Rubber composition for sidewall and tire

Abstract

To provide a rubber composition for sidewall that has superior ozone resistance and maintains high levels of elongation at break (EB) and tensile strength (TB) after aging, even in the absence of the antioxidant 6PPD.SOLUTION: A rubber composition comprising a rubber component and an aminoquinoline-based antioxidant represented by the following general formula (1). [In formula (1), A is a single bond or a double bond; R11 and R12 are each independently hydrogen, a C1-C12 alkyl group, a C3-C6 cycloalkyl group, or a phenyl group; R13 to R19 are each independently hydrogen or a C1-C12 alkyl group].SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] In general, various rubber components constituting tires (particularly sidewalls, etc.) may deteriorate due to the influence of external environments such as the presence of ozone, and as the deterioration progresses, cracks, etc. In response to such problems, rubber compositions containing antioxidants are often used in various rubber components constituting tires. For example, Patent Document 1 below discloses that cracking and discoloration of the tire surface can be suppressed by applying a rubber composition containing a selected blend of a specific quinoline-based antioxidant and N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antiaging agent 6PPD) to the rubber that makes up the tire surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 056384 Summary of the Invention [Problem to be solved by the invention]

[0004] However, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antioxidant 6PPD) used in the above 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. Therefore, a technique that does not use the antioxidant 6PPD in the rubber composition can be considered. However, the inventors of the present invention have conducted research and found that if only a quinoline-based antioxidant is used without the antioxidant 6PPD, the ozone resistance of the rubber composition decreases, and the durability of the rubber composition after aging (particularly the 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 conventional technology and to provide a rubber composition for sidewalls that has excellent ozone resistance even when the antioxidant 6PPD is not used. A further object of the present invention is to provide a tire having excellent ozone resistance in the sidewall portion. [Means for solving the problem]

[0006] As a result of investigations conducted by the present inventors to solve the above problems, they found that the ozone resistance of a rubber composition can be improved and deterioration of other performance properties can be suppressed by using an aminoquinoline antioxidant having a specific structure.

[0007] That is, the rubber composition for a sidewall of the present invention comprises a rubber component, The following general formula (1): [ka] is a single or double bond, and R 11 and R 12 are each independently a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a phenyl group, and R 13 , R 14 , R 15 , R 16 , R 17 , R 18 and R 19 are each independently hydrogen or an alkyl group having 1 to 12 carbon atoms; and The present invention is characterized by comprising: The rubber composition for a sidewall of the present invention has excellent ozone resistance and exhibits high retention of elongation at break (EB) and tensile strength (TB) after aging.

[0008] The rubber composition for a sidewall of the present invention preferably further contains a quinoline antioxidant other than the aminoquinoline antioxidant represented by the general formula (1), which provides better ozone resistance and higher retention rates of elongation at break (EB) and tensile strength (TB) after aging.

[0009] Furthermore, in the rubber composition for sidewalls of the present invention, the rubber component preferably contains at least one rubber selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, butadiene rubber, and chloroprene rubber. In this case, the rubber composition has excellent rubber elasticity, is more suitable for sidewall applications, and the effects of the present invention are more likely to be significantly exhibited.

[0010] Furthermore, in the rubber composition for sidewalls of the present invention, the content of the quinoline antioxidant other than the aminoquinoline antioxidant represented by the general formula (1) is preferably 0.1 to 5 parts by mass per 100 parts by mass of the rubber component, which can further improve ozone resistance and the retention rates of elongation at break (EB) and tensile strength (TB) after aging.

[0011] Furthermore, in the rubber composition for sidewalls of the present invention, the quinoline antioxidant other than the aminoquinoline antioxidant represented by the general formula (1) preferably contains a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline, which is highly effective in improving the ozone resistance of the rubber composition and also makes the rubber composition less susceptible to discoloration.

[0012] In addition, in the rubber composition for a sidewall of the present invention, the aminoquinoline antioxidant is represented by the following general formula (1-1): [ka] In this case, the ozone resistance of the rubber composition is further improved.

[0013] Furthermore, the rubber composition for a sidewall of the present invention preferably further contains a wax, and the content of the wax is preferably 0.1 to 5 parts by mass per 100 parts by mass of the rubber component, which further improves the ozone resistance of the rubber composition.

[0014] Furthermore, the rubber composition for a sidewall of the present invention further 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 preferable that the polybutadiene contains a syndiotactic 1,2-polybutadiene having a molecular weight of 1,2,5 or more, because the retention rate of elongation at break (EB) and tensile strength (TB) after aging can be further increased.

[0015] In addition, the rubber composition for a sidewall of the present invention further comprises a compound represented by the following general formulas (3-1), (3-2) and (3-3): [ka] [A is one selected from the group consisting of an aromatic ring, a substituted or unsubstituted hydantoin ring, and a saturated or unsaturated straight-chain 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; and R1 to R4 are one selected from the group consisting of a hydrogen atom, an alkyl group, a cycloalkyl group, and an aromatic ring having 1 to 18 carbon atoms, and may be the same or different.] It is preferable that the hydrazide compound contains any one of the following: It is possible to improve low heat buildup while suppressing an increase in Mooney viscosity.

[0016] Furthermore, the rubber component contains a modified conjugated diene polymer, The modified conjugated diene polymer preferably has two or more modifying groups in one molecule, the modifying groups are bonded together via a non-covalent bond, and the energy per non-covalent bond is 10 to 250 kJ / mol, thereby further improving low loss properties and durability.

[0017] The tire of the present invention is characterized by using the above-mentioned rubber composition for sidewalls of the present invention. The tire of the present invention has excellent ozone resistance in the sidewall portion and excellent durability after aging. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a rubber composition for a sidewall that is excellent in ozone resistance even when the antioxidant 6PPD is not used. Furthermore, according to the present invention, a tire having excellent ozone resistance in the sidewall portion can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0019] 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.

[0020] <Definition> The compounds described herein may be derived in part or in whole from fossil sources, biological sources such as plant sources, recycled sources such as used tires, or a mixture of two or more of fossil, biological, and recycled sources.

[0021] 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.

[0022] 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.). Such biological resources may be edible or non-edible, but are preferably non-edible from the viewpoint of not competing with food and of effective resource utilization.

[0023] 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, used 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. Furthermore, 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.

[0024] 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.

[0025] <Sidewall rubber composition> The rubber composition for a sidewall of the present invention is a rubber composition used in a sidewall portion of a tire, comprising: a rubber component; The following general formula (1): [ka] is a single or double bond, and R 11 and R 12 are each independently a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a phenyl group, and R 13 , R 14 , R 15 , R 16 , R 17 , R 18 and R 19 are each independently hydrogen or an alkyl group having 1 to 12 carbon atoms; and The present invention is characterized by comprising: By including the aminoquinoline antioxidant represented by the general formula (1) above, the rubber composition for a sidewall of the present invention has excellent ozone resistance.

[0026] Each component constituting the rubber composition of the present invention will be described below. (rubber component) The rubber composition for a sidewall 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, even more preferably 90% by mass or more, and particularly preferably 100% by mass. Here, the "sustainability rate" of the rubber component refers to the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources (recycled resources) in the rubber component.

