JP2020059809A - Rubber composition for base tread and tire - Google Patents

Abstract

To provide a rubber composition for base tread which improves wet property when a base tread of a tire is exposed while highly achieving crack resistance and low rolling resistance.SOLUTION: A rubber composition for base tread contains a rubber component (A) and a reinforcing filler (B), in which the rubber component (A) contains a specific modified conjugated diene-based polymer (A1), an amount of the modified conjugated diene-based polymer (A1) is 7-35 pts.mass with respect to 100 pts.mass of the rubber component (A), and an amount of extension oil added to the modified conjugated diene-based polymer (A1) is 10 pts.mass or less with respect to 100 pts.mass of the modified conjugated diene-based polymer (A1), and the reinforcing filler (B) contains carbon black and silica, and an amount of the carbon black is 1-35 pts.mass with respect to 100 pts.mass of the rubber component (A).SELECTED DRAWING: None

Description

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

  In order to reduce the rolling resistance of a tire, a structure in which rubber with a small energy loss is arranged in a base tread has been proposed (for example, refer to Patent Document 1). Further, the base tread is required to have various properties such as crack resistance and elongation at break, which are different from those of the cap rubber of the tread.

JP 2009-280808 A

  The base tread of the tire may be unexpectedly exposed due to contact between the tire and obstacles or projections on the road, or excessive wear of the tread due to forgetting to replace the tire. Although the base tread of a tire is a part that is supposed not to be exposed, even if it is exposed unexpectedly as described above, it has good wet grip properties (referred to as "wet property when exposed to base tread"). ) Is desirable.

  Therefore, an object of the present invention is to provide a rubber composition for a base tread that improves the wettability of the tire when the base tread is exposed, while achieving both high crack resistance and low rolling resistance.

The rubber composition for a base tread according to the present invention contains a rubber component (A) and a reinforcing filler (B),
The rubber component (A) contains a modified conjugated diene-based polymer (A1),
The modified conjugated diene polymer (A1) has a weight average molecular weight of 20 × 10 ^{4 to} 300 × 10 ⁴ , and has a molecular weight of 200 × 10 ^{4 with} respect to the total amount of the modified conjugated diene polymer (A1). The modified conjugated diene polymer, which is ˜500 × 10 ⁴ , contains 0.25 to 30 mass%, and the contraction factor (g ′) is less than 0.64,
The amount of the modified conjugated diene polymer (A1) is 7 to 35 parts by mass with respect to 100 parts by mass of the rubber component (A),
The amount of extender oil added to the modified conjugated diene polymer (A1) is 10 parts by mass or less with respect to 100 parts by mass of the modified conjugated diene polymer (A1),
The reinforcing filler (B) contains carbon black and silica,
In the rubber composition for a base tread, the amount of the carbon black is 1 to 35 parts by mass with respect to 100 parts by mass of the rubber component (A).
This makes it possible to improve the wettability of the tire when the base tread is exposed, while achieving a high level of both crack resistance and low rolling resistance of the tire.

In the rubber composition for a base tread according to the present invention, it is preferable that the rubber component (A) further contains one or more selected from the group consisting of natural rubber, synthetic isoprene rubber, butadiene rubber and styrene butadiene rubber.
Thereby, crack resistance, wear resistance, or wetness when the base tread is exposed can be further improved.

In the rubber composition for a base tread according to the present invention, the rubber component (A) further contains natural rubber,
The amount of the natural rubber is preferably 65 to 93 parts by mass with respect to 100 parts by mass of the rubber component (A).
Thereby, the crack resistance can be further improved and the balance with the low rolling resistance is further improved.

In the rubber composition for a base tread according to the present invention, the amount of silica is preferably 15 to 70 parts by mass with respect to 100 parts by mass of the rubber component (A).
This further improves the balance between crack resistance and low rolling resistance.

In the rubber composition for a base tread according to the present invention, the modified conjugated diene polymer (A1) is a modified styrene butadiene rubber, and the modified conjugated diene polymer (A1) has a glass transition temperature of -30. It is preferably at least ° C.
Thereby, crack resistance and low rolling resistance can be further improved.

In the rubber composition for a base tread according to the present invention, it is preferable that the modified conjugated diene polymer (A1) has a branch and a branching degree of 5 or more.
This makes it possible to further improve the wettability of the tire when the base tread is exposed, while achieving both crack resistance and low rolling resistance to a higher degree.

In the rubber composition for a base tread according to the present invention, the modified conjugated diene polymer (A1) has one or more coupling residues, and a conjugated diene polymer chain bonded to the coupling residues. Has,
The branch preferably includes a branch in which 5 or more conjugated diene polymer chains are bonded to one coupling residue.
This makes it possible to further improve the wettability of the tire when the base tread is exposed, while achieving both crack resistance and low rolling resistance to a higher degree.

［一般式（Ｉ）中、Ｄは、共役ジエン系重合体鎖を示し、Ｒ^１、Ｒ^２及びＲ^３は、それぞれ独立して単結合又は炭素数１〜２０のアルキレン基を示し、Ｒ^４及びＲ^７は、それぞれ独立して炭素数１〜２０のアルキル基を示し、Ｒ^５、Ｒ^８、及びＲ^９は、それぞれ独立して水素原子又は炭素数１〜２０のアルキル基を示し、Ｒ^６及びＲ^１０は、それぞれ独立して炭素数１〜２０のアルキレン基を示し、Ｒ^１１は、水素原子又は炭素数１〜２０のアルキル基を示し、ｍ及びｘは、それぞれ独立して１〜３の整数を示し、ｘ≦ｍであり、ｐは、１又は２を示し、ｙは、１〜３の整数を示し、ｙ≦（ｐ＋１）であり、ｚは、１又は２を示し、それぞれ複数存在する場合のＤ、Ｒ^１〜Ｒ^１１、ｍ、ｐ、ｘ、ｙ、及びｚは、それぞれ独立しており、ｉは、０〜６の整数を示し、ｊは、０〜６の整数を示し、ｋは、０〜６の整数を示し、（ｉ＋ｊ＋ｋ）は、３〜１０の整数であり、（（ｘ×ｉ）＋（ｙ×ｊ）＋（ｚ×ｋ））は、５〜３０の整数であり、Ａは、炭素数１〜２０の炭化水素基、又は、酸素原子、窒素原子、ケイ素原子、硫黄原子及びリン原子からなる群より選ばれる少なくとも１種の原子を有し、かつ、活性水素を有しない有機基を示す］で表されることが好ましい。
これにより、耐亀裂性と、低転がり抵抗性とをより高度に両立しながら、タイヤのベーストレッド露出時ウェット性をより向上させることができる。 In the rubber composition for a base tread according to the present invention, the modified conjugated diene polymer (A1) has the following general formula (I):

[In the general formula (I), D represents a conjugated diene-based polymer chain, R ¹ , R ² and R ³ each independently represent a single bond or an alkylene group having 1 to 20 carbon atoms, and R ⁴ And R ⁷ each independently represent an alkyl group having 1 to 20 carbon atoms, and R ⁵ , R ⁸ and R ⁹ each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, and 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, and m and x each independently represent 1 to 1. 3 represents an integer of 3, x ≦ m, p represents 1 or 2, y represents an integer of 1 to 3, y ≦ (p + 1), z represents 1 or 2, and respectively. ^D when there are a ^{plurality, R 1 ~R 11, m,} p, x, y, and z are each independently I is an integer of 0 to 6, j is an integer of 0 to 6, k is an integer of 0 to 6, (i + j + k) is an integer of 3 to 10, and (( x × i) + (y × j) + (z × k)) is an integer of 5 to 30, and A is a hydrocarbon group having 1 to 20 carbon atoms, or an oxygen atom, a nitrogen atom, or a silicon atom. Represents an organic group having at least one atom selected from the group consisting of a sulfur atom and a phosphorus atom and having no active hydrogen].
This makes it possible to further improve the wettability of the tire when the base tread is exposed, while achieving both crack resistance and low rolling resistance to a higher degree.

［一般式（ＩＩ）中、Ｂ^１は、単結合又は炭素数１〜２０の炭化水素基を示し、ａは、１〜１０の整数を示し、複数存在する場合のＢ^１は、各々独立している；
一般式（ＩＩＩ）中、Ｂ^２は、単結合又は炭素数１〜２０の炭化水素基を示し、Ｂ^３は、炭素数１〜２０のアルキル基を示し、ａは、１〜１０の整数を示し、それぞれ複数存在する場合のＢ^２及びＢ^３は、各々独立している；
一般式（ＩＶ）中、Ｂ^４は、単結合又は炭素数１〜２０の炭化水素基を示し、ａは、１〜１０の整数を示し、複数存在する場合のＢ^４は、各々独立している；
一般式（Ｖ）中、Ｂ^５は、単結合又は炭素数１〜２０の炭化水素基を示し、ａは、１〜１０の整数を示し、複数存在する場合のＢ^５は、各々独立している］のいずれかで表されることが好ましい。
これにより、耐亀裂性と、低転がり抵抗性とをより高度に両立しながら、タイヤのベーストレッド露出時ウェット性をより向上させることができる。 In the rubber composition for a base tread according to the present invention, in the general formula (I), A is the following general formulas (II) to (V):

[In the general formula (II), B ¹ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, a represents an integer of 1 to 10, and when there are a plurality of B ^{1's, they} are each independently. ing;
In the general formula (III), B ² represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, B ³ represents an alkyl group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10. B ² and B ³ when there are a plurality of each are independent of each other;
In formula (IV), B ⁴ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, a represents an integer of 1 to 10, and B ⁴ in the case where a plurality of them are present, each independently. Is;
In formula (V), B ⁵ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, a represents an integer of 1 to 10, and B ⁵ in the case where a plurality of B ⁵ are present are each independently. Is present].
This makes it possible to further improve the wettability of the tire when the base tread is exposed, while achieving both crack resistance and low rolling resistance to a higher degree.

