JP2015221883A - Rubber composition and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition that meets a request for improved fuel efficiency, prevents embrittlement while maintaining high grip performance, and has excellent wear resistance, and a pneumatic tire having a tread comprising the rubber composition.SOLUTION: A rubber composition comprises, based on 100 pts. mass of a rubber component comprising a modified styrene-butadiene rubber 87-95 mass% and liquid butadiene rubber 5-13 mass%, 50-80 pts. mass of silica.

Description

  The present invention relates to a rubber composition comprising a predetermined modified styrene butadiene rubber, liquid butadiene rubber and silica, and a pneumatic tire having a tread comprising the rubber composition.

  In recent years, demand for lower fuel consumption in passenger cars has increased, and such demand has reached even high-performance vehicles. In a high-performance vehicle, in order to improve grip performance, for example, a solution-polymerized styrene butadiene rubber (S-SBR) having a high glass transition temperature (Tg) is used, and a combination that increases the amount of silica is used.

  However, the use of a high Tg polymer raises the problem that the embrittlement temperature increases and cracks tend to occur in low temperature regions. As a technique for preventing cracks, for example, there is a technique using liquid butadiene (Patent Document 1).

  On the other hand, liquid butadiene has a problem that the grip performance is lowered.

JP 2003-12860 A

  The present invention relates to a rubber composition that responds to demands for lower fuel consumption, prevents brittleness while maintaining high grip performance, and also has excellent wear resistance, and an air having a tread made of the rubber composition An object is to provide a tire entering.

  As a result of intensive studies, the present inventor has found that the above-mentioned problems can be solved by blending silica into a predetermined modified styrene butadiene rubber and liquid butadiene rubber, and further studies are completed to complete the present invention. did.

That is, the present invention relates to 100 parts by mass of a rubber component comprising 87 to 95% by mass of a modified styrene butadiene rubber and 5 to 13% by mass of a liquid butadiene rubber.
The present invention relates to a rubber composition comprising 50 to 80 parts by mass of silica.

  In the rubber composition, the Tan δ peak temperature of the modified styrene butadiene rubber is preferably −15 to −5 ° C.

  In the rubber composition, it is preferable that the modified styrene butadiene rubber is a solution-polymerized styrene butadiene rubber having its ends modified with amino groups and / or alkoxysilyl groups.

  In the rubber composition, the weight average molecular weight of the liquid butadiene rubber is preferably 3000 to 40000.

  The rubber composition is preferably a styrene butadiene rubber modified with a liquid butadiene rubber.

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

  According to the present invention, a rubber composition that prevents brittleness while maintaining high grip performance while meeting demands for low fuel consumption, and also has excellent wear resistance, and a tread composed of the rubber composition are provided. A pneumatic tire having the same can be obtained.

  Hereinafter, the configuration of the present invention will be described in detail.

<Rubber component>
(Modified styrene butadiene rubber)
In the present invention, the modified styrene butadiene rubber (SBR) is a copolymer of styrene and butadiene, and is formed by an amino group (primary amino group, secondary amino group and tertiary amino group) by a conventional method. All of which are treated with an alkoxysilyl group or a modified group such as a combination of an alkoxysilyl group and an amino group. These modifying groups may be bonded to any of the polymerization initiation terminal, polymerization termination terminal, polymer main chain, and side chain, but from the point that energy loss can be suppressed from the polymer terminal to improve the hysteresis loss characteristics. It is preferably introduced at the polymerization initiation terminal or the polymerization termination terminal.

  Here, the SBR is not particularly limited, and both emulsion polymerization SBR (E-SBR) and solution polymerization SBR (S-SBR) can be preferably used, but both rolling resistance and wet grip properties can be achieved. From the viewpoint, S-SBR is preferable.

  The styrene content in SBR is preferably 20% by mass or more, and more preferably 25% by mass or more. When the styrene content is less than 20% by mass, the grip tends to decrease. Moreover, it is preferable that the styrene content rate of SBR is 50 mass% or less, and it is more preferable that it is 45 mass% or less. When the styrene content exceeds 50% by mass, Tg increases, and the low-temperature characteristics and wear tend to deteriorate. Here, the styrene content is a value measured by PGC (gas chromatography).

  The vinyl content in SBR is preferably 18% or more, and more preferably 20% or more. When the vinyl content is less than 18%, the grip performance (dry, wet) tends to decrease. Further, the vinyl content of SBR is preferably 55% by mass or less, and more preferably 50% by mass or less. When the vinyl content exceeds 50% by mass, Tg tends to be high, and the low temperature characteristics and wear resistance tend to deteriorate. Here, the vinyl content is a value measured by PGC (gas chromatography).

