Patent Description:
In general, tire rubbers, which contain a large number of double bonds, tend to become hardened over time due to recrosslinking. Moreover, the plasticizers contained in tire rubbers generally have a low molecular weight and tend to escape from the rubbers. The escape of plasticizers accelerates hardening of the rubbers. The hardening of the rubbers then results in a change in tire performance such as wet grip performance. Thus, there is room for improvement in that tire rubbers may fail to provide stable tire performance.

Patent Literature <NUM> discloses a technique in which a rubber (hydrogenated copolymer) which is hydrogenated to reduce the number of double bonds is used in a tire. This technique can reduce a change in hardness over time to some extent. However, in recent years where tire life has been extended, it has become desirable to further improve enduring performance.

Patent Literature <NUM> discloses a pneumatic tire, formed from a rubber composition, the rubber composition containing: a hydrogenated copolymer obtained by copolymerization of an aromatic vinyl compound and a conjugated diene compound, the hydrogenated copolymer having a degree of hydrogenation of the conjugated diene units of <NUM> mol% or more; and a resin having a softening point of <NUM> to <NUM>.

A further pneumatic tire is described in Patent Literature <NUM>.

The present disclosure aims to solve the above problem and provide a rubber composition and a tire which have excellent enduring performance as well as good fuel economy and wet grip performance.

The present disclosure relates to a rubber composition, containing: at least one hydrogenated conjugated diene polymer (A) having a weight average molecular weight of <NUM>,<NUM> or more and a degree of hydrogenation of <NUM> mol% or higher; at least one hydrogenated conjugated diene polymer (B) having a weight average molecular weight of less than <NUM>,<NUM>; and at least one resin having a softening point of <NUM> or higher,
wherein the hydrogenated conjugated diene polymer (B) is a copolymer of a conjugated diene compound and an aromatic vinyl compound.

Preferably, an absolute value of a difference in degree of hydrogenation between the hydrogenated conjugated diene polymer (A) and the hydrogenated conjugated diene polymer (B) is <NUM> mol% or less.

Preferably, the hydrogenated conjugated diene polymer (B) has a degree of hydrogenation of <NUM> mol% or higher.

Preferably, the hydrogenated conjugated diene polymer (B) is present in an amount of <NUM> parts by mass or more per <NUM> parts by mass of rubber components in the rubber composition.

Preferably, the hydrogenated conjugated diene polymer (B) and the resin are present in a combined amount of <NUM> parts by mass or less per <NUM> parts by mass of rubber components in the rubber composition.

Preferably, a change in hardness of the rubber composition after immersion in acetone for <NUM> hours is <NUM>% or less of the hardness before the immersion.

Preferably, a mass of the rubber composition after immersion in acetone for <NUM> hours is <NUM>% or more of the mass before the immersion.

Preferably, the rubber composition contains at least one filler selected from the group consisting of carbon black and silica.

Preferably, the resin is at least one selected from the group consisting of coumarone-indene resins, styrene resins, and terpene resins.

Preferably, the hydrogenated conjugated diene polymer (A) has a weight average molecular weight of <NUM>,<NUM> to <NUM>,<NUM>,<NUM> and a degree of hydrogenation of <NUM> to <NUM> mol%, and the hydrogenated conjugated diene polymer (B) has a weight average molecular weight of <NUM>,<NUM> to <NUM>,<NUM> and a degree of hydrogenation of <NUM> to <NUM> mol%.

Preferably, the hydrogenated conjugated diene polymer (A) and the hydrogenated conjugated diene polymer (B) are each a copolymer of a conjugated diene compound and an aromatic vinyl compound; the hydrogenated conjugated diene polymer (A) contains <NUM> to <NUM>% by mass of structural units derived from at least one aromatic vinyl compound; and the hydrogenated conjugated diene polymer (B) contains <NUM> to <NUM>% by mass of structural units derived from at least one aromatic vinyl compound.

Preferably, the hydrogenated conjugated diene polymer (A) is present in an amount of <NUM>% by mass or more based on <NUM>% by mass of rubber components in the rubber composition.

Preferably, the resin has a softening point of <NUM> to <NUM>.

Preferably, the rubber composition contains, per <NUM> parts by mass of rubber components therein, <NUM> to <NUM> parts by mass of the resin, <NUM> to <NUM> parts by mass of carbon black, and <NUM> to <NUM> parts by mass of silica.

The present disclosure also relates to a tire, including a tire component containing the rubber composition.

