JP5662265B2 - Rubber composition for tire and pneumatic tire - Google Patents

Description

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

Conventionally, vehicle fuel efficiency has been reduced by reducing the rolling resistance of tires (improving rolling resistance performance). In recent years, there has been an increasing demand for lower fuel consumption of vehicles, and excellent low heat generation (low fuel consumption) is required for rubber compositions for manufacturing tires.

As a method for improving the low fuel consumption of the rubber composition, a method of reducing the reinforcing filler is known. However, in such a method, the handling performance (steering stability), the wet grip performance, and the wear resistance (destructive property) tend to be deteriorated due to a decrease in the hardness, calorific value, and reinforcement of the rubber composition.

As another method for improving fuel efficiency, a method of replacing carbon black, which is a reinforcing filler, with silica is known. However, since silica has hydrophilic silanol groups on its surface, it has a lower affinity for rubber (especially natural rubber, butadiene rubber, styrene butadiene rubber, etc. often used in rubber compositions for tires) than carbon black. In some cases, it is inferior in terms of wear resistance and mechanical strength (tensile strength and elongation at break). Methods such as modifying the rubber for the purpose of improving the affinity between rubber and silica have been studied. However, if the affinity between rubber and silica becomes too high, the interaction between rubber and silica becomes stronger, and kneadability is improved. Tend to get worse.

Further, polybutadiene rubber is generally used for improving the wear resistance, and the wear resistance can be further improved by increasing the molecular weight of the polybutadiene rubber. However, when the molecular weight of the polybutadiene rubber is increased, the kneadability tends to deteriorate.

Patent Document 1 discloses a rubber composition for tires that can significantly improve wet grip performance by containing both anhydrous silica and hydrous silica. However, there is still room for improvement in terms of improving fuel economy, wet grip performance, wear resistance, and kneading workability in a well-balanced manner.

JP 2003-192842 A

An object of the present invention is to solve the above-mentioned problems and to provide a rubber composition capable of improving the fuel efficiency, wet grip performance, wear resistance and kneading workability in a well-balanced manner, and a pneumatic tire using the same. .

（式中、Ｒ^０は水素、炭素数１〜３０の脂肪族炭化水素基、炭素数３〜３０の脂環族炭化水素基又は炭素数５〜３０の芳香族炭化水素基を表す。Ｒ^１及びＲ^２は、同一若しくは異なって、水素、

又は

であり、少なくともＲ^１及びＲ^２のいずれかは水素ではない。Ｒ^３は水素又は炭素数１〜４の炭化水素基を表す。Ｘは２価の飽和炭化水素基を表し、窒素、酸素又は硫黄を含んでいてもよく、

又は

で置換されていてもよい。Ｚは２価の飽和炭化水素基を表し、窒素、酸素又は硫黄を含んでいてもよい。Ｒ^４〜Ｒ^７は、同一若しくは異なって、水素、炭素数１〜３０の脂肪族炭化水素基、炭素数３〜３０の脂環族炭化水素基、炭素数５〜３０の芳香族炭化水素基、又は環構成原子数３〜３０の複素環基を表す。）で表される窒素含有化合物に由来する構成単位を主鎖中に有する変性スチレンブタジエンゴムの含有量が５質量％以上、
（Ａ）ムーニー粘度（ＭＬ）：４０〜４９、（Ｂ）分子量分布（重量平均分子量Ｍｗ／数平均分子量Ｍｎ）：３．０〜３．９及び（Ｃ）ムーニー粘度の速度依存性指数（式（１）のｎ値）：２．３〜３．０の要件を満足し、かつシス含量が９５質量％以上のハイシスポリブタジエンの含有量が１０〜７０質量％であり、
上記ゴム成分１００質量部に対して、上記シリカの含有量が１０〜１５０質量部であるタイヤ用ゴム組成物に関する。
ｌｏｇ（ＭＬ）＝ｌｏｇ（Ｋ）＋ｎ^−１×ｌｏｇ（ＲＳ） 式（１）
（但し、ＲＳはローターの１分間あたりの回転数、Ｋは任意の数、ＭＬはムーニー粘度を表す。） The present invention contains a rubber component and silica,
In 100% by mass of the rubber component, the following general formula:

(In the formula, R ⁰ represents hydrogen, an aliphatic hydrocarbon group having 1 to 30 carbon atoms, an alicyclic hydrocarbon group having 3 to 30 carbon atoms, or an aromatic hydrocarbon group having 5 to 30 carbon atoms. R ¹ And R ² are the same or different and are hydrogen,

Or

And at least ^one of R ¹ and R ² is not hydrogen. R ³ represents hydrogen or a hydrocarbon group having 1 to 4 carbon atoms. X represents a divalent saturated hydrocarbon group and may contain nitrogen, oxygen or sulfur;

