JP7188344B2 - pneumatic tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pneumatic tire excellent in steering stability, low rolling resistance, wet grip performance, low road noise and high-speed durability.

Pneumatic tires are required to be excellent in steering stability, fuel efficiency and durability. More specifically, they are required to be excellent in steering stability, low rolling resistance, wet grip performance, low road noise and high-speed durability. Desired. However, these required performances required for pneumatic tires are in a trade-off relationship, and it has been difficult to combine these performances at a high level.

Patent Document 1 discloses a rubber composition comprising a diene rubber containing a conjugated diene rubber obtained by reacting a conjugated diene polymer chain having an active terminal with a predetermined polyorganosiloxane, and silica and a silane coupling agent blended therein. to improve steering stability, low rolling resistance, and wet grip. However, pneumatic tires using this rubber composition have room for improvement in low road noise and high-speed durability.

Patent No. 6064953

An object of the present invention is to provide a pneumatic tire with improved handling stability, low rolling resistance, wet grip performance, low road noise and high-speed durability over conventional levels.

The pneumatic tire of the present invention for achieving the above object has a plurality of belt layers with the cord directions intersecting between the layers, and polyethylene terephthalate fiber cords are helically wound in the tire circumferential direction outside the belt layers in the tire radial direction. A pneumatic tire having a belt cover layer wound around a belt cover layer, and having an undertread and a cap tread on the outside in the tire radial direction, wherein the thickness of the undertread is 1.5 mm or more, and the rubber hardness of the undertread The ratio Hu/Hc between Hu and the rubber hardness Hc of the cap tread is 0.9 or less, and the cap tread is composed of a rubber composition in which 50 to 150 parts by mass of silica is blended with 100 parts by mass of diene rubber. The diene rubber contains 70% by mass or more of a conjugated diene rubber having a modifying group having at least one selected from a polyorganosiloxane structure, an aminosilane group, and a polysiloxane structure .

The pneumatic tire of the present invention has a belt cover layer in which a polyethylene terephthalate fiber cord is wound in the tire circumferential direction, has an undertread thickness of 1.5 mm or more, and has a rubber hardness ratio Hu/Hc between the undertread and the cap tread. is set to 0.9 or less, and the rubber composition constituting the cap tread contains 70% by mass or more of conjugated diene rubber and silica is blended into the diene rubber. Grip performance, low road noise, and high-speed durability can be improved beyond conventional levels.

（式（１）中、Ｒ_１～Ｒ_８は、炭素数１～６のアルキル基、または炭素数６～１２のアリール基であり、これらは互いに同一であっても相違していてもよい。Ｘ_１およびＸ_４は、炭素数１～６のアルキル基、炭素数６～１２のアリール基、炭素数１～５のアルコキシ基、および、エポキシ基を含有する炭素数４～１２の基からなる群より選ばれるいずれかの基であり、これらは互いに同一であっても相違していてもよい。Ｘ_２は、炭素数１～５のアルコキシ基、またはエポキシ基を含有する炭素数４～１２の基であり、複数あるＸ_２は互いに同一であっても相違していてもよい。Ｘ_３は、２～２０のアルキレングリコールの繰返し単位を含有する基であり、Ｘ_３が複数あるときは、それらは互いに同一であっても相違していてもよい。ｍは３～２００の整数、ｎは０～２００の整数、ｋは０～２００の整数である。） The conjugated diene rubber having the modifying group is formed by bonding the active terminal of the conjugated diene polymer chain having the active terminal with the polyorganosiloxane represented by the following general formula (1), and has the active terminal. The conjugated diene-based polymer chain has a polymer block A and a polymer block B formed continuously with the polymer block A, and the polymer block A contains 80 to 95% by mass of isoprene units and It is preferable that the polymer block B contains 5 to 20% by mass of aromatic vinyl units, has a weight average molecular weight of 500 to 15,000, and contains 1,3-butadiene units and aromatic vinyl units.

(In formula (1), R ₁ to R ₈ are alkyl groups having 1 to 6 carbon atoms or aryl groups having 6 to 12 carbon atoms, which may be the same or different. X ₁ and X ₄ are an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, and a group having 4 to 12 carbon atoms containing an epoxy group. Any group selected from the group, which may be the same or different X ₂ is an alkoxy group having 1 to 5 carbon atoms, or an epoxy group containing 4 to 12 carbon atoms and a plurality of X ₂ may be the same or different, X ₃ is a group containing 2 to 20 alkylene glycol repeating units, and when there are a plurality of X ₃ , they may be the same or different, m is an integer from 3 to 200, n is an integer from 0 to 200, and k is an integer from 0 to 200.)

The rubber composition constituting the cap tread contains 0.1 to 20 parts by mass of alkyltriethoxysilane having an alkyl of 7 to 20 carbon atoms with respect to the amount of silica compounded, thereby achieving low rolling resistance and Wet grip performance can be made more excellent. Further, by setting the CTAB adsorption specific surface area of the silica to 180 to 230 m ² /g, the wet grip performance and low rolling resistance can be further improved.

FIG. 1 is a cross-sectional view along the tire meridian line showing an example of an embodiment of the pneumatic tire of the present invention.

FIG. 1 is a cross-sectional view showing an example of an embodiment of a pneumatic tire. A pneumatic tire consists of a tread portion 1, a sidewall portion 2, and a bead portion 3.

In FIG. 1, two carcass layers 4 are formed by arranging reinforcing cords extending in the tire radial direction between the left and right bead portions 3 at predetermined intervals in the tire circumferential direction and embedding them in the rubber layer. A bead core 5 embedded in the bead portion 3 is folded back from the inner side to the outer side in the tire axial direction so that a bead filler 6 is sandwiched around the bead core 5 . An inner liner layer 7 is arranged inside the carcass layer 4 . On the outer peripheral side of the carcass layer 4 of the tread portion 1, a two-layer belt layer 8 is arranged in which reinforcing cords extending obliquely in the tire circumferential direction are arranged at predetermined intervals in the tire axial direction and embedded in the rubber layer. is set. The reinforcing cords of the two belt layers 8 intersect with each other in the direction of inclination with respect to the circumferential direction of the tire, that is, the direction of the cords being opposite to each other. A belt cover layer 9 is arranged on the outer peripheral side of the belt layer 8 . The belt cover layer 9 may be either a full cover type that covers the entire belt layer or an edge cover type that covers the end of the belt layer in the tire width direction, or both types may be combined. A tread portion 1 is arranged on the outer peripheral side of the belt cover layer 9, and the tread portion 1 is composed of a cap tread 10a and an undertread 10b.

The pneumatic tire has a plurality of belt layers 8 in which the cord direction intersects between the layers on the tire tread, has a belt cover layer 9 outside the belt layers 8 in the tire radial direction, and has a belt cover layer 9 outside the belt layers 8 in the tire radial direction. It has an undertread 10b and a cap tread 10a. Here, the belt layer 8 is composed of a plurality of layers in which reinforcing cords extending obliquely in the tire circumferential direction are arranged at predetermined intervals in the axial direction of the tire and embedded in the coat rubber. They are arranged so that their extending directions intersect each other. The inclination angle of the reinforcing cords with respect to the tire circumferential direction is set, for example, in the range of 10° to 40°. Steel cords, for example, are preferably used as the reinforcing cords of the belt layer 8 .

Furthermore, a belt cover layer 9 is provided on the outer peripheral side of the belt layer 8 for the purpose of improving high-speed durability and reducing road noise. The belt cover layer 9 contains organic fiber cords oriented in the tire circumferential direction. In the belt cover layer 9, the angle of the organic fiber cords with respect to the tire circumferential direction is set to 0° to 5°, for example. The belt cover layer 9 is preferably constructed by spirally winding a strip material in which at least one organic fiber cord is aligned and coated with a coating rubber in the tire circumferential direction, and particularly preferably has a jointless structure.