［一般式（ＶＩ）中、Ｒ^１２、Ｒ^１３及びＲ^１４は、それぞれ独立して単結合又は炭素数１〜２０のアルキレン基を示し、Ｒ^１５、Ｒ^１６、Ｒ^１７、Ｒ^１８及びＲ^２０は、それぞれ独立して炭素数１〜２０のアルキル基を示し、Ｒ^１９及びＲ^２２は、それぞれ独立して炭素数１〜２０のアルキレン基を示し、Ｒ^２１は、炭素数１〜２０の、アルキル基又はトリアルキルシリル基を示し、ｍは、１〜３の整数を示し、ｐは、１又は２を示し、Ｒ^１２〜Ｒ^２２、ｍ及びｐは、複数存在する場合、それぞれ独立しており、ｉ、ｊ及びｋは、それぞれ独立して０〜６の整数を示し、但し、（ｉ＋ｊ＋ｋ）は、３〜１０の整数であり、Ａは、炭素数１〜２０の炭化水素基、又は、酸素原子、窒素原子、ケイ素原子、硫黄原子及びリン原子からなる群から選択される少なくとも一種の原子を有し、かつ、活性水素を有しない有機基を示す］で表されるカップリング剤と反応させてなることが好ましい。
これにより、耐亀裂性と、低転がり抵抗性とをより高度に両立しながら、タイヤのベーストレッド露出時ウェット性をより向上させることができる。 In the rubber composition for a base tread according to the present invention, the modified conjugated diene polymer (A1) is a conjugated diene polymer represented by the following general formula (VI):

[In the general formula ^{(VI), R 12, R} 13 and ^{R 14} is independently a single bond or an alkylene group having a carbon number of ^{1~20, R 15, R 16,} R 17, R 18 and ^{R 20} Are each independently an alkyl group having 1 to 20 carbon atoms, R ¹⁹ and R ²² are each independently an alkylene group having 1 to 20 carbon atoms, and R ²¹ is an alkyl group having 1 to 20 carbon atoms; Represents an alkyl group or a trialkylsilyl group, m represents an integer of 1 to 3, p represents 1 or 2, and R ^{12 to} R ²² , m and p each independently represent a plurality of them. And i, j, and k each independently represent an integer of 0 to 6, provided that (i + j + k) is an integer of 3 to 10 and A is a hydrocarbon group having 1 to 20 carbon atoms, or , Oxygen atom, nitrogen atom, silicon atom, sulfur atom and phosphorus atom? It represents an organic group having at least one atom selected from the group consisting of and having no active hydrogen].
This makes it possible to further improve the wettability of the tire when the base tread is exposed, while achieving both crack resistance and low rolling resistance to a higher degree.

A tire according to the present invention is a tire using the rubber composition for a base tread described in any one of the above as a base tread.
This makes it possible to improve the wettability of the tire when the base tread is exposed, while achieving both high crack resistance and low rolling resistance.

  ADVANTAGE OF THE INVENTION According to this invention, the rubber composition for base treads which improve the wettability at the time of base tread exposure of a tire can be provided, highly satisfying both crack resistance of a tire and low rolling resistance. Moreover, according to the present invention, it is possible to provide a tire having improved wettability when the base tread is exposed, while achieving a high level of both crack resistance and low rolling resistance.

  Hereinafter, embodiments of the present invention will be described. These descriptions are for the purpose of illustrating the present invention and are not intended to limit the present invention in any way.

  Numerical ranges, as used herein, are intended to include the lower and upper limits of the range unless stated otherwise. For example, 0.25 to 30 mass% means 0.25 mass% or more and 30 mass% or less.

  In the following description, the rubber component (A), the reinforcing filler (B), the modified conjugated diene polymer (A1) and the like are referred to as the component (A), the component (B) and the component (A1), respectively. Sometimes.

  The base tread is a layer on the inner side in the radial direction when the tread portion of the tire includes a layer on the outer side in the radial direction (cap tread) that serves as a ground contact portion of the tire and a layer on the inner side in the radial direction.

(Rubber composition for base tread)
The rubber composition for a base tread according to the present invention contains a rubber component (A) and a reinforcing filler (B),
The rubber component (A) contains a modified conjugated diene-based polymer (A1),
The modified conjugated diene polymer (A1) has a weight average molecular weight of 20 × 10 ^{4 to} 300 × 10 ⁴ , and has a molecular weight of 200 × 10 ^{4 with} respect to the total amount of the modified conjugated diene polymer (A1). The modified conjugated diene polymer, which is ˜500 × 10 ⁴ , contains 0.25 to 30 mass%, and the contraction factor (g ′) is less than 0.64,
The amount of the modified conjugated diene polymer (A1) is 7 to 35 parts by mass with respect to 100 parts by mass of the rubber component (A),
The amount of extender oil added to the modified conjugated diene polymer (A1) is 10 parts by mass or less with respect to 100 parts by mass of the modified conjugated diene polymer (A1),
The reinforcing filler (B) contains carbon black and silica,
In the rubber composition for a base tread, the amount of the carbon black is 1 to 35 parts by mass with respect to 100 parts by mass of the rubber component (A).

  Furthermore, when the rubber composition for a base tread according to the present invention is applied to the base tread, the adhesiveness with the belt coating rubber that covers the steel cord of the belt layer of the tire can be more easily maintained.

<Rubber component (A)>
The rubber component (A) contains a modified conjugated diene polymer (A1) described later. This improves the dispersibility of the component (B) silica and the reinforcing property.

-Modified conjugated diene polymer (A1)
The modified conjugated diene polymer (A1) has a weight average molecular weight of 20 × 10 ^{4 to} 300 × 10 ⁴ , and a molecular weight of 200 × 10 ^{4 to} 500 with respect to the total amount of the modified conjugated diene polymer (A1). The modified conjugated diene-based polymer of × 10 ⁴ is contained in an amount of 0.25 to 30% by mass, and the contraction factor (g ′) is less than 0.64. As the component (A1), one type may be used alone, or two or more types may be used in combination.

  The conjugated diene-based polymer that is the base polymer of the component (A1) is a polymer of one type of conjugated diene compound or a copolymer of two or more types of conjugated diene compounds. Further, the conjugated diene-based polymer may be a copolymer of a conjugated diene compound and an aromatic vinyl compound.

  Examples of the conjugated diene compound include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 3-methyl-1, Examples thereof include compounds having 4 to 12 carbon atoms such as 3-pentadiene, 1,3-hexadiene and 1,3-heptadiene. From the viewpoint of industrial availability, 1,3-butadiene and isoprene are preferable as the conjugated diene compound.

  Examples of the aromatic vinyl compound include styrene, p-methylstyrene, α-methylstyrene, vinylxylene, vinylnaphthalene, diphenylethylene 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene and 4-cyclohexyl. Examples include xyl styrene and 2,4,6-trimethyl styrene. The aromatic vinyl compounds may be used alone or in combination of two or more. Styrene is preferred as the aromatic vinyl compound from the viewpoint of industrial availability.

  Examples of the conjugated diene polymer include natural rubber (NR), polybutadiene (BR), synthetic polyisoprene (IR), styrene butadiene rubber (SBR), isoprene butadiene copolymer, ethylene butadiene copolymer, and propylene butadiene copolymer. Examples thereof include polymers. The conjugated diene-based polymer which is the base polymer of the component (A1) is preferably SBR.

  The component (A1) is preferably a modified SBR.

The weight average molecular weight (Mw) of the component (A1) is 20 × 10 ^{4 to} 300 × 10 ⁴ . The Mw is preferably 50 × 10 ⁴ or more, 64 × 10 ⁴ or more, or 80 × 10 ⁴ or more. In addition, the Mw is preferably 250 × 10 ⁴ or less, 180 × 10 ⁴ or less, or 150 × 10 ⁴ or less. When the Mw is 20 × 10 ⁴ or more, low rolling resistance of the tire and wettability when the base tread is exposed can be highly compatible. Moreover, if Mw is 300 × 10 ⁴ or less, the processability of the rubber composition is improved.

The number average molecular weight, the weight average molecular weight, the molecular weight distribution, and the content of a specific high molecular weight component described later of the conjugated diene polymer and the component (A1) are measured as follows. Using a conjugated diene polymer or a modified conjugated diene polymer as a sample, three GPC (gel permeation chromatography) measuring devices (trade name “HLC- manufactured by Tosoh Corporation,” in which three columns having polystyrene gel as a filler are connected 8320GPC ") and a RI detector (trade name" HLC-8020 "manufactured by Tosoh Corporation) is used to measure a chromatogram, and a weight average molecular weight is obtained based on a calibration curve obtained using standard polystyrene. (Mw) to number-average molecular weight (Mn) of the molecular weight distribution (Mw / Mn), a peak top molecular weight of the modified conjugated diene polymer (Mp ₁₎ and a peak top molecular weight of the conjugated diene polymer and (Mp ₂₎ thereof The ratio (Mp ₁ / Mp ₂ ) and the ratio of the modified conjugated diene-based polymer having a molecular weight of 200 × 10 ^{4 to} 500 × 10 ⁴ are obtained. The eluent is THF (tetrahydrofuran) containing 5 mmol / L triethylamine. For the column, three Tosoh product name "TSKgel SuperMultipore HZ-H" are connected, and a Tosoh product name "TSKguardcolumn SuperMP (HZ) -H" is used as a guard column in front of it. 10 mg of a 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 measurement device, and measurement is performed under the conditions of an oven temperature of 40 ° C. and a THF flow rate of 0.35 mL / min.

