JP7494447B2 - Rubber composition, tread, tire and manufacturing method - Google Patents

Description

The present invention relates to a specific rubber composition, a tread made using the same, a tire equipped with the tread, and a method for manufacturing the same.

In recent years, with the implementation of tire labeling systems in various countries, tires are required to achieve a high level of compatibility in each performance category (rolling resistance, wear resistance, wet grip performance). In Japan in particular, there has been remarkable progress in fuel-efficient tires, and reduced rolling resistance will continue to be a required performance in the future. Here, fuel efficiency performance is required to perform over a wide temperature range, not just under certain temperature conditions. In other words, it is necessary to minimize the temperature dependency of rubber.

Patent Document 1 describes how, in a rubber composition containing a rubber component containing 50% by mass or more of a specified isoprene-based rubber, a specified amount of thermoplastic resin, and a filler containing 70% by mass or more of silica, the value of tan δ at 0°C, the difference between the value of tan δ at 30°C and the value of tan δ at 60°C, the value of dynamic strain 1%, and the value of storage modulus (E') at 0°C are all set to specified values, thereby reducing the difference between fuel efficiency in a low temperature environment and that in a normal temperature environment while maintaining the fuel efficiency of the tire in a normal temperature environment, and ensuring wet performance.

Patent No. 5998310

However, Patent Document 1 does not take into consideration wear resistance, and there is room for improvement.

The present invention aims to provide a rubber composition that reduces the difference between fuel efficiency in a low temperature environment and fuel efficiency in a normal temperature environment while maintaining fuel efficiency at normal temperatures, i.e., reduces the temperature dependency of fuel efficiency, has excellent wet grip performance, and also has excellent wear resistance, a tread made using the rubber composition, and a tire equipped with the tread, as well as methods for manufacturing these.

As a result of intensive research to solve the above problems, the present inventors discovered that a rubber composition containing a rubber component containing a predetermined amount of natural rubber, a predetermined amount of silica, and a silane coupling agent having a mercapto group (hereinafter also referred to as a "mercapto-based coupling agent"), which is subjected to a keep kneading process to increase the reaction efficiency of the silica and the silane coupling agent having a mercapto group in the kneading process before adding the vulcanization chemicals, maintains fuel efficiency at room temperature while reducing the difference between fuel efficiency in a low temperature environment and fuel efficiency in a room temperature environment, i.e., reduces the temperature dependency of fuel efficiency, is excellent in wet grip performance, and also has excellent abrasion resistance. After further research, the present 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、それぞれ、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、それぞれ、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。）
［６］前記シリカの窒素吸着比表面積が１８０ｍ²／ｇ以上、好ましくは１８０～５００ｍ²／ｇ、より好ましくは１９０～５００ｍ²／ｇ、より好ましくは１９５～５００ｍ²／ｇ、より好ましくは２００～４００ｍ²／ｇ、より好ましくは２１０～４００ｍ²／ｇ、より好ましくは２１０～３００ｍ²／ｇ、より好ましくは２２０～２８０ｍ²／ｇ、さらに好ましくは２３５～２６０ｍ²／ｇである、上記［１］～［５］のいずれかに記載のゴム組成物、
［７］０℃におけるｔａｎδ_0℃と３０℃におけるｔａｎδ_30℃との差が０．３００以下、好ましくは０．１４０～０．３００、より好ましくは０．１５０～０．２９０、さらに好ましくは０．１６０～０．２８０である、上記［１］～［６］のいずれかに記載のゴム組成物、
［８］上記［１］～［７］のいずれかに記載のゴム組成物を用いて作製されたトレッド、
［９］上記［８］のトレッドを備えたタイヤ、
［１０］天然ゴムを５０質量％以上、好ましくは５５質量％以上、より好ましくは６０質量％以上、より好ましくは６５質量％以上、より好ましくは７０質量％以上、より好ましくは７５質量％以上、より好ましくは８０質量％以上、さらに好ましくは８５質量％以上含むゴム成分１００質量部（天然ゴムの含有量はゴム成分中１００質量％であってもよい）に対して、シリカ４０質量部以上、好ましくは４０～１５０質量部、より好ましくは４５～１５０質量部、より好ましくは５０～１４０質量部、より好ましくは５５～１３０質量部、さらに好ましくは６５～１２０質量部およびメルカプト基を有するシランカップリング剤を含み、
０℃におけるｔａｎδ_0℃が０．５５０以下、好ましくは０．５４０以下、より好ましくは０．５３０以下であり、３０℃におけるｔａｎδ_30℃と６０℃におけるｔａｎδ_60℃との差が０．０７０以下、好ましくは０．０６０以下、より好ましくは０．０５５以下、さらに好ましくは０．０５０以下であるゴム組成物の製造方法であって、
混練工程を含むものであり、
前記混練工程が、前記ゴム成分と、前記シリカと、前記メルカプト基を有するシランカップリング剤とを含む原料（加硫系薬品は含まない）を混練りする第一混練工程を含むものであり、
前記第一混練工程が、シリカとメルカプト基を有するシランカップリング剤の反応効率を高めるキープ練りを含むものである、ゴム組成物の製造方法、
［１１］前記ゴム組成物の、下記式（Ｉ）で示されるΔＧ^*が５００以下、好ましくは４５０以下、より好ましくは４００以下、より好ましくは３５０以下、さらに好ましくは３００以下である、上記［１０］記載のゴム組成物の製造方法、
ΔＧ^*＝Ｇ^*（４％）－Ｇ^*（６４％） （Ｉ）
式（Ｉ）中、Ｇ^*（ｎ％）はｎ％歪印加時のせん断弾性率を表す、
［１２］０℃における貯蔵弾性率Ｅ’が１５ＭＰａ以下、好ましくは１４．５ＭＰａ以下、より好ましくは１４ＭＰａ以下である、上記［１０］または［１１］記載のゴム組成物の製造方法、
［１３］前記キープ練りの温度が１３０～１５７℃、好ましくは１３２～１５６℃、より好ましくは１３４～１５５℃であり、前記キープ練りの時間が１００秒以上、好ましくは１００～４８０秒、より好ましくは１１０～４８０秒、さらに好ましくは１２０～４８０秒である、上記［１０］～［１２］のいずれかに記載のゴム組成物の製造方法、
［１４］前記混練工程が、前記第一混練工程により得られた混練物を再練りする第二混練工程をさらに含むものである、上記［１０］～［１３］のいずれかに記載のゴム組成物の製造方法、
［１５］前記第二混練工程の排出温度が１４０～１７０℃、好ましくは１４２～１６４℃、より好ましくは１４４～１６２℃、さらに好ましくは１４６～１６０℃である、上記［１４］記載のゴム組成物の製造方法、
［１６］タイヤの製造方法であって、
上記［１０］～［１５］のいずれかに記載のゴム組成物の製造方法により、未加硫のゴム組成物を得る工程、
該未加硫のゴム組成物をトレッドの形状に押出し加工して、トレッド部材を得る工程、
該トレッド部材をタイヤ成型機上で他のタイヤ部材とともに貼り合わせ、成型して、未加硫タイヤを得る工程、および、
該未加硫タイヤを加硫機中で加熱加圧して、タイヤを得る工程
を含む、タイヤの製造方法、
に関する。 That is, the present invention provides
[1] 40 parts by mass or more, preferably 40 to 150 parts by mass, more preferably 45 to 150 parts by mass, more preferably 50 to 140 parts by mass, more preferably 55 to 130 parts by mass, and even more preferably 65 to 120 parts by mass of silica per 100 parts by mass of a rubber component containing 50% by mass or more, preferably 55% by mass or more, more preferably 60% by mass or more, more preferably 65% by mass or more, more preferably 70% by mass or more, more preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more of natural rubber (the content of natural rubber in the rubber component may be 100% by mass), and a silane coupling agent having a mercapto group,
A rubber composition having a tan δ _0°C at 0°C of 0.550 or less, preferably 0.540 or less, more preferably 0.530 or less, and a difference between tan δ _30°C at 30°C and tan δ _60°C at 60°C of 0.070 or less, preferably 0.060 or less, more preferably 0.055 or less, and even more preferably 0.050 or less,
a first kneading step in a kneading step of kneading raw materials (excluding vulcanization-related chemicals) containing the rubber component, the silica, and the silane coupling agent having a mercapto group, the first kneading step including a keep kneading step for increasing a reaction efficiency of the silica and the silane coupling agent having a mercapto group;
[2] The rubber composition according to the above [1], wherein ΔG ^* represented by the following formula (I) is 500 or less, preferably 450 or less, more preferably 400 or less, more preferably 350 or less, and even more preferably 300 or less.
ΔG ^* = G ^* (4%) - G ^* (64%) (I)
In formula (I), G ^* (n%) represents the shear modulus when n% strain is applied.
[3] The rubber composition according to the above [1] or [2], wherein the storage modulus E' at 0 ° C. is 15 MPa or less, preferably 14.5 MPa or less, more preferably 14 MPa or less;
[4] The rubber composition according to any one of the above [1] to [3], wherein the temperature of the keep kneading is 130 to 157°C, preferably 132 to 156°C, more preferably 134 to 155°C, and the time of the keep kneading is 100 seconds or more, preferably 100 to 480 seconds, more preferably 110 to 480 seconds, and even more preferably 120 to 480 seconds.
[5] The silane coupling agent having a mercapto group,
The rubber composition according to any one of the above [1] to [4], which is at least one of a compound represented by the following formula (1) and 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.)
[6] The rubber composition according to ^any one of the above [1] to [5], wherein the nitrogen adsorption specific surface area of the silica is 180 m ² /g or more, preferably 180 to 500 m ² /g, more preferably 190 to 500 m ² /g, more preferably 195 to 500 m ² /g, more preferably 200 to 400 m ² /g, more preferably 210 to 400 m ² /g, more preferably 210 to 300 m 2 /g, more preferably 220 to 280 m ² /g, and even more preferably 235 to 260 m ² /g.
[7] The rubber composition according to any one of the above [1] to [6], wherein the difference between tan δ _0°C at 0°C and tan δ _30° C at 30°C is 0.300 or less, preferably 0.140 to 0.300, more preferably 0.150 to 0.290, and even more preferably 0.160 to 0.280.
[8] A tread produced using the rubber composition according to any one of [1] to [7] above.
[9] A tire having the tread according to [8] above.
[10] 40 parts by mass or more, preferably 40 to 150 parts by mass, more preferably 45 to 150 parts by mass, more preferably 50 to 140 parts by mass, more preferably 55 to 130 parts by mass, and even more preferably 65 to 120 parts by mass of silica per 100 parts by mass of a rubber component containing 50% by mass or more, preferably 55% by mass or more, more preferably 60% by mass or more, more preferably 65% by mass or more, more preferably 70% by mass or more, more preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more of natural rubber (the content of natural rubber in the rubber component may be 100% by mass), and a silane coupling agent having a mercapto group,
A method for producing a rubber composition having a tan δ _0°C of 0.550 or less, preferably 0.540 or less, more preferably 0.530 or less, and a difference between a tan δ _30°C at 30°C and a tan δ _60°C at 60°C of 0.070 or less, preferably 0.060 or less, more preferably 0.055 or less, further preferably 0.050 or less,
It includes a kneading process,
the kneading step includes a first kneading step of kneading raw materials (excluding vulcanization-related chemicals) including the rubber component, the silica, and the silane coupling agent having a mercapto group,
The method for producing a rubber composition, wherein the first kneading step includes a keep kneading step for enhancing a reaction efficiency of the silica and the silane coupling agent having a mercapto group.
[11] The method for producing a rubber composition according to the above [10], wherein the rubber composition has a ΔG ^* represented by the following formula (I) of 500 or less, preferably 450 or less, more preferably 400 or less, more preferably 350 or less, and even more preferably 300 or less.
ΔG ^* = G ^* (4%) - G ^* (64%) (I)
In formula (I), G ^* (n%) represents the shear modulus when n% strain is applied.
[12] A method for producing a rubber composition according to the above [10] or [11], wherein the storage modulus E' at 0 ° C. is 15 MPa or less, preferably 14.5 MPa or less, more preferably 14 MPa or less.
[13] The method for producing a rubber composition according to any one of the above [10] to [12], wherein the temperature of the keep kneading is 130 to 157°C, preferably 132 to 156°C, more preferably 134 to 155°C, and the time of the keep kneading is 100 seconds or more, preferably 100 to 480 seconds, more preferably 110 to 480 seconds, and even more preferably 120 to 480 seconds.
[14] The method for producing a rubber composition according to any one of [10] to [13] above, wherein the kneading step further includes a second kneading step of re-kneading the kneaded product obtained in the first kneading step.
[15] The method for producing a rubber composition according to the above [14], wherein the discharge temperature in the second kneading step is 140 to 170°C, preferably 142 to 164°C, more preferably 144 to 162°C, and even more preferably 146 to 160°C.
[16] A method for manufacturing a tire, comprising the steps of:
A step of obtaining an unvulcanized rubber composition by the method for producing a rubber composition according to any one of the above [10] to [15];
extruding the unvulcanized rubber composition into a tread shape to obtain a tread component;
laminating and molding the tread component together with other tire components on a tire building machine to obtain an unvulcanized tire; and
a step of heating and pressurizing the unvulcanized tire in a vulcanizer to obtain a tire;
Regarding.

