JP2019218502A - Cap tread and pneumatic tire - Google Patents

Abstract

To provide a cap tread composed of a tire rubber composition having improved wear resistance and fuel economy while maintaining workability.SOLUTION: A tire rubber composition contains a polybutadiene rubber (i), another rubber (ii), and a rubber reinforcement material (iii), where the polybutadiene rubber (i) contains a polybutadiene (A) satisfying the conditions of the ratio between a 5 wt.% toluene solution viscosity and a Mooney viscosity (Tcp/ML) of 2.5 or more and a weight average molecular weight of 60.0×10or more, and a polybutadiene (B) satisfying the conditions of the ratio between a 5 wt.% toluene solution viscosity and a Mooney viscosity (Tcp/ML) of 3.5 or less and a weight average molecular weight of 56.0×10, with the polybutadiene (A)/the polybutadiene (B) of 10/90-80/20.SELECTED DRAWING: None

Description

  The present invention relates to a pneumatic tire having a cap tread member manufactured using a tire rubber composition containing a polybutadiene rubber having improved processability, abrasion resistance and low fuel consumption.

  Polybutadiene rubber generally has better mechanical properties but lower workability than other rubbers. However, mechanical properties and workability are in a trade-off relationship, and if one is to be improved, the other will be reduced in performance, so various improvements have been made so far.

  For example, by specifying the ratio (Tcp / ML) between the viscosity (Tcp) of a 5% by weight toluene solution of polybutadiene synthesized using a cobalt catalyst and the Mooney viscosity (ML), it is possible to achieve both wear resistance and workability. A polybutadiene composition for tires has been reported (Patent Document 1).

  Further, in addition to defining the ratio (Tcp / ML) between the viscosity (Tcp) of 5% by weight toluene solution of polybutadiene synthesized using a cobalt catalyst and the Mooney viscosity (ML), defining the liquid property (n value). Attempts have been made to achieve both abrasion resistance and workability (Patent Document 2).

JP-A-2004-394467 JP-A-2004-2111048

  However, in the market, there is a demand for a rubber composition for tires having both higher abrasion resistance and processability and improved fuel economy. Accordingly, an object of the present invention is to provide a rubber composition for a tire for a cap tread having improved wear resistance and low fuel consumption while maintaining processability.

As a result of intensive studies, the present inventors have found that the above problems can be solved by using a polybutadiene rubber containing two kinds of predetermined polybutadienes, and have further studied and completed the present invention. That is, the present invention
[1] (a1) The ratio (Tcp / ML _{1 + 4,100 ° C.} ) of 5 wt% toluene solution viscosity (Tcp) to Mooney viscosity (ML _{1 + 4,100 ° C.} ) is 2.5 or more, and (a2) weight average molecular weight ( Mw) a polybutadiene (A) satisfying the condition of 60.0 × 10 ⁴ or more;
(B1) The ratio (Tcp / ML _{1 + 4,100 ° C.} ) of 5 wt% toluene solution viscosity (Tcp) to Mooney viscosity (ML _{1 + 4,100 ° C.} ) is 3.5 or less, and (b2) the weight average molecular weight (Mw) is A polybutadiene (B) satisfying the condition of 56.0 × 10 ⁴ or less,
A polybutadiene rubber (i) having a weight ratio of the polybutadiene (A) / the polybutadiene (B) of 10/90 to 80/20;
Other rubber (ii),
A cap tread composed of a rubber composition for a tire including a rubber reinforcing material (iii);
[2] The cap tread according to the above [1], wherein the weight ratio of the polybutadiene (A) / the polybutadiene (B) is 15/85 to 45/55.
[3] The cap tread according to the above [1] or [2], wherein the polybutadiene (A) is produced using a cobalt catalyst or a neodymium catalyst.
[4] The cap tread according to any of [1] to [3], wherein the polybutadiene (B) is produced using a cobalt catalyst or a neodymium catalyst.
[5] 100 parts by weight of the rubber component (i) + (ii) consisting of 5 to 90 parts by weight of the polybutadiene rubber (i) and 95 to 10 parts by weight of the other rubber (ii), and the rubber reinforcing material (Iii) the cap tread according to any one of the above [1] to [4], wherein 1 to 100 parts by weight is blended;
[6] The cap tread according to any one of [1] to [5] above, wherein the other rubber (ii) includes a styrene butadiene rubber.
[7] The cap tread according to any one of [1] to [6] above, wherein the other rubber (ii) contains at least one of a natural rubber and an isoprene rubber.
[8] A pneumatic tire comprising the cap tread according to any of [1] to [7] above,
About.

  ADVANTAGE OF THE INVENTION According to this invention, the rubber composition for tires which improved abrasion resistance and low fuel consumption can be provided, maintaining processability.

(Polybutadiene (A))
Polybutadiene (A), which is a constituent component of polybutadiene rubber, is a high-molecular-weight, low-branched polybutadiene, and is a component particularly effective for improving abrasion resistance. The polybutadiene (A) preferably has the following physical properties. The polybutadiene (A) may be used alone or in combination of two or more.

The ratio (Tcp / ML _{1 + 4,100 ° C.} ) of the viscosity (Tcp) of the 5% by weight toluene solution of polybutadiene (A) to the Mooney viscosity (ML _{1 + 4,100 ° C.} ) is 2.5 or more. Here, Tcp / ML _{1 + 4,100 ° C.} is an index of the degree of branching (linearity). When Tcp / ML _{1 + 4,100 ° C.} is large, the degree of branching is low (high linearity), and Tcp / ML _{1 + 4,100 ° C.} If it is small, it means that the branching degree is high (low linearity). When Tcp / ML _{1 + 4,100 ° C.} is 2.5 or more, the degree of branching becomes appropriately low, so that the wear resistance is improved. Tcp / ML _{1 + 4,100 ° C.} is preferably at least 3.0, more preferably at least 3.5, even more preferably at least 4.0. In addition, from the viewpoint of hardly causing cold flow and improving the storage stability of the product, Tcp / ML _{1 + 4,100 ° C.} is preferably 15.0 or less, more preferably 10.0 or less, and more preferably 6.0 or less. More preferred.

  The 5 wt% toluene solution viscosity (Tcp) of polybutadiene (A) is preferably 150 or more. By setting Tcp to 150 or more, wear resistance is further improved. Tcp is more preferably 250 or more, and even more preferably 350 or more. On the other hand, if Tcp is too high, the processability tends to decrease, but since polybutadiene (B) having good processability is used in addition to polybutadiene (A), for example, Tcp exceeds 1000 (exceeds the measurement limit). But it doesn't matter. However, from the viewpoint of further improving workability, Tcp is preferably 1,000 or less, and more preferably 800 or less. The 5% by weight toluene solution viscosity (Tcp) was measured by a method described in Examples described later (the same applies hereinafter).

The Mooney viscosity (ML _{1 + 4,100 ° C.} ) of the polybutadiene (A) is preferably 40 or more. By setting ML _{1 + 4,100 ° C.} to 40 or more, wear resistance is further improved. ML _{1 + 4,100 ° C.} is more preferably 55, even more preferably 80 or more. On the other hand, it is preferable to set ML _{1 + 4,100 ° C.} to 250 or less, since workability is further improved. ML _{1 + 4,100 ° C.} is more preferably 200 or less, and even more preferably 150 or less. The Mooney viscosity (ML _{1 + 4,100 ° C.} ) was measured by the method described in Examples described later (the same applies hereinafter).

