JP2007217518A - Rubber composition for tire tread and pneumatic tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a tire tread improving abrasion resistance and crack growth resistance without deteriorating both wet properties (frictional resistance on wet road surfaces) and low heat-buildup properties and to provide a pneumatic tire using the rubber composition in the tread. <P>SOLUTION: The rubber composition for the tire tread comprises 20-100 pts.mass of a reinforcing filler based on 100 pts.mass of a rubber component composed of 20-80 pts.mass of a solution-polymerized styrene-butadiene copolymer rubber having a micro-structure satisfying the following numerical formulas (1) to (4): (1) Vi≥ST, (2) Vi+2ST≥80, (3) Vi≤70, and (4) ST≤50 äwherein, ST represents the bonded styrene content (mass%) in the copolymer rubber; and Vi represents the 1,2 bond content (%) in the bonded butadiene} and 20-80 pts.mass of a polybutadiene rubber having a micro-structure represented by the following numerical formula (5): (5) Vi≤0.25×(cis-97) äwherein, Vi represents the 1,2 bond content (%) in the bonded butadiene; and cis represents the cis-1,4 bond content (%)} and ≥92% cis-1,4 bond content. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rubber composition for a tire tread having reduced rolling resistance, improved wear resistance and crack growth resistance, and a pneumatic tire using the same.

In recent years, demands for reducing the fuel consumption of automobiles are becoming more severe in connection with the movement of global carbon dioxide emission regulations due to the social demand for energy saving and the increasing interest in environmental problems. In order to meet such demands, there has been a demand for reduction in rolling resistance and improvement in durability of tires.
However, the reduction in rolling resistance of the tire (hereinafter referred to as improvement in low heat generation) and the friction resistance on the wet road surface (hereinafter referred to as wet performance) are in a trade-off relationship, and the wet resistance is reduced without lowering the wet performance. It was difficult to improve the exothermic property.
In addition, in order to improve durability, it is necessary to improve wear resistance and crack growth resistance. However, if wear resistance and crack growth resistance are improved, either wet or low heat build-up will decrease. There was also a problem of doing.
In order to solve the above-described problem, Patent Document 1 discloses a microstructure such as a specific cis-1,4 bond content and 1,2 bond content, and a ratio between a weight average molecular weight (Mw) and a number average molecular weight (Mn). It is proposed to use a polybutadiene rubber having (Mw / Mn) for the tire.
However, since a blend of a polybutadiene rubber and a specific styrene-butadiene copolymer rubber is not taken into consideration, it is difficult to improve the wear resistance and crack growth resistance without reducing the wet property.
Thus, there is a demand for a rubber composition for a tire tread that improves wear resistance and crack growth resistance without reducing both wettability and low heat build-up.

JP 2005-15590 A

  Under such circumstances, the present invention provides a rubber composition for tire tread that can improve wear resistance and crack growth resistance without reducing both wettability and low heat build-up, and tread for the rubber composition. It aims at providing the pneumatic tire used for.

As a result of intensive studies to achieve the above object, the present inventors have made a blend of a polybutadiene rubber having a specific microstructure and a specific solution-polymerized styrene-butadiene copolymer rubber as a rubber component. The inventors have found that the object of the present invention can be achieved. The present invention has been completed based on such findings.
That is, the gist of the present invention is as follows.
1. 20 to 80 parts by mass of a solution-polymerized styrene-butadiene copolymer rubber having a microstructure that satisfies the following mathematical formulas (1) to (4);
(1) Vi ≧ ST
(2) Vi + 2ST ≧ 80
(3) Vi ≦ 70
(4) ST ≦ 50
(In the formula, ST represents the amount of bound styrene (% by mass) in the copolymer rubber, and Vi represents the content of 1,2 bonds in the bound butadiene (%)).
Reinforcing filler with respect to 100 parts by mass of a rubber component having 20 to 80 parts by mass of polybutadiene rubber having a microstructure represented by the following formula (5) and having a cis-1,4 bond content of 92% or more A rubber composition for a tire tread containing 20 to 100 parts by mass.
(5) Vi ≦ 0.25 × (cis-97)
(In the formula, Vi represents 1,2 bond content (%), and cis represents cis-1,4 bond content (%)).
2. 2. The polybutadiene rubber obtained by polymerization in an organic solvent using a catalyst containing a lanthanum series rare earth element-containing compound, and the polybutadiene rubber having a microstructure satisfying the following formula (6): Rubber composition for tire treads.
(6) cis ≧ 98.00 (%)
(Wherein cis represents cis-1,4 bond content (%))
3. Furthermore, the rubber composition for tire treads of said 2 whose polybutadiene rubber satisfies the following Numerical formula (7).
(7) Vi ≦ 0.35
(In the formula, Vi represents 1,2 bond content (%))
4). The rubber composition for a tire tread according to any one of the above 1 to 3, wherein the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polybutadiene rubber is 1.6 to 3.5. .
5). 5. The rubber composition for tire treads according to any one of 1 to 4 above, wherein the number average molecular weight (Mn) of the polybutadiene rubber is 100,000 to 500,000.
6). 6. The rubber composition for a tire tread according to any one of 1 to 5 above, wherein the lanthanum series rare earth element-containing compound is a salt soluble in a neodymium hydrocarbon solvent.
7). 7. The tire tread rubber composition according to any one of 1 to 6 above, wherein the reinforcing filler is carbon black and / or silica.
8). A pneumatic tire obtained by disposing the rubber composition according to any one of 1 to 7 on a tread.

