Rubber composition for cap tread and tire

Abstract

To provide a rubber composition for cap tread and a tire having superior comprehensive performance in terms of fuel economy and abrasion resistance.SOLUTION: A rubber composition for a cap tread comprises a rubber component containing isoprene-based rubber and a filler containing silica, wherein the content of the isoprene-based rubber exceeds 5 mass% relative to 100 mass% of the rubber component, the content of the silica exceeds 40 pts.mass relative to 100 pts.mass of the rubber component, a ratio (AE / Ash) of an acetone extract level AE (mass%) to an ash content Ash (mass%) is less than 0.52, a difference ΔG between a complex elastic modulus Ga (MPa) under 0.1% shear strain at 30°C (frequency 10 Hz) and a complex elastic modulus G*b (MPa) under 20% shear strain at 30°C (frequency 10 Hz) is less than 1.50 MPa, and a hardness Hs exceeds 65.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a rubber composition for a cap tread and a tire using the same.

Background Art

[0002] Recently, for tires, from the viewpoint of environmental considerations and the like, improvements in low fuel consumption, wear resistance, and the like have been desired.

Summary of the Invention

Problems to be Solved by the Invention

[0003] However, since low fuel consumption and wear resistance are generally conflicting performances, it is difficult to improve them in a well-balanced manner.

[0004] An object of the present invention is to solve the above problems and provide a rubber composition for a cap tread and a tire having excellent comprehensive performances of low fuel consumption and wear resistance.

Means for Solving the Problems

[0005] The present invention is a rubber composition for a cap tread containing a rubber component containing an isoprene-based rubber and a filler containing silica, wherein the content of the isoprene-based rubber in 100% by mass of the rubber component exceeds 5% by mass, the content of the silica with respect to 100 parts by mass of the rubber component exceeds 40 parts by mass, the ratio (AE / Ash) of the acetone extraction amount AE (% by mass) to the ash content Ash (% by mass) is less than 0.52, the difference ΔG* between the complex elastic modulus G*a (MPa) at 0.1% shear deformation at 30°C (frequency 10 Hz) and the complex elastic modulus G*b (MPa) at 20% shear deformation at 30°C (frequency 10 Hz) is less than 1.50 MPa, and the hardness Hs exceeds 65, and relates to a rubber composition for a cap tread.

Effects of the Invention

[0006] The present invention relates to a rubber composition for a cap tread containing a rubber component containing an isoprene rubber and a filler containing silica, wherein the content of the isoprene rubber in 100% by mass of the rubber component exceeds 5% by mass, the content of the silica with respect to 100 parts by mass of the rubber component exceeds 40 parts by mass, the ratio (AE / Ash) of the acetone extraction amount AE (% by mass) to the ash content Ash (% by mass) is less than 0.52, the difference ΔG* between the complex elastic modulus G*a (MPa) at 0.1% shear deformation at 30°C (frequency 10 Hz) and the complex elastic modulus G*b (MPa) at 20% shear deformation at 30°C (frequency 10 Hz) is less than 1.50 MPa, and the hardness Hs exceeds 65. Since it is a rubber composition for a cap tread, the overall performance of low fuel consumption and wear resistance can be improved.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0008] The rubber composition for a cap tread contains a rubber component containing an isoprene rubber and a filler containing silica, the content of the isoprene rubber in 100% by mass of the rubber component exceeds 5% by mass, the content of the silica with respect to 100 parts by mass of the rubber component exceeds 40 parts by mass, and the ratio (AE / Ash) of the acetone extraction amount AE (% by mass) to the ash content Ash (% by mass) is less than 0.52, the difference ΔG* between the complex elastic modulus G*a (MPa) at 0.1% shear deformation at 30°C (frequency 10 Hz) and the complex elastic modulus G*b (MPa) at 20% shear deformation at 30°C (frequency 10 Hz) is less than 1.50 MPa, and the hardness Hs exceeds 65.

[0009] The reason for obtaining the above-mentioned effects by the rubber composition for a cap tread is not necessarily clear, but it is presumed as follows. In the case of low fuel consumption formulations, the method of reducing the amount of filler is common, but the reinforcing property decreases, and it is generally difficult to achieve both wear resistance. In a rubber composition containing an isoprene rubber and silica in a predetermined formulation, by making the ratio (AE / Ash) of the acetone extraction amount AE to the ash content Ash less than 0.52, the difference ΔG* between the complex elastic modulus G*a at 0.1% shear strain and the complex elastic modulus G*b at 20% shear strain becomes less than 1.50 MPa, and the hardness Hs exceeds 65. And by making ΔG* < 1.50 MPa, the dispersibility of the filler is improved, and at the same time, it becomes easier to deform with respect to the road surface during running, so it is considered that wear is suppressed. Also, it is considered that wear is suppressed by making Hs > 65. Therefore, it is presumed that the comprehensive performance of low fuel consumption and wear resistance is improved by the rubber composition for the cap tread.

[0010] Thus, the present invention solves the problem (objective) of improving the comprehensive performance of low fuel consumption and wear resistance by adopting a configuration that satisfies the relationships of "AE / Ash < 0.52", "ΔG* < 1.50 MPa", and "Hs > 65". That is, the parameters of "AE / Ash < 0.52", "ΔG* < 1.50 MPa", and "Hs > 65" do not define the problem (objective). The problem of the present application is to improve the comprehensive performance of low fuel consumption and wear resistance, and for that purpose, a configuration that satisfies the parameters is adopted.

[0011] Hereinafter, chemicals that can be used in the rubber composition for the cap tread will be described.

[0012] In this specification, the cap tread is a rubber layer that forms the outermost layer in the tire radial direction among the rubber layers that make up the tread. When the tread is a single-layer structure tread, it is the single-layer structure tread itself. When the tread has a two-layer structure of a cap tread and a base tread, it is the rubber layer that forms the surface layer. When the tread has a structure of three or more layers, the rubber layer that forms the outermost layer corresponds to the cap tread.

[0013] The rubber composition for cap tread contains a rubber component. Here, the rubber component is a component that contributes to crosslinking. Generally, a polymer having a weight average molecular weight (Mw) of 10,000 or more and a polymer component that is not extracted by acetone corresponds to the rubber component. The elastomer component is in a solid state at normal temperature (25°C).

[0014] The weight average molecular weight of the rubber component is preferably 50,000 or more, more preferably 150,000 or more, still more preferably 200,000 or more, particularly preferably 270,000 or more, and is preferably 2,000,000 or less, more preferably 1,500,000 or less, still more preferably 1,000,000 or less. When within the above range, the effect tends to be obtained more favorably.

[0015] In this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) can be determined by standard polystyrene conversion based on the measured values by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation). Also, in the case of a polymer having a modified group, since the modified group and the silica gel of the column interact and accurate Mw and Mn cannot be obtained, usually, Mw and Mn are measured before the modification treatment is carried out.

[0016] The rubber component that can be used in the above rubber composition for cap tread may be an unmodified rubber or a modified rubber. Examples of the modified rubber include rubbers having a functional group that interacts with a filler such as silica. For example, a terminal-modified rubber (terminal-modified rubber having the above functional group at the terminal) in which at least one terminal of the rubber is modified with a compound (modifying agent) having the above functional group, a main-chain modified rubber having the above functional group in the main chain, a main-chain and terminal modified rubber having the above functional group in the main chain and at the terminal (for example, a main-chain and terminal modified rubber having the above functional group in the main chain and at least one terminal modified with the above modifying agent), and 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.

[0017] Examples of the above 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, an epoxy group, etc. These functional groups may have a substituent. Among them, an amino group (preferably an amino group in which a hydrogen atom of the 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 preferable.

[0018] The rubber composition for cap tread contains an isoprene-based rubber as a rubber component.

[0019] In the above rubber composition for cap tread, the content of the isoprene-based rubber (total amount of unmodified isoprene-based rubber and modified isoprene-based rubber) in 100% by mass of the rubber component exceeds 5% by mass, preferably 7% by mass or more, more preferably 9% by mass or more, still more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less. When it is within the above range, the effect tends to be obtained better.

[0020] Examples of the isoprene rubber include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, modified IR, etc. As NR, for example, those commonly used in the rubber industry such as SIR20, RSS#3, TSR20, etc. can be used. IR is not particularly limited, and for example, those commonly used in the rubber industry such as IR2200, etc. can be used. Examples of the modified NR include deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), etc., examples of the modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc., and examples of the modified IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. These may be used alone or in combination of two or more.

[0021] From the viewpoint of obtaining more effects, it is desirable that the rubber composition for the cap tread contains a modified isoprene rubber as a rubber component. Examples of the modified isoprene rubber include modified isoprene rubbers into which functional groups similar to those of the modified rubber are introduced.

[0022] In the above rubber composition for the cap tread, the content of the modified isoprene rubber (the total amount of epoxidized natural rubber, hydrogenated natural rubber, grafted natural rubber, epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, isoprene rubber having various modified groups, etc.) in 100% by mass of the rubber component is preferably more than 5% by mass, more preferably 8% by mass or more, still more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less. When within the above range, there is a tendency to obtain better effects.

[0023] Among the modified isoprene rubbers, from the viewpoint of obtaining more effects, a modified isoprene rubber having a modified group containing at least one selected from the group consisting of nitrogen, sulfur, oxygen, and silicon (hereinafter, also referred to as a specific modified isoprene rubber) is desirable.

[0024] When a specific modified isoprene rubber is included, the mechanism by which more effective results can be obtained is not clear. However, it is considered that an interaction occurs between the modifying group in the specific modified isoprene rubber and silica, suppressing the condensation of silica, and thus improving the dispersibility of silica. Therefore, it is considered that the overall performance of low fuel consumption and abrasion resistance is improved.

[0025] The above-mentioned specific modified isoprene rubber is not particularly limited as long as it has a modifying group containing at least one selected from the group consisting of nitrogen, sulfur, oxygen, and silicon. For example, a terminal-modified rubber in which at least one end of the rubber is modified with a compound having the modifying group, a main-chain modified rubber having the modifying group in the main chain, a main-chain terminal-modified rubber having the modifying group in the main chain and at the terminal, etc. may be mentioned. Among them, a modified rubber having the modifying group at least at the terminal is desirable.

[0026] The above-mentioned specific modified isoprene rubber is not particularly limited as long as it has a modifying group containing at least one selected from the group consisting of nitrogen, sulfur, oxygen, and silicon. However, from the viewpoint of obtaining more effective results, a modified isoprene rubber having a modifying group containing nitrogen and silicon (hereinafter also referred to as a nitrogen- and silicon-modified isoprene rubber) is preferable.

[0027] In the above-mentioned nitrogen- and silicon-modified isoprene rubber, the modifying group containing nitrogen and silicon is not particularly limited. However, it is preferably one containing a nitrogen atom as an amino group (-NR 2 : R is a hydrogen atom or a hydrocarbon group), and it is also preferably one containing a silicon atom as a hydrocarbyloxysilyl group (≡SiOR: R is a hydrocarbon group).

[0028] Among them, from the viewpoint of obtaining more effective results, the modifying group containing nitrogen and silicon is preferably a group represented by the following formula (A).

Chemical formula

[0029] The above-mentioned substituent is not particularly limited as long as it is a monovalent substituent. Examples thereof include a halogen atom, a hydroxy group, a nitro group, a carboxy group, an alkoxy group, an amino group, a mercapto group, an acyl group, an imide group, a phosphino group, a phosphinyl group, a silyl group, and a hydrocarbon group which may have a hetero atom. Examples of the above-mentioned halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. Examples of the hetero atom of the hydrocarbon group which may have the above-mentioned hetero atom include an oxygen atom, a nitrogen atom, a sulfur atom, a phosphorus atom, etc. Examples of the hydrocarbon group which may have the above-mentioned hetero atom include an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a group combining these. The above-mentioned aliphatic hydrocarbon group may be linear, branched, or cyclic. Specific examples of the above-mentioned aliphatic hydrocarbon group include a linear or branched alkyl group (preferably having 1 to 30 carbon atoms), a linear or branched alkenyl group (preferably having 2 to 30 carbon atoms), a linear or branched alkynyl group (preferably having 2 to 30 carbon atoms), etc. Examples of the above-mentioned aromatic hydrocarbon group include aromatic hydrocarbon groups having 6 to 18 carbon atoms such as a phenyl group, a tolyl group, a xylyl group, a naphthyl group, etc.