The stress relaxation time (T80) of the polybutadiene (A) is preferably 2.0 seconds or more. In addition, T80 means the time until the value is attenuated by 80% when the torque at the end of ML _{1 + 4,100 ° C.} measurement is 100%. T80 is more preferably 5.0 seconds or more, and more preferably 10.0 seconds or more, from the viewpoint of ensuring sufficient shear stress holding force due to entanglement of rubber molecules and obtaining a good filler dispersion state. Is more preferred. On the other hand, if T80 is too large, residual stress at the time of molding is increased, so that dimensional stability is inferior and workability tends to decrease. However, besides polybutadiene (A), polybutadiene (B) having good workability is also used. Is used together, for example, T80 may be longer than 60.0 seconds (exceeding the measurement limit). However, from the viewpoint of further improving workability, T80 is preferably 60.0 seconds or less, and more preferably 40.0 seconds or less. The stress relaxation time (T80) was measured by a method described in Examples described later (the same applies hereinafter). The transition of the stress relaxation of the rubber is determined by the combination of the elastic component and the viscous component. A slow stress relaxation indicates a large amount of the elastic component, and a fast stress relaxation indicates a large amount of the viscous component.

The weight average molecular weight (Mw) of the polybutadiene (A) is 60.0 × 10 ⁴ or more. When Mw is at least 60.0 × 10 ⁴ , the fuel efficiency will be improved by mixing the high molecular weight compound. Mw is preferably 70.0 × 10 ⁴ or more, and more preferably 80.0 × 10 ⁴ or more. On the other hand, when Mw is too high, the processability tends to decrease, but since polybutadiene (B) having good processability is used in addition to polybutadiene (A), for example, even if Mw exceeds 100.0 × 10 ⁴ , I do not care. However, from the viewpoint of further improving workability, Mw is preferably 100.0 × 10 ⁴ or less, and more preferably 90.0 × 10 ⁴ .

The polybutadiene (A) preferably has a number average molecular weight (Mn) of 15.0 × 10 ⁴ or more. By setting Mn to 15.0 × 10 ⁴ or more, wear resistance is further improved. Mn is more preferably 20.0 × 10 ⁴ or more, further preferably 25.0 × 10 ⁴ or more. On the other hand, Mn is preferably at most 65.0 × 10 ⁴ . By setting Mn to 65.0 × 10 ⁴ or less, workability is further improved. Mn is more preferably 55.0 × 10 ⁴ or less, further preferably 45.0 × 10 ⁴ or less.

  The molecular weight distribution (Mw / Mn) of the polybutadiene (A) is preferably 2.0 or more. By setting Mw / Mn to 2.0 or more, workability is further improved. Mw / Mn is more preferably 2.2 or more, and even more preferably 2.4 or more. On the other hand, Mw / Mn is preferably 4.5 or less. By setting Mw / Mn to 4.5 or less, wear resistance is further improved. Mw / Mn is more preferably no greater than 3.5, and even more preferably no greater than 3.0. The number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution (Mw / Mn) were measured by the methods described in Examples described below (the same applies hereinafter).

  In the polybutadiene (A), the proportion of the cis structure in the microstructure analysis is preferably 99.4 mol% or less, more preferably 99.0 mol% or less, and 98.6 mol% or less. Is more preferred. Further, the ratio of the cis structure is more preferably 97.0 mol% or more, and further preferably 98.0 mol% or more. In the polybutadiene (A), the ratio of the vinyl structure in the microstructure analysis is preferably 1.5 mol% or less, more preferably 1.0 mol% or less. In the polybutadiene (A), the ratio of the vinyl structure in the microstructure analysis is preferably as small as possible, but may be, for example, 0.3 mol% or more. In the polybutadiene (A), the ratio of the trans structure in the microstructure analysis is preferably 1.5 mol% or less, more preferably 1.0 mol% or less. The proportion of the trans structure in the microstructure analysis is preferably as small as possible, but may be, for example, 0.3 mol% or more. The ratio of the microstructure was measured by a method described in Examples described later (the same applies hereinafter).

  The polybutadiene (A) may or may not be modified with disulfur dichloride, monosulfur monochloride, other sulfur compounds, organic peroxides, t-butyl chloride, and the like.

(Polybutadiene (B))
Polybutadiene (B), which is a constituent component of polybutadiene rubber, is a polybutadiene having a low molecular weight and a high branch, and is a component particularly effective for improving processability. The polybutadiene (B) preferably has the following physical properties. The polybutadiene (B) can be used alone or in combination of two or more.

The ratio (Tcp / ML _{1 + 4,100 ° C.} ) of the viscosity (Tcp) of a 5% by weight toluene solution of polybutadiene (B) to the Mooney viscosity (ML _{1 + 4,100 ° C.} ) is 3.5 or less. When Tcp / ML _{1 + 4,100 ° C.} is 3.5 or less, the degree of branching is appropriately increased, so that cold flow is less likely to occur and the storage stability of the product is improved. Tcp / ML _{1 + 4,100 ° C.} is preferably at most 3.0, more preferably at most 2.5, even more preferably at most 2.0. From the viewpoint of preventing the degree of branching from becoming excessively high and maintaining good abrasion resistance, Tcp / ML _{1 + 4,100 ° C.} is preferably 0.8 or more, more preferably 1.0 or more, and 1 or more. .2 or more is more preferable.

  The 5 wt% toluene solution viscosity (Tcp) of the polybutadiene (B) is preferably 120 or less. By setting Tcp to 120 or less, workability is further improved. Tcp is more preferably 100 or less, and even more preferably 70 or less. On the other hand, if the Tcp is too low, the abrasion resistance tends to decrease. However, since a polybutadiene (A) having good abrasion resistance is used in addition to the polybutadiene (B), for example, the Tcp may be less than 20. However, from the viewpoint of further improving wear resistance, Tcp is preferably 20 or more, and more preferably 40 or more.

The Mooney viscosity (ML _{1 + 4,100 ° C.} ) of the polybutadiene (B) is preferably 20 or more. By setting ML _{1 + 4,100 ° C.} to 20 or more, wear resistance is further improved. ML _{1 + 4,100 ° C.} is more preferably 30 or more, and even more preferably 40 or more. On the other hand, ML _{1 + 4,100 ° C.} is preferably 70 or less. By setting ML _{1 + 4,100 ° C.} to 70 or less, workability is further improved. ML _{1 + 4,100 ° C.} is more preferably 60 or less, further preferably 50 or less.

  The stress relaxation time (T80) of the polybutadiene (B) is preferably 90.0 seconds or less from the viewpoint of preventing an increase in residual stress at the time of molding and good dimensional stability and workability. Tcp is more preferably 70.0 seconds or less, and even more preferably 40.0 seconds or less. On the other hand, if T80 is too small, the entanglement of the rubber molecules is small and the retention of shear stress is insufficient, so that it is difficult to obtain a good filler dispersion state. However, other than polybutadiene (B), the filler dispersibility is good. Since the polybutadiene (A) is used in combination, for example, T80 may be less than 2.0 seconds. However, from the viewpoint of further improving the dispersibility of the filler, T80 is preferably 2.0 seconds or more, and more preferably 5.0 seconds or more.

The weight average molecular weight (Mw) of the polybutadiene (B) is 56.0 × 10 ⁴ or less. When Mw is 56.0 × 10 ⁴ or less, workability can be improved by mixing a low molecular weight substance. Mw is preferably 53.0 × 10 ⁴ or less, more preferably 50.0 × 10 ⁴ or less. On the other hand, when Mw is too low, the abrasion resistance tends to decrease. However, since polybutadiene (A) having good abrasion resistance is used in addition to polybutadiene (B), for example, Mw is 20.0 × 10 ^4. It may be less than. However, from the viewpoint of further improving abrasion resistance, Mw is preferably 20.0 × 10 ⁴ or more, and more preferably 35.0 × 10 ⁴ .