[0027] The rubber component is preferably the rubber derived from biological resources or the rubber derived from recycled resources. Here, the proportion of the monomer components 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, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol%. Furthermore, the proportion of the monomer components 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, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may be 100 mol%.

[0028] 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 is 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, for example, by converting it into standard polystyrene based on a measurement value obtained by gel permeation chromatography (GPC) (GPC-8000 series, manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M, manufactured by Tosoh Corporation).

[0029] The rubber component is preferably a diene rubber, and the diene rubber is preferably an isoprene rubber or a butadiene rubber. Here, the isoprene rubber refers to a rubber containing units derived from isoprene as a monomer unit, and the butadiene rubber refers to a rubber containing units derived from butadiene as a monomer unit.

[0030] Examples of the isoprene-based rubber include natural rubber (NR), synthetic isoprene rubber (IR), modified natural rubber (modified NR), modified natural rubber (modified NR), and modified synthetic isoprene rubber (modified IR). Examples of natural rubber (NR) that can be used include those commonly used in the tire industry, such as RSS#3 and TSR20 (e.g., SIR20 and STR20). The origin of the natural rubber (NR) is not particularly limited, and examples include those derived from Hevea brasiliensis, guayule, and Russian dandelion. Examples of synthetic isoprene rubber (IR) are not particularly limited, and examples include those commonly used in the tire industry, such as IR2200. Examples of modified NR include deproteinized natural rubber (DPNR) and highly purified natural rubber (UPNR). Examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Examples of modified IR include epoxidized synthetic isoprene rubber, hydrogenated synthetic isoprene rubber, and grafted synthetic isoprene rubber. These isoprene-based rubbers may be used alone or in combination of two or more. Among these, NR is preferred as the isoprene-based rubber.

[0031] The isoprene-based rubber preferably has a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, still more preferably 60% by mass or more, still 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. To achieve a sustainability ratio of the isoprene-based rubber within the above range, it is preferable to use natural rubber (NR) or a polymer synthesized using isoprene derived from biological resources or isoprene derived from recycled resources as a monomer component. In this case, the synthesized polymer may be a homopolymer of a monomer derived from biological resources, a homopolymer of a monomer derived from recycled resources, a copolymer of a monomer derived from biological resources and a monomer derived from recycled resources, or a copolymer of a monomer derived from biological resources and / or a monomer derived from recycled resources and a monomer derived from fossil resources (petroleum, etc.).

[0032] Examples of the butadiene rubber include butadiene rubber (BR), aromatic vinyl compound-butadiene copolymer rubber (for example, styrene-butadiene rubber (SBR)), etc. Here, butadiene, which is a raw material for butadiene rubber, is preferably derived from biological resources or recycled resources.

[0033] 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.

[0034] 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. Commercially available products can be used as the aromatic vinyl compound-butadiene copolymer rubber, and examples of such commercially available products include products from Asahi Kasei Corporation, ENEOS Materials Corporation, Nippon Zeon Corporation, Sumitomo Chemical Co., Ltd., etc. These aromatic vinyl compound-butadiene copolymer rubbers may be used singly or in combination of two or more.

[0035] The butadiene-based rubber preferably has a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, still more preferably 60% by mass or more, still 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. To achieve the sustainability rate of the butadiene-based rubber within the above range, for example, a polymer synthesized using biological resource-derived butadiene, recycled resource-derived butadiene, biological resource-derived aromatic vinyl compounds (e.g., biological resource-derived styrene), or recycled resource-derived aromatic vinyl compounds (e.g., recycled resource-derived styrene) as monomer components 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. Biological resource (biomass resource)-derived butadiene rubber (B-BR) and biological resource-derived aromatic vinyl compound-butadiene copolymer rubber (e.g., biological resource (biomass resource)-derived styrene-butadiene rubber (B-SBR)) 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.

[0036] 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.

[0037] Generally, the raw materials for rubber compositions for tires (rubber and its monomers, fillers, resins, etc.) require large-scale manufacturing equipment 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 finished 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 rubber, fillers, steel cords, and other tire-constituting materials. In addition, sulfur can be obtained from biological resources or processed products of biological resources by a method including a desulfurization step of desulfurizing biological resources or processed products of biological resources to remove sulfur-containing substances from the biological resources or processed products of biological resources, a recovery step of recovering sulfur from the desulfurization residue generated in the desulfurization step, and a processing step of processing the recovered sulfur into sulfur for vulcanization (e.g., the method described in WO 2024 / 048141), and raw materials for tire rubber compositions can be obtained from various wastes and used items. In this way, the use of sustainable materials (materials derived from biological resources or recycled resources) can reduce the overall environmental impact of tire manufacturing by reducing carbon dioxide emissions over the entire life cycle (LCCO2), reducing energy consumption over the entire life cycle (LCE), reducing life cycle costs (LCC), and reducing the use of fossil resources.

[0038] 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.

[0039] The ratio of each monomer unit (e.g., units derived from isoprene, units derived from butadiene, and units derived from aromatic vinyl compounds) in the entire rubber component can be adjusted appropriately depending on the components to which the rubber is applied. The ratio of each monomer unit in the entire rubber component can be adjusted, for example, by appropriately combining the above-mentioned isoprene-based rubber and butadiene-based rubber. Furthermore, 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 "unit derived from isoprene" refers to a structural unit in a polymer constituted based on the monomer isoprene (including the isoprene unit in natural rubber), the term "unit derived from butadiene" refers to a structural unit in a polymer constituted based on the monomer butadiene, and the term "unit derived from an aromatic vinyl compound" refers to a structural unit in a polymer constituted based on the monomer aromatic vinyl compound. In this specification, the ratio of each monomer unit is measured by NMR.

[0040] The rubber component may contain diene rubbers such as acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), styrene-isoprene-butadiene copolymer rubber (SIBR), etc., in addition to the above-mentioned isoprene-based rubber, butadiene rubber (BR), and aromatic vinyl compound-butadiene copolymer rubber (e.g., SBR). These rubber components may be used singly or in combination of two or more.

[0041] The rubber component may be modified to introduce functional groups that interact 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 also have a substituent. These functional groups may be introduced into the rubber component either individually or in combination. Among these, amino groups, alkoxy groups, and alkoxysilyl groups are preferred, and substituted amino groups in which the hydrogen atom of an amino group is substituted with an alkyl group having 1 to 6 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, and alkoxysilyl groups having 1 to 6 carbon atoms are more preferred.

[0042] 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 modifying functional group that interacts with fillers such as silica and carbon black, and examples thereof include a nitrogen-containing functional group, a silicon-containing functional group, and an oxygen-containing functional group. Examples of compounds (modifiers) having a nitrogen-containing functional group include amino group-containing compounds. 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.

[0043] 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.

[0044] 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 a monomer component, a bioresource (biomass resource)-derived butadiene rubber (B-BR) can be obtained. Furthermore, by using styrene obtained from a bioresource and butadiene obtained from a bioresource as monomer components, a bioresource (biomass resource)-derived styrene-butadiene rubber (B-SBR) can be obtained. 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.

