JP6794869B2 - Rubber composition, tire tread and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition, a tire tread made using the rubber composition, and a pneumatic tire having the tire tread.

In recent years, with the increasing demand for tires, tires having both low temperature crack resistance and grip performance have been demanded.

Conventionally, a technique of blending butadiene rubber as a rubber component has been known in order to improve low-temperature embrittlement of tire rubber, but in this case, there is a problem that grip performance is lowered as a compensation (paragraph of Patent Document 1). [0002]).

Japanese Unexamined Patent Publication No. 5-132583

An object of the present invention is to provide a rubber composition having improved low temperature embrittlement resistance and grip performance in a well-balanced manner, a tire tread produced by using the rubber composition, and a pneumatic tire having the tire tread. And.

As a result of diligent studies to solve the above problems, the present inventor has found that a predetermined rubber component in which at least 90% by mass or more of the rubber component is composed of styrene-butadiene rubber and butadiene rubber has a liquid styrene-butadiene rubber and a softening point. It was found that the above-mentioned problems could be solved by blending with a kumaron inden resin at 110 ° C. to 130 ° C., and further studies were carried out to complete the present invention.

That is, the present invention
[1] With respect to 100 parts by mass of a rubber component composed of styrene-butadiene rubber and butadiene rubber, at least 90% by mass, preferably at least 95% by mass or more, more preferably 100% by mass of the rubber component.
A rubber composition comprising at least 5 parts by mass of liquid styrene-butadiene rubber and a Kumaron indene resin having a softening point of 110 ° C. to 130 ° C.
The blending amount of the butadiene rubber is 2.0 to 6.0 parts by mass, preferably 2.5 to 5.5 parts by mass, and more preferably 3.0 to 5.0 parts by mass with respect to 1 part by mass of the liquid styrene-butadiene rubber. The amount of the Kumaron inden resin having a softening point of 110 ° C. to 130 ° C., preferably 115 to 125 ° C. is 2.0 to 6.0 parts by mass, preferably 2.5 parts by mass with respect to 1 part by mass of the liquid styrene-butadiene rubber. A rubber composition of ~ 5.5 parts by mass, more preferably 3.0 to 5.0 parts by mass.
[2] The blending amount of the liquid styrene-butadiene rubber is less than 5 to 10 parts by mass, preferably 6 to 9 parts by mass, and more preferably 6 to 8 parts by mass with respect to 100 parts by mass of the rubber component. The rubber composition described,
[3] The blending amount of the kumaron inden resin is 10 to 35 parts by mass, preferably 15 to 30 parts by mass, more preferably 20 to 27 parts by mass, and further preferably 20 to 25 parts by mass with respect to 100 parts by mass of the rubber component. The rubber composition according to the above [1] or [2], which is a part.
[4] The content of styrene-butadiene rubber in the rubber component is 65 to 90% by mass, preferably 70 to 80% by mass, and the content of butadiene rubber is 10 to 35% by mass, preferably 120 to 30% by mass. The rubber composition according to any one of the above [1] to [3].
[5] The rubber according to any one of the above [1] to [4], further containing 30 to less than 50 parts by mass of carbon black, preferably 35 to 48 parts by mass, and more preferably 40 to 45 parts by mass. Composition,
[6] The rubber composition according to any one of the above [1] to [5], further containing 40 to 60 parts by mass of silica, preferably 45 to 58 parts by mass, and more preferably 50 to 55 parts by mass. ,
[7] A tire tread prepared by using the rubber composition according to any one of the above [1] to [6].
[8] Pneumatic tires having the tire tread according to [7] above.
Regarding.

According to the present invention, it is possible to provide a rubber composition having improved low temperature embrittlement resistance and grip performance in a well-balanced manner. In the present invention, the low temperature embrittlement resistance is synonymous with the low temperature crack resistance.

Hereinafter, "Kumaron inden having at least 5 parts by mass of liquid styrene-butadiene rubber and a softening point of 110 ° C. to 130 ° C. with respect to 100 parts by mass of a rubber component in which at least 90% by mass of the rubber component is styrene-butadiene rubber and butadiene rubber. A rubber composition containing a resin, wherein the amount of butadiene rubber is 2.0 to 6.0 parts by mass with respect to 1 part by mass of liquid styrene-butadiene rubber, and the softening point is 110 ° C to 130 ° C. A rubber composition in which the blending amount of the malon inden resin is 2.0 to 6.0 parts by mass with respect to 1 part by mass of the liquid styrene-butadiene rubber "will be described. With such a configuration, a rubber composition having improved low temperature embrittlement resistance and grip performance in a well-balanced manner is provided.

