tire

Abstract

To provide a tire with improved persistence of wet grip performance after the lapse of time.SOLUTION: A tire comprises: a cap tread; and a base tread. The cap tread has a content of polymer having an ethylene unit is 50 mass% or more in a rubber component 100 mass%. The tire satisfies the following expression (1): (1) Rc>Oc≥Ob where RC (mass%) is a content of resin, Oc (mass%) is a content of oil, based on the rubber component 100 mass% in the cap tread, and Ob (mass%) is a content of oil based on the rubber component 100 mass% in the base tread.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a tire. [Background technology]

[0002] 2. Description of the Related Art Tires have traditionally been required to have various performance characteristics, such as wet grip performance, and in light of recent environmental considerations, it is desirable to maintain the wet grip performance over time. Summary of the Invention [Problem to be solved by the invention]

[0003] An object of the present invention is to solve the above problems and to provide a tire having improved durability of wet grip performance over time. [Means for solving the problem]

[0004] The present invention relates to a tire having a cap tread and a base tread, The cap tread has a content of a polymer having an ethylene unit of 50% by mass or more in 100% by mass of a rubber component, The tire has a resin content Rc (parts by mass) and an oil content Oc (parts by mass) per 100 parts by mass of the rubber component in the cap tread, and an oil content Ob (parts by mass) per 100 parts by mass of the rubber component in the base tread, which satisfy the following formula (1): (1) Rc>Oc≧Ob Effect of the Invention

[0005] The present invention relates to a tire having a cap tread and a base tread, in which the content of a polymer having an ethylene unit in 100% by mass of the rubber component is 50% by mass or more and the tire satisfies the above formula (1), thereby improving the durability of wet grip performance over time. [Brief description of the drawings]

[0006] [Figure 1] 1 is a cross-sectional view showing a portion of a pneumatic tire. [Diagram 2] FIG. 2 is an enlarged cross-sectional view showing the vicinity of the tread of the tire of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The tire includes a cap tread and a base tread, and the cap tread has a polymer content having an ethylene unit of 50% by mass or more in 100% by mass of a rubber component, and the resin content Rc (parts by mass) and oil content Oc (parts by mass) per 100 parts by mass of the rubber component in the cap tread, and the oil content Ob (parts by mass) per 100 parts by mass of the rubber component in the base tread satisfy formula (1) "Rc>Oc≧Ob".

[0008] The reason why the above-mentioned effects are obtained in the above tire is not entirely clear, but is presumed to be as follows. Polymers having ethylene units have fewer double bonds than styrene-butadiene rubber, butadiene rubber, etc., and have good physical properties after heat aging. Therefore, in a cap tread containing a certain amount or more of such a polymer having an ethylene unit, by compounding a resin content (Rc) greater than the oil content (Oc), the change in hardness Hs over time due to oil bleeding is reduced. In addition, by compounding the oil content (Oc) of the cap tread greater than the oil content (Ob) of the base tread, the change in hardness Hs over time due to oil bleeding can be further suppressed. It is presumed that the above mechanism improves the durability of the wet grip performance of the tire over time.

[0009] The tire has a cap tread and a base tread. The cap tread is composed of a rubber composition for a cap tread, and the base tread is composed of a rubber composition for a base tread.

[0010] Hereinafter, chemicals that can be commonly used for the rubber composition for the cap tread and the rubber composition for the base tread will be described.

[0011] The rubber composition for the cap tread and the rubber composition for the base tread each contain a rubber component. Here, the rubber component is a component that contributes to crosslinking, and generally corresponds to a polymer component that is not extracted with acetone and has a weight average molecular weight (Mw) of 10,000 or more. The rubber component is in a solid state at room temperature (25°C).

[0012] The weight average molecular weight of the rubber component is preferably 50,000 or more, more preferably 150,000 or more, even more preferably 200,000 or more, and particularly preferably 270,000 or more, and is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,000,000 or less. Within the above ranges, the effect tends to be better obtained.

[0013] In this specification, the weight average molecular weight (Mw) can be determined by converting it into standard polystyrene based on the measured value obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation).

[0014] The rubber component usable in the rubber composition for the cap tread and the rubber composition for the base tread may be either a non-modified rubber or a modified rubber. The modified rubber may be a rubber having a functional group that interacts with a filler such as silica. For example, the modified rubber may be a terminal modified rubber (terminal modified rubber having the functional group at the terminal) in which at least one terminal of the rubber is modified with a compound (modifier) ​​having the functional group, a main chain modified rubber having the functional group at the main chain, a main chain terminal modified rubber having the functional group at the main chain and terminal (for example, a main chain terminal modified rubber having the functional group at the main chain and at least one terminal modified with the modifier), or a terminal modified rubber modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule and having a hydroxyl group or an epoxy group introduced therein.

[0015] Examples of the functional group include an amino group, an amide group, a silyl group, an alkoxysilyl group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imide group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, and an epoxy group. These functional groups may have a substituent. Among them, an amino group (preferably an amino group in which a hydrogen atom of an amino group is substituted with an alkyl group having 1 to 6 carbon atoms), an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms), and an alkoxysilyl group (preferably an alkoxysilyl group having 1 to 6 carbon atoms) are preferred.

[0016] The rubber component may, for example, be a diene rubber.

[0017] Examples of diene rubbers include isoprene rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). Examples of rubber components include butyl rubber and fluororubber. These may be used alone or in combination of two or more. These rubber components may be modified or hydrogenated, and extended rubber extended with oil, resin, liquid rubber component, or the like may be used. Among diene rubbers, isoprene rubber, BR, and SBR are preferable. Among them, the cap tread preferably contains at least an isoprene-based rubber. The base tread preferably contains at least one of an isoprene-based rubber and a butadiene rubber, and more preferably contains an isoprene-based rubber and a butadiene rubber.

[0018] Examples of isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, modified IR, etc. As NR, for example, SIR20, RSS♯3, TSR20, etc., which are common in the rubber industry, can be used. As IR, there is no particular limitation, and for example, IR2200, etc., which are common in the rubber industry can be used. As modified NR, deproteinized natural rubber (DPNR), high-purity natural rubber, etc. can be used, as modified NR, epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc. can be used, as modified IR, epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. can be used. These may be used alone or in combination of two or more.

[0019] The BR is not particularly limited, and for example, high cis BR with a high cis content, BR containing syndiotactic polybutadiene crystals, BR synthesized using a rare earth catalyst (rare earth BR), etc. can be used. These may be used alone or in combination of two or more. In particular, the BR preferably contains high cis BR with a cis content of 90% by mass or more. The cis content is more preferably 95% by mass or more. The cis content can be measured by infrared absorption spectroscopy.

[0020] The cis amount of BR means the cis amount of the BR when there is one type of BR, and means the average cis amount when there are multiple types of BR. The average cis content of BR can be calculated by {Σ(content of each BR × cis content of each BR)} / total content of all BRs. For example, when 100% by mass of the rubber component contains 20% by mass of BR with a cis content of 90% by mass and 10% by mass of BR with a cis content of 40% by mass, the average cis content of BR is 73.3% by mass (=(20×90+10×40) / (20+10)).

[0021] In addition, either unmodified or modified BR can be used as the BR. Modified BR includes modified BR in which the same functional group as that of modified rubber is introduced. In addition, hydrogenated butadiene polymer (hydrogenated BR) can also be used as the BR.

[0022] The SBR is not particularly limited, and for example, emulsion polymerized styrene butadiene rubber (E-SBR), solution polymerized styrene butadiene rubber (S-SBR), etc. can be used. These may be used alone or in combination of two or more kinds.

[0023] The styrene content of SBR is preferably 5% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more. The styrene content is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. When it is within the above range, the effect tends to be better obtained. In this specification, the styrene content is 1 It can be measured by H-NMR measurement.

[0024] The styrene amount of SBR means the styrene amount of the SBR when there is one type of SBR, and means the average styrene amount when there are multiple types of SBR. The average styrene amount of SBR can be calculated by {Σ(content of each SBR × styrene amount of each SBR)} / total content of all SBRs. For example, when 100% by mass of the rubber component contains 85% by mass of SBR with a styrene amount of 40% by mass and 5% by mass of SBR with a styrene amount of 25% by mass, the average styrene amount of the SBR is 39.2% by mass (=(85×40+5×25) / (85+5)).

[0025] The vinyl bond content of SBR is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more. When the vinyl bond content is within the above range, preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, the effect tends to be better. In this specification, the vinyl bond amount (1,2-bonded butadiene unit amount) can be measured by infrared absorption spectroscopy.

