Rubber composition, vulcanized rubber for tire tread, tire, and rubber crawler

Abstract

The present invention addresses the problem of providing a rubber composition capable of maintaining ozone resistance without using an antioxidant 6PPD while using a chemical having a small environmental load. A solution to the problem is a rubber composition which contains a diene-based rubber, an antioxidant, sulfur, and a vulcanization accelerator, and in which the vulcanization accelerator includes a thiuram-based vulcanization accelerator, and the antioxidant provides X that is -3.4 to -2.7 as determined by numerical formula (I). 　Numerical formula (I): X=1.2×A+0.31×B+0.28×C+1.25×D+0.04×E

Description

Rubber compositions, vulcanized rubber for tire treads, tires, and rubber tracks 【0001】 The present invention relates to rubber compositions, vulcanized rubber for tire treads, tires, and rubber tracks. 【0002】 In general, various rubber components that make up tires and the like can deteriorate under the influence of external environmental conditions such as the presence of ozone, and as this deterioration progresses, cracks and other problems may occur. To address this problem, rubber compositions containing antioxidants are often applied to the various rubber components that make up tires and the like. For example, Patent Document 1 below discloses that by applying a rubber composition containing a specific quinoline-based antioxidant and N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antioxidant 6PPD) to the rubber that makes up the surface of a tire, cracks and discoloration of the tire surface can be suppressed. 【0003】 International Publication No. 2018 / 056384 【0004】 However, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (anti-aging agent 6PPD) used in the rubber composition disclosed in Patent Document 1 may have environmental impacts. Therefore, considering the possibility of future regulations under European law, it is desirable to use an anti-aging agent that has a lower environmental impact. Thus, it is conceivable not to use the anti-aging agent 6PPD in the rubber composition. However, the inventors have investigated and found that if the anti-aging agent 6PPD is not used, the ozone resistance of the rubber composition decreases. 【0005】 Therefore, the present invention aims to solve the problems of the above-mentioned prior art and provide a rubber composition that can maintain ozone resistance without using the antioxidant 6PPD while using environmentally friendly chemicals. Furthermore, the present invention aims to provide a vulcanized rubber for tire treads obtained by vulcanizing such a rubber composition, a tire equipped with the vulcanized rubber for tire treads, and a rubber crawler equipped with the rubber composition. 【0006】 The gist of the present invention, which solves the above problems, is as follows. 【0007】 [1] A rubber composition comprising a diene rubber, an antioxidant, sulfur, and a vulcanization accelerator, wherein the vulcanization accelerator includes a thiram-based vulcanization accelerator, and the antioxidant satisfies the condition that X, calculated by the following formula (I), is between -3.4 and -2.7: X = 1.2 × A + 0.31 × B + 0.28 × C + 1.25 × D + 0.04 × E ... Formula (I) (In formula (I), A represents the descriptor MinEStateIndex of the antioxidant, B represents the descriptor MinAbsEStateIndex of the antioxidant, C represents the descriptor SlogP_VSA7 of the antioxidant, D represents the descriptor FractionCSP3 of the antioxidant, and E represents the descriptor NumRotatableBonds of the antioxidant.) 【0008】 [2] The rubber composition according to [1], wherein the vulcanization accelerator does not contain diphenylguanidine. 【0009】 [3] The rubber composition according to [1] or [2], wherein the content of the thiram-based vulcanization accelerator is 3 to 30 parts by mass per 100 parts by mass of sulfur. 【0010】 [4] The rubber composition according to any one of [1] to [3], wherein the vulcanization accelerator further comprises a sulfenamide-based vulcanization accelerator. 【0011】 [5] The rubber composition according to [4], wherein the content of the sulfenamide-based vulcanization accelerator is 50 to 120 parts by mass per 100 parts by mass of sulfur. 【0012】 [6] The rubber composition according to any one of [1] to [5], wherein the amount of the antioxidant is less than 5 parts by mass per 100 parts by mass of the diene rubber. 【0013】 [7] The rubber composition according to any one of [1] to [6], wherein the antioxidant is an amine-based antioxidant represented by the following general formula (1). (In general formula (1), R １ and R ２ These are each independently monovalent saturated hydrocarbon groups. 【0014】[8] The rubber composition according to any one of [1] to [7], further comprising one or more fillers selected from carbon black and silica. 【0015】 [9] The rubber composition according to [8], wherein the carbon black is recycled carbon black. 【0016】

[10] The rubber composition according to [8], wherein the silica is silica derived from rice husks. 【0017】

[11] The rubber composition according to [8] or [9], wherein the silica content is 50 parts by mass or more per 100 parts by mass of the diene rubber. 【0018】

[12] A vulcanized rubber for tire treads, obtained by vulcanizing any of the rubber compositions described in [1] to

