JP2018145239A - Rubber composition for tire and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for tire, which shows excellent low heat generation performance and wear resistance when a tire is formed, and a pneumatic tire that uses the rubber composition.SOLUTION: A rubber composition for tire comprises a diene-based rubber and a filler that is at least one kind selected from silica and carbon black, in which the diene-based rubber contains 10 to 40 mass% of an aromatic vinyl-conjugate diene copolymer, and 60 to 90 mass% of natural rubber, and the aromatic vinyl-conjugate diene copolymer has a content of repeating units derived from the aromatic vinyl of 18 mass% or higher, has a glass transition temperature of -60°C or lower, and, has, among the repeating units derived from the conjugate diene compound, a ratio of vinyl structures of 8 mol% or lower, a ratio of 1,4-trans structures of 75 mol% or lower, and a ratio of 1,4-cis structures of 17 to 90 mol%, and has a content of silica of 15 to 45 pts.mass relative to 100 pts.mass of the diene-based rubber, and a silica ratio of 0.4 to 1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a tire rubber composition and a pneumatic tire.

Tires, particularly tires of heavy-duty vehicles such as trucks and buses (heavy-duty tires), are required to have characteristics such as wear resistance and low heat generation. Under such circumstances, generally, a rubber composition in which carbon black or silica is blended with a rubber component mainly composed of natural rubber is used as a rubber composition for heavy load tires.
For example, Patent Document 1 discloses a rubber composition for tire treads suitable for heavy-duty pneumatic tires, which contains a diene rubber containing 50% by weight or more of natural rubber, silica and carbon black. Terms). According to Patent Document 1, it is described that it is possible to achieve both the wear resistance and the low heat generation property of a tire by using the rubber composition having such a configuration.

JP 2011-57967 A

Recently, from the viewpoint of environmental problems and the like, improvement in fuel efficiency is required, and accordingly, further reduction in tire rolling resistance (further improvement in low heat generation) is required. Further, in recent years, further demand for safety of automobiles has been increased, and further improvement of tire wear resistance is desired.
Under these circumstances, when the present inventors prepared a tire rubber composition with reference to Patent Document 1 and manufactured a tire, its low heat buildup and wear resistance are certainly at a high level. Considering the improvement in level, it became clear that further improvement was necessary.

  Therefore, in view of the above circumstances, the present invention provides a rubber composition for a tire that is excellent in low heat buildup and wear resistance when made into a tire, and a pneumatic tire using the rubber composition for a tire. With the goal.

As a result of intensive studies on the above problems, the present inventors have found that, in addition to natural rubber, the content of repeating units derived from aromatic vinyl, each microstructure of repeating units derived from conjugated dienes (vinyl structure, 1, 4 -The above-mentioned problem can be achieved by blending a specific amount of an aromatic vinyl-conjugated diene copolymer having a cis structure, a 1,4-trans structure) ratio, and a glass transition temperature in a specific range, and silica. The inventors have found that this can be solved, and have reached the present invention.
That is, the present inventors have found that the above problem can be solved by the following configuration.

(1) containing a diene rubber and at least one filler selected from the group consisting of silica and carbon black,
The diene rubber contains 10 to 40% by mass of an aromatic vinyl-conjugated diene copolymer that is a copolymer of aromatic vinyl and conjugated diene, and contains 60 to 90% by mass of natural rubber.
The aromatic vinyl-conjugated diene copolymer has a repeating unit content derived from aromatic vinyl of 18% by mass or more, a glass transition temperature of −60 ° C. or less, and a repeating unit derived from conjugated diene. Among them, the proportion of vinyl structure is 8 mol% or less, the proportion of 1,4-trans structure is 75 mol% or less, the proportion of 1,4-cis structure is 17 to 90 mol%,
The content of the silica is 15 to 45 parts by mass with respect to 100 parts by mass of the diene rubber,
A tire rubber composition having a silica ratio of 0.4 to 1.
Here, the said silica ratio represents the ratio of content of the said silica with respect to the total content of the said silica and the said carbon black by mass ratio.
(2) The tire rubber composition according to (1), wherein the proportion of the 1,4-trans structure is 70 mol% or less and the proportion of the 1,4-cis structure is 30 mol% or more.
(3) The aromatic vinyl-conjugated diene copolymer is terminated with a compound represented by the following formula (N): titanium halide, tin halide, cyclic silazane, alkoxysilane, epoxide, amine, ketone. The tire rubber composition according to (1) or (2) above, which is an aromatic vinyl-conjugated diene copolymer modified with at least one modifier selected from the group consisting of:
(4) The rubber composition for a tire according to any one of (1) to (3), wherein the silica has a CTAB adsorption specific surface area of 150 m ² / g or more and less than 300 m ² / g.
(5) A pneumatic tire in which the tire rubber composition according to any one of the above (1) to (3) is disposed on a cap tread.

  As shown below, according to the present invention, there are provided a rubber composition for a tire that is excellent in low heat buildup and wear resistance when made into a tire, and a pneumatic tire using the rubber composition for a tire. Can do.

It is a partial section schematic diagram of the tire showing an example of the embodiment of the pneumatic tire of the present invention.

Below, the rubber composition for tires of this invention and the pneumatic tire using the said rubber composition for tires are demonstrated.
In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[I] Tire Rubber Composition The tire rubber composition of the present invention (hereinafter also referred to as “the composition of the present invention”) is at least one selected from the group consisting of a diene rubber, silica and carbon black. And a filler.
Here, the diene rubber contains 10 to 40% by mass of an aromatic vinyl-conjugated diene copolymer which is a copolymer of aromatic vinyl and conjugated diene, and 60 to 90% by mass of natural rubber. .
The aromatic vinyl-conjugated diene copolymer has a repeating unit content derived from aromatic vinyl of 18% by mass or more, a glass transition temperature of −60 ° C. or less, and a repeating function derived from conjugated diene. Among the units, the proportion of the vinyl structure is 8 mol% or less, the proportion of the 1,4-trans structure is 75 mol% or less, and the proportion of the 1,4-cis structure is 17 to 90 mol%.
Moreover, content of the said silica is 15-45 mass parts with respect to 100 mass parts of said diene rubbers.
The silica ratio is 0.4 or more and 1 or less. Here, the said silica ratio represents the ratio of content of the said silica with respect to the total content of the said silica and the said carbon black by mass ratio.