  According to the present invention, a tire tread rubber composition that can improve wear resistance and crack growth resistance without reducing both wettability and low heat build-up, and air formed by using the rubber composition in a tread. An inset tire can be provided.

The solution-polymerized styrene-butadiene copolymer rubber used in the rubber composition for a tire tread of the present invention satisfies the above mathematical expressions (1) to (4) at the same time. When the bound styrene content (% by mass) and the 1,2 bond content (%) in the bound butadiene are within this range, the wear resistance and wettability can be improved at the same time.
Examples of the solution-polymerized styrene-butadiene copolymer rubber that simultaneously satisfies the above formulas (1) to (4) include trade name SL552 (ST = 24, Vi = 37), manufactured by JSR Corporation), trade name SL574. (ST = 15, Vi = 56, manufactured by JSR Corporation).

Moreover, the polybutadiene rubber used for the rubber composition for tire treads of this invention satisfies the said Numerical formula (5). If the 1,2 bond content (%) is in this range, the crack growth resistance and the low heat build-up can be improved at the same time.
The polybutadiene rubber preferably further satisfies the above formula (6). Thereby, high elongation crystallinity can be obtained and crack growth resistance can be expressed.
In addition to the above mathematical formulas (5) to (6), it is more preferable to satisfy the above mathematical formula (7) from the viewpoint of improving crack growth resistance.

  The above-mentioned polybutadiene rubber used in the tire tread rubber composition of the present invention is preferably obtained by polymerizing 1,3-butadiene in an organic solvent using a catalyst containing a lanthanum series rare earth element-containing compound. is there.

Next, a catalyst system containing a lanthanum series rare earth element-containing compound suitable for the present invention will be described.
As a catalyst system,
(A) component: a rare earth element-containing compound having an atomic number of 57 to 71 in the periodic table, or a reaction product of these compounds with a Lewis base,
(B) component: The following general formula (I):
AlR ¹ R ² R ³ (I)
(In the formula, R ¹ and R ² are the same or different and are a hydrocarbon group having 1 to 10 carbon atoms or a hydrogen atom, and R ³ is a hydrocarbon group having 1 to 10 carbon atoms, provided that R ³ represents the above R ¹ or an organic aluminum compound represented by R ² and may be the same or different), and component (C): a Lewis acid, at least an organic compound containing a complex compound with the metal halide and Lewis base, and an active halogen It is preferable to polymerize the conjugated diene compound with a single catalyst system.

  In the present invention, it is preferable to add an organoaluminum oxy compound, so-called aluminoxane, as the component (D) in addition to the components (A) to (C) to the catalyst system used for the polymerization of the polybutadiene rubber. . Here, it is more preferable that the catalyst system is preliminarily prepared in the presence of the component (A), the component (B), the component (C), the component (D) and the conjugated diene monomer.

  In the present invention, the component (A) of the catalyst system used for the polymerization of the polybutadiene rubber 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 with a Lewis base. 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.

As the rare earth element carboxylate, the following general formula (II):
(R ⁴ -CO ₂ ) ₃ M (II)
(Wherein, R ⁴ is a hydrocarbon group having 1 to 20 carbon atoms, and M is a rare earth element having an atomic number of 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. Specific examples of the carboxylate include 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 the following general formula (III):
(R ⁵ O) ₃ M (III)
(Wherein, R ⁵ is a hydrocarbon group having 1 to 20 carbon atoms, and M is a rare earth element having an atomic number of 57 to 71 in the periodic table). Examples of the alkoxy group represented by R ⁵ O include 2-ethyl-hexyloxy group, oleyloxy group, stearyloxy group, phenoxy group, benzyloxy group and the like. Among these, 2-ethyl-hexyloxy group and benzyloxy 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, and ethylacetylacetone complex. 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 branching 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.

  In the present invention, the organoaluminum compound represented by the above general formula (I) which is the component (B) of the catalyst system used for the polymerization of polybutadiene rubber includes trimethylaluminum, triethylaluminum, tri-n-propylaluminum, triisopropyl. Aluminum, tri-n-butylaluminum, triisobutylaluminum, tri-t-butylaluminum, tripentylaluminum, trihexylaluminum, tricyclohexylaluminum, trioctylaluminum; diethylaluminum hydride, di-n-propylaluminum hydride, Di-n-butylaluminum hydride, diisobutylaluminum hydride, dihexylaluminum hydride, diisohexylaluminum hydride, dioctylaluminum hydride, hydrogen Diisooctyl aluminum, ethyl aluminum dihydride, n- propyl aluminum 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.

  In the present invention, the component (C) of the catalyst system used for the polymerization of the polybutadiene rubber is at least one selected from the group consisting of Lewis acids, complex compounds of metal halides and Lewis bases, and organic compounds containing active halogens. 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.

  The metal halide constituting the complex compound of the above metal halide and Lewis base includes 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 usually reacted at a ratio of 0.01 to 30 mol, preferably 0.5 to 10 mol, per 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.

  Examples of the aluminoxane as component (D) 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, more preferably 0.0001 to 0.5 mmol, per 100 g of the conjugated diene compound. When the amount of component (A) used is within the above range, excellent polymerization activity can be obtained, and the need for a deashing step is eliminated.
Moreover, the ratio of (A) component and (B) component is molar ratio, and (A) component: (B) component is usually 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, as a molar ratio, usually 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 and (A) component in (D) component is molar ratio, and is 1: 1-700: 1 normally, Preferably it is 3: 1-500: 1. By making the amount of these catalysts within the range of the component ratio, it is preferable because it acts as a highly active catalyst and there is no need for 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 above components (A), (B), and (C), a small amount of a conjugated diene compound such as 1,3-butadiene, if necessary, specifically, component (A) You may use it in the ratio of 0-1000 mol per 1 mol of compounds. A conjugated diene compound such as 1,3-butadiene as a catalyst component is not essential, but when used together, there is an advantage that the catalytic activity is further improved.

