Sidewall rubber composition and tire

Abstract

The present invention addresses the problem of providing a sidewall rubber composition that has excellent ozone resistance even when anti-aging agent 6PPD is not used.　In order to solve the problem, the present invention is characterized by comprising: a rubber component containing at least a natural rubber and a conjugated diene-based rubber having a butadiene rubber skeleton; an amine-based anti-aging agent represented by general formula (1) [Each R is independently a hydrogen atom or a C1-6 alkyl group, and the alkyl group may be substituted with an aromatic group. R' is a hydrogen atom, a C1-6 alkyl group, or an aromatic group, and the alkyl group may be substituted with an aromatic group.]; and a quinoline-based anti-aging agent.

Description

Rubber composition for sidewall and tire

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

[0002] In general, various rubber components constituting tires (particularly sidewalls, etc.) can deteriorate due to the influence of external environments such as the presence of ozone, and as this deterioration progresses, cracks and other defects can 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 on 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 (antiaging agent 6PPD) used in the above-mentioned Patent Document 1 may have an impact on the environment, and in consideration of the possibility of future restrictions under European regulations, it has been desired to use an antioxidant with a lower environmental impact. For this reason, technology that does not use the antiaging agent 6PPD in the rubber composition has been considered, but the inventors' investigations have revealed that if only a quinoline-based antiaging agent is used without the antiaging agent 6PPD, the ozone resistance of the rubber composition decreases, and the durability of the rubber composition after aging (particularly elongation at break (EB) and tensile strength (TB)) decreases.

[0005] Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a rubber composition for a sidewall that has excellent ozone resistance even when the antioxidant 6PPD is not used.Furthermore, another object of the present invention is to provide a tire having excellent ozone resistance in the sidewall portion.

[0006] As a result of investigations conducted by the present inventors to solve the above problems, they found that the use of an amine-based antioxidant having a specific structure can improve the ozone resistance of a rubber composition and suppress deterioration of other performance properties.

[0007] That is, the rubber composition for a sidewall of the present invention comprises a rubber component containing at least natural rubber and a conjugated diene rubber having a butadiene rubber skeleton, and a rubber component represented by the following general formula (1): [Each R is independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, which may be substituted with an aromatic group. R' is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aromatic group, which may be substituted with an aromatic group.]; and a quinoline antioxidant. The rubber composition for a sidewall of the present invention has excellent ozone resistance and high retention rates of elongation at break (EB) and tensile strength (TB) after aging.

[0008] The tire of the present invention is characterized by using the rubber composition for sidewalls of the present invention described above. Such a tire of the present invention has excellent ozone resistance in the sidewall portion and excellent durability after aging.

[0009] According to the present invention, even without using the antioxidant 6PPD, it is possible to provide a rubber composition for a sidewall that has excellent ozone resistance and a high retention rate of elongation at break (EB) and tensile strength (TB) after aging. Also, according to the present invention, it is possible to provide a tire that has excellent ozone resistance in the sidewall portion and excellent durability after aging.

[0010] The rubber composition for a sidewall and the tire of the present invention will be described in detail below by way of example based on embodiments thereof.

[0011] <Definitions> The compounds described herein may be derived in part or in whole 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.

[0012] 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 rubber composition, steel cord-rubber composite, and tire in question.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] <Rubber composition for sidewall> The rubber composition for sidewall of the present invention is a rubber composition used in the sidewall portion of a tire, and comprises a rubber component containing at least natural rubber and a conjugated diene rubber having a butadiene rubber skeleton, and a rubber component represented by the following general formula (1): [Each R is independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, which may be substituted with an aromatic group. R' is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aromatic group, which may be substituted with an aromatic group.]; and a quinoline-based antioxidant. By containing the amine-based antioxidant represented by general formula (1), the rubber composition for a sidewall of the present invention has excellent ozone resistance, and by containing the quinoline-based antioxidant, it is also possible to obtain retention rates of elongation at break (EB) and tensile strength (TB) after aging.

[0017] Each component constituting the rubber composition of the present invention will be described below. (Rubber Component) The rubber composition for sidewalls of the present invention contains a rubber component, and the rubber component provides rubber elasticity to the composition. For example, from the viewpoint of increasing the sustainability rate, 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, still 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.

[0018] 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%.

[0019] 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).

[0020] The rubber component contains at least natural rubber and a conjugated diene rubber having a butadiene rubber skeleton. The conjugated diene rubber having a butadiene rubber skeleton refers to a conjugated diene rubber containing units derived from butadiene as monomer units.

[0021] The natural rubber (NR) can be, for example, RSS#3, TSR20 (e.g., SIR20 or STR20), or other rubber commonly used in the tire industry. The origin of the natural rubber (NR) is not particularly limited, and examples include rubber derived from Hevea brasiliensis, guayule, and Russian dandelion. Furthermore, the rubber component can contain synthetic isoprene rubber in addition to the natural rubber. The synthetic isoprene rubber (IR) is not particularly limited, and examples include IR2200 and other rubber commonly used in the tire industry. Examples of modified NR include deproteinized natural rubber (DPNR) and high-purity 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.

[0022] The isoprene-based rubber containing natural 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 the isoprene-based rubber containing natural rubber, 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.).

[0023] Examples of the conjugated diene rubber having a butadiene rubber skeleton include butadiene rubber (BR), aromatic vinyl compound-butadiene copolymer rubber (e.g., styrene-butadiene rubber (SBR)), etc. Here, butadiene, which is a raw material for the conjugated diene rubber having a butadiene rubber skeleton, is preferably derived from biological resources or recycled resources.

[0024] 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.

[0025] 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.

