JP5485651B2 - 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 having a tread produced using the rubber composition.

Conventionally, the fuel consumption of a vehicle has been reduced by reducing the rolling resistance of the tire (improving rolling resistance characteristics). In recent years, there has been an increasing demand for lower fuel consumption of vehicles, and excellent rolling resistance characteristics are required for rubber compositions for producing treads with a high occupation ratio of tires among tire components. ing.

As a method of improving rolling resistance characteristics, a method of reducing the amount of reinforcing filler is known. However, when this method is used, since the hardness of the rubber composition is lowered, there is a problem that steering stability and wet skid performance are lowered.

As a method for solving the above problem, a method using silica as a reinforcing filler is known. Since silica has a low affinity with a rubber component, it is usually used in combination with a silane coupling agent such as sulfide silane or mercaptosilane. For example, Patent Document 1 discloses a rubber composition using bis (3-triethoxysilylpropyl) tetrasulfide.

However, when sulfide silane is used, the viscosity tends to increase during processing, and when mercaptosilane is used, the scorch time tends to be short. Thus, the conventional silane coupling agent has room for improvement in that the processability tends to deteriorate.

Further, silica has room for improvement in that it has a tendency to be unable to sufficiently improve the wear resistance because of its low reinforcement compared to other reinforcing fillers such as carbon black.

Patent Document 2 discloses a method of blending a polymer obtained by polymerizing only an aromatic vinyl monomer as a method for improving rolling resistance characteristics and wet skid performance. However, performances other than rolling resistance characteristics and wet skid performance have not been studied.

JP 2002-363346 A JP 2007-302713 A

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

（式中、ｘ、ｙはそれぞれ１以上の整数である。Ｒ^１は水素、ハロゲン、分岐若しくは非分岐の炭素数１〜３０のアルキル基若しくはアルキレン基、分岐若しくは非分岐の炭素数２〜３０のアルケニル基若しくはアルケニレン基、分岐若しくは非分岐の炭素数２〜３０のアルキニル基若しくはアルキニレン基、又は該アルキル基若しくは該アルケニル基の末端が水酸基若しくはカルボキシル基で置換されたものを示す。Ｒ^２は水素、分岐若しくは非分岐の炭素数１〜３０のアルキレン基若しくはアルキル基、分岐若しくは非分岐の炭素数２〜３０のアルケニレン基若しくはアルケニル基、又は分岐若しくは非分岐の炭素数２〜３０のアルキニレン基若しくはアルキニル基を示す。Ｒ^１とＲ^２とで環構造を形成してもよい。） The present invention includes a rubber component, an aromatic vinyl polymer, silica, and a silane coupling agent, wherein the aromatic vinyl monomer unit content of the aromatic vinyl polymer is 95% by mass or more, and the rubber The content of the silica is 15 to 150 parts by mass with respect to 100 parts by mass of the component, the content of the aromatic vinyl polymer is 2 to 50 parts by mass, and the silane coupling agent is represented by the following general formula (1 ) And a rubber composition for a tread that is obtained by copolymerizing the binding unit B at a ratio of 1 to 70 mol% with respect to the total amount of the binding unit A represented by the following general formula (2). Related to things.

(In the formula, x and y are each an integer of 1 or more. R ¹ is hydrogen, halogen, branched or unbranched alkyl group or alkylene group having 1 to 30 carbon atoms, branched or unbranched carbon atoms 2 to 30. alkenyl or alkenylene group, a branched or unbranched alkynyl or alkynylene group having 2 to 30 carbon atoms, or .R ² the end of the alkyl or alkenyl group indicates those substituted with hydroxyl or carboxyl groups Hydrogen, branched or unbranched alkylene group or alkyl group having 1 to 30 carbon atoms, branched or unbranched alkenylene group or alkenyl group having 2 to 30 carbon atoms, or branched or unbranched alkynylene group having 2 to 30 carbon atoms Or an alkynyl group, R ¹ and R ² may form a ring structure.)

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

The glass transition temperature of the aromatic vinyl polymer is preferably 10 ° C. or lower.

