JP7616244B2 - Rubber composition for tread and tire - Google Patents

Description

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

From the perspective of safety and the environment, treads are required to have various performance characteristics, such as wet grip performance when driving on wet roads, abrasion resistance, and fuel efficiency. For example, the use of modified polymers has been proposed as a technology to improve the balance between wet grip performance and fuel efficiency, but modified polymers generally have high viscosity and poor processability, so low molecular weight polymers tend to be used, resulting in the problem of poor abrasion resistance.

Improvements using existing silane coupling agents have also been proposed, but there is still room for improvement in terms of the balance between fuel economy, wet grip performance, and wear resistance (see Patent Document 1, etc.).

JP 2019-34992 A

The present invention aims to solve the above problems and provide a rubber composition for treads and a tire that improves the overall performance of fuel economy, wet grip performance, and abrasion resistance.

The present invention relates to a rubber composition for treads, which comprises a styrene-butadiene rubber, silica, and a mercapto-silane coupling agent, the content of the styrene-butadiene rubber in 100% by mass of a rubber component is 50% by mass or more, the content of the silica in 100 parts by mass of the rubber component is 30 to 120 parts by mass, and satisfies the following formulas (1) and (2):

The rubber composition preferably satisfies the following formula (1-1).

The rubber composition preferably satisfies the following formula (1-2).

It is preferable that the styrene butadiene rubber contains styrene butadiene rubber having a styrene content of 5 to 50 mass% and a weight average molecular weight of 100,000 to 1,600,000.

It is preferable that the rubber composition contains butadiene rubber.

（式（２－１）中、Ｒ^１０１は－Ｃｌ、－Ｂｒ、－ＯＲ^１０６、－Ｏ（Ｏ＝）ＣＲ^１０６、－ＯＮ＝ＣＲ^１０６Ｒ^１０７、－ＮＲ^１０６Ｒ^１０７及び－（ＯＳｉＲ^１０６Ｒ^１０７）_ｈ（ＯＳｉＲ^１０６Ｒ^１０７Ｒ^１０８）から選択される一価の基（Ｒ^１０６、Ｒ^１０７及びＲ^１０８は同一でも異なっていても良く、各々水素原子又は炭素数１～１８の一価の炭化水素基であり、ｈは平均値が１～４である。）であり、Ｒ^１０２はＲ^１０１、水素原子又は炭素数１～１８の一価の炭化水素基、Ｒ^１０３は－［Ｏ（Ｒ^１０９Ｏ）_ｊ］－基（Ｒ^１０９は炭素数１～１８のアルキレン基、ｊは１～４の整数である。）、Ｒ^１０４は炭素数１～１８の二価の炭化水素基、Ｒ^１０５は炭素数１～１８の一価の炭化水素基を示し、ｘａ、ｙａ及びｚａは、ｘａ＋ｙａ＋２ｚａ＝３、０≦ｘａ≦３、０≦ｙａ≦２、０≦ｚａ≦１の関係を満たす数である。） The mercapto-based silane coupling agent preferably contains a silane coupling agent represented by the following formula (2-1).

In formula (2-1), R ¹⁰¹ is a monovalent group selected from -Cl, -Br, -OR ¹⁰⁶ , -O(O═)CR ¹⁰⁶ , -ON═CR ¹⁰⁶ R ¹⁰⁷ , -NR ¹⁰⁶ R ¹⁰⁷ and -(OSiR ¹⁰⁶ R ¹⁰⁷ ) _h (OSiR ¹⁰⁶ R ¹⁰⁷ R ¹⁰⁸ ) (R ¹⁰⁶ , R ¹⁰⁷ and R ¹⁰⁸ may be the same or different and each is a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, and h has an average value of 1 to 4), R ¹⁰² is R ¹⁰¹ , a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, R ¹⁰³ is a -[O(R ¹⁰⁹ O) _j ]- group (R R ¹⁰⁹ is an alkylene group having 1 to 18 carbon atoms, j is an integer from 1 to 4. R ¹⁰⁴ is a divalent hydrocarbon group having 1 to 18 carbon atoms, R ¹⁰⁵ is a monovalent hydrocarbon group having 1 to 18 carbon atoms, and xa, ya, and za are numbers that satisfy the relationship: xa+ya+2za=3, 0≦xa≦3, 0≦ya≦2, 0≦za≦1.

（式（２－２）及び（２－３）中、ｘｂは０以上の整数、ｙｂは１以上の整数である。Ｒ^２０１は水素、ハロゲン、分岐若しくは非分岐の炭素数１～３０のアルキル基、分岐若しくは非分岐の炭素数２～３０のアルケニル基、分岐若しくは非分岐の炭素数２～３０のアルキニル基、又は該アルキル基の末端の水素が水酸基若しくはカルボキシル基で置換されたものを示す。Ｒ^２０２は分岐若しくは非分岐の炭素数１～３０のアルキレン基、分岐若しくは非分岐の炭素数２～３０のアルケニレン基、又は分岐若しくは非分岐の炭素数２～３０のアルキニレン基を示す。Ｒ^２０１とＲ^２０２とで環構造を形成してもよい。） The mercapto-based silane coupling agent preferably contains a bonding unit A represented by the following formula (2-2) and a bonding unit B represented by the following formula (2-3).

(In formulas (2-2) and (2-3), xb is an integer of 0 or more, and yb is an integer of 1 or more. R ²⁰¹ represents hydrogen, halogen, a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, a branched or unbranched alkynyl group having 2 to 30 carbon atoms, or an alkyl group in which the terminal hydrogen atom has been substituted with a hydroxyl group or a carboxyl group. R ²⁰² represents a branched or unbranched alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group having 2 to 30 carbon atoms, or a branched or unbranched alkynylene group having 2 to 30 carbon atoms. R ²⁰¹ and R ²⁰² may form a ring structure.)

（式中、Ｒ^６～Ｒ^８は、分岐若しくは非分岐の炭素数１～１２のアルキル基、分岐若しくは非分岐の炭素数１～１２のアルコキシ基、又は－Ｏ－（Ｒ^１１１－Ｏ）_ｚ－Ｒ^１１２（ｚ個のＲ^１１１は、分岐若しくは非分岐の炭素数１～３０の２価の炭化水素基を表す。ｚ個のＲ^１１１はそれぞれ同一でも異なっていてもよい。Ｒ^１１２は、分岐若しくは非分岐の炭素数１～３０のアルキル基、分岐若しくは非分岐の炭素数２～３０のアルケニル基、炭素数６～３０のアリール基、又は炭素数７～３０のアラルキル基を表す。ｚは１～３０の整数を表す。）で表される基を表す。Ｒ^６～Ｒ^８はそれぞれ同一でも異なっていてもよい。Ｒ^９は、分岐若しくは非分岐の炭素数１～６のアルキレン基を表す。） The mercapto-based silane coupling agent preferably contains a silane coupling agent represented by the following formula (2-4).

(In the formula, R ⁶ to R ⁸ each represent a branched or unbranched alkyl group having 1 to 12 carbon atoms, a branched or unbranched alkoxy group having 1 to 12 carbon atoms, or a group represented by -O-(R ¹¹¹ -O) _z -R ¹¹² (z R ¹¹¹ represent a branched or unbranched divalent hydrocarbon group having 1 to 30 carbon atoms. z R ¹¹¹ may be the same or different. R ¹¹² represents a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms. z represents an integer from 1 to 30.) ^{R 6} to R ⁸ each may be the same or different. R ⁹ represents a branched or unbranched alkylene group having 1 to 6 carbon atoms.)

The rubber composition preferably contains carbon black.

It is preferable that the rubber composition is obtained by a manufacturing process including a step (I) of kneading silica and a mercapto-based silane coupling agent, and a step (II) of maintaining the kneaded mixture obtained in the step (I) at 130°C or higher.

The present invention also relates to a tire having a tread made of the rubber composition.

According to the present invention, a rubber composition for treads contains styrene-butadiene rubber, silica, and a mercapto-based silane coupling agent, the content of the styrene-butadiene rubber in 100% by mass of the rubber component is 50% by mass or more, the content of the silica per 100 parts by mass of the rubber component is 30 to 120 parts by mass, and satisfies the formulas (1) and (2), thereby improving the overall performance of fuel economy, wet grip performance, and abrasion resistance.

[Rubber composition for tread]
The rubber composition for treads of the present invention contains a styrene-butadiene rubber, silica, and a mercapto-based silane coupling agent in a predetermined ratio and satisfies the above formulas (1) and (2), thereby significantly improving the overall performance of fuel economy, wet grip performance, and abrasion resistance.

The mechanism by which the above-mentioned effects are obtained is not entirely clear, but is presumed to be as follows.
In the silica compound containing styrene-butadiene rubber, when mercapto-based silane coupling agent is used as silane coupling agent and adjusted to satisfy formula (1) and (2), first, good processing is performed by mercapto-based silane coupling agent, the dispersibility of silica and the reaction rate of silica and silane coupling agent are improved, and excellent fuel economy is given without impairing wet grip performance and wear resistance.Furthermore, by satisfying formula (2), good fuel economy is obtained.Therefore, it is presumed that the overall performance of fuel economy, wet grip performance and wear resistance is significantly improved.