[0026] The vinyl content of SBR (amount of 1,2-bonded butadiene units) is the proportion of vinyl bonds when the total mass of the butadiene parts in SBR is taken as 100 (unit: mass%), and is calculated as vinyl content [mass%] + cis content [mass%] + trans content [mass%] = 100 [mass%]. When there is one type of SBR, it means the vinyl content of that SBR, and when there are multiple types, it means the average vinyl content. The average vinyl content of SBR can be calculated by Σ{content of each SBR × (100 [mass%] - styrene content of each SBR [mass%]) × vinyl content of each SBR [mass%]} / Σ{content of each SBR × (100 [mass%] - styrene content of each SBR [mass%])}. For example, in 100 parts by mass of the rubber component, there are 75 parts by mass of SBR with a styrene content of 40 mass% and a vinyl content of 30 mass%, 25 parts by mass of styrene, and 10 parts by mass of vinyl. In the case where SBR with a vinyl content of 20 mass% is 15 parts by mass and the remaining 10 parts by mass is a component other than SBR, the average vinyl content of the SBR is 28 mass% (={75 × (100 [mass%] - 40 [mass%]) × 30 [mass%] + 15 × (100 [mass%] - 25 [mass%]) × 20 [mass%])} / {75 × (100 [mass%] - 40 [mass%]) + 15 × (100 [mass%] - 25 [mass%])}.

[0027] Either unmodified or modified SBR can be used. Modified SBR includes modified SBR in which the same functional groups as those in modified rubber have been introduced.

[0028] The rubber component may, for example, be a polymer having an ethylene unit (structural unit formed from ethylene: -CH2-CH2-). In the present disclosure, the polymer having an ethylene unit used in the cap tread is a polymer having a high molecular weight ethylene unit, which is a component that is not extracted by an organic solvent such as acetone from the rubber composition after vulcanization, and is used as a rubber component. Note that the polymer having a high molecular weight ethylene unit desirably has the weight average molecular weight of the rubber component.

[0029] The polymer having an ethylene unit is not particularly limited as long as it is a polymer having an ethylene unit, but from the viewpoint of obtaining good effects, a multicomponent copolymer containing an ethylene unit, a conjugated diene unit, and an aromatic vinyl unit is preferable.

[0030] In the multicomponent copolymer, the conjugated diene unit is a structural unit derived from a conjugated diene compound. Examples of the conjugated diene compound include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, 1,3-hexadiene, etc. These may be used alone or in combination of two or more kinds, with 1,3-butadiene and isoprene being preferred, and 1,3-butadiene being more preferred.

[0031] In the multicomponent copolymer, the aromatic vinyl unit is a structural unit derived from an aromatic vinyl compound. Examples of the aromatic vinyl compound include styrene, α-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene, 2,4,6-trimethylstyrene, etc. These may be used alone or in combination of two or more kinds, with styrene and α-methylstyrene being preferred, and styrene being more preferred.

[0032] The multicomponent copolymer can be prepared, for example, by a method of copolymerizing ethylene, a conjugated diene compound, and an aromatic vinyl compound, or by a method of copolymerizing a conjugated diene compound and an aromatic vinyl compound, or by copolymerizing ethylene, a conjugated diene compound, and an aromatic vinyl compound, and then converting a part of the conjugated diene units into non-conjugated olefin units by hydrogenation. That is, the multicomponent copolymer may be a copolymer of ethylene, a conjugated diene compound, and an aromatic vinyl compound, or may be a hydrogenated copolymer of a conjugated diene compound and an aromatic vinyl compound, or a hydrogenated copolymer of ethylene, a conjugated diene compound, and an aromatic vinyl compound. These may be used alone or in combination of two or more. Among them, from the viewpoint of obtaining a better effect, a hydrogenated copolymer of a conjugated diene compound and an aromatic vinyl compound is preferable, and a hydrogenated styrene-butadiene copolymer is more preferable.

[0033] In preparing the multicomponent copolymer, the polymerization method is not particularly limited, and may be random polymerization or block polymerization, with random polymerization being preferred.

[0034] When the multicomponent copolymer is a hydrogenated copolymer, the hydrogenation method and reaction conditions are not particularly limited, and hydrogenation may be performed by a known method and under known conditions. Usually, hydrogenation is performed at 20 to 150°C under a hydrogen pressure of 0.1 to 10 MPa in the presence of a hydrogenation catalyst. Other production methods and conditions are also not particularly limited, and for example, the contents described in International Publication No. 2016 / 039005 can be applied.

[0035] In the rubber composition for cap treads, the content of the polymer having the ethylene unit in 100% by mass of the rubber component is 50% by mass or more, preferably 60% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more. The upper limit is not particularly limited and may be 100% by mass, but is preferably 95% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. Within the above range, the effect tends to be preferably obtained.

[0036] In the rubber composition for cap treads, the content of the isoprene-based rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above ranges, the effect tends to be preferably obtained.

[0037] In the rubber composition for base tread, the content of the isoprene-based rubber in 100% by mass of the rubber component is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 75% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. Within the above ranges, the effects tend to be favorably obtained.

[0038] In the rubber composition for base tread, the content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less. Within the above range, the effect tends to be preferably obtained.

[0039] The rubber composition for the cap tread and the rubber composition for the base tread desirably contain a plasticizer. In this specification, the plasticizer is a material that imparts plasticity to the rubber component, and may be liquid or solid at room temperature (25° C.) These may be used alone or in combination of two or more kinds.

[0040] Examples of the plasticizer include oil, liquid polymer, resin, etc. These may be used alone or in combination of two or more kinds.

[0041] The oil is not particularly limited, and may be any conventionally known oil, such as paraffinic process oil, aromatic process oil, naphthenic process oil, low PCA (polycyclic aromatic) process oil such as TDAE and MES, vegetable-derived oil, and mixtures thereof. These may be used alone or in combination of two or more. From the viewpoint of life cycle analysis, lubricating oil or waste edible oil after use in a rubber mixing mixer or automobile engine may be used as appropriate.

[0042] Examples of the plant-derived oils (also called vegetable oils) include castor oil, cottonseed 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.

[0043] As the above oil, for example, products from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corporation, Orisoi Co., Ltd., H&R Corporation, Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., Nisshin Oillio Group Co., Ltd., etc. can be used.

[0044] Examples of the liquid polymer include liquid diene polymers (liquid rubber) and liquid farnesene polymers at 25°C. Examples of liquid rubber include liquid styrene butadiene copolymers (liquid SBR), liquid butadiene polymers (liquid BR), liquid isoprene polymers (liquid IR), liquid styrene isoprene copolymers (liquid SIR), liquid styrene butadiene styrene block copolymers (liquid SBS block polymers), and liquid styrene isoprene styrene block copolymers (liquid SIS block polymers). The ends or main chains of these may be modified with polar groups. Hydrogenated products of these may also be used.

[0045] The liquid diene polymer has a weight average molecular weight (Mw) of 1.0×10 in terms of polystyrene measured by gel permeation chromatography (GPC). 3 ~5.0×10 4 Preferably, it is 3.0×10 3 ~1.5×10 4 The lower or upper limit of Mw of the liquid diene polymer may be 4,500 or 8,500. In this specification, the Mw of the liquid diene-based polymer is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0046] As the liquid diene polymer, for example, products available from Sartomer Co., Ltd., Kuraray Co., Ltd., etc. can be used.

[0047] The resin may be a resin that is commonly used as a tire compound, and may be liquid or solid at room temperature (25°C). Examples of the resin include aromatic vinyl polymers, coumarone-indene resins, coumarone resins, indene resins, phenolic resins, rosin resins, petroleum resins, terpene resins, and acrylic resins. The resin may also be a hydrogenated resin. These may be used alone or in combination of two or more. The resin itself may be a copolymer of monomer components of multiple origins. Among these, hydrogenated resins are preferable from the viewpoint of obtaining better effects. Aromatic vinyl polymers, petroleum resins, terpene resins, and hydrogenated resins thereof are also preferable.

[0048] The mechanism by which hydrogenated resins are more effective is unclear, but it is speculated that the increased compatibility with the polymer containing ethylene units suppresses oil bleeding and inhibits changes in hardness Hs after heat aging, thereby improving the durability of wet grip performance.

[0049] When a resin that is solid at room temperature is used, the softening point of the resin is preferably 50° C. or higher, more preferably 55° C. or higher, even more preferably 60° C. or higher, and particularly preferably 85° C. or higher. Also, the softening point is preferably 160° C. or lower, more preferably 150° C. or lower, even more preferably 140° C. or lower, even more preferably 120° C. or lower, and particularly preferably 100° C. or lower. Within the above range, the effect tends to be better obtained. When the resin is liquid at room temperature, the softening point is preferably 20° C. or lower, more preferably 10° C. or lower, and even more preferably 0° C. or lower. In the case of hydrogenated resins, it is desirable for the softening point to be similar to that mentioned above. The softening point of the resin is the temperature at which the ball drops when the softening point specified in JIS K6220-1:2001 is measured using a ring and ball softening point tester.

[0050] The aromatic vinyl polymer is a polymer containing an aromatic vinyl monomer as a structural unit. For example, it can be a resin obtained by polymerizing α-methylstyrene and / or styrene, and specifically, it can be a homopolymer of styrene (styrene resin), a homopolymer of α-methylstyrene (α-methylstyrene resin), a copolymer of α-methylstyrene and styrene, a copolymer of styrene and another monomer, etc.

[0051] The coumarone-indene resin is a resin containing coumarone and indene as main monomer components constituting the resin skeleton (main chain). Other monomer components contained in the skeleton besides coumarone and indene include styrene, α-methylstyrene, methylindene, vinyltoluene, etc.

[0052] The coumarone resin is a resin containing coumarone as a main monomer component constituting the skeleton (main chain) of the resin.

[0053] The indene resin is a resin containing indene as a main monomer component constituting the skeleton (main chain) of the resin.

