WO2021200098A1 - Tire - Google Patents

Abstract

Provided is a tire comprising a pair of beads, a pair of sidewalls, and a tread communicating with both sidewalls, the tread being divided into at least three sections in the tire width direction by a center part that includes the tire equatorial plane and a pair of shoulder parts that include the tread edges, wherein the tread rubber in the center part is vulcanized rubber with a rubber composition containing a rubber component including at least one type of modified styrene-butadiene copolymer rubber and at least 75 parts by mass of silica per 100 parts by mass of the rubber component, and additionally, ΔE'/E'₄ is 0.900 or less, where ΔE' is the difference between the storage modulus E'_0.1 of the tread rubber in the center part at 25°C and 0.1% strain and the storage modulus E'₄ at 25°C and 4% strain. The tire exhibits excellent abrasion resistance and wet grip.

Description

tire

The present invention relates to a tire.

In the tire tread for two wheels, two types of tread rubber are used by dividing the tread into three in the tire width direction as a tire for motorcycles that has both the performance required for straight running and the performance required for turning to some extent. Is being developed.
For example, in Patent Document 1, a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions are provided, and the tread portion includes a center portion including a tire equatorial plane in the tire width direction. A two-wheeled vehicle tire divided into three by a pair of shoulder portions including a tread end is disclosed. In the two-wheeled vehicle tire of Patent Document 1, both the tread rubber in the center portion and the tread rubber in the shoulder portion are styrene-. A rubber component containing a butadiene rubber and a modified conjugated diene polymer, silica, and a filler containing 40 to 120 parts by mass with respect to 100 parts by mass of the rubber component, and the silica in the filler. The content is 80% by mass or more.

International Publication No. 2017/20236

In a tire tread for two wheels as shown in Patent Document 1, in addition to wear resistance, it is desired that both dry grip performance (grip performance on dry road surface) and wet grip performance (grip performance on wet road surface) are compatible. It is rare. One of the means to achieve this higher compatibility is tread division. Center rubber is required to have both wear resistance and wet grip performance at a high level, and improvement of the dispersibility of the filler in the rubber has been studied conventionally.
When the amount of the filler in the rubber was small, the dispersibility of the filler was improved and the wear resistance was improved, but it was difficult to improve the wet grip performance. Therefore, in the center rubber, there is room for further improvement in the technology for achieving both wet grip at a high level without impairing the wear resistance.

An object of the present invention is to provide a tire having excellent wear resistance and wet grip, and an object of the present invention is to solve the object.

<1> A pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions are provided, and the tread portion includes a center portion including the tire equatorial plane and a tread end in the tire width direction. In a tire that is divided into at least three by a pair of shoulders
The tread rubber in the center portion is a sulfide of a rubber composition containing a rubber component containing at least one modified styrene-butadiene copolymer rubber and 75 parts by mass or more of silica with respect to 100 parts by mass of the rubber component. a rubber, and, 25 ° C. of the tread rubber of the center portion, the storage modulus E _'0.1 and 25 ° C., the storage modulus E of a strain of 4%' of 0.1% strain differences between the ₄ 'as, Delta] E' Delta] E tire / 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, and the tread portion has a center portion including the tire equatorial plane and a tread end in the tire width direction. In a tire that is divided into three parts by a pair of shoulder parts including
The tread rubber in the center portion is a sulfide of a rubber composition containing a rubber component containing at least one modified styrene-butadiene copolymer rubber and 75 parts by mass or more of silica with respect to 100 parts by mass of the rubber component. a rubber, and, 25 ° C. of the tread rubber of the center portion, the storage modulus E _'0.1 and 25 ° C., the storage modulus E of a strain of 4%' of 0.1% strain differences between the ₄ 'as, ΔE' ΔE / E _'4 is preferably a tire is 0.900 or less.

<2> The tire according to <1>, wherein the content of the silica in the rubber composition is 120 parts by mass or less with respect to 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 the ratio of silica to the total amount of the silica and the carbon black is 70% by 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 softening agent with respect to 100 parts by mass of the rubber component.
<5> The softener comprises a resin, the resin is _{C 5} resins, _{C 9 resins,} C 5 -C ₉ resins, terpene resins, terpene - aromatics-based resin, rosin resin, The tire according to <4>, which is at least one selected from the group consisting of a dicyclopentadiene resin and an alkylphenol-based resin.
<6> The tire according to <5>, wherein the ratio of the resin to the total amount of the softener is 20 to 90% by mass.

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

<9> The tire according to any one of <1> to <8>, wherein the modified styrene-butadiene copolymer rubber has a branch and has 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 5 or more of the styrene-butadiene copolymer rubber chains are bonded to 1 of the coupling residue.
<11> The modified styrene-butadiene copolymer rubber is the tire according to any one of <1> to <10> 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 indicates 1 or 2. y represents an integer of 1 to 3, and y ≦ (p + 1). z represents an integer of 1 or 2. i indicates an integer of 0 to 6, j indicates an integer of 0 to 6, k indicates 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 has a hydrocarbon group having 1 to 20 carbon atoms or 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 has active hydrogen. Indicates an organic group that does not have.
<12> In the above formula (I), A is the tire according to <11> represented by the following formula (II), the following formula (III), the following formula (IV), or the following formula (V).

In formula (II), B ¹ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms. a represents an integer from 1 to 10.
In formula (III), B ² represents a single bond or a hydrocarbon group ^{having 1 to 20 carbon atoms, and B 3} represents an alkyl group having 1 to 20 carbon atoms. a represents an integer from 1 to 10.
In formula (IV), B ⁴ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms. a represents an integer from 1 to 10.
In formula (V), B ⁵ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms. a represents an integer from 1 to 10.
<13> The modified styrene-butadiene copolymer rubber is any one of <1> to <12> obtained by reacting the styrene-butadiene copolymer rubber with a coupling agent represented by the following formula (VI). One of the tires listed.

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 indicates 1 or 2. i, j and k each independently represent an integer of 0 to 6. However, (i + j + k) is an integer of 3 to 10. A has a hydrocarbon group having 1 to 20 carbon atoms or 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 has no active hydrogen. Indicates an organic group.

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

According to the present invention, it is possible to provide a tire having excellent wear resistance and wet grip.

The tire of the present invention includes a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions, and the tread portion includes a center portion including the tire equatorial plane and a tread end in the tire width direction. It is divided into at least three parts by a pair of shoulder portions including.
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 toroid shape. The carcass layer is formed by coating a plurality of carcass cords with rubber.
The sidewall portion extends outward from the bead portion in the tire radial direction 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, the tread portion uses a divided tread divided into a center portion and two shoulder portions sandwiching the center portion. In the divided tread, the tread portion is divided into at least three by a center portion including the equatorial plane of the tire and a pair of shoulder portions including the tread end. The divided 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 is, in order from the tread end, the first shoulder portion, the second shoulder portion, the first center portion, the second center portion, the third shoulder portion, and the fourth shoulder portion. , The center portion and the shoulder portion may be separated respectively.
The divided tread is preferably divided into three by a center portion and a pair of shoulder portions.
The tire equator is the latitude line of the tire passing through the center in the tire width direction, and the surface in the tire circumferential direction including the tire equator is called the tire equator surface.
Center section, more specifically, the width direction of the curve length of the tread portion surface (L _C) is 30-60% of the maximum length of the curve length in the width direction of the tread portion the total surface area (L _T) It is preferably present, and more preferably 40 to 50%. The width direction of the curve length of the tread portion surface (L _C) is, if it is more than 30% of the curve length The maximum length of the width direction of the tread portion the total surface area (L _T) can be secured abrasion resistance, 60% If it is the following, the deterioration of the wet grip property is not suppressed. The width direction of the curve length of the tread portion surface (L _C) is, if it is 40-50% of the curve length The maximum length of the width direction of the tread portion the total surface area (L _T), wet grip performance and abrasion resistance It is advantageous in that it has an excellent balance with.
The width direction of the curve length of the tread portion surface of the shoulder portion (L _S) can but be different from the one of the shoulder portion and the other shoulder portion, usually, preferably the same, a shoulder portion (one side the width direction of the curve length) is preferably (100-Lc) / 2% of _{L T.}

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

<Tread rubber>
Tread rubber of the center portion of the tire of the present invention (Center rubber) is, 25 ° C., the storage modulus E at 0.1% strain 'and _0.1 25 ° C., the storage modulus E of a strain of 4%' and ₄ the difference of the (E _'0.1 -E' ₄₎ as Delta] E of, ΔE '/ E' ₄ is 0.900 or less.
The center rubber is a vulcanized rubber having a rubber composition containing at least one modified styrene-butadiene copolymer rubber and 75 parts by mass or more of silica with respect to 100 parts by mass of the rubber component. ..
It is not clear why the tire of the present invention is excellent in wear resistance and wet grip property because the center rubber of the present invention has the above configuration, but it is presumed to be due to the following reason.
It is considered that the rubber composition provides dispersion reinforcement of silica and improves wear resistance. Since the rubber composition contains a large amount of silica, the tire is considered to have excellent wet performance. ΔE '/ E' ₄ from becoming smaller as the vulcanized rubber properties show that the better the dispersibility of the silica.
First, the vulcanized rubber characteristics of the center rubber will be described.

[Storage modulus difference ΔE']
As described above, the storage elastic modulus E'of the center rubber in the present invention is the storage elastic modulus E'at 25 ° C. and 0.1% strain, and the storage elastic modulus E'at _0.1 and 25 ° C. and 4% strain. 'the difference between the ₄ (E''a ₄ Delta] E _0.1 -E)' as, Delta] E '/ E' ₄ is 0.900 or less.
When ΔE '/ E' ₄ exceeds 0.900, it is impossible to improve the wear resistance and wet grip performance of the tire.
As ΔE '/ E' ₄ is small, shows that excellent dispersibility of silica in the vulcanized within the rubber matrix. Furthermore, E _'0.1 represents a possible storage modulus of the small strain. Storage modulus by the distortion changes greatly but, E _'4 exceeds an inflection point represents the storage modulus of the change in storage modulus became mild area. By making the difference firmly, you can clearly see the degree of dispersion.