The peak top molecular weight (Mp ₁ and Mp ₂ ) is determined as follows. In the GPC curve obtained by measurement, the peak detected as the highest molecular weight component 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 component (A1) is the modified conjugated diene-based polymer having a molecular weight of 200 × 10 ^{4 to} 500 × 10 ⁴ with respect to the total amount (100% by mass) of the component (A1) (in the present specification, “specific 0.25 to 30 mass% is included. When the content of the specific high molecular weight component is within this range, the low rolling resistance of the tire and the wettability when the base tread is exposed can be highly compatible with each other.

Further, the ratio of the specific high molecular weight component is calculated by subtracting the ratio occupied by the molecular weight of less than 200 × 10 ⁴ from the ratio occupied by the molecular weight of 500 × 10 ⁴ or less in the whole from the integral molecular weight distribution curve.

  In one example, the component (A1) contains a specific high molecular weight component in an amount of 1.0% by mass or more, 1.4% by mass or more, 1.75% by mass or more, 2.0% by mass or more, 2.15% by mass or more. , Or 2.5 mass% or more. In one example, the component (A1) contains a specific high molecular weight component in an amount of 28% by mass or less, 25% by mass or less, 20% by mass or less, or 18% by mass or less.

  In the present specification, the “molecular weight” is a standard polystyrene-equivalent molecular weight obtained by GPC. In order to obtain the component (A1) in which the content of the specific high molecular weight component is in such a range, it is preferable to control the reaction conditions in the polymerization step and reaction step described later. For example, in the polymerization step, the amount of the organic monolithium compound described below used as a polymerization initiator may be adjusted. Further, in the polymerization step, a method having a residence time distribution may be used, that is, the time distribution of the growth reaction may be widened in both continuous and batchwise polymerization modes.

  In one example, the molecular weight distribution (Mw / Mn) of component (A1) is 1.6-3.0.

The contraction factor (g ') of the component (A1) is less than 0.64. In general, a branched polymer 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 having the absolute molecular weight of. That is, as the degree of branching of the polymer increases, the contraction factor (g ') tends to decrease. In the present embodiment, the intrinsic viscosity is used as an index of the size of the molecule, and the linear polymer is used as one that follows the relational expression of intrinsic viscosity [η] = − 3.883M ^0.771 . The contraction factor (g ') at each absolute molecular weight of the modified conjugated diene polymer was calculated, and the average value of the contraction factor (g') when the absolute molecular weight was 100 x 10 ⁴ to 200 x 10 ⁴ was calculated as The contraction factor (g ') of the modified conjugated diene polymer. Here, the "branch" is formed by directly or indirectly binding one polymer to another polymer. The “branching degree” is the number of polymers directly or indirectly bonded to one branch. For example, the degree of branching is 5 when the following 5 conjugated diene polymer chains are indirectly bonded to each other via a coupling residue described below. The coupling residue is a constituent unit of the modified conjugated diene-based polymer that is bonded to the conjugated diene-based polymer chain, and, for example, reacts the conjugated diene-based polymer described below with a coupling agent. Is a structural unit derived from the coupling agent. Further, the conjugated diene-based polymer chain is a structural unit of the modified conjugated diene-based polymer, for example, generated by reacting a conjugated diene-based polymer and a coupling agent described below, derived from a conjugated diene-based polymer. It is a structural unit.

  The contraction factor (g ') is, for example, 0.63 or less, 0.60 or less, 0.59 or less, or 0.57 or less. The lower limit of the contraction factor (g ′) is not particularly limited and may be equal to or lower than the detection limit value, for example, 0.30 or more, 0.33 or more, 0.35 or more, 0.45 or more, 0. It is 57 or more, or 0.59 or more. By using the component (A1) having a contraction factor (g ') in this range, the processability of the rubber composition is improved.

  Since the contraction factor (g ') tends to depend on the branching degree, for example, the contraction factor (g') can be controlled using the branching degree as an index. Specifically, when a modified conjugated diene polymer having a branching degree of 6 is used, the contraction factor (g ′) thereof tends to be 0.59 to 0.63, and the branching degree is 8. When the modified conjugated diene polymer is used, the contraction factor (g ') tends to be 0.45 to 0.59.

The method for measuring the contraction factor (g ') is as follows. Using a modified conjugated diene polymer as a sample, a GPC measuring device (trade name "GPCmax VE-2001" manufactured by Malvern Co., Ltd.) in which three columns having polystyrene gel as a filler are connected, and a light scattering detector is used. , RI detector, viscosity detector (trade name "TDA305" manufactured by Malvern Co., Ltd.) are used in this order for measurement, and based on standard polystyrene, a light scattering detector and an RI detector are measured. The absolute molecular weight is obtained from the result of 1 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 viscosities corresponding to each molecular weight is calculated. The eluent is THF containing 5 mmol / L of triethylamine. As the column, the product names “TSKgel G4000HXL”, “TSKgel G5000HXL”, and “TSKgel G6000HXL” manufactured by Tosoh Corporation are connected and used. 20 mg of a sample for measurement is dissolved in 10 mL of THF to prepare a measurement solution, and 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.

  The amount of extender oil added to the component (A1) is 10 parts by mass or less based on 100 parts by mass of the component (A1). Preferably, the amount of extending oil added to the component (A1) is more than 0 parts by mass and 10 parts by mass or less. When the amount of the extending oil is 10 parts by mass or less, it is possible to further improve the wettability of the tire when the base tread is exposed, while achieving both crack resistance and low rolling resistance to a higher degree.

  Examples of the extender oil include aroma oil, naphthene oil, paraffin oil, aroma substitute oil and the like. Among these, an aromatic alternative oil having a polycyclic aromatic (PCA) component of 3% by mass or less according to the IP346 method is preferable from the viewpoints of environmental safety, and prevention of oil bleeding and wet grip properties. Examples of aroma substitute oils include TDAE (Treatment Distillate Aromatic Extracts) and MES (Milt Extract Solvate) RicA (R) (E), etc., as well as RA (R) (E).

  The component (A1) can be an oil-extended polymer to which the extender oil is added as long as the amount of the extender oil added is 10 parts by mass or less based on 100 parts by mass of the component (A1). It may be an oil extension or an oil extension.

In the rubber composition for a base tread according to the present invention, it is preferable that the modified conjugated diene polymer (A1) has a branch and a branching degree of 5 or more.
This makes it possible to further improve the wettability of the tire when the base tread is exposed, while achieving both crack resistance and low rolling resistance to a higher degree.

  The component (A1) has one or more coupling residues and a conjugated diene-based polymer chain that binds to the coupling residues, and further, the branching is one coupling residue. On the other hand, it is more preferable to include a branch in which 5 or more conjugated diene polymer chains are bonded. The structure of the modified conjugated diene-based polymer so that the degree of branching is 5 or more, and the branching includes a branch in which 5 or more conjugated diene-based polymer chains are bonded to one coupling residue. By specifying, the contraction factor (g ′) can be made less than 0.64 more reliably. The number of conjugated diene polymer chains bonded to one coupling residue can be confirmed from the value of the contraction factor (g ').

In the rubber composition for a base tread according to the present invention, the modified conjugated diene polymer (A1) has one or more coupling residues, and a conjugated diene polymer chain bonded to the coupling residues. Has,
The branch preferably includes a branch in which 5 or more conjugated diene polymer chains are bonded to one coupling residue.
This makes it possible to further improve the wettability of the tire when the base tread is exposed, while achieving both crack resistance and low rolling resistance to a higher degree.

  Further, it is more preferable that the component (A1) has branching and the branching degree is 6 or more. Further, the component (A1) has one or more coupling residues and a conjugated diene-based polymer chain bonded to the coupling residues, and further the branch has the coupling residue of 1. It is more preferable to include a branch in which 6 or more conjugated diene-based polymer chains are bonded to the group. The structure of the modified conjugated diene-based polymer so that the degree of branching is 6 or more, and the branching includes a branch in which 6 or more conjugated diene-based polymer chains are bonded to one coupling residue. By specifying, the contraction factor (g ′) can be reduced to 0.63 or less.

  Furthermore, the component (A1) preferably has a branching degree of 7 or more, and more preferably 8 or more. The upper limit of the branching degree is not particularly limited, but is preferably 18 or less. Further, the component (A1) has one or more coupling residues and a conjugated diene-based polymer chain bonded to the coupling residues, and further the branch has the coupling residue of 1. It is even more preferable to include a branch in which 7 or more of the conjugated diene-based polymer chains are bonded to a group, and 8 or more of the conjugated diene-based polymer chains for 1 of the coupling residue are more preferable. It is especially preferred to include branches that are linked. The structure of the modified conjugated diene-based polymer so that the degree of branching is 8 or more, and the branch includes a branch in which 8 or more conjugated diene-based polymer chains are bonded to one coupling residue. By specifying, the contraction factor (g ′) can be reduced to 0.59 or less.

