JP2010275427A - Rubber composition and pneumatic tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition achieving the reduction of rolling resistance by exhibiting more superior low heat build-up while improving the compatibility between a rubber component and a filler without increasing the amount of a compounded butadiene polymer, and having excellent breaking resistance, and to provide a pneumatic tire using the rubber composition. <P>SOLUTION: The rubber composition include 10-60 pts.mass of the butadiene polymer having a conjugated modifying group, and carbon black having a nitrogen adsorption specific surface area (N<SB>2</SB>SA) of 70-160 m<SP>2</SP>/g and a DBP adsorption of 90-180 ml/100 g in 100 pts.mass of the rubber component. The butadiene polymer is modified with a modifier of a heterocyclic nitrile compound represented by formula (I): θ-C≡N or (II): θ-R-C≡N (wherein, θ is a heterocyclic group; and R is a divalent hydrocarbon group), and has ≥40% of the cis content in the rubber composition. The pneumatic tire is obtained by using the rubber composition in a cap rubber part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rubber composition that can exhibit excellent physical properties when employed in a cap rubber part of a pneumatic tire, and a pneumatic tire using the rubber composition in the cap rubber part.

In general, as shown in FIG. 1, a pneumatic tire includes a pair of bead portions 3, a pair of sidewall portions 4, and a tread portion 5, and is a carcass layer that is locked to a bead core 2 that extends in a toroid shape. 6, a belt layer 7 located on the outer periphery of the crown portion, and a tread rubber layer 8 located on the outer side in the tire radial direction. The tread rubber layer 8 includes a base rubber portion 9 that covers the belt layer 7, a cap rubber portion 10 that constitutes the tread surface, a wing rubber portion 11 that covers the end of the belt layer 7, and both width ends of the tread rubber layer 8. It is comprised from the end rubber part 12 located in a part.
In recent years, pneumatic tires are required to have excellent durability in order to save fuel consumption of automobiles in response to social demands for energy saving and resource saving. As such, it is strongly desired to exhibit low exothermic property (low loss property) and breakage resistance, which are further superior to those of the prior art.

  Under such circumstances, it is common to use a low heat-generating rubber composition as a method for reducing the rolling resistance of the tire. In order to achieve low heat build-up, a means for increasing the particle size of the filler can be taken, but although rolling resistance can be reduced, there is a concern about deterioration of fracture resistance. In addition, it is possible to adopt a means of realizing low heat build-up by increasing the blending amount of the butadiene-based polymer to lower the glass transition temperature. Tend to deteriorate, and workability may also be reduced.

On the other hand, in order to improve both low heat buildup and fracture resistance, it is an extremely effective means to use a modified polymer introduced with a functional group that interacts with the filler in the rubber composition as a rubber component. It is known (see, for example, Patent Document 1).
However, even if this rubber component is used, depending on the type of the functional group to be introduced, the reactivity with the filler differs, which may greatly affect the performance of the resulting rubber composition. Therefore, there is still room for improvement from the viewpoint of realizing a rubber composition that can further improve both low heat buildup and fracture resistance.

Furthermore, as a rubber composition for a tire cap tread capable of achieving both low fuel consumption and wear resistance, for example, 15% by weight or more of a terminal-modified diene rubber having a number average molecular weight of 150,000 to 400,000 before modification A rubber composition for a tire cap tread containing a rubber component to be contained, a filler, and 0.5 to 5 parts by weight of a specific vulcanizing agent with respect to 100 parts by weight of the rubber component is known (for example, , See Patent Document 2).
However, even with this tire cap tread rubber composition, it is still insufficient to achieve both low fuel consumption and wear resistance.

International Publication No. 2006/112450 Pamphlet JP 2008-1111012 A (Claims, Examples, etc.)

  In view of the above-described conventional problems and current situation, the present invention intends to solve this problem, and without increasing the blending amount of the butadiene polymer, while improving the affinity between the rubber component and the filler, An object of the present invention is to provide a rubber composition that exhibits superior low heat build-up and realizes reduction in rolling resistance, and also has excellent fracture resistance, and a pneumatic tire using the rubber composition.

  As a result of intensive studies to solve the above-mentioned problems, the inventor contains a butadiene-based polymer modified with a specific modifier in a specific range in a rubber component, and carbon black having specific physical properties. By finding the rubber composition to be contained, it is found that the above-mentioned rubber composition can be obtained, and by using this rubber composition in the cap rubber part of the pneumatic tire, the above-mentioned pneumatic tire can be obtained. The inventors have found out that the present invention has been completed.

That is, the present invention resides in the following (1) to (9).
(1) 10 to 60 parts by mass of a butadiene-based polymer having a conjugated modifying group in 100 parts by mass of a rubber component, a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 160 m ² / g, and a DBP absorption amount of 90 A rubber composition comprising carbon black of ~ 180ml / 100g,
The butadiene polymer is modified with a modifier which is a heterocyclic nitrile compound represented by the following formula (I) or the following formula (II), and has a cis content of 40% or more. Rubber composition.
θ-C≡N (I)
θ-R-C≡N (II)
(In the above formulas (I) and (II), θ represents a heterocyclic group, and R represents a divalent hydrocarbon group.)
(2) The rubber composition as described in (1) above, wherein natural rubber is contained in an amount of 40 to 90 parts by mass in 100 parts by mass of the rubber component.
(3) The rubber composition as described in (1) or (2) above, wherein the carbon black is contained in an amount of 35 to 70 parts by mass with respect to 100 parts by mass of the rubber component.
(4) The rubber composition as described in any one of (1) to (3) above, wherein in the formulas (I) and (II), θ is a heterocyclic group containing a nitrogen atom.
(5) In the formulas (I) and (II), θ represents a heterocyclic group containing an oxygen atom, a heterocyclic group containing a sulfur atom, a heterocyclic group containing two or more heteroatoms, and one or more cyano groups. The rubber composition as described in any one of (1) to (4) above, which is at least one heterocyclic group selected from the group consisting of heterocyclic groups.
(6) In the formulas (I) and (II), θ is a heteroaromatic ring group or a heterononaromatic ring group, or a monocyclic, bicyclic, tricyclic, or polycyclic heterocyclic group. The rubber composition as described in any one of (1) to (5) above.
(7) The rubber composition according to any one of (1) to (6) above, wherein the butadiene polymer has a cis content of 90% or more.
(8) The ratio (Mw / Mn) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the butadiene-based polymer is 1.3 to 3.5. The rubber composition according to any one of to (6).
(9) A pneumatic tire using the rubber composition according to any one of (1) to (8) above in a cap rubber part.

  According to the rubber composition of the present invention, the relatively high cis-content butadiene polymer used as the rubber component is a polymer modified with a specific modifier, so that the carbon black having specific physical properties used as a filler is used. The dispersibility of the butadiene polymer can be improved, and the low heat build-up better than the conventional one can be exhibited without increasing the blending of the butadiene-based polymer itself, and the excellent low rolling resistance and fracture resistance can be achieved. A combined rubber composition can be realized.

  If a rubber composition containing such a butadiene-based polymer is employed in the cap rubber portion, a high-performance pneumatic tire having both excellent low rolling resistance and fracture resistance can be easily obtained.

It is a section schematic diagram of a general pneumatic tire.