The polybutadiene (B) preferably has a number average molecular weight (Mn) of 5.0 × 10 ⁴ or more. By setting Mn to 5.0 × 10 ⁴ or more, the wear resistance is further improved. Mn is more preferably 10.0 × 10 ⁴ or more, and further preferably 15.0 × 10 ⁴ or more. On the other hand, Mn is preferably 35.0 × 10 ⁴ or less. By setting Mn to 35.0 × 10 ⁴ or less, workability is further improved. Mn is more preferably 30.0 × 10 ⁴ or less, further preferably 25.0 × 10 ⁴ or less.

  The molecular weight distribution (Mw / Mn) of the polybutadiene (B) is preferably 2.0 or more. By setting Mw / Mn to 2.0 or more, workability is further improved. Mw / Mn is more preferably 2.5 or more, and even more preferably 3.0 or more. On the other hand, Mw / Mn is preferably 4.5 or less. By setting Mw / Mn to 4.5 or less, wear resistance is further improved. Mw / Mn is more preferably 4.2 or less, and still more preferably 3.9 or less.

  In the polybutadiene (B), the proportion of the cis structure in the microstructure analysis is preferably 99.0 mol% or less, more preferably 98.5 mol% or less, and 98.0 mol% or less. Is more preferred. Further, the ratio of the cis structure is more preferably 95.0 mol% or more, and further preferably 96.0 mol% or more. In the polybutadiene (B), the ratio of the vinyl structure in the microstructure analysis is preferably 2.5 mol% or less, more preferably 2.0 mol% or less. In the polybutadiene (B), the proportion of the vinyl structure in the microstructure analysis is preferably as small as possible, but may be, for example, 0.5 mol% or more. In the polybutadiene (B), the proportion of the trans structure in the microstructure analysis is preferably 2.5 mol% or less, more preferably 2.0 mol% or less. The proportion of the trans structure in the microstructure analysis is preferably as small as possible, but may be, for example, 0.5 mol% or more.

  The polybutadiene (B) may or may not be modified with disulfur dichloride, monosulfur monochloride, other sulfur compounds, organic peroxides, t-butyl chloride, and the like.

(Method for producing polybutadiene)
Polybutadiene (A) and polybutadiene (B) can be produced by polymerizing 1,3-butadiene with a transition metal catalyst. More specifically, it can be produced by polymerizing 1,3-butadiene with a catalyst system comprising a transition metal catalyst, an organoaluminum compound, and water.

  As the transition metal catalyst, a cobalt catalyst or a neodymium catalyst is preferable. Cobalt catalysts include cobalt salts such as cobalt chloride, cobalt bromide, cobalt nitrate, cobalt octylate (ethylhexanoate), cobalt naphthenate, cobalt acetate, cobalt malonate; cobalt bisacetylacetonate, cobalt trisacetylacetonate And organic base complexes such as acetoacetic acid ethyl ester cobalt, pyridine complexes of cobalt salts and picoline complexes, and ethyl alcohol complexes. Of these, cobalt octylate (ethylhexanoate) is preferred. Neodymium catalysts include neodymium salts such as neodymium chloride, neodymium bromide, neodymium nitrate, neodymium octylate (ethylhexanoate), neodymium naphthenate, neodymium acetate, and neodymium malonate; neodymium bisacetylacetonate, neodymium trisacetylacetonate And ethyl acetate acetoacetate, organic base complexes such as pyridine complex and picoline complex of neodymium and neodymium salt, and ethyl alcohol complex. Of these, neodymium octylate (ethylhexanoate) is preferred. Note that other catalysts such as a nickel catalyst can be used as long as polybutadiene having desired physical properties can be obtained.

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

  Examples of the organoaluminum compounds include trialkylaluminum; halogen-containing organoaluminum compounds such as dialkylaluminum chloride, dialkylaluminum bromide, alkylaluminum sesquichloride, alkylaluminum sesquibromide, alkylaluminum dichloride, and alkylaluminum dibromide; dialkylaluminum hydride, alkylaluminum Organic aluminum hydride compounds such as sesquihydrite and the like can be mentioned. One type of the organoaluminum compound may be used alone, or two or more types may be used in combination.

  Specific compounds of trialkylaluminum include trimethylaluminum, triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, tridecylaluminum and the like.

  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 alkyl aluminum sesquichloride include methyl aluminum sesquichloride and ethyl aluminum sesquichloride. Examples of the alkyl aluminum sesquibromide include methyl aluminum sesquibromide and ethyl aluminum sesquibromide. Examples of the alkyl aluminum dichloride include methyl aluminum dichloride and ethyl aluminum dichloride. Examples of the alkyl aluminum dibromide include methyl aluminum dibromide and ethyl aluminum dibromide.

  Examples of the dialkyl aluminum hydride include diethyl aluminum hydride, diisobutyl aluminum hydride, and the like. Examples of the alkyl aluminum sesquihydride include ethyl aluminum sesquihydride, isobutyl aluminum sesquihydride, and the like.

  The mixing ratio between the organoaluminum compound and water is preferably within a predetermined range since polybutadiene having desired physical properties is easily obtained. For example, when the ratio of aluminum / water (molar ratio) is 1.0 or more, It is preferably, and more preferably 1.2 or more. Aluminum / water (molar ratio) is preferably 3.0 or less, and more preferably 2.5 or less.

  Furthermore, in order to obtain polybutadiene having desired physical properties, non-conjugated dienes such as cyclooctadiene, arene, and methylallene (1,2-butadiene); and molecular weights such as α-olefins such as ethylene, propylene, and 1-butene Modulators can be used. As the molecular weight regulator, one type may be used alone, or two or more types may be used in combination.

  The polymerization method is not particularly limited, and bulk polymerization (bulk polymerization) in which a monomer is polymerized using a conjugated diene compound monomer such as 1,3-butadiene as a polymerization solvent, or solution polymerization in which the monomer is dissolved in a solvent, is performed. Etc. can be applied. Examples of the solvent used in the solution polymerization include aromatic hydrocarbons such as toluene, benzene and xylene; saturated aliphatic hydrocarbons such as n-hexane, butane, heptane and pentane; alicyclic hydrocarbons such as cyclopentane and cyclohexane; Olefinic hydrocarbons such as cis-2-butene and trans-2-butene; petroleum solvents such as mineral spirits, solvent naphtha, and kerosene; halogenated hydrocarbons such as methylene chloride. Among them, toluene, cyclohexane, or a mixed solvent of cis-2-butene and trans-2-butene is suitably 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 50 to 80 ° C because polybutadiene having desired physical properties is easily obtained. The polymerization time is preferably in the range of 1 minute to 12 hours, more preferably in the range of 5 minutes to 5 hours.

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

  After the polymerization is performed for a predetermined time, the pressure inside the polymerization tank is released as necessary, and a post-treatment such as a washing or drying step is performed, whereby a polybutadiene having desired physical properties can be produced.

(Polybutadiene rubber)
The polybutadiene rubber contains polybutadiene (A) and polybutadiene (B). The weight ratio of polybutadiene (A) / polybutadiene (B) is 10/90 to 80/20. By mixing the polybutadiene (A) and the polybutadiene (B) at such a weight ratio, a polybutadiene rubber having improved abrasion resistance and low fuel consumption while maintaining workability can be obtained. The weight ratio of polybutadiene (A) / polybutadiene (B) is preferably 15/85 to 70/30, more preferably 15/85 to 60/40, and 15/85 to 55/45. More preferably, it is 15 / 85-45 / 55, further preferably, 15 / 85-35 / 65, and further preferably, 20 / 80-35 / 65.

