JP2018083932A - Rubber composition for tread and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for treads, in which higher mileage, wear resistance and wet grip performance are improved with good balance while obtaining good processability, and pneumatic tires using the rubber composition.SOLUTION: A rubber composition for treads, which contains polybutadiene satisfying conditions of (A) a ratio (Tcp/ML) of solution viscosity of 5% by mass of toluene (Tcp) and MOOney viscosity (ML) is 0.9 to 2.3, (B) when a torque at the end of measurement of MLis set to 100%, a stress relaxation time until the value thereof attenuates to 80% (T80) is 10.0 to 40.0 seconds, and (C) a molecular weight distribution (Mw/Mn) is 2.50 to 4.00, and a terpenoid resin having the glass transition temperature (Tg) of 40 to 90°C.SELECTED DRAWING: None

Description

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

Treads are required to have various properties such as low fuel consumption, wear resistance, rubber physical properties such as wet grip performance, and processability, and are being improved. For example, methods have been proposed to improve fuel economy with terminal-modified rubber, wear resistance with high molecular weight polymers, and wet grip performance with polymers with high glass transition temperatures. There is a problem that the hardness of an object increases and processability deteriorates, and it is generally difficult to achieve both of these performances.

Patent Document 1 proposes a technique for improving fuel economy, wear resistance and wet grip performance by using a liquid resin having a softening point of -20 to 45 ° C. and specific silica, but there is still room for improvement. ing.

In recent years, the demand for performance improvement is severe, and further improvement is desired for improving fuel economy, wear resistance, and wet grip performance in a well-balanced manner while obtaining good processability.

JP 2013-053296 A

The present invention solves the above-mentioned problems and obtains good processability while improving fuel economy, wear resistance and wet grip performance in a well-balanced manner, and a pneumatic composition using the rubber composition. The object is to provide a tire.

In the present invention, (A) the ratio of 5 mass% toluene solution viscosity (Tcp) and Mooney viscosity (ML _{1 + 4,100 ° C.} ) (Tcp / ML _{1 + 4,100 ° C.} ) is 0.9 to 2.3, (B) ML When the torque at the time of _{1 + 4,100 ° C.} measurement is 100%, the stress relaxation time (T80) until the value is attenuated to 80% is 10.0 to 40.0 seconds, and (C) molecular weight distribution (Mw / Mn) relates to a rubber composition for a tread containing polybutadiene satisfying a condition of 2.50 to 4.00 and a terpene resin having a glass transition temperature (Tg) of 40 to 90 ° C.

It is preferable that 5 to 90% by mass of the polybutadiene is contained in 100% by mass of the rubber component, and 1 to 20 parts by mass of the terpene resin is contained with respect to 100 parts by mass of the rubber component.
In 100% by mass of the rubber component, it is preferable that 10 to 95% by mass of other rubber components other than the polybutadiene rubber is included, and 10 to 100 parts by mass of silica is included with respect to 100 parts by mass of the rubber component.

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

According to the present invention, since it is a rubber composition for a tread containing polybutadiene satisfying the above (A), (B) and (C) and a terpene resin having a predetermined Tg, while obtaining good processability, Low fuel consumption, wear resistance and wet grip performance can be improved in a well-balanced manner.

The rubber composition for a tread of the present invention has a ratio (Tcp / ML _{1 + 4,100 ° C.} ) of (A) 5 mass% toluene solution viscosity (Tcp) and Mooney viscosity (ML _{1 + 4,100 ° C.} ) of 0.9-2. 3, (B) ML _{1 + 4,} when the torque at the end of measurement at _{100 ° C.} is 100%, the stress relaxation time (T80) until the value is attenuated to 80% is 10.0 to 40.0 seconds, and ( C) Polybutadiene satisfying a molecular weight distribution (Mw / Mn) of 2.50 to 4.00 and a terpene resin having a glass transition temperature (Tg) of 40 to 90 ° C.