In this way, the present invention solves the problem (objective) of improving the overall performance of fuel economy, wet grip performance, and abrasion resistance by configuring a rubber composition for treads that satisfies formulas (1) and (2) in a formulation that contains styrene-butadiene rubber, silica, and a mercapto-silane coupling agent in a predetermined ratio. In other words, the parameters of formulas (1) and (2) do not define the problem (objective); the object of the present application is to improve the overall performance of fuel economy, wet grip performance, and abrasion resistance, and a configuration that satisfies the parameters is used as a means to achieve this.

The rubber composition (rubber composition after vulcanization) satisfies the following formula (1).

From the viewpoints of fuel economy and abrasion resistance, the value (80) of formula (1) is preferably 75 or less, more preferably 71 or less, even more preferably 70 or less, particularly preferably 67 or less, and most preferably 66 or less. The upper limit may be 65 or less, 63 or less, 60 or less, 56 or less, 55 or less, 53 or less, 50 or less, 48 or less, 47 or less, 46 or less, or 40 or less. The lower limit is not particularly limited, but from the viewpoints of wet grip performance and abrasion resistance, it is preferably 10 or more, more preferably 15 or more, and even more preferably 20 or more.

Ｅ＊（０．５％）の下限は、１９ＭＰａ以上がより好ましく、２０ＭＰａ以上が更に好ましく、２１ＭＰａ以上が特に好ましく、２２ＭＰａ以上が最も好ましい。また、下限は、２４ＭＰａ以上、２５ＭＰａ以上、２６ＭＰａ以上でもよい。Ｅ＊（０．５％）の上限は、３７ＭＰａ以下がより好ましく、３６ＭＰａ以下が更に好ましく、３５ＭＰａ以下が特に好ましく、３０ＭＰａ以下が最も好ましい。また、上限は、２９ＭＰａ以下、２８ＭＰａ以下でもよい。 From the viewpoint of overall performance of fuel economy, wet grip performance, and abrasion resistance, the rubber composition (rubber composition after vulcanization) preferably satisfies the following formula (1-1).

The lower limit of E*(0.5%) is more preferably 19 MPa or more, even more preferably 20 MPa or more, particularly preferably 21 MPa or more, and most preferably 22 MPa or more. The lower limit may be 24 MPa or more, 25 MPa or more, or 26 MPa or more. The upper limit of E*(0.5%) is more preferably 37 MPa or less, even more preferably 36 MPa or less, particularly preferably 35 MPa or less, and most preferably 30 MPa or less. The upper limit may be 29 MPa or less, or 28 MPa or less.

Ｅ＊（５％）の下限は、１３ＭＰａ以上がより好ましく、１４ＭＰａ以上が更に好ましく、１５ＭＰａ以上が特に好ましく、１６ＭＰａ以上が最も好ましい。また、下限は、１７ＭＰａ以上でもよい。Ｅ＊（５％）の上限は、２３ＭＰａ以下がより好ましく、２１ＭＰａ以下が更に好ましく、２０ＭＰａ以下が特に好ましく、１９ＭＰａ以下が最も好ましい。また、上限は、１８ＭＰａ以下でもよい。 From the viewpoint of overall performance of fuel economy, wet grip performance, and abrasion resistance, the rubber composition (rubber composition after vulcanization) preferably satisfies the following formula (1-2).

The lower limit of E*(5%) is more preferably 13 MPa or more, even more preferably 14 MPa or more, particularly preferably 15 MPa or more, and most preferably 16 MPa or more. The lower limit may be 17 MPa or more. The upper limit of E*(5%) is more preferably 23 MPa or less, even more preferably 21 MPa or less, particularly preferably 20 MPa or less, and most preferably 19 MPa or less. The upper limit may be 18 MPa or less.

The rubber composition (rubber composition after vulcanization) satisfies the following formula (2).

From the viewpoint of low fuel consumption, the upper limit of tan δ (70°C) is preferably 0.17 or less, more preferably 0.16 or less, even more preferably 0.15 or less, particularly preferably 0.14 or less, and most preferably 0.13 or less. The upper limit may be 0.12 or less. The lower limit is not particularly limited, but from the viewpoint of wet grip performance, it is more preferably 0.05 or more, and even more preferably 0.08 or more.

Here, E*(0.5%), E*(5%) and tan δ(70° C.) can be appropriately adjusted by changing the types and amounts of the rubber, filler and silane coupling agent.
For example, E*(0.5%) and E*(5%) can be increased by using styrene-butadiene rubber as the rubber component or increasing the amount of the rubber, by using silica as the filler or increasing the amount of the rubber, by reducing the amount of the plasticizer, or by reducing the amount of the silane coupling agent.
(E*(0.5%)-E*(5%)) can be reduced by using a modified rubber as the rubber component or increasing the amount of the modified rubber, by using silica as the filler or decreasing the amount of the modified rubber, or by using a mercapto-based silane coupling agent as the silane coupling agent or increasing the amount of the mercapto-silane coupling agent.
Tan δ (70° C.) can be reduced by using a modified rubber as the rubber component, using silica as the filler, using a mercapto-based silane coupling agent as the silane coupling agent, or increasing the amount of the agent.

Specifically, methods for satisfying formula (1) include (a) using a predetermined amount of styrene butadiene rubber as the rubber component, (b) using a predetermined amount of silica as a filler, and (c) using a predetermined amount of a mercapto-based silane coupling agent, either alone or in appropriate combination.

Methods for satisfying formula (2) include (a) using a mercapto-based silane coupling agent as the silane coupling agent, (b) using modified rubber as the rubber component, and (c) using a predetermined amount of silica as a filler, either alone or in appropriate combination.

The complex modulus E* (0.5%) of the rubber composition (rubber composition after vulcanization) under conditions of an initial strain of 10%, dynamic strain of 0.5%, and a temperature of 0°C, the complex modulus E* (5%) under conditions of an initial strain of 10%, dynamic strain of 5%, and a temperature of 0°C, and the loss tangent tan δ (70°C) under conditions of an initial strain of 10%, dynamic strain of 1%, and a temperature of 70°C can each be measured by the methods described in the examples described later.

(Rubber component)
The rubber composition includes styrene-butadiene rubber (SBR).
The content of SBR in 100% by mass of the rubber component is 50% by mass or more, preferably 60% by mass or more, more preferably 65% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more. By making it equal to or more than the lower limit, good abrasion resistance and wet grip performance tend to be obtained. The upper limit is not particularly limited, but from the viewpoint of obtaining good fuel economy, it is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

The SBR is not particularly limited, and examples of the SBR that can be used include emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc. These may be used alone or in combination of two or more types.

The styrene content of the SBR is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 21% by mass or more. The styrene content is preferably 50% by mass or less, more preferably 47% by mass or less, and even more preferably 45% by mass or less. When the styrene content is within the above range, good overall performance such as low fuel consumption, wet grip performance, and abrasion resistance tends to be obtained.
In this specification, the styrene content of SBR is calculated by H ¹ -NMR measurement.

The Mw of the SBR is preferably 100,000 or more, more preferably 200,000 or more, and even more preferably 240,000 or more. The Mw is preferably 1,600,000 or less, more preferably 1,500,000 or less, and even more preferably 1,400,000 or less. Within the above range, there is a tendency for good overall performance in terms of fuel economy, wet grip performance, and abrasion resistance to be obtained.
In this specification, the Mw of SBR can be determined in terms of standard polystyrene based on a measured value obtained by gel permeation chromatography (GPC) (GPC-8000 series, manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M, manufactured by Tosoh Corporation).

The SBR may be unmodified SBR or modified SBR. These may be used alone or in combination of two or more kinds.
The modified SBR may be any SBR having a functional group that interacts with a filler such as silica, and examples thereof include terminally modified SBR (terminally modified SBR having a functional group at the terminal) in which at least one terminal of SBR has been modified with a compound having a functional group (modifying agent), main-chain modified SBR having a functional group in the main chain, main-chain terminal-modified SBR having functional groups in the main chain and at least one terminal (for example, main-chain terminal-modified SBR having a functional group in the main chain and at least one terminal modified with a modifying agent), and terminally modified SBR modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule and having a hydroxyl group or epoxy group introduced therein. These may be used alone or in combination of two or more types.

Examples of the functional groups include amino groups, amide groups, silyl groups, alkoxysilyl groups, isocyanate groups, imino groups, imidazole groups, urea groups, ether groups, carbonyl groups, oxycarbonyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, and epoxy groups. These functional groups may have a substituent. Among them, amino groups (preferably amino groups in which the hydrogen atoms of the amino groups are substituted with alkyl groups having 1 to 6 carbon atoms), alkoxy groups (preferably alkoxy groups having 1 to 6 carbon atoms), and alkoxysilyl groups (preferably alkoxysilyl groups having 1 to 6 carbon atoms) are preferred.

As SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., etc. can be used.

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

The BR is not particularly limited, and for example, BR with a high cis content, BR containing syndiotactic polybutadiene crystals, etc. can be used. These may be used alone or in combination of two or more.

The BR may be unmodified BR or modified BR. These may be used alone or in combination of two or more kinds.
The modified BR may be a modified BR having a functional group similar to that of the modified SBR described above.

As BR, products from, for example, Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Corporation, etc. can be used.

The BR content in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. The content is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and particularly preferably 20% by mass or less. By keeping the content within the above range, good overall performance in terms of fuel economy, wet grip performance, and abrasion resistance tends to be obtained.

Isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, modified IR, etc. NR can be, for example, SIR20, RSS#3, TSR20, etc., which are common in the tire industry. IR is not particularly limited, and can be, for example, IR2200, etc., which are common in the tire industry. Modified NR can be, for example, deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), etc. Modified NR can be, for example, epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc. Modified IR can be, for example, epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. These can be used alone or in combination of two or more.

When isoprene-based rubber is compounded, its content can be selected appropriately; for example, 5 to 50 mass% per 100 mass% of the rubber component.

(silica)
Examples of silica include dry silica (anhydrous silica) and wet silica (hydrated silica). Among them, wet silica is preferred because it has a large number of silanol groups. These may be used alone or in combination of two or more.

The silica content is 30 parts by mass or more, preferably 40 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 60 parts by mass or more, and particularly preferably 75 parts by mass or more, per 100 parts by mass of the rubber component. By making the content above the lower limit, good abrasion resistance and wet grip performance tend to be obtained. The upper limit of the content is 120 parts by mass or less, preferably 110 parts by mass or less, more preferably 105 parts by mass or less, and even more preferably 100 parts by mass or less. By making the content below the upper limit, good fuel economy tends to be obtained.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 80 m ² /g or more, more preferably 120 m ² /g or more, even more preferably 150 m ² /g or more, and particularly preferably 170 m ² /g or more. By making it equal to or more than the lower limit, good wear resistance and wet grip performance tend to be obtained. In addition, the N ₂ SA of silica is preferably 250 m ² /g or less, more preferably 220 m ² /g or less, and even more preferably 200 m ² /g or less. By making it equal to or less than the upper limit, good dispersibility and low fuel consumption tend to be obtained.
The N ₂ SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

As silica, for example, products from Degussa, Rhodia, Tosoh Silica Co., Ltd., Solvay Japan Co., Ltd., Tokuyama Corporation, etc. can be used.

(Mercapto-based silane coupling agent)
The rubber composition uses a mercapto-based silane coupling agent as a silane coupling agent, which allows for suitable processing, improves the dispersibility of silica, and improves the reaction rate between silica and the silane coupling agent, thereby providing excellent fuel economy without impairing wet grip performance or wear resistance.

The content of the mercapto-based silane coupling agent is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, even more preferably 6 parts by mass or more, and particularly preferably 8 parts by mass or more, per 100 parts by mass of silica. If it is above the lower limit, good overall performance in terms of fuel economy, wet grip performance, and abrasion resistance tends to be obtained. In addition, the above content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less. If it is below the upper limit, an effect commensurate with the amount blended tends to be obtained.

Mercapto-based silane coupling agents include silane coupling agents having a mercapto group, silane coupling agents in which the mercapto group is protected, etc. These may be used alone or in combination of two or more.

（式（２－１）中、Ｒ^１０１は－Ｃｌ、－Ｂｒ、－ＯＲ^１０６、－Ｏ（Ｏ＝）ＣＲ^１０６、－ＯＮ＝ＣＲ^１０６Ｒ^１０７、－ＮＲ^１０６Ｒ^１０７及び－（ＯＳｉＲ^１０６Ｒ^１０７）_ｈ（ＯＳｉＲ^１０６Ｒ^１０７Ｒ^１０８）から選択される一価の基（Ｒ^１０６、Ｒ^１０７及びＲ^１０８は同一でも異なっていても良く、各々水素原子又は炭素数１～１８の一価の炭化水素基であり、ｈは平均値が１～４である。）であり、Ｒ^１０２はＲ^１０１、水素原子又は炭素数１～１８の一価の炭化水素基、Ｒ^１０３は－［Ｏ（Ｒ^１０９Ｏ）_ｊ］－基（Ｒ^１０９は炭素数１～１８のアルキレン基、ｊは１～４の整数である。）、Ｒ^１０４は炭素数１～１８の二価の炭化水素基、Ｒ^１０５は炭素数１～１８の一価の炭化水素基を示し、ｘａ、ｙａ及びｚａは、ｘａ＋ｙａ＋２ｚａ＝３、０≦ｘａ≦３、０≦ｙａ≦２、０≦ｚａ≦１の関係を満たす数である。）

（式（２－２）及び（２－３）中、ｘｂは０以上の整数、ｙｂは１以上の整数である。Ｒ^２０１は水素、ハロゲン、分岐若しくは非分岐の炭素数１～３０のアルキル基、分岐若しくは非分岐の炭素数２～３０のアルケニル基、分岐若しくは非分岐の炭素数２～３０のアルキニル基、又は該アルキル基の末端の水素が水酸基若しくはカルボキシル基で置換されたものを示す。Ｒ^２０２は分岐若しくは非分岐の炭素数１～３０のアルキレン基、分岐若しくは非分岐の炭素数２～３０のアルケニレン基、又は分岐若しくは非分岐の炭素数２～３０のアルキニレン基を示す。Ｒ^２０１とＲ^２０２とで環構造を形成してもよい。） Suitable mercapto-based silane coupling agents include (i) a silane coupling agent represented by the following formula (2-1), and (ii) a silane coupling agent containing a bond unit A represented by the following formula (2-2) and a bond unit B represented by the following formula (2-3).

In formula (2-1), R ¹⁰¹ is a monovalent group selected from -Cl, -Br, -OR ¹⁰⁶ , -O(O═)CR ¹⁰⁶ , -ON═CR ¹⁰⁶ R ¹⁰⁷ , -NR ¹⁰⁶ R ¹⁰⁷ and -(OSiR ¹⁰⁶ R ¹⁰⁷ ) _h (OSiR ¹⁰⁶ R ¹⁰⁷ R ¹⁰⁸ ) (R ¹⁰⁶ , R ¹⁰⁷ and R ¹⁰⁸ may be the same or different and each is a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, and h has an average value of 1 to 4), R ¹⁰² is R ¹⁰¹ , a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, R ¹⁰³ is a -[O(R ¹⁰⁹ O) _j ]- group (R R ¹⁰⁹ is an alkylene group having 1 to 18 carbon atoms, j is an integer from 1 to 4. R ¹⁰⁴ is a divalent hydrocarbon group having 1 to 18 carbon atoms, R ¹⁰⁵ is a monovalent hydrocarbon group having 1 to 18 carbon atoms, and xa, ya, and za are numbers that satisfy the relationship: xa+ya+2za=3, 0≦xa≦3, 0≦ya≦2, 0≦za≦1.

(In formulas (2-2) and (2-3), xb is an integer of 0 or more, and yb is an integer of 1 or more. R ²⁰¹ represents hydrogen, halogen, a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, a branched or unbranched alkynyl group having 2 to 30 carbon atoms, or an alkyl group in which the terminal hydrogen atom has been substituted with a hydroxyl group or a carboxyl group. R ²⁰² represents a branched or unbranched alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group having 2 to 30 carbon atoms, or a branched or unbranched alkynylene group having 2 to 30 carbon atoms. R ²⁰¹ and R ²⁰² may form a ring structure.)

Specific examples of R ¹⁰² , R ¹⁰⁵ , R ¹⁰⁶ , R ¹⁰⁷ and R ¹⁰⁸ in the above formula (2-1) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, a cyclopentyl group, a cyclohexyl group, a vinyl group, a propenyl group, an allyl group, a hexenyl group, an octenyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a tolyl group, a xylyl group, a naphthyl group, a benzyl group, a phenethyl group and a naphthylmethyl group.
Examples of R ¹⁰⁹ in the above formula (2-1) include linear alkylene groups such as methylene, ethylene, n-propylene, n-butylene, and hexylene groups, and branched alkylene groups such as isopropylene, isobutylene, and 2-methylpropylene groups.