[Styrene butadiene rubber]
The styrene-butadiene rubber (SBR) is not particularly limited, and examples thereof include emulsion polymerization SBR (E-SBR) and solution polymerization SBR (S-SBR), regardless of whether they are oil-expanded or not. Good. Of these, oil-extended and high-molecular-weight SBR is preferable from the viewpoint of grip performance. In addition, end-modified S-SBR having enhanced interaction with the filler and main chain-modified S-SBR can also be used. One type of these SBRs may be used, or two or more types may be used in combination.

From the viewpoint of grip performance, the styrene content of SBR is preferably 12% by mass or more, more preferably 20% by mass or more, further preferably 25% by mass or more, and particularly preferably 30% by mass or more. On the other hand, 60% by mass or less is preferable, and 50% by mass or less is more preferable. The styrene content of SBR can be measured by ^{1 1} H-NMR.

The vinyl content of SBR is preferably 10 mol% or more, more preferably 15 mol% or more, from the viewpoint of hardness (Hs) and grip performance of the rubber composition. Further, from the viewpoint of grip performance, EB (durability), and wear resistance performance, 90 mol% or less is preferable, 80 mol% or less is more preferable, 70 mol% or less is further preferable, and 60 mol% or less is particularly preferable. The vinyl content of SBR (1,2-bonded butadiene unit amount) can be measured by infrared absorption spectrum analysis.

The SBR also preferably has a glass transition temperature (Tg) of −70 ° C. or higher, more preferably −40 ° C. or higher. The Tg is preferably 10 ° C. or lower, and more preferably 5 ° C. or lower from the viewpoint of preventing embrittlement cracks in the temperate winter season. The glass transition temperature of SBR is measured by differential scanning calorimetry (DSC) under the condition of a heating rate of 10 ° C./min according to JIS K 7121.

The weight average molecular weight (Mw) of SBR is preferably 100,000 or more, more preferably 200,000 or more, from the viewpoint of grip performance and the like. Further, Mw is preferably 2 million or less, more preferably 1 million or less, from the viewpoint of cross-linking uniformity and the like. Mw is based on the value measured by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Toso Co., Ltd., detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M manufactured by Toso Co., Ltd.). In addition, it can be obtained by standard polystyrene conversion.

The content of SBR in the rubber component is preferably 65% by mass or more, more preferably 70% by mass or more, because sufficient grip performance can be obtained. On the other hand, the content is preferably 90% by mass or less, more preferably 80% by mass or less, from the viewpoint of low temperature crack resistance. When two or more types of SBR are used in combination, the total content of all SBR is defined as the content of SBR in the rubber component of the present invention.

[Butadiene rubber]
The butadiene rubber (BR) is not particularly limited, and for example, a BR having a cis 1,4 bond content of less than 50 mol% (Rare earth BR) and a BR having a cis 1,4 bond content of 90 mol% or more. (Hisys BR), rare earth butadiene rubber synthesized using a rare earth element catalyst (rare earth BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (Hisis modified BR, rosis modified BR) ) Etc. can be used. Among them, it is preferable to use at least one selected from the group consisting of high-cis unmodified BR, high-cis modified BR, low-cis unmodified BR and low-cis-modified BR, and it is more preferable to use high-cis unmodified BR.

Examples of the HISIS BR include BR730 and BR51 manufactured by JSR Corporation, BR1220 manufactured by Zeon Corporation, and BR130B, BR150B and BR710 manufactured by Ube Industries, Ltd. Among the high cis BRs, those having a cis 1,4-bond content of 95 mol% or more are more preferable. These may be used alone or in combination of two or more. By containing HISIS BR, low temperature characteristics and wear resistance can be improved. Examples of the locis BR include BR1250 manufactured by Nippon Zeon Corporation. These may be used alone or in combination of two or more. The cis content of BR (cis 1,4 bond content) can be measured by infrared absorption spectrum analysis.

