JP5485650B2 - Rubber composition for tread and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition for a tread and a pneumatic tire using the same.

As a technique for improving the wet skid performance of a pneumatic tire, it is generally known to add silica as a filler to a rubber composition. As a technique related to this technique, Patent Document 1 discloses a rubber composition in which two types of silica having different nitrogen adsorption specific surface areas are blended. However, when silica is highly filled, there is room for improvement in that silica is difficult to disperse and wear resistance, fracture strength, and workability tend to deteriorate.

Further, as another method for improving the wet skid performance of a pneumatic tire, Patent Documents 2 and 3 disclose a rubber composition containing a polymer obtained by polymerizing only an aromatic vinyl monomer. ing. However, when the polymer is blended, there is room for improvement in that the wear resistance tends to deteriorate.

JP 2008-101127 A JP 2007-302713 A JP 2007-112994 A

The present invention solves the above-mentioned problems, and provides a rubber composition for a tread in which workability, wet skid performance, fracture resistance, wear resistance, and steering stability are obtained in a well-balanced manner, and an air having a tread produced using the rubber composition. An object is to provide a tire entering.

The present invention relates to a rubber component, an aromatic vinyl polymer having a glass transition temperature of 10 ° C. or less and an aromatic vinyl monomer unit content of 95% by mass or more, a nitrogen adsorption specific surface area of 130 m ² / The silica (1) which is g or less, the silica (2) whose nitrogen adsorption specific surface area is 150 m ² / g or more, and a silane coupling agent are contained, and the aromatics with respect to 100 parts by mass of the rubber component. The content of the vinyl polymer is 2 to 50 parts by mass, the total content of the silica (1) and (2) is 10 to 120 parts by mass, and the total content of the silica (1) and (2) is 100 masses. The rubber composition for a tread in which the content of the silane coupling agent is 2 to 15 parts by mass with respect to parts, and the content of the silica (1) and the content of the silica (2) satisfy the following formula: Related to things.
[Content of silica (1)] × 0.2 ≦ [Content of silica (2)] ≦ [Content of silica (1)] × 6.5

The content of the aromatic vinyl monomer unit in the aromatic vinyl polymer is preferably 100% by mass.

The present invention also relates to a pneumatic tire having a tread produced using the rubber composition.

According to the present invention, the aromatic vinyl polymer having a glass transition temperature of not more than a certain value and the content of the aromatic vinyl monomer unit being not less than a certain value, silica (1) having a low specific surface area, and a high ratio. A rubber composition containing a predetermined amount of silica (2) having a surface area and a silane coupling agent, and a ratio of the content of silica (1) and the content of silica (2) being within a predetermined range. Therefore, by using the rubber composition in a tread, a pneumatic tire can be provided in which workability, wet skid performance, fracture resistance, wear resistance, and steering stability can be obtained in a well-balanced manner.

The rubber composition of the present invention has an aromatic vinyl polymer having a glass transition temperature of not more than a certain level and an aromatic vinyl monomer unit content of not less than a certain value, silica (1) having a low specific surface area, While containing a predetermined amount of each of the high specific surface area silica (2) and the silane coupling agent, the ratio of the content of silica (1) and the content of silica (2) is within a predetermined range. By using silica (1) and (2) together with a predetermined amount of the silane coupling agent, silica is easily dispersed, and wet skid performance, workability and wear resistance can be improved. Moreover, the handling stability, wet skid performance, workability, and fracture strength can be improved by blending the aromatic vinyl polymer. By these actions, workability, wet skid performance, fracture strength, wear resistance, and steering stability can be obtained in a well-balanced manner.

Examples of the rubber component include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), epoxidized natural rubber (ENR), acrylonitrile butadiene rubber (NBR), chloroprene rubber ( CR), butyl rubber (IIR), styrene-isoprene-butadiene copolymer rubber (SIBR), and the like can be used. These may be used alone or in combination of two or more. Of these, SBR and BR are preferable, and it is more preferable to use SBR and BR in combination since sufficient wet skid performance and wear resistance can be secured.
In addition, it does not specifically limit as SBR and BR, A thing common in a tire industry can be used.