Specific examples of silane coupling agents represented by the above formula (2-1) include 3-hexanoylthiopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, 3-decanoylthiopropyltriethoxysilane, 3-lauroylthiopropyltriethoxysilane, 2-hexanoylthioethyltriethoxysilane, 2-octanoylthioethyltriethoxysilane, 2-decanoylthioethyltriethoxysilane, 2-lauroylthioethyltriethoxysilane, 3-hexanoylthiopropyltrimethoxysilane, 3-octanoylthiopropyltrimethoxysilane, 3-decanoylthiopropyltrimethoxysilane, 3-lauroylthiopropyltrimethoxysilane, 2-hexanoylthioethyltrimethoxysilane, 2-octanoylthioethyltrimethoxysilane, 2-decanoylthioethyltrimethoxysilane, 2-lauroylthioethyltrimethoxysilane, and the like. Among these, 3-octanoylthiopropyltriethoxysilane (NXT manufactured by Momentive Corp.) is particularly preferred. The above silane coupling agents may be used alone or in combination of two or more kinds.

A silane coupling agent containing the bond unit A represented by formula (2-2) and the bond unit B represented by formula (2-3) shows less increase in viscosity during processing than polysulfide silanes such as bis-(3-triethoxysilylpropyl)tetrasulfide. This is thought to be because the sulfide portion of the bond unit A is a C-S-C bond, which is more thermally stable than tetrasulfides and disulfides, resulting in less increase in Mooney viscosity.

In addition, the scorch time is suppressed compared to mercaptosilanes such as 3-mercaptopropyltrimethoxysilane. This is thought to be because although the bonding unit A has a mercaptosilane structure, _{the -C7H15} portion of the bonding unit A covers the -SH group of the bonding unit B, making it difficult to react with the polymer and causing scorch.

In the silane coupling agent of the above structure, the content of bond unit A is preferably 30 mol% or more, more preferably 50 mol% or more, preferably 99 mol% or less, more preferably 90 mol% or less.In addition, from the viewpoint of reactivity with silica, the content of bond unit B is preferably 1 mol% or more, more preferably 5 mol% or more, even more preferably 10 mol% or more, preferably 70 mol% or less, more preferably 65 mol% or less, even more preferably 55 mol% or less.In addition, the total content of bond unit A and B is preferably 95 mol% or more, more preferably 98 mol% or more, particularly preferably 100 mol%.
The content of the bond units A and B includes the case where the bond units A and B are located at the terminals of the silane coupling agent. When the bond units A and B are located at the terminals of the silane coupling agent, the form is not particularly limited, and it is sufficient that the bond units A and B form units corresponding to the formulas (2-2) and (2-3) representing the bond units A and B.

Examples of the halogen atom for R ²⁰¹ include chlorine, bromine, and fluorine.

Examples of the branched or unbranched alkyl group having 1 to 30 carbon atoms for R ²⁰¹ include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, an octyl group, a nonyl group, a decyl group, etc. The number of carbon atoms in the alkyl group is preferably 1 to 12.

Examples of the branched or unbranched alkenyl group having 2 to 30 carbon atoms for R ²⁰¹ include a vinyl group, a 1-propenyl group, a 2-propenyl group, a 1-butenyl group, a 2-butenyl group, a 1-pentenyl group, a 2-pentenyl group, a 1-hexenyl group, a 2-hexenyl group, a 1-octenyl group, etc. The number of carbon atoms in the alkenyl group is preferably 2 to 12.

Examples of the branched or unbranched alkynyl group having 2 to 30 carbon atoms for R ²⁰¹ include an ethynyl group, a propynyl group, a butynyl group, a pentynyl group, a hexynyl group, a heptynyl group, an octynyl group, a nonynyl group, a decynyl group, an undecynyl group, a dodecynyl group, etc. The number of carbon atoms in the alkynyl group is preferably 2 to 12.

Examples of the branched or unbranched alkylene group having 1 to 30 carbon atoms for R ²⁰² include an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, an undecylene group, a dodecylene group, a tridecylene group, a tetradecylene group, a pentadecylene group, a hexadecylene group, a heptadecylene group, an octadecylene group, etc. The number of carbon atoms in the alkylene group is preferably 1 to 12.

Examples of the branched or unbranched alkenylene group having 2 to 30 carbon atoms for R ²⁰² include a vinylene group, a 1-propenylene group, a 2-propenylene group, a 1-butenylene group, a 2-butenylene group, a 1-pentenylene group, a 2-pentenylene group, a 1-hexenylene group, a 2-hexenylene group, a 1-octenylene group, etc. The number of carbon atoms in the alkenylene group is preferably 2 to 12.

Examples of the branched or unbranched alkynylene group having 2 to 30 carbon atoms for R ²⁰² include an ethynylene group, a propynylene group, a butynylene group, a pentynylene group, a hexynylene group, a heptynylene group, an octynylene group, a nonynylene group, a decynylene group, an undecynylene group, a dodecynylene group, etc. The number of carbon atoms in the alkynylene group is preferably 2 to 12.

In a silane coupling agent containing a bonding unit A represented by formula (2-2) and a bonding unit B represented by formula (2-3), the total number of repetitions (xb+yb) of the bonding unit A and the bonding unit B is preferably in the range of 3 to 300. Within this range, the mercaptosilane of the bonding unit B is covered by -C ₇ H ₁₅ of the bonding unit A, so that the scorch time can be prevented from being shortened and good reactivity with silica and rubber components can be ensured.

As a silane coupling agent containing a bond unit A represented by formula (2-2) and a bond unit B represented by formula (2-3), for example, NXT-Z30, NXT-Z45, NXT-Z60, etc. manufactured by Momentive Corp. can be used. These may be used alone or in combination of two or more kinds.

As a mercapto-based silane coupling agent, (iii) a silane coupling agent represented by the following formula (2-4) can also be suitably used.

（式中、Ｒ^６～Ｒ^８は、分岐若しくは非分岐の炭素数１～１２のアルキル基、分岐若しくは非分岐の炭素数１～１２のアルコキシ基、又は－Ｏ－（Ｒ^１１１－Ｏ）_ｚ－Ｒ^１１２（ｚ個のＲ^１１１は、分岐若しくは非分岐の炭素数１～３０の２価の炭化水素基を表す。ｚ個のＲ^１１１はそれぞれ同一でも異なっていてもよい。Ｒ^１１２は、分岐若しくは非分岐の炭素数１～３０のアルキル基、分岐若しくは非分岐の炭素数２～３０のアルケニル基、炭素数６～３０のアリール基、又は炭素数７～３０のアラルキル基を表す。ｚは１～３０の整数を表す。）で表される基を表す。Ｒ^６～Ｒ^８はそれぞれ同一でも異なっていてもよい。Ｒ^９は、分岐若しくは非分岐の炭素数１～６のアルキレン基を表す。）

(In the formula, R ⁶ to R ⁸ each represent a branched or unbranched alkyl group having 1 to 12 carbon atoms, a branched or unbranched alkoxy group having 1 to 12 carbon atoms, or a group represented by -O-(R ¹¹¹ -O) _z -R ¹¹² (z R ¹¹¹ represent a branched or unbranched divalent hydrocarbon group having 1 to 30 carbon atoms. z R ¹¹¹ may be the same or different. R ¹¹² represents a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms. z represents an integer from 1 to 30.) ^{R 6} to R ⁸ each may be the same or different. R ⁹ represents a branched or unbranched alkylene group having 1 to 6 carbon atoms.)

R ⁶ to R ⁸ represent a branched or unbranched alkyl group having 1 to 12 carbon atoms, a branched or unbranched alkoxy group having 1 to 12 carbon atoms, or a group represented by -O-(R ¹¹¹ -O) _z -R ^112. It is preferable that at least one of ^{R 6} to R ⁸ is a group represented by -O-(R ¹¹¹ -O) _z -R ¹¹² , and it is more preferable that two of them are groups represented by -O-(R ¹¹¹ -O) _z -R ¹¹² and one of them is a branched or unbranched alkoxy group having 1 to 12 carbon atoms.

Examples of the branched or unbranched alkyl group having 1 to 12 carbon atoms (preferably 1 to 5 carbon atoms) for R ⁶ to R ⁸ include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, an octyl group, and a nonyl group.

Examples of the branched or unbranched alkoxy group having 1 to 12 carbon atoms (preferably 1 to 5 carbon atoms) for R ⁶ to R ⁸ include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an iso-butoxy group, a sec-butoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, a 2-ethylhexyloxy group, an octyloxy group, and a nonyloxy group.

In —O—(R ¹¹¹ —O) _z —R ¹¹² of R ⁶ to R ⁸ , R ¹¹¹ represents a branched or unbranched divalent hydrocarbon group having 1 to 30 carbon atoms (preferably 1 to 15 carbon atoms, more preferably 1 to 3 carbon atoms).
Examples of the hydrocarbon group include a branched or unbranched alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group having 2 to 30 carbon atoms, a branched or unbranched alkynylene group having 2 to 30 carbon atoms, and an arylene group having 6 to 30 carbon atoms. Among these, a branched or unbranched alkylene group having 1 to 30 carbon atoms is preferred.

Examples of the branched or unbranched alkylene group having 1 to 30 carbon atoms (preferably 1 to 15 carbon atoms, more preferably 1 to 3 carbon atoms) for R ¹¹¹ include a methylene group, ethylene group, propylene group, butylene group, pentylene group, hexylene group, heptylene group, octylene group, nonylene group, decylene group, undecylene group, dodecylene group, tridecylene group, tetradecylene group, pentadecylene group, hexadecylene group, heptadecylene group, and octadecylene group.