ΔE '/ E' ₄ of the center rubber from the viewpoint of further improving the wear resistance and wet grip performance of the tire, preferably at least 0.22, more preferably 0.27 or more, 0.32 The above is more preferable, 0.37 or more is further preferable, and 0.42 or more is further preferable.
But not the center lower rubber ΔE '/ E' ₄ particularly limited, from the viewpoint of preventing aggregation of the filler in the vulcanized rubber, preferably at 0.89 or less, it is 0.87 or less It is more preferably 0.85 or less, and further preferably 0.85 or less.

The ΔE'of the center rubber is preferably 10.0 or less, more preferably 8.0 or less, and 6.0 or less from the viewpoint of further improving the wear resistance and wet grip property of the tire. Is more preferable.
The lower limit of ΔE'of the center rubber is not particularly limited, but from the viewpoint of preventing the filler from agglomerating in the vulcanized rubber, the ΔE'of the center rubber is preferably 0.1 or more, and 0.5 or more. It is more preferably 1.0 or more, and even more preferably 1.5 or more.

25 ° C. of the center rubber, from the viewpoint of the dispersibility of the filler in the storage modulus E _'0.1 at 0.1% strain in vulcanizates, is preferably 6.7 N / mm or more, 6 It is more preferably .8 N / mm or more, further preferably 6.9 N / mm or more, further preferably 7.0 N / mm or more, and more preferably 7.1 N / mm or more. It is 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, and even more preferably 8.2 N / mm. More preferably, it is more preferably 8.5 N / mm or more, further preferably 8.8 N / mm or more, and even more preferably 9.1 N / mm or more. , 9.3 N / mm or more, more preferably 9.5 N / mm or more, and even more preferably 9.9 N / mm or more.
25 ° C. of the center rubber, the storage modulus E _'0.1 at 0.1% strain is preferably at most 15.0 N / mm, more preferably not more than 14.5N / mm, 13. It is more preferably 8 N / mm or less, and even more preferably 13.3 N / mm or less.
The storage elastic modulus E'of the center rubber can be measured using, for example, a viscoelasticity measuring device.
Next, the rubber composition (rubber composition for center rubber) constituting 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 modified styrene-butadiene copolymer rubber and 75 parts by mass or more with respect to 100 parts by mass of the rubber component. Includes with silica.
By center rubber rubber composition is the above-mentioned configuration, ΔE '/ E' ₄ of the center rubber likely to become 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 center rubber, the rubber component contains at least one modified styrene-butadiene copolymer rubber.
Rubber component constituting the center rubber-modified styrene - by including butadiene copolymer rubber, ΔE '/ E' ₄ of the center rubber likely to become 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, 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 mentioned.
Since the modified styrene-butadiene copolymer rubber contains nitrogen atoms and silicon atoms, the processability of the rubber composition for center rubber is improved, and rolling resistance is improved while improving the wet grip property and wear resistance of the tire. It can be further reduced. The fact that the modified styrene-butadiene copolymer rubber body has a nitrogen atom can be confirmed by the method described in Examples described later by the presence or absence of adsorption to a specific column. Further, the fact that the modified styrene-butadiene copolymer rubber has a silicon atom can be confirmed by metal analysis by the method described in Examples described later.

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

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

The modified styrene-butadiene copolymer rubber preferably has a branched structure.
In general, a polymer having a branch tends to have a smaller molecular size when compared with a linear polymer having the same absolute molecular weight, and the contraction factor (g') is assumed to be the same. It is an index of the ratio of the size occupied by the molecule to the linear polymer, which is the absolute molecular weight. That is, as the degree of branching of the polymer increases, the contraction factor (g') tends to decrease. In this embodiment, the intrinsic viscosity is used as an index of the size of the molecule, and the linear polymer follows the relational expression of ^{the intrinsic viscosity [η] = -3.883M 0.771.} Modified styrene - shrinkage factor at the time of the absolute molecular weight of the butadiene copolymer rubber (g ') is calculated and shrinkage factor when the absolute molecular weight of ^{100 × 10 4 ~ 200 × 10} 4 (g' average value) , The shrinkage factor (g') of the modified styrene-butadiene copolymer rubber.
Here, the "branch" is a structure formed by directly or indirectly binding another polymer to one polymer.
The "branch degree" is the number of polymers that are directly or indirectly bonded to each other with respect to one branch. For example, when the five styrene-butadiene copolymer rubber chains described below are indirectly bonded to each other via the coupling residue described later, the degree of branching is 5.
The coupling residue is a structural unit of the modified styrene-butadiene copolymer rubber bonded to the styrene-butadiene copolymer rubber chain, and is, for example, coupled with the styrene-butadiene copolymer rubber described later. It is a structural unit derived from a coupling agent, which is produced by reacting with an agent.
The styrene-butadiene copolymer rubber chain is a constituent unit of the modified styrene-butadiene copolymer rubber, and is produced by, for example, reacting a styrene-butadiene copolymer rubber described later with a coupling agent. -A structural unit derived from butadiene copolymer rubber.

Modified styrene - butadiene copolymer rubber has a weight average molecular weight (Mw), is preferably 20 × 10 ⁴ or more 300 × 10 ⁴ or less.
By weight average molecular weight of 20 × 10 ⁴ or more, to improve the wet grip of the tire, also tends to reduce the rolling resistance. In addition, the weight average molecular weight of 300 × 10 ⁴ or less, it is possible to improve the processability of the center rubber rubber composition.
Modified styrene - weight average molecular weight of butadiene copolymer rubber is more preferably 50 × 10 ⁴ or more, still more preferably 64 × 10 ⁴ or more, more preferably more that is 80 × 10 ⁴ or more .. Further, modified styrene - weight average molecular weight of butadiene copolymer rubber is more preferably 250 × 10 ⁴ or less, still more preferably 180 × 10 ⁴ or less, more not less 0.99 × 10 ⁴ or less More preferred.
In the present specification, the "molecular weight" is 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 is measured by the method described in Examples described later.

Modified styrene - butadiene copolymer rubber, modified styrene - based on the total amount of the butadiene copolymer rubber (100 mass%), modified styrene molecular weight of 200 × 10 ⁴ or more 500 × 10 ⁴ or less - butadiene copolymer It is preferable that the rubber is contained in an amount of 0.25% by mass or more and 30% by mass or less. Hereinafter, modified styrene molecular weight of 200 × 10 ⁴ or more 500 × 10 ⁴ or less - butadiene copolymer rubbers referred to as "specific high molecular weight component".
When the content of a specific high molecular weight component in the total amount of the modified styrene-butadiene copolymer rubber is within the above range, both the wet grip property of the tire and the reduction of rolling resistance can 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% by mass or more, further preferably 1.4% by mass or more. It is more preferably 75% by mass or more, further preferably 2.0% by mass or more, further preferably 2.15% by mass or more, and more preferably 2.5% by mass or more. Even more preferable.
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, further preferably 25% by mass or less, and 20% by mass or less. Is even more preferable, and 18% by mass or less is even more preferable.
A modified styrene-butadiene copolymer rubber having a specific high molecular weight component content in 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 later.
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. Further, in the polymerization step, a method having a residence time distribution can be used in both the continuous type and the batch type polymerization modes. That is, it is preferable to widen the time distribution of the growth reaction.

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 1.6 or more and 3.0 or less. Is preferable. 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 a specific high molecular weight component with respect to the modified styrene-butadiene copolymer rubber and the styrene-butadiene copolymer rubber described later are described in Examples described later. Measure by method.

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 center rubber can be improved.
The shrinkage factor (g') of the modified styrene-butadiene copolymer rubber is more preferably 0.63 or less, further preferably 0.60 or less, and even more preferably 0.59 or less. , 0.57 or less, more preferably.
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 less 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, still more preferably 0.35 or more, and even more preferably 0.35 or more. It is 0.45 or more.

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

The modified styrene-butadiene copolymer rubber preferably has bifurcation and a degree of bifurcation of 5 or more. Further, the modified styrene-butadiene copolymer rubber has one or more coupling residues and a styrene-butadiene copolymer rubber bonded to the coupling residues, and further, the branching is 1. It is more preferable to include a branch in which 5 or more of the styrene-butadiene copolymer rubber chains are bonded to the coupling residue of the above. Modified styrene-butadiene copolymer weight so that the degree of branching is 5 or more and the branching includes a branch in which 5 or more styrene-butadiene copolymer rubber chains are bonded to 1 coupling residue. By specifying the structure of the coalesced rubber, the shrinkage factor (g') can be more reliably reduced 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 shrinkage factor (g').

Further, it is more preferable that the modified styrene-butadiene copolymer rubber has bifurcation and the degree of bifurcation is 6 or more. Further, the modified styrene-butadiene copolymer rubber has one or more coupling residues and a styrene-butadiene copolymer rubber chain bonded to the coupling residues, and the branching further comprises. It is more preferable to include a branch in which 6 or more of the styrene-butadiene copolymer rubber chains are bonded to the coupling residue of 1. Modified styrene-butadiene copolymer weight so that the degree of branching is 6 or more and the branching includes a branch in which 6 or more styrene-butadiene copolymer rubber chains are bonded to 1 coupling residue. By specifying the structure of the coalesced rubber, the shrinkage factor (g') can be set to 0.63 or less.
Further, 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 bifurcation is not particularly limited, but is preferably 18 or less. Further, the modified styrene-butadiene copolymer rubber has one or more coupling residues and a styrene-butadiene copolymer rubber chain bonded to the coupling residues, and the branching further comprises. It is even more preferable to include 7 or more branches to which the styrene-butadiene copolymer rubber chain is bonded to the coupling residue of 1, and 8 or more to the coupling residue of 1. It is particularly preferable to include a branch to which the styrene-butadiene copolymer rubber chain is bonded. Modified styrene-butadiene copolymer weight 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 1 coupling residue. By specifying the structure of the coalesced rubber, the shrinkage factor (g') can be reduced to 0.59 or less.