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

According to the present invention, a rubber composition containing a specific amount of an aromatic vinyl polymer having a certain content of aromatic vinyl monomer units and a predetermined amount of silica and a specific silane coupling agent. Therefore, by using the rubber composition in a tread, it is possible to provide a pneumatic tire in which processability, rolling resistance characteristics, wet skid performance, wear resistance, and steering stability can be obtained in a well-balanced manner.

The rubber composition of the present invention contains a predetermined amount of each of an aromatic vinyl polymer having an aromatic vinyl monomer unit content of a certain level and silica, and a specific silane coupling agent. By blending the aromatic vinyl polymer, steering stability, wet skid performance and processability can be improved. Further, by using the specific silane coupling agent in combination with silica, it is possible to improve rolling resistance characteristics while maintaining processability. Furthermore, wear resistance can be improved by using the aromatic vinyl polymer, silica, and the specific silane coupling agent in combination. In this way, it has been possible to improve in a well-balanced performance (particularly wear resistance, wet skid performance and rolling resistance characteristics) that has been difficult to achieve in the past.

The rubber component used in the rubber composition of the present invention is not particularly limited. For example, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR). ), Chloroprene rubber (CR), butyl rubber (IIR), halogenated butyl rubber (X-IIR), styrene-isoprene-butadiene copolymer rubber (SIBR), and the like. These may be used alone or in combination of two or more. Among these, it is preferable to use SBR because the rolling resistance characteristics and the wet skid performance can be obtained with a good balance.

The SBR is not particularly limited, and for example, those commonly used in the tire industry such as emulsion polymerization styrene butadiene rubber (E-SBR), solution polymerization styrene butadiene rubber (S-SBR) can be used. Moreover, SBR (modified SBR) whose terminal is modified can be suitably used because of its excellent adhesion to silica and the ability to reduce rolling resistance. Examples of the modified SBR include modified SBR modified with an organosilicon compound containing an alkoxy group described in JP-A-2001-114938.

The styrene content of SBR is preferably 5% by mass or more, more preferably 10% by mass or more. When the amount is less than 5% by mass, sufficient grip performance may not be obtained when the rubber composition of the present invention is used for a cap tread. Moreover, the styrene content of SBR is preferably 80% by mass or less, more preferably 70% by mass or less. If it exceeds 80% by mass, the rolling resistance characteristics may be deteriorated, or the compatibility of BR and NR may be reduced. Moreover, since the blending ratio of NR and BR is relatively lowered, there is a risk of causing wear resistance and workability.
In the present specification, the styrene content is calculated by H ¹ -NMR measurement.

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 are poorly compatible with rubber components, so if the content of olefinic monomer units in the aromatic vinyl polymer increases, bleeding out tends to occur. There is. 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 wet skid performance tends to deteriorate. The Tg of the aromatic vinyl polymer is preferably 10 ° C. or less, more preferably 5 ° C. or less. When it exceeds 10 ° C., wear resistance and grip 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, it tends to be difficult to obtain a sufficient improvement effect of rolling resistance characteristics and wet skid performance. 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 10 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 2 parts by mass, a sufficient improvement effect of wet skid performance tends to be difficult to obtain. 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. When it exceeds 50 parts by mass, rolling resistance characteristics and wear resistance tend to deteriorate.

The rubber composition of the present invention contains silica. Examples of the silica that can be used include silica produced by a wet method, silica produced by a dry method, and the like, but there is no particular limitation. In addition, a silica may be used individually by 1 type and may be used in combination of 2 or more type.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 80 m ² / g or more, more preferably 100 m ² / g or more, and further preferably 120 m ² / g or more. When it is less than 80 m ² / g, since the reinforcing effect of silica is small, the wear resistance tends to deteriorate. Further, N ₂ SA of silica is preferably 250 m ² / g or less, more preferably 220 m ² / g or less, and further preferably 200 m ² / g or less. When it exceeds 250 m ² / g, since the dispersibility of silica is lowered, the hysteresis loss is increased, and the rolling resistance characteristic tends to be deteriorated.
The _N 2 SA of silica is a value measured by the BET method in accordance with ASTM D3037-81.

The content of silica is 15 parts by mass or more, preferably 45 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 15 parts by mass, the rubber strength tends to be low. Moreover, content of a silica is 150 mass parts or less with respect to 100 mass parts of rubber components, Preferably it is 120 mass parts or less. When it exceeds 150 parts by mass, silica is difficult to disperse and the processability tends to deteriorate.

