Tread rubber composition, tread rubber, and tire

Abstract

The present invention addresses the problem of providing a tread rubber composition capable of suppressing cracks in tread parts of a tire. A solution to the problem is a tread rubber composition characterized by comprising: a rubber component; an aminoquinoline-based antioxidant represented by general formula (1) [in the formula, R11 and R12 each independently represent hydrogen, an alkyl group having 1-12 carbon atoms, a cycloalkyl group having 3-6 carbon atoms, or a phenyl group, and R13, R14, R15, R16, R17, R18, and R19 each independently represent hydrogen or an alkyl group having 1-12 carbon atoms]; and a quinoline-based antioxidant other than the aminoquinoline-based antioxidant represented by general formula (1). The tread rubber composition is characterized in that the rubber component contains at least one selected from the group consisting of isoprene backbone rubbers, styrene-butadiene rubbers, butadiene rubbers, and chloroprene rubbers.

Description

Rubber composition for tread, tread rubber, and tire

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

[0002] In general, various rubber components constituting tires may deteriorate due to the influence of external environments such as the presence of ozone, and as this deterioration progresses, cracks and other defects may occur. To address this problem, rubber compositions containing antioxidants are often applied to the various rubber components constituting tires. For example, Patent Document 1 below discloses that cracks and discoloration of the tire surface can be suppressed by applying a rubber composition containing a selected blend of a specific quinoline-based antioxidant and N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antiaging agent 6PPD) to the rubber constituting the tire surface.

[0003] International Publication No. 2018 / 056384

[0004] However, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antioxidant 6PPD) used in the above-mentioned Patent Document 1 may have an impact on the environment, and it is desirable to use an antioxidant that places less strain on the environment, taking into account the possibility of future restrictions under European regulations. While it is conceivable to use no or very little antioxidant 6PPD in the rubber that constitutes the tire surface, the inventors' investigations have revealed that when antioxidant 6PPD is not used or very little is used, the ozone resistance of the rubber that constitutes the tire surface, particularly the tread rubber, decreases, making cracks more likely to occur in the tread portion.

[0005] Therefore, an object of the present invention is to provide a rubber composition for a tread and a tread rubber that can suppress cracks in the tread portion of a tire.A further object of the present invention is to provide a tire in which cracks in the tread portion are suppressed.

[0006] The rubber composition for a tread, the tread rubber, and the tire of the present invention that solve the above problems are summarized as follows.

[0007] [1] A rubber component and a compound represented by the following general formula (1): [In the formula, is a single bond or a double bond, R １１ and R １２ are each independently a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a phenyl group; R １３ , R １４ , R １５ , R １６ , R １７ , R １８ and R １９ are each independently hydrogen or an alkyl group having 1 to 12 carbon atoms.] and a quinoline antioxidant other than the aminoquinoline antioxidant represented by the general formula (1), wherein the rubber component contains at least one rubber selected from the group consisting of an isoprene skeleton rubber, a styrene-butadiene rubber, a butadiene rubber, and a chloroprene rubber.

[0008] [2] The rubber composition for treads according to [1], wherein the content of the quinoline-based antioxidant other than the aminoquinoline-based antioxidant represented by the general formula (1) is 0.1 to 5 parts by mass per 100 parts by mass of the rubber component.

[0009] [3] The rubber composition for treads according to [1] or [2], wherein the quinoline-based antioxidant other than the aminoquinoline-based antioxidant represented by the general formula (1) contains a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline.

[0010] [4] The aminoquinoline antioxidant is represented by the following structural formula (1-1): The rubber composition for tread according to any one of [1] to [3], wherein the compound is represented by the formula:

[0011] [5] Furthermore, the following general formula (2): [In the formula, R ２１ and R ２２ are each independently a substituted or unsubstituted monovalent aromatic hydrocarbon group, R ２３is an alkyl group substituted with a halogen.

[0012] [6] The rubber composition for a tread according to any one of [1] to [5], further comprising a cyclic polyol compound having a hydrocarbyl group, and a liquid polymer having a weight average molecular weight in terms of polystyrene measured by gel permeation chromatography of 5,000 or more but less than 40,000.

[0013] [7] Furthermore, the crystal amount is 7 J / g or more and 50 J / g or less, and the number average molecular weight is 3.0 × 10 ４ The rubber composition for tread according to any one of [1] to [6], which contains the above syndiotactic 1,2-polybutadiene.

[0014] [8] Furthermore, the following general formulae (3-1), (3-2) and (3-3): [wherein A is an aromatic group, a substituted or unsubstituted hydantoin ring, or a saturated or unsaturated linear hydrocarbon group having 0 to 8 carbon atoms; B is an aromatic group; the substituent X of B is a hydroxy group or an amino group; Y is a pyridyl group or a hydrazino group; R ３１ , R ３２ , R ３３ and R ３４ are each independently a hydrogen atom, or an alkyl group, a cycloalkyl group, or an aromatic group having 1 to 18 carbon atoms.

[0015] [9] The rubber composition for a tread according to any one of [1] to [8], wherein the rubber component contains a modified conjugated diene polymer, the modified conjugated diene polymer has two or more modifying groups in one molecule of the modified conjugated diene polymer, the modifying groups have a non-covalent bond between the molecules, and the energy per non-covalent bond is 10 to 250 kJ / mol.

[0016]

[10] The rubber composition for a tread according to any one of [1] to [9], wherein the rubber component contains a cyclic olefin ring-opening copolymer containing a structural unit derived from a monocyclic olefin and a structural unit derived from a norbornene compound.

[0017]

[11] The rubber composition for tread according to any one of [1] to

[10] , further comprising at least one foaming agent selected from azodicarbonamide, dinitrosopentamethylenetetramine, ammonium bicarbonate, sodium bicarbonate, and ammonium carbonate.

[0018]

[12] The rubber composition for a tread according to any one of [1] to

[11] , further comprising a silane coupling agent.

[0019]

[13] A tread rubber comprising the rubber composition for a tread according to any one of [1] to

[12] .

[0020]

[14] A tire comprising the tread rubber according to

[13] .

[0021] According to the present invention, it is possible to provide a rubber composition for a tread and a tread rubber that can suppress cracks in the tread portion of a tire. Also, according to the present invention, it is possible to provide a tire in which cracks in the tread portion are suppressed.

[0022] Figure 1 is a cross-sectional view of one embodiment of a tire of the present invention, Figure 2 is a cross-sectional view of another embodiment of a tire of the present invention, Figure 3 is a cross-sectional view of yet another embodiment of a tire of the present invention, Figure 4 is a cross-sectional view of yet another embodiment of a tire of the present invention.

[0023] The rubber composition for tread, the tread rubber, and the tire of the present invention will be described in detail below by way of example based on embodiments thereof.

[0024] <Definitions> The compounds described herein may be derived in whole or in part from fossil resources, from biological resources such as plant resources, from recycled resources such as used tires, or from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0025] In this specification, the "proportion of sustainable materials" refers to the total mass proportion of materials derived from biological resources (biomass resources) and materials derived from renewable resources (recycled resources) in the target rubber composition for tread, tread rubber, and tire.

[0026] In this specification, the term "biological resources (biomass resources)" refers to carbon-neutral organic resources derived from living organisms, and includes, for example, materials stored in the form of starch or cellulose, the bodies of animals that grow by eating plants, and products obtained by processing plants or animals, and is a resource excluding fossil resources (petroleum, coal, natural gas, etc.). The biological resources may be edible or non-edible, but are preferably non-edible in order not to compete with food and from the viewpoint of effective resource utilization.

[0027] Specific examples of the biological resources include cellulosic crops (pulp, kenaf, wheat straw, rice straw, waste paper, papermaking residues, etc.), wood, charcoal, compost, food waste, vegetable oil residues, fishery residues, livestock excrement, food waste, wastewater sludge, natural rubber, cotton, oils and fats (palm oil, castor oil, cottonseed oil, soybean oil, linseed oil, rapeseed oil, coconut oil, peanut oil, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, etc.), and the like. Examples of biological resources include: corn oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, tung oil, coconut oil, etc.), carbohydrate crops (corn, wheat, rice, rice husks, rice bran, old rice, potatoes, buckwheat, cassava, sago palm, sugarcane, etc.), bagasse (i.e., the residue left after sugarcane juicing), soybeans, soybean pulp refuse, essential oils (pine oil, orange oil, eucalyptus oil, etc.), pulp black liquor, and algae. The biological resources may also be processed (i.e., biological resource-derived substances). Examples of processing methods include biological processing methods utilizing the activity of microorganisms, plants, animals, and their tissue cultures; chemical processing methods utilizing acids, alkalis, catalysts, thermal energy, light energy, etc.; and physical processing methods such as pulverization, compression, microwave treatment, and electromagnetic wave treatment. The biological resources may also be extracted and purified from the biological resources or biological resources that have undergone the above-described processing (i.e., biological resource-derived substances). For example, sugars, proteins, amino acids, fatty acids, fatty acid esters, etc., purified from the above-mentioned biological resources can also be used. Examples of the sugars include sucrose, glucose, trehalose, fructose, lactose, galactose, xylose, allose, talose, gulose, altrose, mannose, idose, arabinose, apiose, maltose, cellulose, starch, chitin, etc., derived from biological resources. Examples of the proteins include compounds derived from biological resources and formed by linking amino acids (preferably L-amino acids), including oligopeptides such as dipeptides. Examples of the amino acids include valine, leucine, isoleucine, arginine, lysine, asparagine, glutamine, phenylalanine, etc., derived from biological resources, with valine, leucine, isoleucine, arginine, and phenylalanine being preferred.The amino acids may be either L-amino acids or D-amino acids, but L-amino acids are preferred from the viewpoints of abundance in nature and ease of availability. Examples of the fatty acids include butyric acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, etc., which are derived from biological resources. Examples of the fatty acid esters include modified products of vegetable oils, animal oils, and fats and oils derived from biological resources. These biological resources may contain various materials and impurities.

[0028] In this specification, the term "recycled resources" refers to resources obtained by regenerating (recycling) products that have been used once, or that have been collected without being used, or that have been discarded. For example, recycled resources include resources obtained by regenerating (recycling) used rubber products such as used tires.

[0029] <Rubber Composition for Tread> The rubber composition for tread of the present embodiment comprises a rubber component and a rubber compound represented by the following general formula (1): [In the formula, is a single bond or a double bond, R １１ and R １２ are each independently a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a phenyl group; R １３ , R １４ , R １５ , R １６ , R １７ , R １８ and R １９ are each independently hydrogen or an alkyl group having 1 to 12 carbon atoms.] and a quinoline antioxidant other than the aminoquinoline antioxidant represented by the general formula (1), wherein the rubber component contains at least one rubber selected from the group consisting of isoprene skeleton rubber, styrene-butadiene rubber, butadiene rubber, and chloroprene rubber.

[0030] The rubber composition for a tread of this embodiment contains an aminoquinoline-based antioxidant represented by the general formula (1) above and a quinoline-based antioxidant other than the aminoquinoline-based antioxidant represented by the general formula (1), thereby ensuring sufficient ozone resistance and suppressing cracking. Furthermore, in the rubber composition for a tread of this embodiment, the rubber component contains at least one rubber selected from the group consisting of an isoprene-skeleton rubber, a styrene-butadiene rubber, a butadiene rubber, and a chloroprene rubber, which makes it easier to significantly suppress cracking due to the aminoquinoline-based antioxidant represented by the general formula (1) above and the quinoline-based antioxidant other than the aminoquinoline-based antioxidant represented by the general formula (1). Therefore, the rubber composition for a tread of this embodiment has excellent ozone resistance, and when applied to the tread portion of a tire, it is possible to suppress cracking in the tread portion of the tire.

[0031] (Rubber Component) The rubber composition for treads of this embodiment contains a rubber component, and the rubber component provides rubber elasticity to the composition. The rubber component preferably has a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass. Here, the "sustainability rate" of the rubber component refers to the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources (recycled resources) in the rubber component.

[0032] The rubber component is preferably the rubber derived from biological resources and the rubber derived from recycled resources. Here, the proportion of the monomer component derived from biological resources in 100 mol% of the monomer components constituting the rubber derived from biological resources is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol%. Furthermore, the proportion of the monomer component derived from recycled resources in 100 mol% of the monomer components constituting the rubber derived from recycled resources is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol%.

[0033] The rubber component is a component that contributes to crosslinking, and typically has a weight average molecular weight (Mw) of 10,000 or more, preferably 50,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more, and preferably 5,000,000 or less, more preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,300,000 or less. In this specification, the weight average molecular weight (Mw) of the rubber component can be determined in terms of standard polystyrene based on measurements obtained using, for example, a gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M, manufactured by Tosoh Corporation).

[0034] The rubber component is preferably a diene rubber, and the diene rubber is preferably an isoprene rubber or a butadiene rubber. Here, the isoprene rubber refers to a rubber containing units derived from isoprene as a monomer unit, and the butadiene rubber refers to a rubber containing units derived from butadiene as a monomer unit.

[0035] Examples of the isoprene-based rubber include natural rubber (NR), synthetic isoprene rubber (IR), modified natural rubber (modified NR), modified natural rubber (modified NR), and modified synthetic isoprene rubber (modified IR). Examples of natural rubber (NR) that can be used include those commonly used in the tire industry, such as RSS#3 and TSR20 (e.g., SIR20 and STR20). The origin of the natural rubber (NR) is not particularly limited, and examples include those derived from Hevea brasiliensis, guayule, and Russian dandelion. Examples of synthetic isoprene rubber (IR) are not particularly limited, and examples include those commonly used in the tire industry, such as IR2200. Examples of modified NR include deproteinized natural rubber (DPNR) and highly purified natural rubber (UPNR). Examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Examples of modified IR include epoxidized synthetic isoprene rubber, hydrogenated synthetic isoprene rubber, and grafted synthetic isoprene rubber. These isoprene-based rubbers may be used alone or in combination of two or more. Among these, NR is preferred as the isoprene-based rubber.

[0036] The isoprene-based rubber preferably has a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass. To achieve a sustainability rate within the above range, it is preferable to use natural rubber (NR) or a polymer synthesized using isoprene derived from biological resources or isoprene derived from recycled resources as a monomer component. In this case, the synthesized polymer may be a homopolymer of a monomer derived from biological resources, a homopolymer of a monomer derived from recycled resources, a copolymer of a monomer derived from biological resources and a monomer derived from recycled resources, or a copolymer of a monomer derived from biological resources and / or a monomer derived from recycled resources and a monomer derived from fossil resources (petroleum, etc.).

[0037] Examples of the butadiene-based rubber include butadiene rubber (BR), aromatic vinyl compound-butadiene copolymer rubber (for example, styrene-butadiene rubber (SBR)), etc. Here, butadiene, which is a raw material for butadiene-based rubber, is preferably derived from biological resources or recycled resources.

[0038] Examples of the butadiene rubber (BR) include high-cis butadiene rubber, low-cis butadiene rubber, and butadiene rubber containing syndiotactic polybutadiene crystals. Commercially available butadiene rubbers can be used as the butadiene rubber (BR), and examples of commercially available butadiene rubbers include products from UBE Elastomers Co., Ltd., ENEOS Materials Corporation, Asahi Kasei Corporation, and Zeon Corporation. These butadiene rubbers may be used alone or in combination of two or more.

[0039] Examples of the aromatic vinyl compound-butadiene copolymer rubber (e.g., SBR) include emulsion-polymerized aromatic vinyl compound-butadiene copolymer rubber (e.g., emulsion-polymerized styrene-butadiene rubber (E-SBR)) and solution-polymerized aromatic vinyl compound-butadiene copolymer rubber (e.g., solution-polymerized styrene-butadiene rubber (S-SBR)). In the aromatic vinyl compound-butadiene copolymer rubber, examples of the aromatic vinyl compound (aromatic vinyl monomer) include styrene, vinylnaphthalene, and divinylnaphthalene. These aromatic vinyl compounds may be used alone or in combination of two or more. Among these, styrene is preferred, and styrene derived from biological resources and styrene derived from recycled resources are particularly preferred. That is, SBR is preferred as the aromatic vinyl compound-butadiene copolymer rubber. The styrene may have a substituent. As the aromatic vinyl compound-butadiene copolymer rubber, commercially available products can be used, and examples of such commercially available products include products from Asahi Kasei Corporation, ENEOS Materials Corporation, Zeon Corporation, Sumitomo Chemical Co., Ltd. These aromatic vinyl compound-butadiene copolymer rubbers may be used alone or in combination of two or more.

[0040] The butadiene-based rubber preferably has a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass. To achieve a sustainability rate within the above range, for example, a polymer synthesized using a bioresource-derived butadiene, a recycled resource-derived butadiene, a bioresource-derived aromatic vinyl compound (e.g., bioresource-derived styrene), or a recycled resource-derived aromatic vinyl compound (e.g., recycled resource-derived styrene) as a monomer component may be used. In this case, the synthesized polymer may be a homopolymer of a bioresource-derived monomer, a homopolymer of a recycled resource-derived monomer, a copolymer of a bioresource-derived monomer and a recycled resource-derived monomer, or a copolymer of a bioresource-derived monomer and / or a recycled resource-derived monomer and a fossil resource (e.g., petroleum)-derived monomer. Note that the butadiene rubber (B-BR) derived from biological resources (biomass resources) and aromatic vinyl compound-butadiene copolymer rubber derived from biological resources (for example, styrene-butadiene rubber (B-SBR) derived from biological resources (biomass resources)) include not only rubber obtained by polymerizing butadiene or the like according to conventional methods, but also rubber obtained by reactions involving microorganisms, plants, animals, and tissue cultures thereof (hereinafter also referred to as "microorganisms, etc.") or enzymatic reactions.

[0041] In addition, in order to set the sustainability rate of the entire rubber component within the above range, it is preferable to use natural rubber (NR) as the rubber component or a polymer synthesized using monomer components derived from biological resources or monomer components derived from recycled resources as monomer components.

[0042] Generally, the raw materials for rubber compositions for tires (e.g., rubber and its monomers, fillers, resins, etc.) require large-scale manufacturing equipment for their production, and are therefore typically produced in large factories in specific regions, requiring significant amounts of energy for the storage and transportation of raw materials and products. In contrast, materials derived from biological resources (biomass resources) are derived from local agricultural products, forests, etc., and can be produced on a small scale through microbial fermentation and catalytic reactions. By utilizing local products and waste, the energy required for transporting and storing raw materials can be reduced, and the energy required for transporting and storing the produced materials to tire factories can also be reduced, making them environmentally friendly. Materials derived from recycled resources can be obtained, for example, by dismantling and pyrolyzing used tires to extract the tire-constituting materials, such as rubber, fillers, and steel cords. In addition, sulfur can be obtained from biological resources or processed products of biological resources by a method including a desulfurization step of desulfurizing biological resources or processed products of biological resources to remove sulfur-containing substances from the biological resources or processed products of biological resources, a recovery step of recovering sulfur from the desulfurization residue generated in the desulfurization step, and a processing step of processing the recovered sulfur into sulfur for vulcanization (e.g., the method described in WO 2024 / 048141), and raw materials for tire rubber compositions can be obtained from various wastes and used items. In this way, the use of sustainable materials (materials derived from biological resources or materials derived from recycled resources) can reduce the overall environmental impact in tire manufacturing, such as reducing carbon dioxide emissions (LCCO2) over the entire life cycle, reducing energy consumption (LCE) over the entire life cycle, reducing costs incurred over the entire life cycle (LCC), and reducing the use of fossil resources.

[0043] Furthermore, when producing the rubber composition, the ratios of monomer components derived from biological resources, monomer components derived from recycled resources, and monomer components derived from fossil resources can be appropriately selected depending on the supply situation of biological resources, recycled resources, and fossil resources (e.g., monomer components derived from fossil resources) and / or market demand (e.g., demand for biological resources as food). By polymerizing the monomer components derived from biological resources, monomer components derived from recycled resources, and monomer components derived from fossil resources, rubber derived from sustainable materials (materials derived from biological resources or materials derived from recycled resources) can be obtained that has performance equivalent to that of conventional synthetic rubber. When using monomer components derived from recycled resources, it may be difficult to separate them from monomer components derived from fossil resources due to the manufacturing process of the monomers. In such cases, the environmental impact can be evaluated by adopting the mass balance approach.

[0044] The ratio of each monomer unit (e.g., isoprene-derived units, butadiene-derived units, and aromatic vinyl compound-derived units) in the entire rubber component can be adjusted appropriately depending on the components to which the rubber is applied. The ratio of each monomer unit in the entire rubber component can be adjusted, for example, by appropriately combining the above-mentioned isoprene-based rubber and butadiene-based rubber. The ratio of cis-bond units in the butadiene-derived units can also be adjusted appropriately depending on the components to which the rubber is applied. In this specification, the term "monomer unit" refers to a structural unit of a polymer, the term "isoprene-derived unit" refers to a structural unit in a polymer based on the isoprene monomer (including isoprene units in natural rubber), the term "butadiene-derived unit" refers to a structural unit in a polymer based on the butadiene monomer, and the term "aromatic vinyl compound-derived unit" refers to a structural unit in a polymer based on the aromatic vinyl compound monomer. In this specification, the ratio of each monomer unit is measured by NMR.

[0045] The rubber component may contain diene rubbers such as acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), styrene-isoprene-butadiene copolymer rubber (SIBR), etc., in addition to the above-mentioned isoprene-based rubber, butadiene rubber (BR), and aromatic vinyl compound-butadiene copolymer rubber (e.g., SBR). These rubber components may be used alone or in combination of two or more.

[0046] From the viewpoint of improving durability without reducing low loss properties, the rubber component is preferably a diene rubber, and more preferably an isoprene skeleton rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), or chloroprene rubber (CR). Here, the isoprene skeleton rubber is a rubber having an isoprene unit as the main skeleton, and specific examples include the above-mentioned natural rubber (NR) and synthetic isoprene rubber (IR). The rubber component contains at least one selected from the group consisting of an isoprene skeleton rubber, a styrene-butadiene rubber, a butadiene rubber, and a chloroprene rubber. By including at least one selected from the group consisting of an isoprene skeleton rubber, a styrene-butadiene rubber, a butadiene rubber, and a chloroprene rubber, the rubber composition has excellent rubber elasticity and is more suitable for tread applications. Furthermore, when the rubber component contains at least one rubber selected from the group consisting of an isoprene skeleton rubber, a styrene-butadiene rubber, a butadiene rubber, and a chloroprene rubber, the effect of inhibiting crack generation by the aminoquinoline antioxidant represented by the general formula (1) above or a quinoline antioxidant other than the aminoquinoline antioxidant represented by the general formula (1) above is likely to be significantly exhibited. The content of diene rubber, such as an isoprene skeleton rubber, a styrene-butadiene rubber, a butadiene rubber, or a chloroprene rubber, in the rubber component is preferably 80% by mass or more, more preferably 90% by mass or more, and can even be 100% by mass. The rubber component may be one type alone or a blend of two or more types.

[0047] The rubber component may be modified to introduce a functional group that interacts with fillers such as carbon black and silica. Examples of such functional groups include amino groups, amide groups, isocyanate groups, imino groups, imidazole groups, urea groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, ether groups, carbonyl groups, oxycarbonyl groups, silyl groups, alkoxysilyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, and thiocarbonyl groups. These functional groups may have a substituent. These functional groups may be introduced into the rubber component either individually or in combination. Among these, an amino group, an alkoxy group, and an alkoxysilyl group are preferred, and a substituted amino group in which a hydrogen atom of an amino group is substituted with an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and an alkoxysilyl group having 1 to 6 carbon atoms are more preferred.

[0048] The functional group can be introduced, for example, by reacting a compound (modifier) ​​having the functional group with the rubber component. The functional group is a modified functional group that has interactivity with fillers such as silica and carbon black, and examples thereof include a nitrogen-containing functional group, a silicon-containing functional group, or an oxygen-containing functional group. Examples of compounds (modifiers) having a nitrogen-containing functional group include amino group-containing compounds, and examples of compounds (modifiers) having a silicon-containing functional group include silicon halides and hydrocarbyloxysilane compounds. Examples of compounds (modifiers) having an oxygen-containing functional group include alkoxy group-containing compounds, alkylene oxide group-containing compounds, and trialkylsilyloxy group-containing compounds. More specifically, examples of the compounds described in WO 2016 / 194316 and WO 2019 / 117256 include the compounds described in WO 2016 / 194316 and WO 2019 / 117256. These modifiers may be used alone or in combination of two or more.

[0049] The rubber derived from sustainable materials (materials derived from biological resources or materials derived from recycled resources) can be produced in the same manner as conventional methods for producing synthetic rubber derived from fossil resources, for example, by using monomer components derived from biological resources or monomer components derived from recycled resources, and, if necessary, monomer components derived from fossil resources. Furthermore, the rubber derived from sustainable materials (particularly rubber derived from biological resources) can also be obtained by reactions using microorganisms or enzyme reactions.

[0050] Regarding the method for preparing bioresource-derived rubber from the above-mentioned bioresources, for example, the method described in JP 2022-179158 A can be used. For example, by using butadiene obtained from a bioresource as the monomer component, it is possible to obtain a bioresource (biomass resource)-derived butadiene rubber (B-BR). Furthermore, by using styrene obtained from a bioresource and butadiene obtained from a bioresource as the monomer components, it is possible to obtain a bioresource (biomass resource)-derived styrene-butadiene rubber (B-SBR). Here, methods for obtaining B-BR and B-SBR from bioresources include artificial polymerization methods, in vivo polymerization methods, and polymerization methods using biological enzymes. The molecular weight, branching, microstructure, etc. of the obtained B-BR and B-SBR can be appropriately adjusted by changing the polymerization conditions according to known methods depending on the desired tire performance.

[0051] Suitable butadienes obtained from biological resources include butadienes derived from alkyl alcohols (preferably ethanol and butanol, more preferably butanol), butadienes derived from alkenes (preferably ethylene), and butadienes derived from unsaturated carboxylic acids (preferably tiglic acid). Two or more of these butadienes may be used in combination. Suitable styrenes obtained from biological resources include styrenes obtained from plants (preferably plants belonging to the Hamamelidaceae, Styraxaceae, and Apocynaceae families, more preferably plants belonging to the Liquidambar, Styrax, and Catharanthus roseus, and even more preferably sweetgum, Styrax rostrata, and Catharanthus roseus), and styrenes obtained from microorganisms (preferably microorganisms belonging to the Penicillium and Escherichia genera, more preferably P. citrinum, and transformed E. coli). Suitable styrenes may be used in combination.

[0052] Recently, biomass industrial complexes centered on bioethanol, bioethylene, and the like have been planned. However, bioethanol and bioethylene are produced primarily using sugars and / or cellulose as biological resources, and do not effectively utilize other biological resources such as proteins, lipids, and amino acids. Furthermore, sugars compete with food, and excessive use of cellulose leads to deforestation. Therefore, depending on the supply status of various biological resources, the supply status of renewable resources, the supply status of fossil resources, and market demands (e.g., demand for biomass resources as food), it is preferable to use multiple types of monomer components derived from biological resources as the biological resource-derived monomer component, or to use a combination of monomer components derived from biological resources, monomer components derived from renewable resources, and monomer components derived from fossil resources, and further to appropriately adjust the ratios of these monomer components. This allows for the effective utilization of a wide range of biological resources, such as sugars, proteins, and lipids, as well as renewable resources, without relying on a single type of biological resource. It also allows for a stable supply of rubber derived from sustainable materials and further allows for environmental considerations depending on the production conditions. When multiple types of monomer components derived from biological resources are used, it is preferable to use monomer components derived from different biological resources, i.e., monomer components obtained from different biological resources. Specifically, it is preferable to use a mixture of butadienes derived from multiple types of biological resources with different origins as the biological resource-derived butadiene, and / or to use a mixture of styrenes derived from multiple types of biological resources with different origins as the biological resource-derived styrene. This allows for effective use of multiple types of biological resources.

[0053] -Modified Conjugated Diene Polymer- The rubber component preferably contains a modified conjugated diene polymer. The modified conjugated diene polymer preferably has two or more modifying groups per molecule, the modifying groups being bonded to each other via a non-covalent bond, and the energy per non-covalent bond is preferably 10 to 250 kJ / mol. The modified conjugated diene polymer exhibits low loss (low heat buildup) and excellent durability. While not wishing to be bound by theory, it is believed that the non-covalent bond between the modifying groups in the molecules has a weak bond energy within the above-mentioned specific range. Therefore, in a crosslinked product of the modified conjugated diene polymer, the non-covalent bond is maintained at low strain, resulting in excellent low loss. Meanwhile, the non-covalent bond is broken at high strain, resulting in hysteresis loss, resulting in excellent durability. Furthermore, the modified conjugated diene polymer also exhibits improved wet grip performance. While not wishing to be bound by theory, it is generally believed that when gripping, rubber containing the crosslinked product of the modified conjugated diene polymer undergoes significant deformation, and it is speculated that during this deformation, the non-covalent bonds described above are broken, and the resulting energy loss not only improves durability but also wet grip performance. Therefore, a rubber composition for a tread containing the modified conjugated diene polymer as the rubber component is excellent in low loss properties, durability, and wet grip performance.

[0054] Here, the energy per non-covalent bond between modifying groups in the modified conjugated diene polymer is calculated using M06 / 6-31G(d,p) as a basis function and Gaussian09 as a quantum chemical calculation program. The bond energy is calculated as follows. First, only the monomer units that form non-covalent bonds are extracted, a model of the associated state is created, and the energy of the associated state is calculated. Next, the associated state is sufficiently separated, and the energy of the dissociated state is calculated. The bond energy per molecule is calculated from the difference between the energy of the associated state and the energy of the dissociated state, and this is divided by the number of coordinate bonds to obtain the bond energy per molecule.