First, features of the present invention will be described.
In the present invention, a specific aromatic vinyl-conjugated diene copolymer (fragrance having a high content of repeating units derived from aromatic vinyl, a low proportion of vinyl structure, and a high proportion of 1,4-cis structure is used. It is considered that there is a great feature in that an aromatic vinyl-conjugated diene copolymer) is used.
First, since the specific aromatic vinyl-conjugated diene copolymer described above has a high content of repeating units derived from aromatic vinyl, it is considered that this leads to wear resistance when used as a tire.
In addition, the specific aromatic vinyl-conjugated diene copolymer described above maintains a flexible structure due to a high proportion of 1,4-cis structure, has a small hysteresis loss, and has excellent low heat generation when used as a tire. It can be thought of as indicating.
As a result, the composition of the present invention is presumed to be excellent in wear resistance and low heat build-up when formed into a tire.

  Hereinafter, each component contained in the composition of the present invention will be described.

[1] Diene rubber The diene rubber contained in the composition of the present invention contains 10 to 40% by mass of an aromatic vinyl-conjugated diene copolymer which is a copolymer of aromatic vinyl and conjugated diene, And it contains 60-90 mass% of natural rubber.

[Specific copolymer]
The specific aromatic vinyl-conjugated diene copolymer (hereinafter also referred to as “specific copolymer”) contained in the diene rubber is a copolymer of aromatic vinyl and conjugated diene. Here, the content of the repeating unit derived from the aromatic vinyl is 18% by mass or more. Moreover, the ratio of each microstructure of the repeating unit derived from the conjugated diene is in a specific range. Specifically, among the repeating units derived from conjugated dienes, the proportion of vinyl structure is 8 mol% or less, the proportion of 1,4-trans structure is 75 mol% or less, and 1,4-cis structure The ratio is 17 to 60 mol%. The glass transition temperature is −60 ° C. or lower. The specific copolymer is preferably a solution polymerization type copolymer (particularly, solution polymerization type SBR) because the effects of the present invention are more excellent.

〔monomer〕
The specific copolymer is a copolymer of aromatic vinyl and conjugated diene. That is, the specific copolymer is a copolymer obtained by copolymerizing aromatic vinyl and conjugated diene. The specific copolymer may be a copolymer obtained by copolymerizing another monomer in addition to the aromatic vinyl and the conjugated diene.

(1) Aromatic vinyl The aromatic vinyl is not particularly limited. For example, styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, 2,4-diisopropylstyrene, 2,4-dimethylstyrene, 4-t-butylstyrene, 5-t-butyl-2-methylstyrene, vinylnaphthalene, dimethylaminomethylstyrene, and dimethylaminoethylstyrene And so on. Among these, styrene, α-methylstyrene, and 4-methylstyrene are preferable, and styrene is more preferable because the effect of the present invention is more excellent. These aromatic vinyls can be used alone or in combination of two or more.

  The content of repeating units derived from aromatic vinyl in the specific copolymer (hereinafter also referred to as “aromatic vinyl content”) is 18% by mass or more. Especially, it is preferable that it is 20 mass% or more from the reason which the effect of this invention is more excellent, and it is more preferable that it is 30 mass% or more. The upper limit is not particularly limited, but is preferably 90% by mass or less, more preferably 70% by mass or less, and still more preferably 60% by mass or less because the effect of the present invention is more excellent.

(2) Conjugated diene The conjugated diene is not particularly limited, and examples thereof include butadiene (for example, 1,3-butadiene), isoprene, chloroprene and the like. Among these, 1,3-butadiene and isoprene are preferable because the effects of the present invention are more excellent. These conjugated dienes can be used alone or in combination of two or more.

  The content of the repeating unit derived from the conjugated diene in the specific copolymer is preferably 82% by mass or less, more preferably 80% by mass or less, because the effect of the present invention is more excellent. More preferably, it is at most mass%. Further, the lower limit is preferably 10% by mass or more, more preferably 30% by mass or more, and further preferably 40% by mass or more from the reason that the effect of the present invention is more excellent.

(3) Other monomer As described above, the specific copolymer may be a copolymer obtained by copolymerizing another monomer in addition to the aromatic vinyl and the conjugated diene. Such monomers include α, β-unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids or acid anhydrides such as acrylic acid, methacrylic acid, and maleic anhydride; methyl methacrylate, acrylic acid Unsaturated carboxylic esters such as ethyl and butyl acrylate; non-conjugated dienes such as 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, dicyclopentadiene, and 5-ethylidene-2-norbornene And so on.

[Microstructure]
(1) Vinyl structure In the specific copolymer, the proportion of the vinyl structure in the repeating unit derived from the conjugated diene is 8 mol% or less. Especially, it is preferable that it is 5 mol% or less from the reason for which the effect of this invention is more excellent. The lower limit is not particularly limited and is 0 mol%.
Here, the ratio of the vinyl structure means that the repeating unit having a vinyl structure (for example, 1,2-vinyl structure when the conjugated diene is 1,3-butadiene) out of all repeating units derived from the conjugated diene. The ratio (mol%) is said.

(2) 1,4-trans structure In the specific copolymer, the proportion of the 1,4-trans structure is 75 mol% or less among the repeating units derived from the conjugated diene. Especially, it is preferable that it is 70 mol% or less from the reason which the effect of this invention is more excellent, It is more preferable that it is less than 70 mol%, It is more preferable that it is 60 mol% or less. The lower limit is not particularly limited, but is preferably 10 mol% or more, more preferably 20 mol% or more, and even more preferably 30 mol% or more, because the effect of the present invention is more excellent.
Here, the ratio of the 1,4-trans structure refers to the ratio (mol%) occupied by the repeating unit having the 1,4-trans structure among all the repeating units derived from the conjugated diene.

(3) 1,4-cis structure In the specific copolymer, among the repeating units derived from the conjugated diene, the proportion of the 1,4-cis structure is 17 to 90 mol%. Especially, it is preferable that it is 20-88 mol% from the reason for which the effect of this invention is more excellent, It is more preferable that it is 25-85 mol%, It is more preferable that it is 30-80 mol%, 40- Particularly preferred is 75 mol%. Especially, it is preferable that it is 40-55 mol% from the reason which the effect of this invention is more excellent.
Here, the ratio of the 1,4-cis structure refers to the ratio (mol%) occupied by the repeating unit having a 1,4-cis structure out of all repeating units derived from the conjugated diene.

