JP2008150563A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire having an inner liner prepared by using a rubber composition improved in air permeation resistance with keeping workability at the time of production. <P>SOLUTION: The pneumatic tire has a carcass 4 extended in a toroidal shape between a pair of bead units 1 and an inner liner 6 arranged inside face of a tire in the inside of the carcass 4. In the pneumatic tire, the rubber composition is used for preparing the inner liner 6. The rubber composition comprises 100 pts.mass rubber component (A) consisting of 70-100 mass% butyl-based rubber and 0-30 mass% diene-based rubber blended with 1-20 pts.mass low molecular weight polymer (B) which is an aromatic vinyl compound-conjugated diene compound copolymer or a conjugate diene compound polymer comprising 0-80 mass% amount of the aromatic vinyl compound and 5-80 mass% amount of vinyl bonds in the conjugate diene compound and having 5,000-200,000 weight-average molecular weight in terms of polystyrene, measured by gel permeation chromatography. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pneumatic tire provided with an inner liner, and more particularly to a pneumatic tire using a rubber composition with improved air permeation resistance while maintaining workability during production.

  Conventionally, an inner liner made of a rubber composition mainly composed of a low gas permeable rubber such as butyl rubber or halogenated butyl rubber has been provided on the inner surface of a pneumatic tire to prevent air leakage and keep the tire air pressure constant. Has been placed. As a means for improving the air permeation resistance of such an inner liner, a technique for increasing the content of the butyl rubber is generally used. However, as a further means for improving the air permeation resistance, an inorganic layered structure is added to the rubber composition. For example, a technique of adding a filler such as clay mineral. However, when the content of the butyl rubber is increased, the compatibility with the rubber constituting the carcass ply, that is, the ply rubber is deteriorated, resulting in insufficient tackiness of the inner liner. As a result, problems such as deterioration in workability at the time of tire molding and air entering between the inner liner and the ply arise. Further, when an inorganic layered clay mineral is added to the rubber composition, as the amount of the inorganic layered clay mineral increases, the inorganic layered clay mineral is deposited on the rubber surface, resulting in further lack of tackiness. .

  On the other hand, in response to the recent social demands for energy and resource savings, there is an increasing demand for fuel efficiency reduction of automobiles. In order to meet such demands, the inner liner is used for the purpose of reducing the weight of tires. A method for improving the air permeation resistance of the inner liner and reducing the inner liner thickness has been proposed.

  For example, in JP-A-7-40702 (Patent Document 1) and JP-A-7-81306 (Patent Document 2), instead of a conventional butyl rubber, a nylon film layer or a vinylidene chloride layer is used as an inner liner. The technique used is disclosed. However, in these methods, although the weight of the tire is reduced, a crystalline resin material is used as a layer or film matrix, so that the crack resistance and the bending fatigue resistance are particularly 5 ° C. or less. At a low temperature, it is lower than the inner liner made of a rubber composition mainly composed of a conventional butyl rubber, and in addition, the tire production becomes complicated.

  On the other hand, in JP-A-2002-88209 (Patent Document 3), a layered or plate-like inorganic filler is blended with a rubber component composed of butyl rubber, epichlorohydrin rubber, and conjugated diene rubber. A method of using the rubber composition as an inner liner is disclosed, and the inner liner has good air permeation resistance, bending fatigue resistance and workability, and improved durability at low temperatures. That is.

Japanese Patent Laid-Open No. 7-40702 JP-A-7-81306 JP 2002-88209 A

  However, even with the method disclosed in Japanese Patent Application Laid-Open No. 2002-88209, due to the increase in the blending amount of butyl rubber and filler, the workability at the time of molding the tire described above and the air entering between the inner liner and the ply are increased. Thus, there is still room for improvement in order to achieve an improvement in air permeation resistance and a corresponding reduction in tire weight.

  Accordingly, an object of the present invention is to provide a pneumatic tire provided with an inner liner using a rubber composition having improved air permeation resistance while solving the problems of the prior art and maintaining workability during production. There is to do.

  As a result of intensive studies to achieve the above object, the present inventor has determined that the amount of a specific aromatic vinyl compound in place of a normal softener such as an aroma oil for a rubber component containing a butyl rubber in an inner liner. By using a rubber composition comprising a low molecular weight aromatic vinyl compound-conjugated diene compound copolymer or conjugated diene compound polymer having a vinyl bond amount and a weight average molecular weight of a conjugated diene compound portion, at the time of tire production It was found that the air permeation resistance of the tire can be improved while maintaining the workability, and the present invention has been completed.

That is, the pneumatic tire of the present invention has a pair of bead portions and a pair of sidewall portions, and a tread portion connected to both sidewall portions, and extends in a toroidal shape between the pair of bead portions. A carcass that reinforces each part, a belt composed of at least two belt layers arranged on the outer side in the tire radial direction of the crown part of the carcass, and an inner liner arranged on the inner surface of the tire inside the carcass,
In the inner liner, the amount of aromatic vinyl compound is 0 to 80% by mass with respect to 100 parts by mass of the rubber component (A) composed of 70 to 100% by mass of butyl rubber and 0 to 30% by mass of diene rubber. Aromatic vinyl compound-conjugated diene compound copolymer or conjugated diene compound polymer having a vinyl bond amount of 5 to 80% by mass in the compound portion, and having a polystyrene-reduced weight average molecular weight measured by gel permeation chromatography of 5,000 to A rubber composition comprising 1 to 20 parts by mass of a 200,000 low molecular weight polymer (B) is used.

  In a preferred example of the pneumatic tire of the present invention, the low molecular weight polymer (B) has at least one functional group. Here, in the pneumatic tire of the present invention, the low molecular weight polymer (B) is preferably modified with a tin-containing compound, a silicon-containing compound or a nitrogen-containing compound.

  In another preferred embodiment of the pneumatic tire of the present invention, the aromatic vinyl compound of the low molecular weight polymer (B) is styrene.

  In another preferred embodiment of the pneumatic tire of the present invention, the conjugated diene compound of the low molecular weight polymer (B) is 1,3-butadiene.

  In another preferred embodiment of the pneumatic tire of the present invention, the rubber composition further contains carbon black and / or an inorganic filler.