[11] . 【0019】

[13] A tire having the vulcanized rubber for tire treads described in

[12] in the tread portion. 【0020】

[14] A rubber crawler using the rubber composition described in any of [1] to

[11] . 【0021】 According to the present invention, it is possible to provide a rubber composition that can maintain ozone resistance without using the anti-aging agent 6PPD, while using environmentally friendly chemicals. Furthermore, according to the present invention, it is possible to provide vulcanized rubber for tire treads obtained by vulcanizing such rubber composition, a tire equipped with said vulcanized rubber for tire treads, and a rubber crawler equipped with said rubber composition. 【0022】 The rubber composition, vulcanized rubber for tire treads, tire, and rubber crawler of the present invention will be described in detail below based on their embodiments. 【0023】 The compounds described herein may be derived in part or in whole from fossil resources, from biological resources such as plant resources, or from recycled resources such as used tires. They may also be derived from a mixture of two or more of fossil resources, biological resources, or recycled resources. 【0024】<Rubber Composition> The rubber composition of this embodiment is a rubber composition comprising a diene rubber, an antioxidant, sulfur, and a vulcanization accelerator, wherein the vulcanization accelerator includes a thiram-based vulcanization accelerator, and the antioxidant satisfies the condition that X, calculated by the following formula (I), is between -3.4 and -2.7. X = 1.2 × A + 0.31 × B + 0.28 × C + 1.25 × D + 0.04 × E ... Formula (I) (In Formula (I), A represents the descriptor MinEStateIndex of the antioxidant, B represents the descriptor MinAbsEStateIndex of the antioxidant, C represents the descriptor SlogP_VSA7 of the antioxidant, D represents the descriptor FractionCSP3 of the antioxidant, and E represents the descriptor NumRotatableBonds of the antioxidant.) In the rubber composition of this embodiment, ozone resistance can be maintained by using a thiram-based vulcanization accelerator in combination with an antioxidant that satisfies the condition that X, determined by the above formula (I), is within a specific range. Therefore, the rubber composition of this embodiment can maintain ozone resistance even without using the antioxidant 6PPD. Furthermore, because it does not use the antioxidant 6PPD, it has a low environmental impact. 【0025】 (Diene-based rubber) The rubber composition of this embodiment contains a diene-based rubber, which provides rubber elasticity to the composition. Preferred diene-based rubbers are isoprene-backed rubber, styrene-butadiene rubber (SBR), butadiene rubber (BR), and chloroprene rubber (CR). Here, isoprene-backed rubber is a rubber whose main backbone is isoprene units, and specifically, natural rubber (NR), synthetic isoprene rubber (IR), etc. When the diene-based rubber contains at least one selected from the group consisting of isoprene-backed rubber, styrene-butadiene rubber, butadiene rubber, and chloroprene rubber, the rubber elasticity of the rubber composition is excellent, making it a rubber composition more suitable for tire applications. The content of diene-based rubbers such as isoprene-backed rubber, styrene-butadiene rubber, butadiene rubber, and chloroprene rubber in the diene-based rubber is preferably 80% by mass or more, more preferably 90% by mass or more, and may be 100% by mass. The aforementioned diene-based rubber may be a single type or a blend of two or more types. 【0026】 (Antioxidant) The rubber composition of the present embodiment contains an antioxidant. The antioxidant has the function of preventing the aging of the rubber composition and rubber products using the same. As the antioxidant contained in the rubber composition of the present embodiment, there is no limitation as long as X obtained by the following mathematical formula (I) satisfies -3.4 or more and -2.7 or less. X = 1.2×A + 0.31×B + 0.28×C + 1.25×D + 0.04×E... Mathematical formula (I) (In the mathematical formula (I), A represents the descriptor MinEStateIndex of the antioxidant, B represents the descriptor MinAbsEStateIndex of the antioxidant, C represents the descriptor SlogP_VSA7 of the antioxidant, D represents the descriptor FractionCSP3 of the antioxidant, E represents the descriptor NumRotatableBonds of the antioxidant.) 【0027】 In the present invention, the descriptors of the antioxidant are obtained using the chemoinformatics tool RDKit in a Python environment from the molecular structure of each antioxidant represented by the SMILES notation. 【0028】 Examples of the antioxidant that satisfies X obtained by the above mathematical formula (I) being -3.4 or more and -2.7 or less include N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD, X = -3.3), N,N'-bis(sec-butyl)-p-phenylenediamine (44PD, X = -2.8), etc. 【0029】 The descriptor is a conversion of characteristic quantities such as molecular properties into numbers. 【0030】 The descriptor MinEStateIndex represents the lowest EStateIndex among all atoms in the molecule. EStateIndex is calculated based on a set of predefined atomic parameters such as electronegativity, atomic polarizability, resonance effect, etc. 【0031】 The descriptor MinAbsEStateIndex represents the lowest ESAbstateIndex value among all atoms in the molecule. 【0032】LogP is the logarithm of the partition coefficient (Po / w) of a substance in a 1-octanol / water two-phase solvent. In other words, LogP is an index value indicating the degree of hydrophobicity or hydrophilicity of the antioxidant. The descriptor SLogP is calculated by the calculation method of CCG. 【0033】 The descriptor FractionCSP3 represents the ratio of sp ３ carbon in all carbons in the molecule. 【0034】 The descriptor NumRotatableBonds represents the number of rotatable bonds in the molecule. 【0035】 In the rubber composition of the present embodiment, the content of the antioxidant is preferably less than 5 parts by mass with respect to 100 parts by mass of the diene rubber. When the content of the antioxidant is less than 5 parts by mass with respect to 100 parts by mass of the diene rubber, the product to which the rubber composition is applied is less likely to discolor, and the vulcanization rate is also easily controlled. The content of the antioxidant is more preferably 4.8 parts by mass or less, and still more preferably 4.3 parts by mass or less, with respect to 100 parts by mass of the diene rubber. Also, the content of the antioxidant is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and still more preferably 3.5 parts by mass or more, with respect to 100 parts by mass of the diene rubber. 【0036】 [Amine-based antioxidant] The antioxidant is preferably an amine-based antioxidant that satisfies -3.4 or more and -2.7 or less for X obtained by the above formula (I). More preferably, the amine-based antioxidant is represented by the following general formula (1). That is, it is more preferable that the antioxidant is an amine-based antioxidant that satisfies -3.4 or more and -2.7 or less for X obtained by the above formula (I) and is represented by the following general formula (1). (In the general formula (1), R １ and R ２(where each is independently a monovalent saturated hydrocarbon group.) The amine-based antioxidant represented by the general formula (1) contains a phenylenediamine moiety similar to N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antioxidant 6PPD), but is different from antioxidant 6PPD in that it has no double bond other than the phenylenediamine moiety. Also, the amine-based antioxidant represented by the general formula (1) has an effect of improving the ozone resistance of the rubber composition. Hereinafter, the amine-based antioxidant represented by the following general formula (1) that satisfies the condition that X obtained by the mathematical formula (I) is -3.4 or more and -2.7 or less is referred to as a "specific amine-based antioxidant". 【0037】 In the above general formula (1), R １ and R ２ are each independently a monovalent saturated hydrocarbon group. R １ and R ２ may be the same or different, but from the viewpoint of synthesis, it is preferably the same. 【0038】 The number of carbon atoms of the monovalent saturated hydrocarbon group is preferably 1 to 20, more preferably 3 to 10, and particularly preferably 6 and 7. When the number of carbon atoms of the saturated hydrocarbon group is 20 or less, the number of moles per unit mass increases, so the anti-aging effect increases and the ozone resistance of the rubber composition improves. R １ and R ２ are each independently preferably a linear or cyclic monovalent saturated hydrocarbon group having 1 to 20 carbon atoms from the viewpoint of further improving the ozone resistance of the rubber composition. 