  The weight average molecular weight (Mw) of SBR is preferably 200,000 or more, and more preferably 300,000 or more. When Mw is less than 200,000, the wear resistance tends to deteriorate. The Mw of SBR is preferably 1.2 million or less, and more preferably 1 million or less. When Mw exceeds 1,200,000, the workability tends to deteriorate. Here, Mw is a value obtained by measurement using a gel permeation chromatograph (GPC) and conversion with standard polystyrene.

  The Tan δ peak temperature of SBR is preferably −15 ° C. or higher. When it is less than -15 ° C, grip performance tends to be lowered. On the other hand, the temperature is preferably −5 ° C. or lower. If it exceeds -5 ° C, the embrittlement temperature tends to be high and low temperature cracks tend to occur. Here, the Tan δ peak temperature is a value measured by a viscoelastic spectrometer (for example, a viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho Co., Ltd.).

  As the modified SBR in the present invention, in particular, the polymerization terminal (active terminal) of S-SBR is modified with a compound represented by the following formula (1) (modified S-SBR (JP 2010-111753 A). The modified SBR)) described is preferred. In this case, it is easy to control the molecular weight of the polymer, and there are advantages that the low molecular weight component that increases tan δ can be reduced. In addition, the bond between the silica and the polymer chain is strengthened, and the rolling resistance characteristics and wear resistance are further improved. it can.

（式中、Ｒ¹、Ｒ²およびＲ³は、同一若しくは異なって、アルキル基、アルコキシ基、シリルオキシ基、アセタール基、カルボキシル基（−ＣＯＯＨ）、メルカプト基（−ＳＨ）またはこれらの誘導体を表す。Ｒ⁴およびＲ⁵は、同一若しくは異なって、水素原子またはアルキル基を表す。ｎは整数を表す。）

Wherein R ¹ , R ² and R ³ are the same or different and each represents an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group (—COOH), a mercapto group (—SH) or a derivative thereof. R ⁴ and R ⁵ are the same or different and each represents a hydrogen atom or an alkyl group, and n represents an integer.)

Examples of the alkyl group or alkoxy group in R ¹ , R ² and R ³ include those having 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, and still more preferably 1 to 4 carbon atoms. Examples of the alkyl group for R ⁴ and R ⁵ include those having 1 to 4 carbon atoms. n is preferably 1 to 5, more preferably 2 to 4, and still more preferably 3.

  Specific examples of the compound represented by the above formula (1) include 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 2-dimethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 3 -Dimethylaminopropyltrimethoxysilane etc. are mentioned. These may be used alone or in combination of two or more.

  Examples of the method for modifying the styrene butadiene rubber with the compound (modifier) represented by the above formula (1) are described in JP-B-6-53768, JP-B-6-57767, JP-T2003-514078, and the like. A conventionally known method such as a known method can be used. For example, a styrene butadiene rubber and a modifier may be brought into contact with each other. After a styrene butadiene rubber is synthesized by anionic polymerization, a predetermined amount of a modifier is added to the polymer rubber solution, and a polymerization terminal (active activity of the styrene butadiene rubber is activated. And a method in which a modifier is added to the styrene-butadiene rubber solution and reacted.

  In the present invention, the content of the modified SBR in the rubber component is 100% by mass of the rubber component, preferably 87% by mass or more, more preferably 88% by mass or more, more preferably 89% by mass or more, and further preferably 90% by mass. % Or more. When it is less than 87% by mass, grip performance tends to be lowered. The SBR content is preferably 95% by mass or less, more preferably 94% by mass or less, and still more preferably 93% by mass or less. If it exceeds 95% by mass, the embrittlement temperature tends to be high and low temperature cracks tend to occur.

(Liquid butadiene rubber)
In the present invention, liquid butadiene rubber (BR) refers to butadiene rubber that is in a liquid state at room temperature (25 ° C.). Examples of such a liquid BR include RICON 130 and RICON 150. Liquid BR may be used independently and may use 2 or more types together.

  The weight average molecular weight (Mw) of the liquid BR is preferably 3000 or more, more preferably 5000 or more. When Mw is less than 3000, the rubber composition becomes hard due to the effect of the content decreasing with time, and the grip performance tends to decrease. On the other hand, Mw is preferably 40000 or less, more preferably 30000 or less. When Mw exceeds 40,000, grip performance tends to decrease. The weight average molecular weight (Mw) of liquid BR is gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corporation), detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation. ) Based on standard polystyrene conversion.