Hereinafter, the present invention will be described in detail.
The rubber composition of the present invention comprises 10 to 60 parts by mass of a butadiene-based polymer having a conjugated modifying group, a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 160 m ² / g, in 100 parts by mass of a rubber component, and A rubber composition comprising carbon black having a DBP absorption of 90 to 180 ml / 100 g, wherein the butadiene polymer is a heterocyclic nitrile compound represented by the following formula (I) or the following formula (II): It is modified with a certain modifying agent and has a cis content of 40% or more.
θ-C≡N (I)
θ-R-C≡N (II)
(In the above formulas (I) and (II), θ represents a heterocyclic group, and R represents a divalent hydrocarbon group.)

[Butadiene polymer]
In the rubber composition of the present invention, the rubber component has a cis content (1,4-cis bond content) of 40% or more, preferably 90% or more, more preferably 96% or more, and most preferably 98% or more. A butadiene-based polymer having a conjugated modified group (hereinafter also referred to as “modified butadiene-based polymer”) is used.
In the modified butadiene polymer used in the present invention, if the cis content is less than 40%, the effect of the present invention tends to be hardly exhibited. If the cis content is above the above range, an excellent fracture resistance is obtained due to an increase in stretched crystallinity. In addition to being able to exhibit it, the glass transition temperature is also lowered, and the low temperature characteristics and cold resistance characteristics are improved. In the present invention, “cis content” means the proportion of 1,4-cis bonds in the butadiene compound unit in the butadiene polymer.

  The butadiene-based polymer is preferably composed of 1,3-butadiene monomer, particularly preferably composed of only 1,3-butadiene monomer, and is desirably so-called polybutadiene rubber (BR). The 1,3-butadiene monomer unit is preferably 80 to 100% by mass, and the other monomer unit copolymerizable with 1,3-butadiene is preferably 20 to 0% by mass. When the 1,3-butadiene monomer unit content in the polymer is less than 80% by mass, the 1,4-cis bond content with respect to the whole polymer is lowered, and thus the effect of the present invention is hardly exhibited.

  Here, other monomers copolymerizable with 1,3-butadiene include, for example, conjugated diene monomers having 5 to 8 carbon atoms, aromatic vinyl monomers and the like. Among these, A conjugated diene monomer having 5 to 8 carbon atoms is preferred. Examples of the conjugated diene monomer having 5 to 8 carbon atoms include 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and the like. Can be mentioned. Examples of the aromatic vinyl monomer include styrene, p-methylstyrene, α-methylstyrene, and vinylnaphthalene.

  In addition, the vinyl content (1,2-vinyl bond content) of the butadiene polymer is preferably 1.5% or less, more preferably 1.0% or less. If the vinyl content is outside the above range, the crystallinity of the polymer may be lowered, which is not preferable. Here, the “vinyl content” means the proportion of 1,2-vinyl bonds in the butadiene compound unit in the butadiene polymer.

  Furthermore, the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the butadiene-based polymer (modified butadiene-based polymer) having the conjugated modified group is 1.3-3. 5, Preferably, it is 1.3-3.0. Here, “Mn and Mw / Mn” mean values obtained using polystyrene as a standard substance by gel permeation chromatography (GPC).

  The butadiene-based polymer having a conjugated modified group used in the present invention (modified butadiene-based polymer) is described below in detail in the presence of a catalyst system comprising a component (A), a component (B), and a component (C). A butadiene polymer before modification obtained by polymerizing a monomer containing at least a diene monomer such as 1,3-butadiene at a temperature of 25 ° C. or lower is used. Here, examples of the monomer include 1,3-butadiene and other monomers copolymerizable with the above-described 1,3-butadiene.

  The component (A) of the catalyst system used in the production of the butadiene polymer before modification is a compound containing a rare earth element having an atomic number of 57 to 71 in the periodic table, or a reaction product of these compounds and a Lewis base. It is. Here, among the rare earth elements having atomic numbers 57 to 71, neodymium, praseodymium, cerium, lanthanum, gadolinium, or the like, or a mixture thereof is preferable, and neodymium is particularly preferable.

  The rare earth element-containing compound is preferably a salt soluble in a hydrocarbon solvent, and specifically includes the rare earth element carboxylates, alkoxides, β-diketone complexes, phosphates and phosphites. Of these, carboxylates and phosphates are preferable, and carboxylates are particularly preferable. Here, examples of the hydrocarbon solvent include saturated aliphatic hydrocarbons having 4 to 10 carbon atoms such as butane, pentane, hexane and heptane, saturated alicyclic hydrocarbons having 5 to 20 carbon atoms such as cyclopentane and cyclohexane, -Monoolefins such as butene, 2-butene, aromatic hydrocarbons such as benzene, toluene, xylene, methylene chloride, chloroform, trichloroethylene, perchloroethylene, 1,2-dichloroethane, chlorobenzene, bromobenzene, chlorotoluene, etc. A halogenated hydrocarbon is mentioned.

Examples of the rare earth element carboxylates include compounds represented by the following general formula (III).
(R ⁴ —CO ₂ ) ₃ M (III)
[In the formula (III), R ⁴ is a hydrocarbon group having 1 to 20 carbon atoms, and M is a rare earth element having atomic numbers 57 to 71 in the periodic table.]
Here, R ⁴ may be saturated or unsaturated, is preferably an alkyl group or an alkenyl group, and may be linear, branched or cyclic. The carboxyl group is bonded to a primary, secondary or tertiary carbon atom. As the carboxylate, specifically, octanoic acid, 2-ethylhexanoic acid, oleic acid, neodecanoic acid, stearic acid, benzoic acid, naphthenic acid, Versatic acid [trade names of Shell Chemical Co., Ltd. , A carboxylic acid in which a carboxyl group is bonded to a tertiary carbon atom], and the like. Among these, salts of 2-ethylhexanoic acid, neodecanoic acid, naphthenic acid, and versatic acid are preferable.

Examples of the rare earth element alkoxide include compounds represented by the following general formula (IV).
(R ⁵ O) ₃ M ……… (IV)
[In the above formula (IV), R ⁵ is a hydrocarbon group having 1 to 20 carbon atoms, and M is a rare earth element having atomic numbers 57 to 71 in the periodic table. ]
In the above formula (IV), examples of the alkoxy group represented by R ⁵ O include 2-ethyl-hexylalkoxy group, oleylalkoxy group, stearylalkoxy group, phenoxy group, benzylalkoxy group and the like. Among these, a 2-ethyl-hexylalkoxy group and a benzylalkoxy group are preferable.

  Examples of the rare earth element β-diketone complex include the rare earth element acetylacetone complex, benzoylacetone complex, propionitrileacetone complex, valerylacetone complex, ethylacetylacetone complex, and the like. Among these, an acetylacetone complex and an ethylacetylacetone complex are preferable.

  Examples of the rare earth element phosphate and phosphite include the rare earth element, bis (2-ethylhexyl) phosphate, bis (1-methylheptyl phosphate), bis (p-nonylphenyl) phosphate, phosphorus Acid bis (polyethylene glycol-p-nonylphenyl), phosphoric acid (1-methylheptyl) (2-ethylhexyl), phosphoric acid (2-ethylhexyl) (p-nonylphenyl), 2-ethylhexylphosphonic acid mono-2-ethylhexyl 2-ethylhexylphosphonic acid mono-p-nonylphenyl, bis (2-ethylhexyl) phosphinic acid, bis (1-methylheptyl) phosphinic acid, bis (p-nonylphenyl) phosphinic acid, (1-methylheptyl) (2 -Ethylhexyl) phosphinic acid, (2-ethylhexyl) (p-nonylphenyl) phosphine Among these, the rare earth elements, bis (2-ethylhexyl) phosphate, bis (1-methylheptyl) phosphate, mono-2-ethylhexyl 2-ethylhexylphosphonate, bis A salt with (2-ethylhexyl) phosphinic acid is preferred.