In the production of the catalyst, for example, the components (A) to (C) are dissolved in a solvent, and a conjugated diene compound such as 1,3-butadiene is reacted 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 about 0 to 100 ° C, preferably 20 to 80 ° C. When the temperature is less than 0 ° C., the aging is not sufficiently performed, and when the temperature exceeds 100 ° C., the catalytic activity may be reduced or the molecular weight distribution may be broadened.
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.

  In the production of the polybutadiene rubber, an inert organic solvent is used as a polymerization solvent when solution polymerization of 1,3-butadiene is performed in an organic solvent using a catalyst system containing the lanthanum series rare earth element-containing compound. Use. 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, C5-C6 aliphatic hydrocarbon and alicyclic hydrocarbon are particularly preferable. These solvents may be used alone or in combination of two or more.

  The monomer concentration in the solvent of 1,3-butadiene used for this polymerization is preferably 5 to 50% by mass, more preferably 10 to 30% by mass.

  Further, it is important that the polybutadiene rubber is carried out at a polymerization temperature of 25 ° C. or less, and it is preferably carried out at 10 to −78 ° C. When the polymerization temperature exceeds 25 ° C., it is difficult to sufficiently control the polymerization reaction, and the cis-1,4 bond content of the produced butadiene polymer may decrease, and the 1,2 bond content may increase. is there. 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 may not be performed.

  The production of the polybutadiene rubber may be carried out either batchwise or continuously. In addition, in the production of the polybutadiene rubber, in order not to deactivate the rare earth element compound-based catalyst and the polymer, mixing of a deactivating compound such as oxygen, water and carbon dioxide gas is minimized in the polymerization reaction system. Such consideration is necessary.

In the present invention, it is preferable to modify the active terminal of the polybutadiene thus obtained with a modifier. In the modification, a modifier is added to the active terminal, preferably in a stoichiometric amount or in excess, and reacted with the active terminal bonded to the polybutadiene. Thereby, a modified polybutadiene rubber is obtained.
Examples of the modifying agent include the following general formula (IV):

In the general formula (I), X ^{1 to} X ⁵ are a hydrogen atom, a halogen atom, a carbonyl group, a thiocarbonyl group, an isocyanate group, a thioisocyanate group, an epoxy group, a thioepoxy group. , A monovalent functional group containing at least one selected from a halogenated silyl group, a hydrocarbyloxysilyl group, and a sulfonyloxy group, and not containing an active proton or onium salt. X ^{1 to} X ⁵ may be the same or different, but at least one of them is not a hydrogen atom.
R ^{6 to} R ¹⁰ each independently represent a single bond or a divalent hydrocarbon group having 1 to 18 carbon atoms. Examples of the divalent hydrocarbon group include an alkylene group having 1 to 18 carbon atoms, an alkenylene group having 2 to 18 carbon atoms, an arylene group having 6 to 18 carbon atoms, and an aralkylene group having 7 to 18 carbon atoms. Among these, an alkylene group having 1 to 18 carbon atoms, particularly an alkylene group having 1 to 10 carbon atoms is preferable. The alkylene group may be linear, branched or cyclic, but is particularly preferably linear. Examples of the linear alkylene group include a methylene group, an ethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, an octamethylene group, and a decamethylene group.
Or it may be bonded multiple aziridine ring via any of X ¹ to X ⁵ and R ⁶ to R ^10.
The modifier is preferably one that does not simultaneously satisfy X ¹ = hydrogen atom and R ¹ = single bond in the general formula (I).

  Examples of the modifying agent represented by the general formula (IV) include 1-acetylaziridine, 1-propionylaziridine, 1-butylaziridine, 1-isobutylaziridine, 1-valerylaziridine, 1-isovalerylaziridine, 1 -Pivaloylaziridine, 1-acetyl-2-methylaziridine, 2-methyl-1-propionylaziridine, 1-butyl 2-methylaziridine, 2-methyl-1-isobutylaziridine, 2-methyl-1-valerylaziridine 1-isovaleryl-2-methylaziridine, 2-methyl-1-pivaloylaziridine, ethyl 3- (1-aziridinyl) propionate, propyl 3- (1-aziridinyl) propionate, butyl 3- (1-aziridinyl) propionate , Ethylene glycol bis [3- (1-azimuth Dinyl) propionate], trimethylolpropane tris [3- (1-aziridinyl) propionate], ethyl 3- (2-methyl-1-aziridinyl) propionate, propyl 3- (2-methyl-1-aziridinyl) propionate, butyl 3 -(2-methyl-1-aziridinyl) propionate, ethylene glycol bis [3- (2-methyl-1-aziridinyl) propionate], trimethylolpropane tris [3- (2-methyl-1-aziridinyl) propionate], neo Pentyl glycol bis [3- (1-aziridinyl) propionate], neopentyl glycol bis [3- (2-methyl-1-aziridinyl) propionate], di (1-aziridinylcarbonyl) methane, 1,2-di ( 1-aziridinylcar Nyl) ethane, 1,3-di (1-aziridinylcarbonyl) propane, 1,4-di (1-aziridinylcarbonyl) butane, 1,5-di (1-aziridinylcarbonyl) pentane, di (2-methyl-1-aziridinylcarbonyl) methane, 1,2-di (2-methyl-1-aziridinylcarbonyl) ethane, 1,3-di (2-methyl-1-aziridinylcarbonyl) Examples include, but are not limited to, propane and 1,4-di (2-methyl-1-aziridinylcarbonyl) butane.

