is obtained by reacting a styrene-butadiene copolymer rubber with a coupling agent represented by the following formula (VI):

In formula (VI), R ¹² , R ¹³ and R ¹⁴ each independently represent a single bond or an alkylene group having 1 to 20 carbon atoms. R ¹⁵ , R ¹⁶ , R ¹⁷ , R ¹⁸ and R ²⁰ each independently represent an alkyl group having 1 to 20 carbon atoms. ^{R 19} and R ²² each independently represent an alkylene group having 1 to 20 carbon atoms. R ²¹ represents an alkyl group or a trialkylsilyl group having 1 to 20 carbon atoms, and m represents an integer of 1 to 3. p represents 1 or 2. i, j and k each independently represent an integer of 0 to 6, provided that (i+j+k) is an integer of 3 to 10. A represents a hydrocarbon group having 1 to 20 carbon atoms, or an organic group having at least one atom selected from the group consisting of an oxygen atom, a nitrogen atom, a silicon atom, a sulfur atom and a phosphorus atom, and having no active hydrogen.

<14> The tire according to <13>, wherein the coupling agent represented by formula (VI) is at least one selected from the group consisting of tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine, and tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane.
<15> The tire according to any one of <4> to <14>, wherein the rubber composition has a content of the softener of 72 parts by mass or less per 100 parts by mass of the rubber component.

According to the present invention, a tire having excellent wear resistance and wet grip properties can be provided.

The tire of the present invention comprises a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, and the tread portion is divided into at least three portions in the tire width direction by a center portion including the tire equatorial plane and a pair of shoulder portions including the tread ends.
First, the structure of the tire will be described.

<Tire structure>
Each bead portion usually has a bead core, and one or more carcass layers are provided between the pair of bead cores so as to extend in a toroidal shape. The carcass layer is made of a plurality of carcass cords covered with rubber.
The sidewall portion extends radially outward from the bead portion on the side surface of the tire to reinforce and protect the side surface.

The tread portion extends across both sidewall portions.
In the present invention, a split tread is used in which the tread portion is divided into a center portion and two shoulder portions sandwiching the center portion. The split tread is divided into at least three portions by a center portion including the tire equatorial plane and a pair of shoulder portions including the tread ends. The split tread may have an additional portion between the center portion and the shoulder portion, or the center portion may be divided into a plurality of portions. For example, the tread portion may be divided into a first shoulder portion, a second shoulder portion, a first center portion, a second center portion, a third shoulder portion, and a fourth shoulder portion in order from the tread end.
The divided tread is preferably divided into three by a center portion and a pair of shoulder portions.
The tire equator is a latitude line of the tire that passes through the center of the tire in the width direction, and the surface in the tire circumferential direction that includes the tire equator is called the tire equatorial plane.
More specifically, the center portion has a widthwise curved length (L _C ) of the tread surface that is preferably 30 to 60% of the maximum widthwise curved length (L _T ) of the entire surface area of the tread, and more preferably 40 to 50%. When the widthwise curved length (L _C ) of the tread surface is 30% or more of the maximum widthwise curved length (L _T ) of the entire surface area of the tread, wear resistance can be ensured, and when it is 60% or less, the deterioration of wet grip performance is not suppressed. When the widthwise curved length (L _C ) of the tread surface is 40 to 50% of the maximum widthwise curved length (L _T ) of the entire surface area of the tread, it is advantageous in terms of excellent balance between wet grip performance and wear resistance.
The widthwise curved length (L _S ) of the tread surface of the shoulder portion may be different from one shoulder portion to the other, but is usually preferably the same, and the widthwise curved length of the shoulder portion (one side) is preferably (100-Lc)/2% of L _T .

Hereinafter, the rubber constituting the tread portion may be referred to as "tread rubber." The rubber constituting the shoulder portion may be referred to as "tread rubber of the shoulder portion" or simply as "shoulder rubber." Moreover, the rubber constituting the center portion may be referred to as "tread rubber of the center portion" or simply as "center rubber."
The rubber composition constituting the center rubber before vulcanization may be referred to as a rubber composition for the center rubber. In other words, the rubber obtained by vulcanizing the rubber composition for the center rubber is the center rubber.

<Tread rubber>
The tread rubber (center rubber) of the center portion of the tire of the present invention has a ΔE'/ _E'4 ratio of _0.900 or less, where ΔE is the difference between the storage modulus E'0.1 at 25°C and 0.1% strain and the storage modulus E'4 at _25° C and ₄ % strain (E'0.1- _E'4 ).
The center rubber is a vulcanized rubber of a rubber composition containing a rubber component including at least one modified styrene-butadiene copolymer rubber and 75 parts by mass or more of silica per 100 parts by mass of the rubber component.
The reason why the tire of the present invention has excellent wear resistance and wet grip performance due to the center rubber of the present invention having the above-mentioned configuration is not clear, but is presumed to be due to the following reasons.
It is believed that the above rubber composition provides dispersion reinforcement of silica and improves wear resistance. It is believed that the tire has excellent wet performance because the rubber composition contains a large amount of silica. As a vulcanized rubber property, the smaller ΔE'/ _E'4 indicates that the dispersibility of silica is improved.
First, the vulcanized rubber characteristics of the center rubber will be described.

[Storage modulus difference ΔE′]
As described above, the storage modulus E' of the center rubber in the present invention is such that _ΔE '/ _E'4 is 0.900 or less, where ΔE' is the difference between the storage modulus E'0.1 at 25°C and 0.1% strain and the storage modulus _E'4 at ₂₅ °C and 4% strain (E'0.1- _E'4 ).
If ΔE′/ _E′4 exceeds 0.900, the wear resistance and wet grip performance of the tire cannot be improved.
The smaller ΔE'/ _E'4 is, the better the dispersion of silica in the vulcanized rubber matrix is. _E'0.1 represents the storage modulus of as small a strain as possible. Although the storage modulus changes greatly with strain, _E'4 represents the storage modulus in the region beyond the inflection point where the change in storage modulus becomes mild. By determining the difference, the degree of dispersion can be clearly seen.

From the viewpoint of further improving the abrasion resistance and wet grip performance of the tire, ΔE'/ _E'4 of the center rubber is preferably 0.22 or more, more preferably 0.27 or more, even more preferably 0.32 or more, still more preferably 0.37 or more, and still more preferably 0.42 or more.
The lower limit of ΔE'/ _E'4 of the center rubber is not particularly limited, but from the viewpoint of preventing aggregation of the filler in the vulcanized rubber, it is preferably 0.89 or less, more preferably 0.87 or less, and even more preferably 0.85 or less.

From the viewpoint of further improving the abrasion resistance and wet grip performance of the tire, the ΔE′ of the center rubber is preferably 10.0 or less, more preferably 8.0 or less, and further preferably 6.0 or less.
There is no particular lower limit for ΔE' of the center rubber, but from the viewpoint of preventing aggregation of the filler in the vulcanized rubber, ΔE' of the center rubber is preferably 0.1 or more, more preferably 0.5 or more, even more preferably 1.0 or more, and still more preferably 1.5 or more.

From the viewpoint of dispersibility of the filler in the vulcanized rubber, the storage modulus _E'0.1 of the center rubber at 25°C and strain of 0.1% is preferably 6.7 N/mm or more, more preferably 6.8 N/mm or more, even more preferably 6.9 N/mm or more, even more preferably 7.0 N/mm or more, even more preferably 7.1 N/mm or more, even more preferably 7.2 N/mm or more, even more preferably 7.5 N/mm or more, even more preferably 7.8 N/mm or more, even more preferably 8.2 N/mm or more, even more preferably 8.5 N/mm or more, even more preferably 8.8 N/mm or more, even more preferably 9.1 N/mm or more, even more preferably 9.3 N/mm or more, even more preferably 9.5 N/mm or more, and even more preferably 9.9 N/mm or more.
The storage modulus _E'0.1 of the center rubber at 25°C and 0.1% strain is preferably 15.0 N/mm or less, more preferably 14.5 N/mm or less, even more preferably 13.8 N/mm or less, and even more preferably 13.3 N/mm or less.
The storage modulus E' of the center rubber can be measured, for example, by using a viscoelasticity measuring device.
Next, the rubber composition constituting the center rubber (rubber composition for the center rubber) will be described.

[Rubber composition]
The rubber composition of the center rubber (rubber composition for center rubber) in the present invention contains a rubber component containing at least one type of modified styrene-butadiene copolymer rubber, and 75 parts by mass or more of silica per 100 parts by mass of the rubber component.
When the rubber composition for the center rubber has the above-mentioned composition, the ΔE′/ _E′4 of the center rubber tends to be 0.900 or less.
The rubber composition for the center rubber may further contain a rubber component other than the modified styrene-butadiene copolymer rubber, a filler other than silica, and various other components.

[Rubber component]
In the rubber composition for the center rubber, the rubber component contains at least one type of modified styrene-butadiene copolymer rubber.
When the rubber component constituting the center rubber contains a modified styrene-butadiene copolymer rubber, the ΔE′/ _E′4 of the center rubber tends to be 0.900 or less.

(Modified styrene-butadiene copolymer rubber)
The modified styrene-butadiene copolymer rubber in the present invention is not particularly limited as long as the styrene-butadiene copolymer rubber chain has a structure having a modifying group.
For example, there may be mentioned a structure in which at least one end of a styrene-butadiene copolymer rubber chain has a modifying group containing a nitrogen atom and a silicon atom.
By including nitrogen atoms and silicon atoms in the modified styrene-butadiene copolymer rubber, the processability of the rubber composition for the center rubber is improved, and the rolling resistance can be further reduced while improving the wet grip performance and abrasion resistance of the tire. The presence of nitrogen atoms in the modified styrene-butadiene copolymer rubber body can be confirmed by the presence or absence of adsorption to a specific column using the method described in the Examples below. The presence of silicon atoms in the modified styrene-butadiene copolymer rubber can be confirmed by metal analysis using the method described in the Examples below.

A modified styrene-butadiene copolymer rubber having a structure in which at least one end of a styrene-butadiene copolymer rubber chain has a modifying group containing a nitrogen atom and a silicon atom can be obtained, for example, by reacting a coupling agent containing a nitrogen atom and a silicon atom with a styrene-butadiene copolymer rubber.

It is preferable that at least one end of the styrene-butadiene copolymer rubber chain is bonded to a silicon atom of the coupling residue. In this case, the ends of a plurality of styrene-butadiene copolymer rubbers may be bonded to one silicon atom. In addition, an end of the styrene-butadiene copolymer rubber chain and an alkoxy group or hydroxyl group having 1 to 20 carbon atoms may be bonded to one silicon atom, and as a result, that one silicon atom may constitute an alkoxysilyl group or silanol group having 1 to 20 carbon atoms.