The present disclosure relates to a rubber composition containing a hydrogenated conjugated diene polymer (A) having a weight average molecular weight of <NUM>,<NUM> or more and a degree of hydrogenation of <NUM> mol% or higher, a hydrogenated conjugated diene polymer (B) having a weight average molecular weight of less than <NUM>,<NUM>, and a resin having a softening point of <NUM> or higher. Thus, the rubber composition provides excellent enduring performance, fuel economy, and wet grip performance.

The present disclosure relates to a rubber composition which contains a hydrogenated conjugated diene polymer (A) having a weight average molecular weight of <NUM>,<NUM> or more and a degree of hydrogenation of <NUM> mol% or higher, a hydrogenated conjugated diene polymer (B) having a weight average molecular weight of less than <NUM>,<NUM>, and a resin having a softening point of <NUM> or higher.

The rubber composition combines the hydrogenated conjugated diene polymer (A), the hydrogenated conjugated diene polymer (B), and the resin to provide excellent enduring performance, fuel economy, and wet grip performance.

The hydrogenated conjugated diene polymer (A) has a small number of double bonds and thus is advantageously less likely to change in hardness over time. However, the hydrogenated conjugated diene polymer (A) has a lower polarity than diene rubbers commonly used in tire rubber compositions and thus is less compatible with conventional plasticizers such as liquid rubbers, so that they tend to easily bleed out.

In contrast, the hydrogenated conjugated diene polymer (B) used in the rubber composition is highly compatible with the hydrogenated conjugated diene polymer (A) and thus is less likely to bleed out. Moreover, the presence of the resin having a softening point of <NUM> or higher further inhibits bleeding. It is believed that these actions provide excellent enduring performance.

Furthermore, the combined use of the hydrogenated conjugated diene polymer (A) and the hydrogenated conjugated diene polymer (B) provides a sharp temperature dependence of tan δ, resulting in good overall performance in terms of fuel economy and wet grip performance. In addition, the presence of the resin having a softening point of <NUM> or higher allows the rubber composition to have a Tg within a temperature range under tire service conditions. It is believed that these actions provide excellent fuel economy and wet grip performance.

The rubber composition contains at least one hydrogenated conjugated diene polymer (A) having a weight average molecular weight of <NUM>,<NUM> or more and a degree of hydrogenation of <NUM> mol% or higher, and at least one hydrogenated conjugated diene polymer (B) having a weight average molecular weight of less than <NUM>,<NUM>.

The hydrogenated conjugated diene polymer (A) having a high molecular weight is used as a rubber component. On the other hand, the hydrogenated conjugated diene polymer (B) having a low molecular weight is used as a plasticizer. The hydrogenated conjugated diene polymer (B) is not included in rubber components.

The hydrogenated conjugated diene polymers (A) and (B) are each obtainable by hydrogenating a polymer having structural units derived from at least one conjugated diene compound (conjugated diene units). Examples of the polymer to be hydrogenated include homopolymers of conjugated diene compounds, copolymers of two or more conjugated diene compounds, and copolymers of conjugated diene compounds and other monomers (e.g., aromatic vinyl compounds). Each of these may be used alone, or two or more of these may be used in combination. Copolymers of conjugated diene compounds and aromatic vinyl compounds are preferred among these.

Examples of the conjugated diene compounds include <NUM>,<NUM>-butadiene, isoprene, <NUM>,<NUM>-pentadiene, <NUM>,<NUM>-dimethylbutadiene, <NUM>-phenyl-<NUM>,<NUM>-butadiene, and <NUM>,<NUM>-hexadiene. These may be used alone or in combinations of two or more. Preferred are <NUM>,<NUM>-butadiene and isoprene, with <NUM>,<NUM>-butadiene being more preferred.

Examples of the aromatic vinyl compounds include styrene, α-methylstyrene, <NUM>-vinylnaphthalene, <NUM>-vinyltoluene, ethylvinylbenzene, divinylbenzene, <NUM>-cyclohexylstyrene, and <NUM>,<NUM>,<NUM>-trimethylstyrene. These may be used alone or in combinations of two or more. Preferred are styrene and α-methylstyrene, with styrene being more preferred.

In other words, the hydrogenated conjugated diene polymers (A) and (B) are each preferably a hydrogenated styrene-butadiene copolymer (hydrogenated SBR).

The hydrogenated conjugated diene polymers (A) and (B) may be prepared by any polymerization method, including random polymerization and block polymerization, preferably by random polymerization. The hydrogenation may also be performed by any method under any reaction condition, including known methods and known conditions. Usually, the hydrogenation is performed at <NUM> to <NUM> under an elevated hydrogen pressure of <NUM> to <NUM> MPa in the presence of a hydrogenation catalyst. Other production-related methods and conditions are also not limited, and those described in <CIT>, supra may be used, for example.