[0026] The conjugated diene rubber having a butadiene rubber skeleton 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 the conjugated diene rubber having a butadiene rubber skeleton, for example, a polymer synthesized using a biological resource-derived butadiene, a recycled resource-derived butadiene, a biological resource-derived aromatic vinyl compound (e.g., biological resource-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 biological resource-derived monomer, a homopolymer of a recycled resource-derived monomer, a copolymer of a biological resource-derived monomer and a recycled resource-derived monomer, or a copolymer of a biological resource-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.

[0027] 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.

[0028] 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 (for example, the method described in Japanese Patent Application No. 2022-140390), and raw materials for tire rubber compositions can be obtained from various waste products 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 of 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.

[0029] 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.

[0030] 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 conjugated diene-based rubber having a butadiene rubber skeleton. 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.

[0031] 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 natural 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] Furthermore, modified reclaimed rubber can also be used as the rubber component. This "modified reclaimed rubber" is a rubber material obtained by pulverizing a portion of used rubber products (waste rubber products) such as tires, devulcanizing the resulting material, and then functionalizing the resulting material with a thiuram sulfide compound. The use of modified reclaimed rubber functionalized with a thiuram sulfide compound tends to produce better results. Furthermore, since the crosslinked structure in the rubber is partially cleaved by devulcanization and functionalization, increasing its reactivity, the modified reclaimed rubber is advantageous for overcoming problems such as reduced reinforcing properties that can occur when using recycled materials. For example, reclaimed rubber or vulcanized rubber powder (rubber powder) that has functional groups capable of reacting with unvulcanized diene rubber is functionalized with a modifying compound (introducing a modifying compound). Here, the reclaimed rubber is not particularly limited, and examples thereof include crushed rubber that has been mechanically crushed at room temperature or in a frozen state, devulcanized rubber that has been further desulfurized, recycled rubber from used rubber such as automobile tires, tubes, and other rubber products specified in JIS K6313, and reclaimed rubber with properties equivalent thereto.

[0040] Furthermore, from the viewpoint of improving durability without reducing low loss properties, it is preferable to use a diene rubber as the rubber component, and isoprene-skeleton rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), or chloroprene rubber (CR) is more preferable. Here, the isoprene-skeleton rubber is a rubber whose main skeleton is isoprene units, and specific examples include natural rubber (NR) and synthetic isoprene rubber (IR). When the rubber component contains at least one selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, butadiene rubber, and chloroprene rubber, the rubber composition has excellent rubber elasticity and is more suitable for sidewall applications.

[0041] Furthermore, when 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, the effects of the present invention (the effect of improving ozone resistance by using an amine-based antioxidant in combination with a quinoline-based antioxidant, and the effect of suppressing decreases in elongation at break (EB) and tensile strength (TB) after aging) are more likely to be significantly exhibited. The content of diene rubber, such as isoprene-skeleton rubber, styrene-butadiene rubber, butadiene rubber, or 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 contain one type alone or a blend of two or more types.

[0042] Furthermore, the rubber component preferably contains a modified conjugated diene polymer, which preferably has two or more modifying groups per molecule, the modifying groups being bonded together via a non-covalent bond, and the energy per non-covalent bond being 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 intermolecular modifying groups have a non-covalent bond with a weak bond energy within the above-mentioned specific range, resulting in a crosslinked product of the modified conjugated diene polymer exhibiting excellent low loss properties at low strain by maintaining the non-covalent bond, while at high strain, the non-covalent bond is broken, resulting in hysteresis loss and 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 presumed 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 treads containing the modified conjugated diene polymer as the rubber component has low loss properties and excellent durability.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] (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 in the conventionally known anionic polymerizations described in, for example, JP-A Nos. 2013-249379, 2016-003246, and 2014-227458.

[0048] 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.

[0049] 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.

[0050] 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%.

[0051] 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.

[0052] 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%.

[0053] 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.

[0054] 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.

[0055] 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 a 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.

[0056] (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.

[0057] 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).

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] (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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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).

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] (Amine-Based Antiaging Agent) The rubber composition for a sidewall of the present invention contains an amine-based antiaging agent represented by general formula (1). Unlike N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antiaging agent 6PPD), the amine-based antiaging agent represented by general formula (1) does not contain a phenylenediamine moiety and therefore has a low environmental impact. Furthermore, the amine-based antiaging agent represented by general formula (1) has the effect of significantly improving the ozone resistance of rubber compositions.

[0073] In the general formula (1), each R is independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and the alkyl group may be substituted with a monovalent aromatic group. Examples of the alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,3-dimethylbutyl, n-pentyl, isopentyl, neopentyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, and various hexyl groups. Among these, an isopropyl group is preferred. Furthermore, a hydrogen atom in the alkyl group may be substituted with a monovalent aromatic group, and the aromatic group preferably has 3 to 10 carbon atoms, and more preferably has 3 to 6 carbon atoms. Examples of aromatic groups as substituents on the alkyl group include aromatic hydrocarbon groups such as phenyl, tolyl, xylyl, mesityl, duryl, biphenyl, terphenyl, and naphthyl groups, and aromatic heterocyclic groups such as furyl, thienyl, pyridyl, pyrrolyl, quinolyl, benzofuranyl, and benzothienyl groups. Of these, phenyl and furyl groups (e.g., 2-furyl groups) are preferred. R in the general formula (1) may be the same or different, but from the viewpoint of ease of synthesis, they are preferably the same. Specific examples of R in the general formula (1) include an isopropyl group, a furylmethyl group (e.g., 2-furylmethyl group), a furylethyl group [e.g., 1-(2-furyl)ethyl group], and a phenylethyl group (e.g., 1-phenylethyl group).