The modified styrene-butadiene copolymer rubber preferably has a glass transition temperature (Tg) of more than −50 ° C., more preferably −30 ° C. or higher and −20 ° C. or lower, and −45 ° C. or higher and −15 ° C. or lower. It is more preferable to have. When the glass transition temperature (Tg) of the modified styrene-butadiene copolymer rubber is in the range of −45 ° C. or higher and -15 ° C. or lower, the wet grip property of the tire is further improved, the rolling resistance is reduced, and the wear resistance is improved. Can be improved further.
Regarding the glass transition temperature, the DSC curve is recorded while raising the temperature in a predetermined temperature range in accordance with ISO 22768: 2006, and the peak top (Inflection point) of the DSC differential curve is defined as the glass transition temperature.

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

The modified styrene-butadiene copolymer rubber is preferably represented by the following formula (I) from the viewpoint of further improving the wet grip property and wear resistance of the tire.

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 indicates 1 or 2. y represents an integer of 1 to 3, and y ≦ (p + 1). z represents an integer of 1 or 2. i indicates an integer of 0 to 6, j indicates an integer of 0 to 6, k indicates 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 has a hydrocarbon group having 1 to 20 carbon atoms or 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 has active hydrogen. Indicates an organic group that does not have.

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 constituent unit of the modified styrene-butadiene copolymer rubber, and is, for example, a styrene-butadiene copolymer generated by reacting the styrene-butadiene copolymer rubber with a coupling agent. It is a structural unit derived from coalesced rubber.

In the formula ^{(I), D, R 4} , R 5, and ^R 7 ~ ^{R 9} is, when each plurality of, double ^D, R 4, ^{R 5,} and ^R 7 ~ ^{R 9} is a respectively identical It may be different or it may be different.
Further, when i, j and k are 2 or more and there are a plurality of the following substructures (Ii), (Ij) and (Ik) in the formula (I), the partial structure ( Ii), (Ij) and (Ik) may have the same structure or different structures, respectively.

The hydrocarbon groups indicated by A include saturated, unsaturated, aliphatic, and aromatic hydrocarbon groups.
Examples of the organic group having no active hydrogen include active hydrogen such as a hydroxyl group (-OH), a secondary amino group (> NH), a primary amino group (-NH ₂ ), and a sulfhydryl group (-SH). Examples thereof include a functional group having a functional group and an organic group having no functional group.

In the above formula (I), A is preferably represented by any of the following formulas (II) to (V). By expressing A by any of the formulas (II) to (V), it is possible to improve the low rolling resistance, wear resistance and wet grip property 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 from 1 to 10. If B ¹ by a is 2 or more there are a plurality, the plurality of B ¹ represents may be the same or may be different.

In formula (III), B ² represents a single bond or a hydrocarbon group ^{having 1 to 20 carbon atoms, and B 3} represents an alkyl group having 1 to 20 carbon atoms. a represents an integer from 1 to 10. If B ² and B ³ there are a plurality by a is 2 or more, plural B ² and B ³ may be the same, respectively, may be different.

In formula (IV), B ⁴ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10. If a is B ⁴ by 2 or more there are a plurality, plural of B ⁴ may be the same or may be different.

In formula (V), B ⁵ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10. If B ⁵ by a is 2 or more there are a plurality, plural of B ⁵ may be the same or may be different.

^{Regarding B 1} , B ² , B ⁴ and B ^{5 in the} formulas (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), A is represented by formula (II) or (III) and k is preferably 0, and A is represented by formula (II) or (III) and k is 0. In formula (II) or (III), it is more preferable that a is an integer of 2 to 10.
In formula (I), A is represented by formula (II), which is k0, and in formula (II), a is more preferably an integer of 2 to 10.

(Method for producing modified styrene-butadiene copolymer rubber)
The method for producing the modified styrene-butadiene copolymer rubber is not particularly limited, but it is preferable to have the following steps from the viewpoint of easiness of forming the above-mentioned branched structure. That is, 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 pentafunctionality with respect to the active terminal of the styrene-butadiene copolymer rubber. It is preferable to have a reaction step of reacting the above-mentioned reactive compound (hereinafter, also referred to as “specific coupling agent”). As the specific coupling agent, it is preferable to react a reactive compound having a nitrogen atom and a silicon atom and having a pentafunctionality or higher.

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

The alkoxysilyl group of the specific coupling agent reacts with, for example, the active end of the styrene-butadiene copolymer rubber to dissociate alkoxylithium, and the end of the styrene-butadiene copolymer rubber chain and the coupling residue. Tends to form a bond with silicon. The value obtained by subtracting the number of SiORs reduced by the reaction from the total number of SiORs contained in one molecule of the coupling agent is the number of alkoxysilyl groups contained in the coupling residue. Further, the azasila cycle group contained in the coupling agent forms a> N-Li bond and a bond between the rubber end of the styrene-butadiene copolymer and the silicon of the coupling residue. The> N-Li bond tends to be> NH and LiOH easily due to water or the like at the time of finishing. Further, in the coupling agent, the alkoxysilyl group remaining unreacted tends to easily become silanol (Si—OH group) due to water or the like at the time of finishing.

The specific coupling agent is preferably represented by the formula (VI). That is, the modified styrene-butadiene copolymer rubber is preferably formed by reacting the styrene-butadiene copolymer rubber with the coupling agent represented by the formula (VI). By forming the center rubber with the rubber composition containing the modified styrene-butadiene copolymer rubber formed 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 indicates 1 or 2. i, j and k each independently represent an integer of 0 to 6. However, (i + j + k) is an integer of 3 to 10. A has a hydrocarbon group having 1 to 20 carbon atoms or 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 has no active hydrogen. Indicates an organic group.

Here, in formula (VI), the hydrocarbon group represented by A includes saturated, unsaturated, aliphatic, and aromatic hydrocarbon groups. Examples of the organic group having no active hydrogen include active hydrogen such as a hydroxyl group (-OH), a secondary amino group (> NH), a primary amino group (-NH ₂ ), and a sulfhydryl group (-SH). Examples thereof include a functional group having a functional group and an organic group having no functional group.

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

Examples of such a coupling agent include bis (3-trimethoxysilylpropyl)-[3- (2,2-dimethoxy-1-aza-2-silacyclopentane) propyl] amine and tris (3-trimethoxysilyl). Propyl) amine, tris (3-triethoxysilylpropyl) amine, tris (3-trimethoxysilylpropyl)-[3- (2,2-dimethoxy-1-aza-2-silacyclopentane) propyl] -1, 3-Propyldiamine, Tetrax [3- (2,2-dimethoxy-1-aza-2-silacyclopentane) propyl] -1,3-Propyldiamine, Tetrax (3-trimethoxysilylpropyl) -1,3- Propyldiamine, 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 can be mentioned.
The coupling agent may be used alone or in combination of two or more.
Among these, the coupling agents represented by the formula (VI) are tetrakis [3- (2,2-dimethoxy-1-aza-2-silacyclopentane) propyl] -1,3-propanediamine, and tetrakis. (3-Trimethoxysilylpropyl) -1,3-propanediamine and tetrakis (3-trimethoxysilylpropyl) -1,3-bisaminomethylcyclohexane are particularly preferable.

The amount of the compound represented by the formula (VI) as the coupling agent is such that the number of moles of the styrene-butadiene copolymer rubber and the number of moles of the coupling agent react at a desired stoichiometric ratio. It can be adjusted, 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, based on the number of moles of the coupling agent. In this case, in the formula (VI), the number of functional groups ((m-1) × i + p × j + k) of the coupling agent is preferably an integer of 5 to 10, and more preferably an integer of 6 to 10. ..

In the method for producing a modified styrene-butadiene copolymer rubber, the polymerization step is preferably polymerization by a growth reaction by a living anionic polymerization reaction. Thereby, a styrene-butadiene copolymer rubber having an active terminal can be obtained, and a modified styrene-butadiene copolymer rubber having a high modification rate can be obtained.
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 the polymerization initiator is preferably determined by the molecular weight of the target styrene-butadiene copolymer rubber or modified styrene-butadiene copolymer rubber. The amount of a monomer such as a 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 in the direction of decreasing the polymerization initiator, and in order to decrease the molecular weight, it is preferable to adjust in the direction of increasing the amount of the polymerization initiator.
The organic monolithium compound is preferably an alkyllithium compound from the viewpoint of easy industrial availability and easy control of the polymerization reaction. In this case, a styrene-butadiene copolymer rubber having an alkyl group at the polymerization initiation terminal can be obtained. Examples of the alkyllithium compound include n-butyllithium, sec-butyllithium, tert-butyllithium, n-hexyllithium, benzyllithium, phenyllithium, and stillbenlithium. As the alkyllithium compound, n-butyllithium and sec-butyllithium are preferable from the viewpoint of easy industrial availability and easy control of the polymerization reaction. These organic monolithium compounds may be used alone or in combination of two or more.

In the polymerization step, examples of the polymerization reaction mode include batch type and continuous type polymerization reaction modes. In the continuous equation, one or two or more connected reactors can be used. As the continuous reactor, for example, a tank type or tube type reactor with a stirrer is used. In the continuous system, preferably, the monomer, the inert solvent, and the polymerization initiator are continuously fed to the reactor to obtain a polymer solution containing the polymer in the reactor, and the polymer solution is continuously weighted. The coalesced solution is drained. As the batch reactor, for example, a tank type reactor with a stirrer is used. In the batch formula, preferably, the monomer, inert solvent, and polymerization initiator are fed, and if necessary, the monomer is added continuously or intermittently during the polymerization, and the polymer is added in the reactor. A polymer solution containing the mixture is obtained, and the polymer solution is discharged after the completion of the polymerization. In the present embodiment, in order to obtain a styrene-butadiene copolymer rubber having an active terminal at a high ratio, a continuous formula is preferable in which the polymer can 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 hydrocarbon-based solvents are not limited to the following, but are, for example, aliphatic hydrocarbons such as butane, pentane, hexane, and heptane; alicyclic groups such as cyclopentane, cyclohexane, methylcyclopentane, and methylcyclohexane. Hydrocarbons; examples include hydrocarbons composed of aromatic hydrocarbons such as benzene, toluene and xylene and mixtures thereof. By treating impurities such as allenes and acetylenes with an organic metal compound before subjecting them to a polymerization reaction, a styrene-butadiene copolymer rubber having a high concentration of active terminals tends to be obtained, and a high modification rate is obtained. The modified styrene-butadiene copolymer rubber of the above tends to be obtained, which is preferable.