Examples of the branched or unbranched alkenylene group having 2 to 30 carbon atoms (preferably 2 to 15 carbon atoms, more preferably 2 to 3 carbon atoms) for R ¹¹¹ include a vinylene group, a 1-propenylene group, a 2-propenylene group, a 1-butenylene group, a 2-butenylene group, a 1-pentenylene group, a 2-pentenylene group, a 1-hexenylene group, a 2-hexenylene group, and a 1-octenylene group.

Examples of the branched or unbranched alkynylene group having 2 to 30 carbon atoms (preferably 2 to 15 carbon atoms, more preferably 2 to 3 carbon atoms) for R ¹¹¹ include an ethynylene group, a propynylene group, a butynylene group, a pentynylene group, a hexynylene group, a heptynylene group, an octynylene group, a nonynylene group, a decynylene group, an undecynylene group, and a dodecynylene group.

Examples of the arylene group having 6 to 30 carbon atoms (preferably 6 to 15 carbon atoms) for R ¹¹¹ include a phenylene group, a tolylene group, a xylylene group, and a naphthylene group.

z represents an integer from 1 to 30 (preferably from 2 to 20, more preferably from 3 to 7, and even more preferably from 5 to 6).

R ¹¹² represents a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms. Among these, a branched or unbranched alkyl group having 1 to 30 carbon atoms is preferable.

Examples of the branched or unbranched alkyl group having 1 to 30 carbon atoms (preferably having 3 to 25 carbon atoms, more preferably having 10 to 15 carbon atoms) for R ¹¹² include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, and an octadecyl group.

Examples of the branched or unbranched alkenyl group having 2 to 30 carbon atoms (preferably having 3 to 25 carbon atoms, more preferably having 10 to 15 carbon atoms) for R ¹¹² include a vinyl group, a 1-propenyl group, a 2-propenyl group, a 1-butenyl group, a 2-butenyl group, a 1-pentenyl group, a 2-pentenyl group, a 1-hexenyl group, a 2-hexenyl group, a 1-octenyl group, a decenyl group, an undecenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, a pentadecenyl group, and an octadecenyl group.

Examples of the aryl group having 6 to 30 carbon atoms (preferably 10 to 20 carbon atoms) for R ¹¹² include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a biphenyl group.

Examples of the aralkyl group having 7 to 30 carbon atoms (preferably 10 to 20 carbon atoms) for R ¹¹² include a benzyl group and a phenethyl group.

Specific examples of the group represented by -O-(R ¹¹¹ -O) _z -R ¹¹² include, for example, -O-(C ₂ H ₄ -O) ₅ -C ₁₁ H ₂₃ , -O-(C ₂ H ₄ -O) ₅ -C ₁₂ H ₂₅ , -O-(C ₂ H ₄ -O) ₅ -C ₁₃ H ₂₇ , -O-(C ₂ H ₄ -O) ₅ -C ₁₄ H ₂₉ , -O-(C ₂ H ₄ -O) ₅ -C ₁₅ H ₃₁ , -O-(C ₂ H ₄ -O) ₃ -C ₁₃ H ₂₇ , -O-(C ₂ H ₄ -O) ₄ -C ₁₃ H ₂₇ , -O-(C _{2H4 -} O) _{6 - C13H27} , -O-( _C2H4 - _O ) _{7 -C13H27 ,} etc. Among these, -O-( _{C2H4 -} O) ₅ - _C11H23 , -O- _{( C2H4} -O) _{5 -C13H27 ,} -O-( _{C2H4 -} O _{) 5 - C15H31} , -O-( _{C2H4 -} O) _{6 - C13H27} are preferred.

Examples of the branched or unbranched alkylene group having 1 to 6 carbon atoms (preferably 1 to 5 carbon atoms) for R ⁹ include the same groups as the branched or unbranched alkylene group having 1 to 30 carbon atoms for R ¹¹¹ .

Examples of the compound represented by the formula (2-4) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and the compound represented by the following formula (Si363 manufactured by EVONIK-DEGUSSA), and the compound represented by the following formula can be preferably used. These may be used alone or in combination of two or more kinds.

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

(Other silane coupling agents)
The rubber composition may further contain a silane coupling agent other than the mercapto-based silane coupling agent. By using the other silane coupling agent in combination, the effect of using the mercapto-based silane coupling agent can be suitably obtained while imparting good processability.

When a mercapto-based silane coupling agent and another silane coupling agent are used in combination, the mixing ratio (content of mercapto-based silane coupling agent/content of other silane coupling agent (mass ratio)) is preferably 5/95 to 50/50, more preferably 5/95 to 35/65, and even more preferably 5/95 to 25/75, from the viewpoint of overall performance such as fuel economy, wet grip performance, and abrasion resistance.

The content of the silane coupling agent (total content of mercapto-based silane coupling agent and other silane coupling agents) is preferably 2 parts by mass or more, more preferably 4 parts by mass or more, even more preferably 6 parts by mass or more, and particularly preferably 8 parts by mass or more, per 100 parts by mass of silica. If it is above the lower limit, good overall performance in terms of fuel economy, wet grip performance, and abrasion resistance tends to be obtained. Furthermore, the above content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less. If it is below the upper limit, an effect commensurate with the amount blended tends to be obtained.

Other silane coupling agents are not particularly limited, and examples thereof include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide sulfide-based silane coupling agents such as vinyl triethoxysilane and vinyl trimethoxysilane; amino-based silane coupling agents such as 3-aminopropyl triethoxysilane and 3-aminopropyl trimethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyl triethoxysilane and γ-glycidoxypropyl trimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyl trimethoxysilane and 3-nitropropyl triethoxysilane; chloro-based silane coupling agents such as 3-chloropropyl trimethoxysilane and 3-chloropropyl triethoxysilane; polymer-type alkoxy oligomer type and multifunctional group type silane coupling agents;

Among other silane coupling agents, polymer-type alkoxy oligomer type and multifunctional group type silane coupling agents are preferred from the viewpoint of overall performance such as low fuel consumption, wet grip performance, and abrasion resistance. Specifically, methoxy/ethoxy group-containing oligomer type silane coupling agents having epoxy groups (KR-517 manufactured by Shin-Etsu Silicone Co., Ltd., etc.), methoxy group-containing oligomer type silane coupling agents having epoxy groups (KR-516 manufactured by Shin-Etsu Silicone Co., Ltd., etc.), methoxy/ethoxy group-containing oligomer type silane coupling agents having mercapto groups (X-41-1805 manufactured by Shin-Etsu Silicone Co., Ltd., etc.), methoxy group-containing oligomer type silane coupling agents having mercapto groups (X-41-1810 manufactured by Shin-Etsu Silicone Co., Ltd., etc.), ethoxy group-containing multifunctional group type silane coupling agents having amino groups, coupling agents (such as X-12-972F manufactured by Shin-Etsu Silicones), ethoxy group-containing multifunctional group type silane coupling agents having epoxy groups (such as X-12-981S manufactured by Shin-Etsu Silicones), ethoxy group-containing multifunctional group type silane coupling agents having epoxy groups (such as X-12-984S manufactured by Shin-Etsu Silicones), methoxy group-containing multifunctional group type silane coupling agents having mercapto groups (such as X-12-1154 manufactured by Shin-Etsu Silicones), and methoxy group-containing multifunctional group type silane coupling agents having isocyanate groups (such as X-12-1252 manufactured by Shin-Etsu Silicones).

(Carbon Black)
The rubber composition preferably contains carbon black from the viewpoint of abrasion resistance, wet grip performance, etc. Examples of carbon black include, but are not limited to, GPF, FEF, HAF, ISAF, SAF, etc. Commercially available products include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Co., Ltd., Lion Co., Ltd., Shin-Nichika Carbon Co., Ltd., Columbia Carbon Co., Ltd., etc.

The carbon black content is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the rubber component. By making it above the lower limit, there is a tendency to obtain improved effects such as abrasion resistance and wet grip performance. In addition, the carbon black content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. By making it below the upper limit, there is a tendency to obtain good fuel efficiency, etc.

The nitrogen adsorption specific surface area ( _N2SA ) of carbon black is preferably 65 ^m2 /g or more, more preferably 90 ^m2 /g or more, even more preferably 105 ^m2 /g or more, particularly preferably 110 ^m2 /g or more, and is preferably 250 ^m2 /g or less, more preferably 150 ^m2 /g or less, and even more preferably 130 ^m2 /g or less. By keeping it within the above range, there is a tendency to obtain good overall performance in terms of fuel economy, wet grip performance, and abrasion resistance.
The nitrogen adsorption specific surface area of carbon black is determined in accordance with JIS K 6217-2:2001.