In the following, among the repeating units derived from conjugated dienes, “ratio of vinyl structure (mol%), ratio of 1,4-trans structure (mol%), ratio of 1,4-cis structure (mol%)” Also referred to as “vinyl / trans / cis”.
Moreover, since the repeating unit derived from a conjugated diene consists of a vinyl structure, a 1,4-trans structure, and a 1,4-cis structure, the total of the ratio (mol%) of each structure is 100 mol%.

〔Glass-transition temperature〕
The glass transition temperature (Tg) of the specific copolymer is −60 ° C. or lower. Especially, it is preferable that it is -70 degrees C or less, and it is more preferable that it is -80 degrees C or less from the reason which the effect of this invention is more excellent. The lower limit is not particularly limited, but is preferably −100 ° C. or higher, and more preferably −90 ° C. or higher because the effect of the present invention is more excellent.
In the present specification, the glass transition temperature (Tg) is measured at a rate of temperature increase of 20 ° C./min using a differential scanning calorimeter (DSC) and calculated by the midpoint method.

[Molecular weight]
The molecular weight of the specific copolymer is not particularly limited, but for the reason that the effect of the present invention is more excellent, the weight average molecular weight (Mw) is preferably 1,000 to 10,000,000, and 2,000 to 5, More preferably, it is 3,000,000, and more preferably 3,000 to 2,000,000. Moreover, from the reason that the effect of the present invention is more excellent, the number average molecular weight (Mn) is preferably 500 to 5,000,000, more preferably 1,000 to 2,500,000, More preferably, it is 500-1,000,000.
In the present specification, the number average molecular weight (Mn) and the weight average molecular weight (Mw) are standard polystyrene equivalent values obtained by gel permeation chromatography (GPC) measurement under the following conditions.
・ Solvent: Tetrahydrofuran ・ Detector: RI detector

[Preferred embodiment]
As a preferred embodiment of the specific copolymer, for example, the group consisting of a titanium halide, a tin halide, a cyclic silazane, an alkoxysilane, an epoxide, an amine, a ketone and a compound represented by the formula (N) described later is used. The aspect modified | denatured with the at least 1 sort (s) of modifying agent selected from below (it is also mentioned "specific modifier | denaturant" below) is mentioned. In the case of the said aspect, the effect of this invention is more excellent.
When the specific modifier is a titanium halide, tin halide or a compound represented by the formula (N) described later, the end of the specific copolymer is presumed to interact with carbon black, and the specific modifier is cyclic. In the case of silazane, alkoxysilane or amine, it is assumed that the end of the specific copolymer interacts with silica, and when the specific modifier is an epoxide or ketone, the end of the specific copolymer interacts with silica or carbon black. I guess that.
For the reason that the effect of the present invention is more excellent, the specific modifier is preferably a cyclic silazane, an alkoxysilane, or a compound represented by the formula (N) described later, and represented by the formula (N) described later. More preferably, it is a compound.

<Specific modifier>
Hereinafter, each specific modifier will be described.

(1) Titanium halide Titanium halide is not particularly limited. For example, TiCl ₃ , TiBr ₃ , Ti (OC ₂ H ₅ ) Cl ₂ , Ti (OC ₄ H ₉ ) Cl ₂ , TiCl ₄ , Ti (OC _2). H ₅ ) Cl ₃ , Ti (OC ₄ H ₉ ) Cl _{3 and the} like. Among these, TiCl ₃ (trichlorotitanium) and TiCl ₄ (tetrachlorotitanium) are preferable, and tetrachlorotitanium is more preferable because the effect of the present invention is more excellent.

(2) Tin halide Tin halide is not particularly limited, and examples thereof include tin fluoride, tin chloride, tin bromide, tin iodide, and astatine tin.

(3) Cyclic silazane The cyclic silazane is not particularly limited as long as it is a cyclic silazane.
Here, silazane intends a compound having a structure in which a silicon atom and a nitrogen atom are directly bonded (compound having a Si—N bond).
The cyclic silazane is preferably a compound represented by the following formula (S) because the effects of the present invention are more excellent.

In the above formula (S), R _{1 to} R ₃ each independently represents a hydrogen atom or a substituent. Specific examples of the substituent are the same as R in formula (P) described later.
R ₁ is an alkyl group (preferably 1 to 10 carbon atoms), an alkylsilyl group (preferably 1 to 10 carbon atoms), an aromatic hydrocarbon group (preferably It is preferable that it is C6-C18.
R ₂ is preferably an alkoxy group (preferably having a carbon number of 1 to 10) because the effect of the present invention is more excellent.
In the above formula (S), L represents a divalent organic group.
Examples of the divalent organic group include a substituted or unsubstituted aliphatic hydrocarbon group (for example, an alkylene group, preferably 1 to 8 carbon atoms), a substituted or unsubstituted aromatic hydrocarbon group (for example, an arylene group). Preferably 6 to 12 carbon atoms), —O—, —S—, —SO ₂ —, —N (R) — (R: alkyl group), —CO—, —NH—, —COO—, —CONH. -, or a group comprising a combination thereof (e.g., alkyleneoxy group (-C _m H _{2m O-:} m is a positive integer), alkyleneoxy carbonyl group, an alkylene carbonyl group) and the like.
L is preferably an alkylene group (preferably having a carbon number of 1 to 10) because the effects of the present invention are more excellent.

Examples of the compound represented by the formula (S) include Nn-butyl-1,1-dimethoxy-2-azasilacyclopentane and N-phenyl-1,1-dimethoxy-2-azasilacyclopentane. N-trimethylsilyl-1,1-dimethoxy-2-azasilacyclopentane, N-trimethylsilyl-1,1-diethoxy-2-azasilacyclopentane, and the like.
In addition, it is thought that the silicon atom of cyclic silazane shows electrophilicity.

(4) Alkoxysilane Alkoxysilane is not particularly limited as long as it is a compound having an alkoxysilyl group. For example, tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxy. Silane, phenyltrimethoxysilane, diphenyldimethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane 3-glycidoxypropylmethyldimethoxysilane, N, N-bistrimethylsilyl-3-aminopropyltrimethoxysilane, N, N-bistrimethylsilyl-3-a And minopropyltriethoxysilane.
The number of alkoxy groups in the alkoxysilyl group is not particularly limited, but is preferably 2 or more because the effect of the present invention is more excellent.
In addition, it is thought that the silicon atom of alkoxysilane shows electrophilicity.