Or

May be substituted. Z represents a divalent saturated hydrocarbon group and may contain nitrogen, oxygen or sulfur. R ^{4 to} R ⁷ are the same or different and are hydrogen, an aliphatic hydrocarbon group having 1 to 30 carbon atoms, an alicyclic hydrocarbon group having 3 to 30 carbon atoms, or an aromatic hydrocarbon group having 5 to 30 carbon atoms. Or a heterocyclic group having 3 to 30 ring atoms. ) The content of the modified styrene butadiene rubber having a structural unit derived from the nitrogen-containing compound represented by
(A) Mooney viscosity (ML): 40 to 49, (B) Molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn): 3.0 to 3.9, and (C) Rate dependency index of Mooney viscosity (formula N value of (1)): satisfying the requirement of 2.3 to 3.0, and the content of high cis polybutadiene having a cis content of 95% by mass or more is 10 to 70% by mass,
It is related with the rubber composition for tires whose content of the said silica is 10-150 mass parts with respect to 100 mass parts of said rubber components.
log (ML) = log (K) + n ⁻¹ × log (RS) Formula (1)
(However, RS represents the number of rotations per minute of the rotor, K represents an arbitrary number, and ML represents Mooney viscosity.)

The rubber composition is preferably used as a tread rubber composition.

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 a modified styrene butadiene rubber and a specific high-cis polybutadiene each using a specific nitrogen-containing compound as a monomer, and a specific amount of silica, A pneumatic tire with improved fuel economy, wet grip performance, wear resistance, and kneadability can be provided in a well-balanced manner.

（式中、Ｒ^０は水素、炭素数１〜３０の脂肪族炭化水素基、炭素数３〜３０の脂環族炭化水素基又は炭素数５〜３０の芳香族炭化水素基を表す。Ｒ^１及びＲ^２は、同一若しくは異なって、水素、

又は

であり、少なくともＲ^１及びＲ^２のいずれかは水素ではない。Ｒ^３は水素又は炭素数１〜４の炭化水素基を表す。Ｘは２価の飽和炭化水素基を表し、窒素、酸素又は硫黄を含んでいてもよく、

又は

で置換されていてもよい。Ｚは２価の飽和炭化水素基を表し、窒素、酸素又は硫黄を含んでいてもよい。Ｒ^４〜Ｒ^７は、同一若しくは異なって、水素、炭素数１〜３０の脂肪族炭化水素基、炭素数３〜３０の脂環族炭化水素基、炭素数５〜３０の芳香族炭化水素基、又は環構成原子数３〜３０の複素環基を表す。）で表される窒素含有化合物に由来する構成単位を主鎖中に有する変性スチレンブタジエンゴムと、（Ａ）ムーニー粘度（ＭＬ）：４０〜４９、（Ｂ）分子量分布（重量平均分子量Ｍｗ／数平均分子量Ｍｎ）：３．０〜３．９及び（Ｃ）ムーニー粘度の速度依存性指数（式（１）のｎ値）：２．３〜３．０の要件を満足し、かつシス含量が９５質量％以上のハイシスポリブタジエンと、シリカとを含む。
ｌｏｇ（ＭＬ）＝ｌｏｇ（Ｋ）＋ｎ^−１×ｌｏｇ（ＲＳ） 式（１）
（但し、ＲＳはローターの１分間あたりの回転数、Ｋは任意の数、ＭＬはムーニー粘度を表す。） The rubber composition of the present invention has the following general formula:

(In the formula, R ⁰ represents hydrogen, an aliphatic hydrocarbon group having 1 to 30 carbon atoms, an alicyclic hydrocarbon group having 3 to 30 carbon atoms, or an aromatic hydrocarbon group having 5 to 30 carbon atoms. R ¹ And R ² are the same or different and are hydrogen,

Or

And at least ^one of R ¹ and R ² is not hydrogen. R ³ represents hydrogen or a hydrocarbon group having 1 to 4 carbon atoms. X represents a divalent saturated hydrocarbon group and may contain nitrogen, oxygen or sulfur;

Or

May be substituted. Z represents a divalent saturated hydrocarbon group and may contain nitrogen, oxygen or sulfur. R ^{4 to} R ⁷ are the same or different and are hydrogen, an aliphatic hydrocarbon group having 1 to 30 carbon atoms, an alicyclic hydrocarbon group having 3 to 30 carbon atoms, or an aromatic hydrocarbon group having 5 to 30 carbon atoms. Or a heterocyclic group having 3 to 30 ring atoms. ) Modified styrene butadiene rubber having a structural unit derived from a nitrogen-containing compound represented by the formula (A) Mooney viscosity (ML): 40 to 49, (B) molecular weight distribution (weight average molecular weight Mw / number) Average molecular weight Mn): 3.0 to 3.9 and (C) Mooney viscosity rate dependence index (n value of formula (1)): satisfying the requirements of 2.3 to 3.0, and cis content is 95 mass% or more of high cis polybutadiene and silica are included.
log (ML) = log (K) + n ⁻¹ × log (RS) Formula (1)
(However, RS represents the number of rotations per minute of the rotor, K represents an arbitrary number, and ML represents Mooney viscosity.)