Here, although the usage-amount of the modifier with respect to (A) component of the above-mentioned polymerization catalyst system changes with terminal modification | denaturation rates of the obtained modified polymer polymer, it is 0.1-100 normally by a molar ratio, Preferably it is 1 By making the use amount of the modifier within the above range from 0 to 50, a polymer excellent in low heat buildup and abrasion resistance in which the modification reaction proceeds and no toluene insoluble matter (gel) is generated is obtained. Can do.
This denaturation reaction is usually in the range of 0.5 minutes to 2 hours, preferably 3 minutes to 1 hour, with stirring at room temperature to 100 ° C. By polymerizing polybutadiene with a catalyst and polymerization conditions for obtaining a high terminal living ratio, and subsequently conducting a terminal modification reaction, a modified polybutadiene rubber having a high terminal modification ratio can be obtained.

  The terminal modification rate of the modified polybutadiene rubber used in the rubber composition of the present invention is the ratio of the number of moles of the introduced modifying group in the number of moles of the polymer, and is usually 20% or more, preferably 40% or more, More preferably, it is 60% or more, still more preferably 80% or more, and particularly preferably 95% or more. The cis-1,4 bond content of the modified polybutadiene rubber is 92% or more, preferably 94% or more, more preferably 97% or more, and still more preferably 98% or more. As described above, by using a modified polybutadiene rubber having a high cis-1,4 bond content and a high terminal modification rate, a rubber composition part and a tire excellent in low heat buildup and fracture resistance can be obtained.

Here, the terminal modification rate will be described in detail with reference to FIG.
The vertical axis indicates the value of UV / RI obtained by gel permeation chromatography (GPC) measurement. UV indicates a peak area value obtained from the UV absorbance caused by the modifier that has reacted with the polymer, and RI indicates a peak area value obtained from the differential refractive index (RI) of the polymer itself.
The horizontal axis indicates a value of (1 / Mn) × 10 ³ , and Mn is the absolute molecular weight (number average molecular weight). In FIG. 1, LowCisBR is polymerized by anionic polymerization using a Li-based catalyst and modified with a modifier 4, 4′-bis (diethylaminobenzophenone) (hereinafter abbreviated as DEAB), and has three different number average molecular weights Mn. The UV / RI values of are plotted and can be approximated as a straight line. In the case of anionic polymerization, since it is 100% modified, it is represented by A as shown in the following formula, assuming that UV / RI of LowCisBR is 100%.
UV (Li-Br) / RI (Li-Br) = A
On the other hand, using the catalyst containing the lanthanum series rare earth element (Nd) -containing compound of the present invention, which is coordination polymerization, for HighCisBR modified with DEAB, five types of UV / RI values with different number average molecular weights Mn are plotted. As above, it can be approximated as a straight line. In the case of coordination polymerization, there is a portion that is not living during polymerization, and it is difficult to modify 100%. When the UV / RI of HighCisBR is represented by B as shown in the following formula,
UV (Nd-Br) / RI (Nd-Br) = B
The terminal modification rate in the present invention is defined as follows.
Terminal modification rate = B / A × 100 (%)
The terminal modification rate in the present invention is calculated from the A value and B value obtained using LowCisBR having the same absolute molecular weight (number average molecular weight) as HighCisBR.
Note that the UV / RI value obtained by subtracting the value of the unmodified line shown in FIG. 1 is used as the true value, assuming that the terminal modification rate of the unmodified polymer reacted with isopropanol is 0%.
The A and B values are shown in FIG.
The three straight lines shown in FIG. 1 can be used as a calibration curve. For example, if the absolute molecular weight Mn (number average) of HighCisBR is known, the terminal modification rate in the present invention can be calculated.
As can be seen from FIG. 1, as the absolute molecular weight Mn (number average) increases, the terminal modification rate decreases and it becomes difficult to modify with a modifier.
Moreover, it is necessary to create a calibration curve each time the denaturant changes.

In the present invention, after the above-described modification reaction, a known anti-aging agent or alcohol or the like can be added for the purpose of stopping the polymerization reaction, if desired.
After the modification treatment in this way, a conventionally known post-treatment such as solvent removal can be performed to obtain the desired modified polybutadiene rubber.

The cis-1,4 bond content and 1,2 bond content defining the polybutadiene rubber and solution polymerized styrene-butadiene copolymer rubber of the present invention are measured by Fourier transform infrared spectroscopy (FT-IR). Specifically, it is measured by the following method.
Using the carbon disulfide of the same cell as a blank, the FT-IR transmittance spectrum of a carbon disulfide solution of a butadiene polymer prepared to a concentration of 5 mg / mL was measured, and the peak value near 1130 cm ⁻¹ of the spectrum was measured. a, when the valley peak value b in the vicinity of 967 cm ^-1, a valley peak value c near 911 cm ^-1, a valley peak value around 736cm ^-1 was d, the following matrix equation (8):