[0074] In the general formula (1), R' represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aromatic group. 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, a tert-butyl group, a 1,2-dimethylbutyl group, a 1,3-dimethylbutyl group, a 2,3-dimethylbutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 4-methylpentyl group, and various hexyl groups. Of these, an isopropyl group is preferred. The aromatic group preferably has 3 to 10 carbon atoms, and more preferably 3 to 6 carbon atoms. Examples of the aromatic group as a substituent of the alkyl group include aromatic hydrocarbon groups such as a phenyl group, a tolyl group, a xylyl group, a mesityl group, a duryl group, a biphenyl group, a terphenyl group, and a naphthyl group; and aromatic heterocyclic groups such as a furyl group, a thienyl group, a pyridyl group, a pyrrolyl group, a quinolyl group, a benzofuranyl group, and a benzothienyl group. Of these, a phenyl group and a furyl group (for example, a 2-furyl group) are preferred.

[0075] Here, examples of the amine-based antioxidant represented by general formula (1) include compounds represented by the following general formulas (1-1) to (1-7).

[0076] Furthermore, among the compounds represented by general formulas (1-1) to (1-7), it is preferable to use a compound represented by general formula (1-1) or (1-2) as the amine-based antioxidant, since this allows for obtaining better ozone resistance.

[0077] The content of the amine-based antioxidant is not particularly limited, but is preferably 0.1 to 11 parts by mass per 100 parts by mass of the rubber component. When the content of the amine-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 can be sufficiently ensured, and the decrease in the elongation at break (EB) and tensile strength (TB) of the rubber composition after aging can be sufficiently suppressed. On the other hand, when the content of the amine-based antioxidant 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.) can be more reliably suppressed, making the rubber suitable for tire sidewall applications. From the viewpoint of improving ozone resistance, the content of the amine-based antioxidant is more preferably 1 part by mass or more per 100 parts by mass of the rubber component, even more preferably 2 parts by mass or more, and particularly preferably 3 parts by mass or more. In addition, from the viewpoint of suppressing adverse effects on other rubber physical properties, the content of the amine-based antioxidant is more preferably 10.5 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the rubber component.

[0078] (Quinoline-Based Antiaging Agent) The rubber composition for a sidewall of the present invention further contains a quinoline-based antiaging agent, from the viewpoint of obtaining better ozone resistance and retention rates of elongation at break (EB) and tensile strength (TB) after aging.

[0079] Furthermore, in the rubber composition for sidewalls of the present invention, it is more preferable that the mass ratio of the content of the quinoline-based antioxidant to the content of the amine-based antioxidant (quinoline-based antioxidant content / amine-based antioxidant content) is 0.05 to 0.35. By using the amine-based antioxidant represented by the general formula (1) in combination with a quinoline-based antioxidant and setting the mass ratio of the content of the quinoline-based antioxidant to the content of the amine-based antioxidant within the above range (0.05 to 0.35), the ozone resistance of the rubber composition can be further improved, and the decrease in the elongation at break (EB) and tensile strength (TB) of the rubber composition after aging can be further suppressed. When the mass ratio of the content of the quinoline-based antioxidant to the content of the amine-based antioxidant is 0.05 or more, higher ozone resistance can be ensured when the tire is applied to the sidewall, and sufficient elongation at break (EB) and tensile strength (TB) after aging can be obtained. When the mass ratio is 0.2 or less, the elongation at break (EB) and tensile strength (TB) after aging are good, but sufficient ozone resistance can be obtained when the tire is applied to the sidewall.

[0080] In the rubber composition for sidewalls of the present invention, by setting the mass ratio of the content of the quinoline-based antioxidant to the content of the amine-based antioxidant (quinoline-based antioxidant content / amine-based antioxidant content) to 0.05 to 0.35, adverse effects on rubber physical properties other than ozone resistance (heat buildup, etc.) can be suppressed, making the rubber composition suitable for sidewall applications. Furthermore, from the viewpoint of further improving the ozone resistance of the rubber composition and the retention rates of elongation at break (EB) and tensile strength (TB) after aging while suppressing adverse effects on rubber physical properties other than ozone resistance, the mass ratio of the content of the quinoline-based antioxidant to the content of the amine-based antioxidant (quinoline-based antioxidant content / amine-based antioxidant content) is preferably 0.10 to 0.35, more preferably 0.20 to 0.34, and even more preferably 0.26 to 0.32.

[0081] The quinoline-based antioxidant preferably has a dihydroquinoline moiety, and more preferably has a 1,2-dihydroquinoline moiety. Specific examples of the quinoline-based antioxidant include a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline (antiaging agent TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, and 6-anilino-2,2,4-trimethyl-1,2-dihydroquinoline. The 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. The polymer of 2,2,4-trimethyl-1,2-dihydroquinoline includes a dimer, trimer, tetramer, etc. of 2,2,4-trimethyl-1,2-dihydroquinoline.

[0082] The content of the quinoline-based antioxidant is not particularly limited as long as the mass ratio of the content of the quinoline-based antioxidant to the content of the amine-based antioxidant is in the range of 0.05 to 0.35. For example, from the viewpoint of ensuring sufficient ozone resistance and sufficiently suppressing a decrease in the elongation at break (EB) and tensile strength (TB) of the rubber composition after aging while suppressing adverse effects on rubber physical properties other than ozone resistance, the content of the 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 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 can be sufficiently ensured and a decrease in the elongation at break (EB) and tensile strength (TB) of the rubber composition after aging can be sufficiently suppressed. On the other hand, when the content of the 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 tire suitable for sidewall applications. From the viewpoint of further improving ozone resistance, the content of the 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. Furthermore, from the viewpoint of more reliably suppressing adverse effects on other rubber physical properties, the content 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.

