JP7587342B2 - Rubber composition for tread and tire - Google Patents

Description

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

In recent years, there has been growing social demand for the reduction of carbon dioxide emissions from the standpoint of resource and energy conservation, as well as environmental protection, and various countermeasures are being considered for automobiles, such as weight reduction and the use of electrical energy. For this reason, there is a demand to reduce the rolling resistance of automobile tires and improve fuel efficiency, and there is also a desire to improve performance such as wear resistance.

For example, Patent Document 1 proposes a method of reducing rolling resistance by using a diene rubber (modified rubber) modified with an organosilicon compound containing amino and alkoxy groups.

JP 2000-344955 A

However, in the rubber composition of Patent Document 1, while the reaction efficiency between silica and rubber is improved and fuel economy is improved, the bond between the silica and rubber is too dense, so there is room for improvement in wear resistance. In addition, rubber compositions for automobile tires are required to have excellent wet grip performance from a safety standpoint.

The present invention aims to provide a rubber composition for treads that has excellent overall performance, including wet grip performance, fuel efficiency, and abrasion resistance, and a tire having a tread made of the rubber composition for treads.

After extensive research, the inventors discovered that the above problems could be solved by providing a rubber composition for treads that contains 100 parts by mass of a rubber component that contains a predetermined amount of styrene-butadiene rubber and a predetermined amount of BR, a predetermined amount of carbon black, and a predetermined amount of silica, and that has a tan δ of 0.60 or less at a dynamic strain amplitude of 0.5% at 0°C and a peak temperature of tan δ of -17°C or less. After further research, the inventors have completed the present invention.

（式中、Ｒ¹⁰¹～Ｒ¹⁰³は、直鎖もしくは分岐鎖の炭素数１～１２のアルキル基、直鎖もしくは分岐鎖の炭素数１～１２のアルコキシ基、または－Ｏ－（Ｒ¹¹¹－Ｏ）_z－Ｒ¹¹²（ｚ個のＲ¹¹¹は、直鎖もしくは分岐鎖の炭素数１～３０の２価の炭化水素基を表す。ｚ個のＲ¹¹¹は、それぞれ同一でも異なっていてもよい。Ｒ¹¹²は、直鎖もしくは分岐鎖の炭素数１～３０のアルキル基、直鎖もしくは分岐鎖の炭素数２～３０のアルケニル基、炭素数６～３０のアリール基、または炭素数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。Ｒ¹⁰¹～Ｒ¹⁰³はそれぞれ同一でも異なっていてもよい。Ｒ¹⁰⁴は、直鎖もしくは分岐鎖の炭素数１～６のアルキレン基を表す。）

（式中、ｘは０以上の整数、ｙは１以上の整数である。Ｒ²⁰¹は、水素原子、ハロゲン原子、直鎖もしくは分岐鎖の炭素数１～３０のアルキル基、直鎖もしくは分岐鎖の炭素数２～３０のアルケニル基、直鎖もしくは分岐鎖の炭素数２～３０のアルキニル基、または該アルキル基の末端の水素原子が水酸基もしくはカルボキシル基で置換されたものを表す。Ｒ²⁰²は、直鎖もしくは分岐鎖の炭素数１～３０のアルキレン基、直鎖もしくは分岐鎖の炭素数２～３０のアルケニレン基、または、直鎖もしくは分岐鎖の炭素数２～３０のアルキニレン基を表す。Ｒ²⁰¹とＲ²⁰²とで環構造を形成してもよい。）、ならびに
［５］上記［１］～［４］のいずれかに記載のトレッド用ゴム組成物で構成されるトレッドを備えるタイヤ
に関する。 That is, the present invention provides
[1] 100 parts by mass of a rubber component containing 60 to 80% by mass, preferably 65 to 75% by mass, more preferably 65 to 70% by mass or 70 to 75% by mass of a styrene-butadiene rubber and 20 to 40% by mass, preferably 25 to 35% by mass, more preferably 30 to 35% by mass of a butadiene rubber,
a rubber composition for a tread, comprising 1 to 40 parts by mass, preferably 3 to 30 parts by mass, more preferably 5 to 20 parts by mass of carbon black, and 50 to 150 parts by mass, preferably 55 to 115 parts by mass, more preferably 60 to 100 parts by mass of silica, wherein tan δ at a dynamic strain amplitude of 0.5% at 0°C is 0.60 or less, preferably 0.25 to 0.45, more preferably 0.25 to 0.40, even more preferably 0.25 to 0.35, particularly preferably 0.25 to 0.30, and wherein the peak temperature of tan δ is -17°C or less, preferably -28 to -17°C, more preferably -28 to -18°C, even more preferably -23 to -18°C, particularly preferably -23 to -19°C;
[2] The rubber composition for treads according to the above [1], which contains aluminum hydroxide.
[3] The rubber composition for treads according to the above [1] or [2], containing 10 to 80 parts by mass, preferably 15 to 70 parts by mass, more preferably 20 to 60 parts by mass of oil per 100 parts by mass of the rubber component;
[4] The rubber composition for tread according to any one of the above [1] to [3], which contains a silane coupling agent having a mercapto group, which is a compound represented by the following formula (1) and/or a compound containing a bond unit A represented by the following formula (2) and a bond unit B represented by the following formula (3):

(In the formula, R ¹⁰¹ to R ¹⁰³ each represent a linear or branched alkyl group having 1 to 12 carbon atoms, a linear or branched 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 linear or branched divalent hydrocarbon group having 1 to 30 carbon atoms. z R ¹¹¹ may be the same or different. R ¹¹² represents a linear or branched alkyl group having 1 to 30 carbon atoms, a linear or branched 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 101} to R ¹⁰³ may be the same or different. R ¹⁰⁴ represents a linear or branched alkylene group having 1 to 6 carbon atoms.)

(wherein x is an integer of 0 or more, and y is an integer of 1 or more. R ²⁰¹ represents a hydrogen atom, a halogen atom, a linear or branched alkyl group having 1 to 30 carbon atoms, a linear or branched alkenyl group having 2 to 30 carbon atoms, a linear or branched alkynyl group having 2 to 30 carbon atoms, or an alkyl group in which a terminal hydrogen atom has been substituted with a hydroxyl group or a carboxyl group. ^{R 202} represents a linear or branched alkylene group having 1 to 30 carbon atoms, a linear or branched alkenylene group having 2 to 30 carbon atoms, or a linear or branched alkynylene group having 2 to 30 carbon atoms. R ²⁰¹ and R ²⁰² may together form a ring structure.), and [5] a tire having a tread formed from the rubber composition for tread according to any one of the above [1] to [4].