[0030] R 11 、R 12 each preferably represents a hydrogen atom, an alkyl group (preferably having 1 to 10 carbon atoms), an alkylsilyl group (preferably having 1 to 10 carbon atoms), an aromatic hydrocarbon group (preferably having 6 to 18 carbon atoms), and more preferably a hydrogen atom. R 11 、R 12 may be the same or different, and R 11 、R12 When they are different, R 11 , R 12 The combination is preferably a combination of a hydrogen atom and an alkyl group (preferably having 1 to 10 carbon atoms), an alkylsilyl group (preferably having 1 to 10 carbon atoms), or an aromatic hydrocarbon group (preferably having 6 to 18 carbon atoms), more preferably a combination of a hydrogen atom and an alkylsilyl group (preferably having 1 to 10 carbon atoms), and still more preferably a combination of a hydrogen atom and a trialkylsilyl group (preferably having 1 to 10 carbon atoms). Also, among the above substituents, when there are a plurality of R 11 , R 12 respectively, each R 11 , R 12 may be the same or different.

[0031] R 13 is preferably a hydrocarbyloxy group (-OR group: R is a hydrocarbon group), and more preferably an alkoxy group (preferably having 1 to 10 carbon atoms).

[0032] L 11 Examples of the divalent organic group of include aliphatic hydrocarbon groups such as alkylene groups (preferably having 1 to 10 carbon atoms), aromatic hydrocarbon groups such as arylene groups (preferably having 6 to 18 carbon atoms), -O-, -S-, -SO 2 -, -N(R)-(R is an alkyl group), -CO-, -NH-, -COO-, -CONH-, or a group combining these (for example, an alkyleneoxy group (-C m H 2m O-: m is a positive integer), an alkyleneoxycarbonyl group, an alkylenecarbonyloxy group, etc.). Among them, L 11 is preferably an alkylene group (preferably having 1 to 10 carbon atoms).

[0033] From the viewpoint of obtaining more effects, n is preferably 2, and m is preferably 1.

[0034] The above-mentioned specific modified isoprene rubber preferably has a weight-average molecular weight (Mw) of 100,000 or more, more preferably 200,000 or more, still more preferably 250,000 or more, and preferably 10,000,000 or less, more preferably 1,000,000 or less, still more preferably 800,000 or less. When within the above ranges, the effects tend to be preferably obtained. In addition, it is desirable that the Mw of the above-mentioned nitrogen- and silicon-modified isoprene rubber is also in a similar range.

[0035] The above-mentioned specific modified isoprene rubber preferably has a number-average molecular weight (Mn) of 120,000 or more, more preferably 150,000 or more, and preferably 900,000 or less, more preferably 800,000 or less. When within the above ranges, the effects tend to be preferably obtained. In addition, it is desirable that the Mn of the above-mentioned nitrogen- and silicon-modified isoprene rubber is also in a similar range.

[0036] The above-mentioned nitrogen- and silicon-modified isoprene rubber preferably has a molecular weight distribution (Mw / Mn) of 2.0 or less, more preferably 1.7 or less, still more preferably 1.5 or less, and particularly preferably 1.3 or less. The lower limit is not particularly limited, but is usually 1.0 or more. When within the above ranges, the effects tend to be preferably obtained.

[0037] In the above-mentioned specific modified isoprene rubber, the ratios of the 1,2-structure and 3,4-structure are not particularly limited, but are preferably 0 to 10 mol%, more preferably 0 to 5 mol%. When within the above ranges, the effects tend to be preferably obtained. It is also desirable that the ratios of the 1,2-structure and 3,4-structure of the above-mentioned nitrogen- and silicon-modified isoprene rubber are in a similar range. In addition, in this specification, the ratio of the 1,2-structure refers to the ratio (mol%) of the repeating units having a 1,2-structure among the repeating units derived from isoprene. The ratio of the 3,4-structure refers to the ratio (mol%) of the repeating units having a 3,4-structure among the repeating units derived from isoprene.

[0038] In the above-mentioned specific modified isoprene rubber, the proportion of the 1,4-trans structure is not particularly limited, but is preferably 2 mol% or more, more preferably 5 mol% or more, and is preferably 90 mol% or less, more preferably 70 mol% or less. When it is within the above range, the effect tends to be preferably obtained. The proportion of the 1,4-trans structure of the above-mentioned nitrogen- and silicon-modified isoprene rubber is also preferably in the same range. In this specification, the proportion of the 1,4-trans structure refers to the proportion (mol%) of the repeating units having a 1,4-trans structure among all the repeating units derived from isoprene.

[0039] In the above-mentioned specific modified isoprene rubber, the proportion of the 1,4-cis structure is not particularly limited, but is preferably 10 mol% or less, more preferably 30 mol% or less, and is preferably 98 mol% or less. When it is within the above range, the effect tends to be preferably obtained. The proportion of the 1,4-cis structure of the above-mentioned nitrogen- and silicon-modified isoprene rubber is also preferably in the same range. In this specification, the proportion of the 1,4-cis structure refers to the proportion (mol%) of the repeating units having a 1,4-cis structure among all the repeating units derived from isoprene.

[0040] The above-mentioned specific modified isoprene rubber preferably has a glass transition temperature (Tg) of -100°C or higher, more preferably -90°C or higher, still more preferably -85°C or higher, and preferably -40°C or lower, more preferably -50°C or lower, still more preferably -60°C or lower. When it is within the above range, the effect tends to be preferably obtained. The Tg of the above-mentioned nitrogen- and silicon-modified isoprene rubber is also preferably in the same range. In this specification, the glass transition temperature (Tg) is measured using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min and calculated by the midpoint method.

[0041] The viscosity of the above-mentioned specific modified isoprene rubber is preferably 2,000 Pa·s or more, more preferably 3,000 Pa·s or more, and preferably 100,000 Pa·s or less. When within the above range, the effect tends to be preferably obtained. Also, the viscosity of the isoprene polymer before modifying the above-mentioned specific modified isoprene rubber is not particularly limited, but is preferably 800 Pa·s or more, more preferably 1,200 Pa·s or more, and preferably 8,000 Pa·s. When within the above range, the effect tends to be preferably obtained. The viscosity of the above-mentioned specific modified isoprene rubber is preferably 150 to 240% with respect to the viscosity of the isoprene polymer before modification. The viscosity of the above-mentioned nitrogen and silicon modified isoprene rubber and the viscosity of the isoprene polymer before modifying the above-mentioned nitrogen and silicon modified isoprene rubber are also preferably in the same range. In this specification, the viscosity is measured using a cone plate viscometer in accordance with JIS K5600-2-3. Also, the above viscosity is measured under the condition of 40°C.

[0042] The method for producing the above-mentioned specific modified isoprene rubber is not particularly limited, and a conventionally known method can be used. The method for specifying the molecular weight and molecular weight distribution is not particularly limited, and examples include methods for adjusting the amount ratio of the initiator, monomer, and terminator, the reaction temperature, and the rate of adding the initiator. For example, a method of polymerizing isoprene using an organolithium compound and then terminating the polymerization using an electrophilic agent containing nitrogen and silicon or the like can be mentioned.

[0043] The above-mentioned organolithium compound is not particularly limited. For example, mono-organolithium compounds such as n-butyllithium, sec-butyllithium, tert-butyllithium, n-propyllithium, isopropyllithium, benzyllithium; polyfunctional organolithium compounds such as 1,4-dilithiobutane, 1,5-dilithiopentane, 1,6-dilithiohexane, 1,10-dilithiodecane, 1,1-dilithiodiphenylene, dilithiopolybutadiene, dilithiopolyisoprene, 1,4-dilithiobenzene, 1,2-dilithio-1,2-diphenylethane, 1,4-dilithio-2-ethylcyclohexane, 1,3,5-trilithiobenzene, 1,3,5-trilithio-2,4,6-triethylbenzene can be mentioned. Among them, mono-organolithium compounds are preferred, and n-butyllithium, sec-butyllithium, and tert-butyllithium are more preferred.

[0044] The usage amount of the organolithium compound is not particularly limited, but it is preferably 0.001 to 10 mol% based on isoprene.

[0045] The method for polymerizing isoprene using the organolithium compound is not particularly limited. For example, the above-mentioned organolithium compound is added to an organic solvent solution containing isoprene, and the mixture is stirred in a temperature range of 0°C or higher and 120°C or lower (preferably 30°C or higher and 100°C or lower).

[0046] In the above method, the polymerization of isoprene is terminated using an electrophilic agent containing nitrogen, silicon, etc. By terminating the polymerization using the above electrophilic agent, a modified isoprene polymer having a modified group containing the above nitrogen, silicon, etc. at the terminal can be obtained. For the above electrophilic agent, various compounds containing nitrogen, silicon, etc. can be used. Among them, a compound containing a nitrogen atom as an amino group (-NR 2 : R is a hydrogen atom or a hydrocarbon group) is preferably used, and a compound containing a silicon atom as a hydrocarbyloxysilyl group (≡SiOR: R is a hydrocarbon group) is preferably used.

[0047] As the above-mentioned electron acceptor, silazane is preferable, and cyclic silazane is more preferable. Note that silazane is a compound having a structure in which a silicon atom and a nitrogen atom are directly bonded (a compound having a Si-N bond).

[0048] As the above-mentioned cyclic silazane, a compound represented by the following formula (B) can be preferably used.

Chemical formula

[0049] R 21 , R 22 , R 23 Examples of them include the same as the above R 11 , R 12 . Among them, R 21 is preferably an alkyl group (preferably having 1 to 10 carbon atoms), an alkylsilyl group (preferably having 1 to 10 carbon atoms), or an aromatic hydrocarbon group (preferably having 6 to 18 carbon atoms), and more preferably an alkylsilyl group. R 22 , R 23 are the same or different and are preferably a hydrocarbyloxy group (-OR group: R is a hydrocarbon group), and more preferably an alkoxy group (preferably having 1 to 10 carbon atoms).

[0050] L 21 Examples of it include the same as the above L 11 . Among them, L 21 is preferably an alkylene group (preferably having 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, and even more preferably 3 to 5 carbon atoms).

[0051] Examples of the compound represented by the above formula (B) include N-n-butyl-1,1-dimethoxy-2-azasilacyclopentane, N-phenyl-1,1-dimethoxy-2-azasilacyclopentane, N-trimethylsilyl-1,1-dimethoxy-2-azasilacyclopentane, N-trimethylsilyl-1,1-diethoxy-2-azasilacyclopentane, and the like. It is considered that the silicon atom of the cyclic silazane exhibits electrophilicity.

[0052] The amount of the above electrophile with respect to the organolithium compound is not particularly limited, but in terms of molar ratio, it is preferably 0.1 or more, more preferably 1 or more, and preferably 10 or less, more preferably 5 or less.

[0053] In the above rubber composition for cap tread, the content of the above specific modified isoprene-based rubber in 100% by mass of the rubber component is preferably more than 5% by mass, more preferably 8% by mass or more, still more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less. When it is within the above range, the effect tends to be obtained more favorably. In addition, the content of the above nitrogen- and silicon-modified isoprene-based rubber is also desirably in a similar range.

[0054] The above rubber composition for cap tread may contain a rubber component other than the above isoprene-based rubber. Examples of such rubber components include diene rubbers. Examples of diene rubbers include butadiene rubber (BR), styrene-butadiene rubber (SBR) other than the above-mentioned SBR with a low styrene content, styrene-isoprene-butadiene rubber (SIBR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), and the like. In addition, examples of rubber components also include butyl rubber, fluororubber, and the like. These may be used alone or in combination of two or more. Further, these rubber components may be subjected to modification treatment or hydrogenation treatment, and stretched rubber stretched by an oil, a resin, a liquid rubber component, or the like may also be used. Among them, it is preferably to contain at least one of BR and SBR, and more preferably to contain both BR and SBR.