The modified styrene-butadiene copolymer rubber preferably has a branched structure.
In general, a polymer having branches tends to have a smaller molecular size compared to a linear polymer having the same absolute molecular weight, and the shrinkage factor (g') is an index of the ratio of the molecular size to that of a linear polymer having the same assumed absolute molecular weight. That is, the larger the degree of branching of a polymer, the smaller the shrinkage factor (g') tends to be. In this embodiment, intrinsic viscosity is used as an index of molecular size, and linear polymers are assumed to follow the relational expression of intrinsic viscosity [η] = -3.883 M ^0.771 . The shrinkage factor (g') for each absolute molecular weight of the modified styrene-butadiene copolymer rubber is calculated, and the average value of the shrinkage factor (g') for the absolute molecular weight of 100 x 10 ⁴ to 200 x 10 ⁴ is taken as the shrinkage factor (g') of the modified styrene-butadiene copolymer rubber.
Here, the term "branched" refers to a structure formed by directly or indirectly bonding one polymer to another polymer.
The "degree of branching" is the number of polymers that are directly or indirectly bonded to one branch. For example, when five styrene-butadiene copolymer rubber chains described below are indirectly bonded to one another via coupling residues described below, the degree of branching is 5.
The coupling residue is a structural unit of a modified styrene-butadiene copolymer rubber that is bonded to a styrene-butadiene copolymer rubber chain, and is, for example, a structural unit derived from a coupling agent that is generated by reacting a styrene-butadiene copolymer rubber described later with a coupling agent.
The styrene-butadiene copolymer rubber chain is a structural unit of a modified styrene-butadiene copolymer rubber, and is, for example, a structural unit derived from a styrene-butadiene copolymer rubber produced by reacting a styrene-butadiene copolymer rubber described later with a coupling agent.

The modified styrene-butadiene copolymer rubber preferably has a weight average molecular weight (Mw) of 20×10 ⁴ or more and 300×10 ⁴ or less.
When the weight average molecular weight is 20×10 ⁴ or more, the wet grip performance of the tire is improved and the rolling resistance is easily reduced. When the weight average molecular weight is 300×10 ⁴ or less, the processability of the rubber composition for the center rubber can be improved.
The weight average molecular weight of the modified styrene-butadiene copolymer rubber is more preferably 50×10 ⁴ or more, even more preferably 64×10 ⁴ or more, and even more preferably 80×10 ⁴ or more. The weight average molecular weight of the modified styrene-butadiene copolymer rubber is more preferably 250×10 ⁴ or less, even more preferably 180×10 ⁴ or less, and even more preferably 150×10 ⁴ or less.
In this specification, the term "molecular weight" refers to a standard polystyrene-equivalent molecular weight obtained by GPC (gel permeation chromatography).
The weight average molecular weight of the modified styrene-butadiene copolymer rubber and the styrene-butadiene copolymer rubber described later are measured by the method described in the examples described later.

The modified styrene-butadiene copolymer rubber preferably contains 0.25% by mass or more and 30% by mass or less of a modified styrene-butadiene copolymer rubber having a molecular weight of 200×10 ⁴ or more and 500×10 ⁴ or less, based on the total amount (100% by mass) of the modified styrene-butadiene copolymer rubber. Hereinafter, the modified styrene-butadiene copolymer rubber having a molecular weight of 200×10 ⁴ or more and 500×10 ⁴ or less is also referred to as a "specific high molecular weight component."
When the content of the specific high molecular weight component in the total amount of the modified styrene-butadiene copolymer rubber is within the above range, the wet grip performance of the tire and reduced rolling resistance can both be achieved at a high level.

The content of the specific high molecular weight component in the total amount of the modified styrene-butadiene copolymer rubber is more preferably 1.0 mass% or more, even more preferably 1.4 mass% or more, even more preferably 1.75 mass% or more, even more preferably 2.0 mass% or more, even more preferably 2.15 mass% or more, and even more preferably 2.5 mass% or more.
Further, the content of the specific high molecular weight component in the total amount of the modified styrene-butadiene copolymer rubber is more preferably 28% by mass or less, even more preferably 25% by mass or less, even more preferably 20% by mass or less, and even more preferably 18% by mass or less.
The modified styrene-butadiene copolymer rubber having a content of the specific high molecular weight component within the above range can be easily obtained by controlling the reaction conditions in the polymerization step and the reaction step in the production method described below.
For example, in the polymerization step, the amount of the organic monolithium compound used as a polymerization initiator, which will be described later, may be adjusted. In addition, in the polymerization step, a method having a residence time distribution may be used in both continuous and batch polymerization modes. That is, the time distribution of the growth reaction may be broadened.

In the modified styrene-butadiene copolymer rubber, the molecular weight distribution (Mw/Mn) represented by the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is preferably 1.6 to 3.0. When the molecular weight distribution of the modified styrene-butadiene copolymer rubber is in this range, the processability of the rubber composition for the center rubber can be improved.
The number average molecular weight, weight average molecular weight, molecular weight distribution, and content of specific high molecular weight components for the modified styrene-butadiene copolymer rubber and the styrene-butadiene copolymer rubber described later are measured by the method described in the examples described later.

The modified styrene-butadiene copolymer rubber preferably has a shrinkage factor (g') of less than 0.64. By using a modified styrene-butadiene copolymer rubber having a shrinkage factor (g') of less than 0.64, the processability of the rubber composition for the center rubber can be improved.
The shrinkage factor (g') of the modified styrene-butadiene copolymer rubber is more preferably 0.63 or less, even more preferably 0.60 or less, even more preferably 0.59 or less, and even more preferably 0.57 or less.
The lower limit of the shrinkage factor (g') of the modified styrene-butadiene copolymer rubber is not particularly limited and may be equal to or lower than the detection limit. The shrinkage factor (g') of the modified styrene-butadiene copolymer rubber is preferably 0.30 or more, more preferably 0.33 or more, even more preferably 0.35 or more, and still more preferably 0.45 or more.

Since the shrinkage factor (g') tends to depend on the degree of branching, for example, the shrinkage factor (g') can be controlled using the degree of branching as an index. Specifically, for example, the shrinkage factor (g') of a modified styrene-butadiene copolymer rubber having a degree of branching of 6 tends to be 0.59 or more and 0.63 or less. Also, the shrinkage factor (g') of a modified styrene-butadiene copolymer rubber having a degree of branching of 8 tends to be 0.45 or more and 0.59 or less.
The contraction factor (g') is measured by the method described in the Examples below.

The modified styrene-butadiene copolymer rubber preferably has a branch and a degree of branching of 5 or more. The modified styrene-butadiene copolymer rubber preferably has one or more coupling residues and a styrene-butadiene copolymer rubber bonded to the coupling residue, and more preferably includes a branch in which 5 or more styrene-butadiene copolymer rubber chains are bonded to one coupling residue. By specifying the structure of the modified styrene-butadiene copolymer rubber so that the degree of branching is 5 or more and the branch includes a branch in which 5 or more styrene-butadiene copolymer rubber chains are bonded to one coupling residue, the contraction factor (g') can be more reliably set to less than 0.64. The number of styrene-butadiene copolymer rubber chains bonded to one coupling residue can be confirmed from the value of the contraction factor (g').

Moreover, the modified styrene-butadiene copolymer rubber has branches, and more preferably has a degree of branching of 6 or more. Moreover, the modified styrene-butadiene copolymer rubber has one or more coupling residues and a styrene-butadiene copolymer rubber chain bonded to the coupling residue, and further preferably includes a branch in which 6 or more of the styrene-butadiene copolymer rubber chains are bonded to one coupling residue. By specifying the structure of the modified styrene-butadiene copolymer rubber so that the degree of branching is 6 or more and the branch includes a branch in which 6 or more styrene-butadiene copolymer rubber chains are bonded to one coupling residue, the shrinkage factor (g') can be made 0.63 or less.
Furthermore, the modified styrene-butadiene copolymer rubber has branches, and the degree of branching is more preferably 7 or more, and even more preferably 8 or more. The upper limit of the degree of branching is not particularly limited, but is preferably 18 or less. The modified styrene-butadiene copolymer rubber has one or more coupling residues and a styrene-butadiene copolymer rubber chain bonded to the coupling residue, and further, it is more preferable that the branching includes a branch in which 7 or more styrene-butadiene copolymer rubber chains are bonded to one coupling residue, and it is particularly preferable that the branching includes a branch in which 8 or more styrene-butadiene copolymer rubber chains are bonded to one coupling residue. By specifying the structure of the modified styrene-butadiene copolymer rubber so that the degree of branching is 8 or more and the branching includes a branch in which 8 or more styrene-butadiene copolymer rubber chains are bonded to one coupling residue, the contraction factor (g') can be made 0.59 or less.

The modified styrene-butadiene copolymer rubber preferably has a glass transition temperature (Tg) exceeding −50° C., more preferably from −30° C. to −20° C., and further preferably from −45° C. to −15° C. When the glass transition temperature (Tg) of the modified styrene-butadiene copolymer rubber is in the range of from −45° C. to −15° C., the wet grip performance of the tire can be further improved, the rolling resistance can be reduced, and the wear resistance can be further improved.
The glass transition temperature is measured in accordance with ISO 22768:2006 by recording a DSC curve while increasing the temperature within a predetermined temperature range, and the peak top (inflection point) of the DSC differential curve is determined as the glass transition temperature.

The modified styrene-butadiene copolymer rubber can be an oil-extended polymer to which an extender oil is added.
The modified styrene-butadiene copolymer rubber may be either non-oil-extended or oil-extended, but from the viewpoint of the wear resistance of the tire, the Mooney viscosity measured at 100° C. is preferably 20 or more and 100 or less, and more preferably 30 or more and 80 or less. The Mooney viscosity is measured by the method described in the examples described later.

From the viewpoint of further improving the wet grip performance and abrasion resistance of the tire, it is preferable that the modified styrene-butadiene copolymer rubber is represented by the following formula (I).

In formula (I), D represents a styrene-butadiene copolymer rubber chain. ^{R 1} , R ² and R ³ each independently represent a single bond or an alkylene group having 1 to 20 carbon atoms. ^{R 4} and R ⁷ each independently represent an alkyl group having 1 to 20 carbon atoms. ^{R 5} , R ⁸ and R ⁹ each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. R ⁶ and R ¹⁰ each independently represent an alkylene group having 1 to 20 carbon atoms. R ¹¹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. m and x each independently represent an integer of 1 to 3, and x≦m. p represents 1 or 2. y represents an integer of 1 to 3, and y≦(p+1). z represents an integer of 1 or 2. i represents an integer of 0 to 6, j represents an integer of 0 to 6, k represents an integer of 0 to 6, and (i+j+k) is an integer of 3 to 10. ((x×i)+(y×j)+(z×k)) is an integer of 5 to 30. A represents a hydrocarbon group having 1 to 20 carbon atoms, or an organic group having at least one atom selected from the group consisting of oxygen atoms, nitrogen atoms, silicon atoms, sulfur atoms and phosphorus atoms and having no active hydrogen.

The weight average molecular weight of the styrene-butadiene copolymer rubber chain represented by D is preferably 10×10 ⁴ to 100×10 ^4. The styrene-butadiene copolymer rubber chain is a structural unit of a modified styrene-butadiene copolymer rubber, and is, for example, a structural unit derived from a styrene-butadiene copolymer rubber generated by reacting a styrene-butadiene copolymer rubber with a coupling agent.

In formula (I), when a plurality of D, R ⁴ , R ⁵ , and R ⁷ to R ⁹ are present, the plurality of D, R ⁴ , R ⁵ , and R ⁷ to R ⁹ may be the same or different.
In addition, when i, j, and k are 2 or more, and thus a plurality of the following partial structures (I-i), (I-j), and (I-k) are present in formula (I), the partial structures (I-i), (I-j), and (I-k) may be the same structure or different structures.

The hydrocarbon group represented by A includes saturated, unsaturated, aliphatic, and aromatic hydrocarbon groups.
Examples of organic groups that do not have active hydrogen include organic groups that do not have functional groups that have active hydrogen, such as a hydroxyl group (-OH), a secondary amino group (>NH), a primary amino group (-NH ₂ ), or a sulfhydryl group (-SH).