  In another preferred embodiment of the pneumatic tire of the present invention, the rubber composition optionally contains a softening agent (C), and the blending amount of the softening agent (C) and the low molecular weight polymer (B). Is in the range of 1 to 20 parts by mass with respect to 100 parts by mass of the rubber component (A).

  In the pneumatic tire of the present invention, the low molecular weight polymer (B) preferably has a polystyrene equivalent weight average molecular weight measured by gel permeation chromatography of 30,000 to 150,000, and more preferably 50,000 to 150,000.

  In the pneumatic tire of the present invention, when the low molecular weight polymer (B) has at least one functional group, the low molecular weight polymer (B) is measured by gel permeation chromatography before introducing the functional group. The polystyrene-reduced weight average molecular weight is preferably 5,000 to 200,000.

  According to the present invention, for the rubber component (A) containing butyl rubber in the inner liner, the amount of the specific aromatic vinyl compound, the vinyl bond amount of the conjugated diene compound portion, and the weight average instead of the usual softener By using the rubber composition formed by blending the low molecular weight polymer (B) having a molecular weight, it is possible to provide a pneumatic tire with improved air permeation resistance while maintaining workability during production. .

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a partial cross-sectional view of an example of the pneumatic tire of the present invention. The tire shown in FIG. 1 has a pair of bead portions 1 and a pair of sidewall portions 2, and a tread portion 3 connected to both sidewall portions, and extends in a toroidal shape between the pair of bead portions 1. A carcass 4 that reinforces each of these parts 1, 2, 3, a belt 5 composed of at least two belt layers arranged on the outer side in the tire radial direction of the crown part of the carcass 4, and an inner surface of the tire inside the carcass 4 And an inner liner 6 disposed on the surface.

  In addition, the carcass 4 of the illustrated tire is composed of one carcass ply formed by coating a plurality of cords arranged in parallel with a coating rubber (ply rubber), and the carcass 4 is connected to the bead portion 1. It consists of a main body portion extending in a toroidal shape between each of the embedded bead cores 7 and a folded portion wound around each bead core 7 radially outward from the inner side in the tire width direction to the outer side. The ply number and structure of the carcass 4 are not limited to this.

  Furthermore, although the belt 5 of the illustrated tire is composed of two belt layers, the number of belt layers constituting the belt 5 is not limited to this in the tire of the present invention. Here, the belt layer is usually composed of a rubberized layer of a belt cord extending obliquely with respect to the tire equatorial plane, and the two belt layers are configured such that the belt cords constituting the belt layer sandwich the tire equatorial plane from each other. The belts 5 are laminated so as to intersect with each other. Furthermore, in the illustrated tire, a belt reinforcing layer 8 is disposed so as to cover the entire belt 5 on the outer side in the tire radial direction of the belt 5, and the belt reinforcing layer 8 is usually substantially in the tire circumferential direction. It consists of rubberized layers of cords arranged in parallel. In the tire of the present invention, the belt reinforcing layer 8 is not necessarily provided, and a belt reinforcing layer having a different structure and number of layers can be provided.

  In the pneumatic tire of the present invention, the amount of the aromatic vinyl compound is based on 100 parts by mass of the rubber component (A) composed of 70 to 100% by mass of butyl rubber and 0 to 30% by mass of diene rubber. Is an aromatic vinyl compound-conjugated diene compound copolymer or conjugated diene compound polymer in which the amount of vinyl bonds in the conjugated diene compound portion is 5 to 80% by mass, and gel permeation chromatography It is necessary to use a rubber composition in which 1 to 20 parts by mass of a low molecular weight polymer (B) having a measured polystyrene equivalent weight average molecular weight of 5,000 to 200,000 is blended.

  The rubber composition used for the inner liner that constitutes the pneumatic tire of the present invention has an aromatic vinyl compound content of 0 to 80% by mass instead of a normal softener such as aroma oil, and a vinyl bond in the conjugated diene compound portion. An aromatic vinyl compound-conjugated diene compound copolymer or conjugated diene compound polymer having an amount of 5 to 80% by mass and having a polystyrene equivalent weight average molecular weight of 5,000 to 200,000 measured by gel permeation chromatography Although the blend (B) is used, since the low molecular weight polymer (B) is in a liquid state, workability at the time of tire production is good as in the case of using a normal softener. Furthermore, since the low molecular weight polymer (B) has a carbon-carbon double bond in the conjugated diene compound portion, the conjugated diene compound portion and sulfur form a crosslink during the vulcanization step, and the rubber component (A ) And a three-dimensional network structure. Therefore, since the pneumatic tire of the present invention uses a rubber composition in which a low molecular weight polymer (B) capable of forming a three-dimensional network structure together with the rubber component (A) is used for the inner liner, the air permeation resistance is high. It will be improved.

  In the pneumatic tire of the present invention, the rubber component (A) of the rubber composition used for the inner liner is composed of 70 to 100% by mass of butyl rubber and 0 to 30% by mass of diene rubber. Examples of the butyl rubber include butyl rubber (IIR), halogenated butyl rubber, and the like. When the ratio of the butyl rubber in the rubber component (A) is less than 70% by mass, the tire has sufficient air permeation resistance. Cannot be secured. Further, when the rubber component (A) contains a rubber component other than butyl rubber, diene rubber is included. The diene rubber is not particularly limited, and natural rubber, polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), ethylene-propylene-diene rubber (EPDM). Chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), and the like. Among these, natural rubber, polyisoprene rubber, styrene-butadiene copolymer rubber, and polybutadiene rubber are preferable. In addition, the said diene rubber may be used individually by 1 type, and may blend and use 2 or more types.

  In the pneumatic tire of the present invention, the rubber composition used for the inner liner has an aromatic vinyl compound content of 0 to 80% by mass and a vinyl bond content of the conjugated diene compound part of 5 to 80% by mass. -Low molecular weight polymer (B) having a polystyrene-reduced weight average molecular weight of 5,000 to 200,000 as measured by gel permeation chromatography, which is a conjugated diene compound copolymer or a conjugated diene compound polymer, is 100 masses of the rubber component (A). It is necessary to contain 1 to 20 parts by mass, and preferably 1 to 15 parts by mass. When the content of the low molecular weight polymer (B) is less than 1 part by mass, although air permeation resistance is obtained, workability of the rubber composition is deteriorated and sufficient productivity cannot be obtained. Further, if the content of the low molecular weight polymer (B) exceeds 20 parts by mass, the workability of the rubber composition is improved, while the air permeation resistance is lowered, and it is a sufficient function as an inner liner. Will not demonstrate.