[0055] BR is not particularly limited. For example, high-cis BR with a high cis content, BR containing syndiotactic polybutadiene crystals, BR synthesized using a rare earth-based catalyst (rare earth BR), etc. can be used. These may be used alone or in combination of two or more. Among them, 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 spectrum analysis.

[0056] When BR is one type, the cis amount of BR means the cis amount of that BR. When there are multiple types, it means the average cis amount. The average cis amount of BR can be calculated by {Σ (content of each BR × cis amount of each BR)} / total content of all BR. For example, in 100% by mass of the rubber component, when BR with a cis amount of 90% by mass is 20% by mass and BR with a cis amount of 40% by mass is 10% by mass, the average cis amount of BR is 73.3% by mass (=(20×90 + 10×40) / (20 + 10)).

[0057] In addition, either non-modified BR or modified BR can be used for BR. Examples of modified BR include modified BR into which the same functional groups as those of the modified rubber are introduced. Also, hydrogenated butadiene polymer (hydrogenated BR) can be used for BR.

[0058] In the above rubber composition for cap treads, the content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 8% by mass or more, still more preferably 10% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, still more preferably 20% by mass or less. When it is within the above range, the effect tends to be obtained more favorably.

[0059] SBR is not particularly limited. For example, emulsion polymerization styrene-butadiene rubber (E-SBR), solution polymerization styrene-butadiene rubber (S-SBR), etc. can be used. These may be used alone or in combination of two or more.

[0060] The styrene content of SBR is preferably 5% by mass or more, more preferably 20% by mass or more, still more preferably 30% by mass or more, and still more preferably 35% by mass or more. The styrene content is preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 40% by mass or less. When it is within the above range, the effect tends to be obtained more favorably. In this specification, the styrene content 1 can be measured by 1H-NMR measurement.

[0061] 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. 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, in 100% by mass of the rubber component, when SBR with a styrene amount of 40% by mass is 85% by mass and SBR with a styrene amount of 25% by mass is 5% by mass, the average styrene amount of SBR is 39.2% by mass (=(85×40 + 5×25) / (85 + 5)).

[0062] The vinyl bond content of SBR is preferably 5% by mass or more, more preferably 20% by mass or more, still more preferably 35% by mass or more. When the vinyl bond content is within the range of preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 45% by mass or less, the effects tend to be obtained more favorably. In the present specification, the vinyl bond content (1,2-bond butadiene unit amount) can be measured by infrared absorption spectroscopy.

[0063] The vinyl amount (1,2-bond butadiene unit amount) of SBR is the ratio of vinyl bonds when the total mass of the butadiene part in SBR is 100 (unit: mass%), and vinyl amount [mass%] + cis amount [mass%] + trans amount [mass%] = 100 [mass%]. When there is one type of SBR, it means the vinyl amount of the SBR, and when there are multiple types, it means the average vinyl amount. The average vinyl amount of SBR can be calculated by Σ{content of each SBR × (100 [mass%] - styrene amount of each SBR [mass%]) × vinyl amount of each SBR [mass%]} / Σ{content of each SBR × (100 [mass%] - styrene amount of each SBR [mass%])}. For example, in 100 parts by mass of the rubber component, when 75 parts by mass of SBR has a styrene amount of 40% by mass and a vinyl amount of 30% by mass, 15 parts by mass of SBR has a styrene amount of 25% by mass and a vinyl amount of 20% by mass, and the remaining 10 parts by mass is other than SBR, the average vinyl amount of SBR is 28% by 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%])}).

[0064] Either non-modified SBR or modified SBR can be used for SBR. Examples of the modified SBR include modified SBR into which functional groups similar to those of the modified rubber are introduced. Also, as SBR, a hydrogenated styrene-butadiene copolymer (hydrogenated SBR) can be used.

[0065] In the above rubber composition for cap treads, the content of SBR in 100% by mass of the rubber component is preferably 40% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, and is preferably 90% by mass or less, more preferably 85% by mass or less, still more preferably 80% by mass or less. When it is within the above range, the effect tends to be obtained more favorably.

[0066] The raw materials (monomers) of synthetic rubbers such as SBR and BR may be derived from petroleum, or may be recycled from rubber products such as tires and non-rubber products such as polystyrene. The monomers obtained by recycling (recycled monomers) are not particularly limited, and examples include recycled butadiene and recycled aromatic vinyl. Examples of the butadiene include 1,2-butadiene and 1,3-butadiene. The aromatic vinyl is not particularly limited, and examples include styrene. Among them, it is preferable to use recycled butadiene (recycled butadiene) and / or recycled styrene (recycled styrene) as raw materials.

[0067] The method for producing recycled monomers is not particularly limited, and examples include being synthesized from recycled naphtha obtained by decomposing rubber products such as tires. The method for producing recycled naphtha is not particularly limited, and for example, rubber products such as tires may be decomposed under high temperature and high pressure, decomposed by microwaves, or extracted after mechanical pulverization.

[0068] Furthermore, the raw materials (monomers) of synthetic rubbers such as SBR and BR may be derived from biomass. The monomers derived from biomass (biomass monomers) are not particularly limited, and examples include butadiene derived from biomass and aromatic vinyl derived from biomass. Examples of the butadiene include 1,2-butadiene and 1,3-butadiene. The aromatic vinyl is not particularly limited, and examples include styrene. Also, the method for producing biomass monomers is not particularly limited, and examples include those by biological and / or chemical and / or physical conversion of animals and plants. Fermentation by microorganisms is typical of biological conversion, and examples of chemical and / or physical conversion include those by catalysts, high heat, high pressure, electromagnetic waves, supercritical fluids, and combinations thereof. Examples of the biomass sources of these monomers include sugars, wood, plant residues after obtaining useful components, ethanol derived from plants, biomass naphtha, and the like.

[0069] The polymers synthesized from biomass monomer components (biomass polymers) are not particularly limited, and examples include polybutadiene rubber synthesized from butadiene derived from biomass, and aromatic vinyl / butadiene copolymers synthesized from butadiene derived from biomass and / or aromatic vinyl derived from biomass. Examples of the aromatic vinyl / butadiene copolymers include styrene-butadiene rubber synthesized from butadiene derived from biomass and / or styrene derived from biomass.

[0070] Whether the raw material of the polymer is derived from biomass can be determined by pMC (percent Modern Carbon) measured in accordance with ASTM D6866-10.

[0071] pMC is the ratio of the 14 C concentration of the sample to the 14 C concentration of the standard modern carbon (modern standard reference), and this value is used as an index indicating the biomass ratio of the compound (rubber). The significance of this value will be described below.

[0072] One mole (6.02×10 23 atoms) of carbon atoms contains approximately 6.02×10 11 atoms of 14 C, which is about one trillionth of ordinary carbon atoms. 14 C is called a radioactive isotope, and its half-life is 5730 years, decreasing regularly. It takes 226,000 years for all of these to decay. Therefore, after carbon dioxide in the atmosphere is taken up and fixed by plants, etc., in fossil fuels such as coal, oil, and natural gas, for which more than 226,000 years are considered to have passed since fixation, all of the 14 C element has decayed. Thus, in the current 21st century, fossil fuels such as coal, oil, and natural gas contain 14 no 14 C element at all. Therefore, chemical substances produced from these fossil fuels also

[0073] On the other hand, 14 C is constantly generated by nuclear reactions of cosmic rays in the atmosphere, and is in balance with the decrease due to radioactive decay. In the earth's atmospheric environment, 14 the amount of 14 C is constant. Therefore, the -12 C concentration of substances derived from biomass resources that are circulating in the current environment is about 1×10

[0074] This 14 C is generally measured as follows. Using accelerator mass spectrometry based on a tandem accelerator, 13 the 13 C concentration ( 12 C / 14 C) and 14 the 12 C concentration ( 14As a modern standard reference for the concentration standard of C, the concentration of 14 C in the circulating carbon in nature in 1950 is adopted. As a specific reference material, the oxalic acid standard provided by NIST (National Institute of Standards and Technology) is used. The specific activity of carbon in this oxalic acid (the 14 radioactivity intensity of 13 C per gram of carbon) is separated for each carbon isotope, and for 14 C, it is corrected to a constant value, and the value obtained by applying the decay correction from 1950 AD to the measurement date is used as the value (100%) of the standard

[0075] C concentration. The ratio of this value to the value of the sample actually measured is the pMC value. 14 Therefore, if the rubber is made of materials derived from 100% biomass (natural system), although there are regional differences, etc., it will show a value of approximately 110 pMC (currently, in the normal state, it often does not reach 100). On the other hand, for chemical substances derived from fossil fuels such as petroleum, when the

[0076] C concentration is measured, it will show almost 0 pMC (for example, 0.3 pMC). This value corresponds to a biomass ratio of 0% mentioned above.

[0077] The above rubber composition for cap tread contains silica as a filler. The usable silica is not particularly limited, and for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrous silica), etc., which are common in the tire industry, can be used. The raw material of silica is not particularly limited, and for example, it may be a raw material derived from a mineral such as quartz, or it may be a raw material derived from a living organism such as rice husk (for example, silica using a biomass material such as rice husk as a raw material), or silica recycled from a product containing silica may also be used. Among them, hydrous silica prepared by a wet method is preferred because it has many silanol groups. These silicas may be used alone or in combination of two or more.

[0078] Silica using a biomass material as a raw material can be obtained, for example, by extracting silicate from rice husk ash obtained by burning rice husks using a sodium hydroxide solution, and reacting the silicate with sulfuric acid in the same manner as conventional wet silica to precipitate silicon dioxide, followed by filtration, washing with water, drying, and pulverization.

[0079] As the silica recycled from a product containing silica, for example, silica recovered from products containing silica such as electronic components such as semiconductors, tires, desiccants, and filter materials such as diatomaceous earth can be used. Also, the recovery method is not particularly limited, and examples include thermal decomposition and decomposition by electromagnetic waves. Among them, silica recovered from electronic components such as semiconductors or tires is preferred.

[0080] When silica crystallizes, it does not dissolve in water and the silicic acid that is its component cannot be utilized. By controlling the combustion temperature and combustion time, the crystallization of silica in rice husk ash can be suppressed (see, for example, Japanese Patent Laid-Open No. 2009-2594, Akita Prefectural University Web Journal B / 2019, vol. 6, p. 216-222, etc.).

[0081] Also, from the viewpoint of obtaining more effects, rice husk silica is preferred. Amorphous silica extracted from rice husks can be those commercially available from companies such as Wilmar.

[0082] When rice husk silica is included, the mechanism by which more effective results are obtained is not clear. However, in the case of rice husk silica, it is considered that the effect of improving the dispersibility of silica by blending with isoprene rubber is effectively obtained. Therefore, it is considered that the overall performance of low fuel consumption and wear resistance is improved.

[0083] The nitrogen adsorption specific surface area (N 2 SA) of silica is preferably 50 m 2 / g or more, more preferably 100 m 2 / g or more, still more preferably 150 m 2 / g or more. Also, the upper limit of the N 2 SA of silica is not particularly limited, but is preferably 350 m 2 / g or less, more preferably 300 m 2 / g or less, still more preferably 250 m 2 / g or less. When within the above range, the effect tends to be obtained more favorably. In addition, the N 2 SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

[0084] In the above rubber composition for cap tread, the content of silica with respect to 100 parts by mass of the rubber component exceeds 40 parts by mass, preferably 70 parts by mass or more, more preferably 90 parts by mass or more, still more preferably 100 parts by mass or more, particularly preferably 110 parts by mass or more, and is also preferably 200 parts by mass or less, more preferably 150 parts by mass or less, still more preferably 130 parts by mass or less. When within the above range, the effect tends to be obtained more favorably. In addition, the content of the above plant-derived silica and the content of the above rice husk silica are preferably in the same range.

[0085] When containing silica of a predetermined amount or more, particularly 100 parts by mass or more, the mechanism by which more effective results are obtained is not clear. However, since the dispersibility of silica is improved by blending with isoprene rubber, it becomes possible to blend a large amount of silica, and thereby the reinforcing property is considered to be improved. Therefore, it is considered that the overall performance of low fuel consumption and wear resistance is improved.