  As a method of mixing polybutadiene (A) and polybutadiene (B), a method of mixing a solution of polybutadiene (A) and a solution of polybutadiene (B), and a method of adding solid polybutadiene (B) to a solution of polybutadiene (A) A method of adding solid polybutadiene (A) to a solution of polybutadiene (B), and a method of mixing solid polybutadiene (A) and solid polybutadiene (B). From the viewpoint of improving dispersibility, a method of mixing a solution of polybutadiene (A) and a solution of polybutadiene (B) is preferable. The polybutadiene rubber is obtained by mixing the polybutadiene (A) and the polybutadiene (B) and removing the solvent and the like as necessary. As the solution of polybutadiene (A) and the solution of polybutadiene (B), for example, the polymerization solution in the above-mentioned method for producing polybutadiene can be used.

  The polybutadiene rubber (mixture of polybutadiene (A) and polybutadiene (B)) thus obtained preferably has the following physical properties.

The ratio (Tcp / ML _{1 + 4,100 ° C.} ) of the viscosity (Tcp) of the 5% by weight toluene solution of the polybutadiene rubber to the Mooney viscosity (ML _{1 + 4,100 ° C.} ) is preferably within a predetermined range. It is preferable that it is above. By setting Tcp / ML _{1 + 4,100 ° C.} to 1.0 or more, the degree of branching becomes appropriately low, so that the wear resistance is improved. Tcp / ML _{1 + 4,100 ° C.} is more preferably 1.2 or more, still more preferably 1.4 or more, and particularly preferably 1.6 or more. On the other hand, Tcp / ML _{1 + 4,100 ° C.} is preferably 6.0 or less. By setting Tcp / ML _{1 + 4,100 ° C.} to 6.0 or less, the degree of branching becomes moderately high, so that cold flow hardly occurs and the storage stability of the product is improved. Tcp / ML _{1 + 4,100 ° C.} is more preferably 5.0 or lower, further preferably 4.0 or lower, and particularly preferably 3.0 or lower.

  The 5 wt% toluene solution viscosity (Tcp) of the polybutadiene rubber is preferably within a predetermined range, for example, preferably 40 or more. By setting Tcp to 40 or more, wear resistance is further improved. Tcp is more preferably 70 or more, and even more preferably 100 or more. On the other hand, Tcp is preferably 600 or less. By setting Tcp to 600 or less, workability is further improved. Tcp is more preferably 400 or less, and even more preferably 200 or less.

The Mooney viscosity (ML _{1 + 4,100 ° C.} ) of the polybutadiene rubber is preferably in a predetermined range, for example, preferably 30 or more. By setting ML _{1 + 4,100 ° C.} to 30 or more, wear resistance is further improved. ML _{1 + 4,100 ° C.} is more preferably 40 or more, and even more preferably 50 or more. On the other hand, ML _{1 + 4,100 ° C.} ) is preferably 120 or less. By setting ML _{1 + 4,100 ° C.} to 120 or less, workability is further improved. ML _{1 + 4,100 ° C.} is more preferably 100 or lower, and further preferably 80 or lower.

  The stress relaxation time (T80) of the polybutadiene rubber is preferably within a predetermined range, for example, preferably at least 3.0 seconds. When T80 is set to 3.0 seconds or more, the rubber molecules are entangled with each other, and a sufficient holding force for shear stress is obtained. Therefore, a good filler dispersion state is easily obtained. T80 is more preferably equal to or longer than 5.0 seconds, and further preferably equal to or longer than 8.0 seconds. On the other hand, T80 is preferably 50.0 or less. By setting T80 to 50.0 seconds or less, the residual stress at the time of molding is reduced, so that dimensional stability is improved and workability is improved. T80 is more preferably 30.0 seconds or less, and even more preferably 15.0 seconds or less.

The weight average molecular weight (Mw) of the polybutadiene rubber is preferably within a predetermined range, for example, preferably 30.0 × 10 ⁴ or more. By setting Mw to 30.0 × 10 ⁴ or more, wear resistance is further improved. Mw is more preferably 40.0 × 10 ⁴ or more, and further preferably 50.0 × 10 ⁴ or more. On the other hand, Mw is preferably 90.0 × 10 ⁴ or less. By setting Mw to 90.0 × 10 ⁴ or less, workability is further improved. Mw is more preferably 80.0 × 10 ⁴ or less, further preferably 70.0 × 10 ⁴ or less.

The number average molecular weight (Mn) of the polybutadiene rubber is preferably within a predetermined range, for example, preferably 8.0 × 10 ⁴ or more. By setting Mn to 8.0 × 10 ⁴ or more, wear resistance is further improved. Mn is more preferably 10.0 × 10 ⁴ or more, and further preferably 15.0 × 10 ⁴ or more. On the other hand, Mn is preferably 40.0 × 10 ⁴ or less. By setting Mn to 40.0 × 10 ⁴ or less, workability is further improved. Mn is more preferably 30.0 × 10 ⁴ or less, further preferably 25.0 × 10 ⁴ or less.

  The molecular weight distribution (Mw / Mn) of the polybutadiene rubber is preferably within a predetermined range, for example, preferably 2.0 or more. By setting Mw / Mn to 2.0 or more, workability is further improved. Mw / Mn is more preferably 2.4 or more, even more preferably 2.8 or more. On the other hand, Mw / Mn is preferably 6.0 or less. By setting Mw / Mn to 6.0 or less, wear resistance is further improved. Mw / Mn is more preferably 5.0 or less, and even more preferably 4.0 or less.

  In the polybutadiene rubber, the proportion of the cis structure in the microstructure analysis is preferably 99.0 mol% or less, more preferably 98.5 mol% or less, and further preferably 98.0 mol% or less. preferable. The ratio of the cis structure is more preferably 95.0 mol% or more, and further preferably 96.0 mol% or more. In the polybutadiene rubber, the ratio of the vinyl structure in the microstructure analysis is preferably 2.5 mol% or less, more preferably 2.0 mol% or less. In the polybutadiene rubber, the proportion of the vinyl structure in the microstructure analysis is preferably as small as possible, but may be, for example, 0.5 mol% or more. In the polybutadiene rubber, the ratio of the trans structure in the microstructure analysis is preferably 2.5 mol% or less, more preferably 2.0 mol% or less. The proportion of the trans structure in the microstructure analysis is preferably as small as possible, but may be, for example, 0.5 mol% or more.

(Rubber composition)
The rubber composition for a tire contains the above polybutadiene rubber (i), another rubber (ii), and a rubber reinforcing material (iii).