[0045] 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 also be used in combination. As the styrene obtained from the biological resources, styrene obtained from plants (preferably plants belonging to the Hamamelidaceae, Styraxaceae, and Apocynaceae families, more preferably plants belonging to the genus Liquidambar, Styrax rostrata, and Catharanthus roseus, and even more preferably Sweetgum, Styrax rostrata, and Catharanthus roseus), and styrene obtained from microorganisms (preferably microorganisms belonging to the genus Penicillium or Escherichia, more preferably P. citrinum or transformed E. coli) can be suitably used. Two or more of these styrenes may also be used in combination.

[0046] Recently, biomass industrial complexes focused on bioethanol, bioethylene, and the like have been planned. However, bioethanol and bioethylene are produced primarily from 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, or to combine monomer components derived from biological resources, monomer components derived from renewable resources, and monomer components derived from fossil resources, and to use these monomer components in appropriate ratios. This allows for the effective use 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 contributes to environmental considerations depending on the production conditions.

[0047] 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.

[0048] 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, followed by devulcanization, 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 effects. Furthermore, the modified reclaimed rubber is advantageous for improving problems such as reduced reinforcement that can occur when using reclaimed materials, because the crosslinked structures in the rubber are partially cleaved by devulcanization and functionalization, increasing its reactivity. For example, it can be produced by functionalizing reclaimed rubber or vulcanized rubber powder (powdered rubber) that has functional groups that can react with unvulcanized diene rubber with a modifying compound (introducing a modifying compound). The reclaimed rubber is not particularly limited, and examples include ground rubber that is mechanically ground at room temperature or in a frozen state, devulcanized rubber that has been further devulcanized, recycled rubber from used automobile tires, tubes, and other rubber products as specified in JIS K6313, and reclaimed rubber with equivalent properties.

[0049] Furthermore, from the viewpoint of improving durability without sacrificing 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 rubber 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.

[0050] 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 aminoquinoline-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.

[0051] Furthermore, the rubber component preferably contains a modified conjugated diene polymer, and the modified conjugated diene polymer preferably has two or more modifying groups in one molecule of the modified conjugated diene polymer, the modifying groups have a non-covalent bond between the molecules, and the energy per non-covalent bond is preferably 10 to 250 kJ / mol. The modified conjugated diene polymer has low loss (low heat buildup) and excellent durability. Without wishing to be bound by theory, it is presumed that the intermolecular modifying groups have a non-covalent bond with a weak bond energy within the above-mentioned specific range, and therefore, in a crosslinked product of the modified conjugated diene polymer, the non-covalent bond is maintained at low strain, resulting in excellent low loss, while at high strain, the non-covalent bond is broken, resulting in hysteresis loss, resulting in excellent durability. Furthermore, the modified conjugated diene polymer also improves wet grip performance. Without wishing to be bound by theory, it is generally believed that when gripping, the rubber containing the crosslinked product of the modified conjugated diene polymer undergoes significant deformation, and during this deformation, the above-mentioned non-covalent bonds are broken, and the resulting energy loss is presumed to improve not only durability but also wet grip performance. Therefore, the rubber composition for tread containing the modified conjugated diene polymer as the rubber component has low loss properties and excellent durability.

[0052] Here, the energy per non-covalent bond between modifying groups in the modified conjugated diene polymer is calculated using Gaussian09 as a quantum chemistry calculation program with M06 / 6-31G(d,p) as the basis function. 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.

[0053] The weight-average molecular weight (Mw) of the modified conjugated diene polymer was determined by gel permeation chromatography (GPC: Tosoh HLC-8020, column: Tosoh GMH-XL (two columns in series), detector: differential refractometer (RI)) using a calibration curve prepared from monodisperse polystyrene. When a modifier is used, the polymerization reaction is terminated by adding an appropriate amount of degassed isopropanol to the polymerization system before adding the modifier. 0.5 mL of an isopropanol solution of 2,6-di-t-butyl-p-cresol (BHT) (BHT concentration: 5% by mass) is added, and the polymer is isolated according to a standard method. The weight-average molecular weight of the resulting modified conjugated diene polymer is then measured to determine the weight-average molecular weight in terms of polystyrene before reacting the active terminals with the modifier.

[0054] In the modified conjugated diene 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.

[0055] The modified conjugated diene polymer may be, for example, (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 polymer; (ii) after the step (i), further adding an alkali metal compound to the conjugated diene-based polymer; and (iii) The product obtained in step (ii) is reacted with a modifying agent to introduce a modifying group into the conjugated diene polymer.

[0056] (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, sometimes simply referred to as step (i)) can be carried out in the same manner as the conventionally known anionic polymerizations described in, for example, JP-A Nos. 2013-249379, 2016-003246, and 2014-227458.

[0057] 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 compounds 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, hi another embodiment, the conjugated diene compound is solely 1,3-butadiene.

[0058] 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 polymer in step (i) may be collectively referred to as monomers.

[0059] 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%.

[0060] Examples of aromatic vinyl compounds that can be used in step (i) include styrene, alkylstyrene, halogenated alkylstyrene, etc. The aromatic vinyl compounds may be used alone or in combination of two or more. The number of carbon atoms in the alkyl group of the alkylstyrene is, for example, 1 to 5. Examples of alkylstyrene include 4-methylstyrene, 3-methylstyrene, and 2,4-dimethylstyrene. The number of carbon atoms in the alkyl group of the halogenated alkylstyrene is, for example, 1 to 5. Examples of the halogen in the halogenated alkylstyrene include fluorine, chlorine, bromine, and iodine. Examples of the halogenated alkylstyrene include 4-chloromethylstyrene and 3-chloromethylstyrene. In the production of the modified conjugated diene polymer, the aromatic vinyl compound preferably contains styrene and at least one selected from the group consisting of alkylstyrenes and halogenated alkylstyrenes, which makes it easier to introduce the modifying group. In the production of the modified conjugated diene polymer, it is preferable that the monomers forming the conjugated diene polymer contain at least one selected from the group consisting of alkylstyrenes and halogenated alkylstyrenes in a total amount of 0.1 to 3 mass %, which ensures low loss and excellent durability while ensuring workability during production. In the production of the modified conjugated diene polymer, it is preferable that the alkylstyrene is 4-methylstyrene and the halogenated alkylstyrene is 4-chloromethylstyrene, which makes it easier to introduce the modifying group.

[0061] 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%.

[0062] 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 the non-conjugated olefin 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 olefin 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., at least one 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, it can be efficiently copolymerized with a conjugated diene compound. 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.

[0063] 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.

[0064] Organoalkali metal compounds include, for example, hydrocarbyl lithium and lithium amide compounds. The hydrocarbyllithium is preferably, for example, one having a hydrocarbyl group having 2 to 20 carbon atoms, and examples thereof include 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 with butyllithium. Examples of the lithium amide compound 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, since it allows the modified conjugated diene polymer to be synthesized more efficiently. The amount of the alkali metal compound used in step (i) 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.

[0065] (ii) After step (i), 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-based polymer (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, since it allows the modified conjugated diene polymer to be synthesized more efficiently. 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, because these compounds can be synthesized more efficiently.