［一般式（Ｉ）中、Ｄは、共役ジエン系重合体鎖を示し、Ｒ^１、Ｒ^２及びＲ^３は、それぞれ独立して単結合又は炭素数１〜２０のアルキレン基を示し、Ｒ^４及びＲ^７は、それぞれ独立して炭素数１〜２０のアルキル基を示し、Ｒ^５、Ｒ^８、及びＲ^９は、それぞれ独立して水素原子又は炭素数１〜２０のアルキル基を示し、Ｒ^６及びＲ^１０は、それぞれ独立して炭素数１〜２０のアルキレン基を示し、Ｒ^１１は、水素原子又は炭素数１〜２０のアルキル基を示し、ｍ及びｘは、それぞれ独立して１〜３の整数を示し、ｘ≦ｍであり、ｐは、１又は２を示し、ｙは、１〜３の整数を示し、ｙ≦（ｐ＋１）であり、ｚは、１又は２を示し、それぞれ複数存在する場合のＤ、Ｒ^１〜Ｒ^１１、ｍ、ｐ、ｘ、ｙ、及びｚは、それぞれ独立しており、ｉは、０〜６の整数を示し、ｊは、０〜６の整数を示し、ｋは、０〜６の整数を示し、（ｉ＋ｊ＋ｋ）は、３〜１０の整数であり、（（ｘ×ｉ）＋（ｙ×ｊ）＋（ｚ×ｋ））は、５〜３０の整数であり、Ａは、炭素数１〜２０の炭化水素基、又は、酸素原子、窒素原子、ケイ素原子、硫黄原子及びリン原子からなる群より選ばれる少なくとも１種の原子を有し、かつ、活性水素を有しない有機基を示す］で表されることが好ましい。
これにより、耐亀裂性と、低転がり抵抗性とをより高度に両立しながら、タイヤのベーストレッド露出時ウェット性をより向上させることができる。 In the rubber composition for a base tread according to the present invention, the modified conjugated diene polymer (A1) has the following general formula (I):

[In the general formula (I), D represents a conjugated diene-based polymer chain, R ¹ , R ² and R ³ each independently represent a single bond or an alkylene group having 1 to 20 carbon atoms, and R ⁴ And R ⁷ each independently represent an alkyl group having 1 to 20 carbon atoms, and R ⁵ , R ⁸ and R ⁹ each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, and 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, and m and x each independently represent 1 to 1. 3 represents an integer of 3, x ≦ m, p represents 1 or 2, y represents an integer of 1 to 3, y ≦ (p + 1), z represents 1 or 2, and respectively. ^D when there are a ^{plurality, R 1 ~R 11, m,} p, x, y, and z are each independently I is an integer of 0 to 6, j is an integer of 0 to 6, k is an integer of 0 to 6, (i + j + k) is an integer of 3 to 10, and (( x × i) + (y × j) + (z × k)) is an integer of 5 to 30, and A is a hydrocarbon group having 1 to 20 carbon atoms, or an oxygen atom, a nitrogen atom, or a silicon atom. Represents an organic group having at least one atom selected from the group consisting of a sulfur atom and a phosphorus atom and having no active hydrogen].
This makes it possible to further improve the wettability of the tire when the base tread is exposed, while achieving both crack resistance and low rolling resistance to a higher degree.

In one example, in the general formula (I), the weight average molecular weight of the conjugated diene-based polymer chain represented by D is 10 × 10 ^{4 to} 100 × 10 ⁴ . The conjugated diene-based polymer chain is a structural unit of a modified conjugated diene-based polymer, for example, a structural unit derived from a conjugated diene-based polymer produced by reacting a conjugated diene-based polymer with a coupling agent. is there.

In formula (I), 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 hydroxyl group (—OH), secondary amino group (> NH), primary amino group (—NH ₂ ), and sulfhydryl group (—SH). And an organic group having no functional group.

［一般式（ＩＩ）中、Ｂ^１は、単結合又は炭素数１〜２０の炭化水素基を示し、ａは、１〜１０の整数を示し、複数存在する場合のＢ^１は、各々独立している；
一般式（ＩＩＩ）中、Ｂ^２は、単結合又は炭素数１〜２０の炭化水素基を示し、Ｂ^３は、炭素数１〜２０のアルキル基を示し、ａは、１〜１０の整数を示し、それぞれ複数存在する場合のＢ^２及びＢ^３は、各々独立している；
一般式（ＩＶ）中、Ｂ^４は、単結合又は炭素数１〜２０の炭化水素基を示し、ａは、１〜１０の整数を示し、複数存在する場合のＢ^４は、各々独立している；
一般式（Ｖ）中、Ｂ^５は、単結合又は炭素数１〜２０の炭化水素基を示し、ａは、１〜１０の整数を示し、複数存在する場合のＢ^５は、各々独立している］のいずれかで表されることが好ましい。
これにより、耐亀裂性と、低転がり抵抗性とをより高度に両立しながら、タイヤのベーストレッド露出時ウェット性をより向上させることができる。 In the rubber composition for a base tread according to the present invention, in the general formula (I), A is the following general formulas (II) to (V):

[In the general formula (II), B ¹ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, a represents an integer of 1 to 10, and when there are a plurality of B ^{1's, they} are each independently. ing;
In the general formula (III), B ² represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, B ³ represents an alkyl group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10. B ² and B ³ when there are a plurality of each are independent of each other;
In formula (IV), B ⁴ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, a represents an integer of 1 to 10, and B ⁴ in the case where a plurality of them are present, each independently. Is;
In formula (V), B ⁵ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, a represents an integer of 1 to 10, and B ⁵ in the case where a plurality of B ⁵ are present are each independently. Is present].
This makes it possible to further improve the wettability of the tire when the base tread is exposed, while achieving both crack resistance and low rolling resistance to a higher degree.

  In one example, in the general formula (I), A is represented by the general formula (II) or (III), and k represents 0. In another example, in the general formula (I), A is represented by the general formula (II) or (III), k is 0, and in the general formula (II) or (III), a Represents an integer of 2 to 10. In still another example, in the general formula (I), A is represented by the general formula (II), k is 0, and in the general formula (II), a is an integer of 2 to 10. Indicates.

Regarding B ¹ , B ² , B ⁴ , and B ^{5 in the} general 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.

  The component (A1) preferably has a nitrogen atom and a silicon atom. In this case, the processability of the rubber composition becomes good, and the low rolling resistance can be improved while improving the wettability of the tire when the base tread is exposed and the wear resistance. Regarding the fact that the component (A1) has a nitrogen atom, it is determined that the component (A1) has a nitrogen atom when the calculated modification rate is 10% or more by the modification rate measuring method described later.

  It is judged by the following method that the component (A1) has a silicon atom. 0.5 g of the modified conjugated diene polymer was used as a sample, and it was measured according to JIS K 0101 44.3.1 using an ultraviolet-visible spectrophotometer (trade name "UV-1800" manufactured by Shimadzu Corporation). , Molybdenum blue absorptiometry. As a result, when silicon atoms are detected (lower limit of detection: 10 mass ppm), it is determined that they have silicon atoms.

  In one example of the component (A1), at least one end of the conjugated diene-based polymer chain is bonded to the silicon atom of the coupling residue. In this case, the ends of a plurality of conjugated diene polymer chains may be bonded to one silicon atom. Further, the end of the conjugated diene polymer chain and the alkoxy group or the hydroxyl group having 1 to 20 carbon atoms are bonded to one silicon atom, and as a result, the one silicon atom is alkoxysilyl having 1 to 20 carbon atoms. A group or a silanol group may be formed.

  The amount of bound conjugated diene in the conjugated diene polymer or component (A1) is, for example, 40 to 100% by mass, or 55 to 80% by mass. When the amount of the bound conjugated diene is in the above range, it is possible to further improve the wettability of the tire when the base tread is exposed, while making the crack resistance of the tire and the low rolling resistance highly compatible.

  The amount of the bound aromatic vinyl in the conjugated diene polymer or the component (A1) is, for example, 0% by mass or more, 20% by mass or more, or 35% by mass or more. The amount of bound aromatic vinyl in the conjugated diene polymer or the component (A1) is, for example, 60% by mass or less, or 45% by mass or less. When the amount of the bound aromatic vinyl is 35% by mass or more, the low rolling resistance of the tire can be further improved.

  The amount of bound aromatic vinyl can be measured by ultraviolet absorption of a phenyl group, and the amount of bound conjugated diene can also be obtained from this. Specifically, it measures according to the following. Using the modified conjugated diene polymer as a sample, 100 mg of the sample is made up to 100 mL with chloroform and dissolved to obtain a measurement sample. The amount of the bound aromatic vinyl (mass%) relative to 100% by mass of the sample is measured by the absorption amount of the ultraviolet absorption wavelength (near 254 nm) by the phenyl group of the bound aromatic vinyl (a spectrophotometer manufactured by Shimadzu Corporation “ UV-2450 ").

  When the component (A1) is a modified SBR, the amount of bound styrene is preferably 35% by mass or more.

  In the conjugated diene polymer or the component (A1), the vinyl bond content in the conjugated diene bond unit is, for example, 10 to 75 mol%, or 20 to 65 mol%.

  When the component (A1) is a modified SBR, the 1,2-vinyl bond content in the butadiene portion is, for example, 10 to 75 mol%, preferably 20 to 65 mol%.

When the component (A1) is a modified SBR, the method of Hampton [R. R. [Hampton, Analytical Chemistry, 21, 923 (1949)], the vinyl bond content (1,2-bond content) in the butadiene bond unit can be determined. Specifically, it is as follows. Using the modified SBR as a sample, 50 mg of the sample is dissolved in 10 mL of carbon disulfide to obtain a measurement sample. The infrared spectrum was measured in the range of 600 to 1000 cm ⁻¹ using a solution cell, and the microstructure of the butadiene moiety, ie, the 1,2-vinyl bond, was calculated according to the calculation formula of the above Hampton method by the absorbance at a predetermined wave number. The amount (mol%) is determined (Fourier transform infrared spectrophotometer "FT-IR230" manufactured by JASCO Corporation).

  The glass transition temperature (Tg) of the component (A1) is preferably higher than −50 ° C., more preferably −30 ° C. or higher. When the Tg of the component (A1) is -30 ° C or higher, crack resistance and low rolling resistance can be further improved. Moreover, for example, Tg of the component (A1) is −15 ° C. or lower.