【0039】Examples of the monovalent saturated hydrocarbon group include alkyl groups and cycloalkyl groups. Alkyl groups may be linear or branched, and cycloalkyl groups may have further alkyl groups or the like bonded to them as substituents. Examples of the alkyl groups include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, 1,2-dimethylbutyl group, 1,3-dimethylbutyl group, 2,3-dimethylbutyl group, n-pentyl group, isopentyl group, neopentyl group, 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 4-methylpentyl group, 1,2-dimethylpentyl group, 1,3-dimethylpentyl group, 1,4-dimethylpentyl group, 2,3-dimethylpentyl group, 2,4-dimethylpentyl group, 3,4-dimethylpentyl group, n-hexyl group, 1-methylhexyl group, 2-methylhexyl group, various octyl groups, various decyl groups, various dodecyl groups, etc., and among these, sec-butyl group and 1,4-dimethylpentyl group are preferred. Examples of the cycloalkyl group include cyclopentyl group, methylcyclopentyl group, cyclohexyl group, methylcyclohexyl group, cycloheptyl group, and cyclooctyl group, with the cyclohexyl group being preferred among these. 【0040】 Specific examples of particular amine-based antioxidants include N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine, and N,N'-bis(sec-butyl)-p-phenylenediamine (44PD). Among these, N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD) and N,N'-bis(sec-butyl)-p-phenylenediamine (44PD) are preferred. The amine-based antioxidants may be used individually or in combination of two or more. 【0041】The content of the amine-based antioxidant is preferably 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of sulfur. If the content of the amine-based antioxidant is 1 part by mass or more per 100 parts by mass of sulfur, the ozone resistance of the rubber composition can be sufficiently ensured. On the other hand, if the content of the amine-based antioxidant exceeds 5 parts by mass per 100 parts by mass of sulfur, there is a possibility that it will have a greater adverse effect on rubber properties other than ozone resistance (such as heat generation). From the viewpoint of the effect on other rubber properties, the content of the amine-based antioxidant is more preferably 3 parts by mass or less per 100 parts by mass of sulfur, even more preferably 2.8 parts by mass or less, and still more preferably 2.5 parts by mass or less. 【0042】 (Sulfur) The rubber composition of this embodiment contains sulfur. The inclusion of sulfur in the rubber composition makes it vulcanizable and improves the durability of the rubber composition. Various types of sulfur can be used as the sulfur, but ordinary sulfur (soluble sulfur (powdered sulfur), etc.) is preferred over insoluble sulfur, and oil-treated sulfur is also preferred. Here, insoluble sulfur is sulfur that is insoluble in carbon disulfide (amorphous polymer sulfur), and soluble sulfur (powdered sulfur) is sulfur that is soluble in carbon disulfide. The sulfur content is preferably in the range of 0.1 to 10 parts by mass per 100 parts by mass of diene rubber, and more preferably in the range of 1 to 5 parts by mass. If the sulfur content is 0.1 parts by mass or more per 100 parts by mass of diene rubber, the durability of the vulcanized rubber can be ensured, and if it is 10 parts by mass or less per 100 parts by mass of diene rubber, sufficient rubber elasticity can be ensured. 【0043】 (Vulcanization accelerator) The rubber composition of this embodiment contains a vulcanization accelerator. From the viewpoint of the vulcanization accelerating effect and blooming properties, the content of the vulcanization accelerator is preferably 1 to 4 parts by mass, more preferably 1 to 3.7 parts by mass, even more preferably 1 to 3.5 parts by mass, and still more preferably 1.3 to 3.2 parts by mass, per 100 parts by mass of diene rubber. 【0044】[Thiram-based vulcanization accelerator] The vulcanization accelerator includes a thiram-based vulcanization accelerator. The rubber composition of this embodiment contains an anti-aging agent that satisfies the above-mentioned range of X and a thiram-based vulcanization accelerator, thereby maintaining ozone resistance without the use of the anti-aging agent 6PPD. 【0045】 The content of the thiram-based vulcanization accelerator is preferably 3 to 30 parts by mass per 100 parts by mass of sulfur. By having a content of 3 to 30 parts by mass of thiram-based vulcanization accelerator per 100 parts by mass of sulfur, a higher level of ozone resistance can be maintained. Furthermore, from the viewpoint of maintaining a higher level of ozone resistance, the content of the thiram-based vulcanization accelerator is more preferably 0.1 to 1.5 parts by mass, and even more preferably 0.2 to 1.2 parts by mass, per 100 parts by mass of diene rubber. 【0046】Examples of the thiram-based vulcanization accelerators include tetrakis(2-ethylhexyl)thiram disulfide, tetramethylthiram disulfide, tetraethylthiram disulfide, tetrapropylthiram disulfide, tetraisopropylthiram disulfide, tetrabutylthiram disulfide, tetrapentylthiram disulfide, tetrahexylthiram disulfide, tetraheptylthiram disulfide, tetraoctylthiram disulfide, tetranonylthiram disulfide, tetradecylthiram disulfide, tetradodecylthiram disulfide, tetrastearylthiram disulfide, tetrabenzylthiram disulfide ( Examples of thiram-based vulcanization accelerators include TBzTD, tetramethylthiram monosulfide, tetraethylthiram monosulfide, tetrapropylthiram monosulfide, tetraisopropylthiram monosulfide, tetrabutylthiram monosulfide, tetrapentylthiram monosulfide, tetrahexylthiram monosulfide, tetraheptylthiram monosulfide, tetraoctylthiram monosulfide, tetranonylthiram monosulfide, tetradecylthiram monosulfide, tetradodecylthiram monosulfide, tetrastearylthiram monosulfide, tetrabenzylthiram monosulfide, and dipentamethylenethiram tetrasulfide. Among these, tetrabenzylthiram disulfide (TBzTD) is preferred as a thiram-based vulcanization accelerator. 【0047】 [Sulfenamide-based vulcanization accelerator] The rubber composition of this embodiment preferably further contains a sulfenamide-based vulcanization accelerator. The rubber composition tends to maintain a higher level of ozone resistance when it contains a sulfenamide-based vulcanization accelerator in addition to a thiram-based vulcanization accelerator. 【0048】The content of the sulfenamide-based vulcanization accelerator is preferably 50 to 120 parts by mass per 100 parts by mass of sulfur. By having a content of 50 to 120 parts by mass of sulfenamide-based vulcanization accelerator per 100 parts by mass of sulfur, a higher level of ozone resistance can be maintained. Furthermore, from the viewpoint of maintaining a higher level of ozone resistance, the content of the sulfenamide-based vulcanization accelerator is more preferably 0.1 to 2.5 parts by mass, and even more preferably 0.2 to 2.3 parts by mass, per 100 parts by mass of diene rubber. 【0049】Examples of the sulfenamide-based sulfurization accelerators include N-cyclohexylbenzothiazole-2-sulfenamide, N,N-dicyclohexyl-2-benzothiazolylsulfenamide, N-tert-butyl-2-benzothiazolylsulfenamide, N-oxydiethylene-2-benzothiazolylsulfenamide, N-methyl-2-benzothiazolylsulfenamide, N-ethyl-2-benzothiazolylsulfenamide, and N-propyl-2-benzothiazo Lyl sulfenamide, N-butyl-2-benzothiazolyl sulfenamide, N-pentyl-2-benzothiazolyl sulfenamide, N-hexyl-2-benzothiazolyl sulfenamide, N-heptyl-2-benzothiazolyl sulfenamide, N-octyl-2-benzothiazolyl sulfenamide, N-2-ethylhexyl-2-benzothiazolyl sulfenamide, N-decyl-2-benzothiazolyl sulfenamide, N-dodecyl-2-benzothiazo Lyl sulfenamide, N-stearyl-2-benzothiazolyl sulfenamide, N,N-dimethyl-2-benzothiazolyl sulfenamide, N,N-diethyl-2-benzothiazolyl sulfenamide, N,N-dipropyl-2-benzothiazolyl sulfenamide, N,N-dibutyl-2-benzothiazolyl sulfenamide, N,N-dipentyl-2-benzothiazolyl sulfenamide, N,N-dihexyl-2-benzothiazolyl sulfenamide, N, Examples include N-diheptyl-2-benzothiazolyl sulfenamide, N,N-dioctyl-2-benzothiazolyl sulfenamide, N,N-di-2-ethylhexylbenzothiazolyl sulfenamide, N,N-didecyl-2-benzothiazolyl sulfenamide, N,N-didodecyl-2-benzothiazolyl sulfenamide, N,N-distearyl-2-benzothiazolyl sulfenamide, and N-tert-butyl-2-benzothiazolyl sulfenamide. 