[0066] After step (i), an alkali metal compound is further added separately in step (ii) to introduce an alkali metal atom (substituting a hydrogen atom in the hydrocarbon chain with an alkali metal atom) into a portion of the polymer main chain of the conjugated diene polymer formed in step (i) other than one end (e.g., in the middle of the polymer main chain), 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 the alkali metal compound is added all at once in step (i) without performing step (ii), i.e., without further addition of an alkali metal compound, the number of reaction initiation sites for anionic polymerization when forming a conjugated diene polymer increases, and the molecular weight of the conjugated diene polymer decreases. As described above, the alkali metal atom is not introduced into any portion of the polymer main chain of the conjugated diene polymer other than one end. Therefore, even if a modifying group is introduced by reacting this conjugated diene polymer having an alkali metal compound introduced only into one end with a modifying agent, it is difficult to increase the number of modifying groups to two or more, and it is difficult to obtain the modified conjugated diene polymer. Therefore, in order to introduce an alkali metal atom capable of reacting with a modifier into a portion of the polymer main chain of the conjugated diene-based polymer formed in step (i) other than one end thereof, it is necessary to further add an alkali metal compound after step (i).

[0067] In step (ii), for example, when styrene is used as the aromatic vinyl compound, the alkali metal atom is introduced at the tertiary carbon atom at the bond between styrene and the polymer main chain. Alternatively, when styrene and 4-methylstyrene are used as the aromatic vinyl compounds, alkali metal atoms are introduced at the tertiary carbon atom at the bond between styrene and the polymer main chain, as well as at the tertiary carbon atom at the bond between 4-methylstyrene and the polymer main chain and the primary carbon atom of the methyl group at the 4th position. In this case, the primary carbon atom is less sterically hindered than the tertiary carbon atom, so the alkali metal atom is presumably preferentially introduced to the primary carbon atom. Furthermore, in systems of polymers that do not contain aromatic vinyl compounds, although activity is lower than in the case of aromatic vinyl compounds, it is thought 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.

[0068] 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.

[0069] 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.

[0070] 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 % relative to the monomers forming the modified conjugated diene polymer, and preferably 0.1 to 1 mass %, which ensures low loss and excellent durability while ensuring workability.

[0071] (iii) The product obtained in step (ii) is reacted 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 in this step include carbon dioxide and carbon disulfide. In the production of the modified conjugated diene polymer, the modifying agent is preferably carbon dioxide gas, which allows polar groups to be easily introduced into the non-polar polymer. The amount of the modifier is not particularly limited and may be adjusted as appropriate. For example, when carbon dioxide gas is used as the modifier, carbon dioxide gas may be blown into the solution containing the product of step (ii) until the color disappears. For example, when carbon dioxide gas 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.

[0072] In the modified conjugated diene polymer, the modifying group is preferably at least one selected from the group consisting of -COOM and -OM (M is an alkali metal atom), which allows the introduction of a coordinate bond with an appropriate bond energy. In the modified conjugated diene polymer, the modifying group is preferably at least one selected from the group consisting of -COOLi and -OLi, which allows the introduction of a coordinate bond with an appropriate bond energy. The modified conjugated diene polymer has two or more modifying groups per molecule. From the viewpoint of further improving low loss properties and durability, the number of modifying groups per molecule is preferably three or more. From the viewpoint of handleability, the number of modifying groups per molecule is preferably 30 or less.

[0073] 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). For simplicity of explanation, this example shows an intermediate product in which a 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 can 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. [ka]

[0074] The modified conjugated diene polymer obtained in the above example has -COOLi as a modifying group, and for example, the O atom of the carbonyl group in this modifying group coordinates to a Li atom in the 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, the O atoms of the carbonyl groups in the modifying groups in two more modified conjugated diene polymer molecules can coordinate to the Li atom.

[0075] In producing 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).

[0076] 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.

[0077] 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.

[0078] The molecular weight of the modified conjugated diene polymer is not particularly limited and may be adjusted appropriately. 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 modified conjugated diene polymer preferably has a weight average molecular weight of 100,000 or more, which allows for a high degree of compatibility between low loss properties and durability.

[0079] 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, thereby achieving low loss and excellent durability. The modified conjugated diene polymers may be used singly or in combination of two or more.

[0080] The content 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 content 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.

[0081] (Aminoquinoline antioxidant) The rubber composition for a sidewall of the present invention contains an aminoquinoline antioxidant represented by general formula (1). [ka] By including the aminoquinoline antioxidant represented by general formula (1), the ozone resistance of the rubber composition can be improved.

[0082] In the above general formula (1), TIFF2025169651000007.tif11162 is a single bond or a double bond, preferably a double bond; R 11 and R 12 are each independently a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a phenyl group, and are preferably a hydrogen atom or a phenyl group; R 13 , R 14 , R 15 , R 16 , R 17 , R 18 and R 19 are each independently hydrogen or an alkyl group having 1 to 12 carbon atoms, and are preferably hydrogen or a methyl group. R in the above general formula (1) 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 and R 19 With regard to the above, the alkyl group having 1 to 12 carbon atoms may be linear or branched. Examples of the alkyl group having 1 to 12 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, and various decyl groups. The number of carbon atoms in the alkyl group is preferably in the range of 1 to 8, more preferably 1 to 6, even more preferably 1 to 4, and particularly preferably 1 to 3. R in the above general formula (1) 11 and R 12With regard to the above, examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a 1-methylcyclopentyl group, a 2-methylcyclopentyl group, and a 3-methylcyclopentyl group.

[0083] Specific examples of the aminoquinoline antioxidant represented by the general formula (1) include compounds represented by the following structural formulas (1-1) to (1-47). [ka] [ka]

[0084] Furthermore, among the compounds represented by general formulas (1-1) to (1-47), it is preferable to use the compound represented by general formula (1-1) as the aminoquinoline antioxidant, since this allows for better ozone resistance to be obtained.

[0085] The method for producing the aminoquinoline antioxidant represented by the general formula (1) is not particularly limited. For example, when an aromatic amine compound is used as a starting material, (i) reacting an aromatic amine compound with sodium nitrite in the presence of an acid to produce an aromatic amine compound having a nitroso group; (ii) reducing the generated nitroso group with sodium borohydride or the like to generate an aromatic diamine compound; (iii) The resulting aromatic diamine compound is reacted with a ketone compound such as acetone to form a condensed ring, A compound having a 6-amino-1,2-dihydroquinoline skeleton, that is, a compound represented by the above general formula (1), Compounds can be prepared in which TIFF2025169651000010.tif11154 is a double bond. Also, if desired, (iv) The compound having a 6-amino-1,2-dihydroquinoline skeleton thus produced is reduced with hydrogen in the presence of a palladium-supported carbon catalyst to produce a compound having a 6-amino-1,2,3,4-tetrahydroquinoline skeleton, i.e., a compound represented by the above general formula (1), It is also possible to prepare compounds in which TIFF2025169651000011.tif9154 is a single bond.