  As the other rubber component (ii), for example, a diene rubber other than polybutadiene having the above physical properties can be used. Examples of the diene rubber other than polybutadiene having the above physical properties include polybutadiene rubber, natural rubber, high cis polybutadiene rubber, low cis polybutadiene rubber, syndiotactic-1,2-polybutadiene-containing butadiene rubber (VCR) having no such physical properties. Polymers of diene monomers such as isoprene rubber and chloroprene rubber; butyl rubber; acrylonitrile-diene copolymer rubber such as acrylonitrile butadiene rubber (NBR), nitrile chloroprene rubber and nitrile isoprene rubber; styrene such as emulsion polymerized or solution polymerized styrene butadiene rubber Styrene-diene copolymer rubber such as butadiene rubber (SBR), styrene chloroprene rubber, and styrene isoprene rubber; ethylene propylene diene rubber (EPDM); Above all, butadiene rubber, natural rubber, syndiotactic-1,2-polybutadiene-containing butadiene rubber, isoprene rubber, acrylonitrile butadiene rubber, and styrene butadiene rubber having no physical properties described above are preferable. As the styrene butadiene rubber, a solution polymerized styrene butadiene rubber (s-SBR) is preferable. The other rubber component (ii) preferably contains styrene butadiene rubber, natural rubber, and isoprene rubber. In particular, it is preferable that the rubber contains at least one of natural rubber and isoprene rubber, and it is more preferable that the rubber contains at least one of natural rubber and isoprene rubber, or that it contains styrene butadiene rubber Is preferable, and it is further preferable that the styrene-butadiene rubber is used. As the other rubber component (ii), one type may be used alone, or two or more types may be used in combination.

  Examples of the rubber reinforcing material (iii) include inorganic reinforcing materials such as carbon black, white carbon (silica), activated calcium carbonate, and ultrafine magnesium silicate; polyethylene resin, polypropylene resin, high styrene resin, phenol resin, lignin, and modified melamine. Organic reinforcing materials such as resin, coumarone indene resin, petroleum resin, and the like. Among them, carbon black or silica is preferred. One type of rubber reinforcing material can be used alone, or two or more types can be used in combination.

  Examples of the carbon black include FEF, FF, GPF, SAF, ISAF, SRF, and HAF. From the viewpoint of improving abrasion resistance, ISAF or SAF having a small particle diameter is preferable. The average particle size of the carbon black is preferably 15 nm or more and 90 nm or less. The average particle size of the carbon black is more preferably 70 nm or less, further preferably 50 nm or less, further preferably 30 nm or less, and even more preferably 23 nm or less. The average particle size of the carbon black is a number average particle size and is measured by a transmission electron microscope. The dibutyl phthalate (DBP) oil absorption of carbon black is preferably within a predetermined range, for example, preferably 70 ml / 100 g or more, more preferably 80 ml / 100 g or more, and more preferably 90 ml / 100 g or more. More preferably, there is. On the other hand, the DBP oil absorption is preferably 140 ml / 100 g or less, more preferably 135 ml / 100 g or less, and even more preferably 130 ml / 100 g or less. The DBP oil absorption of carbon black is a value determined by a measuring method according to JIS K 6217-4.

The nitrogen adsorption specific surface area (N ₂ SA) of the carbon black is preferably 100 m ² / g or more, more preferably 120 m ² / g or more, and even more preferably 130 m ² / g or more. When the N ₂ SA of the carbon black is 100 m ² / g or more, the grip performance tends to be improved. Further, the N ₂ SA of the carbon black is preferably 500 m ² / g or less, more preferably 450 m ² / g or less, and still more preferably 300 m ² / g or less. When the N ₂ SA of the carbon black is 500 m ² / g or less, the abrasion resistance tends to be improved. The N ₂ SA of carbon black is determined according to JIS K 6217-7 “Carbon black for rubber-Basic properties-Part 7: Rubber compound-Multipoint method nitrogen specific surface area (NSA) and statistical thickness specific surface area (STSA) )).

  As the silica, any one usually used in this field can be used. Silica can be blended from the viewpoint of improving wear resistance, rolling resistance characteristics and workability. The silica may be prepared by a wet method or may be prepared by a dry method. Specific examples of silica include Nipsil VN3 (trade name, manufactured by Tosoh Silica Co., Ltd.) and Ultrasil 7000GR (trade name, manufactured by Evonik Degussa).

  The mixing ratio of the above components is based on 100 parts by weight of a rubber component (i) + (ii) consisting of 5 to 90 parts by weight of the polybutadiene rubber (i) and 95 to 10 parts by weight of the other rubber (ii). The rubber reinforcing material (iii) is preferably 1 to 100 parts by weight. More preferably, the rubber component (i) + (ii) comprises 10 to 60 parts by weight of the polybutadiene rubber (i) and 90 to 40 parts by weight of the other rubber (ii), and the polybutadiene rubber (i) 20 to 40 parts. More preferably, it is composed of parts by weight and 80 to 60 parts by weight of the other rubber (ii). The rubber reinforcing material (iii) is more preferably 30 to 90 parts by weight, further preferably 50 to 80 parts by weight, based on 100 parts by weight of the rubber component (i) + (ii).

  In the rubber composition for tires, in addition to the above components, if necessary, a silane coupling agent, a vulcanizing agent, a vulcanization accelerator, an antioxidant, a filler, a process oil, zinc white, stearic acid, etc. Compounding agents used in the rubber industry may be kneaded.

  As the silane coupling agent, a silane coupling agent having a functional group capable of reacting with the polybutadiene rubber (i) or the other rubber component (ii) is particularly preferable. As the silane coupling agent, one type may be used alone, or two or more types may be used in combination. Examples of the silane coupling agent include bis (3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, and bis (2-triethoxy). (Silylethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyl Trimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl-N, N-dimethylthiocarba Yltetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyltetrasulfide, 3-trimethoxysilylpropylbenzothiazoletetrasulfide, 3-triethoxysilylpropylbenzothiazolyltetrasulfide, 3-triethoxysilyl Propyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis (3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N, N-dimethylthiocarbamoyltetrasulfide , Dimethoxymethylsilylpropylbenzothiazole tetrasulfide, and the like. When the silane coupling agent is contained, the content of the silane coupling agent with respect to 100 parts by weight of silica is preferably 3 parts by weight or more, more preferably 5 parts by weight or more. Further, the content of the silane coupling agent is preferably 15 parts by weight or less, more preferably 10 parts by weight or less. When the content of the silane coupling agent is in the above range, a sufficient and efficient coupling effect tends to be obtained, and the processability and fracture characteristics of the obtained rubber composition tend to be improved.

  As the vulcanizing agent, known vulcanizing agents, for example, sulfur, organic peroxides, resin vulcanizing agents, metal oxides such as magnesium oxide and the like are used. One type of vulcanizing agent may be used alone, or two or more types may be used in combination.

  As the vulcanization accelerator, known vulcanization aids, for example, sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, Alternatively, a xanthate vulcanization accelerator may be used. These vulcanization accelerators may be used alone or in combination of two or more. Among them, sulfenamide-based vulcanization accelerators are preferable because scorch time and vulcanization time can be well-balanced. For example, N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl 2-Benzothiazolylsulfenamide (CBS), N, N'-dicyclohexyl-2-benzothiazolylsulfenamide (DZ) and the like are preferable. The content of the vulcanization accelerator based on 100 parts by weight of the rubber component is preferably 0.5 parts by weight or more, more preferably 1.0 part by weight or more. Further, the content of the vulcanization accelerator is preferably 5.0 parts by weight or less, more preferably 3.0 parts by weight or less. When the content of the vulcanization accelerator is within the above range, the effects of the invention can be more suitably obtained. One type of vulcanization accelerator may be used alone, or two or more types may be used in combination.

  Examples of the antioxidants include amine / ketone antioxidants, imidazole antioxidants, amine antioxidants, phenol antioxidants, sulfur antioxidants, and phosphorus antioxidants. One type of anti-aging agent may be used alone, or two or more types may be used in combination.

  Examples of the filler include fillers other than the above-described carbon black and silica. Specific examples include inorganic fillers such as calcium carbonate, basic magnesium carbonate, clay, Lissajous, and diatomaceous earth; and organic fillers such as recycled rubber and powdered rubber. As the filler, one type may be used alone, or two or more types may be used in combination.