(5) Epoxide The epoxide is not particularly limited as long as it is a compound having an oxacyclopropane (oxirane) structure.
Specific examples of the epoxide include ethylene oxide, propylene oxide, butylene oxide, cyclohexene oxide, styrene oxide, 1-phenylpropylene oxide, methyl glycidyl ether, ethyl glycidyl ether, glycidyl isopropyl ether, butyl glycidyl ether, 1-methoxy-2- Methyl propylene oxide, allyl glycidyl ether, 2-ethyloxyl glycidyl ether, phenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, lauryl alcohol glycidyl ether, stearyl glycidyl ether, palmityl glycidyl ether, myristyl glycidyl ether, lauryl glycidyl ether, Capryl glycidyl ether and caproyl glycidyl ether And the like.

(6) Amine The amine is not particularly limited as long as it is a compound having an amino group (—NR ₂ : R represents a hydrogen atom or a hydrocarbon group. Two Rs may be the same or different). . Among these, aziridine is preferable because the effect of the present invention is more excellent. Examples of aziridine include N-methylaziridine, N-ethylaziridine, N-isopropylaziridine, N-phenylaziridine, N- (4-methylphenyl) aziridine, N-methyl-2-methylaziridine and the like.

(7) Ketone The ketone is not particularly limited as long as it is a compound having a ketone group (—CO—).
Specific examples of the ketone include acetone, benzophenone, and derivatives thereof.
Derivatives of benzophenone include N, N, N ′, N′-tetramethyl-4,4′-diaminobenzophenone, N, N, N ′, N′-tetraethyl (4,4′-diamino) -benzophenone, N , N-dimethyl-1-aminobenzoquinone, N, N, N ′, N′-tetramethyl-1,3-diaminobenzoquinone, N, N-dimethyl-1-aminoanthraquinone, N, N, N ′, N ′ -Tetramethyl-1,4-diaminoanthraquinone, 4,4'-diacetylbenzophenone and the like.

(8) Compound Represented by Formula (N) Hereinafter, the compound represented by the following formula (N) will be described.

In the formula (N), ^{R 1} (preferably, the number 1 to 10 carbon atoms) is a hydrogen atom or an alkyl group represents, ^{R 2} (preferably, the number 2 to 10 carbon atoms) alkylene group represents a.

Specific examples of the compound represented by the above formula (N) include N-methylpyrrolidone (in the above formula (N), R ₁ is a methyl group and R ₂ is a propylene group).

  As described above, the content of the specific copolymer in the diene rubber is 10 to 40% by mass. Especially, it is preferable that it is 20-35 mass% from the reason which the effect of this invention is more excellent.

[Production method of specific copolymer]
The method for producing the specific copolymer described above is not particularly limited, and a conventionally known method can be used. The method for bringing the aromatic vinyl content, the proportion of the microstructure, and the glass transition temperature into a specific range is not particularly limited. For example, the type of the monomer to be polymerized, the amount ratio of the monomer, the type of the initiator, the type of the initiator By adjusting the quantity ratio, the reaction temperature, etc., the aromatic vinyl content, the proportion of the microstructure, and the glass transition temperature can be set to specific ranges.

[Preferred embodiment]
As a preferred embodiment of the method for producing the specific copolymer, for example, an aromatic compound using an initiator (hereinafter, also referred to as “specific initiator”) prepared using an organolithium compound, an alkylaluminum, and a metal alcoholate is used. And a method of copolymerizing monomers containing vinyl and diene (hereinafter, also referred to as “method of the present invention”). When the above method is used, the composition of the present invention containing the obtained specific copolymer exhibits better mechanical properties and abrasion resistance when formed into a tire.

<Specific initiator>
As described above, in the method of the present invention, an initiator (specific initiator) prepared using an organolithium compound, an alkylaluminum, and a metal alcoholate is used. Since a specific initiator is used in the method of the present invention, it is considered that the proportion of the vinyl structure in the repeating unit derived from diene is suppressed (for example, 8 mol% or less) in the specific polymer obtained.

  The specific initiator is preferably one using aromatic divinyl for the reason that the effect of the present invention is more excellent. That is, it is preferably prepared using an organolithium compound, an alkylaluminum, a metal alcoholate and an aromatic divinyl. By using aromatic divinyl, the resulting copolymer is branched, the molecular weight is increased, and mechanical properties and wear resistance are further improved when a tire is formed.

(1) Organolithium compound Examples of the organolithium compound include monoorganolithium compounds such as n-butyllithium, sec-butyllithium, tert-butyllithium, n-propyllithium, iso-propyllithium, and benzyllithium; 4-dilithiobutane, 1,5-dilithiopentane, 1,6-dilithiohexane, 1,10-dilithiodecane, 1,1-dilithiodiphenylene, dilithiopolybutadiene, dilithiopolyisoprene, 1,4-dilithiobenzene, 1,2-dilithio-1,2-diphenylethane, 1,4-dilithio-2-ethylcyclohexane, 1,3,5-trilithiobenzene, 1,3,5-trilithio-2,4,6-triethylbenzene And other multifunctional organolithium compounds. In particular, a monoorganolithium compound of n-butyllithium, sec-butyllithium, or tert-butyllithium is preferable because the effect of the present invention is more excellent.

  The amount of the organolithium compound used for the preparation of the specific initiator is not particularly limited, but is preferably 0.001 to 10 mol% with respect to the monomer to be polymerized because the effect of the present invention is more excellent.

(2) Alkyl aluminum Alkyl aluminum is not particularly limited as long as it is a compound in which an alkyl group (chain, branched, or cyclic) is bonded to an aluminum atom (Al). The number of carbon atoms of the alkyl group is not particularly limited, but is preferably 1 to 20 and more preferably 1 to 10 because the effects of the present invention are more excellent. Specific examples of the alkylaluminum include trimethylaluminum, triethylaluminum, triisopropylaluminum, tributylaluminum, triisobutylaluminum, tripropylaluminum, tributylaluminum, triisobutylaluminum, pentyldiethylaluminum, 2-methylpentyl-diethylaluminum, dicyclohexylethyl. Aluminum, tripentyl aluminum, trihexyl aluminum, trioctyl aluminum, tri (2-ethylhexyl) aluminum, tricyclohexyl aluminum, tricyclopentyl aluminum, tri (2,2,4-trimethylpentyl) aluminum, tridodecyl aluminum, tri (2 -Methylpentyl) aluminum, diisobutyl Rumi bromide hydride, diethylaluminum hydride, dipropyl aluminum hydride, propyl aluminum dihydride, isobutyl aluminum dihydride. Among them, the reason why the effects of the present invention is more excellent, trioctyl aluminum are preferred.