【0050】[Other vulcanization accelerators] In addition to the sulfenamide-based vulcanization accelerator and thiram-based vulcanization accelerator described above, the rubber composition of this embodiment may also contain other vulcanization accelerators such as thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, and xanthogenic acid-based vulcanization accelerators. 【0051】 Furthermore, from the perspective of reducing environmental impact and the possibility of future regulations, it is preferable that the vulcanization accelerator does not contain diphenylguanidine, which is a guanidine-based vulcanization accelerator. 【0052】 (Filler) The rubber composition may further contain a filler. The inclusion of a filler improves the strength of the rubber composition. The rubber composition preferably contains one or more fillers selected from carbon black and silica. The amount of filler in the rubber composition is preferably 1 to 10 parts by mass, more preferably 2 to 9 parts by mass, and even more preferably 3 to 7 parts by mass, per 100 parts by mass of the diene rubber. 【0053】 -Carbon Black- Carbon black can reinforce rubber compositions and improve their abrasion resistance. Preferred carbon blacks include plant-derived carbon black and carbon black obtained through recycling (also referred to as "recycled carbon black" or "regenerated carbon black"). Examples of plant-derived carbon black include those derived from castor oil and pine resin oil. Recycled carbon black will be described in detail below. 【0054】From the viewpoint of further improving the fracture resistance of the rubber composition, the carbon black content (total of recycled carbon black and carbon black other than recycled carbon black) in the rubber composition is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of diene rubber. Furthermore, from the viewpoint of the workability of the rubber composition, the carbon black content in the rubber composition is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 60 parts by mass or less, per 100 parts by mass of diene rubber. 【0055】--Recycled Carbon Black-- Preferably, the carbon black is recycled carbon black. By using recycled carbon black, the environmental burden can be reduced. In this specification, "recycled carbon black" refers to carbon black obtained by recovering from raw materials that are waste materials that have been recycled. Examples of such waste materials include waste rubber, used tires, and waste oil. Waste rubber is not limited to that generated from rubber products, but refers to all discarded rubber, including unwanted scraps generated in the production or repair of rubber products. Examples of scraps include buffing powder and peeling rubber. Buffing powder is, for example, fine rubber generated in the buffing process that removes the tread portion remaining on the base tire during tire retreading. Peeling rubber is, for example, long pieces of rubber, 1 to 2 cm wide, that are peeled off from the surface of rubber products such as tires. Peeling rubber is generated by using a U-shaped or V-shaped knife like a peeler to scrape the surface of rubber products such as tires. Furthermore, waste rubber is not limited to cross-linked rubber, but also includes unvulcanized rubber. Rubber products include, for example, finished products such as tires and rubber hoses, as well as rubber parts or components used in the manufacturing process of these finished products. Used tires may be retreaded, or they may be tires discarded for any reason, such as tires resulting from tire replacement or vehicle scrapping, or End-of-Life Tires (ELTs) that have reached the end of their lifespan as tires. Waste oil is not limited to that generated when plastics and rubber are decomposed, but also includes used oils discharged from industry, such as animal and vegetable oils, lubricating oils, insulating oils, and cutting oils. Among these, waste oils that do not contain any non-organic composition, such as those derived from silicone rubber or polyvinyl chloride, are desirable. Furthermore, waste oils that contain carbon black or rubber containing carbon black are desirable. "Recycled carbon black" is different from carbon black that is directly manufactured using hydrocarbons such as petroleum, natural gas, and coal as raw materials, i.e., carbon black that is not recycled. Note that "used" here includes not only those that have been discarded after being actually used, but also those that were manufactured but discarded without actually being used. 【0056】 Furthermore, it is preferable that the recycled carbon black is obtained by thermal decomposition of a vulcanized rubber product containing carbon black. Recycled carbon black obtained by thermal decomposition of a vulcanized rubber product containing carbon black is readily available because a large amount of vulcanized rubber product containing carbon black exists and it can be easily obtained by thermal decomposition. Moreover, it is preferable that the recycled carbon black is obtained from the solid residue generated by the thermal decomposition of the vulcanized rubber product containing carbon black. When a rubber product containing carbon black is thermally decomposed, solid residue and volatile components (oil) are obtained, and recycled carbon black can be recovered from either. When recovering carbon black from volatile components, it is possible to recover oil with a specific gravity suitable for producing carbon black and use it to produce carbon black using an existing carbon black production method (for example, Japanese Patent Publication No. 2015-520259). In this case, unlike carbon black recovered from solid residue, there are advantages such as the absence of impurities and the absence of mixtures of different grades. Furthermore, in the production of environmentally friendly carbon black, there are various options besides the oil obtained by recovering volatile components from the thermal decomposition of rubber mentioned above, such as using vegetable oil or oil derived from waste plastics. However, edible resources such as vegetable oil present challenges in securing sufficient quantities due to other uses such as food, and the environmental impact associated with the expansion of cultivated land must also be considered. Similarly, oil derived from waste plastics is used for other purposes such as horizontal recycling of plastics, so supply issues are also a concern. On the other hand, when using volatile components (oil) produced by the thermal decomposition of vulcanized rubber products, particularly tires, the tire industry has a system for continuing to use existing materials, making it possible to continue using existing materials and reduce the consumption of new materials in new tire manufacturing, thereby contributing to reducing the environmental burden on the industry. The grade of carbon black is not particularly limited, but examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. 【0057】The solid residue obtained by thermally decomposing waste materials such as used rubber and used tires contains ash in addition to carbon black. The ash originates from non-volatile components contained in rubber and tires. Therefore, the recycled carbon black obtained from this solid residue has a relatively low carbon black content. On the other hand, considering the various physical properties required for tires manufactured using recycled carbon black, a higher carbon content in recycled carbon black is preferable. In the recycled carbon black, the carbon content is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 87% by mass or more, and particularly preferably 89% by mass or more. Furthermore, the carbon content in the recycled carbon black is preferably 97% by mass or less. Note that the carbon content does not include adsorbed water. 【0058】 The aforementioned ash content specifically includes zinc oxide, zinc sulfide, silica, iron compounds (iron oxide), calcium oxide, aluminum oxide, magnesium oxide, and the like. In the case of recycled carbon black produced from solid residue obtained by thermal decomposition of waste, a certain amount of ash remains even after various processes to remove it. In this embodiment, the presence of ash in recycled carbon black is permitted. In one embodiment, the lower limit of the ash content of the recycled carbon black may be 0.5% by mass. 【0059】Furthermore, the recycled carbon black can be obtained from the pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3427975, "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly pp. 438, 440, and 442, states that it can be obtained by the pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (paragraph