[0055] The weight average molecular weight (Mw) of the modified conjugated diene polymer was determined by gel permeation chromatography (GPC: HLC-8020 manufactured by Tosoh Corporation, column: GMH-XL (two columns in series manufactured by Tosoh Corporation), detector: differential refractometer (RI)), using a calibration curve prepared from monodisperse polystyrene, and determining the polystyrene-equivalent weight average molecular weight (Mw) of each modified conjugated diene polymer. When a modifier is used, an appropriate amount of degassed isopropanol is added to the polymerization reaction system before the addition of the modifier to terminate the polymerization reaction, and 0.5 mL of an isopropanol solution of 2,6-di-t-butyl-p-cresol (BHT) (BHT concentration: 5% by mass) is added, followed by isolation according to a conventional method. The weight average molecular weight of the resulting modified conjugated diene polymer was measured, thereby determining the polystyrene-equivalent weight average molecular weight before the reaction of the modifier with the active polymerization terminal.

[0056] In the modified conjugated diene-based polymer, the energy per non-covalent bond is preferably 50 to 250 kJ / mol from the viewpoint of low loss and excellent durability. In one embodiment, the energy per non-covalent bond is 60 kJ / mol or more, 100 kJ / mol or more, 150 kJ / mol or more, 160 kJ / mol or more, 170 kJ / mol or more, 180 kJ / mol or more, 190 kJ / mol or more, 200 kJ / mol or more, 210 kJ / mol or more, 220 kJ / mol or more, 230 kJ / mol or more, or 240 kJ / mol or more. In another embodiment, the energy per non-covalent bond is 240 kJ / mol or less, 230 kJ / mol or less, 220 kJ / mol or less, 210 kJ / mol or less, 200 kJ / mol or less, 190 kJ / mol or less, 180 kJ / mol or less, 170 kJ / mol or less, 160 kJ / mol or less, or 150 kJ / mol or less.

[0057] The modified conjugated diene polymer can be produced, for example, through the steps of: (i) anionically polymerizing a conjugated diene compound alone or a conjugated diene compound and an aromatic vinyl compound in the presence of an alkali metal compound as a polymerization initiator to form a conjugated diene polymer; (ii) after step (i), further adding an alkali metal compound to the conjugated diene polymer; and (iii) reacting the product obtained in step (ii) with a modifying agent to introduce a modifying group into the conjugated diene polymer.

[0058] (i) A step of anionically polymerizing a conjugated diene compound alone or a conjugated diene compound and an aromatic vinyl compound in the presence of an alkali metal compound as a polymerization initiator to form a conjugated diene-based polymer (hereinafter, this step may be simply referred to as step (i)) can be carried out in the same manner as the conventionally known anionic polymerizations described in, for example, JP-A-2013-249379, JP-A-2016-003246, JP-A-2014-227458, and the like.

[0059] Examples of the conjugated diene compound used in step (i) include 1,3-butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethylbutadiene. In one embodiment, the conjugated diene compound has 4 to 8 carbon atoms. The conjugated diene compound may be used alone or in combination of two or more. In one embodiment, the conjugated diene compound is one or more selected from the group consisting of 1,3-butadiene and isoprene. In another embodiment, the conjugated diene compound is 1,3-butadiene alone.

[0060] In this specification, compounds containing at least a conjugated diene compound (optionally containing an aromatic vinyl compound and a non-conjugated olefin, as described below) used to form a conjugated diene-based polymer in step (i) may be collectively referred to as monomers.

[0061] When a conjugated diene compound and an aromatic vinyl compound are copolymerized in step (i), the content of conjugated diene units (portions derived from the conjugated diene compound) in the resulting modified conjugated diene polymer is not particularly limited. For example, it is 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, 90 mol% or more, or 95 mol% or more, and 95 mol% or less, 90 mol% or less, 80 mol% or less, 60 mol% or less, 40 mol% or less, or 20 mol% or less. In one embodiment, the content of conjugated diene units in the modified conjugated diene polymer is 50 to 100 mol%.

[0062] Examples of aromatic vinyl compounds that can be used in step (i) include styrene, alkylstyrene, and halogenated alkylstyrene. The aromatic vinyl compounds may be used alone or in combination of two or more. The alkyl group of the alkylstyrene may have, for example, 1 to 5 carbon atoms. Examples of alkylstyrenes include 4-methylstyrene, 3-methylstyrene, and 2,4-dimethylstyrene. The alkyl group of the halogenated alkylstyrene may have, for example, 1 to 5 carbon atoms. Examples of halogenated alkylstyrenes include fluorine, chlorine, bromine, and iodine. Examples of halogenated alkylstyrenes include 4-chloromethylstyrene and 3-chloromethylstyrene. In producing the modified conjugated diene polymer, the aromatic vinyl compound preferably contains styrene and one or more selected from the group consisting of alkylstyrenes and halogenated alkylstyrenes. This facilitates the introduction of the modifying group. In producing the modified conjugated diene polymer, it is preferable that one or more selected from the group consisting of alkylstyrenes and halogenated alkylstyrenes are contained in a total amount of 0.1 to 3 mass% relative to the monomers forming the conjugated diene polymer. This ensures low loss and excellent durability while ensuring workability during production. In producing the modified conjugated diene polymer, it is preferable that the alkylstyrene is 4-methylstyrene and the halogenated alkylstyrene is 4-chloromethylstyrene. This further facilitates the introduction of a modifying group.

[0063] When a conjugated diene compound and an aromatic vinyl compound are copolymerized in step (i), the content of aromatic vinyl units (portions derived from the aromatic vinyl compound) in the resulting modified conjugated diene polymer is not particularly limited. For example, it is 0.1 mol% or more, 1 mol% or more, 5 mol% or more, 10 mol% or more, 20 mol% or more, 30 mol% or more, or 40 mol% or more, and 50 mol% or less, 45 mol% or less, 40 mol% or less, 30 mol% or less, 20 mol% or less, 10 mol% or less, 5 mol% or less, 1 mol% or less, or 0.1 mol% or less. In one embodiment, the content of aromatic vinyl units in the modified conjugated diene polymer is 0 to 50 mol%.

[0064] In step (i), when a conjugated diene compound and an aromatic vinyl compound are copolymerized, a non-conjugated olefin may be copolymerized in addition to the conjugated diene compound and the aromatic vinyl compound. Examples of non-conjugated olefins include ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-heptene, and 1-octene. In one embodiment, the non-conjugated olefin has 2 to 10 carbon atoms. The non-conjugated olefins may be used alone or in combination of two or more. In one embodiment, the non-conjugated olefin is an acyclic non-conjugated olefin, i.e., one or more selected from linear non-conjugated olefins and branched non-conjugated olefins. In another embodiment, the non-conjugated olefin is an α-olefin. Since the α-olefin has a double bond at the α-position of the olefin, copolymerization with the conjugated diene compound can be carried out efficiently. In one embodiment, the non-conjugated olefin is one or more selected from the group consisting of ethylene, propylene, and 1-butene. In another embodiment, the non-conjugated olefin is solely ethylene.

[0065] As the alkali metal compound used as a polymerization initiator, alkali metal compounds known in anionic polymerization can be used. Examples of the alkali metal atom (M) include Li, Na, K, Rb, and Cs. Examples of the alkali metal compound include organic alkali metal compounds and organic alkaline earth metal compounds. As the alkali metal compound, organic alkali metal compounds are preferred.

[0066] Examples of organic alkali metal compounds include hydrocarbyllithium and lithium amide compounds. Preferred hydrocarbyllithium compounds include those having a hydrocarbyl group having 2 to 20 carbon atoms, such as ethyllithium, n-propyllithium, isopropyllithium, n-butyllithium, isobutyllithium, sec-butyllithium, tert-butyllithium, tert-octyllithium, n-decyllithium, phenyllithium, 2-naphthyllithium, 2-butylphenyllithium, 4-phenylbutyllithium, cyclohexyllithium, cyclopentyllithium, and the reaction product of diisopropenylbenzene and butyllithium. Examples of lithium amide compounds include lithium hexamethyleneimide, lithium pyrrolidide, lithium piperidide, lithium heptamethyleneimide, lithium dodecamethyleneimide, lithium dimethylamide, lithium diethylamide, lithium dibutylamide, lithium dipropylamide, lithium diheptylamide, lithium dihexylamide, lithium dioctylamide, lithium di-2-ethylhexylamide, lithium didecylamide, lithium-N-methylpiperazide, lithium ethylpropylamide, lithium ethylbutylamide, lithium ethylbenzylamide, and lithium methylphenethylamide. The alkali metal compound used in step (i) is preferably n-butyllithium, as this allows for more efficient synthesis of the modified conjugated diene polymer. The amount of the alkali metal compound used in step (i) may be adjusted as appropriate, but may be, for example, in the range of 0.2 to 20 mmol per 100 parts by mass of the monomers that form the modified conjugated diene polymer.

[0067] (ii) Examples of the alkali metal atom (M) of the alkali metal compound added in the step of further adding an alkali metal compound to the conjugated diene polymer after step (i) (hereinafter, sometimes simply referred to as step (ii)) include Li, Na, K, Rb, and Cs. The alkali metal compound added in step (ii) is the same as the alkali metal compound described in step (i). The alkali metal compounds in steps (i) and (ii) may be the same or different. The alkali metal compound used in step (ii) is preferably sec-butyllithium, as this allows for more efficient synthesis of the modified conjugated diene polymer. The alkali metal compound used in step (i) is preferably n-butyllithium, and the alkali metal compound used in step (ii) is preferably sec-butyllithium, as this allows for more efficient synthesis of the modified conjugated diene polymer.

[0068] After step (i), by separately adding an alkali metal compound in step (ii), an alkali metal atom is introduced (a hydrogen atom in the hydrocarbon chain is substituted with an alkali metal atom) into a portion (e.g., partway along the polymer main chain) other than one end of the polymer main chain of the conjugated diene polymer formed in step (i), and the introduced alkali metal atom reacts with the modifying agent to introduce a modifying group capable of forming a non-covalent bond between molecules. However, for example, if step (ii) is not performed, i.e., if the alkali metal compound is added all at once in step (i), including the amount that would normally be added in step (ii), without further addition of an alkali metal compound, the number of reaction initiation sites for anionic polymerization when forming the conjugated diene polymer increases, and the molecular weight of the conjugated diene polymer decreases, but as described above, the alkali metal atom is not introduced into a portion other than one end of the polymer main chain of the conjugated diene polymer. Therefore, even if a conjugated diene polymer having an alkali metal compound introduced only at one end thereof is reacted with a modifying agent to introduce a modifying group, it is difficult to increase the number of modifying groups to 2 or more, making it difficult to obtain the modified conjugated diene polymer. Therefore, in order to introduce an alkali metal atom capable of reacting with the modifier into a portion other than one end of the polymer main chain of the conjugated diene polymer formed in step (i), it is necessary to further add an alkali metal compound after step (i).

[0069] In step (ii), for example, when styrene is used as the aromatic vinyl compound, the portion into which the alkali metal atom is introduced is the tertiary carbon atom at the bonding portion of styrene to the polymer main chain. Alternatively, when styrene and 4-methylstyrene are used as the aromatic vinyl compounds, for example, an alkali metal atom is introduced to the tertiary carbon atom at the bonding portion of styrene to the polymer main chain, as well as the tertiary carbon atom at the bonding portion of 4-methylstyrene to the polymer main chain and the primary carbon atom of the methyl group at the 4-position. In this case, since the primary carbon atom has less steric hindrance than the tertiary carbon atom, it is believed that the alkali metal atom is preferentially introduced to the primary carbon atom. Furthermore, in a polymer system that does not contain an aromatic vinyl compound, although the activity is lower than in the case of an aromatic vinyl compound, it is believed that the hydrogen atom at the allylic position reacts with the alkali metal atom of the additionally added alkali metal compound, resulting in the introduction of the alkali metal atom.

[0070] The amount of the alkali metal compound added in step (ii) may be adjusted as appropriate, for example, within the range of 0.2 to 20 mmol per 100 parts by mass of the monomer that forms the modified conjugated diene polymer.

[0071] The ratio ((ii) / (i)) of the amount (mmol) of the alkali metal compound added in step (i) to the amount (mmol) of the alkali metal compound added in step (ii) is preferably 0.5 to 100, more preferably 0.9 to 20.

[0072] When the aromatic vinyl compound contains styrene and one or more selected from the group consisting of alkylstyrenes and halogenated alkylstyrenes, the amount of the alkali metal compound added in step (ii) may be, for example, in the range of 0.1 to 3 mass %, preferably 0.1 to 1 mass %, based on the monomers forming the modified conjugated diene polymer, which ensures low loss and excellent durability while ensuring workability.

[0073] (iii) In the step of reacting the product obtained in step (ii) with a modifying agent to introduce a modifying group into the conjugated diene polymer (hereinafter, sometimes simply referred to as step (iii)), examples of the modifying agent used include carbon dioxide and carbon disulfide. In the production of the modified conjugated diene polymer, the modifying agent is preferably carbon dioxide. This allows polar groups to be easily introduced into a non-polar polymer. The amount of the modifying agent can be adjusted appropriately and is not particularly limited. For example, when carbon dioxide is used as the modifying agent, carbon dioxide can be blown into the solution containing the product of step (ii) until the color disappears. For example, when carbon dioxide is used as the modifying agent, the modifying group becomes -COOM. For example, when an aldehyde such as acetaldehyde is used as the modifying agent, the modifying group becomes -OM.

[0074] The modified conjugated diene polymer preferably has one or more modifying groups selected from the group consisting of -COOM and -OM (M is an alkali metal atom). This allows for the introduction of a coordinate bond with appropriate bond energy. The modified conjugated diene polymer preferably has one or more modifying groups selected from the group consisting of -COOLi and -OLi. This allows for the introduction of a coordinate bond with appropriate bond energy. The modified conjugated diene polymer has two or more modifying groups per molecule, and from the viewpoint of further improving low loss properties and durability, the number of modifying groups per molecule is preferably three or more, and from the viewpoint of handleability, the number of modifying groups per molecule is preferably 30 or less.

[0075] The following scheme shows an example of steps (i) to (iii) using butadiene as the conjugated diene compound, styrene and 4-methylstyrene as the aromatic vinyl compounds, n-butyllithium as the alkali metal compound in step (i), sec-butyllithium as the alkali metal compound in step (ii), and carbon dioxide as the modifier in step (iii). Note that, for simplicity of explanation, this example shows an intermediate product in which an Li atom has been introduced only into the methyl moiety at the 4-position of the 4-methylstyrene unit of the conjugated diene polymer in step (ii). However, Li atoms may also be introduced into the carbon atoms marked with * in the formula, i.e., the tertiary carbon atom at the bonding site between styrene and the polymer main chain, and the tertiary carbon atom at the bonding site between 4-methylstyrene and the polymer main chain.

[0076] The modified conjugated diene polymer obtained in the above example has -COOLi as a modifying group, and for example, an O atom of a carbonyl group in this modifying group coordinates to a Li atom in a modifying group of another modified conjugated diene polymer molecule to form a coordinate bond, which is a type of non-covalent bond. Note that, since the Li atom has a coordination number of 4, O atoms of carbonyl groups in modifying groups in two more modified conjugated diene polymer molecules can coordinate to the Li atom.

[0077] In the production of the modified conjugated diene polymer, the steps (ii) and (iii) may be carried out simultaneously, or the step (iii) may be carried out after the step (ii).

[0078] The production of the modified conjugated diene polymer may include, in addition to steps (i), (ii), and (iii), a step of washing the modified conjugated diene polymer obtained in step (iii). The solvent used for washing is not particularly limited and can be appropriately selected depending on the purpose. Examples of the solvent include methanol, ethanol, isopropanol, water, and buffer water.

[0079] It is preferable not to add an acid to the modified conjugated diene polymer, because adding an acid may remove lithium from the modified conjugated diene polymer, resulting in the polymer losing its coordinate bond.

[0080] The molecular weight of the modified conjugated diene polymer is not particularly limited and may be adjusted as appropriate. For example, the weight-average molecular weight (Mw) of the modified conjugated diene polymer is 100,000 or more or 150,000 or more and 1,000,000 or less or 500,000 or less. The weight-average molecular weight of the modified conjugated diene polymer is preferably 100,000 or more. This allows for a high degree of compatibility between low loss properties and durability.

[0081] The modified conjugated diene polymer is preferably at least one selected from the group consisting of a modified styrene-butadiene copolymer and a modified polybutadiene. This provides excellent low loss properties and durability. The modified conjugated diene polymer may be used alone or in combination of two or more.

[0082] The amount of the modified conjugated diene polymer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of the rubber component, and may be 100 parts by mass, but is preferably 90 parts by mass or less, and even more preferably 80 parts by mass or less. When the amount of the modified conjugated diene polymer is 5 parts by mass or more, per 100 parts by mass of the rubber component, the low loss property, durability, and wet grip performance of the rubber composition are further improved.

[0083] - Cyclic olefin ring-opening copolymer - The rubber component preferably contains a cyclic olefin ring-opening copolymer containing structural units derived from a monocyclic olefin and structural units derived from a norbornene compound. A rubber composition for a tread containing the cyclic olefin ring-opening copolymer containing structural units derived from a monocyclic olefin and structural units derived from a norbornene compound as the rubber component has excellent flex fatigue resistance, abrasion resistance, wet grip performance, and low heat buildup.

[0084] The monocyclic olefin is not particularly limited as long as it is an olefin having only one cyclic structure, and examples thereof include cyclic monoolefins such as cyclopropene, cyclobutene, cyclopentene, methylcyclopentene, cyclohexene, methylcyclohexene, cycloheptene, and cyclooctene; and cyclic diolefins such as cyclohexadiene, methylcyclohexadiene, cyclooctadiene, and methylcyclooctadiene.

[0085] The monocyclic olefin may be used alone or in combination of two or more. Preferred monocyclic olefins are cyclopentene, cyclohexene, cycloheptene, cyclooctene, and cyclooctadiene, and more preferred are cyclopentene and cyclooctadiene from the viewpoint of more easily achieving improved bending fatigue resistance, abrasion resistance, wet grip properties, and low heat buildup.

[0086] The norbornene compound is a compound having a norbornene ring structure, and is preferably a norbornene compound represented by the following general formula (4-1).

[0087] In the formula, R ４１ ~R ４４ each independently represents a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, or a substituent containing a halogen atom, a silicon atom, an oxygen atom, or a nitrogen atom; R ４２ and R ４３ may be bonded to each other to form a ring structure, and m is an integer of 0 to 2. Here, examples of the hydrocarbon group having 1 to 20 carbon atoms include alkyl groups such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, neopentyl group, hexyl group, and octyl group; alkenyl groups such as vinyl group, allyl group, 2-pentenyl group, 3-pentenyl group, and 4-methyl-3-pentenyl group; aryl groups such as phenyl group, tolyl group, 2,6-dimethylphenyl group, 2,6-diisopropylphenyl group, and naphthyl group; and aralkyl groups such as benzyl group and phenethyl group.

[0088] Examples of the norbornene compound represented by the general formula (4-1) include 2-norbornene, 5-methyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-hexyl-2-norbornene, 5-decyl-2-norbornene, 5-cyclohexyl-2-norbornene, 5-cyclopentyl-2-norbornene, 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene, 5-propenyl-2-norbornene, 5-cyclohexenyl-2-norbornene, 5-cyclopentenyl-2-norbornene, 5-phenyl-2-norbornene, tetracyclo[9.2.1.0] ２，１０ .0 ３，８ ]tetradeca-3,5,7,12-tetraene (also known as 1,4-methano-1,4,4a,9a-tetrahydro-9H-fluorene), tetracyclo[10.2.1.0 ２，１１ .0 ４，９ ]pentadeca-4,6,8,13-tetraene (also known as 1,4-methano-1,4,4a,9,9a,10-hexahydroanthracene), dicyclopentadiene, methyldicyclopentadiene, and dihydrodicyclopentadiene (tricyclo[5.2.1.0 ２，６ Bicyclo[2.2.1]hept-2-enes, such as unsubstituted or hydrocarbon-substituted cyclo[6.2.1.1]dec-8-ene; ３，６ .0 ２，７ ] dodec-4-ene, 9-methyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-ethyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-cyclohexyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-cyclopentyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-methylenetetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-ethylidenetetracyclo[6.2.1.1 ３，６ .0 ２，７] dodec-4-ene, 9-vinyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-propenyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-cyclohexenyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, 9-cyclopentenyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-ene, and 9-phenyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] tetracyclo[6.2.1.1] unsubstituted or having hydrocarbon substituents, such as dodec-4-ene; ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having an alkoxycarbonyl group such as methyl 5-norbornene-2-carboxylate, ethyl 5-norbornene-2-carboxylate, methyl 2-methyl-5-norbornene-2-carboxylate, and ethyl 2-methyl-5-norbornene-2-carboxylate; tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4-carboxylate methyl, and 4-methyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] tetracyclo[6.2.1.1] having an alkoxycarbonyl group, such as methyl dodec-9-ene-4-carboxylate ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having a hydroxycarbonyl group or an acid anhydride group, such as 5-norbornene-2-carboxylic acid, 5-norbornene-2,3-dicarboxylic acid, and 5-norbornene-2,3-dicarboxylic acid anhydride; tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4-carboxylic acid, tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4,5-dicarboxylic acid, and tetracyclo[6.2.1.1 ３，６ .0 ２，７] dodec-9-ene-4,5-dicarboxylic acid anhydride, or other tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having a hydroxyl group such as 5-hydroxy-2-norbornene, 5-hydroxymethyl-2-norbornene, 5,6-di(hydroxymethyl)-2-norbornene, 5,5-di(hydroxymethyl)-2-norbornene, 5-(2-hydroxyethoxycarbonyl)-2-norbornene, and 5-methyl-5-(2-hydroxyethoxycarbonyl)-2-norbornene; tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4-methanol, and tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-en-4-ol and other hydroxyl-containing tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having a hydrocarbonyl group such as 5-norbornene-2-carbaldehyde; tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4-carbaldehyde, and the like. ３，６ .0 ２，７ ]dodec-4-enes; bicyclo[2.2.1]hept-2-enes having an alkoxycarbonyl group and a hydroxycarbonyl group, such as 3-methoxycarbonyl-5-norbornene-2-carboxylic acid; bicyclo[2.2.1]hept-2-enes having a carbonyloxy group, such as 5-norbornen-2-yl acetate, 2-methyl-5-norbornen-2-yl acetate, 5-norbornen-2-yl acrylate, and 5-norbornen-2-yl methacrylate; 9-tetracyclo[6.2.1.1]acetate ３，６ .0 ２，７ ] dodec-4-enyl acrylate, 9-tetracyclo[6.2.1.1 ３，６ .0 ２，７] dodec-4-enyl, and 9-tetracyclo[6.2.1.1 methacrylate ３，６ .0 ２，７ ] tetracyclo[6.2.1.1] having a carbonyloxy group such as dodec-4-enyl ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having a functional group containing a nitrogen atom, such as 5-norbornene-2-carbonitrile, 5-norbornene-2-carboxamide, and 5-norbornene-2,3-dicarboxylic acid imide; tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4-carbonitrile, tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4-carboxamide, and tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene-4,5-dicarboxylic acid imide and other tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having a halogen atom such as 5-chloro-2-norbornene; 9-chlorotetracyclo[6.2.1.1 ３，６ .0 ２，７ ] tetracyclo[6.2.1.1] dodec-4-ene having a halogen atom, ３，６ .0 ２，７ ] dodec-4-enes; bicyclo[2.2.1]hept-2-enes having a functional group containing a silicon atom, such as 5-trimethoxysilyl-2-norbornene and 5-triethoxysilyl-2-norbornene; 4-trimethoxysilyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] dodec-9-ene, 4-triethoxysilyltetracyclo[6.2.1.1 ３，６ .0 ２，７ ] tetracyclo[6.2.1.1] having a functional group containing a silicon atom, such as dodec-9-ene ３，６ .0 ２，７] dodec-4-enes; etc. The norbornene compounds may be used singly or in combination of two or more.

[0089] The norbornene compound represented by the general formula (4-1) is preferably a norbornene compound represented by the general formula (4-1) in which m is 0 or 1, and more preferably a norbornene compound represented by the general formula (4-1) in which m is 0. ４１ ~R ４４ may be the same or different.

[0090] Furthermore, among the norbornene compounds represented by the above general formula (4-1), from the viewpoint that the obtained cross-linked rubber product can be made more excellent in flex fatigue resistance, abrasion resistance, wet grip properties, and low heat buildup, R ４１ ~R ４４ is preferably a hydrogen atom, a chain hydrocarbon group having 1 to 20 carbon atoms, or a substituent containing a halogen atom, a silicon atom, an oxygen atom, or a nitrogen atom. ４１ ~R ４４ are not particularly limited as long as they are groups that do not bond to each other and do not form a ring, and may be the same or different. R ４１ ~R ４４ is preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. In this case, too, those represented by the general formula in which m is 0 or 1 are preferred, and those represented by the general formula in which m is 0 are more preferred.

[0091] R in the above general formula (4-1) ４１ ~R ４４ The norbornene compounds in which the substituent is a hydrogen atom, a chain hydrocarbon group having 1 to 20 carbon atoms, or a halogen atom, a silicon atom, an oxygen atom, or a nitrogen atom include bicyclo[2.2.1]hept-2-enes and tetracyclo[6.2.1.1]hept-2-enes which are unsubstituted or have a hydrocarbon substituent. ３，６ .0 ２，７] dodec-4-enes are preferred, among which 2-norbornene, 5-methyl-2-norbornene, 5-ethyl-2-norbornene, 5-ethylidene-2-norbornene and tetracyclo[6.2.1.1 ３，６ .0 ２，７ ]dodec-4-ene is more preferred, and from the viewpoint of more easily achieving the above-mentioned effects, 2-norbornene, 5-methyl-2-norbornene and tetracyclo[6.2.1.1 ３，６ .0 ２，７ ]dodec-4-ene is more preferred, 2-norbornene and tetracyclo[6.2.1.1 ３，６ .0 ２，７ ] Dodec-4-ene is particularly preferred.

[0092] Furthermore, as the norbornene compound represented by the general formula (4-1), R ４２ and R ４３ When a compound in which R and R are bonded to each other to form a ring is used, specific examples of the ring structure include a cyclopentane ring, a cyclopentene ring, a cyclohexane ring, a cyclohexene ring, a benzene ring, etc., which may form a polycyclic structure and may further have a substituent. Among these, a cyclopentane ring, a cyclopentene ring, and a benzene ring are preferred, and a compound having a single cyclopentene ring or a polycyclic structure of a cyclopentane ring and a benzene ring is particularly preferred. ４２ , R ４３ Other than R ４１ , R ４４ may be the same or different, and are preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. In this case, those represented by the general formula in which m is 0 are preferred.

[0093] R ４２ and R ４３and 1,4-dimethyl-1,4-propanol-2,4-one are preferably bonded to each other to form a ring, and more preferably, 1,4-dimethyl-1,4-propanol-2,4-one is preferably bonded to each other to form a ring.

[0094] In the cyclic olefin ring-opening copolymer, the content of the structural units derived from a monocyclic cyclic olefin, relative to all repeating structural units, is preferably 20 to 90 mass%, more preferably 30 to 80 mass%, even more preferably 35 to 75 mass%, and particularly preferably 35 to 60 mass%. By setting the content of the structural units derived from a monocyclic cyclic olefin within the above range, the obtained cross-linked rubber product can be made to be more excellent in flex fatigue resistance, abrasion resistance, wet grip performance, and low heat buildup.

[0095] In the cyclic olefin ring-opening copolymer, the content of the structural units derived from a norbornene compound is preferably 10 to 80 mass%, more preferably 20 to 70 mass%, even more preferably 25 to 65 mass%, and particularly preferably 40 to 65 mass%, based on all repeating structural units. By setting the content of the structural units derived from a norbornene compound within the above range, the obtained cross-linked rubber product can be made to have even more excellent flex fatigue resistance, abrasion resistance, wet grip properties, and low heat buildup.

[0096] The cyclic olefin ring-opening copolymer may be a copolymer of a monocyclic olefin and a norbornene compound with another monomer copolymerizable therewith. Examples of such another monomer include a polycyclic cycloolefin having an aromatic ring. Examples of polycyclic cycloolefins having an aromatic ring include phenylcyclooctene, 5-phenyl-1,5-cyclooctadiene, and phenylcyclopentene. The content of structural units derived from other monomers in the cyclic olefin ring-opening copolymer is preferably 40% by mass or less, more preferably 30% by mass or less, based on the total repeating structural units. It is particularly preferred that the cyclic olefin ring-opening copolymer is substantially free of structural units derived from other monomers.

[0097] The weight average molecular weight (Mw) of the cyclic olefin ring-opening copolymer is, as a polystyrene-equivalent weight average molecular weight (Mw) measured by gel permeation chromatography, 50,000 to 1,000,000, preferably 60,000 to 800,000, more preferably 70,000 to 700,000, and even more preferably 80,000 to 600,000. By setting the weight average molecular weight (Mw) within the above range, production and handling can be improved, and the resulting cross-linked rubber product can be made to have excellent flex fatigue resistance, abrasion resistance, wet grip properties, and low heat buildup. The ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the cyclic olefin ring-opening copolymer, measured by gel permeation chromatography in terms of polystyrene, is preferably 1.0 to 5.0, more preferably 1.5 to 2.9, even more preferably 1.5 to 2.5, and particularly preferably 1.5 to 2.3.

[0098] The cis / trans ratio of the cyclic olefin ring-opening copolymer is preferably 0 / 100 to 60 / 40, more preferably 5 / 95 to 55 / 45, even more preferably 10 / 90 to 50 / 50, and particularly preferably 15 / 85 to 39 / 61. The cis / trans ratio refers to the ratio of cis structures to trans structures of double bonds present in the repeating units constituting the cyclic olefin ring-opening copolymer (cis / trans ratio). By setting the cis / trans ratio within the above range, the obtained cross-linked rubber product can be made to have excellent flex fatigue resistance, abrasion resistance, wet grip properties, and low heat buildup.

