Rubber composition for tire and tire

Abstract

To provide a rubber composition for tire and a tire, excellent in rubber strength, chip cut resistance, high mileage performance, high-speed performance (grip performance) on a low-temperature road surface without ice and grip performance on a high-temperature road surface while using a large amount of isoprene rubber.SOLUTION: A rubber composition for tire includes isoprene rubber and styrene-butadiene rubber. A content of the isoprene rubber in a rubber constituent 100 mass% is 90 mass% or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a rubber composition for tires and a tire.

Background Art

[0002] In a rubber composition for tires, natural rubber is desired to be utilized as a rubber component in the future because of its excellent strength and being a natural resource. On the other hand, if the rubber component is only natural rubber, it becomes a so-called single morphology system, and when used as a tire member, there is a risk that fine damage may continuously spread. Conventionally, technologies for improving grip performance and wear resistance have been demanded (such as Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to solve the above problems and provide a rubber composition for tires and a tire that are excellent in rubber strength, chip and cut resistance, low fuel consumption, high - speed performance (grip performance) on a low - temperature road surface without ice and snow, grip performance on a high - temperature road surface, etc., while using a large amount of isoprene - based rubber.

Means for Solving the Problems

[0005] The present invention relates to a rubber composition for tires containing an isoprene - based rubber and a styrene - butadiene rubber, wherein the content of the isoprene - based rubber in 100% by mass of the rubber component is 90% by mass or more.

Effects of the Invention

[0006] The present invention relates to a rubber composition for tires, which contains isoprene rubber and styrene-butadiene rubber, and the content of the isoprene rubber in 100% by mass of the rubber component is 90% by mass or more. Therefore, while using a large amount of isoprene rubber, excellent rubber strength, chip cut resistance, low fuel consumption, high-speed performance (grip performance) on a low-temperature road surface without ice and snow, grip performance on a high-temperature road surface, etc. can be imparted.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0008] The above rubber composition for tires contains isoprene rubber and styrene-butadiene rubber, and the content of the isoprene rubber in 100% by mass of the rubber component is 90% by mass or more.

[0009] The mechanism by which the above-described effects are obtained with the rubber composition for tires is not necessarily clear, but it is presumed as follows. By blending a small amount of styrene-butadiene rubber with isoprene rubber, the styrene-butadiene rubber exists as small island phases in the isoprene rubber phase of the large amount component. Thus, it is considered that the damage generated on the isoprene rubber phase side stops at the island phases of the styrene-butadiene rubber, improving the mechanical strength and chip cut resistance. Also, in a single morphology system, relatively sharp viscoelastic characteristics are exhibited. However, by blending rubber systems with different viscoelastic characteristics, it is considered that the temperature dependence of the wet grip performance is reduced, contributing to excellent tire performance. Based on the above mechanisms, it is presumed that a rubber composition for tires excellent in rubber strength, chip cut resistance, low fuel consumption, high-speed performance (grip performance) on a low-temperature road surface without ice and snow, grip performance on a high-temperature road surface, etc. can be provided, even though a large amount of isoprene rubber is used.

[0010] <Rubber composition for tires> The above rubber composition for tires contains, as a rubber component, an isoprene-based rubber and styrene-butadiene rubber (SBR).

[0011] In this specification, the above 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 above rubber component is in a solid state at 25°C. Further, as the rubber component, not only those blended as a single rubber component before crosslinking, but also those blended as a mixture derived from recycling, etc., and components blended as rubber particles in a state where crosslinked or once crosslinked ones are desulfurized are included.

[0012] The weight-average molecular weight of the above 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. When it is within the above range, the effect tends to be obtained more favorably.

[0013] In this specification, the weight-average molecular weight (Mw) and 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).

[0014] The above rubber component 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 (a 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 terminal-modified rubber having the above functional group in the main chain and at the terminal (for example, a main-chain 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, etc. may be mentioned.

[0015] 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.

[0016] Examples of isoprene rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, modified IR, etc. As NR, for example, SIR20, RSS#3, TSR20, etc., which are common in the rubber industry, can be used. IR is not particularly limited, and for example, IR2200, etc., which are common in the rubber industry, can be used. Examples of modified NR include deproteinized natural rubber (DPNR), high-purity natural rubber, etc. Examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc. Examples of 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.

[0017] SBR is not particularly limited, and 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.

[0018] The styrene content of SBR is preferably 5% by mass or more, more preferably 20% by mass or more, still more preferably 24% by mass or more. The styrene content is preferably 60% by mass or less, more preferably 40% by mass or less, still more preferably 35% by mass or less. When within the above range, the effect tends to be obtained more favorably. In this specification, the styrene content 1 can be measured by H-NMR measurement.

[0019] The styrene content of SBR means the styrene content of the SBR when there is one type of SBR, and means the average styrene content when there are multiple types. The average styrene content of SBR can be calculated by {Σ (content of each SBR × styrene content of each SBR)} / total content of all SBRs. For example, when SBR with a styrene content of 40% by mass is 85% by mass and SBR with a styrene content of 25% by mass is 5% by mass in 100% by mass of the rubber component, the average styrene content of SBR is 39.2% by mass (= (85×40 + 5×25) / (85 + 5)).

[0020] The vinyl content of SBR is preferably 3% by mass or more, more preferably 10% by mass or more, still more preferably 17% by mass or more. When the vinyl content is within the range of preferably 50% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, the effect tends to be obtained more favorably. In the present specification, the vinyl content (1,2-bonded butadiene unit content) can be measured by infrared absorption spectroscopy.

[0021] The vinyl content (1,2-bonded butadiene unit content) of SBR is the ratio of vinyl bonds when the total mass of the butadiene part in SBR is 100 (unit: % by mass), and vinyl content [% by mass] + cis content [% by mass] + trans content [% by mass] = 100 [% by mass]. When there is one type of SBR, it means the vinyl content of that SBR, and when there are multiple types, it means the average vinyl content. The average vinyl content of SBR can be calculated by Σ{content of each SBR × (100 [% by mass] - styrene content of each SBR [% by mass]) × vinyl content of each SBR [% by mass]} / Σ{content of each SBR × (100 [% by mass] - styrene content of each SBR [% by mass])}. For example, in 100 parts by mass of the rubber component, when there are 75 parts by mass of SBR with a styrene content of 40% by mass and a vinyl content of 30% by mass, 15 parts by mass of SBR with a styrene content of 25% by mass and a vinyl content of 20% by mass, and the remaining 10 parts by mass are other than SBR, the average vinyl content of SBR is 28% by mass (={75 × (100 [% by mass] - 40 [% by mass]) × 30 [% by mass] + 15 × (100 [% by mass] - 25 [% by mass]) × 20 [% by mass])} / {75 × (100 [% by mass] - 40 [% by mass]) + 15 × (100 [% by mass] - 25 [% by mass])}).

[0022] SBR preferably has a glass transition temperature (Tg) of -50°C or lower, more preferably -55°C or lower, still more preferably -58°C or lower, and particularly preferably -60°C or lower. The lower limit of the glass transition temperature is preferably -78°C or higher, more preferably -75°C or higher, still more preferably -72°C or higher, and particularly preferably -70°C or higher. In this specification, the glass transition temperature is a value measured by performing differential scanning calorimetry (DSC) in accordance with JIS K7121 under the condition of a heating rate of 10 °C / min.

[0023] Although the mechanism by which more effects can be obtained by including SBR with a Tg of 50 °C or lower is not clear, using SBR with a low Tg improves the affinity with isoprene rubber, and the mechanical strength of the entire rubber component is improved. As a result, it is considered that the rubber strength, chip cut resistance, low fuel consumption, high-speed performance (grip performance) on a low-temperature road surface without ice and snow, and grip performance on a high-temperature road surface are improved.

[0024] As the SBR, either non-modified SBR or modified SBR can be used. Examples of the modified SBR include modified SBR into which functional groups similar to those of modified rubber are introduced. In addition, a hydrogenated styrene-butadiene copolymer (hydrogenated SBR) can also be used as the SBR.

[0025] As the SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., etc. can be used. Alternatively, those synthesized by known methods can also be used.

[0026] The above rubber composition for tires may contain butadiene rubber (BR). 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, it is preferable that the BR 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. Regarding the butadiene monomer that is the basis for BR polymerization, it may be derived from petroleum, but it is more desirable from the perspective of carbon neutrality that it is derived from biomass and / or recycled.