から導かれるｅ、ｆ、ｇの値を用い、下記式（９)、式（１０）、式（１１)：
(シス−１，４結合含量）＝ｅ／(ｅ＋ｆ＋ｇ)×１００(％) ・・・９)
(トランス−１，４結合含量）＝ｆ／(ｅ＋ｆ＋ｇ）×１００(％)・（１０）
(１，２結合含有量）＝ｇ／(ｅ＋ｆ＋ｇ）×１００ (％）・・・ (１１)
に従ってシス−１，４結合含量、トランス−１，４結合含量及び１，２結合含有量を求める。なお、上記スペクトルの１１３０ｃｍ^-1付近の山ピーク値ａはベースラインを、９６７ｃｍ^-1付近の谷ピーク値ｂはトランス−１，４結合を、９１１ｃｍ^-1付近の谷ピーク値ｃはビニル結合を、７３６ｃｍ^-1付近の谷ピーク値ｄはシス−１，４結合を示す。

Using the values of e, f, and g derived from the following equations (9), (10), and (11):
(Cis-1,4 bond content) = e / (e + f + g) × 100 (%) (9)
(Trans-1,4 bond content) = f / (e + f + g) × 100 (%) · (10)
(1,2 bond content) = g / (e + f + g) × 100 (%) (11)
The cis-1,4 bond content, trans-1,4 bond content and 1,2 bond content are determined according to In the above spectrum, the peak value a near 1130 cm ⁻¹ is the baseline, the valley peak value b near 967 cm ⁻¹ is the trans-1,4 bond, and the valley peak value c near 911 cm ⁻¹ is the vinyl bond. , A valley peak value d in the vicinity of 736 cm ⁻¹ indicates a cis-1,4 bond.

As a method for analyzing the microstructure of 1,3-butadiene monomer units in polybutadiene rubber, conventionally, ¹ H-NMR and ¹³ C-NMR are used to determine the cis-1,4 bond content, trans-1,4 bond content, and A method for obtaining the 1,2 bond content is known, but the measurement result by ¹³ C-NMR underestimates the 1,2 bond content, resulting in a value smaller than the actual value. In contrast, the polybutadiene rubber of the present invention is characterized by having a very low 1,2 bond content in addition to a high cis-1,4 bond content. Measured by high FT-IR method.

Moreover, the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polybutadiene rubber in the present invention, that is, the molecular weight distribution (Mw / Mn) is 1.6 to 3.5. Preferably, it is 1.6 to 2.7. Here, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are values in terms of polystyrene measured by gel permeation chromatography (GPC). is there.
Even if the modified butadiene polymer is blended with the rubber composition by setting the molecular weight distribution (Mw / Mn) of the polybutadiene rubber within the above range, the workability of the rubber composition is not lowered and kneading can be performed. It is easy and the physical properties of the rubber composition can be sufficiently improved.

  The polybutadiene rubber in the present invention preferably has a number average molecular weight (Mn) of 100,000 to 500,000, and more preferably 150,000 to 300,000. By making the number average molecular weight of the polybutadiene rubber within the above range, the elastic modulus of the vulcanizate of the rubber composition for tire tread of the present invention is reduced, the increase in hysteresis loss is suppressed, and excellent wear resistance is obtained. Excellent kneading workability can be obtained.

The rubber composition for tire treads of the present invention contains 100 parts by mass of a rubber component composed of 20-80 parts by mass of the above-mentioned solution-polymerized styrene-butadiene copolymer rubber and 20-80 parts by mass of the above-mentioned polybutadiene rubber. When the polybutadiene rubber is 20 parts by mass or more, good interaction with the filler is exhibited, and crack growth resistance is improved. Moreover, if the solution-polymerized styrene-butadiene copolymer rubber is 20 parts by mass or more, excellent wear resistance and wettability can be enjoyed. More preferably, it contains 100 parts by mass of a rubber component consisting of 30 to 70 parts by mass of the solution-polymerized styrene-butadiene copolymer rubber and 30 to 70 parts by mass of the polybutadiene rubber.
The solution-polymerized styrene-butadiene copolymer rubber and the polybutadiene rubber may be used singly or in combination of two or more.

The rubber composition for a tire tread of the present invention needs to contain 20 to 100 parts by mass of a reinforcing filler. This is because if the amount is less than 20 parts by mass, the effect of improving the reinforcing properties and other vulcanized physical properties is not sufficiently exhibited, and if it exceeds 100 parts by mass, the workability is reduced.
The reinforcing filler preferably contains carbon black and / or silica. There is no restriction | limiting in particular as carbon black, Arbitrary things can be selected and used from what is conventionally used as a filler for reinforcement of rubber | gum. Examples of the carbon black include HAF, N339, IISAF, ISAF, and SAF. Preferably nitrogen adsorption specific surface area (N ₂ SA) ^{70~160m 2 / g (JIS K 6217-2} : 2001 compliant) with and dibutyl phthalate (DBP) absorption of 80cm ³ / 100g (JIS K 6217-4 : 2001). By using this carbon black, the effect of improving various physical properties is increased, but in particular, N339, IISAF, ISAF, and SAF, which are excellent in wear resistance, are preferable.

Examples of the silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), and the like. Among these, wet silica that exhibits the most remarkable effect of achieving both crack growth resistance and wettability is preferable. Then, the nitrogen adsorption specific surface area of the silica (N ₂ SA, BET method) is preferably 100 to 400 m ² / g. This is because the wear resistance is further improved if it is 100 m ² / g or more, and the processability of the rubber composition becomes more suitable if it is 400 m ² / g or less. Suitable wet silica includes AQ, VN3, LP, NA, etc. manufactured by Tosoh Silica Co., Ltd., Ultrazil VN3 (N ₂ SA: 210 m ₂ / g) manufactured by Degussa, and the like.
In the present invention, when carbon black and silica are used in combination, the use ratio is mass ratio from the viewpoint of performance, and preferably 95: 5 to 5:95.