In the present invention, polyethylene terephthalate fiber cords (hereinafter sometimes referred to as “PET fiber cords”) are used as the organic fiber cords forming the belt cover layer 9 . By using PET fiber cords as the organic fiber cords forming the belt cover layer 9 in this manner, it is possible to effectively reduce road noise while maintaining good durability of the pneumatic tire. In the belt cover layer 9, PET fiber cords are coated with coat rubber.

The PET fiber cord preferably has a modulus of elasticity of 3.5 cN/(tex.%) to 5.5 cN/(tex.%) at 100° C. under a load of 2.0 cN/dtex.
If the modulus of elasticity under a load of 2.0 cN/dtex at 100° C. is less than 3.5 cN/(tex·%), it may not be possible to sufficiently reduce intermediate frequency road noise. If the modulus of elasticity of the PET fiber cord under a load of 2.0 cN/dtex at 100° C. exceeds 5.5 cN/(tex·%), the fatigue resistance of the cord may be reduced and the durability of the tire may be reduced. be. In the present invention, the elastic modulus [N / (tex %)] at 100 ° C. under a load of 2.0 cN / dtex conforms to JIS-L1017 "Chemical fiber tire cord test method", and the grip interval is 250 mm. , Perform a tensile test under the conditions of a tensile speed of 300 ± 20 mm / min, load - Calculated by converting the slope of the tangent line at the point corresponding to the load of 2.0 cN / dtex of the elongation curve into a value per tex .

Furthermore, when the PET fiber cord is used as the belt cover layer 9, the cord tension in the tire is preferably 0.9 cN/dtex or more, more preferably 1.5 cN/dtex to 2.0 cN/dtex. By setting the cord tension in the tire in this way, heat generation can be suppressed and tire durability can be improved. If the cord tension of the PET fiber cord in the tire is less than 0.9 cN/dtex, the peak of tan δ will increase, and there is a possibility that the effect of improving tire durability may not be sufficiently obtained. The cord tension of the PET fiber cord in the tire is measured at the inner side in the tire width direction of two or more rounds from the end of the strip material that constitutes the belt cover layer.

Further, the PET fiber cord preferably has a thermal shrinkage stress of 0.6 cN/tex or more at 100°C. By setting the thermal contraction stress at 100° C. in this way, road noise can be effectively reduced while maintaining good durability of the pneumatic tire more effectively. If the heat shrinkage stress of the PET fiber cord at 100° C. is less than 0.6 cN/tex, the hoop effect during running cannot be sufficiently improved, making it difficult to sufficiently maintain high-speed durability. Although the upper limit of the heat shrinkage stress at 100° C. of the PET fiber cord is not particularly limited, it is preferably 2.0 cN/tex, for example. In the present invention, the thermal shrinkage stress (cN/tex) at 100 ° C. conforms to JIS-L1017 "Chemical fiber tire cord test method", sample length 500 mm, heating conditions 100 ° C. x 5 minutes. is the heat shrinkage stress of the sample cord measured when heated at .

In order to obtain a PET fiber cord having the physical properties as described above, it is preferable to optimize the dipping treatment, for example. In other words, prior to the calendering process, the PET fiber cord is dipped with an adhesive. is preferably set in the range of 2.2×10 ⁻² N/tex to 6.7×10 ⁻² N/tex. As a result, the PET fiber cord can be imparted with the desired physical properties as described above. If the cord tension in the normalization process is less than 2.2×10 ⁻² N/tex, the cord elastic modulus will be low, ^and medium frequency road noise cannot be sufficiently reduced. If it is larger than ² N/tex, the cord elastic modulus increases and the fatigue resistance of the cord decreases.

The thickness of the undertread 10b arranged outside the belt layer 8 and the belt cover layer 9 in the tire radial direction or outside the belt cover layer 9 in the tire radial direction is 1.5 mm or more, preferably 1.7 to 2.5 mm. . Node noise can be reduced by setting the thickness of the undertread 10b to 1.5 mm or more. In addition, heat generation in the tread portion can be suppressed, and high-speed durability can be maintained and improved. The thickness of the undertread 10b is typically the thickness of the undertread at a portion corresponding to the central portion in the tire width direction. Note that when the circumferential grooves are arranged in the central portion in the tire width direction, the thickness of the undertread portion corresponding to the land portion near the central portion can be the thickness of the undertread.

As for the rubber hardness Hu of the undertread 10b, the ratio Hu/Hc to the rubber hardness Hc of the cap tread 10a is 0.9 or less, preferably 0.5 to 0.9, more preferably 0.7 to 0.9. is. By setting the rubber hardness ratio Hu/Hc between the undertread 10b and the cap tread 10a to 0.9 or less, node noise is increased as the rubber hardness Hc of the cap tread 10a is increased in order to improve steering stability. Even when the tire is under tread 10b, the rubber hardness ratio Hu of the undertread 10b can be made sufficiently small to suppress deterioration of node noise. In addition, by using PET fiber cords for the belt cover layer 9, node noise can be further reduced. As a result, both the steering stability and low node noise of the pneumatic tire can be achieved at a high level. The rubber hardness Hu of the undertread 10b and the rubber hardness Hc of the cap tread 10a refer to the hardness of rubber measured at a temperature of 20° C. with a durometer type A according to JIS K6253.

The rubber composition constituting the cap tread 10a, that is, the rubber composition for the cap tread, contains 100 parts by mass of diene rubber and 50 to 150 parts by mass of silica. By blending 50 to 150 parts by mass of silica, low rolling resistance and wet grip performance can be improved. The amount of silica compounded is preferably 70 to 130 parts by mass, more preferably 80 to 120 parts by mass. By blending 50 parts by mass or more of silica, steering stability, low rolling resistance, and wet grip performance can be improved. Further, deterioration of node noise can be suppressed by blending 150 parts by mass or less of silica.

Examples of silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. These may be used alone or in combination of two or more. The CTAB adsorption specific surface area of silica is not particularly limited, but is preferably 180 m ² /g or more and 230 m ² /g or less, more preferably 185 to 220 m ² /g, particularly preferably 190 to 210 m ² /g. Good to have. By setting the CTAB adsorption specific surface area of silica to 180 m ² /g or more, low rolling resistance and wet grip performance can be further improved. Further, by setting the CTAB adsorption specific surface area of silica to 230 m ² /g or less, the dispersibility of silica can be improved. In this specification, the CTAB specific surface area of silica is a value measured according to ISO 5794.

Alkyltriethoxysilane having an alkyl group of 7 to 20 carbon atoms is preferably blended with silica. By blending alkyltriethoxysilane, the dispersibility of silica in the rubber component can be improved, and the balance between low rolling resistance, wet grip performance, low node noise and high speed durability can be improved. In particular, low rolling resistance can be made excellent.

Examples of alkyl groups having 7 to 20 carbon atoms include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group and dodecyl group. Among them, an octyl group and a nonyl group are preferable from the viewpoint of compatibility with the rubber component.

Alkyltriethoxysilane having 7 to 20 carbon atoms is preferably blended in an amount of 0.1 to 20% by mass, more preferably 1 to 5% by mass, based on the amount of silica blended. If the amount of alkyltriethoxysilane is less than 0.1% by mass of the amount of silica, the dispersion of silica may not be sufficiently improved. If the compounded amount of alkyltriethoxysilane exceeds 20% by mass of the silica compounded amount, the steering stability deteriorates.

Furthermore, a silane coupling agent may be blended with silica. By blending the silane coupling agent, the dispersibility of silica in the rubber component can be improved, and the balance between low rolling resistance, wet grip performance, low node noise and high speed durability can be improved.

The type of silane coupling agent is not particularly limited as long as it can be used in silica-blended rubber compositions. Sulfur-containing silane coupling agents such as triethoxysilylpropyl)disulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane can be exemplified. .

The blending amount of the silane coupling agent is preferably 3 to 15% by mass, more preferably 5 to 10% by mass, based on the weight of silica. If the compounded amount of the silane coupling agent is less than 3% by mass of the silica compounded amount, the dispersion of silica may not be sufficiently improved. If the compounded amount of the silane coupling agent exceeds 15% by mass of the silica compounded amount, the silane coupling agents condense with each other, and the desired hardness and strength cannot be obtained in the rubber composition.