In the polymerization step, a polar compound may be added. By adding a polar compound, the aromatic vinyl compound can be randomly copolymerized with the conjugated diene compound, and the polar compound can also be used as a vinylizing agent for controlling the microstructure of the conjugated diene portion. Tend to be able to.
Examples of the polar compound 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 methylethylenediamine, dipiperidinoethane, trimethylamine, triethylamine, pyridine and quinuclidine; alkali metal alkoxides such as potassium-tert-amylate, potassium-tert-butyrate, sodium-tert-butyrate and sodium amylate. Compound: A phosphine compound such as triphenylphosphine can be used. These polar compounds may be used alone or in combination of two or more.

In the polymerization step, 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, from the viewpoint of productivity. Within such a range, it tends to be possible to sufficiently secure the reaction amount of the coupling agent with respect to the active terminal after the completion of polymerization.

The amount of the bonded conjugated diene in the styrene-butadiene copolymer rubber or the modified styrene-butadiene copolymer rubber is not particularly limited, but is preferably 40% by mass or more and 100% by mass or less, and 55% by mass or more and 80% by mass or more. The following is more preferable.
The amount of bonded 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, and is preferably 20% by mass or more. It is more preferably 45% by mass or less, further 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, and 39% by mass or more and 45% by mass or less. It is extremely preferable, and most preferably 40% by mass or more and 45% by mass or less.
When the amount of the bonded conjugated diene and the amount of the bonded aromatic vinyl are in the above ranges, the wet grip property and the wear resistance of the tire can be improved.
The amount of bound aromatic vinyl can be measured by the ultraviolet absorption of the phenyl group, and the amount of bound conjugated diene can also be determined from this. Specifically, the measurement is performed according to the method described in Examples described later.

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

The mixing in the reaction step may be either mechanical stirring, stirring with a static mixer, or the like. When the polymerization step is a continuous type, it is preferable that the reaction step is also a continuous type. As the reactor in the reaction step, for example, a tank type or tube type reactor with a stirrer is used. The coupling agent may be diluted with an inert solvent and continuously supplied to the reactor. When the polymerization step is a batch type, the reaction step may be carried out by charging the coupling agent into the polymerization reactor or by transferring the coupling agent to another reactor.

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, and more. It is preferably 1.8 or more and 2.2 or less. Further, in the obtained modified styrene-butadiene copolymer rubber (A2), it is preferable that a peak having a single peak in the molecular weight curve by GPC is detected.
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 established.
_{(Mp 1 / Mp 2) <} 1.8 × 10-12 × (Mp 2 -120 × 10 4) 2 +2
More preferably, Mp ₂ is 20 × 10 ⁴ or more and 80 × 10 ⁴ or less, and Mp ₁ is 30 × 10 ⁴ or more and 150 × 10 ⁴ or less. Mp ₁ and Mp ₂ are obtained by the method described in Examples described later.

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 further preferably 70% by mass or more. When the modification rate is 30% by mass or more, the rolling resistance can be reduced while improving the wear resistance of the tire. The denaturation rate is measured by the method described in Examples described later.

After the reaction step, a deactivating agent, a neutralizing agent, or the like may be added to the copolymer solution, if necessary. The inactivating agent is not limited to the following, and examples thereof include water; alcohols such as methanol, ethanol, and isopropanol. The neutralizing agent is not limited to the following, but for example, carboxylic acids such as stearic acid, oleic acid, and versatic acid (a mixture of carboxylic acids having 9 to 11 carbon atoms and mainly 10 branches). Acid: An aqueous solution of an inorganic acid, carbonic acid gas and the like can be mentioned.
Further, the modified styrene-butadiene copolymer rubber is, for example, 2,6-di-tert-butyl-4-hydroxytoluene (from the viewpoint of preventing gel formation after polymerization and improving the stability during processing. BHT), n-octadecyl-3- (4'-hydroxy-3', 5'-di-tert-butylphenol) propinate, 2-methyl-4,6-bis [(octylthio) methyl] phenol and other antioxidants. Is preferably added.

In order to further improve the processability of the modified styrene-butadiene copolymer rubber, extender oil can be added to the modified conjugated diene-based copolymer, if necessary. The method of adding the spreading oil to the modified styrene-butadiene copolymer rubber is not limited to the following, but the spreading oil is added to the polymer solution and mixed to obtain an oil spreading copolymer solution. The method of desolving the solvent is preferable. Examples of the spreading oil include aroma oil, naphthenic oil, paraffin oil and the like. Among these, from the viewpoint of environmental safety, prevention of oil bleeding, and wet performance, an aroma substitute oil having a polycyclic aromatic (PCA) component of 3% by mass or less according to the IP346 method is preferable. Examples of the aroma substitute oil include TDAE (Treated Distillate Aromatic Extracts) shown in Kautschuk Gummi Kunststoffe 52 (12) 799 (1999), MES (Mild Extension Solvate), and RA.

The amount of the spreading oil added is not particularly limited, but is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and 12 parts by mass with respect to 100 parts by mass of the modified styrene-butadiene copolymer rubber. The following is particularly preferable. The amount of the spreading oil added is preferably 1% by mass or more, more preferably 3% by mass or more, and 5% by mass or more, based on 100 parts by mass of the modified styrene-butadiene copolymer rubber. Is particularly preferred.

A known method can be used as a method for obtaining the modified styrene-butadiene copolymer rubber from the polymer solution. As the method, for example, after separating the solvent by steam stripping or the like, the polymer is filtered off, and further dehydrated and dried to obtain the polymer, concentrated in a flushing tank, and further bent extruder or the like. A method of devolatile with a drum dryer or the like, or a method of directly devolatile with a drum dryer or the like can be mentioned.

The content of the modified styrene-butadiene copolymer rubber in the rubber component of the rubber composition for center rubber is preferably 20 to 70% by mass, and more preferably 30 to 50% by mass. When the content of the modified styrene-butadiene copolymer rubber in the rubber component is 20% by mass or more, the wet grip property of the tire can be further improved. Further, when the content of the modified styrene-butadiene copolymer rubber in the rubber component is 70% by 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.
Other rubber components include at least one selected from the group consisting of natural rubber, butadiene rubber, styrene-butadiene copolymer rubber and isoprene rubber (synthetic isoprene rubber). By containing other rubber components, the wet grip property and wear resistance of the tire can be improved, and the rolling resistance can be reduced.
The other rubber component may be unmodified rubber or modified rubber.
The other rubber component is preferably a modified or unmodified butadiene rubber, and more preferably a modified butadiene rubber.
That is, the rubber component of the rubber composition for the center rubber preferably contains a modified styrene-butadiene copolymer rubber and further modified or unmodified butadiene rubber, and is preferably a modified styrene-butadiene copolymer rubber and further modified butadiene. More preferably, it contains rubber.

〔filler〕
The rubber composition for center rubber contains 75 parts by mass or more of silica as a filler with respect to 100 parts by mass of the rubber component.
When the content of silica in the rubber composition for center rubber is 75 parts by mass or more with respect to 100 parts by mass of the rubber component, the wet grip property of the tire is excellent.
From the viewpoint of further improving the wet grip property of the tire, the content of silica in the rubber composition for center rubber is preferably 78 parts by mass or more, preferably 82 parts by mass or more with respect to 100 parts by mass of the rubber component. It is more preferably 85 parts by mass or more, and even more preferably 87 parts by mass or more.
From the viewpoint of processability of the rubber composition, the content of silica in the rubber composition for center rubber is preferably 120 parts by mass or less and 117 parts by mass or less with respect to 100 parts by mass of the rubber component. Is more preferably 115 parts by mass or less, further preferably 112 parts by mass or less, and even more preferably 108 parts by mass or less.

Examples of silica include wet silica (hydrous silicic acid), dry silica (silicic anhydride), calcium silicate, aluminum silicate and the like, and among these, wet silica is preferable. These silicas may be used alone or in combination of two or more.
In addition, precipitated silica can be used as the wet silica. Precipitated silica means that the reaction solution is allowed to react in a relatively high temperature, neutral to alkaline pH range at the initial stage of production to grow silica primary particles, and then controlled to the acidic side to aggregate the primary particles. It is the silica obtained as a result of making it.

Further, silica preferably has a cetyltrimethylammonium bromide adsorption specific surface area (CTAB) of 60 to 200 m ² / g.
If the CTAB is 200 m ² / g or less, the rolling resistance is reduced, and the workability and workability of the rubber composition are unlikely to be lowered.
The CTAB of silica ^{is more preferably 80 m 2} / g or more, ^{further preferably 100 m 2} / g or more, further preferably 130 m ² / g or more, still more preferably 140 m ² / g or more. .. Further, the CTAB of silica ^{is more preferably 190 m 2} / g or less, and ^{further preferably 185 m 2} / g.

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

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 blacks are preferable from the viewpoint of improving the wear resistance of the center rubber. These carbon blacks may be used alone or in combination of two or more.

The content of carbon black in the rubber composition for 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 with respect to 100 parts by mass of the rubber component. By setting the carbon black content to 1 part by mass or more with respect to 100 parts by mass of the rubber component, the wear resistance of the tire is further improved, and by setting the content to 15 parts by mass or less, the rolling resistance of the tire is unlikely to increase.

The ratio of silica to the total amount of silica and carbon black (referred to as silica ratio) is preferably 70% by mass or more.
When the silica ratio is 70% by mass, it is possible to contribute to the improvement of low loss property (and thus the reduction of rolling resistance) of the center rubber and the improvement of wear resistance.
From the viewpoint of processability of the rubber composition, the silica ratio is preferably 99% by mass or less.
From the viewpoint of improving the workability of the rubber composition while improving the wear resistance of the tire, the silica ratio is more preferably 75 to 98% by mass, further preferably 79 to 97% by mass. , 83-96% by mass, more preferably.