（式中、ｘ、ｙはそれぞれ１以上の整数である。Ｒ^１は水素、ハロゲン、分岐若しくは非分岐の炭素数１〜３０のアルキル基若しくはアルキレン基、分岐若しくは非分岐の炭素数２〜３０のアルケニル基若しくはアルケニレン基、分岐若しくは非分岐の炭素数２〜３０のアルキニル基若しくはアルキニレン基、又は該アルキル基若しくは該アルケニル基の末端が水酸基若しくはカルボキシル基で置換されたものを示す。Ｒ^２は水素、分岐若しくは非分岐の炭素数１〜３０のアルキレン基若しくはアルキル基、分岐若しくは非分岐の炭素数２〜３０のアルケニレン基若しくはアルケニル基、又は分岐若しくは非分岐の炭素数２〜３０のアルキニレン基若しくはアルキニル基を示す。Ｒ^１とＲ^２とで環構造を形成してもよい。） The rubber composition of the present invention comprises 1 to 70 mol% of the binding unit B based on the total amount of the binding unit A represented by the following general formula (1) and the binding unit B represented by the following general formula (2) A silane coupling agent copolymerized at a ratio of

(In the formula, x and y are each an integer of 1 or more. R ¹ is hydrogen, halogen, branched or unbranched alkyl group or alkylene group having 1 to 30 carbon atoms, branched or unbranched carbon atoms 2 to 30. alkenyl or alkenylene group, a branched or unbranched alkynyl or alkynylene group having 2 to 30 carbon atoms, or .R ² the end of the alkyl or alkenyl group indicates those substituted with hydroxyl or carboxyl groups Hydrogen, branched or unbranched alkylene group or alkyl group having 1 to 30 carbon atoms, branched or unbranched alkenylene group or alkenyl group having 2 to 30 carbon atoms, or branched or unbranched alkynylene group having 2 to 30 carbon atoms Or an alkynyl group, R ¹ and R ² may form a ring structure.)

The silane coupling agent having the above structure has an increased viscosity during processing as compared with polysulfide silanes such as bis- (3-triethoxysilylpropyl) tetrasulfide because the molar ratio of the bond unit A to the bond unit B satisfies the above conditions. Is suppressed. This is presumably because the increase in Mooney viscosity is small because the sulfide portion of the bond unit A is a C—S—C bond and is thermally stable compared to tetrasulfide and disulfide.

Moreover, when the molar ratio of the bond unit A and the bond unit B satisfies the above conditions, the shortening of the scorch time is suppressed as compared with mercaptosilane such as 3-mercaptopropyltrimethoxysilane. This is because the bonding unit B has a structure of mercaptosilane, but the —C ₇ H ₁₅ part of the bonding unit A covers the —SH group of the bonding unit B, so that it does not easily react with the polymer and scorch is less likely to occur. This is probably because of this.

Examples of the halogen for R ¹ include chlorine, bromine, and fluorine.

Examples of the branched or unbranched alkyl group having 1 to 30 carbon atoms of R ¹ and R ² include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an iso-butyl group, and a sec-butyl group. Tert-butyl group, pentyl group, hexyl group, heptyl group, 2-ethylhexyl group, octyl group, nonyl group, decyl group and the like. The number of carbon atoms of the alkyl group is preferably 1-12.

Examples of the branched or unbranched alkylene group having 1 to 30 carbon atoms of R ¹ and R ² include ethylene group, propylene group, butylene group, pentylene group, hexylene group, heptylene group, octylene group, nonylene group, decylene group, Examples include an undecylene group, a dodecylene group, a tridecylene group, a tetradecylene group, a pentadecylene group, a hexadecylene group, a heptadecylene group, and an octadecylene group. The alkylene group preferably has 1 to 12 carbon atoms.