  The low molecular weight polymer (B) needs to have an aromatic vinyl compound bond amount of 0 to 80% by mass or less. When the binding amount of the aromatic vinyl compound exceeds 80% by mass, it becomes difficult to ensure the workability of the rubber composition, and further, the loss tangent (tan δ) of the rubber composition is reduced.

  Moreover, the said low molecular weight polymer (B) requires that the vinyl bond amount of a conjugated diene compound part is 5-80 mass%. If the vinyl bond content of the conjugated diene compound part is less than 5% by mass or exceeds 80% by mass, it becomes difficult to ensure the workability of the rubber composition, and furthermore, the loss tangent (tan δ) of the rubber composition Will be reduced.

  Further, the low molecular weight polymer (B) requires that the polystyrene-equivalent weight average molecular weight measured by gel permeation chromatography (GPC) is 5,000 to 200,000, preferably 30,000 to 150,000, and preferably 50,000 to 150,000. More preferably. The rubber composition in which the low molecular weight polymer (B) having a polystyrene-reduced weight average molecular weight within the above specified range is in a liquid state, and therefore the normal softener is used. Compared with workability. Here, when the weight average molecular weight in terms of polystyrene is less than 5,000, the effect of improving air permeability is small, while when it exceeds 200,000, the effect of improving air permeability is increased, but the role as a softening agent is insufficient. As a result, the workability of the rubber composition deteriorates and sufficient productivity cannot be obtained. When the low molecular weight polymer (B) has at least one functional group, the low molecular weight polymer (B) has a polystyrene-equivalent weight average molecular weight measured by gel permeation chromatography before introducing the functional group. It is preferably 5,000 to 200,000. In this case, a sufficient effect as a softening agent can be easily obtained by setting the weight average molecular weight after introduction of the functional group in the range of 5,000 to 200,000.

  The low molecular weight polymer (B) preferably has at least one functional group in the molecule, and the functional group is preferably a functional group having an affinity with a filler such as carbon black, and tin. More preferred are functional groups containing, functional groups containing silicon, and functional groups containing nitrogen. When the low molecular weight polymer (B) has at least one functional group in the molecule, the affinity for the filler is higher than that of the low molecular weight polymer (B) having no functional group. When the low molecular weight polymer (B) has at least one functional group in the molecule, the low molecular weight polymer (B) is modified with a modifier such as a tin-containing compound, a silicon-containing compound, or a nitrogen-containing compound. , A tin-containing functional group, a silicon-containing functional group, a nitrogen-containing functional group and the like are preferably used.

  The low molecular weight polymer (B) is not particularly limited. For example, in a hydrocarbon solvent inert to the polymerization reaction, only a mixture of a monomeric aromatic vinyl compound and a conjugated diene compound or only a conjugated diene compound. In the case of introducing at least one functional group into the molecule of the low molecular weight polymer (B), (1) using a polymerization initiator as a monomer (co) After polymerization, a (co) polymer having a polymerization active site is produced, and then the polymerization active site is modified with various modifiers, or (2) a monomer is used with a polymerization initiator having a functional group. It can be obtained by a (co) polymerization method. Here, examples of the aromatic vinyl compound include styrene, p-methylstyrene, m-methylstyrene, p-tert-butylstyrene, α-methylstyrene, chloromethylstyrene, vinyltoluene and the like. Among these, styrene Is preferred. On the other hand, examples of the conjugated diene compound include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, and among these, 1,3-butadiene is preferable.

  As a polymerization initiator used for the synthesis | combination of the said low molecular weight polymer (B), an organolithium compound is preferable and hydrocarbyl lithium and a lithium amide compound are still more preferable. In addition, when an organic lithium compound is used as the polymerization initiator, the low molecular weight polymer (B) is produced by anionic polymerization. When hydrocarbyl lithium is used as the polymerization initiator, a (co) polymer having a hydrocarbyl group at the polymerization initiation terminal and the other terminal being a polymerization active site is obtained. On the other hand, when a lithium amide compound is used as a polymerization initiator, a (co) polymer having a nitrogen-containing functional group at the polymerization initiation terminal and the other terminal being a polymerization active site is obtained, and the (co) polymer is The low molecular weight polymer (B) having at least one functional group in the present invention can be used without being modified with a modifier. In addition, the usage-amount of a polymerization initiator has the preferable range of 0.2-20 mmol per 100g of monomers.

  Examples of the hydrocarbyl lithium include ethyl lithium, n-propyl lithium, isopropyl lithium, n-butyl lithium, sec-butyl lithium, tert-octyl lithium, n-decyl lithium, phenyl lithium, 2-naphthyl lithium, and 2-butyl-phenyl. Examples include lithium, 4-phenyl-butyllithium, cyclohexyllithium, cyclopentyllithium, reaction products of diisopropenylbenzene and butyllithium, and among these, ethyllithium, n-propyllithium, isopropyllithium, n-butyl Alkyl lithium such as lithium, sec-butyl lithium, tert-octyl lithium and n-decyl lithium is preferable, and n-butyl lithium is particularly preferable.

  On the other hand, the lithium amide compounds include lithium hexamethylene imide, lithium pyrrolidide, lithium piperidide, lithium heptamethylene imide, lithium dodecamethylene imide, lithium dimethylamide, lithium diethylamide, lithium dipropylamide, lithium dibutylamide, lithium Dihexylamide, lithium diheptylamide, lithium dioctylamide, lythym-2-ethylhexylamide, lithium didecylamide, lithium-N-methylpiperazide, lithium ethylpropylamide, lithium ethylbutyramide, lithium methylbutyramide, lithium ethylbenzylamide, Examples include lithium methylphenethyl amide, among these, lithium hexamethylene imide, lithium pyrrolidide, lithium Cyclic lithium amide compounds such as piperidide, lithium heptamethylene imide and lithium dodecamethylene imide are preferred, and lithium hexamethylene imide and lithium pyrrolidide are particularly preferred.

