JP5662231B2 - Rubber composition for tire and pneumatic tire - Google Patents

Description

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

As a rubber composition used for tire sidewalls, in addition to natural rubber, which exhibits excellent tear strength, butadiene rubber is blended to improve resistance to flex cracking, and weather resistance and reinforcement are further improved. In order to do so, a blend of carbon black has been used.

On the other hand, while reducing the rolling resistance of tires (improving rolling resistance performance), the fuel efficiency of automobiles has been reduced, but in recent years, the demand for fuel efficiency has become stronger and the ratio of tires occupied is high. An excellent low heat generation property is required not only for a rubber composition for producing a tread but also for a rubber composition for producing a sidewall.

As a method for satisfying low heat build-up in a rubber composition, a method of replacing a part of carbon black with silica and a method of introducing a functional group highly reactive with silica into rubber are known. There has been a problem that the resistance to bending cracking and the strength of rubber are lowered due to the lowering of the property, the low reinforcing property of the silica. A method of reducing the blending amount of the reinforcing filler is also known, but there is a problem that the steering stability of the vehicle is lowered because the hardness of the rubber composition is lowered.

Patent Document 1 proposes a rubber composition containing a modified styrene butadiene rubber, silica or the like and exhibiting good low heat buildup and wet grip properties. However, in this case, a sufficient study has not been made on a compound system including natural rubber, butadiene rubber, and silica. In addition, no study has been made on improving the workability, fuel efficiency, bending fatigue resistance, rubber strength, and steering stability in a well-balanced manner.

JP 2010-111754 A

An object of the present invention is to solve the above-mentioned problems and to provide a rubber composition for a tire and a pneumatic tire that can improve workability, fuel efficiency, bending fatigue resistance, rubber strength, and steering stability in a well-balanced manner. .

（式（１）中、Ｒ^１、Ｒ^２及びＲ^３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、メルカプト基又はこれらの誘導体を表す。Ｒ^４及びＲ^５は、同一若しくは異なって、水素原子又はアルキル基を表す。ｎは整数を表す。） The present invention relates to natural rubber, a modified butadiene rubber modified with a compound represented by the following formula (1), a silica (1) having a nitrogen adsorption specific surface area of 50 m ² / g or more and less than 120 m ² / g, and a nitrogen adsorption specific surface area. Relates to a rubber composition for tires, which contains silica (2) of 120 m ² / g or more, and the cis content of the double bond portion of the modified butadiene rubber is 50 mol% or less.

(In the formula (1), 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, a mercapto group, or a derivative thereof. R ⁴ and R ⁵ is the same or different and represents a hydrogen atom or an alkyl group, and n represents an integer.)

The content of the natural rubber in 100% by mass of the rubber component is 20 to 80% by mass, the content of the modified butadiene rubber is 10 to 80% by mass, and the silica (1 ) And (2) is preferably 10 to 80 parts by mass.

It is preferable that the silicas (1) and (2) satisfy the following relational expression.
(Nitrogen adsorption specific surface area of silica (2)) / (Nitrogen adsorption specific surface area of silica (1)) ≧ 1.4
(Content of silica (1)) × 0.06 ≦ (content of silica (2)) ≦ (content of silica (1)) × 15

In 100% by mass of the rubber component, it is preferable to contain 60% by mass or less of styrene butadiene rubber and / or butadiene rubber having a cis content of the double bond portion of 95 mol% or more. The styrene butadiene rubber and / or the butadiene rubber having a cis content of the double bond portion of 95 mol% or more is preferably modified with the compound represented by the formula (1). The butadiene rubber having a cis content of the double bond portion of 95 mol% or more is preferably obtained by polymerization in the presence of a neodymium catalyst.

The rubber composition is preferably used as a sidewall.
The present invention also relates to a pneumatic tire produced using the rubber composition.

According to the present invention, since it is a rubber composition for tires comprising natural rubber, low-cis butadiene rubber modified with a specific compound, and silica (1) and (2) each having a specific nitrogen adsorption specific surface area, Can improve fuel efficiency, flex fatigue resistance, rubber strength, and handling stability in a well-balanced manner.