In addition, inorganic fillers other than silica can be replaced with part of the reinforcing filler. Examples of inorganic fillers other than silica include γ-alumina, alumina (Al ₂ O ₃ ) such as α-alumina, alumina monohydrate (Al ₂ O ₃ .H ₂ O) such as boehmite and diaspore, gibbsite, Aluminum hydroxide such as bayerite [Al (OH) ₃ ], aluminum carbonate [Al ₂ (CO ₃ ) ₂ ], magnesium hydroxide [Mg (OH) ₂ ], magnesium oxide (MgO), magnesium carbonate (MgCO ₃ ) Talc (3MgO · 4SiO ₂ · H ₂ O), attapulgite (5MgO · 8SiO ₂ · 9H ₂ O), titanium white (TiO ₂ ), titanium black (TiO _2n-1 ), calcium oxide (CaO), calcium hydroxide [Ca (OH) _2], magnesium aluminum oxide _{(MgO · Al 2 O 3)} , clay _{(Al 2 O 3 · 2SiO 2} ), kaolin (Al ₂ O ₃ · SiO ₂ · 2H ₂ O), pyrophyllite _{(Al 2 O 3 · 4SiO 2} · H 2 O), bentonite _{(Al 2 O 3 · 4SiO 2} · 2H 2 O), aluminum silicate (Al ₂ SiO _5, Al ₄ / 3SiO ₄ / 5H ₂ O etc.), magnesium silicate (Mg ₂ SiO ₄ , MgSiO ₃ etc.), calcium silicate (Ca ₂ · SiO ₄ etc.), aluminum calcium silicate (Al ₂ O ₃ · CaO · 2SiO etc.) ₂ ), magnesium calcium silicate (CaMgSiO ₄ ), calcium carbonate (CaCO ₃ ), zirconium oxide (ZrO ₂ ), zirconium hydroxide [ZrO (OH) ₂ .nH ₂ O], zirconium carbonate [Zr (CO ₃ ) ₂ ], crystalline aluminosilicates containing hydrogen, alkali metals or alkaline earth metals that correct the charge, such as various zeolites, can be used. Of the inorganic fillers other than silica, aluminum hydroxide is preferable.

  In the rubber composition of the present invention, when silica is used as the reinforcing filler, a silane coupling agent can be blended for the purpose of further improving the reinforcing property. Examples of the silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, 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-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N-dimethylthioca Bamoylchitrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxy Silylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis (3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N, N-dimethylthiocarbamoyltetra Sulfide, dimethoxymethylsilylpropyl benzothiazole tetrasulfide, etc. are mentioned. Among these, bis 3-triethoxysilylpropyl) tetrasulfide and 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide are preferable. These silane coupling agents may be used singly or in combination of two or more.

In the rubber composition of the present invention, the preferable blending amount of the silane coupling agent varies depending on the type of the silane coupling agent and the like, but is preferably selected in the range of 1 to 20% by mass with respect to silica. When this amount is in the above range, the effect as a coupling agent is sufficiently exhibited and the rubber component is hardly gelled. From the viewpoint of the effect as a coupling agent and the prevention of gelation, the preferred amount of the silane coupling agent is in the range of 5 to 15% by mass.
In the rubber composition of the present invention, various chemicals usually used in the rubber industry, for example, vulcanizing agents, vulcanization accelerators, process oils, anti-aging agents, as long as the object of the present invention is not impaired. A scorch inhibitor, zinc white, stearic acid and the like can be contained.

  The rubber composition of the present invention is usually sulfur crosslinkable, and sulfur or the like is preferably used as a vulcanizing agent. The amount used is preferably 0.1 to 10.0 parts by weight, more preferably 1.0 to 5.0 parts by weight, as the sulfur content, per 100 parts by weight of the rubber component. When the amount is 0.1 parts by mass or more, the vulcanized rubber has good fracture strength, wear resistance, and low heat build-up, and when it is 10.0 parts by mass or less, the rubber elasticity is also good.

The vulcanization accelerator that can be used in the present invention is not particularly limited, and examples thereof include M (2-mercaptobenzothiazole), DM (dibenzothiazyl disulfide), and CZ (N-cyclohexyl-2-benzothiazyl). Sulfenamide) and other guanidine vulcanization accelerators such as DPG (diphenylguanidine) can be used, and the amount used is 0.1-5. 0 mass part is preferable, More preferably, it is 0.2-3.0 mass part.
Examples of the process oil that can be used in the rubber composition of the present invention include paraffinic, naphthenic and aromatic oils. From the viewpoint of emphasizing low heat generation properties and low temperature characteristics, naphthenic or paraffinic compounds are preferred. The amount used is preferably 0 to 100 parts by mass with respect to 100 parts by mass of the rubber component, and if it is 100 parts by mass or less, the tensile strength and low heat build-up of the vulcanized rubber can be suppressed.
Furthermore, examples of the anti-aging agent that can be used in the rubber composition of the present invention include 3C (N-isopropyl-N′-phenyl-p-phenylenediamine, 6C [N- (1,3-dimethylbutyl) -N′- Phenyl-p-phenylenediamine], AW (6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline), high-temperature condensate of diphenylamine and acetone, etc. The amount used is rubber. The amount is preferably 0.1 to 5.0 parts by weight, more preferably 0.3 to 3.0 parts by weight with respect to 100 parts by weight of the component.

  The rubber composition of the present invention is obtained by kneading using a kneading machine such as a Banbury mixer, a roll, an internal mixer or the like according to the above-mentioned blending prescription, vulcanizing after molding, and rubber for tire tread It is suitably used as a composition.