[0083] (Wax) The rubber composition for a sidewall of the present invention preferably further contains a wax. When the rubber composition for a sidewall contains a wax, ozone resistance is further improved. Examples of the wax include natural waxes such as vegetable wax and animal wax; petroleum 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 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.

[0084] The wax may also be a hydrolyzed product of a plant-derived wax. Examples of such plant-derived wax hydrolyzates 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 efficiently produces primary alcohols having the carbon number distribution and component composition described below. Plant-derived wax hydrolyzates 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., although these other components do not necessarily need to be removed. Among these other components, higher fatty acids obtained by hydrolyzing plant waxes 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.

[0085] 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.

[0086] (Sulfur) The rubber composition for a sidewall of the present invention preferably contains sulfur. By including sulfur in the rubber composition, it becomes possible to vulcanize, and the durability of the rubber composition (particularly, elongation at break (EB) and tensile strength (TB)) is improved. Various types of sulfur can be used as the sulfur; however, ordinary sulfur (soluble sulfur (powdered sulfur), etc.) is preferred over insoluble sulfur, and oil treat sulfur is also preferred. Here, insoluble sulfur is sulfur insoluble in carbon disulfide (amorphous polymeric sulfur), and soluble sulfur (powdered sulfur) is sulfur soluble in carbon disulfide. The sulfur content is preferably in the range of 0.1 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component. When the sulfur content is 0.1 part by mass or more per 100 parts by mass of the rubber component, superior durability of the vulcanized rubber can be ensured. When the sulfur content is 10 parts by mass or less per 100 parts by mass of the rubber component, superior rubber elasticity can be ensured.

[0087] (Carbon Black) Furthermore, the rubber composition for a sidewall of the present invention may contain carbon black, if necessary. Carbon black reinforces the rubber composition and can improve the abrasion resistance of the rubber composition. As the carbon black, plant-derived carbon black and carbon black obtained by recycling (also called "recycled carbon black" or "recycled carbon black") are preferred. Here, examples of plant-derived carbon black include those derived from castor oil and pine oil. Recycled carbon black will be described in detail below.

[0088] From the viewpoint of further improving the abrasion resistance of the rubber composition and a tire using the same, the content of the carbon black (total of recycled carbon black and carbon black other than recycled carbon black) in the rubber composition of the present invention 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. Also, from the viewpoint of workability of the rubber composition, the content of the carbon black in the rubber composition is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less, per 100 parts by mass of the rubber component.

[0089] As used herein, "recycled carbon black" refers to carbon black recovered from recycled waste materials. Examples of such waste include waste rubber, used tires, and waste oil. Waste rubber refers to all discarded rubber, including not only waste generated from rubber products but also unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeled rubber. Buffing powder is fine rubber generated during the buffing process of scraping the tread portion remaining on the base tire during tire retreading, for example. Peeled rubber is a long piece of rubber, e.g., 1 to 2 cm wide, peeled from the surface of a rubber product such as a tire. Peeled rubber is generated by scraping the surface of a rubber product such as a tire using a U- or V-shaped knife like a peeler. Furthermore, waste rubber is not limited to crosslinked rubber but also includes unvulcanized rubber. Rubber products include, for example, final products such as tires and rubber hoses, as well as rubber parts or components during the manufacturing process of final products. Used tires may be tires to be retreaded, or may be tires discarded for some reason, such as tires generated during tire replacement or scrapping, or ELTs (End-of-Life Tires) that have reached the end of their service life. Waste oils are not limited to those generated during the decomposition of plastics and rubber, but also include used oils discharged from industry, such as animal and vegetable oils, lubricating oils, insulating oils, and cutting oils. Among these, waste oils that contain no non-organic components, such as those derived from silicone rubber or polyvinyl chloride, are desirable. Furthermore, waste oils containing carbon black or rubber containing carbon black are desirable. "Recycled carbon black" differs from carbon black produced directly from hydrocarbons such as petroleum, natural gas, and coal, i.e., non-recycled carbon black. Note that "used" here refers not only to waste oils discarded after actual use, but also to waste oils that were produced but discarded without actually being used.

[0090] The recycled carbon black is preferably obtained by pyrolysis of a vulcanized rubber product containing carbon black. Recycled carbon black obtained by pyrolysis of a vulcanized rubber product containing carbon black is readily available because vulcanized rubber products containing carbon black are readily available and can be easily obtained by pyrolysis. Furthermore, the recycled carbon black is preferably obtained from the solid residue produced by the pyrolysis of the vulcanized rubber product containing carbon black. When a rubber product containing carbon black is pyrolyzed, a solid residue and a volatile component (oil) are obtained, and recycled carbon black can be recovered from either of them. When recovering carbon black from the volatile component, the oil component with a specific gravity suitable for producing carbon black can be recovered and used to produce carbon black using existing carbon black production methods (e.g., JP 2015-520259 A). Unlike carbon black recovered from solid residues, this method offers advantages such as no impurities and no mixed grades. In addition, in the production of environmentally friendly carbon black, various options are available, including oils obtained by recovering volatile components from rubber pyrolysis, as described above, as well as vegetable oils and oils derived from waste plastics. However, edible resources such as vegetable oils are needed for other uses, such as food, and there are challenges in securing sufficient quantities, as well as the environmental impact of expanding cultivated land. Furthermore, oils derived from waste plastics are also used for other purposes, such as horizontal plastic recycling, so supply issues are also a concern. On the other hand, using volatile components (oils) produced by the pyrolysis of vulcanized rubber products, particularly tires, allows for the continued use of existing materials due to the tire industry's ongoing system of using existing materials, thereby reducing the consumption of new materials in new tire production and contributing to a reduction in the industry's environmental impact. The grade of carbon black is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762.