In treads, it is generally difficult to improve fuel economy, wear resistance, and wet grip performance in a well-balanced manner while obtaining good processability. Since the specific polybutadiene satisfying all the conditions of A), (B), and (C) and the terpene resin having a specific Tg are used in combination, the above-mentioned problems can be solved.

The specific polybutadiene provides excellent kneadability while obtaining excellent silica dispersibility, rolling resistance, abrasion resistance, and wet grip performance, and the terpene resin is inherently difficult to achieve both. As a result of dramatically improving wet grip performance while maintaining other performance, it is presumed that fuel economy, wear resistance, and wet grip performance are improved in a well-balanced manner while obtaining good processability. Therefore, the combined use of both components synergistically improves the performance balance of low fuel consumption, wear resistance and wet grip performance while obtaining good processability.

(Polybutadiene)
The polybutadiene has a ratio (Tcp / ML _{1 + 4,100 ° C.} ) of (A) 5 mass% toluene solution viscosity (Tcp) and Mooney viscosity (ML _{1 + 4,100 ° C.} ) of 0.9 to 2.3; 9-1.7 are preferable, 1.2-1.7 are more preferable, and 1.4-1.7 are still more preferable. The ratio is an index of the degree of branching of polybutadiene, and the larger the ratio, the smaller the degree of branching of polybutadiene, that is, the higher the linearity. By setting the ratio to 0.9 or more, there is a tendency that tan δ of the vulcanized rubber is lowered and good fuel efficiency is obtained. There exists a tendency for favorable workability to be acquired by setting it as 2.3 or less.

The Mooney viscosity (ML _{1 + 4, 100 ° C.} ) of the polybutadiene is preferably 43 to 70, more preferably 48 to 70, and still more preferably 50 to 67. By setting it to 43 or more, good wear resistance tends to be obtained. On the other hand, by making it 70 or less, there exists a tendency for favorable workability to be obtained.
Tcp, ML _{1 + 4, and 100 ° C.} are values obtained by the measurement methods described in Examples described later.

The toluene solution viscosity (Tcp) of the polybutadiene is preferably 42 to 160, more preferably 55 to 135, and still more preferably 68 to 120. By setting it to 42 or more, the wear resistance is further improved. On the other hand, by making Tcp 160 or less, workability is further improved.

The polybutadiene has (B) ML _{1 + 4} , the stress relaxation time (T80) until the value is attenuated to 80% when the torque at the end of measurement at _{100 ° C.} is 100%, and is 10.0 to 40.0 seconds. Yes, preferably 11.0 to 26.0 seconds, more preferably 12.0 to 20.0 seconds. By setting it to 10.0 seconds or more, there is a tendency that the retention of shear stress is sufficient and a good filler dispersion state is obtained. There exists a tendency for favorable workability to be acquired by setting it as 40.0 second or less. The transition of the stress relaxation of rubber is determined by a combination of an elastic component and a viscous component, and a slow stress relaxation indicates that there are many elastic components, and a fast stress indicates that there are many viscous components.
T80 is a value obtained by the measurement method described in the examples described later.

The polybutadiene has a (C) molecular weight distribution (Mw / Mn) of 2.50 to 4.00, preferably 2.60 to 3.60, more preferably 2.70 to 3.20. When it is 2.50 or more, good workability is obtained, and when it is 4.00 or less, good wear resistance tends to be obtained.

The weight average molecular weight (Mw) of the polybutadiene is preferably 40.0 × 10 ^{4 to} 75.0 × 10 ⁴ , more preferably 46.0 × 10 ^{4 to} 65.0 × 10 ⁴ , and even more preferably 52.0. × is ^{10 4 ~62.0} × ¹⁰ 4. When it is at least the lower limit, good wear resistance is obtained, and when it is at most the upper limit, good workability tends to be obtained.
Mw and Mn are values converted from standard polystyrene using a gel permeation chromatograph (GPC).