The present invention provides a rubber composition that maintains fuel efficiency at room temperature while reducing the difference between fuel efficiency in a low temperature environment and fuel efficiency in a room temperature environment, has excellent wet grip performance, and also has excellent wear resistance, a tread made using the rubber composition, and a tire equipped with the tread, as well as methods for manufacturing these.

Although it is not intended to be bound by theory, the mechanism by which the above-mentioned effect is exhibited is thought to be as follows. That is, silica has strong interparticle cohesion, and it is necessary to increase the dispersibility of silica by kneading or using other compounding agents, especially silane coupling agents. In the present invention, (1) a silane coupling agent having a mercapto group that is highly reactive with silica is used as the silane coupling agent, and (2) keep kneading is performed in the kneading process to increase the reaction efficiency of silica and the silane coupling agent having a mercapto group, which is thought to synergistically improve the reactivity of silica and the silane coupling agent and improve the dispersibility of silica. As a result, the number of fracture origins due to silica aggregation is reduced, and the wear resistance is improved and various properties of silica are exhibited, the temperature dependency of fuel efficiency is reduced while maintaining fuel efficiency at room temperature, and the rubber physical properties of wet grip performance and wear resistance are thought to be improved in a balanced manner.

In one embodiment, the rubber composition contains 40 parts by mass or more of silica and a silane coupling agent having a mercapto group relative to 100 parts by mass of a rubber component containing 50% by mass or more of natural rubber, and has a tan δ _0°C of 0.550 or less at 0°C, and a difference between tan δ _30°C at 30°C and tan δ _60°C at 60°C of 0.070 or less, and the rubber component, the silica, and a raw material containing the silane coupling agent having a mercapto group (not including vulcanization-based chemicals) are kneaded in a first kneading step, which includes a keep kneading step that enhances the reaction efficiency of the silane coupling agent having a mercapto group.

Another embodiment is a tread made using the rubber composition.

Another embodiment is a tire having the above tread.