（式（１）中、Ｒ^１、Ｒ^２及びＲ^３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、メルカプト基又はこれらの誘導体を表す。Ｒ^４及びＲ^５は、同一若しくは異なって、水素原子又はアルキル基を表す。ｎは整数を表す。） The rubber composition for tires of the present invention includes natural rubber, a modified butadiene rubber modified with a compound represented by the following formula (1) and having a cis content of a double bond portion of 50 mol% or less, and a nitrogen adsorption ratio. It includes silica (1) having a surface area of 50 m ² / g or more and less than 120 m ² / g, and silica (2) having a nitrogen adsorption specific surface area of 120 m ² / g or more.

(In the formula (1), 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, a mercapto group, or a derivative thereof. R ⁴ and R ⁵ is the same or different and represents a hydrogen atom or an alkyl group, and n represents an integer.)

BR is changed to low-sis modified BR in blended rubber containing natural rubber (NR), butadiene rubber (BR), and silica with insufficient performance balance of processability, fuel efficiency, bending fatigue resistance, rubber strength, and steering stability. Substitution can improve low heat build-up, processability, etc., while lowering bending fatigue resistance. Further, the performance cannot be improved at the same time even if silica is replaced with mixed silica composed of low specific surface area silica and high specific surface area silica. Thus, although it is difficult to improve the above-mentioned performance simultaneously with the compounded rubber containing NR, BR, and silica, in the present invention, NR, a low-sis modified BR modified with a specific compound, and mixed silica are used. The aforementioned performance can be improved simultaneously and in a well-balanced manner. Furthermore, the performance balance can be improved synergistically.

The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20 can be used.

The content of NR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more, and further preferably 40% by mass or more. If it is less than 10% by mass, sufficient rubber strength and low fuel consumption may not be obtained. The content is preferably 80% by mass or less, more preferably 70% by mass or less. When it exceeds 80% by mass, the viscosity of the unvulcanized rubber is high, and the kneading processability and the bending fatigue resistance tend to deteriorate.

The modified butadiene rubber (low cis modified BR) in the present invention is modified with a compound represented by the following formula (1), and the cis content of the double bond portion is 50 mol% or less.

（式（１）中、Ｒ^１、Ｒ^２及びＲ^３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）又はこれらの誘導体を表す。Ｒ^４及びＲ^５は、同一若しくは異なって、水素原子又はアルキル基を表す。ｎは整数を表す。）

(In formula (1), R ¹ , R ² and R ³ are the same or different and are alkyl group, alkoxy group, silyloxy group, acetal group, carboxyl group (—COOH), mercapto group (—SH) or these 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 Rhosis-modified BR include those described in JP 2010-111753 A and the like.

In the formula (1), an alkoxy group is preferable as R ¹ , R ² and R ^{3 in} terms of obtaining excellent rolling resistance characteristics and breaking strength (preferably having 1 to 8 carbon atoms, more preferably carbon. An alkoxy group having 1 to 6, more preferably 1 to 4 carbon atoms). R ⁴ and R ⁵ are preferably an alkyl group (preferably an alkyl group having 1 to 3 carbon atoms). n is preferably 1 to 5, more preferably 2 to 4, and still more preferably 3. By using a preferred compound, the aforementioned performance balance can be remarkably improved.

Specific examples of the compound represented by the formula (1) include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, and 3-dimethylaminopropyltriethoxysilane. 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, 3-diethylaminopropyltriethoxysilane, and the like. Of these, 3-dimethylaminopropyltrimethoxysilane and 3-dimethylaminopropyltriethoxysilane are preferable from the viewpoint that the above-mentioned performance can be improved satisfactorily. These may be used alone or in combination of two or more.

As a method for modifying the butadiene rubber with the compound represented by the formula (1), conventionally known methods such as the methods described in JP-B-6-53768 and JP-B-6-57767 can be used. For example, it can be modified by bringing the butadiene rubber into contact with the compound. Specifically, after the preparation of the butadiene rubber by anionic polymerization, a predetermined amount of the compound is added to the rubber solution, and the polymerization terminal of the butadiene rubber (active And the like, and the like.