The styrene content of SBR is preferably 10% by mass or more, more preferably 15% by mass or more. When the amount is less than 10% by mass, the wet skid performance may not be sufficiently obtained. Further, the styrene content of SBR is preferably 50% by mass or less, more preferably 45% by mass or less. When it exceeds 50 mass%, wear resistance and workability may deteriorate.
In the present specification, the styrene content is calculated by H ¹ -NMR measurement.

The content of SBR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 30% by mass or more, and further preferably 50% by mass or more. When it is less than 10% by mass, there is a high possibility that the wet skid performance cannot be sufficiently obtained. Further, the content of SBR in 100% by mass of the rubber component is preferably 95% by mass or less, more preferably 90% by mass or less, and still more preferably 80% by mass or less. If it exceeds 95 mass%, sufficient wear resistance may not be obtained.

The content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and still more preferably 20% by mass or more. If it is less than 5% by mass, sufficient wear resistance may not be obtained. The content of BR in 100% by mass of the rubber component is preferably 70% by mass or less, more preferably 50% by mass or less, and still more preferably 40% by mass or less. When it exceeds 70 mass%, workability may deteriorate.

The total content of SBR and BR in 100% by mass of the rubber component is preferably 40% by mass or more, more preferably 60% by mass or more, still more preferably 80% by mass or more, and most preferably 100% by mass. If it is less than 40% by mass, sufficient wet skid performance or wear resistance may not be obtained.

The rubber composition of the present invention contains an aromatic vinyl polymer. In this specification, the aromatic vinyl polymer refers to those having an aromatic vinyl monomer unit content of 95% by mass or more. The aromatic vinyl polymer is not included in the rubber component.

Examples of the aromatic vinyl monomer (unit) constituting the aromatic vinyl polymer include styrene, α-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, and 4-cyclohexylstyrene. 2,4,6-trimethylstyrene and the like. These may be one type or two or more types. Among them, it is preferable that it is at least one selected from the group consisting of styrene, α-methylstyrene and 1-vinylnaphthalene because it is economical, easy to process, and excellent in wet skid performance. It is more preferable.

The aromatic vinyl polymer may contain components other than the aromatic vinyl monomer unit (ethylene, propylene, butadiene, isoprene, etc.), but it is preferable to reduce the content of the components as much as possible. Olefinic monomers such as ethylene and propylene have poor compatibility with the rubber component, so that if the content of the olefinic monomer unit in the aromatic vinyl polymer is increased, bleeding out tends to occur. Tend. In addition, since diene monomers such as butadiene and isoprene are reduced in hysteresis loss by co-crosslinking with the rubber component, if the content of diene monomer units in the aromatic vinyl polymer is increased, hysteresis is reduced. As the loss decreases, wet skid performance tends to deteriorate. For these reasons, the content of the aromatic vinyl monomer unit in the aromatic vinyl polymer is 95% by mass or more, preferably 97% by mass or more, more preferably 99% by mass or more, and most preferably 100% by mass. %. That is, the aromatic vinyl polymer is preferably a homopolymer of an aromatic vinyl monomer (polystyrene or the like).

The glass transition temperature (Tg) of the aromatic vinyl polymer is preferably −50 ° C. or higher, more preferably −45 ° C. or higher, and further preferably −40 ° C. or higher. When the temperature is lower than −50 ° C., the hysteresis loss of the aromatic vinyl polymer is small, and the effect of improving wet skid performance tends to be small. The Tg of the aromatic vinyl polymer is 10 ° C. or lower, preferably 5 ° C. or lower, more preferably 0 ° C. or lower. If it exceeds 10 ° C, the wear resistance and wet skid performance at low temperatures tend to deteriorate.
In this specification, Tg is a value measured according to JIS-K7121, using an automatic differential scanning calorimeter (DSC-60A) manufactured by Shimadzu Corporation under the condition of a temperature rising rate of 10 ° C./min. is there.

The weight average molecular weight (Mw) of the aromatic vinyl polymer is preferably 300 or more, more preferably 350 or more. If it is less than 300, the wet skid performance improving effect tends to be small. The weight average molecular weight of the aromatic vinyl polymer is preferably 20000 or less, more preferably 15000 or less. When it exceeds 20000, the rolling resistance characteristic tends to deteriorate.
In this specification, the weight average molecular weight is determined by gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corporation), detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ- manufactured by Tosoh Corporation. It is determined by standard polystyrene conversion based on the measured value by M).