The number average molecular weight (Mn) of the polybutadiene is preferably 12.5 × 10 ^{4 to} 30.0 × 10 ⁴ , more preferably 16.0 × 10 ^{4 to} 23.0 × 10 ⁴ , and even more preferably 17.0. × is ^{10 4 ~20.3} × ¹⁰ 4. When it is at least the lower limit, good wear resistance is obtained, and when it is at most the upper limit, good workability tends to be obtained.

The proportion of the cis structure in the microstructural analysis of the polybutadiene is preferably 98 mol% or less, more preferably 94.0 to 97.8 mol%, and 95.0 to 97.6 mol%. More preferably. By setting it as 98 mol% or less, it has a sufficient branched polymer chain, and the required stress relaxation time is easily obtained. However, if the ratio of the cis structure is too small, the wear resistance tends to be lowered.

The proportion of the vinyl structure in the microstructural analysis of the polybutadiene is preferably 2 mol% or less, and more preferably 1.8 mol% or less. When the proportion of the vinyl structure in the microstructure analysis is 2 mol% or less, the molecular mobility is improved, and the tan δ of the dynamic viscoelastic property after vulcanization is improved. The vinyl structure ratio in the microstructural analysis is preferably as small as possible, but may be, for example, 1.0 mol% or more.

The proportion of the trans structure in the microstructural analysis of the polybutadiene is preferably 2.0 mol% or less, more preferably 1.6 mol% or less, and even more preferably 1.3 mol% or less. . Wear resistance improves more by setting it as 2.0 mol% or less. Note that the ratio of the trans structure in the microstructure analysis is preferably as small as possible, but may be, for example, 1.0 mol% or more.
The proportion of the microstructure is measured by the method described in Examples described later.

The content of the polybutadiene is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 15% by mass or more in 100% by mass of the rubber component. The content is preferably 90% by mass or less, more preferably 50% by mass or less, and still more preferably 40% by mass or less. By setting the content to 5% by mass or more, kneadability, silica dispersion, rolling resistance, wet grip performance, and wear resistance tend to be improved in a well-balanced manner within the above range. In this case, it is preferable to blend 10 to 95% by mass of other rubber components.

(Polybutadiene production method)
The polybutadiene used in the present invention can be produced by a catalyst system comprising a transition metal catalyst, an organoaluminum compound, and water.

A cobalt catalyst is suitable as the transition metal catalyst. Cobalt catalysts include cobalt chloride, cobalt bromide, cobalt nitrate, cobalt octylate (ethylhexanoate), cobalt naphthenate, cobalt acetate, cobalt malonate, etc .; cobalt bisacetylacetonate, cobalt trisacetylacetonate And organic base complexes such as acetoacetic acid ethyl ester cobalt, cobalt salt pyridine complex and picoline complex, or ethyl alcohol complex. Of these, octylic acid (ethylhexanoic acid) cobalt is preferable. If a polybutadiene having the above physical properties can be obtained, other catalysts such as a neodymium catalyst and a nickel catalyst can be used.

The amount of the transition metal catalyst used can be appropriately adjusted so as to obtain a polybutadiene having a desired Mooney viscosity.

Examples of organoaluminum compounds include trialkylaluminum; dialkylaluminum chloride, dialkylaluminum bromide, alkylaluminum sesquichloride, alkylaluminum sesquibromide, alkylaluminum dichloride, alkylaluminum dibromide, and other halogen-containing organoaluminum compounds; dialkylaluminum hydride, alkylaluminum Examples thereof include organic aluminum hydride compounds such as sesquihydride. An organoaluminum compound can be used individually by 1 type, and can also be used together 2 or more types.

Specific examples of the trialkylaluminum include trimethylaluminum, triethylaluminum, triinbutylaluminum, trihexylaluminum, trioctylaluminum, and tridecylaluminum.