The diene rubber constituting the cap tread rubber composition contains 70% by mass or more of a conjugated diene rubber having a modifying group having at least one selected from a polyorganosiloxane structure, an amino group, a hydroxyl group, and a hydrocarbyl group. . Containing a conjugated diene rubber having such a modified group improves the affinity with silica, resulting in better low rolling resistance, wet grip performance, low road noise and high-speed durability. be able to. The content of the conjugated diene rubber having a modifying group is 70% by mass or more, preferably 75 to 100% by mass, more preferably 80 to 95% by mass.

The diene rubber of the cap tread rubber composition can contain other diene rubbers in addition to the conjugated diene rubber having a modifying group. Other diene rubbers include natural rubber, isoprene rubber, butadiene rubber, butyl rubber, unmodified styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene rubber (EPM), and the like.

The diene rubber of the cap tread rubber composition is preferably modified with at least one selected from polyorganosiloxane structures, amino groups, hydroxyl groups, epoxy groups, carbonyl groups, alkoxysilyl groups, silanol groups and hydrocarbyl groups. It is preferably an aromatic vinyl-conjugated diene copolymer. Examples of aromatic vinyl compounds include styrene, α-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene and 2,4,6-trimethylstyrene. Among them, styrene is preferred. These may be used alone or in combination of two or more.

Examples of conjugated diene compounds include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene and 1,3-hexadiene. Among them, 1,3-butadiene is preferred. These may be used alone or in combination of two or more.

The aromatic vinyl-conjugated diene copolymer preferably has an aromatic vinyl unit content of 38 to 48% by mass, a vinyl bond content of preferably 20 to 35% by mass, and a weight average molecular weight of preferably 500,000 to 800. , 000. As the aromatic vinyl-conjugated diene copolymer, a copolymer of styrene and 1,3-butadiene (styrene-butadiene copolymer) is preferred.

（式（１）中、Ｒ_１～Ｒ_８は、炭素数１～６のアルキル基、または炭素数６～１２のアリール基であり、これらは互いに同一であっても相違していてもよい。Ｘ_１およびＸ_４は、炭素数１～６のアルキル基、炭素数６～１２のアリール基、炭素数１～５のアルコキシ基、および、エポキシ基を含有する炭素数４～１２の基からなる群より選ばれるいずれかの基であり、これらは互いに同一であっても相違していてもよい。Ｘ_２は、炭素数１～５のアルコキシ基、またはエポキシ基を含有する炭素数４～１２の基であり、複数あるＸ_２は互いに同一であっても相違していてもよい。Ｘ_３は、２～２０のアルキレングリコールの繰返し単位を含有する基であり、Ｘ_３が複数あるときは、それらは互いに同一であっても相違していてもよい。ｍは３～２００の整数、ｎは０～２００の整数、ｋは０～２００の整数である。） A conjugated diene rubber having a modifying group is formed by bonding an active end of a conjugated diene polymer chain having an active end with a polyorganosiloxane represented by the following general formula (1), resulting in a conjugated diene rubber having an active end. The polymer chain has a polymer block A and a polymer block B formed in series with the polymer block A, and the polymer block A contains 80 to 95% by weight of isoprene units and aromatic vinyl units. It preferably contains 5 to 20% by weight, has a weight average molecular weight of 500 to 15,000, and polymer block B contains 1,3-butadiene units and aromatic vinyl units.

(In formula (1), R ₁ to R ₈ are alkyl groups having 1 to 6 carbon atoms or aryl groups having 6 to 12 carbon atoms, which may be the same or different. X ₁ and X ₄ are an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, and a group having 4 to 12 carbon atoms containing an epoxy group. Any group selected from the group, which may be the same or different X ₂ is an alkoxy group having 1 to 5 carbon atoms, or an epoxy group containing 4 to 12 carbon atoms and a plurality of X ₂ may be the same or different, X ₃ is a group containing 2 to 20 alkylene glycol repeating units, and when there are a plurality of X ₃ , they may be the same or different, m is an integer from 3 to 200, n is an integer from 0 to 200, and k is an integer from 0 to 200.)

A conjugated diene rubber having a modifying group can be produced by a method for producing a conjugated diene rubber comprising the following steps A, B and C in this order.
- Step A: By polymerizing a monomer mixture containing isoprene and aromatic vinyl, the isoprene unit content is 80 to 95% by mass, the aromatic vinyl unit content is 5 to 20% by mass, and the weight Step of forming a polymer block A having an active end and having an average molecular weight of 500 to 15,000 Step B: the polymer block A and a monomer mixture containing 1,3-butadiene and an aromatic vinyl; are mixed to continue the polymerization reaction to form a polymer block B having an active terminal in series with the polymer block A, thereby having the polymer block A and the polymer block B, the active Steps for obtaining a conjugated diene-based polymer chain having a terminal Step C: a step of reacting the active terminal of the conjugated diene-based polymer chain with the polyorganosiloxane represented by the formula (1) Hereinafter, each step will be described in detail. describe.

(Step A)
In step A, by polymerizing a monomer mixture containing isoprene and aromatic vinyl, the isoprene unit content is 80 to 95% by mass, the aromatic vinyl unit content is 5 to 20% by mass, and the weight A polymer block A having an active end is formed with an average molecular weight of 500 to 15,000.

The monomer mixture may contain only isoprene and aromatic vinyl, or may contain monomers other than isoprene and aromatic vinyl.
The aromatic vinyl is not particularly limited, but examples include 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, dimethylaminoethylstyrene and the like. Among these, styrene is preferred. These aromatic vinyls can be used alone or in combination of two or more.

Examples of monomers other than isoprene and vinyl aromatics include 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,3-pentadiene, and conjugated dienes other than isoprene such as 1,3-hexadiene; α,β-unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids or anhydrides such as acrylic acid, methacrylic acid, and maleic anhydride; Unsaturated carboxylic acid esters such as methyl methacrylate, ethyl acrylate, and butyl acrylate; 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, dicyclopentadiene, and 5-ethylidene-2-norbornene Non-conjugated dienes such as; Among these, 1,3-butadiene is preferred. These can be used alone or in combination of two or more.

The monomer mixture is preferably polymerized in an inert solvent.
The inert solvent is not particularly limited as long as it is commonly used in solution polymerization and does not inhibit the polymerization reaction. Specific examples thereof include linear aliphatic hydrocarbons such as butane, pentane, hexane, heptane, and 2-butene; alicyclic hydrocarbons such as cyclopentane, cyclohexane, and cyclohexene; benzene, toluene, and xylene. Aromatic hydrocarbons such as; The amount of the inert solvent used is, for example, 1 to 80% by mass, preferably 10 to 50% by mass, based on the concentration of the monomer mixture.

The monomer mixture is preferably polymerized with a polymerization initiator.
The polymerization initiator is not particularly limited as long as it can polymerize a monomer mixture containing isoprene and an aromatic vinyl to give a polymer chain having an active terminal. As a specific example thereof, for example, a polymerization initiator whose main catalyst is an organic alkali metal compound, an organic alkaline earth metal compound, a lanthanide series metal compound, or the like is preferably used. Examples of organic alkali metal compounds include organic monolithium compounds such as n-butyllithium, sec-butyllithium, t-butyllithium, hexyllithium, phenyllithium, and stilbenelithium; organic polyvalent lithium compounds such as 4-dilithio-2-ethylcyclohexane, 1,3,5-trilithiobenzene, and 1,3,5-tris(lithiomethyl)benzene; organic sodium compounds such as sodium naphthalene; potassium naphthalene, etc. organic potassium compounds; and the like. Examples of organic alkaline earth metal compounds include di-n-butylmagnesium, di-n-hexylmagnesium, diethoxycalcium, calcium distearate, di-t-butoxystrontium, diethoxybarium, and diisopropoxybarium. , diethylmercaptobarium, di-t-butoxybarium, diphenoxybarium, diethylaminobarium, barium distearate, and diketylbarium. Examples of polymerization initiators using lanthanum-based metal compounds as main catalysts include lanthanum-based metals such as lanthanum, cerium, praseodymium, neodymium, samarium, and gadolinium, and lanthanum-based metals composed of carboxylic acids, phosphorus-containing organic acids, and the like. and a polymerization initiator comprising a salt of the main catalyst and a promoter such as an alkylaluminum compound, an organoaluminum hydride compound, or an organoaluminum halide compound. Among these polymerization initiators, it is preferable to use an organic monolithium compound, and it is more preferable to use n-butyllithium. The organic alkali metal compound is reacted in advance with a secondary amine such as dibutylamine, dihexylamine, dibenzylamine, pyrrolidine, hexamethyleneimine, and heptamethyleneimine, and used as an organic alkali metal amide compound. good too. These polymerization initiators can be used alone or in combination of two or more.
The amount of the polymerization initiator to be used may be determined according to the target molecular weight. be.