  The ratio of the alkylaluminum to the organolithium compound used for the preparation of the specific initiator is not particularly limited, but is preferably 0.1 to 50 molar equivalents because the effect of the present invention is more excellent, 0.5 to More preferably, it is 10 molar equivalents. Here, 1 molar equivalent indicates the amount when 1 mol of alkylaluminum is added when 1 mol of an organolithium compound is used. That is, the ratio of the alkylaluminum to the organolithium compound used for the preparation of the specific initiator is not particularly limited, but is preferably 10 to 5000 mol%, more preferably 50 to 1000 mol for the reason that the effect of the present invention is more excellent. % Is more preferable.

(3) Metal alcoholate The metal alcoholate (metal alkoxide) is not particularly limited as long as it is a compound in which the hydrogen of the hydroxy group of the alcohol is replaced with a metal.
Although it does not restrict | limit especially as said metal, An alkali metal, alkaline-earth metal, a transition metal (metal of 3-11 groups), aluminum, germanium, tin, antimony, etc. are mentioned. Especially, since the effect of this invention is more excellent, alkaline-earth metal is preferable and it is more preferable that it is barium.
The alcohol is not particularly limited as long as it is a compound in which a hydrogen atom of a chain, branched or cyclic hydrocarbon is substituted with a hydroxy group. The number of carbon atoms of the alcohol is not particularly limited, but is preferably 1 to 30 and more preferably 1 to 20 because the effect of the present invention is more excellent.

  The metal alcoholate is preferably a barium alcoholate (barium alkoxide) because the effects of the present invention are more excellent. Examples of the barium alkoxide include barium dimethoxide, barium diethoxide, barium dipropoxide, barium dibutoxide, barium bis (2-ethylhexoxide), and the like.

  The ratio of the metal alcoholate to the organolithium compound used for the preparation of the specific initiator is not particularly limited, but is preferably 0.01 to 5 molar equivalents because the effect of the present invention is more excellent. More preferably, it is 3 molar equivalents. Here, 1 molar equivalent indicates an amount when 1 mol of metal alcoholate is added when 1 mol of an organic lithium compound is used. That is, the ratio of the metal alcoholate to the organolithium compound used for the preparation of the specific initiator is not particularly limited, but is preferably 1 to 500 mol%, more preferably 10 to 300 mol for the reason that the effect of the present invention is more excellent. % Is more preferable.

(4) Aromatic divinyl Aromatic divinyl is not particularly limited as long as it is an aromatic compound having two vinyl groups. Among these, divinylbenzene is preferable because the effect of the present invention is more excellent.

  The ratio of the aromatic divinyl to the organolithium compound used for the preparation of the specific initiator is not particularly limited, but is preferably 0.1 to 5 molar equivalents because the effect of the present invention is more excellent. More preferably, it is ˜3 molar equivalents. Here, 1 molar equivalent indicates the amount when 1 mol of aromatic divinyl is added when 1 mol of the organic lithium compound is used. That is, the ratio of the aromatic divinyl to the organolithium compound used for the preparation of the specific initiator is not particularly limited, but is preferably 10 to 500 mol% because the effect of the present invention is more excellent, and 30 to 300 More preferably, it is mol%.

(Method for preparing specific initiator)
A method for preparing the specific initiator is not particularly limited, and examples thereof include a method of dissolving the above-described organolithium compound, alkylaluminum, metal alcoholate, and the like in a solvent.
The type of the solvent is not particularly limited, and for example, an organic solvent can be used, but it is preferably other than alcohol because the effect of the present invention is more excellent.

<Monomer>
Monomers (mixtures) include aromatic vinyls and dienes. Specific examples and preferred embodiments of the aromatic vinyl and diene are as described above.
Although the ratio of the aromatic vinyl in the monomer is not particularly limited, it is preferably 18% by mass or more, more preferably 20% by mass or more, and more preferably 30% by mass or more because the effect of the present invention is more excellent. More preferably it is. The upper limit is not particularly limited, but is preferably 90% by mass or less, more preferably 70% by mass or less, and still more preferably 60% by mass or less because the effect of the present invention is more excellent.
Further, the proportion of diene in the monomer is not particularly limited, but is preferably 82% by mass or less, more preferably 80% by mass or less, and 70% by mass or less because the effect of the present invention is more excellent. More preferably it is. Further, the lower limit is preferably 10% by mass or more, more preferably 30% by mass or more, and further preferably 40% by mass or more from the reason that the effect of the present invention is more excellent.
The monomer may further contain another monomer in addition to the aromatic vinyl and diene. Specific examples of such a monomer are the same as the “other monomers” described above.

<Monomer copolymerization>
As described above, in the method of the present invention, a monomer containing an aromatic vinyl and a diene is copolymerized using a specific initiator. The specific initiator and monomer are as described above.

  Although the monomer copolymerization method is not particularly limited, a method in which the above-described monomer is added to the organic solvent solution containing the above-described specific initiator, and the mixture is stirred in a temperature range of 0 to 120 ° C. (preferably 30 to 100 ° C.) Is mentioned.

  Although the ratio of the organolithium compound in the specific initiator with respect to the monomer is not particularly limited, it is preferably 0.001 to 10 mol% because the effect of the present invention is more excellent.

When the monomers are copolymerized, a phenol compound or an amine compound may be added to a copolymerization system (for example, an organic solvent solution containing the specific initiator described above). Among these, a phenol compound is preferable because the effect of the present invention is more excellent. When a phenol compound is added, in the resulting aromatic vinyl-diene copolymer, the proportion of 1,4-cis structure among the repeating units derived from diene increases.
Here, the phenol compound means a compound having a phenolic hydroxyl group or a metal salt thereof. The amine compound is intended to be a compound having an amino group (—NH ₂ , —NHR, —NR ₂ ). Here, R represents a substituent. Specific examples and preferred embodiments of the substituent are the same as R in formula (P) described later. _Two Rs in —NR ₂ may be the same or different.
As a phenol compound, the compound represented by a following formula (P) is mentioned, for example.