The rubber composition for treads of the present invention contains 100 parts by mass of a rubber component containing 60 to 80% by mass of styrene butadiene rubber and 20 to 40% by mass of butadiene rubber, 1 to 40 parts by mass of carbon black and 50 to 150 parts by mass of silica, and has a tan δ of 0.60 or less at a dynamic strain amplitude of 0.5% at 0°C and a peak tan δ temperature of -17°C or less. When used in tire treads, the rubber composition can be used to produce tires with excellent overall performance, including wet grip performance, low fuel consumption, and wear resistance.

The rubber composition for treads, which is one embodiment of the present invention, is characterized in that it contains 100 parts by mass of a rubber component containing 60 to 80% by mass of styrene butadiene rubber and 20 to 40% by mass of butadiene rubber, 1 to 40 parts by mass of carbon black, and 50 to 150 parts by mass of silica, and has a tan δ of 0.60 or less at a dynamic strain amplitude of 0.5% at 0°C and a tan δ peak temperature of -17°C or less. This characteristic makes it possible to dramatically improve the overall performance of the tire, such as wet grip performance, fuel efficiency, and wear resistance, compared to rubber compositions using the same formulation. Specifically, by setting the tan δ peak temperature to a low value of -17°C or less, it is possible to reduce energy loss at tire temperatures of 30 to 40°C, and it is believed that the RRC (rolling resistance coefficient) can be reduced. In this case, it is believed that the wear resistance can be improved by containing 20% by mass or more of BR and setting the tan δ peak temperature to -17°C or less. In this way, by making tan δ at a dynamic strain amplitude of 0.5% at 0°C 0.60 or less and the tan δ peak temperature -17°C or less, it is believed that even in tires that use an ultra-low fuel consumption compound, it is possible to lower the RRC at the same tan δ (30°C), i.e., to achieve lower fuel consumption, compared to compounds with a higher tan δ peak temperature.

In one embodiment, the tan δ (hereinafter also referred to as tan δ (0°C)) at a dynamic strain amplitude of 0.5% at 0°C of the rubber composition for treads is 0.60 or less, preferably 0.45 or less, more preferably 0.40 or less, even more preferably 0.35 or less, and particularly preferably 0.30 or less. If tan δ (0°C) exceeds 0.60, fuel economy performance in winter may deteriorate. In addition, tan δ (0°C) is preferably 0.25 or more. By making tan δ (0°C) 0.25 or more, good wet grip performance tends to be obtained. Note that tan δ (0°C) is a value obtained by the measurement method described in the examples described later.

The tan δ peak temperature of the rubber composition for treads in one embodiment is -17°C or lower, preferably -18°C or lower, and more preferably -19°C or lower. If the tan δ peak temperature exceeds -17°C, fuel economy performance in winter may deteriorate. In addition, the tan δ peak temperature of the rubber composition for treads of the present invention is preferably -28°C or higher, and more preferably -23°C or higher. By setting the tan δ peak temperature to -28°C or higher, good wet grip performance tends to be obtained. The tan δ peak temperature is a value obtained by the measurement method described in the examples described later.

In a rubber composition containing 100 parts by mass of a rubber component containing 60 to 80% by mass of styrene butadiene rubber and 20 to 40% by mass of butadiene rubber, 1 to 40 parts by mass of carbon black and 50 to 150 parts by mass of silica, it is possible to satisfy tan δ (0°C) ≦ 0.60 and a tan δ peak temperature ≦ -17°C by optimizing and selecting the Tgs of the styrene butadiene rubber and butadiene rubber used, specifically, so that the tan δ peak temperature of the tread rubber composition of the combined rubber components is -17 °C or lower, and by adjusting the amounts of other compounding agents such as oil, resin, etc., without imposing an undue burden on a person skilled in the art.

(Rubber component)
In one embodiment, the rubber component contains 60 to 80 mass% of styrene butadiene rubber (SBR) and 20 to 40 mass% of butadiene rubber (BR). In addition to SBR and BR, the rubber component may contain, for example, natural rubber (NR), deproteinized natural rubber (DPNR), highly purified natural rubber (HPNR), epoxidized natural rubber (ENR), isoprene rubber (IR), etc., but only SBR and BR are preferred.

(SBR)
The SBR is not particularly limited, and examples thereof include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Examples of modified SBR include SBR whose ends and/or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin, silicon compounds, etc. Among these, S-SBR is preferable. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR), etc. can also be used. These SBRs may be used alone, or two or more of them may be used in combination.

Examples of S-SBR that can be used in this embodiment include S-SBR manufactured and sold by JSR Corporation, Ube Industries, Ltd., Asahi Kasei Corporation, ZS Elastomers Co., Ltd., etc.

From the viewpoint of grip performance, the styrene content of the SBR is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. If the styrene content is too high, styrene groups are adjacent to each other, the polymer becomes too hard, crosslinking is likely to be non-uniform, and blowability during high-temperature driving may deteriorate. In addition, temperature dependency increases, and performance changes with temperature change become large, and stable grip performance during driving and in the later stages tend not to be obtained. Therefore, the styrene content of the SBR is preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less. In this specification, the styrene content of the SBR is calculated by ¹ H-NMR measurement.

From the viewpoints of ensuring reactivity with silica, rubber strength and abrasion resistance, the vinyl bond amount of SBR is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 20 mol% or more. From the viewpoints of preventing an increase in temperature dependency, grip performance, EB (durability) and abrasion resistance, the vinyl bond amount of SBR is preferably 70 mol% or less, more preferably 65 mol% or less, and even more preferably 60 mol% or less. In this specification, the vinyl bond amount of SBR (amount of 1,2-bonded butadiene units) is measured by infrared absorption spectroscopy.

From the viewpoints of abrasion resistance and grip performance, the weight average molecular weight (Mw) of SBR is preferably 200,000 or more, more preferably 300,000 or more, even more preferably 400,000 or more, and particularly preferably 500,000 or more. From the viewpoints of crosslinking uniformity, Mw is preferably 2,000,000 or less, more preferably 150 or less, and even more preferably 1,000,000 or less. Mw can be calculated based on the 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) in terms of standard polystyrene.

The content of SBR in the rubber component is 60% by mass or more, preferably 65% by mass or more, and more preferably 70% by mass or more. If the content of SBR in the rubber component is less than 60% by mass, grip performance on wet road surfaces tends to be insufficient. Also, the content of SBR in the rubber component is 80% by mass or less, preferably 75% by mass or less, and more preferably 70% by mass or less. If the content of SBR in the rubber component exceeds 80% by mass, abrasion resistance tends to be insufficient.

(BR)
The BR is not particularly limited, and examples of the BR that can be used include BR having a cis 1,4 bond content of less than 50% (low cis BR), BR having a cis 1,4 bond content of 90% or more (high cis BR), rare earth butadiene rubber synthesized using a rare earth catalyst (rare earth BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), and modified BR (high cis modified BR, low cis modified BR), which are commonly used in the tire industry.