The cis content of the low-cis modified BR is 50 mol% or less, preferably 45 mol% or less, more preferably 40 mol% or less. If it exceeds 50 mol%, the kneading processability may not be improved. The lower limit of the cis content is not particularly limited, but is preferably 5 mol% or more, more preferably 10 mol% or more. If it is less than 5 mol%, the workability is not much different from the high cis BR, and the workability improving effect may not be sufficiently obtained.
In the present specification, the amount of cis component (cis content) is measured by the method described in Examples described later.

The weight average molecular weight (Mw) of the low-cis modified BR is preferably 100,000 or more, more preferably 200,000 or more. If it is less than 100,000, the fracture strength and the bending fatigue resistance tend to decrease. Mw is preferably 2 million or less, more preferably 1 million or less. If it exceeds 2 million, the workability is lowered, causing a dispersion failure, and the fracture strength tends to be lowered.
In addition, in this specification, a weight average molecular weight (Mw) is measured by the method as described in the below-mentioned Example.

The content of Rhosis-modified BR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 30% by mass or more. If it is less than 10% by mass, the effect obtained by blending the modified BR tends to be small. The content is preferably 80% by mass or less, more preferably 60% by mass or less. If it exceeds 80% by mass, the reaction between the polymer and silica tends to be strong, and there is a tendency that sufficient breaking strength cannot be obtained. There is.

The rubber component that can be used in the present invention other than NR and low-modified BR is not particularly limited, and isoprene rubber (IR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber ( IIR) and diene rubbers such as styrene-isoprene-butadiene copolymer rubber (SIBR). Also, butadiene rubbers other than the above-mentioned low-cis modified BR can be used. Among these, BR having a cis content of the double bond portion of 95 mol% or more is preferable from the viewpoint of obtaining good bending fatigue resistance, and SBR is preferable from the viewpoint of obtaining excellent rubber strength.

BR (high cis BR) having a cis content of the double bond portion of 95 mol% or more is not particularly limited, but in the presence of a neodymium catalyst (Nd catalyst) in view of effectively improving the performance balance described above. BR (Nd high cis BR) obtained by polymerization is preferable, and Nd high cis modified BR modified with the compound represented by the above formula (1) is more preferable.

Examples of the Nd-based catalyst include Nd halides, carboxylates, alcoholates, thioalcolates, amides, and the like. Moreover, as a modifier for Nd-based high cis-modified BR (compound represented by the formula (1)), the same compound as the above-mentioned low cis-modified BR is preferable.

Nd-based high-cis BR is a reaction-inactive organic solvent such as aliphatic, alicyclic, and aromatic hydrocarbon compounds. Accordingly, it can be prepared by polymerizing in the presence of a cocatalyst such as an Al or B-containing compound, and an Nd-based high cis-modified BR can be produced by bringing the polymer obtained by the polymerization into contact with a modifier. .

The cis content of the double bond portion of the high cis BR is 95 mol% or more, preferably 97 mol% or more. When the cis content is 95 mol% or more, good bending fatigue resistance can be obtained.

The weight average molecular weight (Mw) of the high cis BR is preferably 100,000 or more, more preferably 200,000 or more. If it is less than 100,000, the fracture strength and the bending fatigue resistance tend to decrease. Mw is preferably 2 million or less, more preferably 1 million or less. If it exceeds 2 million, the workability is lowered, causing a dispersion failure, and the fracture strength tends to be lowered.

The lower limit of the content of the high cis BR in 100% by mass of the rubber component is not particularly limited, but is preferably 10% by mass or more, more preferably 20% by mass or more. If it is less than 10% by mass, the effect of improving the bending fatigue resistance may not be sufficiently obtained. The content is preferably 60% by mass or less, more preferably 30% by mass or less. If it exceeds 60% by mass, the amount of NR and the amount of low-modified BR will be relatively small, and the effects of the present invention may not be sufficiently obtained.