  Regarding Tg, according to ISO 22768: 2006, the DSC curve is recorded while increasing the temperature in a predetermined temperature range, and the peak top (Influence point) of the DSC differential curve is taken as Tg. Specifically, it is as follows. Using the modified conjugated diene polymer as a sample, in accordance with ISO 22768: 2006, using a differential scanning calorimeter "DSC3200S" manufactured by Mac Science Co., Ltd., under flow of helium 50 mL / min, from -100 ° C to 20 ° C / min. The DSC curve is recorded while the temperature is being raised at, and the peak top (Infection point) of the DSC differential curve is taken as Tg.

In the rubber composition for a base tread according to the present invention, the modified conjugated diene polymer (A1) is a modified styrene butadiene rubber, and the modified conjugated diene polymer (A1) has a glass transition temperature of -30. It is preferably at least ° C.
Thereby, crack resistance and low rolling resistance can be further improved.

  The Mooney viscosity measured at 100 ° C. of the component (A1) is, for example, 20 to 100, or 30 to 80. Within this range, the wear resistance is improved.

The method of measuring the Mooney viscosity is as follows. Using a Mooney viscometer (trade name "VR1132" manufactured by Ueshima Seisakusho Co., Ltd.) as a sample of a conjugated diene polymer or a modified conjugated diene polymer, the Mooney viscosity is measured using an L-shaped rotor in accordance with JIS K6300. To do. The measurement temperature is 110 ° C. when the conjugated diene polymer is used as the sample, and 100 ° C. when the modified conjugated diene polymer is used as the 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 the Mooney viscosity (ML _{(1 + 4)} ).

-Method for synthesizing modified conjugated diene polymer (A1) The method for synthesizing the component (A1) is not particularly limited. For example, an organic monolithium compound is used as a polymerization initiator to polymerize at least the conjugated diene compound. A polymerization step of obtaining a conjugated diene polymer, and a reaction step of reacting a reactive compound having 5 or more functional groups (hereinafter, also referred to as “coupling agent”) with an active terminal of the conjugated diene polymer. , And the like.

  Examples of the polymerization step include polymerization by growth reaction by living anion polymerization reaction. As a result, a conjugated diene-based polymer having an active terminal can be obtained, and the component (A1) having a high modification rate can be obtained.

  The amount of the organic monolithium compound used as the polymerization initiator can be adjusted according to the molecular weight of the target conjugated diene polymer or modified conjugated diene polymer. Decreasing the polymerization initiator increases the molecular weight, while increasing the polymerization initiator decreases the molecular weight.

  The organomonolithium compound is preferably an alkyllithium compound from the viewpoint of industrial availability and easy control of the polymerization reaction. In this case, a conjugated diene polymer having an alkyl group at the polymerization initiation terminal is obtained.

  Examples of the alkyl lithium compound include n-butyl lithium, sec-butyl lithium, tert-butyl lithium, n-hexyl lithium, benzyl lithium, phenyl lithium, and stilbene lithium. These organic monolithium compounds may be used alone or in combination of two or more.

  In the polymerization step, a batch or continuous polymerization reaction mode can be appropriately selected and used.

  An inert solvent may be used in the polymerization step.

  Examples of the inert solvent include aliphatic hydrocarbons such as butane, pentane, hexane and heptane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclopentane and methylcyclohexane; aromatics such as benzene, toluene and xylene. Examples include hydrocarbons. The inert solvent may be used alone or in combination of two or more.

  Before using an inert solvent for the polymerization reaction, it may be treated with an organometallic compound in order to remove impurities such as arenes and acetylenes in the inert solvent.

  A polar compound may be used in the polymerization step. By using the polar compound, the aromatic vinyl compound can be randomly copolymerized with the conjugated diene compound. The polar compound can also be used as a vinylating agent for controlling the microstructure of the conjugated diene part.

  Examples of polar compounds 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; tetra. 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. Compounds: phosphine compounds such as triphenylphosphine, and the like. The polar compounds may be used alone or in combination of two or more.

  The polymerization temperature in the polymerization step may be appropriately adjusted, and is, for example, 0 to 120 ° C. or 50 to 100 ° C. from the viewpoint of sufficiently securing the reaction amount of the coupling agent with respect to the active terminal after the polymerization is completed.

  Examples of the coupling agent include pentafunctional or higher reactive compounds having a nitrogen atom and a silicon atom. The reactive compound preferably has at least 3 silicon-containing functional groups. The coupling agent preferably has at least one silicon atom constituting an alkoxysilyl group having 1 to 20 carbon atoms or a silanol group, and more preferably a compound represented by the general formula (VI) described below. Is. The coupling agents may be used alone or in combination of two or more.

  The alkoxysilyl group contained in the coupling agent reacts, for example, with the active terminal of the conjugated diene-based polymer to dissociate the alkoxylithium, thereby binding the terminal of the conjugated diene-based polymer chain to the silicon of the coupling residue. Tend to form. The value obtained by subtracting the SiOR number subtracted by the reaction from the total number of SiOR contained in one molecule of the coupling agent is the number of alkoxysilyl groups contained in the coupling residue. The azasilacycle group of the coupling agent forms a> N-Li bond and a bond between the end of the conjugated diene polymer and the silicon of the coupling residue. The> N-Li bond tends to easily become> NH and LiOH due to water or the like at the time of finishing. Further, in the coupling agent, the unreacted residual alkoxysilyl group can easily become silanol (Si-OH group) due to water or the like at the time of finishing.

［一般式（ＶＩ）中、Ｒ^１２、Ｒ^１３及びＲ^１４は、それぞれ独立して単結合又は炭素数１〜２０のアルキレン基を示し、Ｒ^１５、Ｒ^１６、Ｒ^１７、Ｒ^１８及びＲ^２０は、それぞれ独立して炭素数１〜２０のアルキル基を示し、Ｒ^１９及びＲ^２２は、それぞれ独立して炭素数１〜２０のアルキレン基を示し、Ｒ^２１は、炭素数１〜２０の、アルキル基又はトリアルキルシリル基を示し、ｍは、１〜３の整数を示し、ｐは、１又は２を示し、Ｒ^１２〜Ｒ^２２、ｍ及びｐは、複数存在する場合、それぞれ独立しており、ｉ、ｊ及びｋは、それぞれ独立して０〜６の整数を示し、但し、（ｉ＋ｊ＋ｋ）は、３〜１０の整数であり、Ａは、炭素数１〜２０の炭化水素基、又は、酸素原子、窒素原子、ケイ素原子、硫黄原子及びリン原子からなる群から選択される少なくとも一種の原子を有し、かつ、活性水素を有しない有機基を示す］で表されるカップリング剤と反応させてなることが好ましい。
これにより、耐亀裂性と、低転がり抵抗性とをより高度に両立しながら、タイヤのベーストレッド露出時ウェット性をより向上させることができる。 In the rubber composition for a base tread according to the present invention, the modified conjugated diene polymer (A1) is a conjugated diene polymer represented by the following general formula (VI):

[In the general formula ^{(VI), R 12, R} 13 and ^{R 14} is independently a single bond or an alkylene group having a carbon number of ^{1~20, R 15, R 16,} R 17, R 18 and ^{R 20} Are each independently an alkyl group having 1 to 20 carbon atoms, R ¹⁹ and R ²² are each independently an alkylene group having 1 to 20 carbon atoms, and R ²¹ is an alkyl group having 1 to 20 carbon atoms; Represents an alkyl group or a trialkylsilyl group, m represents an integer of 1 to 3, p represents 1 or 2, and R ^{12 to} R ²² , m and p each independently represent a plurality of them. And i, j, and k each independently represent an integer of 0 to 6, provided that (i + j + k) is an integer of 3 to 10 and A is a hydrocarbon group having 1 to 20 carbon atoms, or , Oxygen atom, nitrogen atom, silicon atom, sulfur atom and phosphorus atom? It represents an organic group having at least one atom selected from the group consisting of and having no active hydrogen].
This makes it possible to further improve the wettability of the tire when the base tread is exposed, while achieving both crack resistance and low rolling resistance to a higher degree.

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 an organic group that does not have a functional group that has.

  In one example, in the general formula (VI), A is represented by the general formula (II) or (III), and k represents 0. In another example, in the general formula (VI), A is represented by the general formula (II) or (III), k is 0, and in the general formula (II) or (III), a Represents an integer of 2 to 10. In still another example, in the general formula (VI), A is represented by the general formula (II), k is 0, and in the general formula (II), a is an integer of 2 to 10. Indicates.

  Examples of such a coupling agent include tetrakis [3- (2,2-dimethoxy-1-aza-2-silacyclopentane) propyl] -1,3-propanediamine and tetrakis (3-trimethoxysilylpropyl). ) -1,3-Propanediamine, Tetrakis (3-trimethoxysilylpropyl) -1,3-bisaminomethylcyclohexane, bis (3-trimethoxysilylpropyl)-[3- (2,2-dimethoxy-1-) Aza-2-silacyclopentane) propyl] amine, tris (3-trimethoxysilylpropyl) amine, tris (3-triethoxysilylpropyl) amine, tris (3-trimethoxysilylpropyl)-[3- (2, 2-dimethoxy-1-aza-2-silacyclopentane) propyl] -1,3-propanediamine Tris (3-trimethoxysilylpropyl) -methyl-1,3-propanediamine, bis [3- (2,2-dimethoxy-1-aza-2-silacyclopentane) propyl]-(3-trismethoxysilylpropyl ) -Methyl-1,3-propanediamine and the like.

  The addition amount of the compound represented by the general formula (VI) as the coupling agent is adjusted so that the number of moles of the conjugated diene polymer and the number of moles of the coupling agent are reacted at a desired stoichiometric ratio. Can be achieved, which tends to achieve the desired degree of branching. The specific number of moles of the polymerization initiator is, for example, 5.0 times or more, or 6.0 times or more the mole number of the coupling agent. In this case, in the general formula (VI), the number of functional groups ((m−1) × i + p × j + k) of the coupling agent is an integer of 5 to 10, or an integer of 6 to 10.