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

[0004] of Japanese Patent Publication No. 6856781 (Comparison of Surface Morphology and Chemistry of Pyrolysis Carbon Black and Commercial Carbon Black, Powder Technology 160 (2005) 190-193). 【0060】 The recycled carbon black may lack functional groups on its surface, or it may have been treated to include functional groups on its surface. Treatment to include functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, in European Patent Application Publication No. 3173251, carbon black obtained from a thermal decomposition process is treated with potassium permanganate under acidic conditions to obtain carbon black containing hydroxyl groups and / or carboxyl groups on its surface. In addition, in Japanese Patent Publication No. 6856781, carbon black obtained from a thermal decomposition process is treated with an amino acid compound containing at least one thiol group or disulfide group to obtain carbon black with an activated surface. The recycled carbon black according to this embodiment also includes carbon black that has been treated to include functional groups on its surface. 【0061】 Furthermore, for the thermal decomposition of cross-linked rubber products (vulcanized rubber products) such as used tires, one example is a thermal decomposition method at a temperature of 650°C or higher. 【0062】The cross-linked rubber products used in the aforementioned decomposition may be grouped by the type of rubber component they contain beforehand, and the decomposition process may be carried out for each group separately. Alternatively, they may be grouped by the type of filler they contain beforehand (for example, the type of carbon black, the type of silica, the mixing ratio of carbon black and silica, etc.), and the decomposition process may be carried out for each group separately. Furthermore, they may be grouped by both the type of rubber component and the type of filler, and the decomposition process may be carried out for each group separately. When the decomposition process is carried out for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and when it is again incorporated into the rubber component, a rubber composition with better performance can be obtained. 【0063】 Furthermore, if the cross-linked rubber product used in the decomposition is derived from a tire, it may be grouped in advance by tire type (for example, for passenger cars, trucks and buses, heavy vehicles such as off-road vehicles, aircraft, agricultural vehicles, etc.) and then the decomposition process may be carried out for each group. Alternatively, it may be grouped in advance by tire component (for example, tread rubber, sidewall rubber, bead rubber, steel cord coated rubber, organic fiber coated rubber, pad rubber, cushion rubber, etc.) and then the decomposition process may be carried out for each group. Moreover, it may be possible to group by both tire type and tire component and then carry out the decomposition process for each group. When the decomposition process is carried out for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and when it is again blended into the rubber component, a rubber composition with better performance can be obtained. 【0064】 The recycled carbon black has a nitrogen adsorption specific surface area of ​​40 to 100 m² obtained by the BET method. ２ It is preferable that the amount be / g, and 50 to 90 m ２ It is more preferable that the amount be / g, and 55 to 75 m ２ It is particularly preferable that the value be / g. Here, in this specification, the nitrogen adsorption specific surface area of ​​recycled carbon black by the BET method is the statistical thickness specific surface area (STSA), which is determined according to ASTM D6556. 【0065】The recycled carbon black preferably has a pH of 4 to 12, more preferably 5 to 11, and particularly preferably 6 to 10. Herein, in this specification, the pH of the recycled carbon black is determined according to ASTM D1512. 【0066】 The recycled carbon black preferably has a toluene staining transmittance of 60% or more, more preferably 70% or more, and particularly preferably 80% or more. Herein, in this specification, the toluene staining transmittance of recycled carbon black is determined according to ASTM D1618. 【0067】 The recycled carbon black preferably has a heating loss of 3% by mass or less at 125°C, more preferably 2.5% by mass or less, and particularly preferably 2% by mass or less. Hereinafter, the heating loss of the recycled carbon black at 125°C is determined according to ASTM D1509. 【0068】 The recycled carbon black preferably has a sulfur content of 5% by mass or less, more preferably 3.5% by mass or less, and particularly preferably 3% by mass or less. 【0069】 The recycled carbon black preferably has a 35-mesh sieve residue of 20 ppm by mass or less, more preferably 15 ppm by mass or less, and particularly preferably 10 ppm by mass or less. Here, in this specification, the 35-mesh sieve residue of the recycled carbon black is determined according to ASTM D1514. 【0070】 The recycled carbon black preferably has a 325-mesh (44 μm) sieve residue of 1,000 ppm by mass or less, more preferably 700 ppm by mass or less, and particularly preferably 300 ppm by mass or less. Here, in this specification, the 325-mesh (44 μm) sieve residue of the recycled carbon black is determined according to ASTM D1514. 【0071】The recycled carbon black preferably has a pellet hardness of 100 cN or less, more preferably 90 cN or less, and particularly preferably 80 cN or less. Hereinafter, the pellet hardness of the recycled carbon black is determined according to ASTM D5230. 【0072】 The recycled carbon black preferably has a pellet fine powder content of 10% by mass or less, more preferably 7% by mass or less, and particularly preferably 5% by mass or less. Hereinafter, the pellet fine powder content of the recycled carbon black is determined according to ASTM D1508. 【0073】 The recycled carbon black preferably has a particle size (D97) of 25 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less. Hereinafter, the particle size (D97) of the recycled carbon black is determined using a laser diffraction particle size analyzer, with the refractive index of water being 1.33 and the refractive index of the filler being 1.75. 【0074】 The recycled carbon black preferably contains 50% or more by volume of particles 5 μm or smaller, more preferably 70% or more by volume, and particularly preferably 80% or more by volume. 【0075】 The recycled carbon black preferably has an ash content of 25% by mass or less, more preferably 20% by mass or less, and particularly preferably 15% by mass or less. When the ash content of the recycled carbon black is 25% by mass or less, the various physical properties of the rubber product to which the rubber composition is applied can be improved. Herein, in this specification, the ash content of the recycled carbon black is determined according to ASTM D8474 / D1506. 【0076】The recycled carbon black preferably has an OAN (oil absorption rate) of 70 to 120 mL / 100 g, more preferably 75 to 110 mL / 100 g, and particularly preferably 80 to 100 mL / 100 g. Herein, in this specification, the OAN (oil absorption rate) of the recycled carbon black is determined according to ASTM D2414. 