SBR is not particularly limited, and for example, emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR) and the like can be used, and above all, the aforementioned performance balance can be remarkably improved. Therefore, SBR modified with the compound represented by the above formula (1) (modified SBR) is preferable. As the modifying agent for the modified SBR (compound represented by the formula (1)), the same compound as the above-mentioned low-cis modified BR is preferable. Moreover, as a modification | denaturation method, the method similar to the said ROSIS modified BR is mentioned.

The styrene content of SBR is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or less. Thereby, the above-mentioned performance balance can be improved effectively.
In addition, in this specification, the styrene content of SBR is measured by the method as described in the below-mentioned Example.

The content of SBR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 60% by mass or less, more preferably 30% by mass or less. Within the above range, the above-mentioned performance can be obtained satisfactorily.

The rubber composition of the present invention comprises a silica (1) having a nitrogen adsorption specific surface area (N ₂ SA) of 50 m ² / g or more and less than 120 m ² / g and a silica (2) having a nitrogen adsorption specific surface area of 120 m ² / g or more. Contains mixed silica.

Examples of silicas (1) and (2) include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and wet process silica is preferred because it has many silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica (1) is 50 m ² / g or more, preferably 80 m ² / g or more. If it is less than 50 m ² / g, sufficient reinforcement cannot be obtained, and the rubber strength and the bending fatigue resistance tend to deteriorate. The N ₂ SA is less than 120 m ² / g, preferably 115 m ² / g or less. The improvement effect by mixed silica is not acquired as it is 120 m < ² > / g or more.

The nitrogen adsorption specific surface area (N ₂ SA) of silica (2) is 120 m ² / g or more, preferably 150 m ² / g or more, more preferably 160 m ² / g or more. If it is less than 120 m < ² > / g, the improvement effect by mixed silica is not acquired. The upper limit of the N ₂ SA is not particularly limited, but is preferably 250 m ² / g or less, more preferably 180 m ² / g or less. If it exceeds 250 m ² / g, the processability deteriorates and the effects of the present invention may not be sufficiently obtained.

In the present invention, N ₂ SA of silica is a value measured by the BET method according to ASTM D3037-81. In addition, when each of silica (1) or (2) is composed of two or more types of silica, each N ₂ SA of silica (1) or (2) is all silica corresponding to silica (1) or (2) Is a value obtained by measuring a sample consisting of

It is preferable to satisfy the relationship of N ₂ SA of silica (2) —N ₂ SA of silica (1) ≧ 40 m ² / g. Further, it is preferable to satisfy a relation of _N ² SA ≦ 120m 2 / g of _N 2 SA - Silica Silica (2) (1), more preferably satisfy the relation of ≦ ^{80 m} 2 / g. By satisfying the above relationship, the aforementioned performance balance can be effectively improved.

(Silica (2) _N 2 SA) of / is preferably satisfies the relationship ≧ 1.4 _(N 2 SA of the silica (1)), more preferably satisfy the relation of ≧ 2.0. If it is less than 1.4, the difference in the particle diameters of silica (1) and (2) tends to be small, and the effect of improving dispersion by blending tends not to be obtained.

The content of silica (1) is preferably 1 part by mass or more, more preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. There exists a possibility that the effect of this invention may not fully be acquired as it is less than 1 mass part. The content is preferably 60 parts by mass or less, more preferably 20 parts by mass or less. If it exceeds 60 parts by mass, the fuel efficiency tends to deteriorate.

The content of silica (2) is preferably 1 part by mass or more, more preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. There exists a possibility that the effect of this invention may not fully be acquired as it is less than 1 mass part. The content is preferably 60 parts by mass or less, more preferably 40 parts by mass or less. When it exceeds 60 parts by mass, the workability is deteriorated and the effects of the present invention may not be sufficiently obtained.

The contents of silica (1) and (2) preferably satisfy the following formula.
(Content of silica (1)) × 0.06 ≦ (content of silica (2)) ≦ (content of silica (1)) × 15
If it is less than 0.06 times, sufficient rubber strength tends not to be obtained, and if it exceeds 15 times, rolling resistance tends to increase. The content of silica (2) is more preferably 0.3 times or more of the content of silica (1), further preferably 0.5 times or more, more preferably 7 times or less, and more preferably 4 times or less. Further preferred.