The dibutyl phthalate oil absorption (DBP) of the carbon black is preferably 50 ml/100 g or more, more preferably 90 ml/100 g or more, even more preferably 105 ml/100 g or more, and particularly preferably 110 ml/100 g or more, and is preferably 250 ml/100 g or less, more preferably 150 ml/100 g or less, and even more preferably 135 ml/100 g or less. By keeping it within the above range, there is a tendency that good overall performance such as low fuel consumption, wet grip performance, and abrasion resistance can be obtained.
The DBP oil absorption of carbon black is measured in accordance with JIS K6217-4:2001.

(Liquid plasticizer)
From the viewpoint of various physical properties of a tire, the rubber composition preferably contains a liquid plasticizer.
The liquid plasticizer is not particularly limited as long as it is a plasticizer that is in a liquid state at room temperature (25° C.), and examples thereof include oil, liquid diene polymer, liquid resin, etc. Among them, oil is preferred from the viewpoint of processability, etc. These may be used alone or in combination of two or more kinds.

The content (total amount) of liquid plasticizer is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, even more preferably 7 parts by mass or more, particularly preferably 10 parts by mass or more, and most preferably 15 parts by mass or more, per 100 parts by mass of the rubber component. By making it above the lower limit, good processability tends to be obtained. In addition, the content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less. By making it below the upper limit, good abrasion resistance tends to be obtained. The content of liquid plasticizer also includes the amount of oil (extending oil) contained in the rubber (oil-extended rubber).

As the oil, in addition to the above-mentioned extending oil, conventionally known oils such as paraffin-based process oil, aromatic process oil, naphthenic process oil, low PCA (polycyclic aromatic) process oil such as TDAE and MES, vegetable oils and fats, and mixtures thereof can be used. Examples of vegetable oils and fats include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. Among them, process oils are preferred. Examples of commercially available oils that can be used include those from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Orisoi Co., Ltd., H&R Corporation, Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., and the like.

The liquid diene polymer preferably has a weight average molecular weight (Mw) of 1.0×10 ³ to 2.0×10 ⁵ , and more preferably 3.0×10 ³ to 1.5×10 ⁴ , in terms of polystyrene, as measured by gel permeation chromatography (GPC).
In this specification, the Mw of the liquid diene polymer is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

Examples of liquid diene polymers include liquid styrene butadiene copolymer (liquid SBR), liquid butadiene polymer (liquid BR), liquid isoprene polymer (liquid IR), liquid styrene isoprene copolymer (liquid SIR), etc.

Liquid resins are not particularly limited, but examples include liquid aromatic vinyl polymers, coumarone-indene resins, indene resins, terpene resins, rosin resins, and hydrogenated versions of these.

Examples of liquid aromatic vinyl polymers include resins obtained by polymerizing α-methylstyrene and/or styrene. Specific examples include liquid resins such as homopolymers of styrene, homopolymers of α-methylstyrene, and copolymers of α-methylstyrene and styrene.

Liquid coumarone-indene resin is a resin that contains coumarone and indene as the main monomer components that make up the resin skeleton (main chain). Here, monomer components that may be contained in the skeleton other than coumarone and indene include liquid resins such as styrene, α-methylstyrene, methylindene, and vinyltoluene.

Liquid indene resin is a liquid resin that contains indene as the main monomer component that makes up the resin's skeleton (main chain).

Liquid terpene resins are resins obtained by polymerizing terpene compounds such as alpha-pinene, beta-pinene, camphor, and dipentene, and liquid terpene resins (terpene phenolic resins, aromatic modified terpene resins, etc.) represented by terpene phenol, which is a resin obtained using terpene compounds and phenolic compounds as raw materials.

Liquid rosin resins include liquid rosin-based resins such as natural rosin, polymerized rosin, modified rosin, their ester compounds, and hydrogenated products of these.

Commercially available liquid diene polymers and liquid resins include products from, for example, CRAY VALLEY, Kuraray Co., Ltd.

(Resin)
The rubber composition may contain a resin (solid resin: a resin that is in a solid state at room temperature (25° C.)).

Examples of resins (solid resins) include aromatic vinyl polymers, coumarone-indene resins, indene resins, rosin resins, terpene resins, and acrylic resins. Commercially available products include those from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Co., Ltd., Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JXTG Nippon Oil & Energy Corporation, Arakawa Chemical Industries Co., Ltd., Taoka Chemical Co., Ltd., and Toagosei Co., Ltd. These may be used alone or in combination of two or more. Among these, aromatic vinyl polymers, coumarone-indene resins, terpene resins, and rosin resins are preferred, and coumarone-indene resins are more preferred.

The resin (solid resin) content is preferably 3 parts by mass or more, and more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less. By keeping it within the above range, good abrasion resistance, etc. tends to be obtained.

The softening point of the resin (solid resin) is preferably 30° C. or higher, more preferably 60° C. or higher, and even more preferably 80° C. or higher. The softening point is preferably 200° C. or lower, and more preferably 160° C. or lower. By keeping the softening point within the above range, good abrasion resistance and the like tend to be obtained.
The softening point of the resin is the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point tester.

(Other ingredients)
The rubber composition may contain a wax.
The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax; natural waxes such as vegetable wax and animal wax; and synthetic waxes such as polymers of ethylene, propylene, etc. These may be used alone or in combination of two or more. Among them, petroleum waxes are preferred, and paraffin wax is more preferred.

As wax, for example, products from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. can be used.

If wax is contained, the content is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 20 parts by mass or less, more preferably 10 parts by mass or less, per 100 parts by mass of the rubber component.

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

When an antioxidant is contained, the content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component.

The rubber composition may contain stearic acid.
As the stearic acid, any of the conventionally known products can be used, for example, products available from NOF Corporation, NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., and the like.

If stearic acid is contained, the content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component.

The rubber composition may contain zinc oxide.
As the zinc oxide, any known zinc oxide can be used, for example, products available from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., and the like.

If zinc oxide is contained, the content is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component.

The rubber composition preferably contains sulfur.
Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, etc., which are generally used in the rubber industry. These may be used alone or in combination of two or more kinds.

As sulfur, for example, products from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzatsu Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. can be used.

If sulfur is contained, the content is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and preferably 10.0 parts by mass or less, more preferably 5.0 parts by mass or less, and even more preferably 3.0 parts by mass or less, per 100 parts by mass of the rubber component.

The rubber composition preferably contains a vulcanization accelerator.
Examples of the vulcanization accelerator include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazyl sulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide, N-t-butyl-2-benzothiazole sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenyl guanidine, di-orthotolyl guanidine, and orthotolyl biguanidine. These may be used alone or in combination of two or more. Among them, sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators are preferred.

If a vulcanization accelerator is contained, the content thereof is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, and preferably 10.0 parts by mass or less, more preferably 7.0 parts by mass or less, per 100 parts by mass of the rubber component.

In addition to the above components, the rubber composition may further contain other compounding agents (such as organic crosslinking agents) that are commonly used in the tire industry. The content of these compounding agents is preferably 0.1 to 200 parts by mass per 100 parts by mass of the rubber component.

The rubber composition can be produced, for example, by kneading the above components using a rubber kneading device such as an open roll or a Banbury mixer, and then vulcanizing the mixture.

As for kneading conditions, in the base kneading process where additives other than the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 70 to 180°C, preferably 80 to 170°C. In the finish kneading process where the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is usually 120°C or lower, preferably 85 to 110°C. Furthermore, the composition kneaded with the vulcanizing agent and vulcanization accelerator is usually subjected to a vulcanization process such as press vulcanization. The vulcanization temperature is usually 140 to 190°C, preferably 150 to 185°C.

Among these, a method for producing the rubber composition is preferred which includes a step (I) of kneading a rubber component containing SBR, silica and a mercapto-based silane coupling agent, and a step (II) of maintaining the kneaded mixture obtained in the step (I) at high temperature.

For the kneading in step (I), a known method can be used that allows the components to be kneaded while controlling the temperature. The kneading temperature in step (I) is preferably 70 to 130°C, more preferably 80 to 125°C, and even more preferably 80 to 120°C. By setting the temperature at or above the lower limit, good abrasion resistance, etc. tends to be obtained. By setting the temperature at or below the upper limit, the dispersibility of the silica during kneading tends to be improved.

The kneading time in step (I) is preferably 30 seconds to 10 minutes, more preferably 2 to 8 minutes, and even more preferably 3 to 7 minutes. By setting the time to above the lower limit, good abrasion resistance, etc. tends to be obtained. By setting the time to below the upper limit, the dispersibility of the silica during kneading tends to be improved.

In step (II), the kneaded material obtained in step (I) is held (left stationary) at a high temperature. The holding method is not particularly limited as long as it is a method that can control the temperature, but for example, a thermostatic device such as an oven can be suitably used. In addition, high temperature holding may be performed in the kneading machine used in step (I).