Examples of high cis BR include BR1220 manufactured by Zeon Corporation, BR130B, BR150B, and BR150L manufactured by Ube Industries, Ltd., and BR730 manufactured by JSR Corporation. The inclusion of high cis BR can improve low temperature properties and wear resistance. Examples of rare earth BR include BUNA-CB25 manufactured by LANXESS KK.

SPB-containing BR is one in which 1,2-syndiotactic polybutadiene crystals are not simply dispersed in BR, but are dispersed after being chemically bonded to the BR. Examples of such SPB-containing BR include VCR-303, VCR-412, and VCR-617 manufactured by Ube Industries, Ltd.

Modified BR is obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and examples of such modified BR include those in which the ends of the modified BR molecule are bonded with tin-carbon bonds (tin-modified BR) and butadiene rubber having a condensed alkoxysilane compound at the active end of the butadiene rubber (silica-modified BR). Examples of such modified BR include BR1250H (tin-modified) and S-modified polymer (silica-modified) manufactured by ZS Elastomers Co., Ltd.

The weight average molecular weight (Mw) of BR is preferably 300,000 or more, more preferably 400,000 or more, and even more preferably 450,000 or more, from the viewpoint of abrasion resistance and grip performance. Also, from the viewpoint of crosslinking uniformity, Mw is preferably 2,000,000 or less, and more preferably 1,000,000 or less. Note that Mw can be calculated by converting it into standard polystyrene based on the 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 content of BR in the rubber component is 20% by mass or more, preferably 25% by mass or more, and more preferably 30% by mass or more. If the content of BR in the rubber component is less than 20% by mass, the abrasion resistance tends to be insufficient. Also, the content of BR in the rubber component is 40% by mass or less, preferably 35% by mass or less, and more preferably 30% by mass or less. If the content of BR in the rubber component exceeds 40% by mass, the grip performance on wet road surfaces tends to be insufficient.

(Carbon Black)
The carbon black is not particularly limited, and those commonly used in the tire industry, such as GPF, FEF, HAF, ISAF, and SAF, can be used. Specifically, N110, N115, N120, N125, N134, N135, N219, N220, N231, N234, N293, N299, N326, N330, N339, N343, and N34 7, N351, N356, N358, N375, N539, N550, N582, N630, N642, N650, N660, N683, N754, N762, N765, N772, N774, N787, N907, N908, N990, N991, etc. can be preferably used, and in addition, products synthesized by the company can also be preferably used. These may be used alone or in combination of two or more kinds.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 50 m ² /g or more, more preferably 80 m ² /g or more, from the viewpoints of weather resistance and reinforcement. Also, the N ₂ SA of carbon black is preferably 250 m ² /g or less, more preferably 220 m ² /g or less, from the viewpoints of fuel economy, dispersibility, fracture properties and durability. The N ₂ SA of carbon black in this specification is a value measured in accordance with Method A of JIS K 6217-2 "Fundamental properties of carbon black for rubber - Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method".

The carbon black content per 100 parts by mass of the rubber component is 1 part by mass or more, preferably 3 parts by mass or more, and more preferably 5 parts by mass or more. If the carbon black content is less than 1 part by mass, weather resistance cannot be ensured and cracks due to ultraviolet rays may occur. In addition, the carbon black content per 100 parts by mass of the rubber component is 40 parts by mass or less, preferably 30 parts by mass or less, and more preferably 15 parts by mass or less. If the carbon black content exceeds 40 parts by mass, there is a possibility that sufficient fuel efficiency performance may not be achieved.

(silica)
In one embodiment, silica is used. By blending silica, fuel economy, wear resistance, and wet grip performance can be improved. The silica is not particularly limited, and for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrated silica), and other silicas commonly used in the tire industry can be used. Among them, hydrated silica prepared by a wet method is preferred because it has a large number of silanol groups. Silica may be used alone or in combination of two or more types.

From the viewpoints of durability and elongation at break, the BET specific surface area of silica is preferably 80 ^m2 /g or more, more preferably 100 ^m2 /g or more, even more preferably 150 ^m2 /g or more, and particularly preferably 180 ^m2 /g or more. From the viewpoints of fuel economy and processability, the BET specific surface area of silica is preferably 300 ^m2 /g or less, more preferably 250 ^m2 /g or less. In this specification, the BET specific surface area of silica is a value measured by the BET method in accordance with ASTM D3037-93.

The silica content is 50 parts by mass or more, preferably 55 parts by mass or more, and more preferably 60 parts by mass or more, per 100 parts by mass of the rubber component. If the silica content is less than 50 parts by mass, the effect of improving fuel efficiency by blending silica tends to be insufficient, the effect of improving wear resistance tends to be insufficient, and grip performance on wet road surfaces may not be sufficiently obtained. The silica content is 150 parts by mass or less, preferably 115 parts by mass or less, and more preferably 100 parts by mass or less, per 100 parts by mass of the rubber component. If the silica content exceeds 150 parts by mass, the dispersion of silica in the rubber may deteriorate, leading to a tendency for fuel efficiency and wear resistance to decrease, and the processability of the rubber may deteriorate, especially the viscosity may become too high, making processing difficult.

In addition to the above-mentioned components, the rubber composition for treads according to one embodiment may contain compounding agents that are conventionally commonly used in the tire industry, such as reinforcing fillers other than carbon black and silica, silane coupling agents, oils, tackifying resins, waxes, processing aids, various antioxidants, softeners, vulcanizing agents such as zinc oxide, stearic acid, and sulfur, and various vulcanization accelerators, as appropriate.

(Other reinforcing fillers)
As reinforcing fillers other than carbon black and silica, those conventionally used in rubber compositions for treads, such as aluminum hydroxide, calcium carbonate, alumina, clay, and talc, can be compounded.

(Aluminum Hydroxide)
As the aluminum hydroxide, aluminum hydroxide generally used in the tire industry can be used, and examples thereof include Higilite (registered trademark) manufactured by Showa Denko K.K. and Apilar (registered trademark) manufactured by Navaltec Co., Ltd. The aluminum hydroxide in the present embodiment also includes alumina hydrate.

The nitrogen adsorption specific surface area (N ₂ SA) of aluminum hydroxide is preferably 4 m ² /g or more, more preferably 5 m ² /g or more, and more preferably 6 m ² /g or more, from the viewpoint of wet grip performance. Moreover, the N ₂ SA of aluminum hydroxide is preferably 50 m ² /g or less, more preferably 45 m ² /g or less, and even more preferably 40 m ² /g or less, from the viewpoint of dispersibility, prevention of re-agglomeration, and wear resistance of aluminum hydroxide. The N ₂ SA of aluminum hydroxide in this specification is a value measured by the BET method in accordance with ASTM D3037-81.