Since the modified styrene butadiene rubber has a strong interaction with silica, it can disperse silica well and can improve fuel economy, wet grip performance, and wear resistance. In comparison, kneadability may be inferior.
In addition, the high-cis polybutadiene is well mixed with silica from the early stage after the start of kneading, so that good kneading workability can be obtained and wear resistance can be improved. On the other hand, low fuel consumption, wet grip In some cases, performance may be degraded. For example, in a rubber composition containing silica, when the high-cis polybutadiene is used in combination with an unmodified styrene butadiene rubber, the fuel efficiency and wet grip performance are greatly reduced.
On the other hand, in the present invention, in the rubber composition containing silica, by using the modified styrene butadiene rubber together with the high cis polybutadiene, excellent fuel economy, wet grip performance, wear resistance and kneading processability are achieved. Can be obtained in a balanced manner. In particular, the wear resistance and kneading workability can be greatly improved.

As the modified styrene butadiene rubber (modified SBR), for example, those described in JP 2010-116545 A and JP 2010-116546 A can be used.

Examples of the saturated hydrocarbon group represented by X include a group represented by (CR ⁸ R ⁹ ) ₁ . Examples of the form in which the saturated hydrocarbon group represented by X contains nitrogen, oxygen, or sulfur include (CR ¹⁰ R ¹¹ ) _m —NR ¹² — (CR ¹³ R ¹⁴ ) _n , (CR ¹⁰ R ¹¹ ) _m — _{^{O- (CR 13 R 14) n}} , and the like _{^{(CR 10 R 11) m -S-}} (CR 13 R 14) n. R ^{8 to} R ¹⁴ are the same or different and are hydrogen, an aliphatic hydrocarbon group having 1 to 30 carbon atoms (preferably 1 to 5), an alicyclic carbon group having 3 to 30 carbon atoms (preferably 3 to 10 carbon atoms). A hydrogen group or an aromatic hydrocarbon group having 5 to 30 (preferably 5 to 10) carbon atoms is represented. l represents an integer of 3 to 10 (preferably 3 to 7). Each of the plurality of (CR ⁸ R ⁹ ) may be the same or different. m and n represent an integer of 1 to 9 (preferably 1 to 6). When m is 2 or more, each of the plurality of (CR ¹⁰ R ¹¹ ) may be the same or different, and when n is 2 or more, each of the plurality of (CR ¹³ R ¹⁴ ) is the same. May be different.

Examples of the saturated hydrocarbon group represented by Z and the form in which the saturated hydrocarbon group contains nitrogen, oxygen or sulfur include the same as the saturated hydrocarbon group represented by X.

R ⁰ is preferably hydrogen or an aliphatic hydrocarbon group having 1 to 2 carbon atoms from the viewpoint that silica can be more favorably dispersed. R ³ is preferably hydrogen or a hydrocarbon group having 1 to 2 carbon atoms. R ^{4 to} R ⁷ are preferably an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a heterocyclic group, and more preferably an aliphatic hydrocarbon group. R ^{8 to} R ¹⁴ are preferably hydrogen or an aliphatic hydrocarbon group having 1 to 2 carbon atoms.

The modified SBR is a copolymer obtained by copolymerizing styrene, butadiene (1,3-butadiene), and a nitrogen-containing compound (monomer) represented by the above general formula, and is derived from the nitrogen-containing compound. The structural unit to be included is included in the main chain portion. Here, the main chain part is a concept including a terminal part.

Examples of the nitrogen-containing compound represented by the above general formula include 3- or 4- (2-azetidinoethyl) styrene, 3- or 4- (2-pyrrolidinoethyl) styrene, 3- or 4- (2-piperidinoethyl). ) Styrene, 3- or 4- (2-hexamethyleneiminoethyl) styrene. These may be used alone or in combination of two or more. Among these, 3- or 4- (2-pyrrolidinoethyl) styrene is preferable from the viewpoint that silica can be more favorably dispersed.

In the modified SBR, at least one terminal is preferably modified with a modifying agent having a functional group containing at least one selected from the group consisting of nitrogen, oxygen, and silicon, and both terminals are the modifying agent. More preferably, it is denatured. Thereby, the improvement effect of each performance can be heightened.

Examples of the functional group possessed by the modifier include amino group, amide group, alkoxysilyl group, isocyanate group, imino group, imidazole group, urea group, ether group, carbonyl group, carboxyl group, hydroxyl group, nitrile group, and pyridyl. Group, and the like, preferably an amino group and an alkoxysilyl group. Examples of the modifier include 3- (N, N-dimethylamino) propyltrimethoxysilane, 3- (N, N-diethylaminopropyl) trimethoxysilane, and 3- (N, N-dimethylamino) propyl. Triethoxysilane, 3- (N, N-diethylaminopropyl) triethoxysilane, 3-glycidoxypropyltrimethoxysilane, 2- (4-pyridylethyl) triethoxysilane, N- (3-triethoxysilylpropyl) Examples include -4,5-dihydroimidazole and silicon tetrachloride, and 3- (N, N-dimethylamino) propyltrimethoxysilane is preferable.