Another embodiment is a method for producing a rubber composition comprising 40 parts by mass or more of silica and a silane coupling agent having a mercapto group relative to 100 parts by mass of a rubber component containing 50% by mass or more of natural rubber, a tan δ _0°C at 0°C being 0.550 or less, and a difference between tan δ _{30°C at 30} °C and tan δ _60° C at 60°C being 0.070 or less, the method including a kneading step, the kneading step including a first kneading step of kneading raw materials (not including vulcanization-based chemicals) including the rubber component, the silica, and the silane coupling agent having a mercapto group, and the first kneading step including a keep kneading step for increasing the reaction efficiency of the silica and the silane coupling agent having a mercapto group.

Another embodiment is a method for producing a tire, including the steps of obtaining an unvulcanized rubber composition by the method for producing a rubber composition of the above embodiment, extruding the unvulcanized rubber composition into a tread shape to obtain a tread component, laminating the tread component together with other tire components on a tire building machine and molding them to obtain an unvulcanized tire, and heating and pressurizing the unvulcanized tire in a vulcanizer to obtain a tire.

<Rubber component>
The rubber component of the present disclosure contains 50% by mass or more of natural rubber (NR).

(Natural rubber)
The NR is not particularly limited, and may be, for example, SIR20, RSS#3, TSR20, or other commonly used NRs in the tire industry (unmodified NRs), or modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, deproteinized natural rubber (DPNR), highly purified natural rubber, etc. NR may be used alone or in combination of two or more types.

The content of NR in the rubber component is 50% by mass or more from the viewpoint of sufficient effect of the present disclosure. The content is preferably 55% by mass or more, more preferably 60% by mass or more, more preferably 65% by mass or more, more preferably 70% by mass or more, more preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more. The upper limit of the content of NR is not particularly limited. The content of NR may be 100% by mass in the rubber component. When NR is contained in the above content, the effect of tan δ _0°C at 0°C being small and excellent low-temperature fuel efficiency performance is obtained.

(Other rubber components)
The rubber component in the rubber composition may contain a rubber component (other rubber component) other than the above NR. Such other rubber components are not particularly limited, and any of those conventionally used in the tire industry, such as diene-based rubber other than NR and butyl-based rubber, can be suitably used. Examples of diene-based rubbers include polyisoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene rubber (SIR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). Examples of butyl-based rubbers include halogenated butyl rubbers including butyl rubber (IIR), brominated butyl rubber (Br-IIR), chlorinated butyl rubber (Cl-IIR), and fluorinated butyl rubber (F-IIR). These rubber components may be used alone or in combination of two or more. Among these, it is preferable that the rubber composition contains BR and/or SBR, or that the rubber composition consists of only BR and SBR, because this allows the effects of the present disclosure to be exhibited more satisfactorily.

The BR is not particularly limited, and any BR commonly used in this field can be suitably used. For example, various BRs such as high cis-1,4-polybutadiene rubber (high cis BR), rare earth butadiene rubber (rare earth BR) synthesized using a rare earth catalyst, butadiene rubber containing 1,2-syndiotactic polybutadiene crystals (SPB-containing BR), and modified butadiene rubber (modified BR) can be used. As such BR, for example, BR manufactured by Ube Industries, Zeon Corporation, JSR Corporation, and LANXESS AG can be suitably used.

High cis BR is butadiene rubber with a cis-1,4 bond content of 90% or more. Of these, those with a cis-1,4 bond content of 95% or more are preferred, those with a cis-1,4 bond content of 96% or more are more preferred, those with a cis-1,4 bond content of 97% or more are even more preferred, and those with a cis-1,4 bond content of 98% or more are even more preferred. The inclusion of high cis BR can improve low-temperature properties and abrasion resistance. The cis-1,4 bond content in BR is a value calculated by infrared absorption spectrum analysis.

As rare earth-based BR, those synthesized using a rare earth catalyst and having a vinyl content (amount of 1,2-bonded butadiene units) of 1.8% or less, preferably 1.0% or less, more preferably 0.8% or less, and a cis content (cis-1,4 bond content) of 90% or more, preferably 93% or more, more preferably 95% or more can be suitably used. By having the vinyl content and cis content within the above ranges, the effect of excellent breaking elongation and abrasion resistance of the obtained rubber composition can be obtained. The vinyl content and cis content of rare earth-based BR are values measured by infrared absorption spectroscopy.

The rare earth element catalyst used in the synthesis of rare earth BR may be any known catalyst, such as a lanthanum series rare earth element compound, an organoaluminum compound, an aluminoxane, a halogen-containing compound, or a catalyst containing a Lewis base as necessary.

In SPB-containing BR, 1,2-syndiotactic polybutadiene crystals are not simply dispersed in the BR, but are dispersed after being chemically bonded to the BR. The complex modulus of elasticity tends to improve as the crystals are dispersed after being chemically bonded to the rubber component.

Examples of modified BR include modified BR whose terminals and/or main chain are modified, modified BR coupled with tin or silicon compounds (condensates, those with branched structures, etc.), modified BR whose terminals and/or main chain are modified with functional groups that interact with silica, and in particular modified BR having at least one group selected from the group consisting of silyl groups, amino groups, amide groups, hydroxyl groups, and epoxy groups. The use of modified BR provides the effect of strengthening the interaction with the filler and providing excellent fuel economy.

When BR is contained, the content in the rubber component is preferably 1 mass% or more from the viewpoint of abrasion resistance, more preferably 5 mass% or more, more preferably 7 mass% or more, and even more preferably 10 mass% or more. In addition, the content of BR is preferably 35 mass% or less, more preferably 30 mass% or less, more preferably 28 mass% or less, and even more preferably 25 mass% or less from the viewpoint of molding processability.

The SBR is not particularly limited, and examples thereof include unmodified emulsion-polymerized styrene butadiene rubber (E-SBR) and solution-polymerized styrene butadiene rubber (S-SBR), as well as modified SBRs such as modified emulsion-polymerized styrene butadiene rubber (modified E-SBR) and modified solution-polymerized styrene butadiene rubber (modified S-SBR). Modified SBRs include modified SBRs whose ends and/or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin or silicon compounds. SBRs include oil-extended types in which the flexibility is adjusted by adding an extender oil, and non-oil-extended types in which no extender oil is added, and either of these can be used. For example, those manufactured by JSR Corporation, Asahi Kasei Chemicals Corporation, Nippon Zeon Corporation, and ZS Elastomers Corporation can be used.

The styrene content of the SBR is preferably 15.0% by mass to 40.0% by mass. From the viewpoint of rubber strength and grip performance, the styrene content is preferably 20.0% by mass or more, more preferably 25.0% by mass or more, more preferably 30.0% by mass or more, and even more preferably 35.0% by mass or more. From the viewpoint of fuel economy, the styrene content of the SBR is preferably 39.0% by mass or less. The styrene content of the SBR is a value calculated by ¹ H-NMR measurement.

The vinyl content (amount of 1,2-bonded butadiene units) of SBR is preferably 10.0 to 30.0%. From the viewpoint of rubber strength and grip performance, the vinyl content is preferably 13.0% or more, and more preferably 15.0% or more. From the viewpoint of fuel economy, the vinyl content is preferably 25.0% or less, and more preferably 20.0% or less. The vinyl content of SBR is a value measured by infrared absorption spectroscopy.

When SBR is contained, the content in the rubber component is preferably 1% by mass or more, more preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 10% by mass or more, because this allows the effects of the present disclosure to be exhibited more effectively. The content of SBR is preferably 35% by mass or less, more preferably 30% by mass or less, more preferably 28% by mass or less, and even more preferably 25% by mass or less. When oil-extended SBR is used as the SBR, the content of SBR itself as a solid content contained in the oil-extended SBR is regarded as the content of SBR in the rubber component.