Examples of the dialkylaluminum chloride include dimethylaluminum chloride and diethylaluminum chloride. Examples of the dialkylaluminum bromide include dimethylaluminum bromide and diethylaluminum bromide. Examples of the alkylaluminum sesquichloride include methylaluminum sesquichloride and ethylaluminum sesquichloride. Examples of the alkylaluminum sesquibromide include methylaluminum sesquibromide and ethylaluminum sesquibromide. Examples of the alkylaluminum dichloride include methylaluminum dichloride and ethylaluminum dichloride. Examples of the alkylaluminum dibromide include methylaluminum dibromide and ethylaluminum dibromide.

Examples of the dialkylaluminum hydride include diethylaluminum hydride and diisobutylaluminum hydride. Examples of the alkylaluminum sesquihydride include ethylaluminum sesquihydride and imptyl aluminum sesquihydride.

Regarding the mixing ratio of the organoaluminum compound and water, since it is easy to obtain a polybutadiene having the desired T80, the aluminum / water (molar ratio) is preferably 1.5 to 3, and preferably 1.7 to 2. 5 is more preferable.

Furthermore, in order to obtain a polybutadiene having a desired Mooney viscosity, non-conjugated dienes such as cyclooctadiene, allene, and methylallene (1,2-butadiene); molecular weights such as α-olefins such as ethylene, propylene, and 1-butene A regulator can also be used. A molecular weight regulator can be used individually by 1 type, and can also be used together 2 or more types.

The polymerization method is not particularly limited, and bulk polymerization (bulk polymerization) in which monomers are polymerized using a conjugated diene compound monomer such as 1,3-butadiene as a polymerization solvent, or solution polymerization in which monomers are dissolved in a solvent is polymerized. Etc. can be applied. Solvents used in the solution polymerization include aromatic hydrocarbons such as toluene, benzene and xylene; saturated aliphatic hydrocarbons such as n-hexane, butane, hebutane and hentan; alicyclic hydrocarbons such as cyclopentane and cyclohexane; Examples thereof include olefinic hydrocarbons such as cis-2-butene and trans-2-butene; petroleum solvents such as mineral spirit, solvent naphtha, and kerosene; halogenated hydrocarbons such as methylene chloride. Of these, toluene, cyclohexane, and a mixed solvent of cis-2-butene and trans-2-butene are preferably used.

The polymerization temperature is preferably in the range of −30 to 150 ° C., more preferably in the range of 30 to 100 ° C., and even more preferably 70 to 80 ° C. because polybutadiene having the desired T80 is easily obtained. The polymerization time is preferably in the range of 1 minute to 12 hours, and more preferably in the range of 5 minutes to 5 hours.

After the polymerization reaction reaches a predetermined polymerization rate, an anti-aging agent can be added as necessary. Anti-aging agents include phenol-based anti-aging agents such as 2,6-di-t-ptyl-p-cresol (BHT), phosphorus-based anti-aging agents such as trinonylphenyl phosphite (TNP), and 4,6 -Sulfur-based antioxidants such as -bis (octylthiomethyl) -o-cresol and dilauryl-3,3'-thiodipropionate (TPL). One type of anti-aging agent can be used alone, or two or more types can be used in combination. The addition amount of the antioxidant is preferably 0.001 to 5 parts by mass with respect to 100 parts by mass of the polybutadiene.

After carrying out the polymerization for a predetermined time, the inside of the polymerization tank is released as necessary, and further post-treatment such as washing and drying steps is performed to produce polybutadiene having desired characteristics.

Moreover, what is manufactured and sold from the Ube Industries, Ltd., Lanxess, etc. can also be used for the said polybutadiene.

In the present invention, other rubber components may be used together with the polybutadiene. Examples of other rubber components include natural rubber (NR), isoprene rubber (IR), other butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene (SIR), and styrene isoprene butadiene rubber (SIBR). And diene rubbers such as ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and butyl rubber (IIR). These rubber components may be used alone or in combination of two or more. Among these, SBR is preferable from the viewpoint that the effects of the present invention can be obtained satisfactorily.