  As the process oil, any of an aromatic process oil, a naphthene process oil, and a paraffin process oil may be used. Further, a low molecular weight liquid polybutadiene or tackifier may be used. One type of process oil can be used alone, or two or more types can be used in combination.

(Production of rubber composition)
As a method for producing the rubber composition for a tire, a known method can be used. For example, the rubber composition can be produced by kneading the above components with a Banbury mixer, a kneader, or an open roll, and then vulcanizing. In kneading, first, components other than the vulcanizing agent and the vulcanization accelerator are kneaded, and then the resulting kneaded product can be kneaded by adding the vulcanizing agent and the vulcanization accelerator. In addition, since the rubber composition for tires exhibits sufficient fuel efficiency while maintaining sufficient wear resistance, it is suitable for cap treads of pneumatic tires for a wide range of vehicles such as passenger cars, trucks, and buses. Can be used.

(Pneumatic tires)
A pneumatic tire can be manufactured by a usual method using the above rubber composition. That is, the rubber composition is extruded according to the shape of the cap tread at the stage of unvulcanization, bonded together with other tire members on a tire molding machine, and molded by an ordinary method, thereby obtaining an unvulcanized tire. Is formed, and the unvulcanized tire is heated and pressurized in a vulcanizer to produce a tire, which is then filled with air to obtain a pneumatic tire.

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

1. Test method (5 wt% toluene solution viscosity (Tcp))
The viscosity (Tcp) of a 5% by weight toluene solution of polybutadiene and polybutadiene rubber was determined by dissolving 2.28 g of a polymer in 50 ml of toluene, and then measuring the viscosity with a Cannon-Fenske viscometer. It was measured at 25 ° C. using a 400. In addition, a standard solution for viscometer calibration (JIS Z 8809) was used as the standard solution.

(Mooney viscosity (ML _{1 + 4,100 ℃} ))
The Mooney viscosity (ML _{1 + 4,100 ° C.} ) of the polybutadiene, polybutadiene rubber and unvulcanized rubber composition was measured at 100 ° C. in accordance with JIS K 6300. The ML _{1 + 4,100 ° C.} of the unvulcanized rubber composition was calculated as an index (processability index) with the value of Comparative Example 1 being 100 (the larger the index, the more ML _{1 + 4,100 ° C.} of the unvulcanized rubber composition). Is small and workability is good).

(Stress relaxation time (T80))
The stress relaxation time (T80) of polybutadiene and polybutadiene rubber was calculated by a stress relaxation measurement according to ASTM D1646-7 of MV2000 manufactured by ALPHA TECHNOLOGIES. Specifically, under the measurement conditions of ML _{1 + 4,100 ° C.} , the torque when the rotor stops (0 second) after 4 minutes from the measurement is set to 100%, and the torque is reduced by 80% (that is, the torque is reduced to 20%). ) Was measured as the 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 and polybutadiene rubber are converted into standard polystyrene by the GPC method (trade name: HLC-8220, manufactured by Tosoh Corporation). Was calculated by Tetrahydrofuran was used as a solvent, two columns of KF-805L (trade name) manufactured by Shodex were connected in series, and a differential refractometer (RI) was used as a detector.

(Micro structure)
The microstructure of polybutadiene and polybutadiene rubber 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.

(Wear resistance)
The test tire was mounted on a 2-D domestic vehicle, the groove depth of the tire tread after 50,000 km was measured, and the mileage when the tire groove depth was reduced by 1 mm was calculated. It was indexed as 100 (wear resistance index). The result is that the larger the index, the better the wear resistance of the tire cap tread.

(Low fuel consumption)
A strip-shaped test piece having a width of 1 mm or 2 mm and a length of 40 mm was punched out from the sheet-like vulcanized rubber composition and subjected to a test. Using a spectrometer manufactured by Ueshima Seisakusho, tan δ was measured at a dynamic strain amplitude of 1%, a frequency of 10 Hz and a temperature of 50 ° C. The value of the reciprocal of tan δ was indicated as an index by setting Comparative Example 1 to 100. The larger the numerical value, the smaller the rolling resistance and the lower the fuel consumption.

2. Preparation of polybutadiene (Preparation of polybutadiene A-1 solution)
1.0 L of a polymerization solution (butadiene (BD): 34.2% by weight, cyclohexane (CH): 31.2% by weight, remaining in a 1.5-L stainless steel reactor equipped with a stirrer and purged with nitrogen gas) Was 2-butenes). Further, 1.52 mmol of water (H ₂ O), 2.08 mmol of diethylaluminum chloride (DEAC), 0.52 mmol of triethylaluminum (TEA) (total aluminum / water = 1.71 (mixing molar ratio)), cobalt octoate ( 20.94 μmol of Co _cat ) and 6.05 mmol of cyclooctadiene (COD) were added, and the mixture was stirred at 72 ° C. for 20 minutes to perform 1,4-cis polymerization. Thereafter, the polymerization was stopped by adding ethanol containing 4,6-bis (octylthiomethyl) -o-cresol to obtain a polybutadiene A-1 solution. Table 1 shows the conditions for preparing the solution.

(Preparation of polybutadiene A-2 solution to polybutadiene A-5 solution)
Polybutadiene A-2 solution to polybutadiene A-5 solution were prepared in the same procedure as the preparation of the polybutadiene A-1 solution. Table 1 shows the conditions for preparing each solution.

(Preparation of polybutadiene A-6 solution)
3.20 mmol of diisobutylaluminum hydride (DIBALH) and 0.16 mmol of neodymium versatate (Nd _v3 ) were added to an eggplant-shaped flask purged with nitrogen, and the mixture was stirred at room temperature for 5 minutes. Next, 0.48 mmol of diethylaluminum chloride (DEAC) was added, and the mixture was further contacted at room temperature for 25 minutes. Next, 1.0 L of the polymerization solution (butadiene (BD): 26.2% by weight, cyclohexane (CH): 73.8% by weight) was placed in a 1.5-L stainless steel reactor equipped with a stirrer that had been previously replaced with nitrogen gas. %) Was kept at 60 ° C. while the aged catalyst component was injected with a special syringe to start the reaction. By stirring at 60 ° C. for 1 hour, 1,4-cis polymerization was carried out. Then, the polymerization was terminated by adding ethanol containing 4,6-bis (octylthiomethyl) -o-cresol to obtain a polybutadiene A-6 solution. Table 1 shows the conditions for preparing the solution.

  Unreacted butadiene and 2-butenes and the solvent were evaporated and removed from the obtained polybutadiene A-1 solution to polybutadiene A-6 solution to obtain polybutadiene A-1 to polybutadiene A-6, and various physical properties were evaluated. . Table 2 shows the results.

(Preparation of polybutadiene B-1 solution)
1.0 L of a polymerization solution (butadiene (BD): 36.0% by weight, cyclohexane (CH): 27.0% by weight, the balance remaining) was placed in a 1.5-L stainless steel reactor equipped with a stirrer and purged with nitrogen gas. Was 2-butenes). Further, 1.72 mmol of water (H ₂ O), 2.32 mmol of diethylaluminum chloride (DEAC), 0.26 mmol of triethylaluminum (TEA) (total aluminum / water = 1.51 (mixing molar ratio)), cobalt octoate ( Co _cat ) 20.00 μmol and cyclooctadiene (COD) 7.00 mmol were added, and the mixture was stirred at 65 ° C. for 20 minutes to perform 1,4-cis polymerization. Thereafter, ethanol containing 4,6-bis (octylthiomethyl) -o-cresol was added to terminate the polymerization, whereby a polybutadiene B-1 solution was obtained. Table 3 shows the conditions for preparing the solution.