<Silica>
Silica is not particularly limited, and for example, silica (anhydrous silicic acid) prepared by dry method, silica (hydrated silicic acid) prepared by wet method, etc. are listed.Among them, silica prepared by wet method is preferred because it has many silanol groups on the surface and many reaction points with silane coupling agent.Silica may be used alone or in combination of two or more kinds.

The nitrogen adsorption specific surface area ( _N2SA ) of silica is not particularly limited, but from the viewpoint of fuel economy and ensuring sufficient reinforcement and further improving wear resistance, it is preferably ¹⁸⁰ m2/g or more, more preferably ¹⁹⁰ m2/g or more, more preferably 195 m2/g or more, more preferably ²⁰⁰ m2/g or more, more preferably ^{210 m2} /g or more, more preferably 220 ^m2 /g or more, and even more preferably ²³⁵ m2/g or more. Also, from the viewpoint of processability, _N2SA is preferably ⁵⁰⁰ m2/g or less, more preferably ⁴⁰⁰ m2/g or less, more preferably ³⁰⁰ m2/g or less, more preferably ²⁸⁰ m2/g or less, and even more preferably 260 ^m2 /g or less. The N ₂ SA of silica is a value measured by the BET method in accordance with ASTM D3037-81.

The content of silica per 100 parts by mass of the rubber component is 40 parts by mass or more, preferably 45 parts by mass or more, more preferably 50 parts by mass or more, more preferably 55 parts by mass or more, and even more preferably 65 parts by mass or more. If it is less than 40 parts by mass, the low heat generation property is impaired and it tends to be difficult to ensure low fuel consumption performance. In addition, from the viewpoint of dispersibility, processability, and wet grip performance of silica, the content of silica is preferably 150 parts by mass or less, more preferably 140 parts by mass or less, more preferably 130 parts by mass or less, and even more preferably 120 parts by mass or less.

In this disclosure, silica is available as a commercially available product, such as Ultrasil 9000GR manufactured by Evonik Degussa.

<Other fillers>
As the filler, other fillers may be used in addition to silica. Such fillers are not particularly limited, and any fillers generally used in this field, such as carbon black, aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, talc, clay, etc., may be used. These fillers may be used alone or in combination of two or more. When a filler other than silica is used as the filler, carbon black is preferred from the viewpoint of rubber strength. That is, the filler preferably contains silica and carbon black, or is preferably composed of only silica and carbon black.

(Carbon black)
The carbon black is not particularly limited, and any carbon black commonly used in the tire industry, such as GPF, FEF, HAF, ISAF, or SAF, can be used.

The N ₂ SA of the carbon black is preferably 50 m ² /g or more, more preferably 70 m ² /g or more, and even more preferably 90 m ² /g or more, from the viewpoint of obtaining sufficient reinforcing properties and abrasion resistance. The N ₂ SA of the carbon black is preferably 500 m ² /g or less, more preferably 450 m ² /g or less, more preferably 300 m ² /g or less, more preferably 250 m ² /g or less, more preferably 200 m ² /g or less, more preferably 180 m ² /g or less, and even more preferably 160 m ² /g or less, from the viewpoint of excellent dispersibility and resistance to heat generation. The N ₂ SA of the carbon black is a value measured in accordance with JIS K 6217-2:2001.

When carbon black is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 3 parts by mass or more, more preferably 4 parts by mass or more, and even more preferably 5 parts by mass or more, from the viewpoint of obtaining sufficient reinforcement and abrasion resistance. In addition, the content of carbon black is preferably 40 parts by mass or less, more 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, from the viewpoint of moldability, fuel efficiency, and abrasion resistance.

（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、それぞれ、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、それぞれ、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。） <Silane coupling agent>
The silane coupling agent having a mercapto group is not particularly limited, and is, for example, at least one of a compound represented by the following formula (1) and 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.)

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 terms of obtaining the effects of the present disclosure satisfactorily, 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 of them are groups represented by -O-(R ¹¹¹ -O) _z -R ¹¹² and one of them is a linear or branched alkoxy group having 1 to 12 carbon atoms.

Examples of the straight-chain or branched-chain 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 a linear or branched alkylene group having 1 to 30 carbon atoms, a linear or branched alkenylene group having 2 to 30 carbon atoms, a linear or branched alkynylene group having 2 to 30 carbon atoms, and an arylene group having 6 to 30 carbon atoms. Of these, a linear or branched alkylene group having 1 to 30 carbon atoms is 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 straight chain or branched chain 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 straight or branched 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 _{2 H} —O) ₆ —C ₁₃ H ₂₇ , —O—(C ₂ H ₄ —O) ₇ —C ₁₃ H ₂₇ , etc. Among these, —O—(C ₂ H ₄ —O) ₅ —C ₁₁ H ₂₃ , —O—(C ₂ H ₄ —O) ₅ —C ₁₃ H ₂₇ , —O—(C ₂ H ₄ —O) ₅ —C ₁₅ H ₃₁ , and —O—(C ₂ H ₄ —O) ₆ —C ₁₃ H ₂₇ 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, 3-mercaptopropylmethyldimethoxysilane, and a 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.

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) representing 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 _-C7H15 of the bonding unit A, so that shortening of the scorch time can be suppressed 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 types.

The content of the silane coupling agent having a mercapto group is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, more preferably 2 parts by mass or more, and more preferably 5 parts by mass or more, per 100 parts by mass of silica, from the viewpoint of sufficiently ensuring effects such as low fuel consumption. In addition, from the viewpoint of obtaining the compounding effect of the silane coupling agent having a mercapto group commensurate with the increase in cost, and from the viewpoint of rubber strength and abrasion resistance, the content is preferably 20 parts by mass or less, more preferably 18 parts by mass or less, more preferably 17 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less.

(Other silane coupling agents)
In the present disclosure, the rubber composition may further contain other silane coupling agents in addition to the silane coupling agent having a mercapto group. Examples of other silane coupling agents include 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazole tetrasulfide, 3-triethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(triethoxysilylpropyl) methacrylate monosulfide, and bis(triethoxysilylpropyl) methacrylate monosulfide. Examples thereof include (3-triethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylpropyl) trisulfide, bis(3-triethoxysilylpropyl) disulfide, bis(2-triethoxysilylethyl) tetrasulfide, bis(3-trimethoxysilylpropyl) tetrasulfide, bis(2-trimethoxysilylethyl) tetrasulfide, bis(3-diethoxymethylsilylpropyl) tetrasulfide, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, and dimethoxymethylsilylpropyl benzothiazole tetrasulfide.

<Other ingredients>
In addition to the above-mentioned components, the rubber composition of the present disclosure may contain other components that are generally used in the manufacture of rubber compositions. Examples of such optional components include softeners, stearic acid, zinc oxide, antioxidants, waxes, vulcanizing agents, vulcanization accelerators, etc.

(Softener)
The softener is not particularly limited, and can be arbitrarily selected from various softeners that have been conventionally used in rubber compositions for tires. For example, the softener is oil, resin, liquid polymer, etc. Among them, from the viewpoint of better exerting the effects of the present disclosure, it is preferable that the softener contains oil and resin, or is preferably composed of only oil and resin. The softener may be used alone or in combination of two or more kinds.

The oil is not particularly limited, and any oil commonly used in the rubber industry can be suitably used, such as process oil, vegetable oil, and animal oil. Examples of process oil include paraffinic process oil, naphthenic process oil, and aromatic process oil. Examples of vegetable oil 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, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, safflower oil, and tung oil. Examples of animal oil include oleyl alcohol, fish oil, and beef tallow. Among them, process oil is preferred because it is advantageous in terms of processability. The oil may be used alone or in combination of two or more.