[0027] When there is one type of BR, the cis content of BR means the cis content of that BR; when there are multiple types, it means the average cis content. The average cis content of BR can be calculated by {Σ(content of each BR × cis content of each BR)} / total content of all BRs. For example, in 100% by mass of the rubber component, if BR with a cis content of 90% by mass is 20% by mass and BR with a cis content of 40% by mass is 10% by mass, the average cis content of BR is 73.3% by mass (=(20×90 + 10×40) / (20 + 10)).

[0028] Either non-modified BR or modified BR can be used for BR. Examples of modified BR include modified BR with functional groups similar to those of modified rubbers. Also, hydrogenated butadiene polymers (hydrogenated BR) can be used for BR.

[0029] As BR, for example, products of Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., etc. can be used.

[0030] The raw materials (monomers) of synthetic rubbers such as IR, SBR, and BR may be derived from underground resources such as petroleum and natural gas, 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 polyisoprene, 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 polyisoprene (recycled isoprene), recycled butadiene (recycled butadiene), and / or recycled styrene (recycled styrene) as raw materials.

[0031] The method for producing recycled monomers is not particularly limited, and examples thereof include those synthesized from recycled naphtha obtained by decomposing rubber products such as tires. Further, 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.

[0032] Furthermore, the raw materials (monomers) of synthetic rubbers such as IR, SBR, and BR may be derived from biomass. In this specification, biomass refers to substances derived from natural resources such as plants. Biomass is not particularly limited, and examples thereof include agricultural and forestry products, sugars, wood chips, plant residues after obtaining useful components, plant-derived ethanol, biomass naphtha, and the like.

[0033] The monomers derived from biomass (biomass monomers) are not particularly limited, and examples thereof 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 thereof include styrene. Further, the method for producing biomass monomers is not particularly limited, and examples thereof include those by biological and / or chemical and / or physical conversion of animals and plants. Fermentation by microorganisms is typical as the biological conversion, and examples of the chemical and / or physical conversion include those by catalysts, high heat, high pressure, electromagnetic waves, supercritical fluids, and combinations thereof.

[0034] The polymers synthesized from biomass monomer components (biomass polymers) are not particularly limited, and examples thereof 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 copolymer include styrene-butadiene rubber synthesized from butadiene derived from biomass and / or styrene derived from biomass.

[0035] 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.

[0036] pMC is the ratio of the 14 C concentration of the sample to the 14 C concentration of the modern standard reference, and is a value used as an index indicating the biomass ratio of a compound. The meaning of this value will be described below.

[0037] In one mole (6.02×10 23 pieces) of carbon atoms, there are approximately 6.02×10 11 pieces 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 and it decreases regularly. It takes 226,000 years for all of these to decay. Therefore, after carbon dioxide in the atmosphere and the like are taken up and fixed by plants and the like, in fossil fuels such as coal, oil, and natural gas, where more than 226,000 years are considered to have passed since fixation, all of the 14 C element contained in them at the beginning of fixation has decayed. Therefore, in the 21st century, fossil fuels such as coal, oil, and natural gas do not contain any 14 C element at all. Therefore, chemical substances produced using these fossil fuels as raw materials also do not contain any 14 C element.

[0038] 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, the amount of 14 C is a certain amount. Therefore, the 14 C concentration of substances derived from biomass resources circulating in the current environment is about 1×10 -12 mol% with respect to the entire C atoms as described above. Therefore, the biomass ratio of a certain compound can be calculated using the difference between these values.

[0039] This 14 C is generally measured as follows. Using accelerator mass spectrometry based on a tandem accelerator, 13 the C concentration ( 13 C / 12 C), 14 the C concentration ( 14 C / 12 C) is measured. In the measurement, 14 as a modern standard reference for the C concentration, the 14 C concentration in the circulating carbon in nature as of 1950 is adopted. As a specific standard substance, 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 C per gram of carbon) is separated for each carbon isotope, 13 corrected to a constant value for 14 C, and the value obtained by applying the decay correction from 1950 AD to the measurement date is used as the value of the standard

[0040] C concentration (100%). 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 100% biomass-derived materials, although there are regional differences, etc., it usually does not reach 100 under normal conditions at present, so it will show a value of about 110 pMC. On the other hand, for chemical substances derived from fossil fuels such as petroleum, when the

[0041] C concentration is measured, it will show a value of about 0 pMC (for example, 0.3 pMC). This value corresponds to the biomass ratio of 0% mentioned above.

[0042] In the above rubber composition for tires, the content of isoprene rubber in 100% by mass of the rubber component is 90% by mass or more, preferably 92% by mass or more, more preferably 94% by mass or more, still more preferably 95% by mass or more, and preferably 99% by mass or less, more preferably 98% by mass or less, still more preferably 97% by mass or less. When it is within the above range, the effects tend to be obtained more favorably.

[0043] Although the mechanism by which more effects are obtained by blending 95% by mass or more of isoprene rubber is not clear, good strength is obtained by containing a very large amount of isoprene rubber, and thereby, it is considered that good rubber strength, chip cut resistance, low fuel consumption, high-speed performance (grip performance) on a low-temperature road surface without ice and snow, grip performance on a high-temperature road surface, etc. can be imparted.

[0044] In the above rubber composition for tires, the content of SBR in 100% by mass of the rubber component is preferably 0.1% by mass or more, more preferably 1.0% by mass or more, still more preferably 1.5% by mass or more, and preferably 10% by mass or less, more preferably 7% by mass or less, still more preferably 5% by mass or less. When it is within the above range, the effects tend to be obtained more favorably.

[0045] When the above rubber composition for tires contains BR, the content of BR in 100% by mass of the rubber component is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and preferably 3% by mass or less, more preferably 2% by mass or less. When it is within the above range, the effects tend to be obtained more favorably.

[0046] Examples of rubber components other than isoprene rubber, BR, and SBR include styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), etc. Also, butyl rubber, fluororubber, etc. are included. These may be used alone or in combination of two or more.

[0047] The above rubber component may be subjected to a modification treatment or a hydrogenation treatment, and an extended rubber stretched by an oil, a resin, a liquid rubber component, etc. may be used.

[0048] It is desirable that the above rubber composition for tires contains a filler. The above filler is not particularly limited, and materials known in the rubber field can be used. For example, inorganic fillers such as carbon black, silica, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, mica, biochar (BIO CHAR); difficult-to-disperse fillers, etc. can be mentioned. The filler may be used alone or in combination of two or more. Among them, from the viewpoint of obtaining more effects, it is preferable that the above rubber composition for tires contains at least one of silica and carbon black, and it is more preferable to contain both silica and carbon black.

[0049] In the above rubber composition for tires, the silica that can be used is not particularly limited. For example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrous silica), etc., those common in the tire industry can be used. The raw material of silica is not particularly limited. For example, it may be a raw material derived from a mineral such as quartz, or 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 be used. Among them, hydrous silica prepared by a wet method is preferable because it has many silanol groups. These silicas may be used alone or in combination of two or more.

[0050] Silica using a biomass material as a raw material can be obtained, for example, by extracting a 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.

[0051] Silica recycled from products containing silica can be, for example, silica recovered from products containing silica such as electronic components such as semiconductors, tires, desiccants, and filter materials such as diatomaceous earth. The method of recovery is not particularly limited, and examples include thermal decomposition and decomposition by electromagnetic waves. Among these, silica recovered from electronic components such as semiconductors or tires is preferred.

[0052] When silica crystallizes, it becomes insoluble in water and the silicic acid that is its component cannot be utilized. By controlling the combustion temperature and combustion time, crystallization of the silica in rice husk ash can be suppressed (see, for example, Japanese Patent Application Laid-Open No. 2009-2594, Akita Prefectural University Web Journal B / 2019, vol. 6, p. 216-222, etc.).

[0053] Amorphous silica extracted from rice husks can be those commercially available from companies such as Wilmar.

[0054] Among the above, from the viewpoint of obtaining more effects, it is desirable to include silica derived from biomass materials (biomass material-derived silica).

[0055] The mechanism by which more effects can be obtained by blending biomass material-derived silica is not clear, but by using such silica, it is considered possible to give good rubber strength, chip cut resistance, low fuel consumption, high-speed performance (grip performance) on a low-temperature road surface without ice and snow, grip performance on a high-temperature road surface, etc., while also considering the environmental aspect.

[0056] When the rubber composition for tires contains silica, the content of silica is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, still more preferably 40 parts by mass or more, based on 100 parts by mass of the rubber component, and is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, still more preferably 70 parts by mass or less. When within the above range, there is a tendency to obtain better effects.