  The reaction temperature in the reaction step may be appropriately adjusted, and is, for example, 0 to 120 ° C, or 50 to 100 ° C. The temperature change from the polymerization step to the addition of the coupling agent is, for example, 10 ° C. or lower, or 5 ° C. or lower.

  The reaction time in the reaction step may be appropriately adjusted, and is, for example, 10 seconds or longer, or 30 seconds or longer. The time from the end of the polymerization step to the start of the reaction step is preferably shorter from the viewpoint of the coupling rate, and is, for example, 5 minutes or less.

  The mixing in the reaction step may be mechanical stirring, stirring with a static mixer, or the like.

  In order to obtain the component (A1) having the specific high molecular weight component, the molecular weight distribution (Mw / Mn) of the conjugated diene-based polymer is set to 1.5 to 2.5, or 1.8 to 2.2. Good to do. Moreover, it is preferable that the obtained component (A1) has a single peak in the molecular weight curve by GPC.

In one example, when the peak molecular weight by GPC of the component (A1) is Mp ₁ and the peak molecular weight of the conjugated diene polymer is Mp ₂ , the following formula is established.
(Mp ₁ / Mp ₂ ) <1.8 × 10 −12 × (Mp ₂ −120 × 10 ⁴ ) ² +2

In one example, Mp ₂ is 20 × 10 ⁴ to 80 × 10 ⁴ , and Mp ₁ is 30 × 10 ^{4 to} 150 × 10 ⁴ .

  The modification rate of the component (A1) is, for example, 30% by mass or more, 50% by mass or more, or 70% by mass or more. When the modification rate is 30% by mass or more, the low rolling resistance can be further improved while improving the wear resistance of the tire.

The method of measuring the modification rate is as follows. The modified conjugated diene polymer is used as a sample, and the property of the modified basic polymer component adsorbing is applied to a GPC column having a silica gel as a packing material for measurement. A sample solution containing a sample and a low molecular weight internal standard polystyrene was adsorbed on a silica column by measuring the difference between the chromatogram measured with a polystyrene column and the chromatogram measured with a silica column to determine the denaturation rate. Ask. Specifically, it is as shown below.
Preparation of sample solution: A sample solution is prepared by dissolving 10 mg of sample and 5 mg of standard polystyrene in 20 mL of THF.
GPC measurement conditions using a polystyrene-based column: using Tosoh's trade name “HLC-8320GPC”, using 5 mmol / L of triethylamine-containing THF as an eluent, injecting 10 μL of the sample solution into the apparatus, and using a column oven A chromatogram is obtained using a RI detector under the conditions of a temperature of 40 ° C. and a THF flow rate of 0.35 mL / min. For the column, three Tosoh product name "TSKgel SuperMultipore HZ-H" are connected, and a Tosoh product name "TSKguardcolumn SuperMP (HZ) -H" is used as a guard column in front of it.
GPC measurement conditions using a silica-based column: using Tosoh Corporation trade name "HLC-8320GPC", using THF as an eluent, injecting 50 μL of a sample solution into the apparatus, column oven temperature 40 ° C, THF flow rate A chromatogram is obtained using an RI detector at 0.5 ml / min. As the column, the product names "Zorbax PSM-1000S", "PSM-300S", and "PSM-60S" manufactured by Agilent Technologies are connected and used, and the product name "GL Science" manufactured by GL Sciences is used as a guard column in front of the column. DIOL 4.6 × 12.5 mm 5micron ”is connected and used.
Calculation method of denaturation ratio: The total peak area of the chromatogram using the polystyrene column is 100, the peak area of the sample is P1, the peak area of the standard polystyrene is P2, and the peak area of the chromatogram of the silica column is The denaturation rate (%) is calculated from the following formula, with the whole being 100, the peak area of the sample being P3, and the peak area of the standard polystyrene being P4.
Denaturation rate (%) = [1- (P2 × P3) / (P1 × P4)] × 100
(However, P1 + P2 = P3 + P4 = 100)

  After the reaction step, a deactivating agent, a neutralizing agent and the like may be added to the copolymer solution, if necessary. Examples of the quenching agent include water; alcohols such as methanol, ethanol, and isopropanol. Examples of the neutralizing agent include carboxylic acids such as stearic acid, oleic acid, versatic acid (mixed carboxylic acid mixture having 9 to 11 carbon atoms and 10 as the center); aqueous solutions of inorganic acids, carbon dioxide gas, etc. Is mentioned.

  Component (A1) is, for example, 2,6-di-tert-butyl-4-hydroxytoluene (BHT), n-, from the viewpoint of preventing gel formation after polymerization and improving the stability during processing. It is possible to add an antioxidant such as octadecyl-3- (4'-hydroxy-3 ', 5'-di-tert-butylphenol) propinate and 2-methyl-4,6-bis [(octylthio) methyl] phenol. preferable.

  In order to further improve the processability of the component (A1), extending oil may be added to the modified conjugated diene polymer, if necessary. Examples of the method of adding the extending oil to the modified conjugated diene polymer include a method of adding the extending oil to the polymer solution, mixing them, and removing the solvent to obtain an oil-extended copolymer solution.

  As a method for obtaining the component (A1) from the polymer solution, a known method can be used. As the method, for example, after separating the solvent by steam stripping, etc., the polymer is filtered off, further dehydration and drying to obtain the polymer, concentrated in a flushing tank, further vent extruder etc. And a method of directly devolatilizing with a drum dryer or the like.

  The amount of the component (A1) is 7 to 35 parts by mass with respect to 100 parts by mass of the component (A). For example, the amount of the component (A1) is 10 parts by mass or more, 20 parts by mass or more, or 30 parts by mass or more with respect to 100 parts by mass of the component (A). Further, for example, the amount of the component (A1) is 30 parts by mass or less, 20 parts by mass or less, or 10 parts by mass or less with respect to 100 parts by mass of the component (A).

-Other rubber components The rubber component (A) may or may not include a known rubber component used in the rubber composition, in addition to the component (A1). Examples of such rubber components include natural rubber (NR), polybutadiene (BR), synthetic polyisoprene (IR), styrene butadiene rubber (SBR), isoprene butadiene copolymer, ethylene butadiene copolymer, propylene butadiene copolymer. Examples thereof include polymers. In addition to these, for example, modified (co) polymers as the polymer component P2 in WO 2017/0777712 and modified polymers such as the modified polymer E described in the examples are also included. The other rubber components may be used alone or in combination of two or more.

In the rubber composition for a base tread according to the present invention, it is preferable that the rubber component (A) further contains one or more selected from the group consisting of natural rubber, synthetic isoprene rubber, butadiene rubber and styrene butadiene rubber.
In the case of NR and IR, the crack resistance can be further improved, in the case of SBR, the wettability when the base tread is exposed can be further improved, and in the case of BR, the wear resistance can be particularly improved. The sex can be further improved.

  In the component (A), the amount of the rubber component other than the component (A1) is 65 to 93 parts by mass with respect to 100 parts by mass of the component (A). For example, the amount of the rubber component other than the component (A1) is 70 parts by mass or more, 80 parts by mass or more, or 90 parts by mass or more with respect to 100 parts by mass of the component (A). Further, for example, the amount of the rubber component other than the component (A1) is 90 parts by mass or less, 80 parts by mass or less, or 70 parts by mass or less with respect to 100 parts by mass of the component (A).

  The rubber component (A) preferably further contains natural rubber.

In the rubber composition for a base tread according to the present invention, the rubber component (A) further contains natural rubber,
The amount of the natural rubber is preferably 65 to 93 parts by mass with respect to 100 parts by mass of the rubber component (A).
Thereby, the crack resistance can be further improved and the balance with the low rolling resistance is further improved.

・ Reinforcing filler (B)
The reinforcing filler (B) contains carbon black and silica.

  The carbon black is not particularly limited, and known carbon black can be appropriately selected and used. As the carbon black, for example, IISAF, ISAF, HAF, FEF, GPF grade carbon black or the like is used. The carbon black may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black may be appropriately adjusted, and is, for example, 30 to 250 m ² / g or 30 to ²⁰⁰ m ² / g, preferably 60 to 160 m ² / g, and more preferably Is 90 to 150 m ² / g. In the present invention, N ₂ SA of carbon black is measured according to JIS K 6217-2.

  The amount of carbon black is 1 to 35 parts by mass with respect to 100 parts by mass of the component (A). For example, the amount of carbon black is 5 parts by mass or more, 10 parts by mass or more, 20 parts by mass or more, or 30 parts by mass or more with respect to 100 parts by mass of the component (A). Further, for example, the amount of carbon black is 30 parts by mass or less, 20 parts by mass or less, 10 parts by mass or less, or 5 parts by mass or less with respect to 100 parts by mass of the component (A).

  The ratio of carbon black in the component (B) may be appropriately adjusted, and is, for example, 10% by mass or more, 12.5% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass. As described above, the content is 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more. Further, for example, the ratio of carbon black in the component (B) is 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less. , 20 mass% or less, or 10 mass% or less.

  The silica is not particularly limited, and known silica can be appropriately selected and used. Examples thereof include wet silica (hydrous silicic acid), dry silica (silicic anhydride), calcium silicate, aluminum silicate and the like. The silica may be used alone or in combination of two or more.

Silica is, for example, hydrous silicic acid described in JP2013-245306A, that is, cetyltrimethylammonium bromide adsorption specific surface area (CTAB) (m ² / g) and ink bottle-like pore index (IB). Examples include hydrous silicic acid satisfying the formula (Y) described in JP 2013-245306 A.