When oil is contained, the content per 100 parts by mass of the rubber component is, for example, preferably 0.5 parts by mass or more, and more preferably 1.0 parts by mass or more. The content of oil per 100 parts by mass of the rubber component is preferably 50 parts by mass or less, and more preferably 45 parts by mass or less. When the oil content is within the above range, the resulting tire has excellent wet grip performance and wear resistance. The oil content includes the amount of oil used in oil extension.

The resin is not particularly limited, and resins commonly used in conventional rubber compositions for tires, such as aromatic petroleum resins, can be used. Examples of aromatic petroleum resins include phenolic resins, coumarone-indene resins, styrene resins, terpene resins, acrylic resins, rosin resins, and dicyclopentadiene resins (DCPD resins). Examples of phenolic resins include those manufactured by BASF and Taoka Chemical Co., Ltd. Examples of coumarone-indene resins include those manufactured by Nippon Steel & Sumikin Chemical Co., Ltd. and JXTG Energy Co., Ltd. Examples of styrene resins include those manufactured by Arizona Chemical Co., Ltd. Examples of terpene resins include those manufactured by Arizona Chemical Co., Ltd. and Yasuhara Chemical Co., Ltd. Examples of rosin resins include those manufactured by Harima Chemical Co., Ltd. and Arakawa Chemical Co., Ltd. These may be used alone or in combination of two or more. Among these, it is preferable to use at least one selected from the group consisting of phenol-based resins, coumarone-indene resins, styrene-based resins, terpene-based resins, and acrylic resins because of their excellent grip performance, and styrene-based resins are particularly preferable in terms of improving wet grip performance.

The styrene resin is not particularly limited, but α-methylstyrene resin is preferably used. Examples of α-methylstyrene resin include homopolymers of α-methylstyrene (poly-α-methylstyrene) and copolymers of α-methylstyrene with other compounds including aromatic compounds and phenolic compounds. Other compounds that can form this copolymer include styrene, methylstyrene, methoxystyrene, and divinylbenzene. Specific examples of α-methylstyrene resins that can be used include those manufactured by Arizona Chemical Company.

The softening point of the resin is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher. By making the softening point of the resin 50°C or higher, wet grip performance tends to improve. Furthermore, the softening point of the resin is preferably 200°C or lower, more preferably 190°C or lower, and even more preferably 180°C or lower. By making the softening point of the resin 200°C or lower, compatibility with the rubber during kneading tends to improve. 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 resin is contained, the content per 100 parts by mass of the rubber component is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more, from the viewpoint of wet grip performance. Also, the content per 100 parts by mass of the resin 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, from the viewpoint of abrasion resistance.

(Anti-aging agent)
The antioxidant is not particularly limited, and may be selected from various antioxidants that have been conventionally used in rubber compositions for tires. Examples of the antioxidant include quinoline-based antioxidants, quinone-based antioxidants, phenol-based antioxidants, phenylenediamine-based antioxidants, carbamic acid metal salts, waxes, and the like. Among them, quinoline-based antioxidants, phenylenediamine-based antioxidants, and waxes can be preferably used. An example of the quinoline-based antioxidant is 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ). An example of the phenylenediamine-based antioxidant is N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD). For example, antioxidants manufactured by Ouchi Shinko Chemical Industry Co., Ltd. and Kawaguchi Chemical Industry Co., Ltd. can be preferably used. The antioxidants may be used alone or in combination of two or more.

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, more preferably 0.8 parts by mass or more, and even more preferably 1.0 parts by mass or more. The content of the antioxidant is preferably 7.0 parts by mass or less, more preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less. When the content of the antioxidant is within the above range, the filler is easily dispersed. Furthermore, the obtained rubber composition is easily kneaded.

(Vulcanizing agent)
The vulcanizing agent is not particularly limited, and known vulcanizing agents can be used, such as organic peroxides, sulfur-based vulcanizing agents, resin vulcanizing agents, and metal oxides such as magnesium oxide. Examples of organic peroxides that can be used include benzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, and 1,3-bis(t-butylperoxypropyl)benzene. Examples of sulfur-based vulcanizing agents that can be used include sulfur and morpholine disulfide. Of these, it is preferable to use sulfur. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur, and any of these can be suitably used. The vulcanizing agent may be used alone or in combination of two or more kinds.

When a vulcanizing agent 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 1.0 parts by mass or more. The content of the vulcanizing agent is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less. When the content of the vulcanizing agent is 0.5 parts by mass or more, the rubber composition is more likely to undergo a good vulcanization reaction. When the content of the vulcanizing agent is 5 parts by mass or less, the resulting tire is more likely to have a good balance between grip performance and wear resistance.

(Vulcanization accelerator)
The vulcanization accelerator is not particularly limited, and known vulcanization accelerators can be used, such as sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, or xanthate-based vulcanization accelerators. Among these, sulfenamide-based, thiuram-based, and guanidine-based are preferred, and sulfenamide-based and thiuram-based are more preferred. The vulcanization accelerators may be used alone or in combination of two or more.

Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazole sulfenamide (TBBS), N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS), and N,N'-dicyclohexyl-2-benzothiazolyl sulfenamide (DZ). Of these, N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS) is preferred.

Examples of thiuram vulcanization accelerators include tetramethylthiuram monosulfide, tetramethylthiuram disulfide, and tetrabenzylthiuram disulfide (TBzTD). Among these, tetrabenzylthiuram disulfide (TBzTD) is preferred.

Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine (DPG), di-orthotolylguanidine, and orthotolylbiguanidine. Among these, 1,3-diphenylguanidine (DPG) is preferred from the viewpoint of shortening the vulcanization time.

In the present disclosure, it is more preferable to use only N-cyclohexyl-2-benzothiazolylsulfenamide (CBS) and tetrabenzylthiuram disulfide (TBzTD) as the vulcanization accelerator, because this allows the effects of the present disclosure to be exhibited more effectively.

When a vulcanization accelerator is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 2.0 parts by mass or more. The content of the vulcanization accelerator is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.5 parts by mass or less. By setting the content in such a range, the effects of the present disclosure can be more effectively exhibited.

<Properties of Rubber Composition>
The rubber composition of the present disclosure has a tan δ _{0° C.} at 0° C. of 0.550 or less, preferably 0.540 or less, and more preferably 0.530 or less, from the viewpoint of low-temperature fuel economy. The lower limit of tan δ _{0° C.} at 0° C. is not particularly limited, but is usually 0.150 or more.

In the rubber composition of the present disclosure, the difference between tan δ _30°C at 30°C and tan δ _60°C at 60°C (hereinafter also referred to as "tan δ _30°C -tan δ _60°C ") is 0.070 or less, preferably 0.060 or less, more preferably 0.055 or less, and even more preferably 0.050 or less, from the viewpoint of the temperature dependency of fuel economy. The lower limit of tan δ _30°C -tan δ _60°C is not particularly limited. tan δ _30°C -tan δ _60°C may be 0.

The difference between tan δ _0°C at 0°C and tan δ _{30°C at 30} °C (hereinafter also referred to as "tan δ _0°C -tan δ _30°C ") of the rubber composition of the present disclosure is not particularly limited, but from the viewpoint of the temperature dependency of wet grip performance and fuel economy, it is preferably 0.300 or less, more preferably 0.290 or less, and even more preferably 0.280 or less. In addition, tan δ _0°C -tan δ _30°C is preferably 0.140 or more, more preferably 0.150 or more, and even more preferably 0.160 or more.

In this specification, tan δ indicates the loss tangent during elongation measured by a viscoelasticity spectrometer under conditions of a dynamic strain amplitude of 1%, a frequency of 10 Hz, and each temperature. The loss tangent tan δ indicates the amount of energy consumed in the process of applying strain, and this consumed energy is converted into heat. In other words, the smaller the value of tan δ, the better the low heat generation and fuel efficiency.