[0054] The phenolic resin may be a known polymer obtained by reacting phenol with an aldehyde such as formaldehyde, acetaldehyde, or furfural in the presence of an acid or alkali catalyst. Among these, those obtained by reacting with an acid catalyst (such as novolac-type phenolic resin) are preferred.

[0055] Examples of the rosin resin include rosin-based resins such as natural rosin, polymerized rosin, modified rosin, ester compounds thereof, and hydrogenated products thereof.

[0056] Examples of the petroleum resin include C5 resin, C9 resin, C5 / C9 resin, dicyclopentadiene (DCPD) resin, C9 / DCPD resin, and hydrogenated versions of these resins. Among these, DCPD resin, hydrogenated DCPD resin, C9 / DCPD resin, and C9 / hydrogenated DCPD resin are preferred.

[0057] The terpene resin is a polymer containing terpene as a constituent unit. For example, polyterpene resin obtained by polymerizing a terpene compound, aromatic modified terpene resin obtained by polymerizing a terpene compound and an aromatic compound, etc. can be mentioned. As the aromatic modified terpene resin, terpene phenol resin made from terpene compounds and phenolic compounds, terpene styrene resin made from terpene compounds and styrene compounds, and terpene phenol styrene resin made from terpene compounds, phenolic compounds, and styrene compounds can also be used. In addition, examples of the terpene compound include α-pinene, β-pinene, etc., examples of the phenolic compound include phenol, bisphenol A, etc., and examples of the aromatic compound include styrene compounds (styrene, α-methylstyrene, etc.). Among them, aromatic modified terpene resin is preferable.

[0058] The acrylic resin is a polymer containing an acrylic monomer as a constituent unit. For example, a styrene-acrylic resin having a carboxyl group and obtained by copolymerizing an aromatic vinyl monomer component and an acrylic monomer component, such as a styrene-acrylic resin, can be used. Among them, a solventless carboxyl group-containing styrene-acrylic resin can be preferably used.

[0059] Examples of the resins that can be used include products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Exxon Mobil Corporation, KRATON, Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., ENEOS Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Co., Ltd.

[0060] From the viewpoint of sustainability, it is desirable to use, as the plasticizer, a plant-derived plasticizer such as the plant-derived oil or farnesene-based polymer.

[0061] Farnesene polymers are polymers obtained by polymerizing farnesene and have structural units based on farnesene. Farnesene has isomers such as α-farnesene ((3E,7E)-3,7,11-trimethyl-1,3,6,10-dodecatetraene) and β-farnesene (7,11-dimethyl-3-methylene-1,6,10-dodecatriene), but (E)-β-farnesene, which has the following structure, is preferred. [ka]

[0062] The farnesene-based polymer may be a homopolymer of farnesene (farnesene homopolymer) or a copolymer of farnesene and a vinyl monomer (farnesene-vinyl monomer copolymer). These may be used alone or in combination of two or more. Among them, a copolymer of farnesene and a vinyl monomer is preferred.

[0063] Examples of vinyl monomers include aromatic vinyl compounds such as styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, α-methylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene, 4-tert-butylstyrene, 5-t-butyl-2-methylstyrene, vinylethylbenzene, divinylbenzene, trivinylbenzene, divinylnaphthalene, tert-butoxystyrene, vinylbenzyldimethylamine, (4-vinylbenzyl)dimethylaminoethylether, N,N-dimethylaminoethylstyrene, N,N-dimethylaminomethylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, 2-t-butylstyrene, 3-t-butylstyrene, 4-t-butylstyrene, vinylxylene, vinylnaphthalene, vinyltoluene, vinylpyridine, diphenylethylene, and tertiary amino group-containing diphenylethylene, as well as conjugated diene compounds such as butadiene and isoprene. These may be used alone or in combination of two or more. Among these, butadiene is preferred. That is, the farnesene-vinyl monomer copolymer is preferably a copolymer of farnesene and butadiene (farnesene-butadiene copolymer).

[0064] In the farnesene-vinyl monomer copolymer, the copolymerization ratio by mass of farnesene and vinyl monomer (farnesene / vinyl monomer) is preferably 40 / 60 to 90 / 10.

[0065] The farnesene-based polymer preferably has a weight average molecular weight (Mw) of 3000 or more and 300,000 or less. The Mw of the farnesene-based polymer is preferably 8000 or more, more preferably 10,000 or more, and is preferably 100,000 or less, more preferably 60,000 or less, and even more preferably 50,000 or less. Within the above ranges, the effect tends to be more preferably obtained.

[0066] The farnesene-based polymer may be either a liquid or solid polymer at room temperature (25° C.), and is preferably a liquid farnesene-based polymer that is a liquid at room temperature (25° C.).

[0067] In the rubber composition for cap treads, the content Pc of the plasticizer (total amount of the plasticizer) is preferably 40 parts by mass or more, more preferably 45 parts by mass or more, even more preferably 50 parts by mass or more, and even more preferably 60 parts by mass or more, relative to 100 parts by mass of the rubber component, and is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 75 parts by mass or less. Although the lower limit is not particularly limited, within the above range, the effect tends to be better obtained. The plasticizer content includes the amount of oil and resin contained in the oil-extended rubber and resin-extended rubber.

[0068] In the rubber composition for cap treads, the content of the solid plasticizer in a solid state at room temperature (25° C.) is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 35 parts by mass or more, relative to 100 parts by mass of the rubber component, and is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less. Within the above ranges, the effect tends to be better obtained.

[0069] In the rubber composition for cap treads, the content of the liquid plasticizer in a liquid state at room temperature (25° C.) is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, particularly preferably 25 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 35 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained. The liquid plasticizer content includes the amount of oil contained in the oil-extended rubber and the amount of liquid resin in the resin-extended rubber that has been extended with the liquid resin.

[0070] In the rubber composition for cap tread, the content Rc of the resin (total amount of resin) is preferably 25 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 35 parts by mass or more, relative to 100 parts by mass of the rubber component, and is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less. When it is within the above range, the effect tends to be better obtained.

[0071] In the rubber composition for cap treads, the oil content Oc (total amount of oil) is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, particularly preferably 25 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 35 parts by mass or less, relative to 100 parts by mass of the rubber component. When it is within the above range, the effect tends to be better obtained. The oil content includes the amount of oil contained in the oil-extended rubber.

[0072] In the rubber composition for base tread, the content Pb of the plasticizer (total amount of the plasticizer) is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and even more preferably 10 parts by mass or more, relative to 100 parts by mass of the rubber component, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. When it is within the above range, the effect tends to be better obtained. The plasticizer content includes the amount of oil and resin contained in the oil-extended rubber and resin-extended rubber.

[0073] In the rubber composition for base tread, the content of the solid plasticizer in a solid state at room temperature (25° C.) is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass or less, and may be 0 parts by mass, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better.

[0074] In the rubber composition for base tread, the content of the liquid plasticizer in a liquid state at room temperature (25° C.) is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. When it is within the above range, the effect tends to be better obtained. The liquid plasticizer content includes the amount of oil contained in the oil-extended rubber and the amount of liquid resin in the resin-extended rubber that has been extended with the liquid resin.

[0075] In the rubber composition for base tread, the oil content Ob (total amount of oil) is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and even more preferably 10 parts by mass or more, relative to 100 parts by mass of the rubber component, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. When it is within the above range, the effect tends to be better obtained. The oil content includes the amount of oil contained in the oil-extended rubber.

[0076] In the above tire, the resin content Rc (parts by mass) per 100 parts by mass of the rubber component in the rubber composition for cap tread, the oil content Oc (parts by mass) per 100 parts by mass of the rubber component in the rubber composition for cap tread, and the oil content Ob (parts by mass) per 100 parts by mass of the rubber component in the rubber composition for base tread satisfy the following formula (1). (1) Rc>Oc≧Ob

[0077] Rc / Oc is preferably 1.1 or more, more preferably 1.2 or more, even more preferably 1.3 or more, and even more preferably 1.4 or more. The upper limit of Rc / Oc is not particularly limited, but is preferably 3.0 or less, more preferably 2.0 or less, even more preferably 1.7 or less, and even more preferably 1.5 or less. Within the above range, the effect tends to be better obtained.

[0078] Oc / Ob is preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more, and even more preferably 2.5 or more. The upper limit of Oc / Ob is not particularly limited, but is preferably 4.0 or less, more preferably 3.5 or less, and even more preferably 3.0 or less. Within the above range, the effect tends to be better obtained.

[0079] Rc / Ob is preferably 2.5 or more, more preferably 3.0 or more, even more preferably 3.3 or more, and even more preferably 3.5 or more. The upper limit of Rc / Ob is not particularly limited, but is preferably 8.0 or less, more preferably 7.5 or less, even more preferably 7.0 or less, and even more preferably 5.0 or less. Within the above range, the effect tends to be better obtained.

[0080] In order to obtain better effects in the above tire, it is desirable that the plasticizer content Pc (parts by mass) per 100 parts by mass of the rubber component in the rubber composition for the cap tread is greater than the plasticizer content Pb (parts by mass) per 100 parts by mass of the rubber component in the rubber composition for the base tread.