The modified BR is not particularly limited, but a modified BR having an alkoxyl group as a modifying group in the BR is preferable, and a high-cis modified BR is more preferable.

The blending amount of BR in the rubber composition is 2.0 to 6.0 parts by mass with respect to 1 part by mass of the liquid styrene-butadiene rubber. The blending amount is preferably 2.5 parts by mass or more, more preferably 3.0 parts by mass or more. The blending amount is preferably 5.5 parts by mass or less, more preferably 5.0 parts by mass or less. When the blending amount is in the above range, the low temperature embrittlement resistance tends to be improved.

The content of BR in the rubber component is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. On the other hand, the content is preferably 35% by mass or less, more preferably 30% by mass or less, further preferably 27% by mass or less, and even more preferably 25% by mass or less. When the content is within the above range, the low temperature embrittlement resistance tends to be improved.

[Main rubber components in rubber components]
The total amount of SBR and BR in the rubber component is preferably at least 90% by mass, more preferably at least 95% by mass or more, and most preferably 100% by mass.

[Other rubber components]
The rubber component may contain a rubber component other than SBR and BR, and the rubber component is not particularly limited, and isoprene-based rubber containing natural rubber (NR) and polyisoprene rubber (IR), styrene-isoprene. Examples thereof include diene rubber components such as −butadiene copolymer rubber (SIBR), chloroprene rubber (CR), and acrylonitrile-butadiene copolymer rubber (NBR), and butyl rubber. Of these, natural rubber is preferable. These rubber components may be used alone or in combination of two or more. When other rubber components are used, the content in the rubber components is 10% by mass or less, preferably 5% by mass or less.

[Kumaron Inden Resin]
The kumaron inden resin is a resin containing kumaron, inden, and styrene as monomer components constituting the skeleton (main chain) of the resin. In the present invention, among these, those having a softening point of 110 to 130 ° C. are particularly used. This is to contribute to the improvement of tan δ at a temperature close to the softening point.

The softening point of the resin is 110 ° C. or higher, preferably 115 ° C. or higher, from the viewpoint of improving the high temperature grip performance. The softening point is 130 ° C. or lower, preferably 125 ° C. or lower. The softening point is the temperature at which the sphere has fallen when the softening point defined in JIS K 6220-1: 2001 is measured by a ring-ball type softening point measuring device.

Specific examples of the above resin include Kumaron (manufactured by Nippon Steel Chemical Co., Ltd.), Esclon (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.), Neopolymer (manufactured by JX Nippon Oil & Energy Co., Ltd.) and the like.

The blending amount of the resin in the rubber composition is 2.0 to 6.0 parts by mass with respect to 1 part by mass of the liquid styrene-butadiene rubber. The blending amount is preferably 2.5 parts by mass or more, more preferably 3.0 parts by mass or more. The blending amount is preferably 5.5 parts by mass or less, more preferably 5.0 parts by mass or less. When the blending amount is in the above range, it tends to contribute to the improvement of grip performance at a temperature close to the softening point.

The amount of the resin to be blended in the rubber composition is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and further preferably 20 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 35 parts by mass or less, more preferably 30 parts by mass or less, still more preferably 27 parts by mass or less, still more preferably 25 parts by mass or less. When the blending amount is within the above range, the high temperature grip performance tends to be improved.

[Liquid styrene-butadiene rubber]
Liquid styrene-butadiene rubber (liquid SBR) is styrene-butadiene rubber in a liquid state at room temperature (25 ° C.).

The weight average molecular weight (Mw) of the liquid SBR is preferably 1.0 × 10 ³ or more, and more preferably 3.0 × 10 ³ or more. By Mw of liquid SBR is 1.0 × 10 ³ or more, to prevent the wear resistance, a decrease in fracture properties tend to be secured sufficient durability. Also, Mw of the liquid SBR is preferably 2.0 × 10 ⁵ or less, more preferably 1.5 × 10 ⁴ or less. Mw of liquid SBR is, by 2.0 × at 10 ⁵ or less, too high viscosity of the polymerization solution, the productivity tends to be prevented from deteriorating. The Mw of the liquid SBR in the present specification is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

The content of the liquid SBR with respect to 100 parts by mass of the rubber component is less than 5 to 10 parts by mass from the viewpoint of improving low temperature crack resistance and the like, but is preferably 6 parts by mass or more. The content of the liquid SBR is preferably 9 parts by mass or less, more preferably 8 parts by mass or less.