[0099] The cyclic olefin ring-opening copolymer is measured using differential scanning calorimetry (DSC) in accordance with JIS K7121 at a heating rate of 10°C / min every 0.13°C, and the difference (ΔTg) between the extrapolated glass transition end temperature (Teg) and the extrapolated glass transition onset temperature (Tig) obtained from the DSC curve is preferably 30°C or less, more preferably 20°C or less, even more preferably 15°C or less, and particularly preferably 10°C or less. By setting ΔTg within the above range, the obtained cross-linked rubber product can be made to be more excellent in flex fatigue resistance, abrasion resistance, wet grip properties, and low heat buildup.

[0100] The cyclic olefin ring-opening copolymer preferably has a glass transition temperature (Tmg) of -80°C to 10°C, more preferably -75°C to 0°C, and even more preferably -70°C to -10°C. By setting the glass transition temperature (Tmg) within the above range, the obtained cross-linked rubber product can be made to have excellent flex fatigue resistance, abrasion resistance, wet grip performance, and low heat buildup. The extrapolated glass transition onset temperature (Tig), extrapolated glass transition end temperature (Teg), and glass transition temperature (Tmg) are determined in accordance with JIS K7121. The difference (ΔTg) between the extrapolated glass transition onset temperature (Tig) and the extrapolated glass transition end temperature (Teg) is calculated using the following formula: The extrapolated glass transition onset temperature (Tig), extrapolated glass transition end temperature (Teg), and glass transition temperature (Tmg) can be controlled, for example, by devising a method for adding the monocyclic olefin and norbornene compound used in the polymerization, a method for adding the ring-opening polymerization catalyst, etc., as will be described later.

[0101] The Mooney viscosity (ML １＋４ , 100°C) is preferably 20 to 150, more preferably 22 to 120, and even more preferably 25 to 90. By setting the Mooney viscosity within the above range, kneading at room temperature and high temperatures can be facilitated, thereby improving processability.

[0102] The cyclic olefin ring-opening copolymer has a very small difference (ΔTg) between the extrapolated glass transition end temperature (Teg) and the extrapolated glass transition onset temperature (Tig), and is therefore considered to be a copolymer with a relatively narrow monomer composition distribution and molecular weight distribution.

[0103] The cyclic olefin ring-opening copolymer can be suitably produced by a production method including a step of copolymerizing a monocyclic olefin and a norbornene compound while continuously or intermittently adding one or both of a monocyclic olefin and a norbornene compound, and a ring-opening polymerization catalyst to a polymerization reactor. In the production of the cyclic olefin ring-opening copolymer, the time for continuously adding the monocyclic olefin and the norbornene compound to the polymerization reactor is usually 15 minutes or more, with no particular upper limit. The monocyclic olefin and the norbornene compound may be added continuously until the polymerization reaction is completed, for example, 15 minutes to 3 hours or 30 minutes to 2 hours. In the production method of the cyclic olefin ring-opening copolymer, the number of times the ring-opening polymerization catalyst is intermittently added to the polymerization reactor is usually two or more times, and may be any number of times as long as the polymerization reaction is being carried out, but may be two to five times.

[0104] The method for adding the monocyclic olefin and the norbornene compound to the polymerization reactor is not particularly limited, and for example, the monocyclic olefin and the norbornene compound may be added separately to the polymerization reactor, or they may be mixed together in advance to prepare a monomer mixture, which is then added to the polymerization reactor. When they are added separately, the monocyclic olefin and the norbornene compound are mixed in the polymerization reactor to form a monomer mixture, and the copolymerization reaction proceeds.

[0105] In the production of the cyclic olefin ring-opening copolymer, it is preferable to prepare a monomer mixture containing a monocyclic cyclic olefin and a norbornene compound. By preparing the monomer mixture in advance, the copolymerization reaction can be smoothly carried out and a cyclic olefin ring-opening copolymer with a small difference (ΔTg) can be easily produced.

[0106] Furthermore, the production of the cyclic olefin ring-opening copolymer preferably includes a step of preparing a solution containing a ring-opening polymerization catalyst. By preparing a solution containing a ring-opening polymerization catalyst in advance, the copolymerization reaction can proceed smoothly and a cyclic olefin ring-opening copolymer with a small difference (ΔTg) can be easily produced. The solution can be prepared, for example, by dissolving the ring-opening polymerization catalyst in a part of the solvent used for polymerization.

[0107] In the production of the cyclic olefin ring-opening copolymer, it is usually preferable to start the copolymerization reaction by adding a monocyclic cyclic olefin and a norbornene compound to a polymerization reactor and then adding a ring-opening polymerization catalyst. After this initiation step, the copolymerization reaction of the monocyclic olefin and the norbornene compound continues in the presence of the ring-opening polymerization catalyst.

[0108] In the production of the cyclic olefin ring-opening copolymer, it is preferable to continuously or intermittently add the monocyclic olefin and the norbornene compound or the ring-opening polymerization catalyst to the polymerization reactor even after the initiation step. A previously prepared monomer mixture may be used as the monocyclic olefin and the norbornene compound to be added after the initiation step. A previously prepared solution containing the ring-opening polymerization catalyst may be used as the ring-opening polymerization catalyst to be added after the initiation step. Alternatively, either the monocyclic olefin and the norbornene compound or the ring-opening polymerization catalyst may be added, or both the monocyclic olefin and the norbornene compound and the ring-opening polymerization catalyst may be added.

[0109] When both the monocyclic olefin, the norbornene compound, and the ring-opening polymerization catalyst are added, they may be added simultaneously or at different times. When both the monocyclic olefin, the norbornene compound, and the ring-opening polymerization catalyst are added, it is preferable to add them separately from separate inlets, as this allows the copolymerization reaction to proceed smoothly and makes it possible to easily produce a cyclic olefin ring-opening copolymer with a small difference (ΔTg). If the monocyclic olefin, the norbornene compound, and the ring-opening polymerization catalyst are mixed in advance before being added to the polymerization reactor, it may be difficult to obtain a cyclic olefin ring-opening copolymer with a small difference (ΔTg).

[0110] In the production of the cyclic olefin ring-opening copolymer, it is preferable to add the monocyclic olefin and norbornene compound, or the ring-opening polymerization catalyst, over a desired period of time after the initiation step by adding them in multiple batches or by continuing the addition. The end of the addition of the monocyclic olefin and norbornene compound, or the ring-opening polymerization catalyst, and the termination of the copolymerization reaction may be simultaneous, or the copolymerization reaction may be continued after the addition is completed. The addition duration of the monocyclic olefin and norbornene compound, and the ring-opening polymerization catalyst, can be set, for example, based on the monomer conversion rate and the temperature of the polymerization reaction system. Furthermore, the ratio of the monocyclic olefin and norbornene compound, and the ring-opening polymerization catalyst, added after the initiation step, to the total amount added can be set based on the monomer conversion rate.

[0111] Alternatively, the monocyclic olefin and the norbornene compound may be copolymerized while continuously or intermittently adding a molecular weight modifier to a polymerization reactor together with either or both of the monocyclic olefin and the norbornene compound and the ring-opening polymerization catalyst. Continuous or intermittent addition of the molecular weight modifier may facilitate the production of a cyclic olefin ring-opening copolymer with a small difference (ΔTg). The molecular weight modifier may be added in advance to the monomer mixture.

[0112] In the production of the cyclic olefin ring-opening copolymer, the proportion of the monocyclic olefin used relative to the total amount of the monocyclic olefin and the norbornene compound used is preferably 20 to 90 mass%, more preferably 30 to 85 mass%, even more preferably 35 to 80 mass%, and particularly preferably 35 to 70 mass%. By setting the proportion of the monocyclic olefin used within the above range, it is possible to more easily produce a cyclic olefin ring-opening copolymer that gives a cross-linked rubber product having excellent flex fatigue resistance, abrasion resistance, wet grip properties, and low heat buildup. Furthermore, by setting the proportion of the monocyclic olefin used within the above range, it is possible to more easily produce a cyclic olefin ring-opening copolymer with a small difference (ΔTg).

[0113] In the production of the cyclic olefin ring-opening copolymer, the proportion of the norbornene compound used relative to the total amount of the monocyclic cyclic olefin and the norbornene compound used is preferably 10 to 80 mass%, more preferably 15 to 70 mass%, even more preferably 20 to 65 mass%, and particularly preferably 30 to 65 mass%. By setting the proportion of the norbornene compound used within the above range, it is possible to more easily produce a cyclic olefin ring-opening copolymer that gives a cross-linked rubber product having excellent flex fatigue resistance, abrasion resistance, wet grip properties, and low heat buildup. Furthermore, by setting the proportion of the norbornene compound used within the above range, it is possible to more easily produce a cyclic olefin ring-opening copolymer with a small difference (ΔTg).

[0114] The ring-opening polymerization catalyst used in the ring-opening polymerization is not particularly limited, as long as it can ring-open polymerize a monocyclic cyclic olefin and a norbornene compound, but it is preferable to use one containing a metal halide compound. Examples of such metal halide compounds include halogen-containing Group 6 transition metal compounds and halogen-containing ruthenium carbene complexes. The Group 6 transition metal compound is a compound containing a Group 6 transition metal atom of the periodic table (long-form periodic table, the same applies hereinafter), specifically a compound containing a chromium atom, a molybdenum atom, or a tungsten atom. Compounds containing molybdenum atoms or compounds containing tungsten atoms are preferred, and compounds containing tungsten atoms are more preferred from the viewpoint of high solubility in monocyclic cyclic olefins. Specific examples of such halogen atom-containing Group 6 transition metal compounds (hereinafter referred to as "Group 6 transition metal compounds") include molybdenum compounds such as molybdenum pentachloride, molybdenum oxotetrachloride, and molybdenum(phenylimido)tetrachloride; and tungsten compounds such as tungsten hexachloride, tungsten oxotetrachloride, tungsten(phenylimido)tetrachloride, monocatecholate tungsten tetrachloride, bis(3,5-ditertiarybutyl)catecholate tungsten dichloride, and bis(2-chloroetherate)tetrachloride. The amount of the Group 6 transition metal compound used is preferably in the range of 1:100 to 1:200,000, more preferably 1:200 to 1:150,000, and even more preferably 1:500 to 1:100,000, in terms of the molar ratio of "Group 6 transition metal atom in the ring-opening polymerization catalyst:monomer used in ring-opening polymerization." If the amount of the Group 6 transition metal compound used is too small, the polymerization reaction may not proceed sufficiently. On the other hand, if the amount is too large, it becomes difficult to remove catalyst residue from the resulting cyclic olefin ring-opening copolymer, and the resulting cross-linked rubber product will have inferior properties.

[0115] When a Group 6 transition metal compound of the periodic table is used as a ring-opening polymerization catalyst, the Group 6 transition metal compound is preferably used in combination with an organoaluminum compound represented by the following general formula (4-2). The organoaluminum compound acts as a ring-opening polymerization catalyst together with the above-mentioned Group 6 transition metal compound. (R ４５ ) ３－ｘ Al (OR ４６ ) ｘ ... (4-2) In the above general formula (4-2), R ４５ and R ４６ is a hydrocarbon group having 1 to 20 carbon atoms, preferably a hydrocarbon group having 1 to 10 carbon atoms. In addition, x is 0<x<3. ４５ and R ４６ Specific examples of R include alkyl groups such as methyl, ethyl, isopropyl, n-propyl, isobutyl, n-butyl, t-butyl, n-hexyl, cyclohexyl, n-octyl, and n-decyl; and aryl groups such as phenyl, 4-methylphenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, and naphthyl. In the general formula (4-2), x satisfies the condition 0<x<3. That is, in the general formula (4-2), R ４５ and OR ４６ The composition ratio of x to x can be any value within the ranges of 0<3-x<3 and 0<x<3, respectively. However, in terms of increasing the polymerization activity, x is preferably 0.5<x<1.5.

[0116] The organoaluminum compound represented by the general formula (4-2) can be synthesized, for example, by reacting trialkylaluminum with an alcohol, as shown in the following general formula (4-3): (R ４５ ) ３ Al + xR ４６ OH → (R ４５ ) ３－ｘ Al (OR ４６ ) ｘ + (R ４６ ) ｘH (4-3) Note that x in the above general formula (4-2) can be arbitrarily controlled by specifying the reaction ratio of the corresponding trialkylaluminum and alcohol, as shown in the above general formula (4-3).

[0117] The amount of the organoaluminum compound used varies depending on the type of organoaluminum compound used, but is preferably 0.1 to 100 times by mole, more preferably 0.2 to 50 times by mole, and even more preferably 0.5 to 20 times by mole, relative to the Group 6 transition metal atoms constituting the Group 6 transition metal compound. If the amount of the organoaluminum compound used is too small, the polymerization activity may be insufficient, whereas if it is too large, side reactions tend to occur more easily during ring-opening polymerization.

[0118] Specific examples of the ruthenium carbene complex containing a halogen atom (hereinafter referred to as "ruthenium carbene complex" where appropriate) include bis(tricyclohexylphosphine)benzylideneruthenium dichloride, bis(triphenylphosphine)-3,3-diphenylpropenylideneruthenium dichloride, bis(tricyclohexylphosphine)t-butylvinylideneruthenium dichloride, dichloro-(3-phenyl-1H-inden-1-ylidene)bis(tricyclohexylphosphine)ruthenium, bis(1,3-diisopropylimidazolin-2-ylidene)benzylideneruthenium dichloride, chloride, bis(1,3-dicyclohexylimidazolin-2-ylidene)benzylidene ruthenium dichloride, (1,3-dimesitylimidazolin-2-ylidene)(tricyclohexylphosphine)benzylidene ruthenium dichloride, (1,3-dimesitylimidazolin-2-ylidene)(tricyclohexylphosphine)benzylidene ruthenium dichloride, (1,3-dimesitylimidazolidin-2-ylidene)(tricyclohexylphosphine)benzylidene ruthenium dichloride, bis(tricyclohexylphosphine)ethoxymethylidene ruthenium dichloride, (1,3-dimesitylimidazolidin-2-ylidene)(tricyclohexylphosphine)ethoxymethylidene ruthenium dichloride. The amount of the ruthenium carbene complex used is, in terms of the molar ratio of (ruthenium carbene complex:monomer used in ring-opening polymerization), usually in the range of 1:500 to 1:2,000,000, preferably 1:700 to 1:1,500,000, and more preferably 1:1,000 to 1:1,000,000.

[0119] The ring-opening polymerization catalysts such as a transition metal compound of Group 6 of the periodic table and a ruthenium carbene complex may be used alone or in combination of two or more.

[0120] Furthermore, when a monomer containing a monocyclic olefin and a norbornene compound is subjected to ring-opening polymerization, an olefin compound or a diolefin compound may be added to the polymerization reaction system as a molecular weight modifier, if necessary, to adjust the molecular weight of the resulting cyclic olefin ring-opening copolymer. The olefin compound is not particularly limited as long as it is an organic compound having an ethylenically unsaturated bond, and examples thereof include α-olefins such as 1-butene, 1-pentene, 1-hexene, and 1-octene; styrenes such as styrene and vinyltoluene; halogen-containing vinyl compounds such as allyl chloride; vinyl ethers such as ethyl vinyl ether and i-butyl vinyl ether; silicon-containing vinyl compounds such as allyltrimethoxysilane, allyltriethoxysilane, allyltrichlorosilane, and styryltrimethoxysilane; and disubstituted olefins such as 2-butene and 3-hexene. Examples of the diolefin compound include non-conjugated diolefins such as 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 1,6-heptadiene, 2-methyl-1,4-pentadiene, and 2,5-dimethyl-1,5-hexadiene. The amount of the olefin compound and diolefin compound used as a molecular weight modifier may be appropriately selected depending on the molecular weight of the cyclic olefin ring-opening copolymer to be produced, and is typically in the range of 1 / 100 to 1 / 100,000, preferably 1 / 200 to 1 / 50,000, and more preferably 1 / 500 to 1 / 10,000, in terms of molar ratio relative to the cyclic olefin-containing monomer used in the polymerization.

[0121] The polymerization reaction may be carried out in a solventless state or in a solution, but is preferably carried out in a solution. When copolymerizing in a solution, the solvent used is not particularly limited as long as it is inert to the polymerization reaction and can dissolve the monocyclic olefin, norbornene compound, ring-opening polymerization catalyst, and the like used in the copolymerization. However, it is preferable to use a hydrocarbon solvent or a halogenated solvent. Examples of hydrocarbon solvents include aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; aliphatic hydrocarbons such as hexane, n-heptane, and n-octane; and alicyclic hydrocarbons such as cyclohexane, cyclopentane, and methylcyclohexane. Examples of halogenated solvents include haloalkanes such as dichloromethane and chloroform; and aromatic halogens such as chlorobenzene and dichlorobenzene. These solvents may be used alone or in combination.

[0122] The lower limit of the polymerization reaction temperature is not particularly limited, but is preferably −100°C or higher, more preferably −50°C or higher, even more preferably 0°C or higher, and particularly preferably 20°C or higher. The upper limit of the polymerization reaction temperature is also not particularly limited, but is preferably less than 120°C, more preferably less than 100°C, even more preferably less than 90°C, and particularly preferably less than 80°C. The polymerization reaction time is also not particularly limited, but is preferably 1 minute to 72 hours, more preferably 10 minutes to 20 hours. The polymerization reaction produces a polymerization solution containing a cyclic olefin ring-opening copolymer. The resulting polymerization solution may be recovered after completion of the polymerization reaction, or may be recovered by continuously or intermittently adding one or both of the monocyclic cyclic olefin and norbornene compound, and the ring-opening polymerization catalyst, while continuously withdrawing a certain amount of the polymerization solution (continuous polymerization method).

[0123] If desired, an antioxidant such as a phenol-based stabilizer, a phosphorus-based stabilizer, or a sulfur-based stabilizer may be added to the cyclic olefin ring-opening copolymer obtained by the polymerization reaction. The amount of the antioxidant to be added may be determined appropriately depending on the type of the antioxidant. Furthermore, if desired, an extender oil may be blended. When the cyclic olefin ring-opening copolymer is obtained as a polymerization solution, a known recovery method may be used to recover the cyclic olefin ring-opening copolymer from the polymerization solution. For example, a method may be used in which the solvent is separated by steam stripping or the like, the solid is filtered off, and the solid is then dried to obtain a solid cyclic olefin ring-opening copolymer.

[0124] The amount of the cyclic olefin ring-opening copolymer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of the rubber component, and may be 100 parts by mass, but is preferably 90 parts by mass or less, and even more preferably 80 parts by mass or less. When the amount of the cyclic olefin ring-opening copolymer is 5 parts by mass or more, per 100 parts by mass of the rubber component, the flex fatigue resistance, abrasion resistance, wet grip performance, and low heat buildup of the rubber composition are further improved.

[0125] (Aminoquinoline-based antioxidant) The rubber composition for treads of this embodiment contains an aminoquinoline-based antioxidant represented by the above general formula (1). The aminoquinoline-based antioxidant represented by general formula (1) has the effect of improving the ozone resistance of the rubber composition, and can suppress cracking of the tread rubber to which the rubber composition is applied.

[0126] In the above general formula (1), is a single bond or a double bond, preferably a double bond; R １１ and R １２ are each independently hydrogen, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a phenyl group, and are preferably hydrogen or a phenyl group; １３ , R １４ , R １５ , R １６ , R １７ , R １８ and R１９ are each independently hydrogen or an alkyl group having 1 to 12 carbon atoms, and are preferably hydrogen or a methyl group. １１ , R １２ , R １３ , R １４ , R １５ , R １６ , R １７ , R １８ and R １９ With regard to the above, the alkyl group having 1 to 12 carbon atoms may be linear or branched. Examples of the alkyl group having 1 to 12 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, and various decyl groups. The number of carbon atoms in the alkyl group is preferably in the range of 1 to 8, more preferably in the range of 1 to 6, even more preferably in the range of 1 to 4, and particularly preferably in the range of 1 to 3. R in the above general formula (1) １１ and R １２ Regarding the above, examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a 1-methylcyclopentyl group, a 2-methylcyclopentyl group, and a 3-methylcyclopentyl group.

[0127] Specific examples of the aminoquinoline antioxidants represented by the general formula (1) include those represented by the following structural formulas (1-1) to (1-47): Among these, from the viewpoint of suppressing cracking in the tread rubber, the compound represented by structural formula (1-1) is particularly preferred. A rubber composition for treads containing the compound represented by structural formula (1-1) can further suppress cracking in the tread portion of a tire.

[0128] There are no particular limitations on the method for producing the aminoquinoline antioxidant represented by the above general formula (1). For example, when an aromatic amine compound is used as a starting material, the method comprises the steps of: (i) reacting the aromatic amine compound with sodium nitrite in the presence of an acid to produce an aromatic amine compound having a nitroso group; (ii) reducing the produced nitroso group with sodium borohydride or the like to produce an aromatic diamine compound; and (iii) reacting the produced aromatic diamine compound with a ketone compound such as acetone to form a condensed ring, thereby producing a compound having a 6-amino-1,2-dihydroquinoline skeleton, i.e., the compound represented by the above general formula (1), In addition, if desired, (iv) the compound having a 6-amino-1,2-dihydroquinoline skeleton thus produced can be reduced with hydrogen in the presence of a palladium-supported carbon catalyst to produce a compound having a 6-amino-1,2,3,4-tetrahydroquinoline skeleton, i.e., a compound represented by the above general formula (1), Compounds can be prepared in which is a single bond.

[0129] The content of the aminoquinoline-based antiaging agent is preferably in the range of 0.1 to 11 parts by mass per 100 parts by mass of the rubber component. When the content of the aminoquinoline-based antiaging agent is 0.1 part by mass or more per 100 parts by mass of the rubber component, the ozone resistance of the rubber composition can be sufficiently ensured. Furthermore, when the content of the aminoquinoline-based antiaging agent is 11 parts by mass or less per 100 parts by mass of the rubber component, adverse effects on rubber physical properties other than ozone resistance (heat buildup, etc.) are reduced, making the rubber suitable for tire tread rubber applications. From the viewpoint of ozone resistance (cracking prevention), the content of the aminoquinoline-based antiaging agent is more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more per 100 parts by mass of the rubber component. Furthermore, from the viewpoint of effects on other rubber physical properties, the content is more preferably 10 parts by mass or less, and even more preferably 9 parts by mass or less per 100 parts by mass of the rubber component.

[0130] (Other Quinoline Antiaging Agent) The rubber composition for tread of this embodiment contains a quinoline antioxidant other than the aminoquinoline antioxidant represented by the general formula (1) above (hereinafter, sometimes simply referred to as "other quinoline antioxidant"). The quinoline antioxidant is an antioxidant having a quinoline moiety or a derivative moiety thereof (dihydroquinoline moiety, tetrahydroquinoline moiety, etc.). The quinoline antioxidant has the effect of improving the ozone resistance of the rubber composition, and a rubber composition for tread containing both the aminoquinoline antioxidant represented by the general formula (1) above and the other quinoline antioxidant can further suppress cracking in the tread portion of a tire.

[0131] The other quinoline-based antioxidant preferably has a dihydroquinoline moiety, and more preferably has a 1,2-dihydroquinoline moiety. Specific examples of the other quinoline-based antioxidant include a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline (antiaging agent TMDQ) and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. The other quinoline-based antioxidant preferably contains a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline (antiaging agent TMDQ). Quinoline-based antioxidants containing a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline are highly effective in improving the ozone resistance of rubber compositions, and also have the advantage of being less likely to discolor the rubber composition. Therefore, a rubber composition containing a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline can further suppress cracking in the tread portion of a tire and is also less susceptible to discoloration. Examples of the polymer of 2,2,4-trimethyl-1,2-dihydroquinoline include a dimer, trimer, and tetramer of 2,2,4-trimethyl-1,2-dihydroquinoline.

[0132] The content of the other quinoline-based antioxidant is preferably 0.1 to 5 parts by mass per 100 parts by mass of the rubber component. When the content of the other quinoline-based antioxidant is 0.1 part by mass or more per 100 parts by mass of the rubber component, the ozone resistance of the rubber composition is improved. Furthermore, when the content of the other quinoline-based antioxidant is 5 parts by mass or less per 100 parts by mass of the rubber component, adverse effects on rubber physical properties other than ozone resistance (such as heat buildup) can be suppressed, making the rubber composition more suitable for tire tread rubber applications. Furthermore, a rubber composition containing the other quinoline-based antioxidant in an amount of 0.1 to 5 parts by mass per 100 parts by mass of the rubber component can further suppress cracks in the tire tread while suppressing adverse effects on other rubber physical properties (such as heat buildup). The content of the other quinoline-based antioxidant is more preferably 0.3 parts by mass or more and even more preferably 0.5 parts by mass or more per 100 parts by mass of the rubber component from the viewpoint of ozone resistance, and is more preferably 4 parts by mass or less and even more preferably 3 parts by mass or less per 100 parts by mass of the rubber component from the viewpoint of influence on other rubber physical properties.

[0133] (Other Antiaging Agents) The rubber composition for treads of this embodiment may contain an antioxidant other than the aminoquinoline-based antioxidant and other quinoline-based antioxidants described above. Examples of such other antioxidants include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N,N'-diphenyl-p-phenylenediamine (DPPD), and N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine. However, it is preferable that the rubber composition does not contain N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD). Commercially available antioxidants can be used, and examples of commercially available antioxidants include products from Ouchi Shinko Chemical Industry Co., Ltd., Sumitomo Chemical Co., Ltd., Seiko Chemical Co., Ltd., Flexis, and the like. These antioxidants may be used alone or in combination of two or more.

[0134] The content of the other antioxidant is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the rubber composition is applied, the target performance, etc. For example, the content of the other antioxidant is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2 parts by mass or more, and is preferably 12 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 8 parts by mass or less, per 100 parts by mass of the rubber component.

[0135] (Vulcanization Retarder) The rubber composition for tread of the present embodiment preferably further contains a vulcanization retarder, and the vulcanization retarder is preferably a vulcanization retarder represented by the following general formula (2): [In the formula, R ２１ and R ２２ are each independently a substituted or unsubstituted monovalent aromatic hydrocarbon group, R ２３ is an alkyl group substituted with a halogen. It is more preferable that the rubber composition for a tread contains a vulcanization retarder represented by the formula (2). When the rubber composition for a tread contains a vulcanization retarder, premature vulcanization (scorch) of the rubber composition can be suppressed. Furthermore, the vulcanization retarder represented by the formula (2) has the effect of suppressing premature vulcanization (scorch) of the rubber composition, and is less likely to bloom even when used in combination with an aminoquinoline-based antiaging agent represented by the formula (1) above or a quinoline-based antiaging agent other than the aminoquinoline-based antiaging agent represented by the formula (1) above. Therefore, by compounding the vulcanization retarder represented by the formula (2) into the rubber composition, premature vulcanization (scorch) of the rubber composition can be suppressed while also suppressing a decrease in the tackiness (tack) of the rubber composition, and workability can be improved both during kneading and molding of the rubber composition.

[0136] In the above general formula (2), R ２１ and R ２２ R are each independently a substituted or unsubstituted monovalent aromatic hydrocarbon group. ２１ and R ２２ may be the same or different, but from the viewpoint of synthesis, they are preferably the same.

[0137] The number of carbon atoms in the monovalent aromatic hydrocarbon group is preferably 6 to 20, more preferably 6 to 10, and particularly preferably 6. When the number of carbon atoms in the aromatic hydrocarbon group is 20 or less, the number of moles per unit mass increases, thereby increasing the vulcanization retardation effect and improving the scorch resistance of the rubber composition.

[0138] The monovalent aromatic hydrocarbon group may be an aryl group or an aralkyl group. The aryl group may be a phenyl group, a tolyl group, a xylyl group, a mesityl group, a duryl group, a biphenyl group, a naphthyl group, an anthryl group, a terphenyl group, a pyrenyl group, or a phenanthrenyl group, and among these, a phenyl group is preferred. The aralkyl group may be a benzyl group, a phenethyl group, a phenylpropyl group, or a naphthylmethyl group.

[0139] The hydrogen atoms in the monovalent aromatic hydrocarbon group may or may not be substituted with a substituent. Here, examples of the substituent include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, and tert-butyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl; alkenyl groups such as vinyl, 1-propenyl, allyl, butenyl, and styryl; alkoxy groups such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tert-butoxy, pentyloxy, hexyloxy, heptyloxy, and octyloxy; acyl groups such as acetyl, propionyl, and butyryl; halogen atoms such as fluorine, chlorine, bromine, and iodine; haloalkyl groups such as methyl chloride, methyl bromide, methyl iodide, fluoromethyl, difluoromethyl, and trifluoromethyl; and a nitro group.

[0140] In the above general formula (2), R ２３is an alkyl group substituted with a halogen (haloalkyl group). The number of carbon atoms in the alkyl group substituted with a halogen is preferably 1 to 10, more preferably 1 to 4, and particularly preferably 1. When the alkyl group substituted with a halogen has 10 or less carbon atoms, the number of moles per unit mass increases, thereby enhancing the vulcanization retardation effect and improving the scorch resistance of the rubber composition. Furthermore, in the alkyl group substituted with a halogen, the number of substitutions by halogen is preferably 1 to 10, more preferably 1 to 5, and particularly preferably 3.

[0141] Examples of the halogen include fluorine, chlorine, bromine, and iodine, with chlorine being preferred among these. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group, with methyl being preferred among these. Specific examples of the alkyl group substituted with a halogen include a fluoromethyl group, a chloromethyl group, a bromomethyl group, a difluoromethyl group, a dichloromethyl group, a trifluoromethyl group, a trichloromethyl group, a fluoroethyl group, a chloroethyl group, and a bromoethyl group, with trichloromethyl being preferred among these.

[0142] The molecular weight of the vulcanization retarder is preferably 300 or more and 800 or less. When the molecular weight of the vulcanization retarder is 300 or more, the vulcanization retarder is more unlikely to bloom, and the bloom resistance of the rubber composition is further improved. Furthermore, when the molecular weight of the vulcanization retarder is 800 or less, the number of moles per unit mass is large, so the vulcanization retarding effect is greater and the scorch resistance of the rubber composition is further improved. From the viewpoint of scorch resistance, the molecular weight of the vulcanization retarder is more preferably 700 or less, even more preferably 600 or less, and even more preferably 500 or less.