The total content of silica (1) and (2) is preferably 10 parts by mass or more, more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 10 parts by mass, the rolling resistance reduction effect due to the blending of silica may not be obtained. The content is preferably 80 parts by mass or less, more preferably 50 parts by mass or less. If it exceeds 80 parts by mass, the bending fatigue resistance deteriorates, and the rubber rigidity becomes too high, and the cushioning performance required for the sidewall and the like tends to deteriorate and the riding comfort performance of the tire tends to deteriorate.

The rubber composition of the present invention preferably contains a silane coupling agent. Examples of the silane coupling agent include sulfide, mercapto, vinyl, amino, glycidoxy, nitro, and chloro silane coupling agents. Among them, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, etc. A sulfide system is preferred, and bis (3-triethoxysilylpropyl) tetrasulfide is more preferred.

The content of the silane coupling agent is preferably 3 parts by mass or more and more preferably 5 parts by mass or more with respect to 100 parts by mass of the total content of silica (1) and (2). If the amount is less than 3 parts by mass, the coupling effect is insufficient and high silica dispersion cannot be obtained, so that the fuel economy performance and the breaking strength tend to decrease. The content is preferably 15 parts by mass or less, and more preferably 10 parts by mass or less. When it exceeds 15 parts by mass, an excess silane coupling agent remains, which may cause deterioration in processability and fracture characteristics of the resulting rubber composition.

The rubber composition of the present invention preferably contains carbon black. Since the reinforcing property is effectively exhibited by blending carbon black in addition to the mixed silica as a filler, the effect of the present invention can be remarkably obtained.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 80 m ² / g or more, and more preferably 100 m ² / g or more. If it is less than 80 m < ² > / g, there exists a possibility that sufficient reinforcement may not be obtained. The _N 2 SA is preferably at most 200m ² / g, more preferably at most 120 m ² / g. If it exceeds 200 m ² / g, the dispersibility of the carbon black is deteriorated and sufficient fuel economy may not be obtained.
Incidentally, _N 2 SA of carbon black, JIS K 6217-2: determined by 2001.

The content of carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and preferably 50 parts by mass or less, more preferably 10 parts by mass or less with respect to 100 parts by mass of the rubber component. is there. Within the above range, the above-mentioned performance can be obtained satisfactorily.

When carbon black is contained, the total content of silica (1) and (2) in a total of 100% by mass of silica (1), (2) and carbon black is preferably 50% by mass or more, more preferably 70%. It is at least 80% by mass, more preferably at least 80% by mass. The effect of this invention is fully acquired by setting it as 50 mass% or more. On the other hand, the total content is preferably 95% by mass or less.

The rubber composition of the present invention preferably contains oil. By using a rubber composition containing the above components and oil, the effects of the present invention can be obtained satisfactorily.
Examples of the oil include process oil. As the process oil, for example, paraffinic process oil, aromatic process oil, naphthenic process oil, and the like can be used, and among them, aromatic process oil can be preferably used.

When the rubber composition contains oil, the oil content is preferably 2 parts by mass or more, and more preferably 8 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 2 mass parts, workability may be deteriorated. The oil content is preferably 20 parts by mass or less, more preferably 12 parts by mass or less. When it exceeds 20 parts by mass, there is a possibility that sufficient rubber strength cannot be obtained.

In the rubber composition of the present invention, in addition to the above components, compounding agents generally used in the production of rubber compositions, for example, stearic acid, various anti-aging agents, vulcanizing agents such as zinc oxide, wax, sulfur, Vulcanization accelerators and the like can 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 the above components with a Banbury mixer, kneader, open roll or the like and then vulcanizing. The rubber composition can be used for each member of a tire such as a sidewall, base tread, clinch apex, carcass, inner liner, and insulation, and among them, it is preferably used for a sidewall.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, a rubber composition containing the above components is extruded in accordance with the shape of each member of the tire at an unvulcanized stage, and is molded together with other tire members by a normal method on a tire molding machine. Thus, an unvulcanized tire is formed. A tire is obtained by heating and pressurizing this unvulcanized tire in a vulcanizer.