  Among the rare earth element-containing compounds, neodymium phosphate and neodymium carboxylate are more preferable, and in particular, neodymium branch such as neodymium 2-ethylhexanoate, neodymium neodecanoate, neodymium versatate, etc. Carboxylate is most preferred.

  The component (A) may be a reaction product of the rare earth element-containing compound and a Lewis base. The reaction product has improved solubility of the rare earth element-containing compound in the solvent due to the Lewis base, and can be stably stored for a long period of time. In order to easily solubilize the rare earth element-containing compound in a solvent and to store stably for a long period of time, the Lewis base is used in a proportion of 0 to 30 mol, preferably 1 to 10 mol, per mol of rare earth element. Or as a mixture of the two or as a product obtained by reacting both in advance. Here, examples of the Lewis base include acetylacetone, tetrahydrofuran, pyridine, N, N-dimethylformamide, thiophene, diphenyl ether, triethylamine, an organic phosphorus compound, and a monovalent or divalent alcohol.

  The rare earth element-containing compound as the component (A) described above or a reaction product of these compounds and a Lewis base can be used singly or in combination of two or more.

Examples of the component (B) of the catalyst system used for the production of the butadiene polymer before modification include an organoaluminum compound represented by the following general formula (V).
AlR ¹ R ² R ³ ……… (V)
In [formula (V), R ¹ and R ² are the same or different, a hydrocarbon group or a hydrogen atom having 1 to 10 carbon atoms, R ³ is a hydrocarbon group having 1 to 10 carbon atoms, provided that, R ³ May be the same as or different from R ¹ or R ² described above. ]

  Examples of the organoaluminum compound of the above formula (V) include trimethylaluminum, triethylaluminum, tri-n-propylaluminum, triisopropylaluminum, tri-n-butylaluminum, triisobutylaluminum, tri-t-butylaluminum, tri Pentyl aluminum, trihexyl aluminum, tricyclohexyl aluminum, trioctyl aluminum; diethyl aluminum hydride, di-n-propyl aluminum hydride, di-n-butyl aluminum hydride, diisobutyl aluminum hydride, dihexyl aluminum hydride, hydrogenated Diisohexyl aluminum, dioctyl aluminum hydride, diisooctyl aluminum hydride; ethyl aluminum dihydride, n-propyl Rumi bromide dihydride, include isobutyl aluminum dihydride and the like, among these, triethylaluminum, triisobutylaluminum, hydrogenated diethylaluminum, hydrogenated diisobutylaluminum are preferred. The organoaluminum compound as component (B) described above can be used alone or in combination of two or more.

  The component (C) of the catalyst system used for the production of the butadiene polymer before modification is selected from the group consisting of Lewis acids, complex compounds of metal halides and Lewis bases, and organic compounds containing active halogens. It is at least one halogen compound.

  The Lewis acid has Lewis acidity and is soluble in hydrocarbons. Specifically, methyl aluminum dibromide, methyl aluminum dichloride, ethyl aluminum dibromide, ethyl aluminum dichloride, butyl aluminum dibromide, butyl aluminum dichloride, dimethyl aluminum bromide, dimethyl aluminum chloride, diethyl bromide Aluminum, diethylaluminum chloride, dibutylaluminum bromide, dibutylaluminum chloride, methylaluminum sesquibromide, methylaluminum sesquichloride, ethylaluminum sesquibromide, ethylaluminum sesquichloride, dibutyltin dichloride, aluminum tribromide, antimony trichloride, Examples include antimony pentachloride, phosphorus trichloride, phosphorus pentachloride, tin tetrachloride, and silicon tetrachloride. Among these, diethylaluminum chloride, sesquiethylaluminum chloride, ethylaluminum dichloride, diethylaluminum bromide, ethylaluminum sesquibromide, and ethylaluminum dibromide are preferable. Alternatively, a reaction product of an alkylaluminum and a halogen such as a reaction product of triethylaluminum and bromine can be used.

  Examples of the metal halide constituting the complex compound of the above metal halide and Lewis base include beryllium chloride, beryllium bromide, beryllium iodide, magnesium chloride, magnesium bromide, magnesium iodide, calcium chloride, calcium bromide, iodine. Calcium chloride, barium chloride, barium bromide, barium iodide, zinc chloride, zinc bromide, zinc iodide, cadmium chloride, cadmium bromide, cadmium iodide, mercury chloride, mercury bromide, mercury iodide, manganese chloride, Manganese bromide, manganese iodide, rhenium chloride, rhenium bromide, rhenium iodide, copper chloride, copper iodide, silver chloride, silver bromide, silver iodide, gold chloride, gold iodide, gold bromide, etc. Of these, magnesium chloride, calcium chloride, barium chloride, manganese chloride, zinc chloride, and copper chloride are preferred. , Magnesium chloride, manganese chloride, zinc chloride, copper chloride being particularly preferred.

  Moreover, as a Lewis base which comprises the complex compound of the said metal halide and a Lewis base, a phosphorus compound, a carbonyl compound, a nitrogen compound, an ether compound, alcohol, etc. are preferable. Specifically, tributyl phosphate, tri-2-ethylhexyl phosphate, triphenyl phosphate, tricresyl phosphate, triethylphosphine, tributylphosphine, triphenylphosphine, diethylphosphinoethane, diphenylphosphinoethane, acetylacetone, benzoylacetone , Propionitrile acetone, valeryl acetone, ethyl acetylacetone, methyl acetoacetate, ethyl acetoacetate, phenyl acetoacetate, dimethyl malonate, diethyl malonate, diphenyl malonate, acetic acid, octanoic acid, 2-ethyl-hexanoic acid, olein Acid, stearic acid, benzoic acid, naphthenic acid, versatic acid, triethylamine, N, N-dimethylacetamide, tetrahydrofuran, diphenyl ether, 2-ethyl-hexyl alcohol Examples include oleyl alcohol, stearyl alcohol, phenol, benzyl alcohol, 1-decanol, and lauryl alcohol. Among these, tri-2-ethylhexyl phosphate, tricresyl phosphate, acetylacetone, 2-ethylhexanoic acid, versatic acid, 2 -Ethylhexyl alcohol, 1-decanol and lauryl alcohol are preferred.

The Lewis base is reacted at a ratio of 0.01 to 30 mol, preferably 0.5 to 10 mol, per 1 mol of the metal halide. When the reaction product with the Lewis base is used, the metal remaining in the polymer can be reduced.
Examples of the organic compound containing the active halogen include benzyl chloride.

  In addition to the components (A) to (C), an organoaluminum oxy compound, so-called aluminoxane, is further added as a component (D) to the catalyst system used for the production of the butadiene-based polymer before modification. preferable. Here, examples of the aluminoxane include methylaluminoxane, ethylaluminoxane, propylaluminoxane, butylaluminoxane, chloroaluminoxane and the like. By adding aluminoxane as the component (D), the molecular weight distribution becomes sharp and the activity as a catalyst is improved.