[0086] The rubber composition for cap tread may contain a filler other than silica. Such fillers are not particularly limited, and materials known in the rubber field can be used. For example, inorganic fillers such as carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, mica, etc., biochar (BIO CHAR); difficult-to-disperse fillers, etc. can be mentioned. Among them, from the viewpoint of obtaining more effects, carbon-derived fillers (carbon-containing fillers) such as carbon black are preferable.

[0087] In the rubber composition for cap tread, the carbon black that can be used is not particularly limited, but examples include 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 Corporation, Lion Corporation, Shin Nippon Carbon Co., Ltd., Columbia Carbon Co., etc. can be used. These may be used alone or in combination of two or more. In addition to carbon black made from conventional mineral oils and the like as raw materials, carbon black made from biomass materials such as lignin can also be used. Further, recycled carbon black obtained by decomposing rubber products, plastic products, etc. containing carbon black such as tires can be appropriately used in an equivalent substitution with the above carbon black.

[0088] The nitrogen adsorption specific surface area (N 2 SA) of carbon black is preferably 50 m 2 / g or more, more preferably 80 m 2 / g or more, and still more preferably 100 m 2 / g or more. Also, the above N 2 SA is preferably 150 m 2 / g or less, more preferably 130 m 2 / g or less, and still more preferably 120 m 2 / g or less. When within the above range, the effects tend to be obtained more favorably. The nitrogen adsorption specific surface area of carbon black is determined in accordance with JIS K6217-2:2001.

[0089] The dibutyl phthalate absorption (DBP) of carbon black is preferably 40 ml / 100 g or more, more preferably 60 ml / 100 g or more, and still more preferably 70 ml / 100 g or more. Also, the above DBP is preferably 200 ml / 100 g or less, more preferably 150 ml / 100 g or less, and still more preferably 100 ml / 100 g or less. When within the above range, the effect tends to be obtained more favorably. Note that the DBP of carbon black is determined by the measuring method of JIS K6217-4:2001.

[0090] In the above 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 still more preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. Also, it is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and still more preferably 10 parts by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0091] Examples of the difficult-to-disperse filler include microfibrillated plant fibers, short fiber-like cellulose, and gel-like compounds. Among them, microfibrillated plant fibers are preferred.

[0092] As the above microfibrillated plant fibers, cellulose microfibrils are preferred in terms of obtaining good reinforcing properties. The cellulose microfibrils are not particularly limited as long as they are derived from natural products. For example, resource biomass such as fruits, grains, and root vegetables, wood, bamboo, hemp, jute, kenaf, and pulp, paper, cloth, agricultural crop residues, food waste, and sewage sludge obtained from these as raw materials, waste biomass such as rice straw, wheat straw, and thinned wood, and those derived from cellulose produced by tunicates, acetic acid bacteria, etc. These microfibrillated plant fibers may be used alone or in combination of two or more.

[0093] In the present specification, the cellulose microfibril typically means a cellulose fiber having an average fiber diameter within the range of 10 μm or less, and more typically a cellulose fiber having a micro-structure with an average fiber diameter of 500 nm or less formed by an aggregation of cellulose molecules. A typical cellulose microfibril is formed, for example, as an aggregate of cellulose fibers having the above-described average fiber diameter.

[0094] When the rubber composition for the cap tread contains a hardly dispersible filler, the content of the hardly dispersible filler is preferably 1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, with respect to 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, still more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0095] In the rubber composition for the cap tread, the content of the filler (total amount of fillers such as silica and carbon black) is preferably 75 parts by mass or more, more preferably 95 parts by mass or more, still more preferably 105 parts by mass or more, particularly preferably 115 parts by mass or more, with respect 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, still more preferably 135 parts by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0096] In the rubber composition for the cap tread, the silica content in the filler (100% by mass) is preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 96% by mass or more. The upper limit is not particularly limited and may be 100% by mass, but is preferably 99% by mass or less, more preferably 98% by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0097] When the silica content is 90% by mass or more, the mechanism by which more effects can be obtained is not clear, but it is considered that the effect of improving fuel efficiency due to the high silica content can be obtained, and the effect of improving the dispersibility of silica by blending an isoprene rubber can also be obtained. Therefore, it is considered that the overall performance of fuel efficiency and wear resistance is improved.

[0098] The rubber composition for the cap tread preferably 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, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, etc. of the sulfide series, 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, mercapto series such as NXT and NXT-Z manufactured by Momentive, vinyl series such as vinyltriethoxysilane and vinyltrimethoxysilane, amino series such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane, glycidoxy series such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, nitro series such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane, chloro series such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane, etc. can be mentioned. As commercially available products, products of Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azmax Co., Ltd., Toray Dow Corning Co., Ltd., etc. can be used. These may be used alone or in combination of two or more kinds.

[0099] In the above rubber composition for cap tread, the content of the silane coupling agent is preferably 0.1 part by mass or more, more preferably 3 parts by mass or more, still more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more with respect to 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, still more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less. When it is within the above range, the effect tends to be obtained more favorably.

[0100] The above rubber composition for cap tread preferably contains a plasticizer. In this specification, a plasticizer is a material that imparts plasticity to a rubber component, and is a concept including both a plasticizer that is liquid (liquid state) at normal temperature (25 °C) and a plasticizer that is solid at normal temperature (25 °C). Examples of plasticizers include resin components, oils, liquid polymers, ester-based plasticizers, etc. These plasticizers may be derived from petroleum, may be derived from biomass, or may be derived from naphtha recycled from rubber products or non-rubber products. Also, a low-molecular-weight hydrocarbon component obtained by thermally decomposing and extracting a used tire or a product containing various components may be used as a plasticizer. These plasticizers may be used alone or in combination of two or more.

[0101] Specific examples of the above plasticizer include oils, liquid polymers, resins, etc. These may be used alone or in combination of two or more.

[0102] Examples of the oil include process oil, vegetable oil, animal oil, etc. Examples of the process oil include paraffinic process oil (mineral oil), naphthenic process oil, aromatic process oil, etc. Specific examples of the process oil include, for example, MES (Mild Extract Solvated), DAE (Distillate Aromatic Extract), TDAE (Treated Distillate Aromatic Extract), TRAE (Treated Residual Aromatic Extract), RAE (Residual Aromatic Extract), etc. Also, a process oil with a low content of polycyclic aromatic (PCA) compounds can be used for environmental protection. Examples of the low-PCA-content process oil include MES, TDAE, heavy naphthenic oil, etc. Further, from the perspective of life cycle assessment, waste oil after being used in a rubber mixer or an engine, or refined waste cooking oil used in a restaurant may be used.

[0103] In this specification, the vegetable oil includes, for example, linseed oil, rapeseed oil, safflower oil, soybean oil, corn oil, cottonseed oil, rice oil, tall oil, sesame oil, perilla oil, castor oil, tung oil, pine oil, pine tar oil, sunflower oil, coconut oil, palm oil, palm kernel oil, olive oil, camellia oil, jojoba oil, macadamia nut oil, peanut oil, grape seed oil, wood rosin, etc. Further, the vegetable oil includes refined oil (such as salad oil) obtained by refining the above oil, transesterified oil obtained by transesterifying the above oil, hydrogenated oil obtained by hydrogenating the above oil, thermally polymerized oil obtained by thermally polymerizing the above oil, oxidatively polymerized oil obtained by oxidizing the above oil, waste cooking oil recovered from those used as edible oil, etc. Note that the vegetable oil may be liquid or solid at room temperature (25°C). These vegetable oils may be used alone or in combination of two or more.

[0104] The vegetable oil according to this embodiment preferably contains acylglycerol, and more preferably contains triacylglycerol. In this specification, acylglycerol refers to a compound in which a hydroxy group of glycerin and a fatty acid are ester-bonded. The acylglycerol is not particularly limited, and may be 1-monoacylglycerol, 2-monoacylglycerol, 1,2-diacylglycerol, 1,3-diacylglycerol, or triacylglycerol. Further, the acylglycerol may be a monomer, a dimer, or a multimer of trimer or higher. Note that acylglycerols of dimer or higher can be obtained by thermal polymerization, oxidative polymerization, or the like. Also, the acylglycerol may be liquid or solid at normal temperature (25°C).

[0105] As a method for confirming whether the acylglycerol is contained in the rubber composition, although not particularly limited, 1 it can be confirmed by 1H-NMR measurement. For example, a rubber composition containing triacylglycerol is immersed in deuterated chloroform at normal temperature (25°C) for 24 hours. After removing the rubber composition, 1 1H-NMR is measured. When the signal of tetramethylsilane (TMS) is set to 0.00 ppm, signals are observed at around 5.26 ppm, around 4.28 ppm, and around 4.15 ppm. These signals are presumed to be signals derived from hydrogen atoms bonded to carbon atoms adjacent to the oxygen atom of the ester group. In this paragraph, "around" means a range of ±0.10 ppm.

[0106] The fatty acid is not particularly limited and may be an unsaturated fatty acid or a saturated fatty acid. Examples of the unsaturated fatty acid include monounsaturated fatty acids such as oleic acid, and polyunsaturated fatty acids such as linoleic acid and linolenic acid. Examples of the saturated fatty acid include butyric acid and lauric acid.

[0107] Among these, as the fatty acid, it is desirable to contain a fatty acid with few double bonds, that is, a saturated fatty acid or a monounsaturated fatty acid, and oleic acid is preferred. As the vegetable oil containing such a fatty acid, for example, a vegetable oil containing a saturated fatty acid or a monounsaturated fatty acid may be used, or a vegetable oil subjected to modification such as transesterification may be used. Further, in order to produce a vegetable oil containing such a fatty acid, plants may be improved by variety improvement, genetic recombination, genome editing, etc.

[0108] As the oil, for example, those commercially available from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Co., Ltd., Orisoy Co., Ltd., H&R Co., Ltd., Toyokuni Oil Co., Ltd., Fuji Kogyo Co., Ltd., Nisshin Oillio Group Co., Ltd., etc. can be used.

[0109] Examples of the liquid polymer include a liquid diene polymer (liquid rubber) and a liquid farnesene polymer at 25°C. Examples of the liquid rubber include a liquid styrene-butadiene copolymer (liquid SBR), a liquid butadiene polymer (liquid BR), a liquid isoprene polymer (liquid IR), a liquid styrene-isoprene copolymer (liquid SIR), a liquid styrene-butadiene-styrene block copolymer (liquid SBS block polymer), a liquid styrene-isoprene-styrene block copolymer (liquid SIS block polymer), etc. These may have their terminals or main chains modified with polar groups. Also, hydrogenated products thereof can be used.

[0110] The weight average molecular weight (Mw) in terms of polystyrene measured by gel permeation chromatography (GPC) of the liquid diene polymer is preferably 1.0×10 3 or more, more preferably 3.0×10 3 or more, and preferably 5.0×10 4 or less, more preferably 1.5×10 4 or less. Also, the lower limit or upper limit of Mw of the liquid diene polymer may be 4500 or 8500. In this specification, the Mw of the liquid diene polymer is a polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0111] As the above liquid diene polymer, for example, products of Sartomer Co., Kuraray Co., Ltd., etc. can be used.

[0112] As the above resin, as a tire compound, resins (resins) usually used can be used, and they may be liquid or solid at normal temperature (25°C). For example, aromatic vinyl polymers, coumarone-indene resins, coumarone resins, indene resins, phenol resins, rosin resins, petroleum resins, terpene resins, acrylic resins, etc. can be mentioned. Further, the resin may be a hydrogenated resin (hydrogenated resin). These may be used alone or in combination of two or more. Also, the resin itself may be a copolymer of monomer components from a plurality of sources. Among them, aromatic vinyl polymers, petroleum resins, terpene resins, and hydrogenated resins thereof are desirable.

[0113] When using a resin that is solid at normal temperature, the softening point of the above resin is preferably 50°C or higher, more preferably 55°C or higher, still more preferably 60°C or higher, and particularly preferably 85°C or higher. Also, it is preferably 160°C or lower, more preferably 150°C or lower, still more preferably 140°C or lower, and particularly preferably 100°C or lower. When within the above range, the effect tends to be obtained more favorably. When the resin is liquid at normal temperature, the softening point is preferably 20°C or lower, preferably 10°C or lower, and preferably 0°C or lower. In the case of a hydrogenated resin, it is desirable that the softening point be the same as above. Incidentally, the softening point of the above resin is measured with a ring and ball softening point measuring device for the softening point defined in JIS K6220-1:2001, and is the temperature at which the ball drops.