Although it is sufficient that the weight average molecular weight (Mw) of the hydrogenated conjugated diene polymer (A) be <NUM>,<NUM> or more, it is preferably <NUM>,<NUM> or more, more preferably <NUM>,<NUM> or more, still more preferably <NUM>,<NUM> or more, but is preferably <NUM>,<NUM>,<NUM> or less, more preferably <NUM>,<NUM> or less, still more preferably <NUM>,<NUM> or less. When the Mw is within the range indicated above, the advantageous effect tends to be better achieved.

The weight average molecular weight (Mw) can be determined by gel permeation chromatography (GPC) (GPC-<NUM> series available from Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M available from Tosoh Corporation) calibrated with polystyrene standards. Moreover, for polymers having a modifying group, the Mw is measured before they are thus modified because the Mw of the polymers cannot be accurately determined due to the interaction between the modifying group and the silica gel in the column.

Although it is sufficient that the degree of hydrogenation of the hydrogenated conjugated diene polymer (A) be <NUM> mol% or higher, based on <NUM> mol% of the total conjugated diene units before hydrogenation, it is preferably <NUM> mol% or higher, more preferably <NUM> mol% or higher, but is preferably <NUM> mol% or lower, more preferably <NUM> mol% or lower. When the degree of hydrogenation is within the range indicated above, the advantageous effect tends to be better achieved.

The degree of hydrogenation can be calculated from the rate of decrease in the unsaturated bond signals in the <NUM>H-NMR spectrum measured.

When the hydrogenated conjugated diene polymer (A) is a copolymer of a conjugated diene compound and an aromatic vinyl compound, the amount of structural units derived from at least one aromatic vinyl compound (aromatic vinyl units) is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, still more preferably <NUM>% by mass or more, but is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less, still more preferably <NUM>% by mass or less, particularly preferably <NUM>% by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The amount of the at least one hydrogenated conjugated diene polymer (A) based on <NUM>% by mass of the rubber components is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, still more preferably <NUM>% by mass or more, and may be <NUM>% by mass. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

Although it is sufficient that the weight average molecular weight (Mw) of the hydrogenated conjugated diene polymer (B) be preferably less than <NUM>,<NUM>, it is preferably <NUM>,<NUM> or less, more preferably <NUM>,<NUM> or less, still more preferably <NUM>,<NUM> or less, particularly preferably <NUM>,<NUM> or less, but is preferably <NUM>,<NUM> or more, more preferably <NUM>,<NUM> or more. When the Mw is within the range indicated above, the advantageous effect tends to be better achieved.

The degree of hydrogenation of the hydrogenated conjugated diene polymer (B) is preferably <NUM> mol% or higher, more preferably <NUM> mol% or higher, still more preferably <NUM> mol% or higher, but is preferably <NUM> mol% or lower, more preferably <NUM> mol% or lower, based on <NUM> mol% of the total conjugated diene units before hydrogenation. When the degree of hydrogenation is within the range indicated above, the hydrogenated copolymers (A) and (B) are better compatible with each other, so that bleeding tends to be further inhibited.

The absolute value of the difference in degree of hydrogenation between the hydrogenated conjugated diene polymer (A) and the hydrogenated conjugated diene polymer (B) is preferably <NUM> mol% or less, more preferably <NUM> mol% or less, still more preferably <NUM> mol% or less, particularly preferably <NUM> mol% or less, and may be <NUM> mol% (the degrees of hydrogenation are substantially the same). When the absolute value is within the range indicated above, the hydrogenated copolymers (A) and (B) are better compatible with each other, so that bleeding tends to be further inhibited.

When the hydrogenated conjugated diene polymer (B) is a copolymer of a conjugated diene compound and an aromatic vinyl compound, the amount of structural units derived from at least one aromatic vinyl compound (aromatic vinyl units) is preferably <NUM>% by mass or more, more preferably <NUM>% by mass or more, still more preferably <NUM>% by mass or more, particularly preferably <NUM>% by mass or more, but is preferably <NUM>% by mass or less, more preferably <NUM>% by mass or less, still more preferably <NUM>% by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The amount of the at least one hydrogenated conjugated diene polymer (B) per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, still more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

Examples of rubber components which may be used in addition to the hydrogenated conjugated diene polymer (A) in the rubber composition include diene rubbers such as natural rubbers (NR), styrene-butadiene rubbers (SBR), polybutadiene rubbers (BR), acrylonitrile-butadiene rubbers (NBR), and styrene-isoprene-butadiene copolymer rubbers (SIBR). Each of these may be used alone, or two or more of these may be used in combination.

The rubber components and the hydrogenated conjugated diene polymer (B) may each be modified to introduce a functional group interactive with a filler such as silica into the polymer.