[0091] Solid residues obtained by pyrolysis of waste materials such as used rubber and used tires contain ash in addition to carbon black. The ash is derived from non-volatile components contained in the rubber and tires. Therefore, recycled carbon black obtained from the solid residues has a relatively low carbon black content. On the other hand, considering the various physical properties required for tires manufactured using recycled carbon black, the higher the carbon content of the recycled carbon black, the better. The carbon content of the recycled carbon black is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 87% by mass or more, and particularly preferably 89% by mass or more. Furthermore, the carbon content of the recycled carbon black is preferably 97% by mass or less. Note that the carbon content does not include adsorbed moisture.

[0092] Specific examples of the ash include zinc oxide, zinc sulfide, silica, iron compounds (iron oxide), calcium oxide, aluminum oxide, and magnesium oxide. In the case of recycled carbon black produced from solid residue obtained by pyrolysis of waste, a certain amount of ash remains even after various processes for removing the ash. In this embodiment, the recycled carbon black is allowed to contain ash. In one embodiment, the lower limit of the ash content of the recycled carbon black may be 0.5% by mass.

[0093] The recycled carbon black can also be obtained from a pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3,427,975, citing "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly pp. 438, 440, and 442, describes that recycled carbon black can be obtained by pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (paragraph

[0027] ). Carbon black obtained from such pyrolysis processes typically lacks functional groups on its surface, as mentioned in paragraph

[0004] of Japanese Patent Publication No. 6,856,781 (Comparison of the Surface Morphology and Chemistry of Pyrolytic Carbon Black and Commercially Available Carbon Black, Powder Technology 160 (2005) pp. 190-193).

[0094] The recycled carbon black may lack functional groups on its surface, or may be treated to include functional groups on its surface. The treatment to include functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, in European Patent Application Publication No. 3,173,251, carbon black obtained by a pyrolysis process is treated with potassium permanganate under acidic conditions to obtain carbon black containing hydroxyl and / or carboxyl groups on its surface. Furthermore, in Japanese Patent Publication No. 6,856,781, carbon black obtained by a pyrolysis process is treated with an amino acid compound containing at least one thiol or disulfide group to obtain surface-activated carbon black. The recycled carbon black according to this embodiment also includes carbon blacks treated to include functional groups on their surfaces.

[0095] Furthermore, examples of thermal decomposition of crosslinked rubber products (vulcanized rubber products) such as used tires include thermal decomposition methods at temperatures of 650° C. or higher.

[0096] The crosslinked rubber products used for the decomposition may be grouped by the type of rubber component previously compounded, and then the decomposition step may be performed for each group. Alternatively, the crosslinked rubber products may be grouped by the type of filler previously compounded (e.g., type of carbon black, type of silica, mixing ratio of carbon black and silica, etc.), and then the decomposition step may be performed for each group. Furthermore, the crosslinked rubber products may be grouped by both type of rubber component and type of filler, and then the decomposition step may be performed for each group. When the decomposition step is performed for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and when the recycled carbon black is compounded again into a rubber component, a rubber composition with better performance can be obtained.

[0097] Furthermore, when the crosslinked rubber product used in the degradation is derived from tires, the tires may be grouped in advance by type (e.g., for passenger cars, for trucks and buses, for large vehicles such as off-road vehicles, for aircraft, for agricultural vehicles, etc.), and the degradation step may be carried out for each group. Alternatively, the tires may be grouped in advance by tire component (e.g., tread rubber, sidewall rubber, bead rubber, steel cord-coated rubber, organic fiber-coated rubber, pad rubber, cushion rubber, etc.), and the degradation step may be carried out for each group. Furthermore, the tires may be grouped both by type and by tire component, and the degradation step may be carried out for each group. When the degradation step is carried out for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and therefore, when the recycled carbon black is blended again into a rubber component, a rubber composition with better performance can be obtained.

[0098] The recycled carbon black has a nitrogen adsorption specific surface area of ​​40 to 100 m as measured by the BET method. ２ / g, and 50 to 90m ２ / g, and more preferably 55 to 75m ２ In this specification, the nitrogen adsorption specific surface area of ​​recycled carbon black measured by the BET method is a statistical thickness specific surface area (STSA) determined in accordance with ASTM D6556.

[0099] The pH of the recycled carbon black is preferably 4 to 12, more preferably 5 to 11, and particularly preferably 6 to 10. In this specification, the pH of the recycled carbon black is determined in accordance with ASTM D1512.

[0100] The recycled carbon black preferably has a toluene color transmittance of 60% or more, more preferably 70% or more, and particularly preferably 80% or more. Herein, the toluene color transmittance of recycled carbon black is determined in accordance with ASTM D1618.

[0101] The recycled carbon black preferably has a heat loss of 3% by mass or less, more preferably 2.5% by mass or less, and particularly preferably 2% by mass or less at 125°C. Herein, the heat loss of recycled carbon black at 125°C is determined in accordance with ASTM D1509.

[0102] The recycled carbon black preferably has a sulfur content of 5% by mass or less, more preferably 3.5% by mass or less, and particularly preferably 3% by mass or less.

[0103] The recycled carbon black preferably has a 35 mesh sieve residue of 20 mass ppm or less, more preferably 15 mass ppm or less, and particularly preferably 10 mass ppm or less. Herein, the 35 mesh sieve residue of recycled carbon black is determined in accordance with ASTM D1514.

[0104] The recycled carbon black preferably has a 325 mesh (44 μm) sieve residue of 1000 mass ppm or less, more preferably 700 mass ppm or less, and particularly preferably 300 mass ppm or less. Herein, the 325 mesh (44 μm) sieve residue of the recycled carbon black is determined in accordance with ASTM D1514.