Silica has the following specific formula (1): cetyltrimethylammonium bromide adsorption specific surface area (CTAB) (m ² / g) and ink bottle-like pore index (IB):
IB ≦ −0.36 × CTAB + 86.8 (1)
[In the formula (1), the ink bottle-like pore index (IB) is represented by the following formula (2):
IB = M2-M1 (2)
Is the value obtained by
In the formula (2), M1 is a measurement using a mercury porosimeter based on the mercury porosimetry method for silica having pores having an outer surface with an opening having a diameter of 1.2 × 10 ⁵ nm to 6 nm. Is the diameter (nm) of the opening showing the maximum value of the mercury intrusion amount when the pressure is increased from 1 PSI to 32,000 PSI, and M2 is the pressure decreased from 32,000 PSI to 1 PSI in the measurement. It is the diameter (nm) of the opening showing the maximum value of the mercury discharge amount]. In this case, the low rolling resistance and wear resistance of the tire can be further improved.

For silica, the cetyltrimethylammonium bromide adsorption specific surface area (CTAB) (m ² / g) and the ink bottle-like pore index (IB) are represented by the following formula (3) or (4):
IB ≦ −0.56 × CTAB + 110.4 (however, CTAB ≦ 140) (3)
IB ≦ −0.20 × CTAB + 60.0 (140 <CTAB) (4)
[In the formulas (3) and (4), the ink bottle-shaped pore index (IB) is represented by the following formula (2):
IB = M2-M1 (2)
Is the value obtained by
In the formula (2), M1 is a measurement using a mercury porosimeter based on the mercury porosimetry method for silica having pores having an outer surface with an opening having a diameter of 1.2 × 10 ⁵ nm to 6 nm. Is the diameter (nm) of the opening showing the maximum value of the mercury intrusion amount when the pressure is increased from 1 PSI to 32,000 PSI, and M2 is the pressure decreased from 32,000 PSI to 1 PSI in the measurement. Is the diameter of the opening (nm) that shows the maximum value of mercury emission when the temperature is increased, and the burning loss (mass reduction after heating at 750 ° C for 3 hours) (mass%) and heating loss (Mass reduction amount when heated at 105 ° C. for 2 hours) (mass%) is represented by the following formula (5):
Burning weight loss-Heating weight loss ≥ 2.5 (mass%) (5)
It is also preferable to satisfy. Also in this case, the low rolling resistance and wear resistance of the tire can be further improved.

Alternatively, BET specific surface area by nitrogen adsorption of the silica, for example, 80~300m ² / g, preferably 90~280m ² / g, more preferably 100 to 250 m ² / g. The BET specific surface area of nitrogen adsorbed on silica is measured in accordance with ISO5794-1.

  The amount of silica may be adjusted appropriately. The amount of silica is, for example, 5 parts by mass or more, 10 parts by mass or more, 20 parts by mass or more, 30 parts by mass or more, 40 parts by mass or more, 50 parts by mass or more, 60 parts by mass, relative to 100 parts by mass of the component (A). Parts or more, 70 parts by mass or more, 80 parts by mass or more, 90 parts by mass or more, or 100 parts by mass or more. Further, for example, the amount of silica is 100 parts by mass or less, 90 parts by mass or less, 80 parts by mass or less, 70 parts by mass or less, 60 parts by mass or less, 50 parts by mass or less, with respect to 100 parts by mass of the component (A). It is 40 parts by mass or less, 30 parts by mass or less, 20 parts by mass or less, 10 parts by mass or less, or 5 parts by mass or less.

In the rubber composition for a base tread according to the present invention, the amount of silica is preferably 15 to 70 parts by mass with respect to 100 parts by mass of the rubber component (A).
This further improves the balance between crack resistance and low rolling resistance.

  As the component (B), silica and carbon black may be contained, and a known reinforcing filler other than silica and carbon black may or may not be contained. Examples of such other component (B) include aluminum hydroxide, clay, alumina, talc, mica, kaolin, glass balloons, glass beads, calcium carbonate, magnesium carbonate, magnesium hydroxide, magnesium oxide, titanium oxide, Examples thereof include potassium titanate and barium sulfate. As the other component (B), one type may be used alone, or two or more types may be used in combination.

  The amount of the component (B) is, for example, 5 parts by mass or more, 10 parts by mass or more, 20 parts by mass or more, 30 parts by mass or more, 40 parts by mass or more, 50 parts by mass or more with respect to 100 parts by mass of the component (A). , 60 parts by mass or more, 70 parts by mass or more, 80 parts by mass or more, 90 parts by mass or more, or 100 parts by mass or more. In addition, for example, the amount of the component (B) is 100 parts by mass or less, 90 parts by mass or less, 80 parts by mass or less, 70 parts by mass or less, 60 parts by mass or less, 50 parts by mass, relative to 100 parts by mass of the component (A). Parts or less, 40 parts by mass or less, 30 parts by mass or less, 20 parts by mass or less, 10 parts by mass or less, or 5 parts by mass or less.

<Other ingredients>
In addition to the above-mentioned components, the rubber composition is a component usually used in the rubber industry, for example, a thermoplastic resin, a softening agent, a vulcanization accelerator, a silane coupling agent, a vulcanizing agent, an antioxidant, a vulcanizing agent. Accelerating aids, organic acid compounds and the like can be appropriately selected and contained within the range not departing from the spirit of the present invention.

  The method for preparing the rubber composition is not particularly limited, and the components such as the component (A) and the component (B) may be kneaded by using a known kneading method.

(tire)
A tire according to the present invention is a tire using the rubber composition for a base tread described in any one of the above as a base tread.
This makes it possible to improve the wettability when the base tread is exposed, while achieving a high level of both crack resistance and low rolling resistance.

  Hereinafter, the present invention will be described in more detail with reference to examples, but these examples are for the purpose of illustrating the present invention and do not limit the present invention in any way. In the following examples, the unit of the compounding amount is part by mass unless otherwise specified.

  The materials in the examples are as follows.

Ingredient (A)
Natural rubber (NR): Tg = -60 ° C
Butadiene rubber (BR): trade name "JSRBR01 (registered trademark)" manufactured by JSR Corporation
Styrene butadiene rubber (SBR): E-SBR made by JSR, trade name "JSR 1723"
Modified conjugated diene polymer (A1): Modified SBR synthesized by the method described below

Ingredient (B)
Carbon black 1: N550, product name “Asahi # 65” manufactured by Asahi Carbon Co., Ltd., N ₂ SA = 42 m ² / g
Silica 1: Tosoh Silica Co., BET specific surface area 105 m ² / g
Silica 2: Product name “Nipsil (registered trademark) AQ” manufactured by Tosoh Silica Co., BET specific surface area 205 m ² / g

(Other)
Silane coupling agent: ethoxy (3-mercaptopropyl) bis (3,6,9,12,15-pentaoxaoctacosan-1-yloxy) silane, trade name "Si363 (registered trademark)" manufactured by Evonik Degussa.
WAX: Microcrystalline wax, trade name "Ozoace 0701" manufactured by Nippon Seiro Co., Ltd.
Anti-aging agent (6PPD): N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine, trade name "Nocrac (registered trademark) 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator (DPG): 1,3-diphenylguanidine, product name “Succinol (registered trademark) DG” manufactured by Sumitomo Chemical Co., Ltd.
Vulcanization accelerator (CBS): N-cyclohexylbenzothiazole-2-sulfenamide, trade name "NOXCELLER (registered trademark) CZ" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator (MBTS): di (2-benzothiazolyl) persulfide, trade name "Noccer (registered trademark) DM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

  The amount of bound styrene, the microstructure of the butadiene portion, 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 the presence or absence of silicon atoms of the modified SBR are as described above. analyse.

<Synthesis of modified SBR (A1)>
The internal volume is 10 L, the internal height (L) to diameter (D) ratio (L / D) is 4.0, the bottom has an inlet, the top has an outlet, and a tank-type reaction with a stirrer A tank type pressure vessel having a stirrer which is a vessel and a jacket for temperature control is used as a polymerization reactor. The water, which has been removed in advance, is mixed under the conditions of 17.2 g / min of 1,3-butadiene, 10.5 g / min of styrene and 145.3 g / min of n-hexane. In a static mixer provided in the middle of a pipe for supplying this mixed solution to the inlet of the reactor, 0.117 mmol / min of n-butyllithium for residual impurity inactivation treatment was added and mixed, and then the mixture was added to the bottom of the reactor. Supply continuously. Further, 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 is fed to the bottom of the polymerization reactor to continuously continue the polymerization reaction. The temperature is controlled so that the temperature of the polymerization solution at the outlet of the top of the reactor is 75 ° C. When the polymerization was sufficiently stable, a small amount of the polymer solution before addition of the coupling agent was withdrawn from the outlet of the top of the reactor, and an antioxidant (BHT) was added so that the amount was 0.2 g per 100 g of the polymer, and then the solvent was added. Remove and measure Mooney viscosity at 110 ° C. and various molecular weights. Next, in the polymer solution flowing out from the outlet of the reactor, 0.0302 mmol / min of tetrakis (3-trimethoxysilylpropyl) -1,3-propanediamine diluted to 2.74 mmol / L as a coupling agent ( A polymer solution to which a coupling agent has been added is continuously added at a rate of 5.2 ppm of water containing n-hexane solution), and the polymer solution is mixed by passing through a static mixer to cause a coupling reaction. 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., the temperature in the polymerization step and the temperature until the modifier was added. Is 7 ° C. The antioxidant (BHT) was continuously added to the polymer solution subjected to the coupling reaction at 0.055 g / min (n-hexane solution) so that the amount was 0.2 g per 100 g of the polymer, and the coupling reaction was completed. To do. Simultaneously with the antioxidant, 10.0 g of oil (“JOMO Process NC140” manufactured by JX Nippon Oil & Energy Corporation) as a extending oil was continuously added to 100 g of the polymer, and mixed with a static mixer. The solvent is removed by steam stripping to obtain a modified SBR as the component (A1).