[0086] The content of the aminoquinoline 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 aminoquinoline 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 aminoquinoline antioxidant is 11 parts by mass or less per 100 parts by mass of the rubber component, adverse effects on rubber properties other than ozone resistance (heat buildup, etc.) can be more reliably suppressed, making the rubber suitable for tire sidewall applications. The content of the aminoquinoline antioxidant is more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, and particularly preferably 3 parts by mass or more, per 100 parts by mass of the rubber component from the viewpoint of improving ozone resistance. Also, the content of the aminoquinoline antioxidant is more preferably 10.5 parts by mass or less, even more preferably 10 parts by mass or less, per 100 parts by mass of the rubber component from the viewpoint of suppressing adverse effects on other rubber physical properties.

[0087] (Other quinoline antioxidants) Furthermore, from the viewpoint of obtaining better ozone resistance and maintaining the elongation at break (EB) and tensile strength (TB) after aging, the rubber composition for a sidewall of the present invention preferably further contains a quinoline-based antioxidant other than the aminoquinoline-based antioxidant represented by the general formula (1) above (hereinafter, sometimes simply referred to as "other quinoline-based antioxidant"). The other quinoline-based antioxidant is an antioxidant having a quinoline moiety or a derivative thereof (dihydroquinoline moiety, tetrahydroquinoline moiety, etc.).

[0088] The other quinoline antioxidant preferably has a dihydroquinoline moiety, more preferably a 1,2-dihydroquinoline moiety. Specific examples of the other quinoline-based antioxidants include a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline (antioxidant TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, and the like. The other quinoline antioxidant preferably contains a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline (antiaging agent TMDQ). Quinoline antioxidants containing a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline are highly effective in improving the ozone resistance of the rubber composition, and also have the advantage of being less likely to discolor the rubber composition. Examples of the polymer of 2,2,4-trimethyl-1,2-dihydroquinoline include a dimer, trimer, and tetramer of 2,2,4-trimethyl-1,2-dihydroquinoline.

[0089] Furthermore, in the rubber composition for sidewalls of the present invention, it is more preferable that the mass ratio of the content of the other quinoline-based antioxidants to the content of the aminoquinoline-based antioxidant (content of quinoline-based antioxidant / content of aminoquinoline-based antioxidant) is 0.05 to 0.35. By using the aminoquinoline antioxidant represented by the general formula (1) in combination with another quinoline antioxidant, and setting the mass ratio of the content of the other quinoline antioxidant to the content of the aminoquinoline antioxidant within the above range (0.05 to 0.35), the ozone resistance of the rubber composition can be further improved, and decreases in the elongation at break (EB) and tensile strength (TB) of the aged rubber composition can be further suppressed. When the mass ratio of the content of the other quinoline antioxidant to the content of the aminoquinoline antioxidant is 0.05 or more, higher ozone resistance can be ensured when applied to the sidewall portion, 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 applied to the sidewall portion.

[0090] In addition, in the rubber composition for sidewalls of the present invention, by setting the mass ratio of the content of the other quinoline-based antioxidants to the content of the aminoquinoline-based antioxidant (content of other quinoline-based antioxidants / content of aminoquinoline-based antioxidants) to 0.05 to 0.35, adverse effects on rubber properties other than ozone resistance (heat buildup, etc.) can be suppressed, making the composition suitable for sidewall applications. Furthermore, from the viewpoint of further improving the ozone resistance of the rubber composition and the retention rate of elongation at break (EB) and tensile strength (TB) after aging while suppressing adverse effects on rubber properties other than ozone resistance, the mass ratio of the content of the other quinoline antioxidants to the content of the aminoquinoline antioxidant (content of other quinoline antioxidants / content of aminoquinoline antioxidant) is preferably 0.10 to 0.35, more preferably 0.20 to 0.34, and even more preferably 0.26 to 0.32.

[0091] 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 properties other than ozone resistance, the content of the other quinoline antioxidant is preferably 0.1 to 5 parts by mass per 100 parts by mass of the rubber component. When the content of the other quinoline 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 other quinoline antioxidant is 5 parts by mass or less per 100 parts by mass of the rubber component, adverse effects on rubber properties other than ozone resistance (such as heat buildup) can be suppressed, making the rubber composition suitable for sidewall applications. In order to further improve ozone resistance, the amount of the other quinoline antioxidant is preferably 0.3 parts by mass or more, and more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, in order to more reliably suppress adverse effects on other rubber physical properties, the amount is 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.

[0092] (Other antioxidants) The rubber composition for sidewalls of the present invention may contain antioxidants other than the aminoquinoline antioxidants and other quinoline antioxidants. Examples of such antioxidants include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N,N'-diphenyl-p-phenylenediamine (DPPD), and N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine. However, it is preferable to exclude N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD). Commercially available antioxidants are available, including those from Ouchi Shinko Chemical Industry Co., Ltd., Sumitomo Chemical Co., Ltd., Seiko Chemical Co., Ltd., and Flexis. These antioxidants may be used alone or in combination of two or more.

[0093] (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, the ozone resistance is further improved. Examples of the wax include natural waxes such as vegetable waxes and animal waxes; 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., etc. These waxes may be used alone or in combination of two or more.

[0094] 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 can efficiently produce 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 of these components 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.

[0095] 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.

[0096] (sulfur) The rubber composition for a sidewall of the present invention preferably contains sulfur. When the rubber composition contains sulfur, it becomes vulcanizable, 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, but ordinary sulfur (soluble sulfur (powdered sulfur) and the like) is preferable to insoluble sulfur, and oil treat sulfur and the like are 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. If the sulfur content is 0.1 part by mass or more per 100 parts by mass of the rubber component, better durability of the vulcanized rubber can be ensured, and if the sulfur content is 10 parts by mass or less per 100 parts by mass of the rubber component, better rubber elasticity can be ensured.

[0097] (carbon black) Furthermore, the rubber composition for a sidewall of the present invention may contain carbon black, if necessary. As the carbon black, plant-derived carbon black and recycled carbon black are particularly preferred. Examples of plant-derived carbon black include those derived from castor oil and pine oil. Examples of recycled carbon black include carbon black obtained by pyrolysis of used tires and carbon black obtained from waste oil. The grade of the carbon black is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available carbon black products can be used, including those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Nippon Steel Carbon Co., Ltd., and Birla Carbon. These carbon blacks may be used alone or in combination.

[0098] Furthermore, the nitrogen adsorption specific surface area (N2SA) of the carbon black is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which it is applied, the tire components, the target performance, etc. For example, the nitrogen adsorption specific surface area (N2SA) of carbon black is 20 m 2 / g or more is preferable, and 50m 2 / g or more is more preferable, and 70m 2 / g or more is more preferable, and 90m 2 / g or more is more preferable, and 200m 2 / g or less is preferable, and 150m 2 / g or less is more preferable, and 130m 2 / g or less is more preferable. In this specification, the nitrogen adsorption specific surface area (N2SA) of carbon black is determined according to JIS K 6217-2:2017 (ISO 4652:2012).

[0099] The content of the carbon black is not particularly limited and can be appropriately adjusted depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of the carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component.