[0057] The nitrogen adsorption specific surface area (N2SA) of the silica is preferably 50 m 2100 m / g or more, more preferably 150 m / g or more 2 150 m / g or more, still more preferably 200 m / g or more 2 200 m / g or more, particularly preferably 250 m / g or more 2 is 250 m / g or more. Although the upper limit of the N2SA of the silica is not particularly limited, it is preferably 350 m / g or less, more preferably 300 m / g or less, still more preferably 250 m / g or less. When within the above range, the effect tends to be obtained more favorably. 2 350 m / g or less, more preferably 300 m / g or less 2 300 m / g or less, still more preferably 250 m / g or less 2 is 250 m / g or less. When within the above range, the effect tends to be obtained more favorably. In this specification, the N2SA of the silica is a value measured by the BET method in accordance with ASTM D3037-93.

[0058] The mechanism by which more effects can be obtained by blending silica with an N2SA of 200 m / g or more is not clear, but it is considered that by using high specific surface area silica, the mechanical strength is improved, and good rubber strength, chip cut resistance, low fuel consumption, high speed performance (grip performance) on a low temperature road surface without ice and snow, grip performance on a high temperature road surface, etc. are imparted. 2 In the rubber composition for tires, the carbon black that can be used is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, N762, etc. The raw material of the carbon black may be a biomass material such as lignin or vegetable oil, or may be a pyrolysis oil obtained by pyrolyzing waste tires. Further, the production method of the carbon black may be by combustion such as the furnace method, by hydrothermal carbonization (HTC), or by thermal decomposition of methane such as the thermal black method. As commercially available products, products of Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Nippon Steel Carbon Co., Ltd., Columbian Carbon Co., etc. can be used. These may be used alone or in combination of two or more.

[0059]

[0060] ​In addition to carbon black made from conventional mineral oil or the like as a raw material, carbon black made from biomass materials such as lignin may also be used.

[0061] The nitrogen adsorption specific surface area (N2SA) of the above carbon black is preferably 30 m 2 / g or more, more preferably 50 m 2 / g or more, still more preferably 70 m 2 / g or more. Also, the above N2SA is preferably 200 m 2 / g or less, more preferably 150 m 2 / g or less, still more preferably 130 m 2 / g or less, particularly preferably 120 m 2 / g or less. When it is within the above range, the effect tends to be obtained more favorably. In this specification, the nitrogen adsorption specific surface area of carbon black is determined according to JIS K6217-2:2001.

[0062] In the above rubber composition for tires, the content of carbon black is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 20 parts by mass or more, based on 100 parts by mass of the rubber component, and is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, still more preferably 40 parts by mass or less. When it is within the above range, the effect tends to be obtained more favorably.

[0063] Examples of the hardly dispersible filler include microfibrillated plant fiber, short fiber-like cellulose, gel-like compounds, etc. Among them, microfibrillated plant fiber is preferable.

[0064] As the microfibrillated plant fiber, cellulose microfibril is preferable from the viewpoint of obtaining good reinforcing properties. The cellulose microfibril is not particularly limited as long as it is derived from natural products. For example, resource biomass such as fruits, grains, and root vegetables, wood, bamboo, hemp, jute, kenaf, pulp, paper, cloth obtained from these as raw materials, waste biomass such as agricultural crop residues, food waste, and sewage sludge, unused biomass such as rice straw, wheat straw, and thinned wood, and those derived from cellulose produced by tunicates, acetic acid bacteria, etc. may be mentioned. These microfibrillated plant fibers may be used alone or in combination of two or more.

[0065] 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-mentioned average fiber diameter.

[0066] When the above rubber composition for tires 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, based on 100 parts by mass of the rubber component. The upper limit of the content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, still more preferably 20 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.

[0067] In the above rubber composition for tires, the content of the above filler (total amount of silica, carbon black, etc.) is preferably 10 parts by mass or more, more preferably 50 parts by mass or more, still more preferably 80 parts by mass or more, based on 100 parts by mass of the rubber component, and is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, still more preferably 100 parts by mass or less. When it is within the above range, the effect tends to be obtained more favorably.

[0068] From the viewpoint of obtaining more effective results, it is desirable that the content of the silica in 100% by mass of the filler is 30% by mass or more and 70% by mass or less. The content of the silica is preferably 40% by mass or more, more preferably 45% by mass or more, and still more preferably 50% by mass or more. The upper limit is not particularly limited, but is preferably 65% by mass or less, more preferably 60% by mass or less, and still more preferably 55% by mass or less. When it is within the above range, the effect tends to be obtained more favorably.

[0069] When the rubber composition for tires contains silica, it is preferably further contained with 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 type, 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, mercapto type such as NXT and NXT-Z manufactured by Momentive, vinyltriethoxysilane, vinyltrimethoxysilane, etc. of the vinyl type, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, etc. of the amino type, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, etc. of the glycidoxy type, 3-nitropropyltrimethoxysilane, 3-nitropropyltriethoxysilane, etc. of the nitro type, 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, etc. of the chloro type, and the like. 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.

[0070] In the above rubber composition for tires, 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.

[0071] From the viewpoint of obtaining more effects, it is desirable that the above rubber composition for tires contains a plasticizer. In this specification, the softening agent is a material that imparts plasticity to the rubber component, and is a concept including both a softening agent that is liquid at 25°C and a softening agent that is solid at 25°C. Examples of the softening agent include a resin component, oil, liquid polymer, ester plasticizer, etc. These softening agents may be derived from mineral resources such as petroleum and natural gas, 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 the softening agent. These softening agents may be used alone or in combination of two or more.

[0072] Specific examples of the above plasticizer include oil, liquid polymer, resin, etc. These may be used alone or in combination of two or more.

[0073] Examples of the oil include mineral oil, vegetable oil, animal oil, etc. Also, from the viewpoint of life cycle assessment, waste oil used in a rubber mixer or an engine, or refined waste cooking oil used in a cooking shop may be used.

[0074] In this specification, mineral oil refers to oil derived from mineral resources such as petroleum and natural gas. Examples of mineral oil include paraffinic oil (mineral oil), naphthenic oil, aromatic oil, etc. Specific examples of mineral 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, oil with a low content of polycyclic aromatic (PCA) compounds can be used for environmental protection. Examples of the low-PCA-content oil include MES, TDAE, heavy naphthenic oil, etc.

[0075] In this specification, vegetable oil refers to, 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 wax, etc. Furthermore, 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 vegetable oil may be liquid or solid at 25°C. These vegetable oils may be used alone or in combination of two or more.

[0076] 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 25°C.

[0077] As a method for confirming whether the acylglycerol is contained in the rubber composition, it is not particularly limited, but 1 it can be confirmed by 1H-NMR measurement. For example, a rubber composition containing triacylglycerol is immersed in deuterated chloroform at 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.

[0078] 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.

[0079] 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 varietal improvement, genetic recombination, genome editing, or the like.

[0080] 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.

[0081] 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.

[0082] 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 ~5.0×10 4 and more preferably 3.0×10 3 ~1.5×10 4 . 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).

[0083] As the above liquid diene polymer, for example, products of Sartomer Co., Kuraray Co., Ltd. etc. can be used.

[0084] As the above resin, as a tire compounding material, resins (resins) usually used can be used, and they may be liquid or solid at 25°C. For example, aromatic vinyl polymers, coumarone-indene resins, coumarone resins, indene resins, phenol resins, rosin resins, petroleum resins, terpene resins, acrylic resins and the like 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. Further, the resin itself may be a copolymer of monomer components derived from a plurality of sources. Among them, aromatic vinyl polymers, petroleum resins, terpene resins, and hydrogenated resins thereof are desirable.

[0085] When using a resin that is solid at 25°C as the above resin, the softening point 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. Further, 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 25°C, 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 is 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.

[0086] 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.

[0087] 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 contained in the skeleton other than coumarone and indene, styrene, α-methylstyrene, methyl indene, vinyl toluene, etc. can be mentioned.

[0088] The above coumarone resin is a resin containing coumarone as the main monomer component constituting the resin skeleton (main chain).

[0089] The above indene resin is a resin containing indene as the main monomer component constituting the resin skeleton (main chain).

[0090] 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.

[0091] Examples of the above rosin resin include rosin-based resins typified by natural rosin, polymerized rosin, modified rosin, ester compounds thereof, and hydrogenated products thereof.