The content of the nitrogen-containing compound in the modified SBR is preferably 0.05% by mass or more, more preferably 0.1% by mass or more. If it is less than 0.05% by mass, there is a tendency that it is difficult to obtain an effect of improving fuel efficiency and wet grip performance. Further, the content of the nitrogen-containing compound in the modified SBR is preferably 10% by mass or less, more preferably 5% by mass or less. When it exceeds 10 mass%, there exists a tendency for the effect corresponding to the increase in cost not to be acquired.
In addition, in this specification, content of a nitrogen-containing compound is measured by the method as described in the below-mentioned Example.

The weight average molecular weight Mw of the modified SBR is preferably 1.0 × 10 ⁵ or more, more preferably 2.0 × 10 ⁵ or more. If it is less than 1.0 × 10 ⁵ , fuel economy and wear resistance tend to deteriorate. The Mw is preferably 2.0 × 10 ⁶ or less, more preferably 1.5 × 10 ⁶ or less. If it exceeds 2.0 × 10 ⁶ , kneading processability tends to deteriorate.
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 the modified SBR in 100% by mass of the rubber component is 5% by mass or more, preferably 30% by mass or more, and more preferably 50% by mass or more. If it is less than 5% by mass, the effect of blending the modified SBR may not be sufficiently obtained. Further, the content of the modified SBR is preferably 90% by mass or less, more preferably 80% by mass or less. When it exceeds 90% by mass, kneadability tends to deteriorate.

In the present invention, the high cis polybutadiene (high cis polybutadiene rubber) is used as the rubber component together with the modified SBR.

The Mooney viscosity (ML (ML _{1 + 4} )) of the high cis polybutadiene is 40 to 49, preferably 40 to 47. When the Mooney viscosity is larger than the above range, the kneading processability is lowered, and when it is smaller than the above range, the wear resistance is lowered. In the present specification, the Mooney viscosity (ML) of high-cis polybutadiene is a value measured at 100 ° C. in accordance with JIS K6300-1: 2001.

The molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) of the high cis polybutadiene is 3.0 to 3.9, preferably 3.0 to 3.6. When the molecular weight distribution is larger than the above range, the wear resistance is lowered, and when the molecular weight distribution is smaller than the above range, the kneading workability is lowered. In this specification, the weight average molecular weight Mw and the number average molecular weight Mn of the high-cis polybutadiene are gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corporation), detector: differential refractometer, column: It is determined by standard polystyrene conversion based on the measured value by TSKGEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation.

The weight average molecular weight Mw of the high cis polybutadiene is preferably 500,000 to 700,000, more preferably 550,000 to 650,000. When the molecular weight is larger than the above range, the kneading processability is lowered, and when it is smaller than the above range, the wear resistance may be lowered.

The number average molecular weight Mn of the high cis polybutadiene is preferably 120,000 to 250,000, more preferably 150,000 to 220,000. When the molecular weight is larger than the above range, the kneading processability is lowered, and when it is smaller than the above range, the wear resistance may be lowered.

The speed dependence index (the n value of the formula (1)) of Mooney viscosity of the high cis polybutadiene is 2.3 to 3.0, preferably 2.4 to 2.9, more preferably 2.4 to 2.8. When the n value is less than 2.3, the kneading property (dispersibility) of silica is deteriorated and the kneading processability is deteriorated, and when it is more than 3.0, the fuel efficiency is deteriorated.

The n value is measured in accordance with JIS K6300-1: 2001 by measuring the Mooney viscosity (ML) by changing the rotational speed (1 / min) of the rotor, and the Mooney viscosity (ML) and the rotor rotational speed (RS) are as follows. It is the reciprocal of the slope of the straight line obtained by equation (1). Here, log (K) is an arbitrary number that means a straight intercept.
log (ML) = log (K) + n ⁻¹ × log (RS) Formula (1)
(However, RS represents the number of rotations per minute of the rotor, K represents an arbitrary number, and ML represents Mooney viscosity.)
In addition, the said Formula (1) can be obtained based on the theoretical formula (following Formula (2)) of the n-power rule with respect to a non-Newtonian flow.
γ = kτ ⁿ formula (2)
(Where γ: velocity gradient, τ: shear stress, k ⁻¹ = η: viscosity coefficient)

The n value is determined by the degree of branching and molecular weight distribution of polybutadiene and has no correlation with Mooney viscosity. The n value increases as the degree of branching and molecular weight distribution of polybutadiene increases, and the value n decreases as the degree of branching and molecular weight distribution of polybutadiene decreases.