The tire of the present invention is produced by an ordinary method using the rubber composition of the present invention. That is, the rubber composition of the present invention containing various chemicals as described above is processed into each member at an unvulcanized stage, and pasted and molded by a normal method on a tire molding machine to form a raw tire. The The green tire is heated and pressed in a vulcanizer to obtain a tire.
The tire of the present invention thus obtained has good fuel efficiency, particularly excellent fracture characteristics and wear resistance, and the processability of the rubber composition is good. Also excellent.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
The physical properties of rubber, unvulcanized rubber composition and vulcanized rubber composition were measured according to the following methods.
《Rubber properties》
<Amount of bound styrene>
It measured based on JISK6236: 2001.
<Analysis method of microstructure by FT-IR>
Measurement was performed by the method described above.
<Measurement of number average molecular weight (Mn), weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn)>
It measured using GPC [The Tosoh make, HLC-8020] using the refractometer as a detector, and showed it by polystyrene conversion which used the monodisperse polystyrene as a standard. The column is GMHXL [manufactured by Tosoh] and the eluent is tetrahydrofuran.
The above method was used.
<< Physical properties of rubber and unvulcanized rubber composition >>
<Mooney viscosity>
In accordance with JIS K 6300-1: 2001, ML1 + 4 was measured at 100 ° C. for the raw rubber and at 128 ° C. for the unvulcanized rubber composition.
<Physical properties of vulcanized rubber composition>
<Abrasion resistance>
Based on the description of JIS K 6264-1993, the amount of wear was measured at room temperature using a Lambone-type wear tester, the reciprocal of the amount of wear was calculated, and the index was displayed with Comparative Example 1 as 100. The larger the index value, the smaller the amount of wear and the better the wear resistance.
<Crack growth resistance>
Using a repeated fatigue tester, a 1 mm long scratch was placed in the center of a rubber sample-shaped dumbbell-shaped rubber sample, and then a repeated fatigue test was performed under the conditions of 100% constant strain, no initial strain, and 300 rpm. Thus, the time until breaking was evaluated. The results were expressed as an index with the time of Comparative Example 1 being 100. The larger the index value, the better the crack growth resistance.
<Wet properties>
Using a viscoelasticity measuring device (Rheometrics), tan δ (0 ° C.) was measured at a temperature of 0 ° C., a strain of 5%, and a frequency of 15 Hz. Based on the measured tan δ (0 ° C.), the comparative example 1 was set to 100 and the index was displayed. The greater the index value, the better the wettability.
<Low heat generation>
Using a viscoelasticity measuring device (Rheometrics), tan δ (60 ° C.) was measured at a temperature of 60 ° C., a strain of 5%, and a frequency of 15 Hz. The reciprocal of tan δ (60 ° C.) was calculated, and indexed with Comparative Example 1 as 100. The larger the index value, the lower the heat buildup.

Production Example 1 <Preparation of Catalyst A>
In a 100 ml glass bottle with a rubber stopper that has been dried and replaced with nitrogen, 7.11 g of a cyclohexane solution of butadiene (15.2% by mass), a cyclohexane solution of neodymium neodecanoate (0.56 mol / liter) 59 ml, toluene solution of methylaluminoxane MAO (PMAO manufactured by Toso-Akzo) (10.32 ml as aluminum concentration), hexane solution of diisobutylaluminum hydride (manufactured by Kanto Chemical) (0.90 mol / liter) ) 7.77 ml was added in this order, and after aging for 4 minutes at room temperature, 2.36 ml of hexane solution (0.95 mol / liter) of diethylaluminum chlorinated (manufactured by Kanto Chemical) was added and stirred occasionally at room temperature. Aged for 15 minutes. The concentration of neodymium in the catalyst A solution thus obtained was 0.011 mol / liter.

Production Example 2 <Preparation of Catalyst B>
In a 100 ml glass bottle with a rubber stopper that has been dried and substituted with nitrogen, in a following order, 7.11 g of a cyclohexane solution of butadiene (15.2 mass%), a cyclohexane solution of neodymium neodecanoate (0.56 mol) / 9) 0.59 ml, a toluene solution of methylaluminoxane MAO (PMAO manufactured by Toso-Akzo) (10.32 mol as an aluminum concentration), a hexane solution of diisobutylaluminum hydride (manufactured by Kanto Chemical) (0 .90 mol / liter) was added in the order of 7.77 ml, and after aging for 2 minutes at room temperature, 1.57 ml of hexane solution (0.95 mol / liter) of chlorinated diethylaluminum (manufactured by Kanto Chemical) was added. Aging for 15 minutes with occasional stirring at room temperature. The concentration of neodymium in the catalyst B solution thus obtained was 0.010 mol / liter.

Production Example 3 <Polybutadiene Rubber A Polymerization>
A glass bottle with a rubber stopper having a volume of about 1 liter was dried and purged with nitrogen, and a dry purified cyclohexane solution of butadiene and a dry cyclohexane were respectively added thereto, and 400 g of a cyclohexane solution of 5.0% by mass of butadiene was charged.
Next, 1.53 ml of catalyst A solution prepared in advance (0.017 mmol in terms of neodymium) was added, and polymerization was carried out in a water bath at 10 ° C. for 4.0 hours. Thereafter, 2 ml of a 5 mass% solution of isopropanol 2,2′-methylene-bis (4-ethyl-6-tert-butylphenol) (hereinafter sometimes abbreviated as NS-5) was added at 50 ° C. Then, the polymerization reaction was stopped, and reprecipitation was carried out in isopropanol containing a trace amount of NS-5, followed by drying with a drum dryer to obtain polybutadiene rubber A with a yield of almost 100%.