（式中、Ｒ¹は、それぞれ独立して炭素数１〜１２のアルキル基、シクロアルキル基又はアラルキル基である）で表される置換アミノ基、及び下記式(II)：

（式中、Ｒ²は、３〜１６のメチレン基を有するアルキレン基、置換アルキレン基、オキシアルキレン基又はＮ-アルキルアミノ-アルキレン基を示す）で表される環状アミノ基である］で表されるリチウムアミド化合物を用いることで、式(I)で表される置換アミノ基及び式(II)で表される環状アミノ基からなる群から選択される少なくとも一種の窒素含有官能基が導入された低分子量重合体（Ｂ）が得られる。 As the lithium amide compound, the formula: Li-AM [wherein AM represents the following formula (I):

(Wherein R ¹ is each independently an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group or an aralkyl group), and the following formula (II):

Wherein R ² is a cyclic amino group represented by an alkylene group having 3 to 16 methylene groups, a substituted alkylene group, an oxyalkylene group or an N-alkylamino-alkylene group. By using the lithium amide compound, at least one nitrogen-containing functional group selected from the group consisting of a substituted amino group represented by the formula (I) and a cyclic amino group represented by the formula (II) was introduced. A low molecular weight polymer (B) is obtained.

In the formula (I), R ¹ is an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group, or an aralkyl group. Specifically, a methyl group, an ethyl group, a butyl group, an octyl group, a cyclohexyl group, a 3- Preferable examples include phenyl-1-propyl group and isobutyl group. R ¹ may be the same or different.

In the formula (II), R ² is an alkylene group having 3 to 16 methylene groups, a substituted alkylene group, an oxyalkylene group or an N-alkylamino-alkylene group. Here, the substituted alkylene group includes a mono- to octa-substituted alkylene group, and examples of the substituent include a linear or branched alkyl group having 1 to 12 carbon atoms, a cycloalkyl group, a bicycloalkyl group, and an aryl group. Groups and aralkyl groups. R ² is specifically preferably a trimethylene group, a tetramethylene group, a hexamethylene group, an oxydiethylene group, an N-alkylazadiethylene group, a dodecamethylene group, a hexadecamethylene group, or the like.

  The lithium amide compound may be preliminarily prepared from a secondary amine and a lithium compound and used for the polymerization reaction, but may be generated in a polymerization system. Here, examples of the secondary amine include dimethylamine, diethylamine, dibutylamine, dioctylamine, dicyclohexylamine, diisobutylamine and the like, as well as azacycloheptane (ie, hexamethyleneimine), 2- (2-ethylhexyl) pyrrolidine, 3 -(2-propyl) pyrrolidine, 3,5-bis (2-ethylhexyl) piperidine, 4-phenylpiperidine, 7-decyl-1-azacyclotridecane, 3,3-dimethyl-1-azacyclotetradecane, 4- Dodecyl-1-azacyclooctane, 4- (2-phenylbutyl) -1-azacyclooctane, 3-ethyl-5-cyclohexyl-1-azacycloheptane, 4-hexyl-1-azacycloheptane, 9-isoamyl -1-Azacycloheptadecane, 2-methyl-1-azacycloheptadec-9-ene, 3-isobutyl-1-azacyclododecane 2-Methyl-7-tert-butyl-1-azacyclododecane, 5-nonyl-1-azacyclododecane, 8- (4′-methylphenyl) -5-pentyl-3-azabicyclo [5.4.0] ] Undecane, 1-butyl-6-azabicyclo [3.2.1] octane, 8-ethyl-3-azabicyclo [3.2.1] octane, 1-propyl-3-azabicyclo [3.2.2] nonane And cyclic amines such as 3- (t-butyl) -7-azabicyclo [4.3.0] nonane and 1,5,5-trimethyl-3-azabicyclo [4.4.0] decane. On the other hand, as the lithium compound, the above hydrocarbyl lithium can be used.

  The method for producing the low molecular weight polymer (B) using the polymerization initiator is not particularly limited as described above. For example, the monomer is polymerized in a hydrocarbon solvent inert to the polymerization reaction. Thus, the low molecular weight polymer (B) can be produced. Here, hydrocarbon solvents inert to the polymerization reaction include propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, cyclohexane, propene, 1-butene, isobutene, trans-2-butene, cis -2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene, ethylbenzene and the like. These may be used alone or in combination of two or more.

  The above polymerization reaction may be carried out in the presence of a randomizer. The randomizer can control the microstructure of the conjugated diene compound portion of the copolymer. More specifically, the randomizer can control the vinyl bond amount of the conjugated diene compound portion of the copolymer, The conjugated diene compound unit and the aromatic vinyl compound unit are randomized. Examples of the randomizer include dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, bistetrahydrofurylpropane, triethylamine, pyridine, N-methylmorpholine, N, N, N ′, N′-tetramethylethylenediamine, 1 , 2-dipiperidinoethane, potassium-t-amylate, potassium-t-butoxide, sodium-t-amylate and the like. The amount of these randomizers used is preferably in the range of 0.01 to 100 molar equivalents per mole of polymerization initiator.

  The anionic polymerization is preferably carried out by solution polymerization, and the concentration of the monomer in the polymerization reaction solution is preferably in the range of 5 to 50% by mass, more preferably in the range of 10 to 30% by mass. Further, the polymerization mode is not particularly limited, and may be batch type or continuous type.

  The polymerization temperature of the anionic polymerization is preferably in the range of 0 to 150 ° C, more preferably in the range of 20 to 130 ° C. The polymerization can be carried out under a generated pressure, but it is usually preferred to carry out the polymerization under a pressure sufficient to keep the monomer used in a substantially liquid phase. Here, when the polymerization reaction is carried out under a pressure higher than the generated pressure, it is preferable to pressurize the reaction system with an inert gas. Moreover, it is preferable to use what removed reaction-inhibiting substances, such as water, oxygen, a carbon dioxide, and a protic compound, as raw materials, such as a monomer used for superposition | polymerization, a polymerization initiator, and a solvent.