The polymerization temperature for polymerizing the monomer mixture is, for example, -80 to +150°C, preferably 0 to 100°C, more preferably 20 to 90°C.
As a polymerization mode, any mode such as a batch system or a continuous system can be adopted. In addition, the binding pattern can be, for example, various binding patterns such as block, tapered, and random.
Methods for adjusting the content of 1,4-bonds in the isoprene units in polymer block A include, for example, a method of adding a polar compound to an inert solvent during polymerization and adjusting the amount added. Polar compounds include ether compounds such as dibutyl ether, tetrahydrofuran, and 2,2-di(tetrahydrofuryl)propane; tertiary amines such as tetramethylethylenediamine; alkali metal alkoxides; phosphine compounds; Among these, ether compounds and tertiary amines are preferred, and among them, those capable of forming a chelate structure with the metal of the polymerization initiator are more preferred, such as 2,2-di(tetrahydrofuryl)propane and tetramethylethylenediamine. is particularly preferred.
The amount of the polar compound to be used may be determined according to the target 1,4-bond content, and is preferably 0.01 to 30 mol, more preferably 0.05 to 10 mol, per 1 mol of the polymerization initiator. When the amount of the polar compound used is within the above range, the content of 1,4-bonds in the isoprene unit can be easily adjusted, and problems due to deactivation of the polymerization initiator are less likely to occur.

The content of 1,4-bonds in isoprene units in polymer block A is preferably 10 to 95% by mass, more preferably 20 to 95% by mass.
In the present specification, the content of 1,4-bonds in isoprene units refers to the ratio (% by mass) of isoprene units with 1,4-bonds to all isoprene units possessed by polymer block A.

The weight average molecular weight (Mw) of the polymer block A is 500 to 15,000 as a polystyrene-equivalent value measured by gel permeation chromatography (GPC). Above all, it is more preferably from 1,000 to 12,000, and even more preferably from 1,500 to 10,000.
If the weight average molecular weight of the polymer block A is less than 500, desired low heat build-up and wet performance are difficult to develop.
If the weight-average molecular weight of the polymer block A exceeds 15,000, there is a possibility that the desired low rolling resistance and the viscoelastic property, which is an index of wet performance, will be out of balance.
The molecular weight distribution represented by the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polymer block A is preferably from 1.0 to 1.5, more preferably from 1.0 to 1.3 is more preferred. When the value of the molecular weight distribution (Mw/Mn) of the polymer block A is within the above range, it becomes easier to produce a conjugated diene rubber having a modifying group. Both Mw and Mn are polystyrene equivalent values measured by GPC.

The isoprene unit content of polymer block A is 80 to 95% by mass, preferably 85 to 95% by mass.
The aromatic vinyl content of polymer block A is 5 to 20% by mass, preferably 5 to 15% by mass, more preferably 5 to 13% by mass.
The content of monomer units other than isoprene and aromatic vinyl in polymer block A is preferably 15% by mass or less, more preferably 10% by mass or less, and 6% by mass or less. is more preferred.

(Step B)
In step B, the polymer block A formed in step A described above is mixed with a monomer mixture containing 1,3-butadiene and an aromatic vinyl to continue the polymerization reaction to produce a polymer having an active terminal. By forming block B continuously with polymer block A, a conjugated diene-based polymer chain having the polymer block A and the polymer block B and having an active end is obtained.

Specific examples and preferred aspects of the aromatic vinyl are as described above.

The monomer mixture is preferably polymerized in an inert solvent.
The definition, specific examples and preferred embodiments of the inert solvent are as described above.
The amount of polymer block A having an active terminal to be used in forming polymer block B may be determined according to the target molecular weight. For example, it is in the range of 0.1 to 5 mmol, preferably 0.15 to 2 mmol, more preferably 0.2 to 1.5 mmol per 100 g.
The method of mixing the polymer block A with the monomer mixture containing 1,3-butadiene and the aromatic vinyl is not particularly limited. A polymer block A having an active terminal may be added, or a monomer mixture containing 1,3-butadiene and an aromatic vinyl may be added to a solution of the polymer block A having an active terminal. From the viewpoint of polymerization control, it is preferable to add polymer block A having an active terminal to the solution of the monomer mixture containing 1,3-butadiene and aromatic vinyl.
When polymerizing a monomer mixture containing 1,3-butadiene and an aromatic vinyl, the polymerization temperature is, for example, -80 to +150°C, preferably 0 to 100°C, more preferably 20 to 90°C. . As a polymerization mode, any mode such as a batch system or a continuous system can be adopted. Among them, a batch system is preferable.
The binding pattern of each monomer of the polymer block B can be, for example, various binding patterns such as block, tapered, and random. Among these, a random shape is preferred. When the bonding pattern of 1,3-butadiene and aromatic vinyl is randomized, the ratio of aromatic vinyl to the total amount of 1,3-butadiene and aromatic vinyl in the polymerization system should not be too high. , 1,3-butadiene and the aromatic vinyl are preferably fed into the polymerization system continuously or intermittently for polymerization.

The 1,3-butadiene unit content of polymer block B is not particularly limited, but is preferably 55 to 95% by mass, more preferably 55 to 90% by mass.
The aromatic vinyl unit content of polymer block B is not particularly limited, but is preferably 5 to 45% by mass, more preferably 10 to 45% by mass.

Polymer block B may further have other monomeric units in addition to 1,3-butadiene units and aromatic vinyl units. Other monomers used to constitute other monomer units include the above-mentioned "Examples of monomers other than isoprene other than aromatic vinyl" except for 1,3-butadiene. and isoprene.
The content of other monomer units in polymer block B is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less.

In order to adjust the vinyl bond content in the 1,3-butadiene units in the polymer block B, it is preferable to add a polar compound to the inert solvent during the polymerization. However, if a sufficient amount of a polar compound is added to the inert solvent during the preparation of polymer block A to adjust the vinyl bond content in the 1,3-butadiene units in polymer block B , it is not necessary to add a new polar compound. Specific examples of polar compounds used to adjust the vinyl bond content are the same as the polar compounds used to form polymer block A described above. The amount of the polar compound to be used may be determined according to the desired vinyl bond content, and is preferably adjusted in the range of 0.01 to 100 mol, more preferably 0.1 to 30 mol, per 1 mol of the polymerization initiator. do it. When the amount of the polar compound used is within this range, the vinyl bond content in the 1,3-butadiene unit can be easily adjusted, and problems due to deactivation of the polymerization initiator are less likely to occur.
The vinyl bond content in the 1,3-butadiene units in the polymer block B is preferably 10-90% by mass, more preferably 20-80% by mass, and particularly preferably 25-70% by mass.