  The content of liquid BR in the rubber component is preferably 5% by mass or more, more preferably 6% by mass or more, and further preferably 7% by mass or more. If it is less than 5% by mass, the embrittlement temperature becomes high and low temperature cracks tend to occur. On the other hand, the content is preferably 13% by mass or less, more preferably 12% by mass or less, more preferably 11% by mass or less, and still more preferably 10% by mass or less. If it exceeds 13% by mass, grip performance tends to be lowered.

(Liquid BR extension modified SBR)
In the present invention, the rubber component is preferably composed of the above-described modified SBR and liquid BR. In this case, it is preferable that the modified SBR is previously extended by liquid BR. The extension provides the advantage of little change over time. The stretching can be performed by a conventional method, for example, by adding and preparing S-SBR.

(Other rubber components)
In the present invention, the rubber component may be added with other rubber components in addition to the above-described modified SBR and liquid BR. Examples of such rubber components include natural rubber (NR) and isoprene rubber (IR). Butadiene rubber (BR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), butyl rubber (IIR) and the like. These rubber components may be used alone or in combination of two or more. Among these, NR and BR are preferable because grip performance and wear resistance can be obtained in a well-balanced manner.

<Filler>
Examples of the filler include fillers usually used in this field such as silica and carbon black.

(silica)
As the silica, any of those usually used in this field can be suitably used. For example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrous silica), etc. Can be mentioned. Of these, hydrous silica is preferred because it has many silanol groups. Specific examples of silica that can be used in the present invention include Ultrasil VN3, 115GR, 1115MP, 1165MP, and 165GR. One or two or more types of silica can be used.

N ₂ SA of silica is preferably 100 m ² / g or more, more preferably 120 m ² / g or more. If it is less than 100 m ² / g, the wet grip performance tends to decrease. On the other hand, N ₂ SA is preferably 200 m ² / g or less, more preferably 180 m ² / g or less. If it exceeds 200 m ² / g, the workability and dispersibility tend to be impaired. N ₂ SA of silica is a value measured by the BET method according to ASTM D3037-81.

  The compounding quantity of a silica is 50 mass parts-80 mass parts with respect to 100 mass parts of rubber components. If the amount is less than 50 parts by mass, the grip performance tends to decrease, and if it exceeds 80 parts by mass, the fuel efficiency tends to deteriorate.

(Silane coupling agent)
The rubber composition of the present invention preferably contains a silane coupling agent. As the silane coupling agent, a conventionally known silane coupling agent can be used. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4- Triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilylbutyl) tetrasulfide, bis (3-triethoxy Silylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) trisulfide, bis (2-trimethoxysilylethyl) ) Sulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4-triethoxysilylbutyl) disulfide, bis (3 -Trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxy Ethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N, N-dimethylthioca Sulfide systems such as vamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-trimethoxysilylpropyl methacrylate monosulfide; 3-mercaptopropyltrimethoxysilane Mercapto type such as 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane; Vinyl type such as vinyltriethoxysilane, vinyltrimethoxysilane; 3-aminopropyltriethoxysilane 3-aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltriethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane Amino systems such as orchid; glycidoxy systems such as γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane Nitro compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, 2-chloroethyltri Chloro type such as ethoxysilane; and the like. These silane coupling agents may be used alone or in combination of two or more. Of these, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide and the like are preferable from the viewpoint of good processability.

  When the silane coupling agent is contained, the blending amount is preferably 2.5 parts by mass or more, more preferably 3 parts by mass or more, and further preferably 3.5 parts by mass with respect to 100 parts by mass of silica. That's it. When the content of the silane coupling agent is less than 2.5 parts by mass, effects such as improvement of dispersibility tend not to be obtained sufficiently. Moreover, it is preferable that it is 10 mass parts or less, and, as for content of a silane coupling agent, it is more preferable that it is 8 mass parts or less. When the compounding amount of the silane coupling agent exceeds 10 parts by mass, a sufficient coupling effect cannot be obtained and the reinforcing property tends to be lowered.

(Carbon black)
As carbon black, those generally used in tire production can be used, for example, SAF, ISAF, HAF, FF, FEF, GPF, etc., and these carbon blacks can be used alone, Two or more kinds may be used in combination. The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is 80 m ² / g or more, preferably 115 m ² / g or more. If N ₂ SA is less than 80 m ² / g, the wear properties tend to be reduced. On the other hand, N ₂ SA of carbon black is 200 m ² / g or less, and preferably 185 m ² / g or less. When N ₂ SA of carbon black is larger than 200 m ² / g, processability and dispersion tend to deteriorate. N ₂ SA of carbon black is determined in accordance with JIS K 6217-2: 2001.