  Further, when the polymerization active site of the (co) polymer having the polymerization active site is modified with a modifier, the modifier used is preferably a tin-containing compound, a silicon-containing compound or a nitrogen-containing compound. In this case, a tin-containing functional group, a silicon-containing functional group, or a nitrogen-containing functional group can be introduced by a modification reaction.

  The nitrogen-containing compound that can be used as the modifier preferably has a substituted or unsubstituted amino group, amide group, imino group, imidazole group, nitrile group, or pyridyl group. Suitable nitrogen-containing compounds as the modifier include isocyanate compounds such as diphenylmethane diisocyanate, crude MDI, trimethylhexamethylene diisocyanate, tolylene diisocyanate, 4- (dimethylamino) benzophenone, 4- (diethylamino) benzophenone, 4-dimethylamino. Examples include benzylideneaniline, 4-dimethylaminobenzylidenebutylamine, dimethylimidazolidinone, N-methylpyrrolidone and the like.

［式中、Ａは(チオ)エポキシ、(チオ)インシアネート、(チオ)ケトン、(チオ)アルデヒド、イミン、アミド、イソシアヌル酸トリエステル、(チオ)カルボン酸ヒドロカルビルエステル、(チオ)カルボン酸の金属塩、カルボン酸無水物、カルボン酸ハロゲン化物、炭酸ジヒドロカルビルエステル、環状三級アミン、非環状三級アミン、ニトリル、ピリジン、スルフィド及びマルチスルフィドの中から選ばれる少なくとも一種の官能基を有する一価の基で；Ｒ³は単結合又は二価の不活性炭化水素基で；Ｒ⁴及びＲ⁵は、それぞれ独立に炭素数１〜２０の一価の脂肪族炭化水素基又は炭素数６〜１８の一価の芳香族炭化水素基で；ｎは０〜２の整数であり；ＯＲ⁵が複数ある場合、複数のＯＲ⁵はたがいに同一でも異なっていてもよく；また分子中には活性プロトン及びオニウム塩は含まれない］で表されるヒドロカルビルオキシシラン化合物及びその部分縮合物、並びに、下記式(IV)：
Ｒ⁶ _p−Ｓｉ−(ＯＲ⁷)_4-p ・・・ (IV)
［式中、Ｒ⁶及びＲ⁷は、それぞれ独立して炭素数１〜２０の一価の脂肪族炭化水素基又は炭素数６〜１８の一価の芳香族炭化水素基であり；ｐは０〜２の整数であり；ＯＲ⁷が複数ある場合、複数のＯＲ⁷はたがいに同一でも異なっていてもよく；また分子中には活性プロトン及びオニウム塩は含まれない］で表されるヒドロカルビルオキシシラン化合物及びその部分縮物も好ましい。 Examples of the silicon-containing compound that can be used as the modifier include the following formula (III):

[Wherein A represents (thio) epoxy, (thio) inocyanate, (thio) ketone, (thio) aldehyde, imine, amide, isocyanuric acid triester, (thio) carboxylic acid hydrocarbyl ester, (thio) carboxylic acid One having at least one functional group selected from metal salts, carboxylic acid anhydrides, carboxylic acid halides, carbonic acid dihydrocarbyl esters, cyclic tertiary amines, acyclic tertiary amines, nitriles, pyridines, sulfides and multisulfides. R ³ is a single bond or a divalent inert hydrocarbon group; R ⁴ and R ⁵ are each independently a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms or 6 to 6 carbon atoms. 18 monovalent aromatic hydrocarbon group; n is an integer from 0 to 2; if OR ⁵ have multiple or different and a plurality of OR ⁵ is identical to each other; in addition the molecule active And a partial condensate thereof, and the following formula (IV):
R ⁶ _p -Si- (OR ⁷ ) _4-p (IV)
[Wherein, R ⁶ and R ⁷ are each independently a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms; It is ~ 2 integer; If oR ⁷ there are a plurality, a plurality of oR ⁷ each other may be the same or different; hydrocarbyloxy represented by not included active proton and onium salt are also in the molecule] Silane compounds and partial condensates thereof are also preferred.

  In the formula (III), among the functional groups in A, imine includes ketimine, aldimine and amidine, and (thio) carboxylic acid ester includes unsaturated carboxylic acid ester such as acrylate and methacrylate, Secondary amines include N, N-disubstituted aromatic amines such as N, N-disubstituted anilines, and cyclic tertiary amines can include (thio) ethers as part of the ring. Examples of the metal of the metal salt of (thio) carboxylic acid include alkali metals, alkaline earth metals, Al, Sn, and Zn.

The divalent inert hydrocarbon group in R ³ is preferably an alkylene group having 1 to 20 carbon atoms. 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, a decamethylene group, and a dodecamethylene group.

Examples of R ⁴ and R ⁵ include an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, an aryl group having 6 to 18 carbon atoms, and an aralkyl group having 7 to 18 carbon atoms. Here, the alkyl group and alkenyl group may be linear, branched, or cyclic, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl, tert-butyl, pentyl, hexyl, octyl, decyl, dodecyl, cyclopentyl, cyclohexyl, vinyl, propenyl, allyl, hexenyl, octenyl, cyclopentenyl Group, cyclohexenyl group and the like. The aryl group may have a substituent such as a lower alkyl group on the aromatic ring, and examples thereof include a phenyl group, a tolyl group, a xylyl group, and a naphthyl group. Furthermore, the aralkyl group may have a substituent such as a lower alkyl group on the aromatic ring, and examples thereof include a benzyl group, a phenethyl group, and a naphthylmethyl group.

  In the formula (III), n is an integer of 0 to 2, but 0 is preferable, and it is necessary that this molecule does not have active protons and onium salts.

  Examples of the hydrocarbyloxysilane compound represented by the formula (III) include (thio) epoxy group-containing hydrocarbyloxysilane compounds such as 2-glycidoxyethyltrimethoxysilane, 2-glycidoxyethyltriethoxysilane, (2 -Glycidoxyethyl) methyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, (3-glycidoxypropyl) methyldimethoxysilane, 2- (3,4-epoxy Cyclohexyl) ethyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltriethoxysilane, 2- (3,4-epoxycyclohexyl) ethyl (methyl) dimethoxysilane and the epoxy groups in these compounds replaced with thioepoxy groups Of these, among these, 3-glycidoxypropyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane are particularly preferred.