When SBR is contained, the content thereof is preferably 5% by mass or more, more preferably 50% by mass or more, and further preferably 60% by mass or more, in 100% by mass of the rubber component. When the content is 5% by mass or more, good wear resistance and wet grip performance tend to be obtained. The content is preferably 95% by mass or less, more preferably 90% by mass or less. When the content is 95% by mass or less, good low heat generation tends to be obtained.

SBR manufactured and sold by JSR Corporation, Sumitomo Chemical Co., Ltd., etc. can be used.

The rubber composition of the present invention contains a terpene resin (terpene resin) having a glass transition temperature (Tg) of 40 to 90 ° C. The Tg is preferably 45 to 80 ° C, more preferably 50 to 70 ° C. By adjusting within the above range, wet grip performance is greatly improved, and the performance balance tends to be remarkably improved.
In addition, Tg is a value (midpoint glass) measured according to JIS-K7121 using a differential scanning calorimeter (Q200) manufactured by TA Instruments Japan Co., Ltd. under a temperature rising rate of 10 ° C./min. Transition temperature).

The weight average molecular weight (Mw) of the terpene resin is preferably 500 or more, more preferably 1000 or more, and still more preferably 1500 or more. The weight average molecular weight is preferably 10,000 or less, more preferably 5000 or less, and still more preferably 3500 or less. By adjusting within the above range, wet grip performance is greatly improved, and the performance balance tends to be remarkably improved.

The content of the terpene resin is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and still more preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 20 parts by mass or less, more preferably 18 parts by mass or less, and still more preferably 15 parts by mass or less. When the amount is 1 part by mass or more, good fuel economy and processability are obtained, and when the amount is 20 parts by mass or less, good wear resistance tends to be obtained.

As the terpene resin, a polyterpene resin obtained by polymerizing a terpene compound, an aromatic modified terpene resin obtained by polymerizing a terpene compound and an aromatic compound, or the like can be used. These hydrogenated products can also be used.

The polyterpene resin is a resin obtained by polymerizing a terpene compound. The terpene compound is a hydrocarbon represented by a composition of (C ₅ H ₈ ) _n and an oxygen-containing derivative thereof. Monoterpene (C ₁₀ H ₁₆ ), sesquiterpene (C ₁₅ H ₂₄ ), diterpene (C ₂₀ H ₃₂₎ Terpenes having a basic skeleton classified into, for example, α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, ocimene, α-ferrandrene, α-terpinene, γ-terpinene, terpinolene 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, γ-terpineol and the like.

Examples of the polyterpene resin include a pinene resin, a limonene resin, a dipentene resin, and a pinene / limonene resin made from the above-mentioned terpene compound. Of these, pinene resin is preferred. The pinene resin usually contains both α-pinene and β-pinene having an isomer relationship, but due to the difference in the components contained, β-pinene resin containing β-pinene as a main component and α-pinene It is classified into α-pinene resin mainly composed of pinene.

Examples of the aromatic modified terpene resin include a terpene phenol resin using the terpene compound and the phenolic compound as raw materials, and a terpene styrene resin using the terpene compound and the styrene compound as raw materials. Moreover, the terpene phenol styrene resin which uses the said terpene compound, a phenol type compound, and a styrene type compound as a raw material can also be used.

As the terpene-based resin, a polyterpene resin is preferable and a β-pinene resin is more preferable because the effects of the present invention can be obtained well.

As the terpene resin, those manufactured and sold by Yashara Chemical Co., Ltd., KRATON CORPORATION, etc. can be used.

The rubber composition of the present invention preferably contains silica from the viewpoint that the effects of the present invention can be obtained satisfactorily.

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. Further, the _N 2 SA is preferably 300 meters ² / g or less, and more preferably not more than 200m ² / g. By setting it to 100 m ² / g or more, good wear resistance can be obtained, and by setting it to 300 m ² / g or more, there is a tendency that good silica dispersion and low fuel consumption can be obtained.
The _N 2 SA of silica can be measured in accordance with ASTMD3037-81.