[0143] The vulcanization retarder preferably has a carbon number of 13 to 30. When the carbon number of the vulcanization retarder is 13 or more, the vulcanization retarder is more resistant to blooming, and the bloom resistance of the rubber composition is further improved. When the carbon number of the vulcanization retarder is 30 or less, the number of moles per unit mass is large, thereby enhancing the vulcanization retarding effect and further improving the scorch resistance of the rubber composition. From the viewpoint of scorch resistance, the carbon number of the vulcanization retarder is more preferably 25 or less, even more preferably 20 or less, and even more preferably 15 or less.

[0144] Specific examples of the vulcanization retarder represented by the general formula (2) include N-phenyl-N-(monochloromethylthio)benzenesulfonamide, N-phenyl-N-(dichloromethylthio)benzenesulfonamide, N-phenyl-N-(trichloromethylthio)benzenesulfonamide, N-phenyl-N-(trichloroethylthio)benzenesulfonamide, N-phenyl-N-(trichloropropylthio)benzenesulfonamide, N-phenyl-N-(monochloromethylthio)toluenesulfonamide, N-phenyl-N-(dichloromethylthio)toluenesulfonamide, and N-phenyl-N-(trichloromethylthio)toluenesulfonamide. Of these, N-phenyl-N-(trichloromethylthio)benzenesulfonamide (also referred to as "N-phenyl-N-(trichloromethylsulfenyl)-benzenesulfonamide") is preferred. The vulcanization retarders may be used alone or in combination of two or more.

[0145] The content of the vulcanization retarder is preferably 0.005 parts by mass or more, more preferably 0.01 parts by mass or more, and preferably 3.5 parts by mass or less, per 100 parts by mass of the rubber component. When the content of the vulcanization retarder is 0.005 parts by mass or more, per 100 parts by mass of the rubber component, premature vulcanization (scorch) of the rubber composition can be sufficiently suppressed. When the content of the vulcanization retarder is 0.01 parts by mass or more, premature vulcanization (scorch) of the rubber composition can be further suppressed, and the scorch resistance of the rubber composition can be further improved. When the content of the vulcanization retarder is 3.5 parts by mass or less, per 100 parts by mass of the rubber component, the vulcanization retarder becomes even less likely to bloom, and the bloom resistance of the rubber composition is further improved. When the content of the vulcanization retarder is 0.01 to 3.5 parts by mass per 100 parts by mass of the rubber component, both scorch resistance and bloom resistance can be highly compatible.

[0146] (Cyclic Polyol Compound Having Hydrocarbyl Group) The rubber composition for treads of this embodiment preferably further contains a cyclic polyol compound having a hydrocarbyl group. The cyclic polyol compound having a hydrocarbyl group contained in the rubber composition can significantly improve the abrasion resistance and cut resistance of the rubber composition. In addition, by enhancing the interaction between the rubber molecules of the rubber component and fillers such as silica and carbon black, which will be described later, the physical properties of the rubber after crosslinking can be homogenized, resulting in improved reinforcement. Furthermore, since the cyclic polyol compound having a hydrocarbyl group has fewer hydrophilic moieties than compounds such as sorbitol, self-aggregation in the rubber composition can be suppressed, and as a result, the elongation fatigue properties of the vulcanized rubber composition can be maintained well.

[0147] Here, the content of the hydrocarbyl group-containing cyclic polyol compound is preferably 0.1 to 5 parts by mass per 100 parts by mass of the rubber component. When the content of the hydrocarbyl group-containing cyclic polyol compound is 0.1 part by mass or more per 100 parts by mass of the rubber component, a sufficient improvement in abrasion resistance is obtained. On the other hand, when the content of the hydrocarbyl group-containing cyclic polyol compound is 5 parts by mass or less per 100 parts by mass of the rubber component, self-aggregation in the rubber composition is reliably suppressed, and elongation fatigue properties can be further improved. From the same viewpoint, the content of the hydrocarbyl group-containing cyclic polyol compound is more preferably 0.1 to 3 parts by mass, and even more preferably 0.3 to 2.5 parts by mass per 100 parts by mass of the rubber component.

[0148] The hydrocarbyl group-containing cyclic polyol compound is preferably dispersed in the rubber component from the viewpoint of improving abrasion resistance and cut resistance. The hydrocarbyl group-containing cyclic polyol compound does not act as a surfactant for other compounding ingredients, but rather disperses in the rubber to improve abrasion resistance and cut resistance, and is therefore distinguished from surfactants.

[0149] Here, the cyclic polyol compound having a hydrocarbyl group preferably has two or more hydroxyl groups, and more preferably has three or more hydroxyl groups. This is because having many hydroxyl groups allows for stronger interaction between the rubber component and the additives, resulting in better abrasion resistance and cut resistance. On the other hand, from the viewpoint of suppressing self-aggregation in the rubber due to an increased number of hydrophilic sites, it is preferable for the compound to have five or less hydroxyl groups, and more preferably four or less hydroxyl groups.

[0150] Furthermore, the cyclic polyol compound having a hydrocarbyl group is preferably a cyclic polyol compound having a hydrocarbyl ester group, since this allows for achieving better abrasion resistance and cut resistance.

[0151] Furthermore, in order to realize better abrasion resistance and cut resistance, the cyclic polyol compound having a hydrocarbyl group is preferably a cyclic polyol compound represented by the following general formula (5-1): It is more preferable that the compound is represented by the following formula:

[0152] In the above general formula (5-1), A is a hydrocarbyl ester group having 6 to 30 carbon atoms or a hydrocarbyl ether group having 6 to 30 carbon atoms, and the number of carbon atoms in the hydrocarbyl group portion of A is preferably 12 to 24. When the number of carbon atoms in the hydrocarbyl group portion of A in general formula (5-1) is in the range of 12 to 24, good elongation fatigue properties are maintained while the abrasion resistance and cut resistance are further improved. It is preferable that A in general formula (5-1) is an oxygen atom at the first atom from the ring portion (i.e., the atom bonded to the ring) or the second atom from the ring portion. Examples of A in which the first atom from the ring portion is an oxygen atom include groups represented by -O-A' and -O-CO-A". Also, examples of A in which the second atom from the ring portion is an oxygen atom include, for example, -CH ２ -O-A'', -CH ２ Examples include groups represented by -O-CO-A''', where A' is preferably a hydrocarbyl group having 6 to 30 carbon atoms, A'' is preferably a hydrocarbyl group having 5 to 29 carbon atoms, and A''' is preferably a hydrocarbyl group having 4 to 28 carbon atoms, and more preferably A', A'' and A''' are each a hydrocarbyl group having 12 to 24 carbon atoms.

[0153] In addition, in the general formula (5-1), X ５１ , X ５２ , X ５３ and X ５４ are each independently —OH or —R (wherein —R is —H or —CH ２ OH), with the proviso that X ５１ , X ５２ , X ５３ and X ５４ At least two of X are —OH. ５１ , X ５２ , X ５３ and X ５４ Preferably, two or more of ５１ , X ５２ , X５３ and X ５４ When three or more of the above are —OH, the abrasion resistance and cut resistance of the rubber composition are further improved.

[0154] Furthermore, among the compounds represented by the above general formula (5-1), compounds represented by the following general formula (5-2) or general formula (5-3): Compounds represented by the general formula (5-2) are more preferred, and compounds represented by the general formula (5-2) are particularly preferred. In general formulas (5-2) and (5-3), n is a natural number, preferably in the range of 11 to 23. By blending a compound represented by the general formula (5-2) or (5-3) as the modified cyclic polyol compound, it is possible to further improve abrasion resistance.

[0155] The cyclic polyol compound having a hydrocarbyl group is not particularly limited, but can be obtained, for example, by reacting a polyol compound such as sorbitol, sorbitan, glucose, or fructose with an aliphatic alcohol such as octanol, decanol, dodecanol, tetradecanol, or hexadecanol, or an aliphatic carboxylic acid such as lauric acid, myristic acid, palmitic acid, stearic acid, or oleic acid.

[0156] Specific examples of the cyclic polyol compound having a hydrocarbyl group include ester compounds such as sorbitan monolaurate, sorbitan monomyristate, sorbitan monopalmitate, sorbitan monostearate, and sorbitan monooleate, and ether compounds such as octyl-β-D-glucopyranoside, decyl-β-D-glucopyranoside, dodecyl-β-D-glucopyranoside, tetradecyl-β-D-glucopyranoside, and hexadecyl-β-D-glucopyranoside. These compounds may be used alone or in combination of two or more. Among these compounds, sorbitan monostearate (sorbitan monoester) is preferred as the cyclic polyol compound having a hydrocarbyl group, from the viewpoint of achieving both higher levels of elongation fatigue resistance and cut resistance.

[0157] Furthermore, the melting point of the cyclic polyol compound having a hydrocarbyl group is preferably 40 to 100° C., and more preferably 45 to 90° C. When the melting point of the cyclic polyol compound having a hydrocarbyl group is 100° C. or lower, the solubility during kneading and vulcanization reaction can be improved, and when the melting point is 40° C. or higher, durability at high temperatures can be improved.

[0158] (Liquid Softener) The rubber composition of this embodiment may contain a liquid softener. Here, the "liquid softener" is a compounding agent that is liquid at 25°C (room temperature) and has the effect of softening the rubber composition. The liquid softener is not particularly limited, and examples thereof include oil and liquid polymer, among which oil is preferred. These liquid softeners may be used alone or in combination of two or more.

[0159] The oil is a general term for extender oils contained in rubber components and liquid oils added as compounding agents to rubber compositions. Examples include vegetable oils, process oils, oils obtained by recycling vegetable oils or process oils, and mixtures thereof. From the viewpoint of reducing environmental impact, vegetable oils and recycled oils are preferred. Examples of vegetable oils include seed oils, grain oils, potato oils, bean oils, and vegetable oils. More specific examples include palm oil, castor oil, cottonseed oil, soybean oil, linseed oil, rapeseed oil, coconut oil, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, tung oil, and coconut oil. Examples of the process oil include paraffin-based process oils, aromatic process oils, and naphthenic process oils. As the oil, commercially available products can be used, and examples of commercially available oils that can be used include products from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., ENEOS Corporation, Oriso Co., Ltd., H&R Corporation, Toyokuni Oil Mills Co., Ltd., and Nisshin Oillio Group Co., Ltd. These oils may be used alone or in combination of two or more.

[0160] The liquid polymer is preferably a liquid diene-based polymer. Examples of the liquid diene-based polymer include liquid styrene-butadiene copolymer (liquid SBR), liquid polybutadiene (liquid BR), liquid polyisoprene (liquid IR), liquid styrene-isoprene copolymer (liquid SIR), liquid styrene-butadiene-styrene block copolymer (liquid SBS block polymer), liquid styrene-isoprene-styrene block copolymer (liquid SIS block polymer), liquid polyfarnesene, and liquid farnesene-butadiene copolymer. These liquid polymers may be hydrogenated, or their terminals or main chains may be modified with functional groups (polar groups). These liquid polymers may be used alone or in combination of two or more.

[0161] The content of the liquid softener is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which it is applied, the tire components, the target performance, etc. For example, the content of the liquid softener is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, and is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, still more preferably 50 parts by mass or less, and still more preferably 30 parts by mass or less, per 100 parts by mass of the rubber component.

[0162] - Liquid polymer having a weight average molecular weight of 5,000 or more and less than 40,000 - The rubber composition for a tread of this embodiment preferably further contains a liquid polymer having a polystyrene-equivalent weight average molecular weight measured by gel permeation chromatography of 5,000 or more and less than 40,000. By including the liquid polymer in the rubber composition for a tread, flexibility of the rubber composition as a whole can be ensured.

[0163] Furthermore, the rubber composition for a tread of this embodiment preferably contains the above-mentioned cyclic polyol compound having a hydrocarbyl group, and a liquid polymer having a polystyrene-equivalent weight average molecular weight measured by gel permeation chromatography of 5,000 to less than 40,000. The rubber composition for a tread containing the cyclic polyol compound having a hydrocarbyl group and the liquid polymer can achieve high levels of both on-ice performance and abrasion resistance while ensuring flexibility of the rubber composition as a whole.

[0164] The liquid polymer is not particularly limited as long as it has a weight-average molecular weight of 5,000 or more and less than 40,000 in terms of polystyrene as measured by gel permeation chromatography, but is preferably an unmodified conjugated diene polymer having a bound styrene content of less than 10% and a vinyl bond content of 20% or more in the conjugated diene compound moiety. This makes it easier for the liquid polymer to be unevenly distributed in the natural rubber phase of the rubber component, thereby achieving better on-ice performance.

[0165] From the viewpoint of obtaining better on-ice performance from the liquid polymer, the vinyl bond content of the conjugated diene compound portion of the liquid polymer is preferably 30% or more, more preferably 40% or more, and even more preferably 45% or more. Furthermore, from the viewpoint of suppressing an increase in rubber hardness, the vinyl bond content of the conjugated diene compound portion of the liquid polymer is preferably 70% or less, more preferably 65% ​​or less, and even more preferably 55% or less.

[0166] Here, the content of the liquid polymer is preferably 1 to 40 parts by mass per 100 parts by mass of the rubber component. This is because it imparts flexibility to the rubber composition, and can improve the on-ice performance of a tire equipped with a vulcanized rubber and a tread portion obtained from the rubber composition, while suppressing a decrease in abrasion resistance. From the same viewpoint, the content of the liquid polymer is more preferably 3 to 30 parts by mass, even more preferably 5 to 25 parts by mass, and particularly preferably 7 to 20 parts by mass per 100 parts by mass of the rubber component.

[0167] The liquid polymer has a low molecular weight so that it does not form a crosslinked structure with the rubber component even when the rubber composition is vulcanized. Specifically, the weight average molecular weight (hereinafter, sometimes simply referred to as "weight average molecular weight") in terms of polystyrene as measured by gel permeation chromatography is 5,000 or more and less than 40,000. If the weight average molecular weight of the liquid polymer is less than 5,000, the vulcanized rubber obtained from the rubber composition and the tire tread may become excessively flexible, potentially impairing wear resistance. If the weight average molecular weight of the liquid polymer is 40,000 or more, flexibility may be lost, potentially impairing the ice performance of the vulcanized rubber obtained from the rubber composition and the tire equipped with the tread. From the same perspective, the weight average molecular weight of the liquid polymer is preferably 5,500 to 30,000, more preferably 6,000 to 25,000, and even more preferably 6,500 to 20,000.

[0168] The liquid polymer is preferably an unmodified conjugated diene polymer having a bound styrene content of less than 10% in the conjugated diene compound portion. When the bound styrene content of the conjugated diene compound portion is less than 10%, the flexibility of the rubber composition can be sufficiently ensured, and the on-ice performance of the vulcanized rubber obtained from the rubber composition and the tire equipped with the tread portion can be further improved. From the same viewpoint, the bound styrene content of the conjugated diene compound portion of the liquid polymer is more preferably 5% or less, even more preferably 3% or less, and particularly preferably 0%. The reason why the liquid polymer is preferably an unmodified polymer is that it is less likely to interact with the filler described below, which prevents the filler from being included in the natural rubber phase and maintains good on-ice performance.

[0169] Here, the conjugated diene polymer is not particularly limited as long as it has a specific weight-average molecular weight, a bound styrene content in the conjugated diene compound moiety that is kept below a certain value, and a specific vinyl bond content. However, a homopolymer of a conjugated diene compound or a copolymer of an aromatic vinyl compound and a conjugated diene compound is preferred. Examples of conjugated diene compounds as monomers include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, and 1,3-hexadiene. Among these, 1,3-butadiene and isoprene are preferred. On the other hand, examples of aromatic vinyl compounds as monomers include styrene, p-methylstyrene, m-methylstyrene, p-tert-butylstyrene, α-methylstyrene, chloromethylstyrene, and vinyltoluene. The liquid polymer is preferably either polybutadiene or polyisoprene, or both, with polybutadiene being more preferred. These monomers may be used alone or in combination.

[0170] Furthermore, when the liquid polymer is an aromatic vinyl compound-conjugated diene compound copolymer, the amount of the aromatic vinyl compound bonded is preferably less than 5% by mass. By keeping the amount of the aromatic vinyl compound bonded to less than 5% by mass, it is possible to prevent an increase in rubber hardness and deterioration of performance on ice.

[0171] The method for producing the conjugated diene polymer as the liquid polymer is not particularly limited, and for example, the conjugated diene polymer can be obtained by polymerizing a conjugated diene compound as a monomer alone or a mixture of an aromatic vinyl compound and a conjugated diene compound as monomers in a hydrocarbon solvent inert to the polymerization reaction. The polymerization initiator used in the synthesis of the conjugated diene polymer is preferably a lithium compound, and more preferably n-butylthium. When a lithium compound is used as the polymerization initiator, the aromatic vinyl compound and the conjugated diene compound are polymerized by anionic polymerization.

[0172] As described above, the method for producing the conjugated diene polymer using a polymerization initiator is not particularly limited, and for example, the conjugated diene polymer can be produced by polymerizing monomers in a hydrocarbon solvent inert to the polymerization reaction. Examples of hydrocarbon solvents inert to the polymerization reaction include propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, cyclohexane, propene, 1-butene, isobutene, trans-2-butene, cis-2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene, and ethylbenzene. These may be used alone or in combination of two or more.

[0173] The polymerization reaction is preferably carried out in the presence of a randomizer. The randomizer can control the microstructure of the conjugated diene compound portion of the (co)polymer. More specifically, the randomizer has the effect of controlling the amount of vinyl bonds in the conjugated diene compound portion of the (co)polymer and randomizing the conjugated diene compound units and aromatic vinyl compound units in the copolymer. Examples of the randomizer include dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, ditetrahydrofurylpropane, triethylamine, pyridine, N-methylmorpholine, N,N,N',N'-tetramethylethylenediamine, 1,2-dipiperidinoethane, potassium t-amylate, potassium t-butoxide, and sodium t-amylate. The amount of these randomizers used is preferably in the range of 0.1 to 100 molar equivalents per mole of the polymerization initiator.

[0174] The anionic polymerization is preferably carried out by solution polymerization, and the concentration of the above-mentioned monomer in the polymerization reaction solution is preferably in the range of 5 to 50% by mass, more preferably in the range of 10 to 30% by mass. When a conjugated diene compound and an aromatic vinyl compound are used in combination, the content of the aromatic vinyl compound in the monomer mixture can be appropriately selected depending on the amount of aromatic vinyl compound in the target copolymer. The polymerization method is not particularly limited, and may be a batch or continuous method.

[0175] The polymerization temperature for the anionic polymerization is preferably in the range of 0 to 150°C, more preferably in the range of 20 to 130°C. The polymerization can be carried out under the generated pressure, but is usually preferably carried out under a pressure sufficient to maintain the monomers used substantially in a liquid phase. When the polymerization reaction is carried out under a pressure higher than the generated pressure, it is preferable to pressurize the reaction system with an inert gas. It is also preferable to use raw materials such as monomers, polymerization initiators, and solvents used in the polymerization from which reaction inhibitors such as water, oxygen, carbon dioxide, and protic compounds have been removed in advance.

[0176] The weight average molecular weight of the liquid polymer, the amount of bound styrene in the conjugated diene compound portion, and the amount of vinyl bonds in the conjugated diene compound portion can be adjusted by the amount of monomer used in polymerization, the degree of polymerization, etc. The amount of bound styrene in the conjugated diene compound portion and the amount of vinyl bonds in the conjugated diene compound portion of the liquid polymer (sometimes referred to as the microstructure of the liquid polymer) can be determined by an infrared method (Morello method).

[0177] (Syndiotactic 1,2-polybutadiene) The rubber composition for a tread of this embodiment preferably further contains syndiotactic 1,2-polybutadiene, which has a crystallinity of 7 J / g or more and 50 J / g or less and a number average molecular weight of 3.0 × 10 ４ It is more preferable that the rubber component contains a syndiotactic 1,2-polybutadiene having the above structure. By definition, the syndiotactic 1,2-polybutadiene is not included in the rubber component.

[0178] Without intending to be bound by theory, the syndiotactic 1,2-polybutadiene is a crystalline polymer, and its crystals undergo sacrificial fracture under high strain, thereby dissipating input energy. Furthermore, the syndiotactic 1,2-polybutadiene has the property of being compatible with the rubber component, particularly natural rubber and synthetic isoprene rubber, and therefore can be partially immobilized in a rubber component containing natural rubber or synthetic isoprene rubber. Therefore, a rubber composition for a tread containing syndiotactic 1,2-polybutadiene can be preferably vulcanized to form a mesh-like three-dimensional network in the matrix of the rubber component, the network having a portion consisting of syndiotactic 1,2-polybutadiene crystals (crystalline portion) and a portion in which the rubber component and syndiotactic 1,2-polybutadiene are compatible (compatible portion).

[0179] In a rubber composition for treads containing syndiotactic 1,2-polybutadiene, the above-mentioned three-dimensional network provides a high energy dissipation effect due to the crystalline portion and flexibility due to the compatible portion, so that a tire using such a rubber composition can achieve excellent mechanical strength. Furthermore, in the rubber composition of this embodiment, by using in combination with an aminoquinoline-based antioxidant represented by general formula (1) or a quinoline-based antioxidant other than the aminoquinoline-based antioxidant represented by general formula (1), high mechanical strength can be significantly maintained even after thermal degradation.

[0180] Whether or not the above-described three-dimensional network in the reticulated form is formed in the rubber composition can be determined, for example, by confirming from an elastic modulus image obtained by an atomic force microscope (AFM) that the syndiotactic 1,2-polybutadiene forms a co-continuous network structure in the rubber component, which is the matrix polymer, particularly in natural rubber and / or isoprene rubber. Furthermore, the presence or absence of a three-dimensional network can also be inferred from the composition of the rubber composition before vulcanization.

[0181] The rubber composition for treads containing syndiotactic 1,2-polybutadiene preferably contains at least one of natural rubber (NR) and synthetic isoprene rubber (IR) as the rubber component. Natural rubber and synthetic isoprene rubber use isoprene as a monomer and have a cis-1,4-polyisoprene structure as the main component. Furthermore, the rubber composition preferably contains 50% by mass or more of the natural rubber and synthetic isoprene rubber in the rubber component. This ensures that the above-described three-dimensional network is formed reliably in the rubber composition, particularly in the vulcanized rubber composition, and when the rubber composition is applied to a tire, high mechanical strength can be achieved. From the same perspective, the total proportion of the natural rubber and synthetic isoprene rubber in 100% by mass of the rubber component is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass (i.e., the rubber component consists solely of natural rubber and / or synthetic isoprene rubber).

[0182] The crystal amount is 7 J / g or more and 50 J / g or less, and the number average molecular weight is 3.0 × 10 ４ By using the above syndiotactic 1,2-polybutadiene in combination with the rubber component, particularly the above-mentioned natural rubber and / or synthetic isoprene rubber, the above-mentioned three-dimensional network can be reliably formed in the rubber composition, particularly in the vulcanized rubber composition, and when the rubber composition is applied to a tire, high mechanical strength can be achieved.

[0183] As described above, the crystalline amount of the syndiotactic 1,2-polybutadiene is preferably 7 J / g or more and 50 J / g or less. When the crystalline amount of the syndiotactic 1,2-polybutadiene is 7 J / g or more, the above-mentioned three-dimensional network can be sufficiently formed. Furthermore, when the crystalline amount of the syndiotactic 1,2-polybutadiene is 50 J / g or less, the melting point of the syndiotactic 1,2-polybutadiene does not become too high, making it easier to set the vulcanization temperature for forming the three-dimensional network, and also preventing the crystals from acting as fracture nuclei, which tends to reduce the breaking elongation of the rubber. From the same viewpoint, the crystalline amount of the syndiotactic 1,2-polybutadiene is more preferably 15 J / g or more, even more preferably 17 J / g or more, and more preferably 40 J / g or less, even more preferably 36 J / g or less, and particularly preferably 31 J / g or less. The crystalline amount of syndiotactic 1,2-polybutadiene is the heat of fusion and is an index showing the percentage of syndiotactic 1,2-polybutadiene that has crystallized. This crystalline amount can be derived as the area of ​​the melting peak observed between −100° C. and 200° C., as measured with a differential scanning calorimeter.

[0184] The number average molecular weight of the syndiotactic 1,2-polybutadiene is 3.0×10 as described above. ４ It is preferable that the number average molecular weight of the syndiotactic 1,2-polybutadiene is 3.0×10 or more. ４ From the same viewpoint, the number average molecular weight of the syndiotactic 1,2-polybutadiene used in this embodiment is 5.0×10 ４ That's it, 6.5 x 10 ４ That's it, 8.9 x 10 ４ That's it, 10.0 x 10 ４ That's it, 11.0 x 10 ４ That's it, 12.0 x 10 ４ That's it, 13.0 x 10 ４ That's it, 14.0 x 10 ４ That's it, 15.0 x 10 ４ That's it, 16.0 x 10 ４That's it, 17.0 x 10 ４ That's it, 17.9 x 10 ４ That's it, 18.0 x 10 ４ That's it, 19.0 x 10 ４ or more, or 20.0 x 10 ４ On the other hand, the number average molecular weight of the syndiotactic 1,2-polybutadiene can be 50.0 × 10 or more from the viewpoint of preventing a decrease in crack growth resistance and ride comfort when applied to a tire. ４ From the same viewpoint, it is preferable that the ratio is 40.0×10 ４ Below, 39.0 x 10 ４ Below, 38.0 x 10 ４ Below, 37.0 x 10 ４ Below, 36.0 x 10 ４ Below, 35.0 x 10 ４ Below, 34.7 x 10 ４ Below, 34.0 x 10 ４ Below, 33.0 x 10 ４ Below, 32.0 x 10 ４ Below, 31.0 x 10 ４ or less, or 30.0 x 10 ４ The number average molecular weight of syndiotactic 1,2-polybutadiene can be calculated by gel permeation chromatography in terms of polystyrene using monodisperse polystyrene as the standard.

[0185] From the same viewpoint as above, the syndiotactic 1,2-polybutadiene has a crystallinity of 15 J / g or more and 40 J / g or less and a number average molecular weight of 5.0 × 10 ４ It is preferable that this is equal to or greater than this.

[0186] The syndiotactic 1,2-polybutadiene preferably has a 1,2-bond content (the amount of 1,2-bonds in the microstructure of syndiotactic 1,2-polybutadiene) of 80% by mass or more. In this case, the above-mentioned three-dimensional network can be more reliably formed in the rubber composition, particularly in the rubber composition after vulcanization. From the same viewpoint, the 1,2-bond content of the syndiotactic 1,2-polybutadiene can be 85% by mass or more, 90% by mass or more, 91% by mass or more, 92% by mass or more, 93% by mass or more, 94% by mass or more, or 95% by mass or more. The 1,2-bond content of the syndiotactic 1,2-polybutadiene is １ H and １３ It can be determined by C nuclear magnetic resonance (NMR) analysis.

[0187] The syndiotactic 1,2-polybutadiene preferably has a syndiotacticity of 60% or more in the 1,2-bond. In this case, the above-mentioned three-dimensional network can be more reliably formed in the rubber composition after vulcanization. From the same viewpoint, the syndiotacticity of the 1,2-bond of the syndiotactic 1,2-polybutadiene can be 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, 95% or more, or 100%. The syndiotacticity of the 1,2-bond of the syndiotactic 1,2-polybutadiene is １ H and １３ It can be determined by C nuclear magnetic resonance (NMR) analysis.

[0188] The syndiotactic 1,2-polybutadiene preferably has a melting point of 85°C or higher and 180°C or lower. By setting the melting point of the syndiotactic 1,2-polybutadiene to 85°C or higher, it is possible to suppress a decrease in the heat resistance or strength of the rubber composition after vulcanization. Furthermore, by setting the melting point of the syndiotactic 1,2-polybutadiene to 180°C or lower, it is possible to facilitate crystallization of the syndiotactic 1,2-polybutadiene during vulcanization of the rubber composition, thereby more reliably forming the above-mentioned three-dimensional network in the rubber composition after vulcanization. From the same viewpoint, the melting point of the syndiotactic 1,2-polybutadiene is more preferably 90°C or higher, even more preferably 100°C or higher, and more preferably 170°C or lower, and even more preferably 160°C or lower. The melting point of the syndiotactic 1,2-polybutadiene can be derived as the melting peak temperature measured with a differential scanning calorimeter.

[0189] The content of the syndiotactic 1,2-polybutadiene is preferably 5 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the rubber component. When the content of syndiotactic 1,2-polybutadiene is 5 parts by mass or more, the energy dissipation effect is sufficiently enhanced, and better mechanical strength can be obtained. Furthermore, when the content of syndiotactic 1,2-polybutadiene is 40 parts by mass or less, other performance properties such as fuel economy can be well maintained. From the same viewpoint, the content of the syndiotactic 1,2-polybutadiene is more preferably 10 parts by mass or more, even more preferably 20 parts by mass or more, and even more preferably 35 parts by mass or less per 100 parts by mass of the rubber component.

[0190] The method for obtaining the syndiotactic 1,2-polybutadiene is not particularly limited, and it may be produced by synthesis, or a commercially available product may be used. For example, syndiotactic 1,2-polybutadiene can be obtained by polymerizing 1,3-butadiene monomer in an organic solvent containing an aliphatic solvent using an iron-based catalyst composition, a chromium-based catalyst composition, a cobalt-based catalyst composition, or the like. Specifically, syndiotactic 1,2-polybutadiene can be obtained by the polymerization methods described in JP 2006-063183 A, JP 2000-119324 A, JP 2004-528410 A, JP 2005-518467 A, JP 2005-527641 A, JP 2009-108330 A, JP 7-25212 A, JP 6-306207 A, JP 6-199103 A, JP 6-92108 A, JP 6-87975 A, etc. In particular, among the above-mentioned catalyst compositions, it is preferable to use an iron-based catalyst composition, since the crystal amount and number average molecular weight of syndiotactic 1,2-polybutadiene can be more reliably controlled within predetermined ranges.