Examples of the branched or unbranched alkenyl group having 2 to 30 carbon atoms of R ¹ and R ² include a vinyl group, 1-propenyl group, 2-propenyl group, 1-butenyl group, 2-butenyl group, 1-pentenyl group, 2-pentenyl group, 1-hexenyl group, 2-hexenyl group, 1-octenyl group and the like can be mentioned. The alkenyl group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched C 2-30 alkenylene group of R ¹ and R ² include vinylene group, 1-propenylene group, 2-propenylene group, 1-butenylene group, 2-butenylene group, 1-pentenylene group, 2-pentenylene group, 1-hexenylene group, 2-hexenylene group, 1-octenylene group and the like can be mentioned. The alkenylene group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched alkynyl group having 2 to 30 carbon atoms of R ¹ and R ² include ethynyl group, propynyl group, butynyl group, pentynyl group, hexynyl group, heptynyl group, octynyl group, noninyl group, decynyl group, An undecynyl group, a dodecynyl group, etc. are mentioned. The alkynyl group preferably has 2 to 12 carbon atoms.

Examples of the branched or unbranched alkynylene group having 2 to 30 carbon atoms represented by R ¹ and R ² include ethynylene group, propynylene group, butynylene group, pentynylene group, hexynylene group, heptynylene group, octynylene group, noninylene group, decynylene group, An undecynylene group, a dodecynylene group, etc. are mentioned. The alkynylene group preferably has 2 to 12 carbon atoms.

In the silane coupling agent having the above structure, the total repeating number (x + y) of the repeating number (x) of the bonding unit A and the repeating number (y) of the bonding unit B is preferably in the range of 3 to 300. Within this range, since the mercaptosilane of the bond unit B is covered by —C ₇ H ₁₅ of the bond unit A, it is possible to suppress the scorch time from being shortened and to have good reactivity with silica and rubber components. Can be secured.

As the silane coupling agent having the above structure, for example, NXT-Z30, NXT-Z45, NXT-Z60 manufactured by Momentive, etc. can be used. These may be used alone or in combination of two or more.

The content of the silane coupling agent having the above structure is preferably 2 parts by mass or more, more preferably 4 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 2 parts by mass, rolling resistance characteristics tend to deteriorate. Further, the content is preferably 20 parts by mass or less, more preferably 16 parts by mass or less, with respect to 100 parts by mass of silica. When it exceeds 20 parts by mass, there is a tendency that an effect commensurate with the increase in cost cannot be obtained.

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

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 method for producing the tread is not particularly limited. For example, the rubber composition in the form of a sheet is pasted into a predetermined shape, or the rubber composition is inserted into two or more extruders, and the head exit of the extruder is used. The method of forming in 2 layers etc. are mentioned.

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 on a tire molding machine by a normal method. 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.
SBR: Asaprene El5 manufactured by Asahi Kasei Corporation (styrene content: 23% by mass)
Silica: Ultrasil VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g, average primary particle size: 15 nm)
Silane coupling agent (1): Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Silane coupling agent (2): A1891 (3-mercaptopropyltriethoxysilane) manufactured by Momentive
Silane coupling agent (3): NXT-Z45 manufactured by Momentive (copolymer of bonding unit A and bonding unit B (bonding unit A: 55 mol%, bonding unit B: 45 mol%))
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)
Oil: Diana Process AH-24 manufactured by Idemitsu Kosan Co., Ltd.
Zinc oxide: 2 types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Anti-aging agent manufactured by NOF Corporation: Antigen 6C manufactured by Sumitomo Chemical Co., Ltd.
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator made by Karuizawa Sulfur Co., Ltd. CZ: Noxeller CZ (N-cyclohexyl-2-benzothiazylsulfenamide) made by Ouchi Shinsei Chemical Co., Ltd.
Vulcanization accelerator DPG: Noxeller D (N, N'-diphenylguanidine) 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).

Examples 1-4 and Comparative Examples 1-7
According to the blending contents shown in Table 1, materials other than sulfur and the vulcanization accelerator were kneaded for 5 minutes at 150 ° C. using a Banbury mixer to obtain a kneaded product. Next, using a biaxial open roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded for 5 minutes at 50 ° C. to obtain an unvulcanized rubber composition.
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 15 minutes. A test tire (tire size: 195 / 65R15) was obtained.

The following evaluation was performed using the obtained unvulcanized rubber composition and the test tire. The results are shown in Table 1.