In addition, since the manipulation of the range of the n value needs to optimize the molecular weight distribution, it can be performed in two steps as follows, for example. First, several types of polybutadiene having a small n value and different molecular weight are polymerized in the butadiene polymerization stage. Next, the n value is adjusted to an optimum range by blending several kinds of polybutadienes having different molecular weights to broaden the molecular weight distribution. The n value in the polymerization stage can be adjusted by the mixing molar ratio of the organoaluminum compound as a promoter and water. That is, by increasing the amount of water added to a predetermined amount of the organoaluminum compound, the mixing molar ratio decreases, and the n value tends to decrease as the mixing molar ratio decreases. The mixing molar ratio of the organoaluminum compound, which is a promoter in the polymerization stage, and water is preferably 2.0 or less, particularly preferably 1.0 to 1.5. When the mixing molar ratio exceeds 2.0, the n value becomes too large, and when it is less than 1.0, the polymerization activity may be remarkably lowered.

The ratio (Tcp / ML) of 5 mass% toluene solution viscosity (Tcp) and Mooney viscosity (ML) of the high cis polybutadiene is preferably 2.5 to 3.5, more preferably 2.5 to 3. 0. When Tcp / ML is larger than the above range, the cold flow property of the base rubber (high cis polybutadiene) becomes large, and when Tcp / ML is smaller than the above range, the wear resistance may be lowered. The viscosity of 5 mass% toluene solution (Tcp) is obtained by dissolving 2.28 g of high-cis polybutadiene in 50 ml of toluene, and then using a standard solution for calibrating viscometer (JIS Z8809) as a standard solution. 400 was used and measured at 25 ° C.

The cis content of the high cis polybutadiene is 95% by mass or more, preferably 97% by mass or more, and more preferably 98% by mass or more. When the cis content is smaller than the above range, the wear resistance is lowered. The cis content is calculated by infrared absorption spectrum analysis.

The high cis polybutadiene can be produced, for example, with a cobalt catalyst. Examples of the cobalt-based catalyst include a catalyst system comprising (a) a cobalt compound, (b) a halogen-containing organoaluminum compound, and (c) water.

As the cobalt compound, a cobalt salt or complex is preferably used. Particularly preferred are cobalt salts such as cobalt chloride, cobalt bromide, cobalt nitrate, cobalt octylate (ethylhexanoate), cobalt naphthenate, cobalt acetate, cobalt malonate, cobalt bisacetylacetonate and trisacetylacetate. Examples thereof include organic base complexes such as nate, ethyl acetoacetate cobalt, pyridine complexes and picoline complexes of cobalt salts, or ethyl alcohol complexes.

Examples of the halogen-containing machine aluminum include trialkylaluminum, dialkylaluminum chloride, dialkylaluminum bromide, alkylaluminum sesquichloride, alkylaluminum sesquibromide, and alkylaluminum dichloride.

Specific examples of the compound include trialkylaluminum such as trimethylaluminum, triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, and tridecylaluminum.

In addition, dialkylaluminum chlorides such as dimethylaluminum chloride and diethylaluminum chloride, organoaluminum halogen compounds such as sesquiethylaluminum chloride and ethylaluminum dichloride, hydrogenated organics such as diethylaluminum hydride, diisobutylaluminum hydride and sesquiethylaluminum hydride Aluminum compounds are also included. Two or more of these organoaluminum compounds can be used in combination.

The molar ratio (b) / (a) between the component (a) and the component (b) is preferably 0.1 to 5000, more preferably 1 to 2000.

The molar ratio (b) / (c) between the component (b) and the component (c) is preferably 0.7 to 5, more preferably 0.8 to 4, particularly preferably 1 to 3. is there.

In addition to butadiene monomer, isoprene, 1,3-pentadiene, 2-ethyl-1,3-butadiene, 2,3-dimethylbutadiene, 2-methylpentadiene, 4-methylpentadiene, conjugated dienes such as 2,4-hexadiene, ethylene , Acyclic monoolefins such as propylene, butene-1, butene-2, isobutene, pentene-1, 4-methylpentene-1, hexene-1, octene-1, cyclic monoolefins such as cyclopentene, cyclohexene, norbornene, and An aromatic vinyl compound such as styrene or α-methylstyrene, a non-conjugated diolefin such as dicyclopentadiene, 5-ethylidene-2-norbornene, or 1,5-hexadiene may be included in a small amount.

The polymerization method is not particularly limited, and bulk polymerization (bulk polymerization) using a conjugated diene compound monomer such as 1,3-butadiene itself as a polymerization solvent, or solution polymerization can be applied. Solvents for solution polymerization include aromatic hydrocarbons such as toluene, benzene and xylene, aliphatic hydrocarbons such as n-hexane, butane, heptane and pentane, alicyclic hydrocarbons such as cyclopentane and cyclohexane, and the like And olefinic hydrocarbons such as cis-2-butene and trans-2-butene, hydrocarbon solvents such as mineral spirit, solvent naphtha and kerosene, and halogenated hydrocarbon solvents such as methylene chloride. .