  The compounding amount of carbon black is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and further preferably 9 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 5 parts by mass, the wear performance tends to deteriorate. On the other hand, the amount is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 35 parts by mass or less. When it exceeds 50 mass parts, there exists a tendency for rolling resistance to deteriorate.

  The total blending amount of the filler is preferably 50 parts by mass or more, more preferably 60 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 50 parts by mass, the wear performance tends to deteriorate. On the other hand, the amount is preferably 110 parts by mass or less, more preferably 100 parts by mass or less. If it exceeds 110 parts by mass, the rolling resistance tends to deteriorate.

<Oil>
In the present invention, it is preferable to blend a softener from the viewpoint of grip performance and the like. Although it does not specifically limit as a softening agent, Oils, such as mineral oil, are mentioned. Examples of the oil include process oils such as paraffinic process oil, aroma based process oil, and naphthenic process oil.

  The blending amount of the oil is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and further preferably 13 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 5 parts by mass, the effect of addition may not be obtained. The blending amount of the oil is preferably 25 parts by mass or less, more preferably 22 parts by mass or less. When it exceeds 25 parts by mass, the wear resistance tends to deteriorate.

<Vulcanization accelerator>
Examples of the vulcanization accelerator include sulfenamide-based, thiazole-based, thiuram-based, and guanidine-based vulcanization accelerators. Among them, in the present invention, sulfenamide-based and guanidine-based vulcanization accelerators are preferably used. Can be used.

  Examples of the sulfenamide vulcanization accelerator include N-tert-butyl-2-benzothiazylsulfenamide. Examples of the thiazole vulcanization accelerator include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and the like. Examples of the thiuram vulcanization accelerator include tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), tetrakis (2-ethylhexyl) thiuram disulfide (TOT-N) and the like. Examples of the guanidine vulcanization accelerator include N, N-diphenylguanidine. As a vulcanization accelerator, 1 type (s) or 2 or more types can be used.

  When the vulcanization accelerator is blended, the content of the vulcanization accelerator is preferably 1 part by mass or more, more preferably 2 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, a sufficient vulcanization rate cannot be obtained, and good grip performance and wear resistance tend to be not obtained. On the other hand, the amount is preferably 5 parts by mass or less, more preferably 4 parts by mass or less. If it exceeds 5 parts by mass, blooming may occur and grip performance and wear resistance may be reduced.

  In addition to the above components, the rubber composition of the present invention suitably contains compounding agents conventionally used in the rubber industry, such as zinc oxide, antioxidants, oils, waxes, sulfur, vulcanization accelerators and the like. be able to.

  The rubber composition of the present invention thus obtained responds to demands for low fuel consumption, prevents brittleness while maintaining high grip performance, and further has excellent wear resistance. It can be used for tires for passenger cars. Moreover, it can use suitably especially for a tire tread from these characteristics.

  When used in a tire, the rubber composition of the present invention can be produced as a tire by an ordinary method. That is, if necessary, a mixture containing the above ingredients is kneaded, extruded in accordance with the shape of each member of the tire at an unvulcanized stage, and molded on a tire molding machine by a normal method. Thus, an unvulcanized tire is formed. A tire can be obtained by heating and pressurizing the unvulcanized tire in a vulcanizer, and air can be put into the tire to obtain a pneumatic tire.

In this specification, Mw and Mn are measured using a gel permeation chromatograph (GPC) and converted from standard polystyrene.
The glass transition temperature (Tg) is measured by a differential scanning calorimeter (DSC).
For example, “1-99 mass%” includes values at both ends.

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

  The various chemicals used in the present specification are collectively shown below. Various chemicals were purified according to conventional methods as needed.