  The amount or composition ratio of each component of the catalyst system used in the present invention is appropriately selected according to its purpose or necessity. Of these, the component (A) is preferably used in an amount of 0.00001 to 1.0 mmol, and more preferably 0.0001 to 0.5 mmol, per 100 g of 1,3-butadiene. When the amount of component (A) used is less than 0.00001 mmol, the polymerization activity is low, and when it exceeds 1.0 mmol, the catalyst concentration increases and a deashing step is required. Moreover, the ratio of (A) component and (B) component is molar ratio, (A) component: (B) component is 1: 1-1: 700, Preferably it is 1: 3-1: 500. Furthermore, the ratio of the halogen in the component (A) and the component (C) is in the molar ratio of 1: 0.1 to 1:30, preferably 1: 0.2 to 1:15, more preferably 1: 2. 0 to 1: 5.0. Moreover, the ratio of the aluminum in (D) component and (A) component is 1: 1-700: 1 by molar ratio, Preferably it is 3: 1-500: 1. Outside the range of these catalyst amounts or component ratios, it is not preferable because it does not act as a highly active catalyst or requires a step of removing the catalyst residue. In addition to the above components (A) to (C), the polymerization reaction may be carried out in the presence of hydrogen gas for the purpose of adjusting the molecular weight of the polymer.

  As a catalyst component, in addition to the components (A), (B), and (C), a small amount of a conjugated diene monomer such as 1,3-butadiene, if necessary, specifically (A ) You may use in the ratio of 0-1000 mol per 1 mol of compounds of a component. A conjugated diene monomer such as 1,3-butadiene as a catalyst component is not essential, but when used in combination, there is an advantage that the catalytic activity is further improved.

  The production of the catalyst is, for example, by dissolving the components (A) to (C) in a solvent and further reacting a monomer such as 1,3-butadiene as necessary. In that case, the addition order of each component is not specifically limited, Furthermore, you may add an aluminoxane as (D) component. From the viewpoint of improving the polymerization activity and shortening the polymerization initiation induction period, it is preferable that these components are mixed in advance, reacted and aged. Here, the aging temperature is 0 to 100 ° C, and preferably 20 to 80 ° C. If the temperature is less than 0 ° C., the aging is not sufficiently performed. If the temperature exceeds 100 ° C., the catalytic activity is lowered and the molecular weight distribution is widened. The aging time is not particularly limited, and can be ripened by contacting in the line before adding to the polymerization reaction tank. Usually, 0.5 minutes or more is sufficient, and stable for several days.

  The production of the butadiene-based polymer before modification is preferably performed by solution polymerization. Here, in the case of solution polymerization, an inert organic solvent is used as the polymerization solvent. Examples of the inert organic solvent include saturated aliphatic hydrocarbons having 4 to 10 carbon atoms such as butane, pentane, hexane and heptane, saturated alicyclic hydrocarbons having 5 to 20 carbon atoms such as cyclopentane and cyclohexane, 1- Monoolefins such as butene and 2-butene, aromatic hydrocarbons such as benzene, toluene and xylene, methylene chloride, chloroform, carbon tetrachloride, trichloroethylene, perchloroethylene, 1,2-dichloroethane, chlorobenzene, bromobenzene, chloro And halogenated hydrocarbons such as toluene. Among these, a C5-C6 aliphatic hydrocarbon and alicyclic hydrocarbon are especially preferable. These solvents may be used alone or in combination of two or more.

  The production of the butadiene-based polymer before the modification needs to be performed at a polymerization temperature of 25 ° C. or less, and is preferably performed at 10 to −78 ° C. When the polymerization temperature exceeds 25 ° C., the polymerization reaction cannot be sufficiently controlled, and the cis-1,4 bond content of the produced butadiene polymer is lowered and the vinyl bond content is raised. On the other hand, when the polymerization temperature is lower than -78 ° C, the freezing point of the solvent falls below, so that the polymerization cannot be performed.

  Production of the butadiene-based polymer before the modification may be performed either batchwise or continuously. In addition, in the production of the butadiene-based polymer, in order not to deactivate the rare earth element compound-based catalyst and the polymer, mixing of a deactivating compound such as oxygen, water, carbon dioxide gas in the polymerization reaction system. Consideration to eliminate as much as possible is necessary.

  The butadiene-based polymer having a conjugated modified group (modified butadiene-based polymer) is a polymer obtained by modifying the butadiene-based polymer before modification with a specific modifying agent described later, which is a conjugated modified group. Have Here, the conjugated modification group means a functional group to be conjugated, and at least a part of the modification group and the polymer having the modification group are conjugated via the modification group. In the case of such a butadiene-based copolymer having a conjugated modification group, delocalized electrons existing in the polymer act to improve the affinity for a filler such as carbon black. It is possible to disperse these fillers extremely effectively, and a more excellent low heat generation property can be realized.

Thus, the modifier capable of introducing a conjugated modifying group into the butadiene polymer introduces a conjugated modifying group that can contribute to improving the dispersibility of the filler, which will be described later. Or it is a heterocyclic nitrile compound represented by Formula (II).
θ-C≡N ……… (I)
θ-R-C≡N ……… (II)

  In the above formulas (I) and (II), θ represents a heterocyclic group. Further, θ is preferably a heterocyclic group containing a nitrogen atom, a heterocyclic group containing an oxygen atom, a heterocyclic group containing a sulfur atom, a heterocyclic group containing two or more heteroatoms, and one or more cyano groups. It is preferably at least one heterocyclic group selected from the group consisting of heterocyclic groups containing. Further, it may be a heteroaromatic group or a non-aromatic ring group such as thiophene, pyridine, furan, piperidine, dioxane, and also a monocyclic, bicyclic, tricyclic, or polycyclic heterocyclic group. It may be.

  Conventionally, the modifying groups that can be introduced into the butadiene-based polymer have been limited to specific groups such as —CN, —SiCl, —SiOR, and C═O. However, in the present invention, more excellent low heat generation is realized. From the viewpoint of conversion, a more preferable conjugated modifying group can be introduced. Such a conjugated modification group can more reliably conjugated a butadiene copolymer or the like, and contributes to an improvement in the dispersibility of the filler.