(Preparation of polybutadiene B-2 solution and polybutadiene B-5 solution)
A polybutadiene B-2 solution and a polybutadiene B-5 solution were prepared in the same procedure as the preparation of the polybutadiene B-1 solution. Table 3 shows the conditions for preparing each solution.

(Preparation of polybutadiene B-3 solution)
1.0 L of the polymerization solution (butadiene (BD): 33.0% by weight, cyclohexane (CH): 22.0% by weight, remaining Was 2-butenes). Further, 1.71 mmol of water (H ₂ O), 3.00 mmol of diethyl aluminum chloride (DEAC) (aluminum / water = 1.75 (mixing molar ratio)), 10.40 μmol of cobalt octoate (Co _cat ), and cyclooctamate 1,20 cis polymerization was performed by adding 8.20 mmol of diene (COD) and 15 μmol of dilauryl thiodipropionate (DLTP) and stirring at 65 ° C. for 20 minutes. Thereafter, ethanol containing 4,6-bis (octylthiomethyl) -o-cresol was added to terminate the polymerization, whereby a polybutadiene B-1 solution was obtained. Table 3 shows the conditions for preparing the solution.

(Preparation of polybutadiene B-4 solution and polybutadiene B-6 solution)
A polybutadiene B-4 solution and a polybutadiene B-6 solution were prepared in the same procedure as in the preparation of the polybutadiene B-3 solution. Table 3 shows the conditions for preparing each solution.

  Unreacted butadiene and 2-butenes were removed by evaporation from the resulting polybutadiene B-1 solution to polybutadiene B-6 solution to obtain polybutadiene B-1 to polybutadiene B-6, and various physical properties were evaluated. Table 4 shows the results.

3. Examples and Comparative Examples Hereinafter, various chemicals used in Examples and Comparative Examples are collectively shown.
Isoprene rubber: Nippol IR 2200, butadiene rubber manufactured by Zeon Corporation: polybutadiene rubber carbon black described in Examples and Comparative Examples: Diablack A (N110) manufactured by Mitsubishi Chemical Corporation (average particle diameter: 19 nm, N ₂₎ (SA = 142 m ² / g, DBP: 116 ml / 100 g)
Zinc oxide: Zinc flower No. 1 stearic acid manufactured by Mitsui Kinzoku Mining Co., Ltd. Stearic acid: Tsubaki “tsubaki” manufactured by NOF Corporation
Antiaging agent: Nocrack 6C (N-phenyl-N '-(1,3-dimethylbutyl) -p-phenylenediamine) (6PPD) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Sulfur: powder sulfur vulcanization accelerator manufactured by Karuizawa Sulfur Co., Ltd .: Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

(Examples 1 to 15)
≪Butadiene rubber≫
The corresponding two kinds of polybutadiene solutions were mixed so that the polybutadiene (A) and the polybutadiene (B) were mixed at the ratios shown in Tables 5 and 6 (this mixing method was referred to as "wet"). Then, unreacted butadiene and 2-butenes were removed by evaporation from the obtained mixed solution to obtain a polybutadiene rubber, and various physical properties were measured. The results are shown in Tables 5 and 6.

≪Rubber composition≫
Next, using the obtained polybutadiene rubber, an unvulcanized rubber composition and a vulcanized rubber composition were prepared according to the formulations shown in Table 7. Specifically, first, materials other than sulfur and a vulcanization accelerator were kneaded for 5 minutes at 150 ° C. using a 1.7 L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded material. Was. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded material, and the mixture was kneaded with an open roll at 80 ° C. for 5 minutes to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press-vulcanized at 150 ° C. for 15 minutes using a 0.5 mm thick mold to obtain a vulcanized rubber composition.

≪ tire ≫
Further, the obtained unvulcanized rubber composition is molded into a cap tread shape, and is bonded together with other tire members on a tire molding machine to form an unvulcanized tire, and vulcanized at 150 ° C. for 30 minutes, A test tire (size: 11R22.5) was manufactured.

(Example 16)
Unreacted butadiene and 2-butenes were removed by evaporation from the polybutadiene A-2 solution to obtain polybutadiene A-2. Unreacted butadiene and 2-butenes were removed by evaporation from the polybutadiene B-2 solution to obtain polybutadiene B-2. Then, both were mixed at the compounding ratio shown in Table 6 to obtain a polybutadiene rubber (this compounding method is referred to as “dry”). Then, an unvulcanized rubber composition, a vulcanized rubber composition and a test tire were produced in the same manner as in Example 1 except that the obtained polybutadiene rubber was used.

(Comparative Examples 1-4)
As shown in Table 6, in place of the polybutadiene rubber of Example, except that each polybutadiene was used alone, in the same manner as in Example 1, the unvulcanized rubber composition, the vulcanized rubber composition and the test Tires were manufactured.

  The workability was evaluated by measuring the Mooney viscosity of the unvulcanized rubber composition prepared above, the fuel economy was evaluated by measuring the tan δ of the vulcanized rubber composition, and the tire tread portion of the test tire was evaluated. The abrasion resistance was evaluated by measuring the groove depth. The results are shown in Tables 5 and 6. In Comparative Example 4, kneading could not be performed at the stage of producing the unvulcanized rubber composition, and subsequent evaluation could not be performed.

  In Tables 5 and 6, the workability index is targeted to be 75 or more. Further, the wear resistance index and the fuel economy index are both 102 or more, and at least one of them is intended to be a value exceeding 102. As described above, by using a polybutadiene rubber having predetermined characteristics, while maintaining processability, a cap tread composed of a rubber composition for a tire having improved abrasion resistance and fuel economy, and A pneumatic tire including a cap tread can be provided.

The Mooney viscosity (ML _{1 + 4,100 ° C.} ) of the polybutadiene (A) is preferably 40 or more. By setting ML _{1 + 4,100 ° C.} to 40 or more, wear resistance is further improved. ML _{1 + 4,100 ° C.} is more preferably 55 or more , and even more preferably 80 or more. On the other hand, it is preferable to set ML _{1 + 4,100 ° C.} to 250 or less, since workability is further improved. ML _{1 + 4,100 ° C.} is more preferably 200 or less, and even more preferably 150 or less. The Mooney viscosity (ML _{1 + 4,100 ° C.} ) was measured by the method described in Examples described later (the same applies hereinafter).

The weight average molecular weight (Mw) of the polybutadiene (A) is 60.0 × 10 ⁴ or more. When Mw is at least 60.0 × 10 ⁴ , the fuel efficiency will be improved by mixing the high molecular weight compound. Mw is preferably 70.0 × 10 ⁴ or more, and more preferably 80.0 × 10 ⁴ or more. On the other hand, when Mw is too high, the processability tends to decrease, but since polybutadiene (B) having good processability is used in addition to polybutadiene (A), for example, even if Mw exceeds 100.0 × 10 ⁴ , I do not care. However, from the viewpoint of further improving workability, Mw is preferably 100.0 × 10 ⁴ or less, and more preferably 90.0 × 10 ⁴ or less .

The stress relaxation time (T80) of the polybutadiene (B) is preferably 90.0 seconds or less from the viewpoint of preventing an increase in residual stress at the time of molding and good dimensional stability and workability. T80 is more preferably 70.0 seconds or less, and further preferably 40.0 seconds or less. On the other hand, if T80 is too small, the entanglement of the rubber molecules is small and the retention of shear stress is insufficient, so that it is difficult to obtain a good filler dispersion state. However, other than polybutadiene (B), the filler dispersibility is good. Since the polybutadiene (A) is used in combination, for example, T80 may be less than 2.0 seconds. However, from the viewpoint of further improving the dispersibility of the filler, T80 is preferably 2.0 seconds or more, and more preferably 5.0 seconds or more.