<Various chemicals used in the production of rubber composition>
Liquid BR stretch modified S-SBR (1): stretched using 5 mass% of the following liquid BR (1) with respect to 95 mass% of the modified S-SBR (1) described below. Tanδ peak temperature: -5 ° C
Liquid BR stretch-modified S-SBR (2): Stretched using 10% by mass of the following liquid BR (2) with respect to 90% by mass of the following modified S-SBR (2). Tan δ peak temperature: −15 ° C.
Liquid BR stretch-modified S-SBR (3): Stretched using 15% by mass of the following liquid BR (1) with respect to 90% by mass of the following modified S-SBR (2). Tan δ peak temperature: −20 ° C.
Liquid BR (1): molecular weight 30000
Liquid BR (2): molecular weight 5000
Modified S-SBR (1): Tan δ peak temperature: −5 ° C.
Modified S-SBR (2): Tan δ peak temperature: −15 ° C.
BR: Ubepol BR150B manufactured by Ube Industries (Tg: -114 ° C, cis content: 97% by mass)
Oil: JOMO process X140 manufactured by Japan Energy Co., Ltd.
Silica (hydrous silica): Ultrazil VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g)
Silane coupling agent: Si-69 manufactured by Degussa
Carbon Black: Show Black N220 (N ₂ SA: 115 m ² / g) manufactured by Cabot Japan
Anti-aging agent: NOCRACK 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Wax: Sannox wax manufactured by Ouchi Shinko Chemical Co., Ltd. Stearic acid: Zinc stearate manufactured by Nippon Oil & Fats Co., Ltd .: Zinc Hua No. 1 manufactured by Mitsui Kinzoku Mining Co., Ltd. Sulfur: manufactured by Karuizawa Sulfur Co., Ltd. Powder Sulfur Vulcanization Accelerator (TBBS): Noxeller NS (N-tert-butyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator (DPG): Noxeller D (N, N'-diphenylguanidine) manufactured by Ouchi Shinsei Chemical Co., Ltd.

<Manufacture of rubber composition and tire>
In accordance with the formulation shown in Table 1, various chemicals (excluding sulfur and vulcanization accelerator) were kneaded at 160 ° C. for 2 minutes in a 1.7 L Banbury mixer to obtain a kneaded product. To the obtained kneaded product, sulfur and a vulcanization accelerator were added and kneaded at 80 ° C. for 3 minutes using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was molded into a tire tread shape, bonded together with other tire members on a tire molding machine, and press vulcanized at 183 ° C. for 10 minutes to obtain a test tire ( Tire size: 205 / 65R15). In addition, when obtaining the vulcanized rubber composition used for various tests, it obtained by press vulcanizing the unvulcanized rubber composition molded into a predetermined shape under the same conditions as described above.

(Rolling resistance index)
About the vulcanized rubber composition (strip shape, 4 mm × 40 mm × 2 mm) obtained above, using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), temperature 70 ° C., initial strain 10%, dynamic strain 2 Tan δ was measured under the condition of%, and the tan δ of Comparative Example 1 was taken as 100, and the result was expressed as an index by the following formula. The larger the index, the better the rolling resistance characteristics.

(Rolling resistance index) = (tan δ of Comparative Example 1) ÷ (tan δ of each formulation) × 100

(Dry grip performance index)
The test tire was attached to a traction test vehicle, and the vehicle was driven on a dry asphalt road test course. At this time, the vehicle was run at 40 km / h, the maximum friction coefficient (Maxμ) from when the brake was applied to when the vehicle was stopped was measured, and an index was displayed according to the following formula. The larger the index, the better the dry grip performance.

(Dry grip performance index) = (Maxμ of each formulation) / (Maxμ of Comparative Example 1) × 100

(Ebrittlement test)
The vulcanized rubber composition obtained above (shape / size: strip / 4 mm × 40 mm × 2 mm) was placed in a refrigerator at −45 ° C. for one day, and a rolling load test was performed. After the test, each sample was examined for chipping.
No chipping: ○
Chips with defects: ×

  The results are shown in Table 1.

  According to the present invention, a rubber composition that prevents brittleness while maintaining high grip performance while meeting demands for low fuel consumption, and also has excellent wear resistance, and a tread composed of the rubber composition are provided. The pneumatic tire which has can be provided.

Claims (6)

With respect to 100 parts by mass of a rubber component comprising 87 to 95% by mass of a modified styrene butadiene rubber and 5 to 13% by mass of a liquid butadiene rubber,
A rubber composition comprising 50 to 80 parts by mass of silica. The rubber composition according to claim 1, wherein the modified styrene-butadiene rubber has a Tan δ peak temperature of -15 to -5 ° C. The rubber composition according to claim 1 or 2, wherein the modified styrene-butadiene rubber is a solution-polymerized styrene-butadiene rubber whose terminal is modified with an amino group and / or an alkoxysilyl group. The rubber composition according to any one of claims 1 to 3, wherein the liquid butadiene rubber has a weight average molecular weight of 3000 to 40000. The rubber composition according to any one of claims 1 to 4, wherein the modified styrene butadiene rubber is stretched by a liquid butadiene rubber. The pneumatic tire which has a tread which consists of a rubber composition of any one of Claims 1-5.