Among these, toluene, cyclohexane, or a mixture of cis-2-butene and trans-2-butene is preferably used.

The polymerization temperature is preferably in the range of -30 to 150 ° C, particularly preferably in the range of 30 to 100 ° C. The polymerization time is preferably in the range of 1 minute to 12 hours, particularly preferably 5 minutes to 5 hours.

After carrying out the polymerization for a predetermined time, the inside of the polymerization tank is released as necessary, and post-treatment such as washing and drying steps is performed to obtain the high-cis polybutadiene. In addition, as a commercial item of the said high cis polybutadiene, BR710 made from Ube Industries, Ltd. is mentioned.

Content of the said high cis polybutadiene in 100 mass% of rubber components is 10 mass% or more, Preferably it is 20 mass% or more. If it is less than 10% by mass, sufficient fuel economy and wear resistance cannot be obtained. The content of the high cis polybutadiene is 70% by mass or less, preferably 60% by mass or less, more preferably 55% by mass or less. When it exceeds 70 mass%, sufficient wet grip performance cannot be obtained.

The total content of the modified SBR and the high-cis polybutadiene in 100% by mass of the rubber component is preferably 80% by mass or more, more preferably 90% by mass or more, and may be 100% by mass. If it is less than 80% by mass, the fuel economy, wet grip performance and wear resistance may not be obtained in a well-balanced manner.

The rubber composition of the present invention may use other rubber components in combination with the modified SBR and the high cis polybutadiene. Examples of the other rubber component include diene rubbers such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), and styrene butadiene rubber (SBR).

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

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 100 m ² / g or more, more preferably 150 m ² / g or more. If it is less than 100 m ² / g, the reinforcing effect is small and sufficient wear resistance may not be obtained. Further, N ₂ SA of silica is preferably 300 m ² / g or less, more preferably 200 m ² / g or less. If it exceeds 300 m ² / g, silica is difficult to disperse and sufficient fuel efficiency may not be obtained.
The _N 2 SA of silica is measured by BET method in accordance with ASTM D3037-81.

The content of silica is 10 parts by mass or more, preferably 60 parts by mass or more with respect to 100 parts by mass of the rubber component. When the amount is less than 10 parts by mass, there is a tendency that a sufficient effect due to silica blending cannot be obtained. The content is 150 parts by mass or less, preferably 90 parts by mass or less. When it exceeds 150 parts by mass, it is difficult to disperse silica in rubber, and the kneadability tends to deteriorate.

The rubber composition of the present invention preferably contains a silane coupling agent together with silica. 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. Sulfide type is preferable, and bis (3-triethoxysilylpropyl) disulfide and bis (3-triethoxysilylpropyl) tetrasulfide are more preferable. Here, the lower limit of the content of the silane coupling agent is preferably 2 parts by mass or more, more preferably 6 parts by mass or more, and the upper limit is preferably 15 parts by mass or less, more preferably 100 parts by mass of silica. It is 10 parts by mass or less.

The rubber composition of the present invention preferably contains carbon black.
Here, the nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 60 m ² / g or more, more preferably 90 m ² / g or more. If it is less than 60 m < ² > / g, there exists a tendency for sufficient reinforcement and abrasion resistance not to be obtained. Also, _N 2 SA of carbon black is preferably 180 m ² / g or less, and more preferably not more than 130m ² / g. If it exceeds 180 m ² / g, the dispersibility tends to deteriorate and the exothermicity tends to increase.
Incidentally, _N 2 SA of carbon black, JIS K 6217-2: determined by 2001.

The content of carbon black is preferably 5 to 20 parts by mass with respect to 100 parts by mass of the rubber component. If the amount is less than 5 parts by mass, sufficient reinforcement may not be obtained. If the amount exceeds 20 parts by mass, sufficient low heat build-up tends to be not obtained.

When the rubber composition of the present invention contains carbon black, the total content of silica and carbon black is preferably 60 to 120 parts by mass with respect to 100 parts by mass of the rubber component. Within the above range, low fuel consumption, wet grip performance, abrasion resistance and kneading workability can be obtained in a well-balanced manner.

The content of silica in a total of 100% by mass of silica and carbon black is 50% by mass or more, preferably 65% by mass or more, and more preferably 75% by mass or more. Moreover, this content rate becomes like this. Preferably it is 95 mass% or less, More preferably, it is 90 mass% or less. Within the above range, low fuel consumption, wet grip performance, abrasion resistance and kneading workability can be obtained in a well-balanced manner.