[0092] Examples of the above petroleum resin include C5-based resins, C9-based resins, C5 / C9-based resins, dicyclopentadiene (DCPD) resins, C9 / DCPD resins, and hydrogenated products thereof. Among them, DCPD resins, hydrogenated DCPD resins, C9 / DCPD resins, and C9 / hydrogenated DCPD resins are preferred.

[0093] 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. Examples of terpene compounds include α-pinene, β-pinene, etc., examples of phenolic compounds include phenol, bisphenol A, etc., and examples of aromatic compounds include styrene compounds (styrene, α-methylstyrene, etc.). Among them, aromatic modified terpene resins are preferred.

[0094] 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, solvent-free carboxyl group-containing styrene acrylic resins can be preferably used.

[0095] 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 Catalyst Co., Ltd., ENEOS Co., Ltd., Arakawa Chemical Industries, Ltd., Tago Chemical Industry Co., Ltd., etc. can be used.

[0096] 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.

[0097] 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]

[0098] 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.

[0099] 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.

[0100] In the farnesene-vinyl monomer copolymer, the copolymerization ratio (farnesene / vinyl monomer) based on the mass of farnesene and the vinyl monomer is preferably 40 / 60 to 90 / 10.

[0101] Farnesene-based polymers with a weight average molecular weight (Mw) of 3,000 or more and 300,000 or less can be preferably used. The Mw of the farnesene-based polymer is preferably 8,000 or more, more preferably 10,000 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.

[0102] The farnesene-based polymer may be in a liquid state or a solid state at 25°C. Among them, a liquid farnesene-based polymer in a liquid state at 25°C is desirable.

[0103] In the above rubber composition for tires, the content of the plasticizer (total amount of plasticizer) is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, still more preferably 30 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, still more preferably 50 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 resin-extended rubber.

[0104] In the above rubber composition for tires, the content of the solid plasticizer in a solid state at 25°C is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 20 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, still more preferably 30 parts by mass or less. When it is within the above range, the effect tends to be obtained more favorably.

[0105] In the above rubber composition for tires, the content of the above resin in a solid state at 25°C is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 20 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, still more preferably 30 parts by mass or less. When it is within the above range, the effect tends to be obtained more favorably.

[0106] The mechanism by which more effects are obtained by blending a predetermined amount of the resin in a solid state at 25°C is not clear, but it is considered that the grip is improved by the resin, and good rubber strength, chip cut resistance, low fuel consumption, high-speed performance (grip performance) on a low-temperature road surface without ice and snow, grip performance on a high-temperature road surface, etc. are imparted.

[0107] In the above rubber composition for tires, the content of the liquid plasticizer in the liquid state at 25°C is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, still more preferably 10 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, still more preferably 20 parts by mass or less. When within the above range, the effect tends to be obtained more favorably. In addition, 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.

[0108] In the above rubber composition for tires, the content of the oil is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, still more preferably 10 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, still more preferably 20 parts by mass or less. When within the above range, the effect tends to be obtained more favorably. In addition, the content of the oil includes the amount of oil contained in the oil-extended rubber.

[0109] The above rubber composition for tires preferably contains an anti-aging agent from the viewpoints of crack resistance, ozone resistance, etc.

[0110] The anti-aging agent is not particularly limited, and examples thereof 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.

[0111] In the above rubber composition for tires, the content of the anti-aging agent is preferably 0.2 parts by mass or more, more preferably 2.0 parts by mass or more, and still more preferably 3.4 parts by mass or more, based on 100 parts by mass of the rubber component. The content is preferably 10.0 parts by mass or less, and more preferably 6.0 parts by mass or less.

[0112] The above rubber composition for tires preferably contains stearic acid. In the above rubber composition for tires, the content of stearic acid is preferably 0.5 parts by mass or more, more preferably 1.5 parts by mass or more, still 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.

[0113] 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., etc. can be used.

[0114] The above rubber composition for tires preferably contains zinc oxide. In the above rubber composition for tires, the content of zinc oxide is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, still more preferably 1.0 parts by mass or more, and preferably 6.0 parts by mass or less, more preferably 4.0 parts by mass or less, based on 100 parts by mass of the rubber component.

[0115] 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., Shodo Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. can be used.

[0116] The above rubber composition for tires may be compounded with wax. In the above rubber composition for tires, the content of wax is preferably 0.5 parts by mass or more, more preferably 1.6 parts by mass or more, and preferably 8.0 parts by mass or less, more preferably 5.0 parts by mass or less, based on 100 parts by mass of the rubber component.

[0117] The wax is not particularly limited, and any wax commonly used in the tire industry can be preferably used. For example, mineral waxes, plant-derived waxes, etc. can be mentioned. Mineral waxes refer to waxes derived from mineral resources such as oil and natural gas. Plant-derived waxes refer to waxes derived from natural resources such as plants. Among them, mineral waxes are preferred. Examples of plant-derived waxes include rice wax, carnauba wax, candelilla wax, etc. Examples of mineral waxes include paraffin wax, microcrystalline wax, these selected special waxes, etc., and paraffin wax is preferred. Note that the wax according to this embodiment does not contain stearic acid. As the wax, those commercially available from, for example, Ouchi Shinsei Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Paramelt Co., etc. can be used. These waxes may be used alone or in combination of two or more.

[0118] In the above rubber composition for tires, it is preferable to compound sulfur as a crosslinking agent in terms of forming appropriate crosslinking chains in the polymer chain and imparting good performance.

[0119] In the above rubber composition for tires, the sulfur content is 1.0 part by mass or more, preferably 1.5 parts by mass or more, more preferably 2.0 parts by mass or more, based on 100 parts by mass of the rubber component. The sulfur content is preferably 7.0 parts by mass or less, more preferably 5.0 parts by mass or less, still more preferably 4.0 parts by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0120] Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, soluble sulfur, etc., which are commonly used in the rubber industry. As commercially available products, products of companies such as Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Kasei Kogyo Co., Ltd., Flexsys Co., Ltd., Nippon Dry Distillation Industry Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. can be used. These may be used alone or in combination of two or more.

[0121] The above rubber composition for tires preferably contains a vulcanization accelerator. In the above rubber composition for tires, 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, it is preferably 1.0 part by mass or more, more preferably 3.0 part by mass or more, and still more preferably 4.7 part by mass or more, based on 100 parts by mass of the rubber component. The upper limit is preferably 8.0 part by mass or less, more preferably 7.0 part by mass or less, and still more preferably 6.0 part by mass or less.

[0122] 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-benzothiazole sulfenamide, N-t-butyl-2-benzothiazolylsulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; 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, from the viewpoint of obtaining more effects, it is preferably to contain at least one selected from the group consisting of sulfenamide-based vulcanization accelerators, guanidine-based vulcanization accelerators, and thiuram-based vulcanization accelerators, and more preferably to contain sulfenamide-based vulcanization accelerators, guanidine-based vulcanization accelerators, and thiuram-based vulcanization accelerators.

[0123] At least one selected from the group consisting of sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, and thiuram vulcanization accelerators, preferably three types of sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, and thiuram vulcanization accelerators, are used. The mechanism by which more effects can be obtained is not clear, but these vulcanization accelerators improve the mechanical hardness of the rubber, thereby imparting good rubber strength, chip cut resistance, low fuel consumption, high-speed performance (grip performance) on a low-temperature road surface without ice and snow, and grip performance on a high-temperature road surface.

[0124] In addition to the above components, the rubber composition for tires may be appropriately blended with compounding agents generally used in the tire industry, such as release agents and other materials.

[0125] 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 above-mentioned blend 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.

[0126] The rubber composition for tires is kneaded using a rubber kneading device such as an open roll or a Banbury mixer for the above components, and then a crosslinked rubber composition is obtained by a method such as crosslinking.

[0127] As the kneading conditions, in the base kneading process of kneading additives other than the vulcanizing agent, the kneading temperature is usually 50 to 200°C, preferably 80 to 190°C, and the kneading time is usually 30 seconds to 30 minutes, preferably 1 minute to 30 minutes. In the finishing kneading process of kneading the vulcanizing agent, vulcanization accelerator, etc., the kneading temperature is usually 100°C or lower, preferably room temperature to 80°C. Further, the composition kneaded with the vulcanizing agent and vulcanization accelerator is usually subjected to a vulcanization treatment such as press vulcanization. The vulcanization temperature is usually 120 to 200°C, preferably 140 to 180°C.