In the above formula (I), A is preferably represented by any one of the following formulas (II) to (V). When A is represented by any one of the formulas (II) to (V), it is possible to improve low rolling resistance, wear resistance, and wet grip performance of the tire.

In formula (II), B ¹ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms. a represents an integer of 1 to 10. When a is 2 or more and thus a plurality of B ^1s are present, the plurality of B ^1s may be the same or different.

In formula (III), ^B2 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and ^B3 represents an alkyl group having 1 to 20 carbon atoms. a represents an integer from 1 to 10. When a is 2 or more and thus a plurality of ^B2s and ^B3s are present, the plurality of ^B2s and ^B3s may be the same or different.

In formula (IV), ^B4 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10. When a is 2 or more and thus a plurality of ^B4s are present, the plurality of ^B4s may be the same or different.

In formula (V), ^B5 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10. When a is 2 or more and thus a plurality of ^B5s are present, the plurality of ^B5s may be the same or different.

With respect to B ¹ , B ² , B ⁴ and B ⁵ in formulae (II) to (V), examples of the hydrocarbon group having 1 to 20 carbon atoms include an alkylene group having 1 to 20 carbon atoms.

In formula (I), it is preferable that A is represented by formula (II) or (III) and k is 0, and it is more preferable that A is represented by formula (II) or (III) and k is 0, and in formula (II) or (III), a is an integer of 2 to 10.
In formula (I), A is represented by formula (II) and k0, and in formula (II), a is an integer of 2 to 10, is even more preferred.

(Method for producing modified styrene-butadiene copolymer rubber)
The method for producing the modified styrene-butadiene copolymer rubber is not particularly limited, but from the viewpoint of ease of forming the branched structure described above, it is preferable to have the following steps. That is, it is preferable to have a polymerization step of polymerizing styrene and butadiene using an organic monolithium compound as a polymerization initiator to obtain a styrene-butadiene copolymer rubber, and a reaction step of reacting an active terminal of the styrene-butadiene copolymer rubber with a pentafunctional or higher reactive compound (hereinafter also referred to as a "specific coupling agent"). As the specific coupling agent, it is preferable to react a pentafunctional or higher reactive compound having a nitrogen atom and a silicon atom.

The reactive compound (coupling agent) is preferably a pentafunctional or higher reactive compound having a nitrogen atom and a silicon atom, and preferably has at least three silicon-containing functional groups. It is more preferable that the specific coupling agent has at least one silicon atom that constitutes an alkoxysilyl group or silanol group having 1 to 20 carbon atoms.

The alkoxysilyl group of a specific coupling agent tends to react with, for example, the active terminal of a styrene-butadiene copolymer rubber, dissociating the alkoxylithium and forming a bond between the terminal of the styrene-butadiene copolymer rubber chain and the silicon of the coupling residue. The number of alkoxysilyl groups in the coupling residue is the total number of SiOR in one molecule of the coupling agent minus the number of SiORs subtracted by the reaction. The azasilacycle group in the coupling agent forms an >N-Li bond and a bond between the terminal of the styrene-butadiene copolymer rubber and the silicon of the coupling residue. The >N-Li bond tends to easily become >NH and LiOH due to water, etc. during finishing. The alkoxysilyl group remaining unreacted in the coupling agent tends to easily become a silanol (Si-OH group) due to water, etc. during finishing.

The specific coupling agent is preferably represented by formula (VI). In other words, the modified styrene-butadiene copolymer rubber is preferably obtained by reacting a styrene-butadiene copolymer rubber with a coupling agent represented by formula (VI). By forming the center rubber from a rubber composition containing the modified styrene-butadiene copolymer rubber obtained by reacting with the coupling agent, the wear resistance of the tire can be improved and the rolling resistance can be reduced.

In formula (VI), R ¹² , R ¹³ and R ¹⁴ each independently represent a single bond or an alkylene group having 1 to 20 carbon atoms. R ¹⁵ , R ¹⁶ , R ¹⁷ , R ¹⁸ and R ²⁰ each independently represent an alkyl group having 1 to 20 carbon atoms. ^{R 19} and R ²² each independently represent an alkylene group having 1 to 20 carbon atoms. R ²¹ represents an alkyl group or a trialkylsilyl group having 1 to 20 carbon atoms, and m represents an integer of 1 to 3. p represents 1 or 2. i, j and k each independently represent an integer of 0 to 6, provided that (i+j+k) is an integer of 3 to 10. A represents a hydrocarbon group having 1 to 20 carbon atoms, or an organic group having at least one atom selected from the group consisting of an oxygen atom, a nitrogen atom, a silicon atom, a sulfur atom and a phosphorus atom, and having no active hydrogen.

In formula (VI), the hydrocarbon group represented by A includes saturated, unsaturated, aliphatic and aromatic hydrocarbon groups. Examples of the organic group not having active hydrogen include organic groups not having a functional group having active hydrogen, such as a hydroxyl group (-OH), a secondary amino group (>NH), a primary amino group (-NH ₂ ) or a sulfhydryl group (-SH).

In formula (VI), A is preferably represented by any one of the above-mentioned formulas (II) to (V). When A has a structure represented by any one of formulas (II) to (V), a modified styrene-butadiene copolymer rubber having better performance can be obtained.
The specific coupling agent preferably has a structure in which A is represented by formula (II) or (III) and k is 0 in formula (VI).
In formula (VI), it is more preferable that A is represented by formula (II) or (III), k is 0, and in formula (II) or (III), a is an integer from 2 to 10, and it is even more preferable that A is represented by formula (II), k is 0, and in formula (II), a is an integer from 2 to 10.

Examples of such coupling agents include bis(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]amine, tris(3-trimethoxysilylpropyl)amine, tris(3-triethoxysilylpropyl)amine, tris(3-trimethoxysilylpropyl)-[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, and tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine. cyclopentane)propyl]-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane, tris(3-trimethoxysilylpropyl)-methyl-1,3-propanediamine, bis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-(3-trismethoxysilylpropyl)-methyl-1,3-propanediamine, and the like.
The above coupling agents may be used alone or in combination of two or more.
Among these, the coupling agent represented by formula (VI) is particularly preferably tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine, or tetrakis(3-trimethoxysilylpropyl)-1,3-bisaminomethylcyclohexane.

The amount of the compound represented by formula (VI) added as the coupling agent can be adjusted so that the moles of the styrene-butadiene copolymer rubber to the moles of the coupling agent react in the desired stoichiometric ratio, which tends to achieve the desired degree of branching. The specific number of moles of the polymerization initiator is preferably 5.0 times or more, more preferably 6.0 times or more, relative to the moles of the coupling agent. In this case, in formula (VI), the number of functional groups of the coupling agent ((m-1) x i + p x j + k) is preferably an integer of 5 to 10, and more preferably an integer of 6 to 10.

In the method for producing the modified styrene-butadiene copolymer rubber, the polymerization step is preferably a polymerization by a propagation reaction by a living anionic polymerization reaction, which can obtain a styrene-butadiene copolymer rubber having an active terminal and a modified styrene-butadiene copolymer rubber with a high modification rate.
The styrene-butadiene copolymer rubber is obtained by copolymerizing at least styrene and butadiene styrene-butadiene copolymer rubber.

The amount of the organic monolithium compound used as a polymerization initiator is preferably determined according to the molecular weight of the target styrene-butadiene copolymer rubber or modified styrene-butadiene copolymer rubber. The amount of the monomer such as the conjugated diene compound used relative to the amount of the polymerization initiator used is related to the degree of polymerization, that is, the number average molecular weight and/or the weight average molecular weight. Therefore, in order to increase the molecular weight, it is preferable to adjust the amount of the polymerization initiator to a smaller amount, and in order to decrease the molecular weight, it is preferable to adjust the amount of the polymerization initiator to a larger amount.
From the viewpoint of industrial availability and ease of control of the polymerization reaction, the organic monolithium compound is preferably an alkyllithium compound. In this case, a styrene-butadiene copolymer rubber having an alkyl group at the polymerization initiation terminal is obtained. Examples of the alkyllithium compound include n-butyllithium, sec-butyllithium, tert-butyllithium, n-hexyllithium, benzyllithium, phenyllithium, and stilbenelithium. From the viewpoint of industrial availability and ease of control of the polymerization reaction, n-butyllithium and sec-butyllithium are preferred as the alkyllithium compound. These organic monolithium compounds may be used alone or in combination of two or more.

In the polymerization process, examples of the polymerization reaction mode include a batch polymerization reaction mode and a continuous polymerization reaction mode. In the continuous polymerization mode, one or more connected reactors can be used. For the continuous polymerization mode, for example, a tank type or a tube type reactor equipped with an agitator is used. In the continuous polymerization mode, preferably, the monomer, the inert solvent, and the polymerization initiator are continuously fed into the reactor, a polymer solution containing the polymer is obtained in the reactor, and the polymer solution is continuously discharged. For the batch polymerization mode, for example, a tank type reactor equipped with an agitator is used. In the batch polymerization mode, preferably, the monomer, the inert solvent, and the polymerization initiator are fed, and if necessary, the monomer is continuously or intermittently added during the polymerization, a polymer solution containing the polymer is obtained in the reactor, and the polymer solution is discharged after the polymerization is completed. In this embodiment, in order to obtain a styrene-butadiene copolymer rubber having a high proportion of active ends, a continuous polymerization mode is preferred, which allows the polymer to be continuously discharged and subjected to the next reaction in a short time.

The polymerization step is preferably carried out in an inert solvent.
Examples of the solvent include hydrocarbon solvents such as saturated hydrocarbons and aromatic hydrocarbons. Specific examples of the hydrocarbon solvent include, but are not limited to, aliphatic hydrocarbons such as butane, pentane, hexane, and heptane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclopentane, and methylcyclohexane; aromatic hydrocarbons such as benzene, toluene, and xylene, and hydrocarbons consisting of mixtures thereof. By treating the impurities, that is, allenes and acetylenes, with an organometallic compound before subjecting the mixture to the polymerization reaction, a styrene-butadiene copolymer rubber having a high concentration of active ends tends to be obtained, and a modified styrene-butadiene copolymer rubber having a high modification rate tends to be obtained, which is preferable.

In the polymerization step, a polar compound may be added. By adding the polar compound, the aromatic vinyl compound can be randomly copolymerized with the conjugated diene compound, and the polar compound tends to be usable as a vinylizing agent for controlling the microstructure of the conjugated diene portion.
Examples of the polar compound that can be used include ethers such as tetrahydrofuran, diethyl ether, dioxane, ethylene glycol dimethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, dimethoxybenzene, and 2,2-bis(2-oxolanyl)propane; tertiary amine compounds such as tetramethylethylenediamine, dipiperidinoethane, trimethylamine, triethylamine, pyridine, and quinuclidine; alkali metal alkoxide compounds such as potassium tert-amylate, potassium tert-butylate, sodium tert-butylate, and sodium tert-amylate; and phosphine compounds such as triphenylphosphine. These polar compounds may be used alone or in combination of two or more.

In the polymerization process, from the viewpoint of productivity, the polymerization temperature is preferably 0°C or higher, more preferably 120°C or lower, and particularly preferably 50°C or higher and 100°C or lower. By keeping the temperature in this range, it tends to be possible to ensure a sufficient amount of reaction of the coupling agent with the active terminals after the polymerization is completed.