The pneumatic tire of the present invention is preferably used as a tire for passenger cars, a tire for trucks and buses, a tire for two-wheeled vehicles, a tire for competitions, and the like, and particularly preferably used as a tire for passenger cars.

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 Production Examples 1 to 4 will be described.
Cyclohexane: cyclohexane 1,3-butadiene manufactured by Kanto Chemical Co., Ltd .: 1,3-butadiene styrene manufactured by Tokyo Chemical Industry Co., Ltd .: styrene tetramethylethylenediamine manufactured by Kanto Chemical Co., Ltd .: manufactured by Kanto Chemical Co., Ltd. Tetramethylethylenediamine n-butyllithium: 1.6M n-butyllithium hexane solution modifier manufactured by Kanto Chemical Co., Inc. (1): 3- (N, N-dimethylaminopropyl) trimethoxysilane manufactured by AMAX Co. (formula In (1), R ¹ , R ² and R ³ = methoxy group, R ⁴ and R ⁵ = methyl group, n = 3)
Denaturant (2): 3- (N, N-dimethylaminopropyl) triethoxysilane manufactured by AMAX Co. (in formula (1), R ¹ , R ² and R ³ = ethoxy group, R ⁴ and R ⁵ = methyl) Group, n = 3)
2,6-tert-butyl-p-cresol: NOCRACK 200 manufactured by Ouchi Shinsei Chemical Co., Ltd.
Neodymium ethyl hexanoate: Neodymium ethyl hexanoate PMAO (polymethylaluminosiloxane) manufactured by Wako Pure Chemical Industries, Ltd .: PMAO (Al: 6.8% by mass) manufactured by Tosoh Finechem Co., Ltd.
DIBAH solution: 1M-isodibutylaluminum hydride / toluene solution manufactured by Tosoh Finechem Corp. DEAC solution: 1M-diethylaluminum chloride / hexane solution manufactured by Tosoh Finechem Corp. TIBA solution: Tosoh Finechem Corp. 1M-triisobutylaluminum / hexane solution

(Production Example 1)
Into a pressure vessel sufficiently substituted with nitrogen, 1500 ml of cyclohexane, 900 mmol of 1,3-butadiene, 0.2 mmol of tetramethylethylenediamine and 0.12 mmol of n-butyllithium were added and stirred at 40 ° C. for 48 hours. Thereafter, 1 g of 2,6-tert-butyl-p-cresol was added to the reaction solution, and BR (2) was obtained by reprecipitation purification. Mw was 450,000.

(Production Example 2)
BR (3) was obtained under the same conditions as in Production Example 1 except that 0.12 mmol of the modifier (1) was added after stirring. Mw was 460000.

(Production Example 3)
The 50 ml glass container was purged with nitrogen, 8 ml of a butadiene cyclohexane solution (2.0 mol / L), 1 ml of a neodymium ethylhexanoate / toluene solution (0.2 mol / L) and 8 ml of PMAO were added and stirred. After 5 minutes, 5 ml of DIBAH solution was added, and further 5 minutes later, 2 ml of DEAC solution was added to obtain catalyst solution (1).
The reaction kettle (3 L pressure-resistant stainless steel container) was replaced with nitrogen, and while maintaining the nitrogen atmosphere, 1800 ml of cyclohexane, 75 g of butadiene, and 1 ml of TIBA solution were sealed and stirred for 5 minutes, and then 1.5 ml of catalyst solution (1). The mixture was added and stirred while maintaining 30 ° C. After 3 hours, 1 mmol of the modifier (2) was added, and 10 ml of 0.01M-2,6-tert-butyl-p-cresol / isopropanol solution was added dropwise to the reaction kettle to complete the reaction. After cooling, the reaction solution was added to 3 L of methanol separately prepared, and the resulting precipitate was air-dried overnight and further dried under reduced pressure for 2 days to obtain BR (5). The yield was about 74.2 g. Mw was 560000.