(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.
Examples of the silane coupling agent include 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). Compounds are preferred.
These silane coupling agents may be used alone or in combination of two or more.

Equation (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)
Here, in formula (VII), 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, and m is 1 to 3 An integer, a is an integer of 1 to 9, and b is an integer of 1 or more. 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 the compound represented by the formula (VII) include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (3-methyldimethoxysilylpropyl) tetrasulfide, and bis ( Examples thereof include 3-triethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, and bis (3-triethoxysilylpropyl) trisulfide.

Equation (VIII) has the following structure.
_{A m B 3-m Si- (} CH 2) c -Y ··· (VIII)
Here, in the 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, and Y is a mercapto group or vinyl. It is a group, an amino group, a glycidoxy group or an epoxy group, where 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 or different from each other, and when m is 2 or 3, A may be the same or different from each other.

Examples of the compound represented by the formula (VIII) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyl-di (tridecane-1-oxy-13-penta (ethylene oxide)) ethoxysilane. , Vinyl triethoxysilane, vinyl trimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxy Examples thereof include propylmethyldiethoxysilane. Examples of these commercially available products include the trade name "VP Si363" manufactured by Evonik Degussa.

Equation (IX) has the following structure.
_{A m B 3-m Si- (} CH 2) a -S b -Z ··· (IX)
Here, in the 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, and N. , N-Dimethylthiocarbamoyl group or methacryloyl group, m may be an integer of 1 to 3, a may be an integer of 1 to 9, and b may be an integer of 1 or more. 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 the compound represented by the formula (IX) include 3-trimethoxysilylpropyl-N, N-dimethylcarbamoyltetrasulfide, 3-trimethoxysilylpropylbenzothiazolyltetrasulfide, and 3-trimethoxysilylpropylmethacryloyl monosulfide. And so on.

Equation (X) has the following structure.
R ³¹ _x R ³² _y R ³³ _z Si-R ^34- S-CO-R ³⁵ ... (X)
Here, in the formula (X), R ³¹ is 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 have 1 to 18 carbon atoms. However, R ³⁶ and R ³⁷ are independently selected from an alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group and an aryl group, have 1 to 18 carbon atoms, 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- (where 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 Is).
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 alkaneylene 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.

With respect to the compound represented by the formula (X), in R ³² , R ³⁵ , R ³⁶ and R ³⁷ in the formula (X), the alkyl group may be linear or branched, and the alkyl group may be used as the alkyl group. Examples thereof include a methyl group, an ethyl group, a propyl group and an isopropyl group. Further, the alkenyl group may be linear or branched, and examples of the alkenyl group include a vinyl group, an allyl group, a methanyl group and the like. Further, 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, in R ⁵ , examples of the aralkyl group include a phenethyl group and the like.

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. Moreover, as a cycloalkylene group, a cyclohexylene group and the like can be mentioned. Furthermore, in R ^34, alkenylene group, as also well, the alkenylene group branched be linear, vinylene group, propenylene group and the like. Further, examples of the cycloalkylalkylene group include a cyclohexylmethylene group, examples of the arylene group include a phenylene group, and examples of the aralkylene group include a xylylene group.
In the above formula (X), in R ³³ ,-[O (R ³⁸ O) _m ] _0.5 -groups include 1,2-ethanedioxy group, 1,3-propanedioxy group, and 1,4-butanedioxy. Groups, 1,5-pentanedioxy groups, 1,6-hexanedioxy groups and the like can be mentioned.
The compound represented by the above formula (X) can be synthesized in the same manner as in the method described in Special Table 2001-505225, and the trade name “NXT” (formula (formula)) manufactured by Momentive Performance Materials Co., Ltd. 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), etc. Commercially available products can also be used.

Further, among the compounds represented by the above formulas (VII), (VIII), (IX) or (X), the compound represented by the above formula (VIII) and the compound represented by the above formula (X) are preferable. ..

The amount of the silane coupling agent blended in the rubber composition for center rubber is preferably 1 part by mass or more with respect to 100 parts by mass of silica from the viewpoint of improving the dispersibility of silica in the rubber matrix, and is preferably 4 parts by mass. The above is more preferable, 20 parts by mass or less is preferable, and 12 parts by mass or less is further preferable.

[Softener]
The rubber composition for the center rubber preferably contains a softening agent.
Since the center rubber can be softened by containing the softening agent in the rubber composition for the center rubber, excellent wet grip property can be realized, and the workability and workability of the rubber composition can be improved. Can be done.
Examples of the softener include oil and resin.
The content of the softening agent in the rubber composition for center rubber is preferably 2 parts by mass or more, more preferably 10 parts by mass or more, and 20 parts by mass or more with respect to 100 parts by mass of the rubber component. It is more preferably 30 parts by mass or more, further preferably 35 parts by mass or more, further preferably 40 parts by mass or more, and 45 parts by mass or more. Even more preferable.
The content of the softening agent in the rubber composition for center rubber is more preferably 85 parts by mass or less, more preferably 80 parts by mass or less, and 78 parts by mass or less with respect to 100 parts by mass of the rubber component. It is 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 with respect to 100 parts by mass of the rubber component, the wet grip property of the tire can be improved, and by setting it to 85 parts by mass or less, the rigidity of the tire Can be suppressed.
The "content of the softening agent in the rubber composition for center rubber" includes not only the content of the softening agent blended with the rubber component as the softening agent, but also the content of the spreading oil pre-blended in the rubber component. Include.

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

(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 softening agent, the wet grip property of the tire can be improved and the rolling resistance can be reduced.

As the resin, _{C 5 resins,} C 5 -C ₉ resins, _{C 9} resins, dicyclopentadiene resins, terpene phenol resins, terpene resins, rosin resins, and alkylphenol resins.
Among them, _{C 5 resins,} C 5 -C ₉ resins, _{C 9} resins, dicyclopentadiene resins, rosin resins, and at least one selected from alkylphenol resin.
If as the resin, C ₅ resins, C ₅ -C ₉ resins, C ₉ resins, dicyclopentadiene resins, terpene phenol resins, terpene resins, rosin resins, and containing at least one alkylphenol resin, wet grip of tire The sex can be further improved.

Among resins, _{C 5 resins,} C 5 -C ₉ resins and _{C 9} resins are particularly preferred. C ₅ -C ₉ resins and C ₉ resin has high compatibility with natural rubber, the elasticity of the high effectively the elastic modulus at low strain region of the rubber composition, as well as in the high strain region of vulcanized rubber The effect of lowering the rate is further increased, and the wet grip property of the tire can be further improved.
The resin may be used alone or in combination of two or more.

The C ₅ resins, refers to _{C 5} type synthetic petroleum resins, examples of the _{C 5} resin, for example, a _{C 5} fraction obtained by thermal cracking of petroleum chemical industry naphtha, such as AlCl _3, BF ₃ Examples thereof include an aliphatic petroleum resin obtained by polymerization using a Friedelcrafts type catalyst. The _C in ₅ fractions, typically, 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, 3-methyl-1-olefin hydrocarbons butene, 2- Diolefin hydrocarbons such as methyl-1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene and 3-methyl-1,2-butadiene are included. Incidentally, examples of the C ₅ resin may be commercially available products, for example, an ExxonMobil Chemical Co. aliphatic petroleum resin "Escorez (registered trademark) 1000 Series", Nippon Zeon Co., Ltd. aliphatic Among the "Quinton (registered trademark) 100 series" which are petroleum resins, "A100, B170, M100, R100", "T-REZ RA100" manufactured by Tonen Chemical Corporation and the like can be mentioned.

The C ₅ -C _{9 resins,} refers to C 5 -C ₉ based synthetic petroleum _resins, as the C 5 -C ₉ resins, for example, a _{C 5} fraction derived from petroleum and _{C 9} fraction, AlCl _{Examples thereof include solid polymers obtained by polymerization using Friedelcraft type catalysts such as 3} and BF ₃ , and more specifically, copolymers containing styrene, vinyltoluene, α-methylstyrene, inden and the like as main components. Examples include polymers. As the C _5- C ₉ series resin, a _{resin having a small amount of C 9} or more components is preferable from the viewpoint of compatibility with the rubber component. Here, " _{there are few components of C 9 or more" means that the components of C 9} or more in the total amount of the resin are less than 50% by mass, preferably 40% by mass or less. Examples of the _C 5 -C ₉ resins, it is possible to use a commercially available product, for example, trade name "Quinton (registered trademark) G100B" (manufactured by Nippon Zeon Co., Ltd.), trade name "ECR213" (ExxonMobil Chemical Company ), Product name "T-REZ RD104" (manufactured by Tonen Chemical Corporation) and the like.

C ₉ resins, for example, by thermal cracking of petroleum chemical industry naphtha, ethylene, C ₉ fraction by-produced together with the petrochemical basic raw materials such as propylene, vinyl toluene, alkyl styrene, indene major monomer It is a resin obtained by polymerizing an aromatic having 9 carbon atoms. Here, specific examples of the C ₉ fraction obtained by thermal decomposition of naphtha, vinyl toluene, alpha-methyl styrene, beta-methyl styrene, .gamma.-methyl styrene, o- methyl styrene, p- methyl styrene, indene and the like Can be mentioned. The C _9- based resin, _{together with the C 9} fraction, is a C ₈ fraction such as styrene, a C ₁₀ fraction such as methylinden and 1,3-dimethylstyrene, and further, naphthalene, vinylnaphthalene, vinylanthracene, p. used as the raw material also -tert- butyl styrene, leave these C _{8 ~} C ₁₀ fraction, etc. a mixture, for example can be obtained by copolymerizing a Friedel-Crafts catalyst. Also, the C ₉ resin, a compound having a hydroxy group may be a modified modified petroleum resin with an unsaturated carboxylic acid compound or the like. Incidentally, examples of the C ₉ resins, can be utilized commercially, for example, the unmodified C ₉ petroleum resin, trade name "Nisseki Neo Polymer (registered trademark) L-90", "Nisseki Examples thereof include "Neopolymer (registered trademark) 120", "Nippon Oil Neopolymer (registered trademark) 130", and "Nippon Oil Neopolymer (registered trademark) 140" (manufactured by JX Nippon Oil Energy Co., Ltd.).