[0100] (silica) Furthermore, the rubber composition for a sidewall of the present invention may 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 can be used, including those from Tosoh Silica Corporation, Evonik, Solvay, Solvay Japan, and Tokuyama Corporation. The silica may also be a commercially available product, for example, Zeosil Premium 200MP (trade name) from Rhodia. The silica may be used alone or in combination of two or more.

[0101] From the viewpoint of reducing environmental impact, silica derived from siliceous plants is preferred. Examples of siliceous plants include mosses, ferns, horsetails, Cucurbitaceae, Urticaceae, and Gramineae. 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 them easy to secure. Therefore, from the viewpoint of availability, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferred. The use of rice husk silica allows for the effective use of rice husks, which are industrial waste. Furthermore, since the raw material can be procured locally near tire manufacturing plants, the energy and costs for transportation and storage can be reduced, 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), 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 a method such as that described in JP 2019-38728 A.

[0102] Furthermore, the silica has a nitrogen adsorption specific surface area (N2SA) of 50 m 2 / g or more, and 100m 2 / g or more is more preferable, and 150m2 / g or more is more preferable, and 2 / g or less, and 250m 2 / g or less is more preferable, and 2 / g or less is more preferable, and 2 It is even more preferable that the saturation coefficient is 1 / g or less. In this specification, the nitrogen adsorption specific surface area (N2SA) of silica is a value measured by the BET method in accordance with ASTM D3037-93.

[0103] The content of 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, relative to 100 parts by mass of the rubber component, is 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 is 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.

[0104] (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 to enhance 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, and 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide. Examples of the silane coupling agent 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. Commercially available silane coupling agents can be used, and examples of commercially available silane coupling agents that can be used include products from Evonik, Momentive, Shin-Etsu Silicones, Dow Corning Toray Co., Ltd., Tokyo Chemical Industry Co., Ltd., and AZMAX Corporation. These silane coupling agents may be used alone or in combination of two or more.

[0105] 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.

[0106] Bioethanol can also be used as a raw material for the silane coupling agent. Bioethanol is produced primarily from 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 monomer components derived from biological resources, monomer components derived from renewable resources, and monomer components derived from fossil resources. This allows for the effective use of a wide range of biological resources and renewable resources, such as sugars, proteins, and lipids, without relying on a single type of biological resource, and also allows for environmental considerations depending on the production conditions.

[0107] (resin) The rubber composition for a sidewall of the present invention may further contain a resin. Examples of such resins include terpene resins, rosin resins, C5 resins, C5-C9 resins, C9 resins, cyclopentadiene resins, aromatic resins, coumarone resins, indene resins, coumarone-indene resins, olefin resins, polyurethane resins, and acrylic resins. These resins may be used alone or in combination of two or more. Among these resins, terpene resins, rosin resins, C5 resins, C5-C9 resins, C9 resins, cyclopentadiene resins, and aromatic resins are preferred, with terpene resins and rosin resins being particularly preferred. Terpene resins and rosin resins are naturally derived, sustainable resins that can further reduce environmental impact and further improve tire performance. C5 resins, C9 resins, C5-C9 resins, and cyclopentadiene resins can improve reinforcement and fuel economy in a well-balanced manner. Furthermore, aromatic resins can improve reinforcement and other properties.

[0108] 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.

[0109] 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.

[0110] The terpene resin is a solid resin obtained by polymerizing turpentine, which is obtained simultaneously with the extraction of rosin from pine trees, or a polymerization component separated from the turpentine, 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. Styrene-terpene resins 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.

[0111] 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.

[0112] Furthermore, maleic acid-modified rosin resins 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 improved. 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).

[0113] 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 due to the influence of ambient 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, forming fracture nuclei, which is undesirable. 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.

[0114] 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 and tensile elongation at break decrease, resulting in poor fracture resistance. 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 temperature exceeds 180°C, heat generation worsens. 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.

[0115] The weight-average molecular weight of the maleic acid-modified rosin resin is preferably 500 to 5000, more preferably 1000 to 4000. By setting 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 as the standard.

[0116] 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 Co., Ltd. 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.

[0117] Examples of the C5 resin include aliphatic petroleum resins obtained by (co)polymerizing C5 fractions obtained by thermal cracking of naphtha in the petrochemical industry. C5 fractions typically include 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.

[0118] The C5-C9 resin refers to a C5-C9 synthetic petroleum resin, and examples of the C5-C9 resin include petroleum-derived C5-C 11 Examples of suitable C5-C9 resins include solid polymers obtained by polymerizing the fraction using a Friedel-Crafts catalyst such as AlCl3 or BF3. More specifically, examples include copolymers primarily composed of styrene, vinyltoluene, α-methylstyrene, indene, etc. As the C5-C9 resin, a resin with a low content of C9 or higher components is preferred from the viewpoint of compatibility with the rubber component. Here, "low content of C9 or higher components" means that the content of C9 or higher components in the total resin is less than 50 mass%, preferably 40 mass% or less.

[0119] The C9 resin refers to a C9 synthetic petroleum resin, such as a solid polymer obtained by polymerizing a C9 fraction using a Friedel-Crafts catalyst such as AlCl3 or BF3. Examples of the C9 resin include copolymers containing indene, α-methylstyrene, vinyltoluene, etc. as main components.

[0120] 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 with another monomer. 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 refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts catalyst such as AlCl3 or BF3. Examples of dicyclopentadiene resins include homopolymers of dicyclopentadiene, copolymers of dicyclopentadiene and aromatic monomers, and copolymers of dicyclopentadiene and C9 fractions (vinyltoluene, indene, etc.).

[0121] The aromatic resin refers to a resin containing a unit derived from an aromatic monomer as a monomer unit. Examples of the aromatic resin include a homopolymer of an aromatic monomer, a copolymer of two or more aromatic monomers, and a copolymer of an aromatic monomer with another monomer. Examples of the aromatic monomer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and p-phenylstyrene; phenolic monomers such as phenol, alkylphenol, and alkoxyphenol; and naphthol monomers such as naphthol, alkylnaphthol, and alkoxynaphthol.

[0122] The resin may also be a mixture (mixed resin) of a hydrogenated styrene resin and an aromatic modified terpene resin.The rosin resin may also be a maleic acid modified rosin resin. The hydrogenated styrene resin is a resin obtained by hydrogenating a styrene resin made from a styrene monomer. Hydrogenating the styrene resin reduces the number of aromatic rings derived from styrene, improving dispersibility in diene rubber and accelerating 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.

[0123] 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.

[0124] The hydrogenated styrene resin is obtained by hydrogenating the aromatic rings in the styrene resin. The hydrogenation method is a conventionally known method 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 due to 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 by IR (infrared spectrophotometer) using the following formula: Hydrogenation rate (%)={(CD) / C}×100 C: Absorbance peak height due to aromatic ring before hydrogenation D: Absorbance peak height due to aromatic ring after hydrogenation The hydrogenated styrene resins may be used alone or in combination of two or more.

[0125] The molecular weight of the hydrogenated styrene resin is, in terms of polystyrene, a weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) 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.

[0126] 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.

[0127] 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).

[0128] 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 a resin is the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2015 (ISO 28641:2010) is measured using a ring and ball softening point tester.