The amount of bound conjugated diene in the styrene-butadiene copolymer rubber or the modified styrene-butadiene copolymer rubber is not particularly limited, but is preferably from 40% by mass to 100% by mass, and more preferably from 55% by mass to 80% by mass.
In addition, the amount of bound aromatic vinyl in the styrene-butadiene copolymer rubber or the modified styrene-butadiene copolymer rubber is not particularly limited, but is preferably 0% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 45% by mass or less, even more preferably 30% by mass or more and 45% by mass or less, particularly preferably 35% by mass or more and 45% by mass or less, extremely preferably 39% by mass or more and 45% by mass or less, and most preferably 40% by mass or more and 45% by mass or less.
When the amount of bound conjugated diene and the amount of bound aromatic vinyl are within the above ranges, the wet grip performance and abrasion resistance of the tire can be improved.
The amount of bound aromatic vinyl can be measured by ultraviolet absorption of the phenyl group, and the amount of bound conjugated diene can also be calculated from the amount. Specifically, the amount is measured according to the method described in the examples below.

The reaction temperature in the reaction step is preferably the same as the polymerization temperature of the styrene-butadiene copolymer rubber, more preferably from 0° C. to 120° C., and further preferably from 50° C. to 100° C. In addition, the temperature change from the end of the polymerization step to the addition of the coupling agent is preferably 10° C. or less, more preferably 5° C. or less.
The reaction time in the reaction step is preferably 10 seconds or more, more preferably 30 seconds or more. From the viewpoint of the coupling rate, the time from the end of the polymerization step to the start of the reaction step is preferably shorter, and is more preferably within 5 minutes.

Mixing in the reaction process may be performed by mechanical stirring or stirring with a static mixer. When the polymerization process is continuous, it is preferable that the reaction process is also continuous. The reactor used in the reaction process may be, for example, a tank type or a tube type equipped with a stirrer. The coupling agent may be diluted with an inert solvent and continuously supplied to the reactor. When the polymerization process is batchwise, the coupling agent may be added to the polymerization reactor or transferred to a separate reactor for the reaction process.

In order to obtain a modified styrene-butadiene copolymer rubber having a specific high molecular weight component, the molecular weight distribution (Mw/Mn) of the styrene-butadiene copolymer rubber is preferably 1.5 or more and 2.5 or less, more preferably 1.8 or more and 2.2 or less. In addition, it is preferable that the obtained modified styrene-butadiene copolymer rubber (A2) is one in which a single peak is detected in the molecular weight curve by GPC.
When the peak molecular weight of the modified styrene-butadiene copolymer rubber by GPC is Mp ₁ and the peak molecular weight of the styrene-butadiene copolymer rubber is Mp ₂ , it is preferable that the following formula is satisfied.
(Mp ₁ /Mp ₂ )<1.8×10-12×(Mp ₂ -120×10 ⁴ ) ² +2
_Mp2 is more preferably from 20×10 ⁴ to 80×10 ⁴ , and _Mp1 is more preferably from 30×10 ⁴ to 150×10 ^4. _Mp1 and _Mp2 are determined by the method described in the examples below.

The modification rate of the modified styrene-butadiene copolymer rubber is preferably 30% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more. A modification rate of 30% by mass or more can improve the wear resistance of the tire while reducing the rolling resistance. The modification rate is measured by the method described in the examples below.

After the reaction step, a deactivator, neutralizing agent, etc. may be added to the copolymer solution as necessary. Examples of deactivators include, but are not limited to, water; alcohols such as methanol, ethanol, isopropanol, etc. Examples of neutralizing agents include, but are not limited to, carboxylic acids such as stearic acid, oleic acid, and versatic acid (a highly branched carboxylic acid mixture having 9 to 11 carbon atoms, with the main carbon atom being 10); aqueous solutions of inorganic acids, and carbon dioxide gas.
In addition, from the viewpoint of preventing gel formation after polymerization and improving stability during processing, it is preferable to add an antioxidant such as 2,6-di-tert-butyl-4-hydroxytoluene (BHT), n-octadecyl-3-(4'-hydroxy-3',5'-di-tert-butylphenol)propionate, or 2-methyl-4,6-bis[(octylthio)methyl]phenol to the modified styrene-butadiene copolymer rubber.

To further improve the processability of the modified styrene-butadiene copolymer rubber, an extender oil can be added to the modified conjugated diene copolymer as necessary. The method of adding the extender oil to the modified styrene-butadiene copolymer rubber is not limited to the following, but a method of adding the extender oil to the polymer solution, mixing, and desolvating the oil-extended copolymer solution is preferred. Examples of extender oils include aromatic oils, naphthenic oils, and paraffin oils. Among these, aromatic substitute oils having a polycyclic aromatic (PCA) content of 3% by mass or less according to the IP346 method are preferred from the viewpoints of environmental safety, prevention of oil bleeding, and wet performance. Examples of aromatic substitute oils include Treated Distillate Aromatic Extracts (TDAE) and Mild Extraction Solvate (MES) as shown in Kautschuk Gummi Kunststoffe 52(12)799 (1999), as well as Residual Aromatic Extracts (RAE).

The amount of extending oil added is not particularly limited, but is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and particularly preferably 12 parts by mass or less, per 100 parts by mass of modified styrene-butadiene copolymer rubber. The amount of extending oil added is preferably 1% by mass or more, more preferably 3% by mass or more, and particularly preferably 5% by mass or more, per 100 parts by mass of modified styrene-butadiene copolymer rubber.

The modified styrene-butadiene copolymer rubber can be obtained from the polymer solution by known methods. Examples of such methods include a method in which the solvent is separated by steam stripping or the like, the polymer is filtered, and then dehydrated and dried to obtain the polymer, a method in which the polymer is concentrated in a flashing tank and then devolatilized using a vent extruder or the like, and a method in which the polymer is directly devolatilized using a drum dryer or the like.

The content of modified styrene-butadiene copolymer rubber in the rubber component of the rubber composition for the center rubber is preferably 20 to 70 mass%, and more preferably 30 to 50 mass%. When the content of modified styrene-butadiene copolymer rubber in the rubber component is 20 mass% or more, the wet grip performance of the tire can be further improved. In addition, when the content of modified styrene-butadiene copolymer rubber in the rubber component is 70 mass% or less, the processability of the rubber composition for the center rubber can be improved.

The rubber component of the rubber composition for the center rubber preferably further contains a rubber component (other rubber component) other than the modified styrene-butadiene copolymer rubber.
The other rubber component may be at least one selected from the group consisting of natural rubber, butadiene rubber, styrene-butadiene copolymer rubber, and isoprene rubber (synthetic isoprene rubber). By including the other rubber component, the wet grip property and abrasion resistance of the tire can be improved, and the rolling resistance can be reduced.
The other rubber component may be an unmodified rubber or a modified rubber.
The other rubber component is preferably a modified or unmodified butadiene rubber, and more preferably a modified butadiene rubber.
In other words, the rubber component of the rubber composition for the center rubber preferably contains a modified styrene-butadiene copolymer rubber and further a modified or unmodified butadiene rubber, and more preferably contains a modified styrene-butadiene copolymer rubber and further a modified butadiene rubber.

[Filler]
The rubber composition for the center rubber contains 75 parts by mass or more of silica as a filler based on 100 parts by mass of the rubber component.
When the content of silica in the rubber composition for the center rubber is 75 parts by mass or more per 100 parts by mass of the rubber component, the tire has excellent wet grip property.
From the viewpoint of further improving the wet grip performance of the tire, the content of silica in the rubber composition for the center rubber is preferably 78 parts by mass or more, more preferably 82 parts by mass or more, even more preferably 85 parts by mass or more, and still more preferably 87 parts by mass or more, per 100 parts by mass of the rubber component.
From the viewpoint of processability of the rubber composition, the content of silica in the rubber composition for the center rubber is preferably 120 parts by mass or less, more preferably 117 parts by mass or less, even more preferably 115 parts by mass or less, even more preferably 112 parts by mass or less, and even more preferably 108 parts by mass or less, per 100 parts by mass of the rubber component.

Examples of silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc., and among these, wet silica is preferred. These silicas may be used alone or in combination of two or more.
The wet silica may be precipitated silica, which is obtained by growing primary silica particles in a reaction solution at a relatively high temperature and in a neutral to alkaline pH range in the early stages of production, and then agglomerating the primary particles by controlling the reaction solution to an acidic pH range.

The silica preferably has a cetyltrimethylammonium bromide adsorption specific surface area (CTAB) of 60 to 200 m ² /g.
When the CTAB is 200 m ² /g or less, the rolling resistance is reduced and the processability and workability of the rubber composition are less likely to decrease.
The CTAB of the silica is more preferably 80 m ² /g or more, even more preferably 100 m ² /g or more, even more preferably 130 m ² /g or more, and even more preferably 140 m ² /g or more. The CTAB of the silica is more preferably 190 m ² /g or less, and even more preferably 185 m ² /g.

Cetyltrimethylammonium bromide adsorption specific surface area (CTAB) (m ² /g) means a value measured in accordance with ASTM D3765-92. However, since ASTM D3765-92 is a method for measuring the CTAB of carbon black, in the present invention, instead of the standard IRB#3 (83.0 ^{m 2} /g), a cetyltrimethylammonium bromide (hereinafter abbreviated as CE-TRAB) standard solution is separately prepared, and a silica OT (di-2-ethylhexyl sodium sulfosuccinate) solution is standardized with this, and the adsorption cross-sectional area per molecule of CE-TRAB on the silica surface is set to 0.35 nm ² , and the specific surface area (m ² /g) calculated from the amount of CE-TRAB adsorbed is taken as the CTAB value. This is because the surfaces of carbon black and silica are different, and therefore it is believed that even with the same surface area, there is a difference in the amount of CE-TRAB adsorbed.

The filler may further contain a reinforcing filler other than silica, and examples thereof include metal oxides other than silica, carbon black, and the like.
The carbon black is not particularly limited, and examples thereof include GPF, FEF, HAF, ISAF, and SAF grade carbon black. Among these, ISAF and SAF grade carbon black are preferred from the viewpoint of improving the abrasion resistance of the center rubber. These carbon blacks may be used alone or in combination of two or more.

The amount of carbon black in the rubber composition for the center rubber is not particularly limited, but is preferably in the range of 1 to 15 parts by mass, and more preferably in the range of 3 to 10 parts by mass, per 100 parts by mass of the rubber component. By making the amount of carbon black 1 part by mass or more per 100 parts by mass of the rubber component, the abrasion resistance of the tire is further improved, and by making the amount 15 parts by mass or less, the rolling resistance of the tire is less likely to increase.

The ratio of silica to the total amount of silica and carbon black (referred to as "silica ratio") is preferably 70 mass % or more.
A silica ratio of 70% by mass can contribute to improving the low loss properties of the center rubber (and thus reducing the rolling resistance) and improving the abrasion resistance.
From the viewpoint of processability of the rubber composition, the silica ratio is preferably equal to or less than 99 mass %.
From the viewpoint of improving the wear resistance of the tire while improving the processability of the rubber composition, the silica ratio is more preferably 75 to 98 mass%, even more preferably 79 to 97 mass%, and even more preferably 83 to 96 mass%.

(Silane coupling agent)
The rubber composition for the center rubber may contain a silane coupling agent in order to improve the compounding effect of silica.
As the silane coupling agent, a compound represented by the following formula (VII), a compound represented by the following formula (VIII), a compound represented by the following formula (IX), and a compound represented by the following formula (X) are preferred.
These silane coupling agents may be used alone or in combination of two or more.