The storage modulus E' at 0°C of the rubber composition of the present disclosure is not particularly limited, but from the viewpoint of wet grip performance, it is preferably 15 MPa or less, more preferably 14.5 MPa or less, and even more preferably 14 MPa or less. The storage modulus E' at 0°C is preferably 3 MPa or more, and more preferably 5 MPa or more. The storage modulus E' at 0°C indicates the dynamic modulus of elasticity during elongation measured by a viscoelasticity spectrometer under the conditions of a dynamic strain amplitude of 1%, a frequency of 10 Hz, and a temperature of 0°C.

In the rubber composition of the present disclosure, ΔG ^* represented by formula (I) is preferably 500 or less, more preferably 450 or less, more preferably 400 or less, more preferably 350 or less, and even more preferably 300 or less. When the reaction between silica and the silane coupling agent is promoted, the silica surface is hydrophobized and the dispersibility of silica is improved. As a physical property for evaluating the dispersibility of silica, there is ΔG ^* (Payne effect) defined as the difference between G ^* in the low strain region and G ^* in the high strain region, and the smaller this value, the smaller the proportion of large filler aggregates in the rubber composition, and the better the silica dispersion state is. Note that G ^* is a value measured by using an RPA2000 manufactured by α Technology Co., Ltd. at a test temperature of 100°C to measure the shear strain G ^* (kPa) of a rubber test piece of an unvulcanized rubber composition from 4% to 64%. By measuring G ^* in the unvulcanized rubber composition, the effect of dispersion of pure silica can be extracted.

<Keep kneading>
The rubber composition of the present disclosure is a rubber composition in which a first kneading step in a kneading process for kneading raw materials (excluding vulcanization-related chemicals) containing a rubber component containing 50% by mass or more of natural rubber, 40 parts by mass or more of silica, and a silane coupling agent having a mercapto group is included, the first kneading step including a keep kneading step for increasing the reaction efficiency of the silica and the silane coupling agent having a mercapto group.

In this specification, "kneading with keeping" refers to a kneading method in which a predetermined temperature range is maintained while kneading for a predetermined time period, and includes a method of kneading for a certain time period while maintaining a certain temperature, and a method of kneading for a certain time period while allowing temperature fluctuations within a certain temperature range. In addition, the temperature for keeping kneading in this specification is the set temperature inside the kneader that is set by the kneader.

In this specification, the "kneading process" refers to a process in which raw materials are mixed and kneaded. The kneading process includes at least a first kneading process and a final kneading process. The "first kneading process" refers to a process in which, when kneading the raw materials in preparing the rubber composition, the raw materials other than the vulcanization chemicals (vulcanizing agent and vulcanization accelerator) are first kneaded to obtain a kneaded product. The "final kneading process" refers to the final stage of the kneading process in which a vulcanizing agent and a vulcanization accelerator are added to the kneaded product obtained in the first kneading process (or the kneaded product obtained in the second kneading process if the second kneading process is performed after the first kneading process) and further kneaded to obtain an unvulcanized rubber composition.

The "temperature in a specified range and the time in a specified range" in the keep kneading process may be "a temperature and time sufficient to increase the reaction efficiency of the silica and the silane coupling agent having a mercapto group". The temperature and time may vary depending on the type of silane coupling agent having a mercapto group used and the types of other raw materials used, but a person skilled in the art can set them appropriately for the above purpose. By performing keep kneading to increase the reaction efficiency of the silica and the silane coupling agent having a mercapto group, the silica dispersion can be improved, so that the starting points of destruction due to filler aggregation are reduced and the wear resistance performance is improved. Furthermore, the heat generation due to the friction between the fillers is also mitigated, so that the fuel efficiency performance is also improved. At the same time, wet grip performance is exhibited by blending silica. It also leads to improved processability.

The temperature in the specified range is not particularly limited as long as it is a temperature that enhances the reaction efficiency between silica and the silane coupling agent having a mercapto group, but is preferably 130 to 157°C. The lower limit is more preferably 132°C or higher, and more preferably 134°C or higher. The upper limit is more preferably 156°C or lower, and more preferably 155°C or lower. Being in such a range is the reaction temperature region of the silane coupling agent having a mercapto group, and is preferable in terms of enhancing the reaction efficiency between silica and the silane coupling agent having a mercapto group.

The time in the specified range may be set appropriately depending on the temperature setting in the above specified range and the type of kneading machine used for kneading, but from the viewpoint of sufficiently increasing the reaction efficiency of the silica and the silane coupling agent having a mercapto group, it is usually preferably 100 seconds or more, more preferably 110 seconds or more, and even more preferably 120 seconds or more. The upper limit of the time in the specified range is not particularly limited, but from the viewpoint of preventing the inflow of machine oil into the kneading machine, it is usually at most 480 seconds or less.

<Production Method>
Rubber compositions, tire components (eg, treads), and methods of making tires are described.

(Method for producing rubber composition)
A method for producing a rubber composition comprising 100 parts by mass of a rubber component containing 50% by mass or more of natural rubber, 40 parts by mass or more of silica, and a silane coupling agent having a mercapto group, wherein the rubber composition has a tan δ _0°C of 0.550 or less and a difference between a tan δ _30°C at 30°C and a tan δ _60°C at 60°C of 0.070 or less, the method comprising a kneading step, the kneading step including a first kneading step of kneading raw materials (excluding vulcanization-related chemicals) including the rubber component, the silica, and the silane coupling agent having a mercapto group, and the first kneading step including a keep kneading step for increasing a reaction efficiency of the silica and the silane coupling agent having a mercapto group.

The kneading process can be carried out in accordance with methods commonly used in the tire and rubber industry.

(First kneading step)
The first kneading step includes the keep kneading. The "first kneading step" and the "kneading" are defined above. The "predetermined range of time and the predetermined range of temperature" in the keep kneading are the same as those explained above.

In the first kneading step, 100 parts by mass of a rubber component containing 50% by mass or more of natural rubber is kneaded with raw materials containing 40 parts by mass or more of silica and a silane coupling agent having a mercapto group. If there are other raw materials to be blended into the rubber composition, all of them other than the vulcanization chemicals are kneaded in this first kneading step.

In the first kneading step, the above-mentioned predetermined raw materials are blended and a predetermined keep kneading is included, and the conditions other than the keep kneading are not particularly limited as long as the effect of the present disclosure is not impaired, and the rotation speed and discharge temperature can be the same as those in the conventional so-called base kneading step. Here, it is preferable to perform the keep kneading after the first kneading step is performed by a conventional method (preferably at the final stage of the first kneading step) in order to increase the reaction efficiency of the silica and the mercapto-based silane coupling agent. In addition, it is preferable that the kneading in the first kneading step is completed when the keep kneading is completed. The first kneading step is completed by discharging the kneaded product at the end of the keep kneading. The kneading speed is usually 20 to 60 rpm, preferably 30 to 50 rpm.

The discharge temperature in the first kneading process is the same as the temperature during keep kneading, since the kneaded material is discharged when keep kneading is completed.

(Second kneading step)
The "second kneading step" refers to a step of kneading the kneaded product obtained by the first kneading step again (re-kneading) to obtain a kneaded product. In the manufacturing method of the present disclosure, it is preferable to perform the second kneading step after the first kneading step, in order to further increase the reaction efficiency of silica and mercapto-based silane coupling agent.

The discharge temperature in the second kneading step is preferably 140 to 170°C. As a lower limit, from the viewpoint of further increasing the reaction efficiency between silica and the mercapto-silane coupling agent, it is more preferable that the temperature is 142°C or higher, more preferably 144°C or higher, and even more preferably 146°C or higher. As an upper limit, from the viewpoint of suppressing the progress of the reaction between the polymer and the mercapto-silane coupling agent and further exerting the effect of improving silica dispersibility, it is more preferable that the temperature is 164°C or lower, more preferably 162°C or lower, and even more preferably 160°C or lower. The kneading time in the second kneading step may be adjusted according to the discharge temperature, but is usually 1 to 6 minutes, preferably 2 to 5 minutes.