[0114] The above aromatic vinyl polymer is a polymer containing an aromatic vinyl monomer as a constituent unit. For example, resins obtained by polymerizing α-methylstyrene and / or styrene can be mentioned. Specifically, homopolymers of styrene (styrene resins), homopolymers of α-methylstyrene (α-methylstyrene resins), copolymers of α-methylstyrene and styrene, copolymers of styrene and other monomers, etc. can be mentioned.

[0115] The above coumarone-indene resin is a resin containing coumarone and indene as the main monomer components constituting the resin skeleton (main chain). As monomer components other than coumarone and indene contained in the skeleton, styrene, α-methylstyrene, methyl indene, vinyl toluene, etc. can be mentioned.

[0116] The above coumarone resin is a resin containing coumarone as the main monomer component constituting the resin skeleton (main chain).

[0117] The above indene resin is a resin containing indene as the main monomer component constituting the resin skeleton (main chain).

[0118] As the above phenol resin, for example, known ones such as polymers obtained by reacting phenol with aldehydes such as formaldehyde, acetaldehyde, and furfural in the presence of an acid or alkali catalyst can be used. Among them, those obtained by reacting with an acid catalyst (such as novolak-type phenol resins) are preferred.

[0119] As the above rosin resin, rosin-based resins typified by natural rosin, polymerized rosin, modified rosin, ester compounds thereof, and hydrogenated products thereof can be mentioned.

[0120] As the above petroleum resin, C5-based resins, C9-based resins, C5 / C9-based resins, dicyclopentadiene (DCPD) resins, C9 / DCPD resins, hydrogenated products thereof, etc. can be mentioned. Among them, DCPD resins, hydrogenated DCPD resins, C9 / DCPD resins, and C9 / hydrogenated DCPD resins are preferred.

[0121] The above terpene resin is a polymer containing terpenes as constituent units. For example, there are polyt terpene resins obtained by polymerizing terpene compounds, aromatic modified terpene resins obtained by polymerizing terpene compounds and aromatic compounds, and the like. Examples of aromatic modified terpene resins include terpene phenol resins using terpene compounds and phenolic compounds as raw materials, terpene styrene resins using terpene compounds and styrene compounds as raw materials, and terpene phenol styrene resins using terpene compounds, phenolic compounds, and styrene compounds as raw materials. As terpene compounds, there are α-pinene, β-pinene, etc.; as phenolic compounds, there are phenol, bisphenol A, etc.; and as aromatic compounds, there are styrene compounds (styrene, α-methylstyrene, etc.). Among them, aromatic modified terpene resins are preferred.

[0122] The above acrylic resin is a polymer containing acrylic monomers as constituent units. For example, there are styrene acrylic resins such as styrene acrylic resins obtained by copolymerizing an aromatic vinyl monomer component and an acrylic monomer component and having a carboxyl group. Among them, a solventless carboxyl group-containing styrene acrylic resin can be preferably used.

[0123] As the above resin, for example, products of Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical, ExxonMobil, KRATON, Nippon Paint Co., Ltd., Nippon Shokubai Co., Ltd., ENEOS Co., Ltd., Arakawa Chemical Industries, Ltd., Tago Chemical Industry Co., Ltd., etc. can be used.

[0124] From the perspective of sustainability, it is desirable to use plant-derived plasticizers such as the above plant-derived oils and farnesene-based polymers as the above plasticizer.

[0125] The farnesene-based polymer is a polymer obtained by polymerizing farnesene and has a structural unit 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 having the following structure is preferred. [Chemical formula]

[0126] 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.

[0127] 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, vinyl ethylbenzene, divinylbenzene, trivinylbenzene, divinylnaphthalene, tert-butoxystyrene, vinylbenzyldimethylamine, (4-vinylbenzyl)dimethylaminoethyl ether, 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, and conjugated diene compounds such as butadiene and isoprene. These may be used alone or in combination of two or more. Among them, butadiene is preferred. That is, as the farnesene-vinyl monomer copolymer, a copolymer of farnesene and butadiene (farnesene-butadiene copolymer) is preferred.

[0128] In the farnesene-vinyl monomer copolymer, the copolymerization ratio by mass (farnesene / vinyl monomer) of farnesene and the vinyl monomer is preferably 40 / 60 to 90 / 10.

[0129] Farnesene-based polymers with a weight average molecular weight (Mw) of 3000 or more and 300,000 or less can be preferably used. The Mw of the farnesene-based polymer is preferably 8000 or more, more preferably 10000 or more, and preferably 100,000 or less, more preferably 60,000 or less, and even more preferably 50,000 or less. When within the above range, the effects tend to be more preferably obtained.

[0130] The farnesene-based polymer may be in a liquid state or a solid state at room temperature (25°C). Among them, a liquid farnesene-based polymer in a liquid state at room temperature (25°C) is desirable.

[0131] In the rubber composition for the cap tread, the content of the plasticizer (total amount of the plasticizer) is preferably 32.5 parts by mass or more, more preferably 35.0 parts by mass or more, and still more preferably 37.5 parts by mass or more with respect to 100 parts by mass of the rubber component. The upper limit is preferably 47.5 parts by mass or less, more preferably 45.0 parts by mass or less, and still more preferably 42.5 parts by mass or less. When it is within the above range, the effect tends to be obtained more favorably. Note that the content of the plasticizer includes the amount of oil and resin contained in the oil-extended rubber and the resin-extended rubber.

[0132] In the rubber composition for the cap tread, the content of the solid plasticizer in a solid state at normal temperature (25 ° C) is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and still more preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. The upper limit is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and still more preferably 15 parts by mass or less. When it is within the above range, the effect tends to be obtained more favorably. Note that the content of the above resin in a solid state at normal temperature (25 ° C) and the above aromatic vinyl polymer in a solid state at normal temperature (25 ° C) are preferably in the same range.

[0133] In the above rubber composition, the content of the liquid plasticizer in a liquid state at normal temperature (25 ° C) is preferably 22.5 parts by mass or more, more preferably 25.0 parts by mass or more, and still more preferably 27.5 parts by mass or more with respect to 100 parts by mass of the rubber component. The upper limit is preferably 37.5 parts by mass or less, more preferably 35.0 parts by mass or less, and still more preferably 32.5 parts by mass or less. When it is within the above range, the effect tends to be obtained more favorably. Note that the content of the liquid plasticizer includes the amount of oil contained in the oil-extended rubber and the amount of the liquid resin of the resin-extended rubber extended with the liquid resin. The content of the oil in a liquid state at normal temperature (25 ° C) is preferably in the same range.

[0134] From the viewpoints of crack resistance, ozone resistance, etc., the above rubber composition for cap tread preferably contains an anti-aging agent.

[0135] The anti-aging agent is not particularly limited, but examples include naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; p-phenylenediamine-based anti-aging agents such as N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N,N'-diphenyl-p-phenylenediamine (DPPD), N,N'-ditoly-p-phenylenediamine (DTPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), and N,N'-di-2-naphthyl-p-phenylenediamine (DNPD); quinoline-based anti-aging agents such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol-based anti-aging agents such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; bis, tris, polyphenol-based anti-aging agents such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, etc. Among them, p-phenylenediamine-based anti-aging agents and quinoline-based anti-aging agents are preferred, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and polymers of 2,2,4-trimethyl-1,2-dihydroquinoline are more preferred. As commercially available products, for example, products of Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinsei Chemical Industry Co., Ltd., Flexsys Co., etc. can be used.

[0136] In the above rubber composition for cap tread, the content of the anti-aging agent is preferably 1.0 part by mass or more, more preferably 3.0 part by mass or more, still more preferably 4.0 part by mass or more, based on 100 parts by mass of the rubber component. The content is preferably 7.0 part by mass or less, more preferably 5.0 part by mass or less.

[0137] The rubber composition for cap tread preferably contains stearic acid. In the rubber composition for cap tread, the content of stearic acid is preferably 0.5 parts by mass or more, more preferably 2.0 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, based on 100 parts by mass of the rubber component.

[0138] As the stearic acid, conventionally known ones can be used. For example, products of NOF Corporation, Kao Corporation, FUJIFILM Wako Pure Chemical Corporation, Chiba Fatty Acids Co., Ltd. and the like can be used.

[0139] The rubber composition for cap tread preferably contains zinc oxide. In the rubber composition for cap tread, the content of zinc oxide is preferably 0.5 parts by mass or more, more preferably 2.0 parts by mass or more, and preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, based on 100 parts by mass of the rubber component.

[0140] As the zinc oxide, conventionally known ones can be used. For example, products of Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Sho-Doh Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd. and the like can be used.

[0141] The rubber composition for cap tread may be blended with wax. In the rubber composition for cap tread, the content of wax is preferably 1.0 parts 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, based on 100 parts by mass of the rubber component.

[0142] The wax is not particularly limited, and examples thereof include petroleum waxes and natural waxes. Synthetic waxes obtained by purifying or chemically treating a plurality of waxes can also be used. These waxes may be used alone or in combination of two or more.

[0143] Examples of petroleum waxes include paraffin wax and microcrystalline wax. Natural waxes are not particularly limited as long as they are waxes derived from non-petroleum resources. For example, plant waxes such as candelilla wax, carnauba wax, wood wax, rice wax, and jojoba wax; animal waxes such as beeswax, lanolin, and whale wax; mineral waxes such as ozokerite, ceresin, and petrolactam; and purified products thereof. As commercially available products, for example, products of Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. can be used.

[0144] In the rubber composition for the cap tread, it is preferable to compound sulfur in terms of forming appropriate crosslinked chains in the polymer chain and imparting good performance.

[0145] In the rubber composition for the cap tread, the sulfur content is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and still more preferably 1.5 parts by mass or more with respect to 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 still more preferably 2.0 parts by mass or less.

[0146] Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, soluble sulfur, etc., which are generally used in the rubber industry. As commercially available products, products of Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Kasei Kogyo Co., Ltd., Flexsys, Nippon Karyu Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. can be used. These may be used alone or in combination of two or more.

[0147] The rubber composition for the cap tread preferably contains a vulcanization accelerator. In the above rubber composition for cap treads, the content of the vulcanization accelerator is not particularly limited and may be freely determined according to the desired vulcanization rate and crosslink density. However, based on 100 parts by mass of the rubber component, it is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and still more preferably 4.0 parts by mass or more. The upper limit is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, and still more preferably 6.0 parts by mass or less.

[0148] The type of the vulcanization accelerator is not particularly limited, and those commonly used can be used. Examples of the vulcanization accelerator include benzothiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyldisulfide, and N-cyclohexyl-2-benzothiazylsulfenamide; 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-benzothiazolesulfenamide, N-t-butyl-2-benzothiazolylsulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, and N,N'-diisopropyl-2-benzothiazolesulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, diorthotolylguanidine, 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.

[0149] In this specification, various materials containing carbon atoms (for example, rubber, oil, resin, vulcanization accelerator, anti-aging agent, surfactant, etc.) may be derived from carbon dioxide in the atmosphere. As a method for obtaining the formulation of the present invention from carbon dioxide, carbon dioxide may be directly converted, or methane obtained through a methanation process of synthesizing methane from carbon dioxide may be converted.

[0150] In addition to the above components, the rubber composition for cap tread may be appropriately blended with compounding agents generally used in the tire industry, such as materials such as mold release agents.

[0151] As kneading conditions, in the base kneading process for kneading additives other than the crosslinking agent (vulcanizing agent) and vulcanization accelerator, the kneading temperature is preferably 100 °C or higher, more preferably 120 °C or higher, and preferably 180 °C or lower, more preferably 170 °C or lower. In the finishing kneading process for kneading the vulcanizing agent and vulcanization accelerator, the kneading temperature is preferably 80 °C or higher, and preferably 120 °C or lower, more preferably 110 °C or lower. Further, the composition kneaded with the vulcanizing agent and vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. As the vulcanization temperature, it is preferably 140 °C or higher, more preferably 150 °C or higher, and preferably 190 °C or lower, more preferably 185 °C or lower.