[0191] Examples of the iron-based catalyst composition include a catalyst composition comprising a mixture of (a) an iron-containing compound, (b) an α-acylphosphonic acid diester, and (c) an organoaluminum compound; a catalyst composition comprising a mixture of (a) an iron-containing compound, (b) an α-acylphosphonic acid diester, (c) an organoaluminum compound, and another organometallic compound or a Lewis base; or a catalyst composition comprising (a) an iron-containing compound, (c) an organoaluminum compound, and (d) a dihydrocarbyl hydrogen phosphite; etc. Examples of the (a) iron-containing compound include iron carboxylate, organic iron phosphate, organic iron phosphonate, organic iron phosphinate, iron carbamate, iron dithiocarbamate, iron xanthate, iron α-diketonate, iron alkoxide or aryloxide, and organic iron compounds.

[0192] Furthermore, from the viewpoint of more reliably controlling the crystal content and number average molecular weight of syndiotactic 1,2-polybutadiene within predetermined ranges, the iron-based catalyst composition more preferably contains iron(III) tris(2-ethylhexanoate), bis(2-ethylhexyl) phosphite, triisobutylaluminum, tri-n-butylaluminum, and tri-n-octylaluminum.

[0193] Examples of the chromium-based catalyst composition include a three-component catalyst system containing (a) a chromium-containing compound, (b) an alkylaluminum hydride compound, and (c) a hydrogen phosphite. As the (a) chromium-containing compound, it is generally advantageous to use a chromium-containing compound that is soluble in a hydrocarbon solvent such as an aromatic hydrocarbon, an aliphatic hydrocarbon, or an alicyclic hydrocarbon. However, it is also possible for an insoluble chromium-containing compound simply dispersed in the polymerization medium to generate catalytically active species. Therefore, there is no need to impose any limitations on the (a) chromium-containing compound in order to ensure solubility. Specific examples of the (a) chromium-containing compound include chromium carboxylates, chromium β-diketonates, chromium alkoxides or aryloxides, chromium halides, pseudo-chromium halides, and organic chromium compounds.

[0194] The cobalt-based catalyst composition may be a catalyst system comprising a soluble cobalt compound (e.g., cobalt octoate, cobalt 1-naphthate, cobalt benzoate, etc.), an organoaluminum compound (e.g., trimethylaluminum, triethylaluminum, tributylaluminum, triphenylaluminum, etc.), and carbon disulfide.

[0195] Commercially available syndiotactic 1,2-polybutadiene products include the JSR RB (registered trademark) series, such as JSR RB (registered trademark) 810, 820, 830, and 840 manufactured by JSR Corporation.

[0196] (Hydrazide Compound) The rubber composition for tread of the present embodiment preferably further contains a hydrazide compound, and the hydrazide compound is represented by the following general formulas (3-1), (3-2), and (3-3): [wherein A is an aromatic group, a substituted or unsubstituted hydantoin ring, or a saturated or unsaturated linear hydrocarbon group having 0 to 8 carbon atoms; B is an aromatic group; the substituent X of B is a hydroxy group or an amino group; Y is a pyridyl group or a hydrazino group; R ３１ , R ３２ , R ３３ and R ３４ are each independently a hydrogen atom, or an alkyl group, a cycloalkyl group, or an aromatic group having 1 to 18 carbon atoms.] A rubber composition for a tread containing a hydrazide compound has excellent low heat buildup properties. Furthermore, a rubber composition for a tread containing a hydrazide compound represented by the above general formula (3-1), (3-2), or (3-3) can improve low heat buildup properties while suppressing an increase in Mooney viscosity.

[0197] The hydrazide compounds represented by the above general formula (3-1), (3-2) or (3-3) have the effect of suppressing viscosity increase while maintaining low heat buildup of the rubber, and their mechanism of action is that the incorporation of the hydrazide compound reduces the reactivity with the rubber polymer and maintains and improves the reactivity with carbon black.

[0198] In the general formula (3-1), A represents an aromatic group (aromatic ring; substituted at the ortho, meta, or para position), a substituted or unsubstituted hydantoin ring, or a saturated or unsaturated linear hydrocarbon group having 0 to 8 carbon atoms. Examples of the saturated or unsaturated linear hydrocarbon group having 0 to 8 carbon atoms include an ethylene group, a tetramethylene group, a heptamethylene group, and an octamethylene group.

[0199] Also, R ３１ , R ３２ , R ３３ and R ３４ are a hydrogen atom, or an alkyl group, a cycloalkyl group, or an aromatic group (aromatic ring; substituted at the ortho, meta, or para position) having 1 to 18 carbon atoms, and may be the same or different (the same applies to the hydrazide compounds represented by the following general formula (3-2) or (3-3)).

[0200] Examples of the hydrazide compound represented by the general formula (3-1) include isophthalic acid dihydrazide and derivatives of adipic acid dihydrazide, such as isophthalic acid di(1-methylethylidene)hydrazide, adipic acid di(1-methylethylidene)hydrazide, isophthalic acid di(1-methylpropylidene)hydrazide, adipic acid di(1-methylpropylidene)hydrazide, isophthalic acid di(1,3-dimethylpropylidene)hydrazide, adipic acid di(1,3-dimethylpropylidene)hydrazide, isophthalic acid di(1-phenylethylidene)hydrazide, and adipic acid di(1-phenylethylidene)hydrazide. However, in addition to these derivatives of isophthalic acid dihydrazide and adipic acid dihydrazide, derivatives of the following dihydrazide compounds can also provide similar effects. Examples include derivatives of terephthalic acid dihydrazide, azelaic acid dihydrazide, succinic acid dihydrazide, etc. Among these, derivatives of isophthalic acid dihydrazide are the most effective, as they provide a high effect of reducing heat buildup and significantly increase the Mooney viscosity, making it possible to reduce the Mooney viscosity while maintaining low heat buildup.

[0201] In the general formula (3-2), B is an aromatic group such as a phenyl group or a naphthyl group, and the substituent X of B is a hydroxy group or an amino group. Examples of the hydrazide compound represented by the general formula (3-2) include derivatives of 2-naphthalene-3-hydroxyhydrazide such as 2-naphthalene-3-hydroxy(1-methylethylidene)hydrazide, 2-naphthalene-3-hydroxy(1-methylpropylidene)hydrazide, 2-naphthalene-3-hydroxy(1,3-dimethylpropylidene)hydrazide, and 2-naphthalene-3-hydroxy(1-phenylethylidene)hydrazide, as well as derivatives of salicylic acid hydrazide, 4-hydroxybenzoic acid hydrazide, anthranilic acid hydrazide, and 1-hydroxy-2-naphthalene acid hydrazide. Among these, derivatives of 2-naphthalene-3-hydroxyhydrazide are particularly effective in that they can keep the Mooney viscosity low while maintaining high low heat buildup.

[0202] The hydrazide compound represented by the above general formula (3-2) is preferably a hydrazide compound represented by the following general formula (3-2-1). (In the formula, R ３１ , R ３２ are each independently an alkyl group having 1 to 18 carbon atoms.

[0203] In the general formula (3-2-1), R ３１ , R ３２ are each independently an alkyl group having 1 to 18 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl. ３１ , R ３２ One of these may be methyl.

[0204] Examples of the hydrazide compound represented by the general formula (3-2-1) include 1-hydroxy-N'-(1-methylethylidene)-2-naphthoic acid hydrazide, 1-hydroxy-N'-(1-methylpropylidene)-2-naphthoic acid hydrazide, 1-hydroxy-N'-(1-methylbutylidene)-2-naphthoic acid hydrazide, 1-hydroxy-N'-(1,3-dimethylbutylidene)-2-naphthoic acid hydrazide, hydrazide, 1-hydroxy-N'-(2-furylmethylene)-2-naphthoic acid hydrazide, 3-hydroxy-N'-(1-methylethylidene)-2-naphthoic acid hydrazide, 3-hydroxy-N'-(1-methylpropylidene)-2-naphthoic acid hydrazide, 3-hydroxy-N'-(1-methylbutylidene)-2-naphthoic acid hydrazide, 3-hydroxy-N'-(1,3-dimethylbutylidene)-2-naphthoic acid hydrazide hydroxy-N'-(1-methylethylidene)-2-naphthoic acid hydrazide, 3-hydroxy-N'-(2-furylmethylene)-2-naphthoic acid hydrazide, and the like can be mentioned, and preferred are 1-hydroxy-N'-(1-methylethylidene)-2-naphthoic acid hydrazide, 1-hydroxy-N'-(1-methylpropylidene)-2-naphthoic acid hydrazide, 1-hydroxy-N'-(1,3-dimethylbutyl ... and 1-hydroxy-N'-(1-methylpropylidene)-2-naphthoic acid hydrazide. Examples include 3-hydroxy-N'-(2-furylmethylene)-2-naphthoic acid hydrazide, 3-hydroxy-N'-(1-methylethylidene)-2-naphthoic acid hydrazide, 3-hydroxy-N'-(1-methylpropylidene)-2-naphthoic acid hydrazide, 3-hydroxy-N'-(1,3-dimethylbutylidene)-2-naphthoic acid hydrazide, and 3-hydroxy-N'-(2-furylmethylene)-2-naphthoic acid hydrazide.

[0205] In the general formula (3-3), Y is a pyridyl group or a hydrazino group. Examples of the hydrazide compound represented by the general formula (3-3) include derivatives of isonicotinic acid hydrazide such as isonicotinic acid (1-methylethylidene) hydrazide, isonicotinic acid (1-methylpropylidene) hydrazide, isonicotinic acid (1,3-dimethylpropylidene) hydrazide, and isonicotinic acid (1-phenylethylidene) hydrazide, as well as derivatives of carbonic acid dihydrazide. Among these, derivatives of isonicotinic acid hydrazide are particularly effective in reducing the Mooney viscosity while maintaining high low heat buildup, and are therefore highly effective in the present invention.

[0206] The synthesis method of the hydrazide compounds represented by the above general formula (3-1), (3-2) or (3-3) is described, for example, in Pant, U.C.; Ramchandran, Reena; Joshi, B.C. Rev. Roum. Chim. (1979) 24(3), 471-82.

[0207] The hydrazide compounds can be used alone or in combination of two or more. The content of the hydrazide compound is preferably in the range of 0.05 to 20 parts by mass, more preferably 0.1 to 2.0 parts by mass, per 100 parts by mass of the rubber component. When the content of the hydrazide compound is 0.05 part by mass or more per 100 parts by mass of the rubber component, the intended effect can be sufficiently obtained. When the content of the hydrazide compound is 10 parts by mass or less, deterioration of other physical properties can be suppressed and costs can be reduced.

[0208] (Foaming Agent) The rubber composition for a tread of the present embodiment preferably further contains a foaming agent. When the rubber composition for a tread contains a foaming agent, the on-ice performance of a tire to which the rubber composition is applied can be improved.

[0209] The foaming agent can be any foaming agent that has been conventionally used as a foaming agent for rubber compositions, and can be any of inorganic and organic foaming agents. Specific examples include azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT), dinitrosopentastyrenetetramine, benzenesulfonyl hydrazide derivatives, p,p'-oxybisbenzenesulfonyl hydrazide (OBSH), ammonium bicarbonate that generates carbon dioxide, sodium bicarbonate, ammonium carbonate, nitrososulfonylazo compounds that generate nitrogen, N,N'-dimethyl-N,N'-dinitrosophthalamide, toluenesulfonyl hydrazide, p-toluenesulfonylsemicarbazide, p,p'-oxybisbenzenesulfonylsemicarbazide, etc. These foaming agents can be used alone or in combination of two or more. Among these, taking into consideration the effect of improving performance on ice, ease of manufacture, etc., azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT), ammonium bicarbonate, sodium bicarbonate, and ammonium carbonate are preferred, with azodicarbonamide (ADCA) and dinitrosopentamethylenetetramine (DPT) being more preferred, and dinitrosopentamethylenetetramine (DPT) being even more preferred. A rubber composition for a tread containing at least one foaming agent selected from azodicarbonamide, dinitrosopentamethylenetetramine, ammonium bicarbonate, sodium bicarbonate, and ammonium carbonate is excellent in the effect of improving performance on ice and in the ease of manufacture.

[0210] The content of the foaming agent is preferably 0.1 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the rubber component, and from the viewpoint of obtaining a better effect of suppressing the deterioration of performance on ice, it is more preferably 0.5 parts by mass or more, even more preferably 1 part by mass or more, and the upper limit is more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less.

[0211] (Foaming Aid) When the rubber composition for a tread of this embodiment contains a foaming agent, it is preferable that the rubber composition further contains a foaming aid. By using a foaming agent and a foaming aid in combination, it is possible to promote the foaming reaction, increase the degree of completion of the reaction, and suppress unnecessary deterioration over time. Examples of the foaming aid include urea, zinc stearate, zinc benzenesulfinate, and zinc oxide. These foaming aids may be used alone or in combination. The mass ratio of the foaming agent to the foaming aid (foaming agent / foaming aid) is preferably 0.3 to 2.0, more preferably 0.6 to 1.8, and even more preferably 1.0 to 1.5.

[0212] (Resin) The rubber composition for a tread of the present embodiment preferably contains a resin. Examples of the resin include a terpene-based resin, a rosin-based resin, a C ５ based resin, C ５ -C ９ based resin, C ９ Examples of suitable resins include cyclopentadiene-based resins, aromatic resins, coumarone resins, indene resins, coumarone-indene-based resins, olefin-based resins, polyurethane resins, and acrylic resins. These resins may be used alone or in combination of two or more. Among these resins, terpene-based resins, rosin-based resins, and C ５ based resin, C ５ -C ９ based resin, C ９ Preferred are cyclopentadiene-based resins, cyclopentadiene-based resins, and aromatic resins, with terpene-based resins and rosin-based resins being particularly preferred. Terpene-based resins and rosin-based resins are naturally derived, sustainable resins that can further reduce the environmental impact and can further improve tire performance, such as grip performance on various road surface conditions, including dry roads, wet roads, snow-covered roads, and frozen roads. ５ based resin, C ９ based resin, C ５ -C ９ The cyclopentadiene-based resin and the cyclopentadiene-based resin can improve abrasion resistance and fuel economy in a balanced manner, while the aromatic resin can improve grip performance, abrasion resistance, and rubber strength in a balanced manner.

[0213] The resin may be hydrogenated, i.e., may be a hydrogenated resin (hydrogenated resin). Furthermore, the resin may be modified to introduce a functional group that interacts with fillers such as carbon black and silica. Examples of such functional groups include amino groups, amide groups, isocyanate groups, imino groups, imidazole groups, urea groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, ether groups, carbonyl groups, oxycarbonyl groups, silyl groups, alkoxysilyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, and thiocarbonyl groups.

[0214] The terpene-based resin is a solid resin obtained by blending turpentine, which is obtained simultaneously when rosin is extracted from pine trees, or a polymerization component separated therefrom, and polymerizing the blend using a Friedel-Crafts catalyst. Examples of such resins include β-pinene resin and α-pinene resin. Terpene-based resins also include terpene-aromatic compound-based resins, which are copolymers of terpenes and aromatic compounds. Examples of terpenes include α-pinene, β-pinene, dipentene, and limonene. Examples of aromatic compounds include styrene, α-methylstyrene, vinyltoluene, and indene. The content of the aromatic compound in the terpene-aromatic compound-based resin is preferably 10 to 50% by mass, more preferably 12 to 45% by mass. Representative examples of the terpene-aromatic compound-based resin include terpene-phenol resin and styrene-terpene resin. The terpene-phenol resin can be obtained by reacting terpenes with various phenols using a Friedel-Crafts catalyst, or by further condensing them with formalin. The styrene-terpene resin can be obtained by reacting styrene with terpenes using a Friedel-Crafts catalyst. The terpenes used as raw materials are not particularly limited, and monoterpene hydrocarbons such as α-pinene and limonene are preferred, with those containing α-pinene being more preferred, and α-pinene being particularly preferred.

[0215] Examples of the rosin-based resin include natural resin rosins such as gum rosin, tall oil rosin, and wood rosin contained in raw pine resin and tall oil, and examples of modified rosins, rosin derivatives, and modified rosin derivatives include polymerized rosin and partially hydrogenated rosin thereof; glycerin ester rosin and partially hydrogenated rosin thereof and fully hydrogenated rosin thereof; pentaerythritol ester rosin and partially hydrogenated rosin thereof and polymerized rosin; and the like.

[0216] The rosin resin may be modified with maleic acid. The maleic acid-modified rosin resin is not particularly limited as long as it is one typically used in rubber compositions for tires. Preferably, the maleic acid-modified rosin resin contains a maleic acid-modified rosin resin having an acid value of 50 KOH mg / g or less. Alternatively, the maleic acid-modified rosin resin may be a mixture of a maleic acid-modified rosin resin having an acid value of 50 KOH mg / g or less and a maleic acid-modified rosin resin having an acid value of more than 50 KOH mg / g. By including a maleic acid-modified rosin resin having an acid value of 50 KOH mg / g or less, both fracture resistance and low heat buildup can be achieved, with fracture resistance being particularly excellent. The acid value of the maleic acid-modified rosin resin can be adjusted by the degree of modification with maleic acid. In this specification, the acid value of the maleic acid-modified rosin resin is the amount of potassium hydroxide required to neutralize the acid contained in 1 g of resin, expressed in milligrams, and can be measured by potentiometric titration (JIS K 0070:1992).

[0217] The softening point of the maleic acid-modified rosin resin is preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher. If the softening point is lower than 80°C, the resin may melt and aggregate under the influence of air temperature, which may adversely affect handleability. The softening point of the maleic acid-modified rosin resin is preferably 160°C or lower, more preferably 150°C or lower. If the softening point exceeds 160°C, the resin component may not dissolve sufficiently in the rubber component and may form fracture nuclei, which is not preferable. The softening point of the maleic acid resin can be measured using a ring and ball softening point analyzer as defined in JIS K 6220-1:2001.

[0218] The maleic acid-modified rosin resin preferably has a glass transition temperature of 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher. If the glass transition temperature is lower than 40°C, the dynamic modulus of elasticity and tensile elongation at break decrease, resulting in poor fracture resistance. Furthermore, the glass transition temperature is preferably 180°C or lower, more preferably 150°C or lower, and even more preferably 120°C or lower. If the glass transition temperature exceeds 180°C, heat generation deteriorates. The glass transition temperature can be determined by measuring a thermogram by differential scanning calorimetry (DSC) at a heating rate of 20°C / min, and determining it as the midpoint of the transition region.

[0219] The weight-average molecular weight of the maleic acid-modified rosin resin is preferably 500 to 5,000, more preferably 1,000 to 4,000. By controlling the weight-average molecular weight within this range, the target performance can be obtained. The weight-average molecular weight can be determined by gel permeation chromatography (GPC) using standard polystyrene standards.

[0220] Examples of the maleic acid-modified rosin resin include Malquid Nos. 1, 2, 5, 6, 8, 31, 32, 33, 34, 382, ​​and 3002 manufactured by Arakawa Chemical Industries, Ltd., and Harimac R-80, T-80, R-100, M-453, M-130A, 135GN, 145P, and R-120AH manufactured by Harima Chemicals, Inc. Of these, Malquid No. 1 (acid value: 25 KOH mg / g) and No. 8 (acid value: 37 KOH mg / g), manufactured by Arakawa Chemical Industries, Ltd., are preferred.

[0221] Said C ５ As a resin based on C, there is C obtained by thermal decomposition of naphtha in the petrochemical industry. ５ and aliphatic petroleum resins obtained by (co)polymerizing the distillate. ５ The fraction usually contains olefinic hydrocarbons such as 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene, and diolefinic hydrocarbons such as 2-methyl-1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene, and 3-methyl-1,2-butadiene.

[0222] Said C ５ -C９ The C-based resin is ５ -C ９ It refers to synthetic petroleum resin, ５ -C ９ Examples of the resin include petroleum-derived C ５ -C １１ The fraction was treated with AlCl ３ , B.F. ３ More specifically, copolymers containing styrene, vinyltoluene, α-methylstyrene, indene, etc. as the main component may be mentioned. ５ -C ９ As the resin, ９ Resins containing less of the above components are preferred from the viewpoint of compatibility with the rubber component. ９ "Low amount of the above components" means that the C ９ This means that the content of the above components is less than 50% by mass, preferably 40% by mass or less.

[0223] Said C ９ The C-based resin is ９ This refers to synthetic petroleum resins, such as AlCl ３ or BF ３ Using a Friedel-Crafts type catalyst such as C ９ It refers to a solid polymer obtained by polymerizing the fraction. ９ Examples of the resin include copolymers containing indene, α-methylstyrene, vinyltoluene, etc. as main components.

[0224] The cyclopentadiene-based resin refers to a resin containing a unit derived from a cyclopentadiene-based monomer as a monomer unit. Examples of the cyclopentadiene-based resin include a homopolymer of a cyclopentadiene-based monomer, a copolymer of two or more cyclopentadiene-based monomers, and a copolymer of a cyclopentadiene-based monomer and another monomer. Here, examples of the cyclopentadiene-based monomer include cyclopentadiene, dicyclopentadiene, and tricyclopentadiene. Among these, dicyclopentadiene is preferred. That is, the cyclopentadiene-based resin is preferably a dicyclopentadiene-based resin. The dicyclopentadiene-based resin is, for example, a copolymer of AlCl３ or BF ３ The term "dicyclopentadiene-based resin" refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts catalyst such as Benzene, etc. Dicyclopentadiene-based resins include homopolymers of dicyclopentadiene, copolymers of dicyclopentadiene and aromatic monomers, copolymers of dicyclopentadiene and C ９ Examples include copolymers with distillates (vinyl toluene, indene, etc.).

[0225] The aromatic resin refers to a resin containing units derived from aromatic monomers as monomer units. Examples of the aromatic resin include homopolymers of aromatic monomers, copolymers of two or more aromatic monomers, and copolymers of aromatic monomers with other monomers. Examples of the aromatic monomer include styrene-based monomers such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and p-phenylstyrene; phenol-based monomers such as phenol, alkylphenol, and alkoxyphenol; and naphthol-based monomers such as naphthol, alkylnaphthol, and alkoxynaphthol.

[0226] The rubber composition for a tread of this embodiment may contain, as the resin, a temperature-responsive resin whose hydrophilicity changes with temperature. The temperature-responsive resin is a compound in which A and B are bonded, A contains a group whose hydrophilicity changes with temperature, B is a terpene-based resin, a rosin-based resin, a styrene-based resin, or C ５ based resin, C ９ based resin, C ５ -C ９ The thermoresponsive resin preferably contains a coumarone-based resin, an indene-based resin, and / or an olefin-based resin. Examples of the thermoresponsive resin whose hydrophilicity changes with temperature include resins described in JP 2022-077145 A.

[0227] Furthermore, the rubber composition for treads of this embodiment may contain a mixed resin consisting of a mixture of hydrogenated styrene resin and the above-mentioned terpene-aromatic compound resin (also referred to as "aromatic-modified terpene resin"). The hydrogenated styrene resin and the terpene-aromatic compound resin may be mixed in advance, or may be added separately to a kneader or the like used to produce the rubber composition and mixed, or may be added together with other raw materials and mixed. The hydrogenated styrene resin and the terpene-aromatic compound resin each improve wet grip properties and low rolling resistance, but when blended alone, they do not have the effect of improving cut and chip resistance. However, by using a hydrogenated styrene resin and a terpene-aromatic compound resin in combination, not only can wet grip properties and low rolling resistance be improved, but also cut and chip resistance can be improved. In 100% by mass of the mixed resin, the hydrogenated styrene resin preferably accounts for 1 to 99% by mass and the terpene-aromatic compound resin for 99 to 1% by mass, more preferably 5 to 95% by mass and 95 to 5% by mass of the terpene-aromatic compound resin, and even more preferably 10 to 90% by mass of the hydrogenated styrene resin and 90 to 10% by mass of the terpene-aromatic compound resin.

[0228] The hydrogenated styrene resin is a resin obtained by hydrogenating (hereinafter sometimes referred to simply as "hydrogenation") a styrene resin made from a styrene monomer. By hydrogenating the styrene resin, the number of aromatic rings derived from styrene is reduced, improving dispersibility in the diene rubber and promoting crosslinking of the diene rubber, thereby uniforming the crosslinking positions between rubber polymers and increasing the modulus of the rubber composition after vulcanization. Furthermore, the uniform and tight crosslinking of the rubber also improves durability.

[0229] The styrene resin that serves as the base of the hydrogenated styrene resin can be obtained by addition polymerization of styrene. The addition polymerization reaction can be carried out according to a known method, such as a solution polymerization method using a living anionic polymerization catalyst, a method using a cationic polymerization catalyst, or a method using a radical polymerization initiator.

[0230] The hydrogenated styrene resin is obtained by hydrogenating the aromatic rings in a styrene resin. The hydrogenation method is conventionally known and is not particularly limited. The hydrogenation rate of the aromatic rings is not particularly limited, but is 0.1 to 100%, preferably 1 to 95%, more preferably 40 to 90%, and even more preferably 50 to 80%. If the hydrogenation rate of the aromatic rings is less than 0.1%, the properties resulting from the hydrogenation are not fully exhibited. Here, the hydrogenation rate of the aromatic rings (hydrogenation rate) is a value calculated from the peak height of the absorbance derived from styrene measured by IR (infrared spectrophotometer) using the following formula: Hydrogenation rate (%) = {(C - D) / C} x 100, where C is the peak height of the absorbance derived from the aromatic rings before hydrogenation, and D is the peak height of the absorbance derived from the aromatic rings after hydrogenation. The hydrogenated styrene resins may be used alone or in combination of two or more.

[0231] The molecular weight of the hydrogenated styrene resin is, as measured by gel permeation chromatography (GPC), a weight average molecular weight (Mw) converted to polystyrene of 500 to 10,000, preferably 1,000 to 7,000, and more preferably 1,500 to 5,000. If the weight average molecular weight is less than 500, the durability of the rubber composition may be poor, and if the weight average molecular weight exceeds 10,000, the effect of improving the grip of the rubber composition may be poor.

[0232] The softening point of the resin is preferably 30 ° C. or higher, more preferably 60 ° C. or higher, more preferably 80 ° C. or higher, more preferably higher than 110 ° C., more preferably 116 ° C. or higher, more preferably 120 ° C. or higher, more preferably 123 ° C. or higher, and even more preferably 127 ° C. or higher. From the viewpoint of processability, the softening point of the resin is preferably 160 ° C. or lower, more preferably 150 ° C. or lower, more preferably 145 ° C. or lower, more preferably 141 ° C. or lower, and even more preferably 136 ° C. or lower. In this specification, the softening point of the resin is the temperature at which the ball drops when the softening point as defined in JIS K 6220-1:2015 (ISO 28641:2010) is measured using a ring and ball softening point tester.

[0233] Commercially available resins can be used, and examples of commercially available resins include products from ENEOS Corporation, Arakawa Chemical Industries, Ltd., ExxonMobil Corporation, Kraton Corporation, Yasuhara Chemical Co., Ltd., Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Kraton Polymers, Inc., Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., and Taoka Chemical Co., Ltd.

[0234] The content of the resin is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the rubber composition is applied, the target performance, etc. For example, the content of the resin is preferably in the range of 5 to 100 parts by mass, and more preferably in the range of 10 to 60 parts by mass, per 100 parts by mass of the rubber component.

[0235] (Silica) The rubber composition for treads of this embodiment preferably contains silica. Examples of the silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Among these, wet silica is preferred because it contains a large number of silanol groups. These silicas may be used alone or in combination of two or more. Commercially available silicas can be used, and examples of commercially available silicas include products from Tosoh Silica Corporation, Evonik, Solvay, Solvay Japan, and Tokuyama Corporation.

[0236] From the viewpoint of reducing environmental impact, silica derived from siliceous plants is preferred as the silica. Examples of siliceous plants include mosses, ferns, horsetails, Cucurbitaceae, Urticaceae, and Gramineae plants. Among these plants, grasses are preferred. Examples of grasses include rice, bamboo, and sugarcane, with rice being preferred. Rice is widely cultivated for food and therefore can be procured locally over a wide area. Furthermore, rice husks are generated in large quantities as industrial waste, making it easy to secure a sufficient supply. Therefore, from the viewpoint of availability, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferred as silica. The use of rice husk silica allows for the effective use of rice husks, which are industrial waste, and also allows for the local procurement of raw materials near tire manufacturing plants, thereby reducing the energy and costs involved in transportation and storage, which is environmentally preferable from various viewpoints. The rice husk silica may be rice husk charcoal powder obtained by carbonizing rice husks by heating, or may be precipitated silica produced by a wet process using an alkali silicate aqueous solution, which is prepared by extracting rice husk ash generated when rice husks are burned as fuel in a biomass boiler with an alkali. The method for producing the rice husk charcoal is not particularly limited, and various known methods can be used. For example, rice husk charcoal can be obtained by pyrolyzing the rice husks by steaming them in a kiln. The rice husk charcoal obtained in this manner is pulverized using a known pulverizer (e.g., a ball mill), and then sorted and classified into a predetermined particle size range to obtain rice husk charcoal powder. The rice husk-derived precipitated silica can be produced by the method described in JP 2019-38728 A. From the perspective of reducing environmental impact, it is also preferable to use silica obtained by extracting silicic acid components from silicon wafer scraps, glass bottles, etc., which are used as raw materials for semiconductors, and recycling the extracted silica.

[0237] The silica has a nitrogen adsorption specific surface area (N ２ SA) is 50m ２ / g or more, and ２ / g or more is more preferable, and 150m ２ / g or more, and ２ / g or less, and ２ / g or less is more preferable, and 230m ２ / g or less is more preferable, and 200m ２ / g or less. In this specification, the nitrogen adsorption specific surface area (N ２ SA) is a value measured by the BET method in accordance with ASTM D3037-93.