[0081] The ratio of Pc to Pb (Pc / Pb) is preferably 4.0 or more, more preferably 4.5 or more, even more preferably 5.0 or more, even more preferably 5.5 or more, even more preferably 6.0 or more, and is preferably 10.0 or less, more preferably 8.0 or less, even more preferably 7.5 or less. Within the above range, the effect tends to be better obtained.

[0082] Although the mechanism by which a greater effect is obtained when Pc>Pb, especially when Pc / Pb is adjusted to 5.0 or more, is not clear, it is believed that by compounding a plasticizer content (Pc) in the cap tread that is greater than the plasticizer content (Pb) in the base tread, the change in hardness Hs over time caused by bleeding of the plasticizer can be suppressed more effectively. Therefore, it is presumed that the durability of the tire is improved.

[0083] The rubber composition for the cap tread and the rubber composition for the base tread desirably contain a filler. The filler is not particularly limited, and materials known in the rubber field can be used, for example, inorganic fillers such as carbon black, silica, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, mica, biochar, poorly dispersible fillers, etc. Among them, carbon-derived fillers (carbon-containing fillers) such as carbon black, and silica are preferred from the viewpoint of obtaining a greater effect.

[0084] In the rubber composition for cap tread and the rubber composition for base tread, usable carbon black is not particularly limited, but includes N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, N762, etc. As commercially available products, products of Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Co., Ltd., Lion Co., Ltd., Shin-Nichika Carbon Co., Ltd., Columbia Carbon Co., Ltd., etc. can be used. These may be used alone or in combination of two or more. In addition to conventional carbon black made from mineral oils, etc., carbon black made from biomass materials such as lignin may be used. In addition, recycled carbon black obtained by decomposing rubber products containing carbon black such as tires, plastic products, etc., may be appropriately substituted for the above carbon black in an equal amount.

[0085] The nitrogen adsorption specific surface area (N2SA) of carbon black is 5m 2 / g or more is preferable, and 10m 2 / g or more is more preferable, and 15m 2 / g or more is more preferable. 2 / g or less is preferable, and 130m 2 / g or less is more preferable, and 120m 2 / g or less is more preferable, 2 When it is within the above range, the effect tends to be better. The nitrogen adsorption specific surface area of ​​carbon black can be determined in accordance with JIS K6217-2:2001.

[0086] The dibutyl phthalate oil absorption (DBP) of the carbon black is preferably 40 ml / 100 g or more, more preferably 60 ml / 100 g or more, and even more preferably 70 ml / 100 g or more. In addition, when the DBP is within the above range of preferably 200 ml / 100 g or less, more preferably 150 ml / 100 g or less, and even more preferably 100 ml / 100 g or less, the effect tends to be better. The DBP of carbon black is determined by the measurement method of JIS K6217-4:2001.

[0087] In the rubber composition for cap tread and the rubber composition for base tread, usable silica includes dry process silica (anhydrous silica) and wet process silica (hydrated silica). Among them, wet process silica is preferred because it has a large number of silanol groups. As commercially available products, products from Degussa, Rhodia, Tosoh Silica Co., Ltd., Solvay Japan Co., Ltd., Tokuyama Co., Ltd., etc. can be used. These may be used alone or in combination of two or more kinds.

[0088] As the silica, plant-derived silica can also be suitably used. Examples of plant-derived silica include silica derived from plants containing silica. Examples of plants containing silica include rice, corn, sugarcane, horsetail, wheat, barley, rye, pearl barley, millet, foxtail millet, Japanese barnyard millet, and Erianthus. In addition, the saccharification residue of the above-mentioned plants containing silica can also be used. Among them, rice husks and straws with high silica content are preferred, and rice husks are more preferred. In addition, the plant containing silica may be one that has been burned to ash or one that has been carbonized.

[0089] The nitrogen adsorption specific surface area (N2SA) of the silica is preferably 50 m 2 / g or more, more preferably 100m2 / g or more, more preferably 150m 2 / g or more, and even more preferably 175m 2 The upper limit of the N2SA of silica is not particularly limited, but is preferably 350 m 2 / g or less, more preferably 300m 2 / g or less, more preferably 250m 2 Within the above range, there is a tendency for the effect to be better obtained. The N2SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

[0090] Examples of the poorly dispersible filler include microfibrillated vegetable fibers, short fiber cellulose, gel compounds, etc. Among these, microfibrillated vegetable fibers are preferred.

[0091] The microfibrillated plant fiber is preferably cellulose microfibril, since it has good reinforcing properties. The cellulose microfibril is not particularly limited as long as it is derived from a natural product, and examples thereof include those derived from resource biomass such as fruits, grains, and root vegetables, wood, bamboo, hemp, jute, and kenaf, and pulp, paper, cloth, agricultural waste, waste biomass such as food waste and sewage sludge obtained from these as raw materials, unused biomass such as rice straw, wheat straw, and thinned wood, as well as cellulose produced by sea squirts, acetic acid bacteria, etc. These microfibrillated plant fibers may be used alone or in combination of two or more.

[0092] In this specification, cellulose microfibrils typically refer to cellulose fibers having an average fiber diameter of 10 μm or less, more typically cellulose fibers having a microstructure formed by the aggregation of cellulose molecules and an average fiber diameter of 500 nm or less. Typical cellulose microfibrils are formed, for example, as an aggregate of cellulose fibers having the above-mentioned average fiber diameter.

[0093] In the rubber composition for cap treads, the filler content Fc (total amount of fillers such as silica, carbon black, etc.) is preferably 70 parts by mass or more, more preferably 75 parts by mass or more, even more preferably 85 parts by mass or more, and even more preferably 105 parts by mass or more, relative to 100 parts by mass of the rubber component, and is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 130 parts by mass or less. Within the above range, the effect tends to be better obtained.

[0094] Although the mechanism by which the effect of adjusting the filler content to 75 parts by mass or more is more clear, it is believed that increasing the filler content reduces the polymer ratio, which in turn suppresses changes in physical properties after heat aging, and therefore improves the durability of wet grip performance.

[0095] In the rubber composition for cap treads, the content of carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 10 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.

[0096] In the rubber composition for cap treads, the content of silica relative to 100 parts by mass of the rubber component is preferably 65 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, and even more preferably 100 parts by mass or more, and is preferably 150 parts by mass or less, more preferably 130 parts by mass or less, and even more preferably 120 parts by mass or less. Within the above range, the effect tends to be better obtained.

[0097] When the rubber composition for cap tread contains a poorly dispersible filler, the content of the poorly dispersible filler is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit of the content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less. Within the above range, the effect tends to be better obtained.

[0098] In the rubber composition for base tread, the content Fb of the filler (total amount of fillers such as silica, carbon black, etc.) is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, relative to 100 parts by mass of the rubber component, and is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less. When it is within the above range, the effect tends to be better obtained.

[0099] In the rubber composition for base tread, the content of carbon black is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, and is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less, based on 100 parts by mass of the rubber component. When the content is within the above range, the effect tends to be better obtained.

[0100] In the rubber composition for base tread, the content of silica per 100 parts by mass of the rubber component is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, further preferably 5 parts by mass or less, and may be 0 parts by mass. When the content is within the above range, the effect tends to be better.

[0101] When the rubber composition for base tread contains a poorly dispersible filler, the content of the poorly dispersible filler is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit of the content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less. Within the above range, the effect tends to be better obtained.

[0102] The ratio (Fc / Fb) of the filler content Fc per 100 parts by mass of the rubber component in the rubber composition for cap tread to the filler content Fb per 100 parts by mass of the rubber component in the rubber composition for base tread is preferably 1.7 or more, more preferably 2.3 or more, even more preferably 2.8 or more, even more preferably 3.2 or more, and particularly preferably 3.5 or more. The upper limit of Fc / Fb is not particularly limited, but is preferably 5.0 or less, more preferably 4.5 or less, and even more preferably 4.0 or less. Within the above range, the effect tends to be better obtained.

[0103] Although the mechanism by which a greater effect is obtained when Fc / Fb is adjusted to a specified value or more, especially 3.2 or more, is not clear, it is believed that by compounding the filler content (Fc) of the cap tread higher than the filler content (Fb) of the base tread, the polymer ratio in the cap tread is reduced, thereby suppressing changes in physical properties after heat aging. Therefore, it is presumed that the performance durability of the wet grip performance is improved.

[0104] The ratio (Cc / Cb) of the carbon black content Cc per 100 parts by mass of the rubber component in the rubber composition for cap tread to the carbon black content Cb per 100 parts by mass of the rubber component in the rubber composition for base tread is preferably 0.10 or more, more preferably 0.15 or more, and even more preferably 0.17 or more. The upper limit of Cc / Cb is not particularly limited, but is preferably 0.30 or less, more preferably 0.23 or less, and even more preferably 0.20 or less. Within the above range, the effect tends to be better obtained.

[0105] Although the mechanism by which a greater effect is obtained when Cc / Cb is adjusted to a specified value or more, especially 0.15 or more, is not clear, it is believed that by compounding the carbon black content (Cc) of the cap tread higher than the carbon black content (Cb) of the base tread, the polymer ratio in the cap tread is reduced, thereby suppressing changes in physical properties after heat aging. Therefore, it is presumed that the performance durability of wet grip performance is improved.