The values of modified SBR are as follows.
Amount of bound styrene = 40% by mass,
Vinyl bond amount (1,2-bond amount) = 41 mol%,
Weight average molecular weight (Mw) = 85.2 × 10 ⁴ g / mol,
Number average molecular weight (Mn) = 38.2 × 10 ⁴ g / mol,
Molecular weight distribution (Mw / Mn) = 2.23,
Peak top molecular weight (Mp ₁ ) = 96.8 × 10 ⁴ g / mol,
Peak top molecular weight ratio (Mp ₁ / Mp ₂ ) = 3.13,
Ratio of molecular weight of 200 × 10 ⁴ or more and 500 × 10 ⁴ or less = 4.6%,
Contraction factor (g ′) = 0.59,
Mooney viscosity (100 ° C) = 65,
Glass transition temperature (Tg) =-24 ° C., and modification rate = 80%.

  The modified SBR has a nitrogen atom and a silicon atom.

  The modified SBR has a “branching degree” corresponding to the number of branches assumed from the number of functional groups of the coupling agent and the amount added (which can also be confirmed from the value of the contraction factor), and the SiOR of one molecule of the coupling agent can be confirmed. The "number of SiOR residues" corresponding to a value obtained by subtracting the number of SiORs subtracted by the reaction from the total number is 4.

<Preparation of rubber composition and manufacture of tire>
According to the formulation shown in Table 1 and Table 2, a rubber composition is prepared using an ordinary Banbury mixer. Further, the rubber composition is used as the rubber of the base tread of the tread portion to prepare a pneumatic radial tire for passenger cars having a tire size of 195 / 65R15.

  With respect to the rubber composition or the tire, crack resistance, wettability when the base tread is exposed, and low rolling resistance are evaluated by the following methods. Each evaluation is shown in Table 2.

<Crack resistance>
As a test piece, a trouser-shaped test piece is prepared, and a tearing test is performed according to JIS K-6252: 2015, and the maximum tearing force until the test piece is cut is measured. The evaluation of Comparative Example 1 is set to 100 and is represented by an index value. The larger the index value, the better the crack resistance.

<Wetness when the base tread is exposed>
Attach the tire to the passenger car and run it for 30,000 km to check the exposure of the base rubber. Next, the vehicle is run on a dry road surface for 100 km and on a wet road surface for 10 km to carry out a preliminary break-in. Next, a concrete road having a water depth of 2 mm is run, and at a speed of 60 km / hour, the brake is depressed to lock the tire, and the distance until the tire is stopped is measured. The reciprocal of the distance in Comparative Example 1 is set to 100 and is represented by an index value. The larger the index value, the better the wet performance after exposure.

<Low rolling resistance>
Regarding the vulcanized rubber obtained by vulcanizing each rubber composition at 145 ° C. for 33 minutes, the loss tangent (tan δ) was measured by a Ueshima Seisakusho spectrometer, temperature 40 ° C., initial strain 2%, dynamic strain 1%, frequency 52 Hz. Measure under the conditions. The reciprocal of the loss tangent of Comparative Example 1 is set to 100 and is displayed as an index. The larger the index value, the lower the rolling resistance and the better the low rolling resistance.

  As shown in Table 2, the tire according to the present invention can improve the wettability of the tire when the base tread is exposed, while achieving both crack resistance and low rolling resistance at a high level. Furthermore, the tire according to the present invention can also obtain good wettability when the base tread is exposed.

  ADVANTAGE OF THE INVENTION According to this invention, the rubber composition for base treads which improve the wettability at the time of base tread exposure of a tire can be provided, highly satisfying both crack resistance of a tire and low rolling resistance. Further, according to the present invention, it is possible to provide a tire having improved wettability when the base tread of the tire is exposed, while achieving both high crack resistance and low rolling resistance.

Claims (11)

Contains a rubber component (A) and a reinforcing filler (B),
The rubber component (A) contains a modified conjugated diene-based polymer (A1),
The modified conjugated diene polymer (A1) has a weight average molecular weight of 20 × 10 ^{4 to} 300 × 10 ⁴ , and has a molecular weight of 200 × 10 ^{4 with} respect to the total amount of the modified conjugated diene polymer (A1). The modified conjugated diene polymer, which is ˜500 × 10 ⁴ , contains 0.25 to 30 mass%, and the contraction factor (g ′) is less than 0.64,
The amount of the modified conjugated diene polymer (A1) is 7 to 35 parts by mass with respect to 100 parts by mass of the rubber component (A),
The amount of extender oil added to the modified conjugated diene polymer (A1) is 10 parts by mass or less with respect to 100 parts by mass of the modified conjugated diene polymer (A1),
The reinforcing filler (B) contains carbon black and silica,
The rubber composition for a base tread, wherein the amount of the carbon black is 1 to 35 parts by mass with respect to 100 parts by mass of the rubber component (A).   The rubber composition for a base tread according to claim 1, wherein the rubber component (A) further contains one or more selected from the group consisting of natural rubber, synthetic isoprene rubber, butadiene rubber and styrene butadiene rubber. The rubber component (A) further contains natural rubber,
The rubber composition for a base tread according to claim 1 or 2, wherein the amount of the natural rubber is 65 to 93 parts by mass with respect to 100 parts by mass of the rubber component (A).   The rubber composition for a base tread according to claim 1, wherein the amount of the silica is 15 to 70 parts by mass with respect to 100 parts by mass of the rubber component (A).   Any of claims 1 to 4, wherein the modified conjugated diene polymer (A1) is a modified styrene-butadiene rubber, and the modified conjugated diene polymer (A1) has a glass transition temperature of -30 ° C or higher. The rubber composition for a base tread according to 1 above.   The rubber composition for a base tread according to any one of claims 1 to 5, wherein the modified conjugated diene-based polymer (A1) has a branch and a branching degree of 5 or more. The modified conjugated diene-based polymer (A1) has one or more coupling residues and a conjugated diene-based polymer chain bonded to the coupling residues,
The rubber composition for a base tread according to claim 6, wherein the branch includes a branch in which 5 or more conjugated diene-based polymer chains are bonded to one coupling residue. The modified conjugated diene polymer (A1) has the following general formula (I):

[In the general formula (I), D represents a conjugated diene-based polymer chain, R ¹ , R ² and R ³ each independently represent a single bond or an alkylene group having 1 to 20 carbon atoms, and R ⁴ And R ⁷ each independently represent an alkyl group having 1 to 20 carbon atoms, and R ⁵ , R ⁸ and R ⁹ each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, and 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, and m and x each independently represent 1 to 1. 3 represents an integer of 3, x ≦ m, p represents 1 or 2, y represents an integer of 1 to 3, y ≦ (p + 1), z represents 1 or 2, and respectively. ^D when there are a ^{plurality, R 1 ~R 11, m,} p, x, y, and z are each independently I is an integer of 0 to 6, j is an integer of 0 to 6, k is an integer of 0 to 6, (i + j + k) is an integer of 3 to 10, and (( x × i) + (y × j) + (z × k)) is an integer of 5 to 30, and A is a hydrocarbon group having 1 to 20 carbon atoms, or an oxygen atom, a nitrogen atom, or a silicon atom. , An organic group having at least one atom selected from the group consisting of a sulfur atom and a phosphorus atom, and having no active hydrogen] is represented by any one of claims 1 to 7. Rubber composition for base tread of. In the general formula (I), A is the following general formulas (II) to (V):

[In the general formula (II), B ¹ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, a represents an integer of 1 to 10, and when there are a plurality of B ^{1's, they} are each independently. ing;
In the general formula (III), B ² represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, B ³ represents an alkyl group having 1 to 20 carbon atoms, and a represents an integer of 1 to 10. B ² and B ³ when there are a plurality of each are independent of each other;
In formula (IV), B ⁴ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, a represents an integer of 1 to 10, and B ⁴ in the case where a plurality of them are present, each independently. Is;
In formula (V), B ⁵ represents a single bond or a hydrocarbon group having 1 to 20 carbon atoms, a represents an integer of 1 to 10, and B ⁵ in the case where a plurality of B ⁵ are present are each independently. The rubber composition for a base tread according to claim 8, which is represented by any of the above. The modified conjugated diene-based polymer (A1) is a conjugated diene-based polymer represented by the following general formula (VI):

[In the general formula ^{(VI), R 12, R} 13 and ^{R 14} is independently a single bond or an alkylene group having a carbon number of ^{1~20, R 15, R 16,} R 17, R 18 and ^{R 20} Are each independently an alkyl group having 1 to 20 carbon atoms, R ¹⁹ and R ²² are each independently an alkylene group having 1 to 20 carbon atoms, and R ²¹ is an alkyl group having 1 to 20 carbon atoms; Represents an alkyl group or a trialkylsilyl group, m represents an integer of 1 to 3, p represents 1 or 2, and R ^{12 to} R ²² , m and p each independently represent a plurality of them. And i, j, and k each independently represent an integer of 0 to 6, provided that (i + j + k) is an integer of 3 to 10 and A is a hydrocarbon group having 1 to 20 carbon atoms, or , Oxygen atom, nitrogen atom, silicon atom, sulfur atom and phosphorus atom? Which has at least one atom selected from the group consisting of, and represents an organic group having no active hydrogen], and is reacted with a coupling agent represented by any one of claims 1 to 9. The rubber composition for a base tread described in.   A tire using the rubber composition for a base tread according to any one of claims 1 to 10 as a base tread.