In the above formula (P), X ¹ represents a hydrogen atom or a metal atom. Examples of the metal atom include a sodium atom and a potassium atom.
In the above formula (P), R represents a hydrogen atom or a substituent. A plurality of R may be the same or different.
The substituent is not particularly limited as long as it is a monovalent substituent. For example, a halogen atom, hydroxy group, nitro group, carboxy group, alkoxy group, amino group, mercapto group, acyl group, imide group, phosphino group , A phosphinyl group, a silyl group, a hydrocarbon group optionally having a hetero atom, and the like.
As said halogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom etc. are mentioned, for example.
Examples of the hetero atom of the hydrocarbon group that may have a hetero atom include an oxygen atom, a nitrogen atom, a sulfur atom, and a phosphorus atom.
Examples of the hydrocarbon group that may have a hetero atom include an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a group obtained by combining these.
The aliphatic hydrocarbon group may be linear, branched or cyclic. Specific examples of the aliphatic hydrocarbon group include a linear or branched alkyl group (particularly having 1 to 30 carbon atoms), a linear or branched alkenyl group (particularly having 2 to 30 carbon atoms), Examples thereof include a linear or branched alkynyl group (particularly having 2 to 30 carbon atoms).
As said aromatic hydrocarbon group, C6-C18 aromatic hydrocarbon groups, such as a phenyl group, a tolyl group, a xylyl group, a naphthyl group, etc. are mentioned, for example.
In the above formula (P), X represents a hydrogen atom, -OX ¹ group or a substituent. X ¹ is as described above. Moreover, the specific example of a substituent is the same as R in the formula (P) mentioned above.

  Although the amount of the phenol compound to be added is not particularly limited, it is preferably 0.01 to 90 mol%, preferably 0.1 to 80 mol% with respect to the organolithium compound, because the effect of the present invention is more excellent. More preferably.

The method for stopping the polymerization is not particularly limited, and examples thereof include a method of adding alcohol (particularly methanol) to the polymerization solution.
The method for stopping the polymerization is selected from titanium halide, tin halide, cyclic silazane, alkoxysilane, epoxide, amine, ketone and a compound represented by the following formula (N) because the effect of the present invention is more excellent. A method of stopping polymerization using an electrophile (hereinafter also referred to as “specific electrophile”) is preferable.
That is, the method of the present invention is preferably a method in which a monomer containing an aromatic vinyl and a diene is copolymerized using a specific initiator, and then the polymerization is stopped using a specific electrophile.
The definition, specific examples and preferred embodiments of the specific electrophile are the same as those of the specific modifier described above.
By stopping the polymerization using a specific electrophile, a copolymer having a terminal modified with a specific electrophile (specific modifier) can be obtained.
Although the amount of the specific electrophile with respect to the specific initiator is not particularly limited, the ratio of the electrophile to the organolithium compound (specific electrophile / organolithium compound) is a molar ratio because the effect of the present invention is more excellent. It is preferable that it is 0.1-10, and it is more preferable that it is 1-5.
For the reason that the effect of the present invention is more excellent, the ratio of the specific electrophile to the alkylaluminum (alkyl Al) (specific electrophile / alkyl Al) is preferably 0.1 to 10 in terms of molar ratio. 5 is more preferable.
For the reason that the effect of the present invention is more excellent, the ratio of the electrophile to the metal alcoholate (electrophile / metal alcoholate) is preferably 0.1 to 20 and more preferably 1 to 10 in terms of molar ratio. preferable.

[Natural rubber]
As described above, the diene rubber contains 60 to 90% by mass of natural rubber. Especially, it is preferable that it is 70-80 mass% from the reason which the effect of this invention is more excellent.

[Other rubber components]
The diene rubber may contain a rubber component other than the specific copolymer and natural rubber. Examples of such other rubber components include isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR) other than the specific copolymer, acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), Halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR) and the like can be mentioned.

[2] Filler As described above, the composition of the present invention contains at least one filler selected from the group consisting of silica and carbon black.

[silica]
The composition of the present invention contains silica as a filler.
The silica contained in the composition of the present invention is not particularly limited, and any conventionally known silica compounded in a rubber composition for uses such as tires can be used.
Examples of the silica include wet silica, dry silica, fumed silica, diatomaceous earth, and the like. As the silica, one type of silica may be used alone, or two or more types of silica may be used in combination.

Although the cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of the silica (hereinafter, “CTAB adsorption specific surface area” is also simply referred to as “CTAB”) is not particularly limited, it is 150 m ² / g because the effect of the present invention is more excellent. is preferably less than or 300m ² / g, more preferably 180~250m ² / g.
In the present specification, the CTAB adsorption specific surface area is a value obtained by measuring the CTAB adsorption amount on the silica surface in accordance with JIS K6217-3: 2001 “Part 3: Determination of specific surface area—CTAB adsorption method”.

  In the composition of the present invention, the content of silica is 15 to 45 parts by mass with respect to 100 parts by mass of the diene rubber. Especially, it is preferable that it is 20-40 mass parts from the reason which the effect of this invention is more excellent, and it is more preferable that it is 25-35 mass parts.

[Carbon black]
The composition of the present invention preferably contains carbon black as a filler because the effects of the present invention are more excellent.
The carbon black is not particularly limited. For example, various grades such as SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS, HAF, HAF-LS, FEF, GPF, SRF, etc. Can be used.
The nitrogen adsorption specific surface area (N ₂ SA) of the carbon black is not particularly limited, but is preferably 50 to ²⁰⁰ m ² / g, more preferably 70 to 150 m ² / g, because the effect of the present invention is more excellent. Is more preferable.
Here, the nitrogen adsorption specific surface area (N ₂ SA) is the nitrogen adsorption amount on the carbon black surface according to JIS K6217-2: 2001 “Part 2: Determination of specific surface area—nitrogen adsorption method—single point method”. It is a measured value.

  Although the content of the carbon black is not particularly limited, it is preferably 1 to 100 parts by mass and 5 to 50 parts by mass with respect to 100 parts by mass of the diene rubber because the effect of the present invention is more excellent. It is more preferable.

[Silica ratio]
In the composition of the present invention, the silica ratio is 0.4 or more and 1 or less. Especially, it is preferable that it is 0.5-1 from the reason which the effect of this invention is more excellent.
Here, the silica ratio represents the ratio of the above-described silica content with respect to the total content of the above-described silica and the above-described carbon black as a mass ratio. For example, in the case of Example 1 described later, the silica ratio is 0.60 (= 30 ÷ (30 + 20)) because the amount of silica is 30 parts by mass and the amount of carbon black is 20 parts by mass. .

[3] Arbitrary component The composition of the present invention can further contain other components (optional component) as long as the effect and purpose are not impaired.
Examples of the optional component include a silane coupling agent, a terpene resin (preferably an aromatic-modified terpene resin), a thermally expandable microcapsule, a filler, zinc oxide (zinc white), stearic acid, an antiaging agent, and a wax. , Processing aids, oils, liquid polymers, thermosetting resins, vulcanizing agents (eg, sulfur), vulcanization accelerators, alkyltriethoxysilanes (particularly those having an alkyl group having 3 to 20 carbon atoms), etc. Examples include various additives generally used in rubber compositions.