  In addition, as imine group-containing hydrocarbyloxysilane compounds, N- (1,3-dimethylbutylidene) -3- (triethoxysilyl) -1-propanamine, N- (1-methylethylidene) -3- (triethoxy Silyl) -1-propanamine, N-ethylidene-3- (triethoxysilyl) -1-propanamine, N- (1-methylpropylidene) -3- (triethoxysilyl) -1-propanamine, N- (4-N, N-dimethylaminobenzylidene) -3- (triethoxysilyl) -1-propanamine, N- (cyclohexylidene) -3- (triethoxysilyl) -1-propanamine and their triethoxy Examples include trimethoxysilyl compounds, methyldiethoxysilyl compounds, ethyldiethoxysilyl compounds, methyldimethoxysilyl compounds, ethyldimethoxysilyl compounds corresponding to silyl compounds. Among these, N- (1-methylpropylidene) -3- (triethoxysilyl) -1-propanamine and N- (1,3-dimethylbutylidene) -3- (triethoxysilyl) -1 -Propanamine is particularly preferred.

  Further, the imine (amidine) group-containing compounds include 1- [3- (triethoxysilyl) propyl] -4,5-dihydroimidazole, 1- [3- (trimethoxysilyl) propyl] -4,5-dihydro. Imidazole, N- (3-triethoxysilylpropyl) -4,5-dihydroimidazole, N- (3-isopropoxysilylpropyl) -4,5-dihydroimidazole, N- (3-methyldiethoxysilylpropyl)- 4,5-dihydroimidazole and the like can be mentioned, and among these, N- (3-triethoxysilylpropyl) -4,5-dihydroimidazole is preferable.

  Furthermore, as the carboxylic acid ester group-containing compound, 3-methacryloyloxypropyltriethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropylmethyldiethoxysilane, 3-methacryloyloxypropyltri Examples include isopropoxysilane, and among these, 3-methacryloyloxypropyltrimethoxysilane is preferable.

  Examples of the isocyanate group-containing compound include 3-isocyanatopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, 3-isocyanatopropylmethyldiethoxysilane, and 3-isocyanatopropyltriisopropoxysilane. Of these, 3-isocyanatopropyltriethoxysilane is preferred.

  Further, examples of the carboxylic acid anhydride-containing compound include 3-triethoxysilylpropyl succinic anhydride, 3-trimethoxysilylpropyl succinic anhydride, 3-methyldiethoxysilylpropyl succinic anhydride, and the like. Among these, 3-triethoxysilylpropyl succinic anhydride is preferable.

  In addition, cyclic tertiary amine group-containing hydrocarbyloxysilane compounds include 3- (1-hexamethyleneimino) propyl (triethoxy) silane, 3- (1-hexamethyleneimino) propyl (trimethoxy) silane, and (1-hexamethylene). Imino) methyl (trimethoxy) silane, (1-hexamethyleneimino) methyl (triethoxy) silane, 2- (1-hexamethyleneimino) ethyl (triethoxy) silane, 2- (1-hexamethyleneimino) ethyl (trimethoxy) silane , 3- (1-pyrrolidinyl) propyl (triethoxy) silane, 3- (1-pyrrolidinyl) propyl (trimethoxy) silane, 3- (1-heptamethyleneimino) propyl (triethoxy) silane, 3- (1-dodecamethyleneimino ) Propyl (triethoxy) silane, 3- (1-hexamethyleneimino) propyl (diethoxy) methylsilane, 3- (1-he Xamethyleneimino) propyl (diethoxy) ethylsilane, 3- [10- (triethoxysilyl) decyl] -4-oxazoline and the like, among which 3- (1-hexamethyleneimino) propyl (triethoxy) silane and (1-Hexamethyleneimino) methyl (trimethoxy) silane is preferred.

  Furthermore, as the hydrocarbyloxysilane compound containing an acyclic tertiary amine group, 3-dimethylaminopropyl (triethoxy) silane, 3-dimethylaminopropyl (trimethoxy) silane, 3-diethylaminopropyl (triethoxy) silane, 3-diethylaminopropyl ( Trimethoxy) silane, 2-dimethylaminoethyl (triethoxy) silane, 2-dimethylaminoethyl (trimethoxy) silane, 3-dimethylaminopropyl (diethoxy) methylsilane, 3-dibutylaminopropyl (triethoxy) silane, and the like. Of these, 3-diethylaminopropyl (triethoxy) silane and 3-dimethylaminopropyl (triethoxy) silane are preferable.

  Still other hydrocarbyloxysilane compounds include 2- (trimethoxysilylethyl) pyridine, 2- (triethoxysilylethyl) pyridine, 2-cyanoethyltriethoxysilane, and the like.

  One of the hydrocarbyloxysilane compounds of the above formula (III) may be used alone, or two or more thereof may be used in combination. Moreover, the partial condensate of the said hydrocarbyl oxysilane compound can also be used.

In the formula (IV), R ⁶ and R ⁷ are as described for R ⁴ and R ⁵ in the formula (III), respectively.

  Examples of the hydrocarbyloxysilane compound represented by the formula (IV) include tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetraisopropoxysilane, tetra-n-butoxysilane, tetraisobutoxysilane, tetra -sec-butoxysilane, tetra-tert-butoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, butyl Trimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, dimethyldimethoxysilane, methylphenyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, divinyldimethoxy Sisilane, divinyldiethoxysilane and the like can be mentioned, and among these, tetraethoxysilane is particularly preferable.

  The hydrocarbyloxysilane compound of the formula (IV) may be used alone or in combination of two or more. Moreover, the partial condensate of these hydrocarbyl oxysilane compounds can also be used.