Examples of the functional group include amino, amide, silyl, alkoxysilyl, isocyanate, imino, imidazole, urea, ether, carbonyl, oxycarbonyl, mercapto, sulfide, disulfide, sulfonyl, sulfinyl, thiocarbonyl, ammonium, imide, hydrazo, azo, diazo, carboxyl, nitrile, pyridyl, alkoxy, hydroxy, oxy, and epoxy groups. These functional groups may be substituted. Preferred among these are amino groups (preferably amino groups whose hydrogen atom is replaced with a C1-C6 alkyl group), alkoxy groups (preferably C1-C6 alkoxy groups), and alkoxysilyl groups (preferably C1-C6 alkoxysilyl groups).

Specific examples of compounds (modifiers) having these functional groups include <NUM>-dimethylaminoethyltrimethoxysilane, <NUM>-dimethylaminopropyltrimethoxysilane, <NUM>-dimethylaminoethyltriethoxysilane, <NUM>-dimethylaminopropyltriethoxysilane, <NUM>-diethylaminoethyltrimethoxysilane, <NUM>-diethylaminopropyltrimethoxysilane, <NUM>-diethylaminoethyltriethoxysilane, and <NUM>-diethylaminopropyltriethoxysilane.

The rubber composition contains at least one resin having a softening point of <NUM> or higher.

Examples of the resin include coumarone-indene resins, styrene resins, terpene resins, C5/C9 resins, and phenol resins. Each of these may be used alone, or two or more of these may be used in combination. Coumarone-indene resins, styrene resins, and terpene resins are preferred among these.

The term "coumarone-indene resins" refers to polymers mainly having structural units derived from coumarone and indene. Examples include copolymers of coumarone and indene and copolymers of coumarone and indene with other monomers (e.g., terpenes, conjugated diene compounds). Coumarone-indene resins (copolymers of coumarone and indene) are preferred among these.

The term "styrene resins" refers to liquid polymers mainly having structural units derived from styrenes. Examples include homopolymers of styrenes (e.g., styrene, α-methylstyrene), copolymers of two or more styrenes, and copolymers of styrenes and other monomers (e.g., terpenes, conjugated diene compounds). Copolymers of α-methylstyrene and styrene are preferred among these.

The term "terpene resins" refers to liquid polymers mainly having structural units derived from terpenes. Examples include homopolymers of terpenes (e.g., α-pinene, β-pinene, farnesene, myrcene), copolymers of two or more terpenes, and copolymers of terpenes and other monomers (e.g., aromatic vinyl compounds, conjugated diene compounds), such as terpene-styrene copolymers and farnesene-butadiene copolymers. Preferred among these are β-pinene resins (homopolymers of β-pinene).

Although it is sufficient that the softening point of the resin be <NUM> or higher, it is preferably <NUM> or higher, but is preferably <NUM> or lower, more preferably <NUM> or lower, still more preferably <NUM> or lower. When the softening point is within the range indicated above, the overall performance in terms of fuel economy and wet grip performance tends to be better.

The softening point is determined as set forth in JIS K <NUM>-<NUM>:<NUM> using a ring and ball softening point measuring apparatus and defined as the temperature at which the ball drops down.

The resin may be commercially available from Maruzen Petrochemical Co. , Sumitomo Bakelite Co. , Yasuhara Chemical Co. , Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical, Nitto Chemical Co. , Nippon Shokubai Co. , JXTG Nippon Oil & Energy Corporation, Arakawa Chemical Industries, Ltd. , Taoka Chemical Co. , ExxonMobil, etc..

The amount of the at least one resin per <NUM> parts by mass of the rubber components is preferably <NUM> part by mass or more, more preferably <NUM> parts by mass or more, still more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, bleeding tends to be further inhibited.

The combined amount of the at least one hydrogenated conjugated diene polymer (B) and the at least one resin per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, still more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less. When the combined amount is within the range indicated above, bleeding tends to be further inhibited.

The rubber composition may contain at least one filler selected from the group consisting of carbon black and silica, preferably a combination of carbon black and silica.

Any carbon black may be used, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Usable commercial products are available from Asahi Carbon Co. , Cabot Japan K. , Tokai Carbon Co. , Mitsubishi Chemical Corporation, Lion Corporation, NSCC Carbon Co. , Columbia Carbon, etc. These may be used alone or in combinations of two or more.

The nitrogen adsorption specific surface area (N<NUM>SA) of the carbon black is preferably <NUM><NUM>/g or more, more preferably <NUM><NUM>/g or more, still more preferably <NUM><NUM>/g or more, but is preferably <NUM><NUM>/g or less, more preferably <NUM><NUM>/g or less, still more preferably <NUM><NUM>/g or less. When the N<NUM>SA is within the range indicated above, the advantageous effect tends to be better achieved.