[0238] The content of the silica can be adjusted appropriately depending on, for example, the tire category to which the rubber composition is applied, the target performance, etc. For example, the content of silica is, relative to 100 parts by mass of the rubber component, preferably 5 parts by mass or more, more preferably 10 parts by mass or more, more preferably 30 parts by mass or more, more preferably 50 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, still more preferably 100 parts by mass or more, particularly preferably 110 parts by mass or more, and preferably 300 parts by mass or less, more preferably 200 parts by mass or less, still more preferably 180 parts by mass or less, and particularly preferably 150 parts by mass or less.

[0239] (Silane Coupling Agent) When the rubber composition for tread of the present embodiment contains silica, the rubber composition preferably contains a silane coupling agent in order to improve the effect of the silica. The rubber composition for tread containing a silane coupling agent is excellent in improving the wet grip performance and fuel economy of the tire. Examples of the silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, Examples of such tetrasulfides include N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, and dimethoxymethylsilylpropyl benzothiazolyl tetrasulfide. As the silane coupling agent, commercially available products can be used, and examples of commercially available silane coupling agents that can be used include products from Evonik, Momentive, Shin-Etsu Silicones Co., Ltd., Dow Corning Toray Co., Ltd., Tokyo Chemical Industry Co., Ltd., and Azumax Co., Ltd. These silane coupling agents may be used alone or in combination of two or more.

[0240] The content of the silane coupling agent can be adjusted appropriately depending on, for example, the tire category to which it is applied, the tire component, the target performance, etc. For example, the content of the silane coupling agent is preferably 1 part by mass or more, more preferably 6 parts by mass or more, and even more preferably 8 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 12 parts by mass or less, and even more preferably 10 parts by mass or less, relative to 100 parts by mass of the silica.

[0241] Bioethanol can also be used as a raw material for the silane coupling agent. Bioethanol is produced primarily using sugars and / or cellulose as biological resources, and does not effectively utilize other biological resources such as proteins, lipids, and amino acids. Furthermore, sugars compete with food, and excessive use of cellulose leads to deforestation. Therefore, depending on the supply status of various biological resources, the supply status of renewable resources, the supply status of fossil resources, and market demands (e.g., demand for biomass resources as food), it is preferable to use multiple types of ethanol derived from biological resources (bioethanol) as the raw material for the silane coupling agent, or to use a combination of ethanol derived from biological resources (bioethanol), ethanol derived from renewable resources, and ethanol derived from fossil resources. This allows for the effective use of a wide range of biological resources and renewable resources, such as sugars, proteins, and lipids, without relying on a single type of biological resource, and also allows for environmental considerations depending on the production conditions.

[0242] (Carbon Black) The rubber composition for treads of this embodiment preferably contains carbon black. As the carbon black, plant-derived carbon black and recycled carbon black are particularly preferred. Examples of plant-derived carbon black include those derived from castor oil and pine oil. Examples of recycled carbon black include carbon black obtained by pyrolysis of used tires and carbon black obtained from waste oil. The grade of the carbon black is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available carbon black products can be used, including those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Nippon Steel Carbon Co., Ltd., and Birla Carbon. These carbon blacks may be used alone or in combination of two or more.

[0243] The nitrogen adsorption specific surface area (N ２ The nitrogen adsorption specific surface area (N SA) of carbon black is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which it is applied, the tire components, the target performance, etc. ２ SA) is 20m ２ / g or more is preferable, and 50m ２ / g or more is more preferable, and 70m ２ / g or more is more preferable, ２ / g or more is more preferable, and ２ / g or less is preferable, and 150m ２ / g or less is more preferable, and 130m ２ / g or less is more preferable. In this specification, the nitrogen adsorption specific surface area (N ２ SA) is determined according to JIS K 6217-2:2017 (ISO 4652:2012).

[0244] The content of the carbon black is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of the carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component.

[0245] The proportion of silica in the total content of silica and carbon black is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which it is applied, the tire components, the target performance, etc. For example, in the case of tread rubber for passenger car tires, the proportion of silica in the total content of silica and carbon black is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. Furthermore, the proportion of silica in the total content of silica and carbon black may be 100% by mass, but is preferably 98% by mass or less.

[0246] (Carbon Black Dispersant) The rubber composition for treads of this embodiment may contain a carbon black dispersant. By containing the carbon black dispersant, a coupling effect between the rubber component and the carbon black can be obtained with high efficiency, and the dispersibility of the carbon black in the rubber composition can be improved. A rubber composition with improved dispersibility of carbon black can achieve excellent low heat buildup and wear resistance.

[0247] —Compound Represented by General Formula (6)— As the carbon black dispersant, a compound represented by the following general formula (6) (hereinafter also referred to as “compound (6)”), a salt of the compound represented by the following general formula (6), a solvate of the compound represented by the following general formula (6), and a solvate of the salt of the compound represented by the following general formula (6) are preferred. [In the formula, R ６１ represents an alkanediyl group having 2 to 12 carbon atoms which may have a substituent, a cycloalkanediyl group having 3 to 12 carbon atoms which may have a substituent, or *-B １ -Ar-B ２ - represents a * group, and * represents a bond. １represents a single bond or an alkanediyl group having 1 to 12 carbon atoms. ２ represents a single bond or an alkanediyl group having 1 to 12 carbon atoms. Ar represents a divalent aromatic hydrocarbon group having 6 to 12 carbon atoms which may have a substituent. R ６２ and R ６３ R each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, a hydroxy group, or an alkoxy group having 1 to 6 carbon atoms, or they combine with each other to form an alkanediyl group having 2 to 12 carbon atoms. ６４ represents a hydroxy group, an alkoxy group having 1 to 6 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, an arylalkoxy group having 7 to 15 carbon atoms, -NR ６５ R ６６ or -O － (Y ｎ＋ ) １／ｎ represents R ６５ and R ６６ each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. X represents —NH— or —O—.]

[0248] The salt of the compound (6) is R ６４ is a hydroxy group, and a carboxylate salt of compound (6) in which the amine moiety (—NH ２ or —NH—) with an acid. The carboxylate salt of the compound (6) includes, for example, a compound or salt represented by formula (6) in which R ６４ Ga-O － (Y ｎ＋ ) １／ｎ Examples of the acid in the addition salt formed with the acid at the amine moiety in the compound (6) include inorganic acids and organic acids. Examples of the solvate of the compound (6) include methanol solvates and hydrates. Examples of the salt formed with the carbon-carbon double bond in the compound (6) and R ６３ and CO-R ６４ The bond with may be a compound in which the configuration of the carbon-carbon double bond is an E-configuration, a Z-configuration, or a mixture of compounds in which the configuration of the carbon-carbon double bond is an E-configuration, or a Z-configuration, and among these, a compound in which the configuration of the carbon-carbon double bond is a Z-configuration is preferred.

[0249] The compound (6) is preferably a compound represented by the following general formula (6-1). [In the formula, R ６１ , R ６２ , R ６３ , R ６４ and X have the same meanings as above.]

[0250] R ６１ Examples of the alkanediyl group having 2 to 12 carbon atoms in the formula (I) include linear alkanediyl groups such as methylene, ethylene, trimethylene, tetramethylene, pentamethylene, and hexamethylene; and branched alkanediyl groups such as isopropylene, isobutylene, 2-methyltrimethylene, isopentylene, isohexylene, isooctylene, 2-ethylhexylene, and isodecylene. Among these, the number of carbon atoms in the alkanediyl group is preferably 3 to 12, and more preferably 3 to 6. Furthermore, linear alkanediyl groups are preferred.

[0251] Examples of the substituent that the alkanediyl group may have include alkoxy groups having 1 to 4 carbon atoms, such as a methoxy group, an ethoxy group, or a butoxy group; halogen atoms, such as chlorine, bromine, iodine, or fluorine; aryl groups having 6 to 12 carbon atoms, such as a phenyl group, a naphthyl group, or a biphenyl group; and a hydroxy group. Examples of the alkanediyl group having a substituent include a phenylmethylene group (also referred to as a "phenylmethane-1,1-diyl group"), a phenylethylene group (also referred to as a "phenylethane-1,2-diyl group"), a 1-phenylpropane-1,3-diyl group, a 2-hydroxypropane-1,3-diyl group, and a 2-methoxypropane-1,3-diyl group.

[0252] R ６１Examples of the cycloalkanediyl group having 3 to 12 carbon atoms include a cyclopropylene group, a cyclopentylene group, a cyclohexylene group, and a cyclododecylene group. Examples of the substituent that the cycloalkanediyl group having 3 to 12 carbon atoms may have include alkyl groups having 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, n-butyl, and t-butyl; aryl groups having 6 to 10 carbon atoms, such as phenyl, 4-methylphenyl, and naphthyl; alkoxy groups having 1 to 4 carbon atoms, such as methoxy, ethoxy, and n-butoxy; acyl groups having 1 to 7 carbon atoms, such as acetyl, benzoyl, formyl, and pivaloyl; alkoxycarbonyl groups having 3 to 4 carbon atoms, such as methoxycarbonyl and ethoxycarbonyl; aryloxycarbonyl groups having 7 to 11 carbon atoms, such as phenoxycarbonyl and naphthyloxycarbonyl; and acyloxy groups having 2 to 7 carbon atoms, such as acetoxy and benzoyloxy. The cycloalkanediyl group having 3 to 12 carbon atoms is preferably a cyclopentylene group, a cyclohexylene group, a methylcyclohexylene group, or a t-butylcyclohexylene group.

[0253] B １ and B ２ Examples of the alkanediyl group having 1 to 12 carbon atoms in Ar include the alkanediyl groups having 3 to 12 carbon atoms mentioned above, as well as a methylene group. Examples of the divalent aromatic hydrocarbon group having 6 to 12 carbon atoms in Ar include a phenylene group, a naphthylene group, and a biphenylene group. ６１ *-B in １ -Ar-B ２ Examples of the -* group include a phenylene group, a naphthylene group, a biphenylene group, an o-xylylene group, an m-xylylene group, a p-xylylene group, etc. The hydrogen atom contained in Ar may be substituted with one or more groups selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a hydroxy group, a nitro group, a cyano group, a sulfo group, and a halogen atom.

[0254] R ６１ As the alkylene group, an alkylene group having 2 to 12 carbon atoms, a phenylene group or a phenylmethylene group is preferred, and a phenylene group is more preferred.

[0255] R ６２ and R ６３ Examples of halogen atoms in R include fluorine, chlorine, bromine and iodine. ６２ and R ６３ Examples of the alkyl group having 1 to 6 carbon atoms in R include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, and an n-hexyl group. ６２ and R ６３ The aryl group having 6 to 12 carbon atoms in R represents a monocyclic or fused polycyclic aromatic hydrocarbon having 6 to 12 carbon atoms, and examples thereof include a phenyl group, a naphthyl group, and a biphenyl group. ６２ and R ６３ Examples of the alkoxy group having 1 to 6 carbon atoms in R include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, an n-pentoxy group, an isopentoxy group, and an n-hexyloxy group. ６２ and R ６３ Examples of the alkanediyl group having 2 to 12 carbon atoms in which R are bonded to each other include the same groups as those exemplified above for the alkanediyl group having 3 to 12 carbon atoms, and an alkanediyl group having 3 or 4 carbon atoms is preferred. ６２ and R ６３ Examples of the cyclic structure formed by combining these with the carbon atoms to which they are attached include a cyclopentene ring and a cyclohexene ring. ６２ and R ６３ As for R ６２ is a hydrogen atom, and R ６３ is preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R ６２ and R ６３ is more preferably a hydrogen atom.

[0256] R ６４ The alkoxy group having 1 to 6 carbon atoms in the above R ６２ and R ６３The alkyl groups having 1 to 6 carbon atoms in R ６４ The aryloxy group having 6 to 12 carbon atoms in the above R ６２ and R ６３ Examples of the aryl group having 6 to 12 carbon atoms in the formula (I) include an aryl group having 6 to 12 carbon atoms bonded to an oxy group, such as a phenyloxy group, a naphthyloxy group, and a biphenyloxy group. ６４ Examples of the arylalkoxy group having 7 to 15 carbon atoms in R include a phenylethyloxy group, a benzyloxy group, and a phenylpropyloxy group. ６４ -NR in ６５ R ６６ Examples of the amino group include a methylamino group, an ethylamino group, a phenylamino group, an ethylmethylamino group, a dimethylamino group, a diethylamino group, a methylphenylamino group, an ethylphenylamino group, and a diphenylamino group.

[0257] R ６４ Y in ｎ＋ represents an n-valent cation capable of forming a carboxylate salt of the compound represented by general formula (6). ＋ Examples of the cation include cations of metals selected from the group consisting of alkali metals, alkaline earth metals, and transition elements of Groups IB and IIB of the periodic table, and cations of organic bases capable of forming salts with carboxyl groups such as amines. For example, Li ＋ , Na ＋ , K. ＋ , Mg ２＋ , Ca ２＋ , Ba ２＋ , Zn ２＋ , Cu ２＋ , Cu ＋ , Ag ＋ , (NH ４ ) ＋ , [NH(C ２ H ５ ) ３ ] ＋ , [NH(C ２ H ５ ) (i-C ３ H ７ ) ２ ] ＋ , ＋ H ３ N-(CH２ ) ２ -NH ３ ＋ , ＋ H ３ N-(CH ２ ) ６ -NH ３ ＋ etc. ６４ is a hydroxy group or —O － (Y ｎ＋ ) １／ｎ is preferred, and a hydroxy group or —O － (Y ｎ＋ ) １／ｎ (Y is an alkali metal) is more preferred.

[0258] Specific examples of the compound represented by the general formula (6) are shown below.

[0259] The compound represented by the general formula (6) can be produced, for example, by carrying out the reactions shown in the following formulas (a), (b) and (c). [In formula (a), formula (b) and formula (c), R ６１ , R ６２ , R ６３ and R ６４ represents the same meaning as above. P1 represents a protecting group. １ Examples of the protecting group represented by the formula (I) include a tert-butoxycarbonyl group, etc. When a protecting group is used, the protecting group can be removed by a commonly used method.

[0260] The compound represented by the above general formula (6-1) can be produced by subjecting the corresponding acid anhydride such as maleic anhydride to an esterification reaction, an amidation reaction, or a salt-forming reaction.

[0261] Compound Represented by General Formula (7) As the carbon black dispersant, a compound represented by the following general formula (7) (hereinafter also referred to as "compound (7)") is also preferred. (In the formula, M ｎ＋ Is, H ＋ or an n-valent metal ion, where n is an integer of 1 or 2. ７１ and R ７２each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, or R ７１ and R ７２ are bonded to each other to form a ring together with the nitrogen atom to which they are bonded. m represents an integer of 2 to 9.

[0262] R ７１ and R ７２ Examples of the alkyl group having 1 to 6 carbon atoms in R include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a heptyl group, and a hexyl group. ７１ and R ７２ and are bonded to each other to form a ring together with the nitrogen atom to which they are bonded, R ７１ and R ７２ Examples of the group formed by bonding R to each other include a polymethylene group, and examples of the polymethylene group include an ethylene group (dimethylene group), a trimethylene group, a tetramethylene group, a pentamethylene group, and a hexamethylene group. ７１ and R ７２ is preferably a hydrogen atom.

[0263] M ｎ＋ As for H ＋ ions, such as lithium ions, sodium ions, potassium ions, cesium ions, magnesium ions, calcium ions, strontium ions, barium ions, manganese ions, iron ions, copper ions, and zinc ions, and preferably H ＋ or alkali metal ions, more preferably H ＋ Or sodium ions.

[0264] Examples of the compound represented by general formula (7) include S-(aminoalkyl)thiosulfuric acid, S-(aminoalkyl)thiosulfate salts, S-(N,N-dialkylaminoalkyl)thiosulfuric acid, S-(N,N-dialkylaminoalkyl)thiosulfate salts, S-(N-monoalkylaminoalkyl)thiosulfuric acid, and S-(N-monoalkylaminoalkyl)thiosulfate salts, and preferably S-(aminoalkyl)thiosulfuric acid or S-(aminoalkyl)thiosulfate salts.

[0265] Here, examples of the S-(aminoalkyl)thiosulfuric acid include S-(aminoethyl)thiosulfuric acid, S-(aminopropyl)thiosulfuric acid, S-(aminobutyl)thiosulfuric acid, S-(aminopentyl)thiosulfuric acid, S-(aminohexyl)thiosulfuric acid, S-(aminoheptyl)thiosulfuric acid, S-(aminooctyl)thiosulfuric acid, S-(aminononyl)thiosulfuric acid, etc. Examples of the S-(aminoalkyl)thiosulfuric acid salts include sodium S-(aminoethyl)thiosulfate, sodium S-(aminopropyl)thiosulfate, sodium S-(aminobutyl)thiosulfate, sodium S-(aminopentyl)thiosulfate, sodium S-(aminohexyl)thiosulfate, sodium S-(aminoheptyl)thiosulfate, sodium S-(aminooctyl)thiosulfate, sodium S-(aminononyl)thiosulfate, etc. Examples of the S-(N,N-dialkylaminoalkyl)thiosulfuric acid include S-(N,N-dimethylaminoethyl)thiosulfuric acid, S-(N,N-dimethylaminopropyl)thiosulfuric acid, S-(N,N-dimethylaminobutyl)thiosulfuric acid, S-(N,N-dimethylaminopentyl)thiosulfuric acid, S-(N,N-dimethylaminohexyl)thiosulfuric acid, S-(N,N-dimethylaminoheptyl)thiosulfuric acid, S-(N,N-dimethylaminooctyl)thiosulfuric acid, and S-(N,N-dimethylaminononyl)thiosulfuric acid. Examples of S-(N,N-dialkylaminoalkyl)thiosulfates include S-(N,N-dimethylaminoethyl)sodium thiosulfate, S-(N,N-dimethylaminopropyl)sodium thiosulfate, S-(N,N-dimethylaminobutyl)sodium thiosulfate, S-(N,N-dimethylaminopentyl)sodium thiosulfate, S-(N,N-dimethylaminohexyl)sodium thiosulfate, S-(N,N-dimethylaminoheptyl)sodium thiosulfate, S-(N,N-dimethylaminooctyl)sodium thiosulfate, and S-(N,N-dimethylaminononyl)sodium thiosulfate.Examples of the S-(N-monoalkylaminoalkyl)thiosulfuric acid include S-(N-methylaminoethyl)thiosulfuric acid, S-(N-methylaminopropyl)thiosulfuric acid, S-(N-methylaminobutyl)thiosulfuric acid, S-(N-methylaminopentyl)thiosulfuric acid, S-(N-methylaminohexyl)thiosulfuric acid, S-(N-methylaminoheptyl)thiosulfuric acid, S-(N-methylaminooctyl)thiosulfuric acid, and S-(N-methylaminononyl)thiosulfuric acid. Examples of the S-(N-monoalkylaminoalkyl)thiosulfates include S-(N-methylaminoethyl)sodium thiosulfate, S-(N-methylaminopropyl)sodium thiosulfate, S-(N-methylaminobutyl)sodium thiosulfate, S-(N-methylaminopentyl)sodium thiosulfate, S-(N-methylaminohexyl)sodium thiosulfate, S-(N-methylaminoheptyl)sodium thiosulfate, S-(N-methylaminooctyl)sodium thiosulfate, and S-(N-methylaminononyl)sodium thiosulfate.

[0266] The compound (7) can be produced, for example, by reacting 3-chloropropylamine hydrochloride with sodium thiosulfate. The metal salt of compound (7) may also be neutralized with a protonic acid such as hydrochloric acid or sulfuric acid to obtain compound (7). The metal salt of compound (7) can be produced by any known method, such as reacting 3-halopropylamine with sodium thiosulfate, or by reacting potassium phthalimide with 1,3-dihalopropane, reacting the resulting compound with sodium thiosulfate, and then hydrolyzing the resulting compound.

[0267] (Rubber Crumb) The rubber composition for treads of this embodiment preferably contains rubber crumb. The rubber crumb may be obtained by pulverizing used rubber products such as used tires and, if desired, removing reinforcing materials such as steel and fibers, dust, glass, sand, stones, etc., or by preparing a new vulcanized rubber composition for producing the rubber crumb and pulverizing the pulverized rubber. For example, rubber crumb can be obtained from vulcanized rubber by the method described in "Rubber Chemistry and Technology." The process of pulverizing vulcanized rubber to obtain rubber crumb may involve mechanical treatment or low-temperature treatment. For example, in mechanical treatment, various crushing devices such as a cracker mill or a granulator can be used to mechanically crush the vulcanized rubber into fine particles. In low-temperature treatment, the finely chopped vulcanized rubber is frozen at a cryogenic temperature and then crushed into fine particles. A magnetic separator or the like can be used to remove steel, and an air separator or the like can be used to remove fibers. The rubber powder may be a commercially available product, such as those from Global Corporation or Nantong Huili Rubber Corporation. From the viewpoint of reducing the environmental impact, it is preferable to use rubber powder obtained by crushing used rubber products such as used tires. The rubber powder may be used alone or in combination of two or more types.

[0268] The composition of the rubber crumb is not particularly limited and depends on the composition of the vulcanized rubber from used rubber products (used tires) or the like that serve as the raw material. In one embodiment, the rubber crumb contains a rubber component, carbon black, silica, etc. The rubber component, carbon black, silica, etc. contained in the rubber crumb may be the same as or different from the rubber component, carbon black, silica, etc. contained in the rubber composition of this embodiment described above.

[0269] The rubber powder preferably has a volume average particle diameter of 1000 μm or less, more preferably 500 μm or less, even more preferably 200 μm or less, and even more preferably 100 μm or less. The smaller the volume average particle diameter of the rubber powder, the better, and there is no particular lower limit. In this specification, the volume average particle diameter is measured with a laser diffraction particle size distribution analyzer, for example, a "CAPA500" manufactured by Horiba, Ltd.

[0270] The rubber powder preferably has a 60-mesh sieve residue of less than 1% by mass, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, with no particular lower limit. The rubber powder preferably has an 80-mesh sieve residue of less than 10% by mass, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, with no particular lower limit. In this specification, the sieve residue is measured in accordance with ASTM D5644-01.

[0271] The rubber crumb has an acetone extractable content of preferably 12% by mass or less, more preferably 11% by mass or less, and even more preferably 10% by mass or less, and preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more. In this specification, the acetone extractable content in the rubber crumb refers to the acetone extractable content (%) determined by the acetone extraction method in accordance with JIS K6350.

[0272] The content of the rubber crumb is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the tire is applied, the tire components, the target performance, etc. For example, the content of the rubber crumb is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, and is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, more preferably 100 parts by mass or less, more preferably 50 parts by mass or less, more preferably 30 parts by mass or less, still more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, per 100 parts by mass of the rubber component.

[0273] The rubber composition for treads of this embodiment may contain a modified rubber material functionalized with a thiuram sulfide compound. The modified rubber material is not particularly limited, and any rubber material modified with a thiuram sulfide compound can be used. Among these, the modified rubber material is preferably a modified diene rubber material functionalized with a thiuram sulfide compound. In this specification, the modified rubber material functionalized with a thiuram sulfide compound is not considered to be a rubber component.

[0274] The thiuram sulfide compounds are not particularly limited and include, for example, alkylthiuram sulfides, arylthiuram sulfides, heterocyclic thiuram sulfides, thiuram disulfides, thiuram polysulfides, tetrabenzylthiuram disulfide, tetraalkylthiuram disulfides, tetramethylthiuram disulfide, tetraethylthiuram disulfide, dipentamethylthiuram monosulfide, etc. These may be used alone or in combination of two or more.

[0275] From the viewpoint of life cycle assessment (LCA), modified reclaimed rubber can be suitably used as the modified rubber material functionalized with a thiuram sulfide compound. In this specification, "modified reclaimed rubber" refers to a rubber material obtained by pulverizing a portion of used rubber products (waste rubber products) such as tires, followed by devulcanization, and then functionalizing the resulting product with a thiuram sulfide compound. The use of modified reclaimed rubber functionalized with a thiuram sulfide compound tends to produce better effects.

[0276] The modified reclaimed rubber is advantageous for improving problems such as reduced reinforcing properties that can occur when using recycled materials, since the crosslinked structure in the rubber is partially cleaved by devulcanization and functionalization, increasing its reactivity. For example, it can be produced by functionalizing reclaimed rubber or vulcanized rubber powder (powdered rubber) that has functional groups that can act on unvulcanized diene rubber with a modifying compound (introducing a modifying compound). The reclaimed rubber is not particularly limited, and examples include ground rubber mechanically pulverized at room temperature or in a frozen state, devulcanized rubber that has been further devulcanized, recycled rubber from used automobile tires, tubes, and other rubber products as specified in JIS K6313, and reclaimed rubber with equivalent properties. The modified reclaimed rubber can be a product of Lehigh or another company.

[0277] (Wax) The rubber composition for a tread of this embodiment may contain a wax. Examples of the wax include natural waxes (naturally derived waxes) such as plant waxes (plant-derived waxes) and animal waxes (animal-derived waxes); petroleum waxes (petroleum-derived waxes) such as paraffin wax and microcrystalline wax; and synthetic waxes such as ethylene polymers and propylene polymers. Commercially available waxes can be used, and examples of commercially available waxes that can be used include products from Seiko Chemical Co., Ltd., Nippon Seiro Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., and the like. These waxes may be used alone or in combination of two or more.

[0278] The plant wax (plant-derived wax) may be hydrolyzed. Examples of plant wax hydrolysates include those obtained by partially or completely hydrolyzing plant waxes such as carnauba wax, candelilla wax, Japan wax, sunflower wax, and rice wax using any method. Among these, rice wax extracted from grasses is particularly suitable because it can efficiently produce primary alcohols having the carbon number distribution and component composition described below. Plant wax hydrolysates typically contain a linear monohydric primary alcohol as an active ingredient, and other components include alkanes, alkenes, alkynes, carboxylic acids, ketones, aldehydes, non-linear and / or unsaturated primary alcohols, secondary alcohols, tertiary alcohols, dihydric or higher polyhydric alcohols, resins, wax esters, etc., but these other components do not necessarily need to be removed. Among these other components, higher fatty acids obtained by hydrolyzing plant wax function as vulcanization aids in rubber compositions, so their removal is less necessary. Of course, any component may be removed using any method. As a specific example, in the case of a hydrolysate of vegetable wax, the fatty acids contained therein may be esterified with a lower alcohol, and then the higher fatty acid esters may be removed and the higher alcohol may be concentrated by utilizing the difference in solubility between the higher alcohol and the ester in a low-polarity solvent.

[0279] The content of the wax is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of the wax is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, per 100 parts by mass of the rubber component.

[0280] (Stearic Acid) The rubber composition for treads of this embodiment may contain stearic acid. Commercially available stearic acids can be used, and examples of commercially available stearic acids include products from NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc. These commercially available stearic acids may be used alone or in combination of two or more.

[0281] The content of stearic acid is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of stearic acid is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, per 100 parts by mass of the rubber component.

[0282] (Zinc Oxide) The rubber composition for treads of this embodiment may contain zinc oxide (zinc white). The zinc oxide is preferably obtained not only from zinc ores but also from recycled zinc or zinc dross (i.e., obtained by recycling). Commercially available zinc oxide can be used, and examples of commercially available zinc oxide include products from Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., Mitsui Mining & Smelting Co., Ltd., and Toho Zinc Co., Ltd. These commercially available zinc oxide products may be used alone or in combination of two or more.

[0283] The content of the zinc oxide is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of the zinc oxide is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, per 100 parts by mass of the rubber component.

[0284] (Sulfur) The rubber composition for treads of this embodiment preferably contains sulfur. The sulfur may be derived from fossil resources, recycled resources, or sulfur obtained by processing biological resource-derived materials. From the perspective of reducing environmental impact, it is particularly preferable to use sulfur obtained from waste derived from biological resources. Examples of methods for obtaining sulfur from waste derived from biological resources include the methods described in International Publication No. 2024 / 048141. The sulfur may also be powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, and the like, which are commonly used as crosslinking agents in the rubber industry. Commercially available sulfur products are available from Tsurumi Chemical Industry Co., Ltd., Hosoi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, and the like. These sulfurs may be used alone or in combination of two or more.

[0285] The sulfur content is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the sulfur content is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.8 parts by mass or more, and is preferably 8 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component.

[0286] (Vulcanization Accelerator) The rubber composition for treads of this embodiment preferably contains a vulcanization accelerator. The vulcanization accelerator may be derived from fossil resources, renewable resources, or biological resources, but is preferably derived from biological resources from the viewpoint of reducing the environmental impact. Vulcanization accelerators derived from biological resources can be obtained, for example, by the method disclosed in JP 2005-139239 A. Examples of the vulcanization accelerator include sulfenamide vulcanization accelerators such as N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide, N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-oxyethylene-2-benzothiazolsulfenamide, and N,N'-diisopropyl-2-benzothiazolsulfenamide; 1,3-diphenylguanidine (DPG), 1,3-dibenzothiazolylsulfenamide, and the like. Examples of suitable vulcanization accelerators include guanidine-based vulcanization accelerators such as o-tolylguanidine and o-tolylbiguanidine; thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole (M) and di-2-benzothiazolyl disulfide (MBTS, DM); and thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrastearylthiuram disulfide, tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N). Commercially available vulcanization accelerators can be used, including those manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Sumitomo Chemical Co., Ltd., and the like. These vulcanization accelerators may be used alone or in combination of two or more.

[0287] The content of the vulcanization accelerator is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the vulcanization accelerator is applied, the tire components, the target performance, etc. For example, the content of the vulcanization accelerator is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, and is preferably 8 parts by mass or less, more preferably 6 parts by mass or less, and even more preferably 5.5 parts by mass or less, per 100 parts by mass of the rubber component.