【0077】 The recycled carbon black preferably has a COAN (oil absorption capacity of compressed material) of 50 to 110 mL / 100 g, more preferably 60 to 100 mL / 100 g, and particularly preferably 70 to 90 mL / 100 g. Hereinafter, the COAN (oil absorption capacity of compressed material) of the recycled carbon black is determined according to ASTM D3493. 【0078】 Commercially available recycled carbon black can be used. Examples of such commercially available products include "PB365" manufactured by Enrestec. PB365 is recycled carbon black produced by the thermal decomposition of used tires, and has a nitrogen adsorption specific surface area of ​​73.6 m² by the BET method. ２ It is 1 / g and also contains approximately 17% by mass of ash. 【0079】 The recycled carbon black content is preferably 1 to 100 parts by mass, more preferably 5 to 80 parts by mass, even more preferably 5 to 50 parts by mass, even more preferably 5 to 30 parts by mass, and particularly preferably 5 to 20 parts by mass, per 100 parts by mass of diene rubber. When the recycled carbon black content is 5 parts by mass or more per 100 parts by mass of diene rubber, it has a great effect in improving the ratio of sustainable materials in rubber products to which the rubber composition is applied, and when it is 50 parts by mass or less, the fracture resistance of the rubber composition can be maintained more reliably. 【0080】(Silica) The rubber composition of this embodiment may contain silica. Examples of silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc., and among these, wet silica is preferred because it has a large amount of silanol groups. These silicas may be used individually or in combination of two or more. Commercially available silica can be used, and examples of commercially available silica include products from Tosoh Silica Co., Ltd., Evonik, Solvay, Solvay Japan Ltd., Tokuyama Corporation, etc. 【0081】As for the silica, silica derived from silicate plants is preferred from the viewpoint of reducing environmental impact. These silicate plants include, for example, mosses, ferns, horsetails, cucurbitaceae, nettleaceae, and grasses. Among these plants, grasses are preferred. Examples of grasses include rice, bamboo grass, and sugarcane, with rice being preferred among these. Rice is widely cultivated for food, so it can be procured locally in a wide area, and rice hulls are generated in large quantities as industrial waste, making it easy to secure the necessary amount. Therefore, from the viewpoint of availability, silica derived from rice hulls (hereinafter also referred to as "rice hull silica") is particularly preferred. By using this rice hull silica, rice hulls that would otherwise be industrial waste can be effectively utilized, and since the raw material can be procured locally near the tire manufacturing plant, the energy and costs of transportation and storage can be reduced, which is environmentally friendly from various perspectives. The aforementioned rice husk silica may be powder of rice husk charcoal obtained by carbonizing rice husks by heating, or it may be precipitated silica produced by a wet process using an alkaline aqueous solution of silicate prepared by extracting rice husk ash generated when rice husks are burned as fuel in a biomass boiler with alkali. The method for producing the aforementioned rice husk charcoal is not particularly limited, and various known methods can be used. For example, rice husk charcoal can be obtained by thermal decomposition by steam-roasting rice husks in a kiln. The rice husk charcoal obtained in this way can be crushed using a known crusher (e.g., a ball mill), sorted into a predetermined particle size range, and classified to obtain powder of rice husk charcoal. Furthermore, the aforementioned precipitated silica derived from rice husks can be produced by the method described in Japanese Patent Application Publication No. 2019-38728, etc. In addition, from the viewpoint of reducing environmental impact, it is also preferable to use silica that has been recycled and used in the production process by extracting silica components from silicon wafer scraps, which are raw materials for semiconductors, or from glass bottles, etc. 【0082】 The silica has a specific surface area (N) for nitrogen adsorption. ２ SA) is 50m ２ It is preferable that it be 100m or more per gram. ２ It is more preferable that the amount is 150m or more per gram. ２ It is even more preferable that it be 350m or more ２It is preferable that the amount is less than or equal to 250m ２ It is more preferable that it be less than or equal to 230m ２ It is even more preferable that it be less than or equal to 200m ２ It is even more preferable that it be less than or equal to / g. In this specification, the specific surface area of ​​silica for nitrogen adsorption (N ２ SA) is a value measured by the BET method in accordance with ASTM D3037-93. 【0083】 The silica content is preferably 35 parts by mass or more, and more preferably 50 parts by mass or more, per 100 parts by mass of the diene rubber. Furthermore, the silica content is preferably 85 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 75 parts by mass or less, per 100 parts by mass of the diene rubber. 【0084】 (Silane coupling agent) When silica is used as the filler, silane coupling agents such as bis(3-triethoxysilylpropyl) polysulfide, bis(3-triethoxysilylpropyl) disulfide, and 3-trimethoxysilylpropylbenzothiadyl tetrasulfide are preferably used. The amount of silane coupling agent is preferably selected in the range of 2 to 20 parts by mass per 100 parts by mass of silica. 【0085】(Wax) The rubber composition of this embodiment preferably further contains wax. When the rubber composition contains wax, the ozone resistance of the rubber composition is further improved. Examples of the wax include paraffin wax and microcrystalline wax. The amount of wax is preferably 0.1 to 5 parts by mass per 100 parts by mass of the diene rubber. If the amount of wax is 0.1 parts by mass or more per 100 parts by mass of the diene rubber, the ozone resistance of the rubber composition is further improved. Also, if the amount of wax is 5 parts by mass or less per 100 parts by mass of the diene rubber, the effect on rubber properties other than ozone resistance is small. From the viewpoint of ozone resistance, the amount of wax is more preferably 0.5 parts by mass or more per 100 parts by mass of the diene rubber, and even more preferably 1 part by mass or more. From the viewpoint of the effect on other rubber properties, it is more preferably 4 parts by mass or less per 100 parts by mass of the diene rubber, and even more preferably 3 parts by mass or less. 【0086】 (Other) In addition to the diene rubber, antioxidant, vulcanization accelerator, and sulfur described above, the rubber composition of this embodiment may also contain, as necessary, various components commonly used in the rubber industry, such as softeners, processing aids, resins, surfactants, organic acids (such as stearic acid), zinc oxide (zinc oxide), and vulcanizing agents other than sulfur, selected appropriately within a range that does not impair the purpose of the present invention. Commercially available products can be suitably used as these compounding agents. 