[0106] When the rubber composition for a cap tread or the rubber composition for a base tread contains silica, it is preferable that the rubber composition further contains a silane coupling agent. The silane coupling agent is not particularly limited, and those known in the rubber field can be used. For example, bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N, Examples of such silylsilanes include sulfide-based silylsilanes such as N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto-based silylsilanes such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and Momentive's NXT and NXT-Z; vinyl-based silylsilanes such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based silylsilanes such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based silylsilanes such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silylsilanes such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silylsilanes such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Commercially available products include those manufactured by Degussa, Momentive, Shin-Etsu Silicones, Tokyo Chemical Industry, Azumax, and Dow Corning Toray Co., Ltd. These may be used alone or in combination of two or more.

[0107] In the rubber composition for cap tread and the rubber composition for base tread, the content of the silane coupling agent is preferably 0.1 parts by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more, based on 100 parts by mass of silica. The upper limit of the content is preferably 50 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less. Within the above range, the effect tends to be better obtained.

[0108] The rubber composition for the cap tread and the rubber composition for the base tread preferably contain an antioxidant from the viewpoints of crack resistance, ozone resistance, and the like.

[0109] The antiaging agent is not particularly limited, and examples thereof include naphthylamine-based antiaging agents such as phenyl-α-naphthylamine; diphenylamine-based antiaging agents such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, Examples of the antioxidant include p-phenylenediamine antioxidants such as amines; quinoline antioxidants such as polymerized 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis, tris, and polyphenol antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Among these, p-phenylenediamine antioxidants and quinoline antioxidants are preferred, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and polymerized 2,2,4-trimethyl-1,2-dihydroquinoline are more preferred. Commercially available products include, for example, products from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Flexis Co., Ltd.

[0110] In the rubber composition for cap tread and the rubber composition for base tread, the content of the antioxidant is preferably 0.2 parts by mass or more, more preferably 2.0 parts by mass or more, and even more preferably 2.5 parts by mass or more, based on 100 parts by mass of the rubber component. The content is preferably 7.0 parts by mass or less, and more preferably 3.5 parts by mass or less.

[0111] The rubber composition for the cap tread and the rubber composition for the base tread preferably contain stearic acid. In the rubber composition for cap treads and the rubber composition for base treads, the content of stearic acid is preferably 0.5 parts by mass or more, more preferably 2.0 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component.

[0112] As the stearic acid, any conventionally known product can be used, for example, products available from NOF Corp., Kao Corp., Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., and the like.

[0113] The rubber composition for the cap tread and the rubber composition for the base tread preferably contain zinc oxide. In the rubber composition for cap treads and the rubber composition for base treads, the content of zinc oxide is preferably 0.5 parts by mass or more, more preferably 2.0 parts by mass or more, and is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, per 100 parts by mass of the rubber component.

[0114] As the zinc oxide, any known zinc oxide can be used, for example, products available from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc.

[0115] Wax may be blended into the rubber composition for the cap tread and the rubber composition for the base tread. In the rubber composition for cap treads and the rubber composition for base treads, the wax content is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, and preferably 10.0 parts by mass or less, more preferably 2.0 parts by mass or less, per 100 parts by mass of the rubber component.

[0116] The wax is not particularly limited, and examples thereof include petroleum waxes, natural waxes, etc. Also, synthetic waxes obtained by refining or chemically treating multiple waxes can be used. These waxes may be used alone or in combination of two or more kinds.

[0117] Examples of petroleum waxes include paraffin wax and microcrystalline wax. Examples of natural waxes are not particularly limited as long as they are derived from resources other than petroleum, and include, for example, vegetable waxes such as candelilla wax, carnauba wax, Japan wax, rice wax, and jojoba wax; animal waxes such as beeswax, lanolin, and spermaceti; mineral waxes such as ozokerite, ceresin, and petrolactam; and refined products thereof. Examples of commercially available products include products from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Seiko Chemical Co., Ltd.

[0118] It is preferable to compound sulfur into the rubber composition for the cap tread and the rubber composition for the base tread in order to form an appropriate amount of crosslinked chains in the polymer chains and to impart good performance.

[0119] In the rubber composition for cap tread, the content of sulfur is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 1.5 parts by mass or more, based on 100 parts by mass of the rubber component. The content is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, and even more preferably 2.0 parts by mass or less.

[0120] In the rubber composition for base tread, the content of sulfur is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, and even more preferably 2.5 parts by mass or more, based on 100 parts by mass of the rubber component. The content is preferably 7.0 parts by mass or less, more preferably 5.0 parts by mass or less, and even more preferably 4.0 parts by mass or less.

[0121] Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, etc., which are commonly used in the rubber industry. Commercially available products include those from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. These may be used alone or in combination of two or more kinds.

[0122] The rubber composition for the cap tread and the rubber composition for the base tread preferably contain a vulcanization accelerator.

[0123] In the rubber composition for cap tread, the content of the vulcanization accelerator is not particularly limited and may be freely determined according to the desired vulcanization speed and crosslink density, but it is preferably 3.0 parts by mass or more, more preferably 5.0 parts by mass or more, and even more preferably 5.3 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, and even more preferably 6.0 parts by mass or less.

[0124] In the rubber composition for base tread, the content of the vulcanization accelerator is not particularly limited and may be freely determined according to the desired vulcanization speed and crosslink density, but is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 1.5 parts by mass or more, relative to 100 parts by mass of the rubber component. The upper limit is preferably 4.0 parts by mass or less, more preferably 3.0 parts by mass or less, and even more preferably 2.0 parts by mass or less.

[0125] The type of vulcanization accelerator is not particularly limited, and commonly used ones can be used. Examples of the vulcanization accelerator include benzothiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazyl sulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide, Nt-butyl-2-benzothiazolyl sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, di-orthotolylguanidine, and orthotolylbiguanidine. These may be used alone or in combination of two or more. Among them, sulfenamide-based, guanidine-based and benzothiazole-based vulcanization accelerators are preferred.

[0126] In addition to the above-mentioned components, the rubber composition for the cap tread and the rubber composition for the base tread may contain compounding agents generally used in the tire industry, such as materials such as a mold release agent, as appropriate.

[0127] The rubber composition for the cap tread and the rubber composition for the base tread can be produced, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or a Banbury mixer, followed by vulcanization.

[0128] As for the kneading conditions, in the base kneading step in which additives other than the crosslinking agent (vulcanizing agent) and the vulcanization accelerator are kneaded, the kneading temperature is preferably 100°C or higher, more preferably 120°C or higher, and also preferably 180°C or lower, more preferably 170°C or lower. In the finish kneading step in which the vulcanizing agent and the vulcanization accelerator are kneaded, the kneading temperature is preferably 80°C or higher, and also preferably 120°C or lower, more preferably 110°C or lower. In addition, the composition kneaded with the vulcanizing agent and the vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. The vulcanization temperature is preferably 140°C or higher, more preferably 150°C or higher, and also preferably 190°C or lower, more preferably 185°C or lower.

[0129] The rubber composition for a cap tread and the rubber composition for a base tread are used for the cap tread and the base tread, respectively, which are tire components.

[0130] In this specification, a cap tread refers to the rubber layer that forms the outermost layer in the radial direction of the tire among the rubber layers that make up the tread. In the case of a tread having a two-layer structure of a cap tread and a base tread, the rubber layer that forms the outermost layer corresponds to the cap tread. In the case of a tread having a structure of three or more layers, the rubber layer that forms the outermost layer corresponds to the cap tread.

[0131] In this specification, the base tread refers to a rubber layer arranged radially inward of a cap tread that forms the outermost layer in the tire radial direction among the rubber layers that make up a multi-layered tread. In the case of a tread having a two-layer structure of a cap tread and a base tread, the rubber layer that forms the radially inner side of the tire corresponds to the base tread. In the case of a tread having a three or more layer structure, one or more rubber layers arranged radially inward of the cap tread correspond to the base tread.

[0132] The above tire is manufactured by a normal method using the above rubber composition for cap tread and rubber composition for base tread. That is, the composition containing various additives as necessary is extruded to match the shapes of the cap tread and base tread in the unvulcanized stage, molded by a normal method on a tire building machine, laminated with other tire components to form an unvulcanized tire, and then heated and pressurized in a vulcanizer to manufacture the tire.

[0133] The tire is not particularly limited, and examples thereof include pneumatic tires, solid tires, airless tires, etc. Among these, pneumatic tires are preferred.

[0134] The above tires are suitably used as passenger car tires, large passenger car tires, large SUV tires, truck and bus tires, motorcycle tires, racing tires, winter tires (studless tires, snow tires, studded tires), all-season tires, run-flat tires, aircraft tires, mining tires, etc.

[0135] In the above tire, the thickness Tc (mm) of the cap tread is preferably 12 mm or less, more preferably 11 mm or less, even more preferably 10 mm or less, and even more preferably 9 mm or less. The lower limit is preferably 5 mm or more, more preferably 6 mm or more, even more preferably 7 mm or more, and even more preferably 8 mm or more. Within the above range, the effect tends to be preferably obtained.