The content of the aromatic vinyl polymer is 2 parts by mass or more, preferably 5 parts by mass or more, more preferably 8 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 2 parts by mass, the wet skid performance improving effect tends to be small. Moreover, content of an aromatic vinyl polymer is 50 mass parts or less with respect to 100 mass parts of rubber components, Preferably it is 30 mass parts or less, More preferably, it is 20 mass parts or less. If it exceeds 50 parts by mass, steering stability and wear resistance tend to deteriorate.

The rubber composition of the present invention contains low specific surface area silica (1) and high specific surface area silica (2). Examples of silica (1) and (2) include silica prepared by a dry method (silicic anhydride), silica prepared by a wet method (hydrous silicic acid), etc., and there are many silanol groups on the surface, Silica prepared by a wet method is preferred because it has many reactive sites with the silane coupling agent.

The nitrogen adsorption specific surface area (hereinafter referred to as N ₂ SA) of silica (1) is 130 m ² / g or less, preferably 125 m ² / g or less, more preferably 120 m ² / g or less. When N ₂ SA of silica (1) exceeds 130 m ² / g, the effect obtained by mixing with silica (2) tends to be small. Further, N ₂ SA of silica (1) is preferably 20 m ² / g or more, more preferably 30 m ² / g or more. If N ₂ SA of silica (1) is less than 20 m ² / g, the fracture resistance tends to decrease.
The nitrogen adsorption specific surface area (N ₂ SA) of silica is a value measured by the BET method according to ASTM D3037-81.

Examples of silica having a nitrogen adsorption specific surface area (N ₂ SA) of 130 m ² / g or less include ULTRASIL 360 (N ₂ SA: 50 m ² / g) manufactured by Degussa and ZEOSIL 115GR (N ₂ SA manufactured by Rhodia). 115 m ² / g) and ZEOSIL 1115MP (N ₂ SA: 115 m ² / g) manufactured by Rhodia.

The content of silica (1) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 20 parts by mass or more with respect to 100 parts by mass of the rubber component. When the content of silica (1) is less than 5 parts by mass, the improvement effect by silica (1) may not be sufficiently obtained. The content of silica (1) is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and still more preferably 45 parts by mass or less. When the content of silica (1) exceeds 80 parts by mass, the fracture resistance tends to decrease.

N ₂ SA of silica (2) is 150 m ² / g or more, preferably 160 m ² / g or more, more preferably 170 m ² / g or more. When N ₂ SA of silica (2) is less than 150 m ² / g, the effect obtained by mixing with silica (1) tends to be small. Also, _N 2 SA of the silica (2) is preferably 300 meters ² / g, more preferably at most 240 m ² / g. When N ₂ SA of silica (2) exceeds 300 m ² / g, processability tends to deteriorate.

Examples of the silica having a nitrogen adsorption specific surface area (N ₂ SA) of 150 m ² / g or more include ULTRASIL VN3 (N ₂ SA: 175 m ² / g) manufactured by Degussa and ZEOSIL 1165MP (N ₂ SA: manufactured by Rhodia). 160 m ² / g) and ZEOSIL 1205MP (N ₂ SA: 200 m ² / g) manufactured by Rhodia.

The content of silica (2) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 20 parts by mass or more with respect to 100 parts by mass of the rubber component. When the content of silica (2) is less than 5 parts by mass, the improvement effect by silica (2) may not be sufficiently obtained. Further, the content of silica (2) is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and still more preferably 45 parts by mass or less. When the content of silica (2) exceeds 60 parts by mass, workability tends to deteriorate.

The total content of silica (1) and (2) is 10 parts by mass or more, preferably 30 parts by mass or more, more preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. When the total content of silica (1) and (2) is less than 10 parts by mass, the improvement effect by silica (1) and (2) may not be sufficiently obtained. The total content of silica (1) and (2) is 120 parts by mass or less, preferably 100 parts by mass or less, more preferably 80 parts by mass or less. When the total content of silica (1) and (2) exceeds 120 parts by mass, silica becomes difficult to disperse, and thus workability and wear resistance tend to deteriorate.