  Specific examples of such θ include, for example, 2-pyridyl, 3-pyridyl, 4-pyridyl, pyrazinyl, 2-pyrimidinyl, 4-pyrimidinyl, 5-pyrimidinyl, 3-pyridazinyl as a heterocyclic group containing a nitrogen atom. 4-pyridazinyl, N-methyl-2-pyrrolyl, N-methyl-3-pyrrolyl, N-methyl-2-imidazolyl, N-methyl-4-imidazolyl, N-methyl-5-imidazolyl, N-methyl-3 -Pyrazolyl, N-methyl-4-pyrazolyl, N-methyl-5-pyrazolyl, N-methyl-1,2,3-triazol-4-yl, N-methyl-1,2,3-triazol-5-yl N-methyl-1,2,4-triazol-3-yl, N-methyl-1,2,4-triazol-5-yl, 1,2,4-triazin-3-yl, 2,4-triazin-5-yl, 1,2,4-triazin-6-yl, 1,3,5-triazinyl, N-methyl-2-pyrrolin-2-yl, N-methyl-2-pyrroline- 3-yl, N-methyl-2-pyrrolin-4-yl, N-methyl-2-pyrrolin-5-yl, N-methyl-3-pyrrolin-2-yl, N-methyl-3-pyrrolin-3- Yl, N-methyl-2-imidazolin-2-yl, N-methyl-2-imidazolin-4-yl, N-methyl-2-imidazolin-5-yl, N-methyl-2-pyrazolin-3-yl, N-methyl-2-pyrazolin-4-yl, N-methyl-2-pyrazolin-5-yl, 2-quinolyl, 3-quinolyl, 4-quinolyl, 1-isoquinolyl, 3-isoquinolyl, 4-isoquinolyl, N- Methylindol-2-yl N-methylindol-3-yl, N-methylisoindol-1-yl, N-methylisoindol-3-yl, 1-indolidinyl, 2-indolidinyl, 3-indolidinyl, 1-phthalazinyl, 2-quinazolinyl, 4-quinazolinyl, 2-quinoxalinyl, 3-cinnolinyl, 4-cinnolinyl, 1-methylindazol-3-yne, 1,5-naphthyridin-2-yl, 1,5-naphthyridin-3-yl, 1,5-naphthyridine -4-yl, 1,8-naphthyridin-2-yl, 1,8-naphthyridin-3-yl, 1,8-naphthyridin-4-yl, 2-pteridinyl, 4-pteridinyl, 6-pteridinyl, 7-pteridinyl 1-methylbenzimidazol-2-yl, 6-phenanthridinyl, N-methyl-2-purinyl, N Methyl-6-purinyl, N-methyl-8-purinyl, N-methyl-β-carbolin-1-yl, N-methyl-β-carbolin-3-yl, N-methyl-β-carbolin-4-yl, 9-acridinyl, 1,7-phenanthroline-2-yl, 1,7-phenanthroline-3-yl, 1,7-phenanthroline-4-yl, 1,10-phenanthroline-2-yl, 1,10-phenanthroline- 3-yl, 1,10-phenanthroline-4-yl, 4,7-phenanthroline-1-yl, 4,7-phenanthroline-2-yl, 4,7-phenanthroline-3-yl, 1-phenazinyl, 2- Examples include phenazinyl, pyrrolidino and piperidino.

  Examples of the heterocyclic group containing an oxygen atom include 2-furyl, 3-furyl, 2-benzo [b] furyl, 3-benzo [b] furyl, 1-isobenzo [b] furyl, 3-isobenzo [b] furyl, 2 -Naphtho [2,3-b] furyl, 3-naphtho [2,3-b] furyl.

  As the heterocyclic group containing a sulfur atom, 2-thienyl, 3-thienyl, 2-benzo [b] thienyl, 3-benzo [b] thienyl, 1-isobenzo [b] thienyl, 3-isobenzo [b] thienyl, 2 -Naphtho [2,3-b] thienyl, 3-naphtho [2,3-b] thienyl.

  Examples of the heterocyclic group containing two or more heteroatoms include 2-oxazolyl, 4-oxazolyl, 5-oxazolyl, 3-isoxazolyl, 4-isoxazolyl, 5-isoxazolyl, 2-thiazolyl, 4-thiazolyl, 5-thiazolyl, 3- Isothiazolyl, 4-isothiazolyl, 5-isothiazolyl, 1,2,3-oxadiazol-4-yl, 1,2,3-oxadiazol-5-yl, 1,3,4-oxadiazol-2- Yl, 1,2,3-thiadiazol-4-yl, 1,2,3-thiadiazol-5-yl, 1,3,4-thiadiazol-2-yl, 2-oxazolin-2-yl, 2-oxazoline- 4-yl, 2-oxazolin-5-yl, 3-isoxazolinyl, 4-isoxazolinyl, 5-isoxazolinyl, 2-thia Phosphorus-2-yl, 2-thiazoline-4-yl, 2-thiazoline-5-yl, 3-isothiazolinyl, 4-isothiazolinyl, 5- isothiazolinyl, 2-benzothiazolyl, and morpholino.

  Among these, θ is preferably a heterocyclic group containing a nitrogen atom, and particularly preferably 2-pyridyl, 3-pyridyl, or 4-pyridyl.

  In the above formulas (I) and (II), R represents a divalent hydrocarbon group, and corresponds to an alkylene group, alkenylene group, arylene group, or the like corresponding to a heterocyclic nitrile compound described later.

  Specific examples of such a heterocyclic nitrile compound include, for example, 2-pyridinecarbonitrile, 3-pyridinecarbonitrile, 4-pyridinecarbonitrile, pyrazinecarbohydrate as compounds having a heterocyclic group containing a nitrogen atom. Nitrile, 2-pyrimidinecarbonitrile, 4-pyrimidinecarbonitrile, 5-pyrimidinecarbonitrile, 3-pyridazinecarbonitrile, 4-pyridazinecarbonitrile, N-methyl-2-pyrrolecarbonitrile, N-methyl-3-pyrrolecarb Nitrile, N-methyl-2-imidazolecarbonitrile, N-methyl-4-imidazolecarbonitrile, N-methyl-5-imidazolecarbonitrile, N-methyl-3-pyrazolecarbonitrile, N-methyl-4-pyrazolecarbonitrile Nitrile, N-me Ru-5-pyrazolecarbonitrile, N-methyl-1,2,3-triazole-4-carbonitrile, N-methyl-1,2,3-triazole-5-carbonitrile, N-methyl-1,2, 4-triazole-3-carbonitrile, N-methyl-1,2,4-triazole-5-carbonitrile, 1,2,4-triazine-3-carbonitrile, 1,2,4-triazine-5-carbonitrile Nitrile, 1,2,4-triazine-6-carbonitrile, 1,3,5-triazinecarbonitrile, N-methyl-2-pyrroline-2-carbonitrile, N-methyl-2-pyrroline-3-carbonitrile N-methyl-2-pyrroline-4-carbonitrile, N-methyl-2-pyrroline-5-carbonitrile, N-methyl-3-pyrroline-2-carbonitrile N-methyl-3-pyrroline-3-carbonitrile, N-methyl-2-imidazoline-2-carbonitrile, N-methyl-2-imidazoline-4-carbonitrile, N-methyl-2-imidazoline-5-carbonitrile Nitrile, N-methyl-2-pyrazolin-3-carbonitrile, N-methyl-2-pyrazoline-4-carbonitrile, N-methyl-2-pyrazoline-5-carbonitrile, 2-quinolinecarbonitrile, 3-quinoline Carbonitrile, 4-quinolinecarbonitrile, 1-isoquinolinecarbonitrile, 3-isoquinolinecarbonitrile, 4-isoquinolinecarbonitrile, N-methylindole-2-carbonitrile, N-methylindole-3-carbonitrile, N-methyl Isoindole-1-carbonitrile, N-methylisoi Ndole-3-carbonitrile, 1-indolizinecarbonitrile, 2-indolizinecarbonitrile, 3-indolizinecarbonitrile, 1-phthalazinecarbonitrile, 2-quinazolinecarbonitrile, 4-quinazolinecarbonitrile, 2-quinoxaline Carbonitrile, 3-cinnolinecarbonitrile, 4-cinnolinecarbonitrile, 1-methylindazole-3-carbonitrile, 1,5-naphthyridine-2-carbonitrile, 1,5-naphthyridine-3-carbonitrile, 1 , 5-naphthyridine-4-carbonitrile, 1,8-naphthyridine-2-carbonitrile, 1,8-naphthyridine-3-carbonitrile, 1,8-naphthyridine-4-carbonitrile, 2-pteridinecarbonitrile, 4 -Pteridinecarbonitrile, 6 Pteridinecarbonitrile, 7-pteridinecarbonitrile, 1-methylbenzimidazole-2-carbonitrile, phenanthridine-6-carbonitrile, N-methyl-2-purinecarbonitrile, N-methyl-6-purinecarbonitrile, N-methyl-8-purinecarbonitrile, N-methyl-β-carboline-1-carbonitrile, N-methyl-β-carboline-3-carbonitrile, N-methyl-β-carboline-4-carbonitrile, 9 -Acridinecarbonitrile, 1,7-phenanthroline-2-carbonitrile, 1,7-phenanthroline-3-carbonitrile, 1,7-phenanthroline-4-carbonitrile, 1,10-phenanthroline-2-carbonitrile, 1 , 10-phenanthroline-3-carbonitrile, , 10-phenanthroline-4-carbonitrile, 4,7-phenanthroline-1-carbonitrile, 4,7-phenanthroline-2-carbonitrile, 4,7-phenanthroline-3-carbonitrile, 1-phenazinecarbonitrile, 2, -Phenazinecarbonitrile, 1-pyrrolidinecarbonitrile, 1-piperidinecarbonitrile are mentioned.