(Final kneading process)
The "final compounding step" is defined above.

The discharge temperature in the final kneading step is not particularly limited, but is preferably 70°C or higher, more preferably 80°C or higher, and even more preferably 90°C or higher. By setting the discharge temperature at 70°C or higher, it tends to be possible to efficiently obtain a kneaded product in which each component is well dispersed. In addition, the discharge temperature in the final kneading step is not particularly limited, but is preferably 120°C or lower, more preferably 115°C or lower, and even more preferably 110°C or lower. By setting the discharge temperature of the kneading step at 120°C or lower, it tends to be possible to prevent scorching (rubber burning).

The kneading can be carried out using a Banbury mixer, kneader, open roll, or other kneading machine commonly used in the rubber industry. Among them, a closed Banbury mixer is preferred because of its excellent workability and productivity. The shape of the Banbury mixer rotor may be either tangential or intermeshing.

(Tire components (e.g., treads) and methods for manufacturing tires)
The rubber composition of the present disclosure can be suitably used for various tire components (e.g., tread, sidewall, carcass covering rubber, clinch, chafer, bead, etc.) Among them, it is preferable to use it for the tread because it has excellent rubber physical properties such as wet grip performance and abrasion resistance.

Tire components (e.g., treads) made using the rubber composition obtained by the above manufacturing method and tires equipped with such tire components can be manufactured by conventional methods in the rubber industry.

For example, a method for producing the tire member includes the steps of:
(1) a step of obtaining an unvulcanized rubber composition by a method for producing a rubber composition comprising the first kneading step;
(2) A step of extruding the unvulcanized rubber composition thus obtained into a shape of a tire component (e.g., a tread) to obtain the tire component (e.g., a tread);
It includes.

In addition to the above steps (1) and (2), the tire manufacturing method further comprises the steps of:
(3) bonding the tire component (e.g., tread) obtained in (2) above together with other tire components in a tire building machine and molding the tire to obtain an unvulcanized tire; and
(4) The method includes a step of heating and pressurizing the thus obtained unvulcanized tire in a vulcanizer to obtain a tire.

The tire of the present disclosure may be either a pneumatic tire or a non-pneumatic tire, but is preferably a pneumatic tire. In addition, various types of pneumatic tires can be used, such as tires for passenger cars, tires for trucks and buses, tires for motorcycles, high-performance tires such as racing tires, and run-flat tires.

＜Other＞
Claim 1 of the present application is an invention of a rubber composition, and "the first kneading step in the kneading step of kneading raw materials (excluding vulcanization chemicals) containing the rubber component, the silica, and the silane coupling agent having a mercapto group includes a keep kneading step for increasing the reaction efficiency of the silica and the silane coupling agent having a mercapto group." As shown in the examples below, the invention according to claim 1 of the present application uses the same compounding, but the physical properties of the resulting rubber composition are different depending on whether or not the keep kneading specified in the present application is performed. This shows that even with the same compounding, the keep kneading specified in the present application affects the physical properties of the rubber composition, and that by performing the keep kneading specified in the present application, rubber compositions with different temperature dependence of fuel economy, low temperature fuel economy, normal temperature fuel economy, wet grip performance, and wear resistance are produced.

However, even if one were to directly identify the differences between such rubber compositions based on their structure or properties, it is unclear what indicators or parameters would be necessary and sufficient to identify them. Therefore, forcing such identification is at least not practical in Japan, which adopts the first-to-file system. Therefore, claim 1 of the present application does not constitute an unclear invention.

The present disclosure will be specifically explained based on examples. The present disclosure is not limited to these examples.

<Various chemicals used in the examples and comparative examples>
NR: TSR20
SBR: NS616 (S-SBR, styrene content: 21% by mass, non-oil extended, available from ZS Elastomers Co., Ltd.)
BR: BR730 (cis 1,4 bond content: 95%, available from JSR Corporation)
Carbon black: N220 ( _N2SA : 114 ^m2 /g, available from Cabot Japan Co., Ltd.)
Silica: Ultrasil 9000GR ( _N2SA : 235 ^m2 /g, available from Evonik Degussa)
Silane coupling agent 1 (sulfide-based coupling agent): Si266 (bis(3-triethoxysilylpropyl) disulfide, available from Evonik Degussa)
Silane coupling agent 2 (mercapto-based coupling agent): NXT-Z45 (a copolymer of bonding unit A and bonding unit B (bonding unit A: 55 mol %, bonding unit B: 45 mol %), available from Momentive Corporation)
Silane coupling agent 3 (mercapto-based coupling agent): Si363 (available from Evonik Degussa)
Resin: SYLVATRAXX4401 (α-methylstyrene resin, softening point: 85° C., SP value: 9.1, available from Arizona Chemical Company)
Oil: Diana Process Oil PA32 (available from Idemitsu Kosan Co., Ltd.)
Antioxidant 1: Nocrac 6C (N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), available from Ouchi Shinko Chemical Industry Co., Ltd.)
Antioxidant 2: Antage RD (2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ), available from Kawaguchi Chemical Industry Co., Ltd.)
Wax: Sunnock N (available from Ouchi Shinko Chemical Industry Co., Ltd.)
Stearic acid: Camellia stearate beads (available from NOF Corp.)
Zinc oxide: Two types of zinc oxide (available from Mitsui Mining & Smelting Co., Ltd.)
Sulfur: Powdered sulfur (available from Karuizawa Sulfur Co., Ltd.)
Vulcanization accelerator 1: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS), available from Ouchi Shinko Chemical Industry Co., Ltd.)
Vulcanization accelerator 2: Sancerer TBZTD (tetrabenzyl thiuram disulfide (TBzTD), available from Sanshin Chemical Industry Co., Ltd.)

Examples 1 to 5 and Comparative Examples 1 to 9
<Unvulcanized rubber composition>
(First kneading step)
According to the compounding recipe shown in Table 1 below, when keep kneading was performed in the first kneading step ("Keep" in the table), chemicals other than sulfur and vulcanization accelerator were kneaded for 2 minutes at a kneading temperature of 155°C or less using a 1.7L closed Banbury mixer, and then keep kneading was performed for a predetermined time at a predetermined temperature shown in Table 1, and discharged according to the discharge temperature shown in Table 1 to obtain a kneaded product. When keep kneading was not performed in the first kneading step ("Normal" in the table), chemicals other than sulfur and vulcanization accelerator were kneaded for 3 minutes at a discharge temperature of 155°C using a 1.7L closed Banbury mixer, and a kneaded product was obtained.

(Second kneading step)
The kneaded product obtained in the first kneading step was kneaded again for 3 minutes under the condition of a discharge temperature of 155° C. in a Banbury mixer to obtain a kneaded product.

(Final kneading process)
Sulfur and a vulcanization accelerator were added to the kneaded product obtained in the second kneading step, and the mixture was kneaded for 3 minutes using a Banbury mixer under conditions of a discharge temperature of 110° C. or less to obtain an unvulcanized rubber composition.

<Vulcanized Rubber Composition>
The unvulcanized rubber composition obtained above was press-vulcanized at 170° C. for 15 minutes to produce a vulcanized rubber composition.

<Test tires>
The unvulcanized rubber composition obtained above was extruded into the shape of a tire tread using an extruder equipped with a die of a predetermined shape, and then laminated together with other tire components to form an unvulcanized tire. A test tire (size: 195/65R15) was manufactured by press-vulcanizing the tire at 170°C for 15 minutes.