[0105] The recycled carbon black preferably has a pellet hardness of 100 cN or less, more preferably 90 cN or less, and particularly preferably 80 cN or less. Herein, the pellet hardness of recycled carbon black is determined in accordance with ASTM D5230.

[0106] The recycled carbon black preferably has a pellet fine powder content of 10% by mass or less, more preferably 7% by mass or less, and particularly preferably 5% by mass or less. Herein, the pellet fine powder content of recycled carbon black is determined in accordance with ASTM D1508.

[0107] The particle size (D97) of the recycled carbon black is preferably 25 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less. Here, in this specification, the particle size (D97) of the recycled carbon black is determined using a laser diffraction particle size distribution analyzer, assuming a refractive index of 1.33 for water and a refractive index of 1.75 for the filler.

[0108] The recycled carbon black preferably contains particles of 5 μm or less in a proportion of 50% by volume or more, more preferably 70% by volume or more, and particularly preferably 80% by volume or more.

[0109] The recycled carbon black preferably has an ash content of 25% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less. When the ash content of the recycled carbon black is 25% by mass or less, the physical properties of the rubber product to which the rubber composition is applied can be improved. Herein, the ash content of the recycled carbon black is determined in accordance with ASTM D8474 and D1506.

[0110] The recycled carbon black preferably has a dibutyl phthalate (DBP) absorption of 70 to 120 mL / 100 g, more preferably 75 to 110 mL / 100 g, and particularly preferably 80 to 100 mL / 100 g. Herein, the DBP absorption of recycled carbon black is determined in accordance with ASTM D2414.

[0111] The recycled carbon black preferably has a compressed dibutyl phthalate (24M4DBP) absorption capacity of 50 to 110 mL / 100 g, more preferably 60 to 100 mL / 100 g, and particularly preferably 70 to 90 mL / 100 g. Herein, the 24M4DBP absorption capacity of the recycled carbon black is determined in accordance with ASTM D3493.

[0112] Commercially available recycled carbon black can be used. For example, Enrestec's product name "PB365" can be mentioned as such a commercially available product. PB365 is a recycled carbon black produced through the thermal decomposition of used tires, and has a nitrogen adsorption specific surface area of ​​73.6 m2 as measured by the BET method. ２ / g and contains about 17% by mass of ash.

[0113] The amount of recycled carbon black is preferably 1 to 100 parts by mass, more preferably 5 to 80 parts by mass, even more preferably 5 to 50 parts by mass, still more preferably 5 to 30 parts by mass, and particularly preferably 5 to 20 parts by mass, per 100 parts by mass of the rubber component. When the amount of recycled carbon black is 5 parts by mass or more per 100 parts by mass of the rubber component, the effect of improving the proportion of sustainable materials in rubber products to which the rubber composition is applied is significant, and when the amount is 50 parts by mass or less, the fracture resistance of the rubber composition can be more reliably maintained.

[0114] (Silica) The rubber composition for sidewalls of the present invention may also contain silica, if necessary. The type of silica is not particularly limited, and examples thereof 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 may be used, such as those from Tosoh Silica Corporation, Evonik Corporation, Solvay, Solvay Japan Co., Ltd., and Tokuyama Corporation. The silica may also be commercially available, such as Zeosil Premium 200MP (trade name) from Rhodia. Only one type of silica may be used, or two or more types may be used.

[0115] 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 a powder of rice husk charcoal 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 rice husks by steaming them in a kiln. The rice husk charcoal obtained in this manner can be 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, for example.

[0116] Furthermore, 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.

[0117] The content of the silica 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 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.

[0118] (Silane Coupling Agent) When the rubber composition for a sidewall of the present invention contains silica, the rubber composition preferably contains a silane coupling agent in order to improve the effect of the silica. 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.

[0119] 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.

[0120] 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 monomer components derived from biological resources as the biological resource-derived monomer component, or to use a combination of a monomer component derived from a biological resource, a monomer component derived from a renewable resource, and a monomer component derived from a fossil resource. 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.

[0121] (Resin) The rubber composition for a sidewall of the present invention may further contain a resin. Examples of the resin include terpene-based resins, rosin-based resins, 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, C９ 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, and therefore can further reduce the environmental impact and further improve tire performance. ５ based resin, C ９ based resin, C ５ -C ９ The cyclopentadiene-based resin and the cyclopentadiene-based resin can improve reinforcement and fuel economy in a well-balanced manner, while the aromatic resin can improve reinforcement and other properties.

[0122] Furthermore, the resin may be a temperature-responsive resin whose hydrophilicity changes with temperature. An example of the temperature-responsive resin is the temperature-responsive resin described in JP 2022-077145 A.

[0123] 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.

[0124] The terpene resin is a solid resin obtained by blending turpentine, which is obtained simultaneously with the extraction of rosin 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 resins also include terpene-aromatic compound resins, representative examples of which include terpene-phenol resin and styrene-terpene resin. Terpene-phenol resins can be obtained by reacting terpenes with various phenols using a Friedel-Crafts catalyst, or by further condensing the terpene 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; monoterpene hydrocarbons such as α-pinene and limonene are preferred, with those containing α-pinene being more preferred, and α-pinene being particularly preferred.

[0125] 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.

[0126] Furthermore, a maleic acid-modified rosin resin can also be used as the rosin-based resin. 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 resin contains a maleic acid-modified rosin resin having an acid value of 50 KOH mg / g or less. Alternatively, the 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 K0070:1992).

[0127] 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.

[0128] 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.

[0129] 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.

[0130] Examples of the maleic acid-modified rosin resin include Marquid 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. Among these, Marquid 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.).