[4] Method for Preparing Tire Rubber Composition The method for producing the composition of the present invention is not particularly limited, and specific examples thereof include, for example, the above-described components using known methods and apparatuses (for example, a Banbury mixer, And a kneading method using a kneader or a roll. When the composition of the present invention contains sulfur or a vulcanization accelerator, components other than sulfur and the vulcanization accelerator are first mixed at a high temperature (preferably 100 to 160 ° C.) and cooled, and then sulfur or It is preferable to mix a vulcanization accelerator.
The composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions.

[II] Pneumatic tire The pneumatic tire of the present invention is a pneumatic tire using the above-described composition of the present invention. Especially, it is preferable that it is a pneumatic tire which used (arrange | positioned) the composition of this invention for the cap tread.
FIG. 1 shows a schematic partial sectional view of a tire representing an example of an embodiment of the pneumatic tire of the present invention, but the pneumatic tire of the present invention is not limited to the embodiment shown in FIG.

In FIG. 1, reference numeral 1 represents a bead portion, reference numeral 2 represents a sidewall portion, and reference numeral 3 represents a tire tread portion.
In addition, a carcass layer 4 in which fiber cords are embedded is mounted between the pair of left and right bead portions 1, and the end portion of the carcass layer 4 extends from the inside of the tire to the outside around the bead core 5 and the bead filler 6. Wrapped and rolled up.
In the tire tread 3, a belt layer 7 is disposed over the circumference of the tire on the outside of the carcass layer 4.
Moreover, in the bead part 1, the rim cushion 8 is arrange | positioned in the part which touches a rim | limb.
The tire tread portion 3 includes an under tread 9 and a cap tread 10 disposed on the outside thereof.
The cap tread 10 is formed of the above-described composition of the present invention.

The pneumatic tire of the present invention can be manufactured, for example, according to a conventionally known method. Moreover, as gas with which a tire is filled, inert gas, such as nitrogen, argon, helium other than the air which adjusted normal or oxygen partial pressure, can be used.
The pneumatic tire of the present invention is useful for various vehicles such as passenger cars, trucks, buses, construction vehicles, and industrial vehicles.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.

(Synthesis example)
A specific copolymer and a specific polysiloxane were synthesized as follows.

<Specific copolymer 1 (unmodified SBR)>
n-BuLi (Kanto Chemical Co., Inc .: 1.60 mol / L (hexane solution), 18 mL, 28.8 mmol), barium bis (2-ethylhexoxide) (Ba (OCH ₂ CH (C ₂ H ₅ ) CH ₂ CH _{2 CH 2 CH 3) 2)} (STREM manufactured: 1M (toluene / hexane solution) 7.5 mL), trioctyl aluminum (Aldrich made: 25 wt% (in hexane), 45 mL) and cyclohexane (manufactured by Kanto Kagaku: 10 mL) of 60 mL of the initiator solution (corresponding to the specific initiator described above) prepared by using 1,3-butadiene (708 g, 13098 mmol), styrene (manufactured by Kanto Chemical Co., Ltd .: 300 g, 2883 mmol) and 4-tert-butylpyrocatechol (4.79 g, 28.8 mmol) In addition to the sun (4.24 kg) solution, the mixture was stirred at 60 ° C. for 14 hours. After cooling to room temperature, methanol (Kanto Chemical Co., Ltd .: 3.44 g) was added to terminate the polymerization. The resulting solution was removed and concentrated under reduced pressure. The concentrated solution was poured into methanol (5 L) to separate methanol insoluble components. As a result, a styrene-butadiene copolymer (unmodified SBR) (895 g, Mn = 360,000, Mw = 500,000, PDI = 1.4) was obtained in a yield of 88%. In addition, it was estimated that vinyl / trans / cis = 3/62/35 by IR analysis. Moreover, aromatic vinyl content (content of the repeating unit derived from styrene) was 31 mass%, and the glass transition temperature was -84 degreeC.

<Specific copolymer 2 (alkoxysilane terminal-modified SBR)>
n-BuLi (Kanto Chemical Co., Inc .: 1.60 mol / L (hexane solution), 18 mL, 28.8 mmol), barium bis (2-ethylhexoxide) (Ba (OCH ₂ CH (C ₂ H ₅ ) CH ₂ CH _{2 CH 2 CH 3) 2)} (STREM manufactured: 1M (toluene / hexane solution) 7.5 mL), trioctyl aluminum (Aldrich made: 25 wt% (in hexane), 45 mL) and cyclohexane (manufactured by Kanto Kagaku: 10 mL) of 60 ml of an initiator solution (corresponding to the specific initiator described above) prepared by using 1,3-butadiene (721 g, 13330 mmol), styrene (manufactured by Kanto Chemical Co., Ltd .: 300 g, 2883 mmol) and 4-tert-butylpyrocatechol (4.79 g, 28.8 mmol) In addition to the sun (4.24 kg) solution, the mixture was stirred at 60 ° C. for 14 hours. After cooling to room temperature, a mixed solution of N, N-bistrimethylsilyl-3-aminopropyltrimethoxysilane (22.4 g) and lithium diisopropylamide (Aldrich (2M solution): 10 mL) in cyclohexane (10 mL) was added to polymerize. Stopped. The resulting solution was removed and concentrated under reduced pressure. The concentrated solution was poured into methanol (5 L) to separate methanol insoluble components. As a result, 81% yield of styrene-butadiene copolymer (alkoxysilane terminal-modified SBR) (827 g, Mn = 350,000, Mw = 490,000, PDI = 1.4) whose terminal was modified with alkoxysilane was obtained. Obtained at a rate. In addition, it was estimated that vinyl / trans / cis = 4/61/35 by IR analysis. Moreover, aromatic vinyl content (content of the repeating unit derived from styrene) was 26 mass%, and the glass transition temperature was -85 degreeC.

[Preparation of rubber composition for tire]
The components shown in Table 1 below were blended in the proportions (parts by mass) shown in Table 1 below.
Specifically, first, components excluding sulfur and a vulcanization accelerator among the components shown in Table 1 below were mixed with a Banbury mixer at 150 ° C. for 2 minutes. Next, sulfur and a vulcanization accelerator were mixed using a roll to obtain a tire rubber composition.