The content of silica is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and still more preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 100 parts by mass or less, more preferably 90 parts by mass or less. When it is 10 parts by mass or more, good fuel economy and wear resistance can be obtained, and when it is 100 parts by mass or less, good silica dispersibility and workability tend to be obtained.

The rubber composition of the present invention preferably contains a silane coupling agent together with silica.
Examples of the silane coupling agent include sulfides such as bis (3-triethoxysilylpropyl) tetrasulfide, mercaptos such as 3-mercaptopropyltrimethoxysilane, vinyls such as vinyltriethoxysilane, and 3-aminopropyltriethoxy. Examples thereof include amino-based compounds such as silane, glycidoxy-based compounds of γ-glycidoxypropyltriethoxysilane, nitro-based compounds such as 3-nitropropyltrimethoxysilane, and chloro-based compounds such as 3-chloropropyltrimethoxysilane. Among these, sulfide type is preferable, and bis (3-triethoxysilylpropyl) tetrasulfide is more preferable. The content of the silane coupling agent is preferably 1 to 20 parts by mass with respect to 100 parts by mass of silica.

The rubber composition of the present invention preferably contains carbon black from the viewpoints of wear resistance, wet grip properties and the like.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 80 m ² / g or more, more preferably 100 m ² / g or more. The N ₂ SA is preferably 200 m ² / g or less, more preferably 150 m ² / g or less. By making it 80 m ² / g or more, good reinforcing properties can be obtained and excellent wear resistance can be obtained, and by making it 200 m ² / g or less, good carbon black dispersion can be obtained, and excellent low fuel consumption. There is a tendency to have sex.
Incidentally, _N 2 SA of carbon black is, JIS-K6217-2: can be measured in conformity with 2001.

The content of carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more with respect to 100 parts by mass of the rubber component. Moreover, this content becomes like this. Preferably it is 15 mass parts or less, More preferably, it is 10 mass parts or less, More preferably, it is 8 mass parts or less. When the amount is 1 part by mass or more, good wear resistance is obtained, and when the amount is 15 parts by mass or less, good fuel efficiency tends to be obtained.

The rubber composition of the present invention can contain other reinforcing fillers, anti-aging agents, vulcanizing agents such as oil, wax, sulfur, vulcanization accelerators, and the like as appropriate in addition to the above components.

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 into a tread shape at an unvulcanized stage and molded together with other tire members on a tire molding machine by a normal method. Form a sulfur tire. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

The pneumatic tire of the present invention can be suitably used for passenger car tires, large passenger car tires, large SUV tires, heavy duty tires such as trucks and buses, and light truck tires.

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

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
SBR: commercial product manufactured by Nippon Zeon Co., Ltd. (solution-polymerized SBR end-modified with N-methylpyrrolidone, styrene content = 21 mass%, Tg = −25 ° C.)
BR1 (polybutadiene): Tcp / ML _{1 + 4, 100 ° C.} = 1.6, ML _{1 + 4, 100 ° C.} = 67, T80 = 20.0 seconds, Mw / Mn = 2.99, Mw = 52.9 × 10 ⁴ , cis Polybutadiene having physical properties of structure = 97.6 mol%, vinyl structure = 1.4 mol%, trans structure = 1.3 mol% (Production Example 1 below)
BR2: Commercial products of Ube Industries, Ltd. (Tcp / ML _{1 + 4, 100 ° C.} = 2.4, ML _{1 + 4, 100 ° C.} = 42, T80 = 3.2 seconds, Mw / Mn = 2.36, Mw = 49. 8 × 10 ⁴ , cis structure = 98.1 mol%, vinyl structure = 0.9 mol%, trans structure = 1.0 mol%)
BR3: Commercial product of Ube Industries, Ltd. (Tcp / ML _{1 + 4, 100 ° C.} = 2.9, ML _{1 + 4, 100 ° C.} = 44, T80 = 3.5 seconds, Mw / Mn = 3.12, Mw = 57. 4 × 10 ⁴ , cis structure = 97.8 mol%, vinyl structure = 1.1 mol%, trans structure = 1.2 mol%)
Silica: Ultrasil VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g)
Carbon Black: Show Black N220 (N ₂ SA: 111 m ² / g, DBP: 115 ml / 100 g) manufactured by Cabot Japan
Terpene resin: SYLVATRAXX4150 (β-pinene resin, β-pinene content: 98% by mass or more, non-hydrogenated, Tg: 61 ° C., Mw2350, Mn830)
Oil: Diana Process AH-24 (aromatic process oil) manufactured by Idemitsu Kosan Co., Ltd.
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Wax: Sunnock wax anti-aging agent manufactured by Ouchi Shinsei Chemical Industry Co., Ltd .: NOCRACK 6C (N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shin Chemical Co., Ltd. )
Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Sulfur stearate manufactured by NOF Corporation: Sulfur powder vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Ouchi Shinsei Chemical Industry ( Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by