[0135] 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.

[0136] The resin may also be a mixture (mixed resin) of a hydrogenated styrene resin and an aromatic-modified terpene resin. The rosin-based resin may also be a maleic acid-modified rosin resin. The hydrogenated styrene resin is a resin obtained by hydrogenating a styrene resin made of a styrene monomer. Hydrogenating the styrene resin reduces the number of aromatic rings derived from styrene, 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. The uniform and tight crosslinking of the rubber also improves durability.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] The aromatic-modified terpene resin is a copolymer of a terpene and an aromatic compound. 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 aromatic-modified terpene resin is preferably 10 to 50% by mass, and more preferably 12 to 45% by mass. By compounding the aromatic-modified terpene resin with a diene rubber, the dynamic viscoelasticity of the rubber composition can be modified, and the wet grip performance and heat buildup can be improved.

[0141] The softening point of the aromatic modified terpene resin is not particularly limited, but is preferably 60°C to 150°C, more preferably 80°C to 130°C. If the softening point of the aromatic modified terpene resin is less than 60°C, the wet grip performance may be reduced. If the softening point of the aromatic modified terpene resin is more than 150°C, the low rolling resistance may be deteriorated. In this specification, the softening point of the aromatic modified terpene resin is measured based on JIS K6220-1 (ring and ball method).

[0142] 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.

[0143] 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.

[0144] 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 tire components, 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.

[0145] (Rubber Crumb) The rubber composition for sidewalls of the present invention may also contain rubber crumb. The rubber crumb may be obtained by crushing 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 rubber crumb and crushing it. For example, rubber crumb can be obtained from vulcanized rubber by the method described in "Rubber Chemistry and Technology." The process of crushing 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] (Liquid Softener) The rubber composition 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.

[0151] 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 perspective of reducing environmental impact, vegetable oils and recycled oils are preferred. Examples of vegetable oils include palm oil, castor oil, cottonseed oil, soybean oil, linseed oil, rapeseed oil, coconut oil, coconut oil, peanut 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, coconut oil, seed oils, grain oils, potato oils, bean oils, and vegetable oils. Examples of process oils include paraffinic 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.

[0152] 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.

[0153] 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.

[0154] (Syndiotactic 1,2-polybutadiene) The rubber composition for sidewalls of the present invention 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.

[0155] 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).

[0156] In a rubber composition for a tread 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 it in combination with an amine-based antioxidant represented by general formula (1), high mechanical strength can be significantly maintained even after thermal degradation.

[0157] 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.

[0158] 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).

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] 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.

[0173] (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): [A is one member selected from the group consisting of an aromatic ring, a substituted or unsubstituted hydantoin ring, and a saturated or unsaturated linear hydrocarbon 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 １ ~R ４ is one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, and an aromatic ring, and may be the same or different.] A rubber composition for a tread containing the 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 (I), (II), or (III) can improve low heat buildup properties while suppressing an increase in Mooney viscosity.

[0174] The hydrazide compounds represented by the above general formula (I), (II) or (III) 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.

[0175] In the above general formula (I), A is 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.

[0176] 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 (II) or (III)).

[0177] Examples of the hydrazide compound represented by the general formula (I) 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.

[0178] In the above general formula (II), 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 above general formula (II) include derivatives of 2-naphthalene acid-3-hydroxyhydrazide such as 2-naphthalene acid-3-hydroxy(1-methylethylidene)hydrazide, 2-naphthalene acid-3-hydroxy(1-methylpropylidene)hydrazide, 2-naphthalene acid-3-hydroxy(1,3-dimethylpropylidene)hydrazide, and 2-naphthalene acid-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.

[0179] As the hydrazide compound represented by the general formula (II), a hydrazide compound represented by the following general formula can be used. (In the formula, R １ , R ２ are each independently an alkyl group having 1 to 18 carbon atoms.

[0180] In the above general formula, R １ , R ２ are each independently an alkyl group having 1 to 18 carbon atoms, and examples thereof include 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. １ , R ２ One of these may be methyl.

[0181] Examples of the hydrazide compound represented by the above general formula 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, 1-hydroxy-N'-(1,3-dimethylbutylidene)-2-naphthoic acid hydrazide, 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 hydrazide, 3-hydroxy-N'-(2-furylmethylene)-2-naphthoic acid hydrazide, and the like, among which 1-hydroxy-N'-(1-methylethylidene)-2-naphthoic acid hydrazide, 1-hydroxy-N'-(1-methylpropylidene)-2-naphthoic acid hydrazide, 1-hydroxy-N'-(1,3-dimethylbutylidene)-2-naphthoic acid hydrazide, 1-hydroxy-N'- Examples include (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.

[0182] In the above general formula (III), Y is a pyridyl group or a hydrazino group. Examples of the hydrazide compound represented by the above general formula (III) 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 capable of reducing the Mooney viscosity value while maintaining high low heat buildup, and are therefore highly effective in the present invention.

[0183] The synthesis method of the hydrazide compounds represented by the above general formula (I), (II) or (III) is described, for example, in Pant, U.C.; Ramchandran, Reena; Joshi, B.C. Rev. Roum. Chim. (1979) 24(3), 471-82.

[0184] 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, and when the content is 10 parts by mass or less, deterioration of other physical properties can be suppressed and costs can be reduced.

[0185] (Other Components) In addition to the above-mentioned components, the rubber composition for sidewalls of the present invention may contain various components (other components) commonly used in the rubber industry, as necessary. Examples of other components include fillers such as silica and carbon black, silane coupling agents, softeners, processing aids, stearic acid, zinc oxide (zinc white), vulcanization accelerators, and vulcanizing agents other than sulfur, which may be appropriately selected and contained within a range that does not impair the object of the present invention. Commercially available products can be suitably used as these compounding ingredients.