(Production Example 4)
Add 1500 ml of n-hexane, 32 g of styrene, 92 g of 1,3-butadiene and 3 g of tetrahydrofuran to a heat-resistant container sufficiently purged with nitrogen, and then add 0.7 ml of 1.6 M n-butyllithium hexane solution, and then at 50 ° C. for 4 hours. Stir. Thereafter, 0.12 mmol of the modifier (1) was added and stirred for 30 minutes. The reaction was stopped by adding 1 g of methanol to the polymer solution, and 27 g of oil and 1 g of 2,6-tert-butyl-p-cresol were added to the reaction solution, followed by drying under reduced pressure at 50 ° C. for 24 hours to obtain SBR (2). . The obtained SBR (2) had an Mw of 230000 and a styrene component content of 32% by mass.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: TSR20
BR (1): BR150B manufactured by Ube Industries, Ltd. (non-modified, cis content: 96 mol%)
BR (2): produced in Production Example 1 above (non-modified, cis content: 40 mol%)
BR (3): produced in Production Example 2 above (modified, cis content: 40 mol%)
BR (4): BUNA-CB24 manufactured by LANXESS (non-modified, BR synthesized using Nd-based catalyst, cis content: 97 mol%, Mw: 500,000)
BR (5): produced in Production Example 3 above (modified, cis content: 98 mol%)
SBR (1): SBR1502 manufactured by Sumitomo Chemical Co., Ltd. (non-denaturing, cis content: 14 mol%)
SBR (2): produced in Production Example 4 above (modified, cis content: 15 mol%)
Carbon black: N220 manufactured by Cabot Japan Co., Ltd. (DBP oil absorption: 115 ml / g, N ₂ SA: 111 m ² / g)
Silica (1-1): ZEOSIL 1085GR manufactured by Rhodia (N ₂ SA: 80 m ² / g)
Silica (1-2): ZEOSIL 115GR (N ₂ SA: 110 m ² / g) manufactured by Rhodia
Silica (2-1): ZEOSIL 1165MP (N ₂ SA: 160 m ² / g) manufactured by Rhodia
Silica (2-2): ZEOSIL 1205MP (N ₂ SA: 200 m ² / g) manufactured by Rhodia
Silane coupling agent: Si75 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Aroma oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Anti-aging agent: Santoflex 13 from Flexis
Stearic acid: Stearic acid “椿” manufactured by NOF Corporation
Zinc oxide: Zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) -2-Benzothiazolylsulfenamide)

In addition, the analysis of BR (1) -BR (5), SBR (1), and (2) was performed with the following method.

(Measurement of weight average molecular weight Mw)
The weight average molecular weight Mw of rubber is measured by gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M, manufactured by Tosoh Corporation). It calculated | required by standard polystyrene conversion based on the value.

(Measurement of cis content in butadiene units)
The cis content of the double bond in the butadiene unit of the rubber was measured using a JNM-ECA series NMR apparatus manufactured by JEOL Ltd. The measurement was performed on 1 g of a rubber sample dissolved in 15 ml of toluene, slowly poured into 30 ml of methanol, purified, dried and purified.

(Measurement of styrene content)
The styrene content was measured using a JNM-ECA series NMR apparatus manufactured by JEOL Ltd.

<Examples and Comparative Examples>
According to the formulation shown in Table 1, chemicals other than sulfur and vulcanization accelerator were kneaded for 4 minutes using a Banbury mixer to obtain a kneaded product. Next, using an open roll, sulfur and a vulcanization accelerator were added to the obtained kneaded material and kneaded for 4 minutes to obtain an unvulcanized rubber composition. Further, the obtained unvulcanized rubber composition was press vulcanized for 12 minutes at 170 ° C. to obtain a vulcanized rubber composition.
Further, the obtained unvulcanized rubber composition was molded into a sidewall shape, bonded together with other tire members on a tire molding machine, press vulcanized at 170 ° C. for 20 minutes, and a test tire (tire size: 195 / 65R15).