Formula (VII) has the following structure:
A _m B _3-m Si-(CH ₂ ) _a -S _b -(CH ₂ ) _a -SiA _m B _3-m ... (VII)
In formula (VII), A is C _n H _2n+1 O (n is an integer from 1 to 3) or a chlorine atom, B is an alkyl group having 1 to 3 carbon atoms, m is an integer from 1 to 3, a is an integer from 1 to 9, and b is an integer of 1 or greater. However, when m is 1, B may be the same or different from each other, and when m is 2 or 3, A may be the same or different from each other.

Examples of compounds represented by formula (VII) include bis(3-triethoxysilylpropyl) tetrasulfide, bis(3-trimethoxysilylpropyl) tetrasulfide, bis(3-methyldimethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylethyl) tetrasulfide, bis(3-triethoxysilylpropyl) disulfide, bis(3-trimethoxysilylpropyl) disulfide, bis(3-triethoxysilylpropyl) trisulfide, etc.

Formula (VIII) is the following structure:
A _m B _3-m Si-(CH ₂ ) _c -Y... (VIII)
In formula (VIII), A is C _n H _2n+1 O (n is an integer of 1 to 3) or a chlorine atom, B is an alkyl group having 1 to 3 carbon atoms, Y is a mercapto group, a vinyl group, an amino group, a glycidoxy group or an epoxy group, m is an integer of 1 to 3, and c is an integer of 0 to 9. However, when m is 1, B may be the same as or different from each other, and when m is 2 or 3, A may be the same as or different from each other.

Examples of compounds represented by formula (VIII) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyl-di(tridecane-1-oxy-13-penta(ethylene oxide))ethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, etc. Commercially available products of these include, for example, the product name "VP Si363" manufactured by Evonik Degussa.

Formula (IX) has the following structure:
A _m B _3-m Si-(CH ₂ ) _a -S _b -Z ... (IX)
In formula (IX), A is C _n H _2n+1 O (n is an integer of 1 to 3) or a chlorine atom, B is an alkyl group having 1 to 3 carbon atoms, Z is a benzothiazolyl group, an N,N-dimethylthiocarbamoyl group or a methacryloyl group, m is an integer of 1 to 3, a is an integer of 1 to 9, and b is an integer of 1 or more and may have a distribution. However, when m is 1, B may be the same as or different from each other, and when m is 2 or 3, A may be the same as or different from each other.

Examples of compounds represented by formula (IX) include 3-trimethoxysilylpropyl-N,N-dimethylcarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-trimethoxysilylpropyl methacryloyl monosulfide, etc.

Formula (X) has the following structure:
R ³¹ _x R ³² _y R ³³ _z Si-R ³⁴ -S-CO-R ³⁵ ... (X)
In formula (X), R ³¹ is selected from R ³⁶ O-, R ³⁶ C(═O)O-, R ³⁶ R ³⁷ C═NO-, R ³⁶ R ³⁷ NO-, R ³⁶ R ³⁷ N-, and -(OSiR ³⁶ R ³⁷ ) _n (OSiR ³⁵ R ³⁶ R ³⁷ ), and has a carbon number of 1 to 18. However, R ³⁶ and R ³⁷ are each independently selected from an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, and an aryl group, and have a carbon number of 1 to 18, and n is 0 to 10.
R ³² is selected from hydrogen, or an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, and an aryl group.
R ³³ is —[O(R ³⁸ O) _m ] _0.5 — (wherein R ³⁸ is selected from an alkylene group and a cycloalkylene group and has 1 to 18 carbon atoms, and m is 1 to 4).
x, y, and z satisfy the relationship of x+y+2z=3, 0≦x≦3, 0≦y≦2, 0≦z≦1.
R ³⁴ is selected from an alkylene group, a cycloalkylene group, a cycloalkylalkylene group, an alkenylene group, an arylene group, and an aralkylene group, and has 1 to 18 carbon atoms.
R ³⁵ is selected from an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, an aryl group, and an aralkyl group, and has 1 to 18 carbon atoms.

In the compound represented by formula (X), in formula (X), the alkyl group in R ³² , R ³⁵ , R ³⁶ and R ³⁷ may be linear or branched, and examples of the alkyl group include a methyl group, an ethyl group, a propyl group, and an isopropyl group. The alkenyl group may be linear or branched, and examples of the alkenyl group include a vinyl group, an allyl group, and a methanyl group. Furthermore, examples of the cycloalkyl group include a cyclohexyl group and an ethylcyclohexyl group, examples of the cycloalkenyl group include a cyclohexenyl group and an ethylcyclohexenyl group, and examples of the aryl group include a phenyl group and a tolyl group. Furthermore, examples of the aralkyl group in R ⁵ include a phenethyl group.

In the above formula (X), in R ³⁴ and R ³⁸ , the alkylene group may be linear or branched, and examples of the alkylene group include a methylene group, an ethylene group, a trimethylene group, and a propylene group. In addition, an example of a cycloalkylene group is a cyclohexylene group. Furthermore, in R ³⁴ , the alkenylene group may be linear or branched, and examples of the alkenylene group include a vinylene group and a propenylene group. In addition, an example of a cycloalkylalkylene group is a cyclohexylmethylene group, and examples of an arylene group are a phenylene group, and examples of an aralkylene group are a xylylene group.
In the above formula (X), examples of the —[O(R ³⁸ O) _m ] _0.5 — group in R ³³ include a 1,2-ethanedioxy group, a 1,3-propanedioxy group, a 1,4-butanedioxy group, a 1,5-pentanedioxy group, and a 1,6-hexanedioxy group.
The compound represented by the above formula (X) can be synthesized in the same manner as the method described in JP-A-2001-505225. Alternatively, a commercially available product such as "NXT" (formula (X), R ³¹ =C ₂ H ₅ O, R ³⁴ =C ₃ H ₆ , R ³⁵ =C ₇ H ₁₅ , x=3, y=0, z=0: 3-octanoylthio-propyltriethoxysilane) manufactured by Momentive Performance Materials, Inc. can also be used.

Furthermore, among the compounds represented by the above formulas (VII), (VIII), (IX) and (X), the compounds represented by the above formulas (VIII) and (X) are preferred.

With regard to the amount of silane coupling agent in the rubber composition for the center rubber, from the viewpoint of improving the dispersibility of silica into the rubber matrix, the amount is preferably 1 part by mass or more, more preferably 4 parts by mass or more, and is preferably 20 parts by mass or less, and even more preferably 12 parts by mass or less, per 100 parts by mass of silica.

[Softener]
The rubber composition for the center rubber preferably contains a softener.
By including a softener in the rubber composition for the center rubber, the center rubber can be softened, thereby achieving excellent wet grip properties and improving the processability and workability of the rubber composition.
The softener may include oil, resin, and the like.
The content of the softener in the rubber composition for the center rubber is preferably 2 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 20 parts by mass or more, still more preferably 30 parts by mass or more, even more preferably 35 parts by mass or more, even more preferably 40 parts by mass or more, and even more preferably 45 parts by mass or more, per 100 parts by mass of the rubber component.
The content of the softener in the rubber composition for the center rubber is, per 100 parts by mass of the rubber component, preferably 85 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 78 parts by mass or less, even more preferably 72 parts by mass or less, and even more preferably 68 parts by mass or less.
By setting the content of the softener to 2 parts by mass or more per 100 parts by mass of the rubber component, the wet grip performance of the tire can be improved, and by setting the content to 85 parts by mass or less, a decrease in the rigidity of the tire can be suppressed.
In addition, the "content of the softener in the rubber composition for the center rubber" includes the content of the softener blended together with the rubber component as a softener, as well as the content of the extender oil blended in advance in the rubber component.

(oil)
Examples of oils include mineral oils derived from minerals, aromatic oils derived from petroleum, paraffin oils, naphthenic oils, palm oils derived from natural products, and octyl oleate.

(resin)
As the resin, it is preferable to use a thermoplastic resin.
When the rubber composition for the center rubber contains a thermoplastic resin as a softener, the wet grip performance of the tire can be improved and the rolling resistance can be reduced.

Resins include _C5 resins, _C5 - _C9 resins, _C9 resins, dicyclopentadiene resins, terpene phenol resins, terpene resins, rosin resins, and alkylphenol resins.
Among them, at least one selected from the group consisting of _C5 resin, _C5 - _C9 resin, _C9 resin, dicyclopentadiene resin, rosin resin, and alkylphenol resin is preferable.
When the resin contains at least one of a _C5 resin, a _C5 - _C9 resin, a _C9 resin, a dicyclopentadiene resin, a terpene phenol resin, a terpene resin, a rosin resin, and an alkylphenol resin, the wet grip performance of the tire can be further improved.

Among the resins, _C5 resins, _C5 - _C9 resins and _C9 resins are particularly preferred. _C5 - _C9 resins and _C9 resins have high compatibility with natural rubber, and further increase the effect of increasing the elastic modulus of the rubber composition in the low strain region and the effect of decreasing the elastic modulus of the vulcanized rubber in the high strain region, thereby enabling further improvement in the wet grip performance of the tire.
The resins may be used alone or in combination of two or more.

_C5 resin refers to _C5 synthetic petroleum resin, and examples of the _C5 resin include aliphatic petroleum resins obtained by polymerizing a _C5 fraction obtained by thermal cracking of naphtha in the petrochemical industry using a Friedel-Crafts catalyst such as AlCl ₃ or BF _3. The _C5 fraction usually includes olefinic hydrocarbons such as 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene, and diolefinic hydrocarbons such as 2-methyl-1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene, and 3-methyl-1,2-butadiene. As the _C5 -based resin, commercially available products can be used. For example, the “ESCOLETS (registered trademark) 1000 series” which is an aliphatic petroleum resin manufactured by ExxonMobil Chemical Corporation, “A100, B170, M100, R100” of the “Quinton (registered trademark) 100 series” which is an aliphatic petroleum resin manufactured by Zeon Corporation, and “T-REZ RA100” manufactured by Tonen Chemical Industry Co., Ltd. can be mentioned.

_C5 - _C9 resin refers to _C5 - _C9 synthetic petroleum resin. Examples of _C5 - _C9 resin include solid polymers obtained by polymerizing petroleum-derived _C5 fraction and _C9 fraction using Friedel-Crafts catalysts such as _AlCl3 and _BF3 , and more specifically, copolymers mainly composed of styrene, vinyltoluene, α-methylstyrene, indene, etc. As the _C5 - _C9 resin, a resin with a small amount of _C9 or more components is preferable from the viewpoint of compatibility with the rubber component. Here, "small amount of C9 or more components" means that the amount of _{C9 or} more components in the total amount of the resin is less than 50 mass%, preferably 40 mass% or less. As the _C5 - _C9 resin, commercially available products can be used, for example, products under the trade name "Quinton (registered trademark) G100B" (manufactured by Zeon Corporation), the trade name "ECR213" (manufactured by ExxonMobil Chemical Corporation), and the trade name "T-REZ RD104" (manufactured by Tonen Chemical Industry Co., Ltd.).