[0136] In the above tire, the thickness Tb (mm) of the base tread is preferably 4 mm or less, more preferably 3 mm or less, and even more preferably 2 mm or less. The lower limit is preferably 0.5 mm or more, and more preferably 1 mm or more. Within the above range, the effect tends to be preferably obtained.

[0137] Tc / Tb is preferably 1.5 or more, more preferably 2.1 or more, even more preferably 2.4 or more, even more preferably 3.0 or more, even more preferably 3.5 or more, even more preferably 4.0 or more, even more preferably 4.5 or more. The upper limit is preferably 9.2 or less, more preferably 7.0 or less, even more preferably 5.5 or less, even more preferably 5.0 or less. Within the above range, the effect tends to be obtained favorably.

[0138] Although the mechanism by which the effect of adjusting Tc / Tb to a specific range is unclear, it is believed that the change in hardness Hs over time caused by bleeding of the plasticizer can be suppressed, and therefore the durability of wet grip performance over time is improved.

[0139] In the above tire, the ratio (Rc / Tc) of the resin content Rc (parts by mass) relative to 100 parts by mass of the rubber component in the rubber composition for cap tread to the thickness Tc (mm) of the cap tread is preferably 2.3 or more, more preferably 3.0 or more, even more preferably 3.5 or more, still more preferably 3.8 or more, still more preferably 3.9 or more, and still more preferably 4.0 or more. The upper limit is preferably 8.0 or less, more preferably 6.0 or less, still more preferably 5.0 or less, still more preferably 4.3 or less, and still more preferably 4.2 or less. Within the above range, the effect tends to be preferably obtained.

[0140] Although the mechanism by which a greater effect is obtained when Rc / Tc is adjusted to a certain level is unclear, it is believed that by compounding a larger amount of resin per thickness, the change in hardness Hs over time caused by oil bleeding can be suppressed more effectively, and therefore it is presumed that the durability of wet grip performance over time will improve.

[0141] In this specification, the thickness Tc of the cap tread (cap layer) refers to the thickness of the cap tread on the tire equatorial plane in the tire radial cross section, and is the straight-line distance from the tread surface (surface of the cap tread) to the tire radial inner surface of the cap tread in the tire radial cross section.

[0142] The thickness Tb of the base tread (base layer) refers to the thickness of the base tread on the tire equatorial plane in the tire radial cross section, and is the straight-line distance from the tire radial outer surface of the base tread to the tire radial inner surface of the base tread in the tire radial cross section.

[0143] The thicknesses of the cap tread and base tread on the tire equatorial plane are values ​​measured from the outermost surface of the cap tread and the outermost surface of the base tread on the tire equatorial plane along the tire equatorial plane, respectively. When a current-carrying member or the like is present on the tire equatorial plane, this value is measured along the tire equatorial plane from a straight line connecting the ends of the interfaces blocked by the current-carrying member. When a groove is present on the tire equatorial plane, the thickness is measured at the center in the tire width direction of the land portion closest to the tire equatorial plane, and is the thickness measured in the normal direction of the radially outer surface of the cap tread and the radially outer surface of the base tread.

[0144] In this specification, dimensions such as thickness are measured with the bead portion of the tire aligned to the standard rim width. During measurement, the tire is cut out in the tire radial direction, and both bead ends of the sample are fixed in a state where they are aligned to the standard rim width.

[0145] In this specification, unless otherwise specified, the dimensions of each part of the tire are values ​​measured under normal conditions. In this specification, the term "normal condition" refers to a condition in which the tire is mounted on a normal rim (not shown), inflated to normal internal pressure, and no load is applied.

[0146] When it is not possible to measure with the tire mounted on a regular rim, the dimensions and angles of each part in the meridian section of the tire are measured by cutting the tire along a plane including the axis of rotation, and the distance between the left and right beads in the cross section is measured so that it corresponds to the distance between the beads of the tire mounted on a regular rim.

[0147] "Genuine rim" refers to the rim that is specified for each tire by the standard system that includes the standard on which the tire is based, for example, "Standard rim" in the applicable size listed in the "JATMA YEAR BOOK" for JATMA (Japan Automobile Tire Manufacturers Association), "Measuring Rim" in the "STANDARDS MANUAL" for ETRTO (The European Tire and Rim Technical Organisation), and "Design Rim" in the "YEAR BOOK" for TRA (The Tire and Rim Association, Inc.). Refer to JATMA, ETRTO, and TRA in that order, and follow the standard if there is an applicable size at the time of reference. In the case of a tire not specified in the standard, it refers to the rim that can be assembled to the rim and can hold internal pressure, that is, the rim with the smallest rim diameter and the next narrowest rim width among the rims that do not leak air from between the rim and tire.

[0148] "Regular internal pressure" refers to the air pressure specified for each tire by each standard in the standard system including the standard on which the tire is based. For JATMA, it refers to the "Maximum Air Pressure", for ETRTO, it refers to the "INFLATION PRESSURE", and for TRA, it refers to the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". As with "regular rims", it refers to JATMA, ETRTO, TRA in that order and follows those standards. For tires not specified in the standard, it refers to the regular internal pressure (250kPa or more) of another tire size (specified in the standard) that is specified with the regular rim as the standard rim. Note that if multiple regular internal pressures of 250kPa or more are specified, it refers to the smallest value among them.

[0149] In this specification, the term "normal load" refers to the load that is determined for each tire by each standard in the standard system including the standard on which the tire is based, and is the maximum load capacity in the case of JATMA, the "LOAD CAPACITY" in the case of ETRTO, and the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA. As in the case of the "normal rim" and "normal internal pressure" mentioned above, JATMA, ETRTO, and TRA are referred to in that order and their standards are followed. In the case of a tire not determined by a standard, the normal load W is calculated as follows: L Request. V = {(Dt / 2) 2 -(Dt / 2-Ht) 2}×π×Wt W L =0.000011×V+175 W L :Normal load (kg) V: Virtual volume of the tire (mm 3 ) Dt: Tire outer diameter (mm) Ht: Section height of the tire (mm) Wt: tire section width (mm)

[0150] The "section width Wt (mm)" of a tire is the maximum width between the outer surfaces of the sidewalls when the tire is in its normal condition, excluding any patterns or lettering on the sidewalls.

[0151] The "outer diameter Dt (mm)" of a tire refers to the outer diameter of the tire under normal conditions.

[0152] The "section height Ht (mm)" of a tire refers to the radial height of the tire at its radial cross section, and corresponds to half the difference between the tire's outer diameter Dt and the rim diameter R, where R is the tire's rim diameter (mm). In other words, the section height Ht can be calculated by (Dt-R) / 2.

[0153] An example of the tire will be described below with reference to the drawings, but the tire is not limited to this embodiment.

[0154] 1, the up-down direction is the radial direction of the tire 2, the left-right direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. The tire 2 is symmetrical. The tread 4 includes a cap layer 30 (cap tread) and a base layer 28 (base tread).

[0155] Although FIG. 1 shows an example of a two-layer tread 4 consisting of a cap layer 30 and a base layer 28, a tread having a structure of three or more layers may also be used.

[0156] In the tire 2 of Fig. 1, the cap layer 30 is composed of the above-mentioned rubber composition for cap tread, the base layer 28 is composed of the rubber composition for base tread, and the content of polymer having ethylene units in 100 mass% of the rubber component in the cap layer 30 is 50 mass% or more. In addition, the resin content Rc (parts by mass) and the oil content Oc (parts by mass) per 100 mass parts of the rubber component in the cap layer 30, and the oil content Ob (parts by mass) per 100 mass parts of the rubber component in the base layer 28 satisfy the formula (1) "Rc>Oc≧Ob".

[0157] In the tire 2, each sidewall 6 extends substantially radially inward from an end of the tread 4. A radially outer portion of each sidewall 6 is joined to the tread 4. A radially inner portion of each sidewall 6 is joined to a clinch 10. Each sidewall 6 can prevent damage to the carcass 14.

[0158] 1 is located between the tread 4 and the sidewall 6. The wing 8 is joined to the tread 4 and the sidewall 6, respectively.

[0159] Each clinch 10 is located approximately radially inward of the sidewall 6 and has at least one or more portions that come into contact with the rim.

[0160] The carcass 14 includes a carcass ply 36. In the tire 2, the carcass 14 is made up of one carcass ply 36, but may be made up of two or more carcass plies.

[0161] In the tire 2, the carcass ply 36 is laid between the bead cores 32 on both sides and extends along the tread 4 and the sidewall 6. The carcass ply 36 is folded back from the inside to the outside in the axial direction around each bead core 32. By this folding back, the carcass ply 36 is formed with a main portion 36a and a pair of folded back portions 36b. That is, the carcass ply 36 includes the main portion 36a and a pair of folded back portions 36b.

[0162] Each bead core 32 includes a bead apex 34 extending radially outward from the bead core 32. The bead core 32 is preferably ring-shaped and includes a wound non-stretchable wire. The bead apex 34 tapers radially outward.

[0163] Although not shown, the carcass ply 36 is preferably made of a number of parallel cords and a topping rubber. The absolute value of the angle that each cord makes with respect to the equatorial plane CL is preferably 75° to 90°. In other words, the carcass 14 preferably has a radial structure.