From the viewpoints of dispersibility of aluminum hydroxide, prevention of re-aggregation, and abrasion resistance, the average particle diameter (D50) of aluminum hydroxide is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. From the viewpoint of abrasion resistance, the average particle diameter (D50) of aluminum hydroxide is preferably 3.0 μm or less, and more preferably 2.0 μm or less. In this specification, the average particle diameter (D50) is the particle diameter at 50% of the cumulative mass value of the particle size distribution curve obtained by a particle size distribution measuring device.

When aluminum hydroxide is contained, the content per 100 parts by mass of the rubber component 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. By making the content of aluminum hydroxide 3 parts by mass or more, wet grip performance tends to be good. Furthermore, when aluminum hydroxide is contained, the content per 100 parts by mass of the rubber component 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 making the content of aluminum hydroxide 30 parts by mass or less, abrasion resistance tends to be good.

(Silane coupling agent)
Since the rubber composition for treads according to one embodiment contains silica, it is preferable to use a silane coupling agent in combination. The silane coupling agent is not particularly limited, and any silane coupling agent that has been conventionally used in combination with silica in the tire industry can be used. Specific examples of the silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(4-trimethoxysilylbutyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-triethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-triethoxysilylbutyl)trisulfide, bis(3-trimethoxysilylpropyl)trisulfide, bis(2-trimethoxysilylethyl)trisulfide, bis(3-trimethoxy ...methoxysilylethyl)trisulfide, bis(2-trimethoxysilylethyl)trisulfide, bis(2-triethoxysilylethyl)trisulfide, bis(2-triethoxysilylethyl)trisulfide, bis(2-triethoxysilylethyl)trisulfide, bis(2-triethoxysilylethyl)trisulfide, bis( , 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, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyltetrasulfide, 2-trimethoxysilyl Silane coupling agents having a sulfide group, such as ethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzothiazolyl tetrasulfide, and 3-trimethoxysilylpropyl methacrylate monosulfide; silane coupling agents having a mercapto group, such as 3-mercaptopropyl trimethoxysilane, 3-mercaptopropyl triethoxysilane, 2-mercaptoethyl trimethoxysilane, 2-mercaptoethyl triethoxysilane, Si363 manufactured by Evonik-Degussa, and NXT-Z30, NXT-Z45, and NXT-Z60 manufactured by Momentive; 3-octanoylthio-1-propanol; Silane coupling agents having a thioester group such as pyrtriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane, etc.; silane coupling agents having a vinyl group such as vinyltriethoxysilane, etc.; silane coupling agents having an amino group such as 3-aminopropyltriethoxysilane, etc.; silane coupling agents having a glycidoxy group such as γ-glycidoxypropyltriethoxysilane, etc.; silane coupling agents having a nitro group such as 3-nitropropyltrimethoxysilane, etc.; silane coupling agents having a chloro group such as 3-chloropropyltrimethoxysilane, etc., etc. are listed, and silane coupling agents having a mercapto group are preferred. These silane coupling agents may be used alone or in combination of two or more.

（式中、Ｒ¹⁰¹～Ｒ¹⁰³は、直鎖もしくは分岐鎖の炭素数１～１２のアルキル基、直鎖もしくは分岐鎖の炭素数１～１２のアルコキシ基、または－Ｏ－（Ｒ¹¹¹－Ｏ）_z－Ｒ¹¹²（ｚ個のＲ¹¹¹は、直鎖もしくは分岐鎖の炭素数１～３０の２価の炭化水素基を表す。ｚ個のＲ¹¹¹は、それぞれ同一でも異なっていてもよい。Ｒ¹¹²は、直鎖もしくは分岐鎖の炭素数１～３０のアルキル基、直鎖もしくは分岐鎖の炭素数２～３０のアルケニル基、炭素数６～３０のアリール基、または炭素数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。Ｒ¹⁰¹～Ｒ¹⁰³はそれぞれ同一でも異なっていてもよい。Ｒ¹⁰⁴は、直鎖もしくは分岐鎖の炭素数１～６のアルキレン基を表す。）

（式中、ｘは０以上の整数、ｙは１以上の整数である。Ｒ²⁰¹は、水素原子、ハロゲン原子、直鎖もしくは分岐鎖の炭素数１～３０のアルキル基、直鎖もしくは分岐鎖の炭素数２～３０のアルケニル基、直鎖もしくは分岐鎖の炭素数２～３０のアルキニル基、または該アルキル基の末端の水素原子が水酸基もしくはカルボキシル基で置換されたものを表す。Ｒ²⁰²は、直鎖もしくは分岐鎖の炭素数１～３０のアルキレン基、直鎖もしくは分岐鎖の炭素数２～３０のアルケニレン基、または、直鎖もしくは分岐鎖の炭素数２～３０のアルキニレン基を表す。Ｒ²⁰¹とＲ²⁰²とで環構造を形成してもよい。） The silane coupling agent having a mercapto group is preferably a compound represented by the following formula (1) and/or a compound containing a bonding unit A represented by the following formula (2) and a bonding unit B represented by the following formula (3).

(In the formula, R ¹⁰¹ to R ¹⁰³ each represent a linear or branched alkyl group having 1 to 12 carbon atoms, a linear or branched 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 linear or branched divalent hydrocarbon group having 1 to 30 carbon atoms. z R ¹¹¹ may be the same or different. R ¹¹² represents a linear or branched alkyl group having 1 to 30 carbon atoms, a linear or branched 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 101} to R ¹⁰³ may be the same or different. R ¹⁰⁴ represents a linear or branched alkylene group having 1 to 6 carbon atoms.)

(In the formula, x is an integer of 0 or more, and y is an integer of 1 or more. R ²⁰¹ represents a hydrogen atom, a halogen atom, a linear or branched alkyl group having 1 to 30 carbon atoms, a linear or branched alkenyl group having 2 to 30 carbon atoms, a linear or branched 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 linear or branched alkylene group having 1 to 30 carbon atoms, a linear or branched alkenylene group having 2 to 30 carbon atoms, or a linear or branched alkynylene group having 2 to 30 carbon atoms. R ²⁰¹ and R ²⁰² may together form a ring structure.)

The compound represented by the above formula (1) is described below.

R ¹⁰¹ to R ¹⁰³ represent a linear or branched alkyl group having 1 to 12 carbon atoms, a linear or branched alkoxy group having 1 to 12 carbon atoms, or a group represented by -O-(R ¹¹¹ -O) _z -R ^112. In order to satisfactorily obtain the desired effects, it is preferable that at least one of R ¹⁰¹ to R ¹⁰³ is a group represented by -O-(R ¹¹¹ -O) _z -R ¹¹² , and it is more preferable that two are groups represented by -O-(R ¹¹¹ -O) _z -R ¹¹² and one is a linear or branched alkoxy group having 1 to 12 carbon atoms.