The _C9 resin is, for example, a resin obtained by polymerizing aromatic compounds having 9 carbon atoms, the main monomers of which are vinyltoluene, alkylstyrene, and indene, which are _C9 fractions by-produced together with petrochemical basic raw materials such as ethylene and propylene by thermal decomposition of naphtha in the petrochemical industry. Specific examples of _C9 fractions obtained by thermal decomposition of naphtha include vinyltoluene, α-methylstyrene, β-methylstyrene, γ-methylstyrene, o-methylstyrene, p-methylstyrene, and indene. The _C9 resin can be obtained by copolymerizing the mixture of these _{C8 to C10 fractions} as they are, for example, with a Friedel-Crafts catalyst, using as raw materials the _C9 fraction, C8 fractions such as styrene, _C10 fractions such as methylindene and 1,3-dimethylstyrene, and further naphthalene, vinylnaphthalene, vinylanthracene, and p-tert-butylstyrene. The _C9 resin may be a modified petroleum resin modified with a compound having a hydroxyl group, an unsaturated carboxylic acid compound, etc. Commercially available products can be used as the _C9 resin. For example, examples of unmodified _C9 petroleum resins include those under the trade names "Nippon Oil Neopolymer (registered trademark) L-90", "Nippon Oil Neopolymer (registered trademark) 120", "Nippon Oil Neopolymer (registered trademark) 130", and "Nippon Oil Neopolymer (registered trademark) 140" (manufactured by JX Nippon Oil & Energy Corporation).

Dicyclopentadiene resin is a petroleum resin produced using dicyclopentadiene, obtained by dimerizing cyclopentadiene, as the main raw material. Commercially available dicyclopentadiene resins can be used, such as 1105, 1325, and 1340 of the Quinton (registered trademark) 1000 series, which is an alicyclic petroleum resin manufactured by Zeon Corporation.

Terpene phenol resins can be obtained, for example, by reacting terpenes with various phenols using a Friedel-Crafts catalyst, or by further condensing with formalin. There are no particular limitations on the terpenes used as raw materials, and monoterpene hydrocarbons such as α-pinene and limonene are preferred, and those containing α-pinene are more preferred, and α-pinene is particularly preferred. As the terpene phenol resin, commercially available products can be used, such as those under the trade names "Tamanol 803L" and "Tamanol 901" (manufactured by Arakawa Chemical Industries Co., Ltd.), the product names "YS Polystar (registered trademark) U" series, "YS Polystar (registered trademark) T" series, "YS Polystar (registered trademark) S" series, "YS Polystar (registered trademark) G" series, "YS Polystar (registered trademark) N" series, "YS Polystar (registered trademark) K" series, and "YS Polystar (registered trademark) TH" series (manufactured by Yasuhara Chemical Co., Ltd.).

Terpene resins are solid resins obtained by blending turpentine oil, which is obtained at the same time as rosin is obtained from pine trees, or polymerization components separated from this, and polymerizing them using a Friedel-Crafts catalyst, and examples of such resins include β-pinene resin and α-pinene resin. Commercially available terpene resins can be used, such as the "YS Resin" series (PX-1250, TR-105, etc.) manufactured by Yasuhara Chemical Co., Ltd. and the "Picolite" series (A115, S115, etc.) manufactured by Hercules.

Rosin resin is the residue remaining after collecting balsams such as pine resin (pine tar), which is the sap of plants in the pine family, and distilling turpentine essential oil. It is a natural resin whose main component is rosin acid (abietic acid, palustric acid, isopimaric acid, etc.), as well as modified and hydrogenated resins that are processed by modifying or hydrogenating them. Examples include natural resin rosin, its polymerized rosin, and partially hydrogenated rosin; glycerin ester rosin, its partially hydrogenated rosin, fully hydrogenated rosin, and polymerized rosin; pentaerythritol ester rosin, its partially hydrogenated rosin, and polymerized rosin. Natural resin rosins include gum rosin, tall oil rosin, and wood rosin, which are contained in raw pine tar and tall oil. The rosin resin may be a commercially available product, and examples thereof include those available under the trade name "Neotoru 105" (manufactured by Harima Chemical Co., Ltd.), those available under the trade name "SN Tac 754" (manufactured by San Nopco Ltd.), those available under the trade name "Lime Resin No. 1", "Pensel A" and "Pensel AD" (manufactured by Arakawa Chemical Industries, Ltd.), those available under the trade name "Polypale" and "Pentalin C" (manufactured by Eastman Chemical Co., Ltd.), and those available under the trade name "Hi-Rosin (registered trademark) S" (manufactured by Taishamatsu Oil Co., Ltd.).

The alkylphenol resin is obtained, for example, by a condensation reaction of alkylphenol and formaldehyde in the presence of a catalyst. Commercially available alkylphenol resins are available, such as those under the trade name "Hitanol 1502P" (alkylphenol formaldehyde resin, manufactured by Hitachi Chemical Co., Ltd.), "Tackirol 201" (alkylphenol formaldehyde resin, manufactured by Taoka Chemical Co., Ltd.), "Tackirol 250-I" (brominated alkylphenol formaldehyde resin, manufactured by Taoka Chemical Co., Ltd.), "Tackirol 250-III" (brominated alkylphenol formaldehyde resin, manufactured by Taoka Chemical Co., Ltd.), and the trade names "R7521P", "SP1068", "R7510PJ", "R7572P" and "R7578P" (manufactured by SI GROUP INC.).

The ratio of the resin in the total amount of the softener is preferably 20 to 90 mass %.
When the ratio of the resin in the total amount of the softener is 20% by mass or more, the wet grip performance of the tire is improved, and when it is 90% by mass or less, the decrease in the elastic modulus of the center rubber can be suppressed.
The proportion of the resin in the total amount of the softener is more preferably 20 to 70 mass %, further preferably 20 to 50 mass %, and even more preferably 20 to 35 mass %.

In addition to the rubber components, fillers, softeners, and silane coupling agents described above, the rubber composition for the center rubber may contain compounding agents commonly used in the rubber industry, such as stearic acid, antioxidants, zinc oxide (zinc oxide), vulcanization accelerators, vulcanizing agents, etc., appropriately selected within the scope that does not impair the objectives of the present invention.

The component compositions of the shoulder rubber rubber composition constituting the shoulder rubber and other rubber compositions such as rubber compositions constituting other tire parts are not particularly limited.
The other rubber composition may contain the rubber component, filler, softener, and silane coupling agent that the rubber composition for the center rubber may contain, and may also contain stearic acid, an antioxidant, zinc oxide (zinc white), a vulcanization accelerator, a vulcanizing agent, etc.
The rubber component of the other rubber composition may not contain a modified styrene-butadiene copolymer rubber. Also, the content of silica in the rubber composition may be 75 parts by mass or less (including 0 part by mass) per 100 parts by mass of the rubber component.

From the viewpoint of grip, it is preferable that the total amount of softener in the rubber composition for the shoulder rubber is greater than the total amount of softener in the rubber composition for the center. The rubber composition for the shoulder rubber does not have to contain modified styrene-butadiene copolymer rubber as a rubber component.

The tire of the present invention can be used for various purposes, not limited to applications such as two-wheeled vehicles and four-wheeled vehicles, but the effects of the present invention can be easily achieved by using it for two-wheeled vehicles in particular.
When used as a motorcycle tire, it may be a front tire or a rear tire, but in the present invention, since it is possible to achieve high levels of both wet grip performance and wear resistance of the tread, the effects of the present invention are particularly likely to be achieved when applied to a rear tire.
The type of motorcycle is not particularly limited and can be appropriately selected depending on the purpose.
Examples of such vehicles include racing motorcycles, motorcycles for general public roads, on-road motorcycles, off-road motorcycles, etc. Among these, motorcycles in which the effects of the present invention are particularly likely to be realized are preferred for general public roads and on-road motorcycles, and more preferred are motorcycles for general public roads.

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

<Preparation of Rubber Composition>
(1) Comparative Example 1 and Examples 1 to 2
A rubber composition for a shoulder tread was prepared in the compounding ratio (parts by mass) shown in Table 1, and a rubber composition for a center tread was prepared in the compounding ratio (parts by mass) shown in Table 2.
(2) Comparative Examples 2 to 4 and Examples 3 to 6
A rubber composition for a tread of a shoulder portion is prepared in the compounding ratio (parts by mass) shown in Table 1, and a rubber composition for a tread of a center portion is prepared in the compounding ratio (parts by mass) shown in Table 2.

[Rubber composition for shoulder rubber]
(1) Comparative Example 1 and Examples 1 and 2
According to the compounding recipe shown in Table 1, a rubber composition for shoulder rubber was produced using a conventional Banbury mixer.
(2) Comparative Examples 2 to 4 and Examples 3 to 6
According to the compounding recipe shown in Table 1, a rubber composition for shoulder rubber is produced using a conventional Banbury mixer.
The components in Table 1 are as follows.
BR: Polybutadiene rubber: manufactured by JSR Corporation, product name "BR01"
SBR: Styrene-butadiene copolymer rubber, manufactured by JSR Corporation, emulsion-polymerized styrene-butadiene copolymer rubber, product name "HP755B"
Carbon black: Asahi Carbon Co., Ltd., product name "ASAHI #105"
Silica: Product name "Nipsil AQ" manufactured by Tosoh Silica Corporation
Softener: Tonen Chemical Co., Ltd., product name "T-REZ RD104" and JX Nippon Oil & Energy Corporation, product name "Oil A/O MIX"
Antiaging agent: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., under the trade name "Nocrac 6C" is included.
Vulcanization package: Contains stearic acid, zinc oxide, thiuram accelerator, and vulcanizing agent.

In addition, the "total amount of softener" in Table 1 means the combined amount of 30 parts by mass of the softener in the compounding components and 32 parts by mass of the oil extender in the rubber component.

[Rubber composition for center rubber]
(1) Comparative Example 1 and Examples 1 and 2
According to the compounding recipe shown in Table 2, a rubber composition for a center rubber was produced using a conventional Banbury mixer.
(2) Comparative Examples 2 to 4 and Examples 3 to 6
According to the compounding recipe shown in Table 2, a rubber composition for a center rubber is produced using a conventional Banbury mixer.
The components in Table 2 are as follows:

1. Rubber Component (1) BR: butadiene rubber, manufactured by JSR Corporation, product name "BR01"
(2) Modified BR: Modified butadiene rubber, manufactured by JSR Corporation, product name "JSR BR54"
(3) SBR: styrene-butadiene copolymer rubber, manufactured by JSR Corporation, emulsion-polymerized styrene-butadiene copolymer rubber, product name "HP755B", containing 37.5 parts by mass of oil per 100 parts by mass of rubber component, bound styrene content = 39.5% by mass, bound vinyl content = 38.5% by mass
(4) Modified SBR: Modified styrene-butadiene copolymer rubber synthesized by the following method, containing 10.0 parts by mass of oil per 100 parts by mass of rubber component, weight average molecular weight (Mw) = 85.2 x 10 ⁴ , proportion of molecular weight from 200 x 10 ⁴ to 500 x 10 ⁴ = 4.6%
Shrinkage factor (g') = 0.59, glass transition temperature (Tg) = -25°C

2. Filler CB: Carbon black, manufactured by Asahi Carbon Co., Ltd., product name "ASAHI #105"
Silica: Tosoh Silica Corporation, product name "Nipsil AQ", CTAB165

3. Other component oil: JX Nippon Oil & Energy Corporation, product name "A/O MIX"
Resin: _C5 - _C9 resin Silane coupling agent: Shin-Etsu Chemical Co., Ltd., product name "ABC-856"
Antiaging agent: Contains at least N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, product name "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization package: Contains guanidine vulcanization accelerator, thiuram vulcanization accelerator, sulfide vulcanization accelerator, stearic acid, zinc oxide and sulfur

The synthesized modified styrene-butadiene copolymer rubber is analyzed for the amount of bound styrene, the microstructure of the butadiene portion, the molecular weight, the shrinkage factor (g'), Mooney viscosity, the glass transition temperature (Tg), the modification rate, the presence or absence of nitrogen atoms, and the presence or absence of silicon atoms using the following methods.