In addition to the above components, the rubber composition of the present invention includes compounding agents generally used in the production of rubber compositions, for example, vulcanization of zinc oxide, stearic acid, various anti-aging agents, wax, oil, sulfur and the like. An agent, a vulcanization accelerator, 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 of the present invention can be used for each member of a tire, and in particular, can be suitably used for a tread.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, if necessary, a rubber composition containing various additives is extruded in accordance with the shape of each member (tread, etc.) of the tire at an unvulcanized stage, and is subjected to a normal method on a tire molding machine. After forming and bonding together with other tire members to form an unvulcanized tire, the tire can be manufactured by heating and pressing 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 the synthesis of the monomer (1) and the polymers (1) to (2) will be described.
Cyclohexane: Kanto Chemical Co., Ltd. Pyrrolidine: Kanto Chemical Co., Ltd. divinylbenzene: Sigma Aldrich 1.6M n-butyllithium hexane solution: Kanto Chemical Co., Ltd. Isopropanol: Kanto Chemical Co., Ltd. Styrene: Kanto Chemical Co., Ltd. Butadiene: Takachiho Chemical Industry Co., Ltd. Tetramethylethylenediamine: Kanto Chemical Co., Ltd. Modifier: Amax Co. 3- (N, N-dimethylamino) propyltrimethoxysilane

Production Example 1 (Synthesis of Monomer (1))
Add 100 ml of cyclohexane, 4.1 ml (3.6 g) of pyrrolidine, and 6.5 g of divinylbenzene to a 100 ml container sufficiently purged with nitrogen, and then add 0.7 ml of 1.6 M n-butyllithium hexane solution at 0 ° C. And stirred.
After 1 hour, isopropanol was added to stop the reaction, and extraction / purification was performed to obtain a monomer (1).

Production Example 2 (Synthesis of Polymer (1))
To a 1000 ml pressure vessel fully purged with nitrogen, add 600 ml of cyclohexane, 12.6 ml (11.4 g) of styrene, 71.0 ml (41.0 g) of butadiene, 0.29 g of monomer (1), and 0.11 ml of tetramethylethylenediamine. Then, 0.2 ml of 1.6M n-butyllithium hexane solution was added at 40 ° C. and stirred.
After 3 hours, 3 ml of isopropanol was added to stop the polymerization. After adding 1 g of 2,6-tert-butyl-p-cresol to the reaction solution, reprecipitation treatment was performed with methanol, followed by heating and drying to obtain a polymer (1).

Production Example 3 (Synthesis of polymer (2))
To a 1000 ml pressure vessel fully purged with nitrogen, add 600 ml of cyclohexane, 12.6 ml (11.4 g) of styrene, 71.0 ml (41.0 g) of butadiene, 0.29 g of monomer (1), and 0.11 ml of tetramethylethylenediamine. Then, 0.2 ml of 1.6M n-butyllithium hexane solution was added at 40 ° C. and stirred.
After 3 hours, 0.5 ml (0.49 g) of 3- (N, N-dimethylamino) propyltrimethoxysilane (modifier) was added and stirred.
After 1 hour, 3 ml of isopropanol was added to terminate the polymerization. After adding 1 g of 2,6-tert-butyl-p-cresol to the reaction solution, reprecipitation treatment was performed with methanol, followed by heating and drying to obtain a polymer (2).

(Measurement of weight average molecular weight Mw of polymer)
The weight average molecular weight Mw of the polymer is determined 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 measured value.

(Measurement of content of nitrogen-containing compound in polymer)
The content (monomer (1) amount) of the nitrogen-containing compound in the polymer was measured using a JNM-ECA series device manufactured by JEOL Ltd.

Hereinafter, the chemical | medical agent used by the Example and the comparative example is demonstrated.
SBR: E15 manufactured by Asahi Kasei Chemicals Corporation
Polymer 1: Main chain modified SBR (manufactured in Production Example 2, Mw: 3.0 × 10 ⁵ , monomer (1) amount: 1.0 mass%)
Polymer 2: Main chain and terminal-modified SBR (produced in Production Example 3, Mw: 3.0 × 10 ⁵ , monomer (1) amount: 1.0 mass%)
BR1: Ubepol BR150B manufactured by Ube Industries, Ltd.
BR2: Ubepol BR150L manufactured by Ube Industries, Ltd.
BR3: Ubepol BR230 manufactured by Ube Industries, Ltd.
BR4: Ubepol BR710 manufactured by Ube Industries, Ltd. (high-cis polybutadiene rubber produced by the method described in Japanese Patent No. 4124273)
NR: RSS # 3
Silica: ULTRASIL VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g)
Carbon black: Dia Black N220 manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 114 m ² / g)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Zinc oxide: Zinc Hua 1 manufactured by Mitsui Mining & Smelting Co., Ltd.
Anti-aging agent: Antigen 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator manufactured by Karuizawa Sulfur Co., Ltd. 1: Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Vulcanization accelerator 2: Noxeller D (N, N'-diphenylguanidine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Table 1 summarizes the results of analysis of BR1 to BR4 by the measurement method described above. Note that BR4 corresponds to the high-cis polybutadiene.