【0087】 (Method for producing the rubber composition) The method for producing the rubber composition is not particularly limited, but for example, it can be produced by mixing the diene rubber, antioxidant, vulcanization accelerator, and sulfur described above with various components selected as needed, and then kneading, heating, extruding, etc. The obtained rubber composition can be vulcanized to produce vulcanized rubber. 【0088】There are no particular restrictions on the mixing conditions, and various conditions such as the input volume of the mixing device, the rotation speed of the rotor, the ram pressure, as well as the mixing temperature, mixing time, and the type of mixing device can be appropriately selected according to the purpose. Examples of mixing devices include Banbury mixers, intermixes, kneaders, and rolls, which are commonly used for mixing rubber compositions. 【0089】 There are no particular restrictions on the heat treatment conditions, and various conditions such as heat treatment temperature, heat treatment time, and heat treatment equipment can be appropriately selected according to the purpose. Examples of such heat treatment equipment include heat treatment roll machines commonly used for heat treatment of rubber compositions. 【0090】 There are no particular restrictions on the extrusion conditions, and various conditions such as extrusion time, extrusion speed, extrusion equipment, and extrusion temperature can be appropriately selected according to the purpose. Examples of extrusion equipment include extruders typically used for extruding rubber compositions. The extrusion temperature can be determined as appropriate. 【0091】 There are no particular restrictions on the apparatus, method, and conditions for performing the vulcanization, and they can be appropriately selected according to the purpose. Examples of vulcanization apparatus include molding vulcanizers that use molds for vulcanizing rubber compositions. As for the vulcanization conditions, the temperature is, for example, around 100 to 190°C. 【0092】 <Vulcanized Rubber for Tire Treads> The vulcanized rubber for tire treads in this embodiment is obtained by vulcanizing the rubber composition described above. Since this vulcanized rubber for tire treads is obtained by vulcanizing the rubber composition of this embodiment, it has a low environmental impact while maintaining ozone resistance. 【0093】 <Tire> The tire of this embodiment is characterized by having the above-described vulcanized rubber for tire treads in the tread portion. Since the tire uses vulcanized rubber obtained by vulcanizing the rubber composition of this embodiment, it has a low environmental impact while maintaining ozone resistance. 【0094】The tire of this embodiment is preferably a pneumatic tire, and as the gas to be filled into the pneumatic tire, in addition to ordinary air or air with adjusted oxygen partial pressure, an inert gas such as nitrogen, argon, or helium can be used. 【0095】 <Rubber Crawler> The rubber crawler of this embodiment is characterized by using the rubber composition described above. Because the rubber crawler uses the rubber composition of this embodiment, it has a low environmental impact while maintaining ozone resistance. 【0096】 In one embodiment, the rubber crawler comprises a steel cord, an intermediate rubber layer covering the steel cord, a core metal positioned on the intermediate rubber layer, and a main rubber layer surrounding the intermediate rubber layer and the core metal. Furthermore, the main rubber layer has a plurality of lugs on the contact surface side. Here, the rubber composition of the present invention may be used in any part of the rubber crawler, but it is preferable to use it in the main rubber layer, and especially in the lugs. 【0097】 The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples. 【0098】 (Preparation of Rubber Compositions) The rubber compositions of the examples and comparative examples were prepared according to the formulations shown in Table 1. The prepared rubber compositions were evaluated as follows. 【0099】 (Descriptors) For each anti-aging agent, the descriptors (descriptors MinEStateIndex, MinAbsEStateIndex, SlogP_VSA7, FractionCSP3, and NumRotatableBonds) were obtained from the molecular structure of each anti-aging agent represented in SMILES notation using the cheminformatics tool RDKit in a Python environment. 【0100】 (Evaluation of rubber composition) - Ozone resistance A dynamic ozone degradation test (a test in which repeated strain is applied) was conducted in accordance with ISO 1431 (JIS K 6259) to evaluate ozone resistance. Products in which no cracks could be seen with the naked eye were evaluated as A, and products in which cracks could be seen with the naked eye were evaluated as B. 【0101】 【0102】 *1 Diene rubber: Styrene-butadiene rubber, manufactured by Asahi Kasei Corporation, trade name "Toughden 2000" *2 Anti-aging agent (1): N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), manufactured by Sumitomo Chemical Co., Ltd., trade name "Antigen 6C", X = -3.9 *3 Anti-aging agent (2): R in general formula (1) １ and R ２ R is a saturated hydrocarbon group (1,4-dimethylpentyl group), an amine-based antioxidant, N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (77PD), manufactured by Eastman, trade name "Santoflex 77PD", X = -3.3 *4 Antioxidant (3): R in general formula (1) １ and R ２*5 Antioxidant (4): Amine-based antioxidant with a saturated hydrocarbon group (sec-butyl group), N,N'-bis(sec-butyl)-p-phenylenediamine (44PD), manufactured by Kanto Chemical Co., Ltd., X = -2.8 *6 Antioxidant (5): Quinoline-based antioxidant, 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrac AW", X = -3.7 *6 Antioxidant (5): Phosphorus-based antioxidant, tris(nonylphenyl)phosphite (TNP), manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrac TNP", X = -3.9 *7 Antioxidant (6): Sulfur-based antioxidant, dilauryl thiodipropionate, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrac 400", X = -3.6 *8 Sulfur: Manufactured by Hosoi Chemical Industry Co., Ltd., product name "HK200-5", 5% oil *9 Sulfenamide-based vulcanization accelerator: N-cyclohexylbenzothiazole-2-sulfenamide (Manufactured by Ouchi Shinko Chemical Industry Co., Ltd., product name "Noxellar CZ-G") *10 Thiazole-based vulcanization accelerator: Dibenzothiazole disulfide, Ouchi Shinko Chemical Industry Co., Ltd., product name "Noxellar DM-P" *11 Thiuram-based vulcanization accelerator: Tetrabenzyl thiuram disulfide, Manufactured by Sanshin Chemical Industry Co., Ltd., product name "Sunceller TBzTD" *12 Carbon black: Manufactured by Cabot Japan, product name "VULCAN 7HJ" *13 Silica: Manufactured by Tosoh Silica Industry Co., Ltd., product name "NipSeal AQ" *14 Silane coupling agent: Manufactured by Osaka Soda Co., Ltd., product name "CABRUS(registered trademark)-2A" 【0103】 Table 1 shows that the rubber composition of this embodiment maintains ozone resistance even without the use of the antioxidant 6PPD. Furthermore, because it uses chemicals that have a low environmental impact, it has a low environmental burden.