The content of silica (1) and the content of silica (2) satisfy the following formula.
[Content of silica (1)] × 0.2 ≦ [Content of silica (2)] ≦ [Content of silica (1)] × 6.5

The content of silica (2) is 0.2 or more times, preferably 0.3 or more times the content of silica (1). When the content of silica (2) is less than the amount obtained by multiplying the content of silica (1) by 0.2, there is a tendency that sufficient fracture resistance is not obtained. The content of silica (2) is not more than 6.5 times, preferably not more than 5.5 times, more preferably not more than 4.0 times the content of silica (1). If the content of silica (2) is more than 6.5 times the content of silica (1), processability and rolling resistance characteristics tend to deteriorate.

The rubber composition of the present invention contains a silane coupling agent. As the silane coupling agent used in the present invention, those commonly used in the tire industry can be used, for example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, Examples thereof include bis (3-triethoxysilylpropyl) disulfide. These silane coupling agents may be used alone or in combination of two or more. Of these, bis (3-triethoxysilylpropyl) tetrasulfide is preferable from the viewpoint of excellent processability.

Content of a silane coupling agent is 2 mass parts or more with respect to 100 mass parts of total content of silica (1) and (2), Preferably it is 4 mass parts or more, More preferably, it is 6 mass parts or more. When the content of the silane coupling agent is less than 2 parts by mass, the wet skid performance improving effect tends to be low. Moreover, content of a silane coupling agent is 15 mass parts or less with respect to 100 mass parts of total content of silica (1) and (2), Preferably it is 12 mass parts or less, More preferably, it is 10 mass parts or less. is there. When content of a silane coupling agent exceeds 15 mass parts, there exists a tendency for the effect corresponding to the increase in cost not to be acquired.

In addition to the above components, the rubber composition of the present invention includes fillers other than silica (carbon black, etc.), oil, tackifiers, antioxidants, antiozonants, antiaging agents, vulcanizing agents, vulcanization accelerators Additives as necessary, such as an agent and a vulcanization accelerator, may be appropriately blended.

The rubber composition of the present invention preferably contains carbon black. Thereby, the reinforcement effect is acquired and abrasion resistance can be improved more. As carbon black, GPF, HAF, FF, ISAF, SAF, etc. can be used, for example.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 40 m ² / g or more, more preferably 45 m ² / g or more. If it is less than 40 m < ² > / g, there exists a tendency for the improvement effect of abrasion resistance to become small. Moreover, the nitrogen adsorption specific surface area of carbon black is preferably 120 m ² / g or less, more preferably 90 m ² / g or less. When it exceeds 120 m ² / g, carbon black is difficult to disperse, and wear resistance and workability tend to decrease.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

The content of carbon black is preferably 5 parts by mass or more, more preferably 15 parts by mass or more, and still more preferably 20 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 improving the wear resistance tends to be small. The content of carbon black is preferably 50 parts by mass or less, more preferably 45 parts by mass or less, and still more preferably 35 parts by mass or less with respect to 100 parts by mass of the rubber component. If it exceeds 50 parts by mass, the workability tends to deteriorate.

The total content of silica and carbon black is preferably 40 parts by mass or more, more preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 40 parts by mass, the rubber hardness tends to be low and the breaking strength tends to be insufficient. The total content is preferably 130 parts by mass or less, more preferably 90 parts by mass or less, and still more preferably 70 parts by mass or less with respect to 100 parts by mass of the rubber component. If it exceeds 130 parts by mass, the heat build-up becomes high and the wear resistance tends to deteriorate.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading each of the above components with a kneader such as a Banbury mixer, a kneader, or an open roll, and then vulcanizing.

The rubber composition of the present invention is used as a tread for a pneumatic tire.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition.
That is, the rubber composition containing the above components is extruded in accordance with the shape of the tread at an unvulcanized stage and molded together with other tire members by a normal method on a tire molding machine. Form a vulcanized tire. The pneumatic tire of the present invention can be manufactured by heating and pressurizing this unvulcanized tire in a vulcanizer.