Through steps A and B, a conjugated diene-based polymer chain having polymer block A and polymer block B and having an active end can be obtained.
From the viewpoint of productivity, the conjugated diene-based polymer chain having the active terminal is preferably composed of polymer block A and polymer block B, and the terminal of polymer block B is preferably the active terminal. It may have a plurality of blocks A, or may have other polymer blocks. Examples thereof include conjugated diene-based polymer chains having active ends, such as polymer block A-polymer block B-polymer block A, and blocks consisting of polymer block A-polymer block B-isoprene only. When forming a block consisting of only isoprene on the active terminal side of the conjugated diene polymer chain, the amount of isoprene used is preferably 10 to 100 mol per 1 mol of the polymerization initiator used in the initial polymerization reaction. , more preferably 15 to 70 mol, particularly preferably 20 to 35 mol.
The mass ratio of the polymer block A to the polymer block B in the conjugated diene polymer chain having the active terminal (when there are a plurality of polymer blocks A and B, the total mass of each is used as a reference) is ( The mass of polymer block A)/(mass of polymer block B) is preferably 0.001 to 0.1, more preferably 0.003 to 0.07, and 0.005 to 0. 0.05 is particularly preferred.
The molecular weight distribution represented by the ratio (Mw/Mn) between the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) of the conjugated diene-based polymer chain having an active terminal is 1.0 to 3.0. is preferred, 1.0 to 2.5 is more preferred, and 1.0 to 2.2 is particularly preferred. When the molecular weight distribution value (Mw/Mn) of the conjugated diene-based polymer chain having active terminals is within the above range, the production of the conjugated diene-based rubber having modifying groups is facilitated. Both Mw and Mn are polystyrene equivalent values measured by GPC.
In the conjugated diene polymer chain having the active terminal, the total content of isoprene units and 1,3-butadiene units is 50 to 99.995% by mass, and the content of aromatic vinyl units is 0.005 to 50% by mass. %, more preferably the total content of isoprene units and 1,3-butadiene units is 55 to 95% by mass, the content of aromatic vinyl units is 5 to 45% by mass, and the isoprene units and 1,3-butadiene units in a total content of 55 to 90% by mass, and an aromatic vinyl unit content of 10 to 45% by mass. Further, the vinyl bond content in the isoprene unit and the 1,3-butadiene unit in the conjugated diene polymer chain having an active terminal is the vinyl bond content in the 1,3-butadiene unit in the polymer block B described above. is similar to

(Process C)
Step C is a step of reacting the active terminal of the conjugated diene polymer chain obtained in Step B with a polyorganosiloxane represented by the following formula (1).

（式（１）中、Ｒ_１～Ｒ_８は、炭素数１～６のアルキル基、または炭素数６～１２のアリール基であり、これらは互いに同一であっても相違していてもよい。Ｘ_１およびＸ_４は、炭素数１～６のアルキル基、炭素数６～１２のアリール基、炭素数１～５のアルコキシ基、および、エポキシ基を含有する炭素数４～１２の基からなる群より選ばれるいずれかの基であり、これらは互いに同一であっても相違していてもよい。Ｘ_２は、炭素数１～５のアルコキシ基、またはエポキシ基を含有する炭素数４～１２の基であり、複数あるＸ_２は互いに同一であっても相違していてもよい。Ｘ_３は、２～２０のアルキレングリコールの繰返し単位を含有する基であり、Ｘ_３が複数あるときは、それらは互いに同一であっても相違していてもよい。ｍは３～２００の整数、ｎは０～２００の整数、ｋは０～２００の整数である。）

(In formula (1), R ₁ to R ₈ are alkyl groups having 1 to 6 carbon atoms or aryl groups having 6 to 12 carbon atoms, which may be the same or different. X ₁ and X ₄ are an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, and a group having 4 to 12 carbon atoms containing an epoxy group. Any group selected from the group, which may be the same or different X ₂ is an alkoxy group having 1 to 5 carbon atoms, or an epoxy group containing 4 to 12 carbon atoms and a plurality of X ₂ may be the same or different, X ₃ is a group containing 2 to 20 alkylene glycol repeating units, and when there are a plurality of X ₃ , they may be the same or different, m is an integer from 3 to 200, n is an integer from 0 to 200, and k is an integer from 0 to 200.)

In the polyorganosiloxane represented by the above formula (1), examples of alkyl groups having 1 to 6 carbon atoms represented by R ₁ to R ₈ , X ₁ and X ₄ include methyl group, ethyl group, n- Examples include propyl, isopropyl, butyl, pentyl, hexyl, and cyclohexyl groups. Examples of the aryl group having 6 to 12 carbon atoms include a phenyl group and a methylphenyl group. Among these, a methyl group and an ethyl group are preferable from the viewpoint of production of the polyorganosiloxane itself.

In the polyorganosiloxane represented by the above formula (1), examples of the alkoxy groups having 1 to 5 carbon atoms represented by X ₁ , X ₂ and X ₄ include methoxy, ethoxy, propoxy, iso propoxy group, butoxy group, and the like. Among them, a methoxy group and an ethoxy group are preferable from the viewpoint of reactivity with the active terminal of the conjugated diene polymer chain.

上記式（２）中、Ｚ_１は、炭素数１～１０のアルキレン基またはアルキルアリーレン基であり、Ｚ_２はメチレン基、硫黄原子、または酸素原子であり、Ｅはエポキシ基を有する炭素数２～１０の炭化水素基である。上記式（２）中、＊は結合位置を表す。 In the polyorganosiloxane represented by the above formula (1), the group having 4 to 12 carbon atoms containing an epoxy group represented by X ₁ , X ₂ and X ₄ is represented by the following formula (2) group.

In the above formula (2), Z ₁ is an alkylene group or alkylarylene group having 1 to 10 carbon atoms, Z ₂ is a methylene group, a sulfur atom, or an oxygen atom, and E is an epoxy group having 2 carbon atoms. ∼10 hydrocarbon groups. In the above formula (2), * represents a bonding position.

In the group represented by the above formula (2), Z ₂ is preferably an oxygen atom, more preferably Z ₂ is an oxygen atom and E is a glycidyl group, and Z ₁ has 1 carbon atom. ∼3 alkylene groups, Z ₂ is an oxygen atom and E is a glycidyl group are particularly preferred.

In the polyorganosiloxane represented by the above formula (1), X ₁ and X ₄ are preferably an epoxy group-containing group having 4 to 12 carbon atoms or an alkyl group having 1 to 6 carbon atoms. Among the above, X ₂ is preferably an epoxy group-containing group having 4 to 12 carbon atoms, X ₁ and X ₄ are alkyl groups having 1 to 6 carbon atoms, and X ₂ is epoxy It is more preferably a group containing 4 to 12 carbon atoms.

上記式（３）中、ｔは２～２０の整数であり、Ｐは炭素数２～１０のアルキレン基またはアルキルアリーレン基であり、Ｒは水素原子またはメチル基であり、Ｑは炭素数１～１０のアルコキシ基またはアリールオキシ基である。上記式（３）中、＊は結合位置を表す。これらの中でも、ｔが２～８の整数であり、Ｐが炭素数３のアルキレン基であり、Ｒが水素原子であり、かつ、Ｑがメトキシ基であるものが好ましい。 In the polyorganosiloxane represented by the above formula (1), X ₃ , that is, the group containing 2 to 20 alkylene glycol repeating units, is preferably a group represented by the following formula (3).

In the above formula (3), t is an integer of 2 to 20, P is an alkylene group or an alkylarylene group having 2 to 10 carbon atoms, R is a hydrogen atom or a methyl group, and Q has 1 to 1 carbon atoms. 10 alkoxy or aryloxy groups. In the above formula (3), * represents a bonding position. Among these, those in which t is an integer of 2 to 8, P is an alkylene group having 3 carbon atoms, R is a hydrogen atom, and Q is a methoxy group are preferred.

In the polyorganosiloxane represented by the above formula (1), m is an integer of 3-200, preferably an integer of 20-150, more preferably an integer of 30-120. Since m is an integer of 3 or more, the conjugated diene rubber having a modifying group has a high affinity with silica, and as a result, the tire obtained from the rubber composition of the present invention exhibits excellent low heat build-up. Moreover, since m is an integer of 200 or less, the polyorganosiloxane itself can be easily produced, and the rubber composition of the present invention has a low viscosity.

In the polyorganosiloxane represented by the above formula (1), n is an integer of 0-200, preferably an integer of 0-150, more preferably an integer of 0-120. In the polyorganosiloxane represented by the above formula (1), k is an integer of 0-200, preferably an integer of 0-150, more preferably an integer of 0-130.