(Production Example 1)
In a 1.5 L stainless steel reactor equipped with a stirrer, the content was replaced with nitrogen gas, 1.0 L of a polymerization solution (butadiene (BD): 34.2% by mass, cyclohexane (CH): 31.2% by mass, the rest) 2-butenes). Further, 1.52 mmol of water (H ₂ 0), 2.08 mmol of diethylaluminum chloride (DEAC), 0.52 mmol of triethylaluminum (aluminum / water = 1.71 (mixing molar ratio)), cobalt octate (Cocat) 20. 94 μmol and 6.05 mmol of cyclooctadiene (COD) were added, and the mixture was stirred at 70 ° C. for 20 minutes to carry out 1,4 cis polymerization. Thereafter, etamer containing 4,6-bis (octylthiomethyl) -orcresol was added to terminate the polymerization, and unreacted butadiene and 2-butenes were removed by evaporation to obtain polybutadiene (BR1).

<Examples and Comparative Examples>
In accordance with the formulation shown in Table 1, various chemicals except sulfur and a vulcanization accelerator were kneaded at 150 ° C. for 5 minutes using a Banbury mixer. Sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded for 12 minutes at 80 ° C. using an open roll to obtain an unvulcanized rubber composition.
The obtained unvulcanized rubber composition was press vulcanized at 170 ° C. for 20 minutes to obtain a vulcanized rubber composition.

Various properties of polybutadiene, Mooney viscosity index, rolling resistance index, wet grip index, and abrasion resistance index of the obtained unvulcanized rubber composition and vulcanized rubber composition were measured and evaluated as follows. The evaluation results are shown in Table 1.

(5 mass% toluene solution viscosity (Tcp))
The 5 mass% toluene solution viscosity (Tcp) of polybutadiene was obtained by dissolving 2.28 g of polymer in 50 ml of toluene, 400 was measured at 25 ° C. As the standard solution, a viscometer calibration standard solution (JIS Z8809) was used.

(Mooney viscosity (ML _{1 + 4, 100 ° C} ))
The Mooney viscosity (ML _{1 + 4, 100 ° C.} ) of polybutadiene was measured at 100 ° C. according to JIS-K6300.

(Stress relaxation time (T80))
The stress relaxation time (T80) of polybutadiene was calculated by stress relaxation measurement according to ASTM D1646-7. Specifically, under the measurement condition of ML _{1 + 4, 100 ° C.} , the torque when the rotor stops after 4 minutes of measurement (0 second) is set to 100%, and the value is attenuated to 80% (ie, attenuates to 20%). ) (Unit: second) was measured as stress relaxation time T80.

(Number average molecular weight (Mn), weight average molecular weight (Mw), molecular weight distribution (Mw / Mn))
The number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw / Mn) of polybutadiene were calculated in terms of standard polystyrene by GPC method (trade name: HLC-8220, manufactured by Tosoh Corporation). Tetrahydrofuran was used as the solvent, two KF-805L (trade name) manufactured by Shodex were connected in series, and a suggestive refractometer (RI) was used as the detector.