[0186] Among the other components, zinc oxide (ZnO) is used as a vulcanization accelerator. By further including zinc oxide in the rubber composition, vulcanization can be accelerated, and strength after vulcanization can be further increased. The zinc oxide is preferably zinc oxide obtained by recycling. Commercially available zinc oxide products can be used, including those 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.

[0187] Here, the content of zinc oxide 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 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.

[0188] Among the other components, commercially available stearic acid can be used, and examples of commercially available stearic acid include products from NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc. These commercially available stearic acid products may be used alone or in combination of two or more.

[0189] 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.

[0190] The amine-based antiaging agent represented by the general formula (1) may be supported on any carrier. For example, the amine-based antiaging agent represented by the general formula (1) may be supported on an inorganic filler such as silica or calcium carbonate. The amine-based antiaging agent 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 amine-based antiaging agent 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 thereof include stearic acid.

[0191] (Method for Producing Rubber Composition for Sidewall) The method for producing the rubber composition for sidewall of the present invention is not particularly limited, but can be produced, for example, by blending the above-mentioned rubber component and amine-based antioxidant with suitable components and other components appropriately selected as necessary, and kneading, heating, extruding, etc. The obtained rubber composition can be vulcanized to form a vulcanized rubber.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] The vulcanization apparatus, method, conditions, etc. are not particularly limited and can be appropriately selected depending on the purpose. Examples of vulcanization apparatus include a molding vulcanizer using a mold used for vulcanizing rubber compositions. The vulcanization temperature is, for example, about 100 to 190°C.

[0196] <Tire> The tire of the present invention is characterized by using the rubber composition for sidewall of the present invention described above. As a result, the tire of the present invention has excellent ozone resistance in the sidewall portion. The rubber composition for sidewall needs to be used in at least the sidewall portion of the tire, but it can also be used in other portions, such as at least one of the tread portion, shoulder portion, bead portion, belt layer (belt coating rubber), and carcass (ply coating rubber).

[0197] Depending on the type of tire to be applied, the tire of the present invention 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 step or the like and then further vulcanizing it. The tire of the present invention is preferably a pneumatic tire, and the gas to be filled into the pneumatic tire may be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

[0198] 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.

[0199] Examples 1 and 2, Comparative Example 1 According to the compounding recipes shown in Table 1, rubber compositions were produced.

[0200] <Evaluation> The ozone resistance of the obtained rubber composition samples was evaluated by the following method. The results are shown in Table 1.

[0201] (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 samples were observed under a microscope at 20x magnification. 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 to less than 3 mm). 5: Cracks of 3 mm or larger or likely to cause breakage.

[0202]

[0203] *1 NR: Natural rubber *2 BR: Butadiene rubber, UBE Corporation, trade name "UBEPOL BR150" *3 Carbon black: Asahi Carbon Co., Ltd., trade name "Asahi #65" *4 Antioxidant A: Quinoline-based antioxidant, 2,2,4-trimethyl-1,2-dihydroquinoline polymer, Seiko Chemical Co., Ltd., trade name "Nonflex RD" *5 Antioxidant B: Amine-based antioxidant represented by the following formula (1-1) *6 Antioxidant C: An amine-based antioxidant represented by the following formula (1-2) *7 Other chemicals: Total amount including at least oil, zinc oxide, stearic acid and vulcanization accelerator

[0204] From the results in Table 1, it was found that the rubber compositions of the examples all had superior ozone resistance compared to the rubber compositions of the comparative examples.

[0205] According to the present invention, a rubber composition for a sidewall having excellent ozone resistance can be provided even when the antioxidant 6PPD is not used. Also, according to the present invention, a tire having excellent ozone resistance in the sidewall portion can be provided.

Claims

1. A rubber component containing at least natural rubber and a conjugated diene rubber having a butadiene rubber skeleton, and a rubber component represented by the following general formula (1): [Each R is independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, which may be substituted with an aromatic group. R' is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aromatic group, which may be substituted with an aromatic group.]; and a quinoline-based antioxidant.

2. The rubber composition for sidewalls according to claim 1 or 2, wherein the content of the quinoline-based antioxidant is 0.1 to 5 parts by mass per 100 parts by mass of the rubber component.

3. The rubber composition for a sidewall according to claim 1 or 2, wherein the quinoline-based antioxidant contains a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline.

4. The amine-based antioxidant is represented by the following general formula (1-1) or (1-2): The rubber composition for a sidewall according to claim 1 or 2, characterized in that the compound is represented by the following formula:

5. The rubber composition for a sidewall according to claim 1 or 2, further comprising a wax, the content of the wax being 0.1 to 5 parts by mass per 100 parts by mass of the rubber component.

6. The amount of crystallinity is 7 J / g or more and 50 J / g or less, and the number average molecular weight is 3.0 × 10 ４ 3. The rubber composition for a sidewall according to claim 1, comprising the syndiotactic 1,2-polybutadiene as described above.

7. Furthermore, the following general formulae (3-1), (3-2) and (3-3): [A is one member selected from the group consisting of an aromatic ring, a substituted or unsubstituted hydantoin ring, and a saturated or unsaturated linear hydrocarbon 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 １ ~R ４ is one selected from the group consisting of a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, and an aromatic ring, and may be the same or different.

8. A rubber composition for sidewalls according to claim 1 or 2, characterized in that 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 non-covalent bonds between the molecules, and the energy per non-covalent bond is 10 to 250 kJ / mol.

9. A tire characterized by using the rubber composition for sidewalls according to claim 1 or 2.