Examples of the linear or branched alkyl group having 1 to 12 carbon atoms (preferably 1 to 5 carbon atoms) for R ¹⁰¹ to R ¹⁰³ 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 straight or branched alkoxy group having 1 to 12 carbon atoms (preferably 1 to 5 carbon atoms) for R ¹⁰¹ to R ¹⁰³ 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 ¹⁰¹ to R ¹⁰³ , R ¹¹¹ represents a linear or branched 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 linear or branched alkylene groups having 1 to 30 carbon atoms, linear or branched alkenylene groups having 2 to 30 carbon atoms, linear or branched alkynylene groups having 2 to 30 carbon atoms, and arylene groups having 6 to 30 carbon atoms. Of these, linear or branched alkylene groups having 1 to 30 carbon atoms are preferred.

Examples of the linear or branched 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 straight-chain or branched-chain alkenylene group having 2 to 30 carbon atoms (preferably 2 to 15 carbon atoms, more preferably 2 or 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 straight chain or branched chain alkynylene group having 2 to 30 carbon atoms (preferably 2 to 15 carbon atoms, more preferably 2 or 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 is an integer from 1 to 30, preferably from 2 to 20, more preferably from 3 to 7, and even more preferably 5 or 6.

R ¹¹² represents a linear or branched alkyl group having 1 to 30 carbon atoms, a linear or branched 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. Of these, a linear or branched alkyl group having 1 to 30 carbon atoms is preferred.

Examples of the linear or branched alkyl group having 1 to 30 carbon atoms (preferably 3 to 25 carbon atoms, more preferably 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 straight or branched alkenyl group having 2 to 30 carbon atoms (preferably 3 to 25 carbon atoms, more preferably 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 linear or branched alkylene group having 1 to 6 carbon atoms (preferably 1 to 5 carbon atoms) for R ¹⁰⁴ include the same groups as the linear or branched alkylene group having 1 to 30 carbon atoms for R ¹¹¹ .

Examples of the compound represented by formula (1) 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.

Next, we will explain a compound containing the bond unit A represented by the above formula (2) and the bond unit B represented by the above formula (3).

Compounds containing the bond unit A represented by the above formula (2) and the bond unit B represented by the above formula (3) exhibit 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 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 B 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 order to enhance the effect of suppressing the increase in viscosity during processing and the effect of suppressing the shortening of the scorch time, the content of the bond unit A in the silane coupling agent of the above structure is preferably 30 mol% or more, more preferably 50 mol% or more, preferably 99 mol% or less, and more preferably 90 mol% or less. The content of the 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, and even more preferably 55 mol% or less. The total content of the bond units A and B is preferably 95 mol% or more, more preferably 98 mol% or more, and 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 ends of the silane coupling agent. When the bond units A and B are located at the ends of the silane coupling agent, the form is not particularly limited, and it is sufficient that they form units corresponding to the formulas (2) and (3) showing the bond units A and B.

Examples of the halogen atom for ^R201 include a chlorine atom, a bromine atom, and a fluorine atom.

Examples of the linear or branched 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 of the alkyl group is preferably 1 to 12.

Examples of the linear or branched 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 of the alkenyl group is preferably 2 to 12.

Examples of the straight or branched 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 of the alkynyl group is preferably 2 to 12.

Examples of the linear or branched 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 of the alkylene group is preferably 1 to 12.

Examples of the linear or branched 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 of the alkenylene group is preferably 2 to 12.

Examples of the linear or branched 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 of the alkynylene group is preferably 2 to 12.

In a compound containing the bonding unit A represented by the above formula (2) and the bonding unit B represented by the above formula (3), the total number of repetitions (x+y) 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 _{the -C7H15} 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 compound containing the bond unit A represented by the above formula (2) and the bond unit B represented by the above formula (3), for example, NXT-Z30, NXT-Z45, NXT-Z60, etc. manufactured by Momentive Corporation can be used. These may be used alone or in combination of two or more kinds.

When a silane coupling agent is contained, the content per 100 parts by mass of silica is preferably 6 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 10 parts by mass or more. By making the content of the silane coupling agent per 100 parts by mass of silica 6 parts by mass or more, there is a tendency that the effect of improving fuel efficiency and the like is easily obtained, and the dispersibility of silica in rubber is likely to be ensured. In addition, when a silane coupling agent is contained, the content per 100 parts by mass of silica is preferably 20 parts by mass or less, more preferably 18 parts by mass or less, and even more preferably 15 parts by mass or less. By making the content of the silane coupling agent per 100 parts by mass of silica 20 parts by mass or less, there is a tendency that the decrease in rubber strength and abrasion resistance can be suppressed.

(oil)
Examples of the oil include aromatic oil, process oil, mineral oil such as paraffin oil, etc. Among them, it is preferable to use process oil because of the reduction of the burden on the environment.

When oil is contained, the content per 100 parts by mass of the rubber component is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more. By making the oil content 10 parts by mass or more, it tends to be possible to ensure the hardness required for a tire and to ensure processability. Furthermore, when oil is contained, the content per 100 parts by mass of the rubber component is preferably 80 parts by mass or less, more preferably 70 parts by mass or less, and even more preferably 60 parts by mass or less. By making the oil content 80 parts by mass or less, it tends to be possible to ensure processability.

(Tackifier resin)
Examples of tackifying resins include cyclopentadiene resins, coumarone resins, petroleum resins (aliphatic petroleum resins, aromatic petroleum resins, alicyclic petroleum resins, etc.), phenolic resins, rosin derivatives, etc., with aromatic petroleum resins being preferred.

Examples of aromatic petroleum resins include the following aromatic vinyl resins and C9 petroleum resins other than aromatic vinyl resins, with aromatic vinyl resins being preferred.

In aromatic vinyl resins, for example, styrene, α-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene, 2,4,6-trimethylstyrene, etc. are used as aromatic vinyl monomers (units), and they may be either homopolymers of the respective monomers or copolymers of two or more monomers. They may also be modified versions of these.

As the aromatic vinyl resin, a homopolymer of α-methylstyrene or styrene or a copolymer of α-methylstyrene and styrene is preferred, and a copolymer of α-methylstyrene and styrene is more preferred, because they are economical, easy to process, and have excellent wet grip performance. As the aromatic vinyl resin, for example, commercially available products such as SYLVARES SA85, SA100, SA120, and SA140 manufactured by Arizona Chemical Company, and R2336 manufactured by Eastman Chemical Company are preferably used. As the copolymer of α-methylstyrene and styrene, for example, SYLVATRAXX4401 manufactured by Arizona Chemical Company is preferably used.

The softening point of the tackifier resin is preferably 40°C or higher, and more preferably 60°C or higher. By setting the softening point to 40°C or higher, sufficient grip performance tends to be obtained. Furthermore, the softening point is preferably 120°C or lower, and more preferably 100°C or lower. By setting the softening point to 120°C or lower, sufficient grip performance tends to be obtained. In this specification, 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 measuring device.