The N<NUM>SA of the carbon black is measured in accordance with JIS K6217-<NUM>:<NUM>.

The amount of carbon black per <NUM> parts by mass of the rubber components is preferably <NUM> part by mass or more, more preferably <NUM> parts by mass or more, still more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

Examples of the silica include dry silica (anhydrous silicic acid) and wet silica (hydrous silicic acid), with wet silica being preferred because it has a large number of silanol groups. Usable commercial products are available from Evonik, Tosoh Silica Corporation, Solvay Japan, Tokuyama Corporation, etc. Each of these may be used alone, or two or more of these may be used in combination.

The nitrogen adsorption specific surface area (N<NUM>SA) of the silica is preferably <NUM><NUM>/g or more, more preferably <NUM><NUM>/g or more, still more preferably <NUM><NUM>/g or more, but is preferably <NUM><NUM>/g or less, more preferably <NUM><NUM>/g or less, still more preferably <NUM><NUM>/g or less. When the N<NUM>SA is within the range indicated above, the advantageous effect tends to be better achieved.

The nitrogen adsorption specific surface area of the silica is measured by a BET method in accordance with ASTM D3037-<NUM>.

The amount of silica per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, still more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The silica is preferably used together with a silane coupling agent.

Any silane coupling agent may be used, and examples include sulfide silane coupling agents such as bis(<NUM>-triethoxysilylpropyl)tetrasulfide, bis(<NUM>-triethoxysilylethyl)tetrasulfide, bis(<NUM>-triethoxysilylbutyl)tetrasulfide, bis(<NUM>-trimethoxysilylpropyl)tetrasulfide, bis(<NUM>-trimethoxysilylethyl)tetrasulfide, bis(<NUM>-triethoxysilylethyl)trisulfide, bis(<NUM>-trimethoxysilylbutyl)trisulfide, bis(<NUM>-triethoxysilylpropyl)disulfide, bis(<NUM>-triethoxysilylethyl)disulfide, bis(<NUM>-triethoxysilylbutyl)disulfide, bis(<NUM>-trimethoxysilylpropyl)disulfide, bis(<NUM>-trimethoxysilylethyl)disulfide, bis(<NUM>-trimethoxysilylbutyl)disulfide, <NUM>-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, <NUM>-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and <NUM>-triethoxysilylpropyl methacrylate monosulfide; mercapto silane coupling agents such as <NUM>-mercaptopropyltrimethoxysilane, <NUM>-mercaptoethyltriethoxysilane, and NXT and NXT-Z both available from Momentive; vinyl silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; amino silane coupling agents such as <NUM>-aminopropyltriethoxysilane and <NUM>-aminopropyltrimethoxysilane; glycidoxy silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro silane coupling agents such as <NUM>-nitropropyltrimethoxysilane and <NUM>-nitropropyltriethoxysilane; and chloro silane coupling agents such as <NUM>-chloropropyltrimethoxysilane and <NUM>-chloropropyltriethoxysilane. Usable commercial products are available from Evonik, Momentive, Shin-Etsu Silicone, Tokyo Chemical Industry Co. , Dow Corning Toray Co. , etc. These may be used alone or in combinations of two or more.

The amount of silane coupling agents per <NUM> parts by mass of the silica is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The rubber composition may contain a wax.

Any wax may be used, and examples include petroleum waxes such as paraffin waxes and microcrystalline waxes; naturally-occurring waxes such as plant waxes and animal waxes; and synthetic waxes such as polymers of ethylene, propylene, or other similar monomers. Usable commercial products are available from Ouchi Shinko Chemical Industrial Co. , Nippon Seiro Co. , Seiko Chemical Co. , etc. Each of these may be used alone, or two or more of these may be used in combination.

The amount of waxes per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> part by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The rubber composition may contain an oil.

Examples of the oil include process oils, plant oils, and mixtures of these oils. Examples of the process oils include paraffinic process oils, aromatic process oils, and naphthenic process oils. Examples of the plant oils include castor oil, cotton seed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. Usable commercial products are available from Idemitsu Kosan Co. , Sankyo Yuka Kogyo K. , JXTG Nippon Oil & Energy Corporation, Olisoy, H&R, Hokoku Corporation, Showa Shell Sekiyu K. , Fuji Kosan Co. , etc. Each of these may be used alone, or two or more of these may be used in combination.

The amount of oils per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less, and may be <NUM> parts by mass (the rubber composition contains substantially no oil). Because the hydrogenated conjugated diene polymer (B) functions as a plasticizer in the rubber composition, the amount of oils can be reduced to provide better fuel economy.