In the polyorganosiloxane represented by the above formula (1), the total number of m, n, and k is preferably 3 to 400, more preferably 20 to 300, and 30 to 250. is particularly preferred.

In the polyorganosiloxane represented by the above formula (1), when the epoxy groups in the polyorganosiloxane react with the active terminals of the conjugated diene polymer chain, at least some of the epoxy groups in the polyorganosiloxane are opened. It is believed that the ringing forms a bond between the carbon atom at the ring-opening portion of the epoxy group and the active terminal of the conjugated diene polymer chain. Also, when the alkoxy groups in the polyorganosiloxane react with the active terminals of the conjugated diene-based polymer chain, at least some of the alkoxy groups in the polyorganosiloxane are eliminated, and the eliminated alkoxy groups are bonded. It is believed that a bond is formed between the silicon atom in the polyorganosiloxane and the active terminal of the conjugated diene polymer chain.

The amount of the above-mentioned polyorganosiloxane (hereinafter also referred to as a modifier) is such that the ratio of the total number of moles of epoxy groups and alkoxy groups in the modifier to 1 mole of the polymerization initiator used for polymerization is in the range of 0.1 to 1. The amount is preferably in the range of 0.2 to 0.9, more preferably in the range of 0.3 to 0.8.

In the method for producing a conjugated diene-based rubber, in addition to modifying the conjugated diene-based polymer chain having an active terminal with the modifier described above, a polymerization terminator, a polymerization terminal modifier other than the modifier described above, and a cup By adding a ring agent or the like to the polymerization system, some of the active terminals of the conjugated diene polymer chains may be inactivated to the extent that the effects of the present invention are not impaired. That is, in the conjugated diene rubber having a modifying group, a polymerization terminator, a polymerization terminal modifying agent other than the above-described modifying agents, as long as the active terminals of some of the conjugated diene polymer chains do not impair the effects of the present invention. , and may be inactivated by a coupling agent or the like.
Polymerization terminal modifiers and coupling agents used at this time include, for example, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-phenyl-2-pyrrolidone, and N-methyl-ε-caprolactam. N-substituted cyclic amides such as 1,3-dimethylethyleneurea and 1,3-diethyl-2-imidazolidinone; 4,4'-bis(dimethylamino)benzophenone, and 4,4′-bis(diethylamino)benzophenone; aromatic isocyanates such as diphenylmethane diisocyanate, and 2,4-tolylene diisocyanate; N,N, such as N,N-dimethylaminopropylmethacrylamide; N-disubstituted aminoalkylmethacrylamides; N-substituted aminoaldehydes such as 4-N,N-dimethylaminobenzaldehyde 1 N-substituted carbodiimides such as dicyclohexylcarbodiimide; N-ethylethylideneimine, N-methylbenzylideneimine, etc. Schiff bases; pyridyl group-containing vinyl compounds such as 4-vinylpyridine; tin tetrachloride; silicon tetrachloride, hexachlorodisilane, bis (trichlorosilyl) methane, 1,2-bis (trichlorosilyl) ethane, 1,3- Silicon halide compounds such as bis(trichlorosilyl)propane, 1,4-bis(trichlorosilyl)butane, 1,5-bis(trichlorosilyl)pentane, and 1,6-bis(trichlorosilyl)hexane; be done. A tire obtained using a highly branched conjugated diene rubber obtained by using a silicon halide compound having 5 or more silicon-halogen atom bonds in one molecule as a coupling agent has excellent steering stability. One of these polymerization terminal modifiers and coupling agents may be used alone, or two or more thereof may be used in combination.

When the active terminal of the conjugated diene polymer chain is reacted with the modifier or the like described above, it is preferable to add the modifier or the like to the solution containing the conjugated diene polymer chain having the active terminal to improve the reaction. From the viewpoint of controlling to , it is more preferable to dissolve the modifier or the like in an inert solvent and add it to the polymerization system. The solution concentration is preferably in the range of 1 to 50% by mass.
The timing of adding a modifier or the like is not particularly limited, but when the polymerization reaction in the conjugated diene polymer chain having an active terminal is not completed and the solution containing the conjugated diene polymer chain having an active terminal is A state containing a monomer, more specifically, a solution containing a conjugated diene polymer chain having an active terminal preferably contains 100 ppm or more, more preferably 300 to 50,000 ppm of the monomer. It is desirable to add a denaturing agent or the like to this solution while it is contained. By adding modifiers and the like in this way, side reactions between the conjugated diene polymer chains having active terminals and impurities contained in the polymerization system can be suppressed, and the reaction can be well controlled. Become.
Conditions for reacting the active terminal of the conjugated diene-based polymer chain with the modifier or the like described above include a temperature range of, for example, 0 to 100° C., preferably 30 to 90° C., and the respective reaction times. is, for example, in the range of 1 minute to 120 minutes, preferably 2 minutes to 60 minutes.
After the active terminal of the conjugated diene polymer chain is reacted with a modifier or the like, a polymerization terminator such as alcohol such as methanol and isopropanol or water can be added to deactivate the unreacted active terminal. preferable.

After deactivating the active terminal of the conjugated diene-based polymer chain, if desired, anti-aging agents such as phenol-based stabilizers, phosphorus-based stabilizers, sulfur-based stabilizers, crumb agents, scale inhibitors, etc. are polymerized. After that, the polymerization solvent is separated from the polymerization solution by direct drying, steam stripping, or the like, and the resulting conjugated diene rubber having modifying groups is recovered. Before separating the polymerization solvent from the polymerization solution, an extender oil may be mixed with the polymerization solution, and the conjugated diene rubber having a modifying group may be recovered as an oil-extended rubber.
Examples of the extender oil used when recovering the conjugated diene rubber having a modifying group as an oil-extended rubber include paraffinic, aromatic and naphthenic petroleum softeners, vegetable softeners, and fatty acids. be done. When petroleum-based softeners are used, it is preferred that the content of polycyclic aromatics extracted by the IP346 method (inspection method of THE INSTITUTE PETROLEUM, UK) is less than 3%. When an extender oil is used, the amount used is, for example, 5 to 100 parts by mass, preferably 10 to 60 parts by mass, and more preferably 20 to 50 parts by mass with respect to 100 parts by mass of the conjugated diene rubber.

A conjugated diene-based rubber having a modifying group has a structure in which three or more conjugated diene-based polymer chains are bonded by reacting a conjugated diene-based polymer chain having an active terminal with the polyorganosiloxane described above. body (hereinafter, "a structure in which three or more conjugated diene-based polymer chains are bonded, which is produced by reacting a conjugated diene-based polymer chain having an active terminal with the above-described polyorganosiloxane" is simply referred to as " (Also referred to as "a structure in which three or more conjugated diene polymer chains are bonded") preferably contains 5 to 40% by mass, more preferably 5 to 30% by mass. It is particularly preferable to contain up to 20% by mass. When the ratio of the structure to which 3 or more conjugated diene-based polymer chains are bonded is within the above range, the coagulability and drying property during production are improved, and furthermore, when silica is blended, the A rubber composition for tires having excellent processability and a tire having excellent low heat build-up can be provided. The ratio (mass fraction) of the structure in which three or more conjugated diene polymer chains are bonded to the total amount of the finally obtained conjugated diene rubber having a modifying group is defined as the conjugated diene polymer It is expressed as the coupling rate of 3 or more branches of the chain. This can be measured by gel permeation chromatography (converted to polystyrene). From the chart obtained by gel permeation chromatography measurement, the area ratio of the peak portion having a peak top molecular weight of 2.8 times or more of the peak top molecular weight indicated by the peak with the lowest molecular weight with respect to the total elution area was Coupling rate of 3 or more branches of the coalesced chain.