The weight average molecular weight (Mw) of the polybutadiene (B) is 56.0 × 10 ⁴ or less. When Mw is 56.0 × 10 ⁴ or less, workability can be improved by mixing a low molecular weight substance. Mw is preferably 53.0 × 10 ⁴ or less, more preferably 50.0 × 10 ⁴ or less. On the other hand, when Mw is too low, the abrasion resistance tends to decrease. However, since polybutadiene (A) having good abrasion resistance is used in addition to polybutadiene (B), for example, Mw is 20.0 × 10 ^4. It may be less than. However, from the viewpoint of further improving the abrasion resistance, Mw is preferably 20.0 × 10 ⁴ or more, and more preferably 35.0 × 10 ⁴ or more .

The Mooney viscosity (ML _{1 + 4,100 ° C.} ) of the polybutadiene rubber is preferably in a predetermined range, for example, preferably 30 or more. By setting ML _{1 + 4,100 ° C.} to 30 or more, wear resistance is further improved. ML _{1 + 4,100 ° C.} is more preferably 40 or more, and even more preferably 50 or more. On the other hand, ML _{1 + 4,100 ° C.} is preferably 120 or less. By setting ML _{1 + 4,100 ° C.} to 120 or less, workability is further improved. ML _{1 + 4,100 ° C.} is more preferably 100 or lower, and further preferably 80 or lower.

The stress relaxation time (T80) of the polybutadiene rubber is preferably within a predetermined range, for example, preferably at least 3.0 seconds. When T80 is set to 3.0 seconds or more, the rubber molecules are entangled with each other, and a sufficient holding force for shear stress is obtained. Therefore, a good filler dispersion state is easily obtained. T80 is more preferably equal to or longer than 5.0 seconds, and further preferably equal to or longer than 8.0 seconds. On the other hand, T80 is preferably 50.0 seconds or less. By setting T80 to 50.0 seconds or less, the residual stress at the time of molding is reduced, so that dimensional stability is improved and workability is improved. T80 is more preferably 30.0 seconds or less, and even more preferably 15.0 seconds or less.

As the other rubber component (ii), for example, a diene rubber other than polybutadiene having the above physical properties can be used. Examples of the diene rubber other than polybutadiene having the above physical properties include polybutadiene rubber, natural rubber, high cis polybutadiene rubber, low cis polybutadiene rubber, syndiotactic-1,2-polybutadiene-containing butadiene rubber (VCR) having no such physical properties. Polymers of diene monomers such as isoprene rubber and chloroprene rubber; butyl rubber; acrylonitrile-diene copolymer rubber such as acrylonitrile butadiene rubber (NBR), nitrile chloroprene rubber and nitrile isoprene rubber; styrene such as emulsion polymerized or solution polymerized styrene butadiene rubber Styrene-diene copolymer rubber such as butadiene rubber (SBR), styrene chloroprene rubber, and styrene isoprene rubber; ethylene propylene diene rubber (EPDM); Among them, poly-butadiene rubber having no above physical properties, natural rubber, syndiotactic 1,2-polybutadiene content butadiene rubber, isoprene rubber, acrylonitrile-butadiene rubber, styrene-butadiene rubber are preferable. As the styrene butadiene rubber, a solution polymerized styrene butadiene rubber (s-SBR) is preferable. The other rubber component (ii) preferably contains styrene butadiene rubber, natural rubber, and isoprene rubber. In particular, it is preferable that the rubber contains at least one of natural rubber and isoprene rubber, and it is more preferable that the rubber contains at least one of natural rubber and isoprene rubber, or that it contains styrene butadiene rubber Is preferable, and it is further preferable that the styrene-butadiene rubber is used. As the other rubber component (ii), one type may be used alone, or two or more types may be used in combination.

(Production of rubber composition)
As a method for producing the rubber composition for a tire, a known method can be used. For example, the rubber composition can be produced by kneading the above components with a Banbury mixer, a kneader, or an open roll, and then vulcanizing. Mixing kneading Rinisaishite can after first kneading the components other than the vulcanizing agent and the vulcanization accelerator are kneaded a vulcanizing agent and vulcanization accelerator kneaded product obtained. In addition, since the rubber composition for tires exhibits sufficient fuel efficiency while maintaining sufficient wear resistance, it is suitable for cap treads of pneumatic tires for a wide range of vehicles such as passenger cars, trucks, and buses. Can be used.

(Preparation of polybutadiene B-3 solution)
1.0 L of the polymerization solution (butadiene (BD): 33.0% by weight, cyclohexane (CH): 22.0% by weight, remaining Was 2-butenes). Further, 1.71 mmol of water (H ₂ O), 3.00 mmol of diethyl aluminum chloride (DEAC) (aluminum / water = 1.75 (mixing molar ratio)), 10.40 μmol of cobalt octoate (Co _cat ), and cyclooctamate 1,20 cis polymerization was performed by adding 8.20 mmol of diene (COD) and 15 μmol of dilauryl thiodipropionate (DLTP) and stirring at 65 ° C. for 20 minutes. Thereafter, the polymerization was stopped by adding ethanol containing 4,6-bis (octylthiomethyl) -o-cresol to obtain a polybutadiene B- 3 solution. Table 3 shows the conditions for preparing the solution.

Claims (8)

(A1) The ratio (Tcp / ML _{1 + 4,100 ° C.} ) of 5 wt% toluene solution viscosity (Tcp) to Mooney viscosity (ML _{1 + 4,100 ° C.} ) is 2.5 or more, and (a2) weight average molecular weight (Mw) is Polybutadiene (A) satisfying the condition of 60.0 × 10 ⁴ or more;
(B1) The ratio (Tcp / ML _{1 + 4,100 ° C.} ) of 5 wt% toluene solution viscosity (Tcp) to Mooney viscosity (ML _{1 + 4,100 ° C.} ) is 3.5 or less, and (b2) the weight average molecular weight (Mw) is A polybutadiene (B) satisfying the condition of 56.0 × 10 ⁴ or less,
A polybutadiene rubber (i) having a weight ratio of the polybutadiene (A) / the polybutadiene (B) of 10/90 to 80/20;
Other rubber (ii),
A cap tread comprising a rubber composition for a tire, comprising a rubber reinforcing material (iii).   The cap tread according to claim 1, wherein the weight ratio of the polybutadiene (A) / the polybutadiene (B) is 15/85 to 45/55.   The cap tread according to claim 1 or 2, wherein the polybutadiene (A) is produced using a cobalt catalyst or a neodymium catalyst.   The cap tread according to any one of claims 1 to 3, wherein the polybutadiene (B) is produced using a cobalt catalyst or a neodymium catalyst.   With respect to 100 parts by weight of a rubber component (i) + (ii) consisting of 5 to 90 parts by weight of the polybutadiene rubber (i) and 95 to 10 parts by weight of the other rubber (ii), the rubber reinforcing material (iii) The cap tread according to any one of claims 1 to 4, wherein 1 to 100 parts by weight is blended.   The cap tread according to any one of claims 1 to 5, wherein the other rubber (ii) includes a styrene butadiene rubber.   The cap tread according to any one of claims 1 to 6, wherein the other rubber (ii) includes at least one of a natural rubber and an isoprene rubber.   A pneumatic tire comprising the cap tread according to any one of claims 1 to 7.