[0129] Commercially available resins can be used, and examples of commercially available resins include those from ENEOS Corporation, Arakawa Chemical Industries, Ltd., ExxonMobil Corporation, Clayton Corporation, Yasuhara Chemical Co., Ltd., Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Clayton Polymers, Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., and Taoka Chemical Co., Ltd.

[0130] 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.

[0131] (rubber powder) 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 the purpose of 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 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 crumb may also be commercially available, such as those from Global Corporation or Nantong Huili Rubber Corporation. From the viewpoint of reducing the environmental load, 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.

[0132] 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.

[0133] The rubber powder has a volume average particle size of preferably 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 size of the rubber powder, the better, and there is no particular lower limit. In this specification, the volume average particle size is measured by a laser diffraction particle size distribution measuring device, for example, "CAPA500" manufactured by Horiba, Ltd.

[0134] The rubber powder preferably has an acetone extractable content of 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 extractables in the rubber crumb refers to the acetone extractables (%) determined by the acetone extraction method in accordance with JIS K6350.

[0135] 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, even more preferably 15 parts by mass or less, still 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.

[0136] (liquid softener) The rubber composition may contain a liquid softener. Here, the "liquid softener" refers to 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.

[0137] 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. The oil may be a commercially available product, such as 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.

[0138] 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.

[0139] 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.

[0140] (syndiotactic 1,2-polybutadiene) The rubber composition for a sidewall of the present invention preferably further contains syndiotactic 1,2-polybutadiene, and 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 polybutadiene contains a syndiotactic 1,2-polybutadiene having a molecular weight of 1,2,5 or more. By definition, the syndiotactic 1,2-polybutadiene is not included in the rubber component.

[0141] 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 is compatible with the rubber component, particularly natural rubber and synthetic isoprene rubber, and can therefore be partially immobilized in the 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 rubber component matrix, comprising a portion consisting of syndiotactic 1,2-polybutadiene crystals (crystalline portion) and a portion where the rubber component and syndiotactic 1,2-polybutadiene are compatible (compatible portion).

[0142] In a rubber composition for treads containing syndiotactic 1,2-polybutadiene, the above-mentioned three-dimensional network provides a high energy dissipation effect due to the crystalline portion and flexibility due to the compatible portion, so that a tire using such a rubber composition can achieve excellent mechanical strength. Furthermore, in the rubber composition of this embodiment, by using it in combination with an aminoquinoline antioxidant represented by general formula (1), high mechanical strength can be significantly maintained even after thermal degradation.

[0143] Whether or not the above-mentioned three-dimensional network is formed in the rubber composition can be determined, for example, by confirming from an atomic force microscope (AFM) elastic modulus image that the syndiotactic 1,2-polybutadiene forms a co-continuous network structure in the rubber component, which is the matrix polymer, particularly 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.

[0144] The rubber composition for a tread 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 viewpoint, 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).

[0145] 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.

[0146] 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 when measured with a differential scanning calorimeter.

[0147] 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 4That's it, 16.0 x 10 4 That's it, 17.0 x 10 4 That's 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 concentration 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 It can be as follows: The number average molecular weight of syndiotactic 1,2-polybutadiene can be determined by gel permeation chromatography in terms of polystyrene using monodisperse polystyrene as the standard.

[0148] 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.

[0149] The syndiotactic 1,2-polybutadiene preferably has a 1,2-bond content (the amount of 1,2-bonds in the microstructure of the 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 syndiotactic 1,2-polybutadiene is 1 H and 13 It can be determined by C nuclear magnetic resonance (NMR) analysis.

[0150] The syndiotactic 1,2-polybutadiene preferably has a syndiotacticity of 60% or more in 1,2-bonds. 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 syndiotactic 1,2-polybutadiene in 1,2-bonds 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 in syndiotactic 1,2-polybutadiene is as follows: 1 H and 13 It can be determined by C nuclear magnetic resonance (NMR) analysis.

[0151] The syndiotactic 1,2-polybutadiene preferably has a melting point of 85°C or higher and 180°C or lower. By making the melting point of the syndiotactic 1,2-polybutadiene 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 making the melting point of the syndiotactic 1,2-polybutadiene 180°C or lower, it is possible to facilitate the 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, 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 by a differential scanning calorimeter.

[0152] 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 the 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 the 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.

[0153] 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 content and number average molecular weight of syndiotactic 1,2-polybutadiene can be more reliably controlled within predetermined ranges.

[0154] 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. Examples of the (a) iron-containing compound include iron carboxylate, iron organophosphate, iron organophosphonate, iron organophosphinate, iron carbamate, iron dithiocarbamate, iron xanthate, iron α-diketonate, iron alkoxide or aryloxide, and organoiron compounds.

[0155] 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.

[0156] 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 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, pseudochromium halides, and organic chromium compounds.

[0157] 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.

[0158] 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.

[0159] (hydrazide compounds) The rubber composition for a tread of the present embodiment preferably further contains a hydrazide compound, and is preferably a hydrazide compound represented by the following general formulas (3-1), (3-2), and (3-3): [ka] [A is one selected from the group consisting of an aromatic ring, a substituted or unsubstituted hydantoin ring, and a saturated or unsaturated straight-chain 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; and R1 to R4 are one selected from the group consisting of a hydrogen atom, an alkyl group, a cycloalkyl group, and an aromatic ring having 1 to 18 carbon atoms, and may be the same or different.] It is more preferable that the rubber composition for a tread contains a hydrazide compound represented by any one of the following general formulas: wherein R is a hydrazide group; ...

[0160] 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.

[0161] 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.

[0162] Also, R 31 , R 32 , R 33 and R 34are a hydrogen atom, or an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, or an aromatic group (aromatic ring; substituted at the ortho, meta, or para position), and may be the same or different (the same applies to hydrazide compounds represented by the following general formula (II) or (III)).

[0163] Examples of the hydrazide compounds represented by the general formula (I) above include isophthalic dihydrazide and derivatives of adipic dihydrazide such as isophthalic di(1-methylethylidene)hydrazide, adipic di(1-methylethylidene)hydrazide, isophthalic di(1-methylpropylidene)hydrazide, adipic di(1-methylpropylidene)hydrazide, isophthalic di(1,3-dimethylpropylidene)hydrazide, adipic di(1,3-dimethylpropylidene)hydrazide, isophthalic di(1-phenylethylidene)hydrazide, and adipic di(1-phenylethylidene)hydrazide. However, in addition to these derivatives of isophthalic dihydrazide and adipic dihydrazide, derivatives of the dihydrazide compounds listed below also have similar effects. For example, derivatives such as terephthalic acid dihydrazide, azelaic acid dihydrazide, and succinic acid dihydrazide are included. Among these, derivatives of isophthalic acid dihydrazide are the most effective in that they provide a high effect of reducing heat buildup and a significant increase in Mooney viscosity, and can reduce the Mooney viscosity while maintaining low heat buildup.

[0164] 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.

[0165] Furthermore, as the hydrazide compound represented by the above general formula (II), a hydrazide compound represented by the following general formula can be used. [ka] (In the formula, R 1 , R 2 are each independently an alkyl group having 1 to 18 carbon atoms.)