The vinyl content of the liquid SBR is preferably 10 mol% or more, more preferably 20 mol% or more, still more preferably 35 mol% or more. When the vinyl content is 10 mol% or more, sufficient grip performance tends to be obtained. The vinyl content is preferably 90 mol% or less, more preferably 75 mol% or less, still more preferably 55 mol% or less. When the vinyl content is 90 mol% or less, deterioration of wear resistance tends to be suppressed. The vinyl content of the liquid SBR can be measured by infrared absorption spectrum analysis. The styrene content of the liquid SBR is 30% by mass or less, preferably 27% by mass or less. When the styrene content is 30% by mass or less, the decrease in heat generation rate under low temperature conditions tends to be suppressed. The styrene content of the liquid SBR is preferably 20% by mass or more, and more preferably 23% by mass or more. When the styrene content is 20% by mass or more, sufficient grip performance tends to be obtained. The styrene content of the liquid SBR is calculated by ^{1 1} H-NMR measurement.

[filler]
In addition to the above-mentioned components, a filler can be further added to the rubber composition. The filler is not particularly limited, and those used in this field such as carbon black and silica can be used in the same manner.

(Carbon black)
The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 100 m ² / g or more, more preferably 120 m ² / g or more, and further preferably 130 m ² / g or more from the viewpoint of grip performance and wear resistance performance. is there. Further, N ₂ SA is preferably 300 m ² / g or less, more preferably 200 m ² / g or less, still more preferably 160 m ² / g or less, from the viewpoint of ensuring good filler dispersibility. The carbon black N ₂ SA is measured by the BET method in accordance with JIS K 6217-2: 2001.

The content of carbon black is preferably 30 parts by mass or more, more preferably 35 parts by mass or more, still more preferably 40 parts by mass or more, with respect to 100 parts by mass of the rubber component, from the viewpoint of grip performance, wear resistance, and the like. is there. The content is preferably less than 50 parts by mass, more preferably 48 parts by mass or less, and further preferably 45 parts by mass or less.

(silica)
The BET specific surface area of silica is preferably 70 m ² / g or more, more preferably 80 m ² / g or more, and further preferably 90 m ² / g or more from the viewpoint of grip performance, wear resistance performance and the like. The BET specific surface area is preferably 300 m ² / g or less, more preferably 280 m ² / g or less, and further preferably 250 m ² / g or less. The N ₂ SA of silica in the present specification is a value measured by the BET method according to ASTM D3037-81.

When silica is contained, the content of the rubber component with respect to 100 parts by mass is preferably 40 parts by mass or more, more preferably 45 parts by mass or more, and further preferably 50 parts by mass or more from the viewpoint of grip performance. The content is preferably 60 parts by mass or less, more preferably 58 parts by mass or less, and further preferably 55 parts by mass or less.

(Silane coupling agent)
When silica is blended, it is preferable to use it in combination with a silane coupling agent. As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry, for example, bis (3-triethoxysilylpropyl) disulfide and bis (3-triethoxy). Cyrilpropyl) Tetrasulfide and other sulfides, 3-mercaptopropyltrimethoxysilane, Momentive's NXT-Z100, NXT-Z45, NXT and other mercaptos (silane coupling agents having a mercapto group), vinyltriethoxysilane Vinyl type such as 3-aminopropyltriethoxysilane, amino type such as γ-glycidoxypropyltriethoxysilane, nitro type such as 3-nitropropyltrimethoxysilane, 3-chloropropyltrimethoxysilane Such as chloro system can be mentioned. These may be used alone or in combination of two or more.

When a silane coupling agent is contained, the content with respect to 100 parts by mass of silica is 4.0 parts by mass or more because an effect of improving sufficient filler dispersibility and an effect of reducing viscosity can be obtained. It is preferably 6.0 parts by mass or more, and more preferably 6.0 parts by mass or more. Further, the content of the silane coupling agent is preferably 12 parts by mass or less, preferably 10 parts by mass, for the reason of preventing the reinforcing property from being lowered due to insufficient coupling effect and silica dispersion effect. The following is more preferable.