<Rubber composition>
(Mooney viscosity index)
In accordance with JIS K6300-1, “Unvulcanized rubber—Physical properties—Part 1: Determination of viscosity and scorch time using Mooney viscometer”, 130 heated with a Mooney viscosity tester by preheating for 1 minute. Under the temperature condition of ° 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. And the Mooney viscosity of the comparative example 1 was set to 100, and it represented by the index | exponent by the following formula. The smaller the value, the lower the Mooney viscosity and the better the workability.
(Mooney viscosity index) = (Mooney viscosity of each formulation) / (Mooney viscosity of Comparative Example 1) × 100

(Scorch time index)
Based on JIS K6300, the time until the vulcanization degree of the unvulcanized rubber composition reached 95% (T ₉₅ ) was measured at 160 ° C. Then, the _{T 95} of Comparative Example 1 as 100, was displayed by indices by the following calculation formula. Larger values indicate better workability.
(Scorch Time Index) = (T _{95 of} Comparative Example 1) / (T _{95 of} each formulation) × 100

(Rolling resistance index)
Using a rolling resistance tester, the rolling resistance is measured when the test tire is run under the conditions of rim (15 × 6JJ), internal pressure (230 kPa), load (3.43 kN), and speed (80 km / h). did. And the rolling resistance of the comparative example 1 was set to 100, and it represented by the index | exponent by the following formula. It shows that rolling resistance characteristic is so favorable that a numerical value is large (rolling resistance is low).
(Rolling resistance index) = (Rolling resistance of Comparative Example 1) / (Rolling resistance of each formulation) × 100

(Wet skid performance index)
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. Larger values indicate better wet skid performance.
(Wet skid performance index) = (Brake distance of Comparative Example 1) / (Brake distance of each formulation) × 100

(Abrasion resistance index)
The test tire was mounted on all the wheels of a vehicle (domestic FF2000cc), and the test course was run on an actual vehicle, and the reduction amount of the pattern groove depth after running about 30000 km was determined. And the reduction amount of the comparative example 1 was set to 100, and the index display was carried out with the following formula. It shows that abrasion resistance is so favorable that a numerical value is large.
(Abrasion resistance index) = (Reduction amount of Comparative Example 1) / (Reduction amount of each formulation) × 100

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

From Table 1, Examples 1-4 which contain a specific silane coupling agent while containing the aromatic vinyl polymer whose content of an aromatic vinyl monomer unit is more than fixed, and a silica respectively. The processability, rolling resistance characteristics, wet skid performance, wear resistance and steering stability were obtained in a well-balanced manner. On the other hand, the comparative examples 1-7 which did not use the said aromatic vinyl polymer and the said specific silane coupling agent together were inferior in performance compared with Examples 1-4.

Claims (4)

Contains a rubber component, an aromatic vinyl polymer, silica and a silane coupling agent,
The aromatic vinyl monomer unit content of the aromatic vinyl polymer is 95% by mass or more,
The content of the silica is 15 to 150 parts by mass with respect to 100 parts by mass of the rubber component, and the content of the aromatic vinyl polymer is 2 to 50 parts by mass,
The silane coupling agent comprises 1 to 70 mol% of the binding unit B with respect to the total amount of the binding unit A represented by the following general formula (1) and the binding unit B represented by the following general formula (2). A rubber composition for a tread which is copolymerized at a ratio.

(In the formula, x and y are each an integer of 1 or more. R ¹ is hydrogen, halogen, branched or unbranched alkyl group or alkylene group having 1 to 30 carbon atoms, branched or unbranched carbon atoms 2 to 30. alkenyl or alkenylene group, a branched or unbranched alkynyl or alkynylene group having 2 to 30 carbon atoms, or .R ² the end of the alkyl or alkenyl group indicates those substituted with hydroxyl or carboxyl groups Hydrogen, branched or unbranched alkylene group or alkyl group having 1 to 30 carbon atoms, branched or unbranched alkenylene group or alkenyl group having 2 to 30 carbon atoms, or branched or unbranched alkynylene group having 2 to 30 carbon atoms Or an alkynyl group, R ¹ and R ² may form a ring structure.) 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 tires according to claim 1 or 2, wherein the glass transition temperature of the aromatic vinyl polymer is 10 ° C or lower. A pneumatic tire having a tread produced using the rubber composition according to claim 1.