[0164] The belt layer 16 in FIG. 1 is located radially inward of the tread 4. The belt layer 16 is laminated with the carcass 14. The belt layer 16 reinforces the carcass 14. In the tire 2 in FIG. 1, the belt layer 16 is composed of an inner layer 38 and an outer layer 40. As is clear from FIG. 1, it is desirable that the width of the inner layer 38 is slightly larger than the width of the outer layer 40 in the axial direction. In this tire 2, the axial width of the belt layer 16 is preferably 0.6 times or more and 0.9 times or less of the cross-sectional width of the tire 2.

[0165] Each of the inner layer 38 and the outer layer 40 is preferably made of a number of parallel single-wire steel cords (steel monofilaments) and a topping rubber (coating rubber). In other words, the belt layer 16 includes a number of parallel steel monofilaments.

[0166] The band 18 in Fig. 1 is located radially outside the belt layer 16. In the axial direction, the band 18 has a width equal to the width of the belt layer 16. The band 18 may also have a width greater than the width of the belt layer 16.

[0167] Although not shown, the band 18 is preferably made of a cord and a topping rubber. The cord is wound in a spiral shape. This band 18 has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is preferably 5° or less, and more preferably 2° or less. Since the belt layer 16 is restrained by the cord, lifting of the belt layer 16 is suppressed.

[0168] 1 constitute a reinforcing layer. The reinforcing layer may be constituted by the belt layer 16 alone.

[0169] FIG. 2 is an enlarged view of the vicinity of the tread 4 in FIG. The tire in FIG. 2 is a tire 2 having a groove 26 on the tire equatorial plane (CL). In this case, the thickness (Tc) of the cap tread is the thickness measured at the center in the tire width direction of the land portion closest to the groove 26 on the tire equatorial plane in the radial cross section of the tire, and is the thickness measured in the normal direction to the surface of the cap layer 30 (cap tread), specifically, it refers to the straight-line distance in the normal direction from the tire radial outer surface of the cap layer 30 to the interface of the base layer 28 on the tire outermost surface side. The thickness (Tb) of the base tread is the thickness measured at the center in the tire width direction of the land portion closest to the groove 26 on the tire equatorial plane in the radial cross section of the tire, and is the thickness measured in the normal direction of the tire radial outer surface of the base layer 28 (base tread); specifically, it refers to the straight-line distance in the normal direction from the outer surface of the base layer 28 to the interface of the band 18 on the outermost side of the tire.

[0170] The inner liner 20 is located inside the carcass 14. The inner liner 20 is bonded to the inner surface of the carcass 14. A typical base rubber of the inner liner 20 is butyl rubber or halogenated butyl rubber. The inner liner 20 holds the internal pressure of the tire 2.

[0171] Each chafer 22 is located adjacent to a bead 12. In this embodiment, the chafer 22 is preferably made of fabric with rubber impregnated into the fabric. The chafer 22 may be integral with the clinch 10.

[0172] In the tire 2, the tread 4 has a main groove 42 as the groove 26. As shown in FIG. 1, a plurality of main grooves 42, specifically three main grooves 42, are formed in the tread 4. These main grooves 42 are arranged at intervals in the axial direction. The three main grooves 42 are formed in the tread 4, thereby forming four ribs 44 extending in the circumferential direction. In other words, the spaces between the ribs 44 constitute the main grooves 42.

[0173] Each of the main grooves 42 extends in the circumferential direction. The main grooves 42 are continuous in the circumferential direction without interruption. The main grooves 42 facilitate the drainage of water present between the road surface and the tire 2, for example, in rainy weather. Therefore, even if the road surface is wet, the tire 2 can make sufficient contact with the road surface.

[0174] In tire 2, the resin content Rc (parts by mass) and oil content Oc (parts by mass) per 100 parts by mass of the rubber component in cap layer 30, the oil content Ob (parts by mass) per 100 parts by mass of the rubber component in base layer 28, the plasticizer content Pc (parts by mass) per 100 parts by mass of the rubber component in cap layer 30, the plasticizer content Pb (parts by mass) per 100 parts by mass of the rubber component in base layer 28, the filler content Fc (parts by mass) per 100 parts by mass of the rubber component in cap layer 30, With regard to the filler content Fb (parts by mass) per 100 parts by mass of the rubber component, the carbon black content Cc (parts by mass) per 100 parts by mass of the rubber component in cap layer 30, the carbon black content Cb (parts by mass) per 100 parts by mass of the rubber component in base layer 28, the thickness Tc (mm) of cap layer 30, and the thickness Tb (mm) of base layer 28, it is desirable that Rc / Oc, Oc / Ob, Rc / Ob, Pc / Pb, Fc / Fb, Cc / Cb, Tc / Tb, and Rc / Tc be within the aforementioned ranges. EXAMPLES

[0175] Below, examples (embodiments) that are considered to be preferable for carrying out the present disclosure will be shown, but the scope of the present disclosure is not limited to the embodiments.

[0176] The various chemicals used during synthesis and polymerization are described below. If necessary, the chemicals are purified according to standard methods. n-Hexane: Kanto Chemical Co., Ltd. Styrene: Kanto Chemical Co., Ltd. Butadiene: 1,3-butadiene manufactured by Tokyo Chemical Industry Co., Ltd. TMEDA: N,N,N',N'-Tetramethylethylenediamine manufactured by Kanto Chemical Co., Ltd. n-Butyllithium solution: 1.6M n-butyllithium hexane solution manufactured by Kanto Chemical Co., Ltd. Ethanol: Kanto Chemical Co., Ltd. 2,6-Di-tert-butyl-p-cresol: Nocrac 200 manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0177] The evaluation methods for the copolymers will be summarized below.

[0178] (Measurement of hydrogenation rate of conjugated diene part of copolymer) A 15% solution was prepared using carbon tetrachloride as a solvent and was operated at 100 MHz. 1 It is calculated from the spectral reduction rate of the unsaturated bond in H-NMR.

[0179] (Measurement of styrene content) At 25°C, using a JEOL JNM-A 400 NMR instrument 1 H-NMR is measured, and the styrene content is determined from the ratio of phenyl protons based on styrene units at 6.5 to 7.2 ppm to vinyl protons based on butadiene units at 4.9 to 5.4 ppm, which is obtained from the spectrum.

[0180] (Measurement of weight average molecular weight (Mw)) The weight average molecular weight (Mw) of the copolymer is determined by converting it into standard polystyrene based on the measured value obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation).

[0181] (Production Example 1: Synthesis of hydrogenated styrene-butadiene copolymer 1: hydrogenation rate 95 mol%) 2000ml of n-hexane, 60g of styrene, 140g of butadiene, 0.93g of TMEDA, and 0.45mmol of n-butyllithium are added to a heat-resistant reaction vessel that has been thoroughly substituted with nitrogen, and the mixture is stirred at 50°C for 5 hours to carry out a polymerization reaction. Next, the mixture is stirred for 20 minutes while supplying hydrogen gas at a pressure of 0.4MPa-Gauge, and reacted with the unreacted lithium at the polymer end to produce lithium hydride. Hydrogen gas is supplied at a pressure of 0.7MPa-Gauge and a reaction temperature of 90°C, and hydrogenation is carried out using a catalyst mainly composed of titanocene dichloride. When the amount of hydrogen absorption reaches an integrated amount that corresponds to the target hydrogenation rate, the reaction temperature is returned to room temperature, the hydrogen pressure is returned to normal pressure, and the reaction vessel is discharged. The reaction solution is stirred and poured into water, and the solvent is removed by steam stripping to obtain hydrogenated styrene-butadiene copolymer 1 (hydrogenation rate 95 mol%, weight average molecular weight (Mw) 450,000, styrene content 30 mass%, butadiene content 70 mass%).

[0182] (Production Example 2: Synthesis of hydrogenated styrene-butadiene copolymer 2: hydrogenation rate 80 mol%) Hydrogenated styrene-butadiene copolymer 2 (hydrogenation rate 80 mol%, weight average molecular weight (Mw) 480,000, styrene content 30 mass%) is obtained by the same recipe as hydrogenated styrene-butadiene copolymer 1, except that the cumulative amount of hydrogen suction is adjusted so as to obtain the desired hydrogenation rate.

[0183] The various chemicals used in the manufacture of the cap tread and base tread are described below. If necessary, the chemicals are refined according to a standard method. (Captread) Hydrogenated styrene-butadiene copolymers 1-2: Production Examples 1-2 above (polymers having ethylene units) NR:TSR20 Carbon black: Show Black N220 (N2SA:111m) manufactured by Cabot Japan Co., Ltd. 2 / g) Silica: Ultrasil VN3 (N2SA: 175m) manufactured by Evonik Degussa 2 / g) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd. Anti-aging agent: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd. Oil: H&R Vivatec 500 (TDAE, aromatic process oil) Resin 1: Sylvatraxx 4401 (styrene α-methylstyrene resin (copolymer of styrene and α-methylstyrene)) manufactured by Arizona Chemical Company Resin 2: ExxonMobil PR120 (hydrogenated dicyclopentadiene resin, softening point 120°C) Stearic acid: Camellia made by NOF Corporation Zinc oxide: Two types of zinc oxide manufactured by Mitsui Metals Co., Ltd. Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator CZ: Noccela CZ-G (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator DPG: Noccelaer D (N,N'-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator TBzTD: Sancerer TBzTD (tetrabenzyl thiuram disulfide) manufactured by Sanshin Chemical Industry Co., Ltd.