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

(Processability)
According to JIS K6300, the Mooney viscosity of a predetermined unvulcanized composition was measured at 130 ° C. and indicated as an index with Comparative Example 1 taken as 100. The larger the index, the lower the viscosity and the easier the processing.
(Processability index) = (Mooney viscosity of Comparative Example 1) / (Mooney viscosity of each formulation) × 100

(Low heat generation)
Loss tangent of the vulcanized rubber sheet at 70 ° C. under the conditions of a frequency of 10 Hz, an initial strain of 10% and a dynamic strain of 2% using the viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. tan δ) was measured, the low exothermic index of Comparative Example 1 was set to 100, and tan δ of each formulation was indicated by an index by the following calculation formula. In addition, it shows that heat_generation | fever is so small that a low exothermic index | exponent is large, and low exothermic property is excellent.
(Low exothermic index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(Bending fatigue resistance)
Using a constant stress / constant strain fatigue tester (FT-3100) manufactured by Ueshima Seisakusho Co., Ltd., the test was conducted in accordance with the method of ISO6943. Using a test piece (vulcanized rubber composition) of dumbbell No. 3, 1 Hz, 30% strain was continuously applied repeatedly, and the number of times until the test piece broke was determined. It shows that it is excellent in bending fatigue resistance, so that a numerical value is large.

(Rubber strength)
A tensile test was performed in accordance with JIS K6251 to measure elongation at break. The measurement results are shown as an index with Comparative Example 1 as 100. The larger the index, the greater the breaking strength.
(Rubber strength index) = (breaking elongation of each compound) / (breaking elongation of Comparative Example 1) × 100

(Maneuvering stability)
The test tires were mounted on all domestic FF2000cc wheels, the vehicle was run on the test course, and the handling stability was evaluated by sensory evaluation of the driver. Evaluation was made into a 10-point perfect score and the comparative example 1 was made into 6 points, and relative evaluation was carried out. The greater the score, the better the steering stability.

According to Table 1, compared to Comparative Example 1 using NR, high cis BR, and one type of silica, in the example using NR, low cis modified BR, mixed silica, workability, low fuel consumption, flex fatigue resistance, It became clear that all the properties of rubber strength and steering stability could be improved simultaneously and significantly.

Claims (8)

Natural rubber, modified butadiene rubber modified with a compound represented by the following formula (1), silica (1) having a nitrogen adsorption specific surface area of 50 m ² / g or more and less than 120 m ² / g, and a nitrogen adsorption specific surface area of 120 m ² / g or more of silica (2),
The cis content of the double bond moiety of the modified butadiene rubber Ri der than 50 mol%,
In 100% by mass of the rubber component, the content of natural rubber is 10 to 80% by mass, the content of the modified butadiene rubber is 10 to 80% by mass,
The content of the silica (1) and (2) is 1 to 60 parts by mass, and the total content of the silica (1) and (2) is 10 to 80 parts by mass with respect to 100 parts by mass of the rubber component. Oh Ru tire rubber composition.

(In the formula ^{(1), R 1, R} 2 and ^{R 3} are .R ⁴ and ^{R 5} represents an alkoxy group having 1 to 8 carbon atoms, .n is 1 represents an alkyl group having 1 to 3 carbon atoms Represents an integer of 5. ) The rubber composition for tires according to claim 1 whose content of said natural rubber in 100 mass% of rubber components is 20-80 mass % . The rubber composition for a tire according to claim 1 or 2, wherein the silica (1) and (2) satisfy the following relational expression.
(Nitrogen adsorption specific surface area of silica (2)) / (Nitrogen adsorption specific surface area of silica (1)) ≧ 1.4
(Content of silica (1)) × 0.06 ≦ (content of silica (2)) ≦ (content of silica (1)) × 15 The rubber composition for tires according to any one of claims 1 to 3, comprising 60% by mass or less of styrene butadiene rubber and / or butadiene rubber having a cis content of 95% by mole or more in 100% by mass of the rubber component. . The tire rubber according to claim 4, wherein the styrene-butadiene rubber and / or the butadiene rubber having a cis content of the double bond portion of 95 mol% or more is modified with the compound represented by the formula (1). Composition. The tire rubber composition according to claim 4 or 5, wherein the butadiene rubber having a cis content of the double bond portion of 95 mol% or more is obtained by polymerization in the presence of a neodymium catalyst. The rubber composition for a tire according to any one of claims 1 to 6, which is used as a sidewall. The pneumatic tire produced using the rubber composition in any one of Claims 1-7.