Dicyclopentadiene resin is a petroleum resin produced using dicyclopentadiene as a main raw material, which is obtained by dimerizing cyclopentadiene. As the dicyclopentadiene resin, a commercially available product can be used. For example, among the trade names "Quinton (registered trademark) 1000 series", which is an alicyclic petroleum resin manufactured by Nippon Zeon Corporation, "1105, 1325, 1340 ”and the like.

The terpene phenol resin can be obtained, for example, by reacting terpenes with various phenols using a Friedel-Crafts type catalyst, or by further condensing with formalin. The raw material terpenes are not particularly limited, and monoterpene hydrocarbons such as α-pinene and limonene are preferable, those containing α-pinene are more preferable, and α-pinene is particularly preferable. Commercially available products can be used as the terpene phenol resin, for example, product names "Tamanol 803L", "Tamanol 901" (manufactured by Arakawa Chemical Industry Co., Ltd.), and product name "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) N" series Examples include the "K" series and the "YS Polystar (registered trademark) TH" series (manufactured by Yasuhara Chemical Co., Ltd.).

The terpene resin is a solid resin obtained by blending turpentine oil obtained at the same time as obtaining rosin from a pine tree or a polymerization component separated from the turpentine and polymerizing it using a Friedelcrafts type catalyst. , Β-Pinene resin, α-pinene resin and the like. Commercially available products can be used as the terpene resin. For example, the product name "YS Resin" series (PX-1250, TR-105, etc.) manufactured by Yasuhara Chemical Co., Ltd. and the product name "Picolite" series manufactured by Hercules Co., Ltd. (A115, S115, etc.) and the like.

Rosin resin is a residue that remains after collecting balsams such as pine fat (pine yani), which is the sap of Pinaceae plants, and distilling terepine essential oil. Natural resins as components, modified resins obtained by modifying them, hydrogenation, etc., and hydrogenated resins. Examples thereof include natural resin rosins, their polymerized rosins and partially hydrogenated rosins; glycerin ester rosins, their partially hydrogenated rosins and fully hydrogenated rosins and polymerized rosins; pentaerythritol ester rosins, their partially hydrogenated rosins and polymerized rosins. .. Examples of natural resin rosin include raw pine tar, gum rosin contained in tall oil, tall oil rosin, and wood rosin. As the rosin resin, a commercially available product can be used, for example, the product name "Neotol 105" (manufactured by Harima Kasei Co., Ltd.), the product name "SN Tuck 754" (manufactured by Sannopco Co., Ltd.), and the product name "Lime Resin". No. 1 ”,“ Pencel A ”and“ Pencel AD ”(manufactured by Arakawa Chemical Industry Co., Ltd.), product names“ Polypale ”and“ Pentalin C ”(manufactured by Eastman Chemical Co., Ltd.), product name“ Hyrosin (registered trademark) "S" (manufactured by Taisha Matsu Seiyu Co., Ltd.) and the like can be mentioned.

The alkylphenol resin is obtained, for example, by a condensation reaction of alkylphenol and formaldehyde under a catalyst. As the alkylphenol resin, a commercially available product can be used. For example, the product name "Hitanol 1502P" (alkylphenol formaldehyde resin, manufactured by Hitachi Kasei Co., Ltd.) and the product name "Tackiroll 201" (alkylphenol formaldehyde resin, Taoka Chemical Industry Co., Ltd.) (Company), Product name "Tackiroll 250-I" (brominated alkylphenol formaldehyde resin, manufactured by Taoka Chemical Industry Co., Ltd.), Product name "Tackiroll 250-III" (brominated alkylphenol formaldehyde resin, manufactured by Taoka Chemical Industry Co., Ltd.), Product names such as "R7521P", "SP1068", "R7510PJ", "R7572P" and "R7578P" (manufactured by SI GROUP INC.) Can be mentioned.

The ratio of the resin in the total amount of the softener is preferably 20 to 90% by mass.
When the ratio of the resin in the total amount of the softener is 20% by mass or more, the wet grip property 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 ratio of the resin in the total amount of the softener is more preferably 20 to 70% by mass, further preferably 20 to 50% by mass, and even more preferably 20 to 35% by mass.

In addition to the rubber components, fillers, softeners, and silane coupling agents described above, the rubber composition for center rubber includes compounding agents commonly used in the rubber industry, such as stearic acid and antiaging agents. Zinc oxide (zinc white), a vulcanization accelerator, a vulcanizing agent and the like can be appropriately selected and contained within a range that does not impair the object of the present invention.

The component composition of other rubber compositions such as the rubber composition for shoulder rubber constituting the shoulder rubber and the rubber composition constituting other tire parts is not particularly limited.
Other rubber compositions can include rubber components, fillers, softeners, and silane coupling agents that can be included in rubber compositions for center rubber, as well as stearic acid, anti-aging agents, zinc oxide (zinc oxide). ), A vulcanization accelerator, a vulcanizing agent and the like may be contained.
The rubber component of the other rubber composition does not have to contain the modified styrene-butadiene copolymer rubber. Further, the content of silica in the rubber composition may be 75 parts by mass or less (including 0 parts by mass) with respect to 100 parts by mass of the rubber component.

From the viewpoint of grip, the total amount of the softener should be larger than the total amount of the softener in the center rubber composition of the rubber composition for shoulder rubber. The rubber composition for shoulder rubber does not have to contain the modified styrene-butadiene copolymer rubber as a rubber component.

The tire of the present invention is not limited to applications such as for two-wheeled vehicles and four-wheeled vehicles, and can be used for various purposes. However, when used for two-wheeled vehicles in particular, the effects of the present invention can be easily realized.
When used as a motorcycle tire, it may be a front tire or a rear tire, but in the present invention, it is applicable to a rear tire because it can achieve both wet grip and wear resistance of the tread at a high level. Then, the effect of the present invention is particularly likely to be exhibited.
The type of motorcycle is not particularly limited and can be appropriately selected according to the purpose.
For example, motorcycles for competition, motorcycles for general public roads, motorcycles for on-road, motorcycles for off-road, and the like can be mentioned. Among them, as the two-wheeled vehicle in which the effect of the present invention is particularly likely to be exhibited, a general public road two-wheeled vehicle and an on-road two-wheeled vehicle are preferable, and a general public road two-wheeled vehicle is more preferable.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

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

[Rubber composition for shoulder rubber]
(1) Comparative Example 1 and Examples 1 and 2
A rubber composition for shoulder rubber was produced using a normal Banbury mixer according to the formulation shown in Table 1.
(2) Comparative Examples 2 to 4 and Examples 3 to 6
A rubber composition for shoulder rubber is produced using a normal Banbury mixer according to the formulation shown in Table 1.
The components in Table 1 are as follows.
BR: Polybutadiene rubber: Made by JSR Corporation, product name "BR01"
SBR: Styrene-butadiene copolymer rubber, manufactured by JSR Corporation, emulsion polymerized styrene-butadiene copolymer rubber, trade name "HP755B"
Carbon Black: Made by Asahi Carbon Co., Ltd., product name "ASAHI # 105"
Silica: Made by Tosoh Silica Co., Ltd., Product name "Nip Seal AQ"
Softener: Tonen Chemical Corporation, trade name "T-REZ RD104" and JX Nippon Oil Energy Co., Ltd., trade name "Oil A / O MIX"
Anti-aging agent: N-phenyl-N'-(1,3-dimethylbutyl) -p-phenylenediamine, manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., and contains at least the trade name "Nocrack 6C".
Vulcanization package: Contains stearic acid, zinc oxide, thiuram-based vulcanization accelerator, and vulcanizing agent.

The "total amount of softener" in Table 1 means the total amount of 30 parts by mass of the softener of the compounding component and 32 parts by mass of the oil spread amount of the rubber component.

[Rubber composition for center rubber]
(1) Comparative Example 1 and Examples 1 and 2
A rubber composition for center rubber was produced using a normal Banbury mixer according to the formulation shown in Table 2.
(2) Comparative Examples 2 to 4 and Examples 3 to 6
A rubber composition for center rubber is produced using a normal Banbury mixer according to the formulation shown in Table 2.
The components in Table 2 are as follows.

1. 1. Rubber component (1) BR: Butadiene rubber, manufactured by JSR Corporation, product name "BR01"
(2) Modified BR: Modified butadiene rubber, manufactured by JSR Corporation, trade name "JSR BR54"
(3) SBR: Styrene-butadiene copolymer rubber, manufactured by JSR Co., Ltd., emulsified polymerized styrene-butadiene copolymer rubber, trade name "HP755B", 37.5 parts by mass of oil with respect to 100 parts by mass of rubber component Including, amount of bonded styrene = 39.5% by mass, amount of bonded vinyl = 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 with respect to 100 parts by mass of rubber component, weight average molecular weight (Mw) = 85.2 × 10 ⁴ , molecular weight 200 × 10 ⁴ or more and 500 × 10 ⁴ or less ratio = 4.6%
Shrinkage factor (g') = 0.59, glass transition temperature (Tg) = -25 ° C

2. Filler CB: Carbon Black, manufactured by Asahi Carbon Co., Ltd., trade name "ASAHI # 105"
Silica: Made by Tosoh Silica Co., Ltd., trade name "Nip Seal AQ", CTAB165

3. 3. Other component oil: JX Nikko Nisseki Energy Co., Ltd., trade name "A / O MIX"
_Resin: C 5 -C ₉ resins silane coupling agent: Shin-Etsu Chemical Co., Ltd. under the trade name "ABC-856"
Anti-aging agent: N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine, manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., and contains at least the trade name "Nocrack 6C".
Vulcanization package: Contains guanidine-based vulcanization accelerator, thiuram-based vulcanization accelerator, sulfide-based vulcanization accelerator, stearate, zinc white and sulfur

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

(1) Amount of bound styrene Using the modified styrene-butadiene copolymer rubber as a sample, 100 mg of the sample is made up to 100 mL with chloroform and dissolved to prepare a measurement sample. The amount of bound styrene (mass%) with respect to 100% by mass of the sample is measured by the amount of ultraviolet absorption wavelength (around 254 nm) absorbed by the phenyl group of styrene (spectrophotometer "UV-2450" manufactured by Shimadzu Corporation). ..