(Other compounding agents)
In addition to the above components, the rubber composition is a compounding agent generally used in the production of the rubber composition, for example, oil (process oil, etc.), zinc oxide, stearic acid, antiaging agent, wax, vulcanizing agent. (Sulfur, etc.), vulcanization accelerator, etc. can be appropriately contained.

The rubber composition of the present invention can be produced by a general method. For example, in a known kneader used in the general rubber industry such as a Banbury mixer, a kneader, and an open roll, among the above-mentioned components, components other than vulcanization chemicals such as a vulcanizing agent and a vulcanization accelerator are used. After kneading, a vulcanizing chemical is added thereto, the mixture is further kneaded, and then vulcanization is performed.

The rubber composition of the present invention can be used not only for tire members such as tire treads, carcasses, sidewalls and beads, but also for anti-vibration rubbers, belts, hoses, other rubber industrial products and the like. In particular, since it is excellent in grip performance and low temperature embrittlement resistance, it is preferable to use a pneumatic tire having a tire tread composed of the rubber composition of the present invention, and more preferably a studless tire.

A pneumatic tire using the rubber composition of the present invention can be produced by a usual method using the rubber composition. That is, the rubber composition in which the above-mentioned compounding agent is blended with the rubber component as necessary is extruded according to the shape of a tread or the like, and is bonded together with other tire members on a tire molding machine. An unvulcanized tire is formed by molding by a method, and the tire can be manufactured by heating and pressurizing the unvulcanized tire in a vulcanizer.

Although not intended to be bound by theory, in the present invention, it is considered that the reason why the low temperature embrittlement resistance (low temperature crack resistance) and the grip performance can be improved in a well-balanced manner is due to the following mechanism. Be done.

That is, in the rubber composition, the BR phase is softer than the SBR phase in the low temperature region and can absorb the strain at the time of deformation. Therefore, by adding this, the low temperature embrittlement resistance is improved. On the other hand, the BR phase has a smaller hysteresis loss (tan δ) than the SBR phase, and the grip performance is lowered.

On the other hand, the Kumaron indene resin having a softening point of 110 to 130 ° C. contributes to the improvement of tan δ at a temperature close to the softening point, and thus improves the grip performance in such a temperature range. However, since they have styrene groups with each other, the compatibility with SBR becomes high, and as a result, there is a concern that the hardness of the SBR phase increases at a temperature lower than the softening point of the resin.

This concern is considered to be resolved by blending liquid SBR. Since liquid SBR has high compatibility with SBR as a rubber component, the SBR phase can be softened and the difference in rigidity between the SBR phase and the BR phase can be reduced. Further, the liquid SBR is considered to contribute to the grip performance (increase in tan δ) in a low temperature range. In addition to increasing the adhesive friction due to the partial blooming of the liquid SBR on the tire surface, the liquid SBR dissolves unevenly in the SBR phase, softening the SBR phase, and as a result, the difference in rigidity between the SBR phase and the BR phase becomes smaller. , Increases the distortion of the SBR phase from a low temperature range and contributes to the improvement of grip.

Although the present invention will be specifically described based on Examples, the present invention is not construed as being limited to these.

Various chemicals used in Examples and Comparative Examples will be described.
Styrene-butadiene rubber (SBR): NS522 manufactured by Nippon Zeon Corporation (styrene content: 39% by mass, containing 37.5 parts by mass of oil spread oil with respect to 100 parts by mass of rubber solid content)
Butadiene rubber (BR): Ube Industries, Ltd. of UBEPOL BR150B (cis content: 97 _{mol%, ML 1 + 4 (100} ℃): 40, Mw: 4.4 × 10 5, Mw / Mn: 3.3 )
Carbon black: SAF class carbon manufactured by Tokai Carbon Co., Ltd., Seest 9H (N ₂ SA: 142m ² / g)
Silica: ULTRASIL VN3 (N ₂ SA: 175m ² / g) manufactured by Evonik Degussa
Silane coupling agent: Si266 manufactured by Evonik Japan Co., Ltd. [bis (3-triethoxysilylpropyl) disulfide]
Kumaron Inden Resin 1: V-120 manufactured by Nikko Kagaku Co., Ltd. (softening point: 120 ° C)
Kumaron Inden Resin 2: G-90 manufactured by Nikko Kagaku Co., Ltd. (softening point: 100 ° C)
Kumaron Inden Resin 3: Nisseki Neopolymer 140 manufactured by JX Nisseki Energy Co., Ltd. (softening point: 140 ° C)
Liquid styrene-butadiene rubber (liquid SBR): RICON100 (Mw: 5000) manufactured by Sartmer.
Wax: Ozoace wax anti-aging agent manufactured by Nippon Seiro Co., Ltd. 1: Antigen 6C (N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Anti-aging agent 2: Nocrack RD (Poly (2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Kagaku Co., Ltd.
Oil: Process oil A / O mixed sulfur manufactured by Sankyo Yuka Kogyo Co., Ltd .: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd. (1): Noxeller CZ manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd. CBS, N-cyclohexyl-2-benzothiazil sulfenamide)
Vulcanization accelerator (2): Noxeller D (DPG, 1,3-diphenylguanidine) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