  Examples of the compound having a heterocyclic group containing an oxygen atom include 2-furonitrile, 3-furonitrile, 2-benzo [b] furancarbonitrile, 3-benzo [b] furancarbonitrile, and isobenzo [b] furan-1-carbohydrate. Examples include nitrile, isobenzo [b] furan-3-carbonitrile, naphth [2,3-b] furan-2-carbonitrile, and naphth [2,3-b] furan-3-carbonitrile.

  As compounds having a heterocyclic group containing a sulfur atom, 2-thiophenecarbonitrile, 3-thiophenecarbonitrile, benzo [b] thiophene-2-carbonitrile, benzo [b] thiophene-3-carbonitrile, isobenzo [b] Examples include thiophene-1-carbonitrile, isobenzo [b] thiophene-3-carbonitrile, naphtho [2,3-b] thiophene-2-carbonitrile, and naphtho [2,3-b] thiophene-3-carbonitrile. .

  Compounds having a heterocyclic group containing two or more heteroatoms include 2-oxazolecarbonitrile, 4-oxazolecarbonitrile, 5-oxazolecarbonitrile, 3-isoxazolecarbonitrile, 4-isoxazolecarbonitrile, 5-isoxazole. Oxazolecarbonitrile, 2-thiazolecarbonitrile, 4-thiazolecarbonitrile, 5-thiazolecarbonitrile, 3-isothiazolecarbonitrile, 4-isothiazolecarbonitrile, 5-isothiazolecarbonitrile, 1,2,3-oxazole -4-carbonitrile, 1,2,3-oxazole-5-carbonitrile, 1,3,4-oxazole-2-carbonitrile, 1,2,3-thiazole-4-carbonitrile, 1,2,3 -Thiazole-5-carbo Tolyl, 1,3,4-thiazole-2-carbonitrile, 2-oxazoline-2-carbonitrile, 2-oxazoline-4-carbonitrile, 2-oxazoline-5-carbonitrile, 3-isoxazolinecarbonitrile, 4 -Isoxazoline carbonitrile, 5-isoxazoline carbonitrile, 2-thiazoline-2-carbonitrile, 2-thiazoline-4-carbonitrile, 2-thiazoline-5-carbonitrile, 3-isothiazoline carbonitrile, 4-isothiazoline carbonitrile Nitriles, 5-isothiazolinecarbonitriles, benzothiazole-2-carbonitriles, 4-morpholinecarbonitriles.

  As compounds having two or more cyano groups, 2,3-pyridinedicarbonitrile, 2,4-pyridinedicarbonitrile, 2,5-pyridinedicarbonitrile, 2,6-pyridinedicarbonitrile, 3,4- Pyridinedicarbonitrile, 2,4-pyrimidinedicarbonitrile, 2,5-pyrimidinedicarbonitrile, 4,5-pyrimidinedicarbonitrile, 4,6-pyrimidinedicarbonitrile, 2,3-pyrazinedicarbonitrile, 2,5-pyrazinedicarbonitrile, 2,6-pyrazinedicarbonitrile, 2,3-furandicarbonitrile, 2,4-furandicarbonitrile, 2,5-furandicarbonitrile, 2,3-thiophenedicarbonitrile 2,4-thiophene dicarbonitrile, 2,5-thiophene dicarbonitrile, N-methyl -2,3-pyrrole dicarbonitrile, N-methyl-2,4-pyrrole dicarbonitrile, N-methyl-2,5-pyrrole dicarbonitrile, 1,3,5-triazine-2,4-dicarb Nitrile, 1,2,4-triazine-3,5-dicarbonitrile, 3,2,4-triazine-3,6-dicarbonitrile, 2,3,4-pyridinetricarbonitrile, 2,3,5 -Pyridine tricarbonitrile, 2,3,6-pyridinetricarbonitrile, 2,4,5-pyridinetricarbonitrile, 2,4,6-pyridinetricarbonitrile, 3,4,5-pyridinetricarbonitrile, 2,4,5-pyrimidine tricarbonitrile, 2,4,6-pyrimidine tricarbonitrile, 4,5,6-pyrimidine tricarbonitrile, pyrazine tricarbonitrile Ril, 2,3,4-furantricarbonitrile, 2,3,5-furantricarbonitrile, 2,3,4-thiophenetricarbonitrile, 2,3,5-thiophenetricarbonitrile, N-methyl- 2,3,4-pyrrole tricarbonitrile, N-methyl-2,3,5-pyrrole tricarbonitrile, 1,3,5-triazine-2,4,6-tricarbonitrile, 1,2,4- Examples include triazine-3,5,6-tricarbonitrile.

  Among these, 2-cyanopyridine (2-pyridinecarbonitrile), 3-cyanopyridine (3-pyridinecarbonitrile), and 4-cyanopyridine (4-pyridinecarbonitrile) are preferable.

  As a method for modifying the butadiene polymer with the heterocyclic nitrile compound as described above, the polymer and the heterocyclic nitrile compound may be reacted. For example, a 1,3-butadiene monomer is required. According to the method, a polymerization mixture is obtained by adding other monomers and mixing and reacting together with a catalyst or an initiator, and adding a heterocyclic nitrile compound thereto. Further, a heterocyclic nitrile compound may be added to the activated polymerization mixture, or a reactive polymer formed by polymerizing a 1,3-butadiene monomer may be reacted with the heterocyclic nitrile compound. Good. Further, a heterocyclic nitrile compound may be added to the activated polymerization mixture, and a functionalizing agent may be added thereto.

  The polymerization mixture thus obtained is cooled and subjected to solvent removal and drying using a conventional method to obtain a modified butadiene-based polymer. For example, the polymer recovered from the polymer cement is poured into a solvent, and then the obtained polymer is dried using a dryer such as a drum dryer. At this time, the polymer may be directly recovered from the polymer cement dried with a drum dryer. The volatile substance in the obtained dry polymer is 1% by weight or less.