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

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
SBR: JSR1502 manufactured by JSR Corporation (styrene content: 23.5% by mass)
BR: BR130B manufactured by Ube Industries, Ltd.
Carbon Black: Show Black N351 (N ₂ SA: 69 m ² / g) manufactured by Cabot Japan
Silica (1): ULTRASIL 360 (N ₂ SA: 50 m ² / g) manufactured by Degussa
Silica (2): ZEOSIL 1205MP (N ₂ SA: 200 m ² / g) manufactured by Rhodia
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Aromatic vinyl polymer (1): synthesized in the following Production Example 1 (aromatic vinyl monomer unit: styrene, styrene content: 100% by mass, glass transition temperature: −20 ° C., weight average molecular weight: 830)
Aromatic vinyl polymer (2): synthesized in Production Example 2 below (aromatic vinyl monomer unit: styrene, styrene content: 100% by mass, glass transition temperature: 0 ° C., weight average molecular weight: 1020)
Aromatic vinyl polymer (3): synthesized in the following Production Example 3 (aromatic vinyl monomer unit: 1-vinylnaphthalene, 1-vinylnaphthalene content: 100 mass%, glass transition temperature: 0 ° C., weight average molecular weight : 860)
Aromatic vinyl polymer (4): synthesized in the following Production Example 4 (aromatic vinyl monomer unit: styrene, styrene content: 100 mass%, glass transition temperature: 50 ° C., weight average molecular weight: 3130)
Zinc oxide: Zinc Hana No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Kashiwa Process Oil manufactured by NOF Corporation: Diana Process Oil AH-24 manufactured by Idemitsu Kosan Co., Ltd.
Anti-aging agent: Antigen 6C manufactured by Sumitomo Chemical Co., Ltd.
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator CZ manufactured by Karuizawa Sulfur Co., Ltd .: Noxeller CZ manufactured by Ouchi Shinsei Chemical Co., Ltd.

Production Example 1 (Synthesis of aromatic vinyl polymer (1))
In a 50 ml container thoroughly purged with nitrogen, 35 ml of hexane, 5 ml of styrene and 2.7 ml of a 1.6 mol / l n-butyllithium hexane solution are mixed, stirred at room temperature for 1 hour, and then reacted by adding methanol. The aromatic vinyl polymer (1) was synthesized by stopping.

Production Example 2 (Synthesis of aromatic vinyl polymer (2))
In a 50 ml container thoroughly purged with nitrogen, 35 ml of hexane, 5 ml of styrene, and 3.4 ml of a 1.6 mol / l n-butyllithium hexane solution are mixed, stirred at room temperature for 1 hour, and then reacted by adding methanol. The aromatic vinyl polymer (2) was synthesized by stopping.

Production Example 3 (Synthesis of aromatic vinyl polymer (3))
In a 50 ml container thoroughly purged with nitrogen, 35 ml of hexane, 5 ml of 1-vinylnaphthalene and 2.3 ml of 1.6 mol / l n-butyllithium hexane solution are mixed, stirred for 1 hour at room temperature, and then added with methanol. Then, the reaction was stopped to synthesize an aromatic vinyl polymer (3).

Production Example 4 (Synthesis of aromatic vinyl polymer (4))
In a 50 ml container fully purged with nitrogen, 35 ml of hexane, 5 ml of styrene, and 0.9 ml of a 1.6 mol / l n-butyllithium hexane solution are mixed, stirred at room temperature for 1 hour, and then reacted by adding methanol. The aromatic vinyl polymer (4) was synthesized by stopping.

Examples 1-6 and Comparative Examples 1-9
According to the contents shown in Table 1, materials other than sulfur and a vulcanization accelerator were kneaded at about 150 ° C. for 3 minutes using a 1.7 L Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded at about 80 ° C. for 5 minutes using a biaxial open roll to obtain an unvulcanized rubber composition.
The obtained unvulcanized rubber composition was press vulcanized at 170 ° C. for 18 minutes to obtain a vulcanized rubber sheet.
The obtained unvulcanized rubber composition is rolled into a sheet having a thickness of about 2 mm, processed into a tread shape, bonded to another tire member, molded into a tire, and vulcanized at 170 ° C. for 18 minutes. A test tire (tire size: 195 / 65R15) was obtained.

The following evaluation was performed using the obtained unvulcanized rubber composition, vulcanized rubber sheet, and test tire. Each test result is shown in Table 1.