When a tackifier resin, particularly an aromatic vinyl resin, is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and particularly preferably 4 parts by mass or more, from the viewpoints of wet grip performance and dry grip performance. Furthermore, when a tackifier resin, particularly an aromatic vinyl resin, is contained, the content per 100 parts by mass of the rubber component is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 35 parts by mass or less, and particularly preferably 10 parts by mass or less, from the viewpoints of abrasion resistance and fuel economy, and embrittlement fracture at low temperatures.

(Processing aids)
Examples of the processing aid include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, mixtures of fatty acid metal salts and fatty acid amides, etc. These may be used alone or in combination of two or more. Among them, fatty acid metal salts, amide esters, mixtures of fatty acid metal salts and amide esters or fatty acid amides are preferred, and mixtures of fatty acid metal salts and fatty acid amides are particularly preferred. Specific examples include fatty acid soap-based processing aids such as EF44 and WB16 manufactured by Struktol.

When a processing aid is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of improving processability. Furthermore, when a processing aid is contained, the content per 100 parts by mass of the rubber component is preferably 10 parts by mass or less, and more preferably 8 parts by mass or less, from the viewpoint of abrasion resistance and breaking strength.

(Anti-aging agent)
The antioxidant is not particularly limited, and may be appropriately selected and blended from, for example, amine-based, quinoline-based, phenol-based, and imidazole-based compounds, carbamic acid metal salts, and the like, and these antioxidants may be used alone or in combination of two or more. Among these, amine-based antioxidants are preferred, and examples thereof include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, N,N'-bis(1-methylheptyl)-p-phenylenediamine, N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine, More preferred are p-phenylenediamines such as N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine, N-4-methyl-2-pentyl-N'-phenyl-p-phenylenediamine, N,N'-diaryl-p-phenylenediamine, hindered diaryl-p-phenylenediamine, phenylhexyl-p-phenylenediamine, and phenyloctyl-p-phenylenediamine, and among these, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine is particularly preferred.

When an antioxidant is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 0.8 parts by mass or more, from the viewpoint of exerting an anti-aging effect. Furthermore, when an antioxidant is contained, the content per 100 parts by mass of the rubber component is preferably 2.0 parts by mass or less, and more preferably 1.5 parts by mass or less, from the viewpoint of preventing browning of the rubber caused by the antioxidant.

(Softener)
Examples of the softening agent include liquid polymers and low-temperature plasticizers. The plasticizer components may be used alone or in combination of two or more. Among them, it is preferable to use liquid polymers because they can improve abrasion resistance and grip performance in a well-balanced manner.

Examples of liquid polymers include liquid SBR, liquid BR, liquid IR, and liquid SIR. Of these, it is preferable to use liquid SBR, since it can improve durability and grip performance in a well-balanced manner.

Examples of low-temperature plasticizers include liquid components such as dioctyl phthalate (DOP), dibutyl phthalate (DBP), tris(2-ethylhexyl) phosphate (TOP), and bis(2-ethylhexyl) sebacate (DOS).

When a softener is included, the content per 100 parts by mass of the rubber component is preferably 15 to 250 parts by mass, and more preferably 20 to 200 parts by mass, in order to obtain a sufficient effect as a softener.

Other than these, wax, zinc oxide, and stearic acid can be those that are conventionally used in the tire industry.

(Vulcanizing agent)
The vulcanizing agent is not particularly limited, and any vulcanizing agent commonly used in the tire industry can be used. However, vulcanizing agents containing sulfur atoms are preferred, such as powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur.

The content of the vulcanizing agent per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, and even more preferably 1.0 parts by mass or more. The content of the vulcanizing agent per 100 parts by mass of the rubber component is 3.0 parts by mass or less, preferably 2.5 parts by mass or less, and more preferably 2.0 parts by mass or less.

(Vulcanization accelerator)
The vulcanization accelerator is not particularly limited, but examples thereof include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, and xanthate-based vulcanization accelerators. Among these, sulfenamide-based and thiuram-based vulcanization accelerators are preferred, since the desired effects can be more suitably obtained, and it is more preferable to use two of these vulcanization accelerators in combination.

Examples of sulfenamide vulcanization accelerators include CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (N-t-butyl-2-benzothiazylsulfenamide), N-oxyethylene-2-benzothiazylsulfenamide, N,N'-diisopropyl-2-benzothiazylsulfenamide, and N,N-dicyclohexyl-2-benzothiazylsulfenamide. Examples of thiazole vulcanization accelerators include 2-mercaptobenzothiazole and dibenzothiazolyl disulfide. Examples of thiuram vulcanization accelerators include tetramethylthiuram monosulfide, tetramethylthiuram disulfide, and tetrabenzylthiuram disulfide (TBzTD). Examples of guanidine vulcanization accelerators include diphenylguanidine (DPG), di-orthotolylguanidine, and orthotolylbiguanidine. These may be used alone or in combination of two or more. Of these, the combination of CBS and TBzTD is particularly preferred because it more effectively achieves the desired effect.

When a vulcanization accelerator is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, and more preferably 2 parts by mass or more. The content per 100 parts by mass of the rubber component is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less. By keeping the content of the vulcanization accelerator within the above range, breaking strength and elongation tend to be ensured.

(Method for producing rubber composition for tread)
The method for producing the rubber composition for tread is not particularly limited, and a known method can be used. For example, the rubber composition for tread can be produced by a method in which the components other than the vulcanizing agent and the vulcanization accelerator among the above-mentioned components are kneaded using a rubber kneading device such as an open roll, a Banbury mixer, a kneader, or an internal kneader (kneading step 1), and then the vulcanizing agent and the vulcanization accelerator are added and further kneaded (kneading step 2) to obtain an unvulcanized rubber composition for tread, which is then vulcanized (vulcanization step).

For example, in kneading step 1, the mixture is kneaded for 1 to 10 minutes at a discharge temperature of 150 to 160°C, and then in kneading step 2, a vulcanizing agent and a vulcanization accelerator are added and kneaded using an open roll or the like. The vulcanization step can be performed, for example, at 150 to 170°C for 10 to 35 minutes.

(tire)
A tire according to one embodiment has a tread constituted by the above-mentioned rubber composition for a tread, and can be used for tires in general, such as tires for passenger cars, high-performance tires for passenger cars, heavy-duty tires for trucks and buses, tires for motorcycles, racing tires, etc. In this specification, the high-performance tire is a tire that is particularly excellent in grip performance, and is a concept that also includes racing tires used for racing vehicles.

(Tire manufacturing method)
A tire having a tread made of the rubber composition for a tread can be manufactured by a normal method using the rubber composition for a tread. That is, an unvulcanized rubber composition obtained by blending the above-mentioned components with a rubber component as necessary is extruded according to the shape of the tread, laminated together with other tire components on a tire building machine, and molded by a normal method to form an unvulcanized tire, and the unvulcanized tire is heated and pressurized in a vulcanizer to manufacture a tire.