  The structure of the resulting modified butadiene polymer is, for example, the conditions used to prepare the reactive polymer, such as the type and amount of catalyst and initiator, and the type and amount of the heterocyclic nitrile compound. Thus, it depends on the conditions used to react the reactive polymer with the heterocyclic nitrile compound.

  The modified butadiene-based polymer is presumed to have a structure represented by the following formula (X) or (Y).

上記式（Ｘ）および（Ｙ）中のＡは、水素原子または金属原子を示し、金属原子は上記触媒に起因するものである。Ｂは単結合またはＲを示し、Ｒは上記式（Ｉ）および（II）と同義である。また、θは上記式（Ｉ）および（II）と同義であり、θ’はθから１つの原子が脱離した２価の置換基を示す。ただし、θ’はθが有するヘテロ原子にさらに水素原子などが付加した場合も含む。π₁およびπ₂は共にブタジエン系重合体のポリマー鎖を示す。

A in the above formulas (X) and (Y) represents a hydrogen atom or a metal atom, and the metal atom originates from the catalyst. B represents a single bond or R, and R is as defined in the above formulas (I) and (II). Θ is as defined in the above formulas (I) and (II), and θ ′ represents a divalent substituent in which one atom is eliminated from θ. However, θ ′ includes a case where a hydrogen atom or the like is further added to the hetero atom of θ. π ₁ and π ₂ both represent a polymer chain of a butadiene polymer.

  Then, when the butadiene-based polymer having the above structure is exposed to water vapor or the like, it is considered that the butadiene-based polymer is hydrolyzed and converted into a ketone-based structure such as the following formula (X ′) or (Y ′). .

上記式（Ｘ’）および（Ｙ’）中のＢ、θ、およびθ’は、上記式（Ｉ）および（II）と同義である。π₁およびπ₂は共にブタジエン系重合体のポリマー鎖を示す。

B, θ, and θ ′ in the above formulas (X ′) and (Y ′) are synonymous with the above formulas (I) and (II). π ₁ and π ₂ both represent a polymer chain of a butadiene polymer.

  Since the butadiene-based polymer can take such a structure, it is presumed that the dispersibility of a filler such as carbon black is further improved, and further excellent low heat generation can be realized.

  The butadiene-based polymer is contained in an amount of 10 to 60 parts by mass, preferably 10 to 40 parts by mass, and more preferably 30 to 40 parts by mass in 100 parts by mass of the rubber component. If the amount is less than 10 parts by mass, which is the lower limit, the low heat build-up effect may not be sufficiently exerted. If the amount exceeds 60 parts by mass, which is the upper limit, the heat insertability is lowered and workability is deteriorated. There is a fear.

[Other rubber components]
Examples of other rubber components other than the butadiene polymer having a functional group such as the butadiene polymer include natural rubber (NR), polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), and polybutadiene. Examples include rubber (BR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), halogenated butyl rubber, and acrylonitrile-butadiene rubber (NBR). Among these, natural rubber or polyisoprene rubber is particularly preferable. These rubber components may be used alone or in a blend of two or more.

  In addition, when blending natural rubber, you may use a ribbed smoke sheet (RSS) or technical rating rubber (TSR) according to the rating in the international quality packaging standard (commonly known as Green Book), or reclaim. Rubber can also be used. These natural rubbers are desirably 40 to 90 parts by mass, preferably 60 to 90 parts by mass, and more preferably 60 to 70 parts by mass in 100 parts by mass of the rubber component. If the amount is less than 40 parts by mass, which is the lower limit, the fracture resistance may not be sufficiently exhibited. If the amount exceeds 90 parts by mass, which is the upper limit, low heat build-up may be reduced.

〔filler〕
The filler used in the rubber composition of the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 160 m ² / g and a DBP absorption of 90 to 180 ml from the viewpoint of further exerting the effects of the present invention. Carbon black having a nitrogen adsorption specific surface area of 90 to 160 m ² / g and a DBP absorption of 90 to 180 ml / 100 g is preferably used.
When the nitrogen adsorption specific surface area and the DBP absorption amount are less than the lower limit (70 m ² / g, 90 ml / 100 g), the fracture resistance may be lowered, and the upper limit (160 m ² / g, 180 ml / 100 g). ) Exceeds the above range, the particle size becomes too small, and the low heat build-up may be deteriorated. Carbon black having a nitrogen adsorption specific surface area (N ₂ SA) and a DBP absorption amount within the above range has a suitable particle diameter, and is well dispersed due to the affinity of the butadiene polymer. Can be sufficiently contributed to the improvement of low heat generation.
As the carbon black that can be used, any carbon black having a nitrogen adsorption specific surface area (N ₂ SA) and a DBP absorption amount within the above ranges may be used. , HAF, FF, FEF, GPF, SRF, and FT grades are listed, and HAF, FEF, and GPF grades are particularly preferable from the viewpoint of improving fracture resistance.
In this invention, you may mix | blend inorganic fillers, such as a silica, a talc, and aluminum hydroxide, in the range which does not impair the effect of this invention other than the carbon black of the said characteristic. In addition, these fillers may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  The carbon black is desirably contained in an amount of 35 to 70 parts by mass, preferably 35 to 50 parts by mass with respect to 100 parts by mass of the rubber component of the rubber composition of the present invention. If the amount is less than 35 parts by mass, which is the lower limit, the reinforcing effect may be insufficient, and thus the fracture resistance may be reduced. If the amount exceeds 70 parts by mass, which is the upper limit, the low heat build-up may be deteriorated. There is.

(Rubber composition)
The rubber composition of the present invention includes a rubber component containing the above butadiene polymer, carbon black as a filler, a vulcanizing agent, a vulcanization accelerator, an anti-aging agent, an oil that contributes to improving workability, and a viscosity. A compounding agent usually used in the rubber industry, such as a reducing agent, an adhesive resin that contributes to improvement of molding workability, and a thermosetting resin that contributes to an improvement in elastic modulus, is appropriately selected within a range that does not impair the purpose of the present invention. Can be blended. As these compounding agents, commercially available products can be suitably used. In addition, the said rubber composition can be manufactured by mix | blending the various compounding agent suitably selected as needed with the rubber component, kneading | mixing, heating, extrusion, etc.

[Pneumatic tire]
In the pneumatic tire of the present invention, the above rubber composition is disposed on the cap rubber portion of the above-described tread portion of the tire, for example, the cap rubber portion 10 in FIG.
In the pneumatic tire of the present invention, a high-performance pneumatic tire having both excellent low rolling resistance and fracture resistance can be easily obtained by disposing the rubber composition having the above characteristics on the cap rubber portion of the pneumatic tire. Can get to.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.
The physical properties of the butadiene polymers A to C used in Examples and the like were measured according to the following methods.

<< Microstructure [cis-1,4 bond content (%), 1,2-vinyl bond content (%)] >>
A Fourier transform infrared spectrophotometer (FT / IR-4100, manufactured by JASCO Corporation) was used, and measurement was performed by an infrared method (Morello method).