As the modifier, the following formula (V):
R ⁸ _a ZX _b ... (V)
[Wherein, R ⁸ each independently comprises an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, and an aralkyl group having 7 to 20 carbon atoms. Selected from the group; Z is tin or silicon; X is each independently chlorine or bromine; a is 0-3, b is 1-4, provided that a + b = 4. The coupling agent represented is also preferred. By modifying with the coupling agent of the formula (V), the cold flow resistance of the polymer (B) can be improved. The polymer (B) obtained by modifying with a coupling agent of the formula (V) has at least one tin-carbon bond or silicon-carbon bond.

Specific examples of R ^{8 in the} formula (V) include a methyl group, an ethyl group, an n-butyl group, a neophyll group, a cyclohexyl group, an n-octyl group, and a 2-ethylhexyl group. Specific examples of the coupling agent of the formula (V) include SnCl ₄ , R ⁸ SnCl ₃ , R ⁸ ₂ SnCl ₂ , R ⁸ ₃ SnCl, SiCl ₄ , R ⁸ SiCl ₃ , R ⁸ ₂ SiCl ₂ , R ⁸ ₃ SiCl and the like are preferable, and SnCl ₄ and SiCl ₄ are particularly preferable.

  The modification reaction of the polymerization active site by the modifying agent is preferably performed by a solution reaction, and the solution may contain a monomer used at the time of polymerization. The reaction mode of the modification reaction is not particularly limited, and may be a batch type or a continuous type. Furthermore, the reaction temperature of the modification reaction is not particularly limited as long as the reaction proceeds, and the reaction temperature of the polymerization reaction may be employed as it is. The amount of modifier used is preferably in the range of 0.25 to 3.0 mol, and more preferably in the range of 0.5 to 1.5 mol, with respect to 1 mol of the polymerization initiator used for the production of the copolymer.

  In the present invention, after the reaction solution containing the low molecular weight polymer (B) is dried to separate the low molecular weight polymer (B), the resulting low molecular weight polymer (B) is converted into the rubber component (A). The reaction solution containing the low molecular weight polymer (B) may be mixed with the rubber cement of the rubber component (A) in a solution state, and then dried to dry the rubber component (A) and the low molecular weight. A mixture (B) may be obtained.

  In the pneumatic tire of the present invention, the rubber composition used for the inner liner preferably further contains 50 to 250 parts by mass of the filler (D) with respect to 100 parts by mass of the rubber component (A). When the blending amount of the filler (D) is less than 50 parts by mass, the fracture characteristics and wear resistance of the vulcanized rubber are not sufficient, while when it exceeds 250 parts by mass, workability and low temperature tend to deteriorate. . Here, as the filler (D), carbon black and inorganic filler are preferable. The carbon black is preferably FEF, SRF, HAF, ISAF, or SAF grade, and more preferably HAF, ISAF, or SAF grade. On the other hand, examples of the inorganic filler include silica, alumina, clay, kaolin, mica, feldspar, talc, aluminum hydroxide, calcium carbonate and the like. Among these, silica is preferable. As the silica, wet silica and dry silica are preferable, and wet silica is more preferable. These reinforcing fillers (D) may be used individually by 1 type, and may mix and use 2 or more types.

  In the pneumatic tire of the present invention, the rubber composition used for the inner liner may optionally contain a softening agent (C). In this case, the total amount of the softener (C) and the low molecular weight polymer (B) is preferably in the range of 1 to 20 parts by mass with respect to 100 parts by mass of the rubber component (A). If the total amount of the softener (C) and the low molecular weight polymer (B) is within the specific range, the air permeability of the tire can be improved while maintaining the workability of the rubber composition. it can. Specific examples of the softening agent (C) include process oils such as paraffin oil, naphthenic oil, and aroma oil. Aromatic oil is preferable from the viewpoint of fracture characteristics and wear resistance, and low exothermicity. From the viewpoint of low temperature characteristics, naphthenic oil and paraffin oil are preferred.

  In the pneumatic tire of the present invention, the rubber composition used for the inner liner includes a rubber factory in addition to the rubber component (A), the low molecular weight polymer (B), the softening agent (C), and the filler (D). A compounding agent usually used in the industry, for example, an anti-aging agent, a silane coupling agent, a vulcanization accelerator, a vulcanization accelerator, a vulcanizer, and the like are appropriately selected within a range that does not impair the object of the present invention. Can be blended. As these compounding agents, commercially available products can be suitably used. The rubber composition is produced by blending the rubber component (A) with the low molecular weight polymer (B) and various compounding agents appropriately selected as necessary, kneading, heating, extruding and the like. can do.

  The pneumatic tire of the present invention can be manufactured by a conventional method by applying the above rubber composition to the inner liner. A tire using the rubber composition as an inner liner has good workability during production and excellent air permeation resistance. In addition, the pneumatic tire of the present invention can reduce the inner liner thickness as the air permeation resistance is improved. As a result, the weight of the tire is reduced, and the rolling resistance can be improved. Moreover, as gas with which this tire is filled, inert gas, such as nitrogen, argon, helium other than normal or the air which adjusted oxygen partial pressure, can be used.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

<Example of production of polymer (B-2)>
In a dry, nitrogen-substituted 800 mL pressure-resistant glass container, 1,3-butadiene in cyclohexane solution (16%) and styrene in cyclohexane solution (21%), 40 g of 1,3-butadiene monomer, styrene monomer Inject to 10 g, inject 0.66 mmol of 2,2-ditetrahydrofurylpropane, add 1.32 mmol of n-butyllithium (n-BuLi), and then polymerize in a hot water bath at 50 ° C. for 1.5 hours. Reaction was performed. The polymerization conversion rate at this time was almost 100%. Thereafter, 0.5 mL of an isopropanol solution (BHT concentration: 5% by mass) of 2,6-di-t-butyl-p-cresol (BHT) was added to the polymerization reaction system to stop the polymerization reaction, and further dried according to a conventional method. As a result, a polymer (B-2) having a weight average molecular weight of 80000 was obtained.

<Production Example of Polymer (B-1) and Polymer (B-3)>
A polymer (B-1) having a weight average molecular weight of 4000 and a polymerization average molecular weight are the same as the production example of the polymer (B-2) except that the amount of n-butyllithium as a polymerization initiator is changed. Of 500,000 (B-3) was obtained.

  The weight average molecular weight (Mw), microstructure, and bound styrene content of the polymers (B-1) to (B-3) produced as described above were measured by the following methods. The results are shown in Table 1.