The aromatic vinyl unit content of the conjugated diene-based rubber having the modifying group is 38 to 48% by mass. Among them, 40 to 45% by mass is preferable. If the aromatic vinyl unit content is less than 38% by mass, the wet performance will be insufficient. Moreover, when the said aromatic vinyl unit content exceeds 48 mass %, low rolling resistance will deteriorate.
The vinyl bond content of the conjugated diene rubber having the modifying group is 20 to 35% by mass. Among them, 25 to 30% by mass is preferable. If the vinyl bond content is less than 20% by mass, low rolling resistance is deteriorated. On the other hand, if the vinyl bond content exceeds 35% by mass, the viscosity increases and processability deteriorates. The vinyl bond content refers to the proportion (% by mass) of the conjugated diene units contained in the conjugated diene rubber having a modifying group, which is occupied by vinyl bonds.
The weight average molecular weight (Mw) of the conjugated diene rubber having the modifying group is 500,000 to 800,000 as a polystyrene-equivalent value measured by gel permeation chromatography (GPC). Among them, it is preferably 600,000 to 700,000. If the weight-average molecular weight is less than 500,000, wear performance will deteriorate. On the other hand, when the weight average molecular weight exceeds 800,000, workability deteriorates.
The molecular weight distribution represented by the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the conjugated diene rubber having the modifying group is preferably 1.1 to 3.0. , more preferably 1.2 to 2.5, and particularly preferably 1.2 to 2.2. Both Mw and Mn are polystyrene equivalent values measured by GPC.
The Mooney viscosity (ML ₁₊₄ , 100° C.) of the conjugated diene rubber having the modifying group is preferably 20-100, more preferably 30-90, and particularly preferably 35-80. When the conjugated diene rubber having a modifying group is used as the oil-extended rubber, the Mooney viscosity of the oil-extended rubber is preferably set within the above range.

In the present invention, the content of the conjugated diene rubber having a modifying group in the diene rubber is 30% by mass or more, preferably 40 to 80% by mass, and more preferably 50 to 70% by mass. more preferred.
If the content of the conjugated diene rubber having a modifying group in the diene rubber is less than 30% by mass, wet performance, low rolling resistance and steering stability will be insufficient.
In addition, "the content of the conjugated diene rubber having the modifying group in the diene rubber" refers to the content (% by mass) of the conjugated diene rubber having the modifying group with respect to the entire diene rubber.

Rubber compositions for cap treads are generally used in tire rubber compositions such as vulcanizing or cross-linking agents, vulcanization accelerators, anti-aging agents, plasticizers, processing aids, terpene resins, and thermosetting resins. Various additives can be blended within a range that does not hinder the object of the present invention. Also, such additives can be kneaded in a conventional manner to form a rubber composition and used for vulcanization or cross-linking. The blending amount of these additives can be a conventional general blending amount as long as it does not contradict the object of the present invention. The rubber composition for cap treads can be produced by mixing the above components using a conventional rubber kneading machine such as a Banbury mixer, a kneader, and a roll.

The rubber compositions constituting the undertread, the belt cover layer and the belt layer of the pneumatic tire are not particularly limited, and commonly used undertread rubber compositions, belt cover layer rubber compositions and belt A rubber composition can be applied.
EXAMPLES The present invention will be further described with reference to examples below, but the scope of the present invention is not limited to these examples.

16 kinds of cap tread rubber compositions (Examples 1 to 8, standard examples, comparative examples 1 to In preparing 7), the ingredients except sulfur and the vulcanization accelerator were kneaded in a 1.7 L Banbury mixer for 5 minutes, and when the temperature reached 145°C, the mixture was discharged and cooled to obtain a masterbatch. Sulfur and a vulcanization accelerator were added to the obtained masterbatch, and the mixture was kneaded with an open roll at 70°C to obtain 17 types of tire rubber compositions. Also, the compounding amount of each additive shown in Table 3 is expressed as parts by mass with respect to 100 parts by mass of the rubber component shown in Tables 1 and 2.

A cap tread is constructed using the obtained rubber composition for cap tread, and as shown in Tables 1 and 2, the thickness of the undertread (referred to as "thickness of UT" in the table) and the rubber hardness of the undertread (In the table, "UT rubber hardness Hu"), the rubber hardness ratio Hu/Hc (-) between the cap tread and the undertread, and the type of fiber cord of the belt cover Pneumatic tires (size 195/65R15 ) was vulcanized. Using the obtained pneumatic tire, steering stability, wet grip performance, road noise, high-speed durability and low rolling resistance were evaluated by the following methods.

Steering Stability A pneumatic tire was assembled to a wheel with a rim size of 15×6J, and mounted on a test vehicle at an air pressure of 230 kPa. The evaluation results were shown by a 5-point scale with the standard example as the standard (5 points). It means that the higher the score, the better the steering stability.

Wet grip performance A pneumatic tire was mounted on a wheel with a rim size of 15 x 6J, and mounted on a test vehicle at an air pressure of 230 kPa. The reciprocals of the obtained values were calculated, and the obtained values were listed in the "Wet performance" column of Tables 1 and 2 as indices with the reciprocal value of the standard example being 100. A larger index means better wet grip performance.

Road noise Pneumatic tires were mounted on wheels with a rim size of 15 x 6J, and mounted as the front and rear wheels of a passenger car (front-wheel drive vehicle) with an engine displacement of 2.5L. A microphone was installed, and the sound pressure level around a frequency of 315 Hz was measured when running on a test course consisting of an asphalt road surface at an average speed of 50 km/h. The reciprocals of the obtained values were calculated, and the reciprocals of the values of the standard example were set to 100, and the indices were listed in the "road noise" column of Tables 1 and 2. The larger the index, the better the road noise is reduced.

High-speed durability A pneumatic tire was mounted on a wheel with a rim size of 15 x 6J, filled with air pressure of 230 kPa, mounted on an indoor drum tester (drum diameter 1707 mm), and subjected to a high-speed durability test specified in JIS D4230. After that, the vehicle was accelerated by 8 km/h every hour, and the distance traveled until the tire failed was measured. The evaluation results were expressed as indices with the standard example being 100, using the measured value of the running distance. The larger the index value, the longer the running distance until failure occurs, and the better the high-speed durability.

Low rolling resistance A pneumatic tire is mounted on a rim (15 x 6J), filled with air to a JATMA specified air pressure of 230 kPa, and subjected to an indoor drum tester (drum diameter 1707 mm) in accordance with JIS D4230. The rolling resistance was measured at a test load of 30 N and a speed of 40 km/h. The reciprocal of the obtained value was calculated, and the index was recorded in the column of "low rolling resistance" in Tables 1 and 2, with the reciprocal of the value of the standard example being 100. A larger index means better low rolling resistance.

得られた変性ＳＢＲ－１は、重量平均分子量が６４０，０００、分子量分布（Ｍｗ/Ｍｎ）が１．６５、３分岐以上のカップリング率が１２．５質量％、芳香族ビニル単位含有量が４２．６質量％、ビニル結合含有量が２９．５質量％、および、ムーニー粘度（ＭＬ_１＋４、１００℃）が５８であった。 The types of raw materials used in Tables 1 and 2 are shown below.
・ Undenatured SBR: 1502 manufactured by Nippon Zeon Co., Ltd.
• Modified SBR-1: A conjugated diene rubber having a modifying group, prepared by the following manufacturing method.
Production Method of Modified SBR-1 Cyclohexane (35 g) and tetramethylethylenediamine (1.4 mmol) were added to a nitrogen-purged 100 mL ampoule bottle, and further n-butyllithium (4.3 mmol) was added. Then, isoprene (21.6 g) and styrene (3.1 g) were slowly added and reacted in an ampoule bottle at 50° C. for 120 minutes to obtain polymer block A having active terminals. This polymer block A has a weight average molecular weight of 8700, a molecular weight distribution (Mw/Mn) of 1.10, an aromatic vinyl unit content of 12.6% by mass, an isoprene unit content of 87.4% by mass, and The 1,4-bond content was 58.0% by weight.
Next, an autoclave equipped with a stirrer was charged with cyclohexane (4000 g), 1,3-butadiene (474.0 g), and styrene (126.0 g) under a nitrogen atmosphere, and then the active terminal obtained above was removed. The total amount of polymer block A was added, and polymerization was initiated at 50°C. After confirming that the polymerization conversion rate was in the range of 95% to 100%, polyorganosiloxane A represented by the formula (1) described later was added to an epoxy group content of 1.42 mmol (used (equivalent to 0.33 moles of n-butyllithium) was added in the form of a xylene solution having a concentration of 20% by mass, and reacted for 30 minutes. Thereafter, methanol was added as a polymerization terminator in an amount corresponding to twice the moles of the n-butyllithium used to obtain a solution containing the specific conjugated diene rubber. To this solution, a small amount of an anti-aging agent (Irganox 1520, manufactured by BASF) was added, and 25% Fuccol Ceramic 30 (manufactured by Nippon Oil Co., Ltd.) was added as an extender oil to 100 parts by mass of the specific conjugated diene rubber. After adding parts by mass, a solid rubber was recovered by a steam stripping method. The resulting solid rubber was dehydrated with rolls and dried in a dryer to obtain modified SBR-1, which is a conjugated diene rubber having modifying groups.
In the above-described polyorganosiloxane A, X ₁ , X ₄ , R ₁ to R ₃ and R ₅ to R ₈ are methyl groups in the above formula (1). Also, m is 80, n is 0, and k is 120. Furthermore, X2 is a group represented by the following formula ( ₄ ) (where * represents a bonding position).