[0152] The rubber composition for cap tread (vulcanized rubber composition) has a ratio (AE / Ash) of the acetone extraction amount AE (mass%) to the ash content Ash (mass%) of less than 0.52. AE / Ash is preferably less than 0.51, more preferably less than 0.46, still more preferably less than 0.42, and particularly preferably less than 0.38. The lower limit of AE / Ash preferably exceeds 0.20, more preferably exceeds 0.25, and still more preferably exceeds 0.28. When within the above range, the effect tends to be preferably obtained.

[0153] When AE / Ash is less than a predetermined value, particularly less than 0.46, the mechanism by which more effects are obtained is not clear, but it is considered that by setting the AE amount to less than a predetermined value with respect to the ash content, the strength of the rubber is ensured and the dispersibility of silica is also improved. Therefore, it is considered that the comprehensive performance of low fuel consumption and wear resistance is improved.

[0154] The acetone extraction amount AE (mass %) of the above rubber composition for cap tread (vulcanized rubber composition) is preferably 13.0 mass % or more, more preferably 15.0 mass % or more, still more preferably 15.5 mass % or more. The upper limit of AE is preferably 19.9 mass % or less, more preferably 18.4 mass % or less, still more preferably 17.0 mass % or less. When it is within the above range, the effect tends to be preferably obtained.

[0155] The ash content Ash (mass %) of the above rubber composition for cap tread (vulcanized rubber composition) is preferably 40.0 mass % or more, more preferably 40.7 mass % or more, still more preferably 41.4 mass % or more. The upper limit of Ash is preferably 45.0 mass % or less, more preferably 43.0 mass % or less, still more preferably 42.2 mass % or less. When it is within the above range, the effect tends to be preferably obtained.

[0156] Incidentally, the acetone extraction amount (AE) and ash content (Ash) of the above rubber composition for cap tread (vulcanized rubber composition) are measured by the following methods. First, the acetone extraction amount (AE) is measured for the above rubber composition (sample) by the measurement method of acetone extraction amount in accordance with JIS K 6229:2015 (unit: mass % in the above rubber composition (sample)). The ash content (Ash) is calculated from the mass of the components (ash) that do not burn by oxidative combustion by heating in air for the sample remaining after the above acetone extraction (unit: mass % in the above rubber composition (sample)). Incidentally, the samples used for these measurements are collected from the cap tread of the tire.

[0157] As a method for adjusting AE and Ash, methods known to those skilled in the art can be adopted. For example, AE tends to increase as the amount of softening agent such as oil in the rubber composition increases. Ash tends to increase as the amount of components that do not burn by oxidative combustion such as silica in the rubber composition increases.

[0158] The above rubber composition for cap tread (vulcanized rubber composition) has a difference ΔG* between the complex elastic modulus G*a (MPa) at 0.1% shear deformation at 30°C (frequency 10 Hz) and the complex elastic modulus G*b (MPa) at 20% shear deformation at 30°C (frequency 10 Hz) of less than 1.50 MPa. ΔG*(=|G*a - G*b|) is preferably 1.20 MPa or less, more preferably 1.14 MPa or less, still more preferably 1.12 MPa or less, and particularly preferably 0.90 MPa or less. The smaller ΔG* is, the more the dispersibility is improved, and at the same time, it is easier to deform with respect to the road surface during running, so wear is suppressed. Therefore, the smaller the value of ΔG* is, the more desirable it is, and the lower limit is not particularly limited, and 0.00 MPa is most preferable.

[0159] The above G*a (complex elastic modulus of the above rubber composition for tread (vulcanized rubber composition) under the conditions of 30°C and 0.1% shear deformation (frequency 10 Hz)) is preferably 3.00 MPa or less, more preferably 2.80 MPa or less, still more preferably 2.60 MPa or less, and particularly preferably 2.50 MPa or less. On the other hand, the lower limit is not particularly limited, but it is preferably 1.00 MPa or more, more preferably 1.50 MPa or more, and still more preferably 2.00 MPa or more. When it is within the above range, the effect tends to be preferably obtained.

[0160] The above G*b (complex elastic modulus of the above rubber composition for tread (vulcanized rubber composition) under the conditions of 30°C and 20% shear deformation (frequency 10 Hz)) is preferably 2.00 MPa or less, more preferably 1.80 MPa or less, and still more preferably 1.60 MPa or less. On the other hand, the lower limit is not particularly limited, but it is preferably 0.50 MPa or more, more preferably 0.80 MPa or more, and still more preferably 1.00 MPa or more. When it is within the above range, the effect tends to be preferably obtained.

[0161] In addition, in this specification, G* of the rubber composition for cap tread means G* of the cap tread after tire molding and corresponds to the elastic modulus after vulcanization.

[0162] In this specification, the complex elastic modulus G* means the complex elastic modulus in torsional shear measured by a rheometer ARES manufactured by TA Instruments. Specifically, it means G* measured by the method described in the examples. The measurement sample is taken in a disc shape with a diameter of Φ10 mm and a thickness of 2 mm from the cap tread of the manufactured tire, and the thickness direction is made to coincide with the radial direction of the tire.

[0163] The value of G*a (the complex elastic modulus of the rubber composition for the cap tread (vulcanized rubber composition) under the conditions of 30 °C and 0.1% shear deformation (frequency 10 Hz)) can be adjusted by the materials used (rubber components, fillers, silane coupling agents, oils, etc.). For example, G*a tends to decrease due to polymer low molecular weightization, modified polymers, larger filler particle sizes, lower filler loadings, etc.

[0164] The value of G*b (the complex elastic modulus of the rubber composition for the cap tread (vulcanized rubber composition) under the conditions of 30 °C and 20% shear deformation (frequency 10 Hz)) can be adjusted by the materials used (rubber components, fillers, silane coupling agents, oils, etc.). For example, G*b tends to decrease due to polymer low molecular weightization, modified polymers, larger filler particle sizes, lower filler loadings, etc.

[0165] ΔG*(=|G*a - G*b|) can have its value reduced by using various methods capable of improving the dispersibility of silica. As described above, G*a and G*b generally show similar tendencies when the compounding materials are changed, and ΔG* can be adjusted by the kneading process or the like. For example, the method of charging the total amount of silica compounded in the cap tread into the kneader all at once (high shear can be applied by charging all at once, and silica dispersion is enhanced), the method of kneading at least a part of the guanidine vulcanization accelerator in the base kneading (since the guanidine vulcanization accelerator makes the pH in the system basic, it has the effect of promoting silanization and improving silica dispersion), the method of using modified rubber, etc. can reduce the value of ΔG*.

[0166] The hardness Hs of the above rubber composition for cap tread (vulcanized rubber composition) exceeds 65, preferably exceeds 70, more preferably exceeds 74, and still more preferably exceeds 76. The upper limit of Hs is preferably less than 85, more preferably less than 82, and still more preferably less than 80. When within the above range, the effect tends to be preferably obtained. In this specification, Hs is a value measured in accordance with JIS K6253-3 (2012), and specifically, it is measured by the method described in the examples below.

[0167] In the case of Hs exceeding a predetermined value, particularly Hs exceeding 70, the mechanism by which a more effective result is obtained is not clear, but it is considered that the strength increases due to the high hardness, and the friction with the road surface decreases. Therefore, it is considered that the comprehensive performance of low fuel consumption and wear resistance is improved.

[0168] The method of adjusting Hs can be, for example, increasing the amount of reinforcing agent, decreasing the amount of softening agent, increasing the amount of sulfur, increasing the amount of vulcanization accelerator, compounding modified rubber, etc. to increase it.

[0169] It is desirable that the amount of isoprene component in the acetone extraction amount AE (100% by mass) of the above rubber composition for cap tread (vulcanized rubber composition) is less than 10% by mass. The amount of the isoprene component is preferably less than 30% by mass, more preferably less than 20% by mass, and still more preferably less than 15% by mass. The lower limit is preferably more than 5% by mass, and more preferably more than 10% by mass. When within the above range, the effect tends to be preferably obtained.

[0170] When the isoprene component content is less than 10% by mass, the mechanism by which more effects can be obtained is not clear, but it is considered that the smaller the isoprene component content, the more effectively the effect of improving the dispersibility of silica by blending the isoprene rubber is exerted. Therefore, it is considered that the overall performance of low fuel consumption and wear resistance is improved.

[0171] The method for adjusting the isoprene component content in the acetone extraction amount AE can be, for example, increased by methods such as increasing the amount of plasticizer components (oil, resin, processing aids, etc.), adopting an oil-extended polymer, etc.

[0172] The rubber composition for the cap tread is used for the cap tread of a tire member.

[0173] The tire of the present invention is manufactured by a usual method using the above rubber composition for the cap tread. That is, a composition blended with various additives as necessary is extruded into the shape of various tire members such as the cap tread at the unvulcanized stage, molded by a usual method on a tire molding machine, bonded together with other tire members to form an unvulcanized tire, and then heated and pressurized in a vulcanizer to manufacture the tire.

[0174] The above tire is not particularly limited, and examples include pneumatic tires, solid tires, airless tires, etc. Among them, pneumatic tires are preferred.

[0175] The above tire is preferably used as a passenger car tire, a large passenger car tire, a large SUV tire, a truck / bus tire, a motorcycle tire, a racing tire, a winter tire (studless tire, snow tire, stud tire), an all-season tire, a run-flat tire, an aircraft tire, a mining tire, etc. can be used.

[0176] In the above tire, the thickness T (mm) of the cap tread is preferably 3.0 mm or more, more preferably 6.0 mm or more, and still more preferably 8.0 mm or more. The upper limit is not particularly limited, but is preferably 20.0 mm or less, more preferably 18.0 mm or less, and still more preferably 15.0 mm or less. When within the above range, the effect tends to be preferably obtained.

[0177] When the thickness T of the cap tread is adjusted to a predetermined range, the mechanism by which more effects can be obtained is not clear, but it is considered that a sufficient amount of silica is highly dispersed throughout the thickness of the cap tread. Therefore, it is considered that the overall performance of low fuel consumption and wear resistance is improved.

[0178] In this specification, the thickness T of the cap tread refers to the thickness of the cap tread on the tire equatorial plane in the radial cross-section of the tire, and in the radial cross-section of the tire, it is the straight-line distance from the tread surface (the surface of the cap tread) to the inner surface of the cap tread in the radial direction of the tire.

[0179] The thickness of the cap tread on the tire equatorial plane is a value measured along the tire equatorial plane from the outermost surface of the cap tread on the tire equatorial plane. When there is an energizing member or the like on the tire equatorial plane, it is a value measured along the tire equatorial plane from a straight line connecting the ends of the interface blocked by the energizing member. When there is a groove on the tire equatorial plane, it is the thickness 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 outer surface of the cap tread in the radial direction of the tire.

[0180] In the above tire, it is desirable that the ratio (Ic / T) of the content Ic (mass%) of the above isoprene rubber in 100 mass% of the rubber component of the cap tread rubber composition to the thickness T (mm) of the cap tread is 0.5 or more. Ic / T is preferably 0.6 or more, more preferably 0.7 or more, still more preferably 0.8 or more, and is preferably 1.7 or less, more preferably 1.5 or less, still more preferably 1.3 or less. When within the above range, the effect tends to be obtained more favorably.

[0181] When Ic / T is adjusted to a predetermined range, the mechanism by which a more effective result is obtained is not clear. However, by including a sufficient amount of isoprene rubber with respect to the thickness of the cap tread, it is considered that the effect of improving the dispersibility of silica due to the blending of isoprene rubber can be effectively obtained. Therefore, it is considered that the overall performance of low fuel consumption and wear resistance is improved.

[0182] In the above tire, it is desirable that the ratio (Sc / T) of the content Sc (parts by mass) of silica to 100 parts by mass of the rubber component of the cap tread rubber composition and the thickness T (mm) of the cap tread is 8 or more. Sc / T is preferably 10 or more, more preferably 12 or more, still more preferably 15 or more, and is preferably 45 or less, more preferably 40 or less, still more preferably 35 or less. When within the above range, the effect tends to be obtained more favorably.

[0183] When Sc / T is adjusted to a predetermined value or more, the mechanism by which a more effective result is obtained is not clear. However, since a sufficient amount of silica with high dispersibility can be blended with respect to the thickness of the cap tread, it is considered that the reinforcing property is improved. Therefore, it is considered that the overall performance of low fuel consumption and wear resistance is improved.

[0184] In the above tire, the groove depth D of the circumferential groove formed in the tread is preferably 3.0 mm or more, more preferably 4.0 mm or more, still more preferably 5.0 mm or more, and is preferably 18.0 mm or less, more preferably 15.0 mm or less, still more preferably 13.0 mm or less. When within the above range, the effect tends to be obtained more favorably.

[0185] When the groove depth D of the circumferential groove formed in the tread is adjusted within a predetermined range, the mechanism by which more effective results can be obtained is not clear. However, by adjusting the groove depth, weight reduction and rubber strength are balanced, and as a result, it is considered that the overall performance of low fuel consumption and wear resistance is improved.

[0186] In this specification, the groove depth D of the circumferential groove means the distance measured along the normal line of the surface extending the surface forming the ground contact surface of the outermost surface of the tread, from the surface extending the surface forming the ground contact surface to the deepest groove bottom, and refers to the maximum distance among the groove depths of the provided circumferential grooves.

[0187] It is desirable that the ratio (Ic / D) of the content Ic (mass%) of the isoprene rubber in 100 mass% of the rubber component of the cap tread rubber composition to the groove depth D (mm) of the circumferential groove formed in the tread is 0.2 or more and 3.0 or less. Ic / D is preferably 0.5 or more, more preferably 1.0 or more, and still more preferably 1.2 or more. Also, the upper limit of Ic / D is preferably 2.5 or less, more preferably 2.3 or less, and still more preferably 2.2 or less. When within the above range, there is a tendency for better effects to be obtained.

[0188] When Ic / D is adjusted within a predetermined range, the mechanism by which more effective results can be obtained is not clear. However, by adjusting the groove depth, weight reduction and rubber strength are balanced, and by containing a sufficient amount of isoprene rubber, it is considered that the effect of improving the dispersibility of silica due to the blending of isoprene rubber can be effectively obtained. Therefore, it is considered that the overall performance of low fuel consumption and wear resistance is improved.

[0189] In this specification, dimensions such as thickness are measured with the bead portion of the tire adjusted to the normal rim width. At the time of 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 adjusted to the width of the normal rim.

[0190] In this specification, unless otherwise specified, the dimensions of each part of the tire are the values measured in the normal state. In this specification, the "normal state" refers to a no-load state in which the tire is mounted on a normal rim (not shown) and filled with the normal internal pressure.

[0191] When it cannot be measured in the state where the tire is mounted on the normal rim, the dimensions and angles of each part in the meridian cross-section of the tire are measured in the cross-section of the tire obtained by cutting the tire along the plane including the rotation axis, by making the distance between the left and right beads coincide with the distance between the beads in the tire mounted on the normal rim.

[0192] The "normal rim" is the rim defined for each tire in the standard system including the standard on which the tire is based. For example, in the case of JATMA, it means the standard rim; in the case of TRA, it means "Design Rim"; or in the case of ETRTO, it means "Measuring Rim". The "normal internal pressure" is the air pressure defined for each tire by the above standard. In the case of JATMA, it is the maximum air pressure; in the case of TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; in the case of ETRTO, it refers to "INFLATION PRESSURE". The "normal load" is the load defined for each tire by the above standard. In the case of JATMA, it is the maximum load capacity; in the case of TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES"; in the case of ETRTO, it means "LOAD CAPACITY".

[0193] Hereinafter, an example of the tire of the present invention will be described with reference to the drawings, but the present invention is not limited to such a form.

[0194] In FIG. 1, the vertical direction is the radial direction of the tire 2, the horizontal 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 symmetric about the left and right. The tread 4 includes a cap layer 30 (cap tread) and a base layer 28 (base tread).

[0195] In FIG. 1, an example of the two-layer structure tread 4 composed of the cap layer 30 and the base layer 28 is shown, but a single-layer structure tread or a tread having a structure of three or more layers may also be used.

[0196] In the tire 2 of FIG. 1, the cap layer 30 is made of the above rubber composition. The cap layer 30 contains a rubber component containing an isoprene-based rubber and a filler containing silica, the content of the isoprene-based rubber in 100% by mass of the rubber component exceeds 5% by mass, and the content of the silica with respect to 100 parts by mass of the rubber component exceeds 40 parts by mass. The cap layer 30 has a ratio (AE / Ash) of the acetone extraction amount AE (% by mass) to the ash content Ash (% by mass) of less than 0.52, and a difference ΔG* between the complex elastic modulus G*a (MPa) at 0.1% shear deformation at 30°C (frequency 10 Hz) and the complex elastic modulus G*b (MPa) at 20% shear deformation at 30°C (frequency 10 Hz) of less than 1.50 MPa, and a hardness Hs exceeding 65.

[0197] In the tire 2, each sidewall 6 extends substantially radially inward from the end of the tread 4. The radially outer portion of this sidewall 6 is joined to the tread 4. The radially inner portion of this sidewall 6 is joined to the clinch 10. This sidewall 6 can prevent damage to the carcass 14.

[0198] Each wing 8 in FIG. 1 is located between the tread 4 and the sidewall 6. The wing 8 is joined to each of the tread 4 and the sidewall 6.

[0199] Each clinch 10 is located substantially radially inside the sidewall 6 and has a portion in contact with the rim at at least one place.

[0200] The carcass 14 includes a carcass ply 36. In this tire 2, the carcass 14 is composed of one carcass ply 36, but it may also be composed of two or more plies.

[0201] In this tire 2, the carcass ply 36 is stretched 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 axial inner side toward the outer side around each bead core 32. Due to this folding, a main portion 36a and a pair of folded-back portions 36b are formed in the carcass ply 36. That is, the carcass ply 36 includes the main portion 36a and the pair of folded-back portions 36b.

[0202] Each bead core 32 is provided with a bead apex 34 that extends radially outward from the bead core 32. The bead core 32 is ring-shaped and preferably includes a wound non-stretchable wire. The bead apex 34 tapers radially outward.

[0203] Although not shown, the carcass ply 36 preferably consists of a number of parallel cords and topping rubber. The absolute value of the angle formed by each cord with respect to the equatorial plane CL is preferably 75° to 90°. In other words, this carcass 14 preferably has a radial structure.

[0204] The belt layer 16 in FIG. 1 is located radially inside 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 of FIG. 1, the belt layer 16 consists of an inner layer 38 and an outer layer 40. As is clear from FIG. 1, in the axial direction, it is desirable that the width of the inner layer 38 is slightly larger than the width of the outer layer 40. In this tire 2, the axial width of the belt layer 16 is preferably not less than 0.6 times and not more than 0.9 times the cross-sectional width of the tire 2.

[0205] Each of the inner layer 38 and the outer layer 40 preferably consists of a number of parallel single-wire steel cords (steel monofilaments) and topping rubber (coating rubber). In other words, the belt layer 16 includes a number of parallel steel monofilaments.

[0206] The band 18 in FIG. 1 is located radially outside the belt layer 16. In the axial direction, the band 18 has the same width as the width of the belt layer 16. This band 18 may have a width larger than the width of this belt layer 16.

[0207] Although not shown, the band 18 preferably consists of cords and topping rubber. The cords are wound spirally. This band 18 has a so-called jointless structure. The cords extend substantially in the circumferential direction. The angle of the cords with respect to the circumferential direction is preferably 5° or less, more preferably 2° or less. Since the belt layer 16 is constrained by these cords, lifting of the belt layer 16 is suppressed.

[0208] The belt layer 16 and the band 18 in FIG. 1 constitute a reinforcing layer. The reinforcing layer may be constituted only by the belt layer 16.

[0209] FIG. 2 is an enlarged view near the tread 4 in FIG. 1. The tire in FIG. 2 is a tire 2 having a groove 26 on the tire equatorial plane (on the CL). In this case, the cap tread thickness (T) 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 surface of the cap layer 30 (cap tread), specifically, the linear distance in the normal direction from the outer surface of the cap layer 30 in the tire radial direction to the interface on the outermost surface side of the tire of the base layer 28.

[0210] The inner liner 20 is located inside the carcass 14. The inner liner 20 is joined 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.

[0211] Each chafing strip 22 is located near the bead 12. In this embodiment, it is desirable that the chafing strip 22 is made of cloth and rubber impregnated in the cloth. This chafing strip 22 may be integrated with the clinch 10.

[0212] In this tire 2, the tread 4 has main grooves 42 as grooves 26. As shown in FIG. 1, a plurality of, specifically, three main grooves 42 are engraved in this tread 4. These main grooves 42 are arranged at intervals in the axial direction. By engraving three main grooves 42 in this tread 4, four ribs 44 extending in the circumferential direction are formed. That is, the main groove 42 is between the ribs 44.

[0213] Each main groove 42 extends in the circumferential direction. The main groove 42 is continuous without interruption in the circumferential direction. The main groove 42 promotes the drainage of water existing between the road surface and the tire 2, for example, in rainy weather. Therefore, even when the road surface is wet, the tire 2 can sufficiently contact the road surface. D in FIG. 2 indicates the groove depth of the circumferential main groove 42 formed in the tread 4.

[0214] In the tire 2, regarding the content Ic of isoprene rubber in 100% by mass of the rubber component of the cap layer 30, the content Sc of silica with respect to 100 parts by mass of the rubber component of the cap layer 30, the thickness T of the cap layer 30, and the groove depth D (mm) of the circumferential groove formed in the tread 4, it is desirable that Ic / T, Sc / T, Ic / D, T, and D are within the aforementioned ranges.

Example

[0215] Hereinafter, various chemicals used in the manufacture of the tire will be collectively described. The chemicals are purified according to established methods as necessary.

[0216] Hereinafter, various chemicals used in the manufacture of the tire will be collectively described. The chemicals are purified according to established methods as necessary. SBR: Modified SBR synthesized in Production Example 1 below (styrene content: 35% by mass, vinyl content: 45% by mass, Mw: 750,000) BR: BR730 (manufactured by JSR Corporation, cis content: 95% by mass) IR: Nipol IR2200 manufactured by Nippon Zeon Co., Ltd. Modified IR: Production Example 2 below Carbon black: Show Black N220 (N manufactured by Cabot Japan Ltd.) 2 SA114m 2 / g Silica 1: Ultrasil 9100GR manufactured by Evonik Degussa GmbH (average particle diameter: 15 nm) Silica 2: Ultrasil VN3 (N manufactured by Evonik Degussa GmbH) 2 SA: 175m 2 / g Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa GmbH Oil: Diana Process AH-24 manufactured by Idemitsu Kosan Co., Ltd. Antioxidant 1: Nocrack 6C (N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Antioxidant 2: Antage RD (polymer of 2,2,4-trimethyl-1,2-dihydroquinoline) manufactured by Kawaguchi Chemical Industry Co., Ltd. Stearic acid: Tsubaki manufactured by NOF Corporation Zinc oxide: Zinc white No. 2 manufactured by Mitsui Mining & Smelting Co., Ltd. Resin: SYLVARES SA85 manufactured by Arizona Chemical Company (α-methylstyrene resin (copolymer of α-methylstyrene and styrene), softening point: 85°C) Wax: Oz Ace Wax manufactured by Nippon Seiro Co., Ltd. Sulfur: Powder sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noxeller D (1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0217] (Production Example 1: Synthesis of Modified SBR) Two autoclaves with an internal volume of 10 liters, each having an inlet at the bottom and an outlet at the top, equipped with a stirrer and a jacket, are connected in series as reactors. Butadiene, styrene, and cyclohexane are mixed at predetermined ratios. This mixed solution is passed through a dehydration column filled with activated alumina to remove impurities, and n-butyllithium is mixed in a static mixer. Then, it is continuously supplied from the bottom of the first reactor. Further, 2,2-bis(2-oxolanyl)propane as a polar substance and n-butyllithium as a polymerization initiator are continuously supplied from the bottom of the first reactor at predetermined rates, and the temperature inside the reactor is maintained at 95°C. The polymer solution is continuously withdrawn from the top of the reactor and supplied to the second reactor. The temperature of the second reactor is maintained at 95°C, and a mixture of tetraglycidyl-1,3-bis(aminomethyl)cyclohexane (monomer) as a modifier and an oligomer component is continuously added at a predetermined rate as a 1000-fold dilution with cyclohexane to carry out a modification reaction. This polymer solution is continuously withdrawn from the reactor, and an antioxidant is continuously added with a static mixer, and then the solvent is removed to obtain SBR (modified SBR).

[0218] (Production Example 2: Synthesis of Modified IR) n-BuLi (manufactured by Kanto Chemical Co., Inc.: 1.60 mol / L (hexane solution), 9.0 mL, 14.4 mmol) is added to a mixed solution of isoprene (816 g, 12.0 mmol) and cyclohexane (4.0 kg), and the mixture is stirred at 50°C for 6 hours. After the reaction, N-trimethylsilyl-1,1-dimethoxy-2-azasilacyclopentane (14 mL, 57.4 mmol) represented by the following formula is added to stop the polymerization. The resulting solution is taken out and concentrated under reduced pressure. The concentrated solution is poured into methanol (5.0 L) to separate the methanol-insoluble component. Thus, modified IR1 having a functional group represented by the following formula (A1) at the end (Mn = 243,000, Mw = 292,000, Mw / Mn = 1.20, Tg = -61°C, ratio of 1,2-structure and 3,4-structure / ratio of 1,4-trans structure / ratio of 1,4-cis structure = 8 / 0 / 92) is obtained.

Chemical formula

Chem.

[0219] <Preparation of Test Tires> According to the compounding ingredients shown in Table 1, using a 1.7 L Banbury mixer manufactured by Kobe Steel, Ltd., materials other than sulfur and vulcanization accelerators are kneaded at 150 °C for 5 minutes to obtain a kneaded product. Sulfur and vulcanization accelerators are added to the kneaded product, and using an open roll, it is kneaded at 80 °C for 5 minutes to obtain a rubber composition for an unvulcanized cap tread. The rubber composition for the unvulcanized cap tread is formed into the shape of a cap tread, and on a tire molding machine, it is laminated together with other tire members to form an unvulcanized tire, which is vulcanized at 170 °C for 10 minutes to manufacture a test tire (size 205 / 70R15, passenger car tire).

[0220] Assuming test tires obtained from compositions with formulations and specifications changed according to Table 1, the results calculated based on the following evaluation methods are shown in each table. Note that the reference comparative examples are as follows. Reference example for low fuel consumption in Table 1: Comparative example 4 Reference example for abrasion resistance in Table 1: Comparative example 2

[0221] <Acetone extraction amount (AE)> Regarding a rubber test piece cut out from the cap tread of a test tire, in accordance with the measurement method of acetone extraction amount conforming to JIS K 6229, the amount of the substance extracted by acetone contained in the test piece is measured. Acetone extraction amount AE (mass%) = (mass of the sample before extraction - mass of the sample after extraction) / mass of the sample before extraction × 100

[0222] <Ash content (Ash)> For the sample after acetone extraction in the above acetone extraction amount (AE), it is oxidized and burned by heating in the air, the mass of the component (ash) that does not burn in the oxidative combustion is measured, and Ash (mass%) is calculated based on this.

[0223] <Measurement of complex elastic modulus G*> Samples with a size of Φ10 mm and a thickness of 2 mm are collected from the cap tread of the test tire (the thickness direction coincides with the tire radius direction), and using a rheometer ARES 2G manufactured by TA Instruments, at a temperature of 30 °C, a frequency of 10 Hz, a dynamic strain amplitude of 0.1% and 20% (shear deformation mode), the complex elastic moduli G*a and G*b are measured. From G*a and G*b, ΔG* (= |G*a - G*b|) is calculated.

[0224] <Hardness> For the test piece cut out from the cap tread of the test tire, in accordance with "Vulcanized Rubber and Thermoplastic Rubber - Method for Determining Hardness - Part 3: Durometer Hardness" of JIS K6253-3 (2012), using a type A durometer, the hardness (JIS-A hardness) at room temperature (25 °C) is measured (Hs).

[0225] <Low fuel consumption (rolling resistance)> Using a rolling resistance tester, the rolling resistance is measured under the following measurement conditions. Used rim: 9.00×22.5 Internal pressure: 830 kPa Load: 36.77 kN Speed: 80 km / h Based on this measurement result, it is expressed as an index when the reference comparison example is 100 (low fuel consumption index). The larger the index, the smaller the rolling resistance, indicating excellent low fuel consumption.

[0226] <Wear resistance> The test tire is mounted on a domestic FF vehicle, and with a load of 400 kg, the groove depth of the tread part after a driving distance of 10,000 km is measured, and the driving distance when the tire groove depth decreases by 1 mm is calculated. The result is expressed as an index based on the following calculation formula. The larger the index, the better the wear resistance. (Abrasion resistance index) = (Travel distance when the groove depth of each formulation decreases by 1 mm) / (Travel distance when the tire groove of the reference comparative example decreases by 1 mm) × 100

[0227] <Overall performance> Evaluate the sum of the low fuel consumption index and the abrasion resistance index as the overall performance. The larger the index, the better the overall performance of low fuel consumption and abrasion resistance.

[0228]

Table 1

[0229] The rubber composition for a cap tread of the present invention (1) contains a rubber component containing an isoprene rubber and a filler containing silica, the content of the isoprene rubber in 100% by mass of the rubber component exceeds 5% by mass, the content of the silica with respect to 100 parts by mass of the rubber component exceeds 40 parts by mass, the ratio (AE / Ash) of the acetone extraction amount AE (% by mass) to the ash content Ash (% by mass) is less than 0.52, the difference ΔG* between the complex elastic modulus G*a (MPa) at 0.1% shear deformation (frequency 10 Hz) at 30°C and the complex elastic modulus G*b (MPa) at 20% shear deformation (frequency 10 Hz) at 30°C is less than 1.50 MPa, and the hardness Hs exceeds 65, which is a rubber composition for a cap tread.

[0230] The rubber composition for a tread of the present invention (2) is the rubber composition for a tread according to the present invention (1) where Hs exceeds 70.

[0231] The rubber composition for a tread of the present invention (3) is the rubber composition for a tread according to the present invention (1) or (2) where the content of silica with respect to 100 parts by mass of the rubber component is 100 parts by mass or more.

[0232] The rubber composition for a tread of the present invention (4) is a rubber composition for a tread in any combination of the present inventions (1) to (3) where AE / Ash is less than 0.46.

[0233] The rubber composition for tread of the present invention (5) is a rubber composition for tread in any combination of any one of the present inventions (1) to (4) in which the isoprene component amount in the acetone extraction amount AE is less than 10% by mass.

[0234] The rubber composition for tread of the present invention (6) is a rubber composition for tread in any combination of any one of the present inventions (1) to (5) in which the silica content in the filler is 90% by mass or more.

[0235] The rubber composition for tread of the present invention (7) is a rubber composition for tread in any combination of any one of the present inventions (1) to (6) in which the silica contains rice husk silica.

[0236] The rubber composition for tread of the present invention (8) is a rubber composition for tread in any combination of any one of the present inventions (1) to (7) in which the isoprene rubber contains a modified isoprene rubber having a modified group containing at least one selected from the group consisting of nitrogen, sulfur, oxygen and silicon.

[0237] The present invention (9) is a tire provided with a cap tread composed of a rubber composition for cap tread in any combination of any one of the present inventions (1) to (8), wherein the thickness T of the cap tread is 6.0 mm or more and 18.0 mm or less.

[0238] The present invention (10) is the tire according to the present invention (9), wherein the ratio (Ic / T) of the content Ic (% by mass) of the isoprene rubber in 100% by mass of the rubber component of the rubber composition for cap tread to the thickness T (mm) of the cap tread is 0.5 or more.

[0239] The present invention (11) is the tire according to the present invention (9) or (10), wherein the ratio (Sc / T) of the content Sc (parts by mass) of silica to 100 parts by mass of the rubber component of the rubber composition for cap tread to the thickness T (mm) of the cap tread is 8 or more.

[0240] The tire of the present invention (12) is a tire in any combination with any one of the present inventions (9) to (11) in which the groove depth D of the circumferential groove formed in the tread is 4.0 mm or more and 15.0 mm or less.

[0241] The tire of the present invention (13) is a tire in any combination with any one of the present inventions (9) to (12) in which the ratio (Ic / D) of the content Ic (mass%) of the isoprene rubber in 100 mass% of the rubber component of the cap tread rubber composition to the groove depth D (mm) of the circumferential groove formed in the tread is 0.2 or more and 3.0 or less.

Explanation of Signs

[0242] 2 Tire 4 Tread 6 Sidewall 8 Wing 10 Clincher 12 Bead 14 Carcass 16 Belt layer 18 Band 20 Inner liner 22 Chafer 24 Tread surface 26 Groove 28 Base layer 30 Cap layer 32 Bead core 34 Bead apex 36 Carcass ply 36a Main part 36b Turn-up part 38 Inner layer 40 Outer layer 42 Main groove 44 Rib CL Equatorial plane of the tire T Thickness of the cap tread D Main groove depth of the circumferential main groove formed in the tread

Claims

1. A rubber composition for a cap tread containing a rubber component containing an isoprene rubber and a filler containing silica, wherein the content of the isoprene rubber in 100% by mass of the rubber component exceeds 5% by mass, the content of the silica with respect to 100 parts by mass of the rubber component exceeds 40 parts by mass, the ratio (AE / Ash) of the acetone extraction amount AE (% by mass) to the ash content Ash (% by mass) is less than 0.52, the difference ΔG* between the complex elastic modulus G*a (MPa) at 0.1% shear deformation at 30°C (frequency 10 Hz) and the complex elastic modulus G*b (MPa) at 20% shear deformation at 30°C (frequency 10 Hz) is less than 1.50 MPa, and the hardness Hs exceeds 65, a rubber composition for a cap tread.

2. The rubber composition for a tread according to claim 1, wherein Hs exceeds 70.

3. The rubber composition for a tread according to claim 1, wherein the content of silica with respect to 100 parts by mass of the rubber component is 100 parts by mass or more.

4. The rubber composition for a tread according to claim 1, wherein AE / Ash is less than 0.

46.

5. The rubber composition for a tread according to claim 1, wherein the amount of isoprene component in the acetone extraction amount AE is less than 10% by mass.

6. The rubber composition for a tread according to claim 1, wherein the silica content rate in the filler is 90% by mass or more.

7. The rubber composition for a tread according to claim 1, wherein the silica includes rice husk silica.

8. The rubber composition for a tread according to claim 1, wherein the isoprene rubber includes a modified isoprene rubber having a modified group containing at least one selected from the group consisting of nitrogen, sulfur, oxygen, and silicon.

9. A tire provided with a cap tread composed of the rubber composition for a cap tread according to claim 1, wherein the thickness T of the cap tread is 6.0 mm or more and 18.0 mm or less.

10. The tire according to claim 9, wherein the ratio (Ic / T) of the content Ic (% by mass) of the isoprene rubber in 100% by mass of the rubber component of the rubber composition for a cap tread to the thickness T (mm) of the cap tread is 0.5 or more.

11. The tire according to claim 9, wherein the ratio (Sc / T) of the content Sc (parts by mass) of the silica with respect to 100 parts by mass of the rubber component of the rubber composition for a cap tread to the thickness T (mm) of the cap tread is 8 or more.

12. The tire according to claim 9, wherein the groove depth D of the circumferential groove formed in the tread is 4.0 mm or more and 15.0 mm or less.

13. The tire according to claim 9, wherein the ratio (Ic / D) of the content Ic (mass%) of the isoprene rubber in 100 mass% of the rubber component of the cap tread rubber composition to the groove depth D (mm) of the circumferential groove formed in the tread is 0.2 or more and 3.0 or less.

Images