[0128] The above rubber composition for tires can be used for various tire members. Examples of the above tire members include a tread (such as a cap tread and a base tread), a sidewall, a clinch, a bead apex, a breaker cushion rubber, a carcass cord coating rubber, an insulation, a chafer, an inner liner, etc., and a tire member such as a side reinforcement layer of a run-flat tire can be applied (as a rubber composition for tires). Among them, from the viewpoint of obtaining more effects, it is desirable to apply the tire member to a surface rubber layer (such as a cap tread) that constitutes the surface of the tire.

[0129] <Tire with a multi-layer structure tread> As one form of the above tire, there is a tire provided with a multi-layer structure tread composed of a surface rubber layer made of the above rubber composition for tires and at least one inner rubber layer arranged on the inner side in the tire radial direction of the above surface rubber layer.

[0130] In this specification, the surface rubber layer means the rubber layer on the outermost surface side in the tire radial direction among the rubber layers constituting the multi-layer structure tread. The inner rubber layer means one or two or more rubber layers arranged on the inner side in the tire radial direction of the surface rubber layer among the rubber layers constituting the multi-layer structure tread. For example, when the tread is composed of a two-layer structure rubber layer, the inner rubber layer is the rubber layer arranged adjacent to the inner side in the tire radial direction of the surface rubber layer. When the tread part is composed of a three-layer or more structure rubber layer, the inner rubber layer is two or more rubber layers arranged on the inner side in the tire radial direction of the surface rubber layer.

[0131] For the multi-layer structure tread, any two or more layers of treads can be used, and examples include a two-layer structure tread, a three-layer structure tread, and a tread with a structure of four or more layers. For example, in the case of a three-layer structure tread, the outermost surface rubber layer (the first layer) of the tread part constitutes the surface rubber layer, and the rubber layer (the second layer) arranged adjacent to the inner side in the tire radial direction of the surface rubber layer and the rubber layer (the third layer) arranged adjacent to the inner side in the tire radial direction of the second layer constitute the inner rubber layer.

[0132] In the above tire, the surface rubber layer is composed of a composition for the surface rubber layer, and the inner rubber layer is composed of a composition for the inner rubber layer.

[0133] (Surface rubber layer (composition for surface rubber layer)) In the above tire, the surface rubber layer is composed of a surface rubber layer composition, and the surface rubber composition is composed of the above rubber composition for tires. It is desirable that the materials used and the contents of the surface rubber layer composition are also in the same range as above.

[0134] (Inner rubber layer (composition for inner rubber layer)) The composition for the inner rubber layer can commonly use the materials used in the above rubber composition for tires and can be manufactured in the same manner.

[0135] In the composition for the inner rubber layer, the content of the isoprene-based rubber in 100% by mass of the rubber component is preferably 90% by mass or more, more preferably 94% by mass or more, still more preferably 95% by mass or more, and may be 100% by mass. When it is within the above range, the effect tends to be obtained more favorably.

[0136] From the viewpoint of obtaining more effects, in a tire provided with a multi-layer structure tread composed of a surface rubber layer composed of the above rubber composition for tires and at least one inner rubber layer disposed on the inner side in the tire radial direction of the surface rubber layer, it is desirable that at least one of the inner rubber layers contains silica.

[0137] The mechanism by which more effects are obtained by compounding silica into the inner rubber layer is not clear, but it improves fuel efficiency and makes the inner rubber layer relatively flexible and excellent in temperature dependence, so that the temperature dependence of the wet grip performance can be further reduced. Therefore, it is considered that good rubber strength, chip and cut resistance, fuel efficiency, high-speed performance (grip performance) on a low-temperature road surface without ice and snow, and grip performance on a high-temperature road surface can be imparted.

[0138] In the composition for the inner rubber layer, the silica content is preferably 10 parts by mass or more, more preferably 40 parts by mass or more, still more preferably 50 parts by mass or more, and preferably 150 parts by mass or less, more preferably 100 parts by mass or less, still more preferably 70 parts by mass or less, based on 100 parts by mass of the rubber component. When it is within the above range, the effect tends to be obtained more favorably.

[0139] In the composition for the inner rubber layer, the nitrogen adsorption specific surface area (N2SA) of the silica is preferably 30 m 2 / g or more, more preferably 50 m 2 / g or more, still more preferably 70 m 2 / g or more. Also, the upper limit of the N2SA of the silica is not particularly limited, but it is preferably 200 m 2 / g or less, more preferably 120 m 2 / g or less, still more preferably 90 m 2 / g or less. When it is within the above range, the effect tends to be obtained more favorably.

[0140] In the composition for the inner rubber layer, the nitrogen adsorption specific surface area (N2SA) of the carbon black is preferably 30 m 2 / g or more, more preferably 50 m 2 / g or more, still more preferably 70 m 2 / g or more. Also, the above N2SA is preferably 200 m 2 / g or less, more preferably 150 m 2 / g or less, still more preferably 130 m 2 / g or less. When it is within the above range, the effect tends to be obtained more favorably.

[0141] In the composition for the inner rubber layer, the carbon black content is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, still more preferably 10 parts by mass or more, and preferably 50 parts by mass or less, more preferably 40 parts by mass or less, still more preferably 30 parts by mass or less, based on 100 parts by mass of the rubber component. When it is within the above range, the effect tends to be obtained more favorably.

[0142] In the composition for the inner rubber layer, the content of the filler (total amount of silica, carbon black, etc.) is preferably 10 parts by mass or more, more preferably 50 parts by mass or more, still more preferably 60 parts by mass or more, and preferably 150 parts by mass or less, more preferably 100 parts by mass or less, still more preferably 80 parts by mass or less, based on 100 parts by mass of the rubber component. When within the above range, the effect tends to be obtained more favorably.

[0143] From the viewpoint of obtaining a more effective composition for the inner rubber layer, it is desirable that the content of the silica in 100% by mass of the filler is 50% by mass or more. The content of the silica is preferably 70% by mass or more, more preferably 75% by mass or more, still more preferably 80% by mass or more. The upper limit is not particularly limited, but is preferably 95% by mass or less, more preferably 92% by mass or less, still more preferably 90% by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0144] The mechanism by which more effects can be obtained by adjusting the silica content of the inner rubber layer to a predetermined level or more is not clear, but it can improve fuel efficiency and make the inner rubber layer relatively flexible and excellent in temperature dependence, so that the temperature dependence of wet grip performance can be further reduced. Therefore, it is considered that good rubber strength, chip cut resistance, fuel efficiency, high-speed performance (grip performance) on a low-temperature road surface without ice and snow, and grip performance on a high-temperature road surface can be imparted.

[0145] In the composition for the inner rubber layer, 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, particularly preferably 7 parts by mass or more, based on 100 parts by mass of the 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, particularly preferably 10 parts by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0146] In the composition for the inner rubber layer, the content of the plasticizer (total amount of plasticizers) is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, still more preferably 50 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, still more preferably 80 parts by mass or less. When 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 resin-extended rubber.

[0147] In the composition for the inner rubber layer, the content of the solid plasticizer in the solid state at 25°C is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, still more preferably 40 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 80 parts by mass or less, more preferably 70 parts by mass or less, still more preferably 60 parts by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0148] In the composition for the inner rubber layer, the content of the resin in the solid state at 25°C is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, still more preferably 40 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 80 parts by mass or less, more preferably 70 parts by mass or less, still more preferably 60 parts by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0149] In the composition for the inner rubber layer, the content of the liquid plasticizer in the liquid state at 25°C is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, still more preferably 10 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, still more preferably 20 parts by mass or less. When 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 liquid resin of the resin-extended rubber extended with the liquid resin.

[0150] In the composition for the inner rubber layer, the oil content is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, still more preferably 10 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, still more preferably 20 parts by mass or less. When within the above range, the effect tends to be obtained more favorably. Note that the oil content also includes the amount of oil contained in the oil-extended rubber.

[0151] In the composition for the inner rubber layer, the content of the antioxidant is preferably 0.5 part by mass or more, more preferably 1.5 parts by mass or more, still more preferably 2.0 parts by mass or more, based on 100 parts by mass of the rubber component. The content is preferably 7.0 parts by mass or less, more preferably 5.0 parts by mass or less.

[0152] In the composition for the inner rubber layer, the content of stearic acid is preferably 0.5 part 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.

[0153] In the composition for the inner rubber layer, the content of zinc oxide is preferably 0.5 part by mass or more, more preferably 3.0 parts by mass or more, and preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, based on 100 parts by mass of the rubber component.

[0154] In the composition for the inner rubber layer, the content of wax is preferably 0.5 part by mass or more, more preferably 2.0 parts by mass or more, and preferably 10.0 parts by mass or less, more preferably 5.0 parts by mass or less, based on 100 parts by mass of the rubber component.