(2) Microstructure of butadiene part (1,2-vinyl bond amount)
Using the modified styrene-butadiene copolymer rubber as a sample, 50 mg of the sample is dissolved in 10 mL of carbon disulfide to prepare a measurement sample. Using a solution cell, the infrared spectrum was ^{measured in the range of 600 to 1000 cm -1} , and the absorbance at a predetermined wave number was used by Hampton's method (method described in RR Hampton, Analytical Chemistry 21, 923 (1949)). The microstructure of the butadiene moiety, that is, the amount of 1,2-vinyl bond (mol%) is determined according to the above formula (Fourier transform infrared spectrophotometer "FT-IR230" manufactured by JASCO Corporation).

(3) Molecular Weight A GPC measuring device (trade name "HLC" manufactured by Toso Co., Ltd.) in which three columns using a polystyrene gel as a filler are connected using a styrene-butadiene copolymer rubber or a modified styrene-butadiene copolymer rubber as a sample. -8320GPC ”) was used to measure the chromatogram using an RI detector (trade name“ HLC8020 ”manufactured by Toso), and the weight average molecular weight (weight average molecular weight) based on the calibration line obtained using standard polystyrene. Mw), number average molecular weight (Mn), molecular weight distribution (Mw / Mn), peak top molecular weight of modified styrene-butadiene copolymer rubber (Mp ₁ ), and peak top molecular weight of styrene-butadiene copolymer rubber (Mp _2). ) and determined and the ratio _(Mp 1 / Mp _2), the ratio of molecular weight 200 × 10 ⁴ or more 500 × 10 ⁴ or less, the. The eluent used is THF (tetrahydrofuran) containing 5 mmol / L triethylamine. For the column, three Tosoh product names "TSKgel SuperMultipore HZ-H" are connected, and a Tosoh product name "TSKguardcolum SuperMP (HZ) -H" is connected and used as a guard column in front of the column. 10 mg of the sample for measurement is dissolved in 10 mL of THF to prepare a measurement solution, and 10 μL of the measurement solution is injected into a GPC measuring device to measure under the conditions of an oven temperature of 40 ° C. and a THF flow rate of 0.35 mL / min.
The above peak top molecular weights (Mp ₁ and Mp ₂ ) are determined as follows. In the GPC curve obtained by measurement, the peak detected as the component having the highest molecular weight 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 molecular weight 200 × 10 ⁴ or more 500 × 10 ⁴ or less of the proportion of the above, calculated by subtracting the percentage of the percentage of the total molecular weight 500 × 10 ⁴ or less from the integral molecular weight distribution curve occupied molecular weight of less than 200 × 10 ⁴ do.

(4) Contraction factor (g')
Light scattering using a GPC measuring device (trade name "GPCmax VE-2001" manufactured by Malvern) in which three columns using a polystyrene gel as a filler are connected using a modified styrene-butadiene copolymer rubber as a sample. Measurement is performed using three detectors connected in the order of a detector, an RI detector, and a viscosity detector (trade name "TDA305" manufactured by Polymer Co., Ltd.). Based on standard polystyrene, the absolute molecular weight is obtained from the results of the light scattering detector and the RI detector, and the intrinsic viscosity is obtained 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') as the ratio of the intrinsic viscosity corresponding to each molecular weight is calculated. The eluent used is THF containing 5 mmol / L triethylamine. The column is used by connecting the trade names "TSKgel G4000HXL", "TSKgel G5000HXL", and "TSKgel G6000HXL" manufactured by Tosoh Corporation. 20 mg of a sample for measurement is dissolved in 10 mL of THF to prepare a measurement solution, 100 μL of the measurement solution is injected into a GPC measuring device, and measurement is performed 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 a modified styrene-butadiene copolymer rubber as a sample, using a Mooney viscometer (trade name "VR1132" manufactured by Ueshima Seisakusho Co., Ltd.), conforming to JIS K6300, L The Mooney viscosity is measured using a shape rotor. The measurement temperature is 110 ° C. when a styrene-butadiene copolymer rubber is used as a sample, and 100 ° C. when a modified styrene-butadiene copolymer rubber is used as a sample. First, after preheating the sample at the test temperature for 1 minute, the rotor is rotated at 2 rpm, and the torque after 4 minutes is measured to obtain Mooney viscosity (ML _{(1 + 4)} ).

(6) Glass transition temperature (Tg)
Using a modified styrene-butadiene copolymer rubber as a sample, using a differential scanning calorimeter "DSC3200S" manufactured by MacScience Co., Ltd. in accordance with ISO 22768: 2006, under a flow of helium 50 mL / min, -100 ° C to 20 ° C. The DSC curve is recorded while raising the temperature at / minute, and the peak top (Inflection point) of the DSC differential curve is defined as the glass transition temperature.

(7) Modification rate Using a modified styrene-butadiene copolymer rubber as a sample, it is measured by applying the property of adsorbing a modified basic polymer component to a GPC column using a silica-based gel as a filler. The amount of adsorption of the sample and the sample solution containing the low molecular weight internal standard polystyrene to the silica-based column was measured from the difference between the chromatogram measured on the polystyrene-based column and the chromatogram measured on the silica-based column, and the modification rate was determined. Ask. Specifically, it is as shown below.
Preparation of sample solution: Dissolve 10 mg of sample and 5 mg of standard polystyrene in 20 mL of THF to prepare a sample solution.

GPC measurement conditions using a polystyrene-based column: Using the trade name "HLC-8320 GPC" manufactured by Tosoh Corporation, using THF containing 5 mmol / L triethylamine as an eluent, injecting 10 μL of the sample solution into the apparatus, and using a column oven. Chromatograms are obtained using an RI detector at a temperature of 40 ° C. and a THF flow rate of 0.35 mL / min. For the column, three Tosoh product names "TSKgel SuperMultipore HZ-H" are connected, and a Tosoh product name "TSKguardcolum SuperMP (HZ) -H" is connected and used as a guard column in front of the column.

GPC measurement conditions using a silica-based column: Using the trade name "HLC-8320GPC" manufactured by Tosoh Corporation, using THF as an eluent, injecting 50 μL of the sample solution into the apparatus, column oven temperature 40 ° C., THF flow rate. Chromatograms are obtained using an RI detector at 0.5 ml / min. The column is used by connecting the product names "Zorbox PSM-1000S", "PSM-300S", and "PSM-60S", and the product name "DIOL 4.6 x 12.5 mm 5 micron" is used as a guard column in front of the column. Connect and use.
Calculation method of modification rate: The peak area of the sample is P1, the peak area of standard polystyrene is P2, and the peak area of the chromatogram using the silica column is 100, assuming that the total peak area of the chromatogram using the polystyrene column is 100. The modification rate (%) is calculated from the following formula, where the whole is 100, the peak area of the sample is P3, and the peak area of the standard polystyrene is P4.
Degeneration rate (%) = [1- (P2 × P3) / (P1 × P4)] × 100
(However, P1 + P2 = P3 + P4 = 100)

(8) Presence or absence of nitrogen atom The same measurement as in (7) above is performed, and if the calculated denaturation rate is 10% or more, it is determined that the substance has a nitrogen atom.

(9) Presence or absence of silicon atom Using 0.5 g of modified styrene-butadiene copolymer rubber as a sample, an ultraviolet visible spectrophotometer (trade name "UV" manufactured by Shimadzu Corporation) in accordance with JIS K 0101 44.3.1. -1800 ") and quantify by molybdenum absorptiometry. As a result, when a silicon atom is detected (detection lower limit of 10 mass ppm), it is determined that the silicon atom is contained.

(Synthesis of modified styrene-styrene-butadiene copolymer rubber)
An internal volume of 10 L, an internal height (L) to diameter (D) ratio (L / D) of 4.0, an inlet at the bottom and an outlet at the top, and a tank reactor with a stirrer. A tank-type pressure vessel having a stirrer and a jacket for temperature control was used as a polymerization reactor. Preliminarily water-removed 1,3-butadiene 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 pipe for supplying this mixed solution to the inlet of the reactive group, n-butyllithium for the residual impurity inactivation treatment was added at 0.117 mmol / min, mixed, and then added to the bottom of the reactive group. Supplied continuously. Further, polymerization in which 2,2-bis (2-oxolanyl) propane as a polar substance is vigorously mixed with a stirrer at a rate of 0.019 g / min and n-butyllithium as a polymerization initiator at a rate of 0.242 mmol / min. It was supplied to the bottom of the reactor and the polymerization reaction was continued continuously. The temperature was controlled so that the temperature of the polymerization solution at the outlet at the top of the reactor was 75 ° C. When the polymerization is sufficiently stable, a small amount of the polymer solution before the addition of the coupling agent is withdrawn from the outlet at the top of the reactor, and an antioxidant (BHT) is added so as to be 0.2 g per 100 g of the polymer, and then the solvent is added. After removal, 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 added to the polymer solution flowing out from the outlet of the reactor at 0.0302 mmol / min (0.0302 mmol / min). The polymer solution was continuously added at a rate of 5.2 ppm of water (n-hexane solution containing 5.2 ppm), and the polymer solution to which the coupling agent was added was mixed by passing through a static mixer and reacted. At this time, the time until the coupling agent was added to the polymerization solution flowing out from the outlet of the reactor was 4.8 minutes, and the temperature was 68 ° C., and the temperature in the polymerization step and the temperature until the modifier was added. The difference from was 7 ° C. Antioxidant (BHT) was continuously added to the polymer solution that had undergone the coupling reaction at 0.055 g / min (n-hexane solution) so as to be 0.2 g per 100 g of the polymer, and the coupling reaction was completed. bottom. At the same time as the antioxidant, oil (JOMO Process NC140 manufactured by JX Nippon Oil Energy Co., Ltd.) was continuously added to 100 g of the polymer so as to be 10.0 g, and mixed with a static mixer. The solvent was removed by steam stripping to obtain a modified styrene-styrene-butadiene copolymer rubber (modified SBR).
By the above method, it was confirmed that the obtained modified SBR had a nitrogen atom and a silicon atom.
The modified SBR has a "branching degree" of 8 (which can also be confirmed from the value of the contractile factor), which corresponds to the number of branches estimated from the number of functional groups and the amount of addition of the coupling agent, and is contained in one molecule of the coupling agent. The “number of SiOR residues” corresponding to the value obtained by subtracting the number of SiORs subtracted by the reaction from the total number of SiORs is 4.