(1) Bound styrene content: 100 mg of modified styrene-butadiene copolymer rubber is used as a sample, and chloroform is added to make a measuring sample, and the sample is dissolved in chloroform to prepare a measurement sample. The bound styrene content (mass%) relative to 100 mass% of the sample is measured based on the amount of absorption of ultraviolet light by the phenyl group of styrene at a wavelength (near 254 nm) (Shimadzu Corporation spectrophotometer "UV-2450").

(2) Microstructure of butadiene portion (1,2-vinyl bond content)
A measurement sample is prepared by dissolving 50 mg of a modified styrene-butadiene copolymer rubber in 10 mL of carbon disulfide. Using a solution cell, an infrared spectrum is measured in the range of 600 to 1000 cm ^-1 , and the microstructure of the butadiene portion, i.e., the amount of 1,2-vinyl bonds (mol%) is calculated from the absorbance at a predetermined wave number according to the calculation formula of the Hampton method (method described in R.R. Hampton, Analytical Chemistry 21, 923 (1949)) (Fourier transform infrared spectrophotometer "FT-IR230" manufactured by JASCO Corporation).

(3) Molecular Weight Using a styrene-butadiene copolymer rubber or modified styrene-butadiene copolymer rubber as a sample, a GPC measuring device (manufactured by Tosoh Corporation under the trade name "HLC-8320GPC") in which three columns using polystyrene-based gel as a packing material are connected is used to measure a chromatogram using an RI detector (manufactured by Tosoh Corporation under the trade name "HLC8020"). Based on a calibration curve obtained using standard polystyrene, the weight average molecular weight (Mw), number average molecular weight (Mn), molecular weight distribution (Mw/Mn), the peak top molecular weight (Mp ₁ ) of the modified styrene-butadiene copolymer rubber, the peak top molecular weight (Mp ₂ ) of the styrene-butadiene copolymer rubber, and the ratio (Mp ₁ /Mp ₂ ), and the proportion of molecular weights of 200×10 ⁴ or more and 500×10 ⁴ or less are obtained. THF (tetrahydrofuran) containing 5 mmol/L triethylamine is used as the eluent. The columns are three columns of Tosoh Corporation's product name "TSKgel SuperMultiporeHZ-H", and a guard column of Tosoh Corporation's product name "TSKguardcolumn SuperMP(HZ)-H" is connected in front of them. 10 mg of the sample to be measured is dissolved in 10 mL of THF to prepare a measurement solution, and 10 μL of the measurement solution is injected into the GPC measurement device and measured under conditions of an oven temperature of 40° C. and a THF flow rate of 0.35 mL/min.
The peak top molecular weights ( _Mp1 and _Mp2 ) are determined as follows: A peak that is detected as the highest molecular weight component in the GPC curve obtained by measurement is selected. For the selected peak, the molecular weight corresponding to the maximum value of the peak is calculated and used as the peak top molecular weight.
The proportion of molecular weights of 200×10 ⁴ or more and 500×10 ⁴ or less is calculated by subtracting the proportion of molecular weights less than 200×10 ⁴ from the proportion of molecular weights of 500×10 ⁴ or less based on the integrated molecular weight distribution curve.

(4) Contraction factor (g')
Using a modified styrene-butadiene copolymer rubber as a sample, a GPC measuring device (trade name "GPCmax VE-2001" manufactured by Malvern) having three columns packed with polystyrene gel connected together is used to measure using three detectors connected in this order: a light scattering detector, an RI detector, and a viscosity detector (trade name "TDA305" manufactured by Malvern). Based on standard polystyrene, the absolute molecular weight is determined from the results of the light scattering detector and the RI detector, and the intrinsic viscosity is determined from the results of the RI detector and the viscosity detector.
The linear polymer is used according to the intrinsic viscosity [η] = -3.883M ^0.771 , and the shrinkage factor (g') is calculated as the ratio of the intrinsic viscosity corresponding to each molecular weight. The eluent is THF containing 5 mmol/L triethylamine. The columns are connected to Tosoh Corporation's product names "TSKgel G4000HXL", "TSKgel G5000HXL", and "TSKgel G6000HXL". 20 mg of the sample to be measured is dissolved in 10 mL of THF to prepare a measurement solution, and 100 μL of the measurement solution is injected into the GPC measurement device and measured under the conditions of an oven temperature of 40°C and a THF flow rate of 1 mL/min.

(5) Mooney Viscosity Using a styrene-butadiene copolymer rubber or modified styrene-butadiene copolymer rubber as a sample, a Mooney viscometer (trade name "VR1132" manufactured by Ueshima Seisakusho Co., Ltd.) is used to measure the Mooney viscosity in accordance with JIS K6300 using an L-shaped rotor. The measurement temperature is 110°C when a styrene-butadiene copolymer rubber is used as the sample, and 100°C when a modified styrene-butadiene copolymer rubber is used as the sample. First, the sample is preheated at the test temperature for 1 minute, and then the rotor is rotated at 2 rpm, and the torque after 4 minutes is measured to obtain the Mooney viscosity (ML ₍₁₊₄₎ ).

(6) Glass transition temperature (Tg)
Using a modified styrene-butadiene copolymer rubber as a sample, a DSC curve is recorded using a differential scanning calorimeter "DSC3200S" manufactured by Mac Science in accordance with ISO 22768:2006 while heating from -100°C at 20°C/min under a helium flow of 50 mL/min, and the peak top (inflection point) of the DSC differential curve is taken as the glass transition temperature.

(7) Modification rate: Using modified styrene-butadiene copolymer rubber as a sample, the rate is measured by applying the property of the modified basic polymer component being adsorbed to a GPC column packed with silica-based gel. The amount of the sample solution containing the sample and low molecular weight internal standard polystyrene adsorbed to the silica-based column is measured from the difference between the chromatogram measured with a polystyrene-based column and the chromatogram measured with a silica-based column, and the modification rate is calculated. Specifically, it is as shown below.
Preparation of sample solution: 10 mg of a sample and 5 mg of standard polystyrene are dissolved in 20 mL of THF to prepare a sample solution.

GPC measurement conditions using a polystyrene column: Using a Tosoh Corporation product name "HLC-8320GPC", 10 μL of sample solution was injected into the device using THF containing 5 mmol/L triethylamine as the eluent, and a chromatogram was obtained using an RI detector under the conditions of a column oven temperature of 40°C and a THF flow rate of 0.35 mL/min. Three Tosoh Corporation product name "TSKgel SuperMultiporeHZ-H" columns were connected, and a Tosoh Corporation product name "TSKguardcolumn SuperMP(HZ)-H" was connected in front of them as a guard column.

GPC measurement conditions using a silica-based column: Using a Tosoh Corporation product name "HLC-8320GPC", THF is used as the eluent, 50 μL of the sample solution is injected into the device, and a chromatogram is obtained using an RI detector under the conditions of a column oven temperature of 40° C. and a THF flow rate of 0.5 ml/min. The columns are connected and used with product names "Zorbax PSM-1000S", "PSM-300S", and "PSM-60S", and a product name "DIOL 4.6×12.5 mm 5 micron" is connected to the front stage as a guard column.
Calculation method of modification rate: The total peak area of the chromatogram using a polystyrene-based column is set to 100, the peak area of the sample is set to P1, the peak area of the standard polystyrene is set to P2, the total peak area of the chromatogram using a silica-based column is set to 100, the peak area of the sample is set to P3, and the peak area of the standard polystyrene is set to P4, and the modification rate (%) is calculated from the following formula.
Denaturation rate (%) = [1 - (P2 x P3) / (P1 x P4)] x 100
(where P1 + P2 = P3 + P4 = 100)

(8) Presence or Absence of Nitrogen Atoms The same measurement as in (7) above is carried out, and when the calculated modification rate is 10% or more, it is determined that nitrogen atoms are present.

(9) Presence or absence of silicon atoms 0.5 g of modified styrene-butadiene copolymer rubber is used as a sample, and is measured using an ultraviolet-visible spectrophotometer (manufactured by Shimadzu Corporation under the trade name "UV-1800") in accordance with JIS K 0101 44.3.1, and quantified by molybdenum blue absorptiometry. If silicon atoms are detected (detection limit 10 ppm by mass), it is determined that silicon atoms are present.

(Synthesis of modified styrene-butadiene copolymer rubber)
The polymerization reactor was a tank-type pressure vessel having an internal volume of 10 L, an internal height (L) to diameter (D) ratio (L/D) of 4.0, an inlet at the bottom, an outlet at the top, and a jacket for temperature control as a tank-type reactor with a stirrer. 1,3-butadiene, which had been previously dehydrated, was mixed at 17.2 g/min, styrene at 10.5 g/min, and n-hexane at 145.3 g/min. In a static mixer provided in the middle of the piping supplying this mixed solution to the inlet of the reaction unit, n-butyllithium for inactivating remaining impurities was added at 0.117 mmol/min, mixed, and then continuously supplied to the bottom of the reaction unit. Furthermore, 2,2-bis(2-oxolanyl)propane as a polar substance was supplied at a rate of 0.019 g/min, and n-butyllithium as a polymerization initiator was supplied at a rate of 0.242 mmol/min to the bottom of the polymerization reactor where the mixture was vigorously mixed with the stirrer, and the polymerization reaction was continued continuously. The temperature was controlled so that the temperature of the polymerization solution at the top outlet of the reactor was 75° C. When the polymerization became sufficiently stable, a small amount of the polymer solution before the addition of the coupling agent was withdrawn from the top outlet of the reactor, and an antioxidant (BHT) was added in an amount of 0.2 g per 100 g of the polymer, after which the solvent was removed and the Mooney viscosity at 110° C. and various molecular weights were measured.

Next, tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine diluted to 2.74 mmol/L as a coupling agent was continuously added at a rate of 0.0302 mmol/min (n-hexane solution containing 5.2 ppm of water) to the polymer solution flowing out from the outlet of the reactor, and the polymer solution to which the coupling agent was added was mixed by passing through a static mixer to undergo a coupling reaction. At this time, the time until the coupling agent was added to the polymer solution flowing out from the outlet of the reactor was 4.8 minutes, the temperature was 68°C, and the difference between the temperature in the polymerization step and the temperature before the modifier was added was 7°C. An antioxidant (BHT) was continuously added to the polymer solution that had undergone the coupling reaction at 0.055 g/min (n-hexane solution) so that the amount was 0.2 g per 100 g of polymer, and the coupling reaction was terminated. Simultaneously with the antioxidant, oil (JOMO Process NC140 manufactured by JX Nippon Oil & Energy Corporation) was continuously added so that the amount was 10.0 g per 100 g of the polymer, and mixed with a static mixer. The solvent was removed by steam stripping to obtain a modified styrene-styrene-butadiene copolymer rubber (modified SBR).
It was confirmed by the above method that the modified SBR obtained contained nitrogen atoms and silicon atoms.
The modified SBR has a "degree of branching," which corresponds to the number of branches estimated from the number of functional groups of the coupling agent and the amount added, of 8 (this can also be confirmed from the value of the shrinkage factor), and has a "number of SiOR residues," which corresponds to the value obtained by subtracting the number of SiOR groups reduced by reaction from the total number of SiOR groups in one molecule of the coupling agent, of 4.