[Evaluation]
The obtained tire rubber composition was evaluated as follows.

<Tan δ (60 ° C.)>
The obtained tire rubber composition was press vulcanized at 170 ° C. for 10 minutes in a predetermined mold to prepare a vulcanized rubber test piece. And about the obtained vulcanized rubber test piece, according to JISK6394: 2007, using a viscoelastic spectrometer (made by Toyo Seiki Seisakusho Co., Ltd.), an elongation deformation strain rate of 10% ± 2%, a frequency of 20 Hz, a temperature of 60 Tan δ (60 ° C.) was measured under the condition of ° C.
The results are shown in Table 1. The results were expressed as an index with Comparative Example 1 as 100. The smaller the index, the smaller the tan δ (60 ° C.), and the better the fuel efficiency when used as a tire.

<Abrasion resistance>
A vulcanized rubber test piece was prepared according to the same procedure as in the evaluation of tan δ (60 ° C.).
The obtained vulcanized rubber test piece was subjected to an applied force of 4.0 kg / cm ³ (= 39 N) and a slip rate of 30 according to JIS K6264-2: 2005 using a Lambourne abrasion tester (manufactured by Iwamoto Seisakusho). %, A wear test time of 4 minutes and a test temperature at room temperature were subjected to a wear test, and the wear mass was measured. And the index was calculated as follows. The results are shown in Table 1. The larger the index, the smaller the amount of wear and the better the wear resistance when made into a tire.
Index = (Abrasion mass of test piece of Comparative Example 1 / Abrasion mass of each example) × 100

The details of each component shown in Table 1 are as follows.
・ NR: TSR20 (natural rubber)
-BR: NIPOL BR 1220 (Butadiene rubber, manufactured by Zeon Corporation)
Specific copolymer 1 (unmodified SBR): Specific copolymer 1 (unmodified SBR) synthesized as described above
Specific copolymer 2 (alkoxysilane terminal-modified SBR): Specific copolymer 2 synthesized as described above (alkoxysilane terminal-modified SBR)
CB (ISAF): Seest 6 (ISAF grade carbon black, N ₂ SA = 119 m ² / g
Silica 1 (CTAB = 160 m ² / g): ZEOSIL 1165MP (silica, CTAB = 160 m ² / g, manufactured by Rhodia)
Silica 2 (CTAB = 200 m ² / g): Premium 200MP (silica, CTAB = 200 m ² / g, manufactured by Rhodia)
Silane coupling agent: Si69 (Silane coupling agent, manufactured by Evonik)
Anti-aging agent: Santoflex 6PPD (manufactured by Flexis)
・ Zinc oxide: 3 types of zinc oxide (manufactured by Shodo Chemical Industry Co., Ltd.)
・ Stearic acid: Stearic acid (manufactured by NOF CORPORATION)
・ Vulcanization accelerator: Noxeller NS-P (Ouchi Shinsei Chemical Co., Ltd.)
・ Sulfur: Fine sulfur with Jinhua stamp oil (manufactured by Tsurumi Chemical Co., Ltd.)

  In Table 1, “silica ratio” represents the “silica ratio” described above.

As can be seen from Table 1, the examples of the present application in which specific copolymers, natural rubber, and silica were blended in specific amounts exhibited excellent low heat buildup and wear resistance when formed into tires.
From the comparison between Examples 1 and 2 (contrast between modes containing specific copolymer 2 and 30 parts by mass of silica with respect to 100 parts by mass of diene rubber), the CTAB of silica is 180 m ² / Example 2 which is g or more showed more excellent wear resistance.
Further, from the comparison of Examples 2 to 4 (contrast between the embodiments containing the specific copolymer 2 and silica 2), the silica content is 40 parts by mass or less with respect to 100 parts by mass of the diene rubber. 2 and 3 showed better wear resistance. Among them, Example 2 in which the content of silica was 35 parts by mass or less with respect to 100 parts by mass of the diene rubber showed further excellent wear resistance.
Moreover, the terminal of the specific copolymer was modified with a specific modifier from a comparison between Examples 2 and 5 (a comparison between modes containing 30 parts by mass of silica 2 with respect to 100 parts by mass of diene rubber). Example 2 showed better wear resistance.

  On the other hand, Comparative Examples 1 and 2 not containing a specific copolymer, Comparative Example 3 containing a specific copolymer but having a silica ratio of less than 0.4, and the content of natural rubber in the diene rubber was 60 The comparative example 4 which is less than the mass part has insufficient low heat generation.

1 Bead part 2 Side wall part 3 Tire tread part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Rim cushion

Claims (5)

Containing a diene rubber and at least one filler selected from the group consisting of silica and carbon black;
The diene rubber contains 10 to 40% by mass of an aromatic vinyl-conjugated diene copolymer that is a copolymer of aromatic vinyl and conjugated diene, and contains 60 to 90% by mass of natural rubber.
The aromatic vinyl-conjugated diene copolymer has a repeating unit content derived from aromatic vinyl of 18% by mass or more, a glass transition temperature of −60 ° C. or less, and a repeating unit derived from conjugated diene. Among them, the proportion of vinyl structure is 8 mol% or less, the proportion of 1,4-trans structure is 75 mol% or less, the proportion of 1,4-cis structure is 17 to 90 mol%,
The silica content is 15 to 45 parts by mass with respect to 100 parts by mass of the diene rubber,
A tire rubber composition having a silica ratio of 0.4 to 1.
Here, the said silica ratio represents the ratio of the content of the said silica with respect to the total content of the said silica and the said carbon black by mass ratio.   The tire rubber composition according to claim 1, wherein a ratio of the 1,4-trans structure is 70 mol% or less, and a ratio of the 1,4-cis structure is 30 mol% or more. The aromatic vinyl-conjugated diene copolymer has a terminal selected from the group consisting of titanium halide, tin halide, cyclic silazane, alkoxysilane, epoxide, amine, ketone, and a compound represented by the following formula (N). The tire rubber composition according to claim 1 or 2, which is an aromatic vinyl-conjugated diene copolymer modified with at least one modifier.
In formula (N), R ¹ represents a hydrogen atom or an alkyl group, and R ² represents an alkylene group. CTAB adsorption specific surface area of the silica is less than 150 meters ² / g or more 300 meters ² / g, tire rubber composition according to any one of claims 1 to 3.   The pneumatic tire which has arrange | positioned the rubber composition for tires of any one of Claims 1-3 in the cap tread.