[0288] (Cellulose Nanofiber) The rubber composition for a tread of this embodiment may contain cellulose nanofiber (CNF). The cellulose nanofiber can be blended into a rubber composition to reinforce the rubber composition. The cellulose nanofiber is preferably a modified cellulose nanofiber, which is a fine fiber made from modified cellulose. The fiber diameter of the cellulose nanofiber is not particularly limited, but is approximately 3 to 500 nm. The average fiber diameter and average fiber length of the cellulose nanofiber can be obtained by averaging the fiber diameters and fiber lengths obtained from the observation of each fiber using a scanning electron microscope (SEM), an atomic force microscope (AFM), or a transmission electron microscope (TEM). The cellulose nanofiber can be obtained by defibrating cellulose. The average fiber length and average fiber diameter of the fine fibers can be adjusted by oxidation treatment or defibration treatment.

[0289] The raw material for the cellulose nanofibers is not particularly limited as long as it contains cellulose, and examples thereof include plants (e.g., wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), bleached kraft pulp (BKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animals (e.g., ascidians), algae, microorganisms (e.g., acetic acid bacteria (Acetobacter)), microbial products, etc. These cellulose raw materials may be used alone or in combination of two or more.

[0290] The content of the cellulose nanofibers is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of the cellulose nanofibers is preferably in the range of 1 to 100 parts by mass, more preferably in the range of 5 to 70 parts by mass, and even more preferably in the range of 10 to 40 parts by mass, per 100 parts by mass of the rubber component.

[0291] (Porous Cellulose Particles) The rubber composition for treads of this embodiment may contain porous cellulose particles. The porous cellulose particles are preferably cellulose particles having a porous structure with a porosity of 75 to 95%, and by compounding them with the rubber composition, performance on ice can be improved. When the porosity of the porous cellulose particles is 75% or more, the effect of improving performance on ice is excellent, and when the porosity is 95% or less, the strength of the particles can be increased. The porosity is more preferably 80 to 90%. The porosity of the porous cellulose particles can be calculated by measuring the volume of a certain mass of sample (i.e., porous cellulose particles) with a measuring cylinder, determining the bulk specific gravity, and using the following formula: Porosity (%) = {1 - [bulk specific gravity of sample (g / mL)] / [true specific gravity of sample (g / mL)]} × 100, where the true specific gravity of cellulose is 1.5.

[0292] The particle size of the porous cellulose particles is not particularly limited, but from the viewpoint of abrasion resistance, an average particle size of 1000 μm or less is preferred. The lower limit of the average particle size is not particularly limited, but it is preferably 5 μm or more. The average particle size is more preferably 100 to 800 μm, and even more preferably 200 to 800 μm. The porous cellulose particles are preferably spherical particles with a major axis / minor axis ratio of 1 to 2. The use of particles with such a spherical structure improves dispersibility in the rubber composition, contributing to improved performance on ice and the maintenance of abrasion resistance. The major axis / minor axis ratio is more preferably 1.0 to 1.5. The average particle size and major axis / minor axis ratio of the porous cellulose particles can be determined as follows. That is, porous cellulose particles are observed under a microscope to obtain an image, and this image is used to measure the long and short diameters of the particles (if the long and short diameters are the same, the length in a certain axis direction and the length in an axis direction perpendicular to it) for 100 particles, and the average particle size is obtained by calculating the average value, and the long diameter / short diameter ratio is obtained by averaging the values ​​obtained by dividing the long diameter by the short diameter.

[0293] The porous cellulose particles are commercially available from Rengo Co., Ltd. under the name "Viscopal" and are also described in JP-A Nos. 2001-323095 and 2004-115284, and can be suitably used.

[0294] The content of the porous cellulose particles is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of the porous cellulose particles is preferably in the range of 0.3 to 20 parts by mass, more preferably in the range of 1 to 15 parts by mass, and even more preferably in the range of 3 to 15 parts by mass, per 100 parts by mass of the rubber component.

[0295] (Solid Particles) The rubber composition for treads of this embodiment may contain solid particles. Blending the solid particles into the rubber composition can improve performance on ice. The solid particles preferably have an average particle diameter of 1 μm or more, preferably 1000 μm or less, and more preferably 300 μm or less. Examples of the solid particles include plant-derived powders obtained from plants, such as rice husks, walnut flour, and walnut shells; animal-derived powders obtained from animals, such as eggshells (eggshell powder) and bone powder; powders derived from natural minerals, such as whitebait; inorganic particles, such as graphite and zinc oxide whiskers; water-soluble metal salt particles, such as magnesium sulfate and metal salts of lignosulfonic acid; and non-metallic fibers, such as glass fibers. Of these, rice husks, walnut shells, eggshells, and whitebait are preferred.

[0296] The content of the solid fine particles is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of the solid fine particles is preferably in the range of 0.3 to 20 parts by mass, more preferably in the range of 1 to 15 parts by mass, and even more preferably in the range of 3 to 15 parts by mass, per 100 parts by mass of the rubber component.

[0297] (Thermal Expandable Microcapsules) The rubber composition for a tread of the present embodiment may contain thermal expandable microcapsules. When the rubber composition for a tread contains thermal expandable microcapsules, the on-ice performance of a tire to which the rubber composition is applied can be improved.

[0298] The shell constituting the thermally expandable microcapsules is preferably made of a thermoplastic resin that is a polymer of polymerizable components containing a monofunctional monomer (A) and a polyfunctional monomer (B), wherein the monofunctional monomer (A) contains a nitrile-based monomer and a carboxyl group-containing monomer, and the polyfunctional monomer (B) has at least two (meth)acryloyl groups and reactive carbon-carbon double bonds other than (meth)acryloyl groups, is represented by the following general formula (8), and has a weight average molecular weight of 500 to 50,000. ８１ -O-R ８２ -O-R ８３ ... (8) (wherein, R ８１ and R ８３ is a (meth)acryloyl group, and R ８２ is a structure containing a polymer chain having the reactive carbon-carbon double bond.) By compounding thermally expandable microcapsules having the specific shell material into a rubber composition for treads, it is possible to improve on-ice performance and abrasion resistance compared to when conventional thermally expandable microcapsules are compounded.

[0299] The shell of the thermally expandable microcapsules is made of a thermoplastic resin, which is a polymer of a polymerizable component containing a monofunctional monomer (A) including a nitrile monomer and a carboxyl group-containing monomer, and a polyfunctional monomer (B). The polymerizable component refers to a monomer having at least one polymerizable group in its molecule, and is a component that becomes the thermoplastic resin that forms the shell of the thermally expandable microcapsules upon polymerization. The polymerizable component includes a monofunctional monomer having one reactive carbon-carbon double bond and a polyfunctional monomer having two or more reactive carbon-carbon double bonds. The polyfunctional monomer can introduce a crosslinked structure into the polymer. The reactive carbon-carbon double bond here refers to a carbon-carbon double bond that exhibits radical reactivity, and does not refer to a carbon-carbon double bond within an aromatic ring, but includes a carbon-carbon double bond contained in a vinyl group, a (meth)acryloyl group, an allyl group, a vinylene group, etc.

[0300] The monofunctional monomer (A) includes a nitrile monomer and a carboxyl group-containing monomer. When the polymerizable component contains such a monofunctional monomer (A), the gas barrier properties of the thermoplastic resin constituting the outer shell are improved, making it difficult for the encapsulated blowing agent to leak when vaporized and allowing for efficient expansion. In addition, the strength of the thermoplastic resin is increased, making it possible to suppress crushing and deformation during preparation of the rubber composition for studless tires.

[0301] The thermally expandable microcapsules have thermal expandability (the property that the entire microcapsule expands upon heating) by incorporating a blowing agent, which is a component that vaporizes upon heating, into an outer shell made of a thermoplastic resin. The blowing agent is not particularly limited, but examples thereof include hydrocarbons having 3 to 13 carbon atoms such as methane, ethane, propane, (iso)butane, (iso)pentane, (iso)hexane, (iso)heptane, (iso)octane, (iso)nonane, (iso)decane, (iso)undecane, (iso)dodecane, and (iso)tridecane; hydrocarbons having more than 13 but 20 or less carbon atoms such as (iso)hexadecane and (iso)eicosane; pseudocumene, petroleum ether, and normal paraffins and isoparaffins having an initial boiling point of 150 to 260°C and / or a distillation range of 70 to 360°C. Examples of the blowing agent include hydrocarbons such as petroleum fractions; halogenated hydrocarbons having 1 to 12 carbon atoms such as methyl chloride, methylene chloride, chloroform, and carbon tetrachloride; fluorine-containing compounds such as hydrofluoroethers; silanes having an alkyl group having 1 to 5 carbon atoms such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, and trimethyl-n-propylsilane; and compounds that generate gas upon thermal decomposition by heating, such as azodicarbonamide, N,N'-dinitrosopentamethylenetetramine, and 4,4'-oxybis(benzenesulfonylhydrazide). The blowing agent may be composed of one type of compound or a mixture of two or more types of compounds. The blowing agent may be linear, branched, or alicyclic, with aliphatic blowing agents being preferred.

[0302] (Particles with a glass transition temperature of -70°C to 0°C) The rubber composition for treads of this embodiment may contain particles with a glass transition temperature of -70°C to 0°C. When the rubber composition for treads contains particles with a glass transition temperature of -70°C to 0°C, the on-ice performance and abrasion resistance are improved. The particles can be prepared, for example, by polymerizing a non-crosslinkable monomer in the presence of a crosslinkable monomer by suspension polymerization, seed polymerization, or dispersion polymerization. Furthermore, the particles are preferably incompatible with diene rubber. Here, "incompatible with diene rubber" does not mean incompatible with all types of rubber components included in diene rubber, but rather means incompatible with the specific diene rubber contained in the rubber composition for tire treads. The particles incompatible with diene rubber form a phase-separated structure with the diene rubber, thereby improving on-ice performance.

[0303] The glass transition temperature of the particles is -70°C to 0°C, preferably -65°C to -10°C, and more preferably -60°C to -15°C. By setting the glass transition temperature of the particles to 0°C or less, the flexibility of the rubber compound can be maintained at low temperatures, and the adhesive strength to ice surfaces can be increased, making it possible to suitably use the particles in the tread portion of tires (especially studless tires). If the glass transition temperature of the particles is less than -70°C, steering stability deteriorates. If the glass transition temperature of the particles is more than 0°C, performance on ice deteriorates. The glass transition temperature is determined by measuring a thermogram by differential scanning calorimetry (DSC) at a heating rate of 20°C / min, and is taken as the temperature at the midpoint of the transition region.

[0304] The resin constituting the particles is preferably made of a polymer of a monomer mixture containing the monomer (A), the monomer (B), and the monomer (C) described below.

[0305] The monomer (A) is a monofunctional (meth)acrylic acid ester monomer. The monofunctional (meth)acrylic acid ester monomer refers to a (meth)acrylic acid ester having one ethylenically unsaturated group per molecule. Examples of the monofunctional (meth)acrylic acid ester monomer include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; (meth)acrylic acid esters of alicyclic alcohols such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; (meth)acrylic acid aryl esters such as phenyl (meth)acrylate; and (meth)acrylic acid alkoxyalkyl esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate. These monofunctional (meth)acrylic acid ester monomers may be used alone or in combination of two or more. Among these, (meth)acrylic acid alkyl esters are preferred, acrylic acid alkyl esters are more preferred, and n-butyl acrylate, isobutyl acrylate, and 2-ethylhexyl acrylate are particularly preferred. Note that (meth)acrylic means acrylic and / or methacrylic.

[0306] The monomer (A), i.e., the monofunctional (meth)acrylic acid ester-based monomer, is used in a proportion of 80% to 99.5% by mass in the monomer mixture. By including the monomer (A) in this manner, the flexibility and crushability of the particles can be ensured, and when used in tires, performance on ice can be effectively demonstrated. If the mass proportion of the monofunctional (meth)acrylic acid ester-based monomer in the monomer mixture is less than 80% by mass, when the particles are added to a rubber composition, it is not possible to eliminate a sticky surface feel while maintaining a soft feel. If the mass proportion of the monofunctional (meth)acrylic acid ester-based monomer in the monomer mixture exceeds 99.5% by mass, the particles aggregate together during drying, resulting in poor handleability. The mass proportion of the monomer (A) in the monomer mixture is preferably 85% to 99% by mass, more preferably 92.5% to 98% by mass.

[0307] The monomer (B) is a diene-based monomer. As the diene-based monomer, in particular, one having at least two (meth)acryloyl groups, a weight average molecular weight of 500 to 50,000, and represented by the following general formula (9) can be suitably used. The compound represented by the following general formula (9) has a reactive carbon-carbon double bond such as a polybutadiene skeleton in the molecule, and is therefore advantageous for enhancing affinity with the diene-based rubber that is the main component of the rubber composition. On the other hand, by having a (meth)acryloyl group, which is a more reactive functional group, the reactive carbon-carbon double bond is not used in the polymerization reaction during particle production, and therefore affinity with the diene-based rubber in the rubber composition can be effectively enhanced. R ９１ -O-R ９２ -O-R ９３ ... (9) (wherein, R ９１ and R ９３ is a (meth)acryloyl group, and R ９２ is a structure containing a polymer chain having a diene as a structural unit.

[0308] In the diene monomer represented by the general formula (9), if there is one or less (meth)acryloyl group, the particle strength decreases. In the diene monomer represented by the general formula (9), it is not possible to improve the affinity with diene rubbers having a weight average molecular weight of less than 500. In the diene monomer represented by the general formula (9), if the weight average molecular weight exceeds 50,000, the reactivity of the diene monomer decreases. Note that the weight average molecular weight refers to the weight average molecular weight in terms of polystyrene analyzed by gel permeation chromatography (GPC). Furthermore, "(meth)acryloyl" refers to acryloyl and / or methacryloyl. In the diene monomer represented by the general formula (9), the weight average molecular weight is more preferably 600 to 35,000, even more preferably 1,000 to 30,000, and particularly preferably 1,500 to 25,000.

[0309] In the diene monomer represented by the general formula (9), ９２ Examples of dienes that are structural units of the polymer chain include conjugated dienes such as butadiene, isoprene, and chloroprene; and non-conjugated dienes such as 1,4-hexadiene and 5-ethylidene-2-norbornene. These dienes may be used alone or in combination of two or more. Among these, conjugated dienes are preferred, and butadiene is particularly preferred. Furthermore, examples of diene-based monomers represented by general formula (9) include polybutadiene di(meth)acrylate and di(meth)acrylates having polyisoprene in the main chain skeleton. These diene-based monomers may be used alone or in combination of two or more. Among these, polybutadiene di(meth)acrylate is preferred. Note that "(meth)acrylate" refers to acrylate and / or methacrylate.

[0310] The monomer (B), i.e., the diene monomer, is used in a proportion of 0.1% to 5% by mass in the monomer mixture. The inclusion of the diene monomer improves the affinity of the particles to the diene rubber, which is the main component of the rubber composition, and the particles are less likely to fall off from the rubber composition, ensuring excellent performance on ice and improving abrasion resistance. If the mass proportion of the diene monomer in the monomer mixture is less than 0.1% by mass, the affinity to the diene rubber cannot be improved. If the mass proportion of the diene monomer in the monomer mixture exceeds 5% by mass, the flexibility of the particles deteriorates. The mass proportion of the diene monomer in the monomer mixture is preferably 0.3% to 3% by mass, more preferably 0.5% to 1.5% by mass.

[0311] The monomer (C) is a polyfunctional vinyl monomer other than the above-mentioned monomer (B). The polyfunctional vinyl monomer means a monomer (crosslinking agent) having at least two ethylenically unsaturated groups in one molecule. Examples of polyfunctional vinyl monomers include aromatic divinyl monomers such as divinylbenzene and divinylnaphthalene, and bifunctional or higher functional (meth)acrylate monomers such as allyl methacrylate, triacrylformal, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, PEG#200 di(meth)acrylate, PEG#400 di(meth)acrylate, PEG#600 di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and 2-butyl-2-ethyl-1,3-propanediol di(meth)acrylate. These polyfunctional vinyl monomers may be used alone or in combination of two or more. Among these, trimethylolpropane trimethacrylate and ethylene glycol dimethacrylate are preferred, with ethylene glycol dimethacrylate being particularly preferred.

[0312] The monomer (C), i.e., the polyfunctional vinyl monomer, is used in a proportion of 0.4% by mass to 15% by mass in the monomer mixture. If the mass proportion of the polyfunctional vinyl monomer in the monomer mixture is less than 0.4% by mass, the particles tend to aggregate when dried due to a low degree of crosslinking, resulting in poor handling. If the mass proportion of the polyfunctional vinyl monomer in the monomer mixture exceeds 15% by mass, the particles become hard, impairing the soft feel when added to a rubber composition. The mass proportion of the polyfunctional vinyl monomer in the monomer mixture is preferably 0.7% by mass to 12% by mass, more preferably 1% by mass to 7.5% by mass.

[0313] The particles preferably have an average particle size of 3 μm to 70 μm, more preferably 5 μm to 60 μm. When the average particle size of the particles is 3 μm or more, the surface of the tread rubber can be deformed to accommodate minute irregularities on the ice surface, improving performance on ice. When the average particle size of the particles exceeds 70 μm, the particles tend to fall off the surface of the tread rubber, which may result in a deterioration in abrasion resistance. Here, the average particle size of the particles is the average value obtained by measuring the particle sizes of at least 100 particles from a microscopic image taken at 1000x to 5000x magnification. When the image of the particles is not circular, the particle size can be determined as the circle-equivalent diameter calculated from its projected area.

[0314] (Temperature-Responsive Crosslinked Product) The rubber composition for a tread of this embodiment may contain a crosslinked product of a copolymer having a repeating unit A1 represented by the following formula (A1) and a repeating unit B1 represented by the following formula (B1), provided that the repeating unit A1 and the repeating unit B1 are different from each other.

[0315] In the above formula (A1), R Ａ１ each independently represents a hydrogen atom or a branched alkyl group having 3 to 10 carbon atoms; R Ａ１ At least one of the above is the alkyl group, and in the above formula (B1), R Ｂ１ each independently represents a hydrogen atom or a linear alkyl group having 1 to 10 carbon atoms or a branched alkyl group having 3 to 10 carbon atoms; R Ｂ１At least one of the repeating units A1 and B1 is the alkyl group. The repeating unit A1 preferably contains a repeating unit derived from N-isopropylacrylamide. The repeating unit B1 preferably contains a repeating unit derived from N-tert-butylacrylamide or N,N-dimethylacrylamide.

[0316] In the crosslinked product, the copolymer is crosslinked to form, for example, a network structure. Therefore, when the crosslinked product comes into contact with water under a temperature condition below the lower critical solution temperature (LCST) with water, the crosslinked product can absorb water and become gel-like. In other words, under these conditions, the crosslinked product in a rubber product does not dissolve in water and flow out of the rubber product with water. When the use environment temperature is changed to a temperature condition above the LCST with water while the crosslinked product is in a gel state as described above, the crosslinked product changes from a gel state (a state in which the degree of hydrophilicity / hydrophobicity is more hydrophilic) to a state in which the degree of hydrophilicity / hydrophobicity is more hydrophobic, and water can be discharged from the crosslinked product. In this way, it is believed that the crosslinked product does not flow out of the rubber product even when the rubber product is wet with water, but remains within the rubber product. Furthermore, because the crosslinked product has an excellent balance of water absorption and drainage, when a rubber composition for a tread containing such a crosslinked product is applied to a tire, the tire's ice performance and wet grip performance can be improved.

[0317] (Others) In addition to the above-mentioned components, the rubber composition for tread of the present embodiment may further contain various additives commonly used in the tire industry, such as fillers such as calcium carbonate, talc, alumina, clay, aluminum hydroxide, and mica; organic peroxides; etc. The content of these additives is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the tire is applied, the target performance, etc., and is preferably, for example, in the range of 0.1 to 200 parts by mass per 100 parts by mass of the rubber component.

[0318] (Method for Producing Rubber Composition) The method for producing the rubber composition for treads of the present embodiment is not particularly limited, but the rubber composition can be produced, for example, by blending the aminoquinoline antioxidant represented by the above general formula (1), a quinoline antioxidant other than the aminoquinoline antioxidant represented by the above general formula (1), and various components appropriately selected as necessary with the rubber component, followed by kneading, heating, extrusion, etc. The obtained rubber composition can be vulcanized to produce a vulcanized rubber.

[0319] The conditions for the kneading are not particularly limited, and various conditions such as the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, the kneading temperature, the kneading time, the type of kneading device, etc. can be appropriately selected depending on the purpose. Examples of the kneading device include a Banbury mixer, an intermix, a kneader, a roll, etc. that are usually used for kneading rubber compositions.

[0320] The conditions for the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, and heat-in device can be appropriately selected depending on the purpose. Examples of the heat-in device include a heat-in roll mill typically used for heat-in of rubber compositions.

[0321] The extrusion conditions are not particularly limited, and various conditions such as extrusion time, extrusion speed, extrusion device, and extrusion temperature can be appropriately selected depending on the purpose. Examples of the extrusion device include an extruder typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

[0322] The vulcanization apparatus, method, conditions, etc. are not particularly limited and can be appropriately selected depending on the purpose. Examples of apparatuses for vulcanization include molding vulcanizers using molds used for vulcanizing rubber compositions. The vulcanization temperature is, for example, about 100 to 190°C.

[0323] <Tread Rubber> The tread rubber of this embodiment is characterized by being made of the above-described rubber composition for a tread. Since the tread rubber of this embodiment is made of the above-described rubber composition for a tread, by applying it to a tire, it is possible to suppress cracks in the tread portion of the tire. The tread rubber of this embodiment may be applied to a new tire or a retread tire. Furthermore, the tread rubber of this embodiment may be applied to a pneumatic tire or a non-pneumatic tire.

[0324] <Tire> The tire of this embodiment is characterized by including the tread rubber described above. Because the tire of this embodiment includes the tread rubber described above, cracks in the tread portion are suppressed.

[0325] Next, an embodiment of a tire of the present invention will be described in detail with reference to the drawings. Fig. 1 is a cross-sectional view of an embodiment of a tire of the present invention. The tire 1 of this embodiment shown in Fig. 1 has a pair of bead portions 2, a pair of sidewall portions 3, and a tread portion 4 continuous with both sidewall portions 3. The tire 1 also has a carcass 5 extending in a toroidal shape between the pair of bead portions 2 to reinforce these portions 2, 3, and 4, and a belt 6 disposed radially outward of a crown portion of the carcass 5.

[0326] The carcass 5 of the tire 1 shown in FIG. 1 is composed of one carcass ply made of a plurality of parallel-arranged cords covered with a coating rubber, and the carcass 5 is composed of a main body portion extending in a toroidal shape between the bead cores 7 respectively embedded in the bead portions 2, and turned-up portions wound up radially outward around each bead core 7 from the inner side toward the outer side in the tire width direction, but the number of plies and the structure of the carcass 5 in the tire of the present invention are not limited to this.

[0327] 1 is composed of two belt layers 6A and 6B, but in the tire of the present invention, the number of belt layers constituting the belt 6 is not limited to this, and the number of belt layers may be three or more. Here, the belt layers 6A and 6B usually consist of rubberized layers of cords (preferably steel cords) extending at an angle with respect to the tire equatorial plane, and the two belt layers 6A and 6B are laminated to constitute the belt 6 such that the cords constituting the belt layers 6A and 6B cross each other with the tire equatorial plane in between.

[0328] The tire 1 of this embodiment has a tread rubber 8 on the outermost surface of the tread portion 4, and the above-described rubber composition for a tread of this embodiment is used for the tread rubber 8. Therefore, the tire 1 of this embodiment is suppressed from cracking in the tread portion.

[0329] The tire of this embodiment may be modified in various ways as long as it includes the tread rubber of this embodiment described above. For example, it is possible to provide a belt reinforcing layer on the radially outer side of the belt 6 of the tire 1 shown in Fig. 1, or to divide the tread rubber 8 into a cap rubber located on the outermost side and a base rubber located on the radially inner side of the cap rubber.

[0330] The tire of this embodiment can be manufactured by a conventional method using the above-mentioned rubber composition as the tread rubber. For example, depending on the type of tire to be applied, the tire of this embodiment may be obtained by molding an unvulcanized rubber composition and then vulcanizing it, or by molding a semi-vulcanized rubber that has been subjected to a pre-vulcanization process or the like and then further vulcanizing it. The tire of this embodiment may be a pneumatic tire or a non-pneumatic tire. As the gas to be filled into the pneumatic tire, normal air or air with an adjusted oxygen partial pressure, as well as inert gases such as nitrogen, argon, and helium, can be used.

[0331] Next, another preferred embodiment of the tire of the present invention will be illustrated below. Figure 2 is a cross-sectional view of another embodiment of the tire of the present invention. The tire 1 shown in Figure 2 has a pair of bead portions 2, a pair of sidewall portions 3, and a tread portion 4 connected to both sidewall portions 3 and having an outer rubber layer 9 and an inner rubber layer 10, in that order from the outer side in the tire radial direction. The tire also includes a carcass 5 extending in a toroidal shape between the pair of bead portions 2 to reinforce these portions 2, 3, and 4, and a metal cord layer 11 disposed radially outward of the crown portion of the carcass 5 and radially inward of the inner rubber layer 10. Here, the outer rubber layer 9 of the tire shown in Figure 2 is generally also referred to as a "cap rubber," the inner rubber layer 10 of the tire shown in Figure 2 is generally also referred to as a "base rubber," and the metal cord layer 11 of the tire shown in Figure 2 is generally also referred to as a "belt."

[0332] The carcass 5 of the tire 1 shown in FIG. 2 is composed of one carcass ply made of a plurality of parallel-arranged cords covered with a coating rubber, and the carcass 5 is composed of a main body portion extending in a toroidal shape between the bead cores 7 respectively embedded in the bead portions 2, and turned-up portions wound up radially outward around each bead core 7 from the inner side toward the outer side in the tire width direction, but the number of plies and the structure of the carcass 5 in the tire of the present invention are not limited to this.

[0333] 2 is composed of two belt layers, the number of belt layers constituting the metal cord layer 11 in the tire of the present invention is not limited to this, and the number of belt layers may be three or more. Here, the belt layer is usually composed of a rubberized layer of metal cords (preferably steel cords) extending at an angle with respect to the tire equatorial plane, and the two belt layers are laminated to constitute the metal cord layer 11 such that the metal cords constituting the belt layers cross each other with the tire equatorial plane in between.

[0334] The tire 1 shown in FIG. 2 comprises, in a tread portion 4, an outer rubber layer 9 that forms the tread surface of the tread portion 4, a metal cord layer 11 disposed radially inward of the outer rubber layer 9, and an inner rubber layer 10 positioned between the outer rubber layer 9 and the metal cord layer 11, and it is preferable that the outer rubber layer 9 contains 0.01 mass % or less of N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (hereinafter also referred to as "antiaging agent 6PPD"), and the inner rubber layer 10 has a storage modulus (E') at 30°C of 2 to 22 MPa and contains 0.45 to 4.8 mass % of an aminoquinoline-based antiaging agent represented by the above general formula (1).

[0335] The outer rubber layer 9 constituting the tread surface of the tread portion 4 of the tire 1 shown in Figure 2 is environmentally friendly if it contains 0.01 mass % or less of the antioxidant 6PPD. In addition, in the tire 1 shown in Figure 2, the inner rubber layer 10 located between the outer rubber layer 9 and the metal cord layer 11 contains 0.45 mass % or more of the aminoquinoline antioxidant represented by the general formula (1). This aminoquinoline antioxidant of general formula (1) migrates to the outer rubber layer 9 over time, thereby ensuring sufficient ozone resistance of the outer rubber layer 9 and suppressing the occurrence of cracks. The aminoquinoline antioxidant of general formula (1) diffuses more slowly than the antioxidant 6PPD, allowing it to be supplied to the outer rubber layer 9 over a long period of time. If the outer rubber layer 9 contains a large amount of an antioxidant other than the antioxidant 6PPD, there is a risk of discoloration of the outer rubber layer 9. However, in the tire 1 shown in Figure 2, the inner rubber layer 10, located radially inward of the outer rubber layer 9, contains the aminoquinoline antioxidant of general formula (1). By transferring the aminoquinoline antioxidant of general formula (1) from the inner rubber layer 10 to the outer rubber layer 9, the ozone resistance of the outer rubber layer 9 is ensured, thereby suppressing the occurrence of cracks in the outer rubber layer 9 without discoloring the outer rubber layer 9. Furthermore, by supplying the aminoquinoline antioxidant of general formula (1) from the inner rubber layer 10 to the outer rubber layer 9 over a long period of time, it is also possible to suppress the occurrence of cracks in the outer rubber layer 9 over a long period of time. Therefore, the tire 1 shown in Figure 2 is suppressed from causing cracks.

[0336] The inner layer rubber 10 preferably has a storage modulus (E') at 30°C of 2 to 22 MPa, and more preferably 4 to 22 MPa. Because the inner layer rubber 10 has a storage modulus (E') at 30°C of 2 MPa or more and is not too soft, the tire 1 shown in FIG. 2 has excellent steering stability, durability, and low heat buildup. Furthermore, the inner layer rubber 10 has a storage modulus (E') at 30°C of 22 MPa or less and is not too hard, which reduces strain between the inner layer rubber 10 and the outer layer rubber 9 that forms the tread surface of the tread portion 4, thereby suppressing the occurrence of cracks due to strain. Furthermore, when the inner layer rubber 10 has a storage modulus (E') at 30°C of 4 MPa or more, the tire's steering stability, durability, and low heat buildup are further improved.

[0337] The inner layer rubber 10 preferably contains an aminoquinoline-based antioxidant represented by the general formula (1). The aminoquinoline-based antioxidant represented by the general formula (1) prevents aging of the rubber (inner layer rubber) and improves ozone resistance. The content of the aminoquinoline-based antioxidant represented by the general formula (1) is preferably 1.0 to 3.5 parts by mass, more preferably 1.5 to 3.0 parts by mass, per 100 parts by mass of the rubber component. This can be expected to improve the groove crack resistance and water-resistant adhesion to the belt layer of a tire using the rubber composition. When the blending amount of the antioxidant is 1.0 part by mass or more, the effect of improving crack resistance and processability is significant, and crack resistance is particularly improved. Furthermore, when the blending amount of the antioxidant is 3.5 parts by mass or less, deterioration of the belt adhesion after aging can be suppressed.