The holding temperature in step (II) is preferably 130°C or higher, more preferably 135°C or higher, even more preferably 140°C or higher, particularly preferably 145°C or higher, and most preferably 150°C or higher. By setting it to above the lower limit, the reaction between the silane coupling agent and the silica is promoted, and the dispersibility of the silica is improved, which tends to improve fuel efficiency. The above holding temperature is preferably 185°C or lower, more preferably 170°C or lower, and even more preferably 160°C or lower. By setting it to below the upper limit, it tends to prevent the reaction between the silica and the silane coupling agent from proceeding too far, causing the rubber composition to gel and making tire molding difficult.

The retention time in step (II) is preferably 30 seconds or more, more preferably 70 seconds or more, even more preferably 100 seconds or more, and particularly preferably 150 seconds or more. By making it equal to or greater than the lower limit, the reaction between the silane coupling agent and silica tends to be promoted. The upper limit of the retention time is not particularly limited, but since no improvement in performance is obtained even if it exceeds 300 seconds, it is preferable that it is 300 seconds or less.

After step (II) is performed, sulfur, a vulcanization accelerator, and the like are further added and kneaded by a known method, and then vulcanized to obtain the rubber composition (rubber composition after vulcanization). The vulcanization temperature may be set appropriately, and the vulcanization temperature described above, etc., may be used.

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

The tires include pneumatic tires and airless (solid) tires, among which pneumatic tires are preferred. The tires can be used as passenger car tires, large passenger car tires, large SUV tires, heavy load tires such as trucks and buses, light truck tires, motorcycle tires, racing tires (high performance tires), etc. They can also be used as all-season tires, summer tires, studless tires (winter tires), etc.

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

スルフィド系シランカップリング剤：デグッサ社製のＳｉ６９（ビス（３－トリエトキシシリルプロピル）テトラスルフィド）
オイル：Ｈ＆Ｒ社製のＶＩＶＡＴＥＣ４００／５００（ＴＤＡＥオイル）
ステアリン酸：日油（株）製の椿
酸化亜鉛：三井金属鉱業（株）製の酸化亜鉛２種
老化防止剤：住友化学（株）製のアンチゲン６Ｃ（老化防止剤、Ｎ－（１，３－ジメチルブチル）－Ｎ’－フェニル－ｐ－フェニレンジアミン）
ワックス：日本精鑞（株）製のオゾエース０３５５
硫黄：鶴見化学工業（株）製の粉末硫黄
加硫促進剤１：大内新興化学工業（株）製のノクセラーＮＳ（Ｎ－ｔｅｒｔ－ブチル－２－ベンゾチアジルスルフェンアミド（ＴＢＢＳ））
加硫促進剤２：大内新興化学工業（株）製のノクセラーＤ（Ｎ，Ｎ’－ジフェニルグアニジン（ＤＰＧ）） SBR: NS616 manufactured by Zeon Co., Ltd. (non-oil-extended SBR, styrene content 21% by mass, vinyl content 66 mol%, Tg -23°C, Mw 240,000)
BR: BR150B (cis content: 97% by mass) manufactured by Ube Industries, Ltd.
Carbon black: Diablack I (N220, _N2SA ^114m2 /g, DBP 114ml/100g) manufactured by Mitsubishi Chemical Corporation
Silica: Ultrasil VN3 ( _N2SA ^175m2 /g) manufactured by Evonik Degussa
Mercapto-based silane coupling agent 1: NXT-Z45 manufactured by Momentive (a copolymer of bond unit A and bond unit B (bond unit A: 55 mol %, bond unit B: 45 mol %))
Mercapto-based silane coupling agent 2: NXT (3-octanoylthiopropyltriethoxysilane) manufactured by Momentive
Mercapto-based silane coupling agent 3: Si363 manufactured by Evonik Degussa (a silane coupling agent represented by the following formula (R ⁶ = -O-(C ₂ H ₄ -O) ₅ -C ₁₃ H ₂₇ , R ⁷ = C ₂ H ₅ -O-, R ⁸ = -O-(C ₂ H ₄ -O) ₅ -C ₁₃ H ₂₇ , R ⁹ = -C ₃ H ₆ - in the above formula (2-4))

Sulfide-based silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by Degussa
Oil: H&R VIVATEC 400/500 (TDAE oil)
Stearic acid: Camellia, manufactured by NOF Corp. Zinc oxide: Zinc oxide type 2, manufactured by Mitsui Mining & Smelting Co., Ltd. Antiaging agent: Antigen 6C (antiaging agent, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine), manufactured by Sumitomo Chemical Co., Ltd.
Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd.
Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd. 1: Noccela NS (N-tert-butyl-2-benzothiazylsulfenamide (TBBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator 2: Noccelaer D (N,N'-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

<Examples and Comparative Examples>
Using a Banbury mixer, materials other than sulfur and vulcanization accelerator shown in step (I) of each table were kneaded for 5 minutes under the conditions of a set temperature of 90 ° C. and a final reaching temperature of about 120 ° C. to obtain a kneaded product. Next, the kneaded product obtained in step (I) was held at a high temperature in the kneader used in step (I) at the holding temperature in each table and left for a predetermined time (step (II)). Thereafter, sulfur and vulcanization accelerator shown in step (III) of each table were added to the kneaded product taken out of the kneader, and kneaded for 5 minutes under the condition of 80 ° C. using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press-vulcanized in a 0.5 mm thick mold at 170 ° C. for 20 minutes to obtain a vulcanized rubber composition.

The following evaluations were carried out using the above vulcanized rubber composition (rubber composition after vulcanization). The results are shown in each table. The reference comparative examples in Tables 1, 2, and 3 are Comparative Examples 1-1, 2-1, and 3-1, respectively.

<Viscoelasticity test>
(1) Measurement of Complex Modulus of Elasticity For vulcanized rubber compositions (test pieces with a width of 4 mm, a length of 2 mm, and a thickness of 2 mm), the complex modulus of elasticity (E*(0.5%)) under conditions of an initial strain of 10%, a dynamic strain of 0.5%, and a temperature of 0°C, and the complex modulus of elasticity (E*(5%)) under conditions of an initial strain of 10%, a dynamic strain of 5%, and a temperature of 0°C were measured using a viscoelasticity spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.).
(2) Measurement of loss tangent The loss tangent (tan δ(70°C)) of the vulcanized rubber composition (a test piece having a width of 4 mm, a length of 2 mm, and a thickness of 2 mm) was measured using a viscoelasticity spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.) under conditions of an initial strain of 10%, a dynamic strain of 1%, and a temperature of 70°C.

<Fuel-efficient>
The tan δ (70° C.) values obtained in the viscoelasticity test were expressed as an index using the following calculation formula, with the tan δ (70° C.) of the reference comparative example being set at 100. A larger index indicates smaller rolling resistance and better fuel economy.
(Rolling resistance index) = (tan δ (70°C) of standard comparative example) / (tan δ (70°C) of each formulation) x 100

<Wet grip performance>
For the vulcanized rubber composition, tan δ was measured using a viscoelasticity spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.) under conditions of a frequency of 10 Hz, a strain of 0.1%, and a temperature of 0° C. Tan δ was expressed as an index, with the tan δ of the reference comparative example being set at 100. A larger index value indicates better wet grip performance.

<Wear resistance>
The abrasion amount of the vulcanized rubber composition was measured using a Lambourn abrasion tester under the conditions of room temperature, a load of 1.0 kgf, and a slip ratio of 30%. The reciprocal of the abrasion amount was expressed as an index, with the reference comparative example being set at 100. The larger the value, the more excellent the abrasion resistance.

From each table, it can be seen that the examples that contained SBR, silica and a mercapto-based silane coupling agent in a specified ratio and satisfied the above formulas (1) and (2) had significantly superior overall fuel economy, wet grip performance and abrasion resistance (expressed as the average of the three indices of fuel economy, wet grip performance and abrasion resistance).

Claims (14)

Contains styrene butadiene rubber, silica and a mercapto-based silane coupling agent,
The content of the styrene-butadiene rubber in 100% by mass of the rubber component is 50% by mass or more,
The content of the silica per 100 parts by mass of the rubber component is 30 to 120 parts by mass,
A rubber composition for a tread which satisfies the following formulas (1) and (2):

Contains styrene butadiene rubber, silica and a mercapto-based silane coupling agent,
The content of the styrene-butadiene rubber in 100% by mass of the rubber component is 50% by mass or more,
The content of the silica per 100 parts by mass of the rubber component is 30 to 120 parts by mass,
A rubber composition for a tread that satisfies the following formulas (1) and (2) (excluding the rubber compositions for a tread of (1) to (4) below).

(1) A rubber composition for a tread, comprising an alkylene group having 3 or more carbon atoms, a polysulfide group bonded to the alkylene group, and a crosslinking agent having a functional group containing a benzene ring.
(2) A rubber composition for treads, comprising at least one surfactant selected from the group consisting of polyoxyalkylene alkenyl ether sulfates and polyoxyalkylene alkyl ether sulfates.
(3) A rubber composition for treads, comprising a conjugated diene-based polymer having a structural unit based on a conjugated diene and a structural unit represented by the following formula (I), in which at least one end of the polymer is modified with a compound represented by the following formula (II):

[Wherein, X ¹ , X ² and X ³ each independently represents a group represented by the following formula (Ia), a hydroxyl group, a hydrocarbyl group or a substituted hydrocarbyl group; X ¹ , X ² and X ³ At least one of the above is a group represented by the following formula (Ia) or a hydroxyl group.