The rubber composition may contain an antioxidant.

Examples of the antioxidant include naphthylamine antioxidants such as phenyl-α-naphthylamine; diphenylamine antioxidants such as octylated diphenylamine and <NUM>,<NUM>'-bis(α,α'-dimethylbenzyl)diphenylamine; p-phenylenediamine antioxidants such as N-isopropyl-N'-phenyl-p-phenylenediamine, N-(<NUM>,<NUM>-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and N,N'-di-<NUM>-naphthyl-p-phenylenediamine; quinoline antioxidants such as polymerized <NUM>,<NUM>,<NUM>-trimethyl-<NUM>,<NUM>-dihydroquinoline; monophenolic antioxidants such as <NUM>,<NUM>-di-t-butyl-<NUM>-methylphenol and styrenated phenol; and bis-, tris-, or polyphenolic antioxidants such as tetrakis[methylene-<NUM>-(<NUM>',<NUM>'-di-t-butyl-<NUM>'-hydroxyphenyl)propionate]methane. Usable commercial products are available from Seiko Chemical Co. , Sumitomo Chemical Co. , Ouchi Shinko Chemical Industrial Co. , Flexsys, etc. Each of these may be used alone, or two or more of these may be used in combination.

The amount of antioxidants per <NUM> parts by mass of the rubber components is preferably <NUM> part by mass or more, more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The stearic acid may be a conventional one. Usable commercial products are available from NOF Corporation, Kao Corporation, FUJIFILM Wako Pure Chemical Corporation, Chiba Fatty Acid Co. , etc. Each of these may be used alone, or two or more of these may be used in combination.

The amount of stearic acid per <NUM> parts by mass of the rubber components is preferably <NUM> part by mass or more, more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The zinc oxide may be a conventional one. Usable commercial products are available from Mitsui Mining & Smelting Co. , Toho Zinc Co. , HakusuiTech Co. , Seido Chemical Industry Co. , Sakai Chemical Industry Co. , etc. Each of these may be used alone, or two or more of these may be used in combination.

The amount of zinc oxide per <NUM> parts by mass of the rubber components is preferably <NUM> part by mass or more, more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

Examples of the sulfur include those commonly used in the rubber industry, such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur. Usable commercial products are available from Tsurumi Chemical Industry Co. , Karuizawa sulfur Co. , Shikoku Chemicals Corporation, Flexsys, Nippon Kanryu Industry Co. , Hosoi Chemical Industry Co. , etc. These may be used alone or in combinations of two or more.

The amount of sulfur per <NUM> parts by mass of the rubber components is preferably <NUM> parts by mass or more, more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

The rubber composition may contain a vulcanization accelerator.

Examples of the vulcanization accelerator include thiazole vulcanization accelerators such as <NUM>-mercaptobenzothiazole and di-<NUM>-benzothiazolyl disulfide; thiuram vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(<NUM>-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide vulcanization accelerators such as N-cyclohexyl-<NUM>-benzothiazylsulfenamide (CBS), N-tert-butyl-<NUM>-benzothiazolylsulfenamide (TBBS), N-oxyethylene-<NUM>-benzothiazole sulfenamide, and N,N'-diisopropyl-<NUM>-benzothiazole sulfenamide; and guanidine vulcanization accelerators such as diphenylguanidine, diorthotolylguanidine, and orthotolylbiguanidine. Usable commercial products are available from Sumitomo Chemical Co. , Ouchi Shinko Chemical Industrial Co. , etc. These may be used alone or in combinations of two or more.

The amount of vulcanization accelerators per <NUM> parts by mass of the rubber components is preferably <NUM> part by mass or more, more preferably <NUM> parts by mass or more, still more preferably <NUM> parts by mass or more, but is preferably <NUM> parts by mass or less, more preferably <NUM> parts by mass or less, still more preferably <NUM> parts by mass or less. When the amount is within the range indicated above, the advantageous effect tends to be better achieved.

In addition to the above-described components, the rubber composition may further contain additives commonly used in the tire industry, including for example organic peroxides and fillers such as calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica. The amounts of such additives are each preferably <NUM> to <NUM> parts by mass per <NUM> parts by mass of the rubber components.

The rubber composition may be prepared, for example, by kneading the above-described components using a rubber kneading machine such as an open roll mill or a Banbury mixer, and then vulcanizing the kneaded mixture.