Examples and Comparative Examples According to the formulation shown in Table 1, chemicals other than sulfur and vulcanization accelerator were kneaded at a discharge temperature of 160 ° C. for 5 minutes using a 1.7 L sealed Bunbury mixer to prepare the kneaded product. Obtained. Next, using a twin-screw open roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded for 4 minutes until the temperature reached 105 ° C. to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press-vulcanized at 170 ° C. for 12 minutes to prepare a test rubber composition.

The obtained unvulcanized rubber composition is molded into a tread shape, bonded together with other tire members on a tire molding machine by adjusting the fiber orientation angle, and press-vulcanized for 12 minutes under the condition of 170 ° C. , A test tire (two-wheel rear tire: 180 / 55ZR17) was obtained.

The obtained unvulcanized rubber composition, test rubber composition and test tire were evaluated as follows. The results are shown in Table 1.

<Grip performance>
The above test tires were mounted on a two-wheeled vehicle (commercial motorcycle), and the driver sensually evaluated the straight traction on a dry asphalt road surface by traveling several laps on a competition paved road circuit (1 lap 6 km). The evaluation results were indexed by the following formula.
Grip performance index = (evaluation of each formulation) / (evaluation of standard comparison example) x 100

<Low temperature embrittlement resistance>
The embrittlement temperature of each rubber composition was measured according to the low temperature impact embrittlement test method described in JIS K 6301. The lower the embrittlement temperature, the better the crack resistance at low temperatures. The evaluation results were indexed by the following formula.
Low temperature embrittlement performance index = (embrittlement temperature of standard comparative example + 273) / (embrittlement temperature of each formulation +
273) x 100

According to the present invention, a rubber composition having improved low temperature embrittlement resistance and grip performance in a well-balanced manner, a tire tread produced by using the rubber composition, and a pneumatic tire having the tire tread are provided. Can be done.

Claims (8)

With respect to 100 parts by mass of the rubber component in which at least 90% by mass of the rubber component is styrene-butadiene rubber and butadiene rubber.
A rubber composition comprising at least 5 parts by mass of liquid styrene-butadiene rubber and a Kumaron indene resin having a softening point of 110 ° C. to 130 ° C.
The blending amount of butadiene rubber is 2.0 to 6.0 parts by mass with respect to 1 part by mass of liquid styrene butadiene rubber, and the blending amount of Kumaron inden resin having a softening point of 110 ° C to 130 ° C is 1 mass of liquid styrene butadiene rubber. A rubber composition that is 2.0 to 6.0 parts by mass with respect to parts. The rubber composition according to claim 1, wherein the amount of the liquid styrene-butadiene rubber blended is less than 5 to 10 parts by mass with respect to 100 parts by mass of the rubber component. The rubber composition according to claim 1 or 2, wherein the amount of the kumaron inden resin is 10 to 35 parts by mass with respect to 100 parts by mass of the rubber component. The rubber composition according to any one of claims 1 to 3, wherein the content of styrene-butadiene rubber in the rubber component is 65 to 90% by mass, and the content of butadiene rubber is 10 to 35% by mass. The rubber composition according to any one of claims 1 to 4, further comprising 30 to 50 parts by mass of carbon black. The rubber composition according to any one of claims 1 to 5, further comprising 40 to 60 parts by mass of silica. A tire tread produced by using the rubber composition according to any one of claims 1 to 6. A pneumatic tire having the tire tread according to claim 7.