<Tire manufacturing>
(1) Comparative Example 1 and Examples 1 to 2
Using each rubber composition for tread, a prototype motorcycle tire (size: 180/55ZR17) was produced in a conventional manner, which had a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, and the tread portion was divided into three in the tire width direction by a center portion including the tire equatorial plane and a pair of shoulder portions including the tread ends, and the tread of the motorcycle tire was formed from the rubber composition.

(2) Comparative Examples 2 to 4 and Examples 3 to 6
Using each of the prepared rubber compositions for treads, a prototype motorcycle tire (size: 180/55ZR17) was produced in a conventional manner, having a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, with the tread portion being divided into three in the tire width direction by a center portion including the tire equatorial plane and a pair of shoulder portions including the tread ends, and the tread of the motorcycle tire was formed from the rubber compositions.

<Evaluation>
(1) Comparative Example 1 and Examples 1 to 2
For each rubber composition for tread used in the tread of a two-wheeled tire, the abrasion resistance and wet grip property were evaluated as follows.

(2) Comparative Examples 2 to 4 and Examples 3 to 6
For each rubber composition for tread used in the tread of a two-wheeled tire, the abrasion resistance and wet grip performance are evaluated as follows.

1. Abrasion Resistance (1) Comparative Example 1 and Examples 1-2
A test rider drove the vehicle 3,500 km at 80 km/h on a paved test course. After the run, the remaining groove depth was measured and the tire wear resistance was evaluated from the remaining groove depth. The evaluation results are shown in the "Wear Resistance" column in Table 2.
The evaluation result of Comparative Example 1 was set at 100, and an index was calculated as a relative evaluation.
A larger index indicates higher abrasion resistance. The acceptable range is 110 or more.

(2) Comparative Examples 2 to 4 and Examples 3 to 6
A test rider drives the vehicle 3,500 km at 80 km/h on a paved test course. After the run, the remaining groove depth is measured and the tire wear resistance is evaluated based on the remaining groove depth. The evaluation results are shown in the "Wear Resistance" column of Table 2.
The evaluation result of Comparative Example 1 is set to 100, and an index is calculated as a relative evaluation.
A higher index indicates higher abrasion resistance. The acceptable range is 110 or more.

2. Wet grip (grip on wet surfaces)
(1) Comparative Example 1 and Examples 1 to 2
A test rider performed various driving tests on a wet road course and evaluated the feeling of the wet grip of the tire while driving. The evaluation results are shown in the "Wet Grip" column of Table 2.
The evaluation result of Comparative Example 1 was set as 100, and an index was calculated as a relative evaluation.
The higher the index, the better the tire's wet grip performance. The acceptable range was set at 102 or more.

(2) Comparative Examples 2 to 4 and Examples 3 to 6
A test rider performs various driving tests on a wet road course and evaluates the feeling of the wet grip of the tire while driving. The evaluation results are shown in the "Wet Grip" column of Table 2.
The evaluation result of Comparative Example 1 is set to 100, and an index is calculated as a relative evaluation.
The higher the index, the better the tire's wet grip performance. The acceptable range is 102 or more.

3. Storage modulus (E') and loss tangent (tan δ) of center rubber
(1) Comparative Example 1 and Examples 1 to 2
Using vulcanized rubber test pieces obtained by vulcanizing the rubber compositions for the center rubber of the Examples and Comparative Examples, the dynamic elastic modulus (E') and loss tangent (tan δ) of the center rubber were measured using a viscoelasticity measuring device.
The dynamic elastic modulus was measured by measuring the storage modulus _E'0.1 at 25°C, a frequency of 52 Hz, and a strain of 0.1%, and the storage modulus _E'4 at 25°C, a frequency of 52 Hz, and a strain of 4%, and calculating the difference ΔE' (= _E'0.1 - _E'4 ). ΔE'/ _E'4 was calculated from the obtained _E'4 and ΔE'.
The loss tangent (tan δ) of the center rubber was measured under the conditions of a temperature of 30° C., a strain of 1%, and a frequency of 52 Hz. The larger the value, the better the grip.

(2) Comparative Examples 2 to 4 and Examples 3 to 6
Using vulcanized rubber test pieces obtained by vulcanizing the rubber compositions for the center rubber of the Examples and Comparative Examples, the dynamic elastic modulus (E') and loss tangent (tan δ) of the center rubber are measured using a viscoelasticity measuring device.
The dynamic elastic modulus is measured by measuring a storage modulus _E'0.1 at 25°C, a frequency of 52 Hz, and a strain of 0.1%, and a storage modulus _E'4 at 25°C, a frequency of 52 Hz, and a strain of 4%, and calculating the difference ΔE' (= _E'0.1 - _E'4 ). ΔE'/ _E'4 is calculated from _E'4 and ΔE'.
The loss tangent (tan δ) of the center rubber is measured under the conditions of a temperature of 30° C., a strain of 1%, and a frequency of 52 Hz. The larger the value, the better the grip.

The amount of SBR in Table 2 is an amount including 70 parts by mass of the rubber component and 26 parts by mass of the extender oil, and the amount of modified SBR is an amount including 70 parts by mass of the rubber component and 7 parts by mass of the extender oil.
In Table 2, "total amount of oil" means the sum of the amount of oil in the compounded components and the amount of oil extended in the rubber component. "Total amount of softener" means the total amount of oil plus the amount of resin.

The results in Table 2 show that the examples show well-balanced and excellent effects in terms of wear resistance, wet grip performance and rolling resistance compared to the samples of each comparison example.

According to the present invention, it is possible to provide a tire that has excellent grip performance on wet road surfaces, while enabling reduced rolling resistance and improved wear resistance.

Claims (14)

A tire comprising a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, the tread portion being divided into at least three portions in the tire width direction by a center portion including a tire equatorial plane and a pair of shoulder portions including tread ends,
a tread rubber of the center portion is a vulcanized rubber of a rubber composition containing a rubber component including at least one modified styrene-butadiene copolymer rubber and 75 parts by mass or more of silica per 100 parts by mass of the rubber component, and wherein, when ΔE′ is the difference between the storage modulus E′ _0.1 at 25° C. and 0.1% strain of the tread rubber of the center portion and the storage modulus E′ ₄ at 25° C. and 4% strain, ΔE′/E′ ₄ is 0.900 or less;
The tire , wherein the rubber component further comprises a modified butadiene rubber . The tire according to claim 1, wherein the content of the silica in the rubber composition is 120 parts by mass or less per 100 parts by mass of the rubber component. The tire according to claim 1 or 2, wherein the rubber composition further contains carbon black, and the ratio of silica to the total amount of the silica and the carbon black is 70 mass % or more. The tire according to any one of claims 1 to 3, wherein the rubber composition further contains 2 to 85 parts by mass of a softener per 100 parts by mass of the rubber component. The tire according to claim 4, wherein the softener contains a resin, and the resin is at least one selected from the group consisting of C5 _- based resins, _C9 -based resins, _C5 - _C9 -based resins, terpene-based resins, terpene-aromatic compound-based resins, rosin-based resins, dicyclopentadiene resins, and alkylphenol-based resins. The tire according to claim 5, wherein the ratio of the resin to the total amount of the softener is 20 to 90 mass %. The modified styrene-butadiene copolymer rubber has a weight average molecular weight of 20×10 ⁴ or more and 300×10 ⁴ or less, contains 0.25 mass % or more and 30 mass % or less of modified styrene-butadiene copolymer rubber having a molecular weight of 200×10 ⁴ or more and 500×10 ⁴ or less with respect to a total amount of the modified styrene-butadiene copolymer rubber, and has a shrinkage factor (g') of less than 0.64. The tire according to any one of claims 1 to 6 . The tire according to any one of claims 1 to 7 , wherein the modified styrene-butadiene copolymer rubber has branches and a degree of branching of 5 or more. The modified styrene-butadiene copolymer rubber has one or more coupling residues and a styrene-butadiene copolymer rubber chain bonded to the coupling residues,
The tire according to claim 8 , wherein the branches include branches in which five or more of the styrene-butadiene copolymer rubber chains are bonded to one of the coupling residues. The tire according to any one of claims 1 to 9 , wherein the modified styrene-butadiene copolymer rubber is represented by the following formula (I):

[In formula (I), D represents a styrene-butadiene copolymer rubber chain. R ¹ , R ² and R ³ each independently represent a single bond or an alkylene group having 1 to 20 carbon atoms. ^{R 4} and R ⁷ each independently represent an alkyl group having 1 to 20 carbon atoms. R ⁵ , R ⁸ and R ⁹ each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. R ⁶ and R ¹⁰ each independently represent an alkylene group having 1 to 20 carbon atoms. R ¹¹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. m and x each independently represent an integer of 1 to 3, and x≦m. p represents 1 or 2. y represents an integer of 1 to 3, and y≦(p+1). z represents an integer of 1 or 2. i represents an integer of 0 to 6, j represents an integer of 0 to 6, k represents an integer of 0 to 6, and (i+j+k) is an integer of 3 to 10. ((x×i)+(y×j)+(z×k)) is an integer of 5 to 30. A represents a hydrocarbon group having 1 to 20 carbon atoms, or an organic group having at least one atom selected from the group consisting of oxygen atoms, nitrogen atoms, silicon atoms, sulfur atoms, and phosphorus atoms, and having no active hydrogen.] The tire according to claim 10 , wherein in the formula (I), A is represented by the following formula (II), the following formula (III), the following formula (IV), or the following formula (V):




In formula (II), ^B1 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10.
In formula (III), ^B2 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, ^B3 represents an alkyl group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10.
In formula (IV), ^B4 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10.
In formula (V), ^B5 represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10. The tire according to any one of claims 1 to 11 , wherein the modified styrene-butadiene copolymer rubber is obtained by reacting a styrene-butadiene copolymer rubber with a coupling agent represented by the following formula (VI):

[In formula (VI), R ¹² , R ¹³ and R ¹⁴ each independently represent a single bond or an alkylene group having 1 to 20 carbon atoms. R ¹⁵ , R ¹⁶ , R ¹⁷ , R ¹⁸ and R ²⁰ each independently represent an alkyl group having 1 to 20 carbon atoms. ^{R 19} and R ²² each independently represent an alkylene group having 1 to 20 carbon atoms. R ²¹ represents an alkyl group or trialkylsilyl group having 1 to 20 carbon atoms, and m represents an integer of 1 to 3. p represents 1 or 2. i, j and k each independently represent an integer of 0 to 6, with the proviso that (i+j+k) is an integer of 3 to 10. A represents a hydrocarbon group having 1 to 20 carbon atoms, or an organic group having at least one atom selected from the group consisting of an oxygen atom, a nitrogen atom, a silicon atom, a sulfur atom and a phosphorus atom, and having no active hydrogen. 〕 The tire according to claim 12, wherein the coupling agent represented by formula (VI) is at least one selected from the group consisting of tetrakis[3-(2,2-dimethoxy-1-aza-2-silacyclopentane)propyl]-1,3-propanediamine, tetrakis(3-trimethoxysilylpropyl)-1,3-propanediamine, and tetrakis(3-trimethoxysilylpropyl) -1,3 -bisaminomethylcyclohexane. The tire according to any one of claims 4 to 13 , wherein the content of the softener in the rubber composition is 72 parts by mass or less per 100 parts by mass of the rubber component.