(Micro structure)
The microstructure of polybutadiene was calculated by infrared absorption spectrum analysis. Specifically, the peak position derived from the microstructure ^{(cis: 740cm -1, vinyl:} 910cm -1, trans: 967cm -1) from the absorption intensity ratio was calculated microstructure of the polymer.

[Processability (Mooney viscosity index)]
About each unvulcanized rubber composition, it measured at 100 degreeC according to the measuring method of the Mooney viscosity based on JISK6300. The Mooney viscosity (ML _{1 + 4} ) of Comparative Example 1 was set to 100, and the result was expressed as an index. The larger the index, the better the workability.

[Low fuel consumption (rolling resistance index)]
A test piece of a predetermined size was cut out from the obtained vulcanized rubber composition, and using a viscoelastic spectrometer manufactured by Ueshima Seisakusho, under conditions of initial strain 10%, dynamic strain 2%, frequency 10 Hz, 60 The loss tangent (tan δ) of the vulcanized rubber sheet at 0 ° C. was measured. The tan δ of Comparative Example 1 was set to 100, and the index was displayed by the following calculation formula. A larger index indicates better fuel efficiency.
(Rolling resistance index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(Wet grip index)
About the test piece prepared from the obtained vulcanized rubber composition, the viscoelastic parameter was measured in the torsion mode using a viscoelasticity tester (ARES) manufactured by Rheometrics Scientific. Tan δ was measured at 0 ° C. with a frequency of 10 Hz and a strain of 1%. The tan δ of Comparative Example 1 was set to 100, and the index was displayed by the following calculation formula. A larger index indicates better wet grip performance.
(Wet grip index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(Abrasion resistance index)
The amount of wear of the resulting vulcanized rubber composition was measured using a Lambone-type wear tester under the conditions of room temperature, applied load of 1.0 kgf, and slip rate of 30%, and indicated by an index using the following formula. It shows that it is excellent in abrasion resistance, so that an index | exponent is large.
(Abrasion resistance index) = (Abrasion amount of Comparative Example 1) / (Abrasion amount of each formulation) × 100

From Table 1, in an example in which polybutadiene satisfying the above (A), (B) and (C) and a terpene resin having a predetermined Tg are used in combination, a comparative example in which these two components are not used, Compared to the comparative example using polybutadiene and further to the comparative example in which no terpene resin is added, the performance balance of fuel efficiency, wear resistance and wet grip performance is synergistically improved while obtaining good processability. It became clear.

Claims (4)

(A) Ratio of 5% by mass toluene solution viscosity (Tcp) and Mooney viscosity (ML _{1 + 4,100 ° C.} ) (Tcp / ML _{1 + 4,100 ° C.} ) is 0.9 to 2.3, (B) ML _{1 + 4,100 ° C.} When the torque at the end of measurement is 100%, the stress relaxation time (T80) until the value is attenuated to 80% is 10.0 to 40.0 seconds, and (C) the molecular weight distribution (Mw / Mn) is Polybutadiene satisfying the condition of 2.50 to 4.00,
A rubber composition for a tread comprising a terpene resin having a glass transition temperature (Tg) of 40 to 90 ° C. In 100% by mass of the rubber component, the polybutadiene is included in an amount of 5 to 90% by mass,
The rubber composition for treads of Claim 1 which contains 1-20 mass parts of said terpene resin with respect to 100 mass parts of rubber components. In a rubber component of 100% by mass, other rubber components other than the polybutadiene rubber are included in an amount of 10 to 95% by mass,
The rubber composition for treads of Claim 1 or 2 which contains 10-100 mass parts of silica with respect to 100 mass parts of rubber components. A pneumatic tire having a tread produced using the rubber composition according to claim 1.