<< Ratio (Mw / Mn) of weight average molecular weight (Mw) and number average molecular weight (Mn) of butadiene-based polymer >>
Using gel permeation chromatography (trade name “HLC-8120GPC”, manufactured by Tosoh Corporation), a differential refractometer was used as a detector, and measurement was performed under the following conditions to calculate a standard polystyrene equivalent value.
Column; Trade name “GMHHXL” (manufactured by Tosoh Corporation) 2 Column temperature: 40 ° C.
Mobile phase: Tetrahydrofuran Flow rate: 1.0 ml / min
Sample concentration: 10mg / 20ml

[Production of Butadiene Polymer A: Production Example 1]
In a nitrogen atmosphere, a 5 L autoclave was charged with 2.4 kg of cyclohexane and 300 g of 1,3-butadiene under a nitrogen atmosphere. To the autoclave, as a catalyst component, a cyclohexane solution of neodymium versatate (0.09 mmol), a toluene solution of methylaluminoxane (MAO, 3.6 mmol), diisobutylaluminum hydride (DIBAH, 5.5 mmol) and diethylaluminum chloride (0. (18 mmol) in toluene and 1,3-butadiene (4.5 mmol) were aged at 40 ° C. for 30 minutes, and a pre-prepared catalyst composition was charged, followed by polymerization at 60 ° C. for 60 minutes. The reaction conversion of 1,3-butadiene was almost 100%.

  Further, the polymer solution was kept at a temperature of 60 ° C., and a toluene solution of 4.16 mmol of 2-cyanopyridine was added and reacted for 15 minutes (primary modification reaction). Thereafter, 200 g of this polymer solution was extracted into a methanol solution containing 1.3 g of 2,4-di-tert-butyl-p-cresol, and after the polymerization was stopped, the solvent was removed by steam stripping, and a roll at 110 ° C. By drying, a polymer A (modified butadiene-based polymer) was obtained. The obtained polymer A had a cis-1,4 bond content of 96.1%, a 1,2-vinyl bond content of 0.62%, and Mw / Mn = 2.2.

[Production of butadiene polymer B: Production Example 2]
To about 900 mL of a pressure-resistant glass container that has been dried and purged with nitrogen, 283 g of cyclohexane, 50 g of 1,3-butadiene, 0.0057 mmol of 2,2-ditetrahydrofurylpropane, and 0.513 mmol of hexamethyleneimine are added, and n-butyllithium ( After adding 0.57 mmol of (BuLi), polymerization was carried out in a hot water bath at 50 ° C. equipped with a stirrer for 4.5 hours. The polymerization conversion rate at this time was almost 100%. Next, 0.100 mmol of tin tetrachloride as a modifying agent (coupling agent) was quickly added to the polymerization reaction system, and the mixture was further stirred at 50 ° C. for 30 minutes to carry out a modification reaction. Thereafter, 0.5 mL of an isopropanol solution (BHT concentration: 5% by mass) of 2,6-di-t-butyl-p-cresol (BHT) was added to the polymerization reaction system to stop the reaction, followed by drying according to a conventional method. Thus, modified polybutadiene rubber (HMI-BR) was obtained. The obtained HMI-BR had a vinyl bond content of the butadiene moiety of 14%, a glass transition temperature (Tg) of -95 ° C, and a coupling efficiency of 65%.
In addition, about the obtained HMI-BR, the peak of the highest molecular weight side with respect to the whole area of the molecular weight distribution curve by gel permeation chromatography (GPC) is calculated from the integration ratio of the ¹ H-NMR spectrum and the vinyl bond amount of the butadiene part. The coupling rate was determined from the area ratio, and the glass transition temperature was determined from the inflection point of the DSC curve.
[Butadiene polymer C]
As an unmodified butadiene-based polymer, polymer C (JSR BR01, cis-1,4 bond content: 96.1%, 1,2-vinyl bond content: 0.62%, Mw / Mn = 2.2) Was used.

[Comparative Examples 1-5, Examples 1-3]
Using the butadiene polymers A to C obtained above, a rubber composition having a formulation shown in Table 1 below was prepared, and this was used for the cap rubber portion 10 of the tire 1 as shown in FIG.
Using the obtained test tire (size: 11R22.5), rolling resistance and fracture resistance were measured according to the following methods.
These results are shown in Table 1 below. In addition, the unit of the numerical value in Table 1 represents a mass part.

<< Rolling resistance: RR >>
Using a rotating drum having a steel smooth surface with an outer diameter of 1707.6 mm and a width of 350 mm, under the action of a load of 4500 N (460 kg), measured using the coasting method when rotated at a speed of 80 km / h, evaluated. The measured values were indexed with the value of Comparative Example 5 being 100. Smaller values indicate better rolling resistance (lower fuel consumption).

<< Destruction resistance >>
Using the prepared tire, in a tensile test based on JIS K6251, the breaking strength (Tb) at 100 ° C. was measured, and the value of Comparative Example 5 was indexed to 100. It shows that it is excellent in fracture resistance, so that a numerical value is large.

  According to the results of Table 1 above, the butadiene-based polymer B and the unmodified butadiene-based polymer C, which have physical properties outside the scope of the present invention, were modified with a specific modifier than Comparative Examples 1 to 5. It can be seen that Examples 1 to 3 using the butadiene-based polymer A within the range of the present invention exhibit good rolling resistance and excellent fracture resistance.

1: Pneumatic tire 2: Bead core 3: Bead part 4: Side wall part 5: Tread part 6: Carcass layer 7: Belt layer 8: Tread rubber layer 9: Base rubber part 10: Cap rubber part 11: Wing rubber part 12 : End rubber part

Claims (9)

10 to 60 parts by mass of a butadiene-based polymer having a conjugated modifying group in 100 parts by mass of the rubber component, a nitrogen adsorption specific surface area (N ₂ SA) of 70 to 160 m ² / g, and a DBP absorption of 90 to 180 ml / A rubber composition comprising 100 g of carbon black,
The butadiene polymer is modified with a modifier which is a heterocyclic nitrile compound represented by the following formula (I) or the following formula (II), and has a cis content of 40% or more. Rubber composition.
θ-C≡N (I)
θ-R-C≡N (II)
(In the above formulas (I) and (II), θ represents a heterocyclic group, and R represents a divalent hydrocarbon group.)   The rubber composition according to claim 1, wherein the rubber component contains 40 to 90 parts by mass of natural rubber in 100 parts by mass of the rubber component.   The rubber composition according to claim 1, wherein the carbon black is contained in an amount of 35 to 70 parts by mass with respect to 100 parts by mass of the rubber component.   In said formula (I) and (II), (theta) is a heterocyclic group containing a nitrogen atom, The rubber composition as described in any one of Claims 1-3 characterized by the above-mentioned.   In the formulas (I) and (II), θ is a heterocyclic group containing an oxygen atom, a heterocyclic group containing a sulfur atom, a heterocyclic group containing two or more heteroatoms, and a heterocyclic ring containing one or more cyano groups. The rubber composition according to any one of claims 1 to 4, wherein the rubber composition is at least one heterocyclic group selected from the group consisting of groups.   In the formulas (I) and (II), θ is a heteroaromatic ring group or a heterononaromatic ring group, or a monocyclic, bicyclic, tricyclic or polycyclic heterocyclic group. The rubber composition according to any one of claims 1 to 5.   The rubber composition according to any one of claims 1 to 6, wherein a cis content of the butadiene-based polymer is 90% or more.   The ratio (Mw / Mn) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the butadiene-based polymer is 1.3 to 3.5. The rubber composition as described in any one of the above.   A pneumatic tire using the rubber composition according to any one of claims 1 to 8 for a cap rubber part.

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