Claims

1. A rubber composition comprising a diene rubber, an antioxidant, sulfur, and a vulcanization accelerator, wherein the vulcanization accelerator includes a thiram-based vulcanization accelerator, and the antioxidant satisfies the condition that X, calculated by the following formula (I), is between -3.4 and -2.7: X = 1.2 × A + 0.31 × B + 0.28 × C + 1.25 × D + 0.04 × E ... Formula (I) (In formula (I), A represents the descriptor MinEStateIndex of the antioxidant, B represents the descriptor MinAbsEStateIndex of the antioxidant, C represents the descriptor SlogP_VSA7 of the antioxidant, D represents the descriptor FractionCSP3 of the antioxidant, and E represents the descriptor NumRotatableBonds of the antioxidant.) 2. The rubber composition according to claim 1, wherein the vulcanization accelerator does not contain diphenylguanidine.

3. The rubber composition according to claim 1, wherein the content of the thiram-based vulcanization accelerator is 3 to 30 parts by mass per 100 parts by mass of sulfur.

4. The rubber composition according to claim 1, wherein the vulcanization accelerator further comprises a sulfenamide-based vulcanization accelerator.

5. The rubber composition according to claim 4, wherein the content of the sulfenamide-based vulcanization accelerator is 50 to 120 parts by mass per 100 parts by mass of sulfur.

6. The rubber composition according to claim 1, wherein the content of the antioxidant is less than 5 parts by mass per 100 parts by mass of the diene rubber.

7. The rubber composition according to claim 1, wherein the antioxidant is an amine-based antioxidant represented by the following general formula (1). (In general formula (1), R １ and R ２ These are each independently monovalent saturated hydrocarbon groups.

8. The rubber composition according to claim 1, further comprising one or more fillers selected from carbon black and silica.

9. The rubber composition according to claim 8, wherein the carbon black is recycled carbon black.

10. The rubber composition according to claim 8, wherein the silica is silica derived from rice husks.

11. The rubber composition according to claim 8, wherein the silica content is 50 parts by mass or more per 100 parts by mass of the diene rubber.

12. A vulcanized rubber for tire treads, obtained by vulcanizing the rubber composition described in claim 1.

13. A tire comprising the vulcanized rubber for tire treads described in claim 12 in the tread portion.

14. A rubber crawler using the rubber composition described in claim 1.

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