[0338] The content of the aminoquinoline antioxidant represented by general formula (1) above in the inner rubber layer 10 is preferably 0.45 to 4.8% by mass. When the content of the aminoquinoline antioxidant of general formula (1) is 0.45% by mass or more, a sufficient amount of the aminoquinoline antioxidant of general formula (1) migrates from the inner rubber layer 10 to the outer rubber layer 9, which ensures sufficient ozone resistance of the outer rubber layer 9 and sufficiently suppresses the occurrence of cracks in the outer rubber layer 9. Furthermore, when the content of the aminoquinoline antioxidant of general formula (1) is 4.8% by mass or less, a decrease in the storage modulus (E') at 30°C of the inner layer rubber 10 is suppressed, and a decrease in the tire's handling stability, durability, and low heat buildup properties can be suppressed. Furthermore, an excessive amount of the aminoquinoline antioxidant of general formula (1) migrating from the inner layer rubber 10 to the outer layer rubber 9 is prevented, and discoloration of the outer layer rubber 9 can be suppressed. The content of the aminoquinoline antioxidant represented by the general formula (1) in the inner layer rubber 10 is preferably 0.6% by mass or more, more preferably 1.0% by mass or more, more preferably 1.6% by mass or more, and even more preferably 1.9% by mass or more, from the viewpoint of ozone resistance; and from the viewpoint of suppressing discoloration of the outer layer rubber 9, it is preferably 4.1% by mass or less, more preferably 3.8% by mass or less, more preferably 3.2% by mass or less, more preferably 2.9% by mass or less, and even more preferably 2.6% by mass or less.

[0339] The outer layer rubber 9 preferably has an N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antioxidant 6PPD) content of 0.01% by mass or less, and more preferably 0% by mass (i.e., no antioxidant 6PPD is contained). If the content of the antioxidant 6PPD in the outer layer rubber 9 is 0.01% by mass or less, the tire 1 is environmentally friendly, and if the content of the antioxidant 6PPD is 0% by mass, the tire 1 is even more environmentally friendly.

[0340] The outer layer rubber 9 preferably contains the other quinoline-based antioxidant described above. The other quinoline-based antioxidant is an antioxidant having a quinoline moiety or a derivative thereof (such as a dihydroquinoline moiety or a tetrahydroquinoline moiety). When the outer layer rubber 9 contains the other quinoline-based antioxidant described above, the ozone resistance of the outer layer rubber 9 is improved, and cracking can be further suppressed.

[0341] The content of the other quinoline-based antioxidant in the outer layer rubber 9 is preferably 0.1 to 1.0% by mass. When the content of the other quinoline-based antioxidant is 0.1% by mass or more, the effect of improving the ozone resistance of the outer layer rubber 9 is enhanced. When the content of the other quinoline-based antioxidant is 1.0% by mass or less, discoloration of the outer layer rubber 9 can be more reliably suppressed.

[0342] It is also preferable that the outer layer rubber 9 contains an aminoquinoline-based antioxidant represented by the above general formula (1). When the outer layer rubber 9 contains the aminoquinoline-based antioxidant of general formula (1), the aminoquinoline-based antioxidant of general formula (1) prevents aging of the outer layer rubber 9, improving the ozone resistance of the outer layer rubber 9 and further suppressing the occurrence of cracks in the outer layer rubber 9.

[0343] The content of the aminoquinoline antioxidant represented by general formula (1) in the outer layer rubber 9 is preferably 0.4 to 2.0% by mass. When the content of the aminoquinoline antioxidant represented by general formula (1) is 0.4% by mass or more, the effect of improving the ozone resistance of the outer layer rubber 9 is enhanced. Furthermore, when the content of the aminoquinoline antioxidant represented by general formula (1) is 2.0% by mass or less, discoloration of the outer layer rubber 9 can be more reliably suppressed.

[0344] It is preferable that the content A of the aminoquinoline antioxidant in the outer rubber layer 9 is more than 0.8% by mass and less than 2.0% by mass, the content B of the aminoquinoline antioxidant in the inner rubber layer 10 is more than 0.7% by mass and less than 1.5% by mass, and the ratio B / A of the content A to the content B is 0.6 or more and 1.2 or less. This improves the physical properties of the inner rubber layer 10, which is advantageous for improving steering stability and durability (particularly, resistance to groove cracking) while reducing rolling resistance. Here, a ratio B / A of 0.6 or more improves the durability (particularly, groove crack resistance) of the tread portion 4, and a ratio B / A of 1.2 or less can suppress a decrease in the water-resistant adhesion of the belt.

[0345] The inner rubber layer 10 may further contain an antioxidant other than the aminoquinoline antioxidant represented by the general formula (1). For example, the inner rubber layer 10 may or may not contain the other quinoline antioxidants described above or the antioxidant 6PPD. The total content of antioxidants in the inner rubber layer 10 is preferably greater than the total content of antioxidants in the outer rubber layer 9. If the total content of antioxidants in the inner rubber layer 10 is greater than the total content of antioxidants in the outer rubber layer 9, migration of the antioxidants from the inner rubber layer 10 to the outer rubber layer 9 is more likely to proceed over a longer period of time, thereby suppressing cracking in the outer rubber layer 9 for an even longer period of time. Furthermore, the relatively small total content of antioxidants in the outer rubber layer 9 also more reliably suppresses discoloration of the outer rubber layer 9.

[0346] 2 , the total antioxidant content, the content of the antioxidant 6PPD, the content of the aminoquinoline antioxidant represented by general formula (1), and the content of other quinoline antioxidants are measured in a region between two surfaces formed by extending both ends of the metal cord layer 11 in the tire width direction in the tire radial direction, and can also be calculated as values ​​based on the total amount of the composition from the composition of the rubber composition used in the inner rubber layer 10 or the outer rubber layer 9. The total antioxidant content, the content of the antioxidant 6PPD, and the content of the aminoquinoline antioxidant represented by general formula (1) in the inner rubber layer 10 are measured in a region based on both ends of the metal cord layer 11 in the tire width direction and in a region between the outer rubber layer 9 and the metal cord layer 11, and can also be calculated as values ​​based on the composition of the rubber composition applied to that region (rubber composition for the inner layer rubber).

[0347] The inner layer rubber 10 and the outer layer rubber 9 contain a rubber component, which provides rubber elasticity to the inner layer rubber 10 and the outer layer rubber 9. The content of the rubber component in the inner layer rubber 10 and the outer layer rubber 9 is preferably 30 to 80% by mass, and more preferably 35 to 75% by mass. The rubber component is preferably a diene rubber, and more preferably the rubber component is selected from natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), and styrene-butadiene rubber (SBR). When the rubber component contains at least one selected from the group consisting of natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), and styrene-butadiene rubber (SBR), the inner layer rubber 10 and the outer layer rubber 9 have excellent rubber elasticity and improved durability. Furthermore, when the rubber component contains at least one selected from the group consisting of natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), and styrene-butadiene rubber (SBR), the effect of the present invention (cracking suppression effect) is more likely to be pronounced. The content of diene rubbers such as natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), and styrene-butadiene rubber (SBR) in the rubber component is preferably 80% by mass or more, more preferably 90% by mass or more, and may even be 100% by mass. The rubber component may be one type alone or a blend of two or more types.

[0348] In addition to the antioxidants and rubber components described above, the inner rubber layer 10 and the outer rubber layer 9 may contain, as necessary, various components commonly used in the rubber industry, such as fillers (silica, carbon black, calcium carbonate, etc.), silane coupling agents, softeners, waxes, surfactants, organic acids (stearic acid, etc.), zinc oxide (zinc white), vulcanization accelerators, vulcanizing agents (sulfur, etc.), etc., appropriately selected within ranges that do not impair the objects of the present invention. Commercially available products can be suitably used as these compounding ingredients.

[0349] The aminoquinoline antioxidant represented by the general formula (1) may be supported on any carrier. For example, the aminoquinoline antioxidant represented by the general formula (1) may be supported on an inorganic filler such as silica or calcium carbonate. The aminoquinoline antioxidant represented by the general formula (1) may also be a masterbatch with a rubber component. The rubber component used in the masterbatch is not particularly limited, and may be a diene rubber such as natural rubber (NR), or ethylene-propylene-diene rubber (EPDM). The aminoquinoline antioxidant represented by the general formula (1) may also be a salt with an organic acid. The organic acid used in the salt formation is not particularly limited, but examples include stearic acid.

[0350] In this embodiment, a rubber composition in which an antioxidant and the like are blended with a rubber component is used for the inner rubber layer 10 and the outer rubber layer 9. The rubber composition used for the inner rubber layer 10 and the outer rubber layer 9 can be produced, for example, by blending an antioxidant and various components appropriately selected as necessary with the rubber component, and kneading, heating, extruding, etc.

[0351] Next, a further preferred embodiment of the tire of the present invention will be described by way of example. Figures 3 and 4 are cross-sectional views of another embodiment of the tire of the present invention.

[0352] The tire 1 shown in Fig. 3 has the same structure as the tire shown in Fig. 2 , except that the tread portion 4 includes, in order from the outside in the tire radial direction (in order from the tire surface (tread surface)), an outer layer rubber 9, a base rubber 12, a tread undercushion rubber 13, and a metal cord layer (belt) 11. Here, the base rubber 12 and the tread undercushion rubber 13 of the tire 1 shown in Fig. 3 correspond to the inner layer rubber 10.

[0353] The base rubber 12 and the tread undercushion rubber 13 preferably have a storage modulus (E') at 30°C of 2 to 22 MPa, and the storage modulus (E') at 30°C of the base rubber 12 and the tread undercushion rubber 13 may be the same or different. Also, at least one of the base rubber 12 and the tread undercushion rubber 13 preferably contains an aminoquinoline-based antioxidant represented by the above general formula (1), and the content of the aminoquinoline-based antioxidant represented by the above general formula (1) in the entire base rubber 12 and the tread undercushion rubber 13 is preferably in the range of 0.45 to 4.8 mass%.

[0354] The tire 1 shown in Fig. 4 has the same structure as the tire shown in Fig. 2 , except that the tread portion 4 includes, in order from the outside in the tire radial direction (from the tire surface (tread surface)), an outer layer rubber 9, a base rubber 12, a tread undercushion rubber 13, a metal cord layer reinforcing layer (belt reinforcing layer) 14, and a metal cord layer (belt) 11. The metal cord layer reinforcing layer 14 of the tire 1 shown in Fig. 4 is arranged so as to cover the entire metal cord layer 11 on the outside in the tire radial direction of the metal cord layer 11. However, the metal cord layer reinforcing layer may be arranged so as to cover only both ends of the metal cord layer 11 on the outside in the tire radial direction of the metal cord layer 11, or may be a combination of a layer covering the entire metal cord layer 11 and a pair of layers covering only both ends of the metal cord layer 11. Here, the base rubber 12, tread undercushion rubber 13, and metal cord layer reinforcing layer 14 of the tire 1 shown in Fig. 4 correspond to the inner layer rubber 10.

[0355] In this embodiment, the reinforcing layer 14 of the metal cord layer is made of a rubberized layer of reinforcing cords arranged substantially parallel to the tire circumferential direction. The reinforcing layer 14 of the metal cord layer is formed by continuously spirally winding narrow strips (cord-rubber composites) prepared by rubberizing reinforcing cords with a coating rubber in the tire circumferential direction. In this case, the absence of joints in the tire circumferential direction improves tire uniformity, and the absence of joints also prevents strain concentration at joints. Organic fiber cords such as polyethylene terephthalate cords, nylon cords, and rayon cords can be used as the reinforcing cords of the reinforcing layer 14 of the metal cord layer.

[0356] The base rubber 12, the tread undercushion rubber 13, and the reinforcing layer 14 of the metal cord layer (the covering rubber of the reinforcing cord) preferably have a storage modulus (E') at 30°C of 2 to 22 MPa, and the storage modulus (E') at 30°C of the base rubber 12, the tread undercushion rubber 13, and the reinforcing layer 14 of the metal cord layer (the covering rubber of the reinforcing cord) may be the same or different. Note that, when a material other than rubber (for example, a reinforcing cord such as an organic fiber cord) is contained in the portion corresponding to the inner layer rubber 10, as in the tire 1 shown in Figure 4, the storage modulus (E') at 30°C is measured in the rubber portion. Furthermore, at least one of the base rubber 12, the tread undercushion rubber 13, and the reinforcing layer 14 of the metal cord layer (the covering rubber of the reinforcing cord) preferably contains the aminoquinoline antioxidant represented by the above general formula (1), and the content of the aminoquinoline antioxidant represented by the above general formula (1) in the entire base rubber 12, the tread undercushion rubber 13, and the reinforcing layer 14 of the metal cord layer (the covering rubber of the reinforcing cord) is preferably in the range of 0.45 to 4.8 mass%.

[0357] The tire of the present invention is not limited to these embodiments, and for example, a tire in which the tread undercushion rubber 13 is omitted from the tire 1 shown in Fig. 4 is also a suitable embodiment of the tire of the present invention. Further, other embodiments of the tire of the present invention will be exemplified below.

[0358] Another embodiment of the tire of the present invention includes a tread having a pair of circumferentially extending shoulder main grooves, each located axially outward of the equatorial plane, the tread including a base rubber and a cap rubber covering the base rubber, the base rubber including a center portion located on the equatorial plane and a pair of side portions, each located axially outward of the center portion, the side portions being spaced apart from the center portion, the shoulder main grooves being located between the center portion and the side portions in the axial direction, and the distance from the shoulder main grooves to the base rubber being 6 mm or more and 25 mm or less, the cap rubber corresponding to the outer rubber layer and the base rubber corresponding to the inner rubber layer, and a layer of metal cords being disposed radially inward of the base rubber.

[0359] A tire according to another embodiment of the present invention includes a cap rubber and a base rubber, and satisfies the following formulas (i) and (ii): 0.4≦Tc / Tb≦1.5 (i) [In formula (i), Tc is the average thickness of the cap rubber, and Tb is the average thickness of the base rubber.] tan δc / E*c≧0.16 (ii) [In formula (ii), tan δc is the cap rubber's -30°C tan δ (loss tangent measured under conditions of a temperature of -30°C, an initial strain of 10%, a dynamic strain of 2.5%, and a frequency of 10 Hz), and E*c is the cap rubber's 0°C E* (complex modulus measured under conditions of a temperature of 0°C, an initial strain of 10%, a dynamic strain of 2.5%, and a frequency of 10 Hz).] Here, the cap rubber corresponds to the outer layer rubber, and the base rubber corresponds to the inner layer rubber. A metal cord layer is disposed radially inward of the base rubber.

[0360] Another embodiment of the present invention provides a motorcycle tire having a tread rubber in the tread portion. The tread rubber includes a cap rubber forming a tread surface and a base rubber disposed radially inward of the cap rubber. The 300% modulus (M300c) of the cap rubber is greater than the 300% modulus (M300b) of the base rubber. The loss tangent (tan δc) of the cap rubber is smaller than the loss tangent (tan δb) of the base rubber. The tread surface includes a crown region centered on the tire equator and shoulder regions axially outward of the crown region. The thickness of the cap rubber in the crown region is greater than the thickness of the cap rubber in the shoulder regions. Here, the cap rubber corresponds to an outer layer rubber, and the base rubber corresponds to an inner layer rubber. A layer of metal cords is disposed radially inward of the base rubber.

[0361] Another embodiment of the tire of the present invention is a pneumatic tire comprising: a tread portion provided with tread rubber, the tread portion including a cap rubber forming the tire contact surface and a base rubber provided radially inward of the cap rubber; and a sidewall portion provided with sidewall rubber. The radially outer side of the sidewall rubber is overlapped on the outer side of the widthwise end of the tread rubber. The base rubber comprises an under-rubber portion provided radially inward of the cap rubber and a turned-up portion extending radially outward from the tire widthwise end of the under-rubber portion and disposed between the cap rubber and the sidewall rubber. The rubber hardness of the cap rubber is greater than that of the base rubber, and the rubber hardness of the base rubber is greater than that of the sidewall rubber. Here, the cap rubber corresponds to an outer layer rubber, and the base rubber corresponds to an inner layer rubber. A layer of metal cords is disposed radially inward of the base rubber.

[0362] A tire according to another embodiment of the present invention has a tread portion in which a cap rubber and a base rubber are laminated, wherein the adhesive strength between the cap rubber composition constituting the cap rubber and the base rubber composition constituting the base rubber is 9 MPa or more, and the cap rubber composition satisfies the following formula (A): Breaking elongation before ozone degradation≦Breaking elongation after ozone degradation (A), where the cap rubber corresponds to an outer layer rubber and the base rubber corresponds to an inner layer rubber, and a metal cord layer is disposed radially inward of the base rubber.

[0363] A tire according to another embodiment of the present invention is a pneumatic tire comprising: at least one carcass layer; a belt layer disposed radially outward of a portion of the carcass layer located in a tread portion, the belt layer having a plurality of belts laminated thereon; and a tread rubber layer disposed radially outward of the belt layer in the tread portion, wherein main grooves extending in the tire circumferential direction are formed in the tread portion, and a plurality of land portions are defined by the main grooves, and the tread portion defines a center region where a center land portion, which is the land portion closest to the tire equatorial plane among the land portions, is located, and defines shoulder regions as regions between a position at 85% of the width in the tire width direction of a widest belt, which is the belt having the widest width in the tire width direction among the plurality of belts included in the belt layer, and an end portion of the widest belt in the tire width direction, wherein a relationship between an average tire thickness (Gc) in the center region and an average tire thickness (Gsh) in the shoulder regions is within a range of 1.05≦(Gc / Gsh)≦1.35, The tread rubber layer is formed by laminating three layers of cap rubber, intermediate rubber, and base rubber from the outer side to the inner side in the tire radial direction, and the relationship among the cap rubber, the intermediate rubber, and the base rubber, among which the modulus (Ma) of the cap rubber at 300% elongation, the modulus (Mb) of the intermediate rubber at 300% elongation, and the modulus (Mc) of the base rubber at 300% elongation, satisfies Ma<Mb<Mc, where the cap rubber corresponds to the outer layer rubber, the intermediate rubber and the base rubber correspond to the inner layer rubber, and the belt layer corresponds to the metal cord layer.

[0364] A tire according to another embodiment of the present invention comprises a tread having a plurality of circumferential grooves, a belt located radially inside the tread, and a pair of cushion layers supporting ends of the belt from the radially inside, wherein the tread comprises a base rubber located radially outside the belt and a cap rubber located radially outside the base rubber, the complex modulus of the base rubber being 1.5 to 1.9 times that of the cushion layer, and the fracture energy of the cushion layer being 1.3 to 1.6 times that of the base rubber, wherein the cap rubber corresponds to the outer layer rubber, the base rubber corresponds to the inner layer rubber, and the belt corresponds to the metal cord layer.

[0365] A tire according to another embodiment of the present invention is a pneumatic tire comprising: a plurality of cross belts laminated in the tire radial direction, the cross belts having steel cords extending at an inclination angle relative to the tire circumferential direction, the steel cords of adjacent belts in the tire radial direction crossing each other; and one or more protection belts provided on the tire radial outer side of the cross belts, the steel cords of which extend at an angle larger than the inclination angle, the belt width of a widest protection belt having the widest belt width among the protection belts being wider than the belt width of any of the cross belts. In a tire profile when the pneumatic tire is cut along the tire radial direction, the maximum width protective belt has a maximum protruding position in the tire radial direction in a shoulder region in the tire width direction, the maximum protruding position is A, the end position of the maximum width protective belt is B, the position where a straight line a that passes through the maximum protruding position A and extends in a direction normal to the tread surface of the pneumatic tire intersects with the tread surface is position A', and the position where a straight line b that passes through the end position B and extends in a direction normal to the tread surface intersects with the tread surface is position B', the angle formed between a first straight line connecting the maximum protruding position A and the end position B and a second straight line connecting the position A' and the position B' is equal to or greater than 0 degrees and equal to 15 degrees. Here, the tread rubber of the pneumatic tire comprises a base rubber located radially outside the protective belt, and a cap rubber that contacts the base rubber and forms the tread surface, the cap rubber corresponding to the outer layer rubber, the base rubber corresponding to the inner layer rubber, and the cross belt and protective belt corresponding to the layer of metal cords.

[0366] A tire according to another embodiment of the present invention is a pneumatic tire comprising a mounting direction indicator that indicates the mounting direction relative to a vehicle, and a tread portion, wherein the tread portion has a laminated structure of a belt layer consisting of a belt and a belt cover provided on the radially outer side of the belt, a base rubber provided on the radially outer side of the belt cover, and a cap rubber provided on the radially outer side of the base rubber, wherein, based on the tire equatorial plane, the ground contact area ratio on the tread surface of the tread portion on the radially outer side of the mounting relative to the vehicle is greater than the ground contact area ratio on the tread surface on the radially inner side of the mounting relative to the vehicle, the tangent loss of the cap rubber is greater than the tangent loss of the base rubber, and based on the tire equatorial plane, the thickness of the base rubber along a normal from the radially outer end of the belt layer on the radially outer side of the mounting relative to the vehicle to the tread surface is greater than the thickness of the base rubber along a normal from the radially outer end of the belt on the radially inner side of the mounting relative to the vehicle to the tread surface, The rigidity per unit length in the tire width direction of the outer side of the belt cover when mounted on the vehicle is higher than the rigidity per unit length in the tire width direction of the inner side of the belt cover when mounted on the vehicle. Here, the cap rubber corresponds to the outer layer rubber, the base rubber corresponds to the inner layer rubber, and the belt corresponds to the metal cord layer. Note that if the belt cover includes metal cords, the belt cover also corresponds to the metal cord layer.

[0367] Another embodiment of the present invention provides a pneumatic tire comprising a circumferentially extending annular tread portion, a pair of sidewall portions disposed on both sides of the tread portion, and a pair of bead portions disposed radially inward of the sidewall portions. The tread portion has a laminated structure of cap rubber and base rubber. The tread portion has a plurality of longitudinal grooves extending circumferentially and a plurality of lateral grooves extending widthwise. The longitudinal grooves and lateral grooves define a row of blocks arranged circumferentially in the tread portion, each block having a plurality of sipes. The bottom contour of each sipe is inclined relative to the boundary surface between the cap rubber and the base rubber, and the sipes become gradually shallower from the center to the ends of each block. Here, the cap rubber corresponds to an outer rubber layer, and the base rubber corresponds to an inner rubber layer. A layer of metal cords is disposed radially inward of the base rubber.

[0368] Another embodiment of the tire of the present invention is a pneumatic tire comprising: a carcass consisting of at least one carcass ply; a belt arranged radially outward of the carcass and including a belt layer including cords; and tread rubber arranged radially outward of the belt and constituting a part of a tread portion, wherein at least one circumferential main groove is formed in the tread portion, the total width of which is 15% or more of the contact width; wherein the tread rubber comprises a base rubber and a cap rubber formed radially outward of the base rubber and made of a rubber harder than the base rubber; and when the tire is mounted on a specified rim, inflated to 92% of the specified internal pressure, and subjected to a load of 75% of the maximum load capacity, in a meridian cross section of the tire, the tire contact width is divided into four in the tire width direction, with two regions at the center in the tire width direction as center regions and the remaining two regions as shoulder regions, the average thickness of the base rubber is greater in the center region than in the shoulder regions; and the loss tangent tanδ at 60°C is higher in the cap rubber than in the base rubber. In the center region, in a region radially inward of an imaginary line extending parallel to a tire profile line at a position 1.6 mm radially outward from the groove bottom of the circumferential main groove, the ratio (CAI / BAI) of the cross-sectional area of ​​the cap rubber (CAI) to the cross-sectional area of ​​the base rubber (BAI) is 0.15 to 0.95. Here, the cap rubber corresponds to an outer layer rubber, and the base rubber corresponds to an inner layer rubber. Furthermore, a metal cord layer is disposed radially inward of the base rubber.

[0369] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0370] Example 1 and Comparative Example 1 Rubber compositions were produced according to the compounding recipes shown in Table 1. The ozone resistance of the obtained rubber composition samples was evaluated by the following method. The results are shown in Table 1.

[0371] (1) Ozone Resistance After conducting a dynamic ozone degradation test (a test in which repeated strain is applied) in accordance with ISO 1431 (JIS K 6259), the sample was observed at 20x magnification using a microscope. The observed samples were ranked according to the size and depth of cracks and classified according to the following criteria (1 to 5), with smaller numbers indicating better results. (Ranking by crack size and depth) 1: Not visible to the naked eye but visible with a 10x magnifying glass. 2: Visible to the naked eye. 3: Deep and relatively large cracks (less than 1 mm). 4: Deep and large cracks (1 mm or more but less than 3 mm). 5: Cracks of 3 mm or more or likely to cause breakage.

[0372]

[0373] * 1 SBR-1: Styrene-butadiene rubber, manufactured by ENEOS Material Co., Ltd., bound styrene amount = 35% by mass, vinyl bond amount in butadiene portion = 26% by mass, glass transition temperature = -60 ° C. * 2 SBR-2: Styrene-butadiene rubber, manufactured by ENEOS Material Co., Ltd., bound styrene amount = 45% by mass, vinyl bond amount in butadiene portion = 19% by mass, glass transition temperature = -30 ° C., oil extender 17 parts by mass included * 3 Carbon black: Manufactured by Asahi Carbon Co., Ltd., trade name "Asahi # 78" * 4 Silica: Manufactured by Tosoh Silica Industry Co., Ltd., trade name "Nipsil AQ" * 5 Silane coupling agent: Bis (triethoxysilylpropyl) polysulfide, manufactured by Shin-Etsu Chemical Co., Ltd., trade name "ABC-856"

[0374] * 6 Antioxidant-1: Another quinoline-based antioxidant, a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline, manufactured by Seiko Chemical Co., Ltd., trade name "Nonflex RD" * 7 Antioxidant-2: An aminoquinoline-based antioxidant represented by the following structural formula (1-1)

[0375] *8 Other chemicals: Total amount including at least oil, zinc oxide, stearic acid, and vulcanization accelerator

[0376] The results in Table 1 show that the rubber composition of Example 1 is superior to the rubber composition of Comparative Example 1 in ozone resistance.

[0377] DESCRIPTION OF SYMBOLS 1: Tire 2: Bead portion 3: Sidewall portion 4: Tread portion 5: Carcass 6: Belt 6A, 6B: Belt layer 7: Bead core 8: Tread rubber 9: Outer layer rubber 10: Inner layer rubber 11: Metal cord layer 12: Base rubber 13: Tread undercushion rubber 14: Reinforcement layer of metal cord layer

Claims

1. A rubber component and a rubber composition represented by the following general formula (1): [In the formula, is a single bond or a double bond, R １１ and R １２ are each independently a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a phenyl group; R １３ , R １４ , R １５ , R １６ , R １７ , R １８ and R １９ are each independently hydrogen or an alkyl group having 1 to 12 carbon atoms.] and a quinoline antioxidant other than the aminoquinoline antioxidant represented by the general formula (1), wherein the rubber component contains at least one rubber selected from the group consisting of an isoprene skeleton rubber, a styrene-butadiene rubber, a butadiene rubber, and a chloroprene rubber.

2. The rubber composition for treads according to claim 1, wherein the content of the quinoline-based antioxidant other than the aminoquinoline-based antioxidant represented by the general formula (1) is 0.1 to 5 parts by mass per 100 parts by mass of the rubber component.

3. The rubber composition for treads according to claim 1, wherein the quinoline antioxidant other than the aminoquinoline antioxidant represented by the general formula (1) above comprises a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline.

4. The aminoquinoline antioxidant is represented by the following structural formula (1-1): The rubber composition for a tread according to claim 1, wherein the compound is a compound represented by the formula:

5. Furthermore, the following general formula (2): [In the formula, R ２１ and R ２２ are each independently a substituted or unsubstituted monovalent aromatic hydrocarbon group, R ２３ The rubber composition for a tread according to claim 1, further comprising a vulcanization retarder represented by the formula: wherein R is an alkyl group substituted with a halogen.

6. The rubber composition for treads according to claim 1, further comprising a cyclic polyol compound having a hydrocarbyl group and a liquid polymer having a weight average molecular weight of 5,000 or more but less than 40,000 in terms of polystyrene as measured by gel permeation chromatography.

7. Furthermore, the crystal amount is 7 J / g or more and 50 J / g or less, and the number average molecular weight is 3.0 × 10 ４ The rubber composition for a tread according to claim 1, comprising the above syndiotactic 1,2-polybutadiene.

8. Furthermore, the following general formulas (3-1), (3-2) and (3-3): [wherein A is an aromatic group, a substituted or unsubstituted hydantoin ring, or a saturated or unsaturated linear hydrocarbon group having 0 to 8 carbon atoms; B is an aromatic group; the substituent X of B is a hydroxy group or an amino group; Y is a pyridyl group or a hydrazino group; R ３１ , R ３２ , R ３３ and R ３４ are each independently a hydrogen atom, or an alkyl group, a cycloalkyl group, or an aromatic group having 1 to 18 carbon atoms.

9. The rubber composition for treads according to claim 1, wherein the rubber component comprises a modified conjugated diene polymer, the modified conjugated diene polymer having two or more modifying groups in one molecule of the modified conjugated diene polymer, the modifying groups being bonded together via non-covalent bonds, and the energy per non-covalent bond being 10 to 250 kJ / mol.

10. The rubber composition for a tread according to claim 1, wherein the rubber component comprises a cyclic olefin ring-opening copolymer containing structural units derived from a monocyclic olefin and structural units derived from a norbornene compound.

11. The rubber composition for treads according to claim 1, further comprising at least one foaming agent selected from the group consisting of azodicarbonamide, dinitrosopentamethylenetetramine, ammonium bicarbonate, sodium bicarbonate and ammonium carbonate.

12. The rubber composition for treads according to claim 1, further comprising a silane coupling agent.

13. A tread rubber comprising the tread rubber composition according to any one of claims 1 to 12.

14. A tire comprising a tread rubber according to claim 13.

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