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

The various chemicals used in the examples and comparative examples are listed below.
SBR1: TRINSEO's SLR6430 (S-SBR, styrene content: 40 mass%, vinyl bond amount: 18 mol%, Mw: 1,460,000, Tg: -39°C, oil-extended product containing 37.5 parts by weight of oil per 100 parts by weight of rubber component)
SBR2: Modified SBR synthesized in Production Example 1 described later (styrene content: 38% by mass, vinyl bond amount: 39 mol%, Mw: 800,000, Tg: -25°C)
SBR3: Modified solution-polymerized SBR produced in Production Example 2 described later (styrene content: 42% by mass, vinyl bond content: 36 mol%, Mw: 800,000, Tg: -21°C)
SBR4: Modified solution-polymerized SBR produced in Production Example 3 described later (styrene content: 30% by mass, vinyl bond content: 52 mol%, Mw: 250,000, Tg: -23°C)
BR1: Modified BR produced in Production Example 4 described later (vinyl bond amount: 12 mol%, cis 1,4-content: 38%, Mw: 500,000)
BR2: UBEPOL BR (registered trademark) 150B manufactured by Ube Industries, Ltd. (vinyl bond amount: 1.5 mol%, cis 1,4-content: 97%, Mw: 440,000)
Carbon black: Show Black N220 ( _N2SA : 111 ^m2 /g) manufactured by Cabot Japan Co., Ltd.
Silica: Ultrasil 9000GR manufactured by Evonik Degussa (BET: 240 ^m2 /g, CTAB: 200 ^m2 /g, pH: 6.9)
Silane coupling agent: 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 %))
Aluminum hydroxide: H-43 manufactured by Showa Denko K.K. (N ₂ SA: 6.7 m ² /g, average primary particle size: 800 nm)
Oil: VivaTec 400 (TDAE oil, Tg: -58°C) manufactured by H&R Corporation
Tackifying resin: Sylvares SA85 (α-methylstyrene/styrene resin, softening point: 85° C.) manufactured by Arizona Chemical Co.
Wax: Ozoace 0355 (paraffin-based) manufactured by Nippon Seiro Co., Ltd.
Processing aid: Struktol WB16 (mixture of fatty acid calcium salts, fatty acid monoethanolamides and esters of fatty acid monoethanolamides) from Schill & Seilacher
Anti-aging agent: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Camellia stearic acid beads manufactured by NOF Corp. Sulfur: HK-200-5 (powdered sulfur containing 5% oil) manufactured by Hosoi Chemical Industry Co., Ltd.
Vulcanization accelerator 1: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator 2: Sancerer TBZTD (tetrabenzyl thiuram disulfide (TBzTD)) manufactured by Sanshin Chemical Industry Co., Ltd.

Production Example 1: Synthesis of SBR2 Two autoclaves with an internal volume of 10 L, an inlet at the bottom and an outlet at the top, and equipped with an agitator and a jacket were connected in series as reactors, and butadiene, styrene, and cyclohexane were mixed in a predetermined ratio. This mixed solution was passed through a dehydration column filled with activated alumina, and mixed with n-butyllithium in a static mixer to remove impurities, and then continuously fed from the bottom of the first reactor, and further 2,2-bis(2-oxolanyl)propane as a polar substance and n-butyllithium as a polymerization initiator were continuously fed from the bottom of the first reactor at a predetermined rate, respectively, and the temperature inside the reactor was maintained at 95° C. The polymer solution was continuously withdrawn from the head of the reactor and fed to the second reactor. The temperature of the second reactor was kept at 95°C, and a mixture of tetraglycidyl-1,3-bisaminomethylcyclohexane (monomer) and its oligomer component (hereinafter referred to as "modifier A") was continuously added as a 1000-fold diluted solution with cyclohexane at a predetermined rate to carry out a modification reaction. This polymer solution was continuously extracted from the reactor, and an antioxidant was continuously added using a static mixer. Furthermore, 25 parts by mass of extender oil NC140 manufactured by Japan Energy per 100 parts by mass of the polymer was added to this polymer solution and mixed, and then the solvent was removed to obtain SBR2.

Production Example 2: Synthesis of SBR3 Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene were charged into a nitrogen-substituted autoclave reactor. After adjusting the temperature of the reactor contents to 20°C, n-butyllithium was added to initiate polymerization. Polymerization was performed under adiabatic conditions, and the maximum temperature reached 85°C. When the polymerization conversion reached 99%, 1,3-butadiene was added, and polymerization was continued for another 5 minutes, after which N,N-bis(trimethylsilyl)-3-aminopropyltrimethoxysilane was added as a modifier to carry out the reaction. After the polymerization reaction was completed, 2,6-di-tert-butyl-p-cresol was added. Next, 10 parts by mass of extender oil was added to 100 parts by mass of the polymer, and the solvent was removed by steam stripping. The mixture was dried with a heated roll adjusted to 110°C, and SBR3 was obtained.

Production Example 3: Synthesis of SBR4 Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene were charged into a nitrogen-substituted autoclave reactor. After adjusting the temperature of the reactor contents to 20°C, n-butyllithium was added to initiate polymerization. Polymerization was performed under adiabatic conditions, with the maximum temperature reaching 85°C. When the polymerization conversion reached 99%, 1,3-butadiene was added, and polymerization was continued for another 5 minutes, after which N,N-bis(trimethylsilyl)-3-aminopropyltrimethoxysilane was added as a modifier to carry out the reaction. After completion of the polymerization reaction, 2,6-di-tert-butyl-p-cresol was added. Next, the solvent was removed by steam stripping, and the mixture was dried with a hot roll adjusted to 110°C to obtain SBR4.

Production Example 4: Synthesis of BR1 <Preparation of Terminal Modifier B>
In a nitrogen atmosphere, 23.6 g of 3-(N,N-dimethylamino)propyltrimethoxysilane (manufactured by Azmax Corporation) was placed in a 100 mL measuring flask, and anhydrous hexane (manufactured by Kanto Chemical Co., Ltd.) was added to make the total volume 100 mL to prepare modifier B.

<Preparation of modified BR>
18 L of n-hexane, 2000 g of butadiene, and 2 mmol of tetramethylethylenediamine (TMEDA) were added to a 30 L pressure vessel that had been thoroughly substituted with nitrogen, and the temperature was raised to 60°C. Next, 10.3 mL of butyl lithium was added, and the temperature was raised to 50°C and stirred for 3 hours. Next, 11.5 mL of modifier B was added and stirred for 30 minutes. After adding 15 mL of methanol and 0.1 g of 2,6-tert-butyl-p-cresol to the reaction solution, the reaction solution was placed in a stainless steel vessel containing 18 L of methanol to recover the aggregates. The obtained aggregates were dried under reduced pressure for 24 hours to obtain BR1.