[Wherein, R ¹ and R ² each independently represents a hydrocarbyl group having 1 to 6 carbon atoms, a substituted hydrocarbyl group having 1 to 6 carbon atoms, a silyl group, or a substituted silyl group; R ¹ and R ² may be bonded to form a ring structure together with the nitrogen atom.

[In the formula, n represents an integer of 1 to 10, R ³ , R ⁴ and R ⁵ each independently represents a hydrocarbyl group having 1 to 4 carbon atoms or a hydrocarbyloxy group having 1 to 4 carbon atoms; R ³ , R ⁴ and R ⁵ At least one of the groups is a hydrocarbyloxy group, and A represents a functional group having a nitrogen atom.
(4) A rubber composition for treads obtained by kneading an amine-based antioxidant in a separate kneading step after kneading the rubber component and all of the silane coupling agents. Contains styrene butadiene rubber, silica and a mercapto-based silane coupling agent,
The content of the styrene-butadiene rubber in 100% by mass of the rubber component is 50% by mass or more,
The content of the silica per 100 parts by mass of the rubber component is 30 to 120 parts by mass,
A rubber composition for a tread that satisfies the following formulas (1) and (2) (excluding the rubber compositions for a tread of (1) to (4) below).

(1) A rubber composition for treads, comprising: a rubber component including a butadiene polymer having a trans content of 45% by mass or more and a vinyl content of 20% by mass or less; silica; a silane coupling agent having two or more functional groups including a sulfur atom capable of bonding to a diene rubber; and a crosslinking agent having an alkylene group having 3 or more carbon atoms, a polysulfide group bonded to the alkylene group, and a functional group including a benzene ring.
(2) A rubber component containing 30% by mass or more of styrene-butadiene rubber having an SiOR group (R is a hydrogen atom or a hydrocarbon group) and a nitrogen adsorption specific surface area of 210 m ² and at least one surfactant selected from the group consisting of polyoxyalkylene alkenyl ether sulfate salts and polyoxyalkylene alkyl ether sulfate salts.
(3) A rubber composition for a tread comprising a rubber component, silica and a silane coupling agent,
In 100% by mass of the rubber component, the content of a conjugated diene-based polymer having a structural unit based on a conjugated diene and a structural unit represented by the following formula (I), at least one end of the polymer being modified with a compound represented by the following formula (II), is 5% by mass or more,
The content of the silica per 100 parts by mass of the rubber component is 5 to 150 parts by mass,
A rubber composition for a tread, wherein the silane coupling agent has a mercapto group.

[Wherein, X ¹ , X ² and X ³ each independently represents a group represented by the following formula (Ia), a hydroxyl group, a hydrocarbyl group or a substituted hydrocarbyl group; X ¹ , X ² and X ³ At least one of the above is a group represented by the following formula (Ia) or a hydroxyl group.

[Wherein, R ¹ and R ² each independently represents a hydrocarbyl group having 1 to 6 carbon atoms, a substituted hydrocarbyl group having 1 to 6 carbon atoms, a silyl group, or a substituted silyl group; R ¹ and R ² may be bonded to form a ring structure together with the nitrogen atom.

[In the formula, n represents an integer of 1 to 10, R ³ , R ⁴ and R ⁵ each independently represents a hydrocarbyl group having 1 to 4 carbon atoms or a hydrocarbyloxy group having 1 to 4 carbon atoms; R ³ , R ⁴ and R ⁵ At least one of the groups is a hydrocarbyloxy group, and A represents a functional group having a nitrogen atom.
(4) A rubber composition for treads, which contains 60 to 200 parts by mass of silica, 1.5 to 5.0 parts by mass of an amine-based antioxidant, and at least one silane coupling agent selected from the group consisting of silane coupling agent 1 having a carbonylthio group (-S-C(=O)-) and no mercapto group (-SH), and silane coupling agent 2 having a mercapto group, relative to 100 parts by mass of a rubber component containing a copolymer obtained by copolymerizing an aromatic vinyl compound and a conjugated diene compound, and which is obtained by kneading the amine-based antioxidant in a separate kneading step after kneading the rubber component and all of the silane coupling agents. Styrene butadiene rubber, butadiene rubber, silica, carbon black and a mercapto-based silane coupling agent are included,
the rubber component is composed only of the styrene-butadiene rubber and the butadiene rubber,
a content of the styrene-butadiene rubber in 100% by mass of the rubber component is 50% by mass or more and 80% by mass or less, and a content of the butadiene rubber is 20% by mass or more and 50% by mass or less,
the content of the silica is 30 to 120 parts by mass and the content of the carbon black is 10 parts by mass or more relative to 100 parts by mass of the rubber component,
A rubber composition for a tread which satisfies the following formulas (1) and (2):

The rubber composition for treads according to any one of claims 1 to 4 , which satisfies the following formula (1-1):

The rubber composition for treads according to any one of claims 1 to 5 , which satisfies the following formula (1-2):

The rubber composition for treads according to any one of claims 1 to 6 , wherein the styrene-butadiene rubber contains a styrene content of 5 to 50 mass % and a weight average molecular weight of 100,000 to 1,600,000. The rubber composition for a tread according to any one of claims 1 to 7, further comprising a butadiene rubber. The rubber composition for tread according to any one of claims 1 to 8 , wherein the mercapto-based silane coupling agent contains a silane coupling agent represented by the following formula (2-1):

In formula (2-1), R ¹⁰¹ is a monovalent group selected from -Cl, -Br, -OR ¹⁰⁶ , -O(O═)CR ¹⁰⁶ , -ON═CR ¹⁰⁶ R ¹⁰⁷ , -NR ¹⁰⁶ R ¹⁰⁷ and -(OSiR ¹⁰⁶ R ¹⁰⁷ ) _h (OSiR ¹⁰⁶ R ¹⁰⁷ R ¹⁰⁸ ) (R ¹⁰⁶ , R ¹⁰⁷ and R ¹⁰⁸ may be the same or different and each is a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, and h has an average value of 1 to 4), R ¹⁰² is R ¹⁰¹ , a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, R ¹⁰³ is a -[O(R ¹⁰⁹ O) _j ]- group (R R ¹⁰⁹ is an alkylene group having 1 to 18 carbon atoms, j is an integer from 1 to 4. R ¹⁰⁴ is a divalent hydrocarbon group having 1 to 18 carbon atoms, R ¹⁰⁵ is a monovalent hydrocarbon group having 1 to 18 carbon atoms, and xa, ya, and za are numbers that satisfy the relationship: xa+ya+2za=3, 0≦xa≦3, 0≦ya≦2, 0≦za≦1. The mercapto-based silane coupling agent includes a silane coupling agent having a bond unit A represented by the following formula (2-2) and a bond unit B represented by the following formula ( 2-3 ).

(In formulas (2-2) and (2-3), xb is an integer of 0 or more, and yb is an integer of 1 or more. R ²⁰¹ represents hydrogen, halogen, a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, a branched or unbranched alkynyl group having 2 to 30 carbon atoms, or an alkyl group in which the terminal hydrogen atom has been substituted with a hydroxyl group or a carboxyl group. R ²⁰² represents a branched or unbranched alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group having 2 to 30 carbon atoms, or a branched or unbranched alkynylene group having 2 to 30 carbon atoms. R ²⁰¹ and R ²⁰² may form a ring structure.) The rubber composition for treads according to any one of claims 1 to 10 , wherein the mercapto-based silane coupling agent includes a silane coupling agent represented by the following formula (2-4):

(In the formula, R ⁶ to R ⁸ each represent a branched or unbranched alkyl group having 1 to 12 carbon atoms, a branched or unbranched alkoxy group having 1 to 12 carbon atoms, or a group represented by -O-(R ¹¹¹ -O) _z -R ¹¹² (z R ¹¹¹ represent a branched or unbranched divalent hydrocarbon group having 1 to 30 carbon atoms. z R ¹¹¹ may be the same or different. R ¹¹² represents a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms. z represents an integer from 1 to 30.) ^{R 6} to R ⁸ each may be the same or different. R ⁹ represents a branched or unbranched alkylene group having 1 to 6 carbon atoms.) The rubber composition for a tread according to any one of claims 1 to 11, further comprising carbon black. The rubber composition for tread according to any one of claims 1 to 12, which is obtained by a manufacturing method including: a step (I) of kneading silica and a mercapto-based silane coupling agent; and a step (II) of holding the kneaded mixture obtained in the step (I ) at 130°C or higher. A tire having a tread made of the rubber composition according to any one of claims 1 to 13 .