The kneading conditions are as follows. In a base kneading step of kneading additives other than vulcanizing agents and vulcanization accelerators, the kneading temperature is usually <NUM> to <NUM>, preferably <NUM> to <NUM>. In a final kneading step of kneading vulcanizing agents and vulcanization accelerators, the kneading temperature is usually <NUM> or lower, preferably <NUM> to <NUM>. Then, the composition obtained after kneading vulcanizing agents and vulcanization accelerators is usually vulcanized by, for example, press vulcanization. The vulcanization temperature is usually <NUM> to <NUM>, preferably <NUM> to <NUM>. The vulcanization time is usually <NUM> to <NUM> minutes.

The change in hardness of the rubber composition after immersion in acetone for <NUM> hours can be used as an index of change in hardness over time.

The change in hardness is preferably <NUM>% or less, more preferably <NUM>% or less, still more preferably <NUM>% or less, particularly preferably <NUM>% or less, of the hardness before the immersion and may be <NUM>% or less, <NUM>% or less, or <NUM>% (the hardnesses before and after immersion in acetone are substantially the same). When the change is within the range indicated above, there tends to be a small change in hardness over time, resulting in good enduring performance.

The change in hardness can be measured as described later in EXAMPLES.

The mass of the rubber composition after immersion in acetone for <NUM> hours can also be used as an index of change in hardness over time.

The mass is preferably <NUM>% or more, more preferably <NUM>% or more, still more preferably <NUM>% or more, particularly preferably <NUM>% or more, of the mass before the immersion and may be <NUM>% or more, <NUM>% or more, <NUM>% or more, or <NUM>% (the masses before and after immersion in acetone are substantially the same). When the mass is within the range indicated above, there tends to be a small change in hardness over time, resulting in good enduring performance.

The mass can be measured as described later in EXAMPLES.

The rubber composition may be used in tire components (i.e., as a tire rubber composition), including treads (cap treads), sidewalls, base treads, undertreads, shoulders, clinches, bead apexes, breaker cushion rubbers, rubbers for carcass cord topping, insulations, chafers, and innerliners, and side reinforcement layers of run-flat tires.

The tire of the present disclosure can be produced from the above-described rubber composition by usual methods.

Specifically, the rubber composition, before vulcanization, may be extruded into the shape of a tire component such as a tread and then assembled with other tire components in a usual manner on a tire building machine to build an unvulcanized tire, which may then be heated and pressurized in a vulcanizer to produce a tire.

Here, it is sufficient that the tire component (e.g., tread) of the tire at least partially contain the rubber composition. The entire tire component may contain the rubber composition.

The tire (e.g., pneumatic tire) may be used as: a tire for passenger cars; a tire for trucks and buses; a tire for two-wheeled vehicles; a high performance tire; a winter tire such as a studless winter tire; a run-flat tire provided with a side reinforcing layer; a noise absorber-equipped tire which includes a noise absorber such as sponge on the tire inner cavity; a sealant-attached tire which includes a sealant capable of sealing punctures either inside the tire or on the tire inner cavity; an electronic component-equipped tire which includes an electronic component such as a sensor or a radio tag either inside the tire or on the tire inner cavity, etc. The tire is suitable for passenger cars.

The present disclosure is specifically described below with reference to examples.

A sufficiently nitrogen-purged heat-resistant reaction vessel was charged with n-hexane, styrene, <NUM>,<NUM>-butadiene, N,N,N',N'-tetramethylethylenediamine (TMEDA), and n-butyllithium, followed by stirring at <NUM> for five hours to perform a polymerization reaction. Thereafter, the reaction solution was stirred for <NUM> minutes while supplying hydrogen gas at a pressure of <NUM> MPa gauge to react unreacted polymer terminal lithium with hydrogen into lithium hydride. Hydrogenation was performed using a titanocene dichloride-based catalyst at a hydrogen gas supply pressure of <NUM> MPa gauge and a reaction temperature of <NUM>. Once the cumulative amount of absorbed hydrogen reached the amount corresponding to the target degree of hydrogenation, the reaction temperature was brought to room temperature, and the hydrogen pressure was returned to an ordinary pressure. Then, the reaction solution was drawn from the reaction vessel and introduced into water with stirring. The solvent was removed by steam stripping to obtain hydrogenated copolymer (<NUM>). The polymerization conversion ratio was almost <NUM>%.

Hydrogenated copolymer (<NUM>) was prepared as in Production Example <NUM>, except that the amounts of the chemicals and the cumulative amount of absorbed hydrogen were changed. The polymerization conversion ratio was almost <NUM>%.

Hydrogenated copolymer (<NUM>) was prepared as in Production Example <NUM>, except that the amounts of the chemicals were changed. The polymerization conversion ratio was almost <NUM>%.