Examples 1 to 13 and Comparative Examples 1 to 7
According to the compounding recipe shown in Table 1 or 2, the chemicals other than sulfur and the vulcanization accelerator were kneaded for 1 to 10 minutes using a 1.7 L closed type Banbury mixer until the discharge temperature reached 150 to 160°C, and a kneaded product was obtained. Next, sulfur and the vulcanization accelerator were added to the kneaded product obtained using a two-screw open roll, and the mixture was kneaded for 4 minutes until the temperature reached 105°C, and an unvulcanized rubber composition was obtained. The unvulcanized rubber composition obtained was press-vulcanized at 170°C for 12 minutes to prepare a test rubber composition. In Tables 1 and 2, when the rubber component is an oil-extended rubber, the amount of the rubber component excluding the oil content is described as the compounding amount of the rubber component such as "SBR1", and the oil content is described as the compounding amount of "oil" by adding the TDAE oil content separately compounded.

The unvulcanized rubber composition was extruded into the shape of a tire tread using an extruder equipped with a nozzle of a specified shape, and then laminated together with other tire components to form an unvulcanized tire. Test tires (size: 195/65R15) were manufactured by press-vulcanizing the tire at 170°C for 12 minutes.

The vulcanized rubber compositions and test tires obtained in each of the Examples and Comparative Examples were evaluated as follows. The results are shown in Tables 1 and 2.

<tan δ (0° C.) and tan δ peak temperature>
Using a spectrometer manufactured by Ueshima Seisakusho Co., Ltd., the tan δ of the vulcanized rubber composition was measured at a dynamic strain amplitude of 0.5%, a frequency of 10 Hz, a temperature rise rate of 2°C/min, and a measurement temperature range of -80°C to 80°C, and the temperature at which tan δ reached its peak was defined as the tan δ peak temperature.

<Wet grip performance>
Wet grip performance was evaluated using a flat belt abrasion tester (FR5010 type) manufactured by Ueshima Seisakusho Co., Ltd. A cylindrical rubber test piece of each vulcanized rubber composition having a width of 20 mm and a diameter of 100 mm was used as a sample, and the slip ratio of the sample against the road surface was changed from 0 to 70% under the conditions of a speed of 20 km/h, a load of 4 kgf, and a road surface temperature of 20°C, and the maximum value of the friction coefficient detected at that time was read. The measurement results were expressed as an index using the following calculation formula. The higher the index, the better the wet grip performance.
(Wet grip performance index)
= (maximum value of friction coefficient of each formulation) / (maximum value of friction coefficient of Comparative Example 1) × 100

<Wear resistance>
The test tires were mounted on a domestically produced FR vehicle with an engine displacement of 2000cc, and the vehicle was driven on a test course with a dry asphalt surface. The tire tread depth was measured after a driving distance of 10,000 km, and the driving distance when the tire groove depth was reduced by 1 mm was calculated and expressed as an index according to the following formula. The higher the index, the better the wear resistance.
(Wear resistance index) = (Running distance for each compound) / (Running distance for Comparative Example 1) x 100

<Fuel efficiency index>
A rectangular test piece having a width of 4 mm, a length of 50 mm, and a thickness of 2 mm was punched out from the sheet-like vulcanized rubber composition and used for testing. The loss tangent (tan δ) of the vulcanized rubber sheet was measured using a spectrometer manufactured by Ueshima Seisakusho Co., Ltd. at dynamic strain amplitude of 1%, frequency of 10 Hz, and temperatures of 50°C and 22.5°C, and the reciprocal value of tan δ was expressed as an index (fuel economy index) with Comparative Example 1 being set at 100. The results obtained at 50°C and 22.5°C were designated fuel economy index A and B, respectively. The larger the value, the smaller the rolling resistance and the better the fuel economy.
(Fuel economy index)=(tan δ of Comparative Example 1)/(tan δ of each formulation)×100

From the results in Tables 1 and 2, it can be seen that in Examples 1 to 13, which contain 100 parts by mass of a rubber component containing 60 to 80% by mass of SBR and 20 to 40% by mass of butadiene rubber, 1 to 40 parts by mass of carbon black, and 50 to 150 parts by mass of silica, and have a tan δ of 0.60 or less at a dynamic strain amplitude of 0.5% at 0°C and a peak temperature of tan δ of -17°C or less, the overall performance such as wet grip performance, abrasion resistance, and fuel economy is improved compared to Comparative Examples 1 and 2, which have a low BR content, Comparative Example 5, which has a high BR content, Comparative Example 6, which has a low silica content, Comparative Example 7, which does not contain carbon black, and Comparative Examples 3 and 4, which have the same composition but do not satisfy at least one of tan δ (0°C) ≦ 0.60 and tan δ peak temperature ≦ -17°C.

Claims (5)

100 parts by mass of a rubber component containing 60 to 80% by mass of styrene-butadiene rubber and 20 to 40% by mass of butadiene rubber,
A rubber composition for a tread, comprising 1 to 40 parts by mass of carbon black and 50 to 150 parts by mass of silica, having a tan δ of 0.60 or less at a dynamic strain amplitude of 0.5% at 0°C and a peak temperature of tan δ of -17°C or less ,
The silica has a BET specific surface area of 180 m ² /g or more. The rubber composition for treads according to claim 1, which contains aluminum hydroxide. The rubber composition for treads according to claim 1 or 2, which contains 10 to 80 parts by mass of oil per 100 parts by mass of the rubber component. The rubber composition for tread according to any one of claims 1 to 3, comprising a silane coupling agent having a mercapto group, which is a compound represented by the following formula (1) and/or a compound containing a bond unit A represented by the following formula (2) and a bond unit B represented by the following formula (3):

(In the formula, R ¹⁰¹ to R ¹⁰³ each represent a linear or branched alkyl group having 1 to 12 carbon atoms, a linear or branched 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 linear or branched divalent hydrocarbon group having 1 to 30 carbon atoms. z R ¹¹¹ may be the same or different. R ¹¹² represents a linear or branched alkyl group having 1 to 30 carbon atoms, a linear or branched 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 101} to R ¹⁰³ may be the same or different. R ¹⁰⁴ represents a linear or branched alkylene group having 1 to 6 carbon atoms.)

(In the formula, x is an integer of 0 or more, and y is an integer of 1 or more. R ²⁰¹ represents a hydrogen atom, a halogen atom, a linear or branched alkyl group having 1 to 30 carbon atoms, a linear or branched alkenyl group having 2 to 30 carbon atoms, a linear or branched 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 linear or branched alkylene group having 1 to 30 carbon atoms, a linear or branched alkenylene group having 2 to 30 carbon atoms, or a linear or branched alkynylene group having 2 to 30 carbon atoms. R ²⁰¹ and R ²⁰² may together form a ring structure.) A tire having a tread made of the rubber composition for a tread according to any one of claims 1 to 4.