<Manufacturing of tires>
(1) Comparative Example 1 and Examples 1 and 2
Using each tread rubber composition, a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions are provided by a conventional method, and the tread portion is provided in the tire width direction at the tire equatorial line. A two-wheeled vehicle tire (size: 180 / 55ZR17) divided into three by a center portion including a surface and a pair of shoulder portions including a tread end was prototyped, and a tread of the two-wheeled 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 tread, a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions are provided by a conventional method, and the tread portions are provided in the tire width direction. A two-wheeled vehicle tire (size: 180 / 55ZR17) divided into three parts by a center portion including the equatorial plane of the tire and a pair of shoulder portions including the tread end was prototyped, and the tread of the two-wheeled tire was used with the rubber composition. To form.

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

(2) Comparative Examples 2 to 4 and Examples 3 to 6
The wear resistance and wet grip property of each tread rubber composition used for the tread of a two-wheeled tire are evaluated as follows.

1. 1. Abrasion resistance (1) Comparative Example 1 and Examples 1 and 2
On a paved road test course, a test rider ran the vehicle at 80 km / h for 3500 km. Then, the amount of the remaining groove after running was measured, and the wear resistance of the tire was evaluated from the amount of the remaining groove. The evaluation results are shown in the "Abrasion resistance" column of Table 2.
An index that is a relative evaluation was calculated with the evaluation result of Comparative Example 1 as 100.
The larger the index, the higher the wear resistance. The permissible range was 110 or more.

(2) Comparative Examples 2 to 4 and Examples 3 to 6
On a paved road test course, a test rider drives the vehicle at 80 km / h for 3500 km. Then, the amount of the remaining groove after running is measured, and the wear resistance of the tire is evaluated from the amount of the remaining groove. The evaluation results are shown in the "Abrasion resistance" column of Table 2.
An index that is a relative evaluation is calculated with the evaluation result of Comparative Example 1 as 100.
The larger the index, the higher the wear resistance. The permissible range is 110 or more.

2. Wet grip (grip on wet roads)
(1) Comparative Example 1 and Examples 1 and 2
On the course of the wet road, the test rider performed various runs and evaluated the feeling of the WET GRIP property of the running tires. The evaluation results are shown in the "Wetness" column of Table 2.
With the evaluation result of Comparative Example 1 as 100, an index to be a relative evaluation was calculated.
The larger the index, the greater the wet grip of the tire. The permissible range was 102 or more.

(2) Comparative Examples 2 to 4 and Examples 3 to 6
On the course of the wet road, the test rider performs various runs and evaluates the feeling of the WET GRIP property of the running tire. The evaluation results are shown in the "Wetness" column of Table 2.
With the evaluation result of Comparative Example 1 as 100, an index to be a relative evaluation is calculated.
The larger the index, the greater the wet grip of the tire. The permissible range is 102 or more.

3. 3. Storage elastic modulus (E') and loss tangent (tan δ) of center rubber
(1) Comparative Example 1 and Examples 1 and 2
Using the vulcanized rubber test piece obtained by vulcanizing the rubber composition for center rubber of Examples and Comparative Examples, the dynamic elastic modulus (E') and loss tangent (tan δ) of the center rubber were measured in viscoelasticity. Measured using the device.
Dynamic modulus was measured 25 ° C., frequency 52 Hz, the storage modulus E at 0.1% strain 'and _0.1, 25 ° C., frequency 52 Hz, storage elastic modulus E of a strain of 4%' and ₄ and it calculates a difference _{ΔE '(= E' 0.1 -E} '4). Since the resulting E _'4 and Delta] E' and was calculated ΔE '/ E' _4.
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 a vulcanized rubber test piece obtained by vulcanizing the rubber composition for center rubber of Examples and Comparative Examples, the dynamic elastic modulus (E') and loss tangent (tan δ) of the center rubber were measured by a viscoelasticity measuring device. Measure using.
Dynamic modulus was measured 25 ° C., frequency 52 Hz, the storage modulus E at 0.1% strain 'and _0.1, 25 ° C., frequency 52 Hz, storage elastic modulus E of a strain of 4%' and ₄ , it calculates a difference _{ΔE '(= E' 0.1 -E} '4). Since the E _'4 and Delta] E' to calculate the ΔE '/ E' _4.
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 includes 70 parts by mass as a rubber component and 26 parts as an oil spread oil amount, and the modified SBR amount includes 70 parts by mass as a rubber component and 7 parts as an oil spread oil amount. The amount to include.
The "total oil amount" in Table 2 means the total amount of the oil amount of the compounding component and the oil spreading amount of the rubber component. The "total amount of softener" means the amount obtained by adding the amount of resin to the total amount of oil.

From the results in Table 2, it can be seen that the examples show well-balanced and excellent effects on wear resistance, wet grip performance, and rolling resistance as compared with the samples of each comparative example.

According to the present invention, it is possible to provide a tire capable of reducing rolling resistance and improving wear resistance while having excellent grip performance on a wet road surface.

Claims (15)

A pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions are provided, and the tread portion includes a center portion including the tire equatorial plane and a pair of shoulders including the tread end in the tire width direction. In a tire that is divided into at least three parts
The tread rubber in the center portion is a sulfide of a rubber composition containing a rubber component containing at least one modified styrene-butadiene copolymer rubber and 75 parts by mass or more of silica with respect to 100 parts by mass of the rubber component. a rubber, and, 25 ° C. of the tread rubber of the center portion, the storage modulus E _'0.1 and 25 ° C., the storage modulus E of a strain of 4%' of 0.1% strain differences between the ₄ 'as, Delta] E' Delta] E tire / E _'4 is 0.900 or less. The tire according to claim 1, wherein the content of the silica in the rubber composition is 120 parts by mass or less with respect to 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% by 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 with respect to 100 parts by mass of the rubber component. The softening agent comprises a resin, the resin is C ₅ resins, C ₉ resins, C ₅ -C ₉ resins, terpene resins, terpene - aromatics-based resin, rosin resin, dicyclopentadiene The tire according to claim 4, which is at least one selected from the group consisting of a resin and an alkylphenol-based resin. The tire according to claim 5, wherein the ratio of the resin to the total amount of the softener is 20 to 90% by mass. The tire according to any one of claims 1 to 6, wherein the rubber component further contains a modified butadiene rubber. The modified styrene - butadiene copolymer rubber, a weight average molecular weight of 20 × 10 ⁴ or more 300 × 10 ⁴ or less, the modified styrene - based on the total amount of the butadiene copolymer rubber, the molecular weight of 200 × 10 ⁴ above 500 × 10 ⁴ or less is modified styrene - containing butadiene copolymer rubber 0.25% by weight to 30% by weight, any one of claims 1 to 7, shrinkage factor (g ') is less than 0.64 The tire described in item 1. The tire according to any one of claims 1 to 8, wherein the modified styrene-butadiene copolymer rubber has a branch and has 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 that binds to the coupling residues.
The tire according to claim 9, wherein the branch includes a branch in which 5 or more of the styrene-butadiene copolymer rubber chains are bonded to the coupling residue of 1. The tire according to any one of claims 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 indicates 1 or 2. y represents an integer of 1 to 3, and y ≦ (p + 1). z represents an integer of 1 or 2. i indicates an integer of 0 to 6, j indicates an integer of 0 to 6, k indicates 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 has a hydrocarbon group having 1 to 20 carbon atoms or 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 has active hydrogen. Indicates an organic group that does not have. ] In the above formula (I), A is the tire according to claim 11, which is represented by the following formula (II), the following formula (III), the following formula (IV), or the following formula (V).

[In formula (II), B ¹ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms. a represents an integer from 1 to 10.
In formula (III), B ² represents a single bond or a hydrocarbon group ^{having 1 to 20 carbon atoms, and B 3} represents an alkyl group having 1 to 20 carbon atoms. a represents an integer from 1 to 10.
In formula (IV), B ⁴ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms. a represents an integer from 1 to 10.
In formula (V), B ⁵ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms. a represents an integer from 1 to 10. ] The modified styrene-butadiene copolymer rubber according to any one of claims 1 to 12, wherein the modified styrene-butadiene copolymer rubber is formed by reacting the styrene-butadiene copolymer rubber with a coupling agent represented by the following formula (VI). tire.

[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 indicates 1 or 2. i, j and k each independently represent an integer of 0 to 6. However, (i + j + k) is an integer of 3 to 10. A has a hydrocarbon group having 1 to 20 carbon atoms or 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 has no active hydrogen. Indicates an organic group. ] The coupling agent represented by the above formula (VI) is tetrakis [3- (2,2-dimethoxy-1-aza-2-silacyclopentane) propyl] -1,3-propanediamine, tetrakis (3-tritri). The tire according to claim 13, which is at least one selected from the group consisting of methoxysilylpropyl) -1,3-propanediamine and tetrakis (3-trimethoxysilylpropyl) -1,3-bisaminomethylcyclohexane. The tire according to any one of claims 4 to 14, wherein the content of the softening agent in the rubber composition is 72 parts by mass or less with respect to 100 parts by mass of the rubber component.