Hexane, butadiene, and styrene together with TMEDA were introduced into a sufficiently nitrogen-purged heat-resistant reaction vessel. Next, a small amount of a solution of n-butyllithium in hexane was introduced into the polymerization vessel as a scavenger for preliminarily detoxifying impurities which serve to deactivate polymerization initiators. Then, a solution of n-butyllithium in hexane was added, followed by performing a polymerization reaction at <NUM> for three hours. Three hours later, a <NUM> isopropanol/hexane solution was dropwise added to terminate the reaction. Subsequently, the polymerization solution was evaporated at room temperature for <NUM> hours and then dried in vacuo at <NUM> for <NUM> hours to obtain a copolymer.

Next, the copolymer, n-hexane, and <NUM>% palladium carbon were added to a pressure-resistant vessel, and the vessel was purged with nitrogen and then with hydrogen at a pressure of <NUM>/cm<NUM>. Then, a reaction was performed until the cumulative amount of absorbed hydrogen reached the amount corresponding to the target degree of hydrogenation. Then, the reaction solution was filtrated to remove the catalyst. Subsequently, the filtrate was evaporated at room temperature for <NUM> hours and then dried in vacuo at <NUM> for <NUM> hours to obtain liquid hydrogenated SBR (<NUM>). The polymerization conversion ratio was almost <NUM>%.

According to the formulation shown in Table <NUM>, the materials other than the sulfur and vulcanization accelerators were kneaded in a <NUM> Banbury mixer (Kobe Steel, Ltd. ) at <NUM> for five minutes to give a kneaded mixture. Then, the sulfur and vulcanization accelerators were added to the kneaded mixture, and they were kneaded in an open roll mill at <NUM> for five minutes to give an unvulcanized rubber composition. The unvulcanized rubber composition was vulcanized at <NUM> for <NUM> minutes to obtain a vulcanized rubber composition.

The test tires prepared as above were evaluated as described below. Table <NUM> shows the results.

It should be noted that all the measurements were conducted within three days after the vulcanization.

The mass of a specimen of each vulcanized rubber composition was measured.

Moreover, the measured specimen was immersed in acetone for <NUM> hours and dried, and then the mass was again measured.

Then, the change in mass after immersion in acetone was expressed as an index using the equation below. In general, the index is <NUM> or lower, and an index closer to <NUM> is better (a smaller change in hardness over time). An index of <NUM> or higher is considered acceptable.

The mass change index can be used to determine the mass after immersion in acetone. For example, a mass change index of <NUM> indicates that the mass after immersion in acetone is <NUM>% of the mass before the immersion.

The hardness (JIS-A hardness) at room temperature (<NUM>) of a specimen of each vulcanized rubber composition was measured in accordance with "Rubber, vulcanized or thermoplastic - Determination of hardness - Part <NUM>: Durometer method" in JIS K6253-<NUM> (<NUM>) using a type A durometer.

Moreover, the measured specimen was immersed in acetone for <NUM> hours and dried, and then the hardness at room temperature was measured as described above.

Then, the change in hardness after immersion in acetone was expressed as an index using the equation below. In general, the index is <NUM> or lower, and an index closer to <NUM> is better (a smaller change in hardness over time). An index of <NUM> or higher is considered acceptable.

The hardness change index can be used to determine the change (%) in hardness after immersion in acetone. For example, a hardness change index of <NUM> indicates that the change in hardness after immersion in acetone is <NUM>% of the hardness before the immersion.

The tan δ of the vulcanized rubber compositions was measured using a viscoelastic spectrometer (RSA available from TA Instruments) at a temperature of <NUM>, an initial strain of <NUM>%, a dynamic strain of <NUM>%, and a frequency of <NUM>. The results are expressed as an index (fuel economy index) relative to the reciprocal of the tan δ value of Comparative Example <NUM> taken as <NUM>. A higher index indicates better fuel economy.

The tan δ of the vulcanized rubber compositions was measured using a viscoelastic spectrometer (RSA available from TA Instruments) at a temperature of <NUM>, an initial strain of <NUM>%, a dynamic strain of <NUM>%, and a frequency of <NUM>. The results are expressed as an index (wet grip performance index) relative to the tan δ value of Comparative Example <NUM> taken as <NUM>. A higher index indicates better wet grip performance.

Claim 1:
A rubber composition, comprising:
at least one hydrogenated conjugated diene polymer (A) having a weight average molecular weight of <NUM>,<NUM> or more and a degree of hydrogenation of <NUM> mol% or higher;
at least one hydrogenated conjugated diene polymer (B) having a weight average molecular weight of less than <NUM>,<NUM>; and
at least one resin having a softening point of <NUM> or higher,
wherein the hydrogenated conjugated diene polymer (B) is a copolymer of a conjugated diene compound and an aromatic vinyl compound.