<Evaluation>
The unvulcanized rubber composition, vulcanized rubber composition and test tire obtained were subjected to the following evaluations. The results are shown in Table 1.

(Payne effect ΔG ^* )
The shear strain G ^* (kPa) of each rubber test piece of the unvulcanized rubber composition at a strain of 4% to 64% was measured using an RPA2000 manufactured by Alpha Technology Co., Ltd. (test temperature 100°C). The Payne effect ΔG ^* was calculated using the following formula. The smaller this value, the better the silica dispersibility.
ΔG ^* =G ^* (4%)-G ^* (64%)
G ^* (n%) represents the shear modulus when a strain of n% is applied.

(Loss tangent tan δ and storage modulus E′)
Using a spectrometer (manufactured by Ueshima Seisakusho Co., Ltd.), the loss tangent (tan δ 0° _C , tan δ 30°C, tan δ 60°C) of the vulcanized rubber composition and the storage modulus E' (MPa) at 0°C were measured under conditions of dynamic strain amplitude of 1%, frequency of 10 Hz, and temperatures of 0°C, _{30 °C} , and _60°C , and tan δ _0°C -tan δ _{30°C and tan δ 30°C} -tan δ _60°C were obtained. The smaller the tan δ, the lower the rolling resistance and the better the fuel economy, and the smaller the tan δ _30°C -tan δ _60°C , the smaller the temperature dependency of fuel economy. Also, the smaller the storage modulus E' at 0°C, the better the wet grip performance.

(Low temperature fuel efficiency/Normal temperature fuel efficiency)
The ambient temperature of the tire chamber of the rolling resistance tester was set to 0°C for the evaluation of low-temperature fuel economy performance and 30°C for the evaluation of normal temperature fuel economy performance, and the rolling resistance was measured. The rolling resistance was measured using a rolling resistance tester when each test tire was run with a rim (15x6JJ), internal pressure (230kPa), load (3.43kN), and speed (80km/h), and the rolling resistance was expressed as an index with the reference comparative example being 100. The smaller the rolling resistance, the better the fuel economy. The higher the index, the better the fuel economy. The target values are a fuel economy performance index of 130 or more in the low temperature range and a fuel economy performance index of 130 or more in the normal temperature range.

(Wet grip performance)
Each test tire was attached to all wheels of a test vehicle (domestic FF vehicle), and the braking distance from an initial speed of 100 km/h was measured on a wet asphalt road surface. The results were expressed as an index using the following formula, with the reference comparative example being set at 100. The higher the index, the better the wet grip performance. The target value for the index is 108 or more.
(Wet grip performance index) =
{(braking distance of the reference comparative tire)/(braking distance of each test tire)}×100

(Wear resistance)
Each test tire was attached to all wheels of a test vehicle (a domestic FF vehicle), and the vehicle was driven on a dry asphalt road surface for 8,000 km. The groove depth of the tire tread was measured, and the running distance when the groove depth of the tire tread was reduced by 1 mm was calculated from the arithmetic mean value of the groove depth of all wheels. The results were expressed as an index using the following formula, with the reference comparative example being set at 100. The higher the index, the better the wear resistance performance. The target value of the index is 115 or more.
(Wear resistance performance index)={(travel distance when tire tread of each test tire is reduced by 1 mm)/(travel distance when tire tread of reference comparative example is reduced by 1 mm)}×100

The results in Table 1 show that the rubber compositions of the examples have better silica dispersibility than those of the comparative examples, maintain fuel economy at room temperature while reducing the temperature dependency of fuel economy, and have better wet grip performance and wear resistance.

Claims (16)

containing 40 parts by mass or more of silica and a silane coupling agent having a mercapto group relative to 100 parts by mass of a rubber component containing 50% by mass or more of natural rubber,
A vulcanized rubber composition having a tan δ _0°C of 0.550 or less at 0°C and a difference between a tan δ _30°C at 30°C and a tan δ _60°C at 60°C of 0.070 or less,
a vulcanized rubber composition, wherein a first kneading step in a kneading step for kneading raw materials (excluding vulcanization-related chemicals) containing the rubber component, the silica, and the silane coupling agent having a mercapto group includes a keep kneading step for kneading for a predetermined range of time while maintaining a predetermined temperature , the predetermined temperature being within a range of 130°C to 157°C, and the predetermined range of time being within a range of 100 seconds to 480 seconds . 2. The vulcanized rubber composition according to claim 1, wherein the unvulcanized rubber composition after the kneading step has a ΔG ^* value represented by the following formula (I) of 500 or less.
ΔG ^* = G ^* (4%) - G ^* (64%) (I)
In formula (I), G ^* (n%) represents the shear modulus when a strain of n% is applied. The vulcanized rubber composition according to claim 1 or 2, having a storage modulus E' at 0°C of 15 MPa or less. The vulcanized rubber composition according to any one of claims 1 to 3, wherein the keep kneading temperature is 132°C to 156°C , and the keep kneading time is 110 seconds to 480 seconds . The silane coupling agent having a mercapto group is
The vulcanized rubber composition according to any one of claims 1 to 4, which is at least one of a compound represented by the following formula (1) and 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.) 6. The vulcanized rubber composition according to claim 1, wherein the silica has a nitrogen adsorption specific surface area of 180 m ² /g or more. 7. The vulcanized rubber composition according to claim 1, wherein the difference between tan δ _0°C at 0°C and tan δ _30°C at 30°C is 0.300 or less. A tread made using the vulcanized rubber composition according to any one of claims 1 to 7. A tire having a tread according to claim 8. containing 40 parts by mass or more of silica and a silane coupling agent having a mercapto group relative to 100 parts by mass of a rubber component containing 50% by mass or more of natural rubber,
A method for producing a vulcanized rubber composition having a tan δ _0°C of 0.550 or less at 0°C and a difference between a tan δ _30°C at 30°C and a tan δ _60°C at 60°C of 0.070 or less, comprising:
The method includes a kneading step for obtaining an unvulcanized rubber composition,
the kneading step includes a first kneading step of kneading raw materials (excluding vulcanization-related chemicals) including the rubber component, the silica, and the silane coupling agent having a mercapto group,
The method for producing a vulcanized rubber composition, wherein the first kneading step includes a keep kneading step of kneading for a predetermined time period while maintaining a predetermined temperature range , the predetermined temperature being within a range of 130°C to 157°C, and the predetermined time period being within a range of 100 seconds to 480 seconds. The method for producing a vulcanized rubber composition according to claim 10, wherein the unvulcanized rubber composition has a ΔG ^* represented by the following formula (I) of 500 or less.
ΔG ^* = G ^* (4%) - G ^* (64%) (I)
In formula (I), G ^* (n%) represents the shear modulus when a strain of n% is applied. The method for producing a vulcanized rubber composition according to claim 10 or 11, wherein the storage modulus E' at 0°C is 15 MPa or less. The method for producing a vulcanized rubber composition according to any one of claims 10 to 12, wherein the keep kneading temperature is 132°C to 156°C , and the keep kneading time is 110 seconds to 480 seconds . The method for producing a vulcanized rubber composition according to any one of claims 10 to 13, wherein the kneading step further includes a second kneading step of re-kneading the kneaded product obtained by the first kneading step, and the first kneading step includes kneading chemicals other than sulfur and the vulcanization accelerator, and then performing keep kneading . The method for producing a vulcanized rubber composition according to claim 14, wherein the discharge temperature of the second kneading step is 140 to 170°C. The method according to any one of claims 10 to 15, wherein the vulcanized rubber composition is a tire,
After the kneading step for obtaining the unvulcanized rubber composition,
extruding the unvulcanized rubber composition into a tread shape to obtain a tread component;
laminating and molding the tread component together with other tire components on a tire building machine to obtain an unvulcanized tire; and
The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.