[0184] (Base tread) NR:SIR20 BR: BR150B manufactured by Ube Industries, Ltd. Carbon black: Show Black N220 (N2SA:111m) manufactured by Cabot Japan Co., Ltd. 2 / g) Oil: Aroma oil made by ENEOS Corporation Stearic acid: Camellia made by NOF Corporation Zinc oxide: Two types of zinc oxide manufactured by Mitsui Metals Co., Ltd. Anti-aging agent: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd. Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd. Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator TBBS: Noccela NS (N-tert-butyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0185] (Preparation of rubber composition for cap tread) According to the composition shown in Table 1, materials other than sulfur and vulcanization accelerator are kneaded for 5 minutes at 150° C. using a 1.7 L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded mixture. Sulfur and a vulcanization accelerator are added to the kneaded mixture, and the mixture is kneaded for 5 minutes at 80° C. using an open roll to obtain an unvulcanized rubber composition.

[0186] (Preparation of Rubber Composition for Base Tread) According to the composition shown in Table 2, materials other than sulfur and vulcanization accelerator are kneaded for 5 minutes at 150° C. using a 1.7 L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded product. Sulfur and a vulcanization accelerator are added to the kneaded mixture, and the mixture is kneaded for 5 minutes at 80° C. using an open roll to obtain an unvulcanized rubber composition.

[0187] <Manufacturing method for test tires> According to the specifications in Table 1, the rubber composition for unvulcanized cap tread is molded into the shape of a cap tread, and the rubber composition for unvulcanized base tread is molded into the shape of a base tread, and these are laminated together with other tire components on a tire building machine to form an unvulcanized tire. The tire is then vulcanized at 170°C for 10 minutes to produce a test tire (size 205 / 70R15, passenger car tire).

[0188] The results are shown in Table 1, which are calculated based on the following evaluation method assuming test tires obtained from compositions whose formulation and specifications are changed according to Table 1.

[0189] <Hardness> (New) For test specimens cut out from the cap tread of each test tire (new), measure the JIS-A hardness (new) at room temperature (25°C) using a Type A durometer in accordance with JIS K6253-3 (2012) "Vulcanized rubber and thermoplastic rubber - Determination of hardness - Part 3: Durometer hardness". (After heat aging) After measuring the hardness (new), the test piece is heat treated at 80°C for 168 hours under conditions of an oxygen concentration of 20%. The JIS-A hardness (after heat aging) at room temperature is measured in the same manner.

[0190] <Sustainability of wet grip performance over time> (New) Each test tire was mounted on a domestically produced 2000cc FF vehicle, and the vehicle was driven on a wet road surface at 25°C. The lock brakes were applied at a speed of 150km / h, and the stopping distance (initial) required to stop the vehicle was measured. (Wet grip performance after aging) After the above-mentioned actual vehicle has been driven for 20,000 km, the stopping distance (after aging) required to stop the vehicle is measured using the same method. The wet grip performance retention rate (%) is calculated based on the stopping distance of each test tire, both new and aged. A higher wet grip performance retention rate indicates better durability of wet grip performance.

[0191] [Table 1]

[0192] [Table 2]

[0193] The present invention (1) is a tire having a cap tread and a base tread, The cap tread has a content of a polymer having an ethylene unit of 50% by mass or more in 100% by mass of a rubber component, The tire is characterized in that the resin content Rc (parts by mass) and oil content Oc (parts by mass) per 100 parts by mass of the rubber component in the cap tread, and the oil content Ob (parts by mass) per 100 parts by mass of the rubber component in the base tread satisfy the following formula (1): (1) Rc>Oc≧Ob

[0194] The present invention (2) is the tire according to the present invention (1), in which the resin contains a hydrogenated resin.

[0195] The present invention (3) is the tire according to the present invention (1) or (2), wherein the cap tread has a filler content of 75 parts by mass or more per 100 parts by mass of the rubber component.

[0196] The present invention (4) is a tire in any combination with any of the present inventions (1) to (3) having an Rc / Oc of 1.5 or less.

[0197] The present invention (5) is a tire in any combination with any of the present inventions (1) to (4) having an Oc / Ob ratio of 2.5 or more.

[0198] The present invention (6) is a tire in any combination with any of the present inventions (1) to (5) having an Rc / Ob of 3.3 or more.

[0199] The present invention (7) is a tire in any combination with any of the present inventions (1) to (6), in which the content Pc (parts by mass) of the plasticizer per 100 parts by mass of the rubber component in the cap tread is greater than the content Pb (parts by mass) of the plasticizer per 100 parts by mass of the rubber component in the base tread.

[0200] The present invention (8) is the tire according to the present invention (7), in which Pc / Pb is 5.0 or more.

[0201] The present invention (9) is a tire comprising a cap tread containing an isoprene-based rubber, a base tread containing an isoprene-based rubber and a butadiene rubber, The cap tread is a tire in any combination with any of the present inventions (1) to (8) in which the content of isoprene-based rubber in 100% by mass of the rubber component is 5 to 40% by mass.

[0202] The present invention (10) is a tire in any combination with any of the present inventions (1) to (9), in which the ratio (Fc / Fb) of the filler content Fc per 100 parts by mass of the rubber component in the cap tread to the filler content Fb per 100 parts by mass of the rubber component in the base tread is 3.2 or more.

[0203] The present invention (11) is a tire in any combination with any of the present inventions (1) to (10), in which the ratio (Cc / Cb) of the carbon black content Cc per 100 parts by mass of the rubber component in the cap tread to the carbon black content Cb per 100 parts by mass of the rubber component in the base tread is 0.15 or more.

[0204] The present invention (12) is a tire in any combination with any of the present inventions (1) to (11), in which the ratio (Tc / Tb) of the cap tread thickness Tc (mm) to the base tread thickness Tb (mm) is 2.1 to 9.2.

[0205] The present invention (13) is a tire in any combination with any of the present inventions (1) to (12), in which the ratio (Rc / Tc) of the resin content Rc (parts by mass) per 100 parts by mass of the rubber component in the cap tread to the thickness Tc (mm) of the cap tread is 3.0 or more. [Explanation of symbols]

[0206] 2 Tires 4 Tread 6 Sidewall 8 Wing 10 Clinch 12 Beads 14 Carcass 16 Belt Layer 18 Bands 20 Inner Liner 22 Chafer 24 Tread Surface 26 Groove 28 Base Layer 30 Cap Layer 32 cores 34 Apex 36 Carcass ply 36a Main part 36b Folded part 38 Inner layer 40 outer layer 42 Main groove 44 Ribs CL Tire equatorial plane Tc Cap tread thickness Tb Base tread thickness

Claims

1. A tire having a cap tread and a base tread, The cap tread has a content of a polymer having an ethylene unit of 50% by mass or more in 100% by mass of a rubber component, A tire in which a resin content Rc (parts by mass) and an oil content Oc (parts by mass) per 100 parts by mass of a rubber component in the cap tread, and an oil content Ob (parts by mass) per 100 parts by mass of the rubber component in the base tread satisfy the following formula (1): (1) Rc>Oc≧Ob

2. 2. The tire of claim 1, wherein the resin comprises a hydrogenated resin.

3. 2. The tire according to claim 1, wherein the cap tread has a filler content of 75 parts by mass or more per 100 parts by mass of the rubber component.

4. 2. The tire according to claim 1, wherein Rc / Oc is 1.5 or less.

5. 2. The tire according to claim 1, wherein Oc / Ob is 2.5 or more.

6. 2. The tire according to claim 1, wherein Rc / Ob is 3.3 or more.

7. 2. The tire according to claim 1, wherein a content Pc (parts by mass) of the plasticizer in the cap tread per 100 parts by mass of the rubber component is greater than a content Pb (parts by mass) of the plasticizer in the base tread per 100 parts by mass of the rubber component.

8. 8. The tire according to claim 7, wherein Pc / Pb is 5.0 or more.

9. The cap tread includes an isoprene-based rubber, and the base tread includes an isoprene-based rubber and a butadiene rubber.

2. The tire according to claim 1, wherein the cap tread has an isoprene-based rubber content of 5 to 40 mass % based on 100 mass % of the rubber component.

10. 2. The tire according to claim 1, wherein a ratio (Fc / Fb) of a filler content Fc per 100 parts by mass of the rubber component in the cap tread to a filler content Fb per 100 parts by mass of the rubber component in the base tread is 3.2 or more.

11. 2. The tire according to claim 1, wherein a ratio (Cc / Cb) of a carbon black content Cc per 100 parts by mass of the rubber component in the cap tread to a carbon black content Cb per 100 parts by mass of the rubber component in the base tread is 0.15 or more.

12. The tire according to claim 1, wherein a ratio (Tc / Tb) of a thickness Tc (mm) of the cap tread to a thickness Tb (mm) of the base tread is 2.1 to 9.

2.

13. 2. The tire according to claim 1, wherein a ratio (Rc / Tc) of a resin content Rc (parts by mass) per 100 parts by mass of the rubber component in the cap tread to a thickness Tc (mm) of the cap tread is 3.0 or more.

Images