[0166] 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 the groups may be methyl.

[0167] 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, 3-Hydroxy-N'-(2-furylmethylene)-2-naphthoic acid hydrazide, 3-Hydroxy-N'-(1-methylethylidene)-2-naphthoic acid hydrazide, 3-Hydroxy-N'-(1-methylpropylidene)-2-naphthoic acid hydrazide, 3-Hydroxy-N'-(1-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 can be mentioned, and preferred are 1-hydroxy-N'-(1-methylethylidene)-2-naphthoic acid hydrazide, 1-hydroxy-N'-(1-methylpropylidene)-2-naphthoic acid hydrazide, 1-hydroxy-N'-(1,3-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.

[0168] In the above general formula (III), Y is a pyridyl group or a hydrazino group. Examples of the hydrazide compounds represented by the 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 effective in reducing the Mooney viscosity while maintaining a high level of low heat buildup, and are therefore highly effective in the present invention.

[0169] The synthesis method of the hydrazide compounds represented by the above general formula (I), (II) or (III) is described, for example, in Pant, UC; Ramchandran, Reena; Joshi, BC Rev. Roum. Chim. (1979) 24(3), 471-82.

[0170] 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.

[0171] (Other ingredients) 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 needed. 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.

[0172] Among the other components, zinc oxide (ZnO) is used as a vulcanization accelerator. When the rubber composition further contains zinc oxide, 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.

[0173] Here, the content of zinc oxide is not particularly limited and can be adjusted appropriately depending on, for example, the tire category to which the rubber composition is applied, the tire components, the target performance, etc. For example, the content of 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.

[0174] 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.

[0175] 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.

[0176] The aminoquinoline antioxidant represented by the general formula (1) may be supported on any carrier, for example, an inorganic filler such as silica or calcium carbonate. The aminoquinoline antioxidant represented by the general formula (1) may be used in the form of 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 an ethylene-propylene-diene rubber (EPDM). The aminoquinoline antioxidant represented by the general formula (1) may be converted into a salt with an organic acid. The organic acid used to convert the salt is not particularly limited, but examples thereof include stearic acid.

[0177] (Method of manufacturing rubber composition for sidewall) The method for producing the rubber composition for a sidewall of the present invention is not particularly limited, but the composition can be produced, for example, by blending the above-mentioned rubber component and aminoquinoline-based antioxidant with suitable components and other components appropriately selected as necessary, and kneading, heating, extruding, etc. The resulting rubber composition can be vulcanized to form a vulcanized rubber.

[0178] 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.

[0179] 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 roller typically used for heat-in of a rubber composition.

[0180] 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.

[0181] 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.

[0182] <Tires> The tire of the present invention is characterized by using the above-mentioned rubber composition for sidewalls of the present invention. As a result, the tire of the present invention has excellent ozone resistance in the sidewall portion. The rubber composition for sidewalls is required to be used in at least the sidewall portion of the tire, but may 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).

[0183] 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. [Example]

[0184] 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.

[0185] <Example 1, Comparative Example 1> According to the compounding recipe shown in Table 1, rubber compositions were produced.

[0186] <Evaluation> The ozone resistance of the obtained rubber composition samples was evaluated by the following method, and the results are shown in Table 1.

[0187] (1) Ozone resistance After a dynamic ozone degradation test (a test in which repeated strain is applied) was conducted in accordance with ISO 1431 (JIS K 6259), the sample was observed under a microscope at 20x magnification. The observed samples were ranked according to the size and depth of the cracks and classified according to the following criteria (1 to 5), with the smaller the number, the better the result. (Ranking based on crack size and depth) 1: Something that cannot be seen with the naked eye but can be seen with a 10x magnification glass. 2: Visible to the naked eye. 3: The crack is deep and relatively large (less than 1 mm). 4: The crack is deep and large (more than 1mm but less than 3mm). 5: Likely to cause cracks or cuts of 3mm or more.

[0188] [Table 1]

[0189] *1 NR: Natural rubber *2 BR: Butadiene rubber, cis-1,4 bond content 96% or more *3 Carbon black: Asahi Carbon Co., Ltd., product name "Asahi #65" *4 Antioxidant A: Other quinoline-based antioxidant, polymer of 2,2,4-trimethyl-1,2-dihydroquinoline, manufactured by Seiko Chemical Co., Ltd., product name "Nonflex RD" *5 Antioxidant B: An aminoquinoline-based antioxidant represented by the following formula (1-1) [ka] *6 Other chemicals: Total amount including at least oil, zinc oxide, stearic acid and vulcanization accelerator

[0190] The results in Table 1 show that all of the rubber compositions of the examples are superior in ozone resistance to the rubber compositions of the comparative examples.

[0191] [Contribution to the United Nations-led Sustainable Development Goals (SDGs)] The SDGs have been proposed to realize a sustainable society. One embodiment of the present invention is thought to be a technology that can contribute to the achievement of goals such as "No. 7 - Affordable and clean energy for all," "No. 12 - Responsible consumption and production," and "No. 13 - Take urgent action against climate change." [Industrial Applicability]

[0192] According to the present invention, it is possible to provide a rubber composition for a sidewall that is excellent in ozone resistance even when the antioxidant 6PPD is not used. Furthermore, according to the present invention, a tire having excellent ozone resistance in the sidewall portion can be provided.

Claims

1. A rubber component, The following general formula (1): 【Chemistry 1】 is a single or double bond, R １１ and R １２ are each independently a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or a phenyl group; R １３ , R １４ , R １５ , R １６ , R １７ , R １８ and R １９ are each independently hydrogen or an alkyl group having 1 to 12 carbon atoms; and A rubber composition for a sidewall, comprising:

2. 2. The rubber composition for a sidewall according to claim 1, further comprising a quinoline-based antioxidant other than the aminoquinoline-based antioxidant represented by the general formula (1).

3. 3. The rubber composition for a sidewall according to claim 1, wherein the rubber component contains at least one rubber selected from the group consisting of an isoprene skeleton rubber, a styrene-butadiene rubber, a butadiene rubber, and a chloroprene rubber.

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

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

6. The aminoquinoline antioxidant is represented by the following general formula (1-1): 【Chemistry 2】 The rubber composition for a sidewall according to claim 1 or 2, characterized in that the compound is a compound represented by the formula:

7. 3. The rubber composition for a sidewall according to claim 1, 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.

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

9. Furthermore, the compounds represented by the following general formulae (3-1), (3-2) and (3-3): 【Transformation 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 are 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 group, and may be the same or different.

3. The rubber composition for a sidewall according to claim 1, further comprising a hydrazide compound represented by any one of the following formulas:

10. The rubber component contains a modified conjugated diene polymer, 3. The rubber composition for a sidewall according to claim 1, wherein the modified conjugated diene polymer has two or more modifying groups in one molecule of the modified conjugated diene polymer, the modifying groups are bonded together via a non-covalent bond, and the energy per non-covalent bond is 10 to 250 kJ / mol.

11. A tire comprising the rubber composition for a sidewall according to claim 1 or 2.

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