(Mooney viscosity)
In accordance with JIS K 6300-1 “Unvulcanized rubber—physical properties—Part 1: Determination of viscosity and scorch time using Mooney viscometer”, it was heated by preheating for 1 minute using a Mooney viscosity tester. Under the temperature condition of 130 ° C., the small rotor was rotated, and the Mooney viscosity (ML _{1 +} 4/130 ° C.) of the unvulcanized rubber composition after 4 minutes was measured. The measurement result was set to 100 as the result of Comparative Example 1, and the Mooney viscosity of each formulation was indicated by an index according to the following formula. The larger the index, the lower the viscosity and the better the workability.
(Mooney viscosity index) = (Mooney viscosity of Comparative Example 1) / (Mooney viscosity of each formulation) × 100

(Wet skid performance)
The test tire was mounted on all wheels of a vehicle (domestic FF2000cc), and the braking distance from the point where the brake was applied was measured on a wet asphalt road surface at a speed of 100 km / h. And the braking distance of the comparative example 1 was set to 100, and the wet skid performance of each formulation was displayed as an index by the following formula. The larger the wet skid performance index, the better the wet skid performance.
(Wet skid performance index) = (Brake distance of Comparative Example 1) / (Brake distance of each formulation) × 100

(Destructive strength)
In accordance with JIS-K6251, a tensile test was carried out using No. 3 dumbbell made of the above vulcanized rubber sheet, and the breaking strength (TB) and elongation at break EB (%) were measured. And the rubber strength (TBxEB / 2) of the comparative example 1 was set to 100, and the rubber strength of each compounding was indicated by an index by the following calculation formula. The larger the rubber strength index, the better the fracture strength.
(Rubber Strength Index) = (Rubber Strength of Each Compound) / (Rubber Strength of Comparative Example 1) × 100

(Abrasion resistance)
Using a Lambourne abrasion tester, the Lambourne abrasion amount of the vulcanized rubber sheet was measured under the conditions of a temperature of 20 ° C., a slip rate of 20% and a test time of 2 minutes. Then, the volume loss amount was calculated from the measured amount of Lambourn wear, the volume loss amount of Comparative Example 1 was set to 100, and the volume loss amount of each formulation was displayed as an index according to the following calculation formula. It shows that it is excellent in abrasion resistance, so that a Lambourn abrasion index is large.
(Lambourn wear index) = (volume loss amount of Comparative Example 1) / (volume loss amount of each formulation) × 100

(Maneuvering stability)
The test tire was mounted on all wheels of a vehicle (domestic FF2000cc), and the vehicle was run on the test course. The steering stability was evaluated by sensory evaluation of the driver. At that time, the relative evaluation was performed with 10 points being the perfect score and the steering stability of Comparative Example 1 being 6 points. The larger the value, the better the steering stability.

From Table 1, the glass transition temperature is below a certain level and the content of the aromatic vinyl monomer unit is above a certain level, an aromatic vinyl polymer having a low specific surface area (1), and a high specific surface area. In the examples containing a predetermined amount of silica (2) and a silane coupling agent, processability, wet skid performance, fracture resistance, wear resistance and steering stability were obtained in a well-balanced manner. On the other hand, each performance was inferior in the comparative example compared with the corresponding Example.

Claims (4)

Rubber components including styrene butadiene rubber and butadiene rubber ;
An aromatic vinyl polymer having a glass transition temperature of 10 ° C. or less and an aromatic vinyl monomer unit content of 95% by mass or more;
Silica (1) having a nitrogen adsorption specific surface area of 130 m ² / g or less;
Silica (2) having a nitrogen adsorption specific surface area of 150 m ² / g or more;
Containing a silane coupling agent,
The content of the aromatic vinyl polymer is 2 to 50 parts by mass with respect to 100 parts by mass of the rubber component, and the total content of the silica (1) and (2) is 10 to 120 parts by mass,
The content of the silane coupling agent is 2 to 15 parts by mass with respect to 100 parts by mass of the total content of the silica (1) and (2).
A rubber composition for a tread in which the content of the silica (1) and the content of the silica (2) satisfy the following formula.
[Content of silica (1)] × 0.2 ≦ [Content of silica (2)] ≦ [Content of silica (1)] × 6.5 The rubber composition for a tread according to claim 1, wherein the content of the aromatic vinyl monomer unit in the aromatic vinyl polymer is 100% by mass. The rubber composition for a tread according to claim 1 or 2, comprising carbon black. The pneumatic tire which has a tread produced using the rubber composition in any one of Claims 1-3.