Production Example 4 <Polybutadiene Rubber B Polymerization>
A glass bottle with a rubber stopper having a volume of about 1 liter was dried and purged with nitrogen, and a dry-purified butadiene cyclohexane solution and a dry cyclohexane were respectively added thereto, and 400 g of a cyclohexane solution containing 12.5% by mass of butadiene was charged.
Next, 3.83 ml of the catalyst B solution prepared in advance (0.043 mmol in terms of neodymium) was added, and polymerization was carried out in a water bath at 50 ° C. for 1.0 hour. Thereafter, the polymerization reaction was stopped by adding 2 ml of a 5% by weight isopropanol NS-5 solution at 50 ° C., followed by reprecipitation in isopropanol containing a small amount of NS-5, and then using a drum dryer. It dried and polybutadiene rubber B was obtained with a yield of almost 100%.
Production Example 5 <Polymerization of Solution Polymerized Styrene-Butadiene Copolymer Rubber>
The autoclave with an internal volume of 50 liters equipped with a stirrer and a jacket was dried and replaced with nitrogen. The autoclave was charged with 25 kg of previously purified and dried cyclohexane, 2 kg of styrene, 3.1 kg of 1,3-butadiene and 0.25 kg of tetrahydrofuran. Next, after the temperature in the autoclave was set to 10 ° C., the cooling water was stopped while stirring at 2 revolutions per minute, 3.0 g of n-butyllithium was added, and polymerization was performed for 30 minutes. , Vi was 60% solution polymerized styrene-butadiene copolymer rubber.

Example 1 and Comparative Examples 1 and 2
The styrene-butadiene copolymer rubber obtained in Production Example 5, the polybutadiene rubbers A and B obtained in Production Examples 3 and 4 shown in Table 1, and the nickel catalyst polybutadiene rubber “BR-01” manufactured by JSR Corporation. 3 types of rubber compositions were prepared according to the blending contents shown in Table 2, and each rubber composition was vulcanized under conditions of 160 ° C. for 15 minutes to obtain the Mooney viscosity and vulcanization of the unvulcanized rubber composition. The rubber composition was measured for abrasion resistance, crack growth resistance, wettability and low heat build-up. The results are shown in Table 2.

  From Table 2, the rubber composition of the present invention (Example 1) is not deteriorated in wet property as compared with the rubber compositions of (Comparative Examples 1 and 2), and wear resistance, crack growth resistance, and low heat generation. It can be seen that the properties are excellent.

  Three types of tread rubber compositions of Example 1 and Comparative Examples 1 and 2 were respectively arranged as a 195 / 60R14 tread to produce three types of pneumatic tires for passenger cars, wear resistance and crack growth resistance. When the vehicle was tested for low heat buildup and wettability, the tire of Example 1 did not deteriorate in wettability compared with the tires of Comparative Examples 1 and 2, and had wear resistance, crack growth resistance and low heat buildup. It was excellent.

  The rubber composition for tire treads of the present invention is suitably used for treads for tires for passenger cars, light vehicles, light trucks, trucks and buses, and construction vehicles.

FIG. 4 is a diagram of a calibration curve for calculating the terminal denaturation rate of one embodiment relating to the present invention.

Claims (8)

20 to 80 parts by mass of a solution-polymerized styrene-butadiene copolymer rubber having a microstructure that satisfies the following mathematical formulas (1) to (4);
(1) Vi ≧ ST
(2) Vi + 2ST ≧ 80
(3) Vi ≦ 70
(4) ST ≦ 50
(In the formula, ST represents the amount of bound styrene (% by mass) in the copolymer rubber, and Vi represents the content of 1,2 bonds in the bound butadiene (%)).
Reinforcing filler 20 with respect to 100 parts by mass of a rubber component having a microstructure represented by the following formula (5) and comprising 20 to 80 parts by mass of polybutadiene rubber having a cis-1,4 bond content of 92% or more. A rubber composition for a tire tread containing ˜100 parts by mass.
(5) Vi ≦ 0.25 × (cis-97)
(In the formula, Vi represents 1,2 bond content (%), and cis represents cis-1,4 bond content (%)). A polybutadiene rubber obtained by polymerization in an organic solvent using a catalyst containing a lanthanum series rare earth element-containing compound, and containing a polybutadiene rubber whose microstructure satisfies the following formula (6): The rubber composition for a tire tread as described.
(6) cis ≧ 98.00 (%)
(Wherein cis represents cis-1,4 bond content (%)) Furthermore, the rubber composition for tire treads of Claim 2 with which polybutadiene rubber satisfies the following Numerical formula (7).
(7) Vi ≦ 0.35
(In the formula, Vi represents 1,2 bond content (%))   The rubber composition for a tire tread according to any one of claims 1 to 3, wherein a ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polybutadiene rubber is 1.6 to 3.5. object.   The rubber composition for a tire tread according to any one of claims 1 to 4, wherein the number average molecular weight (Mn) of the polybutadiene rubber is 100,000 to 500,000.   The rubber composition for a tire tread according to any one of claims 1 to 5, wherein the lanthanum series rare earth element-containing compound is a salt soluble in a neodymium hydrocarbon solvent.   The rubber composition for a tire tread according to any one of claims 1 to 6, wherein the reinforcing filler is carbon black and / or silica.   A pneumatic tire comprising the rubber composition according to claim 1 disposed on a tread.

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