The resulting modified SBR-1 has a weight average molecular weight of 640,000, a molecular weight distribution (Mw/Mn) of 1.65, a coupling ratio of three or more branches of 12.5% by mass, and an aromatic vinyl unit content of 42.6% by weight, a vinyl bond content of 29.5% by weight, and a Mooney viscosity (ML ₁₊₄ , 100° C.) of 58.

・Modified SBR-2: Conjugated diene rubber with aminosilane group, F3420 manufactured by Asahi Kasei Corporation
・Modified SBR-3: Conjugated diene rubber with polysiloxane, NS612 manufactured by Nippon Zeon Co., Ltd.
・NR: natural rubber, STR
・Silica-1: ZEOSIL 1165MP manufactured by Evonik, CTAB adsorption specific surface area of 160 m ² /g
・Silica-2: 200MP manufactured by Evonik, with a CTAB adsorption specific surface area of 200m ² /g
Coupling agent: silane coupling agent, Si69 manufactured by Evonik
・ Carbon black: ISAF manufactured by CABOT
・Alkylsilane: octyoltriethoxysilane, KBE-3083 manufactured by Shin-Etsu Silicone Co., Ltd.
・Process oil: Extract No. 4 S manufactured by Showa Shell Sekiyu K.K.
- Nylon fiber cord used for the belt cover layer: Leona manufactured by Asahi Kasei Corporation, with a structure of 1100 dtex/2.
・PET fiber cord used for the belt cover layer: Elastic modulus at 100 ° C. with a load of 2.0 cN / dtex is 4.5 [cN / (tex %)], cord tension in the tire is 1.8 [cN / dtex] polyethylene terephthalate fiber cord, structure 1100 dtex/2.

The types of raw materials used in Table 3 are shown below.
・Stearic acid: Bead stearic acid YR manufactured by NOF Corporation
・ Zinc white: 3 types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd. ・ Anti-aging agent: SANTOFLEX 6PPD manufactured by Solutia
・ Sulfur: Hosoi Chemical Co., Ltd. oil refinery processing sulfur, sulfur content is 95% by mass
・Vulcanization accelerator-1: Ouchi Shinko Kagaku Kogyo Co., Ltd. Noccellar CZ-G (CBS)
・Vulcanization accelerator-2: Ouchi Shinko Kagaku Kogyo Co., Ltd. Noxceller D (DPG)

As is clear from Tables 1 and 2, the pneumatic tires of Examples 1 to 7 are superior in steering stability, low rolling resistance, wet grip performance, low road noise and high-speed durability to the standard and comparative examples. confirmed to be excellent.

The pneumatic tire of Comparative Example 1 was inferior in road noise and high-speed durability because the belt cover layer was composed of nylon fiber cords.
In the pneumatic tire of Comparative Example 2, the rubber hardness Hu of the undertread is increased, and the rubber hardness ratio Hu/Hc between the undertread and the cap tread exceeds 0.9, resulting in poor road noise and high-speed durability. Also, the steering stability is not sufficient.
Since the pneumatic tire of Comparative Example 3 contained less than 50 parts by mass of silica in the cap tread rubber composition, the rubber hardness of the cap tread was low, and the steering stability and wet grip performance were poor.
In the pneumatic tire of Comparative Example 4, the amount of oil in the rubber composition for cap tread of Comparative Example 3 was reduced to recover the rubber hardness of the cap tread, and the steering stability was slightly recovered, but the wet performance was inferior.
Since the pneumatic tire of Comparative Example 5 contained more than 150 parts by mass of silica in the cap tread rubber composition, the rubber hardness of the cap tread was high, and the low rolling resistance, low road noise and high-speed durability were poor. Also, the steering stability is not sufficient.
In the pneumatic tire of Comparative Example 6, the amount of oil in the cap tread rubber composition of Comparative Example 5 was increased to recover the rubber hardness of the cap tread and slightly improve the road noise, but the rolling resistance and high-speed durability were low. is inferior. Also, the steering stability is not sufficient.
Since the pneumatic tire of Comparative Example 7 has an undertread thickness of less than 1.5 mm, it is inferior in low rolling resistance, low road noise and high-speed durability. Also, the steering stability is not sufficient.
In the pneumatic tire of Comparative Example 8, in the cap tread rubber composition, the modified SBR-1 (conjugated diene rubber having a modifying group) in the diene rubber was less than 70% by mass.
Poor wet performance.

Claims (4)

It has a plurality of belt layers in which the cord direction intersects between layers, and a belt cover layer formed by spirally winding a polyethylene terephthalate fiber cord in the tire circumferential direction on the outer side of the belt layer in the tire radial direction, A pneumatic tire having an undertread and a cap tread on its radially outer side,
The thickness of the undertread is 1.5 mm or more, and the ratio Hu/Hc between the rubber hardness Hu of the undertread and the rubber hardness Hc of the cap tread is 0.9 or less,
The cap tread is composed of a rubber composition in which 50 to 150 parts by mass of silica is blended with 100 parts by mass of diene rubber, and the diene rubber is selected from a polyorganosiloxane structure, an aminosilane group, and a polysiloxane structure . A pneumatic tire containing 70% by mass or more of a conjugated diene rubber having at least one modifying group. The conjugated diene rubber having the modifying group is formed by bonding the active terminal of the conjugated diene polymer chain having the active terminal with the polyorganosiloxane represented by the following general formula (1), and has the active terminal. The conjugated diene-based polymer chain has a polymer block A and a polymer block B formed continuously with the polymer block A, and the polymer block A contains 80 to 95% by mass of isoprene units and It contains 5 to 20% by mass of aromatic vinyl units, has a weight average molecular weight of 500 to 15,000, and the polymer block B contains 1,3-butadiene units and aromatic vinyl units. The pneumatic tire according to claim 1.

(In formula (1), R ₁ to R ₈ are alkyl groups having 1 to 6 carbon atoms or aryl groups having 6 to 12 carbon atoms, which may be the same or different. X ₁ and X ₄ are an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, and a group having 4 to 12 carbon atoms containing an epoxy group. Any group selected from the group, which may be the same or different X ₂ is an alkoxy group having 1 to 5 carbon atoms, or an epoxy group containing 4 to 12 carbon atoms and a plurality of X ₂ may be the same or different, X ₃ is a group containing 2 to 20 alkylene glycol repeating units, and when there are a plurality of X ₃ , they may be the same or different, m is an integer from 3 to 200, n is an integer from 0 to 200, and k is an integer from 0 to 200.) The rubber composition constituting the cap tread is characterized in that 0.1 to 20 parts by mass of alkyltriethoxysilane having an alkyl group of 7 to 20 carbon atoms is blended with respect to the amount of silica blended. 3. The pneumatic tire according to Item 1 or 2. 4. The pneumatic tire according to claim 1, 2 or 3, wherein the silica has a CTAB adsorption specific surface area of 180 to 230 m ² /g.

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