Examples and Comparative Examples According to the formulation shown in Table 2, materials other than sulfur and a vulcanization accelerator were kneaded for 5 minutes at 150 ° C. using a Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 3 minutes at 80 ° C. using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition is molded into a tread shape, bonded to another tire member, molded into a tire, and vulcanized at 170 ° C. for 10 minutes to test tires (tire size: 195 / 65R15). ) Was manufactured.

The following evaluation was performed using the obtained unvulcanized rubber composition and the test tire. The results are shown in Table 2.

(Processability (kneading processability))
The above unvulcanized rubber composition was extruded and the sheet shape of the obtained rubber sheet was visually observed and evaluated according to the following criteria. The worse the sheet shape, the lower the workability (workability). If the result is ◎ or ○, the workability is at a satisfactory level.
A: The sheet shape is very good B: The sheet shape is good B: The sheet shape is bad X: The sheet shape is tattered (very bad)

(Rolling resistance)
Using a rolling resistance tester, the rolling resistance when the test tire was run at a rim (15 × 6JJ), internal pressure (230 kPa), load (3.43 kN), speed (80 km / h) was measured, and Comparative Example 1 Is expressed as an index when the value is 100. A larger index indicates lower rolling resistance and better fuel efficiency.

(Wet grip performance)
The braking distance from the initial speed of 100 km / h was determined on the wet asphalt road surface. The result is expressed as an index. The larger the index, the better the wet skid performance (wet grip performance). The index was calculated by the following formula.
Wet grip performance index = (braking distance of comparative example 1) / (braking distance of each example or each comparative example) × 100

(Abrasion resistance)
The manufactured test tire was mounted on a car, and the amount of decrease in the groove depth after traveling 8000 km in an urban area was measured, and the travel distance when the groove depth decreased by 1 mm was calculated. Then, the wear resistance index of Comparative Example 1 was set to 100, and the amount of decrease in groove depth was displayed as an index according to the following formula. It shows that it is excellent in abrasion resistance, so that an index | exponent is large.
Abrasion resistance index = (travel distance of each example or each comparative example) / (travel distance of comparative example 1) × 100

From Table 2, a rubber component containing a specific amount of modified SBR (polymers 1 and 2) using a specific nitrogen-containing compound as a main chain modifying monomer and a specific high-cis polybutadiene (BR4), and a specific amount of silica In the Example which mix | blended with, compared with the comparative example, the low fuel consumption, wet grip performance, abrasion resistance, and kneading | mixing workability could be improved with sufficient balance. It has also been clarified that the combined use of the modified SBR and high-cis polybutadiene can improve the wear resistance synergistically.

Claims (3)

Containing a rubber component and silica having a nitrogen adsorption specific surface area of 100 to 300 m ² / g ,
In 100% by mass of the rubber component,
The following general formula:

(In the formula, R ⁰ represents hydrogen, an aliphatic hydrocarbon group having 1 to 30 carbon atoms, an alicyclic hydrocarbon group having 3 to 30 carbon atoms, or an aromatic hydrocarbon group having 5 to 30 carbon atoms. R ¹ And R ² are the same or different and are hydrogen,

Or

And at least ^one of R ¹ and R ² is not hydrogen. R ³ represents hydrogen or a hydrocarbon group having 1 to 4 carbon atoms. X represents a divalent saturated hydrocarbon group and may contain nitrogen, oxygen or sulfur;

Or

May be substituted. Z represents a divalent saturated hydrocarbon group and may contain nitrogen, oxygen or sulfur. R ^{4 to} R ⁷ are the same or different and are hydrogen, an aliphatic hydrocarbon group having 1 to 30 carbon atoms, an alicyclic hydrocarbon group having 3 to 30 carbon atoms, or an aromatic hydrocarbon group having 5 to 30 carbon atoms. Or a heterocyclic group having 3 to 30 ring atoms. ) The content of the modified styrene butadiene rubber having a structural unit derived from the nitrogen-containing compound represented by
(A) Mooney viscosity (ML): 40 to 49, (B) Molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn): 3.0 to 3.9, and (C) Rate dependency index of Mooney viscosity (formula N value of (1)): satisfying the requirement of 2.3 to 3.0, and the content of high cis polybutadiene having a cis content of 95% by mass or more is 10 to 70% by mass,
A rubber composition for tires, wherein the silica content is 60 to 150 parts by mass with respect to 100 parts by mass of the rubber component.
log (ML) = log (K) + n ⁻¹ × log (RS) Formula (1)
(However, RS represents the number of rotations per minute of the rotor, K represents an arbitrary number, and ML represents Mooney viscosity.) The tire rubber composition according to claim 1, which is used as a tread rubber composition. A pneumatic tire having a tread produced using the rubber composition according to claim 2.