(1) Weight average molecular weight (Mw)
Gel permeation chromatography [GPC: Tosoh HLC-8020, column: Tosoh GMH-XL (two in series), detector: differential refractometer (RI)], based on monodisperse polystyrene, The weight average molecular weight (Mw) in terms of polystyrene was determined.

(2) Microstructure and bound styrene content The microstructure of the polymer was determined by the infrared method (Morero method), and the bound styrene content of the polymer was determined from the integral ratio of the ¹ H-NMR spectrum.

Next, using the polymers (B-1) to (B-3) or the aroma oil, rubber compositions having the formulation shown in Table 2 were prepared. In addition to the compounding agents shown in Table 2, the rubber composition was compounded with a compounding agent that is usually used in the rubber industry in a range that does not impair the object of the present invention. Further, the Mooney viscosity [ML _{1 + 4} (130 ° C.)] of the obtained rubber composition was measured by the following method to evaluate workability, and further vulcanized rubber obtained by vulcanization under normal conditions. On the other hand, the air permeation resistance was measured by the following method. The results are shown in Table 2.

(3) Workability In accordance with JIS K 6300-1: 2001, the Mooney viscosity [ML _{1 + 4} (130 ° C.)] of the rubber composition was measured at 130 ° C., and the Mooney viscosity of the rubber composition was The product (the rubber composition of Comparative Example 1) was evaluated as workability, with “×” indicating that the Mooney viscosity was increased by 5% or more, and “◯” indicating the other. The rubber composition of Comparative Example 1 was expressed as an index with the Mooney viscosity being 100.

(4) Air permeation resistance The rubber composition of Comparative Example 1 was measured for air permeation resistance in accordance with Method A (differential pressure method) of "Gas Permeability Test Method for Plastic Films and Sheets" (JIS K 7126). The air permeation resistance was expressed as an index. A larger index value indicates better air permeation resistance.

  As a comprehensive judgment, a rubber composition having workability equivalent to that of the current product (comparative example 1 rubber composition) and air permeation resistance improved by 5% or more than that of the current product (comparative example 1 rubber composition). “◎” and the other rubber compositions were “x”.

* 1 Bromobutyl 2245 manufactured by JSR Corporation.
* 2 Asahi Carbon Co., Ltd., Asahi # 55 (N660).

  The rubber composition of Example 1 using a polymer (B-2) having a specific aromatic vinyl compound amount, a vinyl bond amount of a conjugated diene compound portion and a weight average molecular weight is the same as that of Comparative Example 1 using aroma oil. From comparison with the rubber composition, it was found that workability was sufficiently maintained and air permeation resistance was good.

  From the results of Comparative Examples 2 and 3, if the weight average molecular weight of the low molecular weight polymer (B) is less than 5,000, sufficient air permeation resistance cannot be secured, while the weight average molecular weight of the low molecular weight polymer (B) is low. When it exceeded 200,000, although the air permeation resistance increased, it was found that the role as a softening agent was insufficient and the workability deteriorated.

  From the results of Comparative Example 4, it was found that when the blending amount of the low molecular weight polymer (B) is less than 1 part by mass, the air permeability is obtained, but the workability is deteriorated.

  From the result of Comparative Example 5, the amount of the low molecular weight polymer (B) exceeds 20 parts by mass, and the total amount of the normal softener (C) and the low molecular weight polymer (B) is too high. It was found that while the workability was good, the air permeation resistance was lowered.

It is a fragmentary sectional view of an example of the pneumatic tire of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tread part 4 Carcass 5 Belt 6 Inner liner 7 Bead core 8 Belt reinforcement layer

Claims (10)

A carcass having a pair of bead portions and a pair of sidewall portions, and a tread portion connected to both sidewall portions, extending in a toroidal shape between the pair of bead portions, and reinforcing the respective portions; and In a pneumatic tire provided with a belt composed of at least two belt layers disposed on the outer side in the tire radial direction of the crown portion, and an inner liner disposed on the inner surface of the tire inside the carcass,
In the inner liner, the amount of aromatic vinyl compound is 0 to 80% by mass with respect to 100 parts by mass of the rubber component (A) composed of 70 to 100% by mass of butyl rubber and 0 to 30% by mass of diene rubber. Aromatic vinyl compound-conjugated diene compound copolymer or conjugated diene compound polymer having a vinyl bond amount of 5 to 80% by mass in the compound portion, and having a polystyrene-reduced weight average molecular weight measured by gel permeation chromatography of 5,000 to A pneumatic tire using a rubber composition comprising 1 to 20 parts by mass of a 200,000 low molecular weight polymer (B).   The pneumatic tire according to claim 1, wherein the low molecular weight polymer (B) has at least one functional group.   The pneumatic tire according to claim 2, wherein the low molecular weight polymer (B) is modified with a tin-containing compound, a silicon-containing compound, or a nitrogen-containing compound.   The pneumatic tire according to claim 1, wherein the aromatic vinyl compound of the low molecular weight polymer (B) is styrene.   The pneumatic tire according to claim 1, wherein the conjugated diene compound of the low molecular weight polymer (B) is 1,3-butadiene.   The pneumatic tire according to claim 1, wherein the rubber composition further contains carbon black and / or an inorganic filler.   The rubber composition optionally contains a softener (C), and the total amount of the softener (C) and the low molecular weight polymer (B) is 100 parts by weight of the rubber component (A). On the other hand, the range of 1-20 mass parts is a pneumatic tire of Claim 1 characterized by the above-mentioned.   The pneumatic tire according to claim 1, wherein the low molecular weight polymer (B) has a polystyrene-equivalent weight average molecular weight of 30,000 to 150,000 as measured by gel permeation chromatography.   The pneumatic tire according to claim 8, wherein the low molecular weight polymer (B) has a polystyrene-reduced weight average molecular weight of 50,000 to 150,000 as measured by gel permeation chromatography.   The pneumatic tire according to claim 2, wherein the low molecular weight polymer (B) has a polystyrene-equivalent weight average molecular weight of 5,000 to 200,000 as measured by gel permeation chromatography before introducing a functional group.

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