[0155] In the composition for the inner rubber layer, the sulfur content is preferably 0.5 parts by mass or more, more preferably 1.5 parts by mass or more, still more preferably 2.0 parts by mass or more, based on 100 parts by mass of the rubber component. The content is preferably 3.5 parts by mass or less, more preferably 3.0 parts by mass or less, still more preferably 2.5 parts by mass or less. When within the above range, the effect tends to be obtained more favorably.

[0156] In the composition for the inner rubber layer, 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, it is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, still more preferably 2.0 parts by mass or more, based on 100 parts by mass of the rubber component. The upper limit is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, still more preferably 6.0 parts by mass or less.

[0157] The above tire is manufactured by a normal method using the above composition for the surface rubber layer and the above composition for the inner rubber layer. That is, a composition containing various additives as required is extruded in an unvulcanized stage according to the shapes of various tire members such as the above surface rubber layer and the above inner rubber layer, molded by a normal 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.

[0158] The above tire is not particularly limited, and examples include pneumatic tires, solid tires, airless tires, etc. Among them, pneumatic tires are preferred.

[0159] 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 two-wheeler tire, a racing tire, a winter tire (a studless tire, a snow tire, a stud tire), an all-season tire, a run-flat tire, an aircraft tire, a mining tire, etc.

[0160] In the above tire, the thickness Tc (mm) of the surface rubber layer is preferably 1.0 mm or more, more preferably 2.0 mm or more, still more preferably 2.5 mm or more. The upper limit is preferably 50.0 mm or less, more preferably 30.0 mm or less, still more preferably 10.0 mm or less, and particularly preferably 8.0 mm or less. When within the above range, the effect tends to be preferably obtained.

[0161] In the above tire, the total thickness (mm) of the inner rubber layer (the total thickness of the inner rubber layer composed of at least one layer) is preferably 1.0 mm or more, more preferably 2.0 mm or more, still more preferably 3.0 mm or more. The upper limit is preferably 50.0 mm or less, more preferably 30.0 mm or less, still more preferably 10.0 mm or less. When within the above range, the effect tends to be preferably obtained.

[0162] In the above tire, the thickness Tb (mm) of each layer of the inner rubber layer optionally containing silica is preferably 1.0 mm or more, more preferably 2.0 mm or more, still more preferably 3.0 mm or more, and particularly preferably 3.5 mm or more. The upper limit is preferably 50.0 mm or less, more preferably 30.0 mm or less, still more preferably 10.0 mm or less, and particularly preferably 8.0 mm or less. When within the above range, the effect tends to be preferably obtained.

[0163] In the above tire, the total thickness (the thickness of the surface rubber layer + the total thickness of the inner rubber layer) (mm) of the multi-layer tread is preferably 4.0 mm or more, more preferably 6.0 mm or more, still more preferably 8.0 mm or more. The upper limit is preferably 100.0 mm or less, more preferably 50.0 mm or less, still more preferably 30.0 mm or less, and particularly preferably 20.0 mm or less. When within the above range, the effect tends to be preferably obtained.

[0164] In addition, in this specification, the "thickness Tc of the surface rubber layer" refers to the thickness of the surface rubber layer on the tire equatorial plane in the tire radial cross-section, and in the tire radial cross-section, it means the straight-line distance from the tread surface (the surface of the surface rubber layer) to the inner surface of the surface rubber layer in the tire radial direction. The "total thickness of the inner rubber layer" refers to the total thickness of the at least one-layer inner rubber layer on the tire equatorial plane in the tire radial cross-section, and in the tire radial cross-section, it means the straight-line distance from the inner surface of the surface rubber layer in the tire radial direction to the inner surface of the innermost rubber layer of the inner rubber layer in the tire radial direction. The "thickness Tb of each layer of the inner rubber layer" refers to the thickness of each inner rubber layer on the tire equatorial plane in the tire radial cross-section, and in the tire radial cross-section, it means the straight-line distance from the outer surface of each inner rubber layer in the tire radial direction to the inner surface of each inner rubber layer in the tire radial direction. The "total thickness of the multi-layer tread" refers to the total thickness of the multi-layer tread on the tire equatorial plane in the tire radial cross-section, and in the tire radial cross-section, it means the straight-line distance from the tread surface (the surface of the surface rubber layer) to the inner surface of the innermost rubber layer of the inner rubber layer in the tire radial direction. Specifically, it is the straight-line distance from the tread surface to the interface on the outermost surface side in the tire radial direction of the reinforcing layer including other fiber materials such as the belt layer and the carcass layer.

[0165] The "thickness Tc of the surface rubber layer", the "total thickness of the inner rubber layer", the "thickness Tb of each layer of the inner rubber layer", and the "total thickness of the multi-layer tread" are values measured along the tire equatorial plane 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 the 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 it is the thickness measured in the normal direction of the outer surface in the tire radial direction of the surface rubber layer, the inner rubber layer, each layer of the inner rubber layer, and the multi-layer tread.

[0166] In the above tire, the product (Sc × Tc) of the content Sc (mass %) of the styrene-butadiene rubber in 100 mass % of the rubber component in the surface rubber layer composition constituting the surface rubber layer and the thickness Tc (mm) of the surface rubber layer is preferably 0.4 or more, more preferably 4 or more, still more preferably 5 or more. The upper limit of Sc × Tc is preferably 500 or less, more preferably 400 or less, still more preferably 200 or less. When it is within the above range, the effect tends to be preferably obtained.

[0167] When Sc × Tc is in a predetermined range, the mechanism by which more effects can be obtained is not clear. However, by adjusting the thickness of the surface rubber layer containing SBR, it can be adjusted to a desired mechanical strength, whereby the rubber strength, chip cut resistance, low fuel consumption, high-speed performance (grip performance) on a low-temperature road surface without ice and snow, and grip performance on a high-temperature road surface are considered to be improved.

[0168] In the above tire, the groove depth D (mm) of the circumferential groove formed in the multi-layer structure tread is preferably 5.0 mm or more, more preferably 6.0 mm or more, still more preferably 7.0 mm or more, and is preferably 70.0 mm or less, more preferably 50.0 mm or less, still more preferably 30.0 mm or less. When it is within the above range, the effect tends to be obtained more favorably.

[0169] In this specification, the groove depth D of the circumferential groove means the distance measured along the normal line of the surface obtained by extending the surface forming the ground contact surface of the tread outermost surface from the surface obtained by 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.

[0170] In the above tire, the product (Sc × D) of the content Sc (mass %) of the styrene-butadiene rubber in 100 mass % of the rubber component in the surface rubber layer composition constituting the surface rubber layer and the groove depth D (mm) of the circumferential groove formed in the multi-layer structure tread is preferably 0.5 or more, more preferably 5 or more, still more preferably 10 or more. The upper limit of Sc × D is preferably 500 or less, more preferably 300 or less, still more preferably 200 or less. When within the above range, the effect tends to be preferably obtained.

[0171] When Sc × D is within a predetermined range, the mechanism by which more effects can be obtained is not clear, but by adjusting the groove depth formed in the surface rubber layer containing SBR, the desired mechanical strength can be adjusted, and thereby, it is considered that the rubber strength, chip cut resistance, low fuel consumption, high-speed performance (grip performance) on a low-temperature road surface without ice and snow, grip performance on a high-temperature road surface, etc. are improved.

[0172] In this specification, dimensions such as thickness are values measured in a normal state. The "normal state" refers to a state where the tire is mounted on a standard rim, filled with the standard internal pressure, and is in an unloaded condition. Here, the "standard rim" is the rim defined for each tire in the standard system including the standard to which the tire conforms. For example, in the case of JATMA (Japan Automobile Tire Association), it is the standard rim in the applicable sizes described in the "JATMA YEAR BOOK"; in the case of ETRTO (The European Tyre and Rim Technical Organisation), it is the "Measuring Rim" described in the "STANDARDS MANUAL"; in the case of TRA (The Tire and Rim Association, Inc.), it is the "Design Rim" described in the "YEAR BOOK". Refer to JATMA, ETRTO, and TRA in that order, and follow the relevant standard if there is an applicable size during the reference. For a tire not defined in the standard, it refers to the rim with the smallest rim diameter and then the narrowest rim width among the rims that can be mounted on the tire and can hold the internal pressure, i.e., the rim that does not cause air leakage between the rim and the tire. Also, the "standard internal pressure" refers to the air pressure defined for each tire in the standard system including the standard to which the tire conforms. In the case of JATMA, it is the "maximum air pressure"; in the case of ETRTO, it is the "INFLATION PRESSURE"; in the case of TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". Refer to JATMA, ETRTO, and TRA in that order, and follow the relevant standard if there is an applicable size during the reference. For a tire not defined in the standard, it refers to the standard internal pressure (however, 250 KPa or more) of another tire size (defined in the standard) with the standard rim described as the standard rim. If there are multiple standard internal pressures of 250 KPa or more described, it refers to the minimum value among them.

[0173] Hereinafter, an example of the above tire will be described with reference to the drawings, but it is not limited to such a form.

[0174] In FIG. 1, the vertical direction is the radial direction of the tire 2, the left - right direction is the axial direction of the tire 2, and the direction perpendicular to the plane of the paper is the circumferential direction of the tire 2. The tire 2 is bilaterally symmetric. The tread 4 (multi - layer structure tread) includes a cap layer 30 (surface rubber layer) and a base layer 28 (inner rubber layer). The cap layer 30 is composed of the above - mentioned rubber composition for tires (composition for surface rubber layer), and the base layer 28 is composed of the above - mentioned composition for inner rubber layer.

[0175] In FIG. 1, an example of a two - layer structure tread 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.

[0176] In the tire 2 of FIG. 1, the cap layer 30 contains isoprene - based rubber and styrene - butadiene rubber, and the content of the isoprene - based rubber in 100% by mass of the rubber component is 90% by mass or more.

[0177] 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.

[0178] 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.

[0179] Each clinch 10 is located substantially radially inside the sidewall 6 and has a portion that contacts the rim at least at one location or more.

[0180] 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 be composed of two or more plies.

[0181] 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 to 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 on the carcass ply 36. That is, the carcass ply 36 includes the main portion 36a and the pair of folded-back portions 36b.

[0182] Each bead core 32 is provided with a bead apex 34 extending 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.

[0183] 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.

[0184] 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 0.6 times or more and preferably 0.9 times or less of the cross-sectional width of the tire 2.

[0185] 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.

[0186] The band 18 in FIG. 1 is located radially outside the belt layer 16. In the axial direction, the band 18 has a width equal to that of the belt layer 16. This band 18 may have a width larger than that of the belt layer 16.

[0187] Although not shown, the band 18 desirably 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 restrained by these cords, lifting of the belt layer 16 is suppressed.

[0188] 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.

[0189] FIG. 2 is an enlarged cross-sectional view showing the vicinity of the tread 4 (multi-layer structure tread) in FIG. 1. The tire in FIG. 2 is a tire 2 having a groove 26 on the tire equatorial plane (on the CL).

[0190] In this case, the thickness Tc of the cap layer 30, the thickness of the base layer 28 (the thickness Tb of the inner rubber layer, corresponding to the total thickness of the inner rubber layers), and the total thickness of the tread 4 (the total thickness of the multi-layer structure tread) are the thicknesses 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 refer to the thicknesses measured in the normal direction of the surfaces of the cap layer 30 and the base layer 28. Specifically, the thickness Tc of the cap layer 30 means the linear distance in the normal direction from the radially outer surface of the cap layer 30 to the interface on the outermost surface side of the tire of the base layer 28. The thickness Tb of the base layer 28 means the linear distance from the radially outer surface of the base layer 28 to the interface on the outermost surface side of the tire in the radial direction of the band 18. The total thickness of the tread 4 means the straight-line distance 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 in the tire radial direction of the band 18, and is the total thickness of the thickness Tc of the cap layer 30 and the thickness Tb of the base layer 28.

[0191] 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.

[0192] Each chafer 22 is located in the vicinity of the bead 12. In this embodiment, it is desirable that the chafer 22 is composed of a cloth and rubber impregnated in this cloth. This chafer 22 may be integrated with the clinch 10.

[0193] In this tire 2, the tread 4 includes 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.

[0194] 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.

[0195] In the tire 2, the product (Sc × Tc) of the content Sc (mass %) of styrene-butadiene rubber in 100 mass % of the rubber component of the cap layer 30 and the thickness Tc (mm) of the surface rubber layer, and the product (Sc × D) of the content Sc (mass %) of styrene-butadiene rubber in 100 mass % of the rubber component of the cap layer 30 and the groove depth D (mm) of the circumferential groove formed in the multi-layer tread are desirably within the above-mentioned ranges.

Example

[0196] Hereinafter, examples (Examples) considered preferable in implementation will be shown, but the scope of the present invention is not limited to the examples.

[0197] Hereinafter, various chemicals used in the production of the cap layer and the base layer will be collectively described. The chemicals are purified according to a conventional method as necessary. (Cap layer) NR: TSR20 SBR1: NS612 (S-SBR, non-oil extended, styrene content: 15 mass %, vinyl content: 30 mass %, Tg: -65 °C, Mw: 780,000) manufactured by Nippon Zeon Co., Ltd. SBR2: Modified SBR (S-SBR whose terminal is modified with 3-diethylaminopropyltrimethoxysilane, styrene content: 25 mass %, vinyl content: 57 mass %, Tg: -25 °C) manufactured by Sumitomo Chemical Co., Ltd. Silica 1: Ultrasil 9000GR manufactured by Evonik Industries AG (N2SA: 240 m 2 / g, CTAB: 200 m 2 / g) Silica 2: Ultrasil VN3 manufactured by Evonik Industries AG (N2SA: 175 m 2 / g, CTAB: 175 m 2 / g) Silica 3: K160 (rice husk silica, N2SA: 154 m 2 / g) manufactured by Wilmar Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa GmbH Carbon black: Show Black N220 (N2SA: 111 m 2 / g) Oil: vivatec500 manufactured by H&R (TDAE, aromatic process oil) Resin: SYLVARES SA85 manufactured by Arizona Chemical (α-methylstyrene resin (copolymer of α-methylstyrene and styrene), softening point 85°C) Stearic acid: Tsubaki manufactured by NOF Corporation Antioxidant: Antigen 6C manufactured by Sumitomo Chemical Co., Ltd. (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) Zinc oxide: Zinc white No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: HK-200-5 (powder sulfur) manufactured by Hosoi Chemical Industry Co., Ltd. Vulcanization accelerator DPG: Nocceler D (N,N'-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator TBzTD: Nocceler TBzTD (tetrabenzylthiuram disulfide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator CZ: Nocceler CZ-G (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0198] (Base layer) NR: TSR20 Silica 2: Ultrasil VN3 manufactured by Evonik (N2SA: 175 m 2 / g, CTAB: 175 m 2 / g) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa Carbon black: Show Black N220 (N2SA: 111 m 2 / g) Oil: vivatec500 manufactured by H&R (TDAE, aromatic process oil) Resin: SYLVARES SA85 manufactured by Arizona Chemical (α-methylstyrene resin (copolymer of α-methylstyrene and styrene), softening point 85°C) Stearic acid: Tsubaki manufactured by NOF Corporation Anti-aging agent: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd. Zinc oxide: Zinc white No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powder sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator CZ: Nocceler CZ-G (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

[0199] (Preparation of rubber composition for cap layer) According to the compounding content shown in Table 1, using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd., the materials are kneaded at 150 °C for 5 minutes to obtain a kneaded product (base kneading step). According to the compounding content shown in Table 1, materials are added to the kneaded product, and using an open roll, they are kneaded at 80 °C for 5 minutes to obtain an unvulcanized rubber composition (finishing kneading step).

[0200] (Preparation of rubber composition for base layer) According to the compounding content shown in Table 2, using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd., the materials are kneaded at 150 °C for 5 minutes to obtain a kneaded product (base kneading step). According to the compounding content shown in Table 2, materials are added to the kneaded product, and using an open roll, they are kneaded at 80 °C for 5 minutes to obtain an unvulcanized rubber composition (finishing kneading step).

[0201] (Manufacturing method of test tire) According to the specifications in Table 1, the above unvulcanized rubber composition for cap layer (Table 1) is formed into the shape of the cap layer, and the above unvulcanized rubber composition for base layer (Table 2) is formed into the shape of the base layer. On a tire molding machine, they are bonded 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, Figures 1 - 2).

[0202] Assuming a test tire obtained from a composition in which the cap layer formulation and specifications are changed according to Table 1 using the base layer formulation of Table 2, the results calculated based on the following evaluation method are shown in Table 1. Note that the reference comparative example is as follows. Table 1: Comparative Example 1

[0203] <Rubber strength> For a rubber test piece cut from the cap layer of the test tire, a tensile test is carried out using a No. 3 dumbbell in accordance with JIS K 6251 "Methods for Determining Tensile Properties of Vulcanized Rubber and Thermoplastic Rubber", and the elongation at break (EB) and tensile strength at break (TB) of the vulcanized rubber composition are measured. Taking the EB×TB of the reference comparative example as 100, the EB×TB of each formulation is expressed as an index according to the following calculation formula. The larger the index, the better the rubber strength. (Rubber strength index) = (EB×TB of each formulation) / (EB×TB of the reference comparative example) × 100

[0204] <Chip cut resistance> Each test tire is mounted on a domestic 2000cc FF vehicle, and the block chipping state after a driving distance of 8000 km is visually observed and scored. The results are shown as an index according to the following calculation formula with the score of the reference comparative example as 100. The larger the index, the less block chipping has occurred and the higher the chip cut resistance. (Block chipping resistance performance index) = (score of each formulation example) / (score of the reference comparative example) × 100

[0205] <Low fuel consumption> Using a rolling resistance tester, the rolling resistance when each test tire is run at a rim (15×6JJ), internal pressure (230 kPa), load (3.43 kN), and speed (80 km / h) is measured and expressed as an index when the reference comparative example is 100. The larger the index, the better (lower fuel consumption).

[0206] <Low temperature high speed grip performance> Mount the test tire on a domestic 2000 cc FF vehicle and drive it on the road surface at 0°C to 3°C without snow and ice on the Asahikawa Test Course in Hokkaido. Step on the lock brake at a speed of 160 km / h and measure the stopping distance required until it stops. Taking the reference comparative example as 100, it is expressed as an index by the following formula. The larger the index, the better the braking performance at low temperature. (Low-temperature high-speed grip performance index) = (Stopping distance of the reference comparative example) / (Stopping distance of each formulation) × 100

[0207] <High-temperature high-speed grip performance> Except that the road temperature is 45°C, conduct the test under the same conditions as the evaluation method of the above low-temperature high-speed grip performance, and express it as an index by the following formula. The larger the index, the better the braking performance at high temperature. (High-temperature high-speed grip performance index) = (Stopping distance of the reference comparative example) / (Stopping distance of each formulation) × 100

[0208] <Comprehensive performance> Evaluate the comprehensive performance of rubber strength, chip cut resistance, low fuel consumption, high-speed performance (grip performance) on a low-temperature road surface without ice and snow, and grip performance on a high-temperature road surface based on the sum of the five indexes obtained from the evaluations of the above rubber strength, chip cut resistance, low fuel consumption, low-temperature high-speed grip performance, and high-temperature high-speed grip performance. The larger the numerical value, the better the comprehensive performance.

[0209]

Table 1

[0210]

Table 2

[0211] The present invention (1) contains isoprene rubber and styrene-butadiene rubber, and is a rubber composition for tires in which the content of the isoprene rubber in 100% by mass of the rubber component is 90% by mass or more.

[0212] The rubber composition for tires according to the present invention (1), wherein the content of isoprene rubber in 100% by mass of the rubber component is 95% by mass or more, is the rubber composition for tires according to the present invention (2).

[0213] The rubber composition for tires according to the present invention (3) is the rubber composition for tires according to the present invention (1) or (2), which contains styrene-butadiene rubber having a glass transition temperature of -50°C or lower.

[0214] The present invention (4) contains a resin, and is a rubber composition for tires in any combination with any one of the present inventions (1) to (3), wherein the content of the resin with respect to 100 parts by mass of the rubber component is 5 parts by mass or more and 50 parts by mass or less.

[0215] The present invention (5) contains silica, and is a rubber composition for tires in any combination with any one of the present inventions (1) to (4), wherein the content of the silica with respect to 100 parts by mass of the rubber component is 10 parts by mass or more and 150 parts by mass or less.

[0216] The present invention (6) is a rubber composition for tires in any combination with any one of the present inventions (1) to (5), which contains silica derived from biomass materials.

[0217] The present invention (7) is a rubber composition for tires in any combination with any one of the present inventions (1) to (6), which contains silica having a nitrogen adsorption specific surface area of 200 m 2 / g or more.

[0218] The present invention (8) contains carbon black, and is a rubber composition for tires in any combination with any one of the present inventions (1) to (7), wherein the content of the carbon black with respect to 100 parts by mass of the rubber component is 5 parts by mass or more and 100 parts by mass or less.

[0219] The present invention (9) is a rubber composition for tires in any combination with any one of the present inventions (1) to (8), which contains a sulfenamide-based vulcanization accelerator, a guanidine-based vulcanization accelerator, and a thiuram-based vulcanization accelerator.

[0220] The tire of the present invention (10) includes a surface rubber layer composed of a rubber composition for tires in any combination of the present inventions (1) to (9), and at least one inner rubber layer disposed on the inner side in the tire radial direction of the surface rubber layer, and is a tire provided with a multi-layer structure tread, wherein at least one of the inner rubber layers contains silica.

[0221] The tire of the present invention (11) is the tire according to the present invention (10), wherein the content of silica in the inner rubber layer containing silica is 50% by mass or more based on 100% by mass of the filler.

[0222] The tire of the present invention (12) is the tire according to the present invention (10) or (11), wherein the product (Sc × Tc) of the content Sc (% by mass) of styrene-butadiene rubber in 100% by mass of the rubber component of the surface rubber layer and the thickness Tc (mm) of the surface rubber layer is 0.4 or more and 500 or less.

[0223] The tire of the present invention (13) is a tire in any combination of the present inventions (10) to (12), wherein the product (Sc × D) of the content Sc (% by mass) of styrene-butadiene rubber in 100% by mass of the rubber component of the surface rubber layer and the groove depth D (mm) of the circumferential groove formed in the multi-layer structure tread is 0.5 or more and 500 or less.

Explanation of Reference Numerals

[0224] 2 Tire 4 Tread portion (multi-layer structure tread portion) 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 Folded-back Part 38 Inner Layer 40 Outer Layer 42 Main Groove 44 Rib Equatorial Plane of CL Tire

Claims

1. A rubber composition for tires, comprising an isoprene rubber and a styrene-butadiene rubber, wherein the content of the isoprene rubber in 100% by mass of the rubber component is 90% by mass or more.

2. The rubber composition for tires according to claim 1, wherein the content of the isoprene rubber in 100% by mass of the rubber component is 95% by mass or more.

3. The rubber composition for tires according to claim 1, comprising a styrene-butadiene rubber having a glass transition temperature of -50°C or lower.

4. Comprising a resin, wherein the content of the resin with respect to 100 parts by mass of the rubber component is 5 parts by mass or more and 50 parts by mass or less. The rubber composition for tires according to claim 1.

5. Comprising silica, wherein the content of the silica with respect to 100 parts by mass of the rubber component is 10 parts by mass or more and 150 parts by mass or less. The rubber composition for tires according to claim 1.

6. The rubber composition for tires according to claim 1, comprising silica derived from biomass materials.

7. The rubber composition for tires according to claim 1, comprising silica having a nitrogen adsorption specific surface area of 200 m ２ / g or more.

8. Comprising carbon black, wherein the content of the carbon black with respect to 100 parts by mass of the rubber component is 5 parts by mass or more and 100 parts by mass or less. The rubber composition for tires according to claim 1.

9. The rubber composition for tires according to claim 1, comprising a sulfenamide-based vulcanization accelerator, a guanidine-based vulcanization accelerator, and a thiuram-based vulcanization accelerator.

10. A tire comprising a multi-layered tread composed of a surface rubber layer made of the rubber composition for tires according to claim 1 and at least one inner rubber layer disposed on the inner side in the tire radial direction of the surface rubber layer, wherein at least one of the inner rubber layers contains silica.

11. The tire according to claim 10, wherein the inner rubber layer containing silica has a silica content of 50% by mass or more in 100% by mass of the filler.

12. The tire according to claim 10, wherein the product (Sc × Tc) of the content Sc (mass%) of the styrene-butadiene rubber in 100% by mass of the rubber component of the surface rubber layer and the thickness Tc (mm) of the surface rubber layer is 0.4 or more and 500 or less.

13. The tire according to claim 10, wherein the product (Sc × D) of the content Sc (mass%) of the styrene-butadiene rubber in 100% by mass of the rubber component of the surface rubber layer and the groove depth D (mm) of the circumferential